HTTPbis Working Group                                   R. Fielding, Ed.
Internet-Draft                                                     Adobe
Obsoletes: 2616 (if approved)                              Y. Lafon, Ed.
Updates: 2817 (if approved)                                          W3C
Intended status: Standards Track                         J. Reschke, Ed.
Expires: September 13, 2012 January 17, 2013                                     greenbytes
                                                          March 12,
                                                           July 16, 2012

                HTTP/1.1, part 2: Message Semantics
                   draft-ietf-httpbis-p2-semantics-19 and Payloads
                   draft-ietf-httpbis-p2-semantics-20

Abstract

   The Hypertext Transfer Protocol (HTTP) is an application-level
   protocol for distributed, collaborative, hypertext information
   systems.  HTTP has been in use by the World Wide Web global
   information initiative since 1990.  This document is Part 2 of the
   seven-part specification that defines the protocol referred to as
   "HTTP/1.1" and, taken together, obsoletes RFC 2616.

   Part 2 defines the semantics of HTTP messages HTTP/1.1 messages,
   as expressed by request methods, request header fields, response
   status codes, and response header fields. fields, along with the payload of
   messages (metadata and body content) and mechanisms for content
   negotiation.

Editorial Note (To be removed by RFC Editor)

   Discussion of this draft should take takes place on the HTTPBIS working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   <http://lists.w3.org/Archives/Public/ietf-http-wg/>.

   The current issues list is at
   <http://tools.ietf.org/wg/httpbis/trac/report/3> and related
   documents (including fancy diffs) can be found at
   <http://tools.ietf.org/wg/httpbis/>.

   The changes in this draft are summarized in Appendix C.20. F.40.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  6   7
     1.1.  Conformance and Error Handling  . . . . . . . . . . . . .  6   7
     1.2.  Syntax Notation . . . . . . . . . . . . . . . . . . . . .  7
       1.2.1.  Core Rules . . . . . . . .   8
   2.  Methods . . . . . . . . . . . . . .  7
       1.2.2.  ABNF Rules defined in other Parts of the
               Specification . . . . . . . . . . . . .   8
     2.1.  Safe and Idempotent Methods . . . . . . .  7
   2.  Method . . . . . . . .   9
       2.1.1.  Safe Methods  . . . . . . . . . . . . . . . . . . . .  7
     2.1.   Overview of   9
       2.1.2.  Idempotent Methods  . . . . . . . . . . . . . . . . . . .  8   9
     2.2.  Method Registry . . . . . . . . . . . . . . . . . . . . .  8   9
       2.2.1.  Considerations for New Methods  . . . . . . . . . . . .  9
   3.  Header Fields  10
     2.3.  Method Definitions  . . . . . . . . . . . . . . . . . . .  10
       2.3.1.  OPTIONS . . . . .  9
     3.1.   Considerations for Creating Header Fields . . . . . . . .  9
     3.2.   Request Header Fields . . . . . . . . . .  11
       2.3.2.  GET . . . . . . . . 11
     3.3.   Response Header Fields . . . . . . . . . . . . . . . . .  12
   4.  Status Code and Reason Phrase  . .
       2.3.3.  HEAD  . . . . . . . . . . . . . . 12
     4.1.   Overview of Status Codes . . . . . . . . . .  12
       2.3.4.  POST  . . . . . . 13
     4.2.   Status Code Registry . . . . . . . . . . . . . . . . . . 15
       4.2.1.  Considerations for New Status Codes  13
       2.3.5.  PUT . . . . . . . . . 15
   5.  Representation . . . . . . . . . . . . . . . .  14
       2.3.6.  DELETE  . . . . . . . . 16
     5.1.   Identifying the Resource Associated with a
            Representation . . . . . . . . . . . . . . .  16
       2.3.7.  TRACE . . . . . . 16
   6.  Method Definitions . . . . . . . . . . . . . . . . . .  16
       2.3.8.  CONNECT . . . . 17
     6.1.   Safe and Idempotent Methods . . . . . . . . . . . . . . . 17
       6.1.1.  Safe Methods . . . .  17
   3.  Header Fields . . . . . . . . . . . . . . . . . 17
       6.1.2.  Idempotent Methods . . . . . . .  18
     3.1.  Considerations for Creating Header Fields . . . . . . . .  18
     3.2.  Request Header Fields . . . 17
     6.2.   OPTIONS . . . . . . . . . . . . . . .  20
     3.3.  Response Header Fields  . . . . . . . . . . 18
     6.3.   GET . . . . . . .  21
   4.  Status Codes  . . . . . . . . . . . . . . . . . . . . 19
     6.4.   HEAD . . . .  22
     4.1.  Overview of Status Codes  . . . . . . . . . . . . . . . .  22
     4.2.  Status Code Registry  . . . . . . 19
     6.5.   POST . . . . . . . . . . . .  24
       4.2.1.  Considerations for New Status Codes . . . . . . . . .  24
     4.3.  Informational 1xx . . . . . 20
     6.6.   PUT . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     6.7.   DELETE  . . . . . . . . . . . . . . . . . . . . . . . . . 23
     6.8.   TRACE . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     6.9.   CONNECT . . . . . . . . . . . . . . . . . . . . . . . . . 24
   7.  Status Code Definitions  . . . . . . . . . . . . . . . . . . .  25
     7.1.   Informational 1xx . . . . . . . . . . . . . . . . . . . . 26
       7.1.1.
       4.3.1.  100 Continue  . . . . . . . . . . . . . . . . . . . . . 26
       7.1.2.  25
       4.3.2.  101 Switching Protocols . . . . . . . . . . . . . . . 27
     7.2.  25
     4.4.  Successful 2xx  . . . . . . . . . . . . . . . . . . . . . 27
       7.2.1.  26
       4.4.1.  200 OK  . . . . . . . . . . . . . . . . . . . . . . . . 27
       7.2.2.  26
       4.4.2.  201 Created . . . . . . . . . . . . . . . . . . . . . 27
       7.2.3.  26
       4.4.3.  202 Accepted  . . . . . . . . . . . . . . . . . . . . . 28
       7.2.4.  27
       4.4.4.  203 Non-Authoritative Information . . . . . . . . . . 28
       7.2.5.  27
       4.4.5.  204 No Content  . . . . . . . . . . . . . . . . . . . . 28
       7.2.6.  27
       4.4.6.  205 Reset Content . . . . . . . . . . . . . . . . . . 29
     7.3.  28
     4.5.  Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 29
       7.3.1.  28
       4.5.1.  300 Multiple Choices  . . . . . . . . . . . . . . . . . 31
       7.3.2.  29
       4.5.2.  301 Moved Permanently . . . . . . . . . . . . . . . . 31
       7.3.3.  30
       4.5.3.  302 Found . . . . . . . . . . . . . . . . . . . . . . 32
       7.3.4.  30
       4.5.4.  303 See Other . . . . . . . . . . . . . . . . . . . . 32
       7.3.5.  31
       4.5.5.  305 Use Proxy . . . . . . . . . . . . . . . . . . . . 33
       7.3.6.  31
       4.5.6.  306 (Unused)  . . . . . . . . . . . . . . . . . . . . . 33
       7.3.7.  31
       4.5.7.  307 Temporary Redirect  . . . . . . . . . . . . . . . . 33
     7.4.  32
     4.6.  Client Error 4xx  . . . . . . . . . . . . . . . . . . . . 33
       7.4.1.  32
       4.6.1.  400 Bad Request . . . . . . . . . . . . . . . . . . . 33
       7.4.2.  32
       4.6.2.  402 Payment Required  . . . . . . . . . . . . . . . . . 33
       7.4.3.  32
       4.6.3.  403 Forbidden . . . . . . . . . . . . . . . . . . . . 33
       7.4.4.  32
       4.6.4.  404 Not Found . . . . . . . . . . . . . . . . . . . . 34
       7.4.5.  33
       4.6.5.  405 Method Not Allowed  . . . . . . . . . . . . . . . . 34
       7.4.6.  33
       4.6.6.  406 Not Acceptable  . . . . . . . . . . . . . . . . . . 34
       7.4.7.  33
       4.6.7.  408 Request Timeout . . . . . . . . . . . . . . . . . 35
       7.4.8.  33
       4.6.8.  409 Conflict  . . . . . . . . . . . . . . . . . . . . . 35
       7.4.9.  34
       4.6.9.  410 Gone  . . . . . . . . . . . . . . . . . . . . . . . 35
       7.4.10.  34
       4.6.10. 411 Length Required . . . . . . . . . . . . . . . . . 36
       7.4.11.  34
       4.6.11. 413 Request Representation Too Large  . . . . . . . . . 36
       7.4.12.  35
       4.6.12. 414 URI Too Long  . . . . . . . . . . . . . . . . . . . 36
       7.4.13.  35
       4.6.13. 415 Unsupported Media Type  . . . . . . . . . . . . . . 36
       7.4.14.  35
       4.6.14. 417 Expectation Failed  . . . . . . . . . . . . . . . . 36
       7.4.15.  35
       4.6.15. 426 Upgrade Required  . . . . . . . . . . . . . . . . . 37
     7.5.  35
     4.7.  Server Error 5xx  . . . . . . . . . . . . . . . . . . . . 37
       7.5.1.  36
       4.7.1.  500 Internal Server Error . . . . . . . . . . . . . . 37
       7.5.2.  36
       4.7.2.  501 Not Implemented . . . . . . . . . . . . . . . . . 37
       7.5.3.  36
       4.7.3.  502 Bad Gateway . . . . . . . . . . . . . . . . . . . 37
       7.5.4.  36
       4.7.4.  503 Service Unavailable . . . . . . . . . . . . . . . 38
       7.5.5.  36
       4.7.5.  504 Gateway Timeout . . . . . . . . . . . . . . . . . 38
       7.5.6.  37
       4.7.6.  505 HTTP Version Not Supported  . . . . . . . . . . .  37
   5.  Protocol Parameters . 38
   8.  Date/Time Formats . . . . . . . . . . . . . . . . . . . .  37
     5.1.  Date/Time Formats . . 38
   9.  Product Tokens . . . . . . . . . . . . . . . . . .  37
     5.2.  Product Tokens  . . . . . . 41
   10. Header Field Definitions . . . . . . . . . . . . . . .  40
     5.3.  Character Encodings (charset) . . . . 42
     10.1.  Allow . . . . . . . . . .  41
     5.4.  Content Codings . . . . . . . . . . . . . . . . . 42
     10.2.  Date . . . .  41
       5.4.1.  Content Coding Registry . . . . . . . . . . . . . . .  42
     5.5.  Media Types . . . . . . . 42
     10.3.  Expect . . . . . . . . . . . . . . . .  42
       5.5.1.  Canonicalization and Text Defaults  . . . . . . . . .  43
     10.4.  From
       5.5.2.  Multipart Types . . . . . . . . . . . . . . . . . . .  44
     5.6.  Language Tags . . . . . . . 44
     10.5.  Location . . . . . . . . . . . . . . .  44
   6.  Payload . . . . . . . . . 45
     10.6.  Max-Forwards . . . . . . . . . . . . . . . . . .  45
     6.1.  Payload Header Fields . . . . 46
     10.7.  Referer . . . . . . . . . . . . . .  45
     6.2.  Payload Body  . . . . . . . . . . . 46
     10.8.  Retry-After . . . . . . . . . . .  45
   7.  Representation  . . . . . . . . . . . . 47
     10.9.  Server . . . . . . . . . . .  45
     7.1.  Identifying the Resource Associated with a
           Representation  . . . . . . . . . . . . . . 47
     10.10. User-Agent . . . . . . .  46
     7.2.  Representation Header Fields  . . . . . . . . . . . . . .  47
     7.3.  Representation Data . . 48
   11. IANA Considerations . . . . . . . . . . . . . . . . .  48
   8.  Content Negotiation . . . . 49
     11.1.  Method Registry . . . . . . . . . . . . . . . . .  49
     8.1.  Server-driven Negotiation . . . . 49
     11.2.  Status Code Registry . . . . . . . . . . . .  50
     8.2.  Agent-driven Negotiation  . . . . . . 49
     11.3.  Header Field Registration . . . . . . . . . .  51
   9.  Header Field Definitions  . . . . . . 50
   12. Security Considerations . . . . . . . . . . . .  52
     9.1.  Accept  . . . . . . . 51
     12.1.  Transfer of Sensitive Information . . . . . . . . . . . . 51
     12.2.  Encoding Sensitive Information in URIs . . . . . .  52
     9.2.  Accept-Charset  . . . 52
     12.3.  Location Header Fields: Spoofing and Information
            Leakage . . . . . . . . . . . . . . . . . .  54
     9.3.  Accept-Encoding . . . . . . . 53
     12.4.  Security Considerations for CONNECT . . . . . . . . . . . 53
   13. Acknowledgments . . .  55
     9.4.  Accept-Language . . . . . . . . . . . . . . . . . . . . 53
   14. References .  56
     9.5.  Allow . . . . . . . . . . . . . . . . . . . . . . . . . 53
     14.1.  Normative References .  57
     9.6.  Content-Encoding  . . . . . . . . . . . . . . . . . 53
     14.2.  Informative References . . .  57
     9.7.  Content-Language  . . . . . . . . . . . . . . 54
   Appendix A.  Changes from RFC 2616 . . . . . .  58
     9.8.  Content-Location  . . . . . . . . . . . 55
   Appendix B.  Collected ABNF . . . . . . . . .  59
     9.9.  Content-Type  . . . . . . . . . . 56
   Appendix C.  Change Log (to be removed by RFC Editor before
                publication) . . . . . . . . . . . .  61
     9.10. Date  . . . . . . . . 59
     C.1.   Since RFC 2616 . . . . . . . . . . . . . . . . . .  61
     9.11. Expect  . . . 59
     C.2.   Since draft-ietf-httpbis-p2-semantics-00 . . . . . . . . 59
     C.3.   Since draft-ietf-httpbis-p2-semantics-01 . . . . . . . . 60
     C.4.   Since draft-ietf-httpbis-p2-semantics-02 . . . . . .  62
     9.12. From  . . 60
     C.5.   Since draft-ietf-httpbis-p2-semantics-03 . . . . . . . . 61
     C.6.   Since draft-ietf-httpbis-p2-semantics-04 . . . . . . . . 61
     C.7.   Since draft-ietf-httpbis-p2-semantics-05 . . . . . . . . 62
     C.8.   Since draft-ietf-httpbis-p2-semantics-06  63
     9.13. Location  . . . . . . . . 62
     C.9.   Since draft-ietf-httpbis-p2-semantics-07 . . . . . . . . 62
     C.10.  Since draft-ietf-httpbis-p2-semantics-08 . . . . . . . .  63
     C.11.  Since draft-ietf-httpbis-p2-semantics-09
     9.14. Max-Forwards  . . . . . . . . 63
     C.12.  Since draft-ietf-httpbis-p2-semantics-10 . . . . . . . . 63
     C.13.  Since draft-ietf-httpbis-p2-semantics-11 . . . . . .  65
     9.15. Referer . . . 64
     C.14.  Since draft-ietf-httpbis-p2-semantics-12 . . . . . . . . 64
     C.15.  Since draft-ietf-httpbis-p2-semantics-13 . . . . . . . . 66
     C.16.  Since draft-ietf-httpbis-p2-semantics-14 . . . . . .  65
     9.16. Retry-After . . . . . . . 66
     C.17.  Since draft-ietf-httpbis-p2-semantics-15 . . . . . . . . 66
     C.18.  Since draft-ietf-httpbis-p2-semantics-16 . . . . . . . .  66
     C.19.  Since draft-ietf-httpbis-p2-semantics-17
     9.17. Server  . . . . . . . . 67
     C.20.  Since draft-ietf-httpbis-p2-semantics-18 . . . . . . . . 67
   Index . . . . . . . . .  66
     9.18. User-Agent  . . . . . . . . . . . . . . . . . . . . . 68

1.  Introduction

   This document defines HTTP/1.1 request and response semantics.  Each
   HTTP message, as defined in [Part1], is in the form . .  67
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  67
     10.1. Method Registry . . . . . . . . . . . . . . . . . . . . .  67
     10.2. Status Code Registry  . . . . . . . . . . . . . . . . . .  68
     10.3. Header Field Registration . . . . . . . . . . . . . . . .  69
     10.4. Content Coding Registry . . . . . . . . . . . . . . . . .  70
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  71
     11.1. Transfer of either a
   request or a response.  An HTTP server listens on a connection for
   HTTP requests and responds to each request, Sensitive Information . . . . . . . . . . . .  71
     11.2. Encoding Sensitive Information in the order received on
   that connection, with one or more HTTP response messages.  This
   document defines the commonly agreed upon semantics of the HTTP
   uniform interface, the intentions defined by each request method, URIs  . . . . . . . . .  72
     11.3. Location Header Fields: Spoofing and
   the various response messages that might be expected as a result of
   applying that method to the target resource.

   This document is currently disorganized in order Information
           Leakage . . . . . . . . . . . . . . . . . . . . . . . . .  72
     11.4. Security Considerations for CONNECT . . . . . . . . . . .  73
     11.5. Privacy Issues Connected to minimize the
   changes Accept Header Fields  . . . .  73
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  74
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  74
     13.1. Normative References  . . . . . . . . . . . . . . . . . .  74
     13.2. Informative References  . . . . . . . . . . . . . . . . .  75
   Appendix A.  Differences between drafts HTTP and enable reviewers to see the smaller errata
   changes.  A future draft will reorganize the sections to better
   reflect the content.  In particular, the sections will be ordered
   according MIME  . . . . . . . . .  77
     A.1.  MIME-Version  . . . . . . . . . . . . . . . . . . . . . .  78
     A.2.  Conversion to the typical processing Canonical Form  . . . . . . . . . . . . . .  78
     A.3.  Conversion of an HTTP request message (after
   message parsing): resource mapping, methods, request modifying header
   fields, response status, Date Formats  . . . . . . . . . . . . . . .  79
     A.4.  Introduction of Content-Encoding  . . . . . . . . . . . .  79
     A.5.  No Content-Transfer-Encoding  . . . . . . . . . . . . . .  79
     A.6.  MHTML and Line Length Limitations . . . . . . . . . . . .  80
   Appendix B.  Additional Features  . . . . . . . . . . . . . . . .  80
   Appendix C.  Changes from RFC 2616  . . . . . . . . . . . . . . .  80
   Appendix D.  Imported ABNF  . . . . . . . . . . . . . . . . . . .  82
   Appendix E.  Collected ABNF . . . . . . . . . . . . . . . . . . .  83
   Appendix F.  Change Log (to be removed by RFC Editor before
                publication) . . . . . . . . . . . . . . . . . . . .  85
     F.1.  Since RFC 2616  . . . . . . . . . . . . . . . . . . . . .  85
     F.2.  Since draft-ietf-httpbis-p2-semantics-00  . . . . . . . .  86
     F.3.  Since draft-ietf-httpbis-p3-payload-00  . . . . . . . . .  86
     F.4.  Since draft-ietf-httpbis-p2-semantics-01  . . . . . . . .  87
     F.5.  Since draft-ietf-httpbis-p3-payload-01  . . . . . . . . .  88
     F.6.  Since draft-ietf-httpbis-p2-semantics-02  . . . . . . . .  88
     F.7.  Since draft-ietf-httpbis-p3-payload-02  . . . . . . . . .  89
     F.8.  Since draft-ietf-httpbis-p2-semantics-03  . . . . . . . .  89
     F.9.  Since draft-ietf-httpbis-p3-payload-03  . . . . . . . . .  89
     F.10. Since draft-ietf-httpbis-p2-semantics-04  . . . . . . . .  90
     F.11. Since draft-ietf-httpbis-p3-payload-04  . . . . . . . . .  90
     F.12. Since draft-ietf-httpbis-p2-semantics-05  . . . . . . . .  91
     F.13. Since draft-ietf-httpbis-p3-payload-05  . . . . . . . . .  91
     F.14. Since draft-ietf-httpbis-p2-semantics-06  . . . . . . . .  91
     F.15. Since draft-ietf-httpbis-p3-payload-06  . . . . . . . . .  92
     F.16. Since draft-ietf-httpbis-p2-semantics-07  . . . . . . . .  92
     F.17. Since draft-ietf-httpbis-p3-payload-07  . . . . . . . . .  92
     F.18. Since draft-ietf-httpbis-p2-semantics-08  . . . . . . . .  93
     F.19. Since draft-ietf-httpbis-p3-payload-08  . . . . . . . . .  93
     F.20. Since draft-ietf-httpbis-p2-semantics-09  . . . . . . . .  93
     F.21. Since draft-ietf-httpbis-p3-payload-09  . . . . . . . . .  94
     F.22. Since draft-ietf-httpbis-p2-semantics-10  . . . . . . . .  94
     F.23. Since draft-ietf-httpbis-p3-payload-10  . . . . . . . . .  95
     F.24. Since draft-ietf-httpbis-p2-semantics-11  . . . . . . . .  95
     F.25. Since draft-ietf-httpbis-p3-payload-11  . . . . . . . . .  96
     F.26. Since draft-ietf-httpbis-p2-semantics-12  . . . . . . . .  96
     F.27. Since draft-ietf-httpbis-p3-payload-12  . . . . . . . . .  97
     F.28. Since draft-ietf-httpbis-p2-semantics-13  . . . . . . . .  97
     F.29. Since draft-ietf-httpbis-p3-payload-13  . . . . . . . . .  98
     F.30. Since draft-ietf-httpbis-p2-semantics-14  . . . . . . . .  98
     F.31. Since draft-ietf-httpbis-p3-payload-14  . . . . . . . . .  98
     F.32. Since draft-ietf-httpbis-p2-semantics-15  . . . . . . . .  98
     F.33. Since draft-ietf-httpbis-p3-payload-15  . . . . . . . . .  99
     F.34. Since draft-ietf-httpbis-p2-semantics-16  . . . . . . . .  99
     F.35. Since draft-ietf-httpbis-p3-payload-16  . . . . . . . . .  99
     F.36. Since draft-ietf-httpbis-p2-semantics-17  . . . . . . . .  99
     F.37. Since draft-ietf-httpbis-p3-payload-17  . . . . . . . . . 100
     F.38. Since draft-ietf-httpbis-p2-semantics-18  . . . . . . . . 100
     F.39. Since draft-ietf-httpbis-p3-payload-18  . . . . . . . . . 101
     F.40. Since draft-ietf-httpbis-p2-semantics-19 and
           draft-ietf-httpbis-p3-payload-19  . . . . . . . . . . . . 101
   Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

1.  Introduction

   Each HTTP message is either a request or a response.  A server
   listens on a connection for a request, parses each message received,
   interprets the message semantics in relation to the identified
   request target, and responds to that request with one or more
   response messages.  This document defines HTTP/1.1 request and
   response semantics in terms of the architecture, syntax notation, and
   conformance criteria defined in [Part1].

   HTTP provides a uniform interface for interacting with resources
   regardless of their type, nature, or implementation.  HTTP semantics
   includes the intentions defined by each request method, extensions to
   those semantics that might be described in request header fields, the
   meaning of status codes to indicate a machine-readable response, and
   additional control data and resource metadata that might be given in
   response header fields.

   In addition, this document defines the payload of messages (a.k.a.,
   content), the associated metadata header fields that define how the
   payload is intended to be interpreted by a recipient, the request
   header fields that might influence content selection, and the various
   selection algorithms that are collectively referred to as "content
   negotiation".

      Note: This document is currently disorganized in order to minimize
      changes between drafts and enable reviewers to see the smaller
      errata changes.  A future draft will reorganize the sections to
      better reflect the content.  In particular, the sections will be
      ordered according to the typical processing of an HTTP request
      message (after message parsing): resource mapping, methods,
      request modifying header fields, response status, status modifying
      header fields, and resource metadata.  The current mess reflects
      how widely dispersed these topics and associated requirements had
      become in [RFC2616].

1.1.  Conformance and Error Handling

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This specification targets conformance criteria according to the role
   of a participant in HTTP communication.  Hence, HTTP requirements are
   placed on senders, recipients, clients, servers, user agents,
   intermediaries, origin servers, proxies, gateways, or caches,
   depending on what behavior is being constrained by the requirement.
   See Section 2 of [Part1] for definitions of these terms.

   The verb "generate" is used instead of "send" where a requirement
   differentiates between creating a protocol element and merely
   forwarding a received element downstream.

   An implementation is considered conformant if it complies with all of
   the requirements associated with the roles it partakes in HTTP.  Note
   that SHOULD-level requirements are relevant here, unless one of the
   documented exceptions is applicable.

   This document also uses ABNF to define valid protocol elements
   (Section 1.2).  In addition to the prose requirements placed upon
   them, senders MUST NOT generate protocol elements that do not match
   the grammar defined by the ABNF rules for those protocol elements
   that are applicable to the sender's role.  If a received protocol
   element is processed, the recipient MUST be able to parse any value
   that would match the ABNF rules for that protocol element, excluding
   only those rules not applicable to the recipient's role.

   Unless noted otherwise, a recipient MAY attempt to recover a usable
   protocol element from an invalid construct.  HTTP does not define
   specific error handling mechanisms except when they have a direct
   impact on security, since different applications of the protocol
   require different error handling strategies.  For example, a Web
   browser might wish to transparently recover from a response where the
   Location header field doesn't parse according to the ABNF, whereas a
   systems control client might consider any form of error recovery to
   be dangerous.

1.2.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234] with the list rule extension defined in Section
   1.2 of [Part1].  Appendix D describes rules imported from other
   documents.  Appendix E shows the collected ABNF with the list rule
   expanded.

2.  Methods

   The method token indicates the request method to be performed on the
   target resource (Section 5.5 of [Part1]).  The method is case-
   sensitive.

     method         = token

   The list of methods allowed by a resource can be specified in an
   Allow header field (Section 9.5).  The status code of the response
   always notifies the client whether a method is currently allowed on a
   resource, since the set of allowed methods can change dynamically.

   An origin server SHOULD respond with the status code 405 (Method Not
   Allowed) if the method is known by the origin server but not allowed
   for the resource, and 501 (Not Implemented) if the method is
   unrecognized or not implemented by the origin server.  The methods
   GET and HEAD MUST be supported by all general-purpose servers.  All
   other methods are OPTIONAL; however, if the above methods are
   implemented, they MUST be implemented with the same semantics as
   those specified in Section 2.3.

2.1.  Safe and Idempotent Methods

2.1.1.  Safe Methods

   Implementers need to be aware that the software represents the user
   in their interactions over the Internet, and need to allow the user
   to be aware of any actions they take which might have an unexpected
   significance to themselves or others.

   In particular, the convention has been established that the GET,
   HEAD, OPTIONS, and TRACE request methods SHOULD NOT have the
   significance of taking an action other than retrieval.  These request
   methods ought to be considered "safe".  This allows user agents to
   represent other methods, such as POST, PUT and DELETE, in a special
   way, so that the user is made aware of the fact that a possibly
   unsafe action is being requested.

   Naturally, it is not possible to ensure that the server does not
   generate side-effects as a result of performing a GET request; in
   fact, some dynamic resources consider that a feature.  The important
   distinction here is that the user did not request the side-effects,
   so therefore cannot be held accountable for them.

2.1.2.  Idempotent Methods

   Request methods can also have the property of "idempotence" in that,
   aside from error or expiration issues, the intended effect of
   multiple identical requests is the same as for a single request.
   PUT, DELETE, and all safe request methods are idempotent.  It is
   important to note that idempotence refers only to changes requested
   by the client: a server is free to change its state due to multiple
   requests for the purpose of tracking those requests, versioning of
   results, etc.

2.2.  Method Registry

   The HTTP Method Registry defines the name space for the method token
   in the Request line of an HTTP request.

   Registrations MUST include the following fields:

   o  Method Name (see Section 2)

   o  Safe ("yes" or "no", see Section 2.1.1)

   o  Idempotent ("yes" or "no", see Section 2.1.1)

   o  Pointer to specification text

   Values to be added to this name space require IETF Review (see
   [RFC5226], Section 4.1).

   The registry itself is maintained at
   <http://www.iana.org/assignments/http-methods>.

2.2.1.  Considerations for New Methods

   When it is necessary to express new semantics for a HTTP request that
   aren't specific to a single application or media type, and currently
   defined methods are inadequate, it might be appropriate to register a
   new method.

   HTTP methods are generic; that is, they are potentially applicable to
   any resource, not just one particular media type, "type" of resource,
   or application.  As such, it is preferred that new HTTP methods be
   registered in a document that isn't specific to a single application,
   so that this is clear.

   Due to the parsing rules defined in Section 3.3 of [Part1],
   definitions of HTTP methods cannot prohibit the presence of a message
   body on either the request or the response message (with responses to
   HEAD requests being the single exception).  Definitions of new
   methods cannot change this rule, but they can specify that only zero-
   length bodies (as opposed to absent bodies) are allowed.

   New method definitions need to indicate whether they are safe
   (Section 2.1.1), what semantics (if any) the request body has, and
   whether they are idempotent (Section 2.1.2).  They also need to state
   whether they can be cached ([Part6]); in particular under what
   conditions a cache can store the response, and under what conditions
   such a stored response can be used to satisfy a subsequent request.

2.3.  Method Definitions
2.3.1.  OPTIONS

   The OPTIONS method requests information about the communication
   options available on the request/response chain identified by the
   effective request URI.  This method allows a client to determine the
   options and/or requirements associated with a resource, or the
   capabilities of a server, without implying a resource action or
   initiating a resource retrieval.

   Responses to the OPTIONS method are not cacheable.

   If the OPTIONS request includes a message body (as indicated by the
   presence of Content-Length or Transfer-Encoding), then the media type
   MUST be indicated by a Content-Type field.  Although this
   specification does not define any use for such a body, future
   extensions to HTTP might use the OPTIONS body to make more detailed
   queries on the server.

   If the request-target (Section 5.3 of [Part1]) is an asterisk ("*"),
   the OPTIONS request is intended to apply to the server in general
   rather than to a specific resource.  Since a server's communication
   options typically depend on the resource, the "*" request is only
   useful as a "ping" or "no-op" type of method; it does nothing beyond
   allowing the client to test the capabilities of the server.  For
   example, this can be used to test a proxy for HTTP/1.1 conformance
   (or lack thereof).

   If the request-target is not an asterisk, the OPTIONS request applies
   only to the options that are available when communicating with that
   resource.

   A 200 (OK) response SHOULD include any header fields that indicate
   optional features implemented by the server and applicable to that
   resource (e.g., Allow), possibly including extensions not defined by
   this specification.  The response body, if any, SHOULD also include
   information about the communication options.  The format for such a
   body is not defined by this specification, but might be defined by
   future extensions to HTTP.  Content negotiation MAY be used to select
   the appropriate response format.  If no response body is included,
   the response MUST include a Content-Length field with a field-value
   of "0".

   The Max-Forwards header field MAY be used to target a specific proxy
   in the request chain (see Section 9.14).  If no Max-Forwards field is
   present in the request, then the forwarded request MUST NOT include a
   Max-Forwards field.

2.3.2.  GET

   The GET method requests transfer of a current representation of the
   target resource.

   If the target resource is a data-producing process, it is the
   produced data which shall be returned as the representation in the
   response and not the source text of the process, unless that text
   happens to be the output of the process.

   The semantics of the GET method change to a "conditional GET" if the
   request message includes an If-Modified-Since, If-Unmodified-Since,
   If-Match, If-None-Match, or If-Range header field ([Part4]).  A
   conditional GET requests that the representation be transferred only
   under the circumstances described by the conditional header field(s).
   The conditional GET request is intended to reduce unnecessary network
   usage by allowing cached representations to be refreshed without
   requiring multiple requests or transferring data already held by the
   client.

   The semantics of the GET method change to a "partial GET" if the
   request message includes a Range header field ([Part5]).  A partial
   GET requests that only part of the representation be transferred, as
   described in Section 5.4 of [Part5].  The partial GET request is
   intended to reduce unnecessary network usage by allowing partially-
   retrieved representations to be completed without transferring data
   already held by the client.

   Bodies on GET requests have no defined semantics.  Note that sending
   a body on a GET request might cause some existing implementations to
   reject the request.

   The response to a GET request is cacheable and MAY be used to satisfy
   subsequent GET and HEAD requests (see [Part6]).

   See Section 11.2 for security considerations when used for forms.

2.3.3.  HEAD

   The HEAD method is identical to GET except that the server MUST NOT
   return a message body in the response.  The metadata contained in the
   HTTP header fields in response to a HEAD request SHOULD be identical
   to the information sent in response to a GET request.  This method
   can be used for obtaining metadata about the representation implied
   by the request without transferring the representation body.  This
   method is often used for testing hypertext links for validity,
   accessibility, and recent modification.

   The response to a HEAD request is cacheable and MAY be used to
   satisfy a subsequent HEAD request.  It also has potential side
   effects on previously stored responses to GET; see Section 5 of
   [Part6].

   Bodies on HEAD requests have no defined semantics.  Note that sending
   a body on a HEAD request might cause some existing implementations to
   reject the request.

2.3.4.  POST

   The POST method requests that the origin server accept the
   representation enclosed in the request as data to be processed by the
   target resource.  POST is designed to allow a uniform method to cover
   the following functions:

   o  Annotation of existing resources;

   o  Posting a message to a bulletin board, newsgroup, mailing list, or
      similar group of articles;

   o  Providing a block of data, such as the result of submitting a
      form, to a data-handling process;

   o  Extending a database through an append operation.

   The actual function performed by the POST method is determined by the
   server and is usually dependent on the effective request URI.

   The action performed by the POST method might not result in a
   resource that can be identified by a URI.  In this case, either 200
   (OK) or 204 (No Content) is the appropriate response status code,
   depending on whether or not the response includes a representation
   that describes the result.

   If a resource has been created on the origin server, the response
   SHOULD be 201 (Created) and contain a representation which describes
   the status of the request and refers to the new resource, and a
   Location header field (see Section 9.13).

   Responses to POST requests are only cacheable when they include
   explicit freshness information (see Section 4.1.1 of [Part6]).  A
   cached POST response with a Content-Location header field (see
   Section 9.8) whose value is the effective Request URI MAY be used to
   satisfy subsequent GET and HEAD requests.

   Note that POST caching is not widely implemented.  However, the 303
   (See Other) response can be used to direct the user agent to retrieve
   a cacheable representation of the resource.

2.3.5.  PUT

   The PUT method requests that the state of the target resource be
   created or replaced with the state defined by the representation
   enclosed in the request message payload.  A successful PUT of a given
   representation would suggest that a subsequent GET on that same
   target resource will result in an equivalent representation being
   returned in a 200 (OK) response.  However, there is no guarantee that
   such a state change will be observable, since the target resource
   might be acted upon by other user agents in parallel, or might be
   subject to dynamic processing by the origin server, before any
   subsequent GET is received.  A successful response only implies that
   the user agent's intent was achieved at the time of its processing by
   the origin server.

   If the target resource does not have a current representation and the
   PUT successfully creates one, then the origin server MUST inform the
   user agent by sending a 201 (Created) response.  If the target
   resource does have a current representation and that representation
   is successfully modified in accordance with the state of the enclosed
   representation, then either a 200 (OK) or 204 (No Content) response
   SHOULD be sent to indicate successful completion of the request.

   Unrecognized header fields SHOULD be ignored (i.e., not saved as part
   of the resource state).

   An origin server SHOULD verify that the PUT representation is
   consistent with any constraints which the server has for the target
   resource that cannot or will not be changed by the PUT.  This is
   particularly important when the origin server uses internal
   configuration information related to the URI in order to set the
   values for representation metadata on GET responses.  When a PUT
   representation is inconsistent with the target resource, the origin
   server SHOULD either make them consistent, by transforming the
   representation or changing the resource configuration, or respond
   with an appropriate error message containing sufficient information
   to explain why the representation is unsuitable.  The 409 (Conflict)
   or 415 (Unsupported Media Type) status codes are suggested, with the
   latter being specific to constraints on Content-Type values.

   For example, if the target resource is configured to always have a
   Content-Type of "text/html" and the representation being PUT has a
   Content-Type of "image/jpeg", then the origin server SHOULD do one
   of:

   a.  reconfigure the target resource to reflect the new media type;

   b.  transform the PUT representation to a format consistent with that
       of the resource before saving it as the new resource state; or,

   c.  reject the request with a 415 (Unsupported Media Type) response
       indicating that the target resource is limited to "text/html",
       perhaps including a link to a different resource that would be a
       suitable target for the new representation.

   HTTP does not define exactly how a PUT method affects the state of an
   origin server beyond what can be expressed by the intent of the user
   agent request and the semantics of the origin server response.  It
   does not define what a resource might be, in any sense of that word,
   beyond the interface provided via HTTP.  It does not define how
   resource state is "stored", nor how such storage might change as a
   result of a change in resource state, nor how the origin server
   translates resource state into representations.  Generally speaking,
   all implementation details behind the resource interface are
   intentionally hidden by the server.

   The fundamental difference between the POST and PUT methods is
   highlighted by the different intent for the target resource.  The
   target resource in a POST request is intended to handle the enclosed
   representation as a data-accepting process, such as for a gateway to
   some other protocol or a document that accepts annotations.  In
   contrast, the target resource in a PUT request is intended to take
   the enclosed representation as a new or replacement value.  Hence,
   the intent of PUT is idempotent and visible to intermediaries, even
   though the exact effect is only known by the origin server.

   Proper interpretation of a PUT request presumes that the user agent
   knows what target resource is desired.  A service that is intended to
   select a proper URI on behalf of the client, after receiving a state-
   changing request, SHOULD be implemented using the POST method rather
   than PUT.  If the origin server will not make the requested PUT state
   change to the target resource and instead wishes to have it applied
   to a different resource, such as when the resource has been moved to
   a different URI, then the origin server MUST send a 301 (Moved
   Permanently) response; the user agent MAY then make its own decision
   regarding whether or not to redirect the request.

   A PUT request applied to the target resource MAY have side-effects on
   other resources.  For example, an article might have a URI for
   identifying "the current version" (a resource) which is separate from
   the URIs identifying each particular version (different resources
   that at one point shared the same state as the current version
   resource).  A successful PUT request on "the current version" URI
   might therefore create a new version resource in addition to changing
   the state of the target resource, and might also cause links to be
   added between the related resources.

   An origin server SHOULD reject any PUT request that contains a
   Content-Range header field (Section 5.2 of [Part5]), since it might
   be misinterpreted as partial content (or might be partial content
   that is being mistakenly PUT as a full representation).  Partial
   content updates are possible by targeting a separately identified
   resource with state that overlaps a portion of the larger resource,
   or by using a different method that has been specifically defined for
   partial updates (for example, the PATCH method defined in [RFC5789]).

   Responses to the PUT method are not cacheable.  If a PUT request
   passes through a cache that has one or more stored responses for the
   effective request URI, those stored responses will be invalidated
   (see Section 6 of [Part6]).

2.3.6.  DELETE

   The DELETE method requests that the origin server delete the target
   resource.  This method MAY be overridden by human intervention (or
   other means) on the origin server.  The client cannot be guaranteed
   that the operation has been carried out, even if the status code
   returned from the origin server indicates that the action has been
   completed successfully.  However, the server SHOULD NOT indicate
   success unless, at the time the response is given, it intends to
   delete the resource or move it to an inaccessible location.

   A successful response SHOULD be 200 (OK) if the response includes a
   representation describing the status, 202 (Accepted) if the action
   has not yet been enacted, or 204 (No Content) if the action has been
   enacted but the response does not include a representation.

   Bodies on DELETE requests have no defined semantics.  Note that
   sending a body on a DELETE request might cause some existing
   implementations to reject the request.

   Responses to the DELETE method are not cacheable.  If a DELETE
   request passes through a cache that has one or more stored responses
   for the effective request URI, those stored responses will be
   invalidated (see Section 6 of [Part6]).

2.3.7.  TRACE

   The TRACE method requests a remote, application-layer loop-back of
   the request message.  The final recipient of the request SHOULD
   reflect the message received back to the client as the message body
   of a 200 (OK) response.  The final recipient is either the origin
   server or the first proxy to receive a Max-Forwards value of zero (0)
   in the request (see Section 9.14).  A TRACE request MUST NOT include
   a message body.

   TRACE allows the client to see what is being received at the other
   end of the request chain and use that data for testing or diagnostic
   information.  The value of the Via header field (Section 6.2 of
   [Part1]) is of particular interest, since it acts as a trace of the
   request chain.  Use of the Max-Forwards header field allows the
   client to limit the length of the request chain, which is useful for
   testing a chain of proxies forwarding messages in an infinite loop.

   If the request is valid, the response SHOULD have a Content-Type of
   "message/http" (see Section 7.3.1 of [Part1]) and contain a message
   body that encloses a copy of the entire request message.  Responses
   to the TRACE method are not cacheable.

2.3.8.  CONNECT

   The CONNECT method requests that the proxy establish a tunnel to the
   request-target and, if successful, thereafter restrict its behavior
   to blind forwarding of packets until the connection is closed.

   When using CONNECT, the request-target MUST use the authority form
   (Section 5.3 of [Part1]); i.e., the request-target consists of only
   the host name and port number of the tunnel destination, separated by
   a colon.  For example,

     CONNECT server.example.com:80 HTTP/1.1
     Host: server.example.com:80

   Any 2xx (Successful) response to a CONNECT request indicates that the
   proxy has established a connection to the requested host and port,
   and has switched to tunneling the current connection to that server
   connection.  The tunneled data from the server begins immediately
   after the blank line that concludes the successful response's header
   block.

   A server SHOULD NOT send any Transfer-Encoding or Content-Length
   header fields in a successful response.  A client MUST ignore any
   Content-Length or Transfer-Encoding header fields received in a
   successful response.

   Any response other than a successful response indicates that the
   tunnel has not yet been formed and that the connection remains
   governed by HTTP.

   Proxy authentication might be used to establish the authority to
   create a tunnel:

     CONNECT server.example.com:80 HTTP/1.1
     Host: server.example.com:80
     Proxy-Authorization: basic aGVsbG86d29ybGQ=

   A message body on a CONNECT request has no defined semantics.
   Sending a body on a CONNECT request might cause existing
   implementations to reject the request.

   Similar to a pipelined HTTP/1.1 request, data to be tunneled from
   client to server MAY be sent immediately after the request (before a
   response is received).  The usual caveats also apply: data can be
   discarded if the eventual response is negative, and the connection
   can be reset with no response if more than one TCP segment is
   outstanding.

   It might be the case that the proxy itself can only reach the
   requested origin server through another proxy.  In this case, the
   first proxy SHOULD make a CONNECT request of that next proxy,
   requesting a tunnel to the authority.  A proxy MUST NOT respond with
   any 2xx status code unless it has either a direct or tunnel
   connection established to the authority.

   If at any point either one of the peers gets disconnected, any
   outstanding data that came from that peer will be passed to the other
   one, and after that also the other connection will be terminated by
   the proxy.  If there is outstanding data to that peer undelivered,
   that data will be discarded.

   An origin server which receives a CONNECT request for itself MAY
   respond with a 2xx status modifying code to indicate that a connection is
   established.  However, most origin servers do not implement CONNECT.

3.  Header Fields

   Header fields are key value pairs that can be used to communicate
   data about the message, its payload, the target resource, or about
   the connection itself (i.e., control data).  See Section 3.2 of
   [Part1] for a general definition of their syntax.

3.1.  Considerations for Creating Header Fields

   New header fields are registered using the procedures described in
   [RFC3864].

   The requirements for header field names are defined in Section 4.1 of
   [RFC3864].  Authors of specifications defining new fields are advised
   to keep the name as short as practical, and not to prefix them with
   "X-" if they are to be registered (either immediately or in the
   future).

   New header field values typically have their syntax defined using
   ABNF ([RFC5234]), using the extension defined in Appendix B of
   [Part1] as necessary, and are usually constrained to the range of
   ASCII characters.  Header fields needing a greater range of
   characters can use an encoding such as the one defined in [RFC5987].

   Because commas (",") are used as a generic delimiter between field-
   values, they need to be treated with care if they are allowed in the
   field-value's payload.  Typically, components that might contain a
   comma are protected with double-quotes using the quoted-string ABNF
   production (Section 3.2.4 of [Part1]).

   For example, a textual date and a URI (either of which might contain
   a comma) could be safely carried in field-values like these:

     Example-URI-Field: "http://example.com/a.html,foo",
                        "http://without-a-comma.example.com/"
     Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"

   Note that double quote delimiters almost always are used with the
   quoted-string production; using a different syntax inside double
   quotes will likely cause unnecessary confusion.

   Many header fields, and resource
   metadata.  The current mess reflects how widely dispersed these
   topics and associated requirements had become fields use a format including (case-insensitively) named
   parameters (for instance, Content-Type, defined in [RFC2616].

1.1.  Conformance and Error Handling

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", Section 9.9).
   Allowing both unquoted (token) and "OPTIONAL" quoted (quoted-string) syntax for
   the parameter value enables recipients to use existing parser
   components.  When allowing both forms, the meaning of a parameter
   value ought to be independent of the syntax used for it (for an
   example, see the notes on parameter handling for media types in this
   document
   Section 5.5).

   Authors of specifications defining new header fields are advised to
   consider documenting:

   o  Whether the field is a single value, or whether it can be interpreted a list
      (delimited by commas; see Section 3.2 of [Part1]).

      If it does not use the list syntax, document how to treat messages
      where the header field occurs multiple times (a sensible default
      would be to ignore the header field, but this might not always be
      the right choice).

      Note that intermediaries and software libraries might combine
      multiple header field instances into a single one, despite the
      header field not allowing this.  A robust format enables
      recipients to discover these situations (good example: "Content-
      Type", as the comma can only appear inside quoted strings; bad
      example: "Location", as described a comma can occur inside a URI).

   o  Under what conditions the header field can be used; e.g., only in [RFC2119].

   This document defines conformance criteria for several roles
      responses or requests, in HTTP
   communication, including Senders, Recipients, Clients, Servers, User-
   Agents, Origin Servers, Intermediaries, Proxies and Gateways.  See
   Section 2 of [Part1] for definitions of these terms.

   An implementation is considered conformant if it complies with all of messages, only on responses to a
      particular request method.

   o  Whether it is appropriate to list the requirements associated with its role(s).  Note that SHOULD-level
   requirements are relevant here, unless one of field-name in the documented
   exceptions Connection
      header field (i.e., if the header field is applicable.

   This document also uses ABNF to define valid protocol elements
   (Section 1.2).  In addition to the prose requirements placed upon
   them, Senders MUST NOT generate protocol elements that be hop-by-hop, see
      Section 6.1 of [Part1]).

   o  Under what conditions intermediaries are invalid.

   Unless noted otherwise, Recipients MAY take steps allowed to recover a usable
   protocol element from an invalid construct.  However, HTTP does not
   define specific error handling mechanisms, except in cases where it
   has direct impact on security.  This modify the
      header field's value, insert or delete it.

   o  How the header field might interact with caching (see [Part6]).

   o  Whether the header field is because different uses useful or allowable in trailers (see
      Section 4.1 of [Part1]).

   o  Whether the
   protocol require different error handling strategies; for example, a
   Web browser may wish to transparently recover from a response where
   the Location header field doesn't parse according ought to be preserved across redirects.

3.2.  Request Header Fields

   The request header fields allow the client to pass additional
   information about the ABNF,
   whereby in a systems control protocol using HTTP, this type of error
   recovery could lead request, and about the client itself, to dangerous consequences.

1.2.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234]
   server.  These fields act as request modifiers, with semantics
   equivalent to the list rule extension defined in parameters on a programming language method
   invocation.

   +---------------------+------------------------+
   | Header Field Name   | Defined in...          |
   +---------------------+------------------------+
   | Accept              | Section
   1.2 9.1            |
   | Accept-Charset      | Section 9.2            |
   | Accept-Encoding     | Section 9.3            |
   | Accept-Language     | Section 9.4            |
   | Authorization       | Section 4.1 of [Part1].  Appendix B shows the collected ABNF with the list
   rule expanded.

   The following core rules are included by reference, as defined in
   [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
   (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line
   feed), OCTET (any 8-bit sequence [Part7] |
   | Expect              | Section 9.11           |
   | From                | Section 9.12           |
   | Host                | Section 5.4 of data), SP (space), and VCHAR (any
   visible US-ASCII character).

1.2.1.  Core Rules

   The core rules below are defined in [Part1]:

     BWS           = <BWS, defined in [Part1], [Part1] |
   | If-Match            | Section 3.2.1>
     OWS           = <OWS, defined in [Part1], 3.1 of [Part4] |
   | If-Modified-Since   | Section 3.2.1>
     RWS           = <RWS, defined in [Part1], 3.3 of [Part4] |
   | If-None-Match       | Section 3.2.1>
     obs-text      = <obs-text, defined in [Part1], 3.2 of [Part4] |
   | If-Range            | Section 3.2.4>
     quoted-string = <quoted-string, defined in [Part1], 5.3 of [Part5] |
   | If-Unmodified-Since | Section 3.4 of [Part4] |
   | Max-Forwards        | Section 3.2.4>
     token         = <token, defined in [Part1], 9.14           |
   | Proxy-Authorization | Section 3.2.4>

1.2.2.  ABNF Rules defined in other Parts 4.3 of the Specification

   The ABNF rules below are defined in other parts:

     absolute-URI  = <absolute-URI, defined in [Part1], [Part7] |
   | Range               | Section 2.7>
     comment       = <comment, defined in [Part1], 5.4 of [Part5] |
   | Referer             | Section 3.2.4>
     partial-URI   = <partial-URI, defined in [Part1], 9.15           |
   | TE                  | Section 2.7>
     URI-reference = <URI-reference, defined in [Part1], 4.3 of [Part1] |
   | User-Agent          | Section 2.7>

2.  Method 9.18           |
   +---------------------+------------------------+

3.3.  Response Header Fields

   The method token indicates response header fields allow the request method server to be performed on pass additional
   information about the
   target resource (Section 5.5 of [Part1]).  The method is case-
   sensitive.

     method         = token

   The list of methods allowed by a resource can response which cannot be specified placed in an
   Allow header field (Section 10.1).  The status code of the response
   always notifies the client whether a method is currently allowed on a
   resource, since the set of allowed methods can change dynamically.
   An origin server SHOULD respond with the status code 405 (Method Not
   Allowed) if the method is known by status-
   line.  These header fields give information about the origin server but not allowed
   for the resource, and 501 (Not Implemented) if the method is
   unrecognized or not implemented by the origin server.  The methods
   GET and HEAD MUST be supported by all general-purpose servers.  All
   other methods are OPTIONAL; however, if the above methods are
   implemented, they MUST be implemented with
   about further access to the same semantics as
   those specified in Section 6.

2.1.  Overview target resource (Section 5.5 of Methods

   The methods listed below are defined in Section 6.

   +-------------+---------------+ [Part1]).

   +--------------------+------------------------+
   | Method Header Field Name  | Defined in...          |
   +-------------+---------------+
   +--------------------+------------------------+
   | OPTIONS Accept-Ranges      | Section 6.2 5.1 of [Part5] |
   | GET Age                | Section 6.3 7.1 of [Part6] |
   | HEAD Allow              | Section 6.4 9.5            |
   | POST Date               | Section 6.5 9.10           |
   | PUT ETag               | Section 6.6 2.3 of [Part4] |
   | DELETE Location           | Section 6.7 9.13           |
   | TRACE Proxy-Authenticate | Section 6.8 4.2 of [Part7] |
   | CONNECT Retry-After        | Section 6.9 9.16           |
   | Server             |
   +-------------+---------------+

   Note that this list is not exhaustive -- it does not include request
   methods defined in other specifications.

2.2.  Method Registry

   The HTTP Method Registry defines the name space for the method token
   in the Request line of an HTTP request.

   Registrations MUST include the following fields:

   o  Method Name (see Section 2)

   o  Safe ("yes" or "no", see 9.17           |
   | Vary               | Section 6.1.1)

   o  Pointer to specification text

   Values to be added to this name space require IETF Review (see
   [RFC5226], 7.5 of [Part6] |
   | WWW-Authenticate   | Section 4.1). 4.4 of [Part7] |
   +--------------------+------------------------+

4.  Status Codes

   The registry itself is maintained at
   <http://www.iana.org/assignments/http-methods>.

2.2.1.  Considerations for New Methods

   When it status-code element is necessary to express new semantics for a HTTP request that
   aren't specific 3-digit integer result code of the
   attempt to a single application or media type, understand and currently
   defined methods are inadequate, it may be appropriate to register a
   new method. satisfy the request.

   HTTP methods status codes are generic; that is, they extensible.  HTTP applications are potentially applicable to
   any resource, not just one particular media type, "type" of resource,
   or application.  As such, it is preferred that new HTTP methods be
   registered in a document that isn't specific to a single application,
   so that this is clear.

   Due required
   to understand the parsing rules defined in Section 3.3 of [Part1],
   definitions meaning of HTTP methods cannot prohibit all registered status codes, though such
   understanding is obviously desirable.  However, applications MUST
   understand the presence class of a message
   body on either the request or any status code, as indicated by the first
   digit, and treat any unrecognized response message (with responses to
   HEAD requests as being equivalent to the single exception).  Definitions
   x00 status code of new
   methods cannot change this rule, but they can specify that only zero-
   length bodies (as opposed to absent bodies) are allowed.

   New method definitions need to indicate whether they are safe
   (Section 6.1.1), what semantics (if any) class, with the exception that an
   unrecognized response MUST NOT be cached.  For example, if an
   unrecognized status code of 431 is received by the client, it can
   safely assume that there was something wrong with its request body has, and
   whether they are idempotent (Section 6.1.2).  They also need to state
   whether they can be cached ([Part6]); in particular what conditions
   treat the response as if it had received a
   cache may store 400 status code.  In such
   cases, user agents SHOULD present to the user the representation
   enclosed with the response, since that representation is likely to
   include human-readable information which will explain the unusual
   status.

   The first digit of the status-code defines the class of response.
   The last two digits do not have any categorization role.  There are 5
   values for the first digit:

   o  1xx (Informational): Request received, continuing process

   o  2xx (Successful): The action was successfully received,
      understood, and under what conditions such a stored
   response may be used accepted

   o  3xx (Redirection): Further action needs to satisfy a subsequent request.

3.  Header Fields

   Header fields are key value pairs that can be used taken in order to communicate
   data about the message, its payload,
      complete the target resource, request

   o  4xx (Client Error): The request contains bad syntax or about cannot be
      fulfilled

   o  5xx (Server Error): The server failed to fulfill an apparently
      valid request

   For most status codes the connection itself (i.e., control data).  See Section 3.2 of
   [Part1] for response can carry a general definition of their syntax.

3.1.  Considerations for Creating Header Fields

   New header fields are registered using the procedures described payload, in
   [RFC3864].

   The requirements for which case
   a Content-Type header field names indicates the payload's media type
   (Section 9.9).

4.1.  Overview of Status Codes

   The status codes listed below are defined in this specification,
   Section 4 of [Part4], Section 3 of [Part5], and Section 3 of [Part7].
   The reason phrases listed here are only recommendations -- they can
   be replaced by local equivalents without affecting the protocol.

   +-------------+------------------------------+----------------------+
   | status-code | reason-phrase                | Defined in...        |
   +-------------+------------------------------+----------------------+
   | 100         | Continue                     | Section 4.3.1        |
   | 101         | Switching Protocols          | Section 4.3.2        |
   | 200         | OK                           | Section 4.4.1        |
   | 201         | Created                      | Section 4.4.2        |
   | 202         | Accepted                     | Section 4.4.3        |
   | 203         | Non-Authoritative            | Section 4.4.4        |
   |             | Information                  |                      |
   | 204         | No Content                   | Section 4.4.5        |
   | 205         | Reset Content                | Section 4.4.6        |
   | 206         | Partial Content              | Section 3.1 of       |
   |             |                              | [Part5]              |
   | 300         | Multiple Choices             | Section 4.5.1        |
   | 301         | Moved Permanently            | Section 4.5.2        |
   | 302         | Found                        | Section 4.5.3        |
   | 303         | See Other                    | Section 4.5.4        |
   | 304         | Not Modified                 | Section 4.1 of
   [RFC3864].  Authors of specifications defining new fields are advised
   to keep the name as short as practical, and not to prefix them with
   "X-" if they are to be registered (either immediately or in the
   future).

   New header field values typically have their syntax defined using
   ABNF ([RFC5234]), using the extension defined in       |
   |             |                              | [Part4]              |
   | 305         | Use Proxy                    | Section 3.2.5 of
   [Part1] as necessary, and are usually constrained to the range 4.5.5        |
   | 307         | Temporary Redirect           | Section 4.5.7        |
   | 400         | Bad Request                  | Section 4.6.1        |
   | 401         | Unauthorized                 | Section 3.1 of
   ASCII characters.  Header fields needing a greater range       |
   |             |                              | [Part7]              |
   | 402         | Payment Required             | Section 4.6.2        |
   | 403         | Forbidden                    | Section 4.6.3        |
   | 404         | Not Found                    | Section 4.6.4        |
   | 405         | Method Not Allowed           | Section 4.6.5        |
   | 406         | Not Acceptable               | Section 4.6.6        |
   | 407         | Proxy Authentication         | Section 3.2 of
   characters can use an encoding such as the one defined in [RFC5987].

   Because commas (",") are used as a generic delimiter between field-
   values, they need to be treated with care if they are allowed in the
   field-value's payload.  Typically, components that might contain a
   comma are protected with double-quotes using the quoted-string ABNF
   production (Section 3.2.4       |
   |             | Required                     | [Part7]              |
   | 408         | Request Time-out             | Section 4.6.7        |
   | 409         | Conflict                     | Section 4.6.8        |
   | 410         | Gone                         | Section 4.6.9        |
   | 411         | Length Required              | Section 4.6.10       |
   | 412         | Precondition Failed          | Section 4.2 of [Part1]).

   For example, a textual date and a       |
   |             |                              | [Part4]              |
   | 413         | Request Representation Too   | Section 4.6.11       |
   |             | Large                        |                      |
   | 414         | URI (either Too Long                 | Section 4.6.12       |
   | 415         | Unsupported Media Type       | Section 4.6.13       |
   | 416         | Requested range not          | Section 3.2 of which might contain
   a comma) could be safely carried in field-values like these:

     Example-URI-Field: "http://example.com/a.html,foo",
                        "http://without-a-comma.example.com/"
     Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"       |
   |             | satisfiable                  | [Part5]              |
   | 417         | Expectation Failed           | Section 4.6.14       |
   | 426         | Upgrade Required             | Section 4.6.15       |
   | 500         | Internal Server Error        | Section 4.7.1        |
   | 501         | Not Implemented              | Section 4.7.2        |
   | 502         | Bad Gateway                  | Section 4.7.3        |
   | 503         | Service Unavailable          | Section 4.7.4        |
   | 504         | Gateway Time-out             | Section 4.7.5        |
   | 505         | HTTP Version not supported   | Section 4.7.6        |
   +-------------+------------------------------+----------------------+

   Note that double quote delimiters almost always are used with the
   quoted-string production; using a different syntax inside double
   quotes will likely cause unnecessary confusion.

   Many header fields use a format including (case-insensitively) named
   parameters (for instance, Content-Type, this list is not exhaustive -- it does not include
   extension status codes defined in Section 6.8 of
   [Part3]).  Allowing both unquoted (token) and quoted (quoted-string)
   syntax other specifications.

4.2.  Status Code Registry

   The HTTP Status Code Registry defines the name space for the parameter value enables recipients to use existing
   parser components.  When allowing both forms, status-
   code token in the meaning status-line of a
   parameter value ought an HTTP response.

   Values to be independent of the syntax used added to this name space require IETF Review (see
   [RFC5226], Section 4.1).

   The registry itself is maintained at
   <http://www.iana.org/assignments/http-status-codes>.

4.2.1.  Considerations for New Status Codes

   When it
   (for an example, see the notes on parameter handling for media types
   in Section 2.3 of [Part3]).

   Authors of specifications defining is necessary to express new header fields are advised semantics for a HTTP response
   that aren't specific to
   consider documenting:

   o  Whether the field is a single value, application or whether it can be a list
      (delimited by commas; see Section 3.2 of [Part1]).

      If it does not use the list syntax, document how to treat messages
      where the header field occurs multiple times (a sensible default
      would be to ignore the header field, but this might not always be
      the right choice).

      Note that intermediaries media type, and software libraries might combine
      multiple header field instances into a single one, despite the
      header field not allowing this.  A robust format enables
      recipients to discover these situations (good example: "Content-
      Type", as the comma can only appear inside quoted strings; bad
      example: "Location", as a comma can occur inside
   currently defined status codes are inadequate, a URI).

   o  Under what conditions the header field new status code can
   be used; e.g., only in
      responses or requests, in all messages, only on responses registered.

   HTTP status codes are generic; that is, they are potentially
   applicable to a any resource, not just one particular request method.

   o  Whether media type,
   "type" of resource, or application.  As such, it is appropriate preferred that
   new HTTP status codes be registered in a document that isn't specific
   to list a single application, so that this is clear.

   Definitions of new HTTP status codes typically explain the field-name in request
   conditions that produce a response containing the Connection status code (e.g.,
   combinations of request header (i.e., if the fields and/or method(s)), along with
   any interactions with response header is to be hop-by-hop, see Section 6.1 fields (e.g., those that are
   required, those that modify the semantics of [Part1]).

   o  Under what conditions intermediaries the response).

   New HTTP status codes are allowed required to modify fall under one of the
      header field's value, insert or delete it.

   o  How
   categories defined in Section 4.  To allow existing parsers to
   properly handle them, new status codes cannot disallow a response
   body, although they can mandate a zero-length response body.  They
   can require the presence of one or more particular HTTP response
   header might interact with caching field(s).

   Likewise, their definitions can specify that caches are allowed to
   use heuristics to determine their freshness (see [Part6]).

   o  Whether the header field [Part6]; by default,
   it is useful or allowable in trailers not allowed), and can define how to determine the resource
   which they carry a representation for (see Section 4.1 7.1; by default,
   it is anonymous).

4.3.  Informational 1xx

   This class of status code indicates a provisional response,
   consisting only of [Part1]).

   o  Whether the header field should be preserved across redirects.

3.2.  Request Header Fields

   The request status-line and optional header fields, and is
   terminated by an empty line.  There are no required header fields allow the client for
   this class of status code.  Since HTTP/1.0 did not define any 1xx
   status codes, servers MUST NOT send a 1xx response to pass additional
   information about the request, and about the an HTTP/1.0
   client itself, except under experimental conditions.

   A client MUST be prepared to the
   server.  These fields act as request modifiers, with semantics
   equivalent accept one or more 1xx status responses
   prior to a regular response, even if the parameters on client does not expect a programming language method
   invocation.

   +---------------------+------------------------+
   | Header Field Name   | Defined in...          |
   +---------------------+------------------------+
   | Accept              | Section 6.1 of [Part3] |
   | Accept-Charset      | Section 6.2 of [Part3] |
   | Accept-Encoding     | Section 6.3 of [Part3] |
   | Accept-Language     | Section 6.4 of [Part3] |
   | Authorization       | Section 4.1 of [Part7] |
   | Expect              | Section 10.3           |
   | From                | Section 10.4           |
   | Host                | Section 5.4 of [Part1] |
   | If-Match            | Section 3.1 of [Part4] |
   | If-Modified-Since   | Section 3.3 of [Part4] |
   | If-None-Match       | Section 3.2 of [Part4] |
   | If-Range            | Section 5.3 of [Part5] |
   | If-Unmodified-Since | Section 3.4 of [Part4] |
   | Max-Forwards        | Section 10.6           |
   | Proxy-Authorization | Section 4.3 of [Part7] |
   | Range               | Section 5.4 of [Part5] |
   | Referer             | Section 10.7           |
   | TE                  | Section 4.3 100
   (Continue) status message.  Unexpected 1xx status responses MAY be
   ignored by a user agent.

   Proxies MUST forward 1xx responses, unless the connection between the
   proxy and its client has been closed, or unless the proxy itself
   requested the generation of [Part1] |
   | User-Agent          | Section 10.10          |
   +---------------------+------------------------+

3.3.  Response Header Fields the 1xx response.  (For example, if a
   proxy adds an "Expect: 100-continue" field when it forwards a
   request, then it need not forward the corresponding 100 (Continue)
   response(s).)

4.3.1.  100 Continue

   The client SHOULD continue with its request.  This interim response header fields allow the server
   is used to pass additional
   information about inform the response which cannot be placed in client that the status-
   line.  These header fields give information about initial part of the server request has
   been received and
   about further access to has not yet been rejected by the target resource (Section 5.5 of [Part1]).

   +--------------------+------------------------+
   | Header Field Name  | Defined in...          |
   +--------------------+------------------------+
   | Accept-Ranges      | Section 5.1 of [Part5] |
   | Age                | Section 3.1 of [Part6] |
   | Allow              | Section 10.1           |
   | Date               | Section 10.2           |
   | ETag               | Section 2.3 of [Part4] |
   | Location           | Section 10.5           |
   | Proxy-Authenticate | Section 4.2 of [Part7] |
   | Retry-After        | Section 10.8           |
   | Server             | Section 10.9           |
   | Vary               | Section 3.5 of [Part6] |
   | WWW-Authenticate   | Section 4.4 of [Part7] |
   +--------------------+------------------------+

4.  Status Code and Reason Phrase server.  The status-code element is a 3-digit integer result code
   client SHOULD continue by sending the remainder of the
   attempt to understand and satisfy request or, if
   the request. request has already been completed, ignore this response.  The reason-phrase is intended to give
   server MUST send a short textual description final response after the request has been
   completed.  See Section 6.4.3 of
   the status-code and is intended [Part1] for a human user.  The client does
   not need to examine or display the reason-phrase.

     status-code    = 3DIGIT
     reason-phrase  = *( HTAB / SP / VCHAR / obs-text )

   HTTP status codes are extensible.  HTTP applications are not required
   to understand detailed discussion of
   the meaning use and handling of all registered this status codes, though such
   understanding code.

4.3.2.  101 Switching Protocols

   The server understands and is obviously desirable.  However, applications MUST
   understand willing to comply with the class client's
   request, via the Upgrade message header field (Section 6.5 of any status code, as indicated by
   [Part1]), for a change in the first
   digit, and treat any unrecognized response as application protocol being equivalent used on this
   connection.  The server will switch protocols to those defined by the
   x00 status code of that class, with
   response's Upgrade header field immediately after the exception that an
   unrecognized response MUST NOT empty line
   which terminates the 101 response.

   The protocol SHOULD be cached. switched only when it is advantageous to do
   so.  For example, if an
   unrecognized status code switching to a newer version of 431 HTTP is received by the client, it can
   safely assume
   advantageous over older versions, and switching to a real-time,
   synchronous protocol might be advantageous when delivering resources
   that there was something wrong with its use such features.

4.4.  Successful 2xx

   This class of status code indicates that the client's request was
   successfully received, understood, and
   treat accepted.

4.4.1.  200 OK

   The request has succeeded.  The payload returned with the response as if it had received a 400 status code.  In such
   cases, user agents SHOULD present to is
   dependent on the user method used in the request, for example:

   GET  a representation
   enclosed with of the response, since that representation target resource is likely to
   include human-readable information which will explain the unusual
   status.

4.1.  Overview of Status Codes

   The status codes listed below are defined sent in Section 7 of this
   specification, Section 4 of [Part4], Section 3 of [Part5], and
   Section 3 of [Part7].  The reason phrases listed here are only
   recommendations -- they can be replaced by local equivalents the response;

   HEAD  the same representation as GET, except without
   affecting the protocol.

   +-------------+------------------------------+----------------------+
   | status-code | reason-phrase                | Defined in...        |
   +-------------+------------------------------+----------------------+
   | 100         | Continue                     | Section 7.1.1        |
   | 101         | Switching Protocols          | Section 7.1.2        |
   | 200         | OK                           | Section 7.2.1        |
   | 201         | Created                      | Section 7.2.2        |
   | 202         | Accepted                     | Section 7.2.3        |
   | 203         | Non-Authoritative            | Section 7.2.4        |
   |             | Information                  |                      |
   | 204         | No Content                   | Section 7.2.5        |
   | 205         | Reset Content                | Section 7.2.6        |
   | 206         | Partial Content              | Section 3.1 of       |
   |             |                              | [Part5]              |
   | 300         | Multiple Choices             | Section 7.3.1        |
   | 301         | Moved Permanently            | Section 7.3.2        |
   | 302         | Found                        | Section 7.3.3        |
   | 303         | See Other                    | Section 7.3.4        |
   | 304         | Not Modified                 | Section 4.1 of       |
   |             |                              | [Part4]              |
   | 305         | Use Proxy                    | Section 7.3.5        |
   | 307         | Temporary Redirect           | Section 7.3.7        |
   | 400         | Bad Request                  | Section 7.4.1        |
   | 401         | Unauthorized                 | Section 3.1 message
      body;

   POST  a representation describing or containing the result of       |
   |             |                              | [Part7]              |
   | 402         | Payment Required             | Section 7.4.2        |
   | 403         | Forbidden                    | Section 7.4.3        |
   | 404         | Not Found                    | Section 7.4.4        |
   | 405         | Method Not Allowed           | Section 7.4.5        |
   | 406         | Not Acceptable               | Section 7.4.6        |
   | 407         | Proxy Authentication         | the
      action;

   TRACE  a representation containing the request message as received by
      the end server.

   Caches MAY use a heuristic (see Section 3.2 4.1.2 of       |
   |             | Required                     | [Part7]              |
   | 408         | [Part6]) to
   determine freshness for 200 responses.

4.4.2.  201 Created

   The request has been fulfilled and has resulted in one or more new
   resources being created.

   Newly created resources are typically linked to from the response
   payload, with the most relevant URI also being carried in the
   Location header field.  If the newly created resource's URI is the
   same as the Effective Request Time-out             | Section 7.4.7        |
   | 409         | Conflict                     | Section 7.4.8        |
   | 410         | Gone                         | Section 7.4.9        |
   | 411         | Length Required              | Section 7.4.10       |
   | 412         | Precondition Failed          | Section 4.2 URI, this information can be omitted
   (e.g., in the case of       |
   |             |                              | [Part4]              |
   | 413         | a response to a PUT request).

   The origin server MUST create the resource(s) before returning the
   201 status code.  If the action cannot be carried out immediately,
   the server SHOULD respond with 202 (Accepted) response instead.

   A 201 response MAY contain an ETag response header field indicating
   the current value of the entity-tag for the representation of the
   resource identified by the Location header field or, in case the
   Location header field was omitted, by the Effective Request Representation Too   | Section 7.4.11       |
   |             | Large                        |                      |
   | 414         | URI Too Long                 | Section 7.4.12       |
   | 415         | Unsupported Media Type       | (see
   Section 7.4.13       |
   | 416         | Requested range 2.3 of [Part4]).

4.4.3.  202 Accepted

   The request has been accepted for processing, but the processing has
   not          | Section 3.2 been completed.  The request might or might not eventually be
   acted upon, as it might be disallowed when processing actually takes
   place.  There is no facility for re-sending a status code from an
   asynchronous operation such as this.

   The 202 response is intentionally non-committal.  Its purpose is to
   allow a server to accept a request for some other process (perhaps a
   batch-oriented process that is only run once per day) without
   requiring that the user agent's connection to the server persist
   until the process is completed.  The representation returned with
   this response SHOULD include an indication of the request's current
   status and either a pointer to a status monitor or some estimate of
   when the user can expect the request to be fulfilled.

4.4.4.  203 Non-Authoritative Information

   The representation in the response has been transformed or otherwise
   modified by a transforming proxy (Section 2.4 of [Part1]).  Note that
   the behavior of transforming intermediaries is controlled by the no-
   transform Cache-Control directive (Section 7.2 of [Part6]).

   This status code is only appropriate when the response status code
   would have been 200 (OK) otherwise.  When the status code before
   transformation would have been different, the 214 Transformation
   Applied warn-code (Section 7.6 of       |
   |             | satisfiable                  | [Part5]              |
   | 417         | Expectation Failed           | Section 7.4.14       |
   | 426         | Upgrade Required             | Section 7.4.15       |
   | 500         | Internal Server Error        | Section 7.5.1        |
   | 501         | Not Implemented              | Section 7.5.2        |
   | 502         | Bad Gateway                  | Section 7.5.3        |
   | 503         | Service Unavailable          | Section 7.5.4        |
   | 504         | Gateway Time-out             | Section 7.5.5        |
   | 505         | HTTP Version not supported   | [Part6]) is appropriate.

   Caches MAY use a heuristic (see Section 7.5.6        |
   +-------------+------------------------------+----------------------+

   Note 4.1.2 of [Part6]) to
   determine freshness for 203 responses.

4.4.5.  204 No Content

   The 204 (No Content) status code indicates that the server has
   successfully fulfilled the request and that there is no additional
   content to return in the response payload body.  Metadata in the
   response header fields refer to the target resource and its current
   representation after the requested action.

   For example, if a 204 status code is received in response to a PUT
   request and the response contains an ETag header field, then the PUT
   was successful and the ETag field-value contains the entity-tag for
   the new representation of that target resource.

   The 204 response allows a server to indicate that the action has been
   successfully applied to the target resource while implying that the
   user agent SHOULD NOT traverse away from its current "document view"
   (if any).  The server assumes that the user agent will provide some
   indication of the success to its user, in accord with its own
   interface, and apply any new or updated metadata in the response to
   the active representation.

   For example, a 204 status code is commonly used with document editing
   interfaces corresponding to a "save" action, such that this list the document
   being saved remains available to the user for editing.  It is not exhaustive -- it does not also
   frequently used with interfaces that expect automated data transfers
   to be prevalent, such as within distributed version control systems.

   The 204 response MUST NOT include
   extension status codes defined in other specifications.

4.2.  Status Code Registry a message body, and thus is always
   terminated by the first empty line after the header fields.

4.4.6.  205 Reset Content

   The HTTP Status Code Registry defines server has fulfilled the name space request and the user agent SHOULD reset
   the document view which caused the request to be sent.  This response
   is primarily intended to allow input for actions to take place via
   user input, followed by a clearing of the status- form in which the input is
   given so that the user can easily initiate another input action.

   The message body included with the response MUST be empty.  Note that
   receivers still need to parse the response according to the algorithm
   defined in Section 3.3 of [Part1].

4.5.  Redirection 3xx

   This class of status code token indicates that further action needs to be
   taken by the user agent in order to fulfill the request.  If the
   required action involves a subsequent HTTP request, it MAY be carried
   out by the user agent without interaction with the user if and only
   if the method used in the status-line of an HTTP response.

   Values second request is known to be added to this name space require IETF Review (see
   [RFC5226], "safe", as
   defined in Section 4.1).

   The registry itself is maintained at
   <http://www.iana.org/assignments/http-status-codes>.

4.2.1.  Considerations for New Status Codes

   When it is necessary to express new semantics for a HTTP response
   that aren't specific 2.1.1.

   There are several types of redirects:

   1.  Redirects of the request to a single application another URI, either temporarily or media type, and
   currently defined
       permanently.  The new URI is specified in the Location header
       field.  In this specification, the status codes are inadequate, 301 (Moved
       Permanently), 302 (Found), and 307 (Temporary Redirect) fall
       under this category.

   2.  Redirection to a new status code can
   be registered.

   HTTP status codes are generic; location that is, they are potentially
   applicable represents an indirect
       response to any resource, not just one particular media type,
   "type" the request, such as the result of resource, or application.  As such, it is preferred that
   new HTTP status codes be registered in a document that isn't specific POST operation
       to be retrieved with a single application, so that this subsequent GET request.  This is clear.

   Definitions of new HTTP status codes typically explain the request
   conditions that produce
       code 303 (See Other).

   3.  Redirection offering a response containing the choice of matching resources for use by
       agent-driven content negotiation (Section 8.2).  This is status
       code (e.g.,
   combinations of request headers and/or method(s)), along with any
   interactions with response headers (e.g., those that are required,
   those that modify the semantics 300 (Multiple Choices).

   4.  Other kinds of the response).

   New HTTP status codes are required redirection, such as to fall under one a cached result (status
       code 304 (Not Modified), see Section 4.1 of [Part4]).

      Note: In HTTP/1.0, only the
   categories defined in Section 7.  To allow existing parsers to
   properly handle them, new status codes cannot disallow a response
   body, although they can mandate a zero-length response body.  They
   can require 301 (Moved Permanently)
      and 302 (Found) were defined for the presence first type of one or more particular HTTP response
   header(s).

   Likewise, their definitions can specify that caches are allowed to
   use heuristics to determine their freshness (see [Part6]; by default,
   it is not allowed), redirect, and can define how to determine
      the resource
   which they carry a representation for (see second type did not exist at all ([RFC1945], Section 5.1; by default, 9.3).
      However it is anonymous).

5.  Representation

   Request and Response messages MAY transfer a representation if not
   otherwise restricted by turned out that web forms using POST expected redirects
      to change the operation for the subsequent request method or response status code.
   A representation consists to retrieval
      (GET).  To address this use case, HTTP/1.1 introduced the second
      type of metadata (representation header fields)
   and data (representation body).  When a complete or partial
   representation is enclosed in an HTTP message, it is referred redirect with the status code 303 (See Other) ([RFC2068],
      Section 10.3.4).  As user agents did not change their behavior to as
      maintain backwards compatibility, the payload first revision of HTTP/1.1
      added yet another status code, 307 (Temporary Redirect), for which
      the message.  HTTP representations are defined backwards compatibility problems did not apply ([RFC2616],
      Section 10.3.8).  Over 10 years later, most user agents still do
      method rewriting for status codes 301 and 302, therefore this
      specification makes that behavior conformant in
   [Part3]. case the original
      request was POST.

   A representation body is only present in Location header field on a message when 3xx response indicates that a message
   body is present, client MAY
   automatically redirect to the URI provided; see Section 9.13.

   Note that for methods not known to be "safe", as described defined in
   Section 3.3 of [Part1].  The
   representation body is obtained from 2.1.1, automatic redirection needs to done with care, since
   the message body by decoding any
   Transfer-Encoding that redirect might have been applied to ensure safe and
   proper transfer of change the message.

5.1.  Identifying conditions under which the Resource Associated with request was
   issued.

   Clients SHOULD detect and intervene in cyclical redirections (i.e.,
   "infinite" redirection loops).

      Note: An earlier version of this specification recommended a Representation

   It is sometimes necessary
      maximum of five redirections ([RFC2068], Section 10.3).  Content
      developers need to determine an identifier for the be aware that some clients might implement such
      a fixed limitation.

4.5.1.  300 Multiple Choices

   The target resource
   associated has more than one representation, each with its
   own specific location, and agent-driven negotiation information
   (Section 8) is being provided so that the user (or user agent) can
   select a representation.

   An HTTP preferred representation by redirecting its request representation, when present, is always associated
   with an anonymous (i.e., unidentified) resource.

   In to that
   location.

   Unless it was a HEAD request, the common case, an HTTP response is SHOULD include a
   representation containing a list of representation metadata and
   location(s) from which the user or user agent can choose the one most
   appropriate.  Depending upon the format and the capabilities of the
   target resource (see Section 5.5
   user agent, selection of [Part1]). the most appropriate choice MAY be performed
   automatically.  However, this is specification does not
   always define any
   standard for such automatic selection.

   If the case.  To determine server has a preferred choice of representation, it SHOULD
   include the specific URI of for that representation in the Location
   field; user agents MAY use the Location field value for automatic
   redirection.

   Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to
   determine freshness for 300 responses.

4.5.2.  301 Moved Permanently

   The target resource has been assigned a response is
   associated with, new permanent URI and any
   future references to this resource SHOULD use one of the following rules are used (with returned
   URIs.  Clients with link editing capabilities ought to automatically
   re-link references to the first
   applicable effective request URI to one being selected):

   1.  If the response status code is 200 or 203 and more of the request method
       was GET,
   new references returned by the response payload is server, where possible.

   Caches MAY use a representation heuristic (see Section 4.1.2 of [Part6]) to
   determine freshness for 301 responses.

   The new permanent URI SHOULD be given by the target
       resource.

   2.  If Location field in the
   response.  A response status code is 204, 206, or 304 and payload can contain a short hypertext note with
   a hyperlink to the new URI(s).

      Note: For historic reasons, user agents MAY change the request
      method was from POST to GET or HEAD, for the response payload subsequent request.  If this
      behavior is a partial
       representation of the undesired, status code 307 (Temporary Redirect) can be
      used instead.

4.5.3.  302 Found

   The target resource.

   3.  If the response has resource resides temporarily under a Content-Location header field, and that URI
       is different URI.  Since
   the same as redirection might be altered on occasion, the client SHOULD
   continue to use the effective request URI, URI for future requests.

   The temporary URI SHOULD be given by the Location field in the
   response.  A response payload is can contain a representation of the target resource.

   4.  If the response has short hypertext note with
   a Content-Location header field, and that URI
       is not hyperlink to the same as new URI(s).

      Note: For historic reasons, user agents MAY change the effective request URI, then
      method from POST to GET for the response
       asserts that its payload subsequent request.  If this
      behavior is a representation of the resource
       identified by the Content-Location URI.  However, such an
       assertion cannot be trusted unless it undesired, status code 307 (Temporary Redirect) can be verified by other
       means (not defined by HTTP).

   5.  Otherwise,
      used instead.

4.5.4.  303 See Other

   The 303 status code indicates that the response server is redirecting the user
   agent to a representation of an anonymous
       (i.e., unidentified) resource.

   [[TODO-req-uri: The comparison function different resource, as indicated by a URI in the Location
   header field, that is going intended to have provide an indirect response to be
   defined somewhere, because we already need the
   original request.  In order to compare URIs for things
   like cache invalidation.]]

6.  Method Definitions

   The set of common satisfy the original request, a user
   agent SHOULD perform a retrieval request methods for HTTP/1.1 is defined below.
   Although this set can be expanded, additional methods cannot be
   assumed to share using the same semantics for separately extended clients
   and servers.

6.1.  Safe Location URI (a
   GET or HEAD request if using HTTP), which can itself be redirected
   further, and Idempotent Methods

6.1.1.  Safe Methods

   Implementors need present the eventual result as an answer to be aware that the software represents original
   request.  Note that the user new URI in their interactions over the Internet, and need Location header field is not
   considered equivalent to the effective request URI.

   This status code is generally applicable to any HTTP method.  It is
   primarily used to allow the output of a POST action to redirect the
   user agent to be aware of any actions they take which might have an unexpected
   significance a selected resource, since doing so provides the
   information corresponding to themselves or others.

   In particular, the convention has been established POST response in a form that the GET,
   HEAD, OPTIONS, can be
   separately identified, bookmarked, and TRACE cached independent of the
   original request.

   A 303 response to a GET request methods SHOULD NOT indicates that the requested resource
   does not have a representation of its own that can be transferred by
   the
   significance server over HTTP.  The Location URI indicates a resource that is
   descriptive of taking an action other than retrieval.  These request
   methods ought to the target resource, such that the follow-on
   representation might be considered "safe".  This allows user agents useful to
   represent other methods, such as POST, PUT recipients without implying that it
   adequately represents the target resource.  Note that answers to the
   questions of what can be represented, what representations are
   adequate, and DELETE, in what might be a special
   way, so that useful description are outside the user is made aware
   scope of HTTP and thus entirely determined by the URI owner(s).

   Except for responses to a HEAD request, the fact that representation of a possibly
   unsafe action is being requested.

   Naturally, it is not possible 303
   response SHOULD contain a short hypertext note with a hyperlink to ensure that
   the server does not
   generate side-effects as Location URI.

4.5.5.  305 Use Proxy

   The 305 status code was defined in a result previous version of performing a GET request; this
   specification (see Appendix C), and is now deprecated.

4.5.6.  306 (Unused)

   The 306 status code was used in
   fact, some dynamic resources consider that a feature.  The important
   distinction here previous version of the
   specification, is that no longer used, and the user did not request code is reserved.

4.5.7.  307 Temporary Redirect

   The target resource resides temporarily under a different URI.  Since
   the side-effects,
   so therefore cannot be held accountable for them.

6.1.2.  Idempotent Methods

   Request methods redirection can also have the property of "idempotence" in that,
   aside from error or expiration issues, change over time, the intended effect of
   multiple identical requests is client SHOULD continue to
   use the same as effective request URI for future requests.

   The temporary URI SHOULD be given by the Location field in the
   response.  A response payload can contain a single request.
   PUT, DELETE, and all safe request methods are idempotent.  It is
   important to short hypertext note that idempotence refers only with
   a hyperlink to changes requested
   by the client: a server new URI(s).

      Note: This status code is free to change its state due similar to multiple
   requests for the purpose of tracking those requests, versioning of
   results, etc.

6.2.  OPTIONS

   The OPTIONS method requests information about the communication
   options available on the request/response chain identified by 302 (Found), except that it
      does not allow rewriting the
   effective request URI.  This method allows a client from POST to determine GET.
      This specification defines no equivalent counterpart for 301
      (Moved Permanently) ([draft-reschke-http-status-308], however,
      defines the
   options and/or requirements associated with status code 308 (Permanent Redirect) for this
      purpose).

4.6.  Client Error 4xx

   The 4xx class of status code is intended for cases in which the
   client seems to have erred.  Except when responding to a resource, or HEAD
   request, the
   capabilities of server SHOULD include a server, without implying representation containing an
   explanation of the error situation, and whether it is a resource action temporary or
   initiating a resource retrieval.

   Responses to the OPTIONS method
   permanent condition.  These status codes are not cacheable.

   If the OPTIONS applicable to any
   request includes a message body (as indicated by method.  User agents SHOULD display any included
   representation to the
   presence of Content-Length user.

4.6.1.  400 Bad Request

   The server cannot or Transfer-Encoding), then will not process the media type
   MUST be indicated by request, due to a Content-Type field.  Although this
   specification does not define any use client
   error (e.g., malformed syntax).

4.6.2.  402 Payment Required

   This code is reserved for such a body, future
   extensions use.

4.6.3.  403 Forbidden

   The server understood the request, but refuses to HTTP authorize it.
   Providing different user authentication credentials might use be
   successful, but any credentials that were provided in the OPTIONS body to make more detailed
   queries on request are
   insufficient.  The request SHOULD NOT be repeated with the server. same
   credentials.

   If the request-target (Section 5.3 of [Part1]) is an asterisk ("*"), request method was not HEAD and the server wishes to make
   public why the request has not been fulfilled, it SHOULD describe the OPTIONS request is intended to apply to
   reason for the server refusal in general
   rather than to a specific resource.  Since a server's communication
   options typically depend on the resource, representation.  If the "*" request is only
   useful as a "ping" or "no-op" type of method; it server does nothing beyond
   allowing the client not
   wish to make this information available to test the capabilities of client, the server.  For
   example, this can status
   code 404 (Not Found) MAY be used to test a proxy for HTTP/1.1 conformance
   (or lack thereof).

   If the request-target is instead.

4.6.4.  404 Not Found

   The server has not an asterisk, found anything matching the OPTIONS effective request applies
   only to URI.
   No indication is given of whether the options that are available when communicating with that
   resource.

   A 200 response condition is temporary or
   permanent.  The 410 (Gone) status code SHOULD include any header fields that indicate
   optional features implemented by be used if the server and applicable to
   knows, through some internally configurable mechanism, that an old
   resource (e.g., Allow), possibly including extensions not defined by
   this specification.  The response body, if any, SHOULD also include
   information about the communication options.  The format for such a
   body is not defined by this specification, but might be defined by
   future extensions to HTTP.  Content negotiation MAY be permanently unavailable and has no forwarding address.
   This status code is commonly used when the server does not wish to select
   reveal exactly why the appropriate response format.  If request has been refused, or when no other
   response body is included, applicable.

4.6.5.  405 Method Not Allowed

   The method specified in the request-line is not allowed for the
   target resource.  The response MUST include a Content-Length an Allow header field with
   containing a field-value list of "0". valid methods for the requested resource.

4.6.6.  406 Not Acceptable

   The Max-Forwards header field MAY be used to target a specific proxy
   in resource identified by the request chain (see Section 10.6).  If no Max-Forwards field is
   present only capable of generating
   response representations which have content characteristics not
   acceptable according to the Accept and Accept-* header fields sent in
   the request.

   Unless it was a HEAD request, then the forwarded request MUST NOT response SHOULD include a
   Max-Forwards field.

6.3.  GET

   The GET method requests transfer of a current
   representation of the
   target resource.

   If the target resource is containing a data-producing process, it is the
   produced data which shall be returned as the list of available representation in the
   response
   characteristics and not location(s) from which the source text of user or user agent can
   choose the process, unless that text
   happens to be one most appropriate.  Depending upon the output of format and the process.

   The semantics
   capabilities of the GET method change to a "conditional GET" if the
   request message includes an If-Modified-Since, If-Unmodified-Since,
   If-Match, If-None-Match, or If-Range header field.  A conditional GET
   requests that user agent, selection of the representation most appropriate
   choice MAY be transferred only under the
   circumstances described by the conditional header field(s).  The
   conditional GET request is intended performed automatically.  However, this specification
   does not define any standard for such automatic selection.

      Note: HTTP/1.1 servers are allowed to reduce unnecessary network
   usage by allowing cached representations return responses which are
      not acceptable according to be refreshed without
   requiring multiple requests or transferring data already held by the
   client.

   The semantics of accept header fields sent in the GET method change
      request.  In some cases, this might even be preferable to sending
      a "partial GET" if 406 response.  User agents are encouraged to inspect the
   request message includes a Range header field.  A partial GET
   requests that only part
      fields of an incoming response to determine if it is acceptable.

   If the representation response could be transferred, as
   described in Section 5.4 unacceptable, a user agent SHOULD
   temporarily stop receipt of [Part5].  The partial GET request is
   intended to reduce unnecessary network usage by allowing partially-
   retrieved representations to be completed without transferring more data
   already held by and query the client.

   Bodies on GET requests have no defined semantics.  Note that sending user for a body
   decision on further actions.

4.6.7.  408 Request Timeout

   The client did not produce a GET request might cause some existing implementations within the time that the server
   was prepared to
   reject wait.  The client MAY repeat the request. request without
   modifications at any later time.

4.6.8.  409 Conflict

   The response request could not be completed due to a GET request conflict with the current
   state of the resource.  This code is cacheable and MAY only allowed in situations where
   it is expected that the user might be used able to satisfy
   subsequent GET resolve the conflict
   and HEAD requests (see [Part6]).

   See Section 12.2 for security considerations when used for forms.

6.4.  HEAD resubmit the request.  The HEAD method is identical response body SHOULD include enough
   information for the user to GET except that recognize the server MUST NOT
   return a message body in source of the response.  The metadata contained in conflict.
   Ideally, the
   HTTP header fields in response representation would include enough information
   for the user or user agent to a HEAD request SHOULD fix the problem; however, that might
   not be identical possible and is not required.

   Conflicts are most likely to the information sent occur in response to a GET PUT request.  This method
   can be  For
   example, if versioning were being used for obtaining metadata about and the representation implied being
   PUT included changes to a resource which conflict with those made by
   an earlier (third-party) request, the request without transferring server might use the representation body.  This
   method is often used for testing hypertext links for validity,
   accessibility, and recent modification.

   The 409
   response to indicate that it can't complete the request.  In this
   case, the response representation would likely contain a HEAD request list of the
   differences between the two versions.

4.6.9.  410 Gone

   The target resource is cacheable no longer available at the server and MAY no
   forwarding address is known.  This condition is expected to be used
   considered permanent.  Clients with link editing capabilities SHOULD
   delete references to
   satisfy a subsequent HEAD request.  It also the effective request URI after user approval.
   If the server does not know, or has potential side
   effects on previously stored responses to GET; see Section 2.5 of
   [Part6].

   Bodies on HEAD requests have no defined semantics.  Note that sending
   a body on a HEAD request might cause some existing implementations facility to
   reject determine, whether
   or not the request.

6.5.  POST condition is permanent, the status code 404 (Not Found)
   SHOULD be used instead.

   The POST method requests that 410 response is primarily intended to assist the origin server accept task of web
   maintenance by notifying the
   representation enclosed in recipient that the resource is
   intentionally unavailable and that the request as data server owners desire that
   remote links to that resource be processed by removed.  Such an event is common
   for limited-time, promotional services and for resources belonging to
   individuals no longer working at the
   target resource.  POST server's site.  It is designed not
   necessary to allow a uniform method mark all permanently unavailable resources as "gone" or
   to cover keep the following functions:

   o  Annotation mark for any length of existing resources;

   o  Posting a message time -- that is left to a bulletin board, newsgroup, mailing list, or
      similar group of articles;

   o  Providing a block of data, such as the result
   discretion of submitting the server owner.

   Caches MAY use a
      form, heuristic (see Section 4.1.2 of [Part6]) to a data-handling process;

   o  Extending a database through an append operation.
   determine freshness for 410 responses.

4.6.10.  411 Length Required

   The actual function performed by the POST method is determined by the server and is usually dependent on refuses to accept the effective request URI. without a defined Content-
   Length.  The action performed by client MAY repeat the POST method might not result in request if it adds a
   resource that can be identified by valid
   Content-Length header field containing the length of the message body
   in the request message.

4.6.11.  413 Request Representation Too Large

   The server is refusing to process a URI.  In this case, either 200
   (OK) or 204 (No Content) request because the request
   representation is larger than the appropriate response status code,
   depending on whether server is willing or not able to
   process.  The server MAY close the response includes a representation
   that describes connection to prevent the result.

   If a resource has been created on client
   from continuing the origin server, request.

   If the response condition is temporary, the server SHOULD be 201 (Created) and contain include a representation which describes Retry-
   After header field to indicate that it is temporary and after what
   time the status of client MAY try again.

4.6.12.  414 URI Too Long

   The server is refusing to service the request and refers to because the new resource, and a
   Location header field (see Section 10.5).

   Responses effective
   request URI is longer than the server is willing to POST requests are interpret.  This
   rare condition is only cacheable likely to occur when they include
   explicit freshness information (see Section 2.3.1 of [Part6]).  A
   cached a client has improperly
   converted a POST response request to a GET request with long query
   information, when the client has descended into a Content-Location header field (see
   Section 6.7 URI "black hole" of [Part3]) whose value is the effective Request
   redirection (e.g., a redirected URI MAY
   be used to satisfy subsequent GET and HEAD requests.

   Note prefix that POST caching is not widely implemented.  However, the 303
   (See Other) response can be used to direct the user agent points to retrieve a cacheable resource.

6.6.  PUT

   The PUT method requests that the state suffix of the target resource be
   created
   itself), or replaced with when the state defined server is under attack by the representation
   enclosed in the request message payload.  A successful PUT of a given
   representation would suggest that a subsequent GET on that same
   target resource will result in an equivalent representation being
   returned client attempting to
   exploit security holes present in a 200 (OK) response.  However, there some servers using fixed-length
   buffers for reading or manipulating the request-target.

4.6.13.  415 Unsupported Media Type

   The server is no guarantee that
   such refusing to service the request because the request
   payload is in a state change will be observable, since format not supported by this request method on the
   target resource
   might be acted upon by other user agents resource.

4.6.14.  417 Expectation Failed

   The expectation given in parallel, or might an Expect header field (see Section 9.11)
   could not be
   subject to dynamic processing met by the origin this server, before any
   subsequent GET or, if the server is received.  A successful response only implies that a proxy, the user agent's intent was achieved at
   server has unambiguous evidence that the time of its processing request could not be met by
   the origin next-hop server.

   If the target resource does

4.6.15.  426 Upgrade Required

   The request can not have be completed without a current representation and prior protocol upgrade.
   This response MUST include an Upgrade header field (Section 6.5 of
   [Part1]) specifying the
   PUT successfully creates one, then required protocols.

   Example:

     HTTP/1.1 426 Upgrade Required
     Upgrade: HTTP/3.0
     Connection: Upgrade
     Content-Length: 53
     Content-Type: text/plain

     This service requires use of the origin HTTP/3.0 protocol.

   The server MUST inform the
   user agent by sending SHOULD include a 201 (Created) response.  If message body in the target
   resource does have a current representation and that representation
   is successfully modified 426 response which
   indicates in accordance with human readable form the state of reason for the enclosed
   representation, then either a 200 (OK) or 204 (No Content) response
   SHOULD error and
   describes any alternative courses which might be sent available to the
   user.

4.7.  Server Error 5xx

   Response status codes beginning with the digit "5" indicate successful completion cases in
   which the server is aware that it has erred or is incapable of
   performing the request.

   Unrecognized header fields SHOULD be ignored (i.e., not saved as part
   of  Except when responding to a HEAD request,
   the resource state).

   An origin server SHOULD verify that the PUT include a representation containing an explanation
   of the error situation, and whether it is
   consistent with a temporary or permanent
   condition.  User agents SHOULD display any constraints which included representation to
   the user.  These response codes are applicable to any request method.

4.7.1.  500 Internal Server Error

   The server has for encountered an unexpected condition which prevented it
   from fulfilling the target
   resource that cannot or will request.

4.7.2.  501 Not Implemented

   The server does not be changed by support the PUT. functionality required to fulfill the
   request.  This is
   particularly important the appropriate response when the origin server uses internal
   configuration information related to the URI in order to set does not
   recognize the
   values request method and is not capable of supporting it for representation metadata on GET responses.  When
   any resource.

4.7.3.  502 Bad Gateway

   The server, while acting as a PUT
   representation is inconsistent with the target resource, the origin
   server SHOULD either make them consistent, by transforming the
   representation or changing the resource configuration, gateway or respond
   with proxy, received an appropriate error message containing sufficient information invalid
   response from the upstream server it accessed in attempting to explain why
   fulfill the representation is unsuitable. request.

4.7.4.  503 Service Unavailable

   The 409 (Conflict)
   or 415 (Unsupported Media Type) status codes are suggested, with server is currently unable to handle the
   latter being specific request due to constraints on Content-Type values.

   For example, if a
   temporary overloading or maintenance of the target resource server.

   The implication is that this is configured to always have a
   Content-Type temporary condition which will be
   alleviated after some delay.  If known, the length of "text/html" and the representation being PUT has delay MAY
   be indicated in a
   Content-Type of "image/jpeg", then Retry-After header field (Section 9.16).  If no
   Retry-After is given, the origin server client SHOULD do one
   of: (a) reconfigure the target resource to reflect the new media
   type; (b) transform handle the PUT representation to response as it
   would for a format consistent
   with that 500 (Internal Server Error) response.

      Note: The existence of the resource before saving 503 status code does not imply that a
      server has to use it as the new resource state;
   or, (c) reject when becoming overloaded.  Some servers might
      wish to simply refuse the request with connection.

4.7.5.  504 Gateway Timeout

   The server, while acting as a 415 gateway or proxy, did not receive a
   timely response indicating that from the
   target resource is limited upstream server specified by the URI (e.g.,
   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
   to "text/html", perhaps including a link access in attempting to a different resource that would be a suitable target for complete the new
   representation. request.

      Note to implementers: some deployed proxies are known to return
      400 (Bad Request) or 500 (Internal Server Error) when DNS lookups
      time out.

4.7.6.  505 HTTP Version Not Supported

   The server does not define exactly how a PUT method affects support, or refuses to support, the state of an
   origin server beyond what can be expressed by protocol
   version that was used in the intent of request message.  The server is
   indicating that it is unable or unwilling to complete the user
   agent request and
   using the semantics of same major version as the origin server response.  It
   does not define what a resource might be, client, as described in any sense Section
   2.7 of [Part1], other than with this error message.  The response
   SHOULD contain a representation describing why that word,
   beyond the interface provided via HTTP.  It does not define how
   resource state version is "stored", nor how such storage might change as a
   result of a change in resource state, nor how the origin server
   translates resource state into representations.  Generally speaking,
   all implementation details behind the resource interface not
   supported and what other protocols are
   intentionally hidden supported by the that server.

   The fundamental difference between the POST and PUT methods is
   highlighted by the

5.  Protocol Parameters

5.1.  Date/Time Formats

   HTTP applications have historically allowed three different intent formats
   for date/time stamps.  However, the target resource.  The
   target resource in a POST request preferred format is intended to handle the enclosed
   representation as a data-accepting process, such as for a gateway to
   some fixed-
   length subset of that defined by [RFC1123]:

     Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123

   The other protocol or a document formats are described here only for compatibility with
   obsolete implementations.

     Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
     Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format

   HTTP/1.1 clients and servers that accepts annotations.  In
   contrast, parse a date value MUST accept all
   three formats (for compatibility with HTTP/1.0), though they MUST
   only generate the target resource RFC 1123 format for representing HTTP-date values
   in header fields.

   All HTTP date/time stamps MUST be represented in a PUT request is intended to take
   the enclosed representation as a new or replacement value.  Hence, Greenwich Mean Time
   (GMT), without exception.  For the intent purposes of PUT HTTP, GMT is idempotent and visible exactly
   equal to intermediaries, even
   though the exact effect UTC (Coordinated Universal Time).  This is only known indicated in the
   first two formats by the origin server.

   Proper interpretation inclusion of a PUT request presumes that "GMT" as the user agent
   knows what target resource three-letter
   abbreviation for time zone, and MUST be assumed when reading the
   asctime format.  HTTP-date is desired.  A service case sensitive and MUST NOT include
   additional whitespace beyond that is intended to
   select a proper URI on behalf specifically included as SP in the
   grammar.

     HTTP-date    = rfc1123-date / obs-date

   Preferred format:

     rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
     ; fixed length subset of the format defined in
     ; Section 5.2.14 of [RFC1123]

     day-name     = %x4D.6F.6E ; "Mon", case-sensitive
                  / %x54.75.65 ; "Tue", case-sensitive
                  / %x57.65.64 ; "Wed", case-sensitive
                  / %x54.68.75 ; "Thu", case-sensitive
                  / %x46.72.69 ; "Fri", case-sensitive
                  / %x53.61.74 ; "Sat", case-sensitive
                  / %x53.75.6E ; "Sun", case-sensitive

     date1        = day SP month SP year
                  ; e.g., 02 Jun 1982

     day          = 2DIGIT
     month        = %x4A.61.6E ; "Jan", case-sensitive
                  / %x46.65.62 ; "Feb", case-sensitive
                  / %x4D.61.72 ; "Mar", case-sensitive
                  / %x41.70.72 ; "Apr", case-sensitive
                  / %x4D.61.79 ; "May", case-sensitive
                  / %x4A.75.6E ; "Jun", case-sensitive
                  / %x4A.75.6C ; "Jul", case-sensitive
                  / %x41.75.67 ; "Aug", case-sensitive
                  / %x53.65.70 ; "Sep", case-sensitive
                  / %x4F.63.74 ; "Oct", case-sensitive
                  / %x4E.6F.76 ; "Nov", case-sensitive
                  / %x44.65.63 ; "Dec", case-sensitive
     year         = 4DIGIT

     GMT   = %x47.4D.54 ; "GMT", case-sensitive

     time-of-day  = hour ":" minute ":" second
                    ; 00:00:00 - 23:59:59

     hour         = 2DIGIT
     minute       = 2DIGIT
     second       = 2DIGIT

   The semantics of the client, after receiving a state-
   changing request, SHOULD be implemented using the POST method rather
   than PUT.  If the origin server will not make the requested PUT state
   change to the target resource day-name, day, month, year, and instead wishes to have it applied
   to a different resource, such as when the resource has been moved to
   a different URI, then time-of-day are the origin server MUST send a 301 (Moved
   Permanently) response;
   same as those defined for the user agent MAY then make its own decision
   regarding whether or not to redirect RFC 5322 constructs with the request.

   A PUT request applied
   corresponding name ([RFC5322], Section 3.3).

   Obsolete formats:

     obs-date     = rfc850-date / asctime-date
     rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
     date2        = day "-" month "-" 2DIGIT
                    ; day-month-year (e.g., 02-Jun-82)

     day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
            / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
            / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
            / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
            / %x46.72.69.64.61.79 ; "Friday", case-sensitive
            / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
            / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive

     asctime-date = day-name SP date3 SP time-of-day SP year
     date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
                    ; month day (e.g., Jun  2)

      Note: Recipients of date values are encouraged to the target resource MAY have side-effects on
   other resources.  For example, an article be robust in
      accepting date values that might have a URI for
   identifying "the current version" (a resource) which been sent by non-HTTP
      applications, as is separate from sometimes the URIs identifying each particular version (different resources
   that at one point shared case when retrieving or posting
      messages via proxies/gateways to SMTP or NNTP.

      Note: HTTP requirements for the same state as date/time stamp format apply only
      to their usage within the current version
   resource).  A successful PUT protocol stream.  Clients and servers
      are not required to use these formats for user presentation,
      request on "the current version" URI
   might therefore create a new version resource in addition logging, etc.

5.2.  Product Tokens

   Product tokens are used to changing
   the state of the target resource, allow communicating applications to
   identify themselves by software name and might version.  Most fields using
   product tokens also cause links allow sub-products which form a significant part
   of the application to be
   added between listed, separated by whitespace.  By
   convention, the related resources.

   An origin server SHOULD reject any PUT request that contains a
   Content-Range header field, since it might be misinterpreted as
   partial content (or might be partial content that is being mistakenly
   PUT as a full representation).  Partial content updates products are possible
   by targeting a separately identified resource with state that
   overlaps a portion listed in order of their significance
   for identifying the larger resource, application.

     product         = token ["/" product-version]
     product-version = token

   Examples:

     User-Agent: CERN-LineMode/2.15 libwww/2.17b3
     Server: Apache/0.8.4

   Product tokens SHOULD be short and to the point.  They MUST NOT be
   used for advertising or by using a different
   method that has been specifically defined other non-essential information.  Although
   any token octet MAY appear in a product-version, this token SHOULD
   only be used for partial updates (for
   example, a version identifier (i.e., successive versions of
   the PATCH method defined same product SHOULD only differ in [RFC5789]).

   Responses the product-version portion of
   the product value).

5.3.  Character Encodings (charset)

   HTTP uses charset names to indicate the PUT method are not cacheable.  If character encoding of a PUT request
   passes through
   textual representation.

   A character encoding is identified by a cache that has one or more stored responses for the
   effective request URI, those stored responses will be invalidated
   (see Section 2.6 of [Part6]).

6.7.  DELETE case-insensitive token.  The DELETE method requests that the origin server delete the target
   resource.  This method MAY be overridden
   complete set of tokens is defined by human intervention (or
   other means) on the origin server.  The client cannot IANA Character Set registry
   (<http://www.iana.org/assignments/character-sets>).

     charset = token

   Although HTTP allows an arbitrary token to be guaranteed used as a charset
   value, any token that the operation has been carried out, even if a predefined value within the status code
   returned from IANA
   Character Set registry MUST represent the origin server indicates character encoding defined
   by that the action has been
   completed successfully.  However, the server registry.  Applications SHOULD NOT indicate
   success unless, at the time the response is given, it intends limit their use of character
   encodings to
   delete those defined within the resource or move it to IANA registry.

   HTTP uses charset in two contexts: within an inaccessible location.

   A successful response SHOULD be 200 (OK) if Accept-Charset request
   header field (in which the response includes charset value is an
   representation describing the status, 202 (Accepted) if the action
   has not yet been enacted, or 204 (No Content) if the action has been
   enacted but the response does not include unquoted token) and as
   the value of a representation.

   Bodies on DELETE requests have no defined semantics.  Note that
   sending parameter in a body on Content-Type header field (within a DELETE
   request might cause some existing
   implementations to reject or response), in which case the request.

   Responses to parameter value of the DELETE method are not cacheable.  If a DELETE
   request passes through a cache
   charset parameter can be quoted.

   Implementers need to be aware of IETF character set requirements
   [RFC3629] [RFC2277].

5.4.  Content Codings

   Content coding values indicate an encoding transformation that has one
   been or more stored responses
   for the effective request URI, those stored responses will can be
   invalidated (see Section 2.6 of [Part6]).

6.8.  TRACE

   The TRACE method requests applied to a remote, application-layer loop-back of representation.  Content codings are
   primarily used to allow a representation to be compressed or
   otherwise usefully transformed without losing the request message.  The final recipient identity of its
   underlying media type and without loss of information.  Frequently,
   the request SHOULD
   reflect representation is stored in coded form, transmitted directly, and
   only decoded by the message received back to recipient.

     content-coding   = token

   All content-coding values are case-insensitive.  HTTP/1.1 uses
   content-coding values in the client as Accept-Encoding (Section 9.3) and
   Content-Encoding (Section 9.6) header fields.  Although the message body value
   describes the content-coding, what is more important is that it
   indicates what decoding mechanism will be required to remove the
   encoding.

   compress

      See Section 4.2.1 of a 200 (OK) response. [Part1].

   deflate

      See Section 4.2.2 of [Part1].

   gzip

      See Section 4.2.3 of [Part1].

5.4.1.  Content Coding Registry

   The final recipient is either HTTP Content Coding Registry defines the origin
   server or name space for the first proxy
   content coding names.

   Registrations MUST include the following fields:

   o  Name

   o  Description

   o  Pointer to receive a Max-Forwards value specification text

   Names of zero (0)
   in content codings MUST NOT overlap with names of transfer
   codings (Section 4 of [Part1]), unless the encoding transformation is
   identical (as is the request case for the compression codings defined in
   Section 4.2 of [Part1]).

   Values to be added to this name space require IETF Review (see
   Section 10.6).  A TRACE request 4.1 of [RFC5226]), and MUST NOT include
   a message body.

   TRACE allows the client conform to see what is being received at the other
   end purpose of content
   coding defined in this section.

   The registry itself is maintained at
   <http://www.iana.org/assignments/http-parameters>.

5.5.  Media Types

   HTTP uses Internet Media Types [RFC2046] in the request chain Content-Type
   (Section 9.9) and use that Accept (Section 9.1) header fields in order to
   provide open and extensible data for testing or diagnostic
   information. typing and type negotiation.

     media-type = type "/" subtype *( OWS ";" OWS parameter )
     type       = token
     subtype    = token

   The value of type/subtype MAY be followed by parameters in the Via header field (Section 6.2 of
   [Part1]) is of particular interest, since it acts as a trace form of
   attribute/value pairs.

     parameter      = attribute "=" value
     attribute      = token
     value          = word

   The type, subtype, and parameter attribute names are case-
   insensitive.  Parameter values might or might not be case-sensitive,
   depending on the
   request chain.  Use semantics of the Max-Forwards header field allows the
   client parameter name.  The presence or
   absence of a parameter might be significant to limit the length processing of the request chain, which is useful for
   testing a chain of proxies forwarding messages in an infinite loop.

   If
   media-type, depending on its definition within the request is valid, media type
   registry.

   A parameter value that matches the response SHOULD have token production can be
   transmitted as either a Content-Type of
   "message/http" (see Section 7.3.1 of [Part1]) and contain token or within a message
   body quoted-string.  The quoted
   and unquoted values are equivalent.

   Note that encloses a copy of the entire request message.  Responses some older HTTP applications do not recognize media type
   parameters.  When sending data to the TRACE method older HTTP applications,
   implementations SHOULD only use media type parameters when they are not cacheable.

6.9.  CONNECT

   The CONNECT method requests
   required by that type/subtype definition.

   Media-type values are registered with the proxy establish a tunnel to the
   request-target and, if successful, thereafter restrict its behavior
   to blind forwarding Internet Assigned Number
   Authority (IANA).  The media type registration process is outlined in
   [RFC4288].  Use of packets until the connection non-registered media types is closed.

   When using CONNECT, the request-target discouraged.

5.5.1.  Canonicalization and Text Defaults

   Internet media types are registered with a canonical form.  A
   representation transferred via HTTP messages MUST use be in the authority
   appropriate canonical form
   (Section 5.3 of [Part1]); i.e., prior to its transmission except for
   "text" types, as defined in the request-target consists next paragraph.

   When in canonical form, media subtypes of only the host name "text" type use CRLF as
   the text line break.  HTTP relaxes this requirement and port number of allows the tunnel destination, separated by
   transport of text media with plain CR or LF alone representing a colon.  For example,

     CONNECT server.example.com:80 HTTP/1.1
     Host: server.example.com:80

   Any successful (2xx) response to line
   break when it is done consistently for an entire representation.
   HTTP applications MUST accept CRLF, bare CR, and bare LF as
   indicating a CONNECT request indicates that line break in text media received via HTTP.  In
   addition, if the
   proxy has established text is in a connection to the requested host character encoding that does not use
   octets 13 and port, 10 for CR and has switched to tunneling the current connection to that server
   connection.  The tunneled data from LF respectively, as is the server begins immediately
   after case for some
   multi-byte character encodings, HTTP allows the blank line use of whatever octet
   sequences are defined by that concludes the successful response's header
   block.  A server SHOULD NOT send any Transfer-Encoding or Content-
   Length header fields character encoding to represent the
   equivalent of CR and LF for line breaks.  This flexibility regarding
   line breaks applies only to text media in the payload body; a successful response.  A client bare CR
   or LF MUST ignore NOT be substituted for CRLF within any Content-Length or Transfer-Encoding of the HTTP control
   structures (such as header fields received in and multipart boundaries).

   If a
   successful response.

   Any response other than representation is encoded with a successful response indicates that the
   tunnel has not yet been formed and that content-coding, the connection remains
   governed by HTTP.

   Proxy authentication might underlying
   data MUST be used to establish the authority in a form defined above prior to
   create being encoded.

5.5.2.  Multipart Types

   MIME provides for a tunnel:

     CONNECT server.example.com:80 HTTP/1.1
     Host: server.example.com:80
     Proxy-Authorization: basic aGVsbG86d29ybGQ=

   A number of "multipart" types -- encapsulations of
   one or more representations within a single message body on body.  All
   multipart types share a CONNECT request has no common syntax, as defined semantics.
   Sending a body on a CONNECT request might cause existing
   implementations to reject the request.

   Similar to in Section 5.1.1 of
   [RFC2046], and MUST include a pipelined HTTP/1.1 request, data to be tunneled from
   client to server MAY be sent immediately after boundary parameter as part of the request (before a
   response is received). media
   type value.  The usual caveats also apply: data may be
   discarded if the eventual response is negative, and the connection
   may be reset with no response if more than one TCP segment message body is
   outstanding.

   It may be the case that the proxy itself can a protocol element and MUST
   therefore use only reach the requested
   origin server through another proxy. CRLF to represent line breaks between body-parts.

   In this case, general, HTTP treats a multipart message body no differently than
   any other media type: strictly as payload.  HTTP does not use the first proxy
   multipart boundary as an indicator of message body length.  In all
   other respects, an HTTP user agent SHOULD make follow the same or similar
   behavior as a CONNECT request MIME user agent would upon receipt of that next proxy, requesting a tunnel multipart type.
   The MIME header fields within each body-part of a multipart message
   body do not have any significance to HTTP beyond that defined by
   their MIME semantics.

   If an application receives an unrecognized multipart subtype, the authority.  A proxy
   application MUST NOT respond with any 2xx status code
   unless treat it as being equivalent to "multipart/mixed".

      Note: The "multipart/form-data" type has either been specifically defined
      for carrying form data suitable for processing via the POST
      request method, as described in [RFC2388].

5.6.  Language Tags

   A language tag, as defined in [RFC5646], identifies a direct natural
   language spoken, written, or tunnel connection established otherwise conveyed by human beings for
   communication of information to other human beings.  Computer
   languages are explicitly excluded.  HTTP uses language tags within
   the
   authority.

   If at any point either Accept-Language and Content-Language fields.

   In summary, a language tag is composed of one or more parts: A
   primary language subtag followed by a possibly empty series of
   subtags:

     language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>

   White space is not allowed within the peers gets disconnected, any
   outstanding data that came from that peer will be passed to the other
   one, tag and after that also the other connection will be terminated all tags are case-
   insensitive.  The name space of language subtags is administered by
   the proxy.  If there is outstanding data to that peer undelivered,
   that data will be discarded.

   An origin server which receives a CONNECT request IANA (see
   <http://www.iana.org/assignments/language-subtag-registry>).

   Example tags include:

     en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN

   See [RFC5646] for itself further information.

6.  Payload

   HTTP messages MAY
   respond with a 2xx status code to indicate that transfer a connection is
   established.  However, most origin servers do not implement CONNECT.

7.  Status Code Definitions payload if not otherwise restricted by
   the request method or response status code.  The first digit payload consists of
   metadata, in the status-code defines form of header fields, and data, in the class form of response.
   The last two digits do not have any categorization role.  There are 5
   values for the first digit:

   o  1xx: Informational - Request received, continuing process

   o  2xx: Success - The action was successfully received, understood,
      and accepted

   o  3xx: Redirection - Further action must be taken
   sequence of octets in order to
      complete the request

   o  4xx: Client Error - The request contains bad syntax or cannot be
      fulfilled

   o  5xx: Server Error - The server failed to fulfill an apparently
      valid request

   Each status-code is described below, including message body after any metadata required transfer-coding has
   been decoded.

   A "payload" in HTTP is always a partial or complete representation of
   some resource.  We use separate terms for payload and representation
   because some messages contain only the response.

   For most associated representation's
   header fields (e.g., responses to HEAD) or only some part(s) of the
   representation (e.g., the 206 (Partial Content) status codes code).

6.1.  Payload Header Fields

   HTTP header fields that specifically define the response can carry a payload, in which case
   a Content-Type header field indicates rather than
   the payload's media type
   (Section 6.8 associated representation, are referred to as "payload header
   fields".  The following payload header fields are defined by
   HTTP/1.1:

   +-------------------+--------------------------+
   | Header Field Name | Defined in...            |
   +-------------------+--------------------------+
   | Content-Length    | Section 3.3.2 of [Part3]).

7.1.  Informational 1xx

   This class [Part1] |
   | Content-Range     | Section 5.2 of status code indicates a provisional response,
   consisting [Part5]   |
   +-------------------+--------------------------+

6.2.  Payload Body

   A payload body is only present in a message when a message body is
   present, as described in Section 3.3 of the status-line and optional header fields, and [Part1].  The payload body is
   terminated
   obtained from the message body by an empty line.  There are no required header fields for
   this class of status code.  Since HTTP/1.0 did not define decoding any 1xx
   status codes, servers MUST NOT send a 1xx response Transfer-Encoding that
   might have been applied to an HTTP/1.0
   client except under experimental conditions. ensure safe and proper transfer of the
   message.

7.  Representation

   A client MUST "representation" is information in a format that can be prepared to accept readily
   communicated from one or more 1xx status responses
   prior party to a regular response, even if the client does not expect a 100
   (Continue) status message.  Unexpected 1xx status responses MAY be
   ignored by a user agent.

   Proxies MUST forward 1xx responses, unless the connection between the
   proxy and its client has been closed, or unless the proxy itself
   requested another.  A resource representation is
   information that reflects the generation state of that resource, as observed at
   some point in the 1xx response.  (For example, if a
   proxy adds a "Expect: 100-continue" field when it forwards past (e.g., in a request,
   then it need not forward the corresponding 100 (Continue)
   response(s).)

7.1.1.  100 Continue

   The client SHOULD continue with its request.  This interim response
   is used to inform the client that GET) or to be desired
   at some point in the initial part future (e.g., in a PUT request).

   Most, but not all, representations transferred via HTTP are intended
   to be a representation of the request has
   been received and has not yet been rejected target resource (the resource
   identified by the server. effective request URI).  The
   client SHOULD continue precise semantics of a
   representation are determined by sending the remainder type of message (request or
   response), the request or, if method, the request has already been completed, ignore this response.  The
   server MUST send a final response after the request has been
   completed.  See Section 6.4.3 of [Part1] for detailed discussion of
   the use and handling of this status code.

7.1.2.  101 Switching Protocols

   The server understands code, and is willing to comply with the client's
   request, via
   representation metadata.  For example, the Upgrade message header field (Section 6.5 of
   [Part1]), above semantic is true for a change
   the representation in any 200 (OK) response to GET and for the application protocol being used on this
   connection.  The server will switch protocols
   representation in any PUT request.  A 200 response to those defined by PUT, in
   contrast, contains either a representation that describes the
   response's Upgrade
   successful action or a representation of the target resource, with
   the latter indicated by a Content-Location header field immediately after with the empty line
   which terminates same
   value as the 101 response.

   The protocol SHOULD be switched only when it is advantageous to do
   so.  For example, switching to a newer version of HTTP is
   advantageous over older versions, and switching to a real-time,
   synchronous protocol might be advantageous when delivering resources
   that use such features.

7.2.  Successful 2xx

   This class of effective request URI.  Likewise, response messages with
   an error status code indicates usually contain a representation that describes
   the client's request was
   successfully received, understood, error and accepted.

7.2.1.  200 OK

   The request has succeeded.  The payload returned with the response is
   dependent on what next steps are suggested for resolving it.

   Request and Response messages MAY transfer a representation if not
   otherwise restricted by the request method used in the request, for example:

   GET  a or response status code.
   A representation consists of the target resource metadata (representation header fields)
   and data (representation body).  When a complete or partial
   representation is sent enclosed in the response;

   HEAD  the same representation an HTTP message, it is referred to as GET, except without the message
      body;

   POST  a representation describing or containing
   the result payload of the
      action;

   TRACE  a message.

   A representation containing the request body is only present in a message as received by
      the end server.

   Caches MAY use when a heuristic (see message
   body is present, as described in Section 2.3.1.1 3.3 of [Part6]) to
   determine freshness for 200 responses.

7.2.2.  201 Created

   The request has been fulfilled and has resulted in a new resource
   being created. [Part1].  The newly created resource
   representation body is typically linked to obtained from the response
   payload, with the most relevant URI also being carried in the
   Location header field.  If the newly created resource's URI is the
   same as message body by decoding any
   Transfer-Encoding that might have been applied to ensure safe and
   proper transfer of the Effective Request URI, this information can be omitted
   (e.g., in message.

7.1.  Identifying the case of Resource Associated with a response Representation

   It is sometimes necessary to a PUT request).

   The origin server MUST create determine an identifier for the resource before returning the 201
   status code.  If the action cannot be carried out immediately, the
   server SHOULD respond
   associated with 202 (Accepted) response instead.

   A 201 response MAY contain a representation.

   An HTTP request representation, when present, is always associated
   with an anonymous (i.e., unidentified) resource.

   In the common case, an ETag HTTP response header field indicating
   the current value of the entity-tag for the is a representation of the
   target resource just created (see Section 2.3 5.5 of [Part4]).

7.2.3.  202 Accepted

   The request has been accepted for processing, but the processing has
   not been completed.  The request might or might not eventually be
   acted upon, as it might be disallowed when processing actually takes
   place.  There [Part1]).  However, this is no facility for re-sending not
   always the case.  To determine the URI of the resource a status code from an
   asynchronous operation such as this.

   The 202 response is intentionally non-committal.  Its purpose is to
   allow a server to accept a request for some other process (perhaps a
   batch-oriented process that is only run once per day) without
   requiring that
   associated with, the user agent's connection to following rules are used (with the server persist
   until first
   applicable one being selected):

   1.  If the process is completed.  The representation returned with
   this response SHOULD include an indication of the request's current
   status and either a pointer to a status monitor code is 200 (OK) or some estimate of
   when the user can expect 203 (Non-Authoritative
       Information) and the request to be fulfilled.

7.2.4.  203 Non-Authoritative Information

   The representation in method was GET, the response has been transformed or otherwise
   modified by payload
       is a transforming proxy (Section 2.3 representation of [Part1]).  Note that the behavior of transforming intermediaries is controlled by target resource.

   2.  If the no-
   transform Cache-Control directive (Section 3.2 of [Part6]).

   This response status code is only appropriate when 204 (No Content), 206 (Partial
       Content), or 304 (Not Modified) and the request method was GET or
       HEAD, the response payload is a partial representation of the
       target resource.

   3.  If the response status code
   would have been 200 (OK) otherwise.  When has a Content-Location header field, and that URI
       is the status code before
   transformation would have been different, same as the 214 Transformation
   Applied warn-code (Section 3.6 of [Part6]) effective request URI, the response payload is appropriate.

   Caches MAY use
       a heuristic (see Section 2.3.1.1 representation of [Part6]) to
   determine freshness for 203 responses.

7.2.5.  204 No Content

   The 204 (No Content) status code indicates that the server has
   successfully fulfilled target resource.

   4.  If the request response has a Content-Location header field, and that there URI
       is no additional
   content to return in not the same as the effective request URI, then the response
       asserts that its payload body.  Metadata in is a representation of the resource
       identified by the Content-Location URI.  However, such an
       assertion cannot be trusted unless it can be verified by other
       means (not defined by HTTP).

   5.  Otherwise, the response is a representation of an anonymous
       (i.e., unidentified) resource.

   [[TODO-req-uri: The comparison function is going to have to be
   defined somewhere, because we already need to compare URIs for things
   like cache invalidation.]]

7.2.  Representation Header Fields

   Representation header fields refer to define metadata about the target resource and its current representation after
   data enclosed in the requested action.

   For example, message body or, if a 204 status code no message body is received present,
   about the representation that would have been transferred in a 200
   (OK) response to a PUT simultaneous GET request and with the response contains an ETag same effective
   request URI.

   The following header field, then the PUT
   was successful and fields are defined as representation metadata:

   +-------------------+------------------------+
   | Header Field Name | Defined in...          |
   +-------------------+------------------------+
   | Content-Encoding  | Section 9.6            |
   | Content-Language  | Section 9.7            |
   | Content-Location  | Section 9.8            |
   | Content-Type      | Section 9.9            |
   | Expires           | Section 7.3 of [Part6] |
   +-------------------+------------------------+

   We use the ETag field-value contains term "selected representation" to refer to the entity-tag for the new current
   representation of that target resource.

   The 204 response allows a server to indicate that the action has been
   successfully applied to the target resource while implying that the
   user agent SHOULD NOT traverse away from its current "document view"
   (if any).  The server assumes that would have been selected in
   a successful response if the user agent will provide some
   indication of same request had used the success to its user, in accord with its own
   interface, method GET and apply
   excluded any new or updated conditional request header fields.

   Additional header fields define metadata about the selected
   representation, which might differ from the representation included
   in the response message for responses to
   the active representation.

   For example, a 204 status code is commonly used some state-changing methods.  The
   following header fields are defined as selected representation
   metadata:

   +-------------------+------------------------+
   | Header Field Name | Defined in...          |
   +-------------------+------------------------+
   | ETag              | Section 2.3 of [Part4] |
   | Last-Modified     | Section 2.2 of [Part4] |
   +-------------------+------------------------+

7.3.  Representation Data

   The representation body associated with document editing
   interfaces corresponding to a "save" action, such that an HTTP message is either
   provided as the document
   being saved remains available to payload body of the user for editing.  It is also
   frequently used with interfaces that expect automated data transfers message or referred to be prevalent, such as within distributed version control systems. by the
   message semantics and the effective request URI.  The 204 response MUST NOT include representation
   data is in a message body, format and thus is always
   terminated encoding defined by the first empty line after the representation
   metadata header fields.

7.2.6.  205 Reset Content

   The server has fulfilled data type of the request representation data is determined via the header
   fields Content-Type and Content-Encoding.  These define a two-layer,
   ordered encoding model:

     representation-data := Content-Encoding( Content-Type( bits ) )

   Content-Type specifies the user agent SHOULD reset media type of the document view underlying data, which caused
   defines both the request to data format and how that data SHOULD be sent.  This response
   is primarily intended to allow input for actions to take place via
   user input, followed processed by
   the recipient (within the scope of the request method semantics).
   Any HTTP/1.1 message containing a clearing payload body SHOULD include a
   Content-Type header field defining the media type of the form in which associated
   representation unless that metadata is unknown to the input sender.  If the
   Content-Type header field is
   given so not present, it indicates that the user can easily initiate another input action.

   The message body included
   sender does not know the media type of the representation; recipients
   MAY either assume that the media type is "application/octet-stream"
   ([RFC2046], Section 4.5.1) or examine the content to determine its
   type.

   In practice, resource owners do not always properly configure their
   origin server to provide the correct Content-Type for a given
   representation, with the result that some clients will examine a
   response MUST be empty.  Note body's content and override the specified type.  Clients
   that
   receivers still need do so risk drawing incorrect conclusions, which might expose
   additional security risks (e.g., "privilege escalation").
   Furthermore, it is impossible to parse determine the response according sender's intent by
   examining the data format: many data formats match multiple media
   types that differ only in processing semantics.  Implementers are
   encouraged to provide a means of disabling such "content sniffing"
   when it is used.

   Content-Encoding is used to indicate any additional content codings
   applied to the algorithm
   defined in Section 3.3 of [Part1].

7.3.  Redirection 3xx

   This class data, usually for the purpose of status code indicates data compression,
   that further action needs to be
   taken by the user agent in order to fulfill are a property of the request. representation.  If Content-Encoding is
   not present, then there is no additional encoding beyond that defined
   by the
   required action involves a subsequent Content-Type header field.

8.  Content Negotiation

   HTTP request, it MAY be carried
   out responses include a representation which contains information
   for interpretation, whether by the a human user agent without interaction with or for further
   processing.  Often, the user if and only
   if server has different ways of representing the method used
   same information; for example, in different formats, languages, or
   using different character encodings.

   HTTP clients and their users might have different or variable
   capabilities, characteristics or preferences which would influence
   which representation, among those available from the second request is known to server, would be "safe", as
   defined in Section 6.1.1.

   There are several types of redirects:

   1.  Redirects of
   best for the request server to another URI, either temporarily or
       permanently.  The new URI is specified in the Location header
       field.  In this specification, the status codes 301 (Moved
       Permanently), 302 (Found), and 307 (Temporary Redirect) fall
       under deliver.  For this category.

   2.  Redirection to reason, HTTP provides
   mechanisms for "content negotiation" -- a new location that represents an indirect
       response to the request, such as the result process of allowing
   selection of a POST operation
       to be retrieved with representation of a subsequent GET request.  This given resource, when more than one
   is status
       code 303 (See Other).

   3.  Redirection offering available.

   This specification defines two patterns of content negotiation;
   "server-driven", where the server selects the representation based
   upon the client's stated preferences, and "agent-driven" negotiation,
   where the server provides a choice list of matching resources representations for use by
       agent-driven content negotiation (Section 5.2 of [Part3]).  This
       is status code 300 (Multiple Choices).

   4.  Other kinds of redirection, such as the client to a cached result (status
       code 304 (Not Modified), see Section 4.1 of [Part4]).

      Note:
   choose from, based upon their metadata.  In HTTP/1.0, only addition, there are other
   patterns: some applications use an "active content" pattern, where
   the status codes 301 (Moved Permanently) server returns active content which runs on the client and, based
   on client available parameters, selects additional resources to
   invoke.  "Transparent Content Negotiation" ([RFC2295]) has also been
   proposed.

   These patterns are all widely used, and 302 (Found) were defined for have trade-offs in
   applicability and practicality.  In particular, when the first type number of redirect,
   preferences or capabilities to be expressed by a client are large
   (such as when many different formats are supported by a user-agent),
   server-driven negotiation becomes unwieldy, and might not be
   appropriate.  Conversely, when the second type did number of representations to
   choose from is very large, agent-driven negotiation might not exist at all ([RFC1945], Section 9.3).
      However it turned out be
   appropriate.

   Note that web forms using POST expected redirects
      to change in all cases, the operation for supplier of representations has the subsequent request
   responsibility for determining which representations might be
   considered to retrieval
      (GET).  To address this use case, HTTP/1.1 introduced be the second
      type "same information".

8.1.  Server-driven Negotiation

   If the selection of redirect with the status code 303 (See Other) ([RFC2068],
      Section 10.3.4).  As user agents did not change their behavior to
      maintain backwards compatibility, best representation for a response is made by
   an algorithm located at the first revision server, it is called server-driven
   negotiation.  Selection is based on the available representations of HTTP/1.1
      added yet another status code, 307 (Temporary Redirect), for
   the response (the dimensions over which
      the backwards compatibility problems did not apply ([RFC2616],
      Section 10.3.8).  Over 10 years later, most user agents still do
      method rewriting for status codes 301 it can vary; e.g., language,
   content-coding, etc.) and 302, therefore this
      specification makes that behavior conformant the contents of particular header fields in case
   the original request was POST.

   A Location header field message or on a 3xx response indicates that a client MAY
   automatically redirect other information pertaining to the URI provided; see Section 10.5.

   Note that request
   (such as the network address of the client).

   Server-driven negotiation is advantageous when the algorithm for methods not known
   selecting from among the available representations is difficult to be "safe", as defined in
   Section 6.1.1, automatic redirection needs
   describe to done with care, since the redirect might change user agent, or when the conditions under which server desires to send its
   "best guess" to the request was
   issued.

   Clients SHOULD detect and intervene in cyclical redirections (i.e.,
   "infinite" redirection loops).

      Note: An earlier version client along with the first response (hoping to
   avoid the round-trip delay of this specification recommended a
      maximum of five redirections ([RFC2068], Section 10.3).  Content
      developers need subsequent request if the "best
   guess" is good enough for the user).  In order to be aware that some clients might implement improve the
   server's guess, the user agent MAY include request header fields
   (Accept, Accept-Language, Accept-Encoding, etc.) which describe its
   preferences for such a fixed limitation.

7.3.1.  300 Multiple Choices

   The target resource has more than one representation, each with its
   own specific location, and agent-driven response.

   Server-driven negotiation information
   (Section 5 of [Part3]) has disadvantages:

   1.  It is being provided so that impossible for the user (or user
   agent) can select a preferred representation by redirecting its
   request server to that location.

   Unless it was a HEAD request, accurately determine what
       might be "best" for any given user, since that would require
       complete knowledge of both the response SHOULD include a
   representation containing a list capabilities of representation metadata the user agent and
   location(s) from which
       the intended use for the response (e.g., does the user want to
       view it on screen or print it on paper?).

   2.  Having the user agent describe its capabilities in every request
       can choose the one most
   appropriate.  Depending upon the format be both very inefficient (given that only a small percentage
       of responses have multiple representations) and the capabilities a potential
       violation of the
   user agent, selection user's privacy.

   3.  It complicates the implementation of an origin server and the most appropriate choice MAY be performed
   automatically.  However, this specification does not define any
   standard
       algorithms for such automatic selection.

   If the server has generating responses to a preferred choice of representation, it SHOULD
   include request.

   4.  It might limit a public cache's ability to use the specific URI same response
       for that representation in multiple user's requests.

   Server-driven negotiation allows the Location
   field; user agents MAY use agent to specify its
   preferences, but it cannot expect responses to always honor them.
   For example, the Location field value origin server might not implement server-driven
   negotiation, or it might decide that sending a response that doesn't
   conform to them is better than sending a 406 (Not Acceptable)
   response.

   Many of the mechanisms for automatic
   redirection.

   Caches MAY expressing preferences use a heuristic (see quality values
   to declare relative preference.  See Section 2.3.1.1 4.3.1 of [Part6]) to
   determine freshness [Part1] for 300 responses.

7.3.2.  301 Moved Permanently

   The target resource has been assigned a new permanent URI
   more information.

   HTTP/1.1 includes the following header fields for enabling server-
   driven negotiation through description of user agent capabilities and
   user preferences: Accept (Section 9.1), Accept-Charset (Section 9.2),
   Accept-Encoding (Section 9.3), Accept-Language (Section 9.4), and
   User-Agent (Section 9.18).  However, an origin server is not limited
   to these dimensions and MAY vary the response based on any
   future references to this resource SHOULD use one aspect of
   the returned
   URIs.  Clients with link editing capabilities ought to automatically
   re-link references to the effective request URI to one or more request, including aspects of the
   new references returned connection (e.g., IP address)
   or information within extension header fields not defined by the server, where possible.

   Caches MAY use a heuristic (see Section 2.3.1.1 of [Part6]) to
   determine freshness for 301 responses.

   The this
   specification.

      Note: In practice, User-Agent based negotiation is fragile,
      because new permanent URI SHOULD clients might not be given by the Location recognized.

   The Vary header field in the
   response.  A response payload (Section 7.5 of [Part6]) can contain a short hypertext note with
   a hyperlink be used to express
   the new URI(s).

      Note: For historic reasons, user agents MAY change parameters the request
      method from POST server uses to GET for the subsequent request.  If this
      behavior is undesired, status code 307 (Temporary Redirect) can be
      used instead.

7.3.3.  302 Found

   The target resource resides temporarily under select a different URI.  Since
   the redirection might be altered on occasion, the client SHOULD
   continue representation that is
   subject to use server-driven negotiation.

8.2.  Agent-driven Negotiation

   With agent-driven negotiation, selection of the effective request URI best representation
   for future requests.

   The temporary URI SHOULD be given a response is performed by the Location field in the
   response.  A user agent after receiving an
   initial response payload can contain a short hypertext note with from the origin server.  Selection is based on a hyperlink to
   list of the new URI(s).

      Note: For historic reasons, user agents MAY change available representations of the request
      method response included within
   the header fields or body of the initial response, with each
   representation identified by its own URI.  Selection from POST to GET for among the subsequent request.  If this
      behavior is undesired, status code 307 (Temporary Redirect)
   representations can be
      used instead.

7.3.4.  303 See Other

   The 303 status code indicates that the server is redirecting performed automatically (if the user agent to a different resource, as indicated is
   capable of doing so) or manually by a URI in the Location
   header field, that user selecting from a
   generated (possibly hypertext) menu.

   Agent-driven negotiation is intended to provide an indirect advantageous when the response to would vary
   over commonly-used dimensions (such as type, language, or encoding),
   when the
   original request.  In order origin server is unable to satisfy the original request, determine a user
   agent SHOULD perform a retrieval request using agent's
   capabilities from examining the Location URI (a
   GET or HEAD request if using HTTP), which may itself be redirected
   further, request, and present the eventual result as an answer generally when public
   caches are used to distribute server load and reduce network usage.

   Agent-driven negotiation suffers from the original
   request.  Note that the new URI in the Location header field is not
   considered equivalent disadvantage of needing a
   second request to obtain the effective request URI. best alternate representation.  This status code
   second request is generally applicable to any HTTP method.  It only efficient when caching is
   primarily used.  In addition,
   this specification does not define any mechanism for supporting
   automatic selection, though it also does not prevent any such
   mechanism from being developed as an extension and used to allow within
   HTTP/1.1.

   This specification defines the output of a POST action to redirect 300 (Multiple Choices) and 406 (Not
   Acceptable) status codes for enabling agent-driven negotiation when
   the
   user agent server is unwilling or unable to provide a selected resource, since doing so provides the
   information corresponding to varying response using
   server-driven negotiation.

9.  Header Field Definitions

   This section defines the POST response in a form that can be
   separately identified, bookmarked, syntax and cached independent semantics of the
   original request.

   A 303 response HTTP/1.1 header
   fields related to a GET request indicates that and response semantics and to the requested resource
   does not have a representation payload
   of its own that messages.

9.1.  Accept

   The "Accept" header field can be transferred used by
   the server over HTTP.  The Location URI indicates a resource that is
   descriptive of the target resource, such user agents to specify
   response media types that the follow-on
   representation might are acceptable.  Accept header fields can
   be useful used to recipients without implying indicate that it
   adequately represents the target resource.  Note that answers request is specifically limited to the
   questions of what can be represented, what representations are
   adequate, and what might be a useful description are outside the
   scope
   small set of HTTP and thus entirely determined by the URI owner(s).

   Except for responses to a HEAD request, desired types, as in the representation case of a 303
   response SHOULD contain a short hypertext note with a hyperlink request for an in-
   line image.

     Accept = #( media-range [ accept-params ] )

     media-range    = ( "*/*"
                      / ( type "/" "*" )
                      / ( type "/" subtype )
                      ) *( OWS ";" OWS parameter )
     accept-params  = OWS ";" OWS "q=" qvalue *( accept-ext )
     accept-ext     = OWS ";" OWS token [ "=" word ]

   The asterisk "*" character is used to
   the Location URI.

7.3.5.  305 Use Proxy group media types into ranges,
   with "*/*" indicating all media types and "type/*" indicating all
   subtypes of that type.  The 305 status code was defined in media-range MAY include media type
   parameters that are applicable to that range.

   Each media-range MAY be followed by one or more accept-params,
   beginning with the "q" parameter for indicating a previous version of this
   specification (see Appendix A), and is now deprecated.

7.3.6.  306 (Unused) relative quality
   factor.  The 306 status code was used in a previous version first "q" parameter (if any) separates the media-range
   parameter(s) from the accept-params.  Quality factors allow the user
   or user agent to indicate the relative degree of preference for that
   media-range, using the
   specification, qvalue scale from 0 to 1 (Section 4.3.1 of
   [Part1]).  The default value is no longer used, and q=1.

      Note: Use of the code "q" parameter name to separate media type
      parameters from Accept extension parameters is reserved.

7.3.7.  307 Temporary Redirect

   The target resource resides temporarily under due to historical
      practice.  Although this prevents any media type parameter named
      "q" from being used with a different URI.  Since media range, such an event is believed
      to be unlikely given the redirection can change over time, lack of any "q" parameters in the client SHOULD continue to
   use IANA
      media type registry and the effective request URI for future requests. rare usage of any media type
      parameters in Accept.  Future media types are discouraged from
      registering any parameter named "q".

   The temporary URI example
     Accept: audio/*; q=0.2, audio/basic

   SHOULD be given by interpreted as "I prefer audio/basic, but send me any audio
   type if it is the Location field best available after an 80% mark-down in the
   response. quality".

   A response payload can contain a short hypertext note with
   a hyperlink to the new URI(s).

      Note: This status code is similar to 302 Found, except request without any Accept header field implies that it
      does not allow rewriting the user agent
   will accept any media type in response.  If an Accept header field is
   present in a request method from POST to GET.
      This specification defines no equivalent counterpart for 301 Moved
      Permanently.

7.4.  Client Error 4xx

   The 4xx class and none of status code is intended the available representations for cases in which
   the
   client seems to response have erred.  Except when responding to a HEAD
   request, media type that is listed as acceptable, the
   origin server SHOULD include MAY either honor the Accept header field by sending a representation containing an
   explanation of
   406 (Not Acceptable) response or disregard the error situation, and whether Accept header field by
   treating the response as if it is a temporary or
   permanent condition.  These status codes are applicable to any
   request method.  User agents SHOULD display any included
   representation not subject to content negotiation.

   A more elaborate example is

     Accept: text/plain; q=0.5, text/html,
             text/x-dvi; q=0.8, text/x-c

   Verbally, this would be interpreted as "text/html and text/x-c are
   the user.

7.4.1.  400 Bad Request

   The server cannot or will preferred media types, but if they do not process exist, then send the request, due
   text/x-dvi representation, and if that does not exist, send the text/
   plain representation".

   Media ranges can be overridden by more specific media ranges or
   specific media types.  If more than one media range applies to a client
   error (e.g., malformed syntax).

7.4.2.  402 Payment Required

   This code
   given type, the most specific reference has precedence.  For example,

     Accept: text/*, text/plain, text/plain;format=flowed, */*

   have the following precedence:

   1.  text/plain;format=flowed

   2.  text/plain

   3.  text/*

   4.  */*

   The media type quality factor associated with a given type is reserved
   determined by finding the media range with the highest precedence
   which matches that type.  For example,

     Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
             text/html;level=2;q=0.4, */*;q=0.5

   would cause the following values to be associated:

   +-------------------+---------------+
   | Media Type        | Quality Value |
   +-------------------+---------------+
   | text/html;level=1 | 1             |
   | text/html         | 0.7           |
   | text/plain        | 0.3           |
   | image/jpeg        | 0.5           |
   | text/html;level=2 | 0.4           |
   | text/html;level=3 | 0.7           |
   +-------------------+---------------+

   Note: A user agent might be provided with a default set of quality
   values for future use.

7.4.3.  403 Forbidden

   The server understood certain media ranges.  However, unless the request, but refuses user agent is a
   closed system which cannot interact with other rendering agents, this
   default set ought to authorize it.
   Providing different user authentication credentials might be
   successful, but any credentials that were provided in configurable by the request are
   insufficient. user.

9.2.  Accept-Charset

   The request SHOULD NOT "Accept-Charset" header field can be repeated with the same
   credentials.

   If the request method was not HEAD and the server wishes used by user agents to make
   public why the request has not been fulfilled, it SHOULD describe the
   reason for the refusal
   indicate what character encodings are acceptable in the representation.  If the server does not
   wish a response
   payload.  This field allows clients capable of understanding more
   comprehensive or special-purpose character encodings to make this information available signal that
   capability to the client, the status
   code 404 (Not Found) MAY be used instead.

7.4.4.  404 Not Found

   The a server has not found anything matching the effective request URI.
   No indication which is given capable of whether representing documents in
   those character encodings.

     Accept-Charset = 1#( ( charset / "*" )
                            [ OWS ";" OWS "q=" qvalue ] )

   Character encoding values (a.k.a., charsets) are described in
   Section 5.3.  Each charset MAY be given an associated quality value
   which represents the condition user's preference for that charset.  The default
   value is temporary or
   permanent. q=1.  An example is

     Accept-Charset: iso-8859-5, unicode-1-1;q=0.8

   The 410 (Gone) status code SHOULD be used special value "*", if present in the server
   knows, through some internally configurable mechanism, that an old
   resource Accept-Charset field,
   matches every character encoding which is permanently unavailable and has not mentioned elsewhere in
   the Accept-Charset field.  If no forwarding address.
   This status code "*" is commonly used when the server does present in an Accept-Charset
   field, then all character encodings not wish to
   reveal exactly why the explicitly mentioned get a
   quality value of 0.

   A request has been refused, or when no other
   response without any Accept-Charset header field implies that the
   user agent will accept any character encoding in response.  If an
   Accept-Charset header field is applicable.

7.4.5.  405 Method Not Allowed

   The method specified present in a request and none of the request-line is not allowed
   available representations for the
   target resource.  The response MUST include an Allow have a character encoding
   that is listed as acceptable, the origin server MAY either honor the
   Accept-Charset header field
   containing by sending a list of valid methods for the requested resource.

7.4.6. 406 Not Acceptable

   The resource identified (Not Acceptable)
   response or disregard the Accept-Charset header field by treating the request is only capable of generating
   response representations which have content characteristics as if it is not
   acceptable according subject to the Accept and Accept-* content negotiation.

9.3.  Accept-Encoding

   The "Accept-Encoding" header fields sent field can be used by user agents to
   indicate what response content-codings (Section 5.4) are acceptable
   in the request (see Section 6 of [Part3]).

   Unless it was response.  An "identity" token is used as a HEAD request, synonym for "no
   encoding" in order to communicate when no encoding is preferred.

     Accept-Encoding  = #( codings [ OWS ";" OWS "q=" qvalue ] )
     codings          = content-coding / "identity" / "*"

   Each codings value MAY be given an associated quality value which
   represents the response SHOULD include preference for that encoding.  The default value is
   q=1.

   For example,

     Accept-Encoding: compress, gzip
     Accept-Encoding:
     Accept-Encoding: *
     Accept-Encoding: compress;q=0.5, gzip;q=1.0
     Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0

   A server tests whether a
   representation containing content-coding for a list of available given representation
   characteristics and location(s) from which the user or user agent can
   choose the one most appropriate.  Depending upon the format and the
   capabilities of the user agent, selection of the most appropriate
   choice MAY be performed automatically.  However, this specification
   does not define any standard for such automatic selection.

      Note: HTTP/1.1 servers are allowed is
   acceptable, according to return responses which are an Accept-Encoding field, using these rules:

   1.  The special "*" symbol in an Accept-Encoding field matches any
       available content-coding not acceptable according to explicitly listed in the accept header fields sent in
       field.

   2.  If the
      request.  In some cases, this might even be preferable to sending representation has no content-coding, then it is
       acceptable by default unless specifically excluded by the Accept-
       Encoding field stating either "identity;q=0" or "*;q=0" without a 406 response.  User agents are encouraged to inspect
       more specific entry for "identity".

   3.  If the header
      fields representation's content-coding is one of an incoming response to determine if the content-
       codings listed in the Accept-Encoding field, then it is acceptable.
       acceptable unless it is accompanied by a qvalue of 0.  (As
       defined in Section 4.3.1 of [Part1], a qvalue of 0 means "not
       acceptable".)

   4.  If multiple content-codings are acceptable, then the response could be unacceptable, acceptable
       content-coding with the highest non-zero qvalue is preferred.

   An Accept-Encoding header field with a user agent SHOULD
   temporarily stop receipt of more data and query combined field-value that is
   empty implies that the user for a
   decision on further actions.

7.4.7.  408 Request Timeout

   The client did agent does not produce want any content-coding in
   response.  If an Accept-Encoding header field is present in a request within
   and none of the time available representations for the response have a
   content-coding that is listed as acceptable, the origin server
   was prepared to wait.  The client MAY repeat the request SHOULD
   send a response without
   modifications at any later time.

7.4.8.  409 Conflict

   The content-coding.

   A request could not be completed due to without an Accept-Encoding header field implies that the
   user agent will accept any content-coding in response, but a conflict
   representation without content-coding is preferred for compatibility
   with the current
   state widest variety of the resource. user agents.

      Note: Most HTTP/1.0 applications do not recognize or obey qvalues
      associated with content-codings.  This code is only allowed in situations where
   it is expected means that the user might be able to resolve the conflict qvalues will not
      work and resubmit the request. are not permitted with x-gzip or x-compress.

9.4.  Accept-Language

   The response body SHOULD include enough
   information for the "Accept-Language" header field can be used by user agents to recognize
   indicate the source set of natural languages that are preferred in the conflict.
   Ideally,
   response.  Language tags are defined in Section 5.6.

     Accept-Language =
                       1#( language-range [ OWS ";" OWS "q=" qvalue ] )
     language-range  =
               <language-range, defined in [RFC4647], Section 2.1>

   Each language-range can be given an associated quality value which
   represents an estimate of the response representation would include enough information user's preference for the user or user agent to fix the problem; however, languages
   specified by that might
   not be possible and is not required.

   Conflicts are most likely to occur in response range.  The quality value defaults to a PUT request. "q=1".  For
   example, if versioning were being used

     Accept-Language: da, en-gb;q=0.8, en;q=0.7

   would mean: "I prefer Danish, but will accept British English and
   other types of English". (see also Section 2.3 of [RFC4647])

   For matching, Section 3 of [RFC4647] defines several matching
   schemes.  Implementations can offer the representation being
   PUT included changes most appropriate matching
   scheme for their requirements.

      Note: The "Basic Filtering" scheme ([RFC4647], Section 3.3.1) is
      identical to a resource which conflict with those made by
   an earlier (third-party) request, the server matching scheme that was previously defined in
      Section 14.4 of [RFC2616].

   It might use be contrary to the 409
   response privacy expectations of the user to indicate that it can't send
   an Accept-Language header field with the complete linguistic
   preferences of the user in every request.  In this
   case, the response representation would likely contain  For a list discussion of the
   differences between the two versions.

7.4.9.  410 Gone

   The target resource this
   issue, see Section 11.5.

   As intelligibility is no longer available at highly dependent on the server and no
   forwarding address is known.  This condition individual user, it is expected to be
   considered permanent.  Clients with link editing capabilities SHOULD
   delete references
   recommended that client applications make the choice of linguistic
   preference available to the effective request URI after user approval. user.  If the server does choice is not know, or has no facility made
   available, then the Accept-Language header field MUST NOT be given in
   the request.

      Note: When making the choice of linguistic preference available to determine, whether
   or not
      the condition is permanent, user, we remind implementers of the status code 404 (Not Found)
   SHOULD fact that users are not
      familiar with the details of language matching as described above,
      and ought to be used instead.

   The 410 response provided appropriate guidance.  As an example,
      users might assume that on selecting "en-gb", they will be served
      any kind of English document if British English is primarily intended not available.
      A user agent might suggest in such a case to assist add "en" to get the task
      best matching behavior.

9.5.  Allow

   The "Allow" header field lists the set of web
   maintenance methods advertised as
   supported by notifying the target resource.  The purpose of this field is
   strictly to inform the recipient that of valid request methods associated
   with the resource resource.

     Allow = #method

   Example of use:

     Allow: GET, HEAD, PUT

   The actual set of allowed methods is
   intentionally unavailable and that defined by the origin server owners desire that
   remote links to that resource be removed.  Such an event is common
   for limited-time, promotional services and for resources belonging to
   individuals no longer working at
   the server's site.  It is time of each request.

   A proxy MUST NOT modify the Allow header field -- it does not
   necessary need to mark
   understand all permanently unavailable resources as "gone" or the methods specified in order to handle them
   according to keep the mark for any length of time -- that is left generic message handling rules.

9.6.  Content-Encoding

   The "Content-Encoding" header field indicates what content-codings
   have been applied to the
   discretion of representation beyond those inherent in the server owner.

   Caches MAY use a heuristic (see Section 2.3.1.1 of [Part6])
   media type, and thus what decoding mechanisms have to
   determine freshness for 410 responses.

7.4.10.  411 Length Required

   The server refuses be applied in
   order to accept obtain the request without a defined Content-
   Length.  The client MAY repeat media-type referenced by the request if it adds a valid
   Content-Length Content-Type header field containing
   field.  Content-Encoding is primarily used to allow a representation
   to be compressed without losing the length identity of the message body its underlying media
   type.

     Content-Encoding = 1#content-coding

   Content codings are defined in the request message.

7.4.11.  413 Request Representation Too Large Section 5.4.  An example of its use is
     Content-Encoding: gzip

   The server content-coding is refusing to process a request because characteristic of the representation.
   Typically, the request representation body is larger than the server stored with this encoding and
   is willing only decoded before rendering or able to
   process.  The server analogous usage.  However, a
   transforming proxy MAY close the connection to prevent the client
   from continuing modify the request.

   If content-coding if the condition new coding is temporary, the server SHOULD include a Retry-
   After header field
   known to indicate that it is temporary and after what
   time the client MAY try again.

7.4.12.  414 URI Too Long

   The server is refusing be acceptable to service the request because recipient, unless the effective
   request URI "no-transform"
   cache-control directive is longer than present in the server is willing to interpret.  This
   rare condition is only likely to occur when a client has improperly
   converted a POST request to a GET request with long query
   information, when message.

   If the client has descended into a URI "black hole" of
   redirection (e.g., media type includes an inherent encoding, such as a redirected URI prefix data
   format that is always compressed, then that points to encoding would not be
   restated as a suffix Content-Encoding even if it happens to be the same
   algorithm as one of
   itself), or when the server content-codings.  Such a content-coding would
   only be listed if, for some bizarre reason, it is under attack by applied a client attempting second
   time to
   exploit security holes present in some servers using fixed-length
   buffers for reading or manipulating form the request-target.

7.4.13.  415 Unsupported Media Type

   The representation.  Likewise, an origin server is refusing might
   choose to service the request because publish the request same payload is data as multiple representations
   that differ only in a format not supported by this request method on whether the
   target resource.

7.4.14.  417 Expectation Failed

   The expectation given coding is defined as part of Content-
   Type or Content-Encoding, since some user agents will behave
   differently in an Expect their handling of each response (e.g., open a "Save as
   ..." dialog instead of automatic decompression and rendering of
   content).

   A representation that has a content-coding applied to it MUST include
   a Content-Encoding header field (see Section 10.3)
   could not be met by this server, or, if that lists the server is content-coding(s)
   applied.

   If multiple encodings have been applied to a proxy, representation, the
   server has unambiguous evidence that
   content codings MUST be listed in the request could not order in which they were
   applied.  Additional information about the encoding parameters MAY be met
   provided by other header fields not defined by this specification.

   If the next-hop server.

7.4.15.  426 Upgrade Required

   The content-coding of a representation in a request can message is not be completed without a prior protocol upgrade.
   This response MUST include an Upgrade header field (Section 6.5 of
   [Part1]) specifying
   acceptable to the required protocols.

   Example:

     HTTP/1.1 426 Upgrade Required
     Upgrade: HTTP/3.0
     Connection: Upgrade
     Content-Length: 53
     Content-Type: text/plain

     This service requires use of origin server, the HTTP/3.0 protocol.

   The server SHOULD include respond with a message body in
   status code of 415 (Unsupported Media Type).

9.7.  Content-Language

   The "Content-Language" header field describes the 426 response which
   indicates in human readable form natural language(s)
   of the reason intended audience for the error and
   describes any alternative courses which may representation.  Note that this
   might not be available equivalent to all the user.

7.5.  Server Error 5xx

   Response status codes beginning with languages used within the digit "5" indicate cases
   representation.

     Content-Language = 1#language-tag

   Language tags are defined in
   which the server is aware that it has erred or is incapable of
   performing the request.  Except when responding to a HEAD request,
   the server SHOULD include a representation containing an explanation Section 5.6.  The primary purpose of the error situation, and whether it
   Content-Language is to allow a temporary or permanent
   condition.  User agents SHOULD display any included representation user to
   the user.  These response codes are applicable identify and differentiate
   representations according to any request method.

7.5.1.  500 Internal Server Error

   The server encountered an unexpected condition which prevented it
   from fulfilling the request.

7.5.2.  501 Not Implemented

   The server does not support the functionality required to fulfill user's own preferred language.
   Thus, if the
   request.  This body content is intended only for a Danish-literate
   audience, the appropriate response when field is

     Content-Language: da

   If no Content-Language is specified, the server does not
   recognize default is that the request method and content
   is not capable of supporting it intended for
   any resource.

7.5.3.  502 Bad Gateway

   The server, while acting as a gateway or proxy, received an invalid
   response from all language audiences.  This might mean that the upstream server
   sender does not consider it accessed in attempting to
   fulfill the request.

7.5.4.  503 Service Unavailable

   The server is currently unable to handle the request due be specific to a
   temporary overloading any natural language,
   or maintenance of that the server.

   The implication sender does not know for which language it is intended.

   Multiple languages MAY be listed for content that this is intended for
   multiple audiences.  For example, a temporary condition which will be
   alleviated after some delay.  If known, the length rendition of the delay MAY
   be indicated "Treaty of
   Waitangi", presented simultaneously in a Retry-After header field (Section 10.8).  If no
   Retry-After is given, the client SHOULD handle the response as it original Maori and English
   versions, would call for

     Content-Language: mi, en

   However, just because multiple languages are present within a 500 response.

      Note: The existence of the 503 status code
   representation does not imply mean that a
      server must use it when becoming overloaded.  Some servers might
      wish is intended for multiple
   linguistic audiences.  An example would be a beginner's language
   primer, such as "A First Lesson in Latin", which is clearly intended
   to simply refuse be used by an English-literate audience.  In this case, the connection.

7.5.5.  504 Gateway Timeout
   Content-Language would properly only include "en".

   Content-Language MAY be applied to any media type -- it is not
   limited to textual documents.

9.8.  Content-Location

   The server, while acting as "Content-Location" header field supplies a gateway or proxy, did not receive URI that can be used
   as a
   timely response from the upstream server specified by specific identifier for the URI (e.g.,
   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
   to access representation in attempting this message.  In
   other words, if one were to complete perform a GET on this URI at the request.

      Note to implementors: some deployed proxies are known to return
      400 or 500 when DNS lookups time out.

7.5.6.  505 HTTP Version Not Supported

   The server does not support, or refuses to support, of
   this message's generation, then a 200 (OK) response would contain the protocol
   version
   same representation that was used is enclosed as payload in the request this message.

     Content-Location = absolute-URI / partial-URI

   The server is
   indicating that it Content-Location value is unable or unwilling to complete not a replacement for the request
   using effective
   Request URI (Section 5.5 of [Part1]).  It is representation metadata.
   It has the same major version syntax and semantics as the client, as described header field of the same
   name defined for MIME body parts in Section
   2.6 4 of [Part1], other than with this error message.  The response
   SHOULD contain a representation describing why that version is not
   supported and what other protocols are supported by that server.

8.  Date/Time Formats [RFC2557].  However,
   its appearance in an HTTP applications have historically allowed three different formats message has some special implications for date/time stamps.  However, the preferred format
   HTTP recipients.

   If Content-Location is included in a fixed-
   length subset of that defined by [RFC1123]:

     Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123

   The other formats are described here only for compatibility with
   obsolete implementations.

     Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
     Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format

   HTTP/1.1 clients response message and servers that parse a date its value MUST accept all
   three formats (for compatibility with HTTP/1.0), though they MUST
   only generate
   is the RFC 1123 format for representing HTTP-date values
   in header fields.

   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
   (GMT), without exception.  For same as the purposes of HTTP, GMT is exactly
   equal to UTC (Coordinated Universal Time).  This is indicated in effective request URI, then the
   first two formats by response payload
   SHOULD be considered a current representation of that resource.  For
   a GET or HEAD request, this is the inclusion of "GMT" same as the three-letter
   abbreviation for time zone, and MUST be assumed default semantics when reading the
   asctime format.  HTTP-date
   no Content-Location is case sensitive and MUST NOT include
   additional whitespace beyond provided by the server.  For a state-changing
   request like PUT or POST, it implies that specifically included as SP in the
   grammar.

     HTTP-date    = rfc1123-date / obs-date

   Preferred format:

     rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
     ; fixed length subset of server's response
   contains the format defined in
     ; Section 5.2.14 of [RFC1123]

     day-name     = %x4D.6F.6E ; "Mon", case-sensitive
                  / %x54.75.65 ; "Tue", case-sensitive
                  / %x57.65.64 ; "Wed", case-sensitive
                  / %x54.68.75 ; "Thu", case-sensitive
                  / %x46.72.69 ; "Fri", case-sensitive
                  / %x53.61.74 ; "Sat", case-sensitive
                  / %x53.75.6E ; "Sun", case-sensitive

     date1        = day SP month SP year
                  ; e.g., 02 Jun 1982

     day          = 2DIGIT
     month        = %x4A.61.6E ; "Jan", case-sensitive
                  / %x46.65.62 ; "Feb", case-sensitive
                  / %x4D.61.72 ; "Mar", case-sensitive
                  / %x41.70.72 ; "Apr", case-sensitive
                  / %x4D.61.79 ; "May", case-sensitive
                  / %x4A.75.6E ; "Jun", case-sensitive
                  / %x4A.75.6C ; "Jul", case-sensitive
                  / %x41.75.67 ; "Aug", case-sensitive
                  / %x53.65.70 ; "Sep", case-sensitive
                  / %x4F.63.74 ; "Oct", case-sensitive
                  / %x4E.6F.76 ; "Nov", case-sensitive
                  / %x44.65.63 ; "Dec", case-sensitive
     year         = 4DIGIT

     GMT   = %x47.4D.54 ; "GMT", case-sensitive

     time-of-day  = hour ":" minute ":" second
                    ; 00:00:00 - 23:59:59

     hour         = 2DIGIT
     minute       = 2DIGIT
     second       = 2DIGIT

   The semantics new representation of day-name, day, month, year, and time-of-day are that resource, thereby
   distinguishing it from representations that might only report about
   the action (e.g., "It worked!").  This allows authoring applications
   to update their local copies without the
   same as those defined need for a subsequent GET
   request.

   If Content-Location is included in a response message and its value
   differs from the RFC 5322 constructs with effective request URI, then the
   corresponding name ([RFC5322], Section 3.3).

   Obsolete formats:

     obs-date     = rfc850-date / asctime-date
     rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
     date2        = day "-" month "-" 2DIGIT
                    ; day-month-year (e.g., 02-Jun-82)

     day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
            / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
            / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
            / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
            / %x46.72.69.64.61.79 ; "Friday", case-sensitive
            / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
            / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive

     asctime-date = day-name SP date3 SP time-of-day SP year
     date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
                    ; month day (e.g., Jun  2)

      Note: Recipients of date values are encouraged origin server is
   informing recipients that this representation has its own, presumably
   more specific, identifier.  For a GET or HEAD request, this is an
   indication that the effective request URI identifies a resource that
   is subject to content negotiation and the selected representation for
   this response can also be robust in
      accepting date values found at the identified URI.  For other
   methods, such a Content-Location indicates that this representation
   contains a report on the action's status and the same report is
   available (for future access with GET) at the given URI.  For
   example, a purchase transaction made via a POST request might have been sent include
   a receipt document as the payload of the 200 (OK) response; the
   Content-Location value provides an identifier for retrieving a copy
   of that same receipt in the future.

   If Content-Location is included in a request message, then it MAY be
   interpreted by non-HTTP
      applications, the origin server as is sometimes an indication of where the case when retrieving or posting
      messages via proxies/gateways to SMTP or NNTP.

      Note: HTTP requirements for user
   agent originally obtained the date/time stamp format apply only
      to their usage within content of the protocol stream.  Clients and servers
      are not required enclosed representation
   (prior to use these formats for any subsequent modification of the content by that user presentation,
      request logging, etc.

9.  Product Tokens

   Product tokens are
   agent).  In other words, the user agent is providing the same
   representation metadata that it received with the original
   representation.  However, such interpretation MUST NOT be used to allow communicating applications to
   identify themselves
   alter the semantics of the method requested by software name and version.  Most fields using
   product tokens also allow sub-products which form the client.  For
   example, if a significant part
   of client makes a PUT request on a negotiated resource and
   the application origin server accepts that PUT (without redirection), then the
   new set of values for that resource is expected to be listed, separated by whitespace.  By
   convention, consistent with
   the products are listed one representation supplied in order that PUT; the Content-Location
   cannot be used as a form of reverse content selection that identifies
   only one of their significance
   for identifying the application.

     product         = token ["/" product-version]
     product-version = token

   Examples:

     User-Agent: CERN-LineMode/2.15 libwww/2.17b3
     Server: Apache/0.8.4

   Product tokens SHOULD negotiated representations to be short and updated.  If the
   user agent had wanted the latter semantics, it would have applied the
   PUT directly to the point.  They MUST NOT be
   used for advertising or other non-essential information.  Although
   any token octet MAY appear Content-Location URI.

   A Content-Location field received in a product-version, this token request message is transitory
   information that SHOULD
   only NOT be used saved with other representation
   metadata for a version identifier (i.e., successive versions of
   the same product SHOULD only differ use in later responses.  The Content-Location's value
   might be saved for use in other contexts, such as within source links
   or other metadata.

   A cache cannot assume that a representation with a Content-Location
   different from the product-version portion of URI used to retrieve it can be used to respond to
   later requests on that Content-Location URI.

   If the product value).

10.  Header Field Definitions

   This section defines Content-Location value is a partial URI, the syntax and semantics of HTTP/1.1 header
   fields related partial URI is
   interpreted relative to the effective request and response semantics.

10.1.  Allow URI.

9.9.  Content-Type

   The "Allow" "Content-Type" header field lists indicates the set media type of methods advertised as
   supported by the target resource.  The purpose
   representation.  In the case of this field is
   strictly responses to inform the recipient of valid request methods associated
   with HEAD method, the resource.

     Allow = #method

   Example of use:

     Allow: GET, HEAD, PUT

   The actual set of allowed methods
   media type is defined by the origin server at that which would have been sent had the time request been a
   GET.

     Content-Type = media-type

   Media types are defined in Section 5.5.  An example of each request.

   A proxy MUST NOT modify the Allow header field -- it does not need to
   understand all the methods specified is

     Content-Type: text/html; charset=ISO-8859-4

   Further discussion of Content-Type is provided in order to handle them
   according to the generic message handling rules.

10.2. Section 7.3.

9.10.  Date

   The "Date" header field represents the date and time at which the
   message was originated, having the same semantics as the Origination
   Date Field (orig-date) defined in Section 3.6.1 of [RFC5322].  The
   field value is an HTTP-date, as defined in Section 8; 5.1; it MUST be
   sent in rfc1123-date format.

     Date = HTTP-date

   An example is

     Date: Tue, 15 Nov 1994 08:12:31 GMT

   Origin servers MUST include a Date header field in all responses,
   except in these cases:

   1.  If the response status code is 100 (Continue) or 101 (Switching
       Protocols), the response MAY include a Date header field, at the
       server's option.

   2.  If the response status code conveys a server error, e.g., 500
       (Internal Server Error) or 503 (Service Unavailable), and it is
       inconvenient or impossible to generate a valid Date.

   3.  If the server does not have a clock that can provide a reasonable
       approximation of the current time, its responses MUST NOT include
       a Date header field.

   A received message that does not have a Date header field MUST be
   assigned one by the recipient if the message will be cached by that
   recipient.

   Clients can use the Date header field as well; in order to keep
   request messages small, they are advised not to include it when it
   doesn't convey any useful information (as is usually the case for
   requests that do not contain a payload).

   The HTTP-date sent in a Date header field SHOULD NOT represent a date
   and time subsequent to the generation of the message.  It SHOULD
   represent the best available approximation of the date and time of
   message generation, unless the implementation has no means of
   generating a reasonably accurate date and time.  In theory, the date
   ought to represent the moment just before the payload is generated.
   In practice, the date can be generated at any time during the message
   origination without affecting its semantic value.

10.3.

9.11.  Expect

   The "Expect" header field is used to indicate that particular server
   behaviors are required by the client.

     Expect       = 1#expectation

     expectation  = expect-name [ BWS "=" BWS expect-value ]
                                *( OWS ";" [ OWS expect-param ] )
     expect-param = expect-name [ BWS "=" BWS expect-value ]

     expect-name  = token
     expect-value = token / quoted-string

   If all received Expect header field(s) are syntactically valid but
   contain an expectation that the recipient does not understand or
   cannot comply with, the recipient MUST respond with a 417
   (Expectation Failed) status code.  A recipient of a syntactically
   invalid Expectation header field MUST respond with a 4xx status code
   other than 417.

   The only expectation defined by this specification is:

   100-continue

      The "100-continue" expectation is defined Section 6.4.3 of
      [Part1].  It does not support any expect-params.

   Comparison is case-insensitive for names (expect-name), and case-
   sensitive for values (expect-value).

   The Expect mechanism is hop-by-hop: the above requirements apply to
   any server, including proxies.  However, the Expect header field
   itself is end-to-end; it MUST be forwarded if the request is
   forwarded.

   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
   Expect header field.

10.4.

9.12.  From

   The "From" header field, if given, SHOULD contain an Internet e-mail
   address for the human user who controls the requesting user agent.
   The address SHOULD be machine-usable, as defined by "mailbox" in
   Section 3.4 of [RFC5322]:

     From    = mailbox

     mailbox = <mailbox, defined in [RFC5322], Section 3.4>

   An example is:

     From: webmaster@example.org

   This header field MAY be used for logging purposes and as a means for
   identifying the source of invalid or unwanted requests.  It SHOULD
   NOT be used as an insecure form of access protection.  The
   interpretation of this field is that the request is being performed
   on behalf of the person given, who accepts responsibility for the
   method performed.  In particular, robot agents SHOULD include this
   header field so that the person responsible for running the robot can
   be contacted if problems occur on the receiving end.

   The Internet e-mail address in this field MAY be separate from the
   Internet host which issued the request.  For example, when a request
   is passed through a proxy the original issuer's address SHOULD be
   used.

   The client SHOULD NOT send the From header field without the user's
   approval, as it might conflict with the user's privacy interests or
   their site's security policy.  It is strongly recommended that the
   user be able to disable, enable, and modify the value of this field
   at any time prior to a request.

10.5.

9.13.  Location

   The "Location" header field MAY be sent in responses to refer to a
   specific resource in accordance with the semantics of the status
   code.

     Location = URI-reference

   For 201 (Created) responses, the Location is the URI of the new
   resource which was created by the request.  For 3xx (Redirection)
   responses, the location SHOULD indicate the server's preferred URI
   for automatic redirection to the resource.

   The field value consists of a single URI-reference.  When it has the
   form of a relative reference ([RFC3986], Section 4.2), the final
   value is computed by resolving it against the effective request URI
   ([RFC3986], Section 5).  If the original URI, as navigated to by the
   user agent, did contain a fragment identifier, and the final value
   does not, then the original URI's fragment identifier is added to the
   final value.

   For example, the original URI "http://www.example.org/~tim", combined
   with a field value given as:

     Location: /pub/WWW/People.html#tim

   would result in a final value of
   "http://www.example.org/pub/WWW/People.html#tim"

   An original URI "http://www.example.org/index.html#larry", combined
   with a field value given as:

     Location: http://www.example.net/index.html

   would result in a final value of
   "http://www.example.net/index.html#larry", preserving the original
   fragment identifier.

      Note: Some recipients attempt to recover from Location fields that
      are not valid URI references.  This specification does not mandate
      or define such processing, but does allow it (see Section 1.1). it.

   There are circumstances in which a fragment identifier in a Location
   URI would not be appropriate.  For instance, when it appears in a 201
   Created
   (Created) response, where the Location header field specifies the URI
   for the entire created resource.

      Note: The Content-Location header field (Section 6.7 of [Part3]) 9.8) differs from
      Location in that the Content-Location identifies the most specific
      resource corresponding to the enclosed representation.  It is
      therefore possible for a response to contain header fields for
      both Location and Content-Location.

10.6.

9.14.  Max-Forwards

   The "Max-Forwards" header field provides a mechanism with the TRACE
   (Section 6.8) 2.3.7) and OPTIONS (Section 6.2) 2.3.1) methods to limit the
   number of times that the request is forwarded by proxies.  This can
   be useful when the client is attempting to trace a request which
   appears to be failing or looping mid-chain.

     Max-Forwards = 1*DIGIT

   The Max-Forwards value is a decimal integer indicating the remaining
   number of times this request message can be forwarded.

   Each recipient of a TRACE or OPTIONS request containing a Max-
   Forwards header field MUST check and update its value prior to
   forwarding the request.  If the received value is zero (0), the
   recipient MUST NOT forward the request; instead, it MUST respond as
   the final recipient.  If the received Max-Forwards value is greater
   than zero, then the forwarded message MUST contain an updated Max-
   Forwards field with a value decremented by one (1).

   The Max-Forwards header field MAY be ignored for all other request
   methods.

10.7.

9.15.  Referer

   The "Referer" [sic] header field allows the client to specify the URI
   of the resource from which the target URI was obtained (the
   "referrer", although the header field is misspelled.).

   The Referer header field allows servers to generate lists of back-
   links to resources for interest, logging, optimized caching, etc.  It
   also allows obsolete or mistyped links to be traced for maintenance.
   Some servers use Referer as a means of controlling where they allow
   links from (so-called "deep linking"), but legitimate requests do not
   always contain a Referer header field.

   If the target URI was obtained from a source that does not have its
   own URI (e.g., input from the user keyboard), the Referer field MUST
   either be sent with the value "about:blank", or not be sent at all.
   Note that this requirement does not apply to sources with non-HTTP
   URIs (e.g., FTP).

     Referer = absolute-URI / partial-URI

   Example:

     Referer: http://www.example.org/hypertext/Overview.html

   If the field value is a relative URI, it SHOULD be interpreted
   relative to the effective request URI.  The URI MUST NOT include a
   fragment.  See Section 12.2 11.2 for security considerations.

10.8.

9.16.  Retry-After

   The header "Retry-After" field can be used with a 503 (Service
   Unavailable) response to indicate how long the service is expected to
   be unavailable to the requesting client.  This field MAY also be used
   with any 3xx (Redirection) response to indicate the minimum time the
   user-agent is asked to wait before issuing the redirected request.

   The value of this field can be either an HTTP-date or an integer
   number of seconds (in decimal) after the time of the response.

     Retry-After = HTTP-date / delta-seconds

   Time spans are non-negative decimal integers, representing time in
   seconds.

     delta-seconds  = 1*DIGIT

   Two examples of its use are

     Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
     Retry-After: 120

   In the latter example, the delay is 2 minutes.

10.9.

9.17.  Server

   The "Server" header field contains information about the software
   used by the origin server to handle the request.

   The field can contain multiple product tokens (Section 9) 5.2) and
   comments (Section 3.2 of [Part1]) identifying the server and any
   significant subproducts.  The product tokens are listed in order of
   their significance for identifying the application.

     Server = product *( RWS ( product / comment ) )

   Example:

     Server: CERN/3.0 libwww/2.17

   If the response is being forwarded through a proxy, the proxy
   application MUST NOT modify the Server header field.  Instead, it
   MUST include a Via field (as described in Section 6.2 of [Part1]).

      Note: Revealing the specific software version of the server might
      allow the server machine to become more vulnerable to attacks
      against software that is known to contain security holes.  Server
      implementors
      implementers are encouraged to make this field a configurable
      option.

10.10.

9.18.  User-Agent

   The "User-Agent" header field contains information about the user
   agent originating the request.  User agents SHOULD include this field
   with requests.

   Typically, it is used for statistical purposes, the tracing of
   protocol violations, and tailoring responses to avoid particular user
   agent limitations.

   The field can contain multiple product tokens (Section 9) 5.2) and
   comments (Section 3.2 of [Part1]) identifying the agent and its
   significant subproducts.  By convention, the product tokens are
   listed in order of their significance for identifying the
   application.

   Because this field is usually sent on every request a user agent
   makes, implementations are encouraged not to include needlessly fine-
   grained detail, and to limit (or even prohibit) the addition of
   subproducts by third parties.  Overly long and detailed User-Agent
   field values make requests larger and can also be used to identify
   ("fingerprint") the user against their wishes.

   Likewise, implementations are encouraged not to use the product
   tokens of other implementations in order to declare compatibility
   with them, as this circumvents the purpose of the field.  Finally,
   they are encouraged not to use comments to identify products; doing
   so makes the field value more difficult to parse.

     User-Agent = product *( RWS ( product / comment ) )

   Example:

     User-Agent: CERN-LineMode/2.15 libwww/2.17b3

11.

10.  IANA Considerations

11.1.

10.1.  Method Registry

   The registration procedure for HTTP request methods is defined by
   Section 2.2 of this document.

   The HTTP Method Registry shall be created at
   <http://www.iana.org/assignments/http-methods> and be populated with
   the registrations below:

   +---------+------+-------------+ 2.2 of this document.

   The HTTP Method Registry shall be created at
   <http://www.iana.org/assignments/http-methods> and be populated with
   the registrations below:

   +---------+------+------------+---------------+
   | Method  | Safe | Idempotent | Reference     |
   +---------+------+------------+---------------+
   | CONNECT | no   | no         | Section 2.3.8 |
   | DELETE  | no   | yes        | Section 2.3.6 |
   | GET     | yes  | yes        | Section 2.3.2 |
   | HEAD    | yes  | yes        | Section 2.3.3 |
   | OPTIONS | yes  | yes        | Section 2.3.1 |
   | POST    | no   | no         | Section 2.3.4 |
   | PUT     | no   | yes        | Section 2.3.5 |
   | TRACE   | yes  | yes        | Section 2.3.7 |
   +---------+------+------------+---------------+

10.2.  Status Code Registry

   The registration procedure for HTTP Status Codes -- previously
   defined in Section 7.1 of [RFC2817] -- is now defined by Section 4.2
   of this document.

   The HTTP Status Code Registry located at
   <http://www.iana.org/assignments/http-status-codes> shall be updated
   with the registrations below:

   +-------+----------------------------------+----------------+
   | Value | Description                      | Reference      |
   +-------+----------------------------------+----------------+
   | 100   | Continue                         | Section 4.3.1  |
   | 101   | Switching Protocols              | Section 4.3.2  |
   | 200   | OK                               | Section 4.4.1  |
   | 201   | Created                          | Section 4.4.2  |
   | 202   | Accepted                         | Section 4.4.3  |
   | 203   | Non-Authoritative Information    | Section 4.4.4  |
   | 204   | No Content                       | Section 4.4.5  |
   | 205   | Reset Content                    | Section 4.4.6  |
   | 300   | Multiple Choices                 | Section 4.5.1  |
   | 301   | Moved Permanently                | Section 4.5.2  |
   | 302   | Found                            | Section 4.5.3  |
   | 303   | See Other                        | Section 4.5.4  |
   | 305   | Use Proxy                        | Section 4.5.5  | Method
   | Safe 306   | Reference (Unused)                         |
   +---------+------+-------------+ Section 4.5.6  | CONNECT
   | no 307   | Temporary Redirect               | Section 6.9 4.5.7  |
   | DELETE 400   | no Bad Request                      | Section 6.7 4.6.1  |
   | GET 402   | yes Payment Required                 | Section 6.3 4.6.2  |
   | HEAD 403   | yes Forbidden                        | Section 6.4 4.6.3  |
   | OPTIONS 404   | yes Not Found                        | Section 6.2 4.6.4  |
   | POST 405   | no Method Not Allowed               | Section 6.5 4.6.5  |
   | PUT 406   | no Not Acceptable                   | Section 6.6 4.6.6  |
   | TRACE 408   | yes Request Timeout                  | Section 6.8 4.6.7  |
   | 409   | Conflict                         |
   +---------+------+-------------+

11.2.  Status Code Registry

   The registration procedure for HTTP Status Codes -- previously
   defined in Section 7.1 of [RFC2817] -- is now defined by 4.6.8  |
   | 410   | Gone                             | Section 4.2
   of this document.

   The HTTP Status Code Registry located at
   <http://www.iana.org/assignments/http-status-codes> shall be updated
   with the registrations below:

   +-------+----------------------------------+----------------+ 4.6.9  | Value
   | Description 411   | Reference Length Required                  |
   +-------+----------------------------------+----------------+ Section 4.6.10 | 100
   | Continue 413   | Request Representation Too Large | Section 7.1.1 4.6.11 |
   | 101 414   | Switching Protocols URI Too Long                     | Section 7.1.2 4.6.12 |
   | 200 415   | OK Unsupported Media Type           | Section 7.2.1 4.6.13 |
   | 201 417   | Created Expectation Failed               | Section 7.2.2 4.6.14 |
   | 202 426   | Accepted Upgrade Required                 | Section 7.2.3 4.6.15 |
   | 203 500   | Non-Authoritative Information Internal Server Error            | Section 4.7.1  |
   | 501   | Not Implemented                  | Section 4.7.2  |
   | 502   | Bad Gateway                      | Section 4.7.3  |
   | 503   | Service Unavailable              | Section 4.7.4  |
   | 504   | Gateway Timeout                  | Section 4.7.5  |
   | 505   | HTTP Version Not Supported       | Section 4.7.6  |
   +-------+----------------------------------+----------------+

10.3.  Header Field Registration

   The Message Header Field Registry located at <http://www.iana.org/
   assignments/message-headers/message-header-index.html> shall be
   updated with the permanent registrations below (see [RFC3864]):

   +-------------------+----------+----------+--------------+
   | Header Field Name | Protocol | Status   | Reference    |
   +-------------------+----------+----------+--------------+
   | Accept            | http     | standard | Section 7.2.4 9.1  |
   | 204 Accept-Charset    | No Content http     | standard | Section 7.2.5 9.2  |
   | 205 Accept-Encoding   | Reset Content http     | standard | Section 7.2.6 9.3  |
   | 300 Accept-Language   | Multiple Choices http     | standard | Section 7.3.1 9.4  |
   | 301 Allow             | Moved Permanently http     | standard | Section 7.3.2 9.5  |
   | 302 Content-Encoding  | Found http     | standard | Section 7.3.3 9.6  |
   | 303 Content-Language  | See Other http     | standard | Section 7.3.4 9.7  |
   | 305 Content-Location  | Use Proxy http     | standard | Section 7.3.5 9.8  |
   | 306 Content-Type      | (Unused) http     | standard | Section 7.3.6 9.9  |
   | 307 Date              | Temporary Redirect http     | standard | Section 7.3.7 9.10 |
   | 400 Expect            | Bad Request http     | standard | Section 7.4.1 9.11 |
   | 402 From              | Payment Required http     | standard | Section 7.4.2 9.12 |
   | 403 Location          | Forbidden http     | standard | Section 7.4.3 9.13 |
   | 404 MIME-Version      | Not Found http     | Section 7.4.4 standard | Appendix A.1 | 405
   | Method Not Allowed Max-Forwards      | http     | standard | Section 7.4.5 9.14 |
   | 406 Referer           | Not Acceptable http     | standard | Section 7.4.6 9.15 |
   | 408 Retry-After       | Request Timeout http     | standard | Section 7.4.7 9.16 |
   | 409 Server            | Conflict http     | standard | Section 7.4.8 9.17 |
   | 410 User-Agent        | Gone http     | standard | Section 7.4.9 9.18 |
   +-------------------+----------+----------+--------------+

   The change controller is: "IETF (iesg@ietf.org) - Internet
   Engineering Task Force".

10.4.  Content Coding Registry

   The registration procedure for HTTP Content Codings is now defined by
   Section 5.4.1 of this document.

   The HTTP Content Codings Registry located at
   <http://www.iana.org/assignments/http-parameters> shall be updated
   with the registration below:

   +----------+------------------------------------------+-------------+
   | 411 Name     | Length Required Description                              | Section 7.4.10 Reference   |
   +----------+------------------------------------------+-------------+
   | 413 compress | Request Representation Too Large UNIX "compress" program method           | Section 7.4.11     |
   | 414          | URI Too Long                                          | Section 7.4.12 4.2.1 of    |
   | 415          | Unsupported Media Type                                          | Section 7.4.13 [Part1]     |
   | 417 deflate  | Expectation Failed "deflate" compression mechanism          | Section 7.4.14     |
   | 426          | Upgrade Required ([RFC1951]) used inside the "zlib" data  | Section 7.4.15 4.2.2 of    |
   | 500          | Internal Server Error format ([RFC1950])                       | Section 7.5.1 [Part1]     |
   | 501 gzip     | Not Implemented Same as GNU zip [RFC1952]                | Section 7.5.2     |
   | 502          | Bad Gateway                                          | Section 7.5.3 4.2.3 of    |
   | 503          | Service Unavailable                                          | Section 7.5.4 [Part1]     |
   | 504 identity | Gateway Timeout reserved (synonym for "no encoding" in   | Section 7.5.5 9.3 |
   | 505          | Accept-Encoding header field)            |             |
   +----------+------------------------------------------+-------------+

11.  Security Considerations

   This section is meant to inform application developers, information
   providers, and users of the security limitations in HTTP/1.1 as
   described by this document.  The discussion does not include
   definitive solutions to the problems revealed, though it does make
   some suggestions for reducing security risks.

11.1.  Transfer of Sensitive Information

   Like any generic data transfer protocol, HTTP Version Not Supported       | Section 7.5.6  |
   +-------+----------------------------------+----------------+

11.3.  Header Field Registration cannot regulate the
   content of the data that is transferred, nor is there any a priori
   method of determining the sensitivity of any particular piece of
   information within the context of any given request.  Therefore,
   applications SHOULD supply as much control over this information as
   possible to the provider of that information.  Four header fields are
   worth special mention in this context: Server, Via, Referer and From.

   Revealing the specific software version of the server might allow the
   server machine to become more vulnerable to attacks against software
   that is known to contain security holes.  Implementers SHOULD make
   the Server header field a configurable option.

   Proxies which serve as a portal through a network firewall SHOULD
   take special precautions regarding the transfer of header information
   that identifies the hosts behind the firewall.  In particular, they
   SHOULD remove, or replace with sanitized versions, any Via fields
   generated behind the firewall.

   The Message Header Field Registry located at <http://www.iana.org/
   assignments/message-headers/message-header-index.html> shall Referer header field allows reading patterns to be studied and
   reverse links drawn.  Although it can be very useful, its power can
   be abused if user details are not separated from the information
   contained in the Referer.  Even when the personal information has
   been removed, the Referer header field might indicate a private
   document's URI whose publication would be
   updated inappropriate.

   The information sent in the From field might conflict with the permanent registrations below (see [RFC3864]):

   +-------------------+----------+----------+---------------+
   | Header Field Name | Protocol | Status   | Reference     |
   +-------------------+----------+----------+---------------+
   | Allow             | http     | standard | Section 10.1  |
   | Date              | http     | standard | Section 10.2  |
   | Expect            | http     | standard | Section 10.3  |
   | user's
   privacy interests or their site's security policy, and hence it
   SHOULD NOT be transmitted without the user being able to disable,
   enable, and modify the contents of the field.  The user MUST be able
   to set the contents of this field within a user preference or
   application defaults configuration.

   We suggest, though do not require, that a convenient toggle interface
   be provided for the user to enable or disable the sending of From              | http     | standard | Section 10.4  |
   | Location          | http     | standard | Section 10.5  |
   | Max-Forwards      | http     | standard | Section 10.6  |
   | and
   Referer           | http     | standard | Section 10.7  |
   | Retry-After       | http     | standard | Section 10.8  |
   | Server            | http     | standard | Section 10.9  |
   | User-Agent        | http     | standard | Section 10.10 |
   +-------------------+----------+----------+---------------+ information.

   The change controller is: "IETF (iesg@ietf.org) - Internet
   Engineering Task Force".

12.  Security Considerations

   This section User-Agent (Section 9.18) or Server (Section 9.17) header fields
   can sometimes be used to determine that a specific client or server
   has a particular security hole which might be exploited.
   Unfortunately, this same information is meant often used for other valuable
   purposes for which HTTP currently has no better mechanism.

   Furthermore, the User-Agent header field might contain enough entropy
   to inform application developers, be used, possibly in conjunction with other material, to uniquely
   identify the user.

   Some request methods, like TRACE (Section 2.3.7), expose information
   providers, and users
   that was sent in request header fields within the body of their
   response.  Clients SHOULD be careful with sensitive information, like
   Cookies, Authorization credentials, and other header fields that
   might be used to collect data from the security limitations client.

11.2.  Encoding Sensitive Information in HTTP/1.1 as
   described by this document.  The discussion does not include
   definitive solutions to URIs

   Because the problems revealed, though source of a link might be private information or might
   reveal an otherwise private information source, it does make
   some suggestions is strongly
   recommended that the user be able to select whether or not the
   Referer field is sent.  For example, a browser client could have a
   toggle switch for reducing security risks.

12.1.  Transfer browsing openly/anonymously, which would
   respectively enable/disable the sending of Sensitive Information

   Like any generic data transfer protocol, Referer and From
   information.

   Clients SHOULD NOT include a Referer header field in a (non-secure)
   HTTP cannot regulate request if the
   content referring page was transferred with a secure
   protocol.

   Authors of services SHOULD NOT use GET-based forms for the submission
   of sensitive data because that is transferred, nor is there any data will be placed in the request-
   target.  Many existing servers, proxies, and user agents log or
   display the request-target in places where it might be visible to
   third parties.  Such services can use POST-based form submission
   instead.

11.3.  Location Header Fields: Spoofing and Information Leakage

   If a priori
   method of determining the sensitivity of any particular piece of
   information within single server supports multiple organizations that do not trust
   one another, then it MUST check the context values of any given request.  Therefore,
   applications SHOULD supply as much Location and Content-
   Location header fields in responses that are generated under control
   of said organizations to make sure that they do not attempt to
   invalidate resources over this which they have no authority.

   Furthermore, appending the fragment identifier from one URI to
   another one obtained from a Location header field might leak
   confidential information as
   possible to the provider of that information.  Four header fields are
   worth special mention in this context: Server, Via, Referer and From.

   Revealing target server -- although the specific software version of
   fragment identifier is not transmitted in the server final request, it might allow
   be visible to the
   server machine user agent through other means, such as scripting.

11.4.  Security Considerations for CONNECT

   Since tunneled data is opaque to become more vulnerable the proxy, there are additional
   risks to attacks against software
   that is known tunneling to contain security holes.  Implementors other well-known or reserved ports.  A HTTP
   client CONNECTing to port 25 could relay spam via SMTP, for example.
   As such, proxies SHOULD make
   the Server header field a configurable option.

   Proxies which serve as a portal through restrict CONNECT access to a network firewall SHOULD
   take special precautions regarding the transfer small number of header information
   that identifies the hosts behind the firewall.  In particular, they
   SHOULD remove, or replace with sanitized versions, any Via
   known ports.

11.5.  Privacy Issues Connected to Accept Header Fields

   Accept header fields
   generated behind can reveal information about the firewall. user to all
   servers which are accessed.  The Referer Accept-Language header field allows reading patterns to be studied and
   reverse links drawn.  Although it can be very useful, its power in
   particular can
   be abused if reveal information the user details are not separated from would consider to be of a
   private nature, because the information
   contained in understanding of particular languages is
   often strongly correlated to the Referer.  Even when membership of a particular ethnic
   group.  User agents which offer the personal information has
   been removed, option to configure the Referer contents
   of an Accept-Language header field might indicate a private
   document's URI whose publication would to be inappropriate.

   The information sent in every request are
   strongly encouraged to let the From field might conflict with configuration process include a
   message which makes the user's user aware of the loss of privacy interests or their site's security policy, involved.

   An approach that limits the loss of privacy would be for a user agent
   to omit the sending of Accept-Language header fields by default, and hence
   to ask the user whether or not to start sending Accept-Language
   header fields to a server if it
   SHOULD NOT be transmitted without detects, by looking for any Vary
   header fields generated by the server, that such sending could
   improve the quality of service.

   Elaborate user-customized accept header fields sent in every request,
   in particular if these include quality values, can be used by servers
   as relatively reliable and long-lived user being able identifiers.  Such user
   identifiers would allow content providers to disable,
   enable, do click-trail tracking,
   and modify would allow collaborating content providers to match cross-server
   click-trails or form submissions of individual users.  Note that for
   many users not behind a proxy, the contents network address of the field.  The host
   running the user agent will also serve as a long-lived user
   identifier.  In environments where proxies are used to enhance
   privacy, user MUST agents ought to be able conservative in offering accept
   header field configuration options to set end users.  As an extreme
   privacy measure, proxies could filter the contents of this field within a accept header fields in
   relayed requests.  General purpose user preference or
   application defaults configuration.

   We suggest, though do not require, that agents which provide a convenient toggle interface high
   degree of header field configurability SHOULD warn users about the
   loss of privacy which can be provided involved.

12.  Acknowledgments

   See Section 9 of [Part1].

13.  References

13.1.  Normative References

   [Part1]                          Fielding, R., Ed., Lafon, Y., Ed.,
                                    and J. Reschke, Ed., "HTTP/1.1, part
                                    1: Message Routing and Syntax"",
                                    draft-ietf-httpbis-p1-messaging-20
                                    (work in progress), July 2012.

   [Part4]                          Fielding, R., Ed., Lafon, Y., Ed.,
                                    and J. Reschke, Ed., "HTTP/1.1, part
                                    4: Conditional Requests",
                                    draft-ietf-httpbis-p4-conditional-20
                                    (work in progress), July 2012.

   [Part5]                          Fielding, R., Ed., Lafon, Y., Ed.,
                                    and J. Reschke, Ed., "HTTP/1.1, part
                                    5: Range Requests",
                                    draft-ietf-httpbis-p5-range-20 (work
                                    in progress), July 2012.

   [Part6]                          Fielding, R., Ed., Lafon, Y., Ed.,
                                    Nottingham, M., Ed., and J. Reschke,
                                    Ed., "HTTP/1.1, part 6: Caching",
                                    draft-ietf-httpbis-p6-cache-20 (work
                                    in progress), July 2012.

   [Part7]                          Fielding, R., Ed., Lafon, Y., Ed.,
                                    and J. Reschke, Ed., "HTTP/1.1, part
                                    7: Authentication",
                                    draft-ietf-httpbis-p7-auth-20 (work
                                    in progress), July 2012.

   [RFC1950]                        Deutsch, L. and J-L. Gailly, "ZLIB
                                    Compressed Data Format Specification
                                    version 3.3", RFC 1950, May 1996.

   [RFC1951]                        Deutsch, P., "DEFLATE Compressed
                                    Data Format Specification version
                                    1.3", RFC 1951, May 1996.

   [RFC1952]                        Deutsch, P., Gailly, J-L., Adler,
                                    M., Deutsch, L., and G. Randers-
                                    Pehrson, "GZIP file format
                                    specification version 4.3",
                                    RFC 1952, May 1996.

   [RFC2045]                        Freed, N. and N. Borenstein,
                                    "Multipurpose Internet Mail
                                    Extensions (MIME) Part One: Format
                                    of Internet Message Bodies",
                                    RFC 2045, November 1996.

   [RFC2046]                        Freed, N. and N. Borenstein,
                                    "Multipurpose Internet Mail
                                    Extensions (MIME) Part Two: Media
                                    Types", RFC 2046, November 1996.

   [RFC2119]                        Bradner, S., "Key words for the user use in
                                    RFCs to enable or disable the sending Indicate Requirement
                                    Levels", BCP 14, RFC 2119,
                                    March 1997.

   [RFC3986]                        Berners-Lee, T., Fielding, R., and
                                    L. Masinter, "Uniform Resource
                                    Identifier (URI): Generic Syntax",
                                    STD 66, RFC 3986, January 2005.

   [RFC4647]                        Phillips, A., Ed. and M. Davis, Ed.,
                                    "Matching of From Language Tags", BCP 47,
                                    RFC 4647, September 2006.

   [RFC5234]                        Crocker, D., Ed. and
   Referer information.

   The User-Agent (Section 10.10) or Server (Section 10.9) header fields
   can sometimes be used to determine that a specific client or server
   has a particular security hole which might be exploited.
   Unfortunately, this same information is often used P. Overell,
                                    "Augmented BNF for other valuable
   purposes Syntax
                                    Specifications: ABNF", STD 68,
                                    RFC 5234, January 2008.

   [RFC5646]                        Phillips, A., Ed. and M. Davis, Ed.,
                                    "Tags for which HTTP currently has no better mechanism.

   Furthermore, the User-Agent header field may contain enough entropy
   to be used, possibly in conjunction with other material, to uniquely
   identify the user.

   Some request methods, like TRACE (Section 6.8), expose information
   that was sent Identifying Languages",
                                    BCP 47, RFC 5646, September 2009.

13.2.  Informative References

   [RFC1123]                        Braden, R., "Requirements for
                                    Internet Hosts - Application and
                                    Support", STD 3, RFC 1123,
                                    October 1989.

   [RFC1945]                        Berners-Lee, T., Fielding, R., and
                                    H. Nielsen, "Hypertext Transfer
                                    Protocol -- HTTP/1.0", RFC 1945,
                                    May 1996.

   [RFC2049]                        Freed, N. and N. Borenstein,
                                    "Multipurpose Internet Mail
                                    Extensions (MIME) Part Five:
                                    Conformance Criteria and Examples",
                                    RFC 2049, November 1996.

   [RFC2068]                        Fielding, R., Gettys, J., Mogul, J.,
                                    Nielsen, H., and T. Berners-Lee,
                                    "Hypertext Transfer Protocol --
                                    HTTP/1.1", RFC 2068, January 1997.

   [RFC2076]                        Palme, J., "Common Internet Message
                                    Headers", RFC 2076, February 1997.

   [RFC2277]                        Alvestrand, H., "IETF Policy on
                                    Character Sets and Languages",
                                    BCP 18, RFC 2277, January 1998.

   [RFC2295]                        Holtman, K. and A. Mutz,
                                    "Transparent Content Negotiation in request header fields within the body
                                    HTTP", RFC 2295, March 1998.

   [RFC2388]                        Masinter, L., "Returning Values from
                                    Forms:  multipart/form-data",
                                    RFC 2388, August 1998.

   [RFC2557]                        Palme, F., Hopmann, A., Shelness,
                                    N., and E. Stefferud, "MIME
                                    Encapsulation of their
   response.  Clients SHOULD be careful with sensitive information, like
   Cookies, Authorization credentials, Aggregate
                                    Documents, such as HTML (MHTML)",
                                    RFC 2557, March 1999.

   [RFC2616]                        Fielding, R., Gettys, J., Mogul, J.,
                                    Frystyk, H., Masinter, L., Leach,
                                    P., and other header fields that
   might be used T. Berners-Lee, "Hypertext
                                    Transfer Protocol -- HTTP/1.1",
                                    RFC 2616, June 1999.

   [RFC2817]                        Khare, R. and S. Lawrence,
                                    "Upgrading to collect data from the client.

12.2.  Encoding Sensitive Information in URIs

   Because the source of TLS Within HTTP/1.1",
                                    RFC 2817, May 2000.

   [RFC3629]                        Yergeau, F., "UTF-8, a link might be private information or might
   reveal
                                    transformation format of ISO 10646",
                                    STD 63, RFC 3629, November 2003.

   [RFC3864]                        Klyne, G., Nottingham, M., and J.
                                    Mogul, "Registration Procedures for
                                    Message Header Fields", BCP 90,
                                    RFC 3864, September 2004.

   [RFC4288]                        Freed, N. and J. Klensin, "Media
                                    Type Specifications and Registration
                                    Procedures", BCP 13, RFC 4288,
                                    December 2005.

   [RFC5226]                        Narten, T. and H. Alvestrand,
                                    "Guidelines for Writing an otherwise private information source, it is strongly
   recommended that the user be able to select whether or not the
   Referer field is sent.  For example, a browser client could have a
   toggle switch IANA
                                    Considerations Section in RFCs",
                                    BCP 26, RFC 5226, May 2008.

   [RFC5322]                        Resnick, P., "Internet Message
                                    Format", RFC 5322, October 2008.

   [RFC5789]                        Dusseault, L. and J. Snell, "PATCH
                                    Method for HTTP", RFC 5789,
                                    March 2010.

   [RFC5987]                        Reschke, J., "Character Set and
                                    Language Encoding for Hypertext
                                    Transfer Protocol (HTTP) Header
                                    Field Parameters", RFC 5987,
                                    August 2010.

   [RFC6151]                        Turner, S. and L. Chen, "Updated
                                    Security Considerations for browsing openly/anonymously, which would
   respectively enable/disable the sending of Referer MD5
                                    Message-Digest and From
   information.

   Clients SHOULD NOT include a Referer header field in a (non-secure)
   HTTP request if the referring page was transferred with a secure
   protocol.

   Authors HMAC-MD5
                                    Algorithms", RFC 6151, March 2011.

   [RFC6266]                        Reschke, J., "Use of services SHOULD NOT use GET-based forms for the submission
   of sensitive data because that data will be placed Content-
                                    Disposition Header Field in the
                                    Hypertext Transfer Protocol (HTTP)",
                                    RFC 6266, June 2011.

   [draft-reschke-http-status-308]  Reschke, J., "The Hypertext Transfer
                                    Protocol (HTTP) Status Code 308
                                    (Permanent Redirect)",
                                    draft-reschke-http-status-308-07
                                    (work in progress), March 2012.

Appendix A.  Differences between HTTP and MIME

   HTTP/1.1 uses many of the request-
   target.  Many existing servers, proxies, constructs defined for Internet Mail
   ([RFC5322]) and user agents log or
   display the request-target in places where it might be visible Multipurpose Internet Mail Extensions (MIME

   [RFC2045]) to
   third parties.  Such services can use POST-based form submission
   instead.

12.3.  Location Header Fields: Spoofing and Information Leakage

   If allow a single server supports multiple organizations that do not trust
   one another, then it MUST check the values message body to be transmitted in an open
   variety of Location representations and Content-
   Location header fields in responses with extensible mechanisms.  However,
   RFC 2045 discusses mail, and HTTP has a few features that are generated under control
   different from those described in MIME.  These differences were
   carefully chosen to optimize performance over binary connections, to
   allow greater freedom in the use of said organizations new media types, to make sure that they do not attempt date
   comparisons easier, and to
   invalidate resources over which they have no authority.

   Furthermore, appending acknowledge the fragment identifier practice of some early
   HTTP servers and clients.

   This appendix describes specific areas where HTTP differs from one URI MIME.
   Proxies and gateways to
   another one obtained strict MIME environments SHOULD be aware of
   these differences and provide the appropriate conversions where
   necessary.  Proxies and gateways from MIME environments to HTTP also
   need to be aware of the differences because some conversions might be
   required.

A.1.  MIME-Version

   HTTP is not a Location MIME-compliant protocol.  However, HTTP/1.1 messages
   MAY include a single MIME-Version header field might leak
   confidential information to indicate what
   version of the target server -- although MIME protocol was used to construct the
   fragment identifier message.  Use
   of the MIME-Version header field indicates that the message is in
   full conformance with the MIME protocol (as defined in [RFC2045]).
   Proxies/gateways are responsible for ensuring full conformance (where
   possible) when exporting HTTP messages to strict MIME environments.

     MIME-Version = 1*DIGIT "." 1*DIGIT

   MIME version "1.0" is the default for use in HTTP/1.1.  However,
   HTTP/1.1 message parsing and semantics are defined by this document
   and not transmitted in the final request, it might MIME specification.

A.2.  Conversion to Canonical Form

   MIME requires that an Internet mail body-part be visible converted to the user agent through other means, such
   canonical form prior to being transferred, as scripting.

12.4.  Security Considerations described in Section 4
   of [RFC2049].  Section 5.5.1 of this document describes the forms
   allowed for CONNECT

   Since tunneled data is opaque to subtypes of the proxy, there are additional
   risks to tunneling "text" media type when transmitted over
   HTTP.  [RFC2046] requires that content with a type of "text"
   represent line breaks as CRLF and forbids the use of CR or LF outside
   of line break sequences.  HTTP allows CRLF, bare CR, and bare LF to other well-known
   indicate a line break within text content when a message is
   transmitted over HTTP.

   Where it is possible, a proxy or reserved ports.  A gateway from HTTP
   client CONNECTing to port 25 could relay spam via SMTP, for example.
   As such, proxies a strict MIME
   environment SHOULD restrict CONNECT access translate all line breaks within the text media
   types described in Section 5.5.1 of this document to a small number the RFC 2049
   canonical form of
   known ports.

13.  Acknowledgments

   See Section 9 CRLF.  Note, however, that this might be
   complicated by the presence of [Part1].

14.  References

14.1.  Normative References

   [Part1]    Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
              "HTTP/1.1, part 1: URIs, Connections, and Message
              Parsing", draft-ietf-httpbis-p1-messaging-19 (work in
              progress), March 2012.

   [Part3]    Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
              "HTTP/1.1, part 3: Message Payload and Content
              Negotiation", draft-ietf-httpbis-p3-payload-19 (work in
              progress), March 2012.

   [Part4]    Fielding, R., Ed., Lafon, Y., Ed., a Content-Encoding and J. Reschke, Ed.,
              "HTTP/1.1, part 4: Conditional Requests",
              draft-ietf-httpbis-p4-conditional-19 (work in progress),
              March 2012.

   [Part5]    Fielding, R., Ed., Lafon, Y., Ed., by the fact
   that HTTP allows the use of some character encodings which do not use
   octets 13 and J. Reschke, Ed.,
              "HTTP/1.1, part 5: Range Requests 10 to represent CR and Partial Responses",
              draft-ietf-httpbis-p5-range-19 (work LF, respectively, as is the case
   for some multi-byte character encodings.

   Conversion will break any cryptographic checksums applied to the
   original content unless the original content is already in progress),
              March 2012.

   [Part6]    Fielding, R., Ed., Lafon, Y., Ed., Nottingham, M., Ed.,
              and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",
              draft-ietf-httpbis-p6-cache-19 (work canonical
   form.  Therefore, the canonical form is recommended for any content
   that uses such checksums in progress),
              March 2012.

   [Part7]    Fielding, R., Ed., Lafon, Y., Ed., HTTP.

A.3.  Conversion of Date Formats

   HTTP/1.1 uses a restricted set of date formats (Section 5.1) to
   simplify the process of date comparison.  Proxies and J. Reschke, Ed.,
              "HTTP/1.1, part 7: Authentication",
              draft-ietf-httpbis-p7-auth-19 (work gateways from
   other protocols SHOULD ensure that any Date header field present in progress),
              March 2012.

   [RFC2119]  Bradner, S., "Key words a
   message conforms to one of the HTTP/1.1 formats and rewrite the date
   if necessary.

A.4.  Introduction of Content-Encoding

   MIME does not include any concept equivalent to HTTP/1.1's Content-
   Encoding header field.  Since this acts as a modifier on the media
   type, proxies and gateways from HTTP to MIME-compliant protocols MUST
   either change the value of the Content-Type header field or decode
   the representation before forwarding the message.  (Some experimental
   applications of Content-Type for use in RFCs Internet mail have used a media-type
   parameter of ";conversions=<content-coding>" to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., perform a function
   equivalent to Content-Encoding.  However, this parameter is not part
   of the MIME standards).

A.5.  No Content-Transfer-Encoding

   HTTP does not use the Content-Transfer-Encoding field of MIME.
   Proxies and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC5234]  Crocker, D., Ed. gateways from MIME-compliant protocols to HTTP MUST
   remove any Content-Transfer-Encoding prior to delivering the response
   message to an HTTP client.

   Proxies and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

14.2.  Informative References

   [RFC1123]  Braden, R., "Requirements gateways from HTTP to MIME-compliant protocols are
   responsible for Internet Hosts - Application ensuring that the message is in the correct format
   and Support", STD 3, RFC 1123, October 1989.

   [RFC1945]  Berners-Lee, T., Fielding, R., encoding for safe transport on that protocol, where "safe
   transport" is defined by the limitations of the protocol being used.
   Such a proxy or gateway SHOULD label the data with an appropriate
   Content-Transfer-Encoding if doing so will improve the likelihood of
   safe transport over the destination protocol.

A.6.  MHTML and H. Nielsen, "Hypertext
              Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.

   [RFC2068]  Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Line Length Limitations

   HTTP implementations which share code with MHTML [RFC2557]
   implementations need to be aware of MIME line length limitations.
   Since HTTP does not have this limitation, HTTP does not fold long
   lines.  MHTML messages being transported by HTTP follow all
   conventions of MHTML, including line length limitations and T.
              Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
              RFC 2068, January 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., folding,
   canonicalization, etc., since HTTP transports all message-bodies as
   payload (see Section 5.5.2) and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2817]  Khare, R. does not interpret the content or any
   MIME header lines that might be contained therein.

Appendix B.  Additional Features

   [RFC1945] and S. Lawrence, "Upgrading to TLS Within
              HTTP/1.1", RFC 2817, May 2000.

   [RFC3864]  Klyne, G., Nottingham, M., [RFC2068] document protocol elements used by some
   existing HTTP implementations, but not consistently and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC5226]  Narten, T. correctly
   across most HTTP/1.1 applications.  Implementers are advised to be
   aware of these features, but cannot rely upon their presence in, or
   interoperability with, other HTTP/1.1 applications.  Some of these
   describe proposed experimental features, and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section some describe features
   that experimental deployment found lacking that are now addressed in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5322]  Resnick, P., "Internet Message Format", RFC 5322,
              October 2008.

   [RFC5789]  Dusseault, L.
   the base HTTP/1.1 specification.

   A number of other header fields, such as Content-Disposition and J. Snell, "PATCH Method for HTTP",
              RFC 5789, March 2010.

   [RFC5987]  Reschke, J., "Character Set
   Title, from SMTP and Language Encoding for
              Hypertext Transfer Protocol (HTTP) Header Field
              Parameters", RFC 5987, August 2010. MIME are also often implemented (see [RFC6266]
   and [RFC2076]).

Appendix A. C.  Changes from RFC 2616

   This document takes over the Status Code Registry, previously defined
   in Section 7.1 of [RFC2817].

   Introduce Method Registry.  (Section 4.2) 2.2)

   Clarify definition of POST.  (Section 6.5) 2.3.4)

   Remove requirement to handle all Content-* header fields; ban use of
   Content-Range with PUT.  (Section 6.6) 2.3.5)

   Take over definition of CONNECT method from [RFC2817].
   (Section 6.9) 2.3.8)

   Take over the Status Code Registry, previously defined in Section 7.1
   of [RFC2817].  (Section 4.2)

   Broadened the definition of 203 (Non-Authoritative Information) to
   include cases of payload transformations as well.  (Section 7.2.4) 4.4.4)

   Status codes 301, 302, and 307: removed the normative requirements on
   both response payloads and user interaction.  (Section 7.3) 4.5)

   Failed to consider that there are many other request methods that are
   safe to automatically redirect, and further that the user agent is
   able to make that determination based on the request method
   semantics.  Furthermore, allow user agents to rewrite the method from
   POST to GET for status codes 301 and 302.  (Sections 7.3.2, 7.3.3 4.5.2, 4.5.3 and
   7.3.7)
   4.5.7)

   Deprecate 305 Use Proxy (Use Proxy) status code, because user agents did not
   implement it.  It used to indicate that the target resource must needs to
   be accessed through the proxy given by the Location field.  The
   Location field gave the URI of the proxy.  The recipient was expected
   to repeat this single request via the proxy.  (Section 7.3.5) 4.5.5)

   Define status 426 (Upgrade Required) (this was incorporated from
   [RFC2817]).  (Section 7.4.15) 4.6.15)

   Change ABNF productions for header fields to only define the field
   value.  (Section 10) 9)

   Reclassify "Allow" as response header field, removing the option to
   specify it in a PUT request.  Relax the server requirement on the
   contents of the Allow header field and remove requirement on clients
   to always trust the header field value.  (Section 10.1) 9.5)

   The ABNF for the Expect header field has been both fixed (allowing
   parameters for value-less expectations as well) and simplified
   (allowing trailing semicolons after "100-continue" when they were
   invalid before).  (Section 10.3) 9.11)

   Correct syntax of Location header field to allow URI references
   (including relative references and fragments), as referred symbol
   "absoluteURI" wasn't what was expected, and add some clarifications
   as to when use of fragments would not be appropriate. when use of fragments would not be appropriate.  (Section 9.13)

   Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
   extension methods could have used it as well).  (Section 9.14)

   Allow Referer field value of "about:blank" as alternative to not
   specifying it.  (Section 9.15)

   In the description of the Server header field, the Via field was
   described as a SHOULD.  The requirement was and is stated correctly
   in the description of the Via header field in Section 6.2 of [Part1].
   (Section 9.17)

   Clarify contexts that charset is used in.  (Section 5.3)

   Registration of Content Codings now requires IETF Review
   (Section 5.4.1)
   Remove the default character encoding of "ISO-8859-1" for text media
   types; the default now is whatever the media type definition says.
   (Section 5.5.1)

   Change ABNF productions for header fields to only define the field
   value.  (Section 10.5)

   Restrict Max-Forwards 9)

   Remove definition of Content-MD5 header field because it was
   inconsistently implemented with respect to OPTIONS partial responses, and TRACE (previously,
   extension methods could have used it as well).  (Section 10.6)

   Allow Referer field value
   also because of "about:blank" as alternative to not
   specifying it. known deficiencies in the hash algorithm itself (see
   [RFC6151] for details).  (Section 10.7)

   In 9)

   Remove ISO-8859-1 special-casing in Accept-Charset.  (Section 9.2)

   Remove base URI setting semantics for Content-Location due to poor
   implementation support, which was caused by too many broken servers
   emitting bogus Content-Location header fields, and also the description
   potentially undesirable effect of the Server potentially breaking relative links
   in content-negotiated resources.  (Section 9.8)

   Remove reference to non-existant identity transfer-coding value
   tokens.  (Appendix A.5)

   Remove discussion of Content-Disposition header field, the Via field was
   described as a SHOULD. it is now
   defined by [RFC6266].  (Appendix B)

Appendix D.  Imported ABNF

   The requirement was following core rules are included by reference, as defined in
   Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
   CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
   quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF
   (line feed), OCTET (any 8-bit sequence of data), SP (space), and is stated correctly
   VCHAR (any visible US-ASCII character).

   The rules below are defined in [Part1]:

     BWS           = <BWS, defined in [Part1], Section 3.2.1>
     OWS           = <OWS, defined in [Part1], Section 3.2.1>
     RWS           = <RWS, defined in [Part1], Section 3.2.1>
     quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>
     token         = <token, defined in [Part1], Section 3.2.4>
     word          = <word, defined in [Part1], Section 3.2.4>

     absolute-URI  = <absolute-URI, defined in [Part1], Section 2.8>
     comment       = <comment, defined in [Part1], Section 3.2.4>
     partial-URI   = <partial-URI, defined in [Part1], Section 2.8>
     qvalue        = <qvalue, defined in the description of the Via header field [Part1], Section 4.3.1>
     URI-reference = <URI-reference, defined in [Part1], Section 6.2 of [Part1].
   (Section 10.9) 2.8>

Appendix B. E.  Collected ABNF

   Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
    OWS ( media-range [ accept-params ] ) ] ) ]
   Accept-Charset = *( "," OWS ) ( ( charset / "*" ) [ OWS ";" OWS "q="
    qvalue ] ) *( OWS "," [ OWS ( ( charset / "*" ) [ OWS ";" OWS "q="
    qvalue ] ) ] )
   Accept-Encoding = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] ) )
    *( OWS "," [ OWS ( codings [ OWS ";" OWS "q=" qvalue ] ) ] ) ]
   Accept-Language = *( "," OWS ) ( language-range [ OWS ";" OWS "q="
    qvalue ] ) *( OWS "," [ OWS ( language-range [ OWS ";" OWS "q="
    qvalue ] ) ] )
   Allow = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]

   BWS = <BWS, defined in [Part1], Section 3.2.1>

   Content-Encoding = *( "," OWS ) content-coding *( OWS "," [ OWS
    content-coding ] )
   Content-Language = *( "," OWS ) language-tag *( OWS "," [ OWS
    language-tag ] )
   Content-Location = absolute-URI / partial-URI
   Content-Type = media-type

   Date = HTTP-date

   Expect = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )

   From = mailbox

   GMT = %x47.4D.54 ; GMT

   HTTP-date = rfc1123-date / obs-date

   Location = URI-reference

   MIME-Version = 1*DIGIT "." 1*DIGIT
   Max-Forwards = 1*DIGIT

   OWS = <OWS, defined in [Part1], Section 3.2.1>

   RWS = <RWS, defined in [Part1], Section 3.2.1>
   Referer = absolute-URI / partial-URI
   Retry-After = HTTP-date / delta-seconds

   Server = product *( RWS ( product / comment ) )
   URI-reference = <URI-reference, defined in [Part1], Section 2.7> 2.8>
   User-Agent = product *( RWS ( product / comment ) )

   absolute-URI = <absolute-URI, defined in [Part1], Section 2.7> 2.8>
   accept-ext = OWS ";" OWS token [ "=" word ]
   accept-params = OWS ";" OWS "q=" qvalue *accept-ext
   asctime-date = day-name SP date3 SP time-of-day SP year
   attribute = token

   charset = token
   codings = content-coding / "identity" / "*"
   comment = <comment, defined in [Part1], Section 3.2.4>
   content-coding = token

   date1 = day SP month SP year
   date2 = day "-" month "-" 2DIGIT
   date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
   day = 2DIGIT
   day-name = %x4D.6F.6E ; Mon
    / %x54.75.65 ; Tue
    / %x57.65.64 ; Wed
    / %x54.68.75 ; Thu
    / %x46.72.69 ; Fri
    / %x53.61.74 ; Sat
    / %x53.75.6E ; Sun
   day-name-l = %x4D.6F.6E.64.61.79 ; Monday
    / %x54.75.65.73.64.61.79 ; Tuesday
    / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
    / %x54.68.75.72.73.64.61.79 ; Thursday
    / %x46.72.69.64.61.79 ; Friday
    / %x53.61.74.75.72.64.61.79 ; Saturday
    / %x53.75.6E.64.61.79 ; Sunday
   delta-seconds = 1*DIGIT

   expect-name = token
   expect-param = expect-name [ BWS "=" BWS expect-value ]
   expect-value = token / quoted-string
   expectation = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
    OWS expect-param ] )

   hour = 2DIGIT

   language-range = <language-range, defined in [RFC4647], Section 2.1>
   language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>

   mailbox = <mailbox, defined in [RFC5322], Section 3.4>
   media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
    ";" OWS parameter )

   media-type = type "/" subtype *( OWS ";" OWS parameter )
   method = token
   minute = 2DIGIT
   month = %x4A.61.6E ; Jan
    / %x46.65.62 ; Feb
    / %x4D.61.72 ; Mar
    / %x41.70.72 ; Apr
    / %x4D.61.79 ; May
    / %x4A.75.6E ; Jun
    / %x4A.75.6C ; Jul
    / %x41.75.67 ; Aug
    / %x53.65.70 ; Sep
    / %x4F.63.74 ; Oct
    / %x4E.6F.76 ; Nov
    / %x44.65.63 ; Dec

   obs-date = rfc850-date / asctime-date
   obs-text

   parameter = <obs-text, defined in [Part1], Section 3.2.4> attribute "=" value
   partial-URI = <partial-URI, defined in [Part1], Section 2.7> 2.8>
   product = token [ "/" product-version ]
   product-version = token

   quoted-string = <quoted-string, defined in [Part1], Section 3.2.4>

   reason-phrase
   qvalue = *( HTAB / SP / VCHAR / obs-text ) <qvalue, defined in [Part1], Section 4.3.1>

   rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
   rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT

   second = 2DIGIT
   status-code
   subtype = 3DIGIT token

   time-of-day = hour ":" minute ":" second
   token = <token, <token, defined in [Part1], Section 3.2.4>
   type = token

   value = word

   word = <word, defined in [Part1], Section 3.2.4>

   year = 4DIGIT
   ABNF diagnostics:

   ; Allow defined but not used
   ; Date defined but not used
   ; Expect defined but not used
   ; From defined but not used
   ; Location defined but not used
   ; Max-Forwards defined but not used
   ; Referer defined but not used
   ; Retry-After defined but not used
   ; Server defined but not used
   ; User-Agent defined but not used
   ; reason-phrase defined but not used
   ; status-code defined but not used

Appendix C. F.  Change Log (to be removed by RFC Editor before publication)

C.1.

F.1.  Since RFC 2616

   Extracted relevant partitions from [RFC2616].

C.2.

F.2.  Since draft-ietf-httpbis-p2-semantics-00

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/5>: "Via is a MUST"
      (<http://purl.org/NET/http-errata#via-must>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/6>: "Fragments
      allowed in Location"
      (<http://purl.org/NET/http-errata#location-fragments>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/10>: "Safe Methods
      vs Redirection" (<http://purl.org/NET/http-errata#saferedirect>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/17>: "Revise
      description of the POST method"
      (<http://purl.org/NET/http-errata#post>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
      Informative references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/42>: "RFC2606
      Compliance"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/65>: "Informative
      references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/84>: "Redundant
      cross-references"

   Other changes:

   o  Move definitions of 304 and 412 condition codes to [Part4]

C.3.

F.3.  Since draft-ietf-httpbis-p3-payload-00

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/8>: "Media Type
      Registrations" (<http://purl.org/NET/http-errata#media-reg>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/14>: "Clarification
      regarding quoting of charset values"
      (<http://purl.org/NET/http-errata#charactersets>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/16>: "Remove
      'identity' token references"
      (<http://purl.org/NET/http-errata#identity>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/25>: "Accept-
      Encoding BNF"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
      Informative references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700
      references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating to
      RFC4288"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/65>: "Informative
      references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/66>: "ISO-8859-1
      Reference"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/68>: "Encoding
      References Normative"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/86>: "Normative up-
      to-date references"

F.4.  Since draft-ietf-httpbis-p2-semantics-01

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/21>: "PUT side
      effects"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/91>: "Duplicate Host
      header requirements"

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Move "Product Tokens" section (back) into Part 1, as "token" is
      used in the definition of the Upgrade header field.

   o  Add explicit references to BNF syntax and rules imported from
      other parts of the specification.

   o  Copy definition of delta-seconds from Part6 instead of referencing
      it.

C.4.

F.5.  Since draft-ietf-httpbis-p3-payload-01

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Add explicit references to BNF syntax and rules imported from
      other parts of the specification.

F.6.  Since draft-ietf-httpbis-p2-semantics-02

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/24>: "Requiring
      Allow in 405 responses"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/59>: "Status Code
      Registry"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/61>: "Redirection
      vs. Location"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/70>: "Cacheability
      of 303 response"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/76>: "305 Use Proxy"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/105>:
      "Classification for Allow header" header field"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/112>: "PUT - 'store
      under' vs 'store at'"

   Ongoing work on IANA Message Header Field Registration
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):

   o  Reference RFC 3984, and update header field registrations for
      headers
      header fields defined in this document.

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Replace string literals when the string really is case-sensitive
      (method).

C.5.

F.7.  Since draft-ietf-httpbis-p3-payload-02

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/67>: "Quoting
      Charsets"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/105>:
      "Classification for Allow header field"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/115>: "missing
      default for qvalue in description of Accept-Encoding"

   Ongoing work on IANA Message Header Field Registration
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):

   o  Reference RFC 3984, and update header field registrations for
      header fields defined in this document.

F.8.  Since draft-ietf-httpbis-p2-semantics-03

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/98>: "OPTIONS
      request bodies"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/119>: "Description
      of CONNECT should refer to RFC2817"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/125>: "Location
      Content-Location reference request/response mixup"

   Ongoing work on Method Registry
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/72>):

   o  Added initial proposal for registration process, plus initial
      content (non-HTTP/1.1 methods to be added by a separate
      specification).

C.6. be added by a separate
      specification).

F.9.  Since draft-ietf-httpbis-p3-payload-03

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/67>: "Quoting
      Charsets"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/113>: "language tag
      matching (Accept-Language) vs RFC4647"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/121>: "RFC 1806 has
      been replaced by RFC2183"

   Other changes:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/68>: "Encoding
      References Normative" -- rephrase the annotation and reference
      BCP97.

F.10.  Since draft-ietf-httpbis-p2-semantics-04

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/103>: "Content-*"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/132>: "RFC 2822 is
      updated by RFC 5322"

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Use "/" instead of "|" for alternatives.

   o  Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
      whitespace ("OWS") and required whitespace ("RWS").

   o  Rewrite ABNFs to spell out whitespace rules, factor out header
      field value format definitions.

F.11.  Since draft-ietf-httpbis-p2-semantics-04 draft-ietf-httpbis-p3-payload-04

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/103>: "Content-*"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/132>: "RFC 2822 is
      updated by RFC 5322"

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Use "/" instead of "|" for alternatives.

   o  Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
      whitespace ("OWS") and required whitespace ("RWS").

   o  Rewrite ABNFs to spell out whitespace rules, factor out header
      field value format definitions.

C.7.

F.12.  Since draft-ietf-httpbis-p2-semantics-05

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/94>: "reason-phrase
      BNF"

   Final work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Add appendix containing collected and expanded ABNF, reorganize
      ABNF introduction.

C.8.

F.13.  Since draft-ietf-httpbis-p3-payload-05

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/118>: "Join
      "Differences Between HTTP Entities and RFC 2045 Entities"?"

   Final work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Add appendix containing collected and expanded ABNF, reorganize
      ABNF introduction.

   Other changes:

   o  Move definition of quality values into Part 1.

F.14.  Since draft-ietf-httpbis-p2-semantics-06

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/144>: "Clarify when
      Referer is sent"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/164>: "status codes
      vs methods"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/170>: "Do not
      require "updates" relation for specs that register status codes or
      method names"

C.9.

F.15.  Since draft-ietf-httpbis-p3-payload-06

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/80>: "Content-
      Location isn't special"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/155>: "Content
      Sniffing"

F.16.  Since draft-ietf-httpbis-p2-semantics-07

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/27>: "Idempotency"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/33>: "TRACE security
      considerations"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/110>: "Clarify rules
      for determining what entities a response carries"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/140>: "update note
      citing RFC 1945 and 2068"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/182>: "update note
      about redirect limit"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/191>: "Location
      header field ABNF should use 'URI'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/192>: "fragments in
      Location vs status 303"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/198>: "move IANA
      registrations for optional status codes"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/171>: "Are OPTIONS
      and TRACE safe?"

C.10.

F.17.  Since draft-ietf-httpbis-p3-payload-07

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/13>: "Updated
      reference for language tags"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/110>: "Clarify rules
      for determining what entities a response carries"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/154>: "Content-
      Location base-setting problems"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/155>: "Content
      Sniffing"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/188>: "pick IANA
      policy (RFC5226) for Transfer Coding / Content Coding"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/189>: "move
      definitions of gzip/deflate/compress to part 1"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/148>: "update IANA
      requirements wrt Transfer-Coding values" (add the IANA
      Considerations subsection)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/149>: "update IANA
      requirements wrt Content-Coding values" (add the IANA
      Considerations subsection)

F.18.  Since draft-ietf-httpbis-p2-semantics-08

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/10>: "Safe Methods
      vs Redirection" (we missed the introduction to the 3xx status
      codes when fixing this previously)

C.11.

F.19.  Since draft-ietf-httpbis-p3-payload-08

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/81>: "Content
      Negotiation for media types"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/181>: "Accept-
      Language: which RFC4647 filtering?"

F.20.  Since draft-ietf-httpbis-p2-semantics-09

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/43>: "Fragment
      combination / precedence during redirects"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/185>: "Location
      header field payload handling"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the
      requested resource's URI"

C.12.

F.21.  Since draft-ietf-httpbis-p3-payload-09

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/122>: "MIME-Version
      not listed in P1, general header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/143>: "IANA registry
      for content/transfer encodings"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/155>: "Content
      Sniffing"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term
      "word" when talking about header field structure"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the
      requested resource's URI"

F.22.  Since draft-ietf-httpbis-p2-semantics-10

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/69>: "Clarify
      'Requested Variant'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
      entity / representation / variant terminology"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/139>: "Methods and
      Caching"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/190>: "OPTIONS vs
      Max-Forwards"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/199>: "Status codes
      and caching"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
      removing the 'changes from 2068' sections"

C.13.

F.23.  Since draft-ietf-httpbis-p3-payload-10

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/69>: "Clarify
      'Requested Variant'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/80>: "Content-
      Location isn't special"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/90>: "Delimiting
      messages with multipart/byteranges"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
      entity / representation / variant terminology"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/136>: "confusing
      req. language for Content-Location"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/167>: "Content-
      Location on 304 responses"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/183>: "'requested
      resource' in content-encoding definition"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
      removing the 'changes from 2068' sections"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/178>: "Content-MD5
      and partial responses"

F.24.  Since draft-ietf-httpbis-p2-semantics-11

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/229>:
      "Considerations for new status codes"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/230>:
      "Considerations for new methods"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/232>: "User-Agent
      guidelines" (relating to the 'User-Agent' header field)

C.14.

F.25.  Since draft-ietf-httpbis-p3-payload-11

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/123>: "Factor out
      Content-Disposition"

F.26.  Since draft-ietf-httpbis-p2-semantics-12

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/43>: "Fragment
      combination / precedence during redirects" (added warning about
      having a fragid on the redirect may might cause inconvenience in some
      cases)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/79>: "Content-* vs.
      PUT"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/88>: "205 Bodies"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/102>: "Understanding
      Content-* on non-PUT requests"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/103>: "Content-*"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/104>: "Header field
      type defaulting"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/112>: "PUT - 'store
      under' vs 'store at'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/137>: "duplicate
      ABNF for reason-phrase"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/180>: "Note special
      status of Content-* prefix in header field registration
      procedures"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/203>: "Max-Forwards
      vs extension methods"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/213>: "What is the
      value space of HTTP status codes?" (actually fixed in
      draft-ietf-httpbis-p2-semantics-11)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/224>: "Header Field
      Classification"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/225>: "PUT side
      effect: invalidation or just stale?"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/226>: "proxies not
      supporting certain methods"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/239>: "Migrate
      CONNECT from RFC2817 to p2"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/240>: "Migrate
      Upgrade details from RFC2817"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/267>: "clarify PUT
      semantics'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/275>: "duplicate
      ABNF for 'Method'"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
      ABNFs for header fields"

C.15.

F.27.  Since draft-ietf-httpbis-p3-payload-12

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/224>: "Header Field
      Classification"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
      ABNFs for header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/277>: "potentially
      misleading MAY in media-type def"

F.28.  Since draft-ietf-httpbis-p2-semantics-13

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
      ABNFs for header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/251>: "message body
      in CONNECT request"

C.16. CONNECT request"

F.29.  Since draft-ietf-httpbis-p3-payload-13

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/20>: "Default
      charsets for text media types"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/178>: "Content-MD5
      and partial responses"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
      ABNFs for header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/281>: "confusing
      undefined parameter in media range example"

F.30.  Since draft-ietf-httpbis-p2-semantics-14

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/255>: "Clarify
      status code for rate limiting"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/294>: "clarify 403
      forbidden"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/296>: "Clarify 203
      Non-Authoritative Information"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/298>: "update
      default reason phrase for 413"

C.17.

F.31.  Since draft-ietf-httpbis-p3-payload-14

   None.

F.32.  Since draft-ietf-httpbis-p2-semantics-15

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/285>: "Strength of
      requirements on Accept re: 406"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/303>: "400 response
      isn't generic"

C.18.

F.33.  Since draft-ietf-httpbis-p3-payload-15

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/285>: "Strength of
      requirements on Accept re: 406"

F.34.  Since draft-ietf-httpbis-p2-semantics-16

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/160>: "Redirects and
      non-GET methods"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document
      HTTP's error-handling philosophy"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/231>:
      "Considerations for new headers" header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/310>: "clarify 303
      redirect on HEAD"

C.19.

F.35.  Since draft-ietf-httpbis-p3-payload-16

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document
      HTTP's error-handling philosophy"

F.36.  Since draft-ietf-httpbis-p2-semantics-17

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/185>: "Location
      header field payload handling"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/255>: "Clarify
      status code for rate limiting" (change backed out because a new
      status code is being defined for this purpose)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/312>: "should there
      be a permanent variant of 307"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/325>: "When are
      Location's semantics triggered?"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/327>: "'expect'
      grammar missing OWS"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/329>: "header field
      considerations: quoted-string vs use of double quotes"

C.20.

F.37.  Since draft-ietf-httpbis-p3-payload-17

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/323>: "intended
      maturity level vs normative references"

F.38.  Since draft-ietf-httpbis-p2-semantics-18

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/227>: "Combining
      HEAD responses"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/238>: "Requirements
      for user intervention during redirects"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/250>: "message-body
      in CONNECT response"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/295>: "Applying
      original fragment to 'plain' redirected URI"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/302>: "Misplaced
      text on connection handling in p2"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/331>: "clarify that
      201 doesn't require Location header fields"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/332>: "relax
      requirements on hypertext in 3/4/5xx error responses"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/333>: "example for
      426 response should have a payload"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/336>: "drop
      indirection entries for status codes"

F.39.  Since draft-ietf-httpbis-p3-payload-18

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/330>: "is ETag a
      representation header field?"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/338>: "Content-
      Location doesn't constrain the cardinality of representations"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/346>: "make IANA
      policy definitions consistent"

F.40.  Since draft-ietf-httpbis-p2-semantics-19 and
       draft-ietf-httpbis-p3-payload-19

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/312>: "should there
      be a permanent variant of 307"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/347>: "clarify that
      201 can imply *multiple* resources were created"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/351>: "merge P2 and
      P3"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/361>: "ABNF
      requirements for recipients"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/364>: "Capturing
      more information in the method registry"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/368>: "note
      introduction of new IANA registries as normative changes"

Index

   1
      1xx Informational (status code class)  25

   2
      2xx Successful (status code class)  26

   3
      3xx Redirection (status code class)  28

   4
      4xx Client Error (status code class)  32

   5
      5xx Server Error (status code class)  36

   1
      100 Continue (status code)  26  25
      100-continue (expect value)  44  62
      101 Switching Protocols (status code)  27  25

   2
      200 OK (status code)  27  26
      201 Created (status code)  27  26
      202 Accepted (status code)  28  27
      203 Non-Authoritative Information (status code)  28  27
      204 No Content (status code)  28  27
      205 Reset Content (status code)  29  28

   3
      300 Multiple Choices (status code)  31  29
      301 Moved Permanently (status code)  31  30
      302 Found (status code)  32  30
      303 See Other (status code)  32  31
      305 Use Proxy (status code)  33  31
      306 (Unused) (status code)  33  31
      307 Temporary Redirect (status code)  33  32

   4
      400 Bad Request (status code)  33  32
      402 Payment Required (status code)  33  32
      403 Forbidden (status code)  33  32
      404 Not Found (status code)  34  33
      405 Method Not Allowed (status code)  34  33
      406 Not Acceptable (status code)  34  33
      408 Request Timeout (status code)  35  33
      409 Conflict (status code)  35  34
      410 Gone (status code)  35  34
      411 Length Required (status code)  36  34
      413 Request Representation Too Large (status code)  36  35
      414 URI Too Long (status code)  36  35
      415 Unsupported Media Type (status code)  36  35
      417 Expectation Failed (status code)  36  35
      426 Upgrade Required (status code)  37  35

   5
      500 Internal Server Error (status code)  37  36
      501 Not Implemented (status code)  37  36
      502 Bad Gateway (status code)  37  36
      503 Service Unavailable (status code)  38  36
      504 Gateway Timeout (status code)  38  37
      505 HTTP Version Not Supported (status code)  38  37

   A
      Accept header field  52
      Accept-Charset header field  54
      Accept-Encoding header field  55
      Accept-Language header field  56
      Allow header field  42  57

   C
      Coding Format
         compress  42
         deflate  42
         gzip  42
      compress (Coding Format)  42
      CONNECT method  24  17
      content negotiation  7
      Content-Encoding header field  57
      Content-Language header field  58
      Content-Location header field  59
      Content-Transfer-Encoding header field  79
      Content-Type header field  61

   D
      Date header field  61
      deflate (Coding Format)  42
      DELETE method  23  16

   E
      Expect header field  43  62
      Expect Values
         100-continue  44  62

   F
      From header field  44  63

   G
      GET method  19  12
      Grammar
         Accept  52
         Accept-Charset  54
         Accept-Encoding  55
         accept-ext  52
         Accept-Language  56
         accept-params  52
         Allow  42  57
         asctime-date  40
         attribute  43
         charset  41
         codings  55
         content-coding  41
         Content-Encoding  57
         Content-Language  58
         Content-Location  59
         Content-Type  61
         Date  42  61
         date1  40  39
         day  40  39
         day-name  40  39
         day-name-l  40  39
         delta-seconds  47  66
         Expect  43  62
         expect-name  43  62
         expect-param  43  62
         expect-value  43  62
         expectation  43
         extension-code  12  62
         From  44  63
         GMT  40  39
         hour  40
         HTTP-date  39
         HTTP-date  38
         language-range  56
         language-tag  44
         Location  45  64
         Max-Forwards  46  65
         media-range  52
         media-type  42
         method  7  8
         MIME-Version  78
         minute  40  39
         month  40  39
         obs-date  40  39
         parameter  43
         product  41  40
         product-version  41
         reason-phrase  12  40
         Referer  47  65
         Retry-After  47  66
         rfc850-date  41
         rfc1123-date  40
         rfc1123-date  39
         second  40  39
         Server  47
         status-code  12  66
         subtype  42
         time-of-day  40  39
         type  42
         User-Agent  48  67
         value  43
         year  40  39
      gzip (Coding Format)  42

   H
      HEAD method  19  12
      Header Fields
         Accept  52
         Accept-Charset  54
         Accept-Encoding  55
         Accept-Language  56
         Allow  42  57
         Content-Encoding  57
         Content-Language  58
         Content-Location  59
         Content-Transfer-Encoding  79
         Content-Type  61
         Date  42  61
         Expect  43  62
         From  44  63
         Location  45  63
         Max-Forwards  46  65
         MIME-Version  78
         Referer  46  65
         Retry-After  47  66
         Server  47  66
         User-Agent  48  67

   I
      Idempotent Methods  17  9

   L
      Location header field  45  63

   M
      Max-Forwards header field  46  65
      Methods
         CONNECT  24  17
         DELETE  23  16
         GET  19  12
         HEAD  19  12
         OPTIONS  18  11
         POST  20  13
         PUT  21  14
         TRACE  23  16
      MIME-Version header field  78

   O
      OPTIONS method  18  11

   P
      payload  45
      POST method  20  13
      PUT method  21  14

   R
      Referer header field  46  65
      representation  45
      Retry-After header field  47  66

   S
      Safe Methods  17  9
      selected representation  47
      Server header field  47  66
      Status Codes
         100 Continue  26  25
         101 Switching Protocols  27  25
         200 OK  27  26
         201 Created  27  26
         202 Accepted  28  27
         203 Non-Authoritative Information  28  27
         204 No Content  28  27
         205 Reset Content  29  28
         300 Multiple Choices  31  29
         301 Moved Permanently  31  30
         302 Found  32  30
         303 See Other  32  31
         305 Use Proxy  33  31
         306 (Unused)  33  31
         307 Temporary Redirect  33  32
         400 Bad Request  33  32
         402 Payment Required  33  32
         403 Forbidden  33  32
         404 Not Found  34  33
         405 Method Not Allowed  34  33
         406 Not Acceptable  34  33
         408 Request Timeout  35  33
         409 Conflict  35  34
         410 Gone  35  34
         411 Length Required  36  34
         413 Request Representation Too Large  36  35
         414 URI Too Long  36  35
         415 Unsupported Media Type  36  35
         417 Expectation Failed  36  35
         426 Upgrade Required  37  35
         500 Internal Server Error  37  36
         501 Not Implemented  37  36
         502 Bad Gateway  37  36
         503 Service Unavailable  38  36
         504 Gateway Timeout  38  37
         505 HTTP Version Not Supported  38  37
      Status Codes Classes
         1xx Informational  25
         2xx Successful  26
         3xx Redirection  28
         4xx Client Error  32
         5xx Server Error  36

   T
      TRACE method  23  16

   U
      User-Agent header field  48  67

Authors' Addresses

   Roy T. Fielding (editor)
   Adobe Systems Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   EMail: fielding@gbiv.com
   URI:   http://roy.gbiv.com/

   Yves Lafon (editor)
   World Wide Web Consortium
   W3C / ERCIM
   2004, rte des Lucioles
   Sophia-Antipolis, AM  06902
   France

   EMail: ylafon@w3.org
   URI:   http://www.raubacapeu.net/people/yves/
   Julian F. Reschke (editor)
   greenbytes GmbH
   Hafenweg 16
   Muenster, NW  48155
   Germany

   Phone: +49 251 2807760
   Fax:   +49 251 2807761

   EMail: julian.reschke@greenbytes.de
   URI:   http://greenbytes.de/tech/webdav/