draft-ietf-httpbis-p3-payload-10.txt   draft-ietf-httpbis-p3-payload-11.txt 
HTTPbis Working Group R. Fielding, Ed. HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Day Software Internet-Draft Day Software
Obsoletes: 2616 (if approved) J. Gettys Obsoletes: 2616 (if approved) J. Gettys
Intended status: Standards Track Alcatel-Lucent Intended status: Standards Track Alcatel-Lucent
Expires: January 13, 2011 J. Mogul Expires: February 5, 2011 J. Mogul
HP HP
H. Frystyk H. Frystyk
Microsoft Microsoft
L. Masinter L. Masinter
Adobe Systems Adobe Systems
P. Leach P. Leach
Microsoft Microsoft
T. Berners-Lee T. Berners-Lee
W3C/MIT W3C/MIT
Y. Lafon, Ed. Y. Lafon, Ed.
W3C W3C
J. Reschke, Ed. J. Reschke, Ed.
greenbytes greenbytes
July 12, 2010 August 4, 2010
HTTP/1.1, part 3: Message Payload and Content Negotiation HTTP/1.1, part 3: Message Payload and Content Negotiation
draft-ietf-httpbis-p3-payload-10 draft-ietf-httpbis-p3-payload-11
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World Wide Web global systems. HTTP has been in use by the World Wide Web global
information initiative since 1990. This document is Part 3 of the information initiative since 1990. This document is Part 3 of the
seven-part specification that defines the protocol referred to as seven-part specification that defines the protocol referred to as
"HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 3 defines "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 3 defines
HTTP message content, metadata, and content negotiation. HTTP message content, metadata, and content negotiation.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
Discussion of this draft should take place on the HTTPBIS working Discussion of this draft should take place on the HTTPBIS working
group mailing list (ietf-http-wg@w3.org). The current issues list is group mailing list (ietf-http-wg@w3.org). The current issues list is
at <http://tools.ietf.org/wg/httpbis/trac/report/3> and related at <http://tools.ietf.org/wg/httpbis/trac/report/3> and related
documents (including fancy diffs) can be found at documents (including fancy diffs) can be found at
<http://tools.ietf.org/wg/httpbis/>. <http://tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix E.11. The changes in this draft are summarized in Appendix E.12.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 13, 2011. This Internet-Draft will expire on February 5, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 48 skipping to change at page 2, line 48
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6 1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6 1.3. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
1.3.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 6 1.3.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2. ABNF Rules defined in other Parts of the 1.3.2. ABNF Rules defined in other Parts of the
Specification . . . . . . . . . . . . . . . . . . . . 6 Specification . . . . . . . . . . . . . . . . . . . . 6
2. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 7 2. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 6
2.1. Character Sets . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Character Sets . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1. Missing Charset . . . . . . . . . . . . . . . . . . . 8 2.1.1. Missing Charset . . . . . . . . . . . . . . . . . . . 7
2.2. Content Codings . . . . . . . . . . . . . . . . . . . . . 8 2.2. Content Codings . . . . . . . . . . . . . . . . . . . . . 8
2.2.1. Content Coding Registry . . . . . . . . . . . . . . . 9 2.2.1. Content Coding Registry . . . . . . . . . . . . . . . 9
2.3. Media Types . . . . . . . . . . . . . . . . . . . . . . . 9 2.3. Media Types . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1. Canonicalization and Text Defaults . . . . . . . . . . 10 2.3.1. Canonicalization and Text Defaults . . . . . . . . . . 10
2.3.2. Multipart Types . . . . . . . . . . . . . . . . . . . 11 2.3.2. Multipart Types . . . . . . . . . . . . . . . . . . . 11
2.4. Language Tags . . . . . . . . . . . . . . . . . . . . . . 12 2.4. Language Tags . . . . . . . . . . . . . . . . . . . . . . 11
3. Entity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3. Payload . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1. Entity Header Fields . . . . . . . . . . . . . . . . . . . 12 3.1. Payload Header Fields . . . . . . . . . . . . . . . . . . 12
3.2. Entity Body . . . . . . . . . . . . . . . . . . . . . . . 13 3.2. Payload Body . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.1. Type . . . . . . . . . . . . . . . . . . . . . . . . . 13 4. Representation . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.2. Entity Length . . . . . . . . . . . . . . . . . . . . 14 4.1. Representation Header Fields . . . . . . . . . . . . . . . 13
4. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 14 4.2. Representation Data . . . . . . . . . . . . . . . . . . . 13
4.1. Server-driven Negotiation . . . . . . . . . . . . . . . . 15 5. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 14
4.2. Agent-driven Negotiation . . . . . . . . . . . . . . . . . 16 5.1. Server-driven Negotiation . . . . . . . . . . . . . . . . 15
5. Header Field Definitions . . . . . . . . . . . . . . . . . . . 17 5.2. Agent-driven Negotiation . . . . . . . . . . . . . . . . . 16
5.1. Accept . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6. Header Field Definitions . . . . . . . . . . . . . . . . . . . 17
5.2. Accept-Charset . . . . . . . . . . . . . . . . . . . . . . 19 6.1. Accept . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.3. Accept-Encoding . . . . . . . . . . . . . . . . . . . . . 20 6.2. Accept-Charset . . . . . . . . . . . . . . . . . . . . . . 19
5.4. Accept-Language . . . . . . . . . . . . . . . . . . . . . 21 6.3. Accept-Encoding . . . . . . . . . . . . . . . . . . . . . 20
5.5. Content-Encoding . . . . . . . . . . . . . . . . . . . . . 22 6.4. Accept-Language . . . . . . . . . . . . . . . . . . . . . 21
5.6. Content-Language . . . . . . . . . . . . . . . . . . . . . 23 6.5. Content-Encoding . . . . . . . . . . . . . . . . . . . . . 22
5.7. Content-Location . . . . . . . . . . . . . . . . . . . . . 24 6.6. Content-Language . . . . . . . . . . . . . . . . . . . . . 23
5.8. Content-MD5 . . . . . . . . . . . . . . . . . . . . . . . 25 6.7. Content-Location . . . . . . . . . . . . . . . . . . . . . 24
5.9. Content-Type . . . . . . . . . . . . . . . . . . . . . . . 26 6.8. Content-MD5 . . . . . . . . . . . . . . . . . . . . . . . 25
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 6.9. Content-Type . . . . . . . . . . . . . . . . . . . . . . . 27
6.1. Message Header Registration . . . . . . . . . . . . . . . 26 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
6.2. Content Coding Registry . . . . . . . . . . . . . . . . . 27 7.1. Header Field Registration . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 27 7.2. Content Coding Registry . . . . . . . . . . . . . . . . . 27
7.1. Privacy Issues Connected to Accept Headers . . . . . . . . 28 8. Security Considerations . . . . . . . . . . . . . . . . . . . 28
7.2. Content-Disposition Issues . . . . . . . . . . . . . . . . 28 8.1. Privacy Issues Connected to Accept Headers . . . . . . . . 28
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29 8.2. Content-Disposition Issues . . . . . . . . . . . . . . . . 29
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
9.1. Normative References . . . . . . . . . . . . . . . . . . . 29 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.2. Informative References . . . . . . . . . . . . . . . . . . 31 10.1. Normative References . . . . . . . . . . . . . . . . . . . 29
Appendix A. Differences Between HTTP Entities and RFC 2045 10.2. Informative References . . . . . . . . . . . . . . . . . . 31
Entities . . . . . . . . . . . . . . . . . . . . . . 32 Appendix A. Differences between HTTP and MIME . . . . . . . . . . 32
A.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . . 32 A.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . . 33
A.2. Conversion to Canonical Form . . . . . . . . . . . . . . . 33 A.2. Conversion to Canonical Form . . . . . . . . . . . . . . . 33
A.3. Conversion of Date Formats . . . . . . . . . . . . . . . . 33 A.3. Conversion of Date Formats . . . . . . . . . . . . . . . . 34
A.4. Introduction of Content-Encoding . . . . . . . . . . . . . 33 A.4. Introduction of Content-Encoding . . . . . . . . . . . . . 34
A.5. No Content-Transfer-Encoding . . . . . . . . . . . . . . . 34 A.5. No Content-Transfer-Encoding . . . . . . . . . . . . . . . 34
A.6. Introduction of Transfer-Encoding . . . . . . . . . . . . 34 A.6. Introduction of Transfer-Encoding . . . . . . . . . . . . 34
A.7. MHTML and Line Length Limitations . . . . . . . . . . . . 34 A.7. MHTML and Line Length Limitations . . . . . . . . . . . . 35
Appendix B. Additional Features . . . . . . . . . . . . . . . . . 34 Appendix B. Additional Features . . . . . . . . . . . . . . . . . 35
B.1. Content-Disposition . . . . . . . . . . . . . . . . . . . 35 B.1. Content-Disposition . . . . . . . . . . . . . . . . . . . 35
Appendix C. Compatibility with Previous Versions . . . . . . . . 35 Appendix C. Changes from RFC 2616 . . . . . . . . . . . . . . . . 36
C.1. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 35
C.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 36
Appendix D. Collected ABNF . . . . . . . . . . . . . . . . . . . 36 Appendix D. Collected ABNF . . . . . . . . . . . . . . . . . . . 36
Appendix E. Change Log (to be removed by RFC Editor before Appendix E. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 38 publication) . . . . . . . . . . . . . . . . . . . . 38
E.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 38 E.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 38
E.2. Since draft-ietf-httpbis-p3-payload-00 . . . . . . . . . . 38 E.2. Since draft-ietf-httpbis-p3-payload-00 . . . . . . . . . . 38
E.3. Since draft-ietf-httpbis-p3-payload-01 . . . . . . . . . . 39 E.3. Since draft-ietf-httpbis-p3-payload-01 . . . . . . . . . . 39
E.4. Since draft-ietf-httpbis-p3-payload-02 . . . . . . . . . . 39 E.4. Since draft-ietf-httpbis-p3-payload-02 . . . . . . . . . . 39
E.5. Since draft-ietf-httpbis-p3-payload-03 . . . . . . . . . . 40 E.5. Since draft-ietf-httpbis-p3-payload-03 . . . . . . . . . . 40
E.6. Since draft-ietf-httpbis-p3-payload-04 . . . . . . . . . . 40 E.6. Since draft-ietf-httpbis-p3-payload-04 . . . . . . . . . . 40
E.7. Since draft-ietf-httpbis-p3-payload-05 . . . . . . . . . . 41 E.7. Since draft-ietf-httpbis-p3-payload-05 . . . . . . . . . . 40
E.8. Since draft-ietf-httpbis-p3-payload-06 . . . . . . . . . . 41 E.8. Since draft-ietf-httpbis-p3-payload-06 . . . . . . . . . . 41
E.9. Since draft-ietf-httpbis-p3-payload-07 . . . . . . . . . . 41 E.9. Since draft-ietf-httpbis-p3-payload-07 . . . . . . . . . . 41
E.10. Since draft-ietf-httpbis-p3-payload-08 . . . . . . . . . . 42 E.10. Since draft-ietf-httpbis-p3-payload-08 . . . . . . . . . . 42
E.11. Since draft-ietf-httpbis-p3-payload-09 . . . . . . . . . . 42 E.11. Since draft-ietf-httpbis-p3-payload-09 . . . . . . . . . . 42
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 E.12. Since draft-ietf-httpbis-p3-payload-10 . . . . . . . . . . 42
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction 1. Introduction
This document defines HTTP/1.1 message payloads (a.k.a., content), This document defines HTTP/1.1 message payloads (a.k.a., content),
the associated metadata header fields that define how the payload is the associated metadata header fields that define how the payload is
intended to be interpreted by a recipient, the request header fields intended to be interpreted by a recipient, the request header fields
that may influence content selection, and the various selection that might influence content selection, and the various selection
algorithms that are collectively referred to as HTTP content algorithms that are collectively referred to as HTTP content
negotiation. negotiation.
This document is currently disorganized in order to minimize the This document is currently disorganized in order to minimize the
changes between drafts and enable reviewers to see the smaller errata changes between drafts and enable reviewers to see the smaller errata
changes. The next draft will reorganize the sections to better changes. The next draft will reorganize the sections to better
reflect the content. In particular, the sections on entities will be reflect the content. In particular, the sections on entities will be
renamed payload and moved to the first half of the document, while renamed payload and moved to the first half of the document, while
the sections on content negotiation and associated request header the sections on content negotiation and associated request header
fields will be moved to the second half. The current mess reflects fields will be moved to the second half. The current mess reflects
skipping to change at page 5, line 32 skipping to change at page 5, line 32
become in [RFC2616]. become in [RFC2616].
1.1. Terminology 1.1. Terminology
This specification uses a number of terms to refer to the roles This specification uses a number of terms to refer to the roles
played by participants in, and objects of, the HTTP communication. played by participants in, and objects of, the HTTP communication.
content negotiation content negotiation
The mechanism for selecting the appropriate representation when The mechanism for selecting the appropriate representation when
servicing a request. The representation of entities in any servicing a request. The representation in any response can be
response can be negotiated (including error responses). negotiated (including error responses).
entity
The information transferred as the payload of a request or
response. An entity consists of metadata in the form of entity-
header fields and content in the form of an entity-body.
representation
An entity included with a response that is subject to content
negotiation. There may exist multiple representations associated
with a particular response status.
variant
A resource may have one, or more than one, representation(s)
associated with it at any given instant. Each of these
representations is termed a "variant". Use of the term "variant"
does not necessarily imply that the resource is subject to content
negotiation.
1.2. Requirements 1.2. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
An implementation is not compliant if it fails to satisfy one or more An implementation is not compliant if it fails to satisfy one or more
of the "MUST" or "REQUIRED" level requirements for the protocols it of the "MUST" or "REQUIRED" level requirements for the protocols it
implements. An implementation that satisfies all the "MUST" or implements. An implementation that satisfies all the "MUST" or
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2. Protocol Parameters 2. Protocol Parameters
2.1. Character Sets 2.1. Character Sets
HTTP uses the same definition of the term "character set" as that HTTP uses the same definition of the term "character set" as that
described for MIME: described for MIME:
The term "character set" is used in this document to refer to a The term "character set" is used in this document to refer to a
method used with one or more tables to convert a sequence of octets method used with one or more tables to convert a sequence of octets
into a sequence of characters. Note that unconditional conversion in into a sequence of characters. Note that unconditional conversion in
the other direction is not required, in that not all characters may the other direction is not required, in that not all characters might
be available in a given character set and a character set may provide be available in a given character set and a character set might
more than one sequence of octets to represent a particular character. provide more than one sequence of octets to represent a particular
This definition is intended to allow various kinds of character character. This definition is intended to allow various kinds of
encoding, from simple single-table mappings such as US-ASCII to character encoding, from simple single-table mappings such as US-
complex table switching methods such as those that use ISO-2022's ASCII to complex table switching methods such as those that use ISO-
techniques. However, the definition associated with a MIME character 2022's techniques. However, the definition associated with a MIME
set name MUST fully specify the mapping to be performed from octets character set name MUST fully specify the mapping to be performed
to characters. In particular, use of external profiling information from octets to characters. In particular, use of external profiling
to determine the exact mapping is not permitted. information to determine the exact mapping is not permitted.
Note: This use of the term "character set" is more commonly Note: This use of the term "character set" is more commonly
referred to as a "character encoding." However, since HTTP and referred to as a "character encoding". However, since HTTP and
MIME share the same registry, it is important that the terminology MIME share the same registry, it is important that the terminology
also be shared. also be shared.
HTTP character sets are identified by case-insensitive tokens. The HTTP character sets are identified by case-insensitive tokens. The
complete set of tokens is defined by the IANA Character Set registry complete set of tokens is defined by the IANA Character Set registry
(<http://www.iana.org/assignments/character-sets>). (<http://www.iana.org/assignments/character-sets>).
charset = token charset = token
Although HTTP allows an arbitrary token to be used as a charset Although HTTP allows an arbitrary token to be used as a charset
value, any token that has a predefined value within the IANA value, any token that has a predefined value within the IANA
Character Set registry MUST represent the character set defined by Character Set registry MUST represent the character set defined by
that registry. Applications SHOULD limit their use of character sets that registry. Applications SHOULD limit their use of character sets
to those defined by the IANA registry. to those defined by the IANA registry.
HTTP uses charset in two contexts: within an Accept-Charset request HTTP uses charset in two contexts: within an Accept-Charset request
header (in which the charset value is an unquoted token) and as the header (in which the charset value is an unquoted token) and as the
value of a parameter in a Content-Type header (within a request or value of a parameter in a Content-Type header (within a request or
response), in which case the parameter value of the charset parameter response), in which case the parameter value of the charset parameter
may be quoted. can be quoted.
Implementors should be aware of IETF character set requirements Implementors need to be aware of IETF character set requirements
[RFC3629] [RFC2277]. [RFC3629] [RFC2277].
2.1.1. Missing Charset 2.1.1. Missing Charset
Some HTTP/1.0 software has interpreted a Content-Type header without Some HTTP/1.0 software has interpreted a Content-Type header without
charset parameter incorrectly to mean "recipient should guess." charset parameter incorrectly to mean "recipient should guess".
Senders wishing to defeat this behavior MAY include a charset Senders wishing to defeat this behavior MAY include a charset
parameter even when the charset is ISO-8859-1 ([ISO-8859-1]) and parameter even when the charset is ISO-8859-1 ([ISO-8859-1]) and
SHOULD do so when it is known that it will not confuse the recipient. SHOULD do so when it is known that it will not confuse the recipient.
Unfortunately, some older HTTP/1.0 clients did not deal properly with Unfortunately, some older HTTP/1.0 clients did not deal properly with
an explicit charset parameter. HTTP/1.1 recipients MUST respect the an explicit charset parameter. HTTP/1.1 recipients MUST respect the
charset label provided by the sender; and those user agents that have charset label provided by the sender; and those user agents that have
a provision to "guess" a charset MUST use the charset from the a provision to "guess" a charset MUST use the charset from the
content-type field if they support that charset, rather than the content-type field if they support that charset, rather than the
recipient's preference, when initially displaying a document. See recipient's preference, when initially displaying a document. See
Section 2.3.1. Section 2.3.1.
2.2. Content Codings 2.2. Content Codings
Content coding values indicate an encoding transformation that has Content coding values indicate an encoding transformation that has
been or can be applied to an entity. Content codings are primarily been or can be applied to a representation. Content codings are
used to allow a document to be compressed or otherwise usefully primarily used to allow a representation to be compressed or
transformed without losing the identity of its underlying media type otherwise usefully transformed without losing the identity of its
and without loss of information. Frequently, the entity is stored in underlying media type and without loss of information. Frequently,
coded form, transmitted directly, and only decoded by the recipient. the representation is stored in coded form, transmitted directly, and
only decoded by the recipient.
content-coding = token content-coding = token
All content-coding values are case-insensitive. HTTP/1.1 uses All content-coding values are case-insensitive. HTTP/1.1 uses
content-coding values in the Accept-Encoding (Section 5.3) and content-coding values in the Accept-Encoding (Section 6.3) and
Content-Encoding (Section 5.5) header fields. Although the value Content-Encoding (Section 6.5) header fields. Although the value
describes the content-coding, what is more important is that it describes the content-coding, what is more important is that it
indicates what decoding mechanism will be required to remove the indicates what decoding mechanism will be required to remove the
encoding. encoding.
compress compress
See Section 6.2.2.1 of [Part1]. See Section 6.2.2.1 of [Part1].
deflate deflate
See Section 6.2.2.2 of [Part1]. See Section 6.2.2.2 of [Part1].
gzip gzip
See Section 6.2.2.3 of [Part1]. See Section 6.2.2.3 of [Part1].
identity identity
The default (identity) encoding; the use of no transformation The default (identity) encoding; the use of no transformation
whatsoever. This content-coding is used only in the Accept- whatsoever. This content-coding is used only in the Accept-
skipping to change at page 9, line 35 skipping to change at page 9, line 23
o Description o Description
o Pointer to specification text o Pointer to specification text
Names of content codings MUST NOT overlap with names of transfer Names of content codings MUST NOT overlap with names of transfer
codings (Section 6.2 of [Part1]), unless the encoding transformation codings (Section 6.2 of [Part1]), unless the encoding transformation
is identical (as it is the case for the compression codings defined is identical (as it is the case for the compression codings defined
in Section 6.2.2 of [Part1]). in Section 6.2.2 of [Part1]).
Values to be added to this name space require expert review and a Values to be added to this name space require a specification (see
specification (see "Expert Review" and "Specification Required" in "Specification Required" in Section 4.1 of [RFC5226]), and MUST
Section 4.1 of [RFC5226]), and MUST conform to the purpose of content conform to the purpose of content coding defined in this section.
coding defined in this section.
The registry itself is maintained at The registry itself is maintained at
<http://www.iana.org/assignments/http-parameters>. <http://www.iana.org/assignments/http-parameters>.
2.3. Media Types 2.3. Media Types
HTTP uses Internet Media Types [RFC2046] in the Content-Type HTTP uses Internet Media Types [RFC2046] in the Content-Type
(Section 5.9) and Accept (Section 5.1) header fields in order to (Section 6.9) and Accept (Section 6.1) header fields in order to
provide open and extensible data typing and type negotiation. provide open and extensible data typing and type negotiation.
media-type = type "/" subtype *( OWS ";" OWS parameter ) media-type = type "/" subtype *( OWS ";" OWS parameter )
type = token type = token
subtype = token subtype = token
Parameters MAY follow the type/subtype in the form of attribute/value Parameters MAY follow the type/subtype in the form of attribute/value
pairs. pairs.
parameter = attribute "=" value parameter = attribute "=" value
attribute = token attribute = token
value = word value = word
The type, subtype, and parameter attribute names are case- The type, subtype, and parameter attribute names are case-
insensitive. Parameter values might or might not be case-sensitive, insensitive. Parameter values might or might not be case-sensitive,
depending on the semantics of the parameter name. The presence or depending on the semantics of the parameter name. The presence or
absence of a parameter might be significant to the processing of a absence of a parameter might be significant to the processing of a
media-type, depending on its definition within the media type media-type, depending on its definition within the media type
registry. registry.
A parameter value that matches the token production may be A parameter value that matches the token production can be
transmitted as either a token or within a quoted-string. The quoted transmitted as either a token or within a quoted-string. The quoted
and unquoted values are equivalent. and unquoted values are equivalent.
Note that some older HTTP applications do not recognize media type Note that some older HTTP applications do not recognize media type
parameters. When sending data to older HTTP applications, parameters. When sending data to older HTTP applications,
implementations SHOULD only use media type parameters when they are implementations SHOULD only use media type parameters when they are
required by that type/subtype definition. required by that type/subtype definition.
Media-type values are registered with the Internet Assigned Number Media-type values are registered with the Internet Assigned Number
Authority (IANA). The media type registration process is outlined in Authority (IANA). The media type registration process is outlined in
[RFC4288]. Use of non-registered media types is discouraged. [RFC4288]. Use of non-registered media types is discouraged.
2.3.1. Canonicalization and Text Defaults 2.3.1. Canonicalization and Text Defaults
Internet media types are registered with a canonical form. An Internet media types are registered with a canonical form. A
entity-body transferred via HTTP messages MUST be represented in the representation transferred via HTTP messages MUST be in the
appropriate canonical form prior to its transmission except for appropriate canonical form prior to its transmission except for
"text" types, as defined in the next paragraph. "text" types, as defined in the next paragraph.
When in canonical form, media subtypes of the "text" type use CRLF as When in canonical form, media subtypes of the "text" type use CRLF as
the text line break. HTTP relaxes this requirement and allows the the text line break. HTTP relaxes this requirement and allows the
transport of text media with plain CR or LF alone representing a line transport of text media with plain CR or LF alone representing a line
break when it is done consistently for an entire entity-body. HTTP break when it is done consistently for an entire representation.
applications MUST accept CRLF, bare CR, and bare LF as being HTTP applications MUST accept CRLF, bare CR, and bare LF as
representative of a line break in text media received via HTTP. In indicating a line break in text media received via HTTP. In
addition, if the text is represented in a character set that does not addition, if the text is in a character encoding that does not use
use octets 13 and 10 for CR and LF respectively, as is the case for octets 13 and 10 for CR and LF respectively, as is the case for some
some multi-byte character sets, HTTP allows the use of whatever octet multi-byte character encodings, HTTP allows the use of whatever octet
sequences are defined by that character set to represent the sequences are defined by that character encoding to represent the
equivalent of CR and LF for line breaks. This flexibility regarding equivalent of CR and LF for line breaks. This flexibility regarding
line breaks applies only to text media in the entity-body; a bare CR line breaks applies only to text media in the payload body; a bare CR
or LF MUST NOT be substituted for CRLF within any of the HTTP control or LF MUST NOT be substituted for CRLF within any of the HTTP control
structures (such as header fields and multipart boundaries). structures (such as header fields and multipart boundaries).
If an entity-body is encoded with a content-coding, the underlying If a representation is encoded with a content-coding, the underlying
data MUST be in a form defined above prior to being encoded. data MUST be in a form defined above prior to being encoded.
The "charset" parameter is used with some media types to define the The "charset" parameter is used with some media types to define the
character set (Section 2.1) of the data. When no explicit charset character encoding (Section 2.1) of the data. When no explicit
parameter is provided by the sender, media subtypes of the "text" charset parameter is provided by the sender, media subtypes of the
type are defined to have a default charset value of "ISO-8859-1" when "text" type are defined to have a default charset value of
received via HTTP. Data in character sets other than "ISO-8859-1" or "ISO-8859-1" when received via HTTP. Data in character encodings
its subsets MUST be labeled with an appropriate charset value. See other than "ISO-8859-1" or its subsets MUST be labeled with an
Section 2.1.1 for compatibility problems. appropriate charset value. See Section 2.1.1 for compatibility
problems.
2.3.2. Multipart Types 2.3.2. Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of MIME provides for a number of "multipart" types -- encapsulations of
one or more entities within a single message-body. All multipart one or more representations within a single message-body. All
types share a common syntax, as defined in Section 5.1.1 of multipart types share a common syntax, as defined in Section 5.1.1 of
[RFC2046], and MUST include a boundary parameter as part of the media [RFC2046], and MUST include a boundary parameter as part of the media
type value. The message body is itself a protocol element and MUST type value. The message body is itself a protocol element and MUST
therefore use only CRLF to represent line breaks between body-parts. therefore use only CRLF to represent line breaks between body-parts.
Unlike in RFC 2046, the epilogue of any multipart message MUST be
empty; HTTP applications MUST NOT transmit the epilogue (even if the
original multipart contains an epilogue). These restrictions exist
in order to preserve the self-delimiting nature of a multipart
message-body, wherein the "end" of the message-body is indicated by
the ending multipart boundary.
In general, HTTP treats a multipart message-body no differently than In general, HTTP treats a multipart message-body no differently than
any other media type: strictly as payload. The one exception is the any other media type: strictly as payload. HTTP does not use the
"multipart/byteranges" type (Appendix A of [Part5]) when it appears multipart boundary as an indicator of message-body length. In all
in a 206 (Partial Content) response. In all other cases, an HTTP other respects, an HTTP user agent SHOULD follow the same or similar
user agent SHOULD follow the same or similar behavior as a MIME user
agent would upon receipt of a multipart type. The MIME header fields
within each body-part of a multipart message-body do not have any
significance to HTTP beyond that defined by their MIME semantics.
In general, an HTTP user agent SHOULD follow the same or similar
behavior as a MIME user agent would upon receipt of a multipart type. behavior as a MIME user agent would upon receipt of a multipart type.
The MIME header fields within each body-part of a multipart message-
body do not have any significance to HTTP beyond that defined by
their MIME semantics.
If an application receives an unrecognized multipart subtype, the If an application receives an unrecognized multipart subtype, the
application MUST treat it as being equivalent to "multipart/mixed". application MUST treat it as being equivalent to "multipart/mixed".
Note: The "multipart/form-data" type has been specifically defined Note: The "multipart/form-data" type has been specifically defined
for carrying form data suitable for processing via the POST for carrying form data suitable for processing via the POST
request method, as described in [RFC2388]. request method, as described in [RFC2388].
2.4. Language Tags 2.4. Language Tags
A language tag, as defined in [RFC5646], identifies a natural A language tag, as defined in [RFC5646], identifies a natural
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insensitive. The name space of language subtags is administered by insensitive. The name space of language subtags is administered by
the IANA (see the IANA (see
<http://www.iana.org/assignments/language-subtag-registry>). <http://www.iana.org/assignments/language-subtag-registry>).
Example tags include: Example tags include:
en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information. See [RFC5646] for further information.
3. Entity 3. Payload
Request and Response messages MAY transfer an entity if not otherwise HTTP messages MAY transfer a payload if not otherwise restricted by
restricted by the request method or response status code. An entity the request method or response status code. The payload consists of
consists of entity-header fields and an entity-body, although some metadata, in the form of header fields, and data, in the form of the
responses will only include the entity-headers. sequence of octets in the message-body after any transfer-coding has
been decoded.
In this section, both sender and recipient refer to either the client A "payload" in HTTP is always a partial or complete representation of
or the server, depending on who sends and who receives the entity. some resource. We use separate terms for payload and representation
because some messages contain only the associated representation's
header fields (e.g., responses to HEAD) or only some part(s) of the
representation (e.g., the 206 status code).
3.1. Entity Header Fields 3.1. Payload Header Fields
Entity-header fields define metainformation about the entity-body or, HTTP header fields that specifically define the payload, rather than
if no body is present, about the resource identified by the request. the associated representation, are referred to as "payload header
fields". The following payload header fields are defined by
HTTP/1.1:
entity-header = Content-Encoding ; Section 5.5 Content-Length ; [Part1], Section 9.2
/ Content-Language ; Section 5.6 Content-MD5 ; Section 6.8
/ Content-Length ; [Part1], Section 9.2 Content-Range ; [Part5], Section 5.2
/ Content-Location ; Section 5.7
/ Content-MD5 ; Section 5.8
/ Content-Range ; [Part5], Section 5.2
/ Content-Type ; Section 5.9
/ Expires ; [Part6], Section 3.3
/ Last-Modified ; [Part4], Section 6.6
/ extension-header
extension-header = header-field 3.2. Payload Body
The extension-header mechanism allows additional entity-header fields A payload body is only present in a message when a message-body is
to be defined without changing the protocol, but these fields cannot present, as described in Section 3.3 of [Part1]. The payload body is
be assumed to be recognizable by the recipient. Unrecognized header obtained from the message-body by decoding any Transfer-Encoding that
fields SHOULD be ignored by the recipient and MUST be forwarded by might have been applied to ensure safe and proper transfer of the
transparent proxies. message.
3.2. Entity Body 4. Representation
The entity-body (if any) sent with an HTTP request or response is in A "representation" is information in a format that can be readily
a format and encoding defined by the entity-header fields. communicated from one party to another. A resource representation is
information that reflects the state of that resource, as observed at
some point in the past (e.g., in a response to GET) or to be desired
at some point in the future (e.g., in a PUT request).
entity-body = *OCTET Most, but not all, representations transferred via HTTP are intended
to be a representation of the target resource (the resource
identified by the effective request URI). The precise semantics of a
representation are determined by the type of message (request or
response), the request method, the response status code, and the
representation metadata. For example, the above semantic is true for
the representation in any 200 (OK) response to GET and for the
representation in any PUT request. A 200 response to PUT, in
contrast, contains either a representation that describes the
successful action or a representation of the target resource, with
the latter indicated by a Content-Location header field with the same
value as the effective request URI. Likewise, response messages with
an error status code usually contain a representation that describes
the error and what next steps are suggested for resolving it.
An entity-body is only present in a message when a message-body is 4.1. Representation Header Fields
present, as described in Section 3.3 of [Part1]. The entity-body is
obtained from the message-body by decoding any Transfer-Encoding that
might have been applied to ensure safe and proper transfer of the
message.
3.2.1. Type Representation header fields define metadata about the representation
data enclosed in the message-body or, if no message-body is present,
about the representation that would have been transferred in a 200
response to a simultaneous GET request with the same effective
request URI.
When an entity-body is included with a message, the data type of that The following header fields are defined as representation metadata:
body is determined via the header fields Content-Type and Content-
Encoding. These define a two-layer, ordered encoding model:
entity-body := Content-Encoding( Content-Type( data ) ) Content-Encoding ; Section 6.5
Content-Language ; Section 6.6
Content-Location ; Section 6.7
Content-Type ; Section 6.9
Expires ; [Part6], Section 3.3
Last-Modified ; [Part4], Section 6.6
Content-Type specifies the media type of the underlying data. Any 4.2. Representation Data
HTTP/1.1 message containing an entity-body SHOULD include a Content-
Type header field defining the media type of that body, unless that
information is unknown.
If the Content-Type header field is not present, it indicates that The representation body associated with an HTTP message is either
the sender does not know the media type of the data; recipients MAY provided as the payload body of the message or referred to by the
either assume that it is "application/octet-stream" ([RFC2046], message semantics and the effective request URI. The representation
Section 4.5.1) or examine the content to determine its type. data is in a format and encoding defined by the representation
metadata header fields.
In practice, currently-deployed servers sometimes provide a Content- The data type of the representation data is determined via the header
Type header which does not correctly convey the intended fields Content-Type and Content-Encoding. These define a two-layer,
interpretation of the content sent, with the result that some clients ordered encoding model:
will examine the response body's content and override the specified
type.
Client that do so risk drawing incorrect conclusions, which may representation-data := Content-Encoding( Content-Type( bits ) )
expose additional security risks (e.g., "privilege escalation").
Implementers are encouraged to provide a means of disabling such
"content sniffing" when it is used.
Content-Encoding may be used to indicate any additional content Content-Type specifies the media type of the underlying data, which
codings applied to the data, usually for the purpose of data defines both the data format and how that data SHOULD be processed by
compression, that are a property of the requested resource. There is the recipient (within the scope of the request method semantics).
no default encoding. Any HTTP/1.1 message containing a payload body SHOULD include a
Content-Type header field defining the media type of the associated
representation unless that metadata is unknown to the sender. If the
Content-Type header field is not present, it indicates that the
sender does not know the media type of the representation; recipients
MAY either assume that the media type is "application/octet-stream"
([RFC2046], Section 4.5.1) or examine the content to determine its
type.
3.2.2. Entity Length In practice, resource owners do not always properly configure their
origin server to provide the correct Content-Type for a given
representation, with the result that some clients will examine a
response body's content and override the specified type. Clients
that do so risk drawing incorrect conclusions, which might expose
additional security risks (e.g., "privilege escalation").
Furthermore, it is impossible to determine the sender's intent by
examining the data format: many data formats match multiple media
types that differ only in processing semantics. Implementers are
encouraged to provide a means of disabling such "content sniffing"
when it is used.
The entity-length of a message is the length of the message-body Content-Encoding is used to indicate any additional content codings
before any transfer-codings have been applied. Section 3.4 of applied to the data, usually for the purpose of data compression,
[Part1] defines how the transfer-length of a message-body is that are a property of the representation. If Content-Encoding is
determined. not present, then there is no additional encoding beyond that defined
by the Content-Type.
4. Content Negotiation 5. Content Negotiation
HTTP responses include a representation which contains information HTTP responses include a representation which contains information
for interpretation, whether by a human user or for further for interpretation, whether by a human user or for further
processing. Often, the server has different ways of representing the processing. Often, the server has different ways of representing the
same information; for example, in different formats, languages, or same information; for example, in different formats, languages, or
using different character encodings. using different character encodings.
HTTP clients and their users might have different or variable HTTP clients and their users might have different or variable
capabilities, characteristics or preferences which would influence capabilities, characteristics or preferences which would influence
which representation, among those available from the server, would be which representation, among those available from the server, would be
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patterns: some applications use an "active content" pattern, where patterns: some applications use an "active content" pattern, where
the server returns active content which runs on the client and, based the server returns active content which runs on the client and, based
on client available parameters, selects additional resources to on client available parameters, selects additional resources to
invoke. "Transparent Content Negotiation" ([RFC2295]) has also been invoke. "Transparent Content Negotiation" ([RFC2295]) has also been
proposed. proposed.
These patterns are all widely used, and have trade-offs in These patterns are all widely used, and have trade-offs in
applicability and practicality. In particular, when the number of applicability and practicality. In particular, when the number of
preferences or capabilities to be expressed by a client are large preferences or capabilities to be expressed by a client are large
(such as when many different formats are supported by a user-agent), (such as when many different formats are supported by a user-agent),
server-driven negotiation becomes unwieldy, and may not be server-driven negotiation becomes unwieldy, and might not be
appropriate. Conversely, when the number of representations to appropriate. Conversely, when the number of representations to
choose from is very large, agent-driven negotiation may not be choose from is very large, agent-driven negotiation might not be
appropriate. appropriate.
Note that in all cases, the supplier of representations has the Note that in all cases, the supplier of representations has the
responsibility for determining which representations might be responsibility for determining which representations might be
considered to be the "same information". considered to be the "same information".
4.1. Server-driven Negotiation 5.1. Server-driven Negotiation
If the selection of the best representation for a response is made by If the selection of the best representation for a response is made by
an algorithm located at the server, it is called server-driven an algorithm located at the server, it is called server-driven
negotiation. Selection is based on the available representations of negotiation. Selection is based on the available representations of
the response (the dimensions over which it can vary; e.g., language, the response (the dimensions over which it can vary; e.g., language,
content-coding, etc.) and the contents of particular header fields in content-coding, etc.) and the contents of particular header fields in
the request message or on other information pertaining to the request the request message or on other information pertaining to the request
(such as the network address of the client). (such as the network address of the client).
Server-driven negotiation is advantageous when the algorithm for Server-driven negotiation is advantageous when the algorithm for
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view it on screen or print it on paper?). view it on screen or print it on paper?).
2. Having the user agent describe its capabilities in every request 2. Having the user agent describe its capabilities in every request
can be both very inefficient (given that only a small percentage can be both very inefficient (given that only a small percentage
of responses have multiple representations) and a potential of responses have multiple representations) and a potential
violation of the user's privacy. violation of the user's privacy.
3. It complicates the implementation of an origin server and the 3. It complicates the implementation of an origin server and the
algorithms for generating responses to a request. algorithms for generating responses to a request.
4. It may limit a public cache's ability to use the same response 4. It might limit a public cache's ability to use the same response
for multiple user's requests. for multiple user's requests.
HTTP/1.1 includes the following request-header fields for enabling HTTP/1.1 includes the following request-header fields for enabling
server-driven negotiation through description of user agent server-driven negotiation through description of user agent
capabilities and user preferences: Accept (Section 5.1), Accept- capabilities and user preferences: Accept (Section 6.1), Accept-
Charset (Section 5.2), Accept-Encoding (Section 5.3), Accept-Language Charset (Section 6.2), Accept-Encoding (Section 6.3), Accept-Language
(Section 5.4), and User-Agent (Section 9.9 of [Part2]). However, an (Section 6.4), and User-Agent (Section 9.9 of [Part2]). However, an
origin server is not limited to these dimensions and MAY vary the origin server is not limited to these dimensions and MAY vary the
response based on any aspect of the request, including information response based on any aspect of the request, including information
outside the request-header fields or within extension header fields outside the request-header fields or within extension header fields
not defined by this specification. not defined by this specification.
Note: In practice, User-Agent based negotiation is fragile, Note: In practice, User-Agent based negotiation is fragile,
because new clients might not be recognized. because new clients might not be recognized.
The Vary header field (Section 3.5 of [Part6]) can be used to express The Vary header field (Section 3.5 of [Part6]) can be used to express
the parameters the server uses to select a representation that is the parameters the server uses to select a representation that is
subject to server-driven negotiation. subject to server-driven negotiation.
4.2. Agent-driven Negotiation 5.2. Agent-driven Negotiation
With agent-driven negotiation, selection of the best representation With agent-driven negotiation, selection of the best representation
for a response is performed by the user agent after receiving an for a response is performed by the user agent after receiving an
initial response from the origin server. Selection is based on a initial response from the origin server. Selection is based on a
list of the available representations of the response included within list of the available representations of the response included within
the header fields or entity-body of the initial response, with each the header fields or body of the initial response, with each
representation identified by its own URI. Selection from among the representation identified by its own URI. Selection from among the
representations may be performed automatically (if the user agent is representations can be performed automatically (if the user agent is
capable of doing so) or manually by the user selecting from a capable of doing so) or manually by the user selecting from a
generated (possibly hypertext) menu. generated (possibly hypertext) menu.
Agent-driven negotiation is advantageous when the response would vary Agent-driven negotiation is advantageous when the response would vary
over commonly-used dimensions (such as type, language, or encoding), over commonly-used dimensions (such as type, language, or encoding),
when the origin server is unable to determine a user agent's when the origin server is unable to determine a user agent's
capabilities from examining the request, and generally when public capabilities from examining the request, and generally when public
caches are used to distribute server load and reduce network usage. caches are used to distribute server load and reduce network usage.
Agent-driven negotiation suffers from the disadvantage of needing a Agent-driven negotiation suffers from the disadvantage of needing a
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this specification does not define any mechanism for supporting this specification does not define any mechanism for supporting
automatic selection, though it also does not prevent any such automatic selection, though it also does not prevent any such
mechanism from being developed as an extension and used within mechanism from being developed as an extension and used within
HTTP/1.1. HTTP/1.1.
This specification defines the 300 (Multiple Choices) and 406 (Not This specification defines the 300 (Multiple Choices) and 406 (Not
Acceptable) status codes for enabling agent-driven negotiation when Acceptable) status codes for enabling agent-driven negotiation when
the server is unwilling or unable to provide a varying response using the server is unwilling or unable to provide a varying response using
server-driven negotiation. server-driven negotiation.
5. Header Field Definitions 6. Header Field Definitions
This section defines the syntax and semantics of HTTP/1.1 header This section defines the syntax and semantics of HTTP/1.1 header
fields related to the payload of messages. fields related to the payload of messages.
For entity-header fields, both sender and recipient refer to either 6.1. Accept
the client or the server, depending on who sends and who receives the
entity.
5.1. Accept
The "Accept" request-header field can be used by user agents to The "Accept" request-header field can be used by user agents to
specify response media types that are acceptable. Accept headers can specify response media types that are acceptable. Accept headers can
be used to indicate that the request is specifically limited to a be used to indicate that the request is specifically limited to a
small set of desired types, as in the case of a request for an in- small set of desired types, as in the case of a request for an in-
line image. line image.
Accept = "Accept" ":" OWS Accept-v Accept = "Accept" ":" OWS Accept-v
Accept-v = #( media-range [ accept-params ] ) Accept-v = #( media-range [ accept-params ] )
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to be unlikely given the lack of any "q" parameters in the IANA to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type media type registry and the rare usage of any media type
parameters in Accept. Future media types are discouraged from parameters in Accept. Future media types are discouraged from
registering any parameter named "q". registering any parameter named "q".
The example The example
Accept: audio/*; q=0.2, audio/basic Accept: audio/*; q=0.2, audio/basic
SHOULD be interpreted as "I prefer audio/basic, but send me any audio SHOULD be interpreted as "I prefer audio/basic, but send me any audio
type if it is the best available after an 80% mark-down in quality." type if it is the best available after an 80% mark-down in quality".
If no Accept header field is present, then it is assumed that the If no Accept header field is present, then it is assumed that the
client accepts all media types. If an Accept header field is client accepts all media types. If an Accept header field is
present, and if the server cannot send a response which is acceptable present, and if the server cannot send a response which is acceptable
according to the combined Accept field value, then the server SHOULD according to the combined Accept field value, then the server SHOULD
send a 406 (Not Acceptable) response. send a 406 (Not Acceptable) response.
A more elaborate example is A more elaborate example is
Accept: text/plain; q=0.5, text/html, Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8, text/x-c text/x-dvi; q=0.8, text/x-c
Verbally, this would be interpreted as "text/html and text/x-c are Verbally, this would be interpreted as "text/html and text/x-c are
the preferred media types, but if they do not exist, then send the the preferred media types, but if they do not exist, then send the
text/x-dvi entity, and if that does not exist, send the text/plain text/x-dvi representation, and if that does not exist, send the text/
entity." plain representation".
Media ranges can be overridden by more specific media ranges or Media ranges can be overridden by more specific media ranges or
specific media types. If more than one media range applies to a specific media types. If more than one media range applies to a
given type, the most specific reference has precedence. For example, given type, the most specific reference has precedence. For example,
Accept: text/*, text/html, text/html;level=1, */* Accept: text/*, text/html, text/html;level=1, */*
have the following precedence: have the following precedence:
1. text/html;level=1 1. text/html;level=1
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| image/jpeg | 0.5 | | image/jpeg | 0.5 |
| text/html;level=2 | 0.4 | | text/html;level=2 | 0.4 |
| text/html;level=3 | 0.7 | | text/html;level=3 | 0.7 |
+-------------------+---------------+ +-------------------+---------------+
Note: A user agent might be provided with a default set of quality Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is a values for certain media ranges. However, unless the user agent is a
closed system which cannot interact with other rendering agents, this closed system which cannot interact with other rendering agents, this
default set ought to be configurable by the user. default set ought to be configurable by the user.
5.2. Accept-Charset 6.2. Accept-Charset
The "Accept-Charset" request-header field can be used by user agents The "Accept-Charset" request-header field can be used by user agents
to indicate what response character sets are acceptable. This field to indicate what response character sets are acceptable. This field
allows clients capable of understanding more comprehensive or allows clients capable of understanding more comprehensive or
special-purpose character sets to signal that capability to a server special-purpose character sets to signal that capability to a server
which is capable of representing documents in those character sets. which is capable of representing documents in those character sets.
Accept-Charset = "Accept-Charset" ":" OWS Accept-Charset = "Accept-Charset" ":" OWS
Accept-Charset-v Accept-Charset-v
Accept-Charset-v = 1#( ( charset / "*" ) Accept-Charset-v = 1#( ( charset / "*" )
skipping to change at page 20, line 15 skipping to change at page 20, line 8
explicitly mentioned get a quality value of 0, except for ISO-8859-1, explicitly mentioned get a quality value of 0, except for ISO-8859-1,
which gets a quality value of 1 if not explicitly mentioned. which gets a quality value of 1 if not explicitly mentioned.
If no Accept-Charset header is present, the default is that any If no Accept-Charset header is present, the default is that any
character set is acceptable. If an Accept-Charset header is present, character set is acceptable. If an Accept-Charset header is present,
and if the server cannot send a response which is acceptable and if the server cannot send a response which is acceptable
according to the Accept-Charset header, then the server SHOULD send according to the Accept-Charset header, then the server SHOULD send
an error response with the 406 (Not Acceptable) status code, though an error response with the 406 (Not Acceptable) status code, though
the sending of an unacceptable response is also allowed. the sending of an unacceptable response is also allowed.
5.3. Accept-Encoding 6.3. Accept-Encoding
The "Accept-Encoding" request-header field can be used by user agents The "Accept-Encoding" request-header field can be used by user agents
to indicate what response content-codings (Section 2.2) are to indicate what response content-codings (Section 2.2) are
acceptable in the response. acceptable in the response.
Accept-Encoding = "Accept-Encoding" ":" OWS Accept-Encoding = "Accept-Encoding" ":" OWS
Accept-Encoding-v Accept-Encoding-v
Accept-Encoding-v = Accept-Encoding-v =
#( codings [ OWS ";" OWS "q=" qvalue ] ) #( codings [ OWS ";" OWS "q=" qvalue ] )
codings = ( content-coding / "*" ) codings = ( content-coding / "*" )
skipping to change at page 20, line 45 skipping to change at page 20, line 38
Accept-Encoding: * Accept-Encoding: *
Accept-Encoding: compress;q=0.5, gzip;q=1.0 Accept-Encoding: compress;q=0.5, gzip;q=1.0
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0 Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
A server tests whether a content-coding is acceptable, according to A server tests whether a content-coding is acceptable, according to
an Accept-Encoding field, using these rules: an Accept-Encoding field, using these rules:
1. If the content-coding is one of the content-codings listed in the 1. If the content-coding is one of the content-codings listed in the
Accept-Encoding field, then it is acceptable, unless it is Accept-Encoding field, then it is acceptable, unless it is
accompanied by a qvalue of 0. (As defined in Section 6.4 of accompanied by a qvalue of 0. (As defined in Section 6.4 of
[Part1], a qvalue of 0 means "not acceptable.") [Part1], a qvalue of 0 means "not acceptable".)
2. The special "*" symbol in an Accept-Encoding field matches any 2. The special "*" symbol in an Accept-Encoding field matches any
available content-coding not explicitly listed in the header available content-coding not explicitly listed in the header
field. field.
3. If multiple content-codings are acceptable, then the acceptable 3. If multiple content-codings are acceptable, then the acceptable
content-coding with the highest non-zero qvalue is preferred. content-coding with the highest non-zero qvalue is preferred.
4. The "identity" content-coding is always acceptable, unless 4. The "identity" content-coding is always acceptable, unless
specifically refused because the Accept-Encoding field includes specifically refused because the Accept-Encoding field includes
skipping to change at page 21, line 39 skipping to change at page 21, line 30
codings commonly understood by HTTP/1.0 clients (i.e., "gzip" and codings commonly understood by HTTP/1.0 clients (i.e., "gzip" and
"compress") are preferred; some older clients improperly display "compress") are preferred; some older clients improperly display
messages sent with other content-codings. The server might also messages sent with other content-codings. The server might also
make this decision based on information about the particular user- make this decision based on information about the particular user-
agent or client. agent or client.
Note: Most HTTP/1.0 applications do not recognize or obey qvalues Note: Most HTTP/1.0 applications do not recognize or obey qvalues
associated with content-codings. This means that qvalues will not associated with content-codings. This means that qvalues will not
work and are not permitted with x-gzip or x-compress. work and are not permitted with x-gzip or x-compress.
5.4. Accept-Language 6.4. Accept-Language
The "Accept-Language" request-header field can be used by user agents The "Accept-Language" request-header field can be used by user agents
to indicate the set of natural languages that are preferred in the to indicate the set of natural languages that are preferred in the
response. Language tags are defined in Section 2.4. response. Language tags are defined in Section 2.4.
Accept-Language = "Accept-Language" ":" OWS Accept-Language = "Accept-Language" ":" OWS
Accept-Language-v Accept-Language-v
Accept-Language-v = Accept-Language-v =
1#( language-range [ OWS ";" OWS "q=" qvalue ] ) 1#( language-range [ OWS ";" OWS "q=" qvalue ] )
language-range = language-range =
<language-range, defined in [RFC4647], Section 2.1> <language-range, defined in [RFC4647], Section 2.1>
Each language-range can be given an associated quality value which Each language-range can be given an associated quality value which
represents an estimate of the user's preference for the languages represents an estimate of the user's preference for the languages
specified by that range. The quality value defaults to "q=1". For specified by that range. The quality value defaults to "q=1". For
example, example,
Accept-Language: da, en-gb;q=0.8, en;q=0.7 Accept-Language: da, en-gb;q=0.8, en;q=0.7
would mean: "I prefer Danish, but will accept British English and would mean: "I prefer Danish, but will accept British English and
other types of English." (see also Section 2.3 of [RFC4647]) other types of English". (see also Section 2.3 of [RFC4647])
For matching, Section 3 of [RFC4647] defines several matching For matching, Section 3 of [RFC4647] defines several matching
schemes. Implementations can offer the most appropriate matching schemes. Implementations can offer the most appropriate matching
scheme for their requirements. scheme for their requirements.
Note: The "Basic Filtering" scheme ([RFC4647], Section 3.3.1) is Note: The "Basic Filtering" scheme ([RFC4647], Section 3.3.1) is
identical to the matching scheme that was previously defined in identical to the matching scheme that was previously defined in
Section 14.4 of [RFC2616]. Section 14.4 of [RFC2616].
It might be contrary to the privacy expectations of the user to send It might be contrary to the privacy expectations of the user to send
an Accept-Language header with the complete linguistic preferences of an Accept-Language header with the complete linguistic preferences of
the user in every request. For a discussion of this issue, see the user in every request. For a discussion of this issue, see
Section 7.1. Section 8.1.
As intelligibility is highly dependent on the individual user, it is As intelligibility is highly dependent on the individual user, it is
recommended that client applications make the choice of linguistic recommended that client applications make the choice of linguistic
preference available to the user. If the choice is not made preference available to the user. If the choice is not made
available, then the Accept-Language header field MUST NOT be given in available, then the Accept-Language header field MUST NOT be given in
the request. the request.
Note: When making the choice of linguistic preference available to Note: When making the choice of linguistic preference available to
the user, we remind implementors of the fact that users are not the user, we remind implementors of the fact that users are not
familiar with the details of language matching as described above, familiar with the details of language matching as described above,
and should provide appropriate guidance. As an example, users and ought to be provided appropriate guidance. As an example,
might assume that on selecting "en-gb", they will be served any users might assume that on selecting "en-gb", they will be served
kind of English document if British English is not available. A any kind of English document if British English is not available.
user agent might suggest in such a case to add "en" to get the A user agent might suggest in such a case to add "en" to get the
best matching behavior. best matching behavior.
5.5. Content-Encoding 6.5. Content-Encoding
The "Content-Encoding" entity-header field indicates what content- The "Content-Encoding" header field indicates what content-codings
codings have been applied to the entity-body, and thus what decoding have been applied to the representation, and thus what decoding
mechanisms must be applied in order to obtain the media-type mechanisms must be applied in order to obtain the media-type
referenced by the Content-Type header field. Content-Encoding is referenced by the Content-Type header field. Content-Encoding is
primarily used to allow a document to be compressed without losing primarily used to allow a representation to be compressed without
the identity of its underlying media type. losing the identity of its underlying media type.
Content-Encoding = "Content-Encoding" ":" OWS Content-Encoding-v Content-Encoding = "Content-Encoding" ":" OWS Content-Encoding-v
Content-Encoding-v = 1#content-coding Content-Encoding-v = 1#content-coding
Content codings are defined in Section 2.2. An example of its use is Content codings are defined in Section 2.2. An example of its use is
Content-Encoding: gzip Content-Encoding: gzip
The content-coding is a characteristic of the entity identified by The content-coding is a characteristic of the representation.
the Effective Request URI (Section 4.3 of [Part1]). Typically, the Typically, the representation body is stored with this encoding and
entity-body is stored with this encoding and is only decoded before is only decoded before rendering or analogous usage. However, a non-
rendering or analogous usage. However, a non-transparent proxy MAY transparent proxy MAY modify the content-coding if the new coding is
modify the content-coding if the new coding is known to be acceptable known to be acceptable to the recipient, unless the "no-transform"
to the recipient, unless the "no-transform" cache-control directive cache-control directive is present in the message.
is present in the message.
If the content-coding of an entity is not "identity", then the If the content-coding of a representation is not "identity", then the
response MUST include a Content-Encoding entity-header (Section 5.5) representation metadata MUST include a Content-Encoding header field
that lists the non-identity content-coding(s) used. (Section 6.5) that lists the non-identity content-coding(s) used.
If the content-coding of an entity in a request message is not If the content-coding of a representation in a request message is not
acceptable to the origin server, the server SHOULD respond with a acceptable to the origin server, the server SHOULD respond with a
status code of 415 (Unsupported Media Type). status code of 415 (Unsupported Media Type).
If multiple encodings have been applied to an entity, the content If multiple encodings have been applied to a representation, the
codings MUST be listed in the order in which they were applied. content codings MUST be listed in the order in which they were
Additional information about the encoding parameters MAY be provided applied. Additional information about the encoding parameters MAY be
by other entity-header fields not defined by this specification. provided by other header fields not defined by this specification.
5.6. Content-Language 6.6. Content-Language
The "Content-Language" entity-header field describes the natural The "Content-Language" header field describes the natural language(s)
language(s) of the intended audience for the entity. Note that this of the intended audience for the representation. Note that this
might not be equivalent to all the languages used within the entity- might not be equivalent to all the languages used within the
body. representation.
Content-Language = "Content-Language" ":" OWS Content-Language-v Content-Language = "Content-Language" ":" OWS Content-Language-v
Content-Language-v = 1#language-tag Content-Language-v = 1#language-tag
Language tags are defined in Section 2.4. The primary purpose of Language tags are defined in Section 2.4. The primary purpose of
Content-Language is to allow a user to identify and differentiate Content-Language is to allow a user to identify and differentiate
entities according to the user's own preferred language. Thus, if representations according to the user's own preferred language.
the body content is intended only for a Danish-literate audience, the Thus, if the body content is intended only for a Danish-literate
appropriate field is audience, the appropriate field is
Content-Language: da Content-Language: da
If no Content-Language is specified, the default is that the content If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the is intended for all language audiences. This might mean that the
sender does not consider it to be specific to any natural language, sender does not consider it to be specific to any natural language,
or that the sender does not know for which language it is intended. or that the sender does not know for which language it is intended.
Multiple languages MAY be listed for content that is intended for Multiple languages MAY be listed for content that is intended for
multiple audiences. For example, a rendition of the "Treaty of multiple audiences. For example, a rendition of the "Treaty of
Waitangi," presented simultaneously in the original Maori and English Waitangi", presented simultaneously in the original Maori and English
versions, would call for versions, would call for
Content-Language: mi, en Content-Language: mi, en
However, just because multiple languages are present within an entity However, just because multiple languages are present within a
does not mean that it is intended for multiple linguistic audiences. representation does not mean that it is intended for multiple
An example would be a beginner's language primer, such as "A First linguistic audiences. An example would be a beginner's language
Lesson in Latin," which is clearly intended to be used by an English- primer, such as "A First Lesson in Latin", which is clearly intended
literate audience. In this case, the Content-Language would properly to be used by an English-literate audience. In this case, the
only include "en". Content-Language would properly only include "en".
Content-Language MAY be applied to any media type -- it is not Content-Language MAY be applied to any media type -- it is not
limited to textual documents. limited to textual documents.
5.7. Content-Location 6.7. Content-Location
The "Content-Location" entity-header field is used to supply a URI
for the entity in the message when it is accessible from a location
separate from the requested resource's URI.
A server SHOULD provide a Content-Location for the variant The "Content-Location" header field supplies a URI that can be used
corresponding to the response entity, especially in the case where a as a specific identifier for the representation in this message. In
resource has multiple entities associated with it, and those entities other words, if one were to perform a GET on this URI at the time of
actually have separate locations by which they might be individually this message's generation, then a 200 response would contain the same
accessed, the server SHOULD provide a Content-Location for the representation that is enclosed as payload in this message.
particular variant which is returned.
Content-Location = "Content-Location" ":" OWS Content-Location = "Content-Location" ":" OWS
Content-Location-v Content-Location-v
Content-Location-v = Content-Location-v =
absolute-URI / partial-URI absolute-URI / partial-URI
The Content-Location value is not a replacement for the Effective The Content-Location value is not a replacement for the effective
Request URI (Section 4.3 of [Part1]); it is only a statement of the Request URI (Section 4.3 of [Part1]). It is representation metadata.
location of the resource corresponding to this particular entity at It has the same syntax and semantics as the header field of the same
the time of the request. Future requests MAY may be addressed to the name defined for MIME body parts in Section 4 of [RFC2557]. However,
Content-Location URI if the desire is to identify the source of that its appearance in an HTTP message has some special implications for
particular entity. HTTP recipients.
Section 6.1 of [Part2] describes how clients may process the Content- If Content-Location is included in a response message and its value
Location header field. is the same as the effective request URI, then the response payload
SHOULD be considered the current representation of that resource.
For a GET or HEAD request, this is the same as the default semantics
when no Content-Location is provided by the server. For a state-
changing method like PUT or POST, it implies that the server's
response contains the new representation of that resource, thereby
distinguishing it from representations that might only report about
the action (e.g., "It worked!"). This allows authoring applications
to update their local copies without the need for a subsequent GET
request.
A cache cannot assume that an entity with a Content-Location If Content-Location is included in a response message and its value
different from the URI used to retrieve it can be used to respond to differs from the effective request URI, then the origin server is
later requests on that Content-Location URI. However, the Content- informing recipients that this representation has its own, presumably
Location can be used to differentiate between multiple entities more specific, identifier. For a GET or HEAD request, this is an
retrieved from a single requested resource, as described in Section indication that the effective request URI identifies a resource that
2.7 of [Part6]. is subject to content negotiation and the representation selected for
this response can also be found at the identified URI. For other
methods, such a Content-Location indicates that this representation
contains a report on the action's status and the same report is
available (for future access with GET) at the given URI. For
example, a purchase transaction made via the POST method might
include a receipt document as the payload of the 200 response; the
Content-Location value provides an identifier for retrieving a copy
of that same receipt in the future.
If the Content-Location is a relative URI, the relative URI is If Content-Location is included in a request message, then it MAY be
interpreted relative to the Effective Request URI. interpreted by the origin server as an indication of where the user
agent originally obtained the content of the enclosed representation
(prior to any subsequent modification of the content by that user
agent). In other words, the user agent is providing the same
representation metadata that it received with the original
representation. However, such interpretation MUST NOT be used to
alter the semantics of the method requested by the client. For
example, if a client makes a PUT request on a negotiated resource and
the origin server accepts that PUT (without redirection), then the
new set of values for that resource is expected to be consistent with
the one representation supplied in that PUT; the Content-Location
cannot be used as a form of reverse content selection that identifies
only one of the negotiated representations to be updated. If the
user agent had wanted the latter semantics, it would have applied the
PUT directly to the Content-Location URI.
The meaning of the Content-Location header in requests is undefined; A Content-Location field received in a request message is transitory
servers are free to ignore it in those cases. information that SHOULD NOT be saved with other representation
metadata for use in later responses. The Content-Location's value
might be saved for use in other contexts, such as within source links
or other metadata.
5.8. Content-MD5 A cache cannot assume that a representation with a Content-Location
different from the URI used to retrieve it can be used to respond to
later requests on that Content-Location URI.
The "Content-MD5" entity-header field, as defined in [RFC1864], is an If the Content-Location value is a partial URI, the partial URI is
MD5 digest of the entity-body that provides an end-to-end message interpreted relative to the effective request URI.
integrity check (MIC) of the entity-body. Note that a MIC is good
for detecting accidental modification of the entity-body in transit, 6.8. Content-MD5
but is not proof against malicious attacks.
The "Content-MD5" header field, as defined in [RFC1864], is an MD5
digest of the payload body that provides an end-to-end message
integrity check (MIC) of the payload body (the message-body after any
transfer-coding is decoded). Note that a MIC is good for detecting
accidental modification of the payload body in transit, but is not
proof against malicious attacks.
Content-MD5 = "Content-MD5" ":" OWS Content-MD5-v Content-MD5 = "Content-MD5" ":" OWS Content-MD5-v
Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]> Content-MD5-v = <base64 of 128 bit MD5 digest as per [RFC1864]>
The Content-MD5 header field MAY be generated by an origin server or The Content-MD5 header field MAY be generated by an origin server or
client to function as an integrity check of the entity-body. Only client to function as an integrity check of the payload body. Only
origin servers or clients MAY generate the Content-MD5 header field; origin servers or user agents MAY generate the Content-MD5 header
proxies and gateways MUST NOT generate it, as this would defeat its field; proxies and gateways MUST NOT generate it, as this would
value as an end-to-end integrity check. Any recipient of the entity- defeat its value as an end-to-end integrity check. Any recipient MAY
body, including gateways and proxies, MAY check that the digest value check that the digest value in this header field matches a
in this header field matches that of the entity-body as received. corresponding digest calculated on payload body as received.
The MD5 digest is computed based on the content of the entity-body,
including any content-coding that has been applied, but not including
any transfer-encoding applied to the message-body. If the message is
received with a transfer-encoding, that encoding MUST be removed
prior to checking the Content-MD5 value against the received entity.
This has the result that the digest is computed on the octets of the The MD5 digest is computed based on the content of the payload body,
entity-body exactly as, and in the order that, they would be sent if including any content-coding, but not including any transfer-coding
no transfer-encoding were being applied. applied to the message-body because such transfer-codings might be
applied or removed anywhere along the request/response chain. If the
message is received with a transfer-coding, that encoding MUST be
decoded prior to checking the Content-MD5 value against the received
payload.
HTTP extends RFC 1864 to permit the digest to be computed for MIME HTTP extends RFC 1864 to permit the digest to be computed for MIME
composite media-types (e.g., multipart/* and message/rfc822), but composite media-types (e.g., multipart/* and message/rfc822), but
this does not change how the digest is computed as defined in the this does not change how the digest is computed as defined in the
preceding paragraph. preceding paragraph.
There are several consequences of this. The entity-body for There are several consequences of this. The payload for composite
composite types MAY contain many body-parts, each with its own MIME types MAY contain many body-parts, each with its own MIME and HTTP
and HTTP headers (including Content-MD5, Content-Transfer-Encoding, headers (including Content-MD5, Content-Transfer-Encoding, and
and Content-Encoding headers). If a body-part has a Content- Content-Encoding headers). If a body-part has a Content-Transfer-
Transfer-Encoding or Content-Encoding header, it is assumed that the Encoding or Content-Encoding header, it is assumed that the content
content of the body-part has had the encoding applied, and the body- of the body-part has had the encoding applied, and the body-part is
part is included in the Content-MD5 digest as is -- i.e., after the included in the Content-MD5 digest as is -- i.e., after the
application. The Transfer-Encoding header field is not allowed application. The Transfer-Encoding header field is not allowed
within body-parts. within body-parts.
Conversion of all line breaks to CRLF MUST NOT be done before Conversion of all line breaks to CRLF MUST NOT be done before
computing or checking the digest: the line break convention used in computing or checking the digest: the line break convention used in
the text actually transmitted MUST be left unaltered when computing the text actually transmitted MUST be left unaltered when computing
the digest. the digest.
Note: While the definition of Content-MD5 is exactly the same for Note: While the definition of Content-MD5 is exactly the same for
HTTP as in RFC 1864 for MIME entity-bodies, there are several ways HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
in which the application of Content-MD5 to HTTP entity-bodies in which the application of Content-MD5 to HTTP entity-bodies
differs from its application to MIME entity-bodies. One is that differs from its application to MIME entity-bodies. One is that
HTTP, unlike MIME, does not use Content-Transfer-Encoding, and HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
does use Transfer-Encoding and Content-Encoding. Another is that does use Transfer-Encoding and Content-Encoding. Another is that
HTTP more frequently uses binary content types than MIME, so it is HTTP more frequently uses binary content types than MIME, so it is
worth noting that, in such cases, the byte order used to compute worth noting that, in such cases, the byte order used to compute
the digest is the transmission byte order defined for the type. the digest is the transmission byte order defined for the type.
Lastly, HTTP allows transmission of text types with any of several Lastly, HTTP allows transmission of text types with any of several
line break conventions and not just the canonical form using CRLF. line break conventions and not just the canonical form using CRLF.
5.9. Content-Type 6.9. Content-Type
The "Content-Type" entity-header field indicates the media type of The "Content-Type" header field indicates the media type of the
the entity-body. In the case of responses to the HEAD method, the representation. In the case of responses to the HEAD method, the
media type is that which would have been sent had the request been a media type is that which would have been sent had the request been a
GET. GET.
Content-Type = "Content-Type" ":" OWS Content-Type-v Content-Type = "Content-Type" ":" OWS Content-Type-v
Content-Type-v = media-type Content-Type-v = media-type
Media types are defined in Section 2.3. An example of the field is Media types are defined in Section 2.3. An example of the field is
Content-Type: text/html; charset=ISO-8859-4 Content-Type: text/html; charset=ISO-8859-4
Further discussion of methods for identifying the media type of an Further discussion of Content-Type is provided in Section 4.2.
entity is provided in Section 3.2.1.
6. IANA Considerations 7. IANA Considerations
6.1. Message Header Registration 7.1. Header Field Registration
The Message Header Registry located at <http://www.iana.org/ The Message Header Field Registry located at <http://www.iana.org/
assignments/message-headers/message-header-index.html> should be assignments/message-headers/message-header-index.html> shall be
updated with the permanent registrations below (see [RFC3864]): updated with the permanent registrations below (see [RFC3864]):
+---------------------+----------+----------+--------------+ +---------------------+----------+----------+--------------+
| Header Field Name | Protocol | Status | Reference | | Header Field Name | Protocol | Status | Reference |
+---------------------+----------+----------+--------------+ +---------------------+----------+----------+--------------+
| Accept | http | standard | Section 5.1 | | Accept | http | standard | Section 6.1 |
| Accept-Charset | http | standard | Section 5.2 | | Accept-Charset | http | standard | Section 6.2 |
| Accept-Encoding | http | standard | Section 5.3 | | Accept-Encoding | http | standard | Section 6.3 |
| Accept-Language | http | standard | Section 5.4 | | Accept-Language | http | standard | Section 6.4 |
| Content-Disposition | http | | Appendix B.1 | | Content-Disposition | http | standard | Appendix B.1 |
| Content-Encoding | http | standard | Section 5.5 | | Content-Encoding | http | standard | Section 6.5 |
| Content-Language | http | standard | Section 5.6 | | Content-Language | http | standard | Section 6.6 |
| Content-Location | http | standard | Section 5.7 | | Content-Location | http | standard | Section 6.7 |
| Content-MD5 | http | standard | Section 5.8 | | Content-MD5 | http | standard | Section 6.8 |
| Content-Type | http | standard | Section 5.9 | | Content-Type | http | standard | Section 6.9 |
| MIME-Version | http | | Appendix A.1 | | MIME-Version | http | standard | Appendix A.1 |
+---------------------+----------+----------+--------------+ +---------------------+----------+----------+--------------+
The change controller is: "IETF (iesg@ietf.org) - Internet The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force". Engineering Task Force".
6.2. Content Coding Registry 7.2. Content Coding Registry
The registration procedure for HTTP Content Codings is now defined by The registration procedure for HTTP Content Codings is now defined by
Section 2.2.1 of this document. Section 2.2.1 of this document.
The HTTP Content Codings Registry located at The HTTP Content Codings Registry located at
<http://www.iana.org/assignments/http-parameters> should be updated <http://www.iana.org/assignments/http-parameters> shall be updated
with the registration below: with the registration below:
+----------+-----------------------------------------+--------------+ +----------+-----------------------------------------+--------------+
| Name | Description | Reference | | Name | Description | Reference |
+----------+-----------------------------------------+--------------+ +----------+-----------------------------------------+--------------+
| compress | UNIX "compress" program method | Section | | compress | UNIX "compress" program method | Section |
| | | 6.2.2.1 of | | | | 6.2.2.1 of |
| | | [Part1] | | | | [Part1] |
| deflate | "deflate" compression mechanism | Section | | deflate | "deflate" compression mechanism | Section |
| | ([RFC1951]) used inside the "zlib" data | 6.2.2.2 of | | | ([RFC1951]) used inside the "zlib" data | 6.2.2.2 of |
| | format ([RFC1950]) | [Part1] | | | format ([RFC1950]) | [Part1] |
| gzip | Same as GNU zip [RFC1952] | Section | | gzip | Same as GNU zip [RFC1952] | Section |
| | | 6.2.2.3 of | | | | 6.2.2.3 of |
| | | [Part1] | | | | [Part1] |
| identity | No transformation | Section 2.2 | | identity | No transformation | Section 2.2 |
+----------+-----------------------------------------+--------------+ +----------+-----------------------------------------+--------------+
7. Security Considerations 8. Security Considerations
This section is meant to inform application developers, information This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks. some suggestions for reducing security risks.
7.1. Privacy Issues Connected to Accept Headers 8.1. Privacy Issues Connected to Accept Headers
Accept request-headers can reveal information about the user to all Accept request-headers can reveal information about the user to all
servers which are accessed. The Accept-Language header in particular servers which are accessed. The Accept-Language header in particular
can reveal information the user would consider to be of a private can reveal information the user would consider to be of a private
nature, because the understanding of particular languages is often nature, because the understanding of particular languages is often
strongly correlated to the membership of a particular ethnic group. strongly correlated to the membership of a particular ethnic group.
User agents which offer the option to configure the contents of an User agents which offer the option to configure the contents of an
Accept-Language header to be sent in every request are strongly Accept-Language header to be sent in every request are strongly
encouraged to let the configuration process include a message which encouraged to let the configuration process include a message which
makes the user aware of the loss of privacy involved. makes the user aware of the loss of privacy involved.
skipping to change at page 28, line 42 skipping to change at page 29, line 18
many users not behind a proxy, the network address of the host many users not behind a proxy, the network address of the host
running the user agent will also serve as a long-lived user running the user agent will also serve as a long-lived user
identifier. In environments where proxies are used to enhance identifier. In environments where proxies are used to enhance
privacy, user agents ought to be conservative in offering accept privacy, user agents ought to be conservative in offering accept
header configuration options to end users. As an extreme privacy header configuration options to end users. As an extreme privacy
measure, proxies could filter the accept headers in relayed requests. measure, proxies could filter the accept headers in relayed requests.
General purpose user agents which provide a high degree of header General purpose user agents which provide a high degree of header
configurability SHOULD warn users about the loss of privacy which can configurability SHOULD warn users about the loss of privacy which can
be involved. be involved.
7.2. Content-Disposition Issues 8.2. Content-Disposition Issues
[RFC2183], from which the often implemented Content-Disposition (see [RFC2183], from which the often implemented Content-Disposition (see
Appendix B.1) header in HTTP is derived, has a number of very serious Appendix B.1) header in HTTP is derived, has a number of very serious
security considerations. Content-Disposition is not part of the HTTP security considerations. Content-Disposition is not part of the HTTP
standard, but since it is widely implemented, we are documenting its standard, but since it is widely implemented, we are documenting its
use and risks for implementors. See Section 5 of [RFC2183] for use and risks for implementors. See Section 5 of [RFC2183] for
details. details.
8. Acknowledgments 9. Acknowledgments
9. References 10. References
9.1. Normative References 10.1. Normative References
[ISO-8859-1] International Organization for Standardization, [ISO-8859-1] International Organization for Standardization,
"Information technology -- 8-bit single-byte coded "Information technology -- 8-bit single-byte coded
graphic character sets -- Part 1: Latin alphabet No. graphic character sets -- Part 1: Latin alphabet No.
1", ISO/IEC 8859-1:1998, 1998. 1", ISO/IEC 8859-1:1998, 1998.
[Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., [Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y.,
Ed., and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Ed., and J. Reschke, Ed., "HTTP/1.1, part 1: URIs,
Connections, and Message Parsing", Connections, and Message Parsing",
draft-ietf-httpbis-p1-messaging-10 (work in progress), draft-ietf-httpbis-p1-messaging-11 (work in progress),
July 2010. August 2010.
[Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., [Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y.,
Ed., and J. Reschke, Ed., "HTTP/1.1, part 2: Message Ed., and J. Reschke, Ed., "HTTP/1.1, part 2: Message
Semantics", draft-ietf-httpbis-p2-semantics-10 (work in Semantics", draft-ietf-httpbis-p2-semantics-11 (work in
progress), July 2010. progress), August 2010.
[Part4] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., [Part4] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y.,
Ed., and J. Reschke, Ed., "HTTP/1.1, part 4: Ed., and J. Reschke, Ed., "HTTP/1.1, part 4:
Conditional Requests", Conditional Requests",
draft-ietf-httpbis-p4-conditional-10 (work in draft-ietf-httpbis-p4-conditional-11 (work in
progress), July 2010. progress), August 2010.
[Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., [Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y.,
Ed., and J. Reschke, Ed., "HTTP/1.1, part 5: Range Ed., and J. Reschke, Ed., "HTTP/1.1, part 5: Range
Requests and Partial Responses", Requests and Partial Responses",
draft-ietf-httpbis-p5-range-10 (work in progress), draft-ietf-httpbis-p5-range-11 (work in progress),
July 2010. August 2010.
[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., [Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y.,
Ed., Nottingham, M., Ed., and J. Reschke, Ed., Ed., Nottingham, M., Ed., and J. Reschke, Ed.,
"HTTP/1.1, part 6: Caching", "HTTP/1.1, part 6: Caching",
draft-ietf-httpbis-p6-cache-10 (work in progress), draft-ietf-httpbis-p6-cache-11 (work in progress),
July 2010. August 2010.
[RFC1864] Myers, J. and M. Rose, "The Content-MD5 Header Field", [RFC1864] Myers, J. and M. Rose, "The Content-MD5 Header Field",
RFC 1864, October 1995. RFC 1864, October 1995.
[RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data [RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data
Format Specification version 3.3", RFC 1950, May 1996. Format Specification version 3.3", RFC 1950, May 1996.
RFC 1950 is an Informational RFC, thus it may be less RFC 1950 is an Informational RFC, thus it might be less
stable than this specification. On the other hand, stable than this specification. On the other hand,
this downward reference was present since the this downward reference was present since the
publication of RFC 2068 in 1997 ([RFC2068]), therefore publication of RFC 2068 in 1997 ([RFC2068]), therefore
it is unlikely to cause problems in practice. See also it is unlikely to cause problems in practice. See also
[BCP97]. [BCP97].
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format [RFC1951] Deutsch, P., "DEFLATE Compressed Data Format
Specification version 1.3", RFC 1951, May 1996. Specification version 1.3", RFC 1951, May 1996.
RFC 1951 is an Informational RFC, thus it may be less RFC 1951 is an Informational RFC, thus it might be less
stable than this specification. On the other hand, stable than this specification. On the other hand,
this downward reference was present since the this downward reference was present since the
publication of RFC 2068 in 1997 ([RFC2068]), therefore publication of RFC 2068 in 1997 ([RFC2068]), therefore
it is unlikely to cause problems in practice. See also it is unlikely to cause problems in practice. See also
[BCP97]. [BCP97].
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and [RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and
G. Randers-Pehrson, "GZIP file format specification G. Randers-Pehrson, "GZIP file format specification
version 4.3", RFC 1952, May 1996. version 4.3", RFC 1952, May 1996.
RFC 1952 is an Informational RFC, thus it may be less RFC 1952 is an Informational RFC, thus it might be less
stable than this specification. On the other hand, stable than this specification. On the other hand,
this downward reference was present since the this downward reference was present since the
publication of RFC 2068 in 1997 ([RFC2068]), therefore publication of RFC 2068 in 1997 ([RFC2068]), therefore
it is unlikely to cause problems in practice. See also it is unlikely to cause problems in practice. See also
[BCP97]. [BCP97].
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996. Message Bodies", RFC 2045, November 1996.
skipping to change at page 31, line 9 skipping to change at page 31, line 32
Language Tags", BCP 47, RFC 4647, September 2006. Language Tags", BCP 47, RFC 4647, September 2006.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008. January 2008.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for
Identifying Languages", BCP 47, RFC 5646, Identifying Languages", BCP 47, RFC 5646,
September 2009. September 2009.
9.2. Informative References 10.2. Informative References
[BCP97] Klensin, J. and S. Hartman, "Handling Normative [BCP97] Klensin, J. and S. Hartman, "Handling Normative
References to Standards-Track Documents", BCP 97, References to Standards-Track Documents", BCP 97,
RFC 4897, June 2007. RFC 4897, June 2007.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen,
"Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945, "Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945,
May 1996. May 1996.
[RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet
skipping to change at page 32, line 21 skipping to change at page 32, line 45
and Registration Procedures", BCP 13, RFC 4288, and Registration Procedures", BCP 13, RFC 4288,
December 2005. December 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008. RFC 5226, May 2008.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322, [RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008. October 2008.
Appendix A. Differences Between HTTP Entities and RFC 2045 Entities Appendix A. Differences between HTTP and MIME
HTTP/1.1 uses many of the constructs defined for Internet Mail HTTP/1.1 uses many of the constructs defined for Internet Mail
([RFC5322]) and the Multipurpose Internet Mail Extensions (MIME ([RFC5322]) and the Multipurpose Internet Mail Extensions (MIME
[RFC2045]) to allow entities to be transmitted in an open variety of [RFC2045]) to allow a message-body to be transmitted in an open
representations and with extensible mechanisms. However, RFC 2045 variety of representations and with extensible mechanisms. However,
discusses mail, and HTTP has a few features that are different from RFC 2045 discusses mail, and HTTP has a few features that are
those described in RFC 2045. These differences were carefully chosen different from those described in MIME. These differences were
to optimize performance over binary connections, to allow greater carefully chosen to optimize performance over binary connections, to
freedom in the use of new media types, to make date comparisons allow greater freedom in the use of new media types, to make date
easier, and to acknowledge the practice of some early HTTP servers comparisons easier, and to acknowledge the practice of some early
and clients. HTTP servers and clients.
This appendix describes specific areas where HTTP differs from RFC This appendix describes specific areas where HTTP differs from MIME.
2045. Proxies and gateways to strict MIME environments SHOULD be Proxies and gateways to strict MIME environments SHOULD be aware of
aware of these differences and provide the appropriate conversions these differences and provide the appropriate conversions where
where necessary. Proxies and gateways from MIME environments to HTTP necessary. Proxies and gateways from MIME environments to HTTP also
also need to be aware of the differences because some conversions need to be aware of the differences because some conversions might be
might be required. required.
A.1. MIME-Version A.1. MIME-Version
HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages
MAY include a single MIME-Version general-header field to indicate MAY include a single MIME-Version general-header field to indicate
what version of the MIME protocol was used to construct the message. what version of the MIME protocol was used to construct the message.
Use of the MIME-Version header field indicates that the message is in Use of the MIME-Version header field indicates that the message is in
full compliance with the MIME protocol (as defined in [RFC2045]). full compliance with the MIME protocol (as defined in [RFC2045]).
Proxies/gateways are responsible for ensuring full compliance (where Proxies/gateways are responsible for ensuring full compliance (where
possible) when exporting HTTP messages to strict MIME environments. possible) when exporting HTTP messages to strict MIME environments.
MIME-Version = "MIME-Version" ":" OWS MIME-Version-v MIME-Version = "MIME-Version" ":" OWS MIME-Version-v
MIME-Version-v = 1*DIGIT "." 1*DIGIT MIME-Version-v = 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.1. However, MIME version "1.0" is the default for use in HTTP/1.1. However,
HTTP/1.1 message parsing and semantics are defined by this document HTTP/1.1 message parsing and semantics are defined by this document
and not the MIME specification. and not the MIME specification.
A.2. Conversion to Canonical Form A.2. Conversion to Canonical Form
[RFC2045] requires that an Internet mail entity be converted to MIME requires that an Internet mail body-part be converted to
canonical form prior to being transferred, as described in Section 4 canonical form prior to being transferred, as described in Section 4
of [RFC2049]. Section 2.3.1 of this document describes the forms of [RFC2049]. Section 2.3.1 of this document describes the forms
allowed for subtypes of the "text" media type when transmitted over allowed for subtypes of the "text" media type when transmitted over
HTTP. [RFC2046] requires that content with a type of "text" HTTP. [RFC2046] requires that content with a type of "text"
represent line breaks as CRLF and forbids the use of CR or LF outside represent line breaks as CRLF and forbids the use of CR or LF outside
of line break sequences. HTTP allows CRLF, bare CR, and bare LF to of line break sequences. HTTP allows CRLF, bare CR, and bare LF to
indicate a line break within text content when a message is indicate a line break within text content when a message is
transmitted over HTTP. transmitted over HTTP.
Where it is possible, a proxy or gateway from HTTP to a strict MIME Where it is possible, a proxy or gateway from HTTP to a strict MIME
environment SHOULD translate all line breaks within the text media environment SHOULD translate all line breaks within the text media
types described in Section 2.3.1 of this document to the RFC 2049 types described in Section 2.3.1 of this document to the RFC 2049
canonical form of CRLF. Note, however, that this might be canonical form of CRLF. Note, however, that this might be
complicated by the presence of a Content-Encoding and by the fact complicated by the presence of a Content-Encoding and by the fact
that HTTP allows the use of some character sets which do not use that HTTP allows the use of some character sets which do not use
octets 13 and 10 to represent CR and LF, as is the case for some octets 13 and 10 to represent CR and LF, as is the case for some
multi-byte character sets. multi-byte character sets.
Implementors should note that conversion will break any cryptographic Conversion will break any cryptographic checksums applied to the
checksums applied to the original content unless the original content original content unless the original content is already in canonical
is already in canonical form. Therefore, the canonical form is form. Therefore, the canonical form is recommended for any content
recommended for any content that uses such checksums in HTTP. that uses such checksums in HTTP.
A.3. Conversion of Date Formats A.3. Conversion of Date Formats
HTTP/1.1 uses a restricted set of date formats (Section 6.1 of HTTP/1.1 uses a restricted set of date formats (Section 6.1 of
[Part1]) to simplify the process of date comparison. Proxies and [Part1]) to simplify the process of date comparison. Proxies and
gateways from other protocols SHOULD ensure that any Date header gateways from other protocols SHOULD ensure that any Date header
field present in a message conforms to one of the HTTP/1.1 formats field present in a message conforms to one of the HTTP/1.1 formats
and rewrite the date if necessary. and rewrite the date if necessary.
A.4. Introduction of Content-Encoding A.4. Introduction of Content-Encoding
RFC 2045 does not include any concept equivalent to HTTP/1.1's MIME does not include any concept equivalent to HTTP/1.1's Content-
Content-Encoding header field. Since this acts as a modifier on the Encoding header field. Since this acts as a modifier on the media
media type, proxies and gateways from HTTP to MIME-compliant type, proxies and gateways from HTTP to MIME-compliant protocols MUST
protocols MUST either change the value of the Content-Type header either change the value of the Content-Type header field or decode
field or decode the entity-body before forwarding the message. (Some the representation before forwarding the message. (Some experimental
experimental applications of Content-Type for Internet mail have used applications of Content-Type for Internet mail have used a media-type
a media-type parameter of ";conversions=<content-coding>" to perform parameter of ";conversions=<content-coding>" to perform a function
a function equivalent to Content-Encoding. However, this parameter equivalent to Content-Encoding. However, this parameter is not part
is not part of RFC 2045). of the MIME standards).
A.5. No Content-Transfer-Encoding A.5. No Content-Transfer-Encoding
HTTP does not use the Content-Transfer-Encoding field of RFC 2045. HTTP does not use the Content-Transfer-Encoding field of MIME.
Proxies and gateways from MIME-compliant protocols to HTTP MUST Proxies and gateways from MIME-compliant protocols to HTTP MUST
remove any Content-Transfer-Encoding prior to delivering the response remove any Content-Transfer-Encoding prior to delivering the response
message to an HTTP client. message to an HTTP client.
Proxies and gateways from HTTP to MIME-compliant protocols are Proxies and gateways from HTTP to MIME-compliant protocols are
responsible for ensuring that the message is in the correct format responsible for ensuring that the message is in the correct format
and encoding for safe transport on that protocol, where "safe and encoding for safe transport on that protocol, where "safe
transport" is defined by the limitations of the protocol being used. transport" is defined by the limitations of the protocol being used.
Such a proxy or gateway SHOULD label the data with an appropriate Such a proxy or gateway SHOULD label the data with an appropriate
Content-Transfer-Encoding if doing so will improve the likelihood of Content-Transfer-Encoding if doing so will improve the likelihood of
skipping to change at page 35, line 37 skipping to change at page 36, line 12
The receiving user agent SHOULD NOT respect any directory path The receiving user agent SHOULD NOT respect any directory path
information present in the filename-parm parameter, which is the only information present in the filename-parm parameter, which is the only
parameter believed to apply to HTTP implementations at this time. parameter believed to apply to HTTP implementations at this time.
The filename SHOULD be treated as a terminal component only. The filename SHOULD be treated as a terminal component only.
If this header is used in a response with the application/ If this header is used in a response with the application/
octet-stream content-type, the implied suggestion is that the user octet-stream content-type, the implied suggestion is that the user
agent should not display the response, but directly enter a "save agent should not display the response, but directly enter a "save
response as..." dialog. response as..." dialog.
See Section 7.2 for Content-Disposition security issues. See Section 8.2 for Content-Disposition security issues.
Appendix C. Compatibility with Previous Versions
C.1. Changes from RFC 2068
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 self delimiting); it was important
to straighten out exactly how message lengths are computed.
(Section 3.2.2, see also [Part1], [Part5] and [Part6]).
Charset wildcarding is introduced to avoid explosion of character set
names in accept headers. (Section 5.2)
Content-Base was deleted from the specification: it was not
implemented widely, and there is no simple, safe way to introduce it
without a robust extension mechanism. In addition, it is used in a
similar, but not identical fashion in MHTML [RFC2557].
A content-coding of "identity" was introduced, to solve problems
discovered in caching. (Section 2.2)
The Alternates, Content-Version, Derived-From, Link, URI, Public and
Content-Base header fields were defined in previous versions of this
specification, but not commonly implemented. See Section 19.6.2 of
[RFC2068].
C.2. Changes from RFC 2616 Appendix C. Changes from RFC 2616
Clarify contexts that charset is used in. (Section 2.1) Clarify contexts that charset is used in. (Section 2.1)
Remove base URI setting semantics for Content-Location due to poor Remove base URI setting semantics for Content-Location due to poor
implementation support, which was caused by too many broken servers implementation support, which was caused by too many broken servers
emitting bogus Content-Location headers, and also the potentially emitting bogus Content-Location headers, and also the potentially
undesirable effect of potentially breaking relative links in content- undesirable effect of potentially breaking relative links in content-
negotiated resources. (Section 5.7) negotiated resources. (Section 6.7)
Remove reference to non-existant identity transfer-coding value Remove reference to non-existant identity transfer-coding value
tokens. (Appendix A.5) tokens. (Appendix A.5)
Appendix D. Collected ABNF Appendix D. Collected ABNF
Accept = "Accept:" OWS Accept-v Accept = "Accept:" OWS Accept-v
Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v Accept-Charset = "Accept-Charset:" OWS Accept-Charset-v
Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q=" Accept-Charset-v = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q=" qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
skipping to change at page 37, line 42 skipping to change at page 37, line 38
content-disposition = "Content-Disposition:" OWS content-disposition = "Content-Disposition:" OWS
content-disposition-v content-disposition-v
content-disposition-v = disposition-type *( OWS ";" OWS content-disposition-v = disposition-type *( OWS ";" OWS
disposition-parm ) disposition-parm )
disp-extension-parm = token "=" word disp-extension-parm = token "=" word
disp-extension-token = token disp-extension-token = token
disposition-parm = filename-parm / disp-extension-parm disposition-parm = filename-parm / disp-extension-parm
disposition-type = "attachment" / disp-extension-token disposition-type = "attachment" / disp-extension-token
entity-body = *OCTET
entity-header = Content-Encoding / Content-Language / Content-Length
/ Content-Location / Content-MD5 / Content-Range / Content-Type /
Expires / Last-Modified / extension-header
extension-header = header-field
filename-parm = "filename=" quoted-string filename-parm = "filename=" quoted-string
header-field = <header-field, defined in [Part1], Section 3.2> header-field = <header-field, defined in [Part1], Section 3.2>
language-range = <language-range, defined in [RFC4647], Section 2.1> language-range = <language-range, defined in [RFC4647], Section 2.1>
language-tag = <Language-Tag, defined in [RFC5646], Section 2.1> language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
";" OWS parameter ) ";" OWS parameter )
media-type = type "/" subtype *( OWS ";" OWS parameter ) media-type = type "/" subtype *( OWS ";" OWS parameter )
parameter = attribute "=" value parameter = attribute "=" value
partial-URI = <partial-URI, defined in [Part1], Section 2.6> partial-URI = <partial-URI, defined in [Part1], Section 2.6>
quoted-string = <quoted-string, defined in [Part1], Section 1.2.2> quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
qvalue = <qvalue, defined in [Part1], Section 6.4> qvalue = <qvalue, defined in [Part1], Section 6.4>
subtype = token subtype = token
token = <token, defined in [Part1], Section 1.2.2> token = <token, defined in [Part1], Section 1.2.2>
type = token type = token
value = word value = word
skipping to change at page 38, line 32 skipping to change at page 38, line 22
value = word value = word
word = <word, defined in [Part1], Section 1.2.2> word = <word, defined in [Part1], Section 1.2.2>
ABNF diagnostics: ABNF diagnostics:
; Accept defined but not used ; Accept defined but not used
; Accept-Charset defined but not used ; Accept-Charset defined but not used
; Accept-Encoding defined but not used ; Accept-Encoding defined but not used
; Accept-Language defined but not used ; Accept-Language defined but not used
; Content-Encoding defined but not used
; Content-Language defined but not used
; Content-Length defined but not used
; Content-Location defined but not used
; Content-MD5 defined but not used
; Content-Range defined but not used
; Content-Type defined but not used
; Expires defined but not used
; Last-Modified defined but not used
; MIME-Version defined but not used ; MIME-Version defined but not used
; content-disposition defined but not used ; content-disposition defined but not used
; entity-body defined but not used ; header-field defined but not used
; entity-header defined but not used
Appendix E. Change Log (to be removed by RFC Editor before publication) Appendix E. Change Log (to be removed by RFC Editor before publication)
E.1. Since RFC2616 E.1. Since RFC2616
Extracted relevant partitions from [RFC2616]. Extracted relevant partitions from [RFC2616].
E.2. Since draft-ietf-httpbis-p3-payload-00 E.2. Since draft-ietf-httpbis-p3-payload-00
Closed issues: Closed issues:
skipping to change at page 42, line 29 skipping to change at page 42, line 27
o <http://tools.ietf.org/wg/httpbis/trac/ticket/81>: "Content o <http://tools.ietf.org/wg/httpbis/trac/ticket/81>: "Content
Negotiation for media types" Negotiation for media types"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/181>: "Accept- o <http://tools.ietf.org/wg/httpbis/trac/ticket/181>: "Accept-
Language: which RFC4647 filtering?" Language: which RFC4647 filtering?"
E.11. Since draft-ietf-httpbis-p3-payload-09 E.11. Since draft-ietf-httpbis-p3-payload-09
Closed issues: Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/122>: "MIME-Version
not listed in P1, general header fields"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/143>: "IANA registry o <http://tools.ietf.org/wg/httpbis/trac/ticket/143>: "IANA registry
for content/transfer encodings" for content/transfer encodings"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/155>: "Content o <http://tools.ietf.org/wg/httpbis/trac/ticket/155>: "Content
Sniffing" Sniffing"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term o <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term
"word" when talking about header structure" "word" when talking about header structure"
Partly resolved issues: Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the o <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the
requested resource's URI" requested resource's URI"
E.12. Since draft-ietf-httpbis-p3-payload-10
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/69>: "Clarify
'Requested Variant'"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/80>: "Content-
Location isn't special"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/90>: "Delimiting
messages with multipart/byteranges"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
entity / representation / variant terminology"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/136>: "confusing
req. language for Content-Location"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/167>: "Content-
Location on 304 responses"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/183>: "'requested
resource' in content-encoding definition"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
removing the 'changes from 2068' sections"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/178>: "Content-MD5
and partial responses"
Index Index
A A
Accept header 17 Accept header 17
Accept-Charset header 19 Accept-Charset header 19
Accept-Encoding header 20 Accept-Encoding header 20
Accept-Language header 21 Accept-Language header 21
Alternates header 36
C C
Coding Format Coding Format
compress 8 compress 8
deflate 8 deflate 8
gzip 9 gzip 8
identity 9 identity 8
compress (Coding Format) 8 compress (Coding Format) 8
content negotiation 5 content negotiation 5
Content-Base header 36
Content-Disposition header 35 Content-Disposition header 35
Content-Encoding header 22 Content-Encoding header 22
Content-Language header 23 Content-Language header 23
Content-Location header 24 Content-Location header 24
Content-MD5 header 25 Content-MD5 header 25
Content-Type header 26 Content-Type header 27
Content-Version header 36
D D
deflate (Coding Format) 8 deflate (Coding Format) 8
Derived-From header 36
E
entity 5
G G
Grammar Grammar
Accept 17 Accept 17
Accept-Charset 19 Accept-Charset 19
Accept-Charset-v 19 Accept-Charset-v 19
Accept-Encoding 20 Accept-Encoding 20
Accept-Encoding-v 20 Accept-Encoding-v 20
accept-ext 17 accept-ext 17
Accept-Language 21 Accept-Language 21
Accept-Language-v 21 Accept-Language-v 21
accept-params 17 accept-params 17
Accept-v 17 Accept-v 17
attribute 10 attribute 9
charset 7 charset 7
codings 20 codings 20
content-coding 8 content-coding 8
content-disposition 35 content-disposition 35
content-disposition-v 35 content-disposition-v 35
Content-Encoding 22 Content-Encoding 22
Content-Encoding-v 22 Content-Encoding-v 22
Content-Language 23 Content-Language 23
Content-Language-v 23 Content-Language-v 23
Content-Location 24 Content-Location 24
Content-Location-v 24 Content-Location-v 24
Content-MD5 25 Content-MD5 25
Content-MD5-v 25 Content-MD5-v 25
Content-Type 26 Content-Type 27
Content-Type-v 26 Content-Type-v 27
disp-extension-parm 35 disp-extension-parm 35
disp-extension-token 35 disp-extension-token 35
disposition-parm 35 disposition-parm 35
disposition-type 35 disposition-type 35
entity-body 13
entity-header 13
extension-header 13
filename-parm 35 filename-parm 35
language-range 21 language-range 21
language-tag 12 language-tag 11
media-range 17 media-range 17
media-type 9 media-type 9
MIME-Version 32 MIME-Version 33
MIME-Version-v 32 MIME-Version-v 33
parameter 10 parameter 9
subtype 9 subtype 9
type 9 type 9
value 10 value 9
gzip (Coding Format) 9 gzip (Coding Format) 8
H H
Headers Headers
Accept 17 Accept 17
Accept-Charset 19 Accept-Charset 19
Accept-Encoding 20 Accept-Encoding 20
Accept-Language 21 Accept-Language 21
Alternate 36
Content-Base 36
Content-Disposition 35 Content-Disposition 35
Content-Encoding 22 Content-Encoding 22
Content-Language 23 Content-Language 23
Content-Location 24 Content-Location 24
Content-MD5 25 Content-MD5 25
Content-Type 26 Content-Type 27
Content-Version 36 MIME-Version 33
Derived-From 36
Link 36
MIME-Version 32
Public 36
URI 36
I I
identity (Coding Format) 9 identity (Coding Format) 8
L
Link header 36
M M
MIME-Version header 32 MIME-Version header 33
P P
Public header 36 payload 12
R R
representation 5 representation 12
U
URI header 36
V
variant 5
Authors' Addresses Authors' Addresses
Roy T. Fielding (editor) Roy T. Fielding (editor)
Day Software Day Software
23 Corporate Plaza DR, Suite 280 23 Corporate Plaza DR, Suite 280
Newport Beach, CA 92660 Newport Beach, CA 92660
USA USA
Phone: +1-949-706-5300 Phone: +1-949-706-5300
 End of changes. 159 change blocks. 
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