HTTP/1.1, part 1: URIs, Connections, and Message Parsing
draft-ietf-httpbis-p1-messaging-18
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7230.
|
|
|---|---|---|---|
| Authors | Roy T. Fielding , Jim Gettys , Jeffrey Mogul , Henrik Nielsen , Larry M Masinter , Paul J. Leach , Tim Berners-Lee , Yves Lafon , Julian Reschke | ||
| Last updated | 2011-11-14 (Latest revision 2011-10-31) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
GENART Telechat review
(of
-25)
by Meral Shirazipour
Ready w/issues
SECDIR Last Call review
(of
-24)
by Ben Laurie
Serious Issues
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 7230 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Peter Saint-Andre | ||
| Send notices to | httpbis-chairs@tools.ietf.org, draft-ietf-httpbis-p1-messaging@tools.ietf.org |
draft-ietf-httpbis-p1-messaging-18
HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe
Obsoletes: 2145,2616 (if approved) J. Gettys
Updates: 2817 (if approved) Alcatel-Lucent
Intended status: Standards Track J. Mogul
Expires: July 7, 2012 HP
H. Frystyk
Microsoft
L. Masinter
Adobe
P. Leach
Microsoft
T. Berners-Lee
W3C/MIT
Y. Lafon, Ed.
W3C
J. Reschke, Ed.
greenbytes
January 4, 2012
HTTP/1.1, part 1: URIs, Connections, and Message Parsing
draft-ietf-httpbis-p1-messaging-18
Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypertext information
systems. HTTP has been in use by the World Wide Web global
information initiative since 1990. This document is Part 1 of the
seven-part specification that defines the protocol referred to as
"HTTP/1.1" and, taken together, obsoletes RFC 2616 and moves it to
historic status, along with its predecessor RFC 2068.
Part 1 provides an overview of HTTP and its associated terminology,
defines the "http" and "https" Uniform Resource Identifier (URI)
schemes, defines the generic message syntax and parsing requirements
for HTTP message frames, and describes general security concerns for
implementations.
This part also obsoletes RFCs 2145 (on HTTP version numbers) and 2817
(on using CONNECT for TLS upgrades) and moves them to historic
status.
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
Fielding, et al. Expires July 7, 2012 [Page 1]
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<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
The current issues list is at
<http://tools.ietf.org/wg/httpbis/trac/report/3> and related
documents (including fancy diffs) can be found at
<http://tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix C.19.
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 July 7, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
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outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Conformance and Error Handling . . . . . . . . . . . . . . 7
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7
1.2.1. ABNF Extension: #rule . . . . . . . . . . . . . . . . 8
1.2.2. Basic Rules . . . . . . . . . . . . . . . . . . . . . 9
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1. Client/Server Messaging . . . . . . . . . . . . . . . . . 10
2.2. Message Orientation and Buffering . . . . . . . . . . . . 11
2.3. Connections and Transport Independence . . . . . . . . . . 12
2.4. Intermediaries . . . . . . . . . . . . . . . . . . . . . . 12
2.5. Caches . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.6. Protocol Versioning . . . . . . . . . . . . . . . . . . . 15
2.7. Uniform Resource Identifiers . . . . . . . . . . . . . . . 17
2.7.1. http URI scheme . . . . . . . . . . . . . . . . . . . 18
2.7.2. https URI scheme . . . . . . . . . . . . . . . . . . . 19
2.7.3. http and https URI Normalization and Comparison . . . 20
3. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1. Start Line . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.1. Request-Line . . . . . . . . . . . . . . . . . . . . . 22
3.1.2. Response Status-Line . . . . . . . . . . . . . . . . . 23
3.2. Header Fields . . . . . . . . . . . . . . . . . . . . . . 23
3.2.1. Field Parsing . . . . . . . . . . . . . . . . . . . . 25
3.2.2. Field Length . . . . . . . . . . . . . . . . . . . . . 25
3.2.3. Common Field ABNF Rules . . . . . . . . . . . . . . . 26
3.3. Message Body . . . . . . . . . . . . . . . . . . . . . . . 27
3.4. Handling Incomplete Messages . . . . . . . . . . . . . . . 30
3.5. Message Parsing Robustness . . . . . . . . . . . . . . . . 31
4. Message Routing . . . . . . . . . . . . . . . . . . . . . . . 31
4.1. Types of Request Target . . . . . . . . . . . . . . . . . 31
4.2. The Resource Identified by a Request . . . . . . . . . . . 33
4.3. Effective Request URI . . . . . . . . . . . . . . . . . . 34
5. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 35
5.1. Transfer Codings . . . . . . . . . . . . . . . . . . . . . 35
5.1.1. Chunked Transfer Coding . . . . . . . . . . . . . . . 36
5.1.2. Compression Codings . . . . . . . . . . . . . . . . . 38
5.1.3. Transfer Coding Registry . . . . . . . . . . . . . . . 39
5.2. Product Tokens . . . . . . . . . . . . . . . . . . . . . . 39
5.3. Quality Values . . . . . . . . . . . . . . . . . . . . . . 40
6. Connections . . . . . . . . . . . . . . . . . . . . . . . . . 40
6.1. Persistent Connections . . . . . . . . . . . . . . . . . . 40
6.1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 40
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6.1.2. Overall Operation . . . . . . . . . . . . . . . . . . 41
6.1.3. Proxy Servers . . . . . . . . . . . . . . . . . . . . 42
6.1.4. Practical Considerations . . . . . . . . . . . . . . . 45
6.1.5. Retrying Requests . . . . . . . . . . . . . . . . . . 46
6.2. Message Transmission Requirements . . . . . . . . . . . . 46
6.2.1. Persistent Connections and Flow Control . . . . . . . 46
6.2.2. Monitoring Connections for Error Status Messages . . . 46
6.2.3. Use of the 100 (Continue) Status . . . . . . . . . . . 46
7. Miscellaneous notes that might disappear . . . . . . . . . . . 48
7.1. Scheme aliases considered harmful . . . . . . . . . . . . 48
7.2. Use of HTTP for proxy communication . . . . . . . . . . . 49
7.3. Interception of HTTP for access control . . . . . . . . . 49
7.4. Use of HTTP by other protocols . . . . . . . . . . . . . . 49
7.5. Use of HTTP by media type specification . . . . . . . . . 49
8. Header Field Definitions . . . . . . . . . . . . . . . . . . . 49
8.1. Connection . . . . . . . . . . . . . . . . . . . . . . . . 49
8.2. Content-Length . . . . . . . . . . . . . . . . . . . . . . 51
8.3. Host . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
8.4. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
8.5. Trailer . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.6. Transfer-Encoding . . . . . . . . . . . . . . . . . . . . 54
8.7. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 55
8.7.1. Upgrade Token Registry . . . . . . . . . . . . . . . . 56
8.8. Via . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 58
9.1. Header Field Registration . . . . . . . . . . . . . . . . 58
9.2. URI Scheme Registration . . . . . . . . . . . . . . . . . 59
9.3. Internet Media Type Registrations . . . . . . . . . . . . 59
9.3.1. Internet Media Type message/http . . . . . . . . . . . 59
9.3.2. Internet Media Type application/http . . . . . . . . . 61
9.4. Transfer Coding Registry . . . . . . . . . . . . . . . . . 62
9.5. Upgrade Token Registration . . . . . . . . . . . . . . . . 62
10. Security Considerations . . . . . . . . . . . . . . . . . . . 62
10.1. Personal Information . . . . . . . . . . . . . . . . . . . 63
10.2. Abuse of Server Log Information . . . . . . . . . . . . . 63
10.3. Attacks Based On File and Path Names . . . . . . . . . . . 63
10.4. DNS-related Attacks . . . . . . . . . . . . . . . . . . . 63
10.5. Proxies and Caching . . . . . . . . . . . . . . . . . . . 64
10.6. Protocol Element Size Overflows . . . . . . . . . . . . . 64
10.7. Denial of Service Attacks on Proxies . . . . . . . . . . . 65
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 65
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 66
12.1. Normative References . . . . . . . . . . . . . . . . . . . 66
12.2. Informative References . . . . . . . . . . . . . . . . . . 67
Appendix A. HTTP Version History . . . . . . . . . . . . . . . . 69
A.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 70
A.1.1. Multi-homed Web Servers . . . . . . . . . . . . . . . 70
A.1.2. Keep-Alive Connections . . . . . . . . . . . . . . . . 71
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A.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 71
Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 72
Appendix C. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 75
C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 75
C.2. Since draft-ietf-httpbis-p1-messaging-00 . . . . . . . . . 75
C.3. Since draft-ietf-httpbis-p1-messaging-01 . . . . . . . . . 77
C.4. Since draft-ietf-httpbis-p1-messaging-02 . . . . . . . . . 78
C.5. Since draft-ietf-httpbis-p1-messaging-03 . . . . . . . . . 78
C.6. Since draft-ietf-httpbis-p1-messaging-04 . . . . . . . . . 79
C.7. Since draft-ietf-httpbis-p1-messaging-05 . . . . . . . . . 79
C.8. Since draft-ietf-httpbis-p1-messaging-06 . . . . . . . . . 80
C.9. Since draft-ietf-httpbis-p1-messaging-07 . . . . . . . . . 81
C.10. Since draft-ietf-httpbis-p1-messaging-08 . . . . . . . . . 82
C.11. Since draft-ietf-httpbis-p1-messaging-09 . . . . . . . . . 82
C.12. Since draft-ietf-httpbis-p1-messaging-10 . . . . . . . . . 82
C.13. Since draft-ietf-httpbis-p1-messaging-11 . . . . . . . . . 83
C.14. Since draft-ietf-httpbis-p1-messaging-12 . . . . . . . . . 83
C.15. Since draft-ietf-httpbis-p1-messaging-13 . . . . . . . . . 84
C.16. Since draft-ietf-httpbis-p1-messaging-14 . . . . . . . . . 84
C.17. Since draft-ietf-httpbis-p1-messaging-15 . . . . . . . . . 85
C.18. Since draft-ietf-httpbis-p1-messaging-16 . . . . . . . . . 85
C.19. Since draft-ietf-httpbis-p1-messaging-17 . . . . . . . . . 85
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
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1. Introduction
The Hypertext Transfer Protocol (HTTP) is an application-level
request/response protocol that uses extensible semantics and MIME-
like message payloads for flexible interaction with network-based
hypertext information systems. HTTP relies upon the Uniform Resource
Identifier (URI) standard [RFC3986] to indicate the target resource
and relationships between resources. Messages are passed in a format
similar to that used by Internet mail [RFC5322] and the Multipurpose
Internet Mail Extensions (MIME) [RFC2045] (see Appendix A of [Part3]
for the differences between HTTP and MIME messages).
HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by
presenting a uniform interface to clients that is independent of the
types of resources provided. Likewise, servers do not need to be
aware of each client's purpose: an HTTP request can be considered in
isolation rather than being associated with a specific type of client
or a predetermined sequence of application steps. The result is a
protocol that can be used effectively in many different contexts and
for which implementations can evolve independently over time.
HTTP is also designed for use as an intermediation protocol for
translating communication to and from non-HTTP information systems.
HTTP proxies and gateways can provide access to alternative
information services by translating their diverse protocols into a
hypertext format that can be viewed and manipulated by clients in the
same way as HTTP services.
One consequence of HTTP flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent of
received communication, and the expected behavior of recipients. If
the communication is considered in isolation, then successful actions
ought to be reflected in corresponding changes to the observable
interface provided by servers. However, since multiple clients might
act in parallel and perhaps at cross-purposes, we cannot require that
such changes be observable beyond the scope of a single response.
This document is Part 1 of the seven-part specification of HTTP,
defining the protocol referred to as "HTTP/1.1", obsoleting [RFC2616]
and [RFC2145]. Part 1 describes the architectural elements that are
used or referred to in HTTP, defines the "http" and "https" URI
schemes, describes overall network operation and connection
management, and defines HTTP message framing and forwarding
requirements. Our goal is to define all of the mechanisms necessary
for HTTP message handling that are independent of message semantics,
thereby defining the complete set of requirements for message parsers
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and message-forwarding intermediaries.
1.1. Conformance and Error Handling
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document defines conformance criteria for several roles in HTTP
communication, including Senders, Recipients, Clients, Servers, User-
Agents, Origin Servers, Intermediaries, Proxies and Gateways. See
Section 2 for definitions of these terms.
An implementation is considered conformant if it complies with all of
the requirements associated with its role(s). Note that SHOULD-level
requirements are relevant here, unless one of the documented
exceptions is applicable.
This document also uses ABNF to define valid protocol elements
(Section 1.2). In addition to the prose requirements placed upon
them, Senders MUST NOT generate protocol elements that are invalid.
Unless noted otherwise, Recipients MAY take steps to recover a usable
protocol element from an invalid construct. However, HTTP does not
define specific error handling mechanisms, except in cases where it
has direct impact on security. This is because different uses of the
protocol require different error handling strategies; for example, a
Web browser may wish to transparently recover from a response where
the Location header field doesn't parse according to the ABNF,
whereby in a systems control protocol using HTTP, this type of error
recovery could lead to dangerous consequences.
1.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234].
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line
feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any
visible [USASCII] character).
As a syntactic convention, ABNF rule names prefixed with "obs-"
denote "obsolete" grammar rules that appear for historical reasons.
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1.2.1. ABNF Extension: #rule
The #rule extension to the ABNF rules of [RFC5234] is used to improve
readability.
A construct "#" is defined, similar to "*", for defining comma-
delimited lists of elements. The full form is "<n>#<m>element"
indicating at least <n> and at most <m> elements, each separated by a
single comma (",") and optional whitespace (OWS, Section 1.2.2).
Thus,
1#element => element *( OWS "," OWS element )
and:
#element => [ 1#element ]
and for n >= 1 and m > 1:
<n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
For compatibility with legacy list rules, recipients SHOULD accept
empty list elements. In other words, consumers would follow the list
productions:
#element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
Note that empty elements do not contribute to the count of elements
present, though.
For example, given these ABNF productions:
example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 3.2.3
Then these are valid values for example-list (not including the
double quotes, which are present for delimitation only):
"foo,bar"
"foo ,bar,"
"foo , ,bar,charlie "
But these values would be invalid, as at least one non-empty element
is required:
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""
","
", ,"
Appendix B shows the collected ABNF, with the list rules expanded as
explained above.
1.2.2. Basic Rules
This specification uses three rules to denote the use of linear
whitespace: OWS (optional whitespace), RWS (required whitespace), and
BWS ("bad" whitespace).
The OWS rule is used where zero or more linear whitespace octets
might appear. OWS SHOULD either not be produced or be produced as a
single SP. Multiple OWS octets that occur within field-content
SHOULD either be replaced with a single SP or transformed to all SP
octets (each octet other than SP replaced with SP) before
interpreting the field value or forwarding the message downstream.
RWS is used when at least one linear whitespace octet is required to
separate field tokens. RWS SHOULD be produced as a single SP.
Multiple RWS octets that occur within field-content SHOULD either be
replaced with a single SP or transformed to all SP octets before
interpreting the field value or forwarding the message downstream.
BWS is used where the grammar allows optional whitespace for
historical reasons but senders SHOULD NOT produce it in messages.
HTTP/1.1 recipients MUST accept such bad optional whitespace and
remove it before interpreting the field value or forwarding the
message downstream.
OWS = *( SP / HTAB / obs-fold )
; "optional" whitespace
RWS = 1*( SP / HTAB / obs-fold )
; "required" whitespace
BWS = OWS
; "bad" whitespace
obs-fold = CRLF ( SP / HTAB )
; obsolete line folding
; see Section 3.2.1
2. Architecture
HTTP was created for the World Wide Web architecture and has evolved
over time to support the scalability needs of a worldwide hypertext
system. Much of that architecture is reflected in the terminology
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and syntax productions used to define HTTP.
2.1. Client/Server Messaging
HTTP is a stateless request/response protocol that operates by
exchanging messages (Section 3) across a reliable transport or
session-layer "connection". An HTTP "client" is a program that
establishes a connection to a server for the purpose of sending one
or more HTTP requests. An HTTP "server" is a program that accepts
connections in order to service HTTP requests by sending HTTP
responses.
Note that the terms client and server refer only to the roles that
these programs perform for a particular connection. The same program
might act as a client on some connections and a server on others. We
use the term "user agent" to refer to the program that initiates a
request, such as a WWW browser, editor, or spider (web-traversing
robot), and the term "origin server" to refer to the program that can
originate authoritative responses to a request. For general
requirements, we use the term "sender" to refer to whichever
component sent a given message and the term "recipient" to refer to
any component that receives the message.
Note: The term 'user agent' covers both those situations where
there is a user (human) interacting with the software agent (and
for which user interface or interactive suggestions might be made,
e.g., warning the user or given the user an option in the case of
security or privacy options) and also those where the software
agent may act autonomously.
Most HTTP communication consists of a retrieval request (GET) for a
representation of some resource identified by a URI. In the simplest
case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin server
(O).
request >
UA ======================================= O
< response
A client sends an HTTP request to the server in the form of a request
message, beginning with a request-line that includes a method, URI,
and protocol version (Section 3.1.1), followed by MIME-like header
fields containing request modifiers, client information, and payload
metadata (Section 3.2), an empty line to indicate the end of the
header section, and finally a message body containing the payload
body (if any, Section 3.3).
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A server responds to the client's request by sending an HTTP response
message, beginning with a status line that includes the protocol
version, a success or error code, and textual reason phrase
(Section 3.1.2), followed by MIME-like header fields containing
server information, resource metadata, and payload metadata
(Section 3.2), an empty line to indicate the end of the header
section, and finally a message body containing the payload body (if
any, Section 3.3).
Note that 1xx responses (Section 7.1 of [Part2]) are not final;
therefore, a server can send zero or more 1xx responses, followed by
exactly one final response (with any other status code).
The following example illustrates a typical message exchange for a
GET request on the URI "http://www.example.com/hello.txt":
client request:
GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept: */*
server response:
HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 14
Vary: Accept-Encoding
Content-Type: text/plain
Hello World!
2.2. Message Orientation and Buffering
Fundamentally, HTTP is a message-based protocol. Although message
bodies can be chunked (Section 5.1.1) and implementations often make
parts of a message available progressively, this is not required, and
some widely-used implementations only make a message available when
it is complete. Furthermore, while most proxies will progressively
stream messages, some amount of buffering will take place, and some
proxies might buffer messages to perform transformations, check
content or provide other services.
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Therefore, extensions to and uses of HTTP cannot rely on the
availability of a partial message, or assume that messages will not
be buffered. There are strategies that can be used to test for
buffering in a given connection, but it should be understood that
behaviors can differ across connections, and between requests and
responses.
Recipients MUST consider every message in a connection in isolation;
because HTTP is a stateless protocol, it cannot be assumed that two
requests on the same connection are from the same client or share any
other common attributes. In particular, intermediaries might mix
requests from different clients into a single server connection.
Note that some existing HTTP extensions (e.g., [RFC4559]) violate
this requirement, thereby potentially causing interoperability and
security problems.
2.3. Connections and Transport Independence
HTTP messaging is independent of the underlying transport or session-
layer connection protocol(s). HTTP only presumes a reliable
transport with in-order delivery of requests and the corresponding
in-order delivery of responses. The mapping of HTTP request and
response structures onto the data units of the underlying transport
protocol is outside the scope of this specification.
The specific connection protocols to be used for an interaction are
determined by client configuration and the target resource's URI.
For example, the "http" URI scheme (Section 2.7.1) indicates a
default connection of TCP over IP, with a default TCP port of 80, but
the client might be configured to use a proxy via some other
connection port or protocol instead of using the defaults.
A connection might be used for multiple HTTP request/response
exchanges, as defined in Section 6.1.
2.4. Intermediaries
HTTP enables the use of intermediaries to satisfy requests through a
chain of connections. There are three common forms of HTTP
intermediary: proxy, gateway, and tunnel. In some cases, a single
intermediary might act as an origin server, proxy, gateway, or
tunnel, switching behavior based on the nature of each request.
> > > >
UA =========== A =========== B =========== C =========== O
< < < <
The figure above shows three intermediaries (A, B, and C) between the
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user agent and origin server. A request or response message that
travels the whole chain will pass through four separate connections.
Some HTTP communication options might apply only to the connection
with the nearest, non-tunnel neighbor, only to the end-points of the
chain, or to all connections along the chain. Although the diagram
is linear, each participant might be engaged in multiple,
simultaneous communications. For example, B might be receiving
requests from many clients other than A, and/or forwarding requests
to servers other than C, at the same time that it is handling A's
request.
We use the terms "upstream" and "downstream" to describe various
requirements in relation to the directional flow of a message: all
messages flow from upstream to downstream. Likewise, we use the
terms inbound and outbound to refer to directions in relation to the
request path: "inbound" means toward the origin server and "outbound"
means toward the user agent.
A "proxy" is a message forwarding agent that is selected by the
client, usually via local configuration rules, to receive requests
for some type(s) of absolute URI and attempt to satisfy those
requests via translation through the HTTP interface. Some
translations are minimal, such as for proxy requests for "http" URIs,
whereas other requests might require translation to and from entirely
different application-layer protocols. Proxies are often used to
group an organization's HTTP requests through a common intermediary
for the sake of security, annotation services, or shared caching.
An HTTP-to-HTTP proxy is called a "transforming proxy" if it is
designed or configured to modify request or response messages in a
semantically meaningful way (i.e., modifications, beyond those
required by normal HTTP processing, that change the message in a way
that would be significant to the original sender or potentially
significant to downstream recipients). For example, a transforming
proxy might be acting as a shared annotation server (modifying
responses to include references to a local annotation database), a
malware filter, a format transcoder, or an intranet-to-Internet
privacy filter. Such transformations are presumed to be desired by
the client (or client organization) that selected the proxy and are
beyond the scope of this specification. However, when a proxy is not
intended to transform a given message, we use the term "non-
transforming proxy" to target requirements that preserve HTTP message
semantics. See Section 7.2.4 of [Part2] and Section 3.6 of [Part6]
for status and warning codes related to transformations.
A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
as a layer above some other server(s) and translates the received
requests to the underlying server's protocol. Gateways are often
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used to encapsulate legacy or untrusted information services, to
improve server performance through "accelerator" caching, and to
enable partitioning or load-balancing of HTTP services across
multiple machines.
A gateway behaves as an origin server on its outbound connection and
as a user agent on its inbound connection. All HTTP requirements
applicable to an origin server also apply to the outbound
communication of a gateway. A gateway communicates with inbound
servers using any protocol that it desires, including private
extensions to HTTP that are outside the scope of this specification.
However, an HTTP-to-HTTP gateway that wishes to interoperate with
third-party HTTP servers MUST comply with HTTP user agent
requirements on the gateway's inbound connection and MUST implement
the Connection (Section 8.1) and Via (Section 8.8) header fields for
both connections.
A "tunnel" acts as a blind relay between two connections without
changing the messages. Once active, a tunnel is not considered a
party to the HTTP communication, though the tunnel might have been
initiated by an HTTP request. A tunnel ceases to exist when both
ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when
transport-layer security is used to establish private communication
through a shared firewall proxy.
In addition, there may exist network intermediaries that are not
considered part of the HTTP communication but nevertheless act as
filters or redirecting agents (usually violating HTTP semantics,
causing security problems, and otherwise making a mess of things).
Such a network intermediary, often referred to as an "interception
proxy" [RFC3040], "transparent proxy" [RFC1919], or "captive portal",
differs from an HTTP proxy because it has not been selected by the
client. Instead, the network intermediary redirects outgoing TCP
port 80 packets (and occasionally other common port traffic) to an
internal HTTP server. Interception proxies are commonly found on
public network access points, as a means of enforcing account
subscription prior to allowing use of non-local Internet services,
and within corporate firewalls to enforce network usage policies.
They are indistinguishable from a man-in-the-middle attack.
2.5. Caches
A "cache" is a local store of previous response messages and the
subsystem that controls its message storage, retrieval, and deletion.
A cache stores cacheable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent
requests. Any client or server MAY employ a cache, though a cache
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cannot be used by a server while it is acting as a tunnel.
The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting
chain if B has a cached copy of an earlier response from O (via C)
for a request which has not been cached by UA or A.
> >
UA =========== A =========== B - - - - - - C - - - - - - O
< <
A response is "cacheable" if a cache is allowed to store a copy of
the response message for use in answering subsequent requests. Even
when a response is cacheable, there might be additional constraints
placed by the client or by the origin server on when that cached
response can be used for a particular request. HTTP requirements for
cache behavior and cacheable responses are defined in Section 2 of
[Part6].
There are a wide variety of architectures and configurations of
caches and proxies deployed across the World Wide Web and inside
large organizations. These systems include national hierarchies of
proxy caches to save transoceanic bandwidth, systems that broadcast
or multicast cache entries, organizations that distribute subsets of
cached data via optical media, and so on.
2.6. Protocol Versioning
HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
of the protocol. This specification defines version "1.1". The
protocol version as a whole indicates the sender's compliance with
the set of requirements laid out in that version's corresponding
specification of HTTP.
The version of an HTTP message is indicated by an HTTP-Version field
in the first line of the message. HTTP-Version is case-sensitive.
HTTP-Version = HTTP-Prot-Name "/" DIGIT "." DIGIT
HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
The HTTP version number consists of two decimal digits separated by a
"." (period or decimal point). The first digit ("major version")
indicates the HTTP messaging syntax, whereas the second digit ("minor
version") indicates the highest minor version to which the sender is
at least conditionally compliant and able to understand for future
communication. The minor version advertises the sender's
communication capabilities even when the sender is only using a
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backwards-compatible subset of the protocol, thereby letting the
recipient know that more advanced features can be used in response
(by servers) or in future requests (by clients).
When an HTTP/1.1 message is sent to an HTTP/1.0 recipient [RFC1945]
or a recipient whose version is unknown, the HTTP/1.1 message is
constructed such that it can be interpreted as a valid HTTP/1.0
message if all of the newer features are ignored. This specification
places recipient-version requirements on some new features so that a
compliant sender will only use compatible features until it has
determined, through configuration or the receipt of a message, that
the recipient supports HTTP/1.1.
The interpretation of an HTTP header field does not change between
minor versions of the same major version, though the default behavior
of a recipient in the absence of such a field can change. Unless
specified otherwise, header fields defined in HTTP/1.1 are defined
for all versions of HTTP/1.x. In particular, the Host and Connection
header fields ought to be implemented by all HTTP/1.x implementations
whether or not they advertise compliance with HTTP/1.1.
New header fields can be defined such that, when they are understood
by a recipient, they might override or enhance the interpretation of
previously defined header fields. When an implementation receives an
unrecognized header field, the recipient MUST ignore that header
field for local processing regardless of the message's HTTP version.
An unrecognized header field received by a proxy MUST be forwarded
downstream unless the header field's field-name is listed in the
message's Connection header-field (see Section 8.1). These
requirements allow HTTP's functionality to be enhanced without
requiring prior update of all compliant intermediaries.
Intermediaries that process HTTP messages (i.e., all intermediaries
other than those acting as a tunnel) MUST send their own HTTP-Version
in forwarded messages. In other words, they MUST NOT blindly forward
the first line of an HTTP message without ensuring that the protocol
version matches what the intermediary understands, and is at least
conditionally compliant to, for both the receiving and sending of
messages. Forwarding an HTTP message without rewriting the HTTP-
Version might result in communication errors when downstream
recipients use the message sender's version to determine what
features are safe to use for later communication with that sender.
An HTTP client SHOULD send a request version equal to the highest
version for which the client is at least conditionally compliant and
whose major version is no higher than the highest version supported
by the server, if this is known. An HTTP client MUST NOT send a
version for which it is not at least conditionally compliant.
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An HTTP client MAY send a lower request version if it is known that
the server incorrectly implements the HTTP specification, but only
after the client has attempted at least one normal request and
determined from the response status or header fields (e.g., Server)
that the server improperly handles higher request versions.
An HTTP server SHOULD send a response version equal to the highest
version for which the server is at least conditionally compliant and
whose major version is less than or equal to the one received in the
request. An HTTP server MUST NOT send a version for which it is not
at least conditionally compliant. A server MAY send a 505 (HTTP
Version Not Supported) response if it cannot send a response using
the major version used in the client's request.
An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
if it is known or suspected that the client incorrectly implements
the HTTP specification and is incapable of correctly processing later
version responses, such as when a client fails to parse the version
number correctly or when an intermediary is known to blindly forward
the HTTP-Version even when it doesn't comply with the given minor
version of the protocol. Such protocol downgrades SHOULD NOT be
performed unless triggered by specific client attributes, such as
when one or more of the request header fields (e.g., User-Agent)
uniquely match the values sent by a client known to be in error.
The intention of HTTP's versioning design is that the major number
will only be incremented if an incompatible message syntax is
introduced, and that the minor number will only be incremented when
changes made to the protocol have the effect of adding to the message
semantics or implying additional capabilities of the sender.
However, the minor version was not incremented for the changes
introduced between [RFC2068] and [RFC2616], and this revision is
specifically avoiding any such changes to the protocol.
2.7. Uniform Resource Identifiers
Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
HTTP as the means for identifying resources. URI references are used
to target requests, indicate redirects, and define relationships.
HTTP does not limit what a resource might be; it merely defines an
interface that can be used to interact with a resource via HTTP.
More information on the scope of URIs and resources can be found in
[RFC3986].
This specification adopts the definitions of "URI-reference",
"absolute-URI", "relative-part", "port", "host", "path-abempty",
"path-absolute", "query", and "authority" from the URI generic syntax
[RFC3986]. In addition, we define a partial-URI rule for protocol
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elements that allow a relative URI but not a fragment.
URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
relative-part = <relative-part, defined in [RFC3986], Section 4.2>
authority = <authority, defined in [RFC3986], Section 3.2>
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
port = <port, defined in [RFC3986], Section 3.2.3>
query = <query, defined in [RFC3986], Section 3.4>
uri-host = <host, defined in [RFC3986], Section 3.2.2>
partial-URI = relative-part [ "?" query ]
Each protocol element in HTTP that allows a URI reference will
indicate in its ABNF production whether the element allows any form
of reference (URI-reference), only a URI in absolute form (absolute-
URI), only the path and optional query components, or some
combination of the above. Unless otherwise indicated, URI references
are parsed relative to the effective request URI, which defines the
default base URI for references in both the request and its
corresponding response.
2.7.1. http URI scheme
The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
TCP connections on a given port.
http-URI = "http:" "//" authority path-abempty [ "?" query ]
The HTTP origin server is identified by the generic syntax's
authority component, which includes a host identifier and optional
TCP port ([RFC3986], Section 3.2.2). The remainder of the URI,
consisting of both the hierarchical path component and optional query
component, serves as an identifier for a potential resource within
that origin server's name space.
If the host identifier is provided as an IP literal or IPv4 address,
then the origin server is any listener on the indicated TCP port at
that IP address. If host is a registered name, then that name is
considered an indirect identifier and the recipient might use a name
resolution service, such as DNS, to find the address of a listener
for that host. The host MUST NOT be empty; if an "http" URI is
received with an empty host, then it MUST be rejected as invalid. If
the port subcomponent is empty or not given, then TCP port 80 is
assumed (the default reserved port for WWW services).
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Regardless of the form of host identifier, access to that host is not
implied by the mere presence of its name or address. The host might
or might not exist and, even when it does exist, might or might not
be running an HTTP server or listening to the indicated port. The
"http" URI scheme makes use of the delegated nature of Internet names
and addresses to establish a naming authority (whatever entity has
the ability to place an HTTP server at that Internet name or address)
and allows that authority to determine which names are valid and how
they might be used.
When an "http" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the
host to an IP address, establishing a TCP connection to that address
on the indicated port, and sending an HTTP request message
(Section 3) containing the URI's identifying data (Section 4) to the
server. If the server responds to that request with a non-interim
HTTP response message, as described in Section 4 of [Part2], then
that response is considered an authoritative answer to the client's
request.
Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority. An HTTP service
based on some other underlying connection protocol would presumably
be identified using a different URI scheme, just as the "https"
scheme (below) is used for servers that require an SSL/TLS transport
layer on a connection. Other protocols might also be used to provide
access to "http" identified resources -- it is only the authoritative
interface used for mapping the namespace that is specific to TCP.
The URI generic syntax for authority also includes a deprecated
userinfo subcomponent ([RFC3986], Section 3.2.1) for including user
authentication information in the URI. Some implementations make use
of the userinfo component for internal configuration of
authentication information, such as within command invocation
options, configuration files, or bookmark lists, even though such
usage might expose a user identifier or password. Senders MUST NOT
include a userinfo subcomponent (and its "@" delimiter) when
transmitting an "http" URI in a message. Recipients of HTTP messages
that contain a URI reference SHOULD parse for the existence of
userinfo and treat its presence as an error, likely indicating that
the deprecated subcomponent is being used to obscure the authority
for the sake of phishing attacks.
2.7.2. https URI scheme
The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
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namespace governed by a potential HTTP origin server listening for
SSL/TLS-secured connections on a given TCP port.
All of the requirements listed above for the "http" scheme are also
requirements for the "https" scheme, except that a default TCP port
of 443 is assumed if the port subcomponent is empty or not given, and
the TCP connection MUST be secured for privacy through the use of
strong encryption prior to sending the first HTTP request.
https-URI = "https:" "//" authority path-abempty [ "?" query ]
Unlike the "http" scheme, responses to "https" identified requests
are never "public" and thus MUST NOT be reused for shared caching.
They can, however, be reused in a private cache if the message is
cacheable by default in HTTP or specifically indicated as such by the
Cache-Control header field (Section 3.2 of [Part6]).
Resources made available via the "https" scheme have no shared
identity with the "http" scheme even if their resource identifiers
indicate the same authority (the same host listening to the same TCP
port). They are distinct name spaces and are considered to be
distinct origin servers. However, an extension to HTTP that is
defined to apply to entire host domains, such as the Cookie protocol
[RFC6265], can allow information set by one service to impact
communication with other services within a matching group of host
domains.
The process for authoritative access to an "https" identified
resource is defined in [RFC2818].
2.7.3. http and https URI Normalization and Comparison
Since the "http" and "https" schemes conform to the URI generic
syntax, such URIs are normalized and compared according to the
algorithm defined in [RFC3986], Section 6, using the defaults
described above for each scheme.
If the port is equal to the default port for a scheme, the normal
form is to elide the port subcomponent. Likewise, an empty path
component is equivalent to an absolute path of "/", so the normal
form is to provide a path of "/" instead. The scheme and host are
case-insensitive and normally provided in lowercase; all other
components are compared in a case-sensitive manner. Characters other
than those in the "reserved" set are equivalent to their percent-
encoded octets (see [RFC3986], Section 2.1): the normal form is to
not encode them.
For example, the following three URIs are equivalent:
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http://example.com:80/~smith/home.html
http://EXAMPLE.com/%7Esmith/home.html
http://EXAMPLE.com:/%7esmith/home.html
3. Message Format
All HTTP/1.1 messages consist of a start-line followed by a sequence
of octets in a format similar to the Internet Message Format
[RFC5322]: zero or more header fields (collectively referred to as
the "headers" or the "header section"), an empty line indicating the
end of the header section, and an optional message-body.
HTTP-message = start-line
*( header-field CRLF )
CRLF
[ message-body ]
The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field into a hash table
by field name until the empty line, and then use the parsed data to
determine if a message-body is expected. If a message-body has been
indicated, then it is read as a stream until an amount of octets
equal to the message-body length is read or the connection is closed.
Recipients MUST parse an HTTP message as a sequence of octets in an
encoding that is a superset of US-ASCII [USASCII]. Parsing an HTTP
message as a stream of Unicode characters, without regard for the
specific encoding, creates security vulnerabilities due to the
varying ways that string processing libraries handle invalid
multibyte character sequences that contain the octet LF (%x0A).
String-based parsers can only be safely used within protocol elements
after the element has been extracted from the message, such as within
a header field-value after message parsing has delineated the
individual fields.
3.1. Start Line
An HTTP message can either be a request from client to server or a
response from server to client. Syntactically, the two types of
message differ only in the start-line, which is either a Request-Line
(for requests) or a Status-Line (for responses), and in the algorithm
for determining the length of the message-body (Section 3.3). In
theory, a client could receive requests and a server could receive
responses, distinguishing them by their different start-line formats,
but in practice servers are implemented to only expect a request (a
response is interpreted as an unknown or invalid request method) and
clients are implemented to only expect a response.
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start-line = Request-Line / Status-Line
Implementations MUST NOT send whitespace between the start-line and
the first header field. The presence of such whitespace in a request
might be an attempt to trick a server into ignoring that field or
processing the line after it as a new request, either of which might
result in a security vulnerability if other implementations within
the request chain interpret the same message differently. Likewise,
the presence of such whitespace in a response might be ignored by
some clients or cause others to cease parsing.
3.1.1. Request-Line
The Request-Line begins with a method token, followed by a single
space (SP), the request-target, another single space (SP), the
protocol version, and ending with CRLF.
Request-Line = Method SP request-target SP HTTP-Version CRLF
3.1.1.1. Method
The Method token indicates the request method to be performed on the
target resource. The request method is case-sensitive.
Method = token
See Section 2 of [Part2] for further information, such as the list of
methods defined by this specification, the IANA registry, and
considerations for new methods.
3.1.1.2. request-target
The request-target identifies the target resource upon which to apply
the request. The four options for request-target are described in
Section 4.1.
request-target = "*"
/ absolute-URI
/ ( path-absolute [ "?" query ] )
/ authority
HTTP does not place a pre-defined limit on the length of a request-
target. A server MUST be prepared to receive URIs of unbounded
length and respond with the 414 (URI Too Long) status code if the
received request-target would be longer than the server wishes to
handle (see Section 7.4.15 of [Part2]).
Various ad-hoc limitations on request-target length are found in
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practice. It is RECOMMENDED that all HTTP senders and recipients
support request-target lengths of 8000 or more octets.
Note: Fragments ([RFC3986], Section 3.5) are not part of the
request-target and thus will not be transmitted in an HTTP
request.
3.1.2. Response Status-Line
The first line of a Response message is the Status-Line, consisting
of the protocol version, a space (SP), the status code, another
space, a possibly-empty textual phrase describing the status code,
and ending with CRLF.
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
3.1.2.1. Status Code
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. See Section 4 of
[Part2] for further information, such as the list of status codes
defined by this specification, the IANA registry, and considerations
for new status codes.
Status-Code = 3DIGIT
3.1.2.2. Reason Phrase
The Reason Phrase exists for the sole purpose of providing a textual
description associated with the numeric status code, out of deference
to earlier Internet application protocols that were more frequently
used with interactive text clients. A client SHOULD ignore the
content of the Reason Phrase.
Reason-Phrase = *( HTAB / SP / VCHAR / obs-text )
3.2. Header Fields
Each HTTP header field consists of a case-insensitive field name
followed by a colon (":"), optional whitespace, and the field value.
header-field = field-name ":" OWS field-value BWS
field-name = token
field-value = *( field-content / obs-fold )
field-content = *( HTAB / SP / VCHAR / obs-text )
The field-name token labels the corresponding field-value as having
the semantics defined by that header field. For example, the Date
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header field is defined in Section 9.2 of [Part2] as containing the
origination timestamp for the message in which it appears.
HTTP header fields are fully extensible: there is no limit on the
introduction of new field names, each presumably defining new
semantics, or on the number of header fields used in a given message.
Existing fields are defined in each part of this specification and in
many other specifications outside the standards process. New header
fields can be introduced without changing the protocol version if
their defined semantics allow them to be safely ignored by recipients
that do not recognize them.
New HTTP header fields SHOULD be registered with IANA according to
the procedures in Section 3.1 of [Part2]. Unrecognized header fields
MUST be forwarded by a proxy unless the field-name is listed in the
Connection header field (Section 8.1) or the proxy is specifically
configured to block or otherwise transform such fields. Unrecognized
header fields SHOULD be ignored by other recipients.
The order in which header fields with differing field names are
received is not significant. However, it is "good practice" to send
header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST
wait until the entire header section is received before interpreting
a request message, since later header fields might include
conditionals, authentication credentials, or deliberately misleading
duplicate header fields that would impact request processing.
Multiple header fields with the same field name MUST NOT be sent in a
message unless the entire field value for that header field is
defined as a comma-separated list [i.e., #(values)]. Multiple header
fields with the same field name can be combined into one "field-name:
field-value" pair, without changing the semantics of the message, by
appending each subsequent field value to the combined field value in
order, separated by a comma. The order in which header fields with
the same field name are received is therefore significant to the
interpretation of the combined field value; a proxy MUST NOT change
the order of these field values when forwarding a message.
Note: The "Set-Cookie" header field as implemented in practice can
occur multiple times, but does not use the list syntax, and thus
cannot be combined into a single line ([RFC6265]). (See Appendix
A.2.3 of [Kri2001] for details.) Also note that the Set-Cookie2
header field specified in [RFC2965] does not share this problem.
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3.2.1. Field Parsing
No whitespace is allowed between the header field-name and colon. In
the past, differences in the handling of such whitespace have led to
security vulnerabilities in request routing and response handling.
Any received request message that contains whitespace between a
header field-name and colon MUST be rejected with a response code of
400 (Bad Request). A proxy MUST remove any such whitespace from a
response message before forwarding the message downstream.
A field value MAY be preceded by optional whitespace (OWS); a single
SP is preferred. The field value does not include any leading or
trailing white space: OWS occurring before the first non-whitespace
octet of the field value or after the last non-whitespace octet of
the field value is ignored and SHOULD be removed before further
processing (as this does not change the meaning of the header field).
Historically, HTTP header field values could be extended over
multiple lines by preceding each extra line with at least one space
or horizontal tab (obs-fold). This specification deprecates such
line folding except within the message/http media type
(Section 9.3.1). HTTP senders MUST NOT produce messages that include
line folding (i.e., that contain any field-content that matches the
obs-fold rule) unless the message is intended for packaging within
the message/http media type. HTTP recipients SHOULD accept line
folding and replace any embedded obs-fold whitespace with either a
single SP or a matching number of SP octets (to avoid buffer copying)
prior to interpreting the field value or forwarding the message
downstream.
Historically, HTTP has allowed field content with text in the ISO-
8859-1 [ISO-8859-1] character encoding and supported other character
sets only through use of [RFC2047] encoding. In practice, most HTTP
header field values use only a subset of the US-ASCII character
encoding [USASCII]. Newly defined header fields SHOULD limit their
field values to US-ASCII octets. Recipients SHOULD treat other (obs-
text) octets in field content as opaque data.
3.2.2. Field Length
HTTP does not place a pre-defined limit on the length of header
fields, either in isolation or as a set. A server MUST be prepared
to receive request header fields of unbounded length and respond with
a 4xx status code if the received header field(s) would be longer
than the server wishes to handle.
A client that receives response headers that are longer than it
wishes to handle can only treat it as a server error.
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Various ad-hoc limitations on header length are found in practice.
It is RECOMMENDED that all HTTP senders and recipients support
messages whose combined header fields have 4000 or more octets.
3.2.3. Common Field ABNF Rules
Many HTTP/1.1 header field values consist of words (token or quoted-
string) separated by whitespace or special characters. These special
characters MUST be in a quoted string to be used within a parameter
value (as defined in Section 5.1).
word = token / quoted-string
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA
; any VCHAR, except special
special = "(" / ")" / "<" / ">" / "@" / ","
/ ";" / ":" / "\" / DQUOTE / "/" / "["
/ "]" / "?" / "=" / "{" / "}"
A string of text is parsed as a single word if it is quoted using
double-quote marks.
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
obs-text = %x80-FF
The backslash octet ("\") can be used as a single-octet quoting
mechanism within quoted-string constructs:
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
Recipients that process the value of the quoted-string MUST handle a
quoted-pair as if it were replaced by the octet following the
backslash.
Senders SHOULD NOT escape octets in quoted-strings that do not
require escaping (i.e., other than DQUOTE and the backslash octet).
Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
comment = "(" *( ctext / quoted-cpair / comment ) ")"
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ctext = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
The backslash octet ("\") can be used as a single-octet quoting
mechanism within comment constructs:
quoted-cpair = "\" ( HTAB / SP / VCHAR / obs-text )
Senders SHOULD NOT escape octets in comments that do not require
escaping (i.e., other than the backslash octet "\" and the
parentheses "(" and ")").
3.3. Message Body
The message-body (if any) of an HTTP message is used to carry the
payload body associated with the request or response.
message-body = *OCTET
The message-body differs from the payload body only when a transfer-
coding has been applied, as indicated by the Transfer-Encoding header
field (Section 8.6). If more than one Transfer-Encoding header field
is present in a message, the multiple field-values MUST be combined
into one field-value, according to the algorithm defined in
Section 3.2, before determining the message-body length.
When one or more transfer-codings are applied to a payload in order
to form the message-body, the Transfer-Encoding header field MUST
contain the list of transfer-codings applied. Transfer-Encoding is a
property of the message, not of the payload, and thus MAY be added or
removed by any implementation along the request/response chain under
the constraints found in Section 5.1.
If a message is received that has multiple Content-Length header
fields (Section 8.2) with field-values consisting of the same decimal
value, or a single Content-Length header field with a field value
containing a list of identical decimal values (e.g., "Content-Length:
42, 42"), indicating that duplicate Content-Length header fields have
been generated or combined by an upstream message processor, then the
recipient MUST either reject the message as invalid or replace the
duplicated field-values with a single valid Content-Length field
containing that decimal value prior to determining the message-body
length.
The rules for when a message-body is allowed in a message differ for
requests and responses.
The presence of a message-body in a request is signaled by the
inclusion of a Content-Length or Transfer-Encoding header field in
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the request's header fields, even if the request method does not
define any use for a message-body. This allows the request message
framing algorithm to be independent of method semantics.
For response messages, whether or not a message-body is included with
a message is dependent on both the request method and the response
status code (Section 3.1.2.1). Responses to the HEAD request method
never include a message-body because the associated response header
fields (e.g., Transfer-Encoding, Content-Length, etc.) only indicate
what their values would have been if the request method had been GET.
All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
responses MUST NOT include a message-body. All other responses do
include a message-body, although the body MAY be of zero length.
The length of the message-body is determined by one of the following
(in order of precedence):
1. Any response to a HEAD request and any response with a status
code of 100-199, 204, or 304 is always terminated by the first
empty line after the header fields, regardless of the header
fields present in the message, and thus cannot contain a message-
body.
2. If a Transfer-Encoding header field is present and the "chunked"
transfer-coding (Section 5.1) is the final encoding, the message-
body length is determined by reading and decoding the chunked
data until the transfer-coding indicates the data is complete.
If a Transfer-Encoding header field is present in a response and
the "chunked" transfer-coding is not the final encoding, the
message-body length is determined by reading the connection until
it is closed by the server. If a Transfer-Encoding header field
is present in a request and the "chunked" transfer-coding is not
the final encoding, the message-body length cannot be determined
reliably; the server MUST respond with the 400 (Bad Request)
status code and then close the connection.
If a message is received with both a Transfer-Encoding header
field and a Content-Length header field, the Transfer-Encoding
overrides the Content-Length. Such a message might indicate an
attempt to perform request or response smuggling (bypass of
security-related checks on message routing or content) and thus
ought to be handled as an error. The provided Content-Length
MUST be removed, prior to forwarding the message downstream, or
replaced with the real message-body length after the transfer-
coding is decoded.
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3. If a message is received without Transfer-Encoding and with
either multiple Content-Length header fields having differing
field-values or a single Content-Length header field having an
invalid value, then the message framing is invalid and MUST be
treated as an error to prevent request or response smuggling. If
this is a request message, the server MUST respond with a 400
(Bad Request) status code and then close the connection. If this
is a response message received by a proxy, the proxy MUST discard
the received response, send a 502 (Bad Gateway) status code as
its downstream response, and then close the connection. If this
is a response message received by a user-agent, it MUST be
treated as an error by discarding the message and closing the
connection.
4. If a valid Content-Length header field is present without
Transfer-Encoding, its decimal value defines the message-body
length in octets. If the actual number of octets sent in the
message is less than the indicated Content-Length, the recipient
MUST consider the message to be incomplete and treat the
connection as no longer usable. If the actual number of octets
sent in the message is more than the indicated Content-Length,
the recipient MUST only process the message-body up to the field
value's number of octets; the remainder of the message MUST
either be discarded or treated as the next message in a pipeline.
For the sake of robustness, a user-agent MAY attempt to detect
and correct such an error in message framing if it is parsing the
response to the last request on a connection and the connection
has been closed by the server.
5. If this is a request message and none of the above are true, then
the message-body length is zero (no message-body is present).
6. Otherwise, this is a response message without a declared message-
body length, so the message-body length is determined by the
number of octets received prior to the server closing the
connection.
Since there is no way to distinguish a successfully completed, close-
delimited message from a partially-received message interrupted by
network failure, implementations SHOULD use encoding or length-
delimited messages whenever possible. The close-delimiting feature
exists primarily for backwards compatibility with HTTP/1.0.
A server MAY reject a request that contains a message-body but not a
Content-Length by responding with 411 (Length Required).
Unless a transfer-coding other than "chunked" has been applied, a
client that sends a request containing a message-body SHOULD use a
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valid Content-Length header field if the message-body length is known
in advance, rather than the "chunked" encoding, since some existing
services respond to "chunked" with a 411 (Length Required) status
code even though they understand the chunked encoding. This is
typically because such services are implemented via a gateway that
requires a content-length in advance of being called and the server
is unable or unwilling to buffer the entire request before
processing.
A client that sends a request containing a message-body MUST include
a valid Content-Length header field if it does not know the server
will handle HTTP/1.1 (or later) requests; such knowledge can be in
the form of specific user configuration or by remembering the version
of a prior received response.
3.4. Handling Incomplete Messages
Request messages that are prematurely terminated, possibly due to a
cancelled connection or a server-imposed time-out exception, MUST
result in closure of the connection; sending an HTTP/1.1 error
response prior to closing the connection is OPTIONAL.
Response messages that are prematurely terminated, usually by closure
of the connection prior to receiving the expected number of octets or
by failure to decode a transfer-encoded message-body, MUST be
recorded as incomplete. A response that terminates in the middle of
the header block (before the empty line is received) cannot be
assumed to convey the full semantics of the response and MUST be
treated as an error.
A message-body that uses the chunked transfer encoding is incomplete
if the zero-sized chunk that terminates the encoding has not been
received. A message that uses a valid Content-Length is incomplete
if the size of the message-body received (in octets) is less than the
value given by Content-Length. A response that has neither chunked
transfer encoding nor Content-Length is terminated by closure of the
connection, and thus is considered complete regardless of the number
of message-body octets received, provided that the header block was
received intact.
A user agent MUST NOT render an incomplete response message-body as
if it were complete (i.e., some indication must be given to the user
that an error occurred). Cache requirements for incomplete responses
are defined in Section 2.1 of [Part6].
A server MUST read the entire request message-body or close the
connection after sending its response, since otherwise the remaining
data on a persistent connection would be misinterpreted as the next
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request. Likewise, a client MUST read the entire response message-
body if it intends to reuse the same connection for a subsequent
request. Pipelining multiple requests on a connection is described
in Section 6.1.2.2.
3.5. Message Parsing Robustness
Older HTTP/1.0 client implementations might send an extra CRLF after
a POST request as a lame workaround for some early server
applications that failed to read message-body content that was not
terminated by a line-ending. An HTTP/1.1 client MUST NOT preface or
follow a request with an extra CRLF. If terminating the request
message-body with a line-ending is desired, then the client MUST
include the terminating CRLF octets as part of the message-body
length.
In the interest of robustness, servers SHOULD ignore at least one
empty line received where a Request-Line is expected. In other
words, if the server is reading the protocol stream at the beginning
of a message and receives a CRLF first, it SHOULD ignore the CRLF.
Likewise, although the line terminator for the start-line and header
fields is the sequence CRLF, we recommend that recipients recognize a
single LF as a line terminator and ignore any CR.
When a server listening only for HTTP request messages, or processing
what appears from the start-line to be an HTTP request message,
receives a sequence of octets that does not match the HTTP-message
grammar aside from the robustness exceptions listed above, the server
MUST respond with an HTTP/1.1 400 (Bad Request) response.
4. Message Routing
In most cases, the user agent is provided a URI reference from which
it determines an absolute URI for identifying the target resource.
When a request to the resource is initiated, all or part of that URI
is used to construct the HTTP request-target.
4.1. Types of Request Target
The four options for request-target are dependent on the nature of
the request.
The asterisk "*" form of request-target, which MUST NOT be used with
any request method other than OPTIONS, means that the request applies
to the server as a whole (the listening process) rather than to a
specific named resource at that server. For example,
OPTIONS * HTTP/1.1
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The "absolute-URI" form is REQUIRED when the request is being made to
a proxy. The proxy is requested to either forward the request or
service it from a valid cache, and then return the response. Note
that the proxy MAY forward the request on to another proxy or
directly to the server specified by the absolute-URI. In order to
avoid request loops, a proxy that forwards requests to other proxies
MUST be able to recognize and exclude all of its own server names,
including any aliases, local variations, and the numeric IP address.
An example Request-Line would be:
GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
To allow for transition to absolute-URIs in all requests in future
versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
form in requests, even though HTTP/1.1 clients will only generate
them in requests to proxies.
If a proxy receives a host name that is not a fully qualified domain
name, it MAY add its domain to the host name it received. If a proxy
receives a fully qualified domain name, the proxy MUST NOT change the
host name.
The "authority form" is only used by the CONNECT request method
(Section 6.9 of [Part2]).
The most common form of request-target is that used when making a
request to an origin server ("origin form"). In this case, the
absolute path and query components of the URI MUST be transmitted as
the request-target, and the authority component MUST be transmitted
in a Host header field. For example, a client wishing to retrieve a
representation of the resource, as identified above, directly from
the origin server would open (or reuse) a TCP connection to port 80
of the host "www.example.org" and send the lines:
GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.example.org
followed by the remainder of the Request. Note that the origin form
of request-target always starts with an absolute path; if the target
resource's URI path is empty, then an absolute path of "/" MUST be
provided in the request-target.
If a proxy receives an OPTIONS request with an absolute-URI form of
request-target in which the URI has an empty path and no query
component, then the last proxy on the request chain MUST use a
request-target of "*" when it forwards the request to the indicated
origin server.
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For example, the request
OPTIONS http://www.example.org:8001 HTTP/1.1
would be forwarded by the final proxy as
OPTIONS * HTTP/1.1
Host: www.example.org:8001
after connecting to port 8001 of host "www.example.org".
The request-target is transmitted in the format specified in
Section 2.7.1. If the request-target is percent-encoded ([RFC3986],
Section 2.1), the origin server MUST decode the request-target in
order to properly interpret the request. Servers SHOULD respond to
invalid request-targets with an appropriate status code.
A non-transforming proxy MUST NOT rewrite the "path-absolute" and
"query" parts of the received request-target when forwarding it to
the next inbound server, except as noted above to replace a null
path-absolute with "/" or "*".
Note: The "no rewrite" rule prevents the proxy from changing the
meaning of the request when the origin server is improperly using
a non-reserved URI character for a reserved purpose. Implementors
need to be aware that some pre-HTTP/1.1 proxies have been known to
rewrite the request-target.
4.2. The Resource Identified by a Request
The exact resource identified by an Internet request is determined by
examining both the request-target and the Host header field.
An origin server that does not allow resources to differ by the
requested host MAY ignore the Host header field value when
determining the resource identified by an HTTP/1.1 request. (But see
Appendix A.1.1 for other requirements on Host support in HTTP/1.1.)
An origin server that does differentiate resources based on the host
requested (sometimes referred to as virtual hosts or vanity host
names) MUST use the following rules for determining the requested
resource on an HTTP/1.1 request:
1. If request-target is an absolute-URI, the host is part of the
request-target. Any Host header field value in the request MUST
be ignored.
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2. If the request-target is not an absolute-URI, and the request
includes a Host header field, the host is determined by the Host
header field value.
3. If the host as determined by rule 1 or 2 is not a valid host on
the server, the response MUST be a 400 (Bad Request) error
message.
Recipients of an HTTP/1.0 request that lacks a Host header field MAY
attempt to use heuristics (e.g., examination of the URI path for
something unique to a particular host) in order to determine what
exact resource is being requested.
4.3. Effective Request URI
HTTP requests often do not carry the absolute URI ([RFC3986], Section
4.3) for the target resource; instead, the URI needs to be inferred
from the request-target, Host header field, and connection context.
The result of this process is called the "effective request URI".
The "target resource" is the resource identified by the effective
request URI.
If the request-target is an absolute-URI, then the effective request
URI is the request-target.
If the request-target uses the origin form or the asterisk form, and
the Host header field is present, then the effective request URI is
constructed by concatenating
o the scheme name: "http" if the request was received over an
insecure TCP connection, or "https" when received over a SSL/
TLS-secured TCP connection,
o the octet sequence "://",
o the authority component, as specified in the Host header field
(Section 8.3), and
o the request-target obtained from the Request-Line, unless the
request-target is just the asterisk "*".
If the request-target uses the origin form or the asterisk form, and
the Host header field is not present, then the effective request URI
is undefined.
Otherwise, when request-target uses the authority form, the effective
request URI is undefined.
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Example 1: the effective request URI for the message
GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.example.org:8080
(received over an insecure TCP connection) is "http", plus "://",
plus the authority component "www.example.org:8080", plus the
request-target "/pub/WWW/TheProject.html", thus
"http://www.example.org:8080/pub/WWW/TheProject.html".
Example 2: the effective request URI for the message
OPTIONS * HTTP/1.1
Host: www.example.org
(received over an SSL/TLS secured TCP connection) is "https", plus
"://", plus the authority component "www.example.org", thus
"https://www.example.org".
Effective request URIs are compared using the rules described in
Section 2.7.3, except that empty path components MUST NOT be treated
as equivalent to an absolute path of "/".
5. Protocol Parameters
5.1. Transfer Codings
Transfer-coding values are used to indicate an encoding
transformation that has been, can be, or might need to be applied to
a payload body in order to ensure "safe transport" through the
network. This differs from a content coding in that the transfer-
coding is a property of the message rather than a property of the
representation that is being transferred.
transfer-coding = "chunked" ; Section 5.1.1
/ "compress" ; Section 5.1.2.1
/ "deflate" ; Section 5.1.2.2
/ "gzip" ; Section 5.1.2.3
/ transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
Parameters are in the form of attribute/value pairs.
transfer-parameter = attribute BWS "=" BWS value
attribute = token
value = word
All transfer-coding values are case-insensitive. HTTP/1.1 uses
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transfer-coding values in the TE header field (Section 8.4) and in
the Transfer-Encoding header field (Section 8.6).
Transfer-codings are analogous to the Content-Transfer-Encoding
values of MIME, which were designed to enable safe transport of
binary data over a 7-bit transport service ([RFC2045], Section 6).
However, safe transport has a different focus for an 8bit-clean
transfer protocol. In HTTP, the only unsafe characteristic of
message-bodies is the difficulty in determining the exact message
body length (Section 3.3), or the desire to encrypt data over a
shared transport.
A server that receives a request message with a transfer-coding it
does not understand SHOULD respond with 501 (Not Implemented) and
then close the connection. A server MUST NOT send transfer-codings
to an HTTP/1.0 client.
5.1.1. Chunked Transfer Coding
The chunked encoding modifies the body of a message in order to
transfer it as a series of chunks, each with its own size indicator,
followed by an OPTIONAL trailer containing header fields. This
allows dynamically produced content to be transferred along with the
information necessary for the recipient to verify that it has
received the full message.
Chunked-Body = *chunk
last-chunk
trailer-part
CRLF
chunk = chunk-size [ chunk-ext ] CRLF
chunk-data CRLF
chunk-size = 1*HEXDIG
last-chunk = 1*("0") [ chunk-ext ] CRLF
chunk-ext = *( ";" chunk-ext-name
[ "=" chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token / quoted-str-nf
chunk-data = 1*OCTET ; a sequence of chunk-size octets
trailer-part = *( header-field CRLF )
quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
; like quoted-string, but disallowing line folding
qdtext-nf = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
The chunk-size field is a string of hex digits indicating the size of
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the chunk-data in octets. The chunked encoding is ended by any chunk
whose size is zero, followed by the trailer, which is terminated by
an empty line.
The trailer allows the sender to include additional HTTP header
fields at the end of the message. The Trailer header field can be
used to indicate which header fields are included in a trailer (see
Section 8.5).
A server using chunked transfer-coding in a response MUST NOT use the
trailer for any header fields unless at least one of the following is
true:
1. the request included a TE header field that indicates "trailers"
is acceptable in the transfer-coding of the response, as
described in Section 8.4; or,
2. the trailer fields consist entirely of optional metadata, and the
recipient could use the message (in a manner acceptable to the
server where the field originated) without receiving it. In
other words, the server that generated the header (often but not
always the origin server) is willing to accept the possibility
that the trailer fields might be silently discarded along the
path to the client.
This requirement prevents an interoperability failure when the
message is being received by an HTTP/1.1 (or later) proxy and
forwarded to an HTTP/1.0 recipient. It avoids a situation where
compliance with the protocol would have necessitated a possibly
infinite buffer on the proxy.
A process for decoding the "chunked" transfer-coding can be
represented in pseudo-code as:
length := 0
read chunk-size, chunk-ext (if any) and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to decoded-body
length := length + chunk-size
read chunk-size and CRLF
}
read header-field
while (header-field not empty) {
append header-field to existing header fields
read header-field
}
Content-Length := length
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Remove "chunked" from Transfer-Encoding
All HTTP/1.1 applications MUST be able to receive and decode the
"chunked" transfer-coding and MUST ignore chunk-ext extensions they
do not understand.
Since "chunked" is the only transfer-coding required to be understood
by HTTP/1.1 recipients, it plays a crucial role in delimiting
messages on a persistent connection. Whenever a transfer-coding is
applied to a payload body in a request, the final transfer-coding
applied MUST be "chunked". If a transfer-coding is applied to a
response payload body, then either the final transfer-coding applied
MUST be "chunked" or the message MUST be terminated by closing the
connection. When the "chunked" transfer-coding is used, it MUST be
the last transfer-coding applied to form the message-body. The
"chunked" transfer-coding MUST NOT be applied more than once in a
message-body.
5.1.2. Compression Codings
The codings defined below can be used to compress the payload of a
message.
Note: Use of program names for the identification of encoding
formats is not desirable and is discouraged for future encodings.
Their use here is representative of historical practice, not good
design.
Note: For compatibility with previous implementations of HTTP,
applications SHOULD consider "x-gzip" and "x-compress" to be
equivalent to "gzip" and "compress" respectively.
5.1.2.1. Compress Coding
The "compress" format is produced by the common UNIX file compression
program "compress". This format is an adaptive Lempel-Ziv-Welch
coding (LZW).
5.1.2.2. Deflate Coding
The "deflate" format is defined as the "deflate" compression
mechanism (described in [RFC1951]) used inside the "zlib" data format
([RFC1950]).
Note: Some incorrect implementations send the "deflate" compressed
data without the zlib wrapper.
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5.1.2.3. Gzip Coding
The "gzip" format is produced by the file compression program "gzip"
(GNU zip), as described in [RFC1952]. This format is a Lempel-Ziv
coding (LZ77) with a 32 bit CRC.
5.1.3. Transfer Coding Registry
The HTTP Transfer Coding Registry defines the name space for the
transfer coding names.
Registrations MUST include the following fields:
o Name
o Description
o Pointer to specification text
Names of transfer codings MUST NOT overlap with names of content
codings (Section 2.2 of [Part3]), unless the encoding transformation
is identical (as it is the case for the compression codings defined
in Section 5.1.2).
Values to be added to this name space require a specification (see
"Specification Required" in Section 4.1 of [RFC5226]), and MUST
conform to the purpose of transfer coding defined in this section.
The registry itself is maintained at
<http://www.iana.org/assignments/http-parameters>.
5.2. Product Tokens
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by whitespace. By
convention, the products are listed in order of their significance
for identifying the application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
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Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although
any token octet MAY appear in a product-version, this token SHOULD
only be used for a version identifier (i.e., successive versions of
the same product SHOULD only differ in the product-version portion of
the product value).
5.3. Quality Values
Both transfer codings (TE request header field, Section 8.4) and
content negotiation (Section 5 of [Part3]) use short "floating point"
numbers to indicate the relative importance ("weight") of various
negotiable parameters. A weight is normalized to a real number in
the range 0 through 1, where 0 is the minimum and 1 the maximum
value. If a parameter has a quality value of 0, then content with
this parameter is "not acceptable" for the client. HTTP/1.1
applications MUST NOT generate more than three digits after the
decimal point. User configuration of these values SHOULD also be
limited in this fashion.
qvalue = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] )
Note: "Quality values" is a misnomer, since these values merely
represent relative degradation in desired quality.
6. Connections
6.1. Persistent Connections
6.1.1. Purpose
Prior to persistent connections, a separate TCP connection was
established for each request, increasing the load on HTTP servers and
causing congestion on the Internet. The use of inline images and
other associated data often requires a client to make multiple
requests of the same server in a short amount of time. Analysis of
these performance problems and results from a prototype
implementation are available [Pad1995] [Spe]. Implementation
experience and measurements of actual HTTP/1.1 implementations show
good results [Nie1997]. Alternatives have also been explored, for
example, T/TCP [Tou1998].
Persistent HTTP connections have a number of advantages:
o By opening and closing fewer TCP connections, CPU time is saved in
routers and hosts (clients, servers, proxies, gateways, tunnels,
or caches), and memory used for TCP protocol control blocks can be
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saved in hosts.
o HTTP requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single TCP connection to be
used much more efficiently, with much lower elapsed time.
o Network congestion is reduced by reducing the number of packets
caused by TCP opens, and by allowing TCP sufficient time to
determine the congestion state of the network.
o Latency on subsequent requests is reduced since there is no time
spent in TCP's connection opening handshake.
o HTTP can evolve more gracefully, since errors can be reported
without the penalty of closing the TCP connection. Clients using
future versions of HTTP might optimistically try a new feature,
but if communicating with an older server, retry with old
semantics after an error is reported.
HTTP implementations SHOULD implement persistent connections.
6.1.2. Overall Operation
A significant difference between HTTP/1.1 and earlier versions of
HTTP is that persistent connections are the default behavior of any
HTTP connection. That is, unless otherwise indicated, the client
SHOULD assume that the server will maintain a persistent connection,
even after error responses from the server.
Persistent connections provide a mechanism by which a client and a
server can signal the close of a TCP connection. This signaling
takes place using the Connection header field (Section 8.1). Once a
close has been signaled, the client MUST NOT send any more requests
on that connection.
6.1.2.1. Negotiation
An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
maintain a persistent connection unless a Connection header field
including the connection-token "close" was sent in the request. If
the server chooses to close the connection immediately after sending
the response, it SHOULD send a Connection header field including the
connection-token "close".
An HTTP/1.1 client MAY expect a connection to remain open, but would
decide to keep it open based on whether the response from a server
contains a Connection header field with the connection-token close.
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In case the client does not want to maintain a connection for more
than that request, it SHOULD send a Connection header field including
the connection-token close.
If either the client or the server sends the close token in the
Connection header field, that request becomes the last one for the
connection.
Clients and servers SHOULD NOT assume that a persistent connection is
maintained for HTTP versions less than 1.1 unless it is explicitly
signaled. See Appendix A.1.2 for more information on backward
compatibility with HTTP/1.0 clients.
In order to remain persistent, all messages on the connection MUST
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in Section 3.3.
6.1.2.2. Pipelining
A client that supports persistent connections MAY "pipeline" its
requests (i.e., send multiple requests without waiting for each
response). A server MUST send its responses to those requests in the
same order that the requests were received.
Clients which assume persistent connections and pipeline immediately
after connection establishment SHOULD be prepared to retry their
connection if the first pipelined attempt fails. If a client does
such a retry, it MUST NOT pipeline before it knows the connection is
persistent. Clients MUST also be prepared to resend their requests
if the server closes the connection before sending all of the
corresponding responses.
Clients SHOULD NOT pipeline requests using non-idempotent request
methods or non-idempotent sequences of request methods (see Section
6.1.2 of [Part2]). Otherwise, a premature termination of the
transport connection could lead to indeterminate results. A client
wishing to send a non-idempotent request SHOULD wait to send that
request until it has received the response status line for the
previous request.
6.1.3. Proxy Servers
It is especially important that proxies correctly implement the
properties of the Connection header field as specified in
Section 8.1.
The proxy server MUST signal persistent connections separately with
its clients and the origin servers (or other proxy servers) that it
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connects to. Each persistent connection applies to only one
transport link.
A proxy server MUST NOT establish a HTTP/1.1 persistent connection
with an HTTP/1.0 client (but see Section 19.7.1 of [RFC2068] for
information and discussion of the problems with the Keep-Alive header
field implemented by many HTTP/1.0 clients).
6.1.3.1. End-to-end and Hop-by-hop Header Fields
For the purpose of defining the behavior of caches and non-caching
proxies, we divide HTTP header fields into two categories:
o End-to-end header fields, which are transmitted to the ultimate
recipient of a request or response. End-to-end header fields in
responses MUST be stored as part of a cache entry and MUST be
transmitted in any response formed from a cache entry.
o Hop-by-hop header fields, which are meaningful only for a single
transport-level connection, and are not stored by caches or
forwarded by proxies.
The following HTTP/1.1 header fields are hop-by-hop header fields:
o Connection
o Keep-Alive
o Proxy-Authenticate
o Proxy-Authorization
o TE
o Trailer
o Transfer-Encoding
o Upgrade
All other header fields defined by HTTP/1.1 are end-to-end header
fields.
Other hop-by-hop header fields MUST be listed in a Connection header
field (Section 8.1).
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6.1.3.2. Non-modifiable Header Fields
Some features of HTTP/1.1, such as Digest Authentication, depend on
the value of certain end-to-end header fields. A non-transforming
proxy SHOULD NOT modify an end-to-end header field unless the
definition of that header field requires or specifically allows that.
A non-transforming proxy MUST NOT modify any of the following fields
in a request or response, and it MUST NOT add any of these fields if
not already present:
o Allow
o Content-Location
o Content-MD5
o ETag
o Last-Modified
o Server
A non-transforming proxy MUST NOT modify any of the following fields
in a response:
o Expires
but it MAY add any of these fields if not already present. If an
Expires header field is added, it MUST be given a field-value
identical to that of the Date header field in that response.
A proxy MUST NOT modify or add any of the following fields in a
message that contains the no-transform cache-control directive, or in
any request:
o Content-Encoding
o Content-Range
o Content-Type
A transforming proxy MAY modify or add these fields to a message that
does not include no-transform, but if it does so, it MUST add a
Warning 214 (Transformation applied) if one does not already appear
in the message (see Section 3.6 of [Part6]).
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Warning: Unnecessary modification of end-to-end header fields
might cause authentication failures if stronger authentication
mechanisms are introduced in later versions of HTTP. Such
authentication mechanisms MAY rely on the values of header fields
not listed here.
A non-transforming proxy MUST preserve the message payload ([Part3]),
though it MAY change the message-body through application or removal
of a transfer-coding (Section 5.1).
6.1.4. Practical Considerations
Servers will usually have some time-out value beyond which they will
no longer maintain an inactive connection. Proxy servers might make
this a higher value since it is likely that the client will be making
more connections through the same server. The use of persistent
connections places no requirements on the length (or existence) of
this time-out for either the client or the server.
When a client or server wishes to time-out it SHOULD issue a graceful
close on the transport connection. Clients and servers SHOULD both
constantly watch for the other side of the transport close, and
respond to it as appropriate. If a client or server does not detect
the other side's close promptly it could cause unnecessary resource
drain on the network.
A client, server, or proxy MAY close the transport connection at any
time. For example, a client might have started to send a new request
at the same time that the server has decided to close the "idle"
connection. From the server's point of view, the connection is being
closed while it was idle, but from the client's point of view, a
request is in progress.
Clients (including proxies) SHOULD limit the number of simultaneous
connections that they maintain to a given server (including proxies).
Previous revisions of HTTP gave a specific number of connections as a
ceiling, but this was found to be impractical for many applications.
As a result, this specification does not mandate a particular maximum
number of connections, but instead encourages clients to be
conservative when opening multiple connections.
In particular, while using multiple connections avoids the "head-of-
line blocking" problem (whereby a request that takes significant
server-side processing and/or has a large payload can block
subsequent requests on the same connection), each connection used
consumes server resources (sometimes significantly), and furthermore
using multiple connections can cause undesirable side effects in
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congested networks.
Note that servers might reject traffic that they deem abusive,
including an excessive number of connections from a client.
6.1.5. Retrying Requests
Senders can close the transport connection at any time. Therefore,
clients, servers, and proxies MUST be able to recover from
asynchronous close events. Client software MAY reopen the transport
connection and retransmit the aborted sequence of requests without
user interaction so long as the request sequence is idempotent (see
Section 6.1.2 of [Part2]). Non-idempotent request methods or
sequences MUST NOT be automatically retried, although user agents MAY
offer a human operator the choice of retrying the request(s).
Confirmation by user-agent software with semantic understanding of
the application MAY substitute for user confirmation. The automatic
retry SHOULD NOT be repeated if the second sequence of requests
fails.
6.2. Message Transmission Requirements
6.2.1. Persistent Connections and Flow Control
HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
flow control mechanisms to resolve temporary overloads, rather than
terminating connections with the expectation that clients will retry.
The latter technique can exacerbate network congestion.
6.2.2. Monitoring Connections for Error Status Messages
An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
the network connection for an error status code while it is
transmitting the request. If the client sees an error status code,
it SHOULD immediately cease transmitting the body. If the body is
being sent using a "chunked" encoding (Section 5.1), a zero length
chunk and empty trailer MAY be used to prematurely mark the end of
the message. If the body was preceded by a Content-Length header
field, the client MUST close the connection.
6.2.3. Use of the 100 (Continue) Status
The purpose of the 100 (Continue) status code (see Section 7.1.1 of
[Part2]) is to allow a client that is sending a request message with
a request body to determine if the origin server is willing to accept
the request (based on the request header fields) before the client
sends the request body. In some cases, it might either be
inappropriate or highly inefficient for the client to send the body
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if the server will reject the message without looking at the body.
Requirements for HTTP/1.1 clients:
o If a client will wait for a 100 (Continue) response before sending
the request body, it MUST send an Expect header field (Section 9.3
of [Part2]) with the "100-continue" expectation.
o A client MUST NOT send an Expect header field (Section 9.3 of
[Part2]) with the "100-continue" expectation if it does not intend
to send a request body.
Because of the presence of older implementations, the protocol allows
ambiguous situations in which a client might send "Expect: 100-
continue" without receiving either a 417 (Expectation Failed) or a
100 (Continue) status code. Therefore, when a client sends this
header field to an origin server (possibly via a proxy) from which it
has never seen a 100 (Continue) status code, the client SHOULD NOT
wait for an indefinite period before sending the request body.
Requirements for HTTP/1.1 origin servers:
o Upon receiving a request which includes an Expect header field
with the "100-continue" expectation, an origin server MUST either
respond with 100 (Continue) status code and continue to read from
the input stream, or respond with a final status code. The origin
server MUST NOT wait for the request body before sending the 100
(Continue) response. If it responds with a final status code, it
MAY close the transport connection or it MAY continue to read and
discard the rest of the request. It MUST NOT perform the request
method if it returns a final status code.
o An origin server SHOULD NOT send a 100 (Continue) response if the
request message does not include an Expect header field with the
"100-continue" expectation, and MUST NOT send a 100 (Continue)
response if such a request comes from an HTTP/1.0 (or earlier)
client. There is an exception to this rule: for compatibility
with [RFC2068], a server MAY send a 100 (Continue) status code in
response to an HTTP/1.1 PUT or POST request that does not include
an Expect header field with the "100-continue" expectation. This
exception, the purpose of which is to minimize any client
processing delays associated with an undeclared wait for 100
(Continue) status code, applies only to HTTP/1.1 requests, and not
to requests with any other HTTP-version value.
o An origin server MAY omit a 100 (Continue) response if it has
already received some or all of the request body for the
corresponding request.
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o An origin server that sends a 100 (Continue) response MUST
ultimately send a final status code, once the request body is
received and processed, unless it terminates the transport
connection prematurely.
o If an origin server receives a request that does not include an
Expect header field with the "100-continue" expectation, the
request includes a request body, and the server responds with a
final status code before reading the entire request body from the
transport connection, then the server SHOULD NOT close the
transport connection until it has read the entire request, or
until the client closes the connection. Otherwise, the client
might not reliably receive the response message. However, this
requirement is not be construed as preventing a server from
defending itself against denial-of-service attacks, or from badly
broken client implementations.
Requirements for HTTP/1.1 proxies:
o If a proxy receives a request that includes an Expect header field
with the "100-continue" expectation, and the proxy either knows
that the next-hop server complies with HTTP/1.1 or higher, or does
not know the HTTP version of the next-hop server, it MUST forward
the request, including the Expect header field.
o If the proxy knows that the version of the next-hop server is
HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
respond with a 417 (Expectation Failed) status code.
o Proxies SHOULD maintain a record of the HTTP version numbers
received from recently-referenced next-hop servers.
o A proxy MUST NOT forward a 100 (Continue) response if the request
message was received from an HTTP/1.0 (or earlier) client and did
not include an Expect header field with the "100-continue"
expectation. This requirement overrides the general rule for
forwarding of 1xx responses (see Section 7.1 of [Part2]).
7. Miscellaneous notes that might disappear
7.1. Scheme aliases considered harmful
[[TBD-aliases-harmful: describe why aliases like webcal are
harmful.]]
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7.2. Use of HTTP for proxy communication
[[TBD-proxy-other: Configured to use HTTP to proxy HTTP or other
protocols.]]
7.3. Interception of HTTP for access control
[[TBD-intercept: Interception of HTTP traffic for initiating access
control.]]
7.4. Use of HTTP by other protocols
[[TBD-profiles: Profiles of HTTP defined by other protocol.
Extensions of HTTP like WebDAV.]]
7.5. Use of HTTP by media type specification
[[TBD-hypertext: Instructions on composing HTTP requests via
hypertext formats.]]
8. Header Field Definitions
This section defines the syntax and semantics of HTTP header fields
related to message origination, framing, and routing.
+-------------------+---------------+
| Header Field Name | Defined in... |
+-------------------+---------------+
| Connection | Section 8.1 |
| Content-Length | Section 8.2 |
| Host | Section 8.3 |
| TE | Section 8.4 |
| Trailer | Section 8.5 |
| Transfer-Encoding | Section 8.6 |
| Upgrade | Section 8.7 |
| Via | Section 8.8 |
+-------------------+---------------+
8.1. Connection
The "Connection" header field allows the sender to specify options
that are desired only for that particular connection. Such
connection options MUST be removed or replaced before the message can
be forwarded downstream by a proxy or gateway. This mechanism also
allows the sender to indicate which HTTP header fields used in the
message are only intended for the immediate recipient ("hop-by-hop"),
as opposed to all recipients on the chain ("end-to-end"), enabling
the message to be self-descriptive and allowing future connection-
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specific extensions to be deployed in HTTP without fear that they
will be blindly forwarded by previously deployed intermediaries.
The Connection header field's value has the following grammar:
Connection = 1#connection-token
connection-token = token
A proxy or gateway MUST parse a received Connection header field
before a message is forwarded and, for each connection-token in this
field, remove any header field(s) from the message with the same name
as the connection-token, and then remove the Connection header field
itself or replace it with the sender's own connection options for the
forwarded message.
A sender MUST NOT include field-names in the Connection header field-
value for fields that are defined as expressing constraints for all
recipients in the request or response chain, such as the Cache-
Control header field (Section 3.2 of [Part6]).
The connection options do not have to correspond to a header field
present in the message, since a connection-specific header field
might not be needed if there are no parameters associated with that
connection option. Recipients that trigger certain connection
behavior based on the presence of connection options MUST do so based
on the presence of the connection-token rather than only the presence
of the optional header field. In other words, if the connection
option is received as a header field but not indicated within the
Connection field-value, then the recipient MUST ignore the
connection-specific header field because it has likely been forwarded
by an intermediary that is only partially compliant.
When defining new connection options, specifications ought to
carefully consider existing deployed header fields and ensure that
the new connection-token does not share the same name as an unrelated
header field that might already be deployed. Defining a new
connection-token essentially reserves that potential field-name for
carrying additional information related to the connection option,
since it would be unwise for senders to use that field-name for
anything else.
HTTP/1.1 defines the "close" connection option for the sender to
signal that the connection will be closed after completion of the
response. For example,
Connection: close
in either the request or the response header fields indicates that
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the connection SHOULD NOT be considered "persistent" (Section 6.1)
after the current request/response is complete.
An HTTP/1.1 client that does not support persistent connections MUST
include the "close" connection option in every request message.
An HTTP/1.1 server that does not support persistent connections MUST
include the "close" connection option in every response message that
does not have a 1xx (Informational) status code.
8.2. Content-Length
The "Content-Length" header field indicates the size of the message-
body, in decimal number of octets, for any message other than a
response to a HEAD request or a response with a status code of 304.
In the case of a response to a HEAD request, Content-Length indicates
the size of the payload body (not including any potential transfer-
coding) that would have been sent had the request been a GET. In the
case of a 304 (Not Modified) response to a GET request, Content-
Length indicates the size of the payload body (not including any
potential transfer-coding) that would have been sent in a 200 (OK)
response.
Content-Length = 1*DIGIT
An example is
Content-Length: 3495
Implementations SHOULD use this field to indicate the message-body
length when no transfer-coding is being applied and the payload's
body length can be determined prior to being transferred.
Section 3.3 describes how recipients determine the length of a
message-body.
Any Content-Length greater than or equal to zero is a valid value.
Note that the use of this field in HTTP is significantly different
from the corresponding definition in MIME, where it is an optional
field used within the "message/external-body" content-type.
8.3. Host
The "Host" header field in a request provides the host and port
information from the target resource's URI, enabling the origin
server to distinguish between resources while servicing requests for
multiple host names on a single IP address. Since the Host field-
value is critical information for handling a request, it SHOULD be
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sent as the first header field following the Request-Line.
Host = uri-host [ ":" port ] ; Section 2.7.1
A client MUST send a Host header field in all HTTP/1.1 request
messages. If the target resource's URI includes an authority
component, then the Host field-value MUST be identical to that
authority component after excluding any userinfo (Section 2.7.1). If
the authority component is missing or undefined for the target
resource's URI, then the Host header field MUST be sent with an empty
field-value.
For example, a GET request to the origin server for
<http://www.example.org/pub/WWW/> would begin with:
GET /pub/WWW/ HTTP/1.1
Host: www.example.org
The Host header field MUST be sent in an HTTP/1.1 request even if the
request-target is in the form of an absolute-URI, since this allows
the Host information to be forwarded through ancient HTTP/1.0 proxies
that might not have implemented Host.
When an HTTP/1.1 proxy receives a request with a request-target in
the form of an absolute-URI, the proxy MUST ignore the received Host
header field (if any) and instead replace it with the host
information of the request-target. When a proxy forwards a request,
it MUST generate the Host header field based on the received
absolute-URI rather than the received Host.
Since the Host header field acts as an application-level routing
mechanism, it is a frequent target for malware seeking to poison a
shared cache or redirect a request to an unintended server. An
interception proxy is particularly vulnerable if it relies on the
Host header field value for redirecting requests to internal servers,
or for use as a cache key in a shared cache, without first verifying
that the intercepted connection is targeting a valid IP address for
that host.
A server MUST respond with a 400 (Bad Request) status code to any
HTTP/1.1 request message that lacks a Host header field and to any
request message that contains more than one Host header field or a
Host header field with an invalid field-value.
See Sections 4.2 and A.1.1 for other requirements relating to Host.
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8.4. TE
The "TE" header field indicates what extension transfer-codings it is
willing to accept in the response, and whether or not it is willing
to accept trailer fields in a chunked transfer-coding.
Its value consists of the keyword "trailers" and/or a comma-separated
list of extension transfer-coding names with optional accept
parameters (as described in Section 5.1).
TE = #t-codings
t-codings = "trailers" / ( transfer-extension [ te-params ] )
te-params = OWS ";" OWS "q=" qvalue *( te-ext )
te-ext = OWS ";" OWS token [ "=" word ]
The presence of the keyword "trailers" indicates that the client is
willing to accept trailer fields in a chunked transfer-coding, as
defined in Section 5.1.1. This keyword is reserved for use with
transfer-coding values even though it does not itself represent a
transfer-coding.
Examples of its use are:
TE: deflate
TE:
TE: trailers, deflate;q=0.5
The TE header field only applies to the immediate connection.
Therefore, the keyword MUST be supplied within a Connection header
field (Section 8.1) whenever TE is present in an HTTP/1.1 message.
A server tests whether a transfer-coding is acceptable, according to
a TE field, using these rules:
1. The "chunked" transfer-coding is always acceptable. If the
keyword "trailers" is listed, the client indicates that it is
willing to accept trailer fields in the chunked response on
behalf of itself and any downstream clients. The implication is
that, if given, the client is stating that either all downstream
clients are willing to accept trailer fields in the forwarded
response, or that it will attempt to buffer the response on
behalf of downstream recipients.
Note: HTTP/1.1 does not define any means to limit the size of a
chunked response such that a client can be assured of buffering
the entire response.
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2. If the transfer-coding being tested is one of the transfer-
codings listed in the TE field, then it is acceptable unless it
is accompanied by a qvalue of 0. (As defined in Section 5.3, a
qvalue of 0 means "not acceptable".)
3. If multiple transfer-codings are acceptable, then the acceptable
transfer-coding with the highest non-zero qvalue is preferred.
The "chunked" transfer-coding always has a qvalue of 1.
If the TE field-value is empty or if no TE field is present, the only
transfer-coding is "chunked". A message with no transfer-coding is
always acceptable.
8.5. Trailer
The "Trailer" header field indicates that the given set of header
fields is present in the trailer of a message encoded with chunked
transfer-coding.
Trailer = 1#field-name
An HTTP/1.1 message SHOULD include a Trailer header field in a
message using chunked transfer-coding with a non-empty trailer.
Doing so allows the recipient to know which header fields to expect
in the trailer.
If no Trailer header field is present, the trailer SHOULD NOT include
any header fields. See Section 5.1.1 for restrictions on the use of
trailer fields in a "chunked" transfer-coding.
Message header fields listed in the Trailer header field MUST NOT
include the following header fields:
o Transfer-Encoding
o Content-Length
o Trailer
8.6. Transfer-Encoding
The "Transfer-Encoding" header field indicates what transfer-codings
(if any) have been applied to the message body. It differs from
Content-Encoding (Section 2.2 of [Part3]) in that transfer-codings
are a property of the message (and therefore are removed by
intermediaries), whereas content-codings are not.
Transfer-Encoding = 1#transfer-coding
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Transfer-codings are defined in Section 5.1. An example is:
Transfer-Encoding: chunked
If multiple encodings have been applied to a representation, the
transfer-codings MUST be listed in the order in which they were
applied. Additional information about the encoding parameters MAY be
provided by other header fields not defined by this specification.
Many older HTTP/1.0 applications do not understand the Transfer-
Encoding header field.
8.7. Upgrade
The "Upgrade" header field allows the client to specify what
additional communication protocols it would like to use, if the
server chooses to switch protocols. Servers can use it to indicate
what protocols they are willing to switch to.
Upgrade = 1#product
For example,
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
The Upgrade header field is intended to provide a simple mechanism
for transition from HTTP/1.1 to some other, incompatible protocol.
It does so by allowing the client to advertise its desire to use
another protocol, such as a later version of HTTP with a higher major
version number, even though the current request has been made using
HTTP/1.1. This eases the difficult transition between incompatible
protocols by allowing the client to initiate a request in the more
commonly supported protocol while indicating to the server that it
would like to use a "better" protocol if available (where "better" is
determined by the server, possibly according to the nature of the
request method or target resource).
The Upgrade header field only applies to switching application-layer
protocols upon the existing transport-layer connection. Upgrade
cannot be used to insist on a protocol change; its acceptance and use
by the server is optional. The capabilities and nature of the
application-layer communication after the protocol change is entirely
dependent upon the new protocol chosen, although the first action
after changing the protocol MUST be a response to the initial HTTP
request containing the Upgrade header field.
The Upgrade header field only applies to the immediate connection.
Therefore, the upgrade keyword MUST be supplied within a Connection
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header field (Section 8.1) whenever Upgrade is present in an HTTP/1.1
message.
The Upgrade header field cannot be used to indicate a switch to a
protocol on a different connection. For that purpose, it is more
appropriate to use a 3xx redirection response (Section 7.3 of
[Part2]).
Servers MUST include the "Upgrade" header field in 101 (Switching
Protocols) responses to indicate which protocol(s) are being switched
to, and MUST include it in 426 (Upgrade Required) responses to
indicate acceptable protocols to upgrade to. Servers MAY include it
in any other response to indicate that they are willing to upgrade to
one of the specified protocols.
This specification only defines the protocol name "HTTP" for use by
the family of Hypertext Transfer Protocols, as defined by the HTTP
version rules of Section 2.6 and future updates to this
specification. Additional tokens can be registered with IANA using
the registration procedure defined below.
8.7.1. Upgrade Token Registry
The HTTP Upgrade Token Registry defines the name space for product
tokens used to identify protocols in the Upgrade header field. Each
registered token is associated with contact information and an
optional set of specifications that details how the connection will
be processed after it has been upgraded.
Registrations are allowed on a First Come First Served basis as
described in Section 4.1 of [RFC5226]. The specifications need not
be IETF documents or be subject to IESG review. Registrations are
subject to the following rules:
1. A token, once registered, stays registered forever.
2. The registration MUST name a responsible party for the
registration.
3. The registration MUST name a point of contact.
4. The registration MAY name a set of specifications associated with
that token. Such specifications need not be publicly available.
5. The responsible party MAY change the registration at any time.
The IANA will keep a record of all such changes, and make them
available upon request.
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6. The responsible party for the first registration of a "product"
token MUST approve later registrations of a "version" token
together with that "product" token before they can be registered.
7. If absolutely required, the IESG MAY reassign the responsibility
for a token. This will normally only be used in the case when a
responsible party cannot be contacted.
8.8. Via
The "Via" header field MUST be sent by a proxy or gateway to indicate
the intermediate protocols and recipients between the user agent and
the server on requests, and between the origin server and the client
on responses. It is analogous to the "Received" field used by email
systems (Section 3.6.7 of [RFC5322]) and is intended to be used for
tracking message forwards, avoiding request loops, and identifying
the protocol capabilities of all senders along the request/response
chain.
Via = 1#( received-protocol RWS received-by
[ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
protocol-name = token
protocol-version = token
received-by = ( uri-host [ ":" port ] ) / pseudonym
pseudonym = token
The received-protocol indicates the protocol version of the message
received by the server or client along each segment of the request/
response chain. The received-protocol version is appended to the Via
field value when the message is forwarded so that information about
the protocol capabilities of upstream applications remains visible to
all recipients.
The protocol-name is excluded if and only if it would be "HTTP". The
received-by field is normally the host and optional port number of a
recipient server or client that subsequently forwarded the message.
However, if the real host is considered to be sensitive information,
it MAY be replaced by a pseudonym. If the port is not given, it MAY
be assumed to be the default port of the received-protocol.
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each recipient MUST append its information
such that the end result is ordered according to the sequence of
forwarding applications.
Comments MAY be used in the Via header field to identify the software
of each recipient, analogous to the User-Agent and Server header
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fields. However, all comments in the Via field are optional and MAY
be removed by any recipient prior to forwarding the message.
For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which
completes the request by forwarding it to the origin server at
www.example.com. The request received by www.example.com would then
have the following Via header field:
Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
A proxy or gateway used as a portal through a network firewall SHOULD
NOT forward the names and ports of hosts within the firewall region
unless it is explicitly enabled to do so. If not enabled, the
received-by host of any host behind the firewall SHOULD be replaced
by an appropriate pseudonym for that host.
For organizations that have strong privacy requirements for hiding
internal structures, a proxy or gateway MAY combine an ordered
subsequence of Via header field entries with identical received-
protocol values into a single such entry. For example,
Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
could be collapsed to
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
Senders SHOULD NOT combine multiple entries unless they are all under
the same organizational control and the hosts have already been
replaced by pseudonyms. Senders MUST NOT combine entries which have
different received-protocol values.
9. IANA Considerations
9.1. Header Field Registration
The Message Header Field Registry located at <http://www.iana.org/
assignments/message-headers/message-header-index.html> shall be
updated with the permanent registrations below (see [RFC3864]):
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+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Connection | http | standard | Section 8.1 |
| Content-Length | http | standard | Section 8.2 |
| Host | http | standard | Section 8.3 |
| TE | http | standard | Section 8.4 |
| Trailer | http | standard | Section 8.5 |
| Transfer-Encoding | http | standard | Section 8.6 |
| Upgrade | http | standard | Section 8.7 |
| Via | http | standard | Section 8.8 |
+-------------------+----------+----------+-------------+
Furthermore, the header field name "Close" shall be registered as
"reserved", as its use as HTTP header field would be in conflict with
the use of the "close" connection option for the "Connection" header
field (Section 8.1).
+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Close | http | reserved | Section 9.1 |
+-------------------+----------+----------+-------------+
The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force".
9.2. URI Scheme Registration
The entries for the "http" and "https" URI Schemes in the registry
located at <http://www.iana.org/assignments/uri-schemes.html> shall
be updated to point to Sections 2.7.1 and 2.7.2 of this document (see
[RFC4395]).
9.3. Internet Media Type Registrations
This document serves as the specification for the Internet media
types "message/http" and "application/http". The following is to be
registered with IANA (see [RFC4288]).
9.3.1. Internet Media Type message/http
The message/http type can be used to enclose a single HTTP request or
response message, provided that it obeys the MIME restrictions for
all "message" types regarding line length and encodings.
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Type name: message
Subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed message (e.g.,
"1.1"). If not present, the version can be determined from the
first line of the body.
msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first line of the
body.
Encoding considerations: only "7bit", "8bit", or "binary" are
permitted
Security considerations: none
Interoperability considerations: none
Published specification: This specification (see Section 9.3.1).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
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9.3.2. Internet Media Type application/http
The application/http type can be used to enclose a pipeline of one or
more HTTP request or response messages (not intermixed).
Type name: application
Subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed messages (e.g.,
"1.1"). If not present, the version can be determined from the
first line of the body.
msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first line of the
body.
Encoding considerations: HTTP messages enclosed by this type are in
"binary" format; use of an appropriate Content-Transfer-Encoding
is required when transmitted via E-mail.
Security considerations: none
Interoperability considerations: none
Published specification: This specification (see Section 9.3.2).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
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Restrictions on usage: none
Author/Change controller: IESG
9.4. Transfer Coding Registry
The registration procedure for HTTP Transfer Codings is now defined
by Section 5.1.3 of this document.
The HTTP Transfer Codings Registry located at
<http://www.iana.org/assignments/http-parameters> shall be updated
with the registrations below:
+----------+--------------------------------------+-----------------+
| Name | Description | Reference |
+----------+--------------------------------------+-----------------+
| chunked | Transfer in a series of chunks | Section 5.1.1 |
| compress | UNIX "compress" program method | Section 5.1.2.1 |
| deflate | "deflate" compression mechanism | Section 5.1.2.2 |
| | ([RFC1951]) used inside the "zlib" | |
| | data format ([RFC1950]) | |
| gzip | Same as GNU zip [RFC1952] | Section 5.1.2.3 |
+----------+--------------------------------------+-----------------+
9.5. Upgrade Token Registration
The registration procedure for HTTP Upgrade Tokens -- previously
defined in Section 7.2 of [RFC2817] -- is now defined by
Section 8.7.1 of this document.
The HTTP Status Code Registry located at
<http://www.iana.org/assignments/http-upgrade-tokens/> shall be
updated with the registration below:
+-------+---------------------------+-------------------------------+
| Value | Description | Reference |
+-------+---------------------------+-------------------------------+
| HTTP | Hypertext Transfer | Section 2.6 of this |
| | Protocol | specification |
+-------+---------------------------+-------------------------------+
10. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
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10.1. Personal Information
HTTP clients are often privy to large amounts of personal information
(e.g., the user's name, location, mail address, passwords, encryption
keys, etc.), and SHOULD be very careful to prevent unintentional
leakage of this information. We very strongly recommend that a
convenient interface be provided for the user to control
dissemination of such information, and that designers and
implementors be particularly careful in this area. History shows
that errors in this area often create serious security and/or privacy
problems and generate highly adverse publicity for the implementor's
company.
10.2. Abuse of Server Log Information
A server is in the position to save personal data about a user's
requests which might identify their reading patterns or subjects of
interest. This information is clearly confidential in nature and its
handling can be constrained by law in certain countries. People
using HTTP to provide data are responsible for ensuring that such
material is not distributed without the permission of any individuals
that are identifiable by the published results.
10.3. Attacks Based On File and Path Names
Implementations of HTTP origin servers SHOULD be careful to restrict
the documents returned by HTTP requests to be only those that were
intended by the server administrators. If an HTTP server translates
HTTP URIs directly into file system calls, the server MUST take
special care not to serve files that were not intended to be
delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
other operating systems use ".." as a path component to indicate a
directory level above the current one. On such a system, an HTTP
server MUST disallow any such construct in the request-target if it
would otherwise allow access to a resource outside those intended to
be accessible via the HTTP server. Similarly, files intended for
reference only internally to the server (such as access control
files, configuration files, and script code) MUST be protected from
inappropriate retrieval, since they might contain sensitive
information. Experience has shown that minor bugs in such HTTP
server implementations have turned into security risks.
10.4. DNS-related Attacks
HTTP clients rely heavily on the Domain Name Service (DNS), and are
thus generally prone to security attacks based on the deliberate
misassociation of IP addresses and DNS names not protected by DNSSec.
Clients need to be cautious in assuming the validity of an IP number/
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DNS name association unless the response is protected by DNSSec
([RFC4033]).
10.5. Proxies and Caching
By their very nature, HTTP proxies are men-in-the-middle, and
represent an opportunity for man-in-the-middle attacks. Compromise
of the systems on which the proxies run can result in serious
security and privacy problems. Proxies have access to security-
related information, personal information about individual users and
organizations, and proprietary information belonging to users and
content providers. A compromised proxy, or a proxy implemented or
configured without regard to security and privacy considerations,
might be used in the commission of a wide range of potential attacks.
Proxy operators need to protect the systems on which proxies run as
they would protect any system that contains or transports sensitive
information. In particular, log information gathered at proxies
often contains highly sensitive personal information, and/or
information about organizations. Log information needs to be
carefully guarded, and appropriate guidelines for use need to be
developed and followed. (Section 10.2).
Proxy implementors need to consider the privacy and security
implications of their design and coding decisions, and of the
configuration options they provide to proxy operators (especially the
default configuration).
Users of a proxy need to be aware that proxies are no trustworthier
than the people who run them; HTTP itself cannot solve this problem.
The judicious use of cryptography, when appropriate, might suffice to
protect against a broad range of security and privacy attacks. Such
cryptography is beyond the scope of the HTTP/1.1 specification.
10.6. Protocol Element Size Overflows
Because HTTP uses mostly textual, character-delimited fields,
attackers can overflow buffers in implementations, and/or perform a
Denial of Service against implementations that accept fields with
unlimited lengths.
To promote interoperability, this specification makes specific
recommendations for size limits on request-targets (Section 3.1.1.2)
and blocks of header fields (Section 3.2). These are minimum
recommendations, chosen to be supportable even by implementations
with limited resources; it is expected that most implementations will
choose substantially higher limits.
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This specification also provides a way for servers to reject messages
that have request-targets that are too long (Section 7.4.15 of
[Part2]) or request entities that are too large (Section 7.4 of
[Part2]).
Other fields (including but not limited to request methods, response
status phrases, header field-names, and body chunks) SHOULD be
limited by implementations carefully, so as to not impede
interoperability.
10.7. Denial of Service Attacks on Proxies
They exist. They are hard to defend against. Research continues.
Beware.
11. Acknowledgments
This document revision builds on the work that went into RFC 2616 and
its predecessors. See Section 16 of [RFC2616] for detailed
acknowledgements.
Since 1999, many contributors have helped by reporting bugs, asking
smart questions, drafting and reviewing text, and discussing open
issues:
Adam Barth, Adam Roach, Addison Phillips, Adrian Chadd, Adrien de
Croy, Alan Ford, Alan Ruttenberg, Albert Lunde, Alex Rousskov, Alexey
Melnikov, Alisha Smith, Amichai Rothman, Amit Klein, Amos Jeffries,
Andreas Maier, Andreas Petersson, Anne van Kesteren, Anthony Bryan,
Asbjorn Ulsberg, Balachander Krishnamurthy, Barry Leiba, Ben Laurie,
Benjamin Niven-Jenkins, Bil Corry, Bill Burke, Bjoern Hoehrmann, Bob
Scheifler, Boris Zbarsky, Brett Slatkin, Brian Kell, Brian McBarron,
Brian Pane, Brian Smith, Bryce Nesbitt, Cameron Heavon-Jones, Carl
Kugler, Charles Fry, Chris Newman, Cyrus Daboo, Dale Robert Anderson,
Dan Winship, Daniel Stenberg, Dave Cridland, Dave Crocker, Dave
Kristol, David Booth, David Singer, David W. Morris, Diwakar Shetty,
Dmitry Kurochkin, Drummond Reed, Duane Wessels, Edward Lee, Eliot
Lear, Eran Hammer-Lahav, Eric D. Williams, Eric J. Bowman, Eric
Lawrence, Erik Aronesty, Florian Weimer, Frank Ellermann, Fred Bohle,
Geoffrey Sneddon, Gervase Markham, Greg Wilkins, Harald Tveit
Alvestrand, Harry Halpin, Helge Hess, Henrik Nordstrom, Henry S.
Thompson, Henry Story, Herbert van de Sompel, Howard Melman, Hugo
Haas, Ian Hickson, Ingo Struck, J. Ross Nicoll, James H. Manger,
James Lacey, James M. Snell, Jamie Lokier, Jan Algermissen, Jeff
Hodges (for coming up with the term 'effective Request-URI'), Jeff
Walden, Jim Luther, Joe D. Williams, Joe Gregorio, Joe Orton, John C.
Klensin, John C. Mallery, John Cowan, John Kemp, John Panzer, John
Schneider, John Stracke, Jonas Sicking, Jonathan Moore, Jonathan
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Rees, Jordi Ros, Joris Dobbelsteen, Josh Cohen, Julien Pierre,
Jungshik Shin, Justin Chapweske, Justin Erenkrantz, Justin James,
Kalvinder Singh, Karl Dubost, Keith Hoffman, Keith Moore, Koen
Holtman, Konstantin Voronkov, Kris Zyp, Lisa Dusseault, Maciej
Stachowiak, Marc Schneider, Marc Slemko, Mark Baker, Mark Nottingham
(Working Group chair), Mark Pauley, Martin J. Duerst, Martin Thomson,
Matt Lynch, Matthew Cox, Max Clark, Michael Burrows, Michael
Hausenblas, Mike Amundsen, Mike Kelly, Mike Schinkel, Miles Sabin,
Mykyta Yevstifeyev, Nathan Rixham, Nicholas Shanks, Nico Williams,
Nicolas Alvarez, Noah Slater, Pablo Castro, Pat Hayes, Patrick R.
McManus, Paul E. Jones, Paul Hoffman, Paul Marquess, Peter Saint-
Andre, Peter Watkins, Phil Archer, Phillip Hallam-Baker, Poul-Henning
Kamp, Preethi Natarajan, Reto Bachmann-Gmuer, Richard Cyganiak,
Robert Brewer, Robert Collins, Robert O'Callahan, Robert Olofsson,
Robert Sayre, Robert Siemer, Robert de Wilde, Roberto Javier Godoy,
Ronny Widjaja, S. Mike Dierken, Salvatore Loreto, Sam Johnston, Sam
Ruby, Scott Lawrence (for maintaining the original issues list), Sean
B. Palmer, Shane McCarron, Stefan Eissing, Stefan Tilkov, Stefanos
Harhalakis, Stephane Bortzmeyer, Stuart Williams, Subbu Allamaraju,
Sylvain Hellegouarch, Tapan Divekar, Thomas Broyer, Thomas Nordin,
Thomas Roessler, Tim Morgan, Tim Olsen, Travis Snoozy, Tyler Close,
Vincent Murphy, Wenbo Zhu, Werner Baumann, Wilbur Streett, Wilfredo
Sanchez Vega, William A. Rowe Jr., William Chan, Willy Tarreau,
Xiaoshu Wang, Yaron Goland, Yngve Nysaeter Pettersen, Yogesh Bang,
Yutaka Oiwa, and Zed A. Shaw.
12. References
12.1. Normative References
[ISO-8859-1] International Organization for Standardization,
"Information technology -- 8-bit single-byte coded
graphic character sets -- Part 1: Latin alphabet No.
1", ISO/IEC 8859-1:1998, 1998.
[Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y.,
Ed., and J. Reschke, Ed., "HTTP/1.1, part 2: Message
Semantics", draft-ietf-httpbis-p2-semantics-18 (work in
progress), January 2012.
[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-18 (work in progress),
January 2012.
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[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-18 (work in progress),
January 2012.
[RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data
Format Specification version 3.3", RFC 1950, May 1996.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format
Specification version 1.3", RFC 1951, May 1996.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and
G. Randers-Pehrson, "GZIP file format specification
version 4.3", RFC 1952, May 1996.
[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.
[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
12.2. Informative References
[Kri2001] Kristol, D., "HTTP Cookies: Standards, Privacy, and
Politics", ACM Transactions on Internet Technology Vol.
1, #2, November 2001,
<http://arxiv.org/abs/cs.SE/0105018>.
[Nie1997] Frystyk, H., Gettys, J., Prud'hommeaux, E., Lie, H.,
and C. Lilley, "Network Performance Effects of
HTTP/1.1, CSS1, and PNG", ACM Proceedings of the ACM
SIGCOMM '97 conference on Applications, technologies,
architectures, and protocols for computer communication
SIGCOMM '97, September 1997,
<http://doi.acm.org/10.1145/263105.263157>.
[Pad1995] Padmanabhan, V. and J. Mogul, "Improving HTTP Latency",
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Internet-Draft HTTP/1.1, Part 1 January 2012
Computer Networks and ISDN Systems v. 28, pp. 25-35,
December 1995,
<http://portal.acm.org/citation.cfm?id=219094>.
[RFC1919] Chatel, M., "Classical versus Transparent IP Proxies",
RFC 1919, March 1996.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen,
"Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945,
May 1996.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
Extensions) Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996.
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and
T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2068, January 1997.
[RFC2145] Mogul, J., Fielding, R., Gettys, J., and H. Nielsen,
"Use and Interpretation of HTTP Version Numbers",
RFC 2145, May 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
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.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC2965] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, October 2000.
[RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC 3040,
January 2001.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Fielding, et al. Expires July 7, 2012 [Page 68]
Internet-Draft HTTP/1.1, Part 1 January 2012
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications
and Registration Procedures", BCP 13, RFC 4288,
December 2005.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines
and Registration Procedures for New URI Schemes",
BCP 115, RFC 4395, February 2006.
[RFC4559] Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based
Kerberos and NTLM HTTP Authentication in Microsoft
Windows", RFC 4559, June 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
[Spe] Spero, S., "Analysis of HTTP Performance Problems",
<http://sunsite.unc.edu/mdma-release/http-prob.html>.
[Tou1998] Touch, J., Heidemann, J., and K. Obraczka, "Analysis of
HTTP Performance", ISI Research Report ISI/RR-98-463,
Aug 1998, <http://www.isi.edu/touch/pubs/http-perf96/>.
(original report dated Aug. 1996)
Appendix A. HTTP Version History
HTTP has been in use by the World-Wide Web global information
initiative since 1990. The first version of HTTP, later referred to
as HTTP/0.9, was a simple protocol for hypertext data transfer across
the Internet with only a single request method (GET) and no metadata.
HTTP/1.0, as defined by [RFC1945], added a range of request methods
and MIME-like messaging that could include metadata about the data
transferred and modifiers on the request/response semantics.
However, HTTP/1.0 did not sufficiently take into consideration the
effects of hierarchical proxies, caching, the need for persistent
connections, or name-based virtual hosts. The proliferation of
incompletely-implemented applications calling themselves "HTTP/1.0"
further necessitated a protocol version change in order for two
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communicating applications to determine each other's true
capabilities.
HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
requirements that enable reliable implementations, adding only those
new features that will either be safely ignored by an HTTP/1.0
recipient or only sent when communicating with a party advertising
compliance with HTTP/1.1.
It is beyond the scope of a protocol specification to mandate
compliance with previous versions. HTTP/1.1 was deliberately
designed, however, to make supporting previous versions easy. We
would expect a general-purpose HTTP/1.1 server to understand any
valid request in the format of HTTP/1.0 and respond appropriately
with an HTTP/1.1 message that only uses features understood (or
safely ignored) by HTTP/1.0 clients. Likewise, would expect an
HTTP/1.1 client to understand any valid HTTP/1.0 response.
Since HTTP/0.9 did not support header fields in a request, there is
no mechanism for it to support name-based virtual hosts (selection of
resource by inspection of the Host header field). Any server that
implements name-based virtual hosts ought to disable support for
HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in fact,
badly constructed HTTP/1.x requests wherein a buggy client failed to
properly encode linear whitespace found in a URI reference and placed
in the request-target.
A.1. Changes from HTTP/1.0
This section summarizes major differences between versions HTTP/1.0
and HTTP/1.1.
A.1.1. Multi-homed Web Servers
The requirements that clients and servers support the Host header
field (Section 8.3), report an error if it is missing from an
HTTP/1.1 request, and accept absolute URIs (Section 3.1.1.2) are
among the most important changes defined by HTTP/1.1.
Older HTTP/1.0 clients assumed a one-to-one relationship of IP
addresses and servers; there was no other established mechanism for
distinguishing the intended server of a request than the IP address
to which that request was directed. The Host header field was
introduced during the development of HTTP/1.1 and, though it was
quickly implemented by most HTTP/1.0 browsers, additional
requirements were placed on all HTTP/1.1 requests in order to ensure
complete adoption. At the time of this writing, most HTTP-based
services are dependent upon the Host header field for targeting
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requests.
A.1.2. Keep-Alive Connections
In HTTP/1.0, each connection is established by the client prior to
the request and closed by the server after sending the response.
However, some implementations implement the explicitly negotiated
("Keep-Alive") version of persistent connections described in Section
19.7.1 of [RFC2068].
Some clients and servers might wish to be compatible with these
previous approaches to persistent connections, by explicitly
negotiating for them with a "Connection: keep-alive" request header
field. However, some experimental implementations of HTTP/1.0
persistent connections are faulty; for example, if a HTTP/1.0 proxy
server doesn't understand Connection, it will erroneously forward
that header to the next inbound server, which would result in a hung
connection.
One attempted solution was the introduction of a Proxy-Connection
header, targeted specifically at proxies. In practice, this was also
unworkable, because proxies are often deployed in multiple layers,
bringing about the same problem discussed above.
As a result, clients are encouraged not to send the Proxy-Connection
header in any requests.
Clients are also encouraged to consider the use of Connection: keep-
alive in requests carefully; while they can enable persistent
connections with HTTP/1.0 servers, clients using them need will need
to monitor the connection for "hung" requests (which indicate that
the client ought stop sending the header), and this mechanism ought
not be used by clients at all when a proxy is being used.
A.2. Changes from RFC 2616
Empty list elements in list productions have been deprecated.
(Section 1.2.1)
Rules about implicit linear whitespace between certain grammar
productions have been removed; now it's only allowed when
specifically pointed out in the ABNF. (Section 1.2.2)
Clarify that the string "HTTP" in the HTTP-Version ABFN production is
case sensitive. Restrict the version numbers to be single digits due
to the fact that implementations are known to handle multi-digit
version numbers incorrectly. (Section 2.6)
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Require that invalid whitespace around field-names be rejected.
(Section 3.2)
The NUL octet is no longer allowed in comment and quoted-string text.
The quoted-pair rule no longer allows escaping control characters
other than HTAB. Non-ASCII content in header fields and reason
phrase has been obsoleted and made opaque (the TEXT rule was
removed). (Section 3.2.3)
Require recipients to handle bogus Content-Length header fields as
errors. (Section 3.3)
Remove reference to non-existent identity transfer-coding value
tokens. (Sections 3.3 and 5.1)
Update use of abs_path production from RFC 1808 to the path-absolute
+ query components of RFC 3986. State that the asterisk form is
allowed for the OPTIONS request method only. (Section 3.1.1.2)
Clarification that the chunk length does not include the count of the
octets in the chunk header and trailer. Furthermore disallowed line
folding in chunk extensions. (Section 5.1.1)
Remove hard limit of two connections per server. Remove requirement
to retry a sequence of requests as long it was idempotent. Remove
requirements about when servers are allowed to close connections
prematurely. (Section 6.1.4)
Remove requirement to retry requests under certain cirumstances when
the server prematurely closes the connection. (Section 6.2)
Change ABNF productions for header fields to only define the field
value. (Section 8)
Clarify exactly when close connection options must be sent.
(Section 8.1)
Define the semantics of the "Upgrade" header field in responses other
than 101 (this was incorporated from [RFC2817]). (Section 8.7)
Appendix B. Collected ABNF
BWS = OWS
Chunked-Body = *chunk last-chunk trailer-part CRLF
Connection = *( "," OWS ) connection-token *( OWS "," [ OWS
connection-token ] )
Content-Length = 1*DIGIT
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HTTP-Prot-Name = %x48.54.54.50 ; HTTP
HTTP-Version = HTTP-Prot-Name "/" DIGIT "." DIGIT
HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
]
Host = uri-host [ ":" port ]
Method = token
OWS = *( SP / HTAB / obs-fold )
RWS = 1*( SP / HTAB / obs-fold )
Reason-Phrase = *( HTAB / SP / VCHAR / obs-text )
Request-Line = Method SP request-target SP HTTP-Version CRLF
Status-Code = 3DIGIT
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
Trailer = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
transfer-coding ] )
URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
Upgrade = *( "," OWS ) product *( OWS "," [ OWS product ] )
Via = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
*( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
)
absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
attribute = token
authority = <authority, defined in [RFC3986], Section 3.2>
chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
chunk-data = 1*OCTET
chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token / quoted-str-nf
chunk-size = 1*HEXDIG
comment = "(" *( ctext / quoted-cpair / comment ) ")"
connection-token = token
ctext = OWS / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
field-content = *( HTAB / SP / VCHAR / obs-text )
field-name = token
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field-value = *( field-content / obs-fold )
header-field = field-name ":" OWS field-value BWS
http-URI = "http://" authority path-abempty [ "?" query ]
https-URI = "https://" authority path-abempty [ "?" query ]
last-chunk = 1*"0" [ chunk-ext ] CRLF
message-body = *OCTET
obs-fold = CRLF ( SP / HTAB )
obs-text = %x80-FF
partial-URI = relative-part [ "?" query ]
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
port = <port, defined in [RFC3986], Section 3.2.3>
product = token [ "/" product-version ]
product-version = token
protocol-name = token
protocol-version = token
pseudonym = token
qdtext = OWS / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
qdtext-nf = HTAB / SP / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
query = <query, defined in [RFC3986], Section 3.4>
quoted-cpair = "\" ( HTAB / SP / VCHAR / obs-text )
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
received-by = ( uri-host [ ":" port ] ) / pseudonym
received-protocol = [ protocol-name "/" ] protocol-version
relative-part = <relative-part, defined in [RFC3986], Section 4.2>
request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
/ authority
special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
start-line = Request-Line / Status-Line
t-codings = "trailers" / ( transfer-extension [ te-params ] )
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tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
"^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
te-ext = OWS ";" OWS token [ "=" word ]
te-params = OWS ";" OWS "q=" qvalue *te-ext
token = 1*tchar
trailer-part = *( header-field CRLF )
transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
transfer-parameter = attribute BWS "=" BWS value
uri-host = <host, defined in [RFC3986], Section 3.2.2>
value = word
word = token / quoted-string
ABNF diagnostics:
; Chunked-Body defined but not used
; Connection defined but not used
; Content-Length defined but not used
; HTTP-message defined but not used
; Host defined but not used
; TE defined but not used
; Trailer defined but not used
; Transfer-Encoding defined but not used
; URI-reference defined but not used
; Upgrade defined but not used
; Via defined but not used
; http-URI defined but not used
; https-URI defined but not used
; partial-URI defined but not used
; special 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-p1-messaging-00
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/1>: "HTTP Version
should be case sensitive"
(<http://purl.org/NET/http-errata#verscase>)
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/2>: "'unsafe'
characters" (<http://purl.org/NET/http-errata#unsafe-uri>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/3>: "Chunk Size
Definition" (<http://purl.org/NET/http-errata#chunk-size>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/4>: "Message Length"
(<http://purl.org/NET/http-errata#msg-len-chars>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/8>: "Media Type
Registrations" (<http://purl.org/NET/http-errata#media-reg>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/11>: "URI includes
query" (<http://purl.org/NET/http-errata#uriquery>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/15>: "No close on
1xx responses" (<http://purl.org/NET/http-errata#noclose1xx>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/16>: "Remove
'identity' token references"
(<http://purl.org/NET/http-errata#identity>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/26>: "Import query
BNF"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/31>: "qdtext BNF"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
Informative references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/42>: "RFC2606
Compliance"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/45>: "RFC977
reference"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700
references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/47>: "inconsistency
in date format explanation"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/48>: "Date reference
typo"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/65>: "Informative
references"
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/66>: "ISO-8859-1
Reference"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/86>: "Normative up-
to-date references"
Other changes:
o Update media type registrations to use RFC4288 template.
o Use names of RFC4234 core rules DQUOTE and HTAB, fix broken ABNF
for chunk-data (work in progress on
<http://tools.ietf.org/wg/httpbis/trac/ticket/36>)
C.3. Since draft-ietf-httpbis-p1-messaging-01
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/19>: "Bodies on GET
(and other) requests"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating to
RFC4288"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/57>: "Status Code
and Reason Phrase"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/82>: "rel_path not
used"
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Get rid of duplicate BNF rule names ("host" -> "uri-host",
"trailer" -> "trailer-part").
o Avoid underscore character in rule names ("http_URL" -> "http-
URL", "abs_path" -> "path-absolute").
o Add rules for terms imported from URI spec ("absoluteURI",
"authority", "path-absolute", "port", "query", "relativeURI",
"host) -- these will have to be updated when switching over to
RFC3986.
o Synchronize core rules with RFC5234.
o Get rid of prose rules that span multiple lines.
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o Get rid of unused rules LOALPHA and UPALPHA.
o Move "Product Tokens" section (back) into Part 1, as "token" is
used in the definition of the Upgrade header field.
o Add explicit references to BNF syntax and rules imported from
other parts of the specification.
o Rewrite prose rule "token" in terms of "tchar", rewrite prose rule
"TEXT".
C.4. Since draft-ietf-httpbis-p1-messaging-02
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/51>: "HTTP-date vs.
rfc1123-date"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/64>: "WS in quoted-
pair"
Ongoing work on IANA Message Header Field Registration
(<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):
o Reference RFC 3984, and update header field registrations for
headers defined in this document.
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Replace string literals when the string really is case-sensitive
(HTTP-Version).
C.5. Since draft-ietf-httpbis-p1-messaging-03
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/28>: "Connection
closing"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/97>: "Move
registrations and registry information to IANA Considerations"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/120>: "need new URL
for PAD1995 reference"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/127>: "IANA
Considerations: update HTTP URI scheme registration"
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/128>: "Cite HTTPS
URI scheme definition"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/129>: "List-type
headers vs Set-Cookie"
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Replace string literals when the string really is case-sensitive
(HTTP-Date).
o Replace HEX by HEXDIG for future consistence with RFC 5234's core
rules.
C.6. Since draft-ietf-httpbis-p1-messaging-04
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/34>: "Out-of-date
reference for URIs"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/132>: "RFC 2822 is
updated by RFC 5322"
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Use "/" instead of "|" for alternatives.
o Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
o Only reference RFC 5234's core rules.
o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
o Rewrite ABNFs to spell out whitespace rules, factor out header
field value format definitions.
C.7. Since draft-ietf-httpbis-p1-messaging-05
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/30>: "Header LWS"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/52>: "Sort 1.3
Terminology"
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/63>: "RFC2047
encoded words"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/74>: "Character
Encodings in TEXT"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/77>: "Line Folding"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/83>: "OPTIONS * and
proxies"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/94>: "Reason-Phrase
BNF"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/111>: "Use of TEXT"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/118>: "Join
"Differences Between HTTP Entities and RFC 2045 Entities"?"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/134>: "RFC822
reference left in discussion of date formats"
Final work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Rewrite definition of list rules, deprecate empty list elements.
o Add appendix containing collected and expanded ABNF.
Other changes:
o Rewrite introduction; add mostly new Architecture Section.
o Move definition of quality values from Part 3 into Part 1; make TE
request header field grammar independent of accept-params (defined
in Part 3).
C.8. Since draft-ietf-httpbis-p1-messaging-06
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/161>: "base for
numeric protocol elements"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/162>: "comment ABNF"
Partly resolved issues:
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/88>: "205 Bodies"
(took out language that implied that there might be methods for
which a request body MUST NOT be included)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/163>: "editorial
improvements around HTTP-date"
C.9. Since draft-ietf-httpbis-p1-messaging-07
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/93>: "Repeating
single-value headers"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/131>: "increase
connection limit"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/157>: "IP addresses
in URLs"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/172>: "take over
HTTP Upgrade Token Registry"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/173>: "CR and LF in
chunk extension values"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/184>: "HTTP/0.9
support"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/188>: "pick IANA
policy (RFC5226) for Transfer Coding / Content Coding"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/189>: "move
definitions of gzip/deflate/compress to part 1"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/194>: "disallow
control characters in quoted-pair"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/148>: "update IANA
requirements wrt Transfer-Coding values" (add the IANA
Considerations subsection)
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C.10. Since draft-ietf-httpbis-p1-messaging-08
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/201>: "header
parsing, treatment of leading and trailing OWS"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/60>: "Placement of
13.5.1 and 13.5.2"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term
"word" when talking about header structure"
C.11. Since draft-ietf-httpbis-p1-messaging-09
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/73>: "Clarification
of the term 'deflate'"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/83>: "OPTIONS * and
proxies"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/122>: "MIME-Version
not listed in P1, general header fields"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/143>: "IANA registry
for content/transfer encodings"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/165>: "Case-
sensitivity of HTTP-date"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term
"word" when talking about header structure"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/196>: "Term for the
requested resource's URI"
C.12. Since draft-ietf-httpbis-p1-messaging-10
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/28>: "Connection
Closing"
Fielding, et al. Expires July 7, 2012 [Page 82]
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/90>: "Delimiting
messages with multipart/byteranges"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/95>: "Handling
multiple Content-Length headers"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
entity / representation / variant terminology"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
removing the 'changes from 2068' sections"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/159>: "HTTP(s) URI
scheme definitions"
C.13. Since draft-ietf-httpbis-p1-messaging-11
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/193>: "Trailer
requirements"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/204>: "Text about
clock requirement for caches belongs in p6"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/221>: "effective
request URI: handling of missing host in HTTP/1.0"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/248>: "confusing
Date requirements for clients"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/95>: "Handling
multiple Content-Length headers"
C.14. Since draft-ietf-httpbis-p1-messaging-12
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/75>: "RFC2145
Normative"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/159>: "HTTP(s) URI
scheme definitions" (tune the requirements on userinfo)
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/210>: "define
'transparent' proxy"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/224>: "Header
Classification"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/233>: "Is * usable
as a request-uri for new methods?"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/240>: "Migrate
Upgrade details from RFC2817"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
ABNFs for header fields"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/279>: "update RFC
2109 reference"
C.15. Since draft-ietf-httpbis-p1-messaging-13
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/53>: "Allow is not
in 13.5.2"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/95>: "Handling
multiple Content-Length headers"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/276>: "untangle
ABNFs for header fields"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/286>: "Content-
Length ABNF broken"
C.16. Since draft-ietf-httpbis-p1-messaging-14
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/273>: "HTTP-Version
should be redefined as fixed length pair of DIGIT . DIGIT"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/282>: "Recommend
minimum sizes for protocol elements"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/283>: "Set
expectations around buffering"
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/288>: "Considering
messages in isolation"
C.17. Since draft-ietf-httpbis-p1-messaging-15
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/100>: "DNS Spoofing
/ DNS Binding advice"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/254>: "move RFCs
2145, 2616, 2817 to Historic status"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/270>: "\-escaping in
quoted strings"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/305>: "'Close'
should be reserved in the HTTP header field registry"
C.18. Since draft-ietf-httpbis-p1-messaging-16
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/186>: "Document
HTTP's error-handling philosophy"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/215>: "Explain
header registration"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/219>: "Revise
Acknowledgements Sections"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/297>: "Retrying
Requests"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/318>: "Closing the
connection on server error"
C.19. Since draft-ietf-httpbis-p1-messaging-17
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/166>: "Clarify 'User
Agent'"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/300>: "Define non-
final responses"
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/323>: "intended
maturity level vs normative references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/324>: "Intermediary
rewriting of queries"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/158>: "Proxy-
Connection and Keep-Alive"
Index
A
absolute-URI form (of request-target) 32
accelerator 13
application/http Media Type 61
asterisk form (of request-target) 31
authority form (of request-target) 32
B
browser 10
C
cache 14
cacheable 15
captive portal 14
chunked (Coding Format) 36
client 10
Coding Format
chunked 36
compress 38
deflate 38
gzip 39
compress (Coding Format) 38
connection 10
Connection header field 49
Content-Length header field 51
D
deflate (Coding Format) 38
downstream 13
E
effective request URI 34
G
gateway 13
Grammar
absolute-URI 18
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ALPHA 7
attribute 35
authority 18
BWS 9
chunk 36
chunk-data 36
chunk-ext 36
chunk-ext-name 36
chunk-ext-val 36
chunk-size 36
Chunked-Body 36
comment 26
Connection 50
connection-token 50
Content-Length 51
CR 7
CRLF 7
ctext 26
CTL 7
date2 35
date3 35
DIGIT 7
DQUOTE 7
field-content 23
field-name 23
field-value 23
header-field 23
HEXDIG 7
Host 52
HTAB 7
HTTP-message 21
HTTP-Prot-Name 15
http-URI 18
HTTP-Version 15
https-URI 20
last-chunk 36
LF 7
message-body 27
Method 22
obs-text 26
OCTET 7
OWS 9
path-absolute 18
port 18
product 39
product-version 39
protocol-name 57
protocol-version 57
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pseudonym 57
qdtext 26
qdtext-nf 36
query 18
quoted-cpair 27
quoted-pair 26
quoted-str-nf 36
quoted-string 26
qvalue 40
Reason-Phrase 23
received-by 57
received-protocol 57
Request-Line 22
request-target 22
RWS 9
SP 7
special 26
start-line 21
Status-Code 23
Status-Line 23
t-codings 53
tchar 26
TE 53
te-ext 53
te-params 53
token 26
Trailer 54
trailer-part 36
transfer-coding 35
Transfer-Encoding 54
transfer-extension 35
transfer-parameter 35
Upgrade 55
uri-host 18
URI-reference 18
value 35
VCHAR 7
Via 57
word 26
gzip (Coding Format) 39
H
header field 21
Header Fields
Connection 49
Content-Length 51
Host 51
TE 53
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Trailer 54
Transfer-Encoding 54
Upgrade 55
Via 57
header section 21
headers 21
Host header field 51
http URI scheme 18
https URI scheme 19
I
inbound 13
interception proxy 14
intermediary 12
M
Media Type
application/http 61
message/http 59
message 10
message/http Media Type 59
N
non-transforming proxy 13
O
origin form (of request-target) 32
origin server 10
outbound 13
P
proxy 13
R
recipient 10
request 10
resource 17
response 10
reverse proxy 13
S
sender 10
server 10
spider 10
T
target resource 34
TE header field 53
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Trailer header field 54
Transfer-Encoding header field 54
transforming proxy 13
transparent proxy 14
tunnel 14
U
Upgrade header field 55
upstream 13
URI scheme
http 18
https 19
user agent 10
V
Via header field 57
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
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Henrik Frystyk Nielsen
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
USA
EMail: henrikn@microsoft.com
Larry Masinter
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA
EMail: LMM@acm.org
URI: http://larry.masinter.net/
Paul J. Leach
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
EMail: paulle@microsoft.com
Tim Berners-Lee
World Wide Web Consortium
MIT Computer Science and Artificial Intelligence Laboratory
The Stata Center, Building 32
32 Vassar Street
Cambridge, MA 02139
USA
EMail: timbl@w3.org
URI: http://www.w3.org/People/Berners-Lee/
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Yves Lafon (editor)
World Wide Web Consortium
W3C / ERCIM
2004, rte des Lucioles
Sophia-Antipolis, AM 06902
France
EMail: ylafon@w3.org
URI: http://www.raubacapeu.net/people/yves/
Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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