HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe
Obsoletes: 2616 (if approved) J. Reschke, Ed.
Updates: 2817 (if approved) greenbytes
Intended status: Standards Track October 4, 2012
Expires: April 7, 2013
Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content
draft-ietf-httpbis-p2-semantics-21
Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypertext information
systems. This document defines the semantics of HTTP/1.1 messages,
as expressed by request methods, request header fields, response
status codes, and response header fields, along with the payload of
messages (metadata and body content) and mechanisms for content
negotiation.
Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
.
The current issues list is at
and related
documents (including fancy diffs) can be found at
.
The changes in this draft are summarized in Appendix F.41.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1. Conformance and Error Handling . . . . . . . . . . . . . 7
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7
2. Resource . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Representation . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Representation Metadata . . . . . . . . . . . . . . . . . 8
3.1.1. Data Type . . . . . . . . . . . . . . . . . . . . . . 9
3.1.2. Data Encoding . . . . . . . . . . . . . . . . . . . . 12
3.1.3. Audience Language . . . . . . . . . . . . . . . . . . 14
3.1.4. Identification . . . . . . . . . . . . . . . . . . . 15
3.2. Representation Data . . . . . . . . . . . . . . . . . . . 18
3.3. Payload Semantics . . . . . . . . . . . . . . . . . . . . 18
3.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 19
3.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 20
3.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . 21
4. Product Tokens . . . . . . . . . . . . . . . . . . . . . . . 22
5. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 22
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5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2. Common Method Properties . . . . . . . . . . . . . . . . 24
5.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 24
5.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 25
5.2.3. Cacheable Methods . . . . . . . . . . . . . . . . . . 25
5.3. Method Definitions . . . . . . . . . . . . . . . . . . . 25
5.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 26
5.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 30
5.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 30
5.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 33
6. Request Header Fields . . . . . . . . . . . . . . . . . . . . 33
6.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.1. Max-Forwards . . . . . . . . . . . . . . . . . . . . 34
6.1.2. Expect . . . . . . . . . . . . . . . . . . . . . . . 34
6.2. Conditionals . . . . . . . . . . . . . . . . . . . . . . 37
6.3. Content Negotiation . . . . . . . . . . . . . . . . . . . 38
6.3.1. Quality Values . . . . . . . . . . . . . . . . . . . 38
6.3.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 38
6.3.3. Accept-Charset . . . . . . . . . . . . . . . . . . . 41
6.3.4. Accept-Encoding . . . . . . . . . . . . . . . . . . . 41
6.3.5. Accept-Language . . . . . . . . . . . . . . . . . . . 42
6.4. Authentication Credentials . . . . . . . . . . . . . . . 44
6.5. Context . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.5.1. From . . . . . . . . . . . . . . . . . . . . . . . . 44
6.5.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 45
6.5.3. User-Agent . . . . . . . . . . . . . . . . . . . . . 45
7. Response Status Codes . . . . . . . . . . . . . . . . . . . . 46
7.1. Overview of Status Codes . . . . . . . . . . . . . . . . 47
7.2. Informational 1xx . . . . . . . . . . . . . . . . . . . . 49
7.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 49
7.2.2. 101 Switching Protocols . . . . . . . . . . . . . . . 49
7.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 50
7.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 50
7.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 50
7.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 51
7.3.4. 203 Non-Authoritative Information . . . . . . . . . . 51
7.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 51
7.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 52
7.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 52
7.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 54
7.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 54
7.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 55
7.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 55
7.4.5. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 56
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7.4.6. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 56
7.4.7. 307 Temporary Redirect . . . . . . . . . . . . . . . 56
7.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 56
7.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 56
7.5.2. 402 Payment Required . . . . . . . . . . . . . . . . 56
7.5.3. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 57
7.5.4. 404 Not Found . . . . . . . . . . . . . . . . . . . . 57
7.5.5. 405 Method Not Allowed . . . . . . . . . . . . . . . 57
7.5.6. 406 Not Acceptable . . . . . . . . . . . . . . . . . 57
7.5.7. 408 Request Timeout . . . . . . . . . . . . . . . . . 58
7.5.8. 409 Conflict . . . . . . . . . . . . . . . . . . . . 58
7.5.9. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 58
7.5.10. 411 Length Required . . . . . . . . . . . . . . . . . 59
7.5.11. 413 Request Representation Too Large . . . . . . . . 59
7.5.12. 414 URI Too Long . . . . . . . . . . . . . . . . . . 59
7.5.13. 415 Unsupported Media Type . . . . . . . . . . . . . 59
7.5.14. 417 Expectation Failed . . . . . . . . . . . . . . . 60
7.5.15. 426 Upgrade Required . . . . . . . . . . . . . . . . 60
7.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 60
7.6.1. 500 Internal Server Error . . . . . . . . . . . . . . 60
7.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 60
7.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 61
7.6.4. 503 Service Unavailable . . . . . . . . . . . . . . . 61
7.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 61
7.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 61
8. Response Header Fields . . . . . . . . . . . . . . . . . . . 61
8.1. Control Data . . . . . . . . . . . . . . . . . . . . . . 62
8.1.1. Origination Date . . . . . . . . . . . . . . . . . . 62
8.1.2. Location . . . . . . . . . . . . . . . . . . . . . . 65
8.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . . 66
8.2. Selected Representation Header Fields . . . . . . . . . . 67
8.2.1. Vary . . . . . . . . . . . . . . . . . . . . . . . . 67
8.3. Authentication Challenges . . . . . . . . . . . . . . . . 68
8.4. Informative . . . . . . . . . . . . . . . . . . . . . . . 68
8.4.1. Allow . . . . . . . . . . . . . . . . . . . . . . . . 69
8.4.2. Server . . . . . . . . . . . . . . . . . . . . . . . 69
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 70
9.1. Method Registry . . . . . . . . . . . . . . . . . . . . . 70
9.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 70
9.1.2. Considerations for New Methods . . . . . . . . . . . 70
9.1.3. Registrations . . . . . . . . . . . . . . . . . . . . 71
9.2. Status Code Registry . . . . . . . . . . . . . . . . . . 71
9.2.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 71
9.2.2. Considerations for New Status Codes . . . . . . . . . 71
9.2.3. Registrations . . . . . . . . . . . . . . . . . . . . 72
9.3. Header Field Registry . . . . . . . . . . . . . . . . . . 73
9.3.1. Considerations for New Header Fields . . . . . . . . 74
9.3.2. Registrations . . . . . . . . . . . . . . . . . . . . 75
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9.4. Content Coding Registry . . . . . . . . . . . . . . . . . 76
9.4.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 76
9.4.2. Registrations . . . . . . . . . . . . . . . . . . . . 77
10. Security Considerations . . . . . . . . . . . . . . . . . . . 77
10.1. Transfer of Sensitive Information . . . . . . . . . . . . 77
10.2. Encoding Sensitive Information in URIs . . . . . . . . . 78
10.3. Location Header Fields: Spoofing and Information
Leakage . . . . . . . . . . . . . . . . . . . . . . . . . 79
10.4. Security Considerations for CONNECT . . . . . . . . . . . 79
10.5. Privacy Issues Connected to Accept Header Fields . . . . 79
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 80
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 80
12.1. Normative References . . . . . . . . . . . . . . . . . . 80
12.2. Informative References . . . . . . . . . . . . . . . . . 81
Appendix A. Differences between HTTP and MIME . . . . . . . . . 83
A.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . 84
A.2. Conversion to Canonical Form . . . . . . . . . . . . . . 84
A.3. Conversion of Date Formats . . . . . . . . . . . . . . . 84
A.4. Introduction of Content-Encoding . . . . . . . . . . . . 85
A.5. No Content-Transfer-Encoding . . . . . . . . . . . . . . 85
A.6. MHTML and Line Length Limitations . . . . . . . . . . . . 85
Appendix B. Additional Features . . . . . . . . . . . . . . . . 85
Appendix C. Changes from RFC 2616 . . . . . . . . . . . . . . . 86
Appendix D. Imported ABNF . . . . . . . . . . . . . . . . . . . 88
Appendix E. Collected ABNF . . . . . . . . . . . . . . . . . . . 88
Appendix F. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 91
F.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . 91
F.2. Since draft-ietf-httpbis-p2-semantics-00 . . . . . . . . 91
F.3. Since draft-ietf-httpbis-p3-payload-00 . . . . . . . . . 92
F.4. Since draft-ietf-httpbis-p2-semantics-01 . . . . . . . . 93
F.5. Since draft-ietf-httpbis-p3-payload-01 . . . . . . . . . 93
F.6. Since draft-ietf-httpbis-p2-semantics-02 . . . . . . . . 93
F.7. Since draft-ietf-httpbis-p3-payload-02 . . . . . . . . . 94
F.8. Since draft-ietf-httpbis-p2-semantics-03 . . . . . . . . 95
F.9. Since draft-ietf-httpbis-p3-payload-03 . . . . . . . . . 95
F.10. Since draft-ietf-httpbis-p2-semantics-04 . . . . . . . . 95
F.11. Since draft-ietf-httpbis-p3-payload-04 . . . . . . . . . 96
F.12. Since draft-ietf-httpbis-p2-semantics-05 . . . . . . . . 96
F.13. Since draft-ietf-httpbis-p3-payload-05 . . . . . . . . . 96
F.14. Since draft-ietf-httpbis-p2-semantics-06 . . . . . . . . 97
F.15. Since draft-ietf-httpbis-p3-payload-06 . . . . . . . . . 97
F.16. Since draft-ietf-httpbis-p2-semantics-07 . . . . . . . . 97
F.17. Since draft-ietf-httpbis-p3-payload-07 . . . . . . . . . 98
F.18. Since draft-ietf-httpbis-p2-semantics-08 . . . . . . . . 99
F.19. Since draft-ietf-httpbis-p3-payload-08 . . . . . . . . . 99
F.20. Since draft-ietf-httpbis-p2-semantics-09 . . . . . . . . 99
F.21. Since draft-ietf-httpbis-p3-payload-09 . . . . . . . . . 99
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F.22. Since draft-ietf-httpbis-p2-semantics-10 . . . . . . . . 100
F.23. Since draft-ietf-httpbis-p3-payload-10 . . . . . . . . . 100
F.24. Since draft-ietf-httpbis-p2-semantics-11 . . . . . . . . 101
F.25. Since draft-ietf-httpbis-p3-payload-11 . . . . . . . . . 101
F.26. Since draft-ietf-httpbis-p2-semantics-12 . . . . . . . . 101
F.27. Since draft-ietf-httpbis-p3-payload-12 . . . . . . . . . 103
F.28. Since draft-ietf-httpbis-p2-semantics-13 . . . . . . . . 103
F.29. Since draft-ietf-httpbis-p3-payload-13 . . . . . . . . . 103
F.30. Since draft-ietf-httpbis-p2-semantics-14 . . . . . . . . 103
F.31. Since draft-ietf-httpbis-p3-payload-14 . . . . . . . . . 104
F.32. Since draft-ietf-httpbis-p2-semantics-15 . . . . . . . . 104
F.33. Since draft-ietf-httpbis-p3-payload-15 . . . . . . . . . 104
F.34. Since draft-ietf-httpbis-p2-semantics-16 . . . . . . . . 104
F.35. Since draft-ietf-httpbis-p3-payload-16 . . . . . . . . . 104
F.36. Since draft-ietf-httpbis-p2-semantics-17 . . . . . . . . 105
F.37. Since draft-ietf-httpbis-p3-payload-17 . . . . . . . . . 105
F.38. Since draft-ietf-httpbis-p2-semantics-18 . . . . . . . . 105
F.39. Since draft-ietf-httpbis-p3-payload-18 . . . . . . . . . 106
F.40. Since draft-ietf-httpbis-p2-semantics-19 and
draft-ietf-httpbis-p3-payload-19 . . . . . . . . . . . . 106
F.41. Since draft-ietf-httpbis-p2-semantics-20 . . . . . . . . 107
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
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1. Introduction
Each Hypertext Transfer Protocol (HTTP) message is either a request
or a response. A server listens on a connection for a request,
parses each message received, interprets the message semantics in
relation to the identified request target, and responds to that
request with one or more response messages. A client constructs
request messages to communicate specific intentions, and examines
received responses to see if the intentions were carried out and
determine how to interpret the results. This document defines
HTTP/1.1 request and response semantics in terms of the architecture
defined in [Part1].
HTTP provides a uniform interface for interacting with a resource
(Section 2), regardless of its type, nature, or implementation, and
for transferring content in message payloads in the form of a
representation (Section 3).
HTTP semantics include the intentions defined by each request method
(Section 5), extensions to those semantics that might be described in
request header fields (Section 6), the meaning of status codes to
indicate a machine-readable response (Section 7), and the meaning of
other control data and resource metadata that might be given in
response header fields (Section 8).
This document also defines representation metadata that describe how
a payload is intended to be interpreted by a recipient, the request
header fields that might influence content selection, and the various
selection algorithms that are collectively referred to as ""content
negotiation"" (Section 3.4).
1.1. Conformance and Error Handling
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Conformance criteria and considerations regarding error handling are
defined in Section 2.5 of [Part1].
1.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with the list rule extension defined in Section
1.2 of [Part1]. Appendix D describes rules imported from other
documents. Appendix E shows the collected ABNF with the list rule
expanded.
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2. Resource
The target of each HTTP request is called a resource. HTTP does not
limit the nature of a resource; it merely defines an interface that
might be used to interact with resources. Each resource is
identified by a Uniform Resource Identifier (URI), as described in
Section 2.7 of [Part1].
When a client constructs an HTTP/1.1 request message, it sends the
"target URI" in one of various forms, as defined in (Section 5.3 of
[Part1]). When a request is received, the server reconstructs an
"effective request URI" for the target resource (Section 5.5 of
[Part1]).
One design goal of HTTP is to separate resource identification from
request semantics, which is made possible by vesting the request
semantics in the request method (Section 5) and a few request-
modifying header fields (Section 6). Resource owners SHOULD NOT
include request semantics within a URI, such as by specifying an
action to invoke within the path or query components of the effective
request URI, unless those semantics are disabled when they are
inconsistent with the request method.
3. Representation
If we consider that a resource could be anything, and that the
uniform interface provided by HTTP is similar to a window through
which one can observe and act upon such a thing only through the
communication of messages to some independent actor on the other
side, then we need an abstraction to represent ("take the place of")
the current or desired state of that thing in our communications. We
call that abstraction a ""representation"" [REST].
For the purposes of HTTP, a "representation" is information that
reflects the current or desired state of a given resource, in a
format that can be readily communicated via the protocol, consisting
of a set of representation metadata and a potentially unbounded
stream of representation data.
3.1. Representation Metadata
Representation header fields provide metadata about the
representation. When a message includes a payload body, the
representation header fields describe how to interpret the
representation data enclosed in the payload body. In a response to a
HEAD request, the representation header fields describe the
representation data that would have been enclosed in the payload body
if the same request had been a GET.
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The following header fields are defined to convey representation
metadata:
+-------------------+------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------+
| Content-Type | Section 3.1.1.5 |
| Content-Encoding | Section 3.1.2.2 |
| Content-Language | Section 3.1.3.2 |
| Content-Location | Section 3.1.4.2 |
| Expires | Section 7.3 of [Part6] |
+-------------------+------------------------+
3.1.1. Data Type
3.1.1.1. Media Types
HTTP uses Internet Media Types [RFC2046] in the Content-Type
(Section 3.1.1.5) and Accept (Section 6.3.2) header fields in order
to provide open and extensible data typing and type negotiation.
media-type = type "/" subtype *( OWS ";" OWS parameter )
type = token
subtype = token
The type/subtype MAY be followed by parameters in the form of
attribute/value pairs.
parameter = attribute "=" value
attribute = token
value = word
The type, subtype, and parameter attribute names are case-
insensitive. Parameter values might or might not be case-sensitive,
depending on the semantics of the parameter name. The presence or
absence of a parameter might be significant to the processing of a
media-type, depending on its definition within the media type
registry.
A parameter value that matches the token production can be
transmitted as either a token or within a quoted-string. The quoted
and unquoted values are equivalent.
Media-type values are registered with the Internet Assigned Number
Authority (IANA). The media type registration process is outlined in
[RFC4288]. Use of non-registered media types is discouraged.
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3.1.1.2. Character Encodings (charset)
HTTP uses charset names to indicate the character encoding of a
textual representation.
A character encoding is identified by a case-insensitive token. The
complete set of tokens is defined by the IANA Character Set registry
().
charset = token
Although HTTP allows an arbitrary token to be used as a charset
value, any token that has a predefined value within the IANA
Character Set registry MUST represent the character encoding defined
by that registry. Applications SHOULD limit their use of character
encodings to those defined within the IANA registry.
HTTP uses charset in two contexts: within an Accept-Charset request
header field (in which the charset value is an unquoted token) and as
the value of a parameter in a Content-Type header field (within a
request or response), in which case the parameter value of the
charset parameter can be quoted.
Implementers need to be aware of IETF character set requirements
[RFC3629] [RFC2277].
3.1.1.3. Canonicalization and Text Defaults
Internet media types are registered with a canonical form. A
representation transferred via HTTP messages MUST be in the
appropriate canonical form prior to its transmission except for
"text" types, as defined in the next paragraph.
When in canonical form, media subtypes of the "text" type use CRLF as
the text line break. HTTP relaxes this requirement and allows the
transport of text media with plain CR or LF alone representing a line
break when it is done consistently for an entire representation.
HTTP applications MUST accept CRLF, bare CR, and bare LF as
indicating a line break in text media received via HTTP. In
addition, if the text is in a character encoding that does not use
octets 13 and 10 for CR and LF respectively, as is the case for some
multi-byte character encodings, HTTP allows the use of whatever octet
sequences are defined by that character encoding to represent the
equivalent of CR and LF for line breaks. This flexibility regarding
line breaks applies only to text media in the payload body; a bare CR
or LF MUST NOT be substituted for CRLF within any of the HTTP control
structures (such as header fields and multipart boundaries).
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If a representation is encoded with a content-coding, the underlying
data MUST be in a form defined above prior to being encoded.
3.1.1.4. Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of
one or more representations within a single message body. All
multipart types share a common syntax, as defined in Section 5.1.1 of
[RFC2046], and include a boundary parameter as part of the media type
value. The message body is itself a protocol element; a sender MUST
generate only CRLF to represent line breaks between body-parts.
In general, HTTP treats a multipart message body no differently than
any other media type: strictly as payload. HTTP does not use the
multipart boundary as an indicator of message body length. In all
other respects, an HTTP 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.
A recipient MUST treat an unrecognized multipart subtype as being
equivalent to "multipart/mixed".
Note: The "multipart/form-data" type has been specifically defined
for carrying form data suitable for processing via the POST
request method, as described in [RFC2388].
3.1.1.5. Content-Type
The "Content-Type" header field indicates the media type of the
representation, which defines both the data format and how that data
SHOULD be processed by the recipient (within the scope of the request
method semantics) after any Content-Encoding is decoded. For
responses to the HEAD method, the media type is that which would have
been sent had the request been a GET.
Content-Type = media-type
Media types are defined in Section 3.1.1.1. An example of the field
is
Content-Type: text/html; charset=ISO-8859-4
A sender SHOULD include a Content-Type header field in a message
containing a payload body, defining the media type of the enclosed
representation, unless the intended media type is unknown to the
sender. If a Content-Type header field is not present, recipients
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MAY either assume a media type of "application/octet-stream"
([RFC2046], Section 4.5.1) or examine the representation data to
determine its type.
In practice, resource owners do not always properly configure their
origin server to provide the correct Content-Type for a given
representation, with the result that some clients will examine a
payload'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.
3.1.2. Data Encoding
3.1.2.1. Content Codings
Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are
primarily used to allow a representation to be compressed or
otherwise usefully transformed without losing the identity of its
underlying media type and without loss of information. Frequently,
the representation is stored in coded form, transmitted directly, and
only decoded by the recipient.
content-coding = token
All content-coding values are case-insensitive and SHOULD be
registered within the HTTP Content Coding registry, as defined in
Section 9.4. They are used in the Accept-Encoding (Section 6.3.4)
and Content-Encoding (Section 3.1.2.2) header fields.
The following content-coding values are defined by this
specification:
compress (and x-compress): See Section 4.2.1 of [Part1].
deflate: See Section 4.2.2 of [Part1].
gzip (and x-gzip): See Section 4.2.3 of [Part1].
3.1.2.2. Content-Encoding
The "Content-Encoding" header field indicates what content codings
have been applied to the representation, beyond those inherent in the
media type, and thus what decoding mechanisms have to be applied in
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order to obtain data in the media type referenced by the Content-Type
header field. Content-Encoding is primarily used to allow a
representation's data to be compressed without losing the identity of
its underlying media type.
Content-Encoding = 1#content-coding
An example of its use is
Content-Encoding: gzip
If multiple encodings have been applied to a representation, the
content codings MUST be listed in the order in which they were
applied. Additional information about the encoding parameters MAY be
provided by other header fields not defined by this specification.
Unlike Transfer-Encoding (Section 3.3.1 of [Part1]), the codings
listed in Content-Encoding are a characteristic of the
representation; the representation is defined in terms of the coded
form, and all other metadata about the representation is about the
coded form unless otherwise noted in the metadata definition.
Typically, the representation is only decoded just prior to rendering
or analogous usage.
A transforming proxy MAY modify the content coding if the new coding
is known to be acceptable to the recipient, unless the "no-transform"
cache-control directive is present in the message.
If the media type includes an inherent encoding, such as a data
format that is always compressed, then that encoding would not be
restated as a Content-Encoding even if it happens to be the same
algorithm as one of the content codings. Such a content coding would
only be listed if, for some bizarre reason, it is applied a second
time to form the representation. Likewise, an origin server might
choose to publish the same payload data as multiple representations
that differ only in whether the coding is defined as part of Content-
Type or Content-Encoding, since some user agents will behave
differently in their handling of each response (e.g., open a "Save as
..." dialog instead of automatic decompression and rendering of
content).
If the content-coding of a representation in a request message is not
acceptable to the origin server, the server SHOULD respond with a
status code of 415 (Unsupported Media Type).
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3.1.3. Audience Language
3.1.3.1. Language Tags
A language tag, as defined in [RFC5646], identifies a natural
language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer
languages are explicitly excluded. HTTP uses language tags within
the Accept-Language and Content-Language fields.
In summary, a language tag is composed of one or more parts: A
primary language subtag followed by a possibly empty series of
subtags:
language-tag =
White space is not allowed within the tag and all tags are case-
insensitive. The name space of language subtags is administered by
the IANA (see
).
Example tags include:
en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information.
3.1.3.2. Content-Language
The "Content-Language" header field describes the natural language(s)
of the intended audience for the representation. Note that this
might not be equivalent to all the languages used within the
representation.
Content-Language = 1#language-tag
Language tags are defined in Section 3.1.3.1. The primary purpose of
Content-Language is to allow a user to identify and differentiate
representations according to the user's own preferred language.
Thus, if the content is intended only for a Danish-literate audience,
the appropriate field is
Content-Language: da
If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the
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.
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Multiple languages MAY be listed for content that is intended for
multiple audiences. For example, a rendition of the "Treaty of
Waitangi", presented simultaneously in the original Maori and English
versions, would call for
Content-Language: mi, en
However, just because multiple languages are present within a
representation does not mean that it is intended for multiple
linguistic audiences. An example would be a beginner's language
primer, such as "A First Lesson in Latin", which is clearly intended
to be used by an English-literate audience. In this case, the
Content-Language would properly only include "en".
Content-Language MAY be applied to any media type -- it is not
limited to textual documents.
3.1.4. Identification
3.1.4.1. Identifying a Representation
When a complete or partial representation is transferred in a message
payload, it is often desirable for the sender to supply, or the
recipient to determine, an identifier for a resource corresponding to
that representation.
The following rules are used to determine such a URI for the payload
of a request message:
o If the request has a Content-Location header field, then the
sender asserts that the payload is a representation of the
resource identified by the Content-Location field-value. However,
such an assertion cannot be trusted unless it can be verified by
other means (not defined by HTTP). The information might still be
useful for revision history links.
o Otherwise, the payload is unidentified.
The following rules, to be applied in order until a match is found,
are used to determine such a URI for the payload of a response
message:
1. If the request is GET or HEAD and the response status code is 200
(OK), 204 (No Content), 206 (Partial Content), or 304 (Not
Modified), the payload's identifier is the effective request URI
(Section 5.5 of [Part1]).
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2. If the request is GET or HEAD and the response status code is 203
(Non-Authoritative Information), the payload is a potentially
modified representation of the target resource; as such, the
effective request URI might only act as an identifier for the
payload's representation when a request is made via the same
chain of intermediaries.
3. If the response has a Content-Location header field and its
field-value is a reference to the same URI as the effective
request URI, the payload's identifier is the effective request
URI.
4. If the response has a Content-Location header field and its
field-value is a reference to a URI different from the effective
request URI, then the sender asserts that the payload is a
representation of the resource identified by the Content-Location
field-value. However, such an assertion cannot be trusted unless
it can be verified by other means (not defined by HTTP).
5. Otherwise, the payload is unidentified.
3.1.4.2. Content-Location
The "Content-Location" header field references a URI that can be used
as a specific identifier for the representation in this message
payload. In other words, if one were to perform a GET on this URI at
the time of this message's generation, then a 200 (OK) response would
contain the same representation that is enclosed as payload in this
message.
Content-Location = absolute-URI / partial-URI
The Content-Location value is not a replacement for the effective
Request URI (Section 5.5 of [Part1]). It is representation metadata.
It has the same syntax and semantics as the header field of the same
name defined for MIME body parts in Section 4 of [RFC2557]. However,
its appearance in an HTTP message has some special implications for
HTTP recipients.
If Content-Location is included in a 2xx (Successful) response
message and its value refers (after conversion to absolute form) to a
URI that is the same as the effective request URI, then the response
payload SHOULD be considered a 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 request 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
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the action (e.g., "It worked!"). This allows authoring applications
to update their local copies without the need for a subsequent GET
request.
If Content-Location is included in a 2xx (Successful) response
message and its field-value refers to a URI that differs from the
effective request URI, then the origin server claims that the field-
value is an identifier for the payload's representation. Such a
claim can only be trusted if both identifiers share the same resource
owner, which cannot be programmatically determined via HTTP.
o For a response to a GET or HEAD request, this is an indication
that the effective request URI identifies a resource that is
subject to content negotiation and the Content-Location field-
value is a more specific identifier for the selected
representation.
o For a 201 (Created) response to a state-changing method, a
Content-Location field-value that is identical to the Location
field-value indicates that this payload is a current
representation of the newly created resource.
o Otherwise, such a Content-Location indicates that this payload is
a representation reporting on the requested action's status and
that the same report is available (for future access with GET) at
the given URI. For example, a purchase transaction made via a
POST request might include a receipt document as the payload of
the 200 (OK) response; the Content-Location field-value provides
an identifier for retrieving a copy of that same receipt in the
future.
If Content-Location is included in a request message, then it MAY be
interpreted by 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.
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A Content-Location field received in a request message is transitory
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.
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.
3.2. Representation Data
The representation data associated with an HTTP message is either
provided as the payload body of the message or referred to by the
message semantics and the effective request URI. The representation
data is in a format and encoding defined by the representation
metadata header fields.
The data type of the representation data is determined via the header
fields Content-Type and Content-Encoding. These define a two-layer,
ordered encoding model:
representation-data := Content-Encoding( Content-Type( bits ) )
3.3. Payload Semantics
Some HTTP messages transfer a complete or partial representation as
the message ""payload"". In some cases, a payload might only contain
the associated representation's header fields (e.g., responses to
HEAD) or only some part(s) of the representation data (e.g., the 206
(Partial Content) status code).
The purpose of a payload in a request is defined by the method
semantics. In a response, the payload's purpose is defined by both
the request method and the response status code.
For example, a representation in the payload of a PUT request
(Section 5.3.4) represents the desired state of the target resource
if the request is successfully applied, whereas a representation in
the payload of a POST request (Section 5.3.3) represents an anonymous
resource for providing data to be processed, such as the information
that a user entered within an HTML form.
Likewise, the payload of a 200 (OK) response to GET (Section 5.3.1)
contains a representation of the target resource, as observed at the
time of the message origination date (Section 8.1.1.2), whereas the
same status code in a response to POST might contain either a
representation of the processing result or a current representation
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of the target resource after applying the processing. Response
messages with an error status code usually contain a representation
that describes the error and what next steps are suggested for
resolving it.
Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing.
+-------------------+--------------------------+
| Header Field Name | Defined in... |
+-------------------+--------------------------+
| Content-Length | Section 3.3.2 of [Part1] |
| Content-Range | Section 5.2 of [Part5] |
| Transfer-Encoding | Section 3.3.1 of [Part1] |
+-------------------+--------------------------+
3.4. Content Negotiation
HTTP responses include a representation which contains information
for interpretation, whether by a human user or for further
processing. Often, the server has different ways of representing the
same information; for example, in different formats, languages, or
using different character encodings.
HTTP clients and their users might have different or variable
capabilities, characteristics or preferences which would influence
which representation, among those available from the server, would be
best for the server to deliver. For this reason, HTTP provides
mechanisms for "content negotiation" -- a process of allowing
selection of a representation of a given resource, when more than one
is available.
This specification defines two patterns of content negotiation;
"proactive", where the server selects the representation based upon
the client's stated preferences, and "reactive" negotiation, where
the server provides a list of representations for the client to
choose from, based upon their metadata. In addition, there are other
patterns: some applications use an "active content" pattern, where
the server returns active content which runs on the client and, based
on client available parameters, selects additional resources to
invoke. "Transparent Content Negotiation" ([RFC2295]) has also been
proposed.
These patterns are all widely used, and have trade-offs in
applicability and practicality. In particular, when the number of
preferences or capabilities to be expressed by a client are large
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(such as when many different formats are supported by a user-agent),
proactive negotiation becomes unwieldy, and might not be appropriate.
Conversely, when the number of representations to choose from is very
large, reactive negotiation might not be appropriate.
Note that, in all cases, the supplier of representations has the
responsibility for determining which representations might be
considered to be the "same information".
3.4.1. Proactive Negotiation
If the selection of the best representation for a response is made by
an algorithm located at the server, it is called proactive
negotiation. Selection is based on the available representations of
the response (the dimensions over which it can vary; e.g., language,
content-coding, etc.) and the contents of particular header fields in
the request message or on other information pertaining to the request
(such as the network address of the client).
Proactive negotiation is advantageous when the algorithm for
selecting from among the available representations is difficult to
describe to the user agent, or when the server desires to send its
"best guess" to the client along with the first response (hoping to
avoid the round-trip delay of a subsequent request if the "best
guess" is good enough for the user). In order to improve the
server's guess, the user agent MAY include request header fields
(Accept, Accept-Language, Accept-Encoding, etc.) which describe its
preferences for such a response.
Proactive negotiation has disadvantages:
1. It is impossible for the server to accurately determine what
might be "best" for any given user, since that would require
complete knowledge of both the capabilities of the user agent and
the intended use for the response (e.g., does the user want to
view it on screen or print it on paper?).
2. Having the user agent describe its capabilities in every request
can be both very inefficient (given that only a small percentage
of responses have multiple representations) and a potential
violation of the user's privacy.
3. It complicates the implementation of an origin server and the
algorithms for generating responses to a request.
4. It might limit a public cache's ability to use the same response
for multiple user's requests.
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Proactive negotiation allows the user agent to specify its
preferences, but it cannot expect responses to always honor them.
For example, the origin server might not implement proactive
negotiation, or it might decide that sending a response that doesn't
conform to them is better than sending a 406 (Not Acceptable)
response.
HTTP/1.1 includes the following header fields for enabling proactive
negotiation through description of user agent capabilities and user
preferences: Accept (Section 6.3.2), Accept-Charset (Section 6.3.3),
Accept-Encoding (Section 6.3.4), Accept-Language (Section 6.3.5), and
User-Agent (Section 6.5.3). However, an origin server is not limited
to these dimensions and MAY vary the response based on any aspect of
the request, including aspects of the connection (e.g., IP address)
or information within extension header fields not defined by this
specification.
Note: In practice, User-Agent based negotiation is fragile,
because new clients might not be recognized.
The Vary header field (Section 8.2.1) can be used to express the
parameters the server uses to select a representation that is subject
to proactive negotiation.
3.4.2. Reactive Negotiation
With reactive negotiation, selection of the best representation for a
response is performed by the user agent after receiving an initial
response from the origin server. Selection is based on a list of the
available representations of the response included within the header
fields or body of the initial response, with each representation
identified by its own URI. Selection from among the representations
can be performed automatically (if the user agent is capable of doing
so) or manually by the user selecting from a generated (possibly
hypertext) menu.
Reactive negotiation is advantageous when the response would vary
over commonly-used dimensions (such as type, language, or encoding),
when the origin server is unable to determine a user agent's
capabilities from examining the request, and generally when public
caches are used to distribute server load and reduce network usage.
Reactive negotiation suffers from the disadvantage of needing a
second request to obtain the best alternate representation. This
second request is only efficient when caching is used. In addition,
this specification does not define any mechanism for supporting
automatic selection, though it also does not prevent any such
mechanism from being developed as an extension and used within
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HTTP/1.1.
This specification defines the 300 (Multiple Choices) and 406 (Not
Acceptable) status codes for enabling reactive negotiation when the
server is unwilling or unable to provide a varying response using
proactive negotiation.
4. Product Tokens
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by whitespace. By
convention, the products are listed in order of their significance
for identifying the application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although
any token octet MAY appear in a product-version, this token SHOULD
only be used for a version identifier (i.e., successive versions of
the same product SHOULD only differ in the product-version portion of
the product value).
5. Request Methods
5.1. Overview
The request method token is the primary source of request semantics;
it indicates the purpose for which the client has made this request
and what is expected by the client as a successful result. The
request semantics MAY be further specialized by the semantics of some
header fields when present in a request (Section 6) if those
additional semantics do not conflict with the method.
method = token
HTTP was originally designed to be usable as an interface to
distributed object systems. The request method was envisioned as
applying semantics to a target resource in much the same way as
invoking a defined method on an identified object would apply
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semantics. The method token is case-sensitive because it might be
used as a gateway to object-based systems with case-sensitive method
names.
Unlike distributed objects, the standardized request methods in HTTP
are not resource-specific, since uniform interfaces provide for
better visibility and reuse in network-based systems [REST]. Once
defined, a standardized method MUST have the same semantics when
applied to any resource, though each resource determines for itself
whether those semantics are implemented or allowed.
This specification defines a number of standardized methods that are
commonly used in HTTP, as outlined by the following table. By
convention, standardized methods are defined in all-uppercase ASCII
letters.
+---------+-------------------------------------------------+-------+
| Method | Description | Sec. |
+---------+-------------------------------------------------+-------+
| GET | Transfer a current representation of the target | 5.3.1 |
| | resource. | |
| HEAD | Same as GET, but do not include a message body | 5.3.2 |
| | in the response. | |
| POST | Perform resource-specific processing on the | 5.3.3 |
| | request payload. | |
| PUT | Replace all current representations of the | 5.3.4 |
| | target resource with the request payload. | |
| DELETE | Remove all current representations of the | 5.3.5 |
| | target resource. | |
| CONNECT | Establish a tunnel to the server identified by | 5.3.6 |
| | the target resource. | |
| OPTIONS | Describe the communication options for the | 5.3.7 |
| | target resource. | |
| TRACE | Perform a message loop-back test along the path | 5.3.8 |
| | to the target resource. | |
+---------+-------------------------------------------------+-------+
The methods GET and HEAD MUST be supported by all general-purpose
servers. All other methods are OPTIONAL. When implemented, a server
MUST implement the above methods according to the semantics defined
for them in Section 5.3.
Additional methods MAY be used in HTTP; many have already been
standardized outside the scope of this specification and registered
within the HTTP Method Registry maintained by IANA, as defined in
Section 9.1.
The set of methods allowed by a target resource can be listed in an
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Allow header field (Section 8.4.1). However, the set of allowed
methods can change dynamically. When a request message is received
that is unrecognized or not implemented by an origin server, the
origin server SHOULD respond with the 501 (Not Implemented) status
code. When a request message is received that is known by an origin
server but not allowed for the target resource, the origin server
SHOULD respond with the 405 (Method Not Allowed) status code.
5.2. Common Method Properties
5.2.1. Safe Methods
Request methods are considered ""safe"" if their defined semantics
are essentially read-only; i.e., the client does not request, and
does not expect, any state change on the origin server as a result of
applying a safe method to a target resource. Likewise, reasonable
use of a safe method is not expected to cause any harm, loss of
property, or unusual burden on the origin server.
This definition of safe methods does not prevent an implementation
from including behavior that is potentially harmful, not entirely
read-only, or which causes side-effects while invoking a safe method.
What is important, however, is that the client did not request that
additional behavior and cannot be held accountable for it. For
example, most servers append request information to access log files
at the completion of every response, regardless of the method, and
that is considered safe even though the log storage might become full
and crash the server. Likewise, a safe request initiated by
selecting an advertisement on the Web will often have the side-effect
of charging an advertising account.
The GET, HEAD, OPTIONS, and TRACE request methods are defined to be
safe.
The purpose of distinguishing between safe and unsafe methods is to
allow automated retrieval processes (spiders) and cache performance
optimization (pre-fetching) to work without fear of causing harm. In
addition, it allows a user agent to apply appropriate constraints on
the automated use of unsafe methods when processing potentially
untrusted content.
A user agent SHOULD distinguish between safe and unsafe methods when
presenting potential actions to a user, such that the user can be
made aware of an unsafe action before it is requested.
When a resource is constructed such that parameters within the
effective request URI have the effect of selecting an action, it is
the resource owner's responsibility to ensure that the action is
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consistent with the request method semantics. For example, it is
common for Web-based content editing software to use actions within
query parameters, such as "page?do=delete". If the purpose of such a
resource is to perform an unsafe action, then the resource MUST
disable or disallow that action when it is accessed using a safe
request method. Failure to do so will result in unfortunate side-
effects when automated processes perform a GET on every URI reference
for the sake of link maintenance, pre-fetching, building a search
index, etc.
5.2.2. Idempotent Methods
Request methods are considered ""idempotent"" if the intended effect
of multiple identical requests is the same as for a single request.
PUT, DELETE, and all safe request methods are idempotent.
Like the definition of safe, the idempotent property only applies to
what has been requested by the user; a server is free to log each
request separately, retain a revision control history, or implement
other non-idempotent side-effects for each idempotent request.
Idempotent methods are distinguished because the request can be
repeated automatically if a communication failure occurs before the
client is able to read the server's response. For example, if a
client sends a PUT request and the underlying connection is closed
before any response is received, then it can establish a new
connection and retry the idempotent request because it knows that
repeating the request will have the same effect even if the original
request succeeded. Note, however, that repeated failures would
indicate a problem within the server.
5.2.3. Cacheable Methods
Request methods are considered ""cacheable"" if it is possible and
useful to answer a current client request with a stored response from
a prior request. GET and HEAD are defined to be cacheable. In
general, safe methods that do not depend on a current or
authoritative response are cacheable, though the overwhelming
majority of caches only support GET and HEAD. HTTP requirements for
cache behavior and cacheable responses are defined in [Part6].
5.3. Method Definitions
5.3.1. GET
The GET method requests transfer of a current representation of the
target resource.
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If the target resource is a data-producing process, it is the
produced data which shall be returned as the representation in the
response and not the source text of the process, unless that text
happens to be the output of the process.
The semantics of the GET method change to a "conditional GET" if the
request message includes an If-Modified-Since, If-Unmodified-Since,
If-Match, If-None-Match, or If-Range header field ([Part4]). A
conditional GET requests that the representation be transferred only
under the circumstances described by the conditional header field(s).
The conditional GET request is intended to reduce unnecessary network
usage by allowing cached representations to be refreshed without
requiring multiple requests or transferring data already held by the
client.
The semantics of the GET method change to a "partial GET" if the
request message includes a Range header field ([Part5]). A partial
GET requests that only part of the representation be transferred, as
described in Section 5.4 of [Part5]. The partial GET request is
intended to reduce unnecessary network usage by allowing partially-
retrieved representations to be completed without transferring data
already held by the client.
A payload within a GET request message has no defined semantics;
sending a payload body on a GET request might cause some existing
implementations to reject the request.
The response to a GET request is cacheable and MAY be used to satisfy
subsequent GET and HEAD requests (see [Part6]).
See Section 10.2 for security considerations when used for forms.
5.3.2. HEAD
The HEAD method is identical to GET except that the server MUST NOT
return a message body in the response. The metadata contained in the
HTTP header fields in response to a HEAD request SHOULD be identical
to the information sent in response to a GET request. This method
can be used for obtaining metadata about the representation implied
by the request without transferring the representation data. This
method is often used for testing hypertext links for validity,
accessibility, and recent modification.
The response to a HEAD request is cacheable and MAY be used to
satisfy a subsequent HEAD request. It also has potential side
effects on previously stored responses to GET; see Section 5 of
[Part6].
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A payload within a HEAD request message has no defined semantics;
sending a payload body on a HEAD request might cause some existing
implementations to reject the request.
5.3.3. POST
The POST method requests that the origin server accept the
representation enclosed in the request as data to be processed by the
target resource. POST is designed to allow a uniform method to cover
the following functions:
o Annotation of existing resources;
o Posting a message to a bulletin board, newsgroup, mailing list, or
similar group of articles;
o Providing a block of data, such as the result of submitting a
form, to a data-handling process;
o Extending a database through an append operation.
The actual function performed by the POST method is determined by the
server and is usually dependent on the effective request URI.
The action performed by the POST method might not result in a
resource that can be identified by a URI. In this case, either 200
(OK) or 204 (No Content) is the appropriate response status code,
depending on whether or not the response includes a representation
that describes the result.
If a resource has been created on the origin server, the response
SHOULD be 201 (Created) and contain a representation which describes
the status of the request and refers to the new resource, and a
Location header field (see Section 8.1.2).
Responses to POST requests are only cacheable when they include
explicit freshness information (see Section 4.1.1 of [Part6]). A
cached POST response with a Content-Location header field (see
Section 3.1.4.2) whose value is the effective Request URI MAY be used
to satisfy subsequent GET and HEAD (not POST) requests.
Note that POST caching is not widely implemented. However, the 303
(See Other) response can be used to direct the user agent to retrieve
a cacheable representation of the resource.
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5.3.4. PUT
The PUT method requests that the state of the target resource be
created or replaced with the state defined by the representation
enclosed in the request message payload. A successful PUT of a given
representation would suggest that a subsequent GET on that same
target resource will result in an equivalent representation being
returned in a 200 (OK) response. However, there is no guarantee that
such a state change will be observable, since the target resource
might be acted upon by other user agents in parallel, or might be
subject to dynamic processing by the origin server, before any
subsequent GET is received. A successful response only implies that
the user agent's intent was achieved at the time of its processing by
the origin server.
If the target resource does not have a current representation and the
PUT successfully creates one, then the origin server MUST inform the
user agent by sending a 201 (Created) response. If the target
resource does have a current representation and that representation
is successfully modified in accordance with the state of the enclosed
representation, then either a 200 (OK) or 204 (No Content) response
SHOULD be sent to indicate successful completion of the request.
Unrecognized header fields SHOULD be ignored (i.e., not saved as part
of the resource state).
An origin server SHOULD verify that the PUT representation is
consistent with any constraints which the server has for the target
resource that cannot or will not be changed by the PUT. This is
particularly important when the origin server uses internal
configuration information related to the URI in order to set the
values for representation metadata on GET responses. When a PUT
representation is inconsistent with the target resource, the origin
server SHOULD either make them consistent, by transforming the
representation or changing the resource configuration, or respond
with an appropriate error message containing sufficient information
to explain why the representation is unsuitable. The 409 (Conflict)
or 415 (Unsupported Media Type) status codes are suggested, with the
latter being specific to constraints on Content-Type values.
For example, if the target resource is configured to always have a
Content-Type of "text/html" and the representation being PUT has a
Content-Type of "image/jpeg", then the origin server SHOULD do one
of:
a. reconfigure the target resource to reflect the new media type;
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b. transform the PUT representation to a format consistent with that
of the resource before saving it as the new resource state; or,
c. reject the request with a 415 (Unsupported Media Type) response
indicating that the target resource is limited to "text/html",
perhaps including a link to a different resource that would be a
suitable target for the new representation.
HTTP does not define exactly how a PUT method affects the state of an
origin server beyond what can be expressed by the intent of the user
agent request and the semantics of the origin server response. It
does not define what a resource might be, in any sense of that word,
beyond the interface provided via HTTP. It does not define how
resource state is "stored", nor how such storage might change as a
result of a change in resource state, nor how the origin server
translates resource state into representations. Generally speaking,
all implementation details behind the resource interface are
intentionally hidden by the server.
The fundamental difference between the POST and PUT methods is
highlighted by the different intent for the target resource. The
target resource in a POST request is intended to handle the enclosed
representation as a data-accepting process, such as for a gateway to
some other protocol or a document that accepts annotations. In
contrast, the target resource in a PUT request is intended to take
the enclosed representation as a new or replacement value. Hence,
the intent of PUT is idempotent and visible to intermediaries, even
though the exact effect is only known by the origin server.
Proper interpretation of a PUT request presumes that the user agent
knows what target resource is desired. A service that is intended to
select a proper URI on behalf of the client, after receiving a state-
changing request, SHOULD be implemented using the POST method rather
than PUT. If the origin server will not make the requested PUT state
change to the target resource and instead wishes to have it applied
to a different resource, such as when the resource has been moved to
a different URI, then the origin server MUST send a 301 (Moved
Permanently) response; the user agent MAY then make its own decision
regarding whether or not to redirect the request.
A PUT request applied to the target resource MAY have side-effects on
other resources. For example, an article might have a URI for
identifying "the current version" (a resource) which is separate from
the URIs identifying each particular version (different resources
that at one point shared the same state as the current version
resource). A successful PUT request on "the current version" URI
might therefore create a new version resource in addition to changing
the state of the target resource, and might also cause links to be
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added between the related resources.
An origin server SHOULD reject any PUT request that contains a
Content-Range header field (Section 5.2 of [Part5]), since it might
be misinterpreted as partial content (or might be partial content
that is being mistakenly PUT as a full representation). Partial
content updates are possible by targeting a separately identified
resource with state that overlaps a portion of the larger resource,
or by using a different method that has been specifically defined for
partial updates (for example, the PATCH method defined in [RFC5789]).
Responses to the PUT method are not cacheable. If a PUT request
passes through a cache that has one or more stored responses for the
effective request URI, those stored responses will be invalidated
(see Section 6 of [Part6]).
5.3.5. DELETE
The DELETE method requests that the origin server delete the target
resource. This method MAY be overridden by human intervention (or
other means) on the origin server. The client cannot be guaranteed
that the operation has been carried out, even if the status code
returned from the origin server indicates that the action has been
completed successfully. However, the server SHOULD NOT indicate
success unless, at the time the response is given, it intends to
delete the resource or move it to an inaccessible location.
A successful response SHOULD be 200 (OK) if the response includes a
representation describing the status, 202 (Accepted) if the action
has not yet been enacted, or 204 (No Content) if the action has been
enacted but the response does not include a representation.
A payload within a DELETE request message has no defined semantics;
sending a payload body on a DELETE request might cause some existing
implementations to reject the request.
Responses to the DELETE method are not cacheable. If a DELETE
request passes through a cache that has one or more stored responses
for the effective request URI, those stored responses will be
invalidated (see Section 6 of [Part6]).
5.3.6. CONNECT
The CONNECT method requests that the proxy establish a tunnel to the
request-target and, if successful, thereafter restrict its behavior
to blind forwarding of packets until the connection is closed.
When using CONNECT, the request-target MUST use the authority form
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(Section 5.3 of [Part1]); i.e., the request-target consists of only
the host name and port number of the tunnel destination, separated by
a colon. For example,
CONNECT server.example.com:80 HTTP/1.1
Host: server.example.com:80
Any 2xx (Successful) response to a CONNECT request indicates that the
proxy has established a connection to the requested host and port,
and has switched to tunneling the current connection to that server
connection. The tunneled data from the server begins immediately
after the blank line that concludes the successful response's header
block.
A server SHOULD NOT send any Transfer-Encoding or Content-Length
header fields in a successful response. A client MUST ignore any
Content-Length or Transfer-Encoding header fields received in a
successful response.
Any response other than a successful response indicates that the
tunnel has not yet been formed and that the connection remains
governed by HTTP.
Proxy authentication might be used to establish the authority to
create a tunnel:
CONNECT server.example.com:80 HTTP/1.1
Host: server.example.com:80
Proxy-Authorization: basic aGVsbG86d29ybGQ=
A payload within a CONNECT request message has no defined semantics;
sending a payload body on a CONNECT request might cause some existing
implementations to reject the request.
Similar to a pipelined HTTP/1.1 request, data to be tunneled from
client to server MAY be sent immediately after the request (before a
response is received). The usual caveats also apply: data can be
discarded if the eventual response is negative, and the connection
can be reset with no response if more than one TCP segment is
outstanding.
It might be the case that the proxy itself can only reach the
requested origin server through another proxy. In this case, the
first proxy SHOULD make a CONNECT request of that next proxy,
requesting a tunnel to the authority. A proxy MUST NOT respond with
any 2xx status code unless it has either a direct or tunnel
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connection established to the authority.
If at any point either one of the peers gets disconnected, any
outstanding data that came from that peer will be passed to the other
one, and after that also the other connection will be terminated by
the proxy. If there is outstanding data to that peer undelivered,
that data will be discarded.
An origin server which receives a CONNECT request for itself MAY
respond with a 2xx status code to indicate that a connection is
established. However, most origin servers do not implement CONNECT.
5.3.7. OPTIONS
The OPTIONS method requests information about the communication
options available on the request/response chain identified by the
effective request URI. This method allows a client to determine the
options and/or requirements associated with a resource, or the
capabilities of a server, without implying a resource action or
initiating a resource retrieval.
Responses to the OPTIONS method are not cacheable.
If the OPTIONS request includes a payload, then the media type MUST
be indicated by a Content-Type field. Although this specification
does not define any use for such a body, future extensions to HTTP
might use the OPTIONS body to make more detailed queries on the
server.
If the request-target (Section 5.3 of [Part1]) is an asterisk ("*"),
the OPTIONS request is intended to apply to the server in general
rather than to a specific resource. Since a server's communication
options typically depend on the resource, the "*" request is only
useful as a "ping" or "no-op" type of method; it does nothing beyond
allowing the client to test the capabilities of the server. For
example, this can be used to test a proxy for HTTP/1.1 conformance
(or lack thereof).
If the request-target is not an asterisk, the OPTIONS request applies
only to the options that are available when communicating with that
resource.
A 200 (OK) response SHOULD include any header fields that indicate
optional features implemented by the server and applicable to that
resource (e.g., Allow), possibly including extensions not defined by
this specification. The response payload, if any, SHOULD also
include information about the communication options. The format for
such a payload is not defined by this specification, but might be
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defined by future extensions to HTTP. Content negotiation MAY be
used to select the appropriate representation. If no payload body is
included, the response MUST include a Content-Length field with a
field-value of "0".
The Max-Forwards header field MAY be used to target a specific proxy
in the request chain (see Section 6.1.1). If no Max-Forwards field
is present in the request, then the forwarded request MUST NOT
include a Max-Forwards field.
5.3.8. TRACE
The TRACE method requests a remote, application-level loop-back of
the request message. The final recipient of the request SHOULD
reflect the message received back to the client as the message body
of a 200 (OK) response. The final recipient is either the origin
server or the first proxy to receive a Max-Forwards value of zero (0)
in the request (see Section 6.1.1). A TRACE request MUST NOT include
a message body.
TRACE allows the client to see what is being received at the other
end of the request chain and use that data for testing or diagnostic
information. The value of the Via header field (Section 5.7 of
[Part1]) is of particular interest, since it acts as a trace of the
request chain. Use of the Max-Forwards header field allows the
client to limit the length of the request chain, which is useful for
testing a chain of proxies forwarding messages in an infinite loop.
If the request is valid, the response SHOULD have a Content-Type of
"message/http" (see Section 7.3.1 of [Part1]) and contain a message
body that encloses a copy of the entire request message. Responses
to the TRACE method are not cacheable.
6. Request Header Fields
A client sends request header fields to provide more information
about the request context, make the request conditional based on the
target resource state, suggest preferred formats for the response,
supply authentication credentials, or modify the expected request
processing. These fields act as request modifiers, similar to the
parameters on a programming language method invocation.
6.1. Controls
Controls are request header fields that direct specific handling of
the request.
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+-------------------+------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------+
| Host | Section 5.4 of [Part1] |
| Max-Forwards | Section 6.1.1 |
| Expect | Section 6.1.2 |
| Range | Section 5.4 of [Part5] |
+-------------------+------------------------+
6.1.1. Max-Forwards
The "Max-Forwards" header field provides a mechanism with the TRACE
(Section 5.3.8) and OPTIONS (Section 5.3.7) methods to limit the
number of times that the request is forwarded by proxies. This can
be useful when the client is attempting to trace a request which
appears to be failing or looping mid-chain.
Max-Forwards = 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded.
Each recipient of a TRACE or OPTIONS request containing a Max-
Forwards header field MUST check and update its value prior to
forwarding the request. If the received value is zero (0), the
recipient MUST NOT forward the request; instead, it MUST respond as
the final recipient. If the received Max-Forwards value is greater
than zero, then the forwarded message MUST contain an updated Max-
Forwards field with a value decremented by one (1).
The Max-Forwards header field MAY be ignored for all other request
methods.
6.1.2. Expect
The "Expect" header field is used to indicate that particular server
behaviors are required by the client.
Expect = 1#expectation
expectation = expect-name [ BWS "=" BWS expect-value ]
*( OWS ";" [ OWS expect-param ] )
expect-param = expect-name [ BWS "=" BWS expect-value ]
expect-name = token
expect-value = token / quoted-string
If all received Expect header field(s) are syntactically valid but
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contain an expectation that the recipient does not understand or
cannot comply with, the recipient MUST respond with a 417
(Expectation Failed) status code. A recipient of a syntactically
invalid Expectation header field MUST respond with a 4xx status code
other than 417.
The only expectation defined by this specification is:
100-continue
The "100-continue" expectation is defined below. It does not
support any expect-params.
Comparison is case-insensitive for names (expect-name), and case-
sensitive for values (expect-value).
The Expect mechanism is hop-by-hop: the above requirements apply to
any server, including proxies. However, the Expect header field
itself is end-to-end; it MUST be forwarded if the request is
forwarded.
Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
Expect header field.
6.1.2.1. Use of the 100 (Continue) Status
The purpose of the 100 (Continue) status code (Section 7.2.1) is to
allow a client that is sending a request message with a payload to
determine if the origin server is willing to accept the request
(based on the request header fields) before the client sends the
payload body. In some cases, it might either be inappropriate or
highly inefficient for the client to send the payload body if the
server will reject the message without looking at the body.
Requirements for HTTP/1.1 clients:
o If a client will wait for a 100 (Continue) response before sending
the payload body, it MUST send an Expect header field with the
"100-continue" expectation.
o A client MUST NOT send an Expect header field with the "100-
continue" expectation if it does not intend to send a payload
body.
Because of the presence of older implementations, the protocol allows
ambiguous situations in which a client might send "Expect: 100-
continue" without receiving either a 417 (Expectation Failed) or a
100 (Continue) status code. Therefore, when a client sends this
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header field to an origin server (possibly via a proxy) from which it
has never seen a 100 (Continue) status code, the client SHOULD NOT
wait for an indefinite period before sending the payload body.
Requirements for HTTP/1.1 origin servers:
o Upon receiving a request which includes an Expect header field
with the "100-continue" expectation, an origin server MUST either
respond with 100 (Continue) status code and continue to read from
the input stream, or respond with a final status code. The origin
server MUST NOT wait for the payload body before sending the 100
(Continue) response. If it responds with a final status code, it
MAY close the transport connection or it MAY continue to read and
discard the rest of the request. It MUST NOT perform the request
method if it returns a final status code.
o An origin server SHOULD NOT send a 100 (Continue) response if the
request message does not include an Expect header field with the
"100-continue" expectation, and MUST NOT send a 100 (Continue)
response if such a request comes from an HTTP/1.0 (or earlier)
client. There is an exception to this rule: for compatibility
with [RFC2068], a server MAY send a 100 (Continue) status code in
response to an HTTP/1.1 PUT or POST request that does not include
an Expect header field with the "100-continue" expectation. This
exception, the purpose of which is to minimize any client
processing delays associated with an undeclared wait for 100
(Continue) status code, applies only to HTTP/1.1 requests, and not
to requests with any other HTTP-version value.
o An origin server MAY omit a 100 (Continue) response if it has
already received some or all of the payload body for the
corresponding request.
o An origin server that sends a 100 (Continue) response MUST
ultimately send a final status code, once the payload body is
received and processed, unless it terminates the transport
connection prematurely.
o If an origin server receives a request that does not include an
Expect header field with the "100-continue" expectation, the
request includes a payload body, and the server responds with a
final status code before reading the entire payload body from the
transport connection, then the server SHOULD NOT close the
transport connection until it has read the entire request, or
until the client closes the connection. Otherwise, the client
might not reliably receive the response message. However, this
requirement ought not be construed as preventing a server from
defending itself against denial-of-service attacks, or from badly
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broken client implementations.
Requirements for HTTP/1.1 proxies:
o If a proxy receives a request that includes an Expect header field
with the "100-continue" expectation, and the proxy either knows
that the next-hop server complies with HTTP/1.1 or higher, or does
not know the HTTP version of the next-hop server, it MUST forward
the request, including the Expect header field.
o If the proxy knows that the version of the next-hop server is
HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
respond with a 417 (Expectation Failed) status code.
o Proxies SHOULD maintain a record of the HTTP version numbers
received from recently-referenced next-hop servers.
o A proxy MUST NOT forward a 100 (Continue) response if the request
message was received from an HTTP/1.0 (or earlier) client and did
not include an Expect header field with the "100-continue"
expectation. This requirement overrides the general rule for
forwarding of 1xx responses (see Section 7.2.1).
6.2. Conditionals
Conditionals are request header fields that indicate a precondition
to be tested before applying the method semantics to the target
resource. Each precondition is based on metadata that is expected to
change if the selected representation of the target resource is
changed. The HTTP/1.1 conditional request mechanisms are defined in
[Part4].
+---------------------+------------------------+
| Header Field Name | Defined in... |
+---------------------+------------------------+
| If-Match | Section 3.1 of [Part4] |
| If-None-Match | Section 3.2 of [Part4] |
| If-Modified-Since | Section 3.3 of [Part4] |
| If-Unmodified-Since | Section 3.4 of [Part4] |
| If-Range | Section 5.3 of [Part5] |
+---------------------+------------------------+
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6.3. Content Negotiation
+-------------------+---------------+
| Header Field Name | Defined in... |
+-------------------+---------------+
| Accept | Section 6.3.2 |
| Accept-Charset | Section 6.3.3 |
| Accept-Encoding | Section 6.3.4 |
| Accept-Language | Section 6.3.5 |
+-------------------+---------------+
6.3.1. Quality Values
Many of the request header fields for proactive content negotiation
use a common parameter, named "q" (case-insensitive), to assign a
relative "weight" to the preference for that associated kind of
content. This weight is referred to as a "quality value" (or
"qvalue") because the same parameter name is often used within server
configurations to assign a weight to the relative quality of the
various representations that can be selected for a resource.
The weight is normalized to a real number in the range 0 through 1,
where 0.001 is the least preferred and 1 is the most preferred; a
value of 0 means "not acceptable". If no "q" parameter is present,
the default weight is 1.
weight = OWS ";" OWS "q=" qvalue
qvalue = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] )
A sender of qvalue MUST NOT generate more than three digits after the
decimal point. User configuration of these values ought to be
limited in the same fashion.
6.3.2. Accept
The "Accept" header field can be used by user agents to specify
response media types that are acceptable. Accept header fields can
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-
line image.
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Accept = #( media-range [ accept-params ] )
media-range = ( "*/*"
/ ( type "/" "*" )
/ ( type "/" subtype )
) *( OWS ";" OWS parameter )
accept-params = weight *( accept-ext )
accept-ext = OWS ";" OWS token [ "=" word ]
The asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The media-range MAY include media type
parameters that are applicable to that range.
Each media-range MAY be followed by one or more accept-params,
beginning with the "q" parameter for indicating a relative weight, as
defined in Section 6.3.1. The first "q" parameter (if any) separates
the media-range parameter(s) from the accept-params.
Note: Use of the "q" parameter name to separate media type
parameters from Accept extension parameters is due to historical
practice. Although this prevents any media type parameter named
"q" from being used with a media range, such an event is believed
to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type
parameters in Accept. Future media types are discouraged from
registering any parameter named "q".
The example
Accept: audio/*; q=0.2, audio/basic
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".
A request without any Accept header field implies that the user agent
will accept any media type in response. If an Accept header field is
present in a request and none of the available representations for
the response have a media type that is listed as acceptable, the
origin server MAY either honor the Accept header field by sending a
406 (Not Acceptable) response or disregard the Accept header field by
treating the response as if it is not subject to content negotiation.
A more elaborate example is
Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8, text/x-c
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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
text/x-dvi representation, and if that does not exist, send the text/
plain representation".
Media ranges can be overridden by more specific media ranges or
specific media types. If more than one media range applies to a
given type, the most specific reference has precedence. For example,
Accept: text/*, text/plain, text/plain;format=flowed, */*
have the following precedence:
1. text/plain;format=flowed
2. text/plain
3. text/*
4. */*
The media type quality factor associated with a given type is
determined by finding the media range with the highest precedence
which matches that type. For example,
Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
text/html;level=2;q=0.4, */*;q=0.5
would cause the following values to be associated:
+-------------------+---------------+
| Media Type | Quality Value |
+-------------------+---------------+
| text/html;level=1 | 1 |
| text/html | 0.7 |
| text/plain | 0.3 |
| image/jpeg | 0.5 |
| text/html;level=2 | 0.4 |
| text/html;level=3 | 0.7 |
+-------------------+---------------+
Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is a
closed system which cannot interact with other rendering agents, this
default set ought to be configurable by the user.
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6.3.3. Accept-Charset
The "Accept-Charset" header field can be used by user agents to
indicate what character encodings are acceptable in a response
payload. This field allows clients capable of understanding more
comprehensive or special-purpose character encodings to signal that
capability to a server which is capable of representing documents in
those character encodings.
Accept-Charset = 1#( ( charset / "*" ) [ weight ] )
Character encoding values (a.k.a., charsets) are described in
Section 3.1.1.2. Each charset MAY be given an associated quality
value which represents the user's preference for that charset, as
defined in Section 6.3.1. An example is
Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
The special value "*", if present in the Accept-Charset field,
matches every character encoding which is not mentioned elsewhere in
the Accept-Charset field. If no "*" is present in an Accept-Charset
field, then any character encodings not explicitly mentioned in the
field are considered "not acceptable" to the client.
A request without any Accept-Charset header field implies that the
user agent will accept any character encoding in response.
If an Accept-Charset header field is present in a request and none of
the available representations for the response have a character
encoding that is listed as acceptable, the origin server MAY either
honor the Accept-Charset header field by sending a 406 (Not
Acceptable) response or disregard the Accept-Charset header field by
treating the response as if it is not subject to content negotiation.
6.3.4. Accept-Encoding
The "Accept-Encoding" header field can be used by user agents to
indicate what response content-codings (Section 3.1.2.1) are
acceptable in the response. An "identity" token is used as a synonym
for "no encoding" in order to communicate when no encoding is
preferred.
Accept-Encoding = #( codings [ weight ] )
codings = content-coding / "identity" / "*"
Each codings value MAY be given an associated quality value which
represents the preference for that encoding, as defined in
Section 6.3.1.
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For example,
Accept-Encoding: compress, gzip
Accept-Encoding:
Accept-Encoding: *
Accept-Encoding: compress;q=0.5, gzip;q=1.0
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
A server tests whether a content-coding for a given representation is
acceptable, according to an Accept-Encoding field, using these rules:
1. The special "*" symbol in an Accept-Encoding field matches any
available content-coding not explicitly listed in the header
field.
2. If the representation has no content-coding, then it is
acceptable by default unless specifically excluded by the Accept-
Encoding field stating either "identity;q=0" or "*;q=0" without a
more specific entry for "identity".
3. If the representation's content-coding is one of the content-
codings listed in the Accept-Encoding field, then it is
acceptable unless it is accompanied by a qvalue of 0. (As
defined in Section 6.3.1, a qvalue of 0 means "not acceptable".)
4. If multiple content-codings are acceptable, then the acceptable
content-coding with the highest non-zero qvalue is preferred.
An Accept-Encoding header field with a combined field-value that is
empty implies that the user agent does not want any content-coding in
response. If an Accept-Encoding header field is present in a request
and none of the available representations for the response have a
content-coding that is listed as acceptable, the origin server SHOULD
send a response without any content-coding.
A request without an Accept-Encoding header field implies that the
user agent will accept any content-coding in response.
Note: Most HTTP/1.0 applications do not recognize or obey qvalues
associated with content-codings. This means that qvalues will not
work and are not permitted with x-gzip or x-compress.
6.3.5. Accept-Language
The "Accept-Language" header field can be used by user agents to
indicate the set of natural languages that are preferred in the
response. Language tags are defined in Section 3.1.3.1.
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Accept-Language = 1#( language-range [ weight ] )
language-range =
Each language-range can be given an associated quality value which
represents an estimate of the user's preference for the languages
specified by that range, as defined in Section 6.3.1. For example,
Accept-Language: da, en-gb;q=0.8, en;q=0.7
would mean: "I prefer Danish, but will accept British English and
other types of English". (see also Section 2.3 of [RFC4647])
For matching, Section 3 of [RFC4647] defines several matching
schemes. Implementations can offer the most appropriate matching
scheme for their requirements.
Note: The "Basic Filtering" scheme ([RFC4647], Section 3.3.1) is
identical to the matching scheme that was previously defined in
Section 14.4 of [RFC2616].
It might be contrary to the privacy expectations of the user to send
an Accept-Language header field with the complete linguistic
preferences of the user in every request. For a discussion of this
issue, see Section 10.5.
As intelligibility is highly dependent on the individual user, it is
recommended that client applications make the choice of linguistic
preference available to the user. If the choice is not made
available, then the Accept-Language header field MUST NOT be given in
the request.
Note: When making the choice of linguistic preference available to
the user, we remind implementers of the fact that users are not
familiar with the details of language matching as described above,
and ought to be provided appropriate guidance. As an example,
users might assume that on selecting "en-gb", they will be served
any kind of English document if British English is not available.
A user agent might suggest in such a case to add "en" to get the
best matching behavior.
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6.4. Authentication Credentials
+---------------------+------------------------+
| Header Field Name | Defined in... |
+---------------------+------------------------+
| Authorization | Section 4.1 of [Part7] |
| Proxy-Authorization | Section 4.3 of [Part7] |
+---------------------+------------------------+
6.5. Context
+-------------------+------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------+
| From | Section 6.5.1 |
| Referer | Section 6.5.2 |
| TE | Section 4.3 of [Part1] |
| User-Agent | Section 6.5.3 |
+-------------------+------------------------+
6.5.1. From
The "From" header field, if given, SHOULD contain an Internet e-mail
address for the human user who controls the requesting user agent.
The address SHOULD be machine-usable, as defined by "mailbox" in
Section 3.4 of [RFC5322]:
From = mailbox
mailbox =
An example is:
From: webmaster@example.org
This header field MAY be used for logging purposes and as a means for
identifying the source of invalid or unwanted requests. It SHOULD
NOT be used as an insecure form of access protection. The
interpretation of this field is that the request is being performed
on behalf of the person given, who accepts responsibility for the
method performed. In particular, robot agents SHOULD include this
header field so that the person responsible for running the robot can
be contacted if problems occur on the receiving end.
The Internet e-mail address in this field MAY be separate from the
Internet host which issued the request. For example, when a request
is passed through a proxy the original issuer's address SHOULD be
used.
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The client SHOULD NOT send the From header field without the user's
approval, as it might conflict with the user's privacy interests or
their site's security policy. It is strongly recommended that the
user be able to disable, enable, and modify the value of this field
at any time prior to a request.
6.5.2. Referer
The "Referer" [sic] header field allows the client to specify the URI
of the resource from which the target URI was obtained (the
"referrer", although the header field is misspelled.).
The Referer header field allows servers to generate lists of back-
links to resources for interest, logging, optimized caching, etc. It
also allows obsolete or mistyped links to be traced for maintenance.
Some servers use Referer as a means of controlling where they allow
links from (so-called "deep linking"), but legitimate requests do not
always contain a Referer header field.
If the target URI was obtained from a source that does not have its
own URI (e.g., input from the user keyboard), the Referer field MUST
either be sent with the value "about:blank", or not be sent at all.
Note that this requirement does not apply to sources with non-HTTP
URIs (e.g., FTP).
Referer = absolute-URI / partial-URI
Example:
Referer: http://www.example.org/hypertext/Overview.html
If the field value is a relative URI, it SHOULD be interpreted
relative to the effective request URI. The URI MUST NOT include a
fragment. See Section 10.2 for security considerations.
6.5.3. User-Agent
The "User-Agent" header field contains information about the user
agent originating the request. User agents SHOULD include this field
with requests.
Typically, it is used for statistical purposes, the tracing of
protocol violations, and tailoring responses to avoid particular user
agent limitations.
The field can contain multiple product tokens (Section 4) and
comments (Section 3.2 of [Part1]) identifying the agent and its
significant subproducts. By convention, the product tokens are
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listed in order of their significance for identifying the
application.
Because this field is usually sent on every request a user agent
makes, implementations are encouraged not to include needlessly fine-
grained detail, and to limit (or even prohibit) the addition of
subproducts by third parties. Overly long and detailed User-Agent
field values make requests larger and can also be used to identify
("fingerprint") the user against their wishes.
Likewise, implementations are encouraged not to use the product
tokens of other implementations in order to declare compatibility
with them, as this circumvents the purpose of the field. Finally,
they are encouraged not to use comments to identify products; doing
so makes the field value more difficult to parse.
User-Agent = product *( RWS ( product / comment ) )
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
7. Response Status Codes
The status-code element is a 3-digit integer result code of the
attempt to understand and satisfy the request.
HTTP status codes are extensible. HTTP applications are not required
to understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, applications MUST
understand the class of any status code, as indicated by the first
digit, and treat any unrecognized response as being equivalent to the
x00 status code of that class, with the exception that an
unrecognized response MUST NOT be cached. For example, if an
unrecognized status code of 431 is received by the client, it can
safely assume that there was something wrong with its request and
treat the response as if it had received a 400 status code. In such
cases, user agents SHOULD present to the user the representation
enclosed with the response, since that representation is likely to
include human-readable information which will explain the unusual
status.
The first digit of the status-code defines the class of response.
The last two digits do not have any categorization role. There are 5
values for the first digit:
o 1xx (Informational): Request received, continuing process
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o 2xx (Successful): The action was successfully received,
understood, and accepted
o 3xx (Redirection): Further action needs to be taken in order to
complete the request
o 4xx (Client Error): The request contains bad syntax or cannot be
fulfilled
o 5xx (Server Error): The server failed to fulfill an apparently
valid request
For most status codes the response can carry a payload, in which case
a Content-Type header field indicates the payload's media type
(Section 3.1.1.5).
7.1. Overview of Status Codes
The status codes listed below are defined in this specification,
Section 4 of [Part4], Section 3 of [Part5], and Section 3 of [Part7].
The reason phrases listed here are only recommendations -- they can
be replaced by local equivalents without affecting the protocol.
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+-------------+------------------------------+----------------------+
| status-code | reason-phrase | Defined in... |
+-------------+------------------------------+----------------------+
| 100 | Continue | Section 7.2.1 |
| 101 | Switching Protocols | Section 7.2.2 |
| 200 | OK | Section 7.3.1 |
| 201 | Created | Section 7.3.2 |
| 202 | Accepted | Section 7.3.3 |
| 203 | Non-Authoritative | Section 7.3.4 |
| | Information | |
| 204 | No Content | Section 7.3.5 |
| 205 | Reset Content | Section 7.3.6 |
| 206 | Partial Content | Section 3.1 of |
| | | [Part5] |
| 300 | Multiple Choices | Section 7.4.1 |
| 301 | Moved Permanently | Section 7.4.2 |
| 302 | Found | Section 7.4.3 |
| 303 | See Other | Section 7.4.4 |
| 304 | Not Modified | Section 4.1 of |
| | | [Part4] |
| 305 | Use Proxy | Section 7.4.5 |
| 307 | Temporary Redirect | Section 7.4.7 |
| 400 | Bad Request | Section 7.5.1 |
| 401 | Unauthorized | Section 3.1 of |
| | | [Part7] |
| 402 | Payment Required | Section 7.5.2 |
| 403 | Forbidden | Section 7.5.3 |
| 404 | Not Found | Section 7.5.4 |
| 405 | Method Not Allowed | Section 7.5.5 |
| 406 | Not Acceptable | Section 7.5.6 |
| 407 | Proxy Authentication | Section 3.2 of |
| | Required | [Part7] |
| 408 | Request Time-out | Section 7.5.7 |
| 409 | Conflict | Section 7.5.8 |
| 410 | Gone | Section 7.5.9 |
| 411 | Length Required | Section 7.5.10 |
| 412 | Precondition Failed | Section 4.2 of |
| | | [Part4] |
| 413 | Request Representation Too | Section 7.5.11 |
| | Large | |
| 414 | URI Too Long | Section 7.5.12 |
| 415 | Unsupported Media Type | Section 7.5.13 |
| 416 | Requested range not | Section 3.2 of |
| | satisfiable | [Part5] |
| 417 | Expectation Failed | Section 7.5.14 |
| 426 | Upgrade Required | Section 7.5.15 |
| 500 | Internal Server Error | Section 7.6.1 |
| 501 | Not Implemented | Section 7.6.2 |
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| 502 | Bad Gateway | Section 7.6.3 |
| 503 | Service Unavailable | Section 7.6.4 |
| 504 | Gateway Time-out | Section 7.6.5 |
| 505 | HTTP Version not supported | Section 7.6.6 |
+-------------+------------------------------+----------------------+
Note that this list is not exhaustive -- it does not include
extension status codes defined in other specifications.
7.2. Informational 1xx
This class of status code indicates a provisional response,
consisting only of the status-line and optional header fields, and is
terminated by an empty line. There are no required header fields for
this class of status code. Since HTTP/1.0 did not define any 1xx
status codes, servers MUST NOT send a 1xx response to an HTTP/1.0
client except under experimental conditions.
A client MUST be prepared to accept one or more 1xx status responses
prior to a regular response, even if the client does not expect a 100
(Continue) status message. Unexpected 1xx status responses MAY be
ignored by a user agent.
Proxies MUST forward 1xx responses, unless the connection between the
proxy and its client has been closed, or unless the proxy itself
requested the generation of the 1xx response. (For example, if a
proxy adds an "Expect: 100-continue" field when it forwards a
request, then it need not forward the corresponding 100 (Continue)
response(s).)
7.2.1. 100 Continue
The client SHOULD continue with its request. This interim response
is used to inform the client that the initial part of the request has
been received and has not yet been rejected by the server. The
client SHOULD continue by sending the remainder of the request or, if
the request has already been completed, ignore this response. The
server MUST send a final response after the request has been
completed. See Section 6.1.2.1 for detailed discussion of the use
and handling of this status code.
7.2.2. 101 Switching Protocols
The server understands and is willing to comply with the client's
request, via the Upgrade message header field (Section 6.3 of
[Part1]), for a change in the application protocol being used on this
connection. The server will switch protocols to those defined by the
response's Upgrade header field immediately after the empty line
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which terminates the 101 response.
The protocol SHOULD be switched only when it is advantageous to do
so. For example, switching to a newer version of HTTP is
advantageous over older versions, and switching to a real-time,
synchronous protocol might be advantageous when delivering resources
that use such features.
7.3. Successful 2xx
This class of status code indicates that the client's request was
successfully received, understood, and accepted.
7.3.1. 200 OK
The request has succeeded. The payload returned with the response is
dependent on the method used in the request, for example:
GET a representation of the target resource is sent in the response;
HEAD the same representation as GET, except without the message
body;
POST a representation describing or containing the result of the
action;
TRACE a representation containing the request message as received by
the end server.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to
determine freshness for 200 responses.
7.3.2. 201 Created
The request has been fulfilled and has resulted in one or more new
resources being created.
Newly created resources are typically linked to from the response
payload, with the most relevant URI also being carried in the
Location header field. If the newly created resource's URI is the
same as the Effective Request URI, this information can be omitted
(e.g., in the case of a response to a PUT request).
The origin server MUST create the resource(s) before returning the
201 status code. If the action cannot be carried out immediately,
the server SHOULD respond with 202 (Accepted) response instead.
A 201 response MAY contain an ETag response header field indicating
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the current value of the entity-tag for the representation of the
resource identified by the Location header field or, in case the
Location header field was omitted, by the Effective Request URI (see
Section 2.3 of [Part4]).
7.3.3. 202 Accepted
The request has been accepted for processing, but the processing has
not been completed. The request might or might not eventually be
acted upon, as it might be disallowed when processing actually takes
place. There is no facility for re-sending a status code from an
asynchronous operation such as this.
The 202 response is intentionally non-committal. Its purpose is to
allow a server to accept a request for some other process (perhaps a
batch-oriented process that is only run once per day) without
requiring that the user agent's connection to the server persist
until the process is completed. The representation returned with
this response SHOULD include an indication of the request's current
status and either a pointer to a status monitor or some estimate of
when the user can expect the request to be fulfilled.
7.3.4. 203 Non-Authoritative Information
The representation in the response has been transformed or otherwise
modified by a transforming proxy (Section 2.3 of [Part1]). Note that
the behavior of transforming intermediaries is controlled by the no-
transform Cache-Control directive (Section 7.2 of [Part6]).
This status code is only appropriate when the response status code
would have been 200 (OK) otherwise. When the status code before
transformation would have been different, the 214 Transformation
Applied warn-code (Section 7.5 of [Part6]) is appropriate.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to
determine freshness for 203 responses.
7.3.5. 204 No Content
The 204 (No Content) status code indicates that the server has
successfully fulfilled the request and that there is no additional
content to return in the response payload body. Metadata in the
response header fields refer to the target resource and its current
representation after the requested action.
For example, if a 204 status code is received in response to a PUT
request and the response contains an ETag header field, then the PUT
was successful and the ETag field-value contains the entity-tag for
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the new representation of that target resource.
The 204 response allows a server to indicate that the action has been
successfully applied to the target resource while implying that the
user agent SHOULD NOT traverse away from its current "document view"
(if any). The server assumes that the user agent will provide some
indication of the success to its user, in accord with its own
interface, and apply any new or updated metadata in the response to
the active representation.
For example, a 204 status code is commonly used with document editing
interfaces corresponding to a "save" action, such that the document
being saved remains available to the user for editing. It is also
frequently used with interfaces that expect automated data transfers
to be prevalent, such as within distributed version control systems.
The 204 response MUST NOT include a message body, and thus is always
terminated by the first empty line after the header fields.
7.3.6. 205 Reset Content
The server has fulfilled the request and the user agent SHOULD reset
the document view which caused the request to be sent. This response
is primarily intended to allow input for actions to take place via
user input, followed by a clearing of the form in which the input is
given so that the user can easily initiate another input action.
The message body included with the response MUST be empty. Note that
receivers still need to parse the response according to the algorithm
defined in Section 3.3 of [Part1].
7.4. Redirection 3xx
This class of status code indicates that further action needs to be
taken by the user agent in order to fulfill the request. If the
required action involves a subsequent HTTP request, it MAY be carried
out by the user agent without interaction with the user if and only
if the method used in the second request is known to be "safe", as
defined in Section 5.2.1.
There are several types of redirects:
1. Redirects of the request to another URI, either temporarily or
permanently. The new URI is specified in the Location header
field. In this specification, the status codes 301 (Moved
Permanently), 302 (Found), and 307 (Temporary Redirect) fall
under this category.
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2. Redirection to a new location that represents an indirect
response to the request, such as the result of a POST operation
to be retrieved with a subsequent GET request. This is status
code 303 (See Other).
3. Redirection offering a choice of matching resources for use by
reactive content negotiation (Section 3.4.2). This is status
code 300 (Multiple Choices).
4. Other kinds of redirection, such as to a cached result (status
code 304 (Not Modified), see Section 4.1 of [Part4]).
Note: In HTTP/1.0, only the status codes 301 (Moved Permanently)
and 302 (Found) were defined for the first type of redirect, and
the second type did not exist at all ([RFC1945], Section 9.3).
However it turned out that web forms using POST expected redirects
to change the operation for the subsequent request to retrieval
(GET). To address this use case, HTTP/1.1 introduced the second
type of redirect with the status code 303 (See Other) ([RFC2068],
Section 10.3.4). As user agents did not change their behavior to
maintain backwards compatibility, the first revision of HTTP/1.1
added yet another status code, 307 (Temporary Redirect), for which
the backwards compatibility problems did not apply ([RFC2616],
Section 10.3.8). Over 10 years later, most user agents still do
method rewriting for status codes 301 and 302, therefore this
specification makes that behavior conformant in case the original
request was POST.
A Location header field on a 3xx response indicates that a client MAY
automatically redirect to the URI provided; see Section 8.1.2.
Note that for methods not known to be "safe", as defined in
Section 5.2.1, automatic redirection needs to done with care, since
the redirect might change the conditions under which the request was
issued.
Clients SHOULD detect and intervene in cyclical redirections (i.e.,
"infinite" redirection loops).
Note: An earlier version of this specification recommended a
maximum of five redirections ([RFC2068], Section 10.3). Content
developers need to be aware that some clients might implement such
a fixed limitation.
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7.4.1. 300 Multiple Choices
The target resource has more than one representation, each with its
own specific location, and reactive negotiation information
(Section 3.4) is being provided so that the user (or user agent) can
select a preferred representation by redirecting its request to that
location.
Unless it was a HEAD request, the response SHOULD include a
representation containing a list of representation metadata and
location(s) from which the user or user agent can choose the one most
appropriate. Depending upon the format and the capabilities of the
user agent, selection of the most appropriate choice MAY be performed
automatically. However, this specification does not define any
standard for such automatic selection.
If the server has a preferred choice of representation, it SHOULD
include the specific URI for that representation in the Location
field; user agents MAY use the Location field value for automatic
redirection.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to
determine freshness for 300 responses.
7.4.2. 301 Moved Permanently
The target resource has been assigned a new permanent URI and any
future references to this resource SHOULD use one of the returned
URIs. Clients with link editing capabilities ought to automatically
re-link references to the effective request URI to one or more of the
new references returned by the server, where possible.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to
determine freshness for 301 responses.
The new permanent URI SHOULD be given by the Location field in the
response. A response payload can contain a short hypertext note with
a hyperlink to the new URI(s).
Note: For historic reasons, user agents MAY change the request
method from POST to GET for the subsequent request. If this
behavior is undesired, status code 307 (Temporary Redirect) can be
used instead.
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7.4.3. 302 Found
The target resource resides temporarily under a different URI. Since
the redirection might be altered on occasion, the client SHOULD
continue to use the effective request URI for future requests.
The temporary URI SHOULD be given by the Location field in the
response. A response payload can contain a short hypertext note with
a hyperlink to the new URI(s).
Note: For historic reasons, user agents MAY change the request
method from POST to GET for the subsequent request. If this
behavior is undesired, status code 307 (Temporary Redirect) can be
used instead.
7.4.4. 303 See Other
The 303 status code indicates that the server is redirecting the user
agent to a different resource, as indicated by a URI in the Location
header field, that is intended to provide an indirect response to the
original request. In order to satisfy the original request, a user
agent SHOULD perform a retrieval request using the Location URI (a
GET or HEAD request if using HTTP), which can itself be redirected
further, and present the eventual result as an answer to the original
request. Note that the new URI in the Location header field is not
considered equivalent to the effective request URI.
This status code is generally applicable to any HTTP method. It is
primarily used to allow the output of a POST action to redirect the
user agent to a selected resource, since doing so provides the
information corresponding to the POST response in a form that can be
separately identified, bookmarked, and cached independent of the
original request.
A 303 response to a GET request indicates that the requested resource
does not have a representation of its own that can be transferred by
the server over HTTP. The Location URI indicates a resource that is
descriptive of the target resource, such that the follow-on
representation might be useful to recipients without implying that it
adequately represents the target resource. Note that answers to the
questions of what can be represented, what representations are
adequate, and what might be a useful description are outside the
scope of HTTP and thus entirely determined by the URI owner(s).
Except for responses to a HEAD request, the representation of a 303
response SHOULD contain a short hypertext note with a hyperlink to
the Location URI.
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7.4.5. 305 Use Proxy
The 305 status code was defined in a previous version of this
specification (see Appendix C), and is now deprecated.
7.4.6. 306 (Unused)
The 306 status code was used in a previous version of the
specification, is no longer used, and the code is reserved.
7.4.7. 307 Temporary Redirect
The target resource resides temporarily under a different URI. Since
the redirection can change over time, the client SHOULD continue to
use the effective request URI for future requests.
The temporary URI SHOULD be given by the Location field in the
response. A response payload can contain a short hypertext note with
a hyperlink to the new URI(s).
Note: This status code is similar to 302 (Found), except that it
does not allow rewriting the request method from POST to GET.
This specification defines no equivalent counterpart for 301
(Moved Permanently) ([status-308], however, defines the status
code 308 (Permanent Redirect) for this purpose).
7.5. Client Error 4xx
The 4xx class of status code is intended for cases in which the
client seems to have erred. Except when responding to a HEAD
request, the server SHOULD include a representation containing an
explanation of the error situation, and whether it is a temporary or
permanent condition. These status codes are applicable to any
request method. User agents SHOULD display any included
representation to the user.
7.5.1. 400 Bad Request
The server cannot or will not process the request, due to a client
error (e.g., malformed syntax).
7.5.2. 402 Payment Required
This code is reserved for future use.
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7.5.3. 403 Forbidden
The server understood the request, but refuses to authorize it.
Providing different user authentication credentials might be
successful, but any credentials that were provided in the request are
insufficient. The request SHOULD NOT be repeated with the same
credentials.
If the request method was not HEAD and the server wishes to make
public why the request has not been fulfilled, it SHOULD describe the
reason for the refusal in the representation. If the server does not
wish to make this information available to the client, the status
code 404 (Not Found) MAY be used instead.
7.5.4. 404 Not Found
The server has not found anything matching the effective request URI.
No indication is given of whether the condition is temporary or
permanent. The 410 (Gone) status code SHOULD be used if the server
knows, through some internally configurable mechanism, that an old
resource is permanently unavailable and has no forwarding address.
This status code is commonly used when the server does not wish to
reveal exactly why the request has been refused, or when no other
response is applicable.
7.5.5. 405 Method Not Allowed
The method specified in the request-line is not allowed for the
target resource. The response MUST include an Allow header field
containing a list of valid methods for the requested resource.
7.5.6. 406 Not Acceptable
The resource identified by the request is only capable of generating
response representations which have content characteristics not
acceptable according to the Accept and Accept-* header fields sent in
the request.
Unless it was a HEAD request, the response SHOULD include a
representation containing a list of available representation
characteristics and location(s) from which the user or user agent can
choose the one most appropriate. Depending upon the format and the
capabilities of the user agent, selection of the most appropriate
choice MAY be performed automatically. However, this specification
does not define any standard for such automatic selection.
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Note: HTTP/1.1 servers are allowed to return responses which are
not acceptable according to the accept header fields sent in the
request. In some cases, this might even be preferable to sending
a 406 response. User agents are encouraged to inspect the header
fields of an incoming response to determine if it is acceptable.
If the response could be unacceptable, a user agent SHOULD
temporarily stop receipt of more data and query the user for a
decision on further actions.
7.5.7. 408 Request Timeout
The client did not produce a request within the time that the server
was prepared to wait. The client MAY repeat the request without
modifications at any later time.
7.5.8. 409 Conflict
The request could not be completed due to a conflict with the current
state of the resource. This code is only allowed in situations where
it is expected that the user might be able to resolve the conflict
and resubmit the request. The payload SHOULD include enough
information for the user to recognize the source of the conflict.
Ideally, the response representation would include enough information
for the user or user agent to fix the problem; however, that might
not be possible and is not required.
Conflicts are most likely to occur in response to a PUT request. For
example, if versioning were being used and the representation being
PUT included changes to a resource which conflict with those made by
an earlier (third-party) request, the server might use the 409
response to indicate that it can't complete the request. In this
case, the response representation would likely contain a list of the
differences between the two versions.
7.5.9. 410 Gone
The target resource is no longer available at the server and no
forwarding address is known. This condition is expected to be
considered permanent. Clients with link editing capabilities SHOULD
delete references to the effective request URI after user approval.
If the server does not know, or has no facility to determine, whether
or not the condition is permanent, the status code 404 (Not Found)
SHOULD be used instead.
The 410 response is primarily intended to assist the task of web
maintenance by notifying the recipient that the resource is
intentionally unavailable and that the server owners desire that
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remote links to that resource be removed. Such an event is common
for limited-time, promotional services and for resources belonging to
individuals no longer working at the server's site. It is not
necessary to mark all permanently unavailable resources as "gone" or
to keep the mark for any length of time -- that is left to the
discretion of the server owner.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to
determine freshness for 410 responses.
7.5.10. 411 Length Required
The server refuses to accept the request without a defined Content-
Length. The client MAY repeat the request if it adds a valid
Content-Length header field containing the length of the message body
in the request message.
7.5.11. 413 Request Representation Too Large
The server is refusing to process a request because the request
representation is larger than the server is willing or able to
process. The server MAY close the connection to prevent the client
from continuing the request.
If the condition is temporary, the server SHOULD include a Retry-
After header field to indicate that it is temporary and after what
time the client MAY try again.
7.5.12. 414 URI Too Long
The server is refusing to service the request because the effective
request URI is longer than the server is willing to interpret. This
rare condition is only likely to occur when a client has improperly
converted a POST request to a GET request with long query
information, when the client has descended into a URI "black hole" of
redirection (e.g., a redirected URI prefix that points to a suffix of
itself), or when the server is under attack by a client attempting to
exploit security holes present in some servers using fixed-length
buffers for reading or manipulating the request-target.
7.5.13. 415 Unsupported Media Type
The server is refusing to service the request because the request
payload is in a format not supported by this request method on the
target resource.
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7.5.14. 417 Expectation Failed
The expectation given in an Expect header field (see Section 6.1.2)
could not be met by this server, or, if the server is a proxy, the
server has unambiguous evidence that the request could not be met by
the next-hop server.
7.5.15. 426 Upgrade Required
The request can not be completed without a prior protocol upgrade.
This response MUST include an Upgrade header field (Section 6.3 of
[Part1]) specifying the required protocols.
Example:
HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/3.0
Connection: Upgrade
Content-Length: 53
Content-Type: text/plain
This service requires use of the HTTP/3.0 protocol.
The server SHOULD include a message body in the 426 response which
indicates in human readable form the reason for the error and
describes any alternative courses which might be available to the
user.
7.6. Server Error 5xx
Response status codes beginning with the digit "5" indicate cases in
which the server is aware that it has erred or is incapable of
performing the request. Except when responding to a HEAD request,
the server SHOULD include a representation containing an explanation
of the error situation, and whether it is a temporary or permanent
condition. User agents SHOULD display any included representation to
the user. These response codes are applicable to any request method.
7.6.1. 500 Internal Server Error
The server encountered an unexpected condition which prevented it
from fulfilling the request.
7.6.2. 501 Not Implemented
The server does not support the functionality required to fulfill the
request. This is the appropriate response when the server does not
recognize the request method and is not capable of supporting it for
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any resource.
7.6.3. 502 Bad Gateway
The server, while acting as a gateway or proxy, received an invalid
response from the upstream server it accessed in attempting to
fulfill the request.
7.6.4. 503 Service Unavailable
The server is currently unable to handle the request due to a
temporary overloading or maintenance of the server.
The implication is that this is a temporary condition which will be
alleviated after some delay. If known, the length of the delay MAY
be indicated in a Retry-After header field (Section 8.1.3). If no
Retry-After is given, the client SHOULD handle the response as it
would for a 500 (Internal Server Error) response.
Note: The existence of the 503 status code does not imply that a
server has to use it when becoming overloaded. Some servers might
wish to simply refuse the connection.
7.6.5. 504 Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a
timely response from the upstream server specified by the URI (e.g.,
HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
to access in attempting to complete the request.
Note to implementers: some deployed proxies are known to return
400 (Bad Request) or 500 (Internal Server Error) when DNS lookups
time out.
7.6.6. 505 HTTP Version Not Supported
The server does not support, or refuses to support, the protocol
version that was used in the request message. The server is
indicating that it is unable or unwilling to complete the request
using the same major version as the client, as described in Section
2.6 of [Part1], other than with this error message. The response
SHOULD contain a representation describing why that version is not
supported and what other protocols are supported by that server.
8. Response Header Fields
The response header fields allow the server to pass additional
information about the response which cannot be placed in the status-
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line. These header fields give information about the server and
about further access to the target resource (Section 5.5 of [Part1]).
8.1. Control Data
Response header fields can supply control data that supplements the
status code or instructs the client where to go next.
+-------------------+------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------+
| Age | Section 7.1 of [Part6] |
| Date | Section 8.1.1.2 |
| Location | Section 8.1.2 |
| Retry-After | Section 8.1.3 |
+-------------------+------------------------+
8.1.1. Origination Date
8.1.1.1. Date/Time Formats
HTTP applications have historically allowed three different formats
for date/time stamps. However, the preferred format is a fixed-
length subset of that defined by [RFC1123]:
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 1123
The other formats are described here only for compatibility with
obsolete implementations.
Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
HTTP/1.1 clients and servers that parse a date value MUST accept all
three formats (for compatibility with HTTP/1.0), though they MUST
only generate the RFC 1123 format for representing HTTP-date values
in header fields.
All HTTP date/time stamps MUST be represented in Greenwich Mean Time
(GMT), without exception. For the purposes of HTTP, GMT is exactly
equal to UTC (Coordinated Universal Time). This is indicated in the
first two formats by the inclusion of "GMT" as the three-letter
abbreviation for time zone, and MUST be assumed when reading the
asctime format. HTTP-date is case sensitive and MUST NOT include
additional whitespace beyond that specifically included as SP in the
grammar.
HTTP-date = rfc1123-date / obs-date
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Preferred format:
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
; fixed length subset of the format defined in
; Section 5.2.14 of [RFC1123]
day-name = %x4D.6F.6E ; "Mon", case-sensitive
/ %x54.75.65 ; "Tue", case-sensitive
/ %x57.65.64 ; "Wed", case-sensitive
/ %x54.68.75 ; "Thu", case-sensitive
/ %x46.72.69 ; "Fri", case-sensitive
/ %x53.61.74 ; "Sat", case-sensitive
/ %x53.75.6E ; "Sun", case-sensitive
date1 = day SP month SP year
; e.g., 02 Jun 1982
day = 2DIGIT
month = %x4A.61.6E ; "Jan", case-sensitive
/ %x46.65.62 ; "Feb", case-sensitive
/ %x4D.61.72 ; "Mar", case-sensitive
/ %x41.70.72 ; "Apr", case-sensitive
/ %x4D.61.79 ; "May", case-sensitive
/ %x4A.75.6E ; "Jun", case-sensitive
/ %x4A.75.6C ; "Jul", case-sensitive
/ %x41.75.67 ; "Aug", case-sensitive
/ %x53.65.70 ; "Sep", case-sensitive
/ %x4F.63.74 ; "Oct", case-sensitive
/ %x4E.6F.76 ; "Nov", case-sensitive
/ %x44.65.63 ; "Dec", case-sensitive
year = 4DIGIT
GMT = %x47.4D.54 ; "GMT", case-sensitive
time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:59
hour = 2DIGIT
minute = 2DIGIT
second = 2DIGIT
The semantics of day-name, day, month, year, and time-of-day are the
same as those defined for the RFC 5322 constructs with the
corresponding name ([RFC5322], Section 3.3).
Obsolete formats:
obs-date = rfc850-date / asctime-date
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rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
date2 = day "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82)
day-name-l = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
/ %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
/ %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
/ %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
/ %x46.72.69.64.61.79 ; "Friday", case-sensitive
/ %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
/ %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; month day (e.g., Jun 2)
Note: Recipients of date values are encouraged to be robust in
accepting date values that might have been sent by non-HTTP
applications, as is sometimes the case when retrieving or posting
messages via proxies/gateways to SMTP or NNTP.
Note: HTTP requirements for the date/time stamp format apply only
to their usage within the protocol stream. Clients and servers
are not required to use these formats for user presentation,
request logging, etc.
8.1.1.2. Date
The "Date" header field represents the date and time at which the
message was originated, having the same semantics as the Origination
Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The
field value is an HTTP-date, as defined in Section 8.1.1.1; it MUST
be sent in rfc1123-date format.
Date = HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
Origin servers MUST include a Date header field in all responses,
except in these cases:
1. If the response status code is 100 (Continue) or 101 (Switching
Protocols), the response MAY include a Date header field, at the
server's option.
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2. If the response status code conveys a server error, e.g., 500
(Internal Server Error) or 503 (Service Unavailable), and it is
inconvenient or impossible to generate a valid Date.
3. If the server does not have a clock that can provide a reasonable
approximation of the current time, its responses MUST NOT include
a Date header field.
A received message that does not have a Date header field MUST be
assigned one by the recipient if the message will be cached by that
recipient.
Clients can use the Date header field as well; in order to keep
request messages small, they are advised not to include it when it
doesn't convey any useful information (as is usually the case for
requests that do not contain a payload).
The HTTP-date sent in a Date header field SHOULD NOT represent a date
and time subsequent to the generation of the message. It SHOULD
represent the best available approximation of the date and time of
message generation, unless the implementation has no means of
generating a reasonably accurate date and time. In theory, the date
ought to represent the moment just before the payload is generated.
In practice, the date can be generated at any time during the message
origination without affecting its semantic value.
8.1.2. Location
The "Location" header field MAY be sent in responses to refer to a
specific resource in accordance with the semantics of the status
code.
Location = URI-reference
For 201 (Created) responses, the Location is the URI of the new
resource which was created by the request. For 3xx (Redirection)
responses, the location SHOULD indicate the server's preferred URI
for automatic redirection to the resource.
The field value consists of a single URI-reference. When it has the
form of a relative reference ([RFC3986], Section 4.2), the final
value is computed by resolving it against the effective request URI
([RFC3986], Section 5). If the original URI, as navigated to by the
user agent, did contain a fragment identifier, and the final value
does not, then the original URI's fragment identifier is added to the
final value.
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For example, the original URI "http://www.example.org/~tim", combined
with a field value given as:
Location: /pub/WWW/People.html#tim
would result in a final value of
"http://www.example.org/pub/WWW/People.html#tim"
An original URI "http://www.example.org/index.html#larry", combined
with a field value given as:
Location: http://www.example.net/index.html
would result in a final value of
"http://www.example.net/index.html#larry", preserving the original
fragment identifier.
Note: Some recipients attempt to recover from Location fields that
are not valid URI references. This specification does not mandate
or define such processing, but does allow it.
There are circumstances in which a fragment identifier in a Location
URI would not be appropriate. For instance, when it appears in a 201
(Created) response, where the Location header field specifies the URI
for the entire created resource.
Note: The Content-Location header field (Section 3.1.4.2) differs
from Location in that the Content-Location identifies the most
specific resource corresponding to the enclosed representation.
It is therefore possible for a response to contain header fields
for both Location and Content-Location.
8.1.3. Retry-After
The header "Retry-After" field can be used with a 503 (Service
Unavailable) response to indicate how long the service is expected to
be unavailable to the requesting client. This field MAY also be used
with any 3xx (Redirection) response to indicate the minimum time the
user-agent is asked to wait before issuing the redirected request.
The value of this field can be either an HTTP-date or an integer
number of seconds (in decimal) after the time of the response.
Retry-After = HTTP-date / delta-seconds
Time spans are non-negative decimal integers, representing time in
seconds.
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delta-seconds = 1*DIGIT
Two examples of its use are
Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
Retry-After: 120
In the latter example, the delay is 2 minutes.
8.2. Selected Representation Header Fields
We use the term ""selected representation"" to refer to the the
current representation of a target resource that would have been
selected in a successful response if the same request had used the
method GET and excluded any conditional request header fields.
Additional header fields define metadata about the selected
representation, which might differ from the representation included
in the message for responses to some state-changing methods. The
following header fields are defined as selected representation
metadata:
+-------------------+------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------+
| ETag | Section 2.3 of [Part4] |
| Last-Modified | Section 2.2 of [Part4] |
| Vary | Section 8.2.1 |
+-------------------+------------------------+
8.2.1. Vary
The "Vary" header field conveys the set of header fields that were
used to select the representation.
Caches use this information as part of determining whether a stored
response can be used to satisfy a given request (Section 4.3 of
[Part6]).
In uncacheable or stale responses, the Vary field value advises the
user agent about the criteria that were used to select the
representation.
Vary = "*" / 1#field-name
The set of header fields named by the Vary field value is known as
the selecting header fields.
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A server SHOULD include a Vary header field with any cacheable
response that is subject to proactive negotiation. Doing so allows a
cache to properly interpret future requests on that resource and
informs the user agent about the presence of negotiation on that
resource. A server MAY include a Vary header field with a non-
cacheable response that is subject to proactive negotiation, since
this might provide the user agent with useful information about the
dimensions over which the response varies at the time of the
response.
A Vary field value of "*" signals that unspecified parameters not
limited to the header fields (e.g., the network address of the
client), play a role in the selection of the response representation;
therefore, a cache cannot determine whether this response is
appropriate. A proxy MUST NOT generate the "*" value.
The field-names given are not limited to the set of standard header
fields defined by this specification. Field names are case-
insensitive.
8.3. Authentication Challenges
Authentication challenges indicate what mechanisms are available for
the client to provide authentication credentials in future requests.
+--------------------+------------------------+
| Header Field Name | Defined in... |
+--------------------+------------------------+
| WWW-Authenticate | Section 4.4 of [Part7] |
| Proxy-Authenticate | Section 4.2 of [Part7] |
+--------------------+------------------------+
8.4. Informative
The remaining response header fields provide more information about
the target resource for potential use in later requests.
+-------------------+------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------+
| Accept-Ranges | Section 5.1 of [Part5] |
| Allow | Section 8.4.1 |
| Server | Section 8.4.2 |
+-------------------+------------------------+
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8.4.1. Allow
The "Allow" header field lists the set of methods advertised as
supported by the target resource. The purpose of this field is
strictly to inform the recipient of valid request methods associated
with the resource.
Allow = #method
Example of use:
Allow: GET, HEAD, PUT
The actual set of allowed methods is defined by the origin server at
the time of each request.
A proxy MUST NOT modify the Allow header field -- it does not need to
understand all the methods specified in order to handle them
according to the generic message handling rules.
8.4.2. Server
The "Server" header field contains information about the software
used by the origin server to handle the request.
The field can contain multiple product tokens (Section 4) and
comments (Section 3.2 of [Part1]) identifying the server and any
significant subproducts. The product tokens are listed in order of
their significance for identifying the application.
Server = product *( RWS ( product / comment ) )
Example:
Server: CERN/3.0 libwww/2.17
If the response is being forwarded through a proxy, the proxy
application MUST NOT modify the Server header field. Instead, it
MUST include a Via field (as described in Section 5.7 of [Part1]).
Note: Revealing the specific software version of the server might
allow the server machine to become more vulnerable to attacks
against software that is known to contain security holes. Server
implementers are encouraged to make this field a configurable
option.
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9. IANA Considerations
9.1. Method Registry
The HTTP Method Registry defines the name space for the request
method token (Section 5). The method registry is maintained at
.
9.1.1. Procedure
HTTP method registrations MUST include the following fields:
o Method Name (see Section 5)
o Safe ("yes" or "no", see Section 5.2.1)
o Idempotent ("yes" or "no", see Section 5.2.2)
o Pointer to specification text
Values to be added to this name space require IETF Review (see
[RFC5226], Section 4.1).
9.1.2. Considerations for New Methods
Standardized methods are generic; that is, they are potentially
applicable to any resource, not just one particular media type, kind
of resource, or application. As such, it is preferred that new
methods be registered in a document that isn't specific to a single
application or data format, since orthogonal technologies deserve
orthogonal specification.
Since message parsing (Section 3.3 of [Part1]) needs to be
independent of method semantics (aside from responses to HEAD),
definitions of new methods cannot change the parsing algorithm or
prohibit the presence of a message body on either the request or the
response message. Definitions of new methods can specify that only a
zero-length message body is allowed by requiring a Content-Length
header field with a value of "0".
New method definitions need to indicate whether they are safe
(Section 5.2.1), idempotent (Section 5.2.2), cacheable
(Section 5.2.3), and what semantics are to be associated with the
payload body if any is present in the request. If a method is
cacheable, the method definition ought to describe how, and under
what conditions, a cache can store a response and use it to satisfy a
subsequent request.
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9.1.3. Registrations
The HTTP Method Registry shall be populated with the registrations
below:
+---------+------+------------+---------------+
| Method | Safe | Idempotent | Reference |
+---------+------+------------+---------------+
| CONNECT | no | no | Section 5.3.6 |
| DELETE | no | yes | Section 5.3.5 |
| GET | yes | yes | Section 5.3.1 |
| HEAD | yes | yes | Section 5.3.2 |
| OPTIONS | yes | yes | Section 5.3.7 |
| POST | no | no | Section 5.3.3 |
| PUT | no | yes | Section 5.3.4 |
| TRACE | yes | yes | Section 5.3.8 |
+---------+------+------------+---------------+
9.2. Status Code Registry
The HTTP Status Code Registry defines the name space for the response
status-code token (Section 7). The status code registry is
maintained at .
This section replaces the registration procedure for HTTP Status
Codes previously defined in Section 7.1 of [RFC2817].
9.2.1. Procedure
Values to be added to the HTTP status code name space require IETF
Review (see [RFC5226], Section 4.1).
9.2.2. Considerations for New Status Codes
When it is necessary to express semantics for a response that are not
defined by current status codes, a new status code can be registered.
HTTP status codes are generic; they are potentially applicable to any
resource, not just one particular media type, "type" of resource, or
application. As such, it is preferred that new status codes be
registered in a document that isn't specific to a single application.
New status codes are required to fall under one of the categories
defined in Section 7. To allow existing parsers to properly handle
them, new status codes cannot disallow a payload, although they can
mandate a zero-length payload body.
A definition for a new status code ought to explain the request
conditions that produce a response containing that status code (e.g.,
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combinations of request header fields and/or method(s)) along with
any dependencies on response header fields (e.g., what fields are
required and what fields can modify the semantics). A response that
can transfer a payload ought to specify expected cache behavior
(e.g., cacheability and freshness criteria, as described in [Part6])
and whether the payload has any implied association with an
identified resource (Section 3.1.4.1).
9.2.3. Registrations
The HTTP Status Code Registry shall be updated with the registrations
below:
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+-------+----------------------------------+----------------+
| Value | Description | Reference |
+-------+----------------------------------+----------------+
| 100 | Continue | Section 7.2.1 |
| 101 | Switching Protocols | Section 7.2.2 |
| 200 | OK | Section 7.3.1 |
| 201 | Created | Section 7.3.2 |
| 202 | Accepted | Section 7.3.3 |
| 203 | Non-Authoritative Information | Section 7.3.4 |
| 204 | No Content | Section 7.3.5 |
| 205 | Reset Content | Section 7.3.6 |
| 300 | Multiple Choices | Section 7.4.1 |
| 301 | Moved Permanently | Section 7.4.2 |
| 302 | Found | Section 7.4.3 |
| 303 | See Other | Section 7.4.4 |
| 305 | Use Proxy | Section 7.4.5 |
| 306 | (Unused) | Section 7.4.6 |
| 307 | Temporary Redirect | Section 7.4.7 |
| 400 | Bad Request | Section 7.5.1 |
| 402 | Payment Required | Section 7.5.2 |
| 403 | Forbidden | Section 7.5.3 |
| 404 | Not Found | Section 7.5.4 |
| 405 | Method Not Allowed | Section 7.5.5 |
| 406 | Not Acceptable | Section 7.5.6 |
| 408 | Request Timeout | Section 7.5.7 |
| 409 | Conflict | Section 7.5.8 |
| 410 | Gone | Section 7.5.9 |
| 411 | Length Required | Section 7.5.10 |
| 413 | Request Representation Too Large | Section 7.5.11 |
| 414 | URI Too Long | Section 7.5.12 |
| 415 | Unsupported Media Type | Section 7.5.13 |
| 417 | Expectation Failed | Section 7.5.14 |
| 426 | Upgrade Required | Section 7.5.15 |
| 500 | Internal Server Error | Section 7.6.1 |
| 501 | Not Implemented | Section 7.6.2 |
| 502 | Bad Gateway | Section 7.6.3 |
| 503 | Service Unavailable | Section 7.6.4 |
| 504 | Gateway Timeout | Section 7.6.5 |
| 505 | HTTP Version Not Supported | Section 7.6.6 |
+-------+----------------------------------+----------------+
9.3. Header Field Registry
HTTP header fields are registered within the Message Header Field
Registry located at , as defined by [RFC3864].
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9.3.1. Considerations for New Header Fields
Header fields are key:value pairs that can be used to communicate
data about the message, its payload, the target resource, or the
connection (i.e., control data). See Section 3.2 of [Part1] for a
general definition of header field syntax in HTTP messages.
The requirements for header field names are defined in Section 4.1 of
[RFC3864]. Authors of specifications defining new fields are advised
to keep the name as short as practical, and not to prefix them with
"X-" if they are to be registered (either immediately or in the
future).
New header field values typically have their syntax defined using
ABNF ([RFC5234]), using the extension defined in Appendix B of
[Part1] as necessary, and are usually constrained to the range of
ASCII characters. Header fields needing a greater range of
characters can use an encoding such as the one defined in [RFC5987].
Because commas (",") are used as a generic delimiter between field-
values, they need to be treated with care if they are allowed in the
field-value's payload. Typically, components that might contain a
comma are protected with double-quotes using the quoted-string ABNF
production (Section 3.2.4 of [Part1]).
For example, a textual date and a URI (either of which might contain
a comma) could be safely carried in field-values like these:
Example-URI-Field: "http://example.com/a.html,foo",
"http://without-a-comma.example.com/"
Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
Note that double-quote delimiters almost always are used with the
quoted-string production; using a different syntax inside double-
quotes will likely cause unnecessary confusion.
Many header fields use a format including (case-insensitively) named
parameters (for instance, Content-Type, defined in Section 3.1.1.5).
Allowing both unquoted (token) and quoted (quoted-string) syntax for
the parameter value enables recipients to use existing parser
components. When allowing both forms, the meaning of a parameter
value ought to be independent of the syntax used for it (for an
example, see the notes on parameter handling for media types in
Section 3.1.1.1).
Authors of specifications defining new header fields are advised to
consider documenting:
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o Whether the field is a single value, or whether it can be a list
(delimited by commas; see Section 3.2 of [Part1]).
If it does not use the list syntax, document how to treat messages
where the header field occurs multiple times (a sensible default
would be to ignore the header field, but this might not always be
the right choice).
Note that intermediaries and software libraries might combine
multiple header field instances into a single one, despite the
header field not allowing this. A robust format enables
recipients to discover these situations (good example: "Content-
Type", as the comma can only appear inside quoted strings; bad
example: "Location", as a comma can occur inside a URI).
o Under what conditions the header field can be used; e.g., only in
responses or requests, in all messages, only on responses to a
particular request method.
o Whether it is appropriate to list the field-name in the Connection
header field (i.e., if the header field is to be hop-by-hop, see
Section 6.1 of [Part1]).
o Under what conditions intermediaries are allowed to modify the
header field's value, insert or delete it.
o How the header field might interact with caching (see [Part6]).
o Whether the header field is useful or allowable in trailers (see
Section 4.1 of [Part1]).
o Whether the header field ought to be preserved across redirects.
9.3.2. Registrations
The Message Header Field Registry shall be updated with the following
permanent registrations:
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+-------------------+----------+----------+-----------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-----------------+
| Accept | http | standard | Section 6.3.2 |
| Accept-Charset | http | standard | Section 6.3.3 |
| Accept-Encoding | http | standard | Section 6.3.4 |
| Accept-Language | http | standard | Section 6.3.5 |
| Allow | http | standard | Section 8.4.1 |
| Content-Encoding | http | standard | Section 3.1.2.2 |
| Content-Language | http | standard | Section 3.1.3.2 |
| Content-Location | http | standard | Section 3.1.4.2 |
| Content-Type | http | standard | Section 3.1.1.5 |
| Date | http | standard | Section 8.1.1.2 |
| Expect | http | standard | Section 6.1.2 |
| From | http | standard | Section 6.5.1 |
| Location | http | standard | Section 8.1.2 |
| MIME-Version | http | standard | Appendix A.1 |
| Max-Forwards | http | standard | Section 6.1.1 |
| Referer | http | standard | Section 6.5.2 |
| Retry-After | http | standard | Section 8.1.3 |
| Server | http | standard | Section 8.4.2 |
| User-Agent | http | standard | Section 6.5.3 |
| Vary | http | standard | Section 8.2.1 |
+-------------------+----------+----------+-----------------+
The change controller for the above registrations is: "IETF
(iesg@ietf.org) - Internet Engineering Task Force".
9.4. Content Coding Registry
The HTTP Content Coding Registry defines the name space for content
coding names (Section 4.2 of [Part1]). The content coding registry
is maintained at .
9.4.1. Procedure
Content Coding registrations MUST include the following fields:
o Name
o Description
o Pointer to specification text
Names of content codings MUST NOT overlap with names of transfer
codings (Section 4 of [Part1]), unless the encoding transformation is
identical (as is the case for the compression codings defined in
Section 4.2 of [Part1]).
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Values to be added to this name space require IETF Review (see
Section 4.1 of [RFC5226]), and MUST conform to the purpose of content
coding defined in this section.
9.4.2. Registrations
The HTTP Content Codings Registry shall be updated with the
registrations below:
+----------+----------------------------------------+---------------+
| Name | Description | Reference |
+----------+----------------------------------------+---------------+
| compress | UNIX "compress" program method | Section 4.2.1 |
| | | of [Part1] |
| deflate | "deflate" compression mechanism | Section 4.2.2 |
| | ([RFC1951]) used inside the "zlib" | of [Part1] |
| | data format ([RFC1950]) | |
| gzip | Same as GNU zip [RFC1952] | Section 4.2.3 |
| | | of [Part1] |
| identity | reserved (synonym for "no encoding" in | Section 6.3.4 |
| | Accept-Encoding header field) | |
+----------+----------------------------------------+---------------+
10. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
10.1. Transfer of Sensitive Information
Like any generic data transfer protocol, HTTP cannot regulate the
content of the data that is transferred, nor is there any a priori
method of determining the sensitivity of any particular piece of
information within the context of any given request. Therefore,
applications SHOULD supply as much control over this information as
possible to the provider of that information. Four header fields are
worth special mention in this context: Server, Via, Referer and From.
Revealing the specific software version of the server might allow the
server machine to become more vulnerable to attacks against software
that is known to contain security holes. Implementers SHOULD make
the Server header field a configurable option.
Proxies which serve as a portal through a network firewall SHOULD
take special precautions regarding the transfer of header information
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that identifies the hosts behind the firewall. In particular, they
SHOULD remove, or replace with sanitized versions, any Via fields
generated behind the firewall.
The Referer header field allows reading patterns to be studied and
reverse links drawn. Although it can be very useful, its power can
be abused if user details are not separated from the information
contained in the Referer. Even when the personal information has
been removed, the Referer header field might indicate a private
document's URI whose publication would be inappropriate.
The information sent in the From field might conflict with the user's
privacy interests or their site's security policy, and hence it
SHOULD NOT be transmitted without the user being able to disable,
enable, and modify the contents of the field. The user MUST be able
to set the contents of this field within a user preference or
application defaults configuration.
We suggest, though do not require, that a convenient toggle interface
be provided for the user to enable or disable the sending of From and
Referer information.
The User-Agent (Section 6.5.3) or Server (Section 8.4.2) header
fields can sometimes be used to determine that a specific client or
server has a particular security hole which might be exploited.
Unfortunately, this same information is often used for other valuable
purposes for which HTTP currently has no better mechanism.
Furthermore, the User-Agent header field might contain enough entropy
to be used, possibly in conjunction with other material, to uniquely
identify the user.
Some request methods, like TRACE (Section 5.3.8), expose information
that was sent in request header fields within the body of their
response. Clients SHOULD be careful with sensitive information, like
Cookies, Authorization credentials, and other header fields that
might be used to collect data from the client.
10.2. Encoding Sensitive Information in URIs
Because the source of a link might be private information or might
reveal an otherwise private information source, it is strongly
recommended that the user be able to select whether or not the
Referer field is sent. For example, a browser client could have a
toggle switch for browsing openly/anonymously, which would
respectively enable/disable the sending of Referer and From
information.
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Clients SHOULD NOT include a Referer header field in a (non-secure)
HTTP request if the referring page was transferred with a secure
protocol.
Authors of services SHOULD NOT use GET-based forms for the submission
of sensitive data because that data will be placed in the request-
target. Many existing servers, proxies, and user agents log or
display the request-target in places where it might be visible to
third parties. Such services can use POST-based form submission
instead.
10.3. Location Header Fields: Spoofing and Information Leakage
If a single server supports multiple organizations that do not trust
one another, then it MUST check the values of Location and Content-
Location header fields in responses that are generated under control
of said organizations to make sure that they do not attempt to
invalidate resources over which they have no authority.
Furthermore, appending the fragment identifier from one URI to
another one obtained from a Location header field might leak
confidential information to the target server -- although the
fragment identifier is not transmitted in the final request, it might
be visible to the user agent through other means, such as scripting.
10.4. Security Considerations for CONNECT
Since tunneled data is opaque to the proxy, there are additional
risks to tunneling to other well-known or reserved ports. A HTTP
client CONNECTing to port 25 could relay spam via SMTP, for example.
As such, proxies SHOULD restrict CONNECT access to a small number of
known ports.
10.5. Privacy Issues Connected to Accept Header Fields
Accept header fields can reveal information about the user to all
servers which are accessed. The Accept-Language header field in
particular can reveal information the user would consider to be of a
private nature, because the understanding of particular languages is
often strongly correlated to the membership of a particular ethnic
group. User agents which offer the option to configure the contents
of an Accept-Language header field to be sent in every request are
strongly encouraged to let the configuration process include a
message which makes the user aware of the loss of privacy involved.
An approach that limits the loss of privacy would be for a user agent
to omit the sending of Accept-Language header fields by default, and
to ask the user whether or not to start sending Accept-Language
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header fields to a server if it detects, by looking for any Vary
header fields generated by the server, that such sending could
improve the quality of service.
Elaborate user-customized accept header fields sent in every request,
in particular if these include quality values, can be used by servers
as relatively reliable and long-lived user identifiers. Such user
identifiers would allow content providers to do click-trail tracking,
and would allow collaborating content providers to match cross-server
click-trails or form submissions of individual users. Note that for
many users not behind a proxy, the network address of the host
running the user agent will also serve as a long-lived user
identifier. In environments where proxies are used to enhance
privacy, user agents ought to be conservative in offering accept
header field configuration options to end users. As an extreme
privacy measure, proxies could filter the accept header fields in
relayed requests. General purpose user agents which provide a high
degree of header field configurability SHOULD warn users about the
loss of privacy which can be involved.
11. Acknowledgments
See Section 9 of [Part1].
12. References
12.1. Normative References
[Part1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and
Routing", draft-ietf-httpbis-p1-messaging-21 (work in
progress), October 2012.
[Part4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Conditional Requests",
draft-ietf-httpbis-p4-conditional-21 (work in
progress), October 2012.
[Part5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range
Requests", draft-ietf-httpbis-p5-range-21 (work in
progress), October 2012.
[Part6] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
draft-ietf-httpbis-p6-cache-21 (work in progress),
October 2012.
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[Part7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Authentication",
draft-ietf-httpbis-p7-auth-21 (work in progress),
October 2012.
[RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data
Format Specification version 3.3", RFC 1950, May 1996.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format
Specification version 1.3", RFC 1951, May 1996.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and
G. Randers-Pehrson, "GZIP file format specification
version 4.3", RFC 1952, May 1996.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types",
RFC 2046, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005.
[RFC4647] Phillips, A., Ed. and M. Davis, Ed., "Matching of
Language Tags", BCP 47, RFC 4647, September 2006.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008.
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for
Identifying Languages", BCP 47, RFC 5646,
September 2009.
12.2. Informative References
[REST] Fielding, R., "Architectural Styles and the Design of
Network-based Software Architectures", Doctoral
Dissertation, University of California, Irvine ,
September 2000,
.
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[RFC1123] Braden, R., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
October 1989.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen,
"Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945,
May 1996.
[RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Five: Conformance Criteria
and Examples", RFC 2049, November 1996.
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and
T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2068, January 1997.
[RFC2076] Palme, J., "Common Internet Message Headers", RFC 2076,
February 1997.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC2295] Holtman, K. and A. Mutz, "Transparent Content
Negotiation in HTTP", RFC 2295, March 1998.
[RFC2388] Masinter, L., "Returning Values from Forms: multipart/
form-data", RFC 2388, August 1998.
[RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud,
"MIME Encapsulation of Aggregate Documents, such as
HTML (MHTML)", RFC 2557, March 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, May 2000.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications
and Registration Procedures", BCP 13, RFC 4288,
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December 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, March 2010.
[RFC5987] Reschke, J., "Character Set and Language Encoding for
Hypertext Transfer Protocol (HTTP) Header Field
Parameters", RFC 5987, August 2010.
[RFC6151] Turner, S. and L. Chen, "Updated Security
Considerations for the MD5 Message-Digest and the HMAC-
MD5 Algorithms", RFC 6151, March 2011.
[RFC6266] Reschke, J., "Use of the Content-Disposition Header
Field in the Hypertext Transfer Protocol (HTTP)",
RFC 6266, June 2011.
[status-308] Reschke, J., "The Hypertext Transfer Protocol (HTTP)
Status Code 308 (Permanent Redirect)",
draft-reschke-http-status-308-07 (work in progress),
March 2012.
Appendix A. Differences between HTTP and MIME
HTTP/1.1 uses many of the constructs defined for Internet Mail
([RFC5322]) and the Multipurpose Internet Mail Extensions (MIME
[RFC2045]) to allow a message body to be transmitted in an open
variety of representations and with extensible mechanisms. However,
RFC 2045 discusses mail, and HTTP has a few features that are
different from those described in MIME. These differences were
carefully chosen to optimize performance over binary connections, to
allow greater freedom in the use of new media types, to make date
comparisons easier, and to acknowledge the practice of some early
HTTP servers and clients.
This appendix describes specific areas where HTTP differs from MIME.
Proxies and gateways to strict MIME environments SHOULD be aware of
these differences and provide the appropriate conversions where
necessary. Proxies and gateways from MIME environments to HTTP also
need to be aware of the differences because some conversions might be
required.
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A.1. MIME-Version
HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages
MAY include a single MIME-Version header field to indicate 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
full conformance with the MIME protocol (as defined in [RFC2045]).
Proxies/gateways are responsible for ensuring full conformance (where
possible) when exporting HTTP messages to strict MIME environments.
MIME-Version = 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.1. However,
HTTP/1.1 message parsing and semantics are defined by this document
and not the MIME specification.
A.2. Conversion to Canonical Form
MIME requires that an Internet mail body-part be converted to
canonical form prior to being transferred, as described in Section 4
of [RFC2049]. Section 3.1.1.3 of this document describes the forms
allowed for subtypes of the "text" media type when transmitted over
HTTP. [RFC2046] requires that content with a type of "text"
represent line breaks as CRLF and forbids the use of CR or LF outside
of line break sequences. HTTP allows CRLF, bare CR, and bare LF to
indicate a line break within text content when a message is
transmitted over HTTP.
Where it is possible, a proxy or gateway from HTTP to a strict MIME
environment SHOULD translate all line breaks within the text media
types described in Section 3.1.1.3 of this document to the RFC 2049
canonical form of CRLF. Note, however, that this might be
complicated by the presence of a Content-Encoding and by the fact
that HTTP allows the use of some character encodings which do not use
octets 13 and 10 to represent CR and LF, respectively, as is the case
for some multi-byte character encodings.
Conversion will break any cryptographic checksums applied to the
original content unless the original content is already in canonical
form. Therefore, the canonical form is recommended for any content
that uses such checksums in HTTP.
A.3. Conversion of Date Formats
HTTP/1.1 uses a restricted set of date formats (Section 8.1.1.1) to
simplify the process of date comparison. Proxies and gateways from
other protocols SHOULD ensure that any Date header field present in a
message conforms to one of the HTTP/1.1 formats and rewrite the date
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if necessary.
A.4. Introduction of Content-Encoding
MIME does not include any concept equivalent to HTTP/1.1's Content-
Encoding header field. Since this acts as a modifier on the media
type, proxies and gateways from HTTP to MIME-compliant protocols MUST
either change the value of the Content-Type header field or decode
the representation before forwarding the message. (Some experimental
applications of Content-Type for Internet mail have used a media-type
parameter of ";conversions=" to perform a function
equivalent to Content-Encoding. However, this parameter is not part
of the MIME standards).
A.5. No Content-Transfer-Encoding
HTTP does not use the Content-Transfer-Encoding field of MIME.
Proxies and gateways from MIME-compliant protocols to HTTP MUST
remove any Content-Transfer-Encoding prior to delivering the response
message to an HTTP client.
Proxies and gateways from HTTP to MIME-compliant protocols are
responsible for ensuring that the message is in the correct format
and encoding for safe transport on that protocol, where "safe
transport" is defined by the limitations of the protocol being used.
Such a proxy or gateway SHOULD label the data with an appropriate
Content-Transfer-Encoding if doing so will improve the likelihood of
safe transport over the destination protocol.
A.6. MHTML and Line Length Limitations
HTTP implementations which share code with MHTML [RFC2557]
implementations need to be aware of MIME line length limitations.
Since HTTP does not have this limitation, HTTP does not fold long
lines. MHTML messages being transported by HTTP follow all
conventions of MHTML, including line length limitations and folding,
canonicalization, etc., since HTTP transports all message-bodies as
payload (see Section 3.1.1.4) and does not interpret the content or
any MIME header lines that might be contained therein.
Appendix B. Additional Features
[RFC1945] and [RFC2068] document protocol elements used by some
existing HTTP implementations, but not consistently and correctly
across most HTTP/1.1 applications. Implementers are advised to be
aware of these features, but cannot rely upon their presence in, or
interoperability with, other HTTP/1.1 applications. Some of these
describe proposed experimental features, and some describe features
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that experimental deployment found lacking that are now addressed in
the base HTTP/1.1 specification.
A number of other header fields, such as Content-Disposition and
Title, from SMTP and MIME are also often implemented (see [RFC6266]
and [RFC2076]).
Appendix C. Changes from RFC 2616
Remove base URI setting semantics for "Content-Location" due to poor
implementation support, which was caused by too many broken servers
emitting bogus Content-Location header fields, and also the
potentially undesirable effect of potentially breaking relative links
in content-negotiated resources. (Section 3.1.4.2)
Clarify definition of POST. (Section 5.3.3)
Remove requirement to handle all Content-* header fields; ban use of
Content-Range with PUT. (Section 5.3.4)
Take over definition of CONNECT method from [RFC2817].
(Section 5.3.6)
Restrict "Max-Forwards" header field to OPTIONS and TRACE
(previously, extension methods could have used it as well).
(Section 6.1.1)
The ABNF for the "Expect" header field has been both fixed (allowing
parameters for value-less expectations as well) and simplified
(allowing trailing semicolons after "100-continue" when they were
invalid before). (Section 6.1.2)
Remove ISO-8859-1 special-casing in Accept-Charset. (Section 6.3.3)
Allow "Referer" field value of "about:blank" as alternative to not
specifying it. (Section 6.5.2)
Broadened the definition of 203 (Non-Authoritative Information) to
include cases of payload transformations as well. (Section 7.3.4)
Status codes 301, 302, and 307: removed the normative requirements on
both response payloads and user interaction. (Section 7.4)
Failed to consider that there are many other request methods that are
safe to automatically redirect, and further that the user agent is
able to make that determination based on the request method
semantics. Furthermore, allow user agents to rewrite the method from
POST to GET for status codes 301 and 302. (Sections 7.4.2, 7.4.3 and
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7.4.7)
Deprecate 305 (Use Proxy) status code, because user agents did not
implement it. It used to indicate that the target resource needs to
be accessed through the proxy given by the Location field. The
Location field gave the URI of the proxy. The recipient was expected
to repeat this single request via the proxy. (Section 7.4.5)
Define status 426 (Upgrade Required) (this was incorporated from
[RFC2817]). (Section 7.5.15)
Correct syntax of "Location" header field to allow URI references
(including relative references and fragments), as referred symbol
"absoluteURI" wasn't what was expected, and add some clarifications
as to when use of fragments would not be appropriate.
(Section 8.1.2)
Reclassify "Allow" as response header field, removing the option to
specify it in a PUT request. Relax the server requirement on the
contents of the Allow header field and remove requirement on clients
to always trust the header field value. (Section 8.4.1)
In the description of the "Server" header field, the "Via" field was
described as a SHOULD. The requirement was and is stated correctly
in the description of the Via header field in Section 5.7 of [Part1].
(Section 8.4.2)
Clarify contexts that charset is used in. (Section 3.1.1.2)
Remove the default character encoding of "ISO-8859-1" for text media
types; the default now is whatever the media type definition says.
(Section 3.1.1.3)
Registration of Content Codings now requires IETF Review
(Section 9.4)
Remove definition of "Content-MD5 header" field because it was
inconsistently implemented with respect to partial responses, and
also because of known deficiencies in the hash algorithm itself (see
[RFC6151] for details).
Introduce Method Registry. (Section 9.1)
Take over the Status Code Registry, previously defined in Section 7.1
of [RFC2817]. (Section 9.2)
Remove reference to non-existant identity transfer-coding value
tokens. (Appendix A.5)
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Remove discussion of Content-Disposition header field, it is now
defined by [RFC6266]. (Appendix B)
Appendix D. Imported ABNF
The following core rules are included by reference, as defined in
Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF
(line feed), OCTET (any 8-bit sequence of data), SP (space), and
VCHAR (any visible US-ASCII character).
The rules below are defined in [Part1]:
BWS =
OWS =
RWS =
URI-reference =
absolute-URI =
comment =
field-name =
partial-URI =
quoted-string =
token =
word =
Appendix E. Collected ABNF
Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
OWS ( media-range [ accept-params ] ) ] ) ]
Accept-Charset = *( "," OWS ) ( ( charset / "*" ) [ weight ] ) *( OWS
"," [ OWS ( ( charset / "*" ) [ weight ] ) ] )
Accept-Encoding = [ ( "," / ( codings [ weight ] ) ) *( OWS "," [ OWS
( codings [ weight ] ) ] ) ]
Accept-Language = *( "," OWS ) ( language-range [ weight ] ) *( OWS
"," [ OWS ( language-range [ weight ] ) ] )
Allow = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
BWS =
Content-Encoding = *( "," OWS ) content-coding *( OWS "," [ OWS
content-coding ] )
Content-Language = *( "," OWS ) language-tag *( OWS "," [ OWS
language-tag ] )
Content-Location = absolute-URI / partial-URI
Content-Type = media-type
Date = HTTP-date
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Expect = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
From = mailbox
GMT = %x47.4D.54 ; GMT
HTTP-date = rfc1123-date / obs-date
Location = URI-reference
MIME-Version = 1*DIGIT "." 1*DIGIT
Max-Forwards = 1*DIGIT
OWS =
RWS =
Referer = absolute-URI / partial-URI
Retry-After = HTTP-date / delta-seconds
Server = product *( RWS ( product / comment ) )
URI-reference =
User-Agent = product *( RWS ( product / comment ) )
Vary = "*" / ( *( "," OWS ) field-name *( OWS "," [ OWS field-name ]
) )
absolute-URI =
accept-ext = OWS ";" OWS token [ "=" word ]
accept-params = weight *accept-ext
asctime-date = day-name SP date3 SP time-of-day SP year
attribute = token
charset = token
codings = content-coding / "identity" / "*"
comment =
content-coding = token
date1 = day SP month SP year
date2 = day "-" month "-" 2DIGIT
date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
day = 2DIGIT
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day-name = %x4D.6F.6E ; Mon
/ %x54.75.65 ; Tue
/ %x57.65.64 ; Wed
/ %x54.68.75 ; Thu
/ %x46.72.69 ; Fri
/ %x53.61.74 ; Sat
/ %x53.75.6E ; Sun
day-name-l = %x4D.6F.6E.64.61.79 ; Monday
/ %x54.75.65.73.64.61.79 ; Tuesday
/ %x57.65.64.6E.65.73.64.61.79 ; Wednesday
/ %x54.68.75.72.73.64.61.79 ; Thursday
/ %x46.72.69.64.61.79 ; Friday
/ %x53.61.74.75.72.64.61.79 ; Saturday
/ %x53.75.6E.64.61.79 ; Sunday
delta-seconds = 1*DIGIT
expect-name = token
expect-param = expect-name [ BWS "=" BWS expect-value ]
expect-value = token / quoted-string
expectation = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
OWS expect-param ] )
field-name =
hour = 2DIGIT
language-range =
language-tag =
mailbox =
media-range = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
";" OWS parameter )
media-type = type "/" subtype *( OWS ";" OWS parameter )
method = token
minute = 2DIGIT
month = %x4A.61.6E ; Jan
/ %x46.65.62 ; Feb
/ %x4D.61.72 ; Mar
/ %x41.70.72 ; Apr
/ %x4D.61.79 ; May
/ %x4A.75.6E ; Jun
/ %x4A.75.6C ; Jul
/ %x41.75.67 ; Aug
/ %x53.65.70 ; Sep
/ %x4F.63.74 ; Oct
/ %x4E.6F.76 ; Nov
/ %x44.65.63 ; Dec
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obs-date = rfc850-date / asctime-date
parameter = attribute "=" value
partial-URI =
product = token [ "/" product-version ]
product-version = token
quoted-string =
qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
second = 2DIGIT
subtype = token
time-of-day = hour ":" minute ":" second
token =
type = token
value = word
weight = OWS ";" OWS "q=" qvalue
word =
year = 4DIGIT
Appendix F. Change Log (to be removed by RFC Editor before publication)
F.1. Since RFC 2616
Extracted relevant partitions from [RFC2616].
F.2. Since draft-ietf-httpbis-p2-semantics-00
Closed issues:
o : "Via is a MUST"
()
o : "Fragments
allowed in Location"
()
o : "Safe Methods
vs Redirection" ()
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o : "Revise
description of the POST method"
()
o : "Normative and
Informative references"
o : "RFC2606
Compliance"
o : "Informative
references"
o : "Redundant
cross-references"
Other changes:
o Move definitions of 304 and 412 condition codes to [Part4]
F.3. Since draft-ietf-httpbis-p3-payload-00
Closed issues:
o : "Media Type
Registrations" ()
o : "Clarification
regarding quoting of charset values"
()
o : "Remove
'identity' token references"
()
o : "Accept-
Encoding BNF"
o : "Normative and
Informative references"
o : "RFC1700
references"
o : "Updating to
RFC4288"
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o : "Informative
references"
o : "ISO-8859-1
Reference"
o : "Encoding
References Normative"
o : "Normative up-
to-date references"
F.4. Since draft-ietf-httpbis-p2-semantics-01
Closed issues:
o : "PUT side
effects"
o : "Duplicate Host
header requirements"
Ongoing work on ABNF conversion
():
o Move "Product Tokens" section (back) into Part 1, as "token" is
used in the definition of the Upgrade header field.
o Add explicit references to BNF syntax and rules imported from
other parts of the specification.
o Copy definition of delta-seconds from Part6 instead of referencing
it.
F.5. Since draft-ietf-httpbis-p3-payload-01
Ongoing work on ABNF conversion
():
o Add explicit references to BNF syntax and rules imported from
other parts of the specification.
F.6. Since draft-ietf-httpbis-p2-semantics-02
Closed issues:
o : "Requiring
Allow in 405 responses"
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o : "Status Code
Registry"
o : "Redirection
vs. Location"
o : "Cacheability
of 303 response"
o : "305 Use Proxy"
o :
"Classification for Allow header field"
o : "PUT - 'store
under' vs 'store at'"
Ongoing work on IANA Message Header Field Registration
():
o Reference RFC 3984, and update header field registrations for
header fields defined in this document.
Ongoing work on ABNF conversion
():
o Replace string literals when the string really is case-sensitive
(method).
F.7. Since draft-ietf-httpbis-p3-payload-02
Closed issues:
o : "Quoting
Charsets"
o :
"Classification for Allow header field"
o : "missing
default for qvalue in description of Accept-Encoding"
Ongoing work on IANA Message Header Field Registration
():
o Reference RFC 3984, and update header field registrations for
header fields defined in this document.
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F.8. Since draft-ietf-httpbis-p2-semantics-03
Closed issues:
o : "OPTIONS
payload bodies"
o : "Description
of CONNECT should refer to RFC2817"
o : "Location
Content-Location reference request/response mixup"
Ongoing work on Method Registry
():
o Added initial proposal for registration process, plus initial
content (non-HTTP/1.1 methods to be added by a separate
specification).
F.9. Since draft-ietf-httpbis-p3-payload-03
Closed issues:
o : "Quoting
Charsets"
o : "language tag
matching (Accept-Language) vs RFC4647"
o : "RFC 1806 has
been replaced by RFC2183"
Other changes:
o : "Encoding
References Normative" -- rephrase the annotation and reference
BCP97.
F.10. Since draft-ietf-httpbis-p2-semantics-04
Closed issues:
o : "Content-*"
o : "RFC 2822 is
updated by RFC 5322"
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Ongoing work on ABNF conversion
():
o Use "/" instead of "|" for alternatives.
o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
o Rewrite ABNFs to spell out whitespace rules, factor out header
field value format definitions.
F.11. Since draft-ietf-httpbis-p3-payload-04
Closed issues:
o : "RFC 2822 is
updated by RFC 5322"
Ongoing work on ABNF conversion
():
o Use "/" instead of "|" for alternatives.
o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
o Rewrite ABNFs to spell out whitespace rules, factor out header
field value format definitions.
F.12. Since draft-ietf-httpbis-p2-semantics-05
Closed issues:
o : "reason-phrase
BNF"
Final work on ABNF conversion
():
o Add appendix containing collected and expanded ABNF, reorganize
ABNF introduction.
F.13. Since draft-ietf-httpbis-p3-payload-05
Closed issues:
o : "Join
"Differences Between HTTP Entities and RFC 2045 Entities"?"
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Final work on ABNF conversion
():
o Add appendix containing collected and expanded ABNF, reorganize
ABNF introduction.
Other changes:
o Move definition of quality values into Part 1.
F.14. Since draft-ietf-httpbis-p2-semantics-06
Closed issues:
o : "Clarify when
Referer is sent"
o : "status codes
vs methods"
o : "Do not
require "updates" relation for specs that register status codes or
method names"
F.15. Since draft-ietf-httpbis-p3-payload-06
Closed issues:
o : "Content-
Location isn't special"
o : "Content
Sniffing"
F.16. Since draft-ietf-httpbis-p2-semantics-07
Closed issues:
o : "Idempotency"
o : "TRACE security
considerations"
o : "Clarify rules
for determining what entities a response carries"
o : "update note
citing RFC 1945 and 2068"
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o : "update note
about redirect limit"
o : "Location
header field ABNF should use 'URI'"
o : "fragments in
Location vs status 303"
o : "move IANA
registrations for optional status codes"
Partly resolved issues:
o : "Are OPTIONS
and TRACE safe?"
F.17. Since draft-ietf-httpbis-p3-payload-07
Closed issues:
o : "Updated
reference for language tags"
o : "Clarify rules
for determining what entities a response carries"
o : "Content-
Location base-setting problems"
o : "Content
Sniffing"
o : "pick IANA
policy (RFC5226) for Transfer Coding / Content Coding"
o : "move
definitions of gzip/deflate/compress to part 1"
Partly resolved issues:
o : "update IANA
requirements wrt Transfer-Coding values" (add the IANA
Considerations subsection)
o : "update IANA
requirements wrt Content-Coding values" (add the IANA
Considerations subsection)
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F.18. Since draft-ietf-httpbis-p2-semantics-08
Closed issues:
o : "Safe Methods
vs Redirection" (we missed the introduction to the 3xx status
codes when fixing this previously)
F.19. Since draft-ietf-httpbis-p3-payload-08
Closed issues:
o : "Content
Negotiation for media types"
o : "Accept-
Language: which RFC4647 filtering?"
F.20. Since draft-ietf-httpbis-p2-semantics-09
Closed issues:
o : "Fragment
combination / precedence during redirects"
Partly resolved issues:
o : "Location
header field payload handling"
o : "Term for the
requested resource's URI"
F.21. Since draft-ietf-httpbis-p3-payload-09
Closed issues:
o : "MIME-Version
not listed in P1, general header fields"
o : "IANA registry
for content/transfer encodings"
o : "Content
Sniffing"
o : "use of term
"word" when talking about header field structure"
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Partly resolved issues:
o : "Term for the
requested resource's URI"
F.22. Since draft-ietf-httpbis-p2-semantics-10
Closed issues:
o : "Clarify
'Requested Variant'"
o : "Clarify
entity / representation / variant terminology"
o : "Methods and
Caching"
o : "OPTIONS vs
Max-Forwards"
o : "Status codes
and caching"
o : "consider
removing the 'changes from 2068' sections"
F.23. Since draft-ietf-httpbis-p3-payload-10
Closed issues:
o : "Clarify
'Requested Variant'"
o : "Content-
Location isn't special"
o : "Delimiting
messages with multipart/byteranges"
o : "Clarify
entity / representation / variant terminology"
o : "confusing
req. language for Content-Location"
o : "Content-
Location on 304 responses"
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o : "'requested
resource' in content-encoding definition"
o : "consider
removing the 'changes from 2068' sections"
Partly resolved issues:
o : "Content-MD5
and partial responses"
F.24. Since draft-ietf-httpbis-p2-semantics-11
Closed issues:
o :
"Considerations for new status codes"
o :
"Considerations for new methods"
o : "User-Agent
guidelines" (relating to the 'User-Agent' header field)
F.25. Since draft-ietf-httpbis-p3-payload-11
Closed issues:
o : "Factor out
Content-Disposition"
F.26. Since draft-ietf-httpbis-p2-semantics-12
Closed issues:
o : "Fragment
combination / precedence during redirects" (added warning about
having a fragid on the redirect might cause inconvenience in some
cases)
o : "Content-* vs.
PUT"
o : "205 Bodies"
o : "Understanding
Content-* on non-PUT requests"
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o : "Content-*"
o : "Header field
type defaulting"
o : "PUT - 'store
under' vs 'store at'"
o : "duplicate
ABNF for reason-phrase"
o : "Note special
status of Content-* prefix in header field registration
procedures"
o : "Max-Forwards
vs extension methods"
o : "What is the
value space of HTTP status codes?" (actually fixed in
draft-ietf-httpbis-p2-semantics-11)
o : "Header Field
Classification"
o : "PUT side
effect: invalidation or just stale?"
o : "proxies not
supporting certain methods"
o : "Migrate
CONNECT from RFC2817 to p2"
o : "Migrate
Upgrade details from RFC2817"
o : "clarify PUT
semantics'"
o : "duplicate
ABNF for 'Method'"
o : "untangle
ABNFs for header fields"
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F.27. Since draft-ietf-httpbis-p3-payload-12
Closed issues:
o : "Header Field
Classification"
o : "untangle
ABNFs for header fields"
o : "potentially
misleading MAY in media-type def"
F.28. Since draft-ietf-httpbis-p2-semantics-13
Closed issues:
o : "untangle
ABNFs for header fields"
o : "message body
in CONNECT request"
F.29. Since draft-ietf-httpbis-p3-payload-13
Closed issues:
o : "Default
charsets for text media types"
o : "Content-MD5
and partial responses"
o : "untangle
ABNFs for header fields"
o : "confusing
undefined parameter in media range example"
F.30. Since draft-ietf-httpbis-p2-semantics-14
Closed issues:
o : "Clarify
status code for rate limiting"
o : "clarify 403
forbidden"
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o : "Clarify 203
Non-Authoritative Information"
o : "update
default reason phrase for 413"
F.31. Since draft-ietf-httpbis-p3-payload-14
None.
F.32. Since draft-ietf-httpbis-p2-semantics-15
Closed issues:
o : "Strength of
requirements on Accept re: 406"
o : "400 response
isn't generic"
F.33. Since draft-ietf-httpbis-p3-payload-15
Closed issues:
o : "Strength of
requirements on Accept re: 406"
F.34. Since draft-ietf-httpbis-p2-semantics-16
Closed issues:
o : "Redirects and
non-GET methods"
o : "Document
HTTP's error-handling philosophy"
o :
"Considerations for new header fields"
o : "clarify 303
redirect on HEAD"
F.35. Since draft-ietf-httpbis-p3-payload-16
Closed issues:
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o : "Document
HTTP's error-handling philosophy"
F.36. Since draft-ietf-httpbis-p2-semantics-17
Closed issues:
o : "Location
header field payload handling"
o : "Clarify
status code for rate limiting" (change backed out because a new
status code is being defined for this purpose)
o : "should there
be a permanent variant of 307"
o : "When are
Location's semantics triggered?"
o : "'expect'
grammar missing OWS"
o : "header field
considerations: quoted-string vs use of double quotes"
F.37. Since draft-ietf-httpbis-p3-payload-17
Closed issues:
o : "intended
maturity level vs normative references"
F.38. Since draft-ietf-httpbis-p2-semantics-18
Closed issues:
o : "Combining
HEAD responses"
o : "Requirements
for user intervention during redirects"
o : "message-body
in CONNECT response"
o : "Applying
original fragment to 'plain' redirected URI"
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o : "Misplaced
text on connection handling in p2"
o : "clarify that
201 doesn't require Location header fields"
o : "relax
requirements on hypertext in 3/4/5xx error responses"
o : "example for
426 response should have a payload"
o : "drop
indirection entries for status codes"
F.39. Since draft-ietf-httpbis-p3-payload-18
Closed issues:
o : "is ETag a
representation header field?"
o : "Content-
Location doesn't constrain the cardinality of representations"
o : "make IANA
policy definitions consistent"
F.40. Since draft-ietf-httpbis-p2-semantics-19 and
draft-ietf-httpbis-p3-payload-19
Closed issues:
o : "should there
be a permanent variant of 307"
o : "clarify that
201 can imply *multiple* resources were created"
o : "merge P2 and
P3"
o : "ABNF
requirements for recipients"
o : "Capturing
more information in the method registry"
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o : "note
introduction of new IANA registries as normative changes"
F.41. Since draft-ietf-httpbis-p2-semantics-20
Closed issues:
o : "is 'q=' case-
sensitive?"
Other changes:
o Conformance criteria and considerations regarding error handling
are now defined in Part 1.
o Properly explain what HTTP semantics are and why. Rewrite
introductory description of methods. Rewrite definition of "safe"
to be more operable and weaken the original same-origin
restrictions to be more consistent with modern UAs. Rewrite
definition of "idempotent", add definition of "cacheable".
o Conneg terminology change: "server-driven" => "proactive" (UA
sends Accept* fields), "agent-driven" => "reactive" (UA waits for
300/Alternatives)
o Move description of "100-continue" from Part 1 over here.
o Move definition of "Vary" header field from Part 6 over here.
o Rewrite definition of "representation".
Index
1
1xx Informational (status code class) 49
2
2xx Successful (status code class) 50
3
3xx Redirection (status code class) 52
4
4xx Client Error (status code class) 56
5
5xx Server Error (status code class) 60
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1
100 Continue (status code) 49
100-continue (expect value) 35
101 Switching Protocols (status code) 49
2
200 OK (status code) 50
201 Created (status code) 50
202 Accepted (status code) 51
203 Non-Authoritative Information (status code) 51
204 No Content (status code) 51
205 Reset Content (status code) 52
3
300 Multiple Choices (status code) 54
301 Moved Permanently (status code) 54
302 Found (status code) 55
303 See Other (status code) 55
305 Use Proxy (status code) 56
306 (Unused) (status code) 56
307 Temporary Redirect (status code) 56
4
400 Bad Request (status code) 56
402 Payment Required (status code) 56
403 Forbidden (status code) 57
404 Not Found (status code) 57
405 Method Not Allowed (status code) 57
406 Not Acceptable (status code) 57
408 Request Timeout (status code) 58
409 Conflict (status code) 58
410 Gone (status code) 58
411 Length Required (status code) 59
413 Request Representation Too Large (status code) 59
414 URI Too Long (status code) 59
415 Unsupported Media Type (status code) 59
417 Expectation Failed (status code) 60
426 Upgrade Required (status code) 60
5
500 Internal Server Error (status code) 60
501 Not Implemented (status code) 60
502 Bad Gateway (status code) 61
503 Service Unavailable (status code) 61
504 Gateway Timeout (status code) 61
505 HTTP Version Not Supported (status code) 61
A
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Accept header field 38
Accept-Charset header field 41
Accept-Encoding header field 41
Accept-Language header field 42
Allow header field 69
C
cacheable 25
compress (content coding) 12
CONNECT method 30
content coding 12
content negotiation 7
Content-Encoding header field 12
Content-Language header field 14
Content-Location header field 16
Content-Transfer-Encoding header field 85
Content-Type header field 11
D
Date header field 64
deflate (content coding) 12
DELETE method 30
E
Expect header field 34
Expect Values
100-continue 35
F
From header field 44
G
GET method 25
Grammar
Accept 39
Accept-Charset 41
Accept-Encoding 41
accept-ext 39
Accept-Language 43
accept-params 39
Allow 69
asctime-date 64
attribute 9
charset 10
codings 41
content-coding 12
Content-Encoding 13
Content-Language 14
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Content-Location 16
Content-Type 11
Date 64
date1 63
day 63
day-name 63
day-name-l 63
delta-seconds 66
Expect 34
expect-name 34
expect-param 34
expect-value 34
expectation 34
From 44
GMT 63
hour 63
HTTP-date 62
language-range 43
language-tag 14
Location 65
Max-Forwards 34
media-range 39
media-type 9
method 22
MIME-Version 84
minute 63
month 63
obs-date 63
parameter 9
product 22
product-version 22
qvalue 38
Referer 45
Retry-After 66
rfc850-date 64
rfc1123-date 63
second 63
Server 69
subtype 9
time-of-day 63
type 9
User-Agent 46
value 9
Vary 67
weight 38
year 63
gzip (content coding) 12
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H
HEAD method 26
I
idempotent 25
L
Location header field 65
M
Max-Forwards header field 34
MIME-Version header field 84
O
OPTIONS method 32
P
payload 18
POST method 27
PUT method 28
R
Referer header field 45
representation 8
Retry-After header field 66
S
safe 24
selected representation 67
Server header field 69
Status Codes Classes
1xx Informational 49
2xx Successful 50
3xx Redirection 52
4xx Client Error 56
5xx Server Error 60
T
TRACE method 33
U
User-Agent header field 45
V
Vary header field 67
X
x-compress (content coding) 12
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x-gzip (content coding) 12
Authors' Addresses
Roy T. Fielding (editor)
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA
EMail: fielding@gbiv.com
URI: http://roy.gbiv.com/
Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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