HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe
Obsoletes: 2616 (if approved) J. Gettys
Updates: 2817 (if approved) Alcatel-Lucent
Intended status: Standards Track J. Mogul
Expires: October 20, 2011 HP
H. Frystyk
Microsoft
L. Masinter
Adobe
P. Leach
Microsoft
T. Berners-Lee
W3C/MIT
Y. Lafon, Ed.
W3C
J. Reschke, Ed.
greenbytes
April 18, 2011
HTTP/1.1, part 2: Message Semantics
draft-ietf-httpbis-p2-semantics-14
Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World Wide Web global
information initiative since 1990. This document is Part 2 of the
seven-part specification that defines the protocol referred to as
"HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 2 defines
the semantics of HTTP messages as expressed by request methods,
request header fields, response status codes, and response header
fields.
Editorial Note (To be removed by RFC Editor)
Discussion of this draft should take place on the HTTPBIS working
group mailing list (ietf-http-wg@w3.org), 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 C.15.
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Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 20, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6
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1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
1.2.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 7
1.2.2. ABNF Rules defined in other Parts of the
Specification . . . . . . . . . . . . . . . . . . . . 7
2. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Overview of Methods . . . . . . . . . . . . . . . . . . . 8
2.2. Method Registry . . . . . . . . . . . . . . . . . . . . . 8
2.2.1. Considerations for New Methods . . . . . . . . . . . . 8
3. Request Header Fields . . . . . . . . . . . . . . . . . . . . 9
4. Status Code and Reason Phrase . . . . . . . . . . . . . . . . 10
4.1. Overview of Status Codes . . . . . . . . . . . . . . . . . 10
4.2. Status Code Registry . . . . . . . . . . . . . . . . . . . 12
4.2.1. Considerations for New Status Codes . . . . . . . . . 12
5. Response Header Fields . . . . . . . . . . . . . . . . . . . . 13
6. Representation . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Identifying the Resource Associated with a
Representation . . . . . . . . . . . . . . . . . . . . . . 13
7. Method Definitions . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Safe and Idempotent Methods . . . . . . . . . . . . . . . 14
7.1.1. Safe Methods . . . . . . . . . . . . . . . . . . . . . 14
7.1.2. Idempotent Methods . . . . . . . . . . . . . . . . . . 15
7.2. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.3. GET . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.4. HEAD . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.5. POST . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.6. PUT . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.7. DELETE . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.9. CONNECT . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.9.1. Establishing a Tunnel with CONNECT . . . . . . . . . . 22
8. Status Code Definitions . . . . . . . . . . . . . . . . . . . 23
8.1. Informational 1xx . . . . . . . . . . . . . . . . . . . . 23
8.1.1. 100 Continue . . . . . . . . . . . . . . . . . . . . . 23
8.1.2. 101 Switching Protocols . . . . . . . . . . . . . . . 23
8.2. Successful 2xx . . . . . . . . . . . . . . . . . . . . . . 24
8.2.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . . 24
8.2.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 24
8.2.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . . 25
8.2.4. 203 Non-Authoritative Information . . . . . . . . . . 25
8.2.5. 204 No Content . . . . . . . . . . . . . . . . . . . . 25
8.2.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 26
8.2.7. 206 Partial Content . . . . . . . . . . . . . . . . . 26
8.3. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 26
8.3.1. 300 Multiple Choices . . . . . . . . . . . . . . . . . 27
8.3.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 27
8.3.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 28
8.3.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 28
8.3.5. 304 Not Modified . . . . . . . . . . . . . . . . . . . 29
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8.3.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 29
8.3.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . . 29
8.3.8. 307 Temporary Redirect . . . . . . . . . . . . . . . . 29
8.4. Client Error 4xx . . . . . . . . . . . . . . . . . . . . . 30
8.4.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 30
8.4.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . . 30
8.4.3. 402 Payment Required . . . . . . . . . . . . . . . . . 30
8.4.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 30
8.4.5. 404 Not Found . . . . . . . . . . . . . . . . . . . . 31
8.4.6. 405 Method Not Allowed . . . . . . . . . . . . . . . . 31
8.4.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . . 31
8.4.8. 407 Proxy Authentication Required . . . . . . . . . . 32
8.4.9. 408 Request Timeout . . . . . . . . . . . . . . . . . 32
8.4.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . . 32
8.4.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . . 32
8.4.12. 411 Length Required . . . . . . . . . . . . . . . . . 33
8.4.13. 412 Precondition Failed . . . . . . . . . . . . . . . 33
8.4.14. 413 Request Entity Too Large . . . . . . . . . . . . . 33
8.4.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . . 33
8.4.16. 415 Unsupported Media Type . . . . . . . . . . . . . . 33
8.4.17. 416 Requested Range Not Satisfiable . . . . . . . . . 34
8.4.18. 417 Expectation Failed . . . . . . . . . . . . . . . . 34
8.4.19. 426 Upgrade Required . . . . . . . . . . . . . . . . . 34
8.5. Server Error 5xx . . . . . . . . . . . . . . . . . . . . . 34
8.5.1. 500 Internal Server Error . . . . . . . . . . . . . . 34
8.5.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 35
8.5.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 35
8.5.4. 503 Service Unavailable . . . . . . . . . . . . . . . 35
8.5.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 35
8.5.6. 505 HTTP Version Not Supported . . . . . . . . . . . . 35
9. Header Field Definitions . . . . . . . . . . . . . . . . . . . 36
9.1. Allow . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.2. Expect . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.3. From . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.4. Location . . . . . . . . . . . . . . . . . . . . . . . . . 38
9.5. Max-Forwards . . . . . . . . . . . . . . . . . . . . . . . 39
9.6. Referer . . . . . . . . . . . . . . . . . . . . . . . . . 39
9.7. Retry-After . . . . . . . . . . . . . . . . . . . . . . . 40
9.8. Server . . . . . . . . . . . . . . . . . . . . . . . . . . 40
9.9. User-Agent . . . . . . . . . . . . . . . . . . . . . . . . 41
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
10.1. Method Registry . . . . . . . . . . . . . . . . . . . . . 41
10.2. Status Code Registry . . . . . . . . . . . . . . . . . . . 42
10.3. Header Field Registration . . . . . . . . . . . . . . . . 43
11. Security Considerations . . . . . . . . . . . . . . . . . . . 44
11.1. Transfer of Sensitive Information . . . . . . . . . . . . 44
11.2. Encoding Sensitive Information in URIs . . . . . . . . . . 45
11.3. Location Headers and Spoofing . . . . . . . . . . . . . . 46
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11.4. Security Considerations for CONNECT . . . . . . . . . . . 46
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 46
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 46
13.1. Normative References . . . . . . . . . . . . . . . . . . . 46
13.2. Informative References . . . . . . . . . . . . . . . . . . 47
Appendix A. Changes from RFC 2616 . . . . . . . . . . . . . . . . 48
Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 49
Appendix C. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 51
C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 51
C.2. Since draft-ietf-httpbis-p2-semantics-00 . . . . . . . . . 51
C.3. Since draft-ietf-httpbis-p2-semantics-01 . . . . . . . . . 52
C.4. Since draft-ietf-httpbis-p2-semantics-02 . . . . . . . . . 52
C.5. Since draft-ietf-httpbis-p2-semantics-03 . . . . . . . . . 53
C.6. Since draft-ietf-httpbis-p2-semantics-04 . . . . . . . . . 53
C.7. Since draft-ietf-httpbis-p2-semantics-05 . . . . . . . . . 54
C.8. Since draft-ietf-httpbis-p2-semantics-06 . . . . . . . . . 54
C.9. Since draft-ietf-httpbis-p2-semantics-07 . . . . . . . . . 54
C.10. Since draft-ietf-httpbis-p2-semantics-08 . . . . . . . . . 55
C.11. Since draft-ietf-httpbis-p2-semantics-09 . . . . . . . . . 55
C.12. Since draft-ietf-httpbis-p2-semantics-10 . . . . . . . . . 55
C.13. Since draft-ietf-httpbis-p2-semantics-11 . . . . . . . . . 56
C.14. Since draft-ietf-httpbis-p2-semantics-12 . . . . . . . . . 56
C.15. Since draft-ietf-httpbis-p2-semantics-13 . . . . . . . . . 58
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
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1. Introduction
This document defines HTTP/1.1 request and response semantics. Each
HTTP message, as defined in [Part1], is in the form of either a
request or a response. An HTTP server listens on a connection for
HTTP requests and responds to each request, in the order received on
that connection, with one or more HTTP response messages. This
document defines the commonly agreed upon semantics of the HTTP
uniform interface, the intentions defined by each request method, and
the various response messages that might be expected as a result of
applying that method to the target resource.
This document is currently disorganized in order to minimize the
changes between drafts and enable reviewers to see the smaller errata
changes. A future draft will reorganize the sections to better
reflect the content. In particular, the sections will be ordered
according to the typical processing of an HTTP request message (after
message parsing): resource mapping, methods, request modifying header
fields, response status, status modifying header fields, and resource
metadata. The current mess reflects how widely dispersed these
topics and associated requirements had become in [RFC2616].
1.1. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
An implementation is not compliant if it fails to satisfy one or more
of the "MUST" or "REQUIRED" level requirements for the protocols it
implements. An implementation that satisfies all the "MUST" or
"REQUIRED" level and all the "SHOULD" level requirements for its
protocols is said to be "unconditionally compliant"; one that
satisfies all the "MUST" level requirements but not all the "SHOULD"
level requirements for its protocols is said to be "conditionally
compliant".
1.2. Syntax Notation
This specification uses the ABNF syntax defined in Section 1.2 of
[Part1] (which extends the syntax defined in [RFC5234] with a list
rule). Appendix B shows the collected ABNF, with the list rule
expanded.
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
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sequence of data), SP (space), VCHAR (any visible USASCII character),
and WSP (whitespace).
1.2.1. Core Rules
The core rules below are defined in Section 1.2.2 of [Part1]:
quoted-string =
token =
OWS =
RWS =
obs-text =
1.2.2. ABNF Rules defined in other Parts of the Specification
The ABNF rules below are defined in other parts:
absolute-URI =
comment =
HTTP-date =
partial-URI =
product =
URI-reference =
2. Method
The Method token indicates the request method to be performed on the
target resource (Section 4.3 of [Part1]). The method is case-
sensitive.
Method = token
The list of methods allowed by a resource can be specified in an
Allow header field (Section 9.1). The status code of the response
always notifies the client whether a method is currently allowed on a
resource, since the set of allowed methods can change dynamically.
An origin server SHOULD respond with the status code 405 (Method Not
Allowed) if the method is known by the origin server but not allowed
for the resource, and 501 (Not Implemented) if the method is
unrecognized or not implemented by the origin server. The methods
GET and HEAD MUST be supported by all general-purpose servers. All
other methods are OPTIONAL; however, if the above methods are
implemented, they MUST be implemented with the same semantics as
those specified in Section 7.
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2.1. Overview of Methods
The methods listed below are defined in Section 7.
+-------------+---------------+
| Method Name | Defined in... |
+-------------+---------------+
| OPTIONS | Section 7.2 |
| GET | Section 7.3 |
| HEAD | Section 7.4 |
| POST | Section 7.5 |
| PUT | Section 7.6 |
| DELETE | Section 7.7 |
| TRACE | Section 7.8 |
| CONNECT | Section 7.9 |
+-------------+---------------+
Note that this list is not exhaustive -- it does not include request
methods defined in other specifications.
2.2. Method Registry
The HTTP Method Registry defines the name space for the Method token
in the Request line of an HTTP request.
Registrations MUST include the following fields:
o Method Name (see Section 2)
o Safe ("yes" or "no", see Section 7.1.1)
o Pointer to specification text
Values to be added to this name space are subject to IETF review
([RFC5226], Section 4.1).
The registry itself is maintained at
.
2.2.1. Considerations for New Methods
When it is necessary to express new semantics for a HTTP request that
aren't specific to a single application or media type, and currently
defined methods are inadequate, it may be appropriate to register a
new method.
HTTP methods are generic; that is, they are potentially applicable to
any resource, not just one particular media type, "type" of resource,
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or application. As such, it is preferred that new HTTP methods be
registered in a document that isn't specific to a single application,
so that this is clear.
Due to the parsing rules defined in Section 3.3 of [Part1],
definitions of HTTP methods cannot prohibit the presence of a
message-body on either the request or the response message (with
responses to HEAD requests being the single exception). Definitions
of new methods cannot change this rule, but they can specify that
only zero-length bodies (as opposed to absent bodies) are allowed.
New method definitions need to indicate whether they are safe
(Section 7.1.1), what semantics (if any) the request body has, and
whether they are idempotent (Section 7.1.2). They also need to state
whether they can be cached ([Part6]); in particular what conditions a
cache may store the response, and under what conditions such a stored
response may be used to satisfy a subsequent request.
3. Request Header Fields
The request header fields allow the client to pass additional
information about the request, and about the client itself, to the
server. These fields act as request modifiers, with semantics
equivalent to the parameters on a programming language method
invocation.
+---------------------+------------------------+
| Header Field Name | Defined in... |
+---------------------+------------------------+
| Accept | Section 6.1 of [Part3] |
| Accept-Charset | Section 6.2 of [Part3] |
| Accept-Encoding | Section 6.3 of [Part3] |
| Accept-Language | Section 6.4 of [Part3] |
| Authorization | Section 4.1 of [Part7] |
| Expect | Section 9.2 |
| From | Section 9.3 |
| Host | Section 9.4 of [Part1] |
| If-Match | Section 3.1 of [Part4] |
| If-Modified-Since | Section 3.3 of [Part4] |
| If-None-Match | Section 3.2 of [Part4] |
| If-Range | Section 5.3 of [Part5] |
| If-Unmodified-Since | Section 3.4 of [Part4] |
| Max-Forwards | Section 9.5 |
| Proxy-Authorization | Section 4.3 of [Part7] |
| Range | Section 5.4 of [Part5] |
| Referer | Section 9.6 |
| TE | Section 9.5 of [Part1] |
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| User-Agent | Section 9.9 |
+---------------------+------------------------+
4. Status Code and Reason Phrase
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request.
The Reason-Phrase is intended to give a short textual description of
the Status-Code and is intended for a human user. The client does
not need to examine or display the Reason-Phrase.
Status-Code = 3DIGIT
Reason-Phrase = *( WSP / VCHAR / obs-text )
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.
4.1. Overview of Status Codes
The status codes listed below are defined in Section 8 of this
specification, Section 4 of [Part4], Section 3 of [Part5], and
Section 3 of [Part7]. The reason phrases listed here are only
recommendations -- they can be replaced by local equivalents without
affecting the protocol.
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+-------------+------------------------------+----------------------+
| Status-Code | Reason-Phrase | Defined in... |
+-------------+------------------------------+----------------------+
| 100 | Continue | Section 8.1.1 |
| 101 | Switching Protocols | Section 8.1.2 |
| 200 | OK | Section 8.2.1 |
| 201 | Created | Section 8.2.2 |
| 202 | Accepted | Section 8.2.3 |
| 203 | Non-Authoritative | Section 8.2.4 |
| | Information | |
| 204 | No Content | Section 8.2.5 |
| 205 | Reset Content | Section 8.2.6 |
| 206 | Partial Content | Section 3.1 of |
| | | [Part5] |
| 300 | Multiple Choices | Section 8.3.1 |
| 301 | Moved Permanently | Section 8.3.2 |
| 302 | Found | Section 8.3.3 |
| 303 | See Other | Section 8.3.4 |
| 304 | Not Modified | Section 4.1 of |
| | | [Part4] |
| 305 | Use Proxy | Section 8.3.6 |
| 307 | Temporary Redirect | Section 8.3.8 |
| 400 | Bad Request | Section 8.4.1 |
| 401 | Unauthorized | Section 3.1 of |
| | | [Part7] |
| 402 | Payment Required | Section 8.4.3 |
| 403 | Forbidden | Section 8.4.4 |
| 404 | Not Found | Section 8.4.5 |
| 405 | Method Not Allowed | Section 8.4.6 |
| 406 | Not Acceptable | Section 8.4.7 |
| 407 | Proxy Authentication | Section 3.2 of |
| | Required | [Part7] |
| 408 | Request Time-out | Section 8.4.9 |
| 409 | Conflict | Section 8.4.10 |
| 410 | Gone | Section 8.4.11 |
| 411 | Length Required | Section 8.4.12 |
| 412 | Precondition Failed | Section 4.2 of |
| | | [Part4] |
| 413 | Request Entity Too Large | Section 8.4.14 |
| 414 | URI Too Long | Section 8.4.15 |
| 415 | Unsupported Media Type | Section 8.4.16 |
| 416 | Requested range not | Section 3.2 of |
| | satisfiable | [Part5] |
| 417 | Expectation Failed | Section 8.4.18 |
| 426 | Upgrade Required | Section 8.4.19 |
| 500 | Internal Server Error | Section 8.5.1 |
| 501 | Not Implemented | Section 8.5.2 |
| 502 | Bad Gateway | Section 8.5.3 |
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| 503 | Service Unavailable | Section 8.5.4 |
| 504 | Gateway Time-out | Section 8.5.5 |
| 505 | HTTP Version not supported | Section 8.5.6 |
+-------------+------------------------------+----------------------+
Note that this list is not exhaustive -- it does not include
extension status codes defined in other specifications.
4.2. Status Code Registry
The HTTP Status Code Registry defines the name space for the Status-
Code token in the Status-Line of an HTTP response.
Values to be added to this name space are subject to IETF review
([RFC5226], Section 4.1).
The registry itself is maintained at
.
4.2.1. Considerations for New Status Codes
When it is necessary to express new semantics for a HTTP response
that aren't specific to a single application or media type, and
currently defined status codes are inadequate, a new status code can
be registered.
HTTP status codes are generic; that is, they are potentially
applicable to any resource, not just one particular media type,
"type" of resource, or application. As such, it is preferred that
new HTTP status codes be registered in a document that isn't specific
to a single application, so that this is clear.
Definitions of new HTTP status codes typically explain the request
conditions that produce a response containing the status code (e.g.,
combinations of request headers and/or method(s)), along with any
interactions with response headers (e.g., those that are required,
those that modify the semantics of the response).
New HTTP status codes are required to fall under one of the
categories defined in Section 8. To allow existing parsers to
properly handle them, new status codes cannot disallow a response
body, although they can mandate a zero-length response body. They
can require the presence of one or more particular HTTP response
header(s).
Likewise, their definitions can specify that caches are allowed to
use heuristics to determine their freshness (see [Part6]; by default,
it is not allowed), and can define how to determine the resource
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which they carry a representation for (see Section 6.1; by default,
it is anonymous).
5. Response Header Fields
The response header fields allow the server to pass additional
information about the response which cannot be placed in the Status-
Line. These header fields give information about the server and
about further access to the target resource (Section 4.3 of [Part1]).
+--------------------+------------------------+
| Header Field Name | Defined in... |
+--------------------+------------------------+
| Accept-Ranges | Section 5.1 of [Part5] |
| Age | Section 3.1 of [Part6] |
| Allow | Section 9.1 |
| ETag | Section 2.2 of [Part4] |
| Location | Section 9.4 |
| Proxy-Authenticate | Section 4.2 of [Part7] |
| Retry-After | Section 9.7 |
| Server | Section 9.8 |
| Vary | Section 3.5 of [Part6] |
| WWW-Authenticate | Section 4.4 of [Part7] |
+--------------------+------------------------+
6. Representation
Request and Response messages MAY transfer a representation if not
otherwise restricted by the request method or response status code.
A representation consists of metadata (representation header fields)
and data (representation body). When a complete or partial
representation is enclosed in an HTTP message, it is referred to as
the payload of the message. HTTP representations are defined in
[Part3].
A representation body is only present in a message when a message-
body is present, as described in Section 3.3 of [Part1]. The
representation body is obtained from the message-body by decoding any
Transfer-Encoding that might have been applied to ensure safe and
proper transfer of the message.
6.1. Identifying the Resource Associated with a Representation
It is sometimes necessary to determine an identifier for the resource
associated with a representation.
An HTTP request representation, when present, is always associated
with an anonymous (i.e., unidentified) resource.
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In the common case, an HTTP response is a representation of the
target resource (see Section 4.3 of [Part1]). However, this is not
always the case. To determine the URI of the resource a response is
associated with, the following rules are used (with the first
applicable one being selected):
1. If the response status code is 200 or 203 and the request method
was GET, the response payload is a representation of the target
resource.
2. If the response status code is 204, 206, or 304 and the request
method was GET or HEAD, the response payload is a partial
representation of the target resource (see Section 2.8 of
[Part6]).
3. If the response has a Content-Location header field, and that URI
is the same as the effective request URI, the response payload is
a representation of the target resource.
4. If the response has a Content-Location header field, and that URI
is not the same as the effective request URI, then the response
asserts that its payload is a representation of the resource
identified by the Content-Location URI. However, such an
assertion cannot be trusted unless it can be verified by other
means (not defined by HTTP).
5. Otherwise, the response is a representation of an anonymous
(i.e., unidentified) resource.
[[TODO-req-uri: The comparison function is going to have to be
defined somewhere, because we already need to compare URIs for things
like cache invalidation.]]
7. Method Definitions
The set of common request methods for HTTP/1.1 is defined below.
Although this set can be expanded, additional methods cannot be
assumed to share the same semantics for separately extended clients
and servers.
7.1. Safe and Idempotent Methods
7.1.1. Safe Methods
Implementors need to be aware that the software represents the user
in their interactions over the Internet, and need to allow the user
to be aware of any actions they take which might have an unexpected
significance to themselves or others.
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In particular, the convention has been established that the GET,
HEAD, OPTIONS, and TRACE request methods SHOULD NOT have the
significance of taking an action other than retrieval. These request
methods ought to be considered ""safe"". This allows user agents to
represent other methods, such as POST, PUT and DELETE, in a special
way, so that the user is made aware of the fact that a possibly
unsafe action is being requested.
Naturally, it is not possible to ensure that the server does not
generate side-effects as a result of performing a GET request; in
fact, some dynamic resources consider that a feature. The important
distinction here is that the user did not request the side-effects,
so therefore cannot be held accountable for them.
7.1.2. Idempotent Methods
Request methods can also have the property of "idempotence" in that,
aside from error or expiration issues, the intended effect of
multiple identical requests is the same as for a single request.
PUT, DELETE, and all safe request methods are idempotent. It is
important to note that idempotence refers only to changes requested
by the client: a server is free to change its state due to multiple
requests for the purpose of tracking those requests, versioning of
results, etc.
7.2. OPTIONS
The OPTIONS method requests information about the communication
options available on the request/response chain identified by the
effective request URI. This method allows a client to determine the
options and/or requirements associated with a resource, or the
capabilities of a server, without implying a resource action or
initiating a resource retrieval.
Responses to the OPTIONS method are not cacheable.
If the OPTIONS request includes a message-body (as indicated by the
presence of Content-Length or Transfer-Encoding), then the media type
MUST be indicated by a Content-Type field. Although this
specification does not define any use for such a body, future
extensions to HTTP might use the OPTIONS body to make more detailed
queries on the server.
If the request-target 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
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the capabilities of the server. For example, this can be used to
test a proxy for HTTP/1.1 compliance (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 response SHOULD include any header fields that indicate
optional features implemented by the server and applicable to that
resource (e.g., Allow), possibly including extensions not defined by
this specification. The response body, if any, SHOULD also include
information about the communication options. The format for such a
body is not defined by this specification, but might be defined by
future extensions to HTTP. Content negotiation MAY be used to select
the appropriate response format. If no response body is included,
the response MUST include a Content-Length field with a field-value
of "0".
The Max-Forwards header field MAY be used to target a specific proxy
in the request chain (see Section 9.5). If no Max-Forwards field is
present in the request, then the forwarded request MUST NOT include a
Max-Forwards field.
7.3. GET
The GET method requests transfer of a current representation of the
target resource.
If the target resource is a data-producing process, it is the
produced data which shall be returned as the representation in the
response and not the source text of the process, unless that text
happens to be the output of the process.
The semantics of the GET method change to a "conditional GET" if the
request message includes an If-Modified-Since, If-Unmodified-Since,
If-Match, If-None-Match, or If-Range header field. 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. 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-
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retrieved representations to be completed without transferring data
already held by the client.
Bodies on GET requests have no defined semantics. Note that sending
a body on a GET request might cause some existing implementations to
reject the request.
The response to a GET request is cacheable and MAY be used to satisfy
subsequent GET and HEAD requests (see [Part6]).
See Section 11.2 for security considerations when used for forms.
7.4. HEAD
The HEAD method is identical to GET except that the server MUST NOT
return a message-body in the response. The metadata contained in the
HTTP header fields in response to a HEAD request SHOULD be identical
to the information sent in response to a GET request. This method
can be used for obtaining metadata about the representation implied
by the request without transferring the representation body. This
method is often used for testing hypertext links for validity,
accessibility, and recent modification.
The response to a HEAD request is cacheable and MAY be used to
satisfy a subsequent HEAD request; see [Part6]. It also MAY be used
to update a previously cached representation from that resource; if
the new field values indicate that the cached representation differs
from the current representation (as would be indicated by a change in
Content-Length, Content-MD5, ETag or Last-Modified), then the cache
MUST treat the cache entry as stale.
Bodies on HEAD requests have no defined semantics. Note that sending
a body on a HEAD request might cause some existing implementations to
reject the request.
7.5. 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;
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o Providing a block of data, such as the result of submitting a
form, to a data-handling process;
o Extending a database through an append operation.
The actual function performed by the POST method is determined by the
server and is usually dependent on the effective request URI.
The action performed by the POST method might not result in a
resource that can be identified by a URI. In this case, either 200
(OK) or 204 (No Content) is the appropriate response status code,
depending on whether or not the response includes a representation
that describes the result.
If a resource has been created on the origin server, the response
SHOULD be 201 (Created) and contain a representation which describes
the status of the request and refers to the new resource, and a
Location header field (see Section 9.4).
Responses to POST requests are only cacheable when they include
explicit freshness information (see Section 2.3.1 of [Part6]). A
cached POST response with a Content-Location header field (see
Section 6.7 of [Part3]) whose value is the effective Request URI MAY
be used to satisfy subsequent GET and HEAD requests.
Note that POST caching is not widely implemented. However, the 303
(See Other) response can be used to direct the user agent to retrieve
a cacheable resource.
7.6. 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
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is successfully modified in accordance with the state of the enclosed
representation, then either a 200 (OK) or 204 (No Content) response
SHOULD be sent to indicate successful completion of the request.
Unrecognized header fields SHOULD be ignored (i.e., not saved as part
of the resource state).
An origin server SHOULD verify that the PUT representation is
consistent with any constraints which the server has for the target
resource that cannot or will not be changed by the PUT. This is
particularly important when the origin server uses internal
configuration information related to the URI in order to set the
values for representation metadata on GET responses. When a PUT
representation is inconsistent with the target resource, the origin
server SHOULD either make them consistent, by transforming the
representation or changing the resource configuration, or respond
with an appropriate error message containing sufficient information
to explain why the representation is unsuitable. The 409 (Conflict)
or 415 (Unsupported Media Type) status codes are suggested, with the
latter being specific to constraints on Content-Type values.
For example, if the target resource is configured to always have a
Content-Type of "text/html" and the representation being PUT has a
Content-Type of "image/jpeg", then the origin server SHOULD do one
of: (a) reconfigure the target resource to reflect the new media
type; (b) transform the PUT representation to a format consistent
with that of the resource before saving it as the new resource state;
or, (c) reject the request with a 415 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
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contrast, the target resource in a PUT request is intended to take
the enclosed representation as a new or replacement value. Hence,
the intent of PUT is idempotent and visible to intermediaries, even
though the exact effect is only known by the origin server.
Proper interpretation of a PUT request presumes that the user agent
knows what target resource is desired. A service that is intended to
select a proper URI on behalf of the client, after receiving a state-
changing request, SHOULD be implemented using the POST method rather
than PUT. If the origin server will not make the requested PUT state
change to the target resource and instead wishes to have it applied
to a different resource, such as when the resource has been moved to
a different URI, then the origin server MUST send a 301 (Moved
Permanently) response; the user agent MAY then make its own decision
regarding whether or not to redirect the request.
A PUT request applied to the target resource MAY have side-effects on
other resources. For example, an article might have a URI for
identifying "the current version" (a resource) which is separate from
the URIs identifying each particular version (different resources
that at one point shared the same state as the current version
resource). A successful PUT request on "the current version" URI
might therefore create a new version resource in addition to changing
the state of the target resource, and might also cause links to be
added between the related resources.
An origin server SHOULD reject any PUT request that contains a
Content-Range header field, 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 2.5 of [Part6]).
7.7. 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
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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 an
representation describing the status, 202 (Accepted) if the action
has not yet been enacted, or 204 (No Content) if the action has been
enacted but the response does not include a representation.
Bodies on DELETE requests have no defined semantics. Note that
sending a body on a DELETE request might cause some existing
implementations to reject the request.
Responses to the DELETE method are not cacheable. If a DELETE
request passes through a cache that has one or more stored responses
for the effective request URI, those stored responses will be
invalidated (see Section 2.5 of [Part6]).
7.8. TRACE
The TRACE method requests a remote, application-layer loop-back of
the request message. The final recipient of the request SHOULD
reflect the message received back to the client as the message-body
of a 200 (OK) response. The final recipient is either the origin
server or the first proxy to receive a Max-Forwards value of zero (0)
in the request (see Section 9.5). 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 9.9 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 10.3.1 of [Part1]) and contain a message-
body that encloses a copy of the entire request message. Responses
to the TRACE method are not cacheable.
7.9. CONNECT
The CONNECT method requests that the proxy establish a tunnel to the
request-target and then restrict its behavior to blind forwarding of
packets until the connection is closed.
When using CONNECT, the request-target MUST use the authority form
(Section 4.1.2 of [Part1]); i.e., the request-target consists of only
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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
Other HTTP mechanisms can be used normally with the CONNECT method --
except end-to-end protocol Upgrade requests, since the tunnel must be
established first.
For example, 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=
Bodies on CONNECT requests have no defined semantics. Note that
sending a body on a CONNECT request might cause some existing
implementations to reject the request.
Like any other pipelined HTTP/1.1 request, data to be tunnel may be
sent immediately after the blank line. The usual caveats also apply:
data may be discarded if the eventual response is negative, and the
connection may be reset with no response if more than one TCP segment
is outstanding.
7.9.1. Establishing a Tunnel with CONNECT
Any successful (2xx) 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.
It may be the case that the proxy itself can only reach the requested
origin server through another proxy. In this case, the first proxy
SHOULD make a CONNECT request of that next proxy, requesting a tunnel
to the authority. A proxy MUST NOT respond with any 2xx status code
unless it has either a direct or tunnel connection established to the
authority.
An origin server which receives a CONNECT request for itself MAY
respond with a 2xx status code to indicate that a connection is
established.
If at any point either one of the peers gets disconnected, any
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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.
8. Status Code Definitions
Each Status-Code is described below, including any metadata required
in the response.
8.1. 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 a "Expect: 100-continue" field when it forwards a request,
then it need not forward the corresponding 100 (Continue)
response(s).)
8.1.1. 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 7.2.3 of [Part1] for detailed discussion of
the use and handling of this status code.
8.1.2. 101 Switching Protocols
The server understands and is willing to comply with the client's
request, via the Upgrade message header field (Section 9.8 of
[Part1]), for a change in the application protocol being used on this
connection. The server will switch protocols to those defined by the
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response's Upgrade header field immediately after the empty line
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.
8.2. Successful 2xx
This class of status code indicates that the client's request was
successfully received, understood, and accepted.
8.2.1. 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 2.3.1.1 of [Part6]) to
determine freshness for 200 responses.
8.2.2. 201 Created
The request has been fulfilled and has resulted in a new resource
being created. The newly created resource can be referenced by the
URI(s) returned in the payload of the response, with the most
specific URI for the resource given by a Location header field. The
response SHOULD include a payload containing a list of resource
characteristics and location(s) from which the user or user agent can
choose the one most appropriate. The payload format is specified by
the media type given in the Content-Type header field. The origin
server MUST create the resource 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 just created (see Section 2.2 of [Part4]).
8.2.3. 202 Accepted
The request has been accepted for processing, but the processing has
not been completed. The request might or might not eventually be
acted upon, as it might be disallowed when processing actually takes
place. There 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.
8.2.4. 203 Non-Authoritative Information
The returned metadata in the header fields is not the definitive set
as available from the origin server, but is gathered from a local or
a third-party copy. The set presented MAY be a subset or superset of
the original version. For example, including local annotation
information about the resource might result in a superset of the
metadata known by the origin server. Use of this response code is
not required and is only appropriate when the response would
otherwise be 200 (OK).
Caches MAY use a heuristic (see Section 2.3.1.1 of [Part6]) to
determine freshness for 203 responses.
8.2.5. 204 No Content
The 204 (No Content) status code indicates that the server has
successfully fulfilled the request and that there is no additional
content to return in the response payload body. Metadata in the
response header fields refer to the target resource and its current
representation after the requested action.
For example, if a 204 status code is received in response to a PUT
request and the response contains an ETag header field, then the PUT
was successful and the ETag field-value contains the entity-tag for
the new representation of that target resource.
The 204 response allows a server to indicate that the action has been
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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.
8.2.6. 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].
8.2.7. 206 Partial Content
The server has fulfilled the partial GET request for the resource and
the enclosed payload is a partial representation as defined in
Section 3.1 of [Part5].
Caches MAY use a heuristic (see Section 2.3.1.1 of [Part6]) to
determine freshness for 206 responses.
8.3. 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. The action
required 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 7.1.1. A client SHOULD
detect infinite redirection loops, since such loops generate network
traffic for each redirection.
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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.
8.3.1. 300 Multiple Choices
The target resource has more than one representation, each with its
own specific location, and agent-driven negotiation information
(Section 5 of [Part3]) 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. The data format is specified by the media type given in
the Content-Type header field. 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 2.3.1.1 of [Part6]) to
determine freshness for 300 responses.
8.3.2. 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 2.3.1.1 of [Part6]) to
determine freshness for 301 responses.
The new permanent URI SHOULD be given by the Location field in the
response. Unless the request method was HEAD, the representation of
the response SHOULD contain a short hypertext note with a hyperlink
to the new URI(s).
If the 301 status code is received in response to a request method
that is known to be "safe", as defined in Section 7.1.1, then the
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request MAY be automatically redirected by the user agent without
confirmation. Otherwise, the user agent MUST NOT automatically
redirect the request unless it can be confirmed by the user, since
this might change the conditions under which the request was issued.
Note: When automatically redirecting a POST request after
receiving a 301 status code, some existing HTTP/1.0 user agents
will erroneously change it into a GET request.
8.3.3. 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. Unless the request method was HEAD, the representation of
the response SHOULD contain a short hypertext note with a hyperlink
to the new URI(s).
If the 302 status code is received in response to a request method
that is known to be "safe", as defined in Section 7.1.1, then the
request MAY be automatically redirected by the user agent without
confirmation. Otherwise, the user agent MUST NOT automatically
redirect the request unless it can be confirmed by the user, since
this might change the conditions under which the request was issued.
Note: HTTP/1.0 ([RFC1945], Section 9.3) and the first version of
HTTP/1.1 ([RFC2068], Section 10.3.3) specify that the client is
not allowed to change the method on the redirected request.
However, most existing user agent implementations treat 302 as if
it were a 303 response, performing a GET on the Location field-
value regardless of the original request method. Therefore, a
previous version of this specification ([RFC2616], Section 10.3.3)
has added the status codes 303 and 307 for servers that wish to
make unambiguously clear which kind of reaction is expected of the
client.
8.3.4. 303 See Other
The server directs the user agent to a different resource, indicated
by a URI in the Location header field, that provides an indirect
response to the original request. The user agent MAY perform a GET
request on the URI in the Location field in order to obtain a
representation corresponding to the response, be redirected again, or
end with an error status. The Location URI is not a substitute
reference for the effective request URI.
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The 303 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.
8.3.5. 304 Not Modified
The response to the request has not been modified since the
conditions indicated by the client's conditional GET request, as
defined in Section 4.1 of [Part4].
8.3.6. 305 Use Proxy
The 305 status code was defined in a previous version of this
specification (see Appendix A), and is now deprecated.
8.3.7. 306 (Unused)
The 306 status code was used in a previous version of the
specification, is no longer used, and the code is reserved.
8.3.8. 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. Unless the request method was HEAD, the representation of
the response SHOULD contain a short hypertext note with a hyperlink
to the new URI(s), since many pre-HTTP/1.1 user agents do not
understand the 307 status code. Therefore, the note SHOULD contain
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the information necessary for a user to repeat the original request
on the new URI.
If the 307 status code is received in response to a request method
that is known to be "safe", as defined in Section 7.1.1, then the
request MAY be automatically redirected by the user agent without
confirmation. Otherwise, the user agent MUST NOT automatically
redirect the request unless it can be confirmed by the user, since
this might change the conditions under which the request was issued.
8.4. 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.
If the client is sending data, a server implementation using TCP
SHOULD be careful to ensure that the client acknowledges receipt of
the packet(s) containing the response, before the server closes the
input connection. If the client continues sending data to the server
after the close, the server's TCP stack will send a reset packet to
the client, which might erase the client's unacknowledged input
buffers before they can be read and interpreted by the HTTP
application.
8.4.1. 400 Bad Request
The request could not be understood by the server due to malformed
syntax. The client SHOULD NOT repeat the request without
modifications.
8.4.2. 401 Unauthorized
The request requires user authentication (see Section 3.1 of
[Part7]).
8.4.3. 402 Payment Required
This code is reserved for future use.
8.4.4. 403 Forbidden
The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request SHOULD NOT be repeated.
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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) can be used instead.
8.4.5. 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.
8.4.6. 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.
8.4.7. 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 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. The data format is specified by the
media type given in the Content-Type header field. Depending upon
the format and the capabilities of the user agent, selection of the
most appropriate choice MAY be performed automatically. However,
this specification does not define any standard for such automatic
selection.
Note: HTTP/1.1 servers are allowed 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.
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8.4.8. 407 Proxy Authentication Required
This code is similar to 401 (Unauthorized), but indicates that the
client must first authenticate itself with the proxy (see Section 3.2
of [Part7]).
8.4.9. 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.
8.4.10. 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 response body 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 in a format defined by the
response Content-Type.
8.4.11. 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
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
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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 2.3.1.1 of [Part6]) to
determine freshness for 410 responses.
8.4.12. 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.
8.4.13. 412 Precondition Failed
The precondition given in one or more of the header fields evaluated
to false when it was tested on the server, as defined in Section 4.2
of [Part4].
8.4.14. 413 Request Entity 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.
8.4.15. 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 effective request URI.
8.4.16. 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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8.4.17. 416 Requested Range Not Satisfiable
The request included a Range header field (Section 5.4 of [Part5])
and none of the range-specifier values in this field overlap the
current extent of the selected resource. See Section 3.2 of [Part5].
8.4.18. 417 Expectation Failed
The expectation given in an Expect header field (see Section 9.2)
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.
8.4.19. 426 Upgrade Required
The request can not be completed without a prior protocol upgrade.
This response MUST include an Upgrade header field (Section 9.8 of
[Part1]) specifying the required protocols.
Example:
HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/2.0
Connection: Upgrade
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 may be available to the user.
8.5. 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.
8.5.1. 500 Internal Server Error
The server encountered an unexpected condition which prevented it
from fulfilling the request.
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8.5.2. 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
any resource.
8.5.3. 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.
8.5.4. 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. If no Retry-After is given, the client
SHOULD handle the response as it would for a 500 response.
Note: The existence of the 503 status code does not imply that a
server must use it when becoming overloaded. Some servers might
wish to simply refuse the connection.
8.5.5. 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 implementors: some deployed proxies are known to return
400 or 500 when DNS lookups time out.
8.5.6. 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
2.5 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.
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9. Header Field Definitions
This section defines the syntax and semantics of HTTP/1.1 header
fields related to request and response semantics.
9.1. 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.
9.2. Expect
The "Expect" header field is used to indicate that particular server
behaviors are required by the client.
Expect = 1#expectation
expectation = "100-continue" / expectation-extension
expectation-extension = token [ "=" ( token / quoted-string )
*expect-params ]
expect-params = ";" token [ "=" ( token / quoted-string ) ]
A server that does not understand or is unable to comply with any of
the expectation values in the Expect field of a request MUST respond
with appropriate error status code. The server MUST respond with a
417 (Expectation Failed) status code if any of the expectations
cannot be met or, if there are other problems with the request, some
other 4xx status code.
This header field is defined with extensible syntax to allow for
future extensions. If a server receives a request containing an
Expect field that includes an expectation-extension that it does not
support, it MUST respond with a 417 (Expectation Failed) status code.
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Comparison of expectation values is case-insensitive for unquoted
tokens (including the 100-continue token), and is case-sensitive for
quoted-string expectation-extensions.
The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
return a 417 (Expectation Failed) status code if it receives a
request with an expectation that it cannot meet. 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.
See Section 7.2.3 of [Part1] for the use of the 100 (Continue) status
code.
9.3. 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.
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
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user be able to disable, enable, and modify the value of this field
at any time prior to a request.
9.4. Location
The "Location" header field is used to identify a newly created
resource, or to redirect the recipient to a different location for
completion of the request.
For 201 (Created) responses, the Location is the URI of the new
resource which was created by the request. For 3xx 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).
Location = URI-reference
Examples are:
Location: http://www.example.org/pub/WWW/People.html#tim
Location: /index.html
There are circumstances in which a fragment identifier in a Location
URI would not be appropriate:
o With a 201 Created response, because in this usage the Location
header field specifies the URI for the entire created resource.
o With 305 Use Proxy.
Note: This specification does not define precedence rules for the
case where the original URI, as navigated to by the user agent,
and the Location header field value both contain fragment
identifiers. Thus be aware that including fragment identifiers
might inconvenience anyone relying on the semantics of the
original URI's fragment identifier.
Note: The Content-Location header field (Section 6.7 of [Part3])
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.
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9.5. Max-Forwards
The "Max-Forwards" header field provides a mechanism with the TRACE
(Section 7.8) and OPTIONS (Section 7.2) 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 in 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.
9.6. Referer
The "Referer" [sic] header field allows the client to specify the URI
of the resource from which the effective request 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 effective request 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
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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 11.2 for security considerations.
9.7. 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 wait before issuing the redirected request.
The value of this field can be either an HTTP-date or an integer
number of seconds (in decimal) after the time of the response.
Retry-After = HTTP-date / delta-seconds
Time spans are non-negative decimal integers, representing time in
seconds.
delta-seconds = 1*DIGIT
Two examples of its use are
Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
Retry-After: 120
In the latter example, the delay is 2 minutes.
9.8. 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 6.3 of
[Part1]) 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 9.9 of [Part1]).
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Note: Revealing the specific software version of the server might
allow the server machine to become more vulnerable to attacks
against software that is known to contain security holes. Server
implementors are encouraged to make this field a configurable
option.
9.9. 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 6.3 of
[Part1]) and comments (Section 3.2 of [Part1]) identifying the agent
and its significant subproducts. By convention, the product tokens
are listed in order of their significance for identifying the
application.
Because this field is usually sent on every request a user agent
makes, implementations are encouraged not to include needlessly fine-
grained detail, and to limit (or even prohibit) the addition of
subproducts by third parties. Overly long and detailed User-Agent
field values make requests larger and can also be used to identify
("fingerprint") the user against their wishes.
Likewise, implementations are encouraged not to use the product
tokens of other implementations in order to declare compatibility
with them, as this circumvents the purpose of the field. Finally,
they are encouraged not to use comments to identify products; doing
so makes the field value more difficult to parse.
User-Agent = product *( RWS ( product / comment ) )
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
10. IANA Considerations
10.1. Method Registry
The registration procedure for HTTP request methods is defined by
Section 2.2 of this document.
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The HTTP Method Registry shall be created at
and be populated with
the registrations below:
+---------+------+-------------+
| Method | Safe | Reference |
+---------+------+-------------+
| CONNECT | no | Section 7.9 |
| DELETE | no | Section 7.7 |
| GET | yes | Section 7.3 |
| HEAD | yes | Section 7.4 |
| OPTIONS | yes | Section 7.2 |
| POST | no | Section 7.5 |
| PUT | no | Section 7.6 |
| TRACE | yes | Section 7.8 |
+---------+------+-------------+
10.2. Status Code Registry
The registration procedure for HTTP Status Codes -- previously
defined in Section 7.1 of [RFC2817] -- is now defined by Section 4.2
of this document.
The HTTP Status Code Registry located at
shall be updated
with the registrations below:
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+-------+-------------------------------+----------------+
| Value | Description | Reference |
+-------+-------------------------------+----------------+
| 100 | Continue | Section 8.1.1 |
| 101 | Switching Protocols | Section 8.1.2 |
| 200 | OK | Section 8.2.1 |
| 201 | Created | Section 8.2.2 |
| 202 | Accepted | Section 8.2.3 |
| 203 | Non-Authoritative Information | Section 8.2.4 |
| 204 | No Content | Section 8.2.5 |
| 205 | Reset Content | Section 8.2.6 |
| 300 | Multiple Choices | Section 8.3.1 |
| 301 | Moved Permanently | Section 8.3.2 |
| 302 | Found | Section 8.3.3 |
| 303 | See Other | Section 8.3.4 |
| 305 | Use Proxy | Section 8.3.6 |
| 306 | (Unused) | Section 8.3.7 |
| 307 | Temporary Redirect | Section 8.3.8 |
| 400 | Bad Request | Section 8.4.1 |
| 402 | Payment Required | Section 8.4.3 |
| 403 | Forbidden | Section 8.4.4 |
| 404 | Not Found | Section 8.4.5 |
| 405 | Method Not Allowed | Section 8.4.6 |
| 406 | Not Acceptable | Section 8.4.7 |
| 407 | Proxy Authentication Required | Section 8.4.8 |
| 408 | Request Timeout | Section 8.4.9 |
| 409 | Conflict | Section 8.4.10 |
| 410 | Gone | Section 8.4.11 |
| 411 | Length Required | Section 8.4.12 |
| 413 | Request Entity Too Large | Section 8.4.14 |
| 414 | URI Too Long | Section 8.4.15 |
| 415 | Unsupported Media Type | Section 8.4.16 |
| 417 | Expectation Failed | Section 8.4.18 |
| 426 | Upgrade Required | Section 8.4.19 |
| 500 | Internal Server Error | Section 8.5.1 |
| 501 | Not Implemented | Section 8.5.2 |
| 502 | Bad Gateway | Section 8.5.3 |
| 503 | Service Unavailable | Section 8.5.4 |
| 504 | Gateway Timeout | Section 8.5.5 |
| 505 | HTTP Version Not Supported | Section 8.5.6 |
+-------+-------------------------------+----------------+
10.3. Header Field Registration
The Message Header Field Registry located at shall be
updated with the permanent registrations below (see [RFC3864]):
Fielding, et al. Expires October 20, 2011 [Page 43]
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+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Allow | http | standard | Section 9.1 |
| Expect | http | standard | Section 9.2 |
| From | http | standard | Section 9.3 |
| Location | http | standard | Section 9.4 |
| Max-Forwards | http | standard | Section 9.5 |
| Referer | http | standard | Section 9.6 |
| Retry-After | http | standard | Section 9.7 |
| Server | http | standard | Section 9.8 |
| User-Agent | http | standard | Section 9.9 |
+-------------------+----------+----------+-------------+
The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force".
11. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
11.1. Transfer of Sensitive Information
Like any generic data transfer protocol, HTTP 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. Implementors SHOULD make
the Server header field a configurable option.
Proxies which serve as a portal through a network firewall SHOULD
take special precautions regarding the transfer of header information
that identifies the hosts behind the firewall. In particular, they
SHOULD remove, or replace with sanitized versions, any Via fields
generated behind the firewall.
The Referer header field allows reading patterns to be studied and
reverse links drawn. Although it can be very useful, its power can
Fielding, et al. Expires October 20, 2011 [Page 44]
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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 9.9) or Server (Section 9.8) header fields
can sometimes be used to determine that a specific client or server
have 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 may contain enough entropy
to be used, possibly in conjunction with other material, to uniquely
identify the user.
Some request methods, like TRACE (Section 7.8), 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.
11.2. 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.
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-
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target. Many existing servers, proxies, and user agents log or
display the request-target in places where it might be visible to
third parties. Such services can use POST-based form submission
instead.
11.3. Location Headers and Spoofing
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.
11.4. 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.
12. Acknowledgments
13. References
13.1. Normative References
[Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,
and Message Parsing", draft-ietf-httpbis-p1-messaging-14
(work in progress), April 2011.
[Part3] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload
and Content Negotiation", draft-ietf-httpbis-p3-payload-14
(work in progress), April 2011.
[Part4] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 4: Conditional
Requests", draft-ietf-httpbis-p4-conditional-14 (work in
progress), April 2011.
[Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
Fielding, et al. Expires October 20, 2011 [Page 46]
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Partial Responses", draft-ietf-httpbis-p5-range-14 (work
in progress), April 2011.
[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part
6: Caching", draft-ietf-httpbis-p6-cache-14 (work in
progress), April 2011.
[Part7] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 7: Authentication",
draft-ietf-httpbis-p7-auth-14 (work in progress),
April 2011.
[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.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
13.2. Informative References
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2068, January 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., 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.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Fielding, et al. Expires October 20, 2011 [Page 47]
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[RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, March 2010.
Appendix A. Changes from RFC 2616
This document takes over the Status Code Registry, previously defined
in Section 7.1 of [RFC2817]. (Section 4.2)
Clarify definition of POST. (Section 7.5)
Remove requirement to handle all Content-* header fields; ban use of
Content-Range with PUT. (Section 7.6)
Take over definition of CONNECT method from [RFC2817]. (Section 7.9)
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. (Sections 8.3.2, 8.3.3 and 8.3.8)
Deprecate 305 Use Proxy status code, because user agents did not
implement it. It used to indicate that the target resource must 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 8.3.6)
Define status 426 (Upgrade Required) (this was incorporated from
[RFC2817]). (Section 8.4.19)
Change ABNF productions for header fields to only define the field
value. (Section 9)
Reclassify "Allow" as response header field, removing the option to
specify it in a PUT request. Relax the server requirement on the
contents of the Allow header field and remove requirement on clients
to always trust the header field value. (Section 9.1)
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 9.4)
Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
extension methods could have used it as well). (Section 9.5)
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Allow Referer field value of "about:blank" as alternative to not
specifying it. (Section 9.6)
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 9.9 of [Part1].
(Section 9.8)
Appendix B. Collected ABNF
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Allow = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
Expect = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
From = mailbox
HTTP-date =
Location = URI-reference
Max-Forwards = 1*DIGIT
Method = token
OWS =
RWS =
Reason-Phrase = *( WSP / VCHAR / obs-text )
Referer = absolute-URI / partial-URI
Retry-After = HTTP-date / delta-seconds
Server = product *( RWS ( product / comment ) )
Status-Code = 3DIGIT
URI-reference =
User-Agent = product *( RWS ( product / comment ) )
absolute-URI =
comment =
delta-seconds = 1*DIGIT
expect-params = ";" token [ "=" ( token / quoted-string ) ]
expectation = "100-continue" / expectation-extension
expectation-extension = token [ "=" ( token / quoted-string )
*expect-params ]
mailbox =
obs-text =
partial-URI =
product =
quoted-string =
token =
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ABNF diagnostics:
; Allow defined but not used
; Expect defined but not used
; From defined but not used
; Location defined but not used
; Max-Forwards defined but not used
; Reason-Phrase defined but not used
; Referer defined but not used
; Retry-After defined but not used
; Server defined but not used
; Status-Code defined but not used
; User-Agent defined but not used
Appendix C. Change Log (to be removed by RFC Editor before publication)
C.1. Since RFC 2616
Extracted relevant partitions from [RFC2616].
C.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" ()
o : "Revise
description of the POST method"
()
o : "Normative and
Informative references"
o : "RFC2606
Compliance"
o : "Informative
references"
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o : "Redundant
cross-references"
Other changes:
o Move definitions of 304 and 412 condition codes to [Part4]
C.3. 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.
C.4. Since draft-ietf-httpbis-p2-semantics-02
Closed issues:
o : "Requiring
Allow in 405 responses"
o : "Status Code
Registry"
o : "Redirection
vs. Location"
o : "Cacheability
of 303 response"
o : "305 Use Proxy"
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o :
"Classification for Allow header"
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
headers defined in this document.
Ongoing work on ABNF conversion
():
o Replace string literals when the string really is case-sensitive
(method).
C.5. Since draft-ietf-httpbis-p2-semantics-03
Closed issues:
o : "OPTIONS
request 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).
C.6. Since draft-ietf-httpbis-p2-semantics-04
Closed issues:
o : "Content-*"
o : "RFC 2822 is
updated by RFC 5322"
Ongoing work on ABNF conversion
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():
o Use "/" instead of "|" for alternatives.
o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
o Rewrite ABNFs to spell out whitespace rules, factor out header
field value format definitions.
C.7. 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.
C.8. 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"
C.9. 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"
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o : "update note
citing RFC 1945 and 2068"
o : "update note
about redirect limit"
o : "Location
header 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?"
C.10. 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)
C.11. Since draft-ietf-httpbis-p2-semantics-09
Closed issues:
o : "Fragment
combination / precedence during redirects"
Partly resolved issues:
o : "Location
header payload handling"
o : "Term for the
requested resource's URI"
C.12. Since draft-ietf-httpbis-p2-semantics-10
Closed issues:
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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"
C.13. 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)
C.14. Since draft-ietf-httpbis-p2-semantics-12
Closed issues:
o : "Fragment
combination / precedence during redirects" (added warning about
having a fragid on the redirect may 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 type
defaulting"
o : "PUT - 'store
under' vs 'store at'"
o : "duplicate
ABNF for Reason-Phrase"
o : "Note special
status of Content-* prefix in header 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
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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C.15. Since draft-ietf-httpbis-p2-semantics-13
Closed issues:
o : "untangle
ABNFs for header fields"
o : "message-body
in CONNECT request"
Index
1
100 Continue (status code) 23
101 Switching Protocols (status code) 23
2
200 OK (status code) 24
201 Created (status code) 24
202 Accepted (status code) 25
203 Non-Authoritative Information (status code) 25
204 No Content (status code) 25
205 Reset Content (status code) 26
206 Partial Content (status code) 26
3
300 Multiple Choices (status code) 27
301 Moved Permanently (status code) 27
302 Found (status code) 28
303 See Other (status code) 28
304 Not Modified (status code) 29
305 Use Proxy (status code) 29
306 (Unused) (status code) 29
307 Temporary Redirect (status code) 29
4
400 Bad Request (status code) 30
401 Unauthorized (status code) 30
402 Payment Required (status code) 30
403 Forbidden (status code) 30
404 Not Found (status code) 31
405 Method Not Allowed (status code) 31
406 Not Acceptable (status code) 31
407 Proxy Authentication Required (status code) 32
408 Request Timeout (status code) 32
409 Conflict (status code) 32
410 Gone (status code) 32
411 Length Required (status code) 33
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412 Precondition Failed (status code) 33
413 Request Entity Too Large (status code) 33
414 URI Too Long (status code) 33
415 Unsupported Media Type (status code) 33
416 Requested Range Not Satisfiable (status code) 34
417 Expectation Failed (status code) 34
426 Upgrade Required (status code) 34
5
500 Internal Server Error (status code) 34
501 Not Implemented (status code) 35
502 Bad Gateway (status code) 35
503 Service Unavailable (status code) 35
504 Gateway Timeout (status code) 35
505 HTTP Version Not Supported (status code) 35
A
Allow header field 36
C
CONNECT method 21
D
DELETE method 20
E
Expect header field 36
F
From header field 37
G
GET method 16
Grammar
Allow 36
delta-seconds 40
Expect 36
expect-params 36
expectation 36
expectation-extension 36
extension-code 10
From 37
Location 38
Max-Forwards 39
Method 7
Reason-Phrase 10
Referer 39
Retry-After 40
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Server 40
Status-Code 10
User-Agent 41
H
HEAD method 17
Header Fields
Allow 36
Expect 36
From 37
Location 38
Max-Forwards 39
Referer 39
Retry-After 40
Server 40
User-Agent 41
I
Idempotent Methods 15
L
Location header field 38
M
Max-Forwards header field 39
Methods
CONNECT 21
DELETE 20
GET 16
HEAD 17
OPTIONS 15
POST 17
PUT 18
TRACE 21
O
OPTIONS method 15
P
POST method 17
PUT method 18
R
Referer header field 39
Retry-After header field 40
S
Safe Methods 14
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Server header field 40
Status Codes
100 Continue 23
101 Switching Protocols 23
200 OK 24
201 Created 24
202 Accepted 25
203 Non-Authoritative Information 25
204 No Content 25
205 Reset Content 26
206 Partial Content 26
300 Multiple Choices 27
301 Moved Permanently 27
302 Found 28
303 See Other 28
304 Not Modified 29
305 Use Proxy 29
306 (Unused) 29
307 Temporary Redirect 29
400 Bad Request 30
401 Unauthorized 30
402 Payment Required 30
403 Forbidden 30
404 Not Found 31
405 Method Not Allowed 31
406 Not Acceptable 31
407 Proxy Authentication Required 32
408 Request Timeout 32
409 Conflict 32
410 Gone 32
411 Length Required 33
412 Precondition Failed 33
413 Request Entity Too Large 33
414 URI Too Long 33
415 Unsupported Media Type 33
416 Requested Range Not Satisfiable 34
417 Expectation Failed 34
426 Upgrade Required 34
500 Internal Server Error 34
501 Not Implemented 35
502 Bad Gateway 35
503 Service Unavailable 35
504 Gateway Timeout 35
505 HTTP Version Not Supported 35
T
TRACE method 21
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U
User-Agent header field 41
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/
Jim Gettys
Alcatel-Lucent Bell Labs
21 Oak Knoll Road
Carlisle, MA 01741
USA
EMail: jg@freedesktop.org
URI: http://gettys.wordpress.com/
Jeffrey C. Mogul
Hewlett-Packard Company
HP Labs, Large Scale Systems Group
1501 Page Mill Road, MS 1177
Palo Alto, CA 94304
USA
EMail: JeffMogul@acm.org
Henrik Frystyk Nielsen
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
USA
EMail: henrikn@microsoft.com
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Larry Masinter
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA
EMail: LMM@acm.org
URI: http://larry.masinter.net/
Paul J. Leach
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
EMail: paulle@microsoft.com
Tim Berners-Lee
World Wide Web Consortium
MIT Computer Science and Artificial Intelligence Laboratory
The Stata Center, Building 32
32 Vassar Street
Cambridge, MA 02139
USA
EMail: timbl@w3.org
URI: http://www.w3.org/People/Berners-Lee/
Yves Lafon (editor)
World Wide Web Consortium
W3C / ERCIM
2004, rte des Lucioles
Sophia-Antipolis, AM 06902
France
EMail: ylafon@w3.org
URI: http://www.raubacapeu.net/people/yves/
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Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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