HTTPbis Working Group                                   R. Fielding, Ed.
Internet-Draft                                              Day Software
Obsoletes: 2616 (if approved)                                  J. Gettys
Intended status: Standards Track
Updates: 2817 (if approved)                         One Laptop per Child
Expires: January 14, 2010
Intended status: Standards Track                                J. Mogul
Expires: April 29, 2010                                               HP
                                                              H. Frystyk
                                                               Microsoft
                                                             L. Masinter
                                                           Adobe Systems
                                                                P. Leach
                                                               Microsoft
                                                          T. Berners-Lee
                                                                 W3C/MIT
                                                           Y. Lafon, Ed.
                                                                     W3C
                                                         J. Reschke, Ed.
                                                              greenbytes
                                                           July 13,
                                                        October 26, 2009

        HTTP/1.1, part 1: URIs, Connections, and Message Parsing
                   draft-ietf-httpbis-p1-messaging-07
                   draft-ietf-httpbis-p1-messaging-08

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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 1 of the
   seven-part specification that defines the protocol referred to as
   "HTTP/1.1" and, taken together, obsoletes RFC 2616.  Part 1 provides
   an overview of HTTP and its associated terminology, defines the
   "http" and "https" Uniform Resource Identifier (URI) schemes, defines
   the generic message syntax and parsing requirements for HTTP message
   frames, and describes general security concerns for implementations.

Editorial Note (To be removed by RFC Editor)

   Discussion of this draft should take place on the HTTPBIS working
   group mailing list (ietf-http-wg@w3.org).  The current issues list is
   at <http://tools.ietf.org/wg/httpbis/trac/report/11> 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 E.8. D.9.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  7
     1.2.  Syntax Notation  . . . . . . . . . . . . . . . . . . . . .  7
       1.2.1.  ABNF Extension: #rule  . . . . . . . . . . . . . . . .  7
       1.2.2.  Basic Rules  . . . . . . . . . . . . . . . . . . . . .  8
       1.2.3.  ABNF Rules defined in other Parts of the
               Specification  . . . . . . . . . . . . . . . . . . . .  9
   2.  HTTP architecture  . . . . . . . . . . . . . . . . . . . . . . 10
     2.1.  Uniform Resource Identifiers  Client/Server Operation  . . . . . . . . . . . . . . . 10
       2.1.1.  http URI scheme . . 10
     2.2.  Intermediaries . . . . . . . . . . . . . . . . . 11
       2.1.2.  https URI scheme . . . . . 11
     2.3.  Caches . . . . . . . . . . . . . . 11
       2.1.3.  URI Comparison . . . . . . . . . . . . 12
     2.4.  Transport Independence . . . . . . . . 11
       2.1.4.  Scheme aliases considered harmful . . . . . . . . . . 12
     2.2.  Overall Operation 13
     2.5.  HTTP Version . . . . . . . . . . . . . . . . . . . . 12
     2.3.  Use of HTTP for proxy communication . . . 14
     2.6.  Uniform Resource Identifiers . . . . . . . . 14
     2.4.  Interception of HTTP for access control . . . . . . . 15
       2.6.1.  http URI scheme  . . 14
     2.5.  Use of HTTP by other protocols . . . . . . . . . . . . . . 14
     2.6.  Use of HTTP by media type specification . . . 16
       2.6.2.  https URI scheme . . . . . . 14
   3.  Protocol Parameters . . . . . . . . . . . . . 17
       2.6.3.  http and https URI Normalization and Comparison  . . . 17
   3.  HTTP Message . . . . . 14
     3.1.  HTTP Version . . . . . . . . . . . . . . . . . . . . 18
     3.1.  Message Parsing Robustness . . . 14
     3.2.  Date/Time Formats: Full Date . . . . . . . . . . . . . 19
     3.2.  Header Fields  . . 15
     3.3.  Transfer Codings . . . . . . . . . . . . . . . . . . . . 19
     3.3.  Message Body . 18
       3.3.1.  Chunked Transfer Coding . . . . . . . . . . . . . . . 19
     3.4.  Product Tokens . . . . . . . 21
     3.4.  Message Length . . . . . . . . . . . . . . . 21
     3.5.  Quality Values . . . . . . . 22
     3.5.  General Header Fields  . . . . . . . . . . . . . . . 22
   4.  HTTP Message . . . 23
   4.  Request  . . . . . . . . . . . . . . . . . . . . . . 22
     4.1.  Message Types . . . . . 24
     4.1.  Request-Line . . . . . . . . . . . . . . . . . 22
     4.2.  Message Headers . . . . . . 24
       4.1.1.  Method . . . . . . . . . . . . . . . 23
     4.3.  Message Body . . . . . . . . . 24
       4.1.2.  request-target . . . . . . . . . . . . . . 24
     4.4.  Message Length . . . . . . 24
     4.2.  The Resource Identified by a Request . . . . . . . . . . . 26
   5.  Response . . . . . 25
     4.5.  General Header Fields . . . . . . . . . . . . . . . . . . 27
   5.  Request . . . . 27
     5.1.  Status-Line  . . . . . . . . . . . . . . . . . . . . . . . 27
     5.1.  Request-Line
       5.1.1.  Status Code and Reason Phrase  . . . . . . . . . . . . 28
   6.  Protocol Parameters  . . . . . . . . . . . . 27
       5.1.1.  Method . . . . . . . . . 28
     6.1.  Date/Time Formats: Full Date . . . . . . . . . . . . . . . 28
       5.1.2.  request-target .
     6.2.  Transfer Codings . . . . . . . . . . . . . . . . . . . 28
     5.2.  The Resource Identified by a Request . . 31
       6.2.1.  Chunked Transfer Coding  . . . . . . . . . 30
   6.  Response . . . . . . 32
       6.2.2.  Compression Codings  . . . . . . . . . . . . . . . . . 34
       6.2.3.  Transfer Coding Registry . . . . 30
     6.1.  Status-Line . . . . . . . . . . . 35
     6.3.  Product Tokens . . . . . . . . . . . . . . . 31
       6.1.1.  Status Code and Reason Phrase . . . . . . . 35
     6.4.  Quality Values . . . . . 31 . . . . . . . . . . . . . . . . . 36
   7.  Connections  . . . . . . . . . . . . . . . . . . . . . . . . . 32 36
     7.1.  Persistent Connections . . . . . . . . . . . . . . . . . . 32 36
       7.1.1.  Purpose  . . . . . . . . . . . . . . . . . . . . . . . 32 36
       7.1.2.  Overall Operation  . . . . . . . . . . . . . . . . . . 32 37
       7.1.3.  Proxy Servers  . . . . . . . . . . . . . . . . . . . . 34 38
       7.1.4.  Practical Considerations . . . . . . . . . . . . . . . 34 39
     7.2.  Message Transmission Requirements  . . . . . . . . . . . . 35 40
       7.2.1.  Persistent Connections and Flow Control  . . . . . . . 35 40
       7.2.2.  Monitoring Connections for Error Status Messages . . . 35 40
       7.2.3.  Use of the 100 (Continue) Status . . . . . . . . . . . 36 40
       7.2.4.  Client Behavior if Server Prematurely Closes
               Connection . . . . . . . . . . . . . . . . . . . . . . 38 42
   8.  Header Field Definitions . .  Miscellaneous notes that may disappear . . . . . . . . . . . . 43
     8.1.  Scheme aliases considered harmful  . . . . . 38
     8.1.  Connection . . . . . . . 43
     8.2.  Use of HTTP for proxy communication  . . . . . . . . . . . 43
     8.3.  Interception of HTTP for access control  . . . . . . 39
     8.2.  Content-Length . . . 43
     8.4.  Use of HTTP by other protocols . . . . . . . . . . . . . . 44
     8.5.  Use of HTTP by media type specification  . . . . . 40
     8.3.  Date . . . . 44
   9.  Header Field Definitions . . . . . . . . . . . . . . . . . . . 44
     9.1.  Connection . . . . 40
       8.3.1.  Clockless Origin Server Operation . . . . . . . . . . 41
     8.4.  Host . . . . . . . . . . 44
     9.2.  Content-Length . . . . . . . . . . . . . . . . . 42
     8.5.  TE . . . . . 45
     9.3.  Date . . . . . . . . . . . . . . . . . . . . . . . 42
     8.6.  Trailer . . . . 46
       9.3.1.  Clockless Origin Server Operation  . . . . . . . . . . 47
     9.4.  Host . . . . . . . . . . . 44
     8.7.  Transfer-Encoding . . . . . . . . . . . . . . . . 47
     9.5.  TE . . . . 44
     8.8.  Upgrade . . . . . . . . . . . . . . . . . . . . . . . . 48
     9.6.  Trailer  . 45
     8.9.  Via . . . . . . . . . . . . . . . . . . . . . . . . 49
     9.7.  Transfer-Encoding  . . . 46
   9.  IANA Considerations . . . . . . . . . . . . . . . . . 49
     9.8.  Upgrade  . . . . 47
     9.1.  Message Header Registration . . . . . . . . . . . . . . . 47
     9.2.  URI Scheme Registration . . . . . . 50
       9.8.1.  Upgrade Token Registry . . . . . . . . . . . 48
     9.3.  Internet Media Type Registrations . . . . . 51
     9.9.  Via  . . . . . . . 48
       9.3.1.  Internet Media Type message/http . . . . . . . . . . . 48
       9.3.2.  Internet Media Type application/http . . . . . . . . . 49 52
   10. Security IANA Considerations  . . . . . . . . . . . . . . . . . . . 50 . . 53
     10.1. Personal Information Message Header Registration  . . . . . . . . . . . . . . . 53
     10.2. URI Scheme Registration  . . . . 51
     10.2. Abuse of Server Log Information . . . . . . . . . . . . . 51 54
     10.3. Attacks Based On File and Path Names Internet Media Type Registrations  . . . . . . . . . . . 51
     10.4. DNS Spoofing . 54
       10.3.1. Internet Media Type message/http . . . . . . . . . . . 54
       10.3.2. Internet Media Type application/http . . . . . . . . . 55
     10.4. Transfer Coding Registry . . 51
     10.5. Proxies and Caching . . . . . . . . . . . . . . . 56
     10.5. Upgrade Token Registration . . . . 52
     10.6. . . . . . . . . . . . . 57
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 57
     11.1. Personal Information . . . . . . . . . . . . . . . . . . . 57
     11.2. Abuse of Server Log Information  . . . . . . . . . . . . . 58
     11.3. Attacks Based On File and Path Names . . . . . . . . . . . 58
     11.4. DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . . 58
     11.5. Proxies and Caching  . . . . . . . . . . . . . . . . . . . 59
     11.6. Denial of Service Attacks on Proxies . . . . . . . . . . . 53
   11. 60
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 53
   12. 60
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 54
     12.1. 61
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 54
     12.2. 61
     13.2. Informative References . . . . . . . . . . . . . . . . . . 55 62
   Appendix A.  Tolerant Applications . . . . . . . . . . . . . . . . 57 64
   Appendix B.  Compatibility with Previous Versions  . . . . . . . . 58 65
     B.1.  Changes from HTTP/1.0  . . . . . . . . . . . . . . . . . . 59 66
       B.1.1.  Changes to Simplify Multi-homed Web Servers and
               Conserve IP Addresses  . . . . . . . . . . . . . . . . 59 66
     B.2.  Compatibility with HTTP/1.0 Persistent Connections . . . . 59 67
     B.3.  Changes from RFC 2068  . . . . . . . . . . . . . . . . . . 60 67
     B.4.  Changes from RFC 2616  . . . . . . . . . . . . . . . . . . 61 68
   Appendix C.  Terminology . . . . . . . . . . . . . . . . . . . . . 61
   Appendix D.  Collected ABNF  . . . . . . . . . . . . . . . . . . . 64 69
   Appendix E. D.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . . 69
     E.1. 73
     D.1.  Since RFC2616  . . . . . . . . . . . . . . . . . . . . . . 69
     E.2. 73
     D.2.  Since draft-ietf-httpbis-p1-messaging-00 . . . . . . . . . 69
     E.3. 73
     D.3.  Since draft-ietf-httpbis-p1-messaging-01 . . . . . . . . . 70
     E.4. 75
     D.4.  Since draft-ietf-httpbis-p1-messaging-02 . . . . . . . . . 71
     E.5. 76
     D.5.  Since draft-ietf-httpbis-p1-messaging-03 . . . . . . . . . 72
     E.6. 76
     D.6.  Since draft-ietf-httpbis-p1-messaging-04 . . . . . . . . . 72
     E.7. 77
     D.7.  Since draft-ietf-httpbis-p1-messaging-05 . . . . . . . . . 73
     E.8. 77
     D.8.  Since draft-ietf-httpbis-p1-messaging-06 . . . . . . . . . 74 78
     D.9.  Since draft-ietf-httpbis-p1-messaging-07 . . . . . . . . . 79
   Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 79
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 78 84

1.  Introduction

   The Hypertext Transfer Protocol (HTTP) is an application-level
   request/response protocol that uses extensible semantics and MIME-
   like message payloads for flexible interaction with network-based
   hypertext information systems.  HTTP relies upon the Uniform Resource
   Identifier (URI) standard [RFC3986] to indicate request targets and
   relationships between resources.  Messages are passed in a format
   similar to that used by Internet mail [RFC5322] and the Multipurpose
   Internet Mail Extensions (MIME) [RFC2045] (see Appendix A of [Part3]
   for the differences between HTTP and MIME messages).

   HTTP is a generic interface protocol for information systems.  It is
   designed to hide the details of how a service is implemented by
   presenting a uniform interface to clients that is independent of the
   types of resources provided.  Likewise, servers do not need to be
   aware of each client's purpose: an HTTP request can be considered in
   isolation rather than being associated with a specific type of client
   or a predetermined sequence of application steps.  The result is a
   protocol that can be used effectively in many different contexts and
   for which implementations can evolve independently over time.

   HTTP is also designed for use as a generic protocol for translating
   communication to and from other Internet information systems.  HTTP
   proxies and gateways provide access to alternative information
   services by translating their diverse protocols into a hypertext
   format that can be viewed and manipulated by clients in the same way
   as HTTP services.

   One consequence of HTTP flexibility is that the protocol cannot be
   defined in terms of what occurs behind the interface.  Instead, we
   are limited to defining the syntax of communication, the intent of
   received communication, and the expected behavior of recipients.  If
   the communication is considered in isolation, then successful actions
   should be reflected in corresponding changes to the observable
   interface provided by servers.  However, since multiple clients may
   act in parallel and perhaps at cross-purposes, we cannot require that
   such changes be observable beyond the scope of a single response.

   This document is Part 1 of the seven-part specification of HTTP,
   defining the protocol referred to as "HTTP/1.1" and obsoleting
   [RFC2616].  Part 1 describes the architectural elements that are used
   or referred to in HTTP and HTTP, defines the "http" and "https" URI schemes specific to HTTP-
   based resources, schemes,
   describes overall network operation, operation and connection management, and
   defines HTTP message framing and forwarding requirements.  Our goal
   is to define all of the mechanisms necessary for HTTP message
   handling that are independent of message semantics, thereby defining
   the complete set of requirements for message parsers and message-forwarding message-
   forwarding intermediaries.

1.1.  Requirements

   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].

   An implementation is not compliant if it fails to satisfy one or more
   of the MUST or REQUIRED level requirements for the protocols it
   implements.  An implementation that satisfies all the MUST or
   REQUIRED level and all the SHOULD level requirements for its
   protocols is said to be "unconditionally compliant"; one that
   satisfies all the MUST level requirements but not all the SHOULD
   level requirements for its protocols is said to be "conditionally
   compliant."

1.2.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234].

   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), LF (line feed), OCTET (any 8-bit
   sequence of data), SP (space), VCHAR (any visible [USASCII]
   character), and WSP (whitespace).

1.2.1.  ABNF Extension: #rule

   One extension to the ABNF rules of [RFC5234] is used to improve
   readability.

   A construct "#" is defined, similar to "*", for defining lists of
   elements.  The full form is "<n>#<m>element" indicating at least <n>
   and at most <m> elements, each separated by a single comma (",") and
   optional whitespace (OWS).

   Thus,

     1#element => element *( OWS "," OWS element )

   and:

     #element => [ 1#element ]

   and for n >= 1 and m > 1:

     <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )

   For compatibility with legacy list rules, recipients SHOULD accept
   empty list elements.  In other words, consumers would follow the list
   productions:

     #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]

     1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )

   Appendix D C shows the collected ABNF, with the list rules expanded as
   explained above.

1.2.2.  Basic Rules

   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
   protocol elements except the entity-body (see Appendix A for tolerant
   applications).  The end-of-line marker within an entity-body is
   defined by its associated media type, as described in Section 2.3 of
   [Part3].

   This specification uses three rules to denote the use of linear
   whitespace: OWS (optional whitespace), RWS (required whitespace), and
   BWS ("bad" whitespace).

   The OWS rule is used where zero or more linear whitespace characters
   may appear.  OWS SHOULD either not be produced or be produced as a
   single SP character.  Multiple OWS characters that occur within
   field-content SHOULD be replaced with a single SP before interpreting
   the field value or forwarding the message downstream.

   RWS is used when at least one linear whitespace character is required
   to separate field tokens.  RWS SHOULD be produced as a single SP
   character.  Multiple RWS characters that occur within field-content
   SHOULD be replaced with a single SP before interpreting the field
   value or forwarding the message downstream.

   BWS is used where the grammar allows optional whitespace for
   historical reasons but senders SHOULD NOT produce it in messages.
   HTTP/1.1 recipients MUST accept such bad optional whitespace and
   remove it before interpreting the field value or forwarding the
   message downstream.

     OWS            = *( [ obs-fold ] WSP )
                    ; "optional" whitespace
     RWS            = 1*( [ obs-fold ] WSP )
                    ; "required" whitespace
     BWS            = OWS
                    ; "bad" whitespace
     obs-fold       = CRLF
                    ; see Section 4.2 3.2

   Many HTTP/1.1 header field values consist of words separated by
   whitespace or special characters.  These special characters MUST be
   in a quoted string to be used within a parameter value (as defined in
   Section 3.3). 6.2).

     tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
                    / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
                    / DIGIT / ALPHA

     token          = 1*tchar

   A string of text is parsed as a single word if it is quoted using
   double-quote marks.

     quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
     qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
                    ; OWS / <VCHAR except DQUOTE and "\"> / obs-text
     obs-text       = %x80-FF

   The backslash character ("\") MAY can be used as a single-character
   quoting mechanism only within quoted-string and comment constructs.

     quoted-text    = %x01-09 /
                      %x0B-0C /
                      %x0E-FF ; Characters excluding NUL, CR and LF constructs:

     quoted-pair    = "\" quoted-text

1.2.3.  ABNF Rules defined in other Parts ( WSP / VCHAR / obs-text )

   Producers SHOULD NOT escape characters that do not require escaping
   (i.e., other than DQUOTE and the backslash character).

1.2.3.  ABNF Rules defined in other Parts of the Specification

   The ABNF rules below are defined in other parts:

     request-header  = <request-header, defined in [Part2], Section 3>
     response-header = <response-header, defined in [Part2], Section 5>

     entity-body     = <entity-body, defined in [Part3], Section 3.2>
     entity-header   = <entity-header, defined in [Part3], Section 3.1>
     Cache-Control   = <Cache-Control, defined in [Part6], Section 3.4>
     Pragma          = <Pragma, defined in [Part6], Section 3.4>
     Warning         = <Warning, defined in [Part6], Section 3.6>

2.  HTTP architecture

   HTTP was created with a specific architecture in mind, for the World Wide
   Web, Web architecture and has evolved
   over time to support the scalability needs of a worldwide hypertext
   system.  Much of that architecture is reflected in the terminology
   and syntax productions used to define HTTP.

2.1.  Uniform Resource Identifiers

   Uniform Resource Identifiers (URIs) [RFC3986] are used throughout  Client/Server Operation

   HTTP as the means for identifying resources.  URI references are used is a request/response protocol that operates by exchanging
   messages across a reliable transport or session-layer connection.  An
   HTTP client is a program that establishes a connection to target requests, redirect responses, and define relationships. a server
   for the purpose of sending one or more HTTP does not limit what requests.  An HTTP server
   is a resource may be; it merely defines an
   interface program that can be used accepts connections in order to interact with service HTTP
   requests by sending HTTP responses.

   Note that the terms "client" and "server" refer only to the roles
   that these programs perform for a resource via HTTP.
   More information particular connection.  The same
   program may act as a client on some connections and a server on
   others.  We use the scope of URIs term "user agent" to refer to the program that
   initiates a request, such as a WWW browser, editor, or spider (web-
   traversing robot), and resources can be found in
   [RFC3986].

   This specification adopts the definitions term "origin server" to refer to the
   program that can originate authoritative responses to a request.

   Most HTTP communication consists of "URI-reference",
   "absolute-URI", "relative-part", "fragment", "port", "host", "path-
   abempty", "path-absolute", "query", and "authority" from [RFC3986].
   In addition, we define a partial-URI rule retrieval request (GET) for protocol elements that
   allow a relative URI without
   representation of some resource identified by a fragment.

     URI           = <URI, defined in [RFC3986], Section 3>
     URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
     absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
     relative-part = <relative-part, defined in [RFC3986], Section 4.2>
     authority     = <authority, defined in [RFC3986], Section 3.2>
     fragment      = <fragment, defined in [RFC3986], Section 3.5>
     path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
     path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
     port          = <port, defined in [RFC3986], Section 3.2.3>
     query         = <query, defined in [RFC3986], Section 3.4>
     uri-host      = <host, defined in [RFC3986], Section 3.2.2>

     partial-URI   = relative-part [ "?" query ]

   Each protocol element in HTTP that allows a URI reference will
   indicate in its ABNF production whether URI.  In the element allows only simplest
   case, this may be accomplished via a URI
   in absolute form (absolute-URI), any relative reference (relative-
   ref), or some other subset of single connection (v) between
   the URI-reference grammar.  Unless
   otherwise indicated, URI references are parsed relative to user agent (UA) and the origin server (O).

          request target (the default base URI for both the chain ------------------------>
       UA -------------------v------------------- O
          <----------------------- response chain

   A client sends an HTTP request and its
   corresponding response).

2.1.1.  http URI scheme

   The "http" scheme is used to locate network resources via the HTTP
   protocol.

     http-URI = "http:" "//" authority path-abempty [ "?" query ]

   If server in the port is form of a request
   message (Section 4), beginning with a method, URI, and protocol
   version, followed by MIME-like header fields containing request
   modifiers, client information, and payload metadata, an empty or not given, port 80 is assumed.  The semantics
   are that line to
   indicate the identified resource is located at end of the header section, and finally the payload body
   (if any).

   A server listening
   for TCP connections on that port of that host, and the request-target
   for responds to the resource is path-absolute client's request by sending an HTTP response
   message (Section 5.1.2).  The use of IP
   addresses in URLs SHOULD be avoided whenever possible (see
   [RFC1900]).  If the path-absolute is not present in the URL, it MUST
   be given as "/" when used as 5), beginning with a request-target for status line that includes the
   protocol version, a success or error code, and textual reason phrase,
   followed by MIME-like header fields containing server information,
   resource
   (Section 5.1.2).  If a proxy receives a host name which is not a
   fully qualified domain name, it MAY add its domain metadata, and payload metadata, an empty line to indicate
   the host name
   it received.  If a proxy receives a fully qualified domain name, the
   proxy MUST NOT change end of the host name.

2.1.2.  https URI scheme

   [[anchor1: TBD: Define header section, and explain purpose of https scheme.]]

      Note: finally the "https" scheme is defined in [RFC2818].

2.1.3.  URI Comparison

   When comparing two URIs to decide if they match or not, payload body (if any).

   The following example illustrates a client
   SHOULD use typical message exchange for a case-sensitive octet-by-octet comparison of
   GET request on the entire
   URIs, with these exceptions:

   o URI "http://www.example.com/hello.txt":

   client request:

     GET /hello.txt HTTP/1.1
     User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
     Host: www.example.com
     Accept: */*

   server response:

     HTTP/1.1 200 OK
     Date: Mon, 27 Jul 2009 12:28:53 GMT
     Server: Apache
     Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
     ETag: "34aa387-d-1568eb00"
     Accept-Ranges: bytes
     Content-Length: 14
     Vary: Accept-Encoding
     Content-Type: text/plain

     Hello World!

2.2.  Intermediaries

   A port that is empty more complicated situation occurs when one or not given is equivalent to more intermediaries
   are present in the default
      port for that URI-reference;

   o  Comparisons of host names MUST be case-insensitive;

   o  Comparisons request/response chain.  There are three common
   forms of scheme names MUST be case-insensitive;

   o  An empty path-absolute is equivalent to a path-absolute of "/".

   o  Characters other than those in the "reserved" set are equivalent
      to their percent-encoded octets (see [RFC3986], Section 2.1).

   For example, the following three URIs are equivalent:

      http://example.com:80/~smith/home.html
      http://EXAMPLE.com/%7Esmith/home.html
      http://EXAMPLE.com:/%7esmith/home.html

2.1.4.  Scheme aliases considered harmful

2.2.  Overall Operation

   HTTP is a request/response protocol.  A client sends intermediary: proxy, gateway, and tunnel.  In some cases, a request to the
   server in
   single intermediary may act as an origin server, proxy, gateway, or
   tunnel, switching behavior based on the form nature of a request method, URI, and protocol version,
   followed by a MIME-like message containing each request.

          request modifiers, client
   information, and possible body content over a connection with a
   server. chain -------------------------------------->
       UA -----v----- A -----v----- B -----v----- C -----v----- O
          <------------------------------------- response chain

   The server responds with a status line, including the
   message's protocol version and a success or error code, followed by a
   MIME-like message containing server information, entity
   metainformation, figure above shows three intermediaries (A, B, and possible entity-body content.

   Most HTTP communication is initiated by a C) between the
   user agent and consists of
   a request to be applied to a resource on some origin server.  In  A request or response message that
   travels the
   simplest case, this whole chain will pass through four separate connections.
   Some HTTP communication options may be accomplished via a single apply only to the connection (v)
   between with
   the user agent (UA) and nearest, non-tunnel neighbor, only to the origin server (O).

          request chain ------------------------>
       UA -------------------v------------------- O
          <----------------------- response chain

   A more complicated situation occurs when one end-points of the
   chain, or more intermediaries
   are present in the request/response chain.  There are three common
   forms of intermediary: proxy, gateway, and tunnel.  A proxy is a
   forwarding agent, receiving requests for a URI in its absolute form,
   rewriting all or part of the message, and forwarding the reformatted
   request toward the server identified by the URI.  A gateway is a
   receiving agent, acting as a layer above some other server(s) and, if
   necessary, translating the requests to the underlying server's
   protocol.  A tunnel acts as a relay point between two connections
   without changing the messages; tunnels are used when the
   communication needs to pass through an intermediary (such as a
   firewall) even when the intermediary cannot understand the contents
   of the messages.

          request chain -------------------------------------->
       UA -----v----- A -----v----- B -----v----- C -----v----- O
          <------------------------------------- response chain

   The figure above shows three intermediaries (A, B, and C) between the
   user agent and origin server.  A request or response message that
   travels the whole chain will pass through four separate connections.
   This distinction is important because some HTTP communication options
   may apply only to the connection with the nearest, non-tunnel
   neighbor, only to the end-points of the chain, or to all connections
   along to all connections along the chain.  Although the diagram
   is linear, each participant may be engaged in multiple, simultaneous
   communications.  For example, B may be receiving requests from many
   clients other than A, and/or forwarding requests to servers other
   than C, at the same time that it is handling A's request.

   Any party

   We use the terms "upstream" and "downstream" to describe various
   requirements in relation to the communication which is not acting as a tunnel may
   employ an internal cache for handling requests.  The effect directional flow of a
   cache is that message: all
   messages flow from upstream to downstream.  Likewise, we use the request/response chain is shortened if one of
   terms "inbound" and "outbound" to refer to directions in relation to
   the
   participants along request path: "inbound" means toward the chain has a cached response applicable to that
   request.  The following illustrates origin server and
   "outbound" means toward the resulting chain if B has a
   cached copy of an earlier response from O (via C) for user agent.

   A proxy is a request which
   has not been cached message forwarding agent that is selected by UA or A.

             request chain ---------->
          UA -----v----- A -----v----- B - - - - - - C - - - - - - O
             <--------- response chain

   Not all responses are usefully cacheable, and some the client,
   usually via local configuration rules, to receive requests may
   contain modifiers which place special requirements on cache behavior.
   HTTP requirements for cache behavior and cacheable responses are
   defined in Section 1 of [Part6].

   In fact, there are a wide variety of architectures and configurations some
   type(s) of caches absolute URI and proxies currently being experimented with or deployed
   across the World Wide Web. These systems include national hierarchies
   of proxy caches attempt to save transoceanic bandwidth, systems that
   broadcast or multicast cache entries, organizations that distribute
   subsets of cached data satisfy those requests via CD-ROM, and so on.
   translation through the HTTP systems interface.  Some translations are used
   in corporate intranets over high-bandwidth links, and
   minimal, such as for access via
   PDAs with low-power radio links proxy requests for "http" URIs, whereas other
   requests may require translation to and intermittent connectivity.  The
   goal of HTTP/1.1 is from entirely different
   application-layer protocols.  Proxies are often used to support group an
   organization's HTTP requests through a common intermediary for the wide diversity
   sake of configurations
   already deployed while introducing protocol constructs security, annotation services, or shared caching.

   A gateway (a.k.a., reverse proxy) is a receiving agent that meet acts as a
   layer above some other server(s) and translates the
   needs of those who build web applications that require high
   reliability and, failing that, at least reliable indications of
   failure.

   HTTP communication usually takes place over TCP/IP connections.  The
   default port is TCP 80
   (<http://www.iana.org/assignments/port-numbers>), but other ports can
   be used.  This does not preclude HTTP from being implemented on top
   of any other protocol on received requests
   to the Internet, underlying server's protocol.  Gateways are often used for
   load balancing or on other networks. partitioning HTTP
   only presumes services across multiple
   machines.  Unlike a reliable transport; any protocol that provides such
   guarantees can proxy, a gateway receives requests as if it were
   the origin server for the requested resource; the requesting client
   will not be used; aware that it is communicating with a gateway.  A gateway
   communicates with the mapping of client as if the HTTP/1.1 request and
   response structures onto gateway is the transport data units origin server
   and thus is subject to all of the requirements on origin servers for
   that connection.  A gateway communicates with inbound servers using
   any protocol in
   question is it desires, including private extensions to HTTP that
   are outside the scope of this specification.

   In HTTP/1.0, most implementations used a new connection for each
   request/response exchange.  In HTTP/1.1,

   A tunnel acts as a connection may be used for
   one or more request/response exchanges, although blind relay between two connections may be
   closed for without
   changing the messages.  Once active, a variety of reasons (see Section 7.1).

2.3.  Use of HTTP for proxy communication

   [[anchor2: TBD: Configured tunnel is not considered a
   party to use the HTTP to proxy communication, though the tunnel may have been
   initiated by an HTTP or other
   protocols.]]

2.4.  Interception request.  A tunnel ceases to exist when both
   ends of HTTP for access control

   [[anchor3: TBD: Interception of HTTP traffic for initiating access
   control.]]

2.5.  Use of HTTP by other protocols

   [[anchor4: TBD: Profiles of HTTP defined by other protocol.
   Extensions of HTTP like WebDAV.]]

2.6.  Use of HTTP by media type specification

   [[anchor5: TBD: Instructions on composing HTTP requests via hypertext
   formats.]]

3.  Protocol Parameters

3.1.  HTTP Version

   HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
   of the protocol.  The protocol versioning policy is intended to allow the sender relayed connection are closed.  Tunnels are used to indicate the format of
   extend a message and its capacity for
   understanding further HTTP communication, rather than the features
   obtained via that communication.  No change virtual connection through an intermediary, such as when
   transport-layer security is made used to the version
   number for the addition of message components which do not affect establish private communication behavior or which only add
   through a shared firewall proxy.

2.3.  Caches

   Any party to extensible field values.
   The <minor> number HTTP communication that is incremented when the changes made to the
   protocol add features which do not change the general message parsing
   algorithm, but which may add to the message semantics and imply
   additional capabilities of the sender.  The <major> number is
   incremented when the format of acting as a message within the protocol is
   changed.  See [RFC2145] tunnel may
   employ an internal cache for handling requests.  A cache is a fuller explanation.

   The version local
   store of an HTTP previous response messages and the subsystem that controls
   its message is indicated by an HTTP-Version field storage, retrieval, and deletion.  A cache stores
   cacheable responses in order to reduce the first line of the message.  HTTP-Version is case-sensitive.

     HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
     HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive

   Note that the major and minor numbers MUST be treated as separate
   integers response time and that each MAY be incremented higher than network
   bandwidth consumption on future, equivalent requests.  Any client or
   server may include a single digit.
   Thus, HTTP/2.4 is cache, though a lower version than HTTP/2.13, which in turn is
   lower than HTTP/12.3.  Leading zeros MUST cache cannot be ignored used by recipients
   and MUST NOT be sent.

   An application that sends a request or response message that includes
   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
   with this specification.  Applications that are at least
   conditionally compliant with this specification SHOULD use an HTTP-
   Version of "HTTP/1.1" in their messages, and MUST do so for any
   message that server
   while it is not compatible with HTTP/1.0.  For more details on
   when to send specific HTTP-Version values, see [RFC2145]. acting as a tunnel.

   The HTTP version effect of an application a cache is that the highest HTTP version for
   which the application request/response chain is at least conditionally compliant.

   Proxy and gateway applications need to be careful when forwarding
   messages in protocol versions different from that shortened
   if one of the application.
   Since the protocol version indicates the protocol capability of participants along the
   sender, a proxy/gateway MUST NOT send chain has a message with cached response
   applicable to that request.  The following illustrates the resulting
   chain if B has a version
   indicator which is greater than its actual version.  If cached copy of an earlier response from O (via C)
   for a higher
   version request is received, the proxy/gateway MUST either downgrade
   the request version, or respond with an error, which has not been cached by UA or switch to tunnel
   behavior.

   Due to interoperability problems with HTTP/1.0 proxies discovered
   since the publication of [RFC2068], caching proxies MUST, gateways
   MAY, and tunnels MUST NOT upgrade the A.

             request chain ---------->
          UA -----v----- A -----v----- B - - - - - - C - - - - - - O
             <--------- response chain

   A response is cacheable if a cache is allowed to store a copy of the highest version
   they support.  The proxy/gateway's
   response to that request MUST be message for use in the same major version as the request.

      Note: Converting between versions of HTTP answering subsequent requests.  Even when
   a response is cacheable, there may involve modification
      of header fields required be additional constraints placed
   by the client or forbidden by the versions involved.

3.2.  Date/Time Formats: Full Date origin server on when that cached response
   can be used for a particular request.  HTTP applications have historically allowed three different formats requirements for the representation of date/time stamps:

     Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
     Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
     Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format

   The first format is preferred as an Internet standard cache
   behavior and represents
   a fixed-length subset of that cacheable responses are defined by [RFC1123].  The other
   formats in Section 2 of [Part6].

   There are described here only for compatibility with obsolete
   implementations.  HTTP/1.1 clients a wide variety of architectures and servers that parse configurations of
   caches and proxies deployed across the date
   value MUST accept all three formats (for compatibility with
   HTTP/1.0), though they MUST only generate the RFC 1123 format for
   representing HTTP-date values in header fields.  See Appendix A for
   further information.

   All World Wide Web and inside
   large organizations.  These systems include national hierarchies of
   proxy caches to save transoceanic bandwidth, systems that broadcast
   or multicast cache entries, organizations that distribute subsets of
   cached data via optical media, and so on.

2.4.  Transport Independence

   HTTP date/time stamps MUST be represented systems are used in Greenwich Mean Time
   (GMT), without exception.  For the purposes a wide variety of HTTP, GMT is exactly
   equal environments, from
   corporate intranets with high-bandwidth links to UTC (Coordinated Universal Time).  This long-distance
   communication over low-power radio links and intermittent
   connectivity.

   HTTP communication usually takes place over TCP/IP connections.  The
   default port is indicated in TCP 80
   (<http://www.iana.org/assignments/port-numbers>), but other ports can
   be used.  This does not preclude HTTP from being implemented on top
   of any other protocol on the
   first two formats by Internet, or on other networks.  HTTP
   only presumes a reliable transport; any protocol that provides such
   guarantees can be used; the inclusion mapping of "GMT" as the three-letter
   abbreviation for time zone, HTTP/1.1 request and MUST be assumed when reading
   response structures onto the
   asctime format.  HTTP-date is case sensitive and MUST NOT include
   additional whitespace beyond that specifically included as SP transport data units of the protocol in
   question is outside the
   grammar.

     HTTP-date    = rfc1123-date / obs-date

   Preferred format:

     rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT

     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 scope of this specification.

   In HTTP/1.0, most implementations used a new connection for each
   request/response exchange.  In HTTP/1.1, a connection may be used for
   one or more request/response exchanges, although connections may be
   closed for a variety of reasons (see Section 7.1).

2.5.  HTTP Version

   HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
   of the protocol.  The semantics protocol versioning policy is intended to allow
   the sender to indicate the format of day-name, day, month, year, a message and time-of-day are its capacity for
   understanding further HTTP communication, rather than the
   same as those defined features
   obtained via that communication.  No change is made to the version
   number for the RFC 5322 constructs with addition of message components which do not affect
   communication behavior or which only add to extensible field values.
   The <minor> number is incremented when 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 changes made to be robust in
      accepting date values that the
   protocol add features which do not change the general message parsing
   algorithm, but which may have been sent by non-HTTP
      applications, as is sometimes add to the case message semantics and imply
   additional capabilities of the sender.  The <major> number is
   incremented when retrieving or posting
      messages via proxies/gateways to SMTP or NNTP.

      Note: HTTP requirements for the date/time stamp format apply only
      to their usage of a message within the protocol stream.  Clients and servers
      are not required to use these formats is
   changed.  See [RFC2145] for user presentation,
      request logging, etc.

3.3.  Transfer Codings

   Transfer-coding values are used to indicate a fuller explanation.

   The version of an encoding
   transformation that has been, can be, or may need to be applied to HTTP message is indicated by an
   entity-body in order to ensure "safe transport" through the network.
   This differs from a content coding HTTP-Version field
   in that the transfer-coding is a
   property first line of the message, not of the original entity.

     transfer-coding         = "chunked" / transfer-extension
     transfer-extension      = token *( OWS ";" OWS transfer-parameter )

   Parameters are in the form of attribute/value pairs.

     transfer-parameter      = attribute BWS "=" BWS value
     attribute message.  HTTP-Version is case-sensitive.

     HTTP-Version   = token
     value HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
     HTTP-Prot-Name = token / quoted-string

   All transfer-coding values are case-insensitive.  HTTP/1.1 uses
   transfer-coding values in %x48.54.54.50 ; "HTTP", case-sensitive

   Note that the TE header field (Section 8.5) major and in
   the Transfer-Encoding header field (Section 8.7).

   Whenever minor numbers MUST be treated as separate
   integers and that each MAY be incremented higher than a transfer-coding single digit.
   Thus, HTTP/2.4 is applied to a message-body, the set of
   transfer-codings MUST include "chunked", unless the message indicates
   it is terminated by closing the connection.  When the "chunked"
   transfer-coding lower version than HTTP/2.13, which in turn is used, it
   lower than HTTP/12.3.  Leading zeros MUST be the last transfer-coding applied
   to the message-body.  The "chunked" transfer-coding ignored by recipients
   and MUST NOT be
   applied more than once to sent.

   An application that sends a message-body.  These rules allow the
   recipient to determine the transfer-length of the request or response message
   (Section 4.4).

   Transfer-codings are analogous to the Content-Transfer-Encoding
   values of MIME [RFC2045], which were designed to enable safe
   transport that includes
   HTTP-Version of binary data over a 7-bit transport service.  However,
   safe transport has a different focus for "HTTP/1.1" MUST be at least conditionally compliant
   with this specification.  Applications that are at least
   conditionally compliant with this specification SHOULD use an 8bit-clean transfer
   protocol.  In HTTP, the only unsafe characteristic HTTP-
   Version of message-bodies
   is the difficulty "HTTP/1.1" in determining the exact body length (Section 4.4),
   or the desire their messages, and MUST do so for any
   message that is not compatible with HTTP/1.0.  For more details on
   when to encrypt data over a shared transport. send specific HTTP-Version values, see [RFC2145].

   The Internet Assigned Numbers Authority (IANA) acts as a registry for
   transfer-coding value tokens.  Initially, HTTP version of an application is the registry contains highest HTTP version for
   which the
   following tokens: "chunked" (Section 3.3.1), "gzip", "compress", application is at least conditionally compliant.

   Proxy and
   "deflate" (Section 2.2 of [Part3]).

   New transfer-coding value tokens SHOULD gateway applications need to be registered careful when forwarding
   messages in protocol versions different from that of the same way
   as new content-coding value tokens (Section 2.2 application.
   Since the protocol version indicates the protocol capability of [Part3]).

   A server which receives an entity-body with a transfer-coding it does
   not understand SHOULD return 501 (Not Implemented), and close the
   connection.  A server
   sender, a proxy/gateway MUST NOT send transfer-codings to an HTTP/1.0
   client.

3.3.1.  Chunked Transfer Coding

   The chunked encoding modifies the body of a message in order to
   transfer it as a series of chunks, each with a version
   indicator which is greater than its own size indicator,
   followed by actual version.  If a higher
   version request is received, the proxy/gateway MUST either downgrade
   the request version, or respond with an OPTIONAL trailer containing entity-header fields.
   This allows dynamically produced content error, or switch to be transferred along tunnel
   behavior.

   Due to interoperability problems with HTTP/1.0 proxies discovered
   since the information necessary for publication of [RFC2068], caching proxies MUST, gateways
   MAY, and tunnels MUST NOT upgrade the recipient request to the highest version
   they support.  The proxy/gateway's response to verify that it has
   received request MUST be
   in the full message.

     Chunked-Body   = *chunk
                      last-chunk
                      trailer-part
                      CRLF

     chunk          = chunk-size *WSP [ chunk-ext ] CRLF
                      chunk-data CRLF
     chunk-size     = 1*HEXDIG
     last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF

     chunk-ext      = *( ";" *WSP chunk-ext-name
                         [ "=" chunk-ext-val ] *WSP )
     chunk-ext-name = token
     chunk-ext-val  = token / quoted-string
     chunk-data     = 1*OCTET ; a sequence of chunk-size octets
     trailer-part   = *( entity-header CRLF )

   The chunk-size field is a string of hex digits indicating same major version as the size request.

      Note: Converting between versions of
   the chunk-data in octets.  The chunked encoding is ended by any chunk
   whose size is zero, followed by the trailer, which is terminated by
   an empty line.

   The trailer allows the sender to include additional HTTP may involve modification
      of header fields at required or forbidden by the end of versions involved.

2.6.  Uniform Resource Identifiers

   Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
   HTTP as the message.  The Trailer header field can be means for identifying resources.  URI references are used
   to target requests, indicate which header fields are included in redirects, and define relationships.
   HTTP does not limit what a trailer (see
   Section 8.6).

   A server using chunked transfer-coding in resource may be; it merely defines an
   interface that can be used to interact with a response MUST NOT use resource via HTTP.
   More information on the
   trailer for any header fields unless at least one scope of the following is
   true:

   1.  the request included a TE header field that indicates "trailers"
       is acceptable URIs and resources can be found in
   [RFC3986].

   This specification adopts the transfer-coding definitions of the response, as
       described in Section 8.5; or,

   2.  the server is the origin server for the response, the trailer
       fields consist entirely of optional metadata, "URI-reference",
   "absolute-URI", "relative-part", "port", "host", "path-abempty",
   "path-absolute", "query", and the recipient
       could use the message (in "authority" from [RFC3986].  In
   addition, we define a manner acceptable to the origin
       server) partial-URI rule for protocol elements that
   allow a relative URI without receiving this metadata.  In a fragment.

     URI           = <URI, defined in [RFC3986], Section 3>
     URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
     absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
     relative-part = <relative-part, defined in [RFC3986], Section 4.2>
     authority     = <authority, defined in [RFC3986], Section 3.2>
     path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
     path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
     port          = <port, defined in [RFC3986], Section 3.2.3>
     query         = <query, defined in [RFC3986], Section 3.4>
     uri-host      = <host, defined in [RFC3986], Section 3.2.2>

     partial-URI   = relative-part [ "?" query ]

   Each protocol element in HTTP that allows a URI reference will
   indicate in its ABNF production whether the element allows only a URI
   in absolute form (absolute-URI), any relative reference (relative-
   ref), or some other words, subset of the
       origin server is willing URI-reference grammar.  Unless
   otherwise indicated, URI references are parsed relative to accept the possibility that
   request target (the default base URI for both the
       trailer fields might be silently discarded along request and its
   corresponding response).

2.6.1.  http URI scheme

   The "http" URI scheme is hereby defined for the path purpose of minting
   identifiers according to their association with the
       client.

   This requirement prevents an interoperability failure when the
   message is being received hierarchical
   namespace governed by an HTTP/1.1 (or later) proxy and
   forwarded to an HTTP/1.0 recipient.  It avoids a situation where
   compliance with the protocol would have necessitated a possibly
   infinite buffer on the proxy.

   A process potential HTTP origin server listening for decoding
   TCP connections on a given port.  The HTTP server is identified via
   the "chunked" transfer-coding can be
   represented in pseudo-code as:

     length := 0
     read chunk-size, chunk-ext (if any) and CRLF
     while (chunk-size > 0) {
        read chunk-data and CRLF
        append chunk-data to entity-body
        length := length + chunk-size
        read chunk-size generic syntax's authority component, which includes a host
   identifier and CRLF
     }
     read entity-header
     while (entity-header not empty) {
        append entity-header to existing header fields
        read entity-header
     }
     Content-Length := length
     Remove "chunked" from Transfer-Encoding

   All HTTP/1.1 applications MUST be able to receive optional TCP port, and decode the
   "chunked" transfer-coding, and MUST ignore chunk-ext extensions they
   do not understand.

3.4.  Product Tokens

   Product tokens are used to allow communicating applications to
   identify themselves by software name and version.  Most fields using
   product tokens also allow sub-products which form a significant part remainder of the application URI is
   considered to be listed, separated by whitespace.  By
   convention, the products are listed in order 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 be short and data corresponding to the point.  They MUST NOT be
   used for advertising or other non-essential information.  Although
   any token character MAY appear in a product-version, this token
   SHOULD only be used resource for a version identifier (i.e., successive
   versions of the same product SHOULD only differ in the product-
   version portion of the product value).

3.5.  Quality Values

   Both transfer codings (TE request header, Section 8.5) and content
   negotiation (Section 4 of [Part3]) use short "floating point" numbers
   to indicate the relative importance ("weight") of various negotiable
   parameters.  A weight
   which that server might provide an HTTP interface.

     http-URI = "http:" "//" authority path-abempty [ "?" query ]

   The host identifier within an authority component is normalized to a real number defined in the range 0
   through 1, where 0
   [RFC3986], Section 3.2.2.  If host is provided as an IP literal or
   IPv4 address, then the minimum and 1 HTTP server is any listener on the maximum value. indicated
   TCP port at that IP address.  If host is a
   parameter has a quality value of 0, registered name, then content with this parameter that
   name is `not acceptable' for considered an indirect identifier and the client.  HTTP/1.1 applications MUST NOT
   generate more than three digits after recipient might use
   a name resolution service, such as DNS, to find the decimal point.  User
   configuration address of these values SHOULD also a
   listener for that host.  The host MUST NOT be limited in this fashion.

     qvalue         = ( "0" [ "." 0*3DIGIT ] )
                    / ( "1" [ "." 0*3("0") ] )

      Note: "Quality values" empty; if an "http" URI
   is a misnomer, since these values merely
      represent relative degradation in desired quality.

4.  HTTP Message

4.1.  Message Types

   HTTP messages consist received with an empty host, then it MUST be rejected as invalid.
   If the port subcomponent is empty or not given, then TCP port 80 is
   assumed (the default reserved port for WWW services).

   Regardless of requests from client to server and responses
   from server the form of host identifier, access to client.

     HTTP-message   = Request / Response     ; HTTP/1.1 messages

   Request (Section 5) and Response (Section 6) messages use the generic
   message format of [RFC5322] for transferring entities (the payload of that host is not
   implied by the message).  Both types of message consist mere presence of a start-line, zero its name or
   more header fields (also known as "headers"), address.  The host may or
   may not exist and, even when it does exist, may or may not be running
   an empty line (i.e., a
   line with nothing preceding the CRLF) indicating HTTP server or listening to the end indicated port.  The "http" URI
   scheme makes use of the
   header fields, and possibly a message-body.

     generic-message = start-line
                       *( message-header CRLF )
                       CRLF
                       [ message-body ]
     start-line      = Request-Line / Status-Line

   In the interest delegated nature of robustness, servers SHOULD ignore any empty
   line(s) received where Internet names and
   addresses to establish a Request-Line is expected.  In other words,
   if naming authority (whatever entity has the
   ability to place an HTTP server is reading the protocol stream at the beginning of a
   message that Internet name or address) and receives
   allows that authority to determine which names are valid and how they
   might be used.

   When an "http" URI is used within a CRLF first, it should ignore context that calls for access to
   the CRLF.

   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
   after indicated resource, a POST request.  To restate what is explicitly forbidden client MAY attempt access by resolving the
   BNF,
   host to an HTTP/1.1 client MUST NOT preface or follow IP address, establishing a request with an
   extra CRLF.

   Whitespace (WSP) MUST NOT be sent between TCP connection to that address
   on the start-line indicated port, and the
   first header field.  The presence of whitespace might be sending an attempt HTTP request message to trick a noncompliant implementation of HTTP into ignoring that
   field or processing the next line
   server containing the URI's identifying data as a new request, either of which
   may result described in security issues when implementations within
   Section 4.  If the server responds to that request
   chain interpret the same message differently.  HTTP/1.1 servers MUST
   reject such a message with a 400 (Bad Request) response.

4.2.  Message Headers non-interim
   HTTP header fields follow the same general format response message, as Internet
   messages described in Section 2.1 of [RFC5322].  Each header field consists of
   a name followed by a colon (":"), optional whitespace, and the field
   value.  Field names are case-insensitive.

     message-header = field-name ":" OWS [ field-value ] OWS
     field-name     = token
     field-value    = *( field-content / OWS )
     field-content  = *( WSP / VCHAR / obs-text )

   Historically, HTTP has allowed field-content with text in 5, then that response
   is considered an authoritative answer to the ISO-
   8859-1 [ISO-8859-1] character encoding (allowing other character sets
   through use of [RFC2047] encoding).  In practice, most client's request.

   Although HTTP header
   field-values use only a subset is independent of the US-ASCII charset [USASCII].
   Newly defined header fields SHOULD constrain their field-values transport protocol, the "http"
   scheme is specific to
   US-ASCII characters.  Recipients SHOULD treat TCP-based services because the name delegation
   process depends on TCP for establishing authority.  An HTTP service
   based on some other (obs-text) octets
   in field-content underlying connection protocol would presumably
   be identified using a different URI scheme, just as opaque data.

   No whitespace is allowed between the header field-name and colon.
   For security reasons, any request message received containing such
   whitespace MUST be rejected with "https"
   scheme (below) is used for servers that require an SSL/TLS transport
   layer on a response code of 400 (Bad Request)
   and any such whitespace in a response message MUST connection.  Other protocols may also be removed. used to provide
   access to "http" identified resources --- it is only the
   authoritative interface used for mapping the namespace that is
   specific to TCP.

2.6.2.  https URI scheme

   The field value MAY be preceded "https" URI scheme is hereby defined for the purpose of minting
   identifiers according to their association with the hierarchical
   namespace governed by optional whitespace; a single SP
   is preferred. potential HTTP origin server listening for
   SSL/TLS-secured connections on a given TCP port.  The field-value does not include any leading or
   trailing white space: OWS occurring before host and port
   are determined in the first non-whitespace
   character same way as for the "http" scheme, except that
   a default TCP port of 443 is assumed if the field-value port subcomponent is
   empty or after not given.

     https-URI = "https:" "//" authority path-abempty [ "?" query ]

   The primary difference between the last non-whitespace
   character of "http" and "https" schemes is that
   interaction with the field-value latter is ignored and MAY required to be removed without
   changing secured for privacy
   through the meaning use of the header field.

   Historically, HTTP header field values could strong encryption.  The URI cannot be extended over
   multiple lines by preceding each extra line with at least one space
   or horizontal tab character (line folding).  This specification
   deprecates such line folding except within sent in a
   request until the message/http media
   type (Section 9.3.1).  HTTP/1.1 senders MUST NOT produce messages
   that include line folding (i.e., connection is secure.  Likewise, the default for
   caching is that contain any field-content each response that
   matches the obs-fold rule) unless would be considered "public" under
   the message "http" scheme is intended instead treated as "private" and thus not
   eligible for
   packaging within the message/http media type.  HTTP/1.1 recipients
   SHOULD accept line folding shared caching.

   The process for authoritative access to an "https" identified
   resource is defined in [RFC2818].

2.6.3.  http and replace any embedded obs-fold
   whitespace with a single SP prior https URI Normalization and Comparison

   Since the "http" and "https" schemes conform to interpreting the field value or
   forwarding URI generic
   syntax, such URIs are normalized and compared according to the message downstream.

   Comments can be included
   algorithm defined in some HTTP header fields by surrounding [RFC3986], Section 6, using the comment text with parentheses.  Comments are only allowed in
   fields containing "comment" as part of their field value definition.
   In all other fields, parentheses are considered part of defaults
   described above for each scheme.

   If the field
   value.

     comment        = "(" *( ctext / quoted-pair / comment ) ")"
     ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
                    ; OWS / <VCHAR except "(", ")", and "\"> / obs-text

   The order in which header fields with differing field names are
   received is not significant.  However, it port is "good practice" equal to send
   general-header fields first, followed by request-header or response-
   header fields, and ending with the entity-header fields.

   Multiple message-header fields with the same field-name MAY be
   present in default port for a message if and only if scheme, the entire field-value for that
   header field normal
   form is defined as a comma-separated list [i.e., #(values)].
   It MUST be possible to combine the multiple header fields into one
   "field-name: field-value" pair, without changing elide the semantics port subcomponent.  Likewise, an empty path
   component is equivalent to an absolute path of "/", so the
   message, by appending each subsequent field-value normal
   form is to the first, each
   separated by provide a comma. path of "/" instead.  The order scheme and host are
   case-insensitive and normally provided in lowercase; all other
   components are compared in a case-sensitive manner.  Characters other
   than those in which header fields with the same
   field-name "reserved" set are received equivalent to their percent-
   encoded octets (see [RFC3986], Section 2.1): the normal form is therefore significant to
   not encode them.

   For example, the
   interpretation of following three URIs are equivalent:

      http://example.com:80/~smith/home.html
      http://EXAMPLE.com/%7Esmith/home.html
      http://EXAMPLE.com:/%7esmith/home.html

   [[anchor1: [[This paragraph does not belong here. --Roy]]]] If path-
   abempty is the combined field value, and thus empty string (i.e., there is no slash "/" path
   separator following the authority), then the "http" URI MUST be given
   as "/" when used as a request-target (Section 4.1.2).  If a proxy
   receives a host name which is not a fully qualified domain name, it
   MAY add its domain to the host name it received.  If a proxy receives
   a fully qualified domain name, the proxy MUST NOT change the order host
   name.

3.  HTTP Message

   All HTTP/1.1 messages consist of these field values when a message is forwarded.

      Note: start-line followed by a sequence
   of characters in a format similar to the "Set-Cookie" Internet Message Format
   [RFC5322]: zero or more header as implemented in practice (as
      opposed fields (collectively referred to how it is specified in [RFC2109]) can occur multiple
      times, but does not use as
   the list syntax, and thus cannot be
      combined into a single line.  (See Appendix A.2.3 "headers" or the "header section"), an empty line indicating the
   end of [Kri2001] for
      details.)  Also note that the Set-Cookie2 header specified in
      [RFC2965] does not share this problem.

4.3.  Message Body

   The message-body (if any) of section, and an optional message-body.

   An HTTP message is used to carry the
   entity-body associated with the can either be a request from client to server or response.  The message-
   body differs a
   response from the entity-body only when a transfer-coding has
   been applied, as indicated by the Transfer-Encoding header field
   (Section 8.7).

     message-body = entity-body
                  / <entity-body encoded as per Transfer-Encoding>

   Transfer-Encoding MUST be used to indicate any transfer-codings
   applied by an application server to ensure safe and proper transfer client.  Syntactically, the two types of
   message differ only in the
   message.  Transfer-Encoding start-line, which is either a property of the message, not of the
   entity, and thus MAY be added Request-Line
   (for requests) or removed by any application along a Status-Line (for responses), and in the
   request/response chain.  (However, Section 3.3 places restrictions on
   when certain transfer-codings may be used.)

   The rules algorithm
   for when a determining the length of the message-body is allowed in (Section 3.4).  In
   theory, a message differ for client could receive requests and responses.

   The presence of a message-body server could receive
   responses, distinguishing them by their different start-line formats,
   but in practice servers are implemented to only expect a request (a
   response is signaled by interpreted as an unknown or invalid request method) and
   clients are implemented to only expect a response.

     HTTP-message    = start-line
                       *( header-field CRLF )
                       CRLF
                       [ message-body ]
     start-line      = Request-Line / Status-Line

   Whitespace (WSP) MUST NOT be sent between the
   inclusion start-line and the
   first header field.  The presence of whitespace might be an attempt
   to trick a Content-Length or Transfer-Encoding header noncompliant implementation of HTTP into ignoring that
   field in or processing the request's message-headers.  When next line as a new request, either of which
   may result in security issues when implementations within the request
   chain interpret the same message contains both differently.  HTTP/1.1 servers MUST
   reject such a message-body of non-zero length and message with a method that does not define
   any semantics for that request message-body, then an origin server 400 (Bad Request) response.

3.1.  Message Parsing Robustness

   In the interest of robustness, servers SHOULD either ignore at least one
   empty line received where a Request-Line is expected.  In other
   words, if the message-body or respond with an appropriate
   error message (e.g., 413).  A proxy or gateway, when presented the
   same request, SHOULD either forward server is reading the request inbound with protocol stream at the
   message-body or beginning
   of a message and receives a CRLF first, it should ignore the CRLF.

   Some old HTTP/1.0 client implementations generate an extra CRLF after
   a POST request as a lame workaround for some early server
   applications that failed to read message-body when determining content that was not
   terminated by a response.

   For response messages, whether line-ending.  An HTTP/1.1 client MUST NOT preface or not
   follow a request with an extra CRLF.  If terminating the request
   message-body is included with a message line-ending is dependent on both the request method and the response
   status code (Section 6.1.1).  All responses to desired, then the HEAD request
   method client MUST NOT
   include a message-body, even though the presence of
   entity-header fields might lead one to believe they do.  All 1xx
   (informational), 204 (No Content), and 304 (Not Modified) responses
   MUST NOT include a message-body.  All other responses do include a
   message-body, although it MAY be terminating CRLF octets as part of zero the message-body
   length.

4.4.  Message Length

   The transfer-length of a normal procedure for parsing an HTTP message is to read the length of the message-body as
   it appears in the message; that is, after any transfer-codings have
   been applied.  When
   start-line into a message-body is included with structure, read each header field into a message, the
   transfer-length of that body is determined hash table
   by one of the following
   (in order of precedence):

   1.  Any response message which "MUST NOT" include a message-body
       (such as field name until the 1xx, 204, and 304 responses empty line, and any response then use the parsed data to
   determine if a
       HEAD request) message-body is always terminated by the first empty line after
       the header fields, regardless of the entity-header fields present
       in the message.

   2. expected.  If a Transfer-Encoding header field (Section 8.7) message-body has been
   indicated, then it is present and read as a stream until an amount of OCTETs
   equal to the "chunked" transfer-coding (Section 3.3) message-length is used, read or the
       transfer-length connection is defined by the use closed.
   Care must be taken to parse an HTTP message as a sequence of this transfer-coding.
       If OCTETs
   in an encoding that is a Transfer-Encoding superset of US-ASCII.  Attempting to parse
   HTTP as a stream of Unicode characters in a character encoding like
   UTF-16 may introduce security flaws due to the differing ways that
   such parsers interpret invalid characters.

3.2.  Header Fields

   Each HTTP header field is present and the "chunked"
       transfer-coding is not present, the transfer-length is defined consists of a case-insensitive field name
   followed by
       the sender closing the connection.

   3.  If a Content-Length header colon (":"), optional whitespace, and the field (Section 8.2) value.

     header-field   = field-name ":" OWS [ field-value ] OWS
     field-name     = token
     field-value    = *( field-content / OWS )
     field-content  = *( WSP / VCHAR / obs-text )

   No whitespace is present, its
       value in OCTETs represents both the entity-length and allowed between the
       transfer-length.  The Content-Length header field name and colon.
   For security reasons, any request message received containing such
   whitespace MUST NOT be
       sent if these two lengths are different (i.e., if a Transfer-
       Encoding header field is present).  If a message is received rejected with
       both a Transfer-Encoding header field and a Content-Length header
       field, the latter MUST be ignored.

   4.  If the message uses the media type "multipart/byteranges", and
       the transfer-length is not otherwise specified, then this self-
       delimiting media type defines the transfer-length.  This media
       type MUST NOT be used unless the sender knows that the recipient
       can parse it; the presence in a request response code of a Range header with
       multiple byte-range specifiers 400 (Bad
   Request).  A proxy MUST remove any such whitespace from a 1.1 client implies that response
   message before forwarding the
       client can parse multipart/byteranges responses. message downstream.

   A range header might field value MAY be forwarded preceded by optional whitespace (OWS); a 1.0 proxy that single
   SP is preferred.  The field value does not
          understand multipart/byteranges; in this case the server MUST
          delimit the message using methods defined in items 1, 3 include any leading or 5
   trailing white space: OWS occurring before the first non-whitespace
   character of this section.

   5.  By the server closing field value or after the connection.  (Closing last non-whitespace
   character of the connection
       cannot field value is ignored and SHOULD be used to indicate removed without
   changing the end meaning of a request body, since that
       would leave no possibility for the server to send back a
       response.)

   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
   containing a message-body MUST include a valid Content-Length header field.

   The order in which header fields with differing field unless the server names are
   received is known not significant.  However, it is "good practice" to be HTTP/1.1 compliant.  If a
   request contains a message-body send
   header fields that contain control data first, such as Host on
   requests and a Content-Length is not given,
   the server SHOULD respond with 400 (Bad Request) if it cannot
   determine the length of the message, or with 411 (Length Required) if
   it wishes to insist Date on receiving a valid Content-Length.

   All HTTP/1.1 applications responses, so that receive entities MUST accept the
   "chunked" transfer-coding (Section 3.3), thus allowing this mechanism
   to be used for messages implementations can decide
   when the not to handle a message length cannot be determined
   in advance.

   Messages as early as possible.  A server MUST NOT include both a Content-Length
   wait until the entire header field and section is received before interpreting
   a
   transfer-coding.  If the message does request message, since later header fields might include a transfer-coding,
   conditionals, authentication credentials, or deliberately misleading
   duplicate header fields that would impact request processing.

   Multiple header fields with the
   Content-Length same field name MUST NOT be ignored.

   When a Content-Length is given sent in a
   message where a message-body is
   allowed, its unless the entire field value MUST exactly match for that header field is
   defined as a comma-separated list [i.e., #(values)].  Multiple header
   fields with the number same field name can be combined into one "field-name:
   field-value" pair, without changing the semantics of OCTETs in the message-body.  HTTP/1.1 user agents MUST notify message, by
   appending each subsequent field value to the user when an
   invalid length is received and detected.

4.5.  General Header Fields

   There are combined field value in
   order, separated by a few comma.  The order in which header fields which have general applicability for
   both request and response messages, but which do not apply to with
   the
   entity being transferred.  These header fields apply only same field name are received is therefore significant to the
   message being transmitted.

     general-header = Cache-Control            ; [Part6], Section 3.2
                    / Connection               ; Section 8.1
                    / Date                     ; Section 8.3
                    / Pragma                   ; [Part6], Section 3.4
                    / Trailer                  ; Section 8.6
                    / Transfer-Encoding        ; Section 8.7
                    / Upgrade                  ; Section 8.8
                    / Via                      ; Section 8.9
                    / Warning                  ; [Part6], Section 3.6

   General-header
   interpretation of the combined field names can be extended reliably only in
   combination with value; a proxy MUST NOT change in the protocol version.  However, new or
   experimental header fields may be given
   the semantics order of general
   header fields if all parties in these field values when forwarding a message.

      Note: the communication recognize them to
   be general-header fields.  Unrecognized "Set-Cookie" header fields are treated as
   entity-header fields.

5.  Request

   A request message from a client implemented in practice (as
      opposed to a server includes, within how it is specified in [RFC2109]) can occur multiple
      times, but does not use the
   first line list syntax, and thus cannot be
      combined into a single line.  (See Appendix A.2.3 of [Kri2001] for
      details.)  Also note that message, the method to Set-Cookie2 header specified in
      [RFC2965] does not share this problem.

   Historically, HTTP header field values could be applied to the resource, extended over
   multiple lines by preceding each extra line with at least one space
   or horizontal tab character (line folding).  This specification
   deprecates such line folding except within the identifier of message/http media
   type (Section 10.3.1).  HTTP/1.1 senders MUST NOT produce messages
   that include line folding (i.e., that contain any field-content that
   matches the resource, and obs-fold rule) unless the protocol version in use.

     Request       = Request-Line              ; Section 5.1
                     *(( general-header        ; Section 4.5
                      / request-header         ; [Part2], Section 3
                      / entity-header ) CRLF )  ; [Part3], Section 3.1
                     CRLF
                     [ message-body ]          ; Section 4.3

5.1.  Request-Line

   The Request-Line begins with a method token, followed by the request-
   target and message is intended for
   packaging within the protocol version, message/http media type.  HTTP/1.1 recipients
   SHOULD accept line folding and ending replace any embedded obs-fold
   whitespace with CRLF.  The elements
   are separated by a single SP characters.  No CR prior to interpreting the field value or LF is
   forwarding the message downstream.

   Historically, HTTP has allowed except field content with text in the
   final CRLF sequence.

     Request-Line   = Method SP request-target SP HTTP-Version CRLF

5.1.1.  Method

   The Method token indicates ISO-
   8859-1 [ISO-8859-1] character encoding and supported other character
   sets only through use of [RFC2047] encoding.  In practice, most HTTP
   header field values use only a subset of the method US-ASCII character
   encoding [USASCII].  Newly defined header fields SHOULD limit their
   field values to US-ASCII characters.  Recipients SHOULD treat other
   (obs-text) octets in field content as opaque data.

   Comments can be performed on the resource
   identified included in some HTTP header fields by surrounding
   the request-target.  The method is case-sensitive.

     Method         = token

5.1.2.  request-target

   The request-target identifies the resource upon which to apply the
   request.

     request-target comment text with parentheses.  Comments are only allowed in
   fields containing "comment" as part of their field value definition.

     comment        = "*" "(" *( ctext / absolute-URI quoted-cpair / ( path-absolute [ "?" query ] comment ) ")"
     ctext          = OWS / authority

   The four options for request-target are dependent on the nature of
   the request. %x21-27 / %x2A-5B / %x5D-7E / obs-text
                    ; OWS / <VCHAR except "(", ")", and "\"> / obs-text

   The asterisk "*" means backslash character ("\") can be used as a single-character
   quoting mechanism within comment constructs:

     quoted-cpair    = "\" ( WSP / VCHAR / obs-text )

   Producers SHOULD NOT escape characters that the request does do not apply
   to a particular resource, but to require escaping
   (i.e., other than the server itself, backslash character "\" and is only
   allowed when the method used does not necessarily apply to a
   resource.  One example would be

     OPTIONS * HTTP/1.1

   The absolute-URI form is REQUIRED when the request is being made to a
   proxy. parentheses "("
   and ")").

3.3.  Message Body

   The proxy message-body (if any) of an HTTP message is requested used to forward the request or service it
   from a valid cache, and return the response.  Note that carry the proxy MAY
   forward
   entity-body associated with the request on to another proxy or directly to response.  The message-
   body differs from the server
   specified entity-body only when a transfer-coding has
   been applied, as indicated by the absolute-URI.  In order to avoid request loops, a
   proxy Transfer-Encoding header field
   (Section 9.7).

     message-body = entity-body
                  / <entity-body encoded as per Transfer-Encoding>

   Transfer-Encoding MUST be able used to recognize all of its server names, including indicate any aliases, local variations, transfer-codings
   applied by an application to ensure safe and proper transfer of the numeric IP address.  An
   example Request-Line would be:

     GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1

   To allow for transition to absolute-URIs in all requests in future
   versions
   message.  Transfer-Encoding is a property of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
   form in requests, even though HTTP/1.1 clients will only generate
   them message, not of the
   entity, and thus MAY be added or removed by any application along the
   request/response chain.  (However, Section 6.2 places restrictions on
   when certain transfer-codings may be used.)

   The rules for when a message-body is allowed in a message differ for
   requests to proxies. and responses.

   The authority form presence of a message-body in a request is only used signaled by the CONNECT method (Section 7.9
   inclusion of
   [Part2]).

   The most common form a Content-Length or Transfer-Encoding header field in
   the request's header fields.  When a request message contains both a
   message-body of request-target is that used to identify non-zero length and a
   resource on method that does not define any
   semantics for that request message-body, then an origin server or gateway.  In this case SHOULD
   either ignore the absolute
   path of message-body or respond with an appropriate error
   message (e.g., 413).  A proxy or gateway, when presented the URI MUST be transmitted (see Section 2.1.1, path-
   absolute) as same
   request, SHOULD either forward the request-target, and request inbound with the network location of message-
   body or ignore the URI
   (authority) MUST be transmitted in message-body when determining a Host header field. response.

   For example, response messages, whether or not a client wishing to retrieve the resource above directly from the
   origin server would create message-body is included with
   a TCP connection to port 80 of message is dependent on both the host
   "www.example.org" request method and send the lines:

     GET /pub/WWW/TheProject.html HTTP/1.1
     Host: www.example.org

   followed by the remainder of response
   status code (Section 5.1.1).  All responses to the Request.  Note that HEAD request
   method MUST NOT include a message-body, even though the absolute
   path cannot be empty; if none is present in the original URI, it presence of
   entity-header fields might lead one to believe they do.  All 1xx
   (informational), 204 (No Content), and 304 (Not Modified) responses
   MUST
   be given as "/" (the server root).

   If NOT include a proxy receives message-body.  All other responses do include a request without any path
   message-body, although it MAY be of zero length.

3.4.  Message Length

   The transfer-length of a message is the length of the message-body as
   it appears in the request-target
   and message; that is, after any transfer-codings have
   been applied.  When a message-body is included with a message, the method specified
   transfer-length of that body is capable determined by one of supporting the asterisk form following
   (in order of request-target, then the last proxy on the request chain MUST
   forward the request with "*" precedence):

   1.  Any response message which "MUST NOT" include a message-body
       (such as the final request-target.

   For example, the request

     OPTIONS http://www.example.org:8001 HTTP/1.1

   would be forwarded 1xx, 204, and 304 responses and any response to a
       HEAD request) is always terminated by the proxy as

     OPTIONS * HTTP/1.1
     Host: www.example.org:8001 first empty line after connecting to port 8001
       the header fields, regardless of host "www.example.org".

   The request-target is transmitted in the format specified entity-header fields present
       in
   Section 2.1.1.  If the request-target message.

   2.  If a Transfer-Encoding header field (Section 9.7) is percent-encoded ([RFC3986],
   Section 2.1), the origin server MUST decode present and
       the request-target in
   order to properly interpret "chunked" transfer-coding (Section 6.2) is used, the request.  Servers SHOULD respond to
   invalid request-targets with an appropriate status code.

   A transparent proxy MUST NOT rewrite
       transfer-length is defined by the "path-absolute" part use of the
   received request-target when forwarding it to the next inbound
   server, except as noted above to replace this transfer-coding.
       If a null path-absolute with
   "/".

      Note: The "no rewrite" rule prevents Transfer-Encoding header field is present and the proxy from changing "chunked"
       transfer-coding is not present, the
      meaning of transfer-length is defined by
       the request when sender closing the origin server is improperly using
      a non-reserved URI character for connection.

   3.  If a reserved purpose.  Implementors
      should be aware that some pre-HTTP/1.1 proxies have been known to
      rewrite Content-Length header field (Section 9.2) is present, its
       value in OCTETs represents both the request-target.

   HTTP does not place a pre-defined limit on entity-length and the length of a request-
   target.  A server
       transfer-length.  The Content-Length header field MUST NOT be prepared to receive URIs of unbounded
   length and respond with the 414 (URI Too Long) status
       sent if the received
   request-target would be longer than the server wishes to handle (see
   Section 8.4.15 of [Part2]).

   Various ad-hoc limitations on request-target length these two lengths are found in
   practice.  It different (i.e., if a Transfer-
       Encoding header field is RECOMMENDED that all HTTP senders and recipients
   support request-target lengths of 8000 or more OCTETs.

5.2.  The Resource Identified by present).  If a Request

   The exact resource identified by an Internet request message is determined by
   examining received with
       both the request-target a Transfer-Encoding header field and the Host a Content-Length header field.

   An origin server that does not allow resources to differ by
       field, the
   requested host MAY ignore latter MUST be ignored.

   4.  If the Host header field value when
   determining message uses the resource identified by an HTTP/1.1 request.  (But see
   Appendix B.1.1 for other requirements on Host support in HTTP/1.1.)

   An origin server that does differentiate resources based on the host
   requested (sometimes referred to as virtual hosts or vanity host
   names) MUST use the following rules for determining the requested
   resource on an HTTP/1.1 request:

   1.  If request-target is an absolute-URI, media type "multipart/byteranges", and
       the host transfer-length is part of the
       request-target.  Any Host header field value in not otherwise specified, then this self-
       delimiting media type defines the request transfer-length.  This media
       type MUST NOT be ignored.

   2.  If used unless the request-target is not an absolute-URI, and sender knows that the recipient
       can parse it; the presence in a request
       includes of a Host Range header field, with
       multiple byte-range specifiers from a 1.1 client implies that the host is determined
       client can parse multipart/byteranges responses.

          A range header might be forwarded by a 1.0 proxy that does not
          understand multipart/byteranges; in this case the Host
       header field value.

   3.  If server MUST
          delimit the host as determined by rule 1 message using methods defined in items 1, 3 or 2 is not a valid host on 5
          of this section.

   5.  By the server, server closing the response MUST connection.  (Closing the connection
       cannot be a 400 (Bad Request) error
       message.

   Recipients used to indicate the end of an HTTP/1.0 a request body, since that lacks
       would leave no possibility for the server to send back a Host
       response.)

   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
   containing a message-body MUST include a valid Content-Length header
   field MAY
   attempt to use heuristics (e.g., examination of unless the URI path for
   something unique server is known to a particular host) in order to determine what
   exact resource is being requested.

6.  Response

   After receiving and interpreting be HTTP/1.1 compliant.  If a
   request message, contains a message-body and a Content-Length is not given,
   the server responds SHOULD respond with 400 (Bad Request) if it cannot
   determine the length of the message, or with 411 (Length Required) if
   it wishes to insist on receiving a valid Content-Length.

   All HTTP/1.1 applications that receive entities MUST accept the
   "chunked" transfer-coding (Section 6.2), thus allowing this mechanism
   to be used for messages when the message length cannot be determined
   in advance.

   Messages MUST NOT include both a Content-Length header field and a
   transfer-coding.  If the message does include a transfer-coding, the
   Content-Length MUST be ignored.

   When a Content-Length is given in a message where a message-body is
   allowed, its field value MUST exactly match the number of OCTETs in
   the message-body.  HTTP/1.1 user agents MUST notify the user when an HTTP
   invalid length is received and detected.

3.5.  General Header Fields

   There are a few header fields which have general applicability for
   both request and response message.

     Response messages, but which do not apply to the
   entity being transferred.  These header fields apply only to the
   message being transmitted.

     general-header = Status-Line Cache-Control            ; [Part6], Section 6.1
                     *(( general-header 3.2
                    / Connection               ; Section 4.5 9.1
                    / response-header Date                     ; [Part2], Section 5 9.3
                    / entity-header ) CRLF ) Pragma                   ; [Part3], [Part6], Section 3.1
                     CRLF
                     [ message-body ] 3.4
                    / Trailer                  ; Section 4.3

6.1.  Status-Line

   The first line of a Response message is the Status-Line, consisting
   of the protocol version followed by a numeric status code and its
   associated textual phrase, with each element 9.6
                    / Transfer-Encoding        ; Section 9.7
                    / Upgrade                  ; Section 9.8
                    / Via                      ; Section 9.9
                    / Warning                  ; [Part6], Section 3.6

   General-header field names can be extended reliably only in
   combination with a change in the protocol version.  However, new or
   experimental header fields may be given the semantics of general
   header fields if all parties in the communication recognize them to
   be general-header fields.  Unrecognized header fields are treated as
   entity-header fields.

4.  Request

   A request message from a client to a server includes, within the
   first line of that message, the method to be applied to the resource,
   the identifier of the resource, and the protocol version in use.

     Request       = Request-Line              ; Section 4.1
                     *(( general-header        ; Section 3.5
                      / request-header         ; [Part2], Section 3
                      / entity-header ) CRLF ) ; [Part3], Section 3.1
                     CRLF
                     [ message-body ]          ; Section 3.3

4.1.  Request-Line

   The Request-Line begins with a method token, followed by the request-
   target and the protocol version, and ending with CRLF.  The elements
   are separated by SP characters.  No CR or LF is allowed except in the
   final CRLF sequence.

     Status-Line

     Request-Line   = HTTP-Version Method SP Status-Code request-target SP Reason-Phrase HTTP-Version CRLF

6.1.1.  Status Code and Reason Phrase

4.1.1.  Method

   The Status-Code element Method token indicates the method to be performed on the resource
   identified by the request-target.  The method is a 3-digit integer result code of case-sensitive.

     Method         = token

4.1.2.  request-target

   The request-target identifies the
   attempt resource upon which to understand and satisfy apply the
   request.  These codes are fully
   defined in Section 8 of [Part2].

     request-target = "*"
                    / absolute-URI
                    / ( path-absolute [ "?" query ] )
                    / authority

   The Reason Phrase exists four options for request-target are dependent on the
   sole purpose nature of providing a textual description associated with
   the
   numeric status code, out of deference to earlier Internet application
   protocols request.  The asterisk "*" means that were more frequently used with interactive text
   clients.  A client SHOULD ignore the content of the Reason Phrase.

   The first digit of request does not apply
   to a particular resource, but to the Status-Code defines server itself, and is only
   allowed when the class of response.
   The last two digits do method used does not have any categorization role.  There are 5
   values for necessarily apply to a
   resource.  One example would be

     OPTIONS * HTTP/1.1

   The absolute-URI form is REQUIRED when the first digit:

   o  1xx: Informational - Request received, continuing process

   o  2xx: Success - request is being made to a
   proxy.  The action was successfully received, understood,
      and accepted

   o  3xx: Redirection - Further action must be taken in order proxy is requested to
      complete forward the request

   o  4xx: Client Error - The or service it
   from a valid cache, and return the response.  Note that the proxy MAY
   forward the request contains bad syntax on to another proxy or cannot be
      fulfilled

   o  5xx: Server Error - The directly to the server failed
   specified by the absolute-URI.  In order to fulfill an apparently
      valid avoid request

     Status-Code    = 3DIGIT
     Reason-Phrase  = *( WSP / VCHAR / obs-text )

7.  Connections

7.1.  Persistent Connections

7.1.1.  Purpose

   Prior to persistent connections, loops, a separate TCP connection was
   established
   proxy MUST be able to fetch each URL, increasing the load on HTTP servers recognize all of its server names, including
   any aliases, local variations, and causing congestion on the Internet.  The use of inline images and
   other associated data often require a client numeric IP address.  An
   example Request-Line would be:

     GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1

   To allow for transition to make multiple absolute-URIs in all requests in future
   versions of HTTP, all HTTP/1.1 servers MUST accept the same server absolute-URI
   form in a short amount of time.  Analysis of
   these performance problems and results from a prototype
   implementation are available [Pad1995] [Spe].  Implementation
   experience and measurements of actual requests, even though HTTP/1.1 implementations show
   good results [Nie1997].  Alternatives have also been explored, for
   example, T/TCP [Tou1998].

   Persistent HTTP connections have a number clients will only generate
   them in requests to proxies.

   The authority form is only used by the CONNECT method (Section 7.9 of advantages:

   o  By opening and closing fewer TCP connections, CPU time
   [Part2]).

   The most common form of request-target is saved in
      routers and hosts (clients, servers, proxies, gateways, tunnels,
      or caches), and memory that used for TCP protocol control blocks can to identify a
   resource on an origin server or gateway.  In this case the absolute
   path of the URI MUST be
      saved in hosts.

   o  HTTP requests transmitted (see Section 2.6.1, path-
   absolute) as the request-target, and responses can the network location of the URI
   (authority) MUST be pipelined on transmitted in a connection.
      Pipelining allows Host header field.  For example,
   a client wishing to make multiple requests without
      waiting for each response, allowing retrieve the resource above directly from the
   origin server would create a single TCP connection to be
      used much more efficiently, with much lower elapsed time.

   o  Network congestion is reduced by reducing the number port 80 of packets
      caused by TCP opens, the host
   "www.example.org" and send the lines:

     GET /pub/WWW/TheProject.html HTTP/1.1
     Host: www.example.org

   followed by allowing TCP sufficient time to
      determine the congestion state remainder of the network.

   o  Latency on subsequent requests is reduced since there Request.  Note that the absolute
   path cannot be empty; if none is no time
      spent present in TCP's connection opening handshake.

   o  HTTP can evolve more gracefully, since errors can the original URI, it MUST
   be reported given as "/" (the server root).

   If a proxy receives a request without any path in the penalty of closing request-target
   and the TCP connection.  Clients using
      future versions of HTTP might optimistically try a new feature,
      but if communicating with an older server, retry with old
      semantics after an error method specified is reported.

   HTTP implementations SHOULD implement persistent connections.

7.1.2.  Overall Operation

   A significant difference between HTTP/1.1 and earlier versions capable of
   HTTP is that persistent connections are supporting the default behavior asterisk form
   of any
   HTTP connection.  That is, unless otherwise indicated, request-target, then the client
   SHOULD assume that last proxy on the server will maintain a persistent connection,
   even after error responses from request chain MUST
   forward the server.

   Persistent connections provide a mechanism request with "*" as the final request-target.

   For example, the request

     OPTIONS http://www.example.org:8001 HTTP/1.1

   would be forwarded by which a client and a
   server can signal the close proxy as

     OPTIONS * HTTP/1.1
     Host: www.example.org:8001

   after connecting to port 8001 of a TCP connection.  This signaling
   takes place using host "www.example.org".

   The request-target is transmitted in the Connection header field (Section 8.1).  Once a
   close has been signaled, format specified in
   Section 2.6.1.  If the client MUST NOT send any more requests
   on that connection.

7.1.2.1.  Negotiation

   An HTTP/1.1 request-target is percent-encoded ([RFC3986],
   Section 2.1), the origin server MAY assume that a HTTP/1.1 client intends to
   maintain a persistent connection unless a Connection header including MUST decode the connection-token "close" was sent request-target in
   order to properly interpret the request.  If the server
   chooses  Servers SHOULD respond to close
   invalid request-targets with an appropriate status code.

   A transparent proxy MUST NOT rewrite the connection immediately after sending "path-absolute" part of the
   response,
   received request-target when forwarding it SHOULD send a Connection header including the
   connection-token close.

   An HTTP/1.1 client MAY expect a connection to remain open, but would
   decide the next inbound
   server, except as noted above to keep it open based on whether replace a null path-absolute with
   "/".

      Note: The "no rewrite" rule prevents the response proxy from a changing the
      meaning of the request when the origin server
   contains is improperly using
      a Connection header with the connection-token close.  In
   case non-reserved URI character for a reserved purpose.  Implementors
      should be aware that some pre-HTTP/1.1 proxies have been known to
      rewrite the client request-target.

   HTTP does not want to maintain place a connection for more than
   that request, it SHOULD send pre-defined limit on the length of a Connection header including request-
   target.  A server MUST be prepared to receive URIs of unbounded
   length and respond with the
   connection-token close.

   If either 414 (URI Too Long) status if the client or received
   request-target would be longer than the server sends the close token wishes to handle (see
   Section 8.4.15 of [Part2]).

   Various ad-hoc limitations on request-target length are found in the
   Connection header, that request becomes the last one for the
   connection.

   Clients and servers SHOULD NOT assume that a persistent connection
   practice.  It is
   maintained for RECOMMENDED that all HTTP versions less than 1.1 unless it is explicitly
   signaled.  See Appendix B.2 for senders and recipients
   support request-target lengths of 8000 or more information on backward
   compatibility with HTTP/1.0 clients.

   In order to remain persistent, all messages on the connection MUST
   have OCTETs.

4.2.  The Resource Identified by a self-defined message length (i.e., one not defined Request

   The exact resource identified by closure
   of an Internet request is determined by
   examining both the connection), as described in Section 4.4.

7.1.2.2.  Pipelining

   A client request-target and the Host header field.

   An origin server that supports persistent connections does not allow resources to differ by the
   requested host MAY "pipeline" its
   requests (i.e., send multiple requests without waiting ignore the Host header field value when
   determining the resource identified by an HTTP/1.1 request.  (But see
   Appendix B.1.1 for each
   response).  A server MUST send its responses to those requests other requirements on Host support in the
   same order HTTP/1.1.)
   An origin server that does differentiate resources based on the requests were received.

   Clients which assume persistent connections and pipeline immediately
   after connection establishment SHOULD be prepared host
   requested (sometimes referred to retry their
   connection if as virtual hosts or vanity host
   names) MUST use the first pipelined attempt fails. following rules for determining the requested
   resource on an HTTP/1.1 request:

   1.  If a client does
   such a retry, it MUST NOT pipeline before it knows request-target is an absolute-URI, the connection host is
   persistent.  Clients MUST also be prepared to resend their requests
   if the server closes the connection before sending all part of the
   corresponding responses.

   Clients SHOULD NOT pipeline requests using non-idempotent methods or
   non-idempotent sequences of methods (see Section 7.1.2 of [Part2]).
   Otherwise, a premature termination of
       request-target.  Any Host header field value in the transport connection could
   lead to indeterminate results.  A client wishing to send a non-
   idempotent request SHOULD wait to send that request until it has
   received the response status for MUST
       be ignored.

   2.  If the previous request.

7.1.3.  Proxy Servers

   It request-target is especially important that proxies correctly implement not an absolute-URI, and the
   properties of request
       includes a Host header field, the Connection host is determined by the Host
       header field value.

   3.  If the host as specified in
   Section 8.1.

   The proxy server MUST signal persistent connections separately with
   its clients and determined by rule 1 or 2 is not a valid host on
       the origin servers (or other proxy servers) that it
   connects to.  Each persistent connection applies to only one
   transport link.

   A proxy server server, the response MUST NOT establish be a HTTP/1.1 persistent connection
   with 400 (Bad Request) error
       message.

   Recipients of an HTTP/1.0 client (but see Section 19.7.1 request that lacks a Host header field MAY
   attempt to use heuristics (e.g., examination of [RFC2068] the URI path for
   information
   something unique to a particular host) in order to determine what
   exact resource is being requested.

5.  Response

   After receiving and discussion of the problems interpreting a request message, a server responds
   with the Keep-Alive header
   implemented by many HTTP/1.0 clients).

7.1.4.  Practical Considerations

   Servers will usually have some time-out value beyond which they will
   no longer maintain an inactive connection.  Proxy servers might make
   this a higher value since it is likely that the client will be making
   more connections through the same server. HTTP response message.

     Response      = Status-Line               ; Section 5.1
                     *(( general-header        ; Section 3.5
                      / response-header        ; [Part2], Section 5
                      / entity-header ) CRLF ) ; [Part3], Section 3.1
                     CRLF
                     [ message-body ]          ; Section 3.3

5.1.  Status-Line

   The use first line of persistent
   connections places no requirements on a Response message is the length (or existence) Status-Line, consisting
   of
   this time-out for either the client or the server.

   When protocol version followed by a client numeric status code and its
   associated textual phrase, with each element separated by SP
   characters.  No CR or server wishes to time-out it SHOULD issue LF is allowed except in the final CRLF
   sequence.

     Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF

5.1.1.  Status Code and Reason Phrase

   The Status-Code element is a graceful
   close on 3-digit integer result code of the transport connection.  Clients
   attempt to understand and servers SHOULD both
   constantly watch satisfy the request.  These codes are fully
   defined in Section 8 of [Part2].  The Reason Phrase exists for the other side
   sole purpose of providing a textual description associated with the transport close, and
   respond
   numeric status code, out of deference to it as appropriate.  If a earlier Internet application
   protocols that were more frequently used with interactive text
   clients.  A client or server does not detect SHOULD ignore the other side's close promptly it could cause unnecessary resource
   drain on content of the network.

   A client, server, or proxy MAY close the transport connection at any
   time.  For example, a client might have started to send a new request
   at the same time that the server has decided to close Reason Phrase.

   The first digit of the "idle"
   connection.  From Status-Code defines the server's point class of view, response.
   The last two digits do not have any categorization role.  There are 5
   values for the connection is being
   closed while it first digit:

   o  1xx: Informational - Request received, continuing process

   o  2xx: Success - The action was idle, but from the client's point of view, a
   request is in progress.

   This means that clients, servers, successfully received, understood,
      and proxies MUST accepted

   o  3xx: Redirection - Further action must be able taken in order to recover
   from asynchronous close events.  Client software SHOULD reopen the
   transport connection and retransmit the aborted sequence of requests
   without user interaction so long as
      complete the request sequence is
   idempotent (see Section 7.1.2 of [Part2]).  Non-idempotent methods

   o  4xx: Client Error - The request contains bad syntax or
   sequences MUST NOT cannot be automatically retried, although user agents MAY
   offer a human operator the choice of retrying the request(s).
   Confirmation by user-agent software with semantic understanding of
   the application MAY substitute for user confirmation.
      fulfilled

   o  5xx: Server Error - The automatic
   retry SHOULD NOT be repeated if the second sequence of requests
   fails.

   Servers SHOULD always respond server failed to at least one fulfill an apparently
      valid request per connection,
   if at all possible.  Servers SHOULD NOT close a connection in the
   middle of transmitting a response, unless a network or client failure
   is suspected.

   Clients that use persistent connections SHOULD limit

     Status-Code    = 3DIGIT
     Reason-Phrase  = *( WSP / VCHAR / obs-text )

6.  Protocol Parameters

6.1.  Date/Time Formats: Full Date

   HTTP applications have historically allowed three different formats
   for the number representation of
   simultaneous connections that they maintain to a given server.  A
   single-user client SHOULD NOT maintain more than 2 connections with
   any server or proxy.  A proxy SHOULD use up to 2*N connections to
   another server or proxy, where N date/time stamps:

     Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
     Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
     Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format

   The first format is the number preferred as an Internet standard and represents
   a fixed-length subset of simultaneously
   active users.  These guidelines that defined by [RFC1123].  The other
   formats are intended to improve HTTP response
   times and avoid congestion.

7.2.  Message Transmission Requirements

7.2.1.  Persistent Connections and Flow Control described here only for compatibility with obsolete
   implementations.  HTTP/1.1 servers SHOULD maintain persistent connections clients and use TCP's
   flow control mechanisms to resolve temporary overloads, rather than
   terminating connections servers that parse the date
   value MUST accept all three formats (for compatibility with
   HTTP/1.0), though they MUST only generate the expectation that clients will retry.
   The latter technique can exacerbate network congestion.

7.2.2.  Monitoring Connections RFC 1123 format for Error Status Messages

   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
   the network connection
   representing HTTP-date values in header fields.  See Appendix A for an error status while it is transmitting
   the request.  If the client sees an error status, it SHOULD
   immediately cease transmitting the body.  If the body is being sent
   using a "chunked" encoding (Section 3.3), a zero length chunk and
   empty trailer MAY be used to prematurely mark the end of the message.
   If the body was preceded by a Content-Length header, the client
   further information.

   All HTTP date/time stamps MUST
   close the connection.

7.2.3.  Use of the 100 (Continue) Status

   The purpose of be represented in Greenwich Mean Time
   (GMT), without exception.  For the 100 (Continue) status (see Section 8.1.1 purposes of
   [Part2]) is to allow a client that HTTP, GMT is sending a request message with
   a request body exactly
   equal to determine if the origin server UTC (Coordinated Universal Time).  This is willing to accept
   the request (based on the request headers) before the client sends
   the request body.  In some cases, it might either be inappropriate or
   highly inefficient for the client to send the body if indicated in the server will
   reject
   first two formats by the message without looking at inclusion of "GMT" as the body.

   Requirements for HTTP/1.1 clients:

   o  If a client will wait three-letter
   abbreviation for a 100 (Continue) response before sending
      the request body, it time zone, and MUST send an Expect request-header field
      (Section 9.2 of [Part2]) with be assumed when reading the "100-continue" expectation.

   o  A client
   asctime format.  HTTP-date is case sensitive and MUST NOT send an Expect request-header field (Section 9.2
      of [Part2]) with the "100-continue" expectation if it does not
      intend to send a request body.

   Because of the presence of older implementations, include
   additional whitespace beyond that specifically included as SP in the protocol allows
   ambiguous situations
   grammar.

     HTTP-date    = rfc1123-date / obs-date

   Preferred format:

     rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT

     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 day-name, day, month, year, and time-of-day are the
   same as those defined for the RFC 5322 constructs with 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 to be robust in
      accepting date values that may have been sent by non-HTTP
      applications, as is sometimes the case when retrieving or posting
      messages via proxies/gateways to SMTP or NNTP.

      Note: HTTP requirements for the date/time stamp format apply only
      to their usage within the protocol stream.  Clients and servers
      are not required to use these formats for user presentation,
      request logging, etc.

6.2.  Transfer Codings

   Transfer-coding values are used to indicate an encoding
   transformation that has been, can be, or may need to be applied to an
   entity-body in order to ensure "safe transport" through the network.
   This differs from a content coding in that the transfer-coding is a
   property of the message, not of the original entity.

     transfer-coding         = "chunked" ; Section 6.2.1
                             / "compress" ; Section 6.2.2.1
                             / "deflate" ; Section 6.2.2.2
                             / "gzip" ; Section 6.2.2.3
                             / transfer-extension
     transfer-extension      = token *( OWS ";" OWS transfer-parameter )

   Parameters are in the form of attribute/value pairs.

     transfer-parameter      = attribute BWS "=" BWS value
     attribute               = token
     value                   = token / quoted-string

   All transfer-coding values are case-insensitive.  HTTP/1.1 uses
   transfer-coding values in the TE header field (Section 9.5) and in
   the Transfer-Encoding header field (Section 9.7).

   Whenever a transfer-coding is applied to a message-body, the set of
   transfer-codings MUST include "chunked", unless the message indicates
   it is terminated by closing the connection.  When the "chunked"
   transfer-coding is used, it MUST be the last transfer-coding applied
   to the message-body.  The "chunked" transfer-coding MUST NOT be
   applied more than once to a message-body.  These rules allow the
   recipient to determine the transfer-length of the message
   (Section 3.4).

   Transfer-codings are analogous to the Content-Transfer-Encoding
   values of MIME, which were designed to enable safe transport of
   binary data over a 7-bit transport service ([RFC2045], Section 6).
   However, safe transport has a different focus for an 8bit-clean
   transfer protocol.  In HTTP, the only unsafe characteristic of
   message-bodies is the difficulty in determining the exact body length
   (Section 3.4), or the desire to encrypt data over a shared transport.

   A server which receives an entity-body with a client may transfer-coding it does
   not understand SHOULD return 501 (Not Implemented), and close the
   connection.  A server MUST NOT send "Expect: 100-
   continue" without receiving either transfer-codings to an HTTP/1.0
   client.

6.2.1.  Chunked Transfer Coding

   The chunked encoding modifies the body of a 417 (Expectation Failed) status
   or message in order to
   transfer it as a 100 (Continue) status.  Therefore, when series of chunks, each with its own size indicator,
   followed by an OPTIONAL trailer containing entity-header fields.
   This allows dynamically produced content to be transferred along with
   the information necessary for the recipient to verify that it has
   received the full message.

     Chunked-Body   = *chunk
                      last-chunk
                      trailer-part
                      CRLF

     chunk          = chunk-size *WSP [ chunk-ext ] CRLF
                      chunk-data CRLF
     chunk-size     = 1*HEXDIG
     last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF

     chunk-ext      = *( ";" *WSP chunk-ext-name
                         [ "=" chunk-ext-val ] *WSP )
     chunk-ext-name = token
     chunk-ext-val  = token / quoted-str-nf
     chunk-data     = 1*OCTET ; a client sends this sequence of chunk-size octets
     trailer-part   = *( entity-header CRLF )

     quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
                    ; like quoted-string, but disallowing line folding
     qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
                    ; WSP / <VCHAR except DQUOTE and "\"> / obs-text

   The chunk-size field is a string of hex digits indicating the size of
   the chunk-data in octets.  The chunked encoding is ended by any chunk
   whose size is zero, followed by the trailer, which is terminated by
   an empty line.

   The trailer allows the sender to include additional HTTP header
   fields at the end of the message.  The Trailer header field can be
   used to an origin server (possibly via a proxy) from indicate which it
   has never seen header fields are included in a 100 (Continue) status, the client SHOULD trailer (see
   Section 9.6).

   A server using chunked transfer-coding in a response MUST NOT wait use the
   trailer for an indefinite period before sending any header fields unless at least one of the following is
   true:

   1.  the request body.

   Requirements for HTTP/1.1 origin servers:

   o  Upon receiving included a request which includes an Expect request-header TE header field with that indicates "trailers"
       is acceptable in the transfer-coding of the response, as
       described in Section 9.5; or,

   2.  the server is the "100-continue" expectation, an origin server MUST
      either respond with 100 (Continue) status for the response, the trailer
       fields consist entirely of optional metadata, and continue to read
      from the input stream, or respond with recipient
       could use the message (in a final status code.  The manner acceptable to the origin
       server) without receiving this metadata.  In other words, the
       origin server MUST NOT wait for is willing to accept the request body before sending possibility that the 100 (Continue) response.  If it responds
       trailer fields might be silently discarded along the path to the
       client.

   This requirement prevents an interoperability failure when the
   message is being received by an HTTP/1.1 (or later) proxy and
   forwarded to an HTTP/1.0 recipient.  It avoids a situation where
   compliance with the protocol would have necessitated a final status
      code, it MAY close possibly
   infinite buffer on the transport connection or it MAY continue proxy.

   A process for decoding the "chunked" transfer-coding can be
   represented in pseudo-code as:

     length := 0
     read chunk-size, chunk-ext (if any) and CRLF
     while (chunk-size > 0) {
        read chunk-data and CRLF
        append chunk-data to entity-body
        length := length + chunk-size
        read chunk-size and CRLF
     }
     read entity-header
     while (entity-header not empty) {
        append entity-header to existing header fields
        read entity-header
     }
     Content-Length := length
     Remove "chunked" from Transfer-Encoding

   All HTTP/1.1 applications MUST be able to receive and discard the rest of decode the request.  It
   "chunked" transfer-coding, and MUST NOT perform ignore chunk-ext extensions they
   do not understand.

6.2.2.  Compression Codings

   The codings defined below can be used to compress the
      requested method if it returns a final status code.

   o  An origin server SHOULD NOT send payload of a 100 (Continue) response if
   message.

      Note: Use of program names for the
      request message does identification of encoding
      formats is not include an Expect request-header field
      with the "100-continue" expectation, desirable and MUST NOT send a 100
      (Continue) response if such a request comes from an HTTP/1.0 (or
      earlier) client.  There is an exception to this rule: discouraged for future encodings.
      Their use here is representative of historical practice, not good
      design.

      Note: For compatibility with [RFC2068], a server MAY send a 100 (Continue)
      status in response previous implementations of HTTP,
      applications SHOULD consider "x-gzip" and "x-compress" to be
      equivalent to "gzip" and "compress" respectively.

6.2.2.1.  Compress Coding

   The "compress" format is produced by the common UNIX file compression
   program "compress".  This format is an HTTP/1.1 PUT or POST request that does
      not include an Expect request-header field adaptive Lempel-Ziv-Welch
   coding (LZW).

6.2.2.2.  Deflate Coding

   The "zlib" format is defined in [RFC1950] in combination with the "100-continue"
      expectation.
   "deflate" compression mechanism described in [RFC1951].

6.2.2.3.  Gzip Coding

   The "gzip" format is produced by the file compression program "gzip"
   (GNU zip), as described in [RFC1952].  This exception, format is a Lempel-Ziv
   coding (LZ77) with a 32 bit CRC.

6.2.3.  Transfer Coding Registry

   The HTTP Transfer Coding Registry defines the name space for the
   transfer coding names.

   Registrations MUST include the following fields:

   o  Name

   o  Description

   o  Pointer to specification text

   Values to be added to this name space require expert review and a
   specification (see "Expert Review" and "Specification Required" in
   Section 4.1 of [RFC5226]), and MUST conform to the purpose of which
   transfer coding defined in this section.

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

6.3.  Product Tokens

   Product tokens are used to minimize
      any client processing delays associated with an undeclared wait
      for 100 (Continue) status, applies only allow communicating applications to HTTP/1.1 requests,
   identify themselves by software name and
      not to requests with any other HTTP-version value.

   o  An origin server MAY omit version.  Most fields using
   product tokens also allow sub-products which form a 100 (Continue) response if it has
      already received some or all significant part
   of the request body application to be listed, separated by whitespace.  By
   convention, the products are listed in order of their significance
   for identifying the
      corresponding request.

   o  An origin server that sends a 100 (Continue) response 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
      ultimately send NOT be
   used for advertising or other non-essential information.  Although
   any token character MAY appear in a final status code, once product-version, this token
   SHOULD only be used for a version identifier (i.e., successive
   versions of the same product SHOULD only differ in the product-
   version portion of the product value).

6.4.  Quality Values

   Both transfer codings (TE request body is
      received header, Section 9.5) and processed, unless it terminates content
   negotiation (Section 4 of [Part3]) use short "floating point" numbers
   to indicate the transport
      connection prematurely.

   o  If an origin server receives a request that does not include an
      Expect request-header field with relative importance ("weight") of various negotiable
   parameters.  A weight is normalized to a real number in the "100-continue" expectation, range 0
   through 1, where 0 is the request includes a request body, minimum and 1 the server responds with maximum value.  If a final status code before reading the entire request body from
      the transport connection,
   parameter has a quality value of 0, then content with this parameter
   is `not acceptable' for the server SHOULD client.  HTTP/1.1 applications MUST NOT close
   generate more than three digits after the
      transport decimal point.  User
   configuration of these values SHOULD also be limited in this fashion.

     qvalue         = ( "0" [ "." 0*3DIGIT ] )
                    / ( "1" [ "." 0*3("0") ] )

      Note: "Quality values" is a misnomer, since these values merely
      represent relative degradation in desired quality.

7.  Connections

7.1.  Persistent Connections

7.1.1.  Purpose

   Prior to persistent connections, a separate TCP connection until it has read the entire request, or
      until the client closes was
   established to fetch each URL, increasing the connection.  Otherwise, load on HTTP servers
   and causing congestion on the Internet.  The use of inline images and
   other associated data often require a client
      might not reliably receive to make multiple
   requests of the response message.  However, this
      requirement is not be construed as preventing a same server in a short amount of time.  Analysis of
   these performance problems and results from
      defending itself against denial-of-service attacks, a prototype
   implementation are available [Pad1995] [Spe].  Implementation
   experience and measurements of actual HTTP/1.1 implementations show
   good results [Nie1997].  Alternatives have also been explored, for
   example, T/TCP [Tou1998].

   Persistent HTTP connections have a number of advantages:

   o  By opening and closing fewer TCP connections, CPU time is saved in
      routers and hosts (clients, servers, proxies, gateways, tunnels,
      or from badly
      broken client implementations.

   Requirements caches), and memory used for HTTP/1.1 proxies: TCP protocol control blocks can be
      saved in hosts.

   o  If  HTTP requests and responses can be pipelined on a proxy receives connection.
      Pipelining allows a request that includes an Expect request-
      header field client to make multiple requests without
      waiting for each response, allowing a single TCP connection to be
      used much more efficiently, with much lower elapsed time.

   o  Network congestion is reduced by reducing the "100-continue" expectation, number of packets
      caused by TCP opens, and by allowing TCP sufficient time to
      determine the proxy
      either knows that the next-hop server complies with HTTP/1.1 or
      higher, or does not know the HTTP version congestion state of the next-hop server,
      it MUST forward the request, including the Expect header field. network.

   o  If the proxy knows that  Latency on subsequent requests is reduced since there is no time
      spent in TCP's connection opening handshake.

   o  HTTP can evolve more gracefully, since errors can be reported
      without the version penalty of closing the next-hop server TCP connection.  Clients using
      future versions of HTTP might optimistically try a new feature,
      but if communicating with an older server, retry with old
      semantics after an error is
      HTTP/1.0 or lower, it MUST NOT forward the request, reported.

   HTTP implementations SHOULD implement persistent connections.

7.1.2.  Overall Operation

   A significant difference between HTTP/1.1 and it MUST
      respond with a 417 (Expectation Failed) status.

   o  Proxies earlier versions of
   HTTP is that persistent connections are the default behavior of any
   HTTP connection.  That is, unless otherwise indicated, the client
   SHOULD assume that the server will maintain a cache recording the HTTP version numbers
      received persistent connection,
   even after error responses from recently-referenced next-hop servers.

   o  A proxy MUST NOT forward a 100 (Continue) response if the request
      message was received from an HTTP/1.0 (or earlier) server.

   Persistent connections provide a mechanism by which a client and did
      not include an Expect request-header field with a
   server can signal the "100-continue"
      expectation. close of a TCP connection.  This requirement overrides signaling
   takes place using the general rule for
      forwarding of 1xx responses (see Section 8.1 of [Part2]).

7.2.4.  Client Behavior if Server Prematurely Closes Connection

   If an header field (Section 9.1).  Once a
   close has been signaled, the client MUST NOT send any more requests
   on that connection.

7.1.2.1.  Negotiation

   An HTTP/1.1 server MAY assume that a HTTP/1.1 client sends intends to
   maintain a request which includes persistent connection unless a request body,
   but which does not include an Expect request-header field with the
   "100-continue" expectation, and if Connection header including
   the client is not directly
   connected to an HTTP/1.1 origin server, and if connection-token "close" was sent in the client sees request.  If the
   connection server
   chooses to close before receiving any status from the server, connection immediately after sending the
   client
   response, it SHOULD retry the request.  If send a Connection header including the
   connection-token close.

   An HTTP/1.1 client does retry this
   request, it MAY use expect a connection to remain open, but would
   decide to keep it open based on whether the following "binary exponential backoff"
   algorithm response from a server
   contains a Connection header with the connection-token close.  In
   case the client does not want to be assured of obtaining a reliable response:

   1.  Initiate maintain a new connection to the server

   2.  Transmit the request-headers

   3.  Initialize for more than
   that request, it SHOULD send a variable R to Connection header including the estimated round-trip time to
   connection-token close.

   If either the
       server (e.g., based on client or the time it took to establish server sends the
       connection), or to a constant value of 5 seconds if close token in the round-
       trip time is not available.

   4.  Compute T = R * (2**N), where N is
   Connection header, that request becomes the number of previous retries
       of this request.

   5.  Wait either last one for an error response from the server, or
   connection.

   Clients and servers SHOULD NOT assume that a persistent connection is
   maintained for T
       seconds (whichever comes first)

   6.  If no error response HTTP versions less than 1.1 unless it is received, after T seconds transmit explicitly
   signaled.  See Appendix B.2 for more information on backward
   compatibility with HTTP/1.0 clients.

   In order to remain persistent, all messages on the
       body connection MUST
   have a self-defined message length (i.e., one not defined by closure
   of the request.

   7.  If connection), as described in Section 3.4.

7.1.2.2.  Pipelining

   A client sees that supports persistent connections MAY "pipeline" its
   requests (i.e., send multiple requests without waiting for each
   response).  A server MUST send its responses to those requests in the connection is closed prematurely, repeat
       from step 1 until the request is accepted, an error response is
       received, or the user becomes impatient and terminates
   same order that the requests were received.

   Clients which assume persistent connections and pipeline immediately
   after connection establishment SHOULD be prepared to retry
       process.

   If at any point an error status is received, their
   connection if the first pipelined attempt fails.  If a client

   o  SHOULD does
   such a retry, it MUST NOT continue and

   o  SHOULD close pipeline before it knows the connection is
   persistent.  Clients MUST also be prepared to resend their requests
   if it has not completed sending the
      request message.

8.  Header Field Definitions

   This section defines server closes the syntax and semantics connection before sending all of HTTP/1.1 header
   fields related to message framing and transport protocols.

   For entity-header fields, both sender and recipient refer to either the client
   corresponding responses.

   Clients SHOULD NOT pipeline requests using non-idempotent methods or
   non-idempotent sequences of methods (see Section 7.1.2 of [Part2]).
   Otherwise, a premature termination of the server, depending on who sends and who receives the
   entity.

8.1.  Connection

   The general-header field "Connection" allows the sender transport connection could
   lead to specify
   options that are desired for indeterminate results.  A client wishing to send a non-
   idempotent request SHOULD wait to send that particular connection and MUST NOT
   be communicated by proxies over further connections.

   The Connection header's value request until it has
   received the following grammar:

     Connection       = "Connection" ":" OWS Connection-v
     Connection-v     = 1#connection-token
     connection-token = token

   HTTP/1.1 proxies MUST parse the Connection header field before a
   message is forwarded and, response status for each connection-token in this field,
   remove any header field(s) from the message with the same name as the
   connection-token.  Connection options are signaled by previous request.

7.1.3.  Proxy Servers

   It is especially important that proxies correctly implement the presence
   properties of
   a connection-token in the Connection header field, not by any
   corresponding additional header field(s), since the additional header field may not be sent if there are no parameters associated as specified in
   Section 9.1.

   The proxy server MUST signal persistent connections separately with
   its clients and the origin servers (or other proxy servers) that it
   connects to.  Each persistent connection option.

   Message headers listed in the Connection header applies to only one
   transport link.

   A proxy server MUST NOT include end-
   to-end headers, such as Cache-Control. establish a HTTP/1.1 defines the "close" persistent connection option
   with an HTTP/1.0 client (but see Section 19.7.1 of [RFC2068] for
   information and discussion of the sender to
   signal problems with the Keep-Alive header
   implemented by many HTTP/1.0 clients).

7.1.4.  Practical Considerations

   Servers will usually have some time-out value beyond which they will
   no longer maintain an inactive connection.  Proxy servers might make
   this a higher value since it is likely that the connection client will be closed after completion making
   more connections through the same server.  The use of persistent
   connections places no requirements on the
   response.  For example,

     Connection: close

   in length (or existence) of
   this time-out for either the request client or the response header fields indicates that server.

   When a client or server wishes to time-out it SHOULD issue a graceful
   close on the connection transport connection.  Clients and servers SHOULD NOT be considered `persistent' (Section 7.1)
   after both
   constantly watch for the current request/response is complete.

   An HTTP/1.1 client that does not support persistent connections MUST
   include other side of the "close" connection option in every request message.

   An HTTP/1.1 transport close, and
   respond to it as appropriate.  If a client or server that does not support persistent connections MUST
   include detect
   the "close" other side's close promptly it could cause unnecessary resource
   drain on the network.

   A client, server, or proxy MAY close the transport connection option in every response message that
   does not at any
   time.  For example, a client might have started to send a 1xx (informational) status code.

   A system receiving an HTTP/1.0 (or lower-version) message new request
   at the same time that
   includes the server has decided to close the "idle"
   connection.  From the server's point of view, the connection is being
   closed while it was idle, but from the client's point of view, a Connection header MUST, for each connection-token
   request is in this
   field, remove progress.

   This means that clients, servers, and ignore any header field(s) proxies MUST be able to recover
   from asynchronous close events.  Client software SHOULD reopen the message with
   transport connection and retransmit the same name aborted sequence of requests
   without user interaction so long as the connection-token.  This protects against
   mistaken forwarding request sequence is
   idempotent (see Section 7.1.2 of such header fields by pre-HTTP/1.1 proxies.
   See Appendix B.2.

8.2.  Content-Length

   The entity-header field "Content-Length" indicates [Part2]).  Non-idempotent methods or
   sequences MUST NOT be automatically retried, although user agents MAY
   offer a human operator the size choice of retrying the
   entity-body, in number request(s).
   Confirmation by user-agent software with semantic understanding of OCTETs, sent to
   the recipient or, application MAY substitute for user confirmation.  The automatic
   retry SHOULD NOT be repeated if the second sequence of requests
   fails.

   Servers SHOULD always respond to at least one request per connection,
   if at all possible.  Servers SHOULD NOT close a connection in the
   case of the HEAD method, the size
   middle of the entity-body that would have
   been sent had the request been transmitting a GET.

     Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
     Content-Length-v = 1*DIGIT

   An example response, unless a network or client failure
   is

     Content-Length: 3495

   Applications suspected.

   Clients (including proxies) SHOULD use this field to indicate limit the transfer-length number of
   the message-body, unless simultaneous
   connections that they maintain to a given server (including proxies).

   Previous revisions of HTTP gave a specific number of connections as a
   ceiling, but this is prohibited by the rules in
   Section 4.4.

   Any Content-Length greater than or equal was found to zero is be impractical for many applications.
   As a valid value.
   Section 4.4 describes how result, this specification does not mandate a particular maximum
   number of connections, but instead encourages clients to determine be
   conservative when opening multiple connections.

   In particular, while using multiple connections avoids the length of "head-of-
   line blocking" problem (whereby a message-body
   if request that takes significant
   server-side processing and/or has a Content-Length is not given. large payload can block
   subsequent requests on the same connection), each connection used
   consumes server resources (sometimes significantly), and furthermore
   using multiple connections can cause undesirable side effects in
   congested networks.

   Note that the meaning servers might reject traffic that they deem abusive,
   including an excessive number of this field is significantly different connections from a client.

7.2.  Message Transmission Requirements

7.2.1.  Persistent Connections and Flow Control

   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
   flow control mechanisms to resolve temporary overloads, rather than
   terminating connections with the corresponding definition in MIME, where expectation that clients will retry.
   The latter technique can exacerbate network congestion.

7.2.2.  Monitoring Connections for Error Status Messages

   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
   the network connection for an error status while it is an optional field
   used within transmitting
   the "message/external-body" content-type.  In HTTP, request.  If the client sees an error status, it SHOULD be sent whenever
   immediately cease transmitting the message's body.  If the body is being sent
   using a "chunked" encoding (Section 6.2), a zero length can chunk and
   empty trailer MAY be determined prior used to being transferred, unless this is prohibited by prematurely mark the rules in
   Section 4.4.

8.3.  Date

   The general-header field "Date" represents end of the date and time at which message.
   If the message body was originated, having preceded by a Content-Length header, the same semantics as orig-date in
   Section 3.6.1 client MUST
   close the connection.

7.2.3.  Use of [RFC5322]. the 100 (Continue) Status

   The field value is an HTTP-date, as
   described in purpose of the 100 (Continue) status (see Section 3.2; it MUST be sent in rfc1123-date format.

     Date   = "Date" ":" OWS Date-v
     Date-v = HTTP-date

   An example 8.1.1 of
   [Part2]) is

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

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

   1.  If client that is sending a request message with
   a request body to determine if the response status code origin server is 100 (Continue) or 101 (Switching
       Protocols), willing to accept
   the response MAY include a Date header field, at request (based on the
       server's option.

   2.  If request headers) before the response status code conveys a server error, e.g. 500
       (Internal Server Error) or 503 (Service Unavailable), and client sends
   the request body.  In some cases, it is
       inconvenient might either be inappropriate or impossible
   highly inefficient for the client to generate a valid Date.

   3.  If send the body if the server does not have will
   reject the message without looking at the body.

   Requirements for HTTP/1.1 clients:

   o  If a clock that can provide client will wait for a reasonable
       approximation 100 (Continue) response before sending
      the request body, it MUST send an Expect request-header field
      (Section 9.2 of [Part2]) with the current time, its responses "100-continue" expectation.

   o  A client MUST NOT include
       a Date header field.  In this case, send an Expect request-header field (Section 9.2
      of [Part2]) with the rules in Section 8.3.1
       MUST be followed.

   A received message that "100-continue" expectation if it does not have
      intend to send a Date header field MUST be
   assigned one by request body.

   Because of the recipient if presence of older implementations, the message will be cached by that
   recipient or gatewayed via a protocol allows
   ambiguous situations in which requires a Date.  An HTTP
   implementation without a clock MUST NOT cache responses client may send "Expect: 100-
   continue" without
   revalidating them on every use.  An HTTP cache, especially a shared
   cache, SHOULD use receiving either a mechanism, such as NTP [RFC1305], to synchronize
   its clock with 417 (Expectation Failed) status
   or a reliable external standard.

   Clients SHOULD only send 100 (Continue) status.  Therefore, when a Date header field in messages that include
   an entity-body, as in the case of the PUT and POST requests, and even
   then it is optional.  A client without a clock MUST NOT send a Date sends this
   header field in a request.

   The HTTP-date sent in to an origin server (possibly via a Date header proxy) from which it
   has never seen a 100 (Continue) status, the client SHOULD NOT represent wait
   for an indefinite period before sending the request body.

   Requirements for HTTP/1.1 origin servers:

   o  Upon receiving a date request which includes an Expect request-header
      field with the "100-continue" expectation, an origin server MUST
      either respond with 100 (Continue) status and
   time subsequent continue to read
      from the generation of the message.  It SHOULD
   represent the best available approximation of input stream, or respond with a final status code.  The
      origin server MUST NOT wait for the date and time of
   message generation, unless request body before sending
      the implementation has no means of
   generating 100 (Continue) response.  If it responds with a reasonably accurate date and time.  In theory, final status
      code, it MAY close the date
   ought transport connection or it MAY continue to represent the moment just before
      read and discard the entity is generated.
   In practice, rest of the date can be generated at any time during request.  It MUST NOT perform the message
   origination without affecting its semantic value.

8.3.1.  Clockless Origin Server Operation

   Some origin server implementations might not have
      requested method if it returns a clock available. final status code.

   o  An origin server without a clock MUST SHOULD NOT assign Expires or Last-
   Modified values to send a response, unless these values were associated
   with 100 (Continue) response if the resource by a system or user with a reliable clock.  It MAY
   assign
      request message does not include an Expires value that is known, at or before server
   configuration time, to be in the past (this allows "pre-expiration"
   of responses without storing separate Expires values for each
   resource).

8.4.  Host

   The Expect request-header field "Host" specifies
      with the Internet host "100-continue" expectation, and port
   number of the resource being requested, as obtained MUST NOT send a 100
      (Continue) response if such a request comes from the original
   URI given by the user or referring resource (generally an http URI,
   as described HTTP/1.0 (or
      earlier) client.  There is an exception to this rule: for
      compatibility with [RFC2068], a server MAY send a 100 (Continue)
      status in Section 2.1.1).  The Host response to an HTTP/1.1 PUT or POST request that does
      not include an Expect request-header field value MUST represent with the naming authority of "100-continue"
      expectation.  This exception, the purpose of which is to minimize
      any client processing delays associated with an undeclared wait
      for 100 (Continue) status, applies only to HTTP/1.1 requests, and
      not to requests with any other HTTP-version value.

   o  An origin server MAY omit a 100 (Continue) response if it has
      already received some or gateway given by all of the
   original URL.  This allows request body for the
      corresponding request.

   o  An origin server or gateway to
   differentiate between internally-ambiguous URLs, such as the root "/"
   URL of that sends a server for multiple host names on 100 (Continue) response MUST
      ultimately send a single IP address.

     Host   = "Host" ":" OWS Host-v
     Host-v = uri-host [ ":" port ] ; Section 2.1.1

   A "host" without any trailing port information implies the default
   port for final status code, once the service requested (e.g., "80" for an HTTP URL).  For
   example, a request on body is
      received and processed, unless it terminates the origin server for
   <http://www.example.org/pub/WWW/> would properly include:

     GET /pub/WWW/ HTTP/1.1
     Host: www.example.org

   A client MUST include transport
      connection prematurely.

   o  If an origin server receives a Host header field in all HTTP/1.1 request
   messages.  If the requested URI that does not include an Internet host
   name for the service being requested, then the Host header
      Expect request-header field MUST
   be given with an empty value.  An HTTP/1.1 proxy MUST ensure that any
   request message it forwards does contain an appropriate Host header
   field that identifies the service being requested by "100-continue" expectation,
      the proxy.  All
   Internet-based HTTP/1.1 servers MUST respond request includes a request body, and the server responds with
      a 400 (Bad Request) final status code to any HTTP/1.1 before reading the entire request message which lacks a Host header
   field.

   See Sections 5.2 and B.1.1 for other requirements relating to Host.

8.5.  TE

   The request-header field "TE" indicates what extension transfer-
   codings body from
      the transport connection, then the server SHOULD NOT close the
      transport connection until it is willing to accept in has read the response and whether entire request, or
      until the client closes the connection.  Otherwise, the client
      might not it
   is willing to accept trailer fields in a chunked transfer-coding.
   Its value may consist of reliably receive the keyword "trailers" and/or response message.  However, this
      requirement is not be construed as preventing a comma-
   separated list of extension transfer-coding names with optional
   accept parameters (as described in Section 3.3).

     TE        = "TE" ":" OWS TE-v
     TE-v      = #t-codings
     t-codings = "trailers" / ( transfer-extension [ te-params ] )
     te-params = OWS ";" OWS "q=" qvalue *( te-ext )
     te-ext    = OWS ";" OWS token [ "=" ( token / quoted-string ) ]

   The presence of server from
      defending itself against denial-of-service attacks, or from badly
      broken client implementations.

   Requirements for HTTP/1.1 proxies:

   o  If a proxy receives a request that includes an Expect request-
      header field with the keyword "trailers" indicates "100-continue" expectation, and the proxy
      either knows that the client is
   willing to accept trailer fields in a chunked transfer-coding, as
   defined in Section 3.3.1.  This keyword is reserved for use next-hop server complies with
   transfer-coding values even though it HTTP/1.1 or
      higher, or does not itself represent a
   transfer-coding.

   Examples know the HTTP version of its use are:

     TE: deflate
     TE:
     TE: trailers, deflate;q=0.5

   The TE the next-hop server,
      it MUST forward the request, including the Expect header field only applies to field.

   o  If the immediate connection.
   Therefore, proxy knows that the keyword version of the next-hop server is
      HTTP/1.0 or lower, it MUST be supplied within NOT forward the request, and it MUST
      respond with a Connection header 417 (Expectation Failed) status.

   o  Proxies SHOULD maintain a cache recording the HTTP version numbers
      received from recently-referenced next-hop servers.

   o  A proxy MUST NOT forward a 100 (Continue) response if the request
      message was received from an HTTP/1.0 (or earlier) client and did
      not include an Expect request-header field (Section 8.1) whenever TE is present in with the "100-continue"
      expectation.  This requirement overrides the general rule for
      forwarding of 1xx responses (see Section 8.1 of [Part2]).

7.2.4.  Client Behavior if Server Prematurely Closes Connection

   If an HTTP/1.1 message.

   A server tests whether client sends a transfer-coding is acceptable, according to request which includes a TE field, using these rules:

   1.  The "chunked" transfer-coding is always acceptable.  If request body,
   but which does not include an Expect request-header field with the
       keyword "trailers" is listed,
   "100-continue" expectation, and if the client indicates that it is
       willing not directly
   connected to accept trailer fields in the chunked response on
       behalf of itself an HTTP/1.1 origin server, and any downstream clients.  The implication is
       that, if given, the client is stating that either all downstream
       clients are willing to accept trailer fields in the forwarded
       response, or that it will attempt to buffer sees the response on
       behalf of downstream recipients.

       Note: HTTP/1.1 does not define
   connection close before receiving any means to limit status from the server, the size of a
       chunked response such that a
   client can SHOULD retry the request.  If the client does retry this
   request, it MAY use the following "binary exponential backoff"
   algorithm to be assured of buffering obtaining a reliable response:

   1.  Initiate a new connection to the entire response. server

   2.  If  Transmit the transfer-coding being tested is one of request-headers

   3.  Initialize a variable R to the transfer-
       codings listed in estimated round-trip time to the TE field, then it is acceptable unless
       server (e.g., based on the time it
       is accompanied by a qvalue of 0.  (As defined in Section 3.5, took to establish the
       connection), or to a
       qvalue constant value of 0 means "not acceptable.")

   3.  If multiple transfer-codings are acceptable, then the acceptable
       transfer-coding with 5 seconds if the highest non-zero qvalue round-
       trip time is preferred.
       The "chunked" transfer-coding always has a qvalue not available.

   4.  Compute T = R * (2**N), where N is the number of 1.

   If previous retries
       of this request.

   5.  Wait either for an error response from the TE field-value is empty server, or if for T
       seconds (whichever comes first)

   6.  If no TE field error response is present, received, after T seconds transmit the only
   transfer-coding is "chunked".  A message with no transfer-coding is
   always acceptable.

8.6.  Trailer

   The general field "Trailer" indicates
       body of the request.

   7.  If client sees that the given set of header
   fields connection is present in closed prematurely, repeat
       from step 1 until the trailer of a message encoded with chunked
   transfer-coding.

     Trailer   = "Trailer" ":" OWS Trailer-v
     Trailer-v = 1#field-name

   An HTTP/1.1 message SHOULD include a Trailer header field in a
   message using chunked transfer-coding with a non-empty trailer.
   Doing so allows request is accepted, an error response is
       received, or the recipient to know which header fields to expect
   in user becomes impatient and terminates the trailer. retry
       process.

   If no Trailer header field at any point an error status is present, received, the trailer client

   o  SHOULD NOT include
   any header fields.  See Section 3.3.1 continue and

   o  SHOULD close the connection if it has not completed sending the
      request message.

8.  Miscellaneous notes that may disappear

8.1.  Scheme aliases considered harmful

   [[anchor2: TBS: describe why aliases like webcal are harmful.]]

8.2.  Use of HTTP for restrictions proxy communication

   [[anchor3: TBD: Configured to use HTTP to proxy HTTP or other
   protocols.]]

8.3.  Interception of HTTP for access control

   [[anchor4: TBD: Interception of HTTP traffic for initiating access
   control.]]

8.4.  Use of HTTP by other protocols

   [[anchor5: TBD: Profiles of HTTP defined by other protocol.
   Extensions of HTTP like WebDAV.]]

8.5.  Use of HTTP by media type specification

   [[anchor6: TBD: Instructions on composing HTTP requests via hypertext
   formats.]]

9.  Header Field Definitions

   This section defines the use syntax and semantics of
   trailer fields in a "chunked" transfer-coding.

   Message HTTP/1.1 header
   fields listed in the Trailer header field MUST NOT
   include the following header fields:

   o  Transfer-Encoding

   o  Content-Length

   o  Trailer

8.7.  Transfer-Encoding

   The general-header "Transfer-Encoding" field indicates what (if any)
   type of transformation has been applied related to the message body in order
   to safely transfer it between the framing and transport protocols.

   For entity-header fields, both sender and the recipient.  This
   differs from the content-coding in that the transfer-coding is a
   property of the message, not of the entity.

     Transfer-Encoding   = "Transfer-Encoding" ":" OWS
                           Transfer-Encoding-v
     Transfer-Encoding-v = 1#transfer-coding

   Transfer-codings are defined in Section 3.3.  An example is:

     Transfer-Encoding: chunked

   If multiple encodings have been applied recipient refer to an entity, the transfer-
   codings MUST be listed in either
   the order in which they were applied.
   Additional information about client or the encoding parameters MAY be provided
   by other entity-header fields not defined by this specification.

   Many older HTTP/1.0 applications do not understand server, depending on who sends and who receives the Transfer-
   Encoding header.

8.8.  Upgrade
   entity.

9.1.  Connection

   The "Connection" general-header "Upgrade" field allows the client sender to specify what
   additional communication protocols it supports
   options that are desired for that particular connection and would like to use
   if the server finds it appropriate to switch protocols.  The server MUST use NOT
   be communicated by proxies over further connections.

   The Connection header's value has the Upgrade header field within a 101 (Switching Protocols)
   response to indicate which protocol(s) are being switched.

     Upgrade following grammar:

     Connection       = "Upgrade" "Connection" ":" OWS Upgrade-v
     Upgrade-v Connection-v
     Connection-v     = 1#product

   For example,

     Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11

   The Upgrade 1#connection-token
     connection-token = token

   HTTP/1.1 proxies MUST parse the Connection header field is intended to provide before a simple mechanism
   message is forwarded and, for transition each connection-token in this field,
   remove any header field(s) from HTTP/1.1 to some other, incompatible protocol.
   It does so by allowing the client to advertise its desire to use
   another protocol, such as a later version of HTTP message with a higher major
   version number, even though the current request has been made using
   HTTP/1.1.  This eases same name as the difficult transition between incompatible
   protocols
   connection-token.  Connection options are signaled by allowing the client to initiate presence of
   a request connection-token in the more
   commonly supported protocol while indicating Connection header field, not by any
   corresponding additional header field(s), since the additional header
   field may not be sent if there are no parameters associated with that
   connection option.

   Message headers listed in the Connection header MUST NOT include end-
   to-end headers, such as Cache-Control.

   HTTP/1.1 defines the "close" connection option for the sender to
   signal that the connection will be closed after completion of the
   response.  For example,
     Connection: close

   in either the request or the response header fields indicates that
   the connection SHOULD NOT be considered `persistent' (Section 7.1)
   after the current request/response is complete.

   An HTTP/1.1 client that does not support persistent connections MUST
   include the "close" connection option in every request message.

   An HTTP/1.1 server that it
   would like to use does not support persistent connections MUST
   include the "close" connection option in every response message that
   does not have a 1xx (informational) status code.

   A system receiving an HTTP/1.0 (or lower-version) message that
   includes a "better" protocol if available (where "better" is
   determined by Connection header MUST, for each connection-token in this
   field, remove and ignore any header field(s) from the server, possibly according to message with
   the nature of same name as the
   method and/or resource being requested).

   The Upgrade connection-token.  This protects against
   mistaken forwarding of such header field only applies to switching application-layer
   protocols upon the existing transport-layer connection.  Upgrade
   cannot be used to insist on a protocol change; its acceptance and use fields by the server is optional. pre-HTTP/1.1 proxies.
   See Appendix B.2.

9.2.  Content-Length

   The capabilities and nature of the
   application-layer communication after the protocol change is entirely
   dependent upon "Content-Length" entity-header field indicates the new protocol chosen, although size of the first action
   after changing
   entity-body, in number of OCTETs.  In the protocol MUST be a response case of responses to the initial HTTP
   request containing
   HEAD method, it indicates the Upgrade header field.

   The Upgrade header field only applies to size of the immediate connection.
   Therefore, entity-body that would have
   been sent had the upgrade keyword MUST be supplied within request been a Connection
   header field (Section 8.1) whenever Upgrade GET.

     Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
     Content-Length-v = 1*DIGIT

   An example is present in an HTTP/1.1
   message.

   The Upgrade header

     Content-Length: 3495

   Applications SHOULD use this field cannot be used to indicate a switch to a
   protocol on a different connection.  For that purpose, it is more
   appropriate to use a 301, 302, 303, or 305 redirection response.

   This specification only defines the protocol name "HTTP" for use by the family transfer-length of Hypertext Transfer Protocols, as defined
   the message-body, unless this is prohibited by the HTTP
   version rules of in
   Section 3.1 and future updates 3.4.

   Any Content-Length greater than or equal to zero is a valid value.
   Section 3.4 describes how to determine the length of a message-body
   if a Content-Length is not given.

   Note that the meaning of this
   specification.  Any token can be field is significantly different from
   the corresponding definition in MIME, where it is an optional field
   used as a protocol name; however, within the "message/external-body" content-type.  In HTTP, it
   will only
   SHOULD be useful if both sent whenever the client message's length can be determined prior
   to being transferred, unless this is prohibited by the rules in
   Section 3.4.

9.3.  Date

   The "Date" general-header field represents the date and server associate time at which
   the name
   with message was originated, having the same protocol.

8.9.  Via semantics as orig-date in
   Section 3.6.1 of [RFC5322].  The general-header field "Via" value is an HTTP-date, as
   described in Section 6.1; it MUST be used by gateways and proxies
   to indicate sent in rfc1123-date format.

     Date   = "Date" ":" OWS Date-v
     Date-v = 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 intermediate protocols and recipients between response status code is 100 (Continue) or 101 (Switching
       Protocols), the
   user agent and response MAY include a Date header field, at the server on requests, and between
       server's option.

   2.  If the origin response status code conveys a server error, e.g. 500
       (Internal Server Error) or 503 (Service Unavailable), and the client on responses.  It is analogous to the "Received" field
   defined in Section 3.6.7 of [RFC5322] and it is intended
       inconvenient or impossible to be used for
   tracking message forwards, avoiding request loops, and identifying generate a valid Date.

   3.  If the protocol capabilities server does not have a clock that can provide a reasonable
       approximation of all senders along the request/response
   chain.

     Via               = "Via" ":" OWS Via-v
     Via-v             = 1#( received-protocol RWS received-by
                             [ RWS comment ] )
     received-protocol = [ protocol-name "/" ] protocol-version
     protocol-name     = token
     protocol-version  = token
     received-by       = ( uri-host [ ":" port ] ) / pseudonym
     pseudonym         = token

   The received-protocol indicates the protocol version of current time, its responses MUST NOT include
       a Date header field.  In this case, the message rules in Section 9.3.1
       MUST be followed.

   A received message that does not have a Date header field MUST be
   assigned one by the server or client along each segment of the request/
   response chain.  The received-protocol version is appended to the Via
   field value when recipient if the message is forwarded so will be cached by that information about
   the
   recipient or gatewayed via a protocol capabilities of upstream applications remains visible which requires a Date.  An HTTP
   implementation without a clock MUST NOT cache responses without
   revalidating them on every use.  An HTTP cache, especially a shared
   cache, SHOULD use a mechanism, such as NTP [RFC1305], to
   all recipients.

   The protocol-name is optional if and synchronize
   its clock with a reliable external standard.

   Clients SHOULD only if it would be "HTTP".  The
   received-by field is normally the host and optional port number of send a
   recipient server or client Date header field in messages that subsequently forwarded include
   an entity-body, as in the message.
   However, if case of the real host is considered to be sensitive information, PUT and POST requests, and even
   then it MAY be replaced by a pseudonym.  If the port is not given, it MAY
   be assumed optional.  A client without a clock MUST NOT send a Date
   header field in a request.

   The HTTP-date sent in a Date header SHOULD NOT represent a date and
   time subsequent to be the default port generation of the received-protocol.

   Multiple Via field values represents each proxy or gateway that has
   forwarded the message.  Each recipient MUST append its information
   such that the end result is ordered according to  It SHOULD
   represent the sequence best available approximation of
   forwarding applications.

   Comments MAY be used in the Via header field to identify date and time of
   message generation, unless the software implementation has no means of
   generating a reasonably accurate date and time.  In theory, the recipient proxy or gateway, analogous date
   ought to represent the User-Agent and
   Server header fields.  However, all comments in moment just before the Via field are
   optional and MAY entity is generated.
   In practice, the date can be removed by generated at any recipient prior to forwarding time during the
   message.

   For example, a request message could be sent from an HTTP/1.0 user
   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
   forward the request
   origination without affecting its semantic value.

9.3.1.  Clockless Origin Server Operation

   Some origin server implementations might not have a clock available.
   An origin server without a clock MUST NOT assign Expires or Last-
   Modified values to a public proxy at p.example.net, which
   completes response, unless these values were associated
   with the request resource by forwarding it a system or user with a reliable clock.  It MAY
   assign an Expires value that is known, at or before server
   configuration time, to be in the origin server at
   www.example.com. past (this allows "pre-expiration"
   of responses without storing separate Expires values for each
   resource).

9.4.  Host

   The request received by www.example.com would then
   have "Host" request-header field specifies the following Via header field:

     Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)

   Proxies Internet host and gateways used port
   number of the resource being requested, allowing the origin server or
   gateway to differentiate between internally-ambiguous URLs, such as
   the root "/" URL of a portal through server for multiple host names on a network firewall
   SHOULD NOT, by default, forward single IP
   address.

   The Host field value MUST represent the names and ports naming authority of hosts within the firewall region.  This information SHOULD only be propagated if
   explicitly enabled.  If not enabled,
   origin server or gateway given by the received-by host of any host
   behind original URL obtained from the firewall SHOULD be replaced by
   user or referring resource (generally an appropriate pseudonym http URI, as described in
   Section 2.6.1).

     Host   = "Host" ":" OWS Host-v
     Host-v = uri-host [ ":" port ] ; Section 2.6.1

   A "host" without any trailing port information implies the default
   port for that host.

   For organizations that have strong privacy requirements the service requested (e.g., "80" for hiding
   internal structures, a proxy MAY combine an ordered subsequence of
   Via HTTP URL).  For
   example, a request on the origin server for
   <http://www.example.org/pub/WWW/> would properly include:

     GET /pub/WWW/ HTTP/1.1
     Host: www.example.org

   A client MUST include a Host header field entries with identical received-protocol values into
   a single such entry.  For example,

     Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy

   could be collapsed to

     Via: 1.0 ricky, 1.1 mertz, 1.0 lucy

   Applications SHOULD NOT combine multiple entries unless they are in all
   under HTTP/1.1 request
   messages.  If the same organizational control and requested URI does not include an Internet host
   name for the hosts have already been
   replaced by pseudonyms.  Applications service being requested, then the Host header field MUST NOT combine entries which
   have different received-protocol values.

9.  IANA Considerations

9.1.  Message Header Registration

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

   +-------------------+----------+----------+-------------+
   | Header Field Name | Protocol | Status   | Reference   |
   +-------------------+----------+----------+-------------+
   | Connection        | http     | standard | Section 8.1 |
   | Content-Length    | http     | standard | Section 8.2 |
   | Date              | http     | standard | Section 8.3 |
   | an empty value.  An HTTP/1.1 proxy MUST ensure that any
   request message it forwards does contain an appropriate Host              | http     | standard | Section 8.4 |
   | TE                | http     | standard | Section 8.5 |
   | Trailer           | http     | standard | Section 8.6 |
   | Transfer-Encoding | http     | standard | Section 8.7 |
   | Upgrade           | http     | standard | Section 8.8 |
   | Via               | http     | standard | Section 8.9 |
   +-------------------+----------+----------+-------------+

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

9.2.  URI Scheme Registration

   The entry header
   field that identifies the service being requested by the proxy.  All
   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
   status code to any HTTP/1.1 request message which lacks a Host header
   field.

   See Sections 4.2 and B.1.1 for the "http" URI Scheme in the registry located at
   <http://www.iana.org/assignments/uri-schemes.html> should be updated other requirements relating to point Host.

9.5.  TE

   The "TE" request-header field indicates what extension transfer-
   codings it is willing to Section 2.1.1 of this document (see [RFC4395]).

9.3.  Internet Media Type Registrations

   This document serves as the specification for accept in the Internet media
   types "message/http" response, and "application/http".  The following whether or not
   it is willing to be
   registered accept trailer fields in a chunked transfer-coding.

   Its value may consist of the keyword "trailers" and/or a comma-
   separated list of extension transfer-coding names with IANA (see [RFC4288]).

9.3.1.  Internet Media Type message/http optional
   accept parameters (as described in Section 6.2).

     TE        = "TE" ":" OWS TE-v
     TE-v      = #t-codings
     t-codings = "trailers" / ( transfer-extension [ te-params ] )
     te-params = OWS ";" OWS "q=" qvalue *( te-ext )
     te-ext    = OWS ";" OWS token [ "=" ( token / quoted-string ) ]

   The message/http type can be used to enclose a single HTTP request or
   response message, provided presence of the keyword "trailers" indicates that it obeys the MIME restrictions client is
   willing to accept trailer fields in a chunked transfer-coding, as
   defined in Section 6.2.1.  This keyword is reserved for
   all "message" types regarding line length and encodings.

   Type name:  message

   Subtype name:  http

   Required parameters:  none

   Optional parameters:  version, msgtype

      version: use with
   transfer-coding values even though it does not itself represent a
   transfer-coding.

   Examples of its use are:

     TE: deflate
     TE:
     TE: trailers, deflate;q=0.5

   The HTTP-Version number of TE header field only applies to the enclosed message (e.g.,
         "1.1").  If not present, immediate connection.
   Therefore, the version can keyword MUST be determined from the
         first line of the body.

      msgtype: supplied within a Connection header
   field (Section 9.1) whenever TE is present in an HTTP/1.1 message.

   A server tests whether a transfer-coding is acceptable, according to
   a TE field, using these rules:

   1.  The message type -- "request" or "response". "chunked" transfer-coding is always acceptable.  If not
         present, the type can be determined from the first line of
       keyword "trailers" is listed, the
         body.

   Encoding considerations:  only "7bit", "8bit", or "binary" are
      permitted

   Security considerations:  none

   Interoperability considerations:  none

   Published specification:  This specification (see Section 9.3.1).

   Applications client indicates that use this media type:

   Additional information:

      Magic number(s):  none

      File extension(s):  none

      Macintosh file type code(s):  none

   Person and email address it is
       willing to contact for further information:  See
      Authors Section.

   Intended usage:  COMMON

   Restrictions accept trailer fields in the chunked response on usage:  none

   Author/Change controller:  IESG

9.3.2.  Internet Media Type application/http
       behalf of itself and any downstream clients.  The application/http type can be used implication is
       that, if given, the client is stating that either all downstream
       clients are willing to enclose a pipeline of one or
   more HTTP request accept trailer fields in the forwarded
       response, or that it will attempt to buffer the response messages (not intermixed).

   Type name:  application

   Subtype name:  http

   Required parameters:  none

   Optional parameters:  version, msgtype
      version:  The HTTP-Version number on
       behalf of the enclosed messages (e.g.,
         "1.1").  If downstream recipients.

       Note: HTTP/1.1 does not present, define any means to limit the version size of a
       chunked response such that a client can be determined from the
         first line assured of buffering
       the body.

      msgtype:  The message type -- "request" or "response". entire response.

   2.  If not
         present, the type can be determined from the first line transfer-coding being tested is one of the
         body.

   Encoding considerations:  HTTP messages enclosed by this type are transfer-
       codings listed in
      "binary" format; use of an appropriate Content-Transfer-Encoding the TE field, then it is required when transmitted via E-mail.

   Security considerations:  none

   Interoperability considerations:  none

   Published specification:  This specification (see Section 9.3.2).

   Applications that use this media type:

   Additional information:

      Magic number(s):  none

      File extension(s):  none

      Macintosh file type code(s):  none

   Person and email address to contact for further information:  See
      Authors Section.

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author/Change controller:  IESG

10.  Security Considerations

   This section acceptable unless it
       is meant to inform application developers, information
   providers, and users accompanied by a qvalue of the security limitations 0.  (As defined 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.

10.1.  Personal Information

   HTTP clients are often privy to large amounts Section 6.4, a
       qvalue of personal information
   (e.g. 0 means "not acceptable.")

   3.  If multiple transfer-codings are acceptable, then the user's name, location, mail address, passwords, encryption
   keys, etc.), and SHOULD be very careful to prevent unintentional
   leakage acceptable
       transfer-coding with the highest non-zero qvalue is preferred.
       The "chunked" transfer-coding always has a qvalue of this information.  We very strongly recommend 1.

   If the TE field-value is empty or if no TE field is present, the only
   transfer-coding is "chunked".  A message with no transfer-coding is
   always acceptable.

9.6.  Trailer

   The "Trailer" general-header field indicates that a
   convenient interface be provided for the user to control
   dissemination given set of such information, and that designers and
   implementors be particularly careful in this area.  History shows
   that errors
   header fields is present in this area often create serious security and/or privacy
   problems and generate highly adverse publicity for the implementor's
   company.

10.2.  Abuse trailer of Server Log Information

   A server is a message encoded with
   chunked transfer-coding.

     Trailer   = "Trailer" ":" OWS Trailer-v
     Trailer-v = 1#field-name

   An HTTP/1.1 message SHOULD include a Trailer header field in a
   message using chunked transfer-coding with a non-empty trailer.
   Doing so allows the position recipient to save personal data about a user's
   requests know which might identify their reading patterns or subjects of
   interest.  This information header fields to expect
   in the trailer.

   If no Trailer header field is clearly confidential present, the trailer SHOULD NOT include
   any header fields.  See Section 6.2.1 for restrictions on the use of
   trailer fields in nature and its
   handling can be constrained by law a "chunked" transfer-coding.

   Message header fields listed in certain countries.  People
   using HTTP the Trailer header field MUST NOT
   include the following header fields:

   o  Transfer-Encoding

   o  Content-Length

   o  Trailer

9.7.  Transfer-Encoding

   The "Transfer-Encoding" general-header field indicates what transfer-
   codings (if any) have been applied to provide data are responsible for ensuring that such
   material is not distributed without the permission message body.  It differs
   from Content-Encoding (Section 2.2 of any individuals [Part3]) in that transfer-
   codings are identifiable by the published results.

10.3.  Attacks Based On File and Path Names

   Implementations a property of HTTP origin servers SHOULD be careful to restrict the documents returned message (and therefore are removed by HTTP requests
   intermediaries), whereas content-codings are not.

     Transfer-Encoding   = "Transfer-Encoding" ":" OWS
                           Transfer-Encoding-v
     Transfer-Encoding-v = 1#transfer-coding

   Transfer-codings are defined in Section 6.2.  An example is:

     Transfer-Encoding: chunked

   If multiple encodings have been applied to an entity, the transfer-
   codings MUST be only those that listed in the order in which they were
   intended applied.
   Additional information about the encoding parameters MAY be provided
   by other entity-header fields not defined by this specification.

   Many older HTTP/1.0 applications do not understand the Transfer-
   Encoding header.

9.8.  Upgrade

   The "Upgrade" general-header field allows the client to specify what
   additional communication protocols it would like to use, if the
   server administrators.  If an HTTP server translates
   HTTP URIs directly into file system calls, chooses to switch protocols.  Additionally, the server MUST take
   special care not
   use the Upgrade header field within a 101 (Switching Protocols)
   response to serve files that were not indicate which protocol(s) are being switched to.

     Upgrade   = "Upgrade" ":" OWS Upgrade-v
     Upgrade-v = 1#product

   For example,

     Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11

   The Upgrade header field is intended to be
   delivered provide a simple mechanism
   for transition from HTTP/1.1 to some other, incompatible protocol.
   It does so by allowing the client to advertise its desire to HTTP clients.  For example, UNIX, Microsoft Windows, and
   other operating systems use ".."
   another protocol, such as a path component to indicate later version of HTTP with a
   directory level above higher major
   version number, even though the current request has been made using
   HTTP/1.1.  This eases the current one.  On such difficult transition between incompatible
   protocols by allowing the client to initiate a system, an HTTP
   server MUST disallow any such construct request in the request-target if more
   commonly supported protocol while indicating to the server that it
   would otherwise allow access like to use a resource outside those intended "better" protocol if available (where "better" is
   determined by the server, possibly according to
   be accessible via the HTTP server.  Similarly, files intended for
   reference nature of the
   method and/or resource being requested).

   The Upgrade header field only internally applies to switching application-layer
   protocols upon the existing transport-layer connection.  Upgrade
   cannot be used to insist on a protocol change; its acceptance and use
   by the server (such as access control
   files, configuration files, is optional.  The capabilities and script code) nature of the
   application-layer communication after the protocol change is entirely
   dependent upon the new protocol chosen, although the first action
   after changing the protocol MUST be protected from
   inappropriate retrieval, since they might contain sensitive
   information.  Experience has shown that minor bugs in such HTTP
   server implementations have turned into security risks.

10.4.  DNS Spoofing

   Clients using a response to the initial HTTP rely heavily on
   request containing the Domain Name Service, and are
   thus generally prone Upgrade header field.

   The Upgrade header field only applies to security attacks based on the deliberate mis-
   association of IP addresses and DNS names.  Clients need immediate connection.
   Therefore, the upgrade keyword MUST be supplied within a Connection
   header field (Section 9.1) whenever Upgrade is present in an HTTP/1.1
   message.

   The Upgrade header field cannot be used to indicate a switch to be
   cautious in assuming the continuing validity of an IP number/DNS name
   association.

   In particular, HTTP clients SHOULD rely a
   protocol on their a different connection.  For that purpose, it is more
   appropriate to use a 301, 302, 303, or 305 redirection response.

   This specification only defines the protocol name resolver "HTTP" for
   confirmation use by
   the family of an IP number/DNS name association, rather than
   caching Hypertext Transfer Protocols, as defined by the result HTTP
   version rules of previous host name lookups.  Many platforms
   already can cache host name lookups locally when appropriate, Section 2.5 and
   they SHOULD be configured to do so.  It is proper for these lookups future updates to this
   specification.  Additional tokens can be cached, however, only when the TTL (Time To Live) information
   reported by the name server makes it likely that registered with IANA using
   the cached
   information will remain useful.

   If registration procedure defined below.

9.8.1.  Upgrade Token Registry

   The HTTP clients cache Upgrade Token Registry defines the results of host name lookups in order space for product
   tokens used to
   achieve a performance improvement, they MUST observe identify protocols in the TTL
   information reported by DNS.

   If HTTP clients do not observe this rule, they could Upgrade header field.  Each
   registered token should be spoofed when associated with one or a previously-accessed server's IP address changes.  As network
   renumbering is expected to become increasingly common [RFC1900], the
   possibility set of this form
   specifications, and with contact information.

   Registrations should be allowed on a First Come First Served basis as
   described in Section 4.1 of attack will grow.  Observing this
   requirement thus reduces this potential security vulnerability.

   This requirement also improves [RFC5226].  These specifications need not
   be IETF documents or be subject to IESG review, but should obey the load-balancing behavior of clients
   following rules:

   1.  A token, once registered, stays registered forever.

   2.  The registration MUST name a responsible party for replicated servers using the same DNS
       registration.

   3.  The registration MUST name and reduces the
   likelihood a point of contact.

   4.  The registration MAY name the documentation required for the
       token.

   5.  The responsible party MAY change the registration at any time.
       The IANA will keep a user's experiencing failure in accessing sites which
   use that strategy.

10.5.  Proxies and Caching

   By their very nature, HTTP proxies are men-in-the-middle, record of all such changes, and
   represent an opportunity make them
       available upon request.

   6.  The responsible party for man-in-the-middle attacks.  Compromise the first registration of a "product"
       token MUST approve later registrations of a "version" token
       together with that "product" token before they can be registered.

   7.  If absolutely required, the systems on which IESG MAY reassign the proxies run can result in serious
   security and privacy problems.  Proxies have access to security-
   related information, personal information about individual users and
   organizations, and proprietary information belonging to users and
   content providers.  A compromised proxy, or responsibility
       for a proxy implemented or
   configured without regard to security and privacy considerations,
   might token.  This will normally only be used in the commission of case when a wide range of potential attacks.

   Proxy operators should protect the systems on which proxies run as
   they would protect any system
       responsible party cannot be contacted.

   It is not required that contains or transports sensitive
   information.  In particular, log information gathered at proxies
   often contains highly sensitive personal information, and/or
   information about organizations.  Log specifications for upgrade tokens be made
   publicly available, but the contact information for the registration
   should be.

9.9.  Via

   The "Via" general-header field MUST be carefully
   guarded, and appropriate guidelines for use developed used by gateways and followed.
   (Section 10.2).

   Proxy implementors should consider proxies
   to indicate the privacy intermediate protocols and security
   implications of their design recipients between the
   user agent and coding decisions, the server on requests, and of between the
   configuration options they provide origin server
   and the client on responses.  It is analogous to proxy operators (especially the
   default configuration).

   Users "Received" field
   defined in Section 3.6.7 of a proxy need [RFC5322] and is intended to be aware that they are no trustworthier than used for
   tracking message forwards, avoiding request loops, and identifying
   the people who run protocol capabilities of all senders along the proxy; HTTP itself cannot solve this problem. request/response
   chain.

     Via               = "Via" ":" OWS Via-v
     Via-v             = 1#( received-protocol RWS received-by
                             [ RWS comment ] )
     received-protocol = [ protocol-name "/" ] protocol-version
     protocol-name     = token
     protocol-version  = token
     received-by       = ( uri-host [ ":" port ] ) / pseudonym
     pseudonym         = token

   The judicious use of cryptography, when appropriate, may suffice to
   protect against a broad range of security and privacy attacks.  Such
   cryptography is beyond received-protocol indicates the scope protocol version of the HTTP/1.1 specification.

10.6.  Denial message
   received by the server or client along each segment of Service Attacks on Proxies

   They exist.  They are hard the request/
   response chain.  The received-protocol version is appended to defend against.  Research continues.
   Beware.

11.  Acknowledgments

   HTTP has evolved considerably over the years.  It has benefited from
   a large and active developer community--the many people who have
   participated on Via
   field value when the www-talk mailing list--and it message is forwarded so that community
   which has been most responsible for information about
   the success protocol capabilities of HTTP upstream applications remains visible to
   all recipients.

   The protocol-name is optional if and of only if it would be "HTTP".  The
   received-by field is normally the
   World-Wide Web in general.  Marc Andreessen, Robert Cailliau, Daniel
   W. Connolly, Bob Denny, John Franks, Jean-Francois Groff, Phillip M.
   Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli,
   Dave Raggett, Tony Sanders, host and Marc VanHeyningen deserve special
   recognition for their efforts in defining early aspects optional port number of a
   recipient server or client that subsequently forwarded the
   protocol.

   This document has benefited greatly from the comments of all those
   participating in message.
   However, if the HTTP-WG.  In addition real host is considered to those already
   mentioned, be sensitive information,
   it MAY be replaced by a pseudonym.  If the following individuals have contributed port is not given, it MAY
   be assumed to this
   specification:

   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc
   Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann, Bob Jernigan, Shel
   Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut,
   David M. Kristol, Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert
   Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David
   Morris, Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott
   Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich
   Salz, Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
   Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart)
   Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen.

   Thanks be the default port of the received-protocol.

   Multiple Via field values represents each proxy or gateway that has
   forwarded the message.  Each recipient MUST append its information
   such that the end result is ordered according to the "cave men" of Palo Alto.  You know who you are.

   Jim Gettys (the editor sequence of [RFC2616]) wishes particularly
   forwarding applications.

   Comments MAY be used in the Via header field to thank Roy
   Fielding, identify the editor software
   of [RFC2068], along with John Klensin, Jeff
   Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh
   Cohen, Alex Hopmann, Scott Lawrence, and Larry Masinter for their
   help.  And thanks go particularly the recipient proxy or gateway, analogous to Jeff Mogul and Scott Lawrence
   for performing the "MUST/MAY/SHOULD" audit.

   The Apache Group, Anselm Baird-Smith, author of Jigsaw, User-Agent and Henrik
   Frystyk implemented RFC 2068 early,
   Server header fields.  However, all comments in the Via field are
   optional and we wish MAY be removed by any recipient prior to thank them for forwarding the
   discovery of many
   message.

   For example, a request message could be sent from an HTTP/1.0 user
   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
   forward the request to a public proxy at p.example.net, which
   completes the request by forwarding it to the origin server at
   www.example.com.  The request received by www.example.com would then
   have the following Via header field:

     Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)

   Proxies and gateways used as a portal through a network firewall
   SHOULD NOT, by default, forward the names and ports of hosts within
   the firewall region.  This information SHOULD only be propagated if
   explicitly enabled.  If not enabled, the problems that this document attempts to
   rectify.

   This specification makes heavy use received-by host of any host
   behind the augmented BNF and generic
   constructs defined firewall SHOULD be replaced by David H. Crocker an appropriate pseudonym
   for [RFC5234].  Similarly, it
   reuses many that host.

   For organizations that have strong privacy requirements for hiding
   internal structures, a proxy MAY combine an ordered subsequence of
   Via header field entries with identical received-protocol values into
   a single such entry.  For example,

     Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy

   could be collapsed to

     Via: 1.0 ricky, 1.1 mertz, 1.0 lucy

   Applications SHOULD NOT combine multiple entries unless they are all
   under the definitions provided by Nathaniel Borenstein same organizational control and
   Ned Freed for MIME [RFC2045].  We hope that their inclusion in this
   specification will help reduce past confusion over the relationship
   between HTTP and hosts have already been
   replaced by pseudonyms.  Applications MUST NOT combine entries which
   have different received-protocol values.

10.  IANA Considerations

10.1.  Message Header Registration

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

   +-------------------+----------+----------+-------------+
   | Header Field Name | Protocol | Status   | Reference   |
   +-------------------+----------+----------+-------------+
   | Connection        | http     | standard | Section 9.1 |
   | Content-Length    | http     | standard | Section 9.2 |
   | Date              | http     | standard | Section 9.3 |
   | Host              | http     | standard | Section 9.4 |
   | TE                | http     | standard | Section 9.5 |
   | Trailer           | http     | standard | Section 9.6 |
   | Transfer-Encoding | http     | standard | Section 9.7 |
   | Upgrade           | http     | standard | Section 9.8 |
   | Via               | http     | standard | Section 9.9 |
   +-------------------+----------+----------+-------------+

   The change controller is: "IETF (iesg@ietf.org) - Internet mail message formats.

12.  References

12.1.  Normative References

   [ISO-8859-1]
              International Organization
   Engineering Task Force".

10.2.  URI Scheme Registration

   The entries for Standardization,
              "Information technology -- 8-bit single-byte coded graphic
              character sets -- Part 1: Latin alphabet No. 1", ISO/
              IEC 8859-1:1998, 1998.

   [Part2]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              and J. Reschke, Ed., "HTTP/1.1, part 2: Message
              Semantics", draft-ietf-httpbis-p2-semantics-07 (work in
              progress), July 2009.

   [Part3]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload
              and Content Negotiation", draft-ietf-httpbis-p3-payload-07
              (work in progress), July 2009.

   [Part5]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
              Partial Responses", draft-ietf-httpbis-p5-range-07 (work
              in progress), July 2009.

   [Part6]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              Nottingham, M., Ed., the "http" and J. Reschke, Ed., "HTTP/1.1, part
              6: Caching", draft-ietf-httpbis-p6-cache-07 (work in
              progress), July 2009.

   [RFC2119]  Bradner, S., "Key words for use "https" URI Schemes in RFCs the registry
   located at <http://www.iana.org/assignments/uri-schemes.html> should
   be updated to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., point to Sections 2.6.1 and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", RFC 3986,
              STD 66, January 2005.

   [RFC5234]  Crocker, D., Ed. 2.6.2 of this document (see
   [RFC4395]).

10.3.  Internet Media Type Registrations

   This document serves as the specification for the Internet media
   types "message/http" and P. Overell, "Augmented BNF "application/http".  The following is to be
   registered with IANA (see [RFC4288]).

10.3.1.  Internet Media Type message/http

   The message/http type can be used to enclose a single HTTP request or
   response message, provided that it obeys the MIME restrictions for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [USASCII]  American National Standards Institute, "Coded Character
              Set
   all "message" types regarding line length and encodings.

   Type name:  message

   Subtype name:  http

   Required parameters:  none

   Optional parameters:  version, msgtype
      version:  The HTTP-Version number of the enclosed message (e.g.,
         "1.1").  If not present, the version can be determined from the
         first line of the body.

      msgtype:  The message type -- 7-bit American Standard Code for Information
              Interchange", ANSI X3.4, 1986.

12.2.  Informative References

   [Kri2001]  Kristol, D., "HTTP Cookies: Standards, Privacy, "request" or "response".  If not
         present, the type can be determined from the first line of the
         body.

   Encoding considerations:  only "7bit", "8bit", or "binary" are
      permitted

   Security considerations:  none

   Interoperability considerations:  none

   Published specification:  This specification (see Section 10.3.1).

   Applications that use this media type:

   Additional information:

      Magic number(s):  none

      File extension(s):  none

      Macintosh file type code(s):  none

   Person and
              Politics", ACM Transactions email address to contact for further information:  See
      Authors Section.

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author/Change controller:  IESG

10.3.2.  Internet Technology Vol. 1,
              #2, November 2001, <http://arxiv.org/abs/cs.SE/0105018>.

   [Nie1997]  Nielsen, H., Gettys, J., Prud'hommeaux, E., Lie, H., and
              C. Lilley, "Network Performance Effects Media Type application/http

   The application/http type can be used to enclose a pipeline of HTTP/1.1, CSS1,
              and PNG", ACM Proceedings one or
   more HTTP request or response messages (not intermixed).

   Type name:  application

   Subtype name:  http
   Required parameters:  none

   Optional parameters:  version, msgtype

      version:  The HTTP-Version number of the ACM SIGCOMM '97
              conference on Applications, technologies, architectures,
              and protocols for computer communication SIGCOMM '97,
              September 1997,
              <http://doi.acm.org/10.1145/263105.263157>.

   [Pad1995]  Padmanabhan, V. and J. Mogul, "Improving enclosed messages (e.g.,
         "1.1").  If not present, the version can be determined from the
         first line of the body.

      msgtype:  The message type -- "request" or "response".  If not
         present, the type can be determined from the first line of the
         body.

   Encoding considerations:  HTTP Latency",
              Computer Networks messages enclosed by this type are in
      "binary" format; use of an appropriate Content-Transfer-Encoding
      is required when transmitted via E-mail.

   Security considerations:  none

   Interoperability considerations:  none

   Published specification:  This specification (see Section 10.3.2).

   Applications that use this media type:

   Additional information:

      Magic number(s):  none

      File extension(s):  none

      Macintosh file type code(s):  none

   Person and ISDN Systems v. 28, pp. 25-35,
              December 1995,
              <http://portal.acm.org/citation.cfm?id=219094>.

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

   [RFC1305]  Mills, D., "Network Time Protocol (Version 3)
              Specification, Implementation", RFC 1305, March 1992.

   [RFC1900]  Carpenter, B. and Y. Rekhter, "Renumbering Needs Work",
              RFC 1900, February 1996.

   [RFC1945]  Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext further information:  See
      Authors Section.

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author/Change controller:  IESG

10.4.  Transfer Coding Registry

   The registration procedure for HTTP Transfer Codings is now defined
   by Section 6.2.3 of this document.

   The HTTP Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format Codings Registry located at
   <http://www.iana.org/assignments/http-parameters> should be updated
   with the registrations below:

   +----------+--------------------------------------+-----------------+
   | Name     | Description                          | Reference       |
   +----------+--------------------------------------+-----------------+
   | chunked  | Transfer in a series of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2047]  Moore, K., "MIME (Multipurpose Internet Mail Extensions)
              Part Three: Message Header Extensions chunks       | Section 6.2.1   |
   | compress | UNIX "compress" program method       | Section 6.2.2.1 |
   | deflate  | "zlib" format [RFC1950] with         | Section 6.2.2.2 |
   |          | "deflate" compression                |                 |
   | gzip     | Same as GNU zip [RFC1952]            | Section 6.2.2.3 |
   +----------+--------------------------------------+-----------------+

10.5.  Upgrade Token Registration

   The registration procedure for Non-ASCII Text",
              RFC 2047, November 1996.

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

   [RFC2109]  Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2109, February 1997.

   [RFC2145]  Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, "Use
              and Interpretation previously
   defined in Section 7.2 of [RFC2817] -- is now defined by
   Section 9.8.1 of this document.

   The HTTP Version Numbers", RFC 2145,
              May 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Status Code Registry located at
   <http://www.iana.org/assignments/http-upgrade-tokens/> should be
   updated with the registration below:

   +-------+---------------------------+-------------------------------+
   | Value | Description               | Reference                     |
   +-------+---------------------------+-------------------------------+
   | HTTP  | Hypertext Transfer        | Section 2.5 of this           |
   |       | Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC2965]  Kristol, D.                  | specification                 |
   +-------+---------------------------+-------------------------------+

11.  Security Considerations

   This section is meant to inform application developers, information
   providers, and L. Montulli, "HTTP State Management
              Mechanism", RFC 2965, October 2000.

   [RFC3864]  Klyne, G., Nottingham, M., 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.  Personal Information

   HTTP clients are often privy to large amounts of personal information
   (e.g. the user's name, location, mail address, passwords, encryption
   keys, etc.), and J. Mogul, "Registration
              Procedures SHOULD be very careful to prevent unintentional
   leakage of this information.  We very strongly recommend that a
   convenient interface be provided for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

   [RFC4288]  Freed, N. the user to control
   dissemination of such information, and J. Klensin, "Media Type Specifications that designers and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC4395]  Hansen, T., Hardie, T.,
   implementors be particularly careful in this area.  History shows
   that errors in this area often create serious security and/or privacy
   problems and L. Masinter, "Guidelines generate highly adverse publicity for the implementor's
   company.

11.2.  Abuse of Server Log Information

   A server is in the position to save personal data about a user's
   requests which might identify their reading patterns or subjects of
   interest.  This information is clearly confidential in nature and
              Registration Procedures its
   handling can be constrained by law in certain countries.  People
   using HTTP to provide data are responsible for New URI Schemes", BCP 115,
              RFC 4395, February 2006.

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

   [Spe]      Spero, S., "Analysis ensuring that such
   material is not distributed without the permission of HTTP Performance Problems",
              <http://sunsite.unc.edu/mdma-release/http-prob.html>.

   [Tou1998]  Touch, J., Heidemann, J., any individuals
   that are identifiable by the published results.

11.3.  Attacks Based On File and K. Obraczka, "Analysis Path Names

   Implementations of HTTP Performance", ISI Research Report ISI/RR-98-463,
              Aug 1998, <http://www.isi.edu/touch/pubs/http-perf96/>.

              (original report dated Aug. 1996)

Appendix A.  Tolerant Applications

   Although this document specifies origin servers SHOULD be careful to restrict
   the requirements for documents returned by HTTP requests to be only those that were
   intended by the generation
   of HTTP/1.1 messages, server administrators.  If an HTTP server translates
   HTTP URIs directly into file system calls, the server MUST take
   special care not all applications will be correct in their
   implementation.  We therefore recommend to serve files that operational applications were not intended to be tolerant of deviations whenever
   delivered to HTTP clients.  For example, UNIX, Microsoft Windows, and
   other operating systems use ".." as a path component to indicate a
   directory level above the current one.  On such a system, an HTTP
   server MUST disallow any such construct in the request-target if it
   would otherwise allow access to a resource outside those deviations can intended to
   be
   interpreted unambiguously. accessible via the HTTP server.  Similarly, files intended for
   reference only internally to the server (such as access control
   files, configuration files, and script code) MUST be protected from
   inappropriate retrieval, since they might contain sensitive
   information.  Experience has shown that minor bugs in such HTTP
   server implementations have turned into security risks.

11.4.  DNS Spoofing

   Clients using HTTP rely heavily on the Domain Name Service, and are
   thus generally prone to security attacks based on the deliberate mis-
   association of IP addresses and DNS names.  Clients SHOULD need to be tolerant
   cautious in parsing the Status-Line and servers
   tolerant when parsing assuming the Request-Line. continuing validity of an IP number/DNS name
   association.

   In particular, they HTTP clients SHOULD
   accept any amount of WSP characters between fields, even though only
   a single SP is required.

   The line terminator rely on their name resolver for message-header fields is
   confirmation of an IP number/DNS name association, rather than
   caching the sequence CRLF.
   However, we recommend that applications, result of previous host name lookups.  Many platforms
   already can cache host name lookups locally when parsing such headers,
   recognize a single LF as a line terminator appropriate, and ignore the leading CR.

   The character set of an entity-body
   they SHOULD be labeled as configured to do so.  It is proper for these lookups
   to be cached, however, only when the lowest
   common denominator of TTL (Time To Live) information
   reported by the character codes used within name server makes it likely that body, with the exception that not labeling cached
   information will remain useful.

   If HTTP clients cache the entity results of host name lookups in order to
   achieve a performance improvement, they MUST observe the TTL
   information reported by DNS.

   If HTTP clients do not observe this rule, they could be spoofed when
   a previously-accessed server's IP address changes.  As network
   renumbering is preferred over labeling expected to become increasingly common [RFC1900], the entity with
   possibility of this form of attack will grow.  Observing this
   requirement thus reduces this potential security vulnerability.

   This requirement also improves the labels US-ASCII or ISO-8859-1.  See [Part3].

   Additional rules load-balancing behavior of clients
   for requirements on parsing replicated servers using the same DNS name and encoding reduces the
   likelihood of dates a user's experiencing failure in accessing sites which
   use that strategy.

11.5.  Proxies and other potential problems with date encodings include:

   o  HTTP/1.1 clients Caching

   By their very nature, HTTP proxies are men-in-the-middle, and caches SHOULD assume that
   represent an RFC-850 date opportunity for man-in-the-middle attacks.  Compromise
   of the systems on which appears to be more than 50 years in the future is proxies run can result in fact serious
   security and privacy problems.  Proxies have access to security-
   related information, personal information about individual users and
   organizations, and proprietary information belonging to users and
   content providers.  A compromised proxy, or a proxy implemented or
   configured without regard to security and privacy considerations,
   might be used in the past (this helps solve the "year 2000" problem).

   o  An HTTP/1.1 implementation MAY internally represent commission of a parsed
      Expires date as earlier than wide range of potential attacks.

   Proxy operators should protect the proper value, but MUST NOT
      internally represent a parsed Expires date systems on which proxies run as later than the
      proper value.

   o  All expiration-related calculations MUST
   they would protect any system that contains or transports sensitive
   information.  In particular, log information gathered at proxies
   often contains highly sensitive personal information, and/or
   information about organizations.  Log information should be done in GMT.  The
      local time zone MUST NOT influence carefully
   guarded, and appropriate guidelines for use developed and followed.
   (Section 11.2).

   Proxy implementors should consider the privacy and security
   implications of their design and coding decisions, and of the
   configuration options they provide to proxy operators (especially the calculation or comparison
   default configuration).

   Users of an age or expiration time.

   o  If an HTTP header incorrectly carries a date value with a time
      zone other than GMT, it MUST proxy need to be converted into GMT using aware that they are no trustworthier than
   the most
      conservative possible conversion.

Appendix B.  Compatibility with Previous Versions

   HTTP has been in use by people who run the World-Wide Web global information
   initiative since 1990. proxy; HTTP itself cannot solve this problem.

   The first version judicious use of HTTP, later referred cryptography, when appropriate, may suffice to
   as HTTP/0.9, was a simple protocol for hypertext data transfer across
   the Internet with only a single method and no metadata.  HTTP/1.0, as
   defined by [RFC1945], added
   protect against a broad range of request methods security and MIME-like
   messaging that could include metadata about privacy attacks.  Such
   cryptography is beyond the data transferred scope of the HTTP/1.1 specification.

11.6.  Denial of Service Attacks on Proxies

   They exist.  They are hard to defend against.  Research continues.
   Beware.

12.  Acknowledgments

   HTTP has evolved considerably over the years.  It has benefited from
   a large and
   modifiers active developer community--the many people who have
   participated on the request/response semantics.  However, HTTP/1.0 did
   not sufficiently take into consideration www-talk mailing list--and it is that community
   which has been most responsible for the effects success of HTTP and of the
   World-Wide Web in general.  Marc Andreessen, Robert Cailliau, Daniel
   W. Connolly, Bob Denny, John Franks, Jean-Francois Groff, Phillip M.
   Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli,
   Dave Raggett, Tony Sanders, and Marc VanHeyningen deserve special
   recognition for their efforts in defining early aspects of hierarchical
   proxies, caching, the need for persistent connections, or name-based
   virtual hosts.  The proliferation
   protocol.

   This document has benefited greatly from the comments of incompletely-implemented
   applications calling themselves "HTTP/1.0" further necessitated a
   protocol version change all those
   participating in order for two communicating applications the HTTP-WG.  In addition to determine each other's true capabilities.

   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
   requirements that enable reliable implementations, adding only those
   new features that will either be safely ignored by an HTTP/1.0
   recipient or only sent when communicating with a party advertising
   compliance already
   mentioned, the following individuals have contributed to this
   specification:

   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc
   Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann, Bob Jernigan, Shel
   Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut,
   David M. Kristol, Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert
   Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David
   Morris, Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott
   Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich
   Salz, Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
   Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart)
   Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen.

   Thanks to the "cave men" of Palo Alto.  You know who you are.

   Jim Gettys (the editor of [RFC2616]) wishes particularly to thank Roy
   Fielding, the editor of [RFC2068], along with HTTP/1.1.

   It is beyond John Klensin, Jeff
   Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh
   Cohen, Alex Hopmann, Scott Lawrence, and Larry Masinter for their
   help.  And thanks go particularly to Jeff Mogul and Scott Lawrence
   for performing the scope "MUST/MAY/SHOULD" audit.

   The Apache Group, Anselm Baird-Smith, author of a protocol specification to mandate
   compliance with previous versions.  HTTP/1.1 was deliberately
   designed, however, Jigsaw, and Henrik
   Frystyk implemented RFC 2068 early, and we wish to make supporting previous versions easy.  It is
   worth noting that, at thank them for the time
   discovery of composing many of the problems that this document attempts to
   rectify.

   This specification
   (1996), we would expect commercial HTTP/1.1 servers to:

   o  recognize makes heavy use of the format augmented BNF and generic
   constructs defined by David H. Crocker for [RFC5234].  Similarly, it
   reuses many of the Request-Line definitions provided by Nathaniel Borenstein and
   Ned Freed for HTTP/0.9, 1.0, MIME [RFC2045].  We hope that their inclusion in this
   specification will help reduce past confusion over the relationship
   between HTTP and Internet mail message formats.

13.  References

13.1.  Normative References

   [ISO-8859-1]
              International Organization for Standardization,
              "Information technology -- 8-bit single-byte coded graphic
              character sets -- Part 1: Latin alphabet No. 1", ISO/
              IEC 8859-1:1998, 1998.

   [Part2]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              and J. Reschke, Ed., "HTTP/1.1, part 2: Message
              Semantics", draft-ietf-httpbis-p2-semantics-08 (work in
              progress), October 2009.

   [Part3]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload
              and Content Negotiation", draft-ietf-httpbis-p3-payload-08
              (work in progress), October 2009.

   [Part5]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              and
      1.1 requests;

   o  understand any valid request J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
              Partial Responses", draft-ietf-httpbis-p5-range-08 (work
              in the format of HTTP/0.9, 1.0, or
      1.1;

   o  respond appropriately with a message progress), October 2009.

   [Part6]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
              Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part
              6: Caching", draft-ietf-httpbis-p6-cache-08 (work in the same major
              progress), October 2009.

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

              RFC 1950 is an Informational RFC, thus it may be less
              stable than this specification.  On the client.

   And we would expect HTTP/1.1 clients to:

   o  recognize other hand, this
              downward reference was present since the format publication of the Status-Line for HTTP/1.0 and 1.1
      responses;

   o  understand any valid response
              RFC 2068 in the format of HTTP/0.9, 1.0, or
      1.1.

   For most implementations of HTTP/1.0, each connection 1997 ([RFC2068]), therefore it is established
   by the client prior unlikely to the request and closed by the server after
   sending the response.  Some implementations implement the Keep-Alive
   version of persistent connections described
              cause problems in Section 19.7.1 of
   [RFC2068].

B.1.  Changes from HTTP/1.0

   This section summarizes major differences between versions HTTP/1.0
   and HTTP/1.1.

B.1.1.  Changes to Simplify Multi-homed Web Servers and Conserve IP
        Addresses

   The requirements that clients and servers support the Host request-
   header, report an error if the Host request-header (Section 8.4) is
   missing from an HTTP/1.1 request, and accept absolute URIs
   (Section 5.1.2) are among the most important changes defined by practice.  See also [BCP97].

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

              RFC 1951 is an Informational RFC, thus it may be less
              stable than this specification.

   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
   addresses and servers; there was no  On the other established mechanism for
   distinguishing hand, this
              downward reference was present since the intended server publication of a request
              RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to
              cause problems in practice.  See also [BCP97].

   [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.

              RFC 1952 is an Informational RFC, thus it may be less
              stable than this specification.  On the IP address
   to which that request other hand, this
              downward reference was directed.  The changes outlined above will
   allow present since the Internet, once older HTTP clients are no longer common, to
   support multiple Web sites from a single IP address, greatly
   simplifying large operational Web servers, where allocation publication of many
   IP addresses
              RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to a single host has created serious problems.  The
   Internet will
              cause problems in practice.  See also be able [BCP97].

   [RFC2119]  Bradner, S., "Key words for use in RFCs to recover the IP addresses that have been
   allocated Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for the sole purpose of allowing special-purpose domain
   names Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [USASCII]  American National Standards Institute, "Coded Character
              Set -- 7-bit American Standard Code for Information
              Interchange", ANSI X3.4, 1986.

13.2.  Informative References

   [BCP97]    Klensin, J. and S. Hartman, "Handling Normative References
              to be used in root-level HTTP URLs.  Given the rate Standards-Track Documents", BCP 97, RFC 4897,
              June 2007.

   [Kri2001]  Kristol, D., "HTTP Cookies: Standards, Privacy, and
              Politics", ACM Transactions on Internet Technology Vol. 1,
              #2, November 2001, <http://arxiv.org/abs/cs.SE/0105018>.

   [Nie1997]  Nielsen, H., Gettys, J., Prud'hommeaux, E., Lie, H., and
              C. Lilley, "Network Performance Effects of growth HTTP/1.1, CSS1,
              and PNG", ACM Proceedings of the Web, ACM SIGCOMM '97
              conference on Applications, technologies, architectures,
              and the number protocols for computer communication SIGCOMM '97,
              September 1997,
              <http://doi.acm.org/10.1145/263105.263157>.

   [Pad1995]  Padmanabhan, V. and J. Mogul, "Improving HTTP Latency",
              Computer Networks and ISDN Systems v. 28, pp. 25-35,
              December 1995,
              <http://portal.acm.org/citation.cfm?id=219094>.

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

   [RFC1305]  Mills, D., "Network Time Protocol (Version 3)
              Specification, Implementation", RFC 1305, March 1992.

   [RFC1900]  Carpenter, B. and Y. Rekhter, "Renumbering Needs Work",
              RFC 1900, February 1996.

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

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of servers already deployed, it is
   extremely important that all implementations Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2047]  Moore, K., "MIME (Multipurpose Internet Mail Extensions)
              Part Three: Message Header Extensions for Non-ASCII Text",
              RFC 2047, 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.

   [RFC2109]  Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2109, February 1997.

   [RFC2145]  Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, "Use
              and Interpretation of HTTP (including
   updates to existing HTTP/1.0 applications) correctly implement these
   requirements:

   o  Both clients Version Numbers", RFC 2145,
              May 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and servers MUST support the Host request-header.

   o  A client that sends an HTTP/1.1 request MUST send a Host header.

   o  Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
      request does not include a Host request-header.

   o  Servers MUST accept absolute URIs.

B.2.  Compatibility with HTTP/1.0 Persistent Connections

   Some clients T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2817]  Khare, R. and servers might wish S. Lawrence, "Upgrading to be compatible with some
   previous implementations of persistent connections in HTTP/1.0
   clients TLS Within
              HTTP/1.1", RFC 2817, May 2000.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC2965]  Kristol, D. and servers.  Persistent connections L. Montulli, "HTTP State Management
              Mechanism", RFC 2965, October 2000.

   [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.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 115,
              RFC 4395, February 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in HTTP/1.0 are
   explicitly negotiated as they are not the default behavior.  HTTP/1.0
   experimental implementations RFCs", BCP 26, RFC 5226,
              May 2008.

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

   [Spe]      Spero, S., "Analysis of persistent connections are faulty, HTTP Performance Problems",
              <http://sunsite.unc.edu/mdma-release/http-prob.html>.

   [Tou1998]  Touch, J., Heidemann, J., and K. Obraczka, "Analysis of
              HTTP Performance", ISI Research Report ISI/RR-98-463,
              Aug 1998, <http://www.isi.edu/touch/pubs/http-perf96/>.

              (original report dated Aug. 1996)

Appendix A.  Tolerant Applications

   Although this document specifies the new facilities in requirements for the generation
   of HTTP/1.1 are designed to rectify these
   problems.  The problem was that some existing 1.0 clients may messages, not all applications will be
   sending Keep-Alive to a proxy server correct in their
   implementation.  We therefore recommend that doesn't understand
   Connection, which would then erroneously forward it to the next
   inbound server, which would establish operational applications
   be tolerant of deviations whenever those deviations can be
   interpreted unambiguously.

   Clients SHOULD be tolerant in parsing the Keep-Alive connection Status-Line and
   result in servers
   tolerant when parsing the Request-Line.  In particular, they SHOULD
   accept any amount of WSP characters between fields, even though only
   a hung HTTP/1.0 proxy waiting single SP is required.

   The line terminator for header fields is the close on sequence CRLF.  However,
   we recommend that applications, when parsing such headers, recognize
   a single LF as a line terminator and ignore the
   response. leading CR.

   The result is that HTTP/1.0 clients must character set of an entity-body SHOULD be prevented from
   using Keep-Alive when talking to proxies.

   However, talking to proxies is labeled as the most important use lowest
   common denominator of persistent
   connections, so the character codes used within that prohibition is clearly unacceptable.  Therefore,
   we need some other mechanism for indicating a persistent connection
   is desired, which is safe to use even when talking to an old proxy body, with
   the exception that ignores Connection.  Persistent connections are not labeling the entity is preferred over labeling
   the default for
   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
   declaring non-persistence. entity with the labels US-ASCII or ISO-8859-1.  See Section 8.1.

   The original HTTP/1.0 form of persistent connections (the Connection:
   Keep-Alive [Part3].

   Additional rules for requirements on parsing and Keep-Alive header) is documented in Section 19.7.1 encoding of
   [RFC2068].

B.3.  Changes from RFC 2068

   This specification has been carefully audited to correct dates
   and
   disambiguate key word usage; RFC 2068 had many other potential problems in respect with date encodings include:

   o  HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
      which appears to be more than 50 years in the conventions laid out future is in [RFC2119].

   Transfer-coding and message lengths all interact fact in ways that
   required fixing exactly when chunked encoding is used (to allow for
   transfer encoding that may not
      the past (this helps solve the "year 2000" problem).

   o  An HTTP/1.1 implementation MAY internally represent a parsed
      Expires date as earlier than the proper value, but MUST NOT
      internally represent a parsed Expires date as later than the
      proper value.

   o  All expiration-related calculations MUST be self delimiting); it was important
   to straighten out exactly how message lengths are computed.
   (Sections 3.3, 4.4, 8.2, see also [Part3], [Part5] and [Part6]) done in GMT.  The use and interpretation
      local time zone MUST NOT influence the calculation or comparison
      of an age or expiration time.

   o  If an HTTP header incorrectly carries a date value with a time
      zone other than GMT, it MUST be converted into GMT using the most
      conservative possible conversion.

Appendix B.  Compatibility with Previous Versions

   HTTP version numbers has been clarified in use by [RFC2145].  Require proxies to upgrade requests to highest
   protocol the World-Wide Web global information
   initiative since 1990.  The first version they support to deal with problems discovered in
   HTTP/1.0 implementations (Section 3.1)

   Quality Values of zero should indicate that "I don't want something"
   to allow clients HTTP, later referred to refuse a representation.  (Section 3.5)

   Transfer-coding had significant problems, particularly with
   interactions with chunked encoding.  The solution is that transfer-
   codings become
   as full fledged as content-codings.  This involves
   adding an IANA registry for transfer-codings (separate from content
   codings), HTTP/0.9, was a new header field (TE) and enabling trailer headers in simple protocol for hypertext data transfer across
   the
   future.  Transfer encoding is a major performance benefit, so it was
   worth fixing [Nie1997].  TE also solves another, obscure, downward
   interoperability problem that could have occurred due to interactions
   between authentication trailers, chunked encoding and HTTP/1.0
   clients.(Section 3.3, 3.3.1, and 8.5)

B.4.  Changes from RFC 2616

   Empty list elements in list productions have been deprecated.
   (Section 1.2.1)

   Rules about implicit linear whitespace between certain grammar
   productions have been removed; now it's Internet with only allowed when
   specifically pointed out in the ABNF.  The NUL character is no longer
   allowed in comment a single method and quoted-string text.  The quoted-pair rule no
   longer allows escaping NUL, CR or LF.  Non-ASCII content in header
   fields and reason phrase has been obsoleted and made opaque (the TEXT
   rule was removed) (Section 1.2.2)

   Clarify that HTTP-Version is case sensitive.  (Section 3.1)

   Remove reference to non-existant identity transfer-coding value
   tokens.  (Sections 3.3 metadata.  HTTP/1.0, as
   defined by [RFC1945], added a range of request methods and 4.4)

   Clarification MIME-like
   messaging that could include metadata about the chunk length does data transferred and
   modifiers on the request/response semantics.  However, HTTP/1.0 did
   not include sufficiently take into consideration the count effects of hierarchical
   proxies, caching, the
   octets need for persistent connections, or name-based
   virtual hosts.  The proliferation of incompletely-implemented
   applications calling themselves "HTTP/1.0" further necessitated a
   protocol version change in the chunk header and trailer.  (Section 3.3.1)

   Require order for two communicating applications
   to determine each other's true capabilities.

   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
   requirements that invalid whitespace around field-names enable reliable implementations, adding only those
   new features that will either be rejected.
   (Section 4.2)

   Update use of abs_path production from RFC1808 to the path-absolute +
   query components of RFC3986.  (Section 5.1.2)

   Clarify exactly safely ignored by an HTTP/1.0
   recipient or only sent when close connection options must be sent.
   (Section 8.1)

Appendix C.  Terminology

   This specification uses communicating with a number party advertising
   compliance with HTTP/1.1.

   It is beyond the scope of terms a protocol specification to refer mandate
   compliance with previous versions.  HTTP/1.1 was deliberately
   designed, however, to make supporting previous versions easy.  It is
   worth noting that, at the roles
   played by participants in, and objects of, time of composing this specification, we
   would expect general-purpose HTTP/1.1 servers to:

   o  understand any valid request in the HTTP communication.

   cache

      A program's local store format of response messages HTTP/1.0 and the subsystem
      that controls its 1.1;

   o  respond appropriately with a message storage, retrieval, and deletion.  A
      cache stores cacheable responses in order to reduce the response
      time and network bandwidth consumption on future, equivalent
      requests.  Any client or server may include a cache, though a
      cache cannot be same major version
      used by a server that is acting as a tunnel.

   cacheable

      A the client.

   And we would expect HTTP/1.1 clients to:

   o  understand any valid response in the format of HTTP/1.0 or 1.1.

   For most implementations of HTTP/1.0, each connection is cacheable if a cache is allowed established
   by the client prior to store a copy of the response message for use in answering subsequent requests.
      The rules for determining request and closed by the server after
   sending the cacheability response.  Some implementations implement the Keep-Alive
   version of HTTP responses are
      defined persistent connections described in Section 1 19.7.1 of [Part6].  Even
   [RFC2068].

B.1.  Changes from HTTP/1.0

   This section summarizes major differences between versions HTTP/1.0
   and HTTP/1.1.

B.1.1.  Changes to Simplify Multi-homed Web Servers and Conserve IP
        Addresses

   The requirements that clients and servers support the Host request-
   header, report an error if a resource the Host request-header (Section 9.4) is cacheable,
      there may be additional constraints on whether a cache can use
   missing from an HTTP/1.1 request, and accept absolute URIs
   (Section 4.1.2) are among the
      cached copy for most important changes defined by this
   specification.

   Older HTTP/1.0 clients assumed a particular request.

   client

      A program that establishes connections for the purpose one-to-one relationship of sending
      requests.

   connection

      A transport layer virtual circuit IP
   addresses and servers; there was no other established between two programs mechanism for
   distinguishing the purpose intended server of a request than the IP address
   to which that request was directed.  The changes outlined above will
   allow the Internet, once older HTTP clients are no longer common, to
   support multiple Web sites from a single IP address, greatly
   simplifying large operational Web servers, where allocation of communication.

   content negotiation many
   IP addresses to a single host has created serious problems.  The mechanism
   Internet will also be able to recover the IP addresses that have been
   allocated for selecting the appropriate representation when
      servicing a request, as described in Section 4 of [Part3].  The
      representation sole purpose of entities in any response can allowing special-purpose domain
   names to be negotiated
      (including error responses).

   entity

      The information transferred as used in root-level HTTP URLs.  Given the payload rate of a request or
      response.  An entity consists growth
   of metainformation in the form of
      entity-header fields Web, and content in the form number of an entity-body, as
      described in Section 3 servers already deployed, it is
   extremely important that all implementations of [Part3].

   gateway HTTP (including
   updates to existing HTTP/1.0 applications) correctly implement these
   requirements:

   o  Both clients and servers MUST support the Host request-header.

   o  A server which acts as client that sends an intermediary for some other server.
      Unlike HTTP/1.1 request MUST send a proxy, Host header.

   o  Servers MUST report a gateway receives requests as 400 (Bad Request) error if it were the
      origin server for the requested resource; the requesting client
      may an HTTP/1.1
      request does not be aware that it is communicating with include a gateway.

   inbound/outbound

      Inbound Host request-header.

   o  Servers MUST accept absolute URIs.

B.2.  Compatibility with HTTP/1.0 Persistent Connections

   Some clients and outbound refer servers might wish to the request and response paths for
      messages: "inbound" means "traveling toward the origin server",
      and "outbound" means "traveling toward the user agent"

   message

      The basic unit of HTTP communication, consisting of a structured
      sequence be compatible with some
   previous implementations of octets matching persistent connections in HTTP/1.0
   clients and servers.  Persistent connections in HTTP/1.0 are
   explicitly negotiated as they are not the syntax defined in Section 4 default behavior.  HTTP/1.0
   experimental implementations of persistent connections are faulty,
   and
      transmitted via the connection.

   origin server new facilities in HTTP/1.1 are designed to rectify these
   problems.  The problem was that some existing 1.0 clients may be
   sending Keep-Alive to a proxy server on that doesn't understand
   Connection, which a given resource resides or is would then erroneously forward it to be created.

   proxy

      An intermediary program the next
   inbound server, which acts as both a server would establish the Keep-Alive connection and
   result in a client hung HTTP/1.0 proxy waiting for the purpose of making requests close on behalf of other clients.
      Requests are serviced internally or by passing them on, with
      possible translation, to other servers.  A proxy MUST implement
      both the client and server requirements of this specification.  A
      "transparent proxy"
   response.  The result is a proxy that does not modify HTTP/1.0 clients must be prevented from
   using Keep-Alive when talking to proxies.

   However, talking to proxies is the request or
      response beyond what most important use of persistent
   connections, so that prohibition is required clearly unacceptable.  Therefore,
   we need some other mechanism for proxy authentication and
      identification.  A "non-transparent proxy" is indicating a proxy that
      modifies the request or response in order persistent connection
   is desired, which is safe to provide some added
      service use even when talking to the user agent, such as group annotation services,
      media type transformation, protocol reduction, or anonymity
      filtering.  Except where either transparent or non-transparent
      behavior is explicitly stated, the HTTP an old proxy requirements apply
      to both types of proxies.

   request

      An HTTP request message, as defined in Section 5.

   resource

      A network data object or service
   that can be identified by ignores Connection.  Persistent connections are the default for
   HTTP/1.1 messages; we introduce a URI,
      as defined in new keyword (Connection: close) for
   declaring non-persistence.  See Section 2.1.  Resources may be available in multiple
      representations (e.g. multiple languages, data formats, size, 9.1.

   The original HTTP/1.0 form of persistent connections (the Connection:
   Keep-Alive and
      resolutions) or vary in other ways.

   response

      An HTTP response message, as defined in Section 6.

   representation

      An entity included with a response that Keep-Alive header) is subject to content
      negotiation, as described documented in Section 4 19.7.1 of [Part3].  There may
      exist multiple representations associated with a particular
      response status.

   server

      An application program that accepts connections
   [RFC2068].

B.3.  Changes from RFC 2068

   This specification has been carefully audited to correct and
   disambiguate key word usage; RFC 2068 had many problems in order respect to
      service requests by sending back responses.  Any given program
   the conventions laid out in [RFC2119].

   Transfer-coding and message lengths all interact in ways that
   required fixing exactly when chunked encoding is used (to allow for
   transfer encoding that may not be capable of being both a client self delimiting); it was important
   to straighten out exactly how message lengths are computed.
   (Sections 6.2, 3.4, 9.2, see also [Part3], [Part5] and a server; our [Part6])

   The use and interpretation of these
      terms refers only to the role being performed HTTP version numbers has been clarified
   by the program [RFC2145].  Require proxies to upgrade requests to highest
   protocol version they support to deal with problems discovered in
   HTTP/1.0 implementations (Section 2.5)

   Quality Values of zero should indicate that "I don't want something"
   to allow clients to refuse a representation.  (Section 6.4)

   Transfer-coding had significant problems, particularly with
   interactions with chunked encoding.  The solution is that transfer-
   codings become as full fledged as content-codings.  This involves
   adding an IANA registry for transfer-codings (separate from content
   codings), a
      particular connection, rather than to the program's capabilities new header field (TE) and enabling trailer headers in general.  Likewise, any server may act as an origin server,
      proxy, gateway, or tunnel, switching behavior based on the nature
      of each request.

   tunnel

      An intermediary program which is acting as a blind relay between
      two connections.  Once active, a tunnel
   future.  Transfer encoding is not considered a party major performance benefit, so it was
   worth fixing [Nie1997].  TE also solves another, obscure, downward
   interoperability problem that could have occurred due to the HTTP communication, though the tunnel may interactions
   between authentication trailers, chunked encoding and HTTP/1.0
   clients.(Section 6.2, 6.2.1, and 9.5)

B.4.  Changes from RFC 2616

   Empty list elements in list productions have been
      initiated by an HTTP request.  The tunnel ceases to exist deprecated.
   (Section 1.2.1)

   Rules about implicit linear whitespace between certain grammar
   productions have been removed; now it's only allowed when
      both ends of
   specifically pointed out in the relayed connections are closed.

   upstream/downstream

      Upstream ABNF.  The NUL character is no longer
   allowed in comment and downstream describe the flow of a message: all
      messages flow from upstream to downstream.

   user agent quoted-string text.  The client which initiates a request.  These are often browsers,
      editors, spiders (web-traversing robots), or quoted-pair rule no
   longer allows escaping control characters other end user tools.

   variant

      A resource may have one, or more than one, representation(s)
      associated with it at any given instant.  Each HTAB.  Non-ASCII
   content in header fields and reason phrase has been obsoleted and
   made opaque (the TEXT rule was removed) (Section 1.2.2)

   Clarify that HTTP-Version is case sensitive.  (Section 2.5)

   Remove reference to non-existant identity transfer-coding value
   tokens.  (Sections 6.2 and 3.4)

   Require that invalid whitespace around field-names be rejected.
   (Section 3.2)
   Update use of these
      representations is termed a `variant'.  Use abs_path production from RFC1808 to the path-absolute +
   query components of RFC3986.  (Section 4.1.2)

   Clarification that the term `variant' chunk length does not necessarily imply that include the resource is subject to content
      negotiation. count of the
   octets in the chunk header and trailer.  Furthermore disallowed line
   folding in chunk extensions.  (Section 6.2.1)

   Remove hard limit of two connections per server.  (Section 7.1.4)

   Clarify exactly when close connection options must be sent.
   (Section 9.1)

Appendix D. C.  Collected ABNF

   BWS = OWS

   Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
   Chunked-Body = *chunk last-chunk trailer-part CRLF
   Connection = "Connection:" OWS Connection-v
   Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
    connection-token ] )
   Content-Length = "Content-Length:" OWS 1*Content-Length-v
   Content-Length-v = 1*DIGIT

   Date = "Date:" OWS Date-v
   Date-v = HTTP-date

   GMT = %x47.4D.54 ; GMT

   HTTP-Prot-Name = %x48.54.54.50 ; HTTP
   HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
   HTTP-date = rfc1123-date / obs-date
   HTTP-message = Request / Response start-line *( header-field CRLF ) CRLF [ message-body
    ]
   Host = "Host:" OWS Host-v
   Host-v = uri-host [ ":" port ]

   Method = token

   OWS = *( [ obs-fold ] WSP )

   Pragma = <Pragma, defined in [Part6], Section 3.4>

   RWS = 1*( [ obs-fold ] WSP )
   Reason-Phrase = *( WSP / VCHAR / obs-text )
   Request = Request-Line *( ( general-header / request-header /
    entity-header ) CRLF ) CRLF [ message-body ]

   Request-Line = Method SP request-target SP HTTP-Version CRLF
   Response = Status-Line *( ( general-header / response-header /
    entity-header ) CRLF ) CRLF [ message-body ]

   Status-Code = 3DIGIT
   Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF

   TE = "TE:" OWS TE-v
   TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
   Trailer = "Trailer:" OWS Trailer-v
   Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
   Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
   Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
    transfer-coding ] )

   URI = <URI, defined in [RFC3986], Section 3>
   URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
   Upgrade = "Upgrade:" OWS Upgrade-v
   Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )

   Via = "Via:" OWS Via-v
   Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
    ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
    ] )

   Warning = <Warning, defined in [Part6], Section 3.6>

   absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
   asctime-date = day-name SP date3 SP time-of-day SP year
   attribute = token
   authority = <authority, defined in [RFC3986], Section 3.2>

   chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
   chunk-data = 1*OCTET
   chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
   chunk-ext-name = token
   chunk-ext-val = token / quoted-string quoted-str-nf
   chunk-size = 1*HEXDIG
   comment = "(" *( ctext / quoted-pair quoted-cpair / comment ) ")"
   connection-token = token
   ctext = OWS / %x21-27 ; '!'-'''
    / %x2A-5B ; '*'-'['
    / %x5D-7E ; ']'-'~'
    / obs-text

   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

   entity-body = <entity-body, defined in [Part3], Section 3.2>
   entity-header = <entity-header, defined in [Part3], Section 3.1>

   field-content = *( WSP / VCHAR / obs-text )
   field-name = token
   field-value = *( field-content / OWS )
   fragment = <fragment, defined in [RFC3986], Section 3.5>

   general-header = Cache-Control / Connection / Date / Pragma / Trailer
    / Transfer-Encoding / Upgrade / Via / Warning
   generic-message

   header-field = start-line *( message-header CRLF ) CRLF field-name ":" OWS [
    message-body field-value ] OWS
   hour = 2DIGIT
   http-URI = "http://" authority path-abempty [ "?" query ]
   https-URI = "https://" authority path-abempty [ "?" query ]

   last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF

   message-body = entity-body /
    <entity-body encoded as per Transfer-Encoding>
   message-header = field-name ":" OWS [ field-value ] OWS
   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-fold = CRLF
   obs-text = %x80-FF

   partial-URI = relative-part [ "?" query ]
   path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
   path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
   port = <port, defined in [RFC3986], Section 3.2.3>
   product = token [ "/" product-version ]
   product-version = token
   protocol-name = token
   protocol-version = token
   pseudonym = token

   qdtext = OWS / "!" / %x23-5B ; '#'-'['
    / %x5D-7E ; ']'-'~'
    / obs-text
   qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
    / %x5D-7E ; ']'-'~'
    / obs-text
   query = <query, defined in [RFC3986], Section 3.4>
   quoted-cpair = "\" ( WSP / VCHAR / obs-text )
   quoted-pair = "\" quoted-text
   quoted-string ( WSP / VCHAR / obs-text )
   quoted-str-nf = DQUOTE *( qdtext qdtext-nf / quoted-pair ) DQUOTE
   quoted-text
   quoted-string = %x01-09 / %x0B-0C DQUOTE *( qdtext / %x0E-FF quoted-pair ) DQUOTE
   qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )

   received-by = ( uri-host [ ":" port ] ) / pseudonym
   received-protocol = [ protocol-name "/" ] protocol-version
   relative-part = <relative-part, defined in [RFC3986], Section 4.2>
   request-header = <request-header, defined in [Part2], Section 3>
   request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
    / authority
   response-header = <response-header, defined in [Part2], Section 5>
   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
   start-line = Request-Line / Status-Line

   t-codings = "trailers" / ( transfer-extension [ te-params ] )
   tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
    "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
   te-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
   te-params = OWS ";" OWS "q=" qvalue *te-ext
   time-of-day = hour ":" minute ":" second
   token = 1*tchar
   trailer-part = *( entity-header CRLF )
   transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
    transfer-extension
   transfer-extension = token *( OWS ";" OWS transfer-parameter )
   transfer-parameter = attribute BWS "=" BWS value

   uri-host = <host, defined in [RFC3986], Section 3.2.2>

   value = token / quoted-string

   year = 4DIGIT

   ABNF diagnostics:

   ; Chunked-Body defined but not used
   ; Content-Length defined but not used
   ; HTTP-message defined but not used
   ; Host defined but not used
   ; TE Request defined but not used
   ; URI Response defined but not used
   ; URI-reference TE defined but not used
   ; fragment URI defined but not used
   ; generic-message URI-reference defined but not used
   ; http-URI defined but not used
   ; https-URI defined but not used
   ; partial-URI defined but not used

Appendix E. D.  Change Log (to be removed by RFC Editor before publication)

E.1.

D.1.  Since RFC2616

   Extracted relevant partitions from [RFC2616].

E.2.

D.2.  Since draft-ietf-httpbis-p1-messaging-00

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/1>: "HTTP Version
      should be case sensitive"
      (<http://purl.org/NET/http-errata#verscase>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/2>: "'unsafe'
      characters" (<http://purl.org/NET/http-errata#unsafe-uri>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/3>: "Chunk Size
      Definition" (<http://purl.org/NET/http-errata#chunk-size>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/4>: "Message Length"
      (<http://purl.org/NET/http-errata#msg-len-chars>)

   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/11>: "URI includes
      query" (<http://purl.org/NET/http-errata#uriquery>)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/15>: "No close on
      1xx responses" (<http://purl.org/NET/http-errata#noclose1xx>)

   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/26>: "Import query
      BNF"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/31>: "qdtext BNF"

   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/45>: "RFC977
      reference"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700
      references"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/47>: "inconsistency
      in date format explanation"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/48>: "Date reference
      typo"

   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/86>: "Normative up-
      to-date references"

   Other changes:

   o  Update media type registrations to use RFC4288 template.

   o  Use names of RFC4234 core rules DQUOTE and WSP, fix broken ABNF
      for chunk-data (work in progress on
      <http://tools.ietf.org/wg/httpbis/trac/ticket/36>)

E.3.

D.3.  Since draft-ietf-httpbis-p1-messaging-01

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/19>: "Bodies on GET
      (and other) requests"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating to
      RFC4288"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/57>: "Status Code
      and Reason Phrase"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/82>: "rel_path not
      used"

   Ongoing work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Get rid of duplicate BNF rule names ("host" -> "uri-host",
      "trailer" -> "trailer-part").

   o  Avoid underscore character in rule names ("http_URL" -> "http-
      URL", "abs_path" -> "path-absolute").

   o  Add rules for terms imported from URI spec ("absoluteURI",
      "authority", "path-absolute", "port", "query", "relativeURI",
      "host) -- these will have to be updated when switching over to
      RFC3986.

   o  Synchronize core rules with RFC5234.

   o  Get rid of prose rules that span multiple lines.

   o  Get rid of unused rules LOALPHA and UPALPHA.

   o  Move "Product Tokens" section (back) into Part 1, as "token" is
      used in the definition of the Upgrade header.

   o  Add explicit references to BNF syntax and rules imported from
      other parts of the specification.

   o  Rewrite prose rule "token" in terms of "tchar", rewrite prose rule
      "TEXT".

E.4.

D.4.  Since draft-ietf-httpbis-p1-messaging-02

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/51>: "HTTP-date vs.
      rfc1123-date"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/64>: "WS in quoted-
      pair"

   Ongoing work on IANA Message Header Registration
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):

   o  Reference RFC 3984, and update header registrations for headers
      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
      (HTTP-Version).

E.5.

D.5.  Since draft-ietf-httpbis-p1-messaging-03

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/28>: "Connection
      closing"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/97>: "Move
      registrations and registry information to IANA Considerations"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/120>: "need new URL
      for PAD1995 reference"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/127>: "IANA
      Considerations: update HTTP URI scheme registration"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/128>: "Cite HTTPS
      URI scheme definition"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/129>: "List-type
      headers vs Set-Cookie"

   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
      (HTTP-Date).

   o  Replace HEX by HEXDIG for future consistence with RFC 5234's core
      rules.

E.6.

D.6.  Since draft-ietf-httpbis-p1-messaging-04

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/34>: "Out-of-date
      reference for URIs"

   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  Get rid of RFC822 dependency; use RFC5234 plus extensions instead.

   o  Only reference RFC 5234's core rules.

   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
      value format definitions.

E.7.

D.7.  Since draft-ietf-httpbis-p1-messaging-05

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/30>: "Header LWS"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/52>: "Sort 1.3
      Terminology"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/63>: "RFC2047
      encoded words"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/74>: "Character
      Encodings in TEXT"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/77>: "Line Folding"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/83>: "OPTIONS * and
      proxies"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/94>: "Reason-Phrase
      BNF"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/111>: "Use of TEXT"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/118>: "Join
      "Differences Between HTTP Entities and RFC 2045 Entities"?"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/134>: "RFC822
      reference left in discussion of date formats"

   Final work on ABNF conversion
   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):

   o  Rewrite definition of list rules, deprecate empty list elements.

   o  Add appendix containing collected and expanded ABNF.

   Other changes:

   o  Rewrite introduction; add mostly new Architecture Section.

   o  Move definition of quality values from Part 3 into Part 1; make TE
      request header grammar independent of accept-params (defined in
      Part 3).

E.8.

D.8.  Since draft-ietf-httpbis-p1-messaging-06

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/161>: "base for
      numeric protocol elements"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/162>: "comment ABNF"

   Partly resolved issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/88>: "205 Bodies"
      (took out language that implied that there may be methods for
      which a request body MUST NOT be included)

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/163>: "editorial
      improvements around HTTP-date"

D.9.  Since draft-ietf-httpbis-p1-messaging-07

   Closed issues:

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/93>: "Repeating
      single-value headers"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/131>: "increase
      connection limit"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/157>: "IP addresses
      in URLs"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/172>: "take over
      HTTP Upgrade Token Registry"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/173>: "CR and LF in
      chunk extension values"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/184>: "HTTP/0.9
      support"

   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"

   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/194>: "disallow
      control characters in quoted-pair"

   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)

Index

   A
      application/http Media Type  49  55

   C
      cache  61  12
      cacheable  62  13
      chunked (Coding Format)  32
      client  62  10
      Coding Format
         chunked  32
         compress  34
         deflate  35
         gzip  35
      compress (Coding Format)  34
      connection  62  10
      Connection header  39
      content negotiation  62  44
      Content-Length header  40  45

   D
      Date header  40  46
      deflate (Coding Format)  35
      downstream  64

   E
      entity  62  12

   G
      gateway  62  12
      Grammar
         absolute-URI  10  15
         ALPHA  7
         asctime-date  18  31
         attribute  18  31
         authority  10  15
         BWS  9
         chunk  20  33
         chunk-data  20  33
         chunk-ext  20  33
         chunk-ext-name  20  33
         chunk-ext-val  20  33
         chunk-size  20  33
         Chunked-Body  20  33
         comment  24  21
         Connection  39  44
         connection-token  39  44
         Connection-v  39  44
         Content-Length  40  45
         Content-Length-v  40  45
         CR  7
         CRLF  7
         ctext  24  21
         CTL  7
         Date  40  46
         Date-v  40  46
         date1  17  30
         date2  18  31
         date3  18  31
         day  17  30
         day-name  17  30
         day-name-l  17  30
         DIGIT  7
         DQUOTE  7
         extension-code  31
         extension-method  28
         extension-method  24
         field-content  23  19
         field-name  23  19
         field-value  23  19
         general-header  27
         generic-message  22  23
         GMT  17  30
         header-field  19
         HEXDIG  7
         Host  42  47
         Host-v  42  47
         hour  17  30
         HTTP-date  16  29
         HTTP-message  22  18
         HTTP-Prot-Name  14
         http-URI  11  16
         HTTP-Version  14
         https-URI  17
         last-chunk  20  33
         LF  7
         message-body  25
         message-header  23  21
         Method  28  24
         minute  17  30
         month  17  30
         obs-date  17  30
         obs-text  9
         OCTET  7
         OWS  9
         path-absolute  10  15
         port  10  15
         product  21  35
         product-version  21  35
         protocol-name  46  52
         protocol-version  46  52
         pseudonym  46  52
         qdtext  9
         qdtext-nf  33
         query  10  15
         quoted-cpair  21
         quoted-pair  9
         quoted-str-nf  33
         quoted-string  9
         quoted-text  9
         qvalue  22  36
         Reason-Phrase  31  28
         received-by  46  52
         received-protocol  46  52
         Request  27  24
         Request-Line  28  24
         request-target  28  24
         Response  31  27
         rfc850-date  18  31
         rfc1123-date  17  30
         RWS  9
         second  17  30
         SP  7
         start-line  22
         Status-Code  31  28
         Status-Line  31  27
         t-codings  42  48
         tchar  9
         TE  42  48
         te-ext  42  48
         te-params  42  48
         TE-v  42  48
         time-of-day  17  30
         token  9
         Trailer  44  49
         trailer-part  20  33
         Trailer-v  44  49
         transfer-coding  18  31
         Transfer-Encoding  44  50
         Transfer-Encoding-v  44  50
         transfer-extension  18  31
         transfer-parameter  18  31
         Upgrade  45  50
         Upgrade-v  45  50
         uri-host  10  15
         URI-reference  10  15
         value  18  31
         VCHAR  7
         Via  46  52
         Via-v  46  52
         WSP  7
         year  17  30
      gzip (Coding Format)  35

   H
      header field  18
      header section  18
      Headers
         Connection  39  44
         Content-Length  40  45
         Date  40  46
         Host  42  47
         TE  42  48
         Trailer  44  49
         Transfer-Encoding  44  49
         Upgrade  45  50
         Via  46  52
      headers  18
      Host header  42  47
      http URI scheme  11  16
      https URI scheme  11  17

   I
      inbound  62  12

   M
      Media Type
         application/http  49  55
         message/http  48  54
      message  63  10
      message/http Media Type  48  54

   O
      origin server  63  10
      outbound  62  12

   P
      proxy  63  12

   R
      representation  63
      request  63  10
      resource  63  15
      response  63  10
      reverse proxy  12

   S
      server  64  10

   T
      TE header  42  48
      Trailer header  44  49
      Transfer-Encoding header  44  49
      tunnel  64  12

   U
      Upgrade header  45  50
      upstream  64  12
      URI scheme
         http  11  16
         https  11  17
      user agent  64  10

   V
      variant  64
      Via header  46  52

Authors' Addresses

   Roy T. Fielding (editor)
   Day Software
   23 Corporate Plaza DR, Suite 280
   Newport Beach, CA  92660
   USA

   Phone: +1-949-706-5300
   Fax:   +1-949-706-5305
   Email: fielding@gbiv.com
   URI:   http://roy.gbiv.com/

   Jim Gettys
   One Laptop per Child
   21 Oak Knoll Road
   Carlisle, MA  01741
   USA

   Email: jg@laptop.org
   URI:   http://www.laptop.org/

   Jeffrey C. Mogul
   Hewlett-Packard Company
   HP Labs, Large Scale Systems Group
   1501 Page Mill Road, MS 1177
   Palo Alto, CA  94304
   USA

   Email: JeffMogul@acm.org
   Henrik Frystyk Nielsen
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA  98052
   USA

   Email: henrikn@microsoft.com

   Larry Masinter
   Adobe Systems, Incorporated
   345 Park Ave
   San Jose, CA  95110
   USA

   Email: LMM@acm.org
   URI:   http://larry.masinter.net/

   Paul J. Leach
   Microsoft Corporation
   1 Microsoft Way
   Redmond, WA  98052

   Email: paulle@microsoft.com

   Tim Berners-Lee
   World Wide Web Consortium
   MIT Computer Science and Artificial Intelligence Laboratory
   The Stata Center, Building 32
   32 Vassar Street
   Cambridge, MA  02139
   USA

   Email: timbl@w3.org
   URI:   http://www.w3.org/People/Berners-Lee/
   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/