- From: Julian Reschke <julian.reschke@greenbytes.de>
- Date: Mon, 16 Dec 2013 17:10:21 +0100
- To: HTTP Working Group <ietf-http-wg@w3.org>
- Message-ID: <52AF25ED.2030206@greenbytes.de>
-------- Original Message --------
Subject: draft-ietf-httpbis-p1-messaging-25
Resent-To: barryleiba@gmail.com, fielding@gbiv.com,
julian.reschke@greenbytes.de, mnot@pobox.com,
Date: Mon, 16 Dec 2013 10:49:42 -0500
From: Thomas Nadeau <tnadeau@lucidvision.com>
To: draft-ietf-httpbis-p1-messaging.all@tools.ietf.org, ops-dir@ietf.org
Hello,
I am the assigned OPS-DIR reviewer for
draft-ietf-httpbis-p1-messaging-25. The OPS-DIR review have as principal
goal helping the OPS ADs in their evaluation and balloting of documents
at IESG reviews. Please consider these comments together with the other
IETF Last Call comments.
This document is of high quality and ready generally speaking, but can
be improved with a few editorial clarifications as mentioned below. My
comments begin with "TOM:" so you can easily search for them below.
--Tom
HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe
Obsoletes: 2145,2616 (if approved) J. Reschke, Ed.
Updates: 2817,2818 (if approved) greenbytes
Intended status: Standards Track November 17, 2013
Expires: May 21, 2014
Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing
draft-ietf-httpbis-p1-messaging-25
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 provides an
overview of HTTP architecture and its associated terminology, defines
the "http" and "https" Uniform Resource Identifier (URI) schemes,
defines the HTTP/1.1 message syntax and parsing requirements, and
describes general security concerns for implementations.
Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
<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.2.
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
Fielding & Reschke Expires May 21, 2014 [Page 1]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 21, 2014.
Copyright Notice
Copyright (c) 2013 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
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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Requirement Notation . . . . . . . . . . . . . . . . . . . 6
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Client/Server Messaging . . . . . . . . . . . . . . . . . 7
2.2. Implementation Diversity . . . . . . . . . . . . . . . . . 8
2.3. Intermediaries . . . . . . . . . . . . . . . . . . . . . . 9
2.4. Caches . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5. Conformance and Error Handling . . . . . . . . . . . . . . 12
2.6. Protocol Versioning . . . . . . . . . . . . . . . . . . . 14
2.7. Uniform Resource Identifiers . . . . . . . . . . . . . . . 16
2.7.1. http URI scheme . . . . . . . . . . . . . . . . . . . 17
2.7.2. https URI scheme . . . . . . . . . . . . . . . . . . . 18
2.7.3. http and https URI Normalization and Comparison . . . 19
3. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 19
Fielding & Reschke Expires May 21, 2014 [Page 2]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
3.1. Start Line . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.1. Request Line . . . . . . . . . . . . . . . . . . . . . 21
3.1.2. Status Line . . . . . . . . . . . . . . . . . . . . . 22
3.2. Header Fields . . . . . . . . . . . . . . . . . . . . . . 22
3.2.1. Field Extensibility . . . . . . . . . . . . . . . . . 23
3.2.2. Field Order . . . . . . . . . . . . . . . . . . . . . 23
3.2.3. Whitespace . . . . . . . . . . . . . . . . . . . . . . 24
3.2.4. Field Parsing . . . . . . . . . . . . . . . . . . . . 24
3.2.5. Field Limits . . . . . . . . . . . . . . . . . . . . . 26
3.2.6. Field value components . . . . . . . . . . . . . . . . 26
3.3. Message Body . . . . . . . . . . . . . . . . . . . . . . . 27
3.3.1. Transfer-Encoding . . . . . . . . . . . . . . . . . . 28
3.3.2. Content-Length . . . . . . . . . . . . . . . . . . . . 30
3.3.3. Message Body Length . . . . . . . . . . . . . . . . . 31
3.4. Handling Incomplete Messages . . . . . . . . . . . . . . . 33
3.5. Message Parsing Robustness . . . . . . . . . . . . . . . . 34
4. Transfer Codings . . . . . . . . . . . . . . . . . . . . . . . 35
4.1. Chunked Transfer Coding . . . . . . . . . . . . . . . . . 35
4.1.1. Chunk Extensions . . . . . . . . . . . . . . . . . . . 36
4.1.2. Chunked Trailer Part . . . . . . . . . . . . . . . . . 36
4.1.3. Decoding Chunked . . . . . . . . . . . . . . . . . . . 37
4.2. Compression Codings . . . . . . . . . . . . . . . . . . . 38
4.2.1. Compress Coding . . . . . . . . . . . . . . . . . . . 38
4.2.2. Deflate Coding . . . . . . . . . . . . . . . . . . . . 38
4.2.3. Gzip Coding . . . . . . . . . . . . . . . . . . . . . 38
4.3. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.4. Trailer . . . . . . . . . . . . . . . . . . . . . . . . . 40
5. Message Routing . . . . . . . . . . . . . . . . . . . . . . . 40
5.1. Identifying a Target Resource . . . . . . . . . . . . . . 40
5.2. Connecting Inbound . . . . . . . . . . . . . . . . . . . . 40
5.3. Request Target . . . . . . . . . . . . . . . . . . . . . . 41
5.4. Host . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.5. Effective Request URI . . . . . . . . . . . . . . . . . . 44
5.6. Associating a Response to a Request . . . . . . . . . . . 46
5.7. Message Forwarding . . . . . . . . . . . . . . . . . . . . 46
5.7.1. Via . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.7.2. Transformations . . . . . . . . . . . . . . . . . . . 48
6. Connection Management . . . . . . . . . . . . . . . . . . . . 49
6.1. Connection . . . . . . . . . . . . . . . . . . . . . . . . 49
6.2. Establishment . . . . . . . . . . . . . . . . . . . . . . 51
6.3. Persistence . . . . . . . . . . . . . . . . . . . . . . . 51
6.3.1. Retrying Requests . . . . . . . . . . . . . . . . . . 52
6.3.2. Pipelining . . . . . . . . . . . . . . . . . . . . . . 53
6.4. Concurrency . . . . . . . . . . . . . . . . . . . . . . . 53
6.5. Failures and Time-outs . . . . . . . . . . . . . . . . . . 54
6.6. Tear-down . . . . . . . . . . . . . . . . . . . . . . . . 55
6.7. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 56
7. ABNF list extension: #rule . . . . . . . . . . . . . . . . . . 58
Fielding & Reschke Expires May 21, 2014 [Page 3]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 59
8.1. Header Field Registration . . . . . . . . . . . . . . . . 59
8.2. URI Scheme Registration . . . . . . . . . . . . . . . . . 60
8.3. Internet Media Type Registration . . . . . . . . . . . . . 60
8.3.1. Internet Media Type message/http . . . . . . . . . . . 60
8.3.2. Internet Media Type application/http . . . . . . . . . 61
8.4. Transfer Coding Registry . . . . . . . . . . . . . . . . . 63
8.4.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 63
8.4.2. Registration . . . . . . . . . . . . . . . . . . . . . 63
8.5. Content Coding Registration . . . . . . . . . . . . . . . 64
8.6. Upgrade Token Registry . . . . . . . . . . . . . . . . . . 64
8.6.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 64
8.6.2. Upgrade Token Registration . . . . . . . . . . . . . . 65
9. Security Considerations . . . . . . . . . . . . . . . . . . . 65
9.1. DNS-related Attacks . . . . . . . . . . . . . . . . . . . 65
9.2. Intermediaries and Caching . . . . . . . . . . . . . . . . 65
9.3. Buffer Overflows . . . . . . . . . . . . . . . . . . . . . 66
9.4. Message Integrity . . . . . . . . . . . . . . . . . . . . 66
9.5. Server Log Information . . . . . . . . . . . . . . . . . . 67
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 68
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 69
11.1. Normative References . . . . . . . . . . . . . . . . . . . 69
11.2. Informative References . . . . . . . . . . . . . . . . . . 71
Appendix A. HTTP Version History . . . . . . . . . . . . . . . . 72
A.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 73
A.1.1. Multi-homed Web Servers . . . . . . . . . . . . . . . 73
A.1.2. Keep-Alive Connections . . . . . . . . . . . . . . . . 74
A.1.3. Introduction of Transfer-Encoding . . . . . . . . . . 74
A.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 74
Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 77
Appendix C. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 79
C.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 79
C.2. Since draft-ietf-httpbis-p1-messaging-24 . . . . . . . . . 79
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Fielding & Reschke Expires May 21, 2014 [Page 4]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
1. Introduction
The Hypertext Transfer Protocol (HTTP) is an application-level
request/response protocol that uses extensible semantics and self-
descriptive message payloads for flexible interaction with network-
based hypertext information systems. This document is the first in a
series of documents that collectively form the HTTP/1.1
specification:
RFC xxx1: Message Syntax and Routing
RFC xxx2: Semantics and Content
RFC xxx3: Conditional Requests
RFC xxx4: Range Requests
RFC xxx5: Caching
RFC xxx6: Authentication
This HTTP/1.1 specification obsoletes and moves to historic status
RFC 2616, its predecessor RFC 2068, and RFC 2145 (on HTTP
versioning). This specification also updates the use of CONNECT to
establish a tunnel, previously defined in RFC 2817, and defines the
"https" URI scheme that was described informally in RFC 2818.
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 this 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
Fielding & Reschke Expires May 21, 2014 [Page 5]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 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 and message-
forwarding intermediaries.
1.1. Requirement Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Conformance criteria and considerations regarding error handling are
defined in Section 2.5.
1.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with the list rule extension defined in
Section 7. Appendix B shows the collected ABNF with the list rule
expanded.
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line
feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any
visible [USASCII] character).
As a convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons.
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
and syntax productions used to define HTTP.
Fielding & Reschke Expires May 21, 2014 [Page 6]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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" (Section 6). 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.
TOM: Change "HTTP responses" to "HTTP response messages in order to
reply to HTTP requests."
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 any of the various client programs
that initiate a request, including (but not limited to) browsers,
spiders (web-based robots), command-line tools, native applications,
and mobile apps. The term "origin server" is used to refer to the
program that can originate authoritative responses to a request. For
general requirements, we use the terms "sender" and "recipient" to
refer to any component that sends or receives, respectively, a given
message.
HTTP relies upon the Uniform Resource Identifier (URI) standard
[RFC3986] to indicate the target resource (Section 5.1) 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 [Part2]
for the differences between HTTP and MIME messages).
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 a 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 header fields
containing request modifiers, client information, and representation
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).
A server responds to a client's request by sending one or more HTTP
Fielding & Reschke Expires May 21, 2014 [Page 7]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
response messages, each beginning with a status line that includes
the protocol version, a success or error code, and textual reason
phrase (Section 3.1.2), possibly followed by header fields containing
server information, resource metadata, and representation 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).
A connection might be used for multiple request/response exchanges,
as defined in Section 6.3.
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-Language: en, mi
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: 51
Vary: Accept-Encoding
Content-Type: text/plain
Hello World! My payload includes a trailing CRLF.
2.2. Implementation Diversity
When considering the design of HTTP, it is easy to fall into a trap
of thinking that all user agents are general-purpose browsers and all
origin servers are large public websites. That is not the case in
practice. Common HTTP user agents include household appliances,
stereos, scales, firmware update scripts, command-line programs,
TOM: scales? Do you mean like a "weight scale"?
mobile apps, and communication devices in a multitude of shapes and
sizes. Likewise, common HTTP origin servers include home automation
units, configurable networking components, office machines,
autonomous robots, news feeds, traffic cameras, ad selectors, and
video delivery platforms.
Fielding & Reschke Expires May 21, 2014 [Page 8]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
The term "user agent" does not imply that there is a human user
directly interacting with the software agent at the time of a
request. In many cases, a user agent is installed or configured to
run in the background and save its results for later inspection (or
save only a subset of those results that might be interesting or
erroneous). Spiders, for example, are typically given a start URI
and configured to follow certain behavior while crawling the Web as a
hypertext graph.
The implementation diversity of HTTP means that we cannot assume the
user agent can make interactive suggestions to a user or provide
adequate warning for security or privacy options. In the few cases
where this specification requires reporting of errors to the user, it
is acceptable for such reporting to only be observable in an error
console or log file. Likewise, requirements that an automated action
be confirmed by the user before proceeding might be met via advance
configuration choices, run-time options, or simple avoidance of the
unsafe action; confirmation does not imply any specific user
interface or interruption of normal processing if the user has
already made that choice.
2.3. 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
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. Likewise, later requests might be sent through a different
path of connections, often based on dynamic configuration for load
balancing.
We use the terms "upstream" and "downstream" to describe various
Fielding & Reschke Expires May 21, 2014 [Page 9]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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-level 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 6.3.4 of [Part2] and Section 5.5 of [Part6]
for status and warning codes related to transformations.
A "gateway" (a.k.a., "reverse proxy") is an intermediary that acts as
an origin server for the outbound connection, but translates received
requests and forwards them inbound to another server or servers.
Gateways are often 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.
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 ought to conform to user agent requirements
on the gateway's inbound connection.
Fielding & Reschke Expires May 21, 2014 [Page 10]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 (TLS, [RFC5246]) is used to establish
confidential communication through a shared firewall proxy.
The above categories for intermediary only consider those acting as
participants in the HTTP communication. There are also
intermediaries that can act on lower layers of the network protocol
stack, filtering or redirecting HTTP traffic without the knowledge or
permission of message senders. Network intermediaries often
introduce security flaws or interoperability problems by violating
HTTP semantics. For example, an "interception proxy" [RFC3040] (also
commonly known as a "transparent proxy" [RFC1919] or "captive
portal") differs from an HTTP proxy because it is not selected by the
client. Instead, an interception proxy filters or redirects outgoing
TCP port 80 packets (and occasionally other common port traffic).
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.
HTTP is defined as a stateless protocol, meaning that each request
message can be understood in isolation. Many implementations depend
on HTTP's stateless design in order to reuse proxied connections or
dynamically load-balance requests across multiple servers. Hence, a
server MUST NOT assume that two requests on the same connection are
from the same user agent unless the connection is secured and
specific to that agent. Some non-standard HTTP extensions (e.g.,
TOM: Do you mean "non-standards track"? Many people regard anything
with an RFC number to be some form of "standard".
[RFC4559]) have been known to violate this requirement, resulting in
security and interoperability problems.
2.4. 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
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
Fielding & Reschke Expires May 21, 2014 [Page 11]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
chain if B has a cached copy of an earlier response from O (via C)
for a request that 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
TOM: You should say, "store a copy of the response message for some
usually non-permanent period of time..."
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 deployed across the World Wide Web and inside large
organizations. These include national hierarchies of proxy caches to
save transoceanic bandwidth, collaborative systems that broadcast or
multicast cache entries, archives of pre-fetched cache entries for
use in off-line or high-latency environments, and so on.
2.5. Conformance and Error Handling
This specification targets conformance criteria according to the role
of a participant in HTTP communication. Hence, HTTP requirements are
placed on senders, recipients, clients, servers, user agents,
intermediaries, origin servers, proxies, gateways, or caches,
depending on what behavior is being constrained by the requirement.
Additional (social) requirements are placed on implementations,
resource owners, and protocol element registrations when they apply
beyond the scope of a single communication.
The verb "generate" is used instead of "send" where a requirement
differentiates between creating a protocol element and merely
forwarding a received element downstream.
An implementation is considered conformant if it complies with all of
the requirements associated with the roles it partakes in HTTP.
Conformance includes both the syntax and semantics of protocol
elements. A sender MUST NOT generate protocol elements that convey a
meaning that is known by that sender to be false. A sender MUST NOT
generate protocol elements that do not match the grammar defined by
the corresponding ABNF rules. Within a given message, a sender MUST
NOT generate protocol elements or syntax alternatives that are only
allowed to be generated by participants in other roles (i.e., a role
that the sender does not have for that message).
Fielding & Reschke Expires May 21, 2014 [Page 12]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
When a received protocol element is parsed, the recipient MUST be
able to parse any value of reasonable length that is applicable to
the recipient's role and matches the grammar defined by the
corresponding ABNF rules. Note, however, that some received protocol
elements might not be parsed. For example, an intermediary
forwarding a message might parse a header-field into generic field-
name and field-value components, but then forward the header field
without further parsing inside the field-value.
HTTP does not have specific length limitations for many of its
protocol elements because the lengths that might be appropriate will
vary widely, depending on the deployment context and purpose of the
implementation. Hence, interoperability between senders and
recipients depends on shared expectations regarding what is a
reasonable length for each protocol element. Furthermore, what is
commonly understood to be a reasonable length for some protocol
elements has changed over the course of the past two decades of HTTP
use, and is expected to continue changing in the future.
At a minimum, a recipient MUST be able to parse and process protocol
element lengths that are at least as long as the values that it
generates for those same protocol elements in other messages. For
example, an origin server that publishes very long URI references to
its own resources needs to be able to parse and process those same
references when received as a request target.
A recipient MUST interpret a received protocol element according to
the semantics defined for it by this specification, including
extensions to this specification, unless the recipient has determined
(through experience or configuration) that the sender incorrectly
implements what is implied by those semantics. For example, an
origin server might disregard the contents of a received Accept-
Encoding header field if inspection of the User-Agent header field
indicates a specific implementation version that is known to fail on
receipt of certain content codings.
Unless noted otherwise, a recipient MAY attempt to recover a usable
protocol element from an invalid construct. HTTP does not define
specific error handling mechanisms except when they have a direct
impact on security, since different applications of the protocol
require different error handling strategies. For example, a Web
browser might wish to transparently recover from a response where the
Location header field doesn't parse according to the ABNF, whereas a
systems control client might consider any form of error recovery to
be dangerous.
Fielding & Reschke Expires May 21, 2014 [Page 13]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 conformance 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-name "/" DIGIT "." DIGIT
HTTP-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 within that major
version to which the sender is conformant and able to understand for
future communication. The minor version advertises the sender's
communication capabilities even when the sender is only using a
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
conformant 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 a header field does not change between minor
versions of the same major HTTP 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 conformance with HTTP/1.1.
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. Header field extensibility is
discussed in Section 3.2.1.
Intermediaries that process HTTP messages (i.e., all intermediaries
Fielding & Reschke Expires May 21, 2014 [Page 14]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
other than those acting as tunnels) MUST send their own HTTP-version
in forwarded messages. In other words, they are not allowed to
blindly forward the first line of an HTTP message without ensuring
that the protocol version in that message matches a version to which
that intermediary is conformant 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.
A client SHOULD send a request version equal to the highest version
to which the client is conformant and whose major version is no
higher than the highest version supported by the server, if this is
known. A client MUST NOT send a version to which it is not
conformant.
A 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 code or header fields (e.g., Server) that
the server improperly handles higher request versions.
A server SHOULD send a response version equal to the highest version
to which the server is conformant that has a major version less than
or equal to the one received in the request. A server MUST NOT send
a version to which it is not conformant. A server can send a 505
(HTTP Version Not Supported) response if it wishes, for any reason,
to refuse service of the client's major protocol version.
A server MAY send an HTTP/1.0 response to a 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 conform to 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 has
specifically avoided any such changes to the protocol.
Fielding & Reschke Expires May 21, 2014 [Page 15]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
When an HTTP message is received with a major version number that the
recipient implements, but a higher minor version number than what the
recipient implements, the recipient SHOULD process the message as if
it were in the highest minor version within that major version to
which the recipient is conformant. A recipient can assume that a
message with a higher minor version, when sent to a recipient that
has not yet indicated support for that higher version, is
sufficiently backwards-compatible to be safely processed by any
implementation of the same major version.
2.7. Uniform Resource Identifiers
Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
HTTP as the means for identifying resources (Section 2 of [Part2]).
URI references are used to target requests, indicate redirects, and
define relationships.
This specification adopts the definitions of "URI-reference",
"absolute-URI", "relative-part", "authority", "port", "host", "path-
abempty", "segment", "query", and "fragment" from the URI generic
syntax. In addition, we define an "absolute-path" rule (that differs
from RFC 3986's "path-absolute" in that it allows a leading "//") and
a "partial-URI" rule for protocol 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>
uri-host = <host, defined in [RFC3986], Section 3.2.2>
port = <port, defined in [RFC3986], Section 3.2.3>
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
segment = <segment, defined in [RFC3986], Section 3.3>
query = <query, defined in [RFC3986], Section 3.4>
fragment = <fragment, defined in [RFC3986], Section 3.5>
absolute-path = 1*( "/" segment )
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 (Section 5.5).
Fielding & Reschke Expires May 21, 2014 [Page 16]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 ([RFC0793]) connections on a given port.
http-URI = "http:" "//" authority path-abempty [ "?" query ]
[ "#" fragment ]
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.
A sender MUST NOT generate an "http" URI with an empty host
identifier. A recipient that processes such a URI reference MUST
reject it as invalid.
If the host identifier is provided as an IP 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. If the port subcomponent is empty or not given, then TCP port
80 is assumed (the default reserved port for WWW services).
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 5) to the
server. If the server responds to that request with a non-interim
HTTP response message, as described in Section 6 of [Part2], then
that response is considered an authoritative answer to the client's
request.
Fielding & Reschke Expires May 21, 2014 [Page 17]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 resources that require an end-to-end
secured connection. Other protocols might also be used to provide
access to "http" identified resources -- it is only the authoritative
interface 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. A sender MUST NOT
generate the userinfo subcomponent (and its "@" delimiter) when an
"http" URI reference is generated within a message as a request
target or header field value. Before making use of an "http" URI
reference received from an untrusted source, a recipient ought to
parse for userinfo and treat its presence as an error; it is likely
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
namespace governed by a potential HTTP origin server listening to a
given TCP port for TLS-secured connections ([RFC0793], [RFC5246]).
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 user agent MUST ensure that its connection to the origin server
is secured through the use of strong encryption, end-to-end, prior to
TOM: Rather than "end-to-end" I would rather use "..., on the connection
between the client and server, ..."
sending the first HTTP request.
https-URI = "https:" "//" authority path-abempty [ "?" query ]
[ "#" fragment ]
Note that the "https" URI scheme depends on both TLS and TCP for
establishing authority. 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
Fielding & Reschke Expires May 21, 2014 [Page 18]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 omit the port subcomponent. When not being used in
absolute form as the request target of an OPTIONS request, 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:
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
Fielding & Reschke Expires May 21, 2014 [Page 19]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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.
A recipient 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.
An HTTP message can be parsed as a stream for incremental processing
or forwarding downstream. However, recipients cannot rely on
incremental delivery of partial messages, since some implementations
will buffer or delay message forwarding for the sake of network
efficiency, security checks, or payload transformations.
A sender MUST NOT send whitespace between the start-line and the
first header field. A recipient that receives whitespace between the
start-line and the first header field MUST either reject the message
as invalid or consume each whitespace-preceded line without further
processing of it (i.e., ignore the entire line, along with any
subsequent lines preceded by whitespace, until a properly formed
header field is received or the header section is terminated).
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. 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
Fielding & Reschke Expires May 21, 2014 [Page 20]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
clients are implemented to only expect a response.
start-line = request-line / status-line
3.1.1. Request Line
A 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
The method token indicates the request method to be performed on the
target resource. The request method is case-sensitive.
method = token
The request methods defined by this specification can be found in
Section 4 of [Part2], along with information regarding the HTTP
method registry and considerations for defining new methods.
The request-target identifies the target resource upon which to apply
the request, as defined in Section 5.3.
Recipients typically parse the request-line into its component parts
by splitting on whitespace (see Section 3.5), since no whitespace is
allowed in the three components. Unfortunately, some user agents
fail to properly encode or exclude whitespace found in hypertext
references, resulting in those disallowed characters being sent in a
request-target.
Recipients of an invalid request-line SHOULD respond with either a
400 (Bad Request) error or a 301 (Moved Permanently) redirect with
the request-target properly encoded. A recipient SHOULD NOT attempt
to autocorrect and then process the request without a redirect, since
the invalid request-line might be deliberately crafted to bypass
security filters along the request chain.
HTTP does not place a pre-defined limit on the length of a request-
line. A server that receives a method longer than any that it
implements SHOULD respond with a 501 (Not Implemented) status code.
A server ought to be prepared to receive URIs of unbounded length, as
described in Section 2.5, and MUST respond with a 414 (URI Too Long)
status code if the received request-target is longer than the server
wishes to parse (see Section 6.5.12 of [Part2]).
Various ad-hoc limitations on request-line length are found in
practice. It is RECOMMENDED that all HTTP senders and recipients
Fielding & Reschke Expires May 21, 2014 [Page 21]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
support, at a minimum, request-line lengths of 8000 octets.
3.1.2. 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
The status-code element is a 3-digit integer code describing the
result of the server's attempt to understand and satisfy the client's
corresponding request. The rest of the response message is to be
interpreted in light of the semantics defined for that status code.
See Section 6 of [Part2] for information about the semantics of
status codes, including the classes of status code (indicated by the
first digit), the status codes defined by this specification,
considerations for the definition of new status codes, and the IANA
registry.
status-code = 3DIGIT
The reason-phrase element exists for the sole purpose of providing a
textual description associated with the numeric status code, mostly
out of deference to earlier Internet application protocols that were
more frequently used with interactive text clients. A client SHOULD
ignore the reason-phrase content.
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 leading whitespace, the field
value, and optional trailing whitespace.
header-field = field-name ":" OWS field-value OWS
field-name = token
field-value = *( field-content / obs-fold )
field-content = *( HTAB / SP / VCHAR / obs-text )
obs-fold = CRLF ( SP / HTAB )
; obsolete line folding
; see Section 3.2.4
The field-name token labels the corresponding field-value as having
the semantics defined by that header field. For example, the Date
header field is defined in Section 7.1.1.2 of [Part2] as containing
Fielding & Reschke Expires May 21, 2014 [Page 22]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
the origination timestamp for the message in which it appears.
3.2.1. Field Extensibility
Header fields are fully extensible: there is no limit on the
introduction of new field names, each presumably defining new
semantics, nor 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 core
standard.
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, define preconditions on request
evaluation, or refine the meaning of responses.
A proxy MUST forward unrecognized header fields unless the field-name
is listed in the Connection header field (Section 6.1) or the proxy
is specifically configured to block, or otherwise transform, such
fields. Other recipients SHOULD ignore unrecognized header fields.
These requirements allow HTTP's functionality to be enhanced without
requiring prior update of deployed intermediaries.
All defined header fields ought to be registered with IANA in the
Message Header Field Registry, as described in Section 8.3 of
[Part2].
3.2.2. Field Order
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.
A sender MUST NOT generate multiple header fields with the same field
name in a message unless either the entire field value for that
header field is defined as a comma-separated list [i.e., #(values)]
or the header field is a well-known exception (as noted below).
A recipient MAY combine multiple header fields with the same field
name 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
Fielding & Reschke Expires May 21, 2014 [Page 23]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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: In practice, the "Set-Cookie" header field ([RFC6265]) often
appears multiple times in a response message and does not use the
list syntax, violating the above requirements on multiple header
fields with the same name. Since it cannot be combined into a
single field-value, recipients ought to handle "Set-Cookie" as a
special case while processing header fields. (See Appendix A.2.3
of [Kri2001] for details.)
3.2.3. Whitespace
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. For protocol elements where optional whitespace is
preferred to improve readability, a sender SHOULD generate the
optional whitespace as a single SP; otherwise, a sender SHOULD NOT
generate optional whitespace except as needed to white-out invalid or
unwanted protocol elements during in-place message filtering.
The RWS rule is used when at least one linear whitespace octet is
required to separate field tokens. A sender SHOULD generate RWS as a
single SP.
The BWS rule is used where the grammar allows optional whitespace
only for historical reasons. A sender MUST NOT generate BWS in
messages. A recipient MUST parse for such bad whitespace and remove
it before interpreting the protocol element.
OWS = *( SP / HTAB )
; optional whitespace
RWS = 1*( SP / HTAB )
; required whitespace
BWS = OWS
; "bad" whitespace
3.2.4. 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. A
Fielding & Reschke Expires May 21, 2014 [Page 24]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
server MUST reject any received request message that contains
whitespace between a header field-name and colon 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 is 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 ought to be excluded by parsers when extracting the
field value from a header field.
A recipient of field-content containing multiple sequential octets of
optional (OWS) or required (RWS) whitespace SHOULD either replace the
sequence with a single SP or transform any non-SP octets in the
sequence to SP octets before interpreting the field value or
forwarding the message downstream.
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 8.3.1). A sender MUST NOT generate a message that includes
line folding (i.e., that has any field-value that contains a match to
the obs-fold rule) unless the message is intended for packaging
within the message/http media type.
A server that receives an obs-fold in a request message that is not
within a message/http container MUST either reject the message by
sending a 400 (Bad Request), preferably with a representation
explaining that obsolete line folding is unacceptable, or replace
each received obs-fold with one or more SP octets prior to
interpreting the field value or forwarding the message downstream.
A proxy or gateway that receives an obs-fold in a response message
that is not within a message/http container MUST either discard the
message and replace it with a 502 (Bad Gateway) response, preferably
with a representation explaining that unacceptable line folding was
received, or replace each received obs-fold with one or more SP
octets prior to interpreting the field value or forwarding the
message downstream.
A user agent that receives an obs-fold in a response message that is
not within a message/http container MUST replace each received obs-
fold with one or more SP octets prior to interpreting the field
value.
Historically, HTTP has allowed field content with text in the ISO-
Fielding & Reschke Expires May 21, 2014 [Page 25]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
8859-1 [ISO-8859-1] charset, supporting other charsets only through
use of [RFC2047] encoding. In practice, most HTTP header field
values use only a subset of the US-ASCII charset [USASCII]. Newly
defined header fields SHOULD limit their field values to US-ASCII
octets. A recipient SHOULD treat other octets in field content (obs-
text) as opaque data.
3.2.5. Field Limits
HTTP does not place a pre-defined limit on the length of each header
field or on the length of the header section as a whole, as described
in Section 2.5. Various ad-hoc limitations on individual header
field length are found in practice, often depending on the specific
field semantics.
A server ought to be prepared to receive request header fields of
unbounded length and MUST respond with an appropriate 4xx (Client
Error) status code if the received header field(s) are larger than
the server wishes to process.
A client ought to be prepared to receive response header fields of
unbounded length. A client MAY discard or truncate received header
fields that are larger than the client wishes to process if the field
semantics are such that the dropped value(s) can be safely ignored
without changing the message framing or response semantics.
3.2.6. Field value components
Many HTTP header field values consist of words (token or quoted-
string) separated by whitespace or special characters.
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.
Fielding & Reschke Expires May 21, 2014 [Page 26]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = HTAB / SP /%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 a quoted-string MUST handle a
quoted-pair as if it were replaced by the octet following the
backslash.
A sender SHOULD NOT generate a quoted-pair in a quoted-string except
where necessary to quote DQUOTE and backslash octets occurring within
that string.
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 ) ")"
ctext = HTAB / SP / %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 )
A sender 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 of that request or response. The message body is
identical to the payload body unless a transfer coding has been
applied, as described in Section 3.3.1.
message-body = *OCTET
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 a Content-
Length or Transfer-Encoding header field. Request message framing is
independent of method semantics, even if the method does not define
Fielding & Reschke Expires May 21, 2014 [Page 27]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
any use for a message body.
The presence of a message body in a response depends on both the
request method to which it is responding and the response status code
(Section 3.1.2). Responses to the HEAD request method never include
a message body because the associated response header fields (e.g.,
Transfer-Encoding, Content-Length, etc.), if present, indicate only
what their values would have been if the request method had been GET
(Section 4.3.2 of [Part2]). 2xx (Successful) responses to CONNECT
switch to tunnel mode instead of having a message body (Section 4.3.6
of [Part2]). All 1xx (Informational), 204 (No Content), and 304 (Not
Modified) responses do not include a message body. All other
responses do include a message body, although the body might be of
zero length.
3.3.1. Transfer-Encoding
The Transfer-Encoding header field lists the transfer coding names
corresponding to the sequence of transfer codings that have been (or
will be) applied to the payload body in order to form the message
body. Transfer codings are defined in Section 4.
Transfer-Encoding = 1#transfer-coding
Transfer-Encoding is analogous to the Content-Transfer-Encoding field
of MIME, which was 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's case, Transfer-Encoding is primarily intended to accurately
delimit a dynamically generated payload and to distinguish payload
encodings that are only applied for transport efficiency or security
from those that are characteristics of the selected resource.
A recipient MUST be able to parse the chunked transfer coding
TOM: Do you mean "encoding" rather than "coding"?
(Section 4.1) because it plays a crucial role in framing messages
when the payload body size is not known in advance. A sender MUST
NOT apply chunked more than once to a message body (i.e., chunking an
TOM: "NOT apply chunked" does not parse well. Please consider rewriting.
Please look over the remainder of this section to maintain consistent
use of "chunked" as a verb, adjective or both.
already chunked message is not allowed). If any transfer coding
other than chunked is applied to a request payload body, the sender
MUST apply chunked as the final transfer coding to ensure that the
message is properly framed. If any transfer coding other than
TOM: coding -> encoding. Please look over the rest of this section as
there are other instances of this.
chunked is applied to a response payload body, the sender MUST either
apply chunked as the final transfer coding or terminate the message
by closing the connection.
Fielding & Reschke Expires May 21, 2014 [Page 28]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
For example,
Transfer-Encoding: gzip, chunked
indicates that the payload body has been compressed using the gzip
coding and then chunked using the chunked coding while forming the
message body.
Unlike Content-Encoding (Section 3.1.2.1 of [Part2]), Transfer-
Encoding is a property of the message, not of the representation, and
any recipient along the request/response chain MAY decode the
received transfer coding(s) or apply additional transfer coding(s) to
the message body, assuming that corresponding changes are made to the
Transfer-Encoding field-value. Additional information about the
encoding parameters MAY be provided by other header fields not
defined by this specification.
Transfer-Encoding MAY be sent in a response to a HEAD request or in a
304 (Not Modified) response (Section 4.1 of [Part4]) to a GET
request, neither of which includes a message body, to indicate that
the origin server would have applied a transfer coding to the message
body if the request had been an unconditional GET. This indication
is not required, however, because any recipient on the response chain
(including the origin server) can remove transfer codings when they
are not needed.
A server MUST NOT send a Transfer-Encoding header field in any
response with a status code of 1xx (Informational) or 204 (No
Content). A server MUST NOT send a Transfer-Encoding header field in
any 2xx (Successful) response to a CONNECT request (Section 4.3.6 of
[Part2]).
Transfer-Encoding was added in HTTP/1.1. It is generally assumed
that implementations advertising only HTTP/1.0 support will not
understand how to process a transfer-encoded payload. A client MUST
NOT send a request containing Transfer-Encoding unless it knows the
server will handle HTTP/1.1 (or later) requests; such knowledge might
be in the form of specific user configuration or by remembering the
version of a prior received response. A server MUST NOT send a
response containing Transfer-Encoding unless the corresponding
request indicates HTTP/1.1 (or later).
A server that receives a request message with a transfer coding it
does not understand SHOULD respond with 501 (Not Implemented).
Fielding & Reschke Expires May 21, 2014 [Page 29]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
3.3.2. Content-Length
When a message does not have a Transfer-Encoding header field, a
Content-Length header field can provide the anticipated size, as a
decimal number of octets, for a potential payload body. For messages
that do include a payload body, the Content-Length field-value
provides the framing information necessary for determining where the
body (and message) ends. For messages that do not include a payload
body, the Content-Length indicates the size of the selected
representation (Section 3 of [Part2]).
Content-Length = 1*DIGIT
An example is
Content-Length: 3495
A sender MUST NOT send a Content-Length header field in any message
that contains a Transfer-Encoding header field.
A user agent SHOULD send a Content-Length in a request message when
no Transfer-Encoding is sent and the request method defines a meaning
for an enclosed payload body. For example, a Content-Length header
field is normally sent in a POST request even when the value is 0
(indicating an empty payload body). A user agent SHOULD NOT send a
Content-Length header field when the request message does not contain
a payload body and the method semantics do not anticipate such a
body.
A server MAY send a Content-Length header field in a response to a
HEAD request (Section 4.3.2 of [Part2]); a server MUST NOT send
Content-Length in such a response unless its field-value equals the
decimal number of octets that would have been sent in the payload
body of a response if the same request had used the GET method.
A server MAY send a Content-Length header field in a 304 (Not
Modified) response to a conditional GET request (Section 4.1 of
[Part4]); a server MUST NOT send Content-Length in such a response
unless its field-value equals the decimal number of octets that would
have been sent in the payload body of a 200 (OK) response to the same
request.
A server MUST NOT send a Content-Length header field in any response
with a status code of 1xx (Informational) or 204 (No Content). A
server MUST NOT send a Content-Length header field in any 2xx
(Successful) response to a CONNECT request (Section 4.3.6 of
[Part2]).
Fielding & Reschke Expires May 21, 2014 [Page 30]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Aside from the cases defined above, in the absence of Transfer-
Encoding, an origin server SHOULD send a Content-Length header field
when the payload body size is known prior to sending the complete
header section. This will allow downstream recipients to measure
transfer progress, know when a received message is complete, and
potentially reuse the connection for additional requests.
Any Content-Length field value greater than or equal to zero is
valid. Since there is no predefined limit to the length of a
payload, a recipient MUST anticipate potentially large decimal
numerals and prevent parsing errors due to integer conversion
overflows (Section 9.3).
If a message is received that has multiple Content-Length header
fields 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 or forwarding the message.
Note: HTTP's use of Content-Length for message framing differs
significantly from the same field's use in MIME, where it is an
optional field used only within the "message/external-body" media-
type.
3.3.3. Message Body Length
The length of a 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 1xx
(Informational), 204 (No Content), or 304 (Not Modified) status
code 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. Any 2xx (Successful) response to a CONNECT request implies that
the connection will become a tunnel immediately after the empty
line that concludes the header fields. A client MUST ignore any
Content-Length or Transfer-Encoding header fields received in
such a message.
3. If a Transfer-Encoding header field is present and the chunked
transfer coding (Section 4.1) is the final encoding, the message
Fielding & Reschke Expires May 21, 2014 [Page 31]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 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. A sender MUST remove the received Content-
Length field prior to forwarding such a message downstream.
4. 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 the
recipient MUST treat it as an unrecoverable 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 close the connection to the server,
discard the received response, and send a 502 (Bad Gateway)
response to the client. If this is a response message received
by a user agent, the user agent MUST close the connection to the
server and discard the received response.
5. If a valid Content-Length header field is present without
Transfer-Encoding, its decimal value defines the expected message
body length in octets. If the sender closes the connection or
the recipient times out before the indicated number of octets are
received, the recipient MUST consider the message to be
incomplete and close the connection.
6. 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).
7. 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.
Fielding & Reschke Expires May 21, 2014 [Page 32]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Since there is no way to distinguish a successfully completed, close-
delimited message from a partially-received message interrupted by
network failure, a server SHOULD generate 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
valid Content-Length header field if the message body length is known
in advance, rather than the chunked transfer coding, since some
existing services respond to chunked with a 411 (Length Required)
status code even though they understand the chunked transfer coding.
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 user agent that sends a request containing a message body MUST send
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.
If the final response to the last request on a connection has been
completely received and there remains additional data to read, a user
agent MAY discard the remaining data or attempt to determine if that
data belongs as part of the prior response body, which might be the
case if the prior message's Content-Length value is incorrect. A
client MUST NOT process, cache, or forward such extra data as a
separate response, since such behavior would be vulnerable to cache
poisoning.
3.4. Handling Incomplete Messages
A server that receives an incomplete request message, usually due to
a canceled request or a triggered time-out exception, MAY send an
error response prior to closing the connection.
TOM: Isn't this a case where the server SHOULD send an error rather than
MAY?
A client that receives an incomplete response message, which can
occur when a connection is closed prematurely or when decoding a
supposedly chunked transfer coding fails, MUST record the message as
incomplete. Cache requirements for incomplete responses are defined
in Section 3 of [Part6].
If a response terminates in the middle of the header section (before
Fielding & Reschke Expires May 21, 2014 [Page 33]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
the empty line is received) and the status code might rely on header
fields to convey the full meaning of the response, then the client
cannot assume that meaning has been conveyed; the client might need
to repeat the request in order to determine what action to take next.
A message body that uses the chunked transfer coding 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 coding 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 section was
received intact.
3.5. Message Parsing Robustness
Older HTTP/1.0 user agent implementations might send an extra CRLF
after a POST request as a 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 user agent 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 user agent MUST
count the terminating CRLF octets as part of the message body length.
In the interest of robustness, a server that is expecting to receive
and parse a request-line SHOULD ignore at least one empty line (CRLF)
received prior to the request-line.
Although the line terminator for the start-line and header fields is
the sequence CRLF, a recipient MAY recognize a single LF as a line
terminator and ignore any preceding CR.
Although the request-line and status-line grammar rules require that
each of the component elements be separated by a single SP octet,
recipients MAY instead parse on whitespace-delimited word boundaries
and, aside from the CRLF terminator, treat any form of whitespace as
the SP separator while ignoring preceding or trailing whitespace;
such whitespace includes one or more of the following octets: SP,
HTAB, VT (%x0B), FF (%x0C), or bare 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
SHOULD respond with a 400 (Bad Request) response.
Fielding & Reschke Expires May 21, 2014 [Page 34]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
4. Transfer Codings
Transfer coding names 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 4.1
/ "compress" ; Section 4.2.1
/ "deflate" ; Section 4.2.2
/ "gzip" ; Section 4.2.3
/ 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 names are case-insensitive and ought to be
registered within the HTTP Transfer Coding registry, as defined in
Section 8.4. They are used in the TE (Section 4.3) and Transfer-
Encoding (Section 3.3.1) header fields.
4.1. Chunked Transfer Coding
The chunked transfer coding wraps the payload body in order to
transfer it as a series of chunks, each with its own size indicator,
followed by an OPTIONAL trailer containing header fields. Chunked
enables content streams of unknown size to be transferred as a
sequence of length-delimited buffers, which enables the sender to
retain connection persistence and the recipient to know when it has
received the entire 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-data = 1*OCTET ; a sequence of chunk-size octets
Fielding & Reschke Expires May 21, 2014 [Page 35]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
The chunk-size field is a string of hex digits indicating the size of
the chunk-data in octets. The chunked transfer coding is complete
when a chunk with a chunk-size of zero is received, possibly followed
by a trailer, and finally terminated by an empty line.
A recipient MUST be able to parse and decode the chunked transfer
coding.
4.1.1. Chunk Extensions
The chunked encoding allows each chunk to include zero or more chunk
extensions, immediately following the chunk-size, for the sake of
supplying per-chunk metadata (such as a signature or hash), mid-
message control information, or randomization of message body size.
chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token / quoted-str-nf
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 chunked encoding is specific to each connection and is likely to
be removed or recoded by each recipient (including intermediaries)
before any higher-level application would have a chance to inspect
the extensions. Hence, use of chunk extensions is generally limited
to specialized HTTP services such as "long polling" (where client and
server can have shared expectations regarding the use of chunk
extensions) or for padding within an end-to-end secured connection.
A recipient MUST ignore unrecognized chunk extensions. A server
ought to limit the total length of chunk extensions received in a
request to an amount reasonable for the services provided, in the
same way that it applies length limitations and timeouts for other
parts of a message, and generate an appropriate 4xx (Client Error)
response if that amount is exceeded.
4.1.2. Chunked Trailer Part
A trailer allows the sender to include additional fields at the end
of a chunked message in order to supply metadata that might be
dynamically generated while the message body is sent, such as a
message integrity check, digital signature, or post-processing
status. The trailer fields are identical to header fields, except
they are sent in a chunked trailer instead of the message's header
section.
Fielding & Reschke Expires May 21, 2014 [Page 36]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
trailer-part = *( header-field CRLF )
A sender MUST NOT generate a trailer that contains a field which
needs to be known by the recipient before it can begin processing the
message body. For example, most recipients need to know the values
of Content-Encoding and Content-Type in order to select a content
handler, so placing those fields in a trailer would force the
recipient to buffer the entire body before it could begin, greatly
increasing user-perceived latency and defeating one of the main
advantages of using chunked to send data streams of unknown length.
A sender MUST NOT generate a trailer containing a Transfer-Encoding,
Content-Length, or Trailer field.
A server MUST generate an empty trailer with the chunked transfer
coding 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 4.3; or,
2. the trailer fields consist entirely of optional metadata and the
recipient could use the message (in a manner acceptable to the
generating server) without receiving that metadata. In other
words, the generating server is willing to accept the possibility
that the trailer fields might be silently discarded along the
path to the client.
The above requirement prevents the need for an infinite buffer when a
message is being received by an HTTP/1.1 (or later) proxy and
forwarded to an HTTP/1.0 recipient.
4.1.3. Decoding Chunked
A process for decoding the chunked transfer coding can be represented
in pseudo-code as:
Fielding & Reschke Expires May 21, 2014 [Page 37]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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, chunk-ext (if any), and CRLF
}
read header-field
while (header-field not empty) {
append header-field to existing header fields
read header-field
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
Remove Trailer from existing header fields
4.2. Compression Codings
The codings defined below can be used to compress the payload of a
message.
4.2.1. Compress Coding
The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
[Welch] that is commonly produced by the UNIX file compression
program "compress". A recipient SHOULD consider "x-compress" to be
equivalent to "compress".
4.2.2. Deflate Coding
The "deflate" coding is a "zlib" data format [RFC1950] containing a
"deflate" compressed data stream [RFC1951] that uses a combination of
the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.
Note: Some incorrect implementations send the "deflate" compressed
data without the zlib wrapper.
4.2.3. Gzip Coding
The "gzip" coding is an LZ77 coding with a 32 bit CRC that is
commonly produced by the gzip file compression program [RFC1952]. A
recipient SHOULD consider "x-gzip" to be equivalent to "gzip".
4.3. TE
The "TE" header field in a request indicates what transfer codings,
besides chunked, the client is willing to accept in response, and
Fielding & Reschke Expires May 21, 2014 [Page 38]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
whether or not the client is willing to accept trailer fields in a
chunked transfer coding.
The TE field-value consists of a comma-separated list of transfer
coding names, each allowing for optional parameters (as described in
Section 4), and/or the keyword "trailers". A client MUST NOT send
the chunked transfer coding name in TE; chunked is always acceptable
for HTTP/1.1 recipients.
TE = #t-codings
t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
t-ranking = OWS ";" OWS "q=" rank
rank = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] )
Three examples of TE use are below.
TE: deflate
TE:
TE: trailers, deflate;q=0.5
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 4.1.2, on behalf of itself and any downstream
clients. For requests from an intermediary, this implies that
either: (a) all downstream clients are willing to accept trailer
fields in the forwarded response; or, (b) the intermediary will
attempt to buffer the response on behalf of downstream recipients.
Note that HTTP/1.1 does not define any means to limit the size of a
chunked response such that an intermediary can be assured of
buffering the entire response.
When multiple transfer codings are acceptable, the client MAY rank
the codings by preference using a case-insensitive "q" parameter
(similar to the qvalues used in content negotiation fields, Section
5.3.1 of [Part2]). The rank value is a real number in the range 0
through 1, where 0.001 is the least preferred and 1 is the most
preferred; a value of 0 means "not acceptable".
If the TE field-value is empty or if no TE field is present, the only
acceptable transfer coding is chunked. A message with no transfer
coding is always acceptable.
Since the TE header field only applies to the immediate connection, a
sender of TE MUST also send a "TE" connection option within the
Connection header field (Section 6.1) in order to prevent the TE
field from being forwarded by intermediaries that do not support its
semantics.
Fielding & Reschke Expires May 21, 2014 [Page 39]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
4.4. Trailer
When a message includes a message body encoded with the chunked
transfer coding and the sender desires to send metadata in the form
of trailer fields at the end of the message, the sender SHOULD
generate a Trailer header field before the message body to indicate
which fields will be present in the trailers. This allows the
recipient to prepare for receipt of that metadata before it starts
processing the body, which is useful if the message is being streamed
and the recipient wishes to confirm an integrity check on the fly.
Trailer = 1#field-name
5. Message Routing
HTTP request message routing is determined by each client based on
the target resource, the client's proxy configuration, and
establishment or reuse of an inbound connection. The corresponding
response routing follows the same connection chain back to the
client.
5.1. Identifying a Target Resource
HTTP is used in a wide variety of applications, ranging from general-
purpose computers to home appliances. In some cases, communication
options are hard-coded in a client's configuration. However, most
HTTP clients rely on the same resource identification mechanism and
configuration techniques as general-purpose Web browsers.
HTTP communication is initiated by a user agent for some purpose.
The purpose is a combination of request semantics, which are defined
in [Part2], and a target resource upon which to apply those
semantics. A URI reference (Section 2.7) is typically used as an
identifier for the "target resource", which a user agent would
resolve to its absolute form in order to obtain the "target URI".
The target URI excludes the reference's fragment component, if any,
since fragment identifiers are reserved for client-side processing
([RFC3986], Section 3.5).
5.2. Connecting Inbound
Once the target URI is determined, a client needs to decide whether a
network request is necessary to accomplish the desired semantics and,
if so, where that request is to be directed.
If the client has a cache [Part6] and the request can be satisfied by
it, then the request is usually directed there first.
Fielding & Reschke Expires May 21, 2014 [Page 40]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
If the request is not satisfied by a cache, then a typical client
will check its configuration to determine whether a proxy is to be
used to satisfy the request. Proxy configuration is implementation-
dependent, but is often based on URI prefix matching, selective
authority matching, or both, and the proxy itself is usually
identified by an "http" or "https" URI. If a proxy is applicable,
the client connects inbound by establishing (or reusing) a connection
to that proxy.
If no proxy is applicable, a typical client will invoke a handler
routine, usually specific to the target URI's scheme, to connect
directly to an authority for the target resource. How that is
accomplished is dependent on the target URI scheme and defined by its
associated specification, similar to how this specification defines
origin server access for resolution of the "http" (Section 2.7.1) and
"https" (Section 2.7.2) schemes.
HTTP requirements regarding connection management are defined in
Section 6.
5.3. Request Target
Once an inbound connection is obtained, the client sends an HTTP
request message (Section 3) with a request-target derived from the
target URI. There are four distinct formats for the request-target,
depending on both the method being requested and whether the request
is to a proxy.
request-target = origin-form
/ absolute-form
/ authority-form
/ asterisk-form
origin-form = absolute-path [ "?" query ]
absolute-form = absolute-URI
authority-form = authority
asterisk-form = "*"
origin-form
The most common form of request-target is the origin-form. When
making a request directly to an origin server, other than a CONNECT
or server-wide OPTIONS request (as detailed below), a client MUST
send only the absolute path and query components of the target URI as
the request-target. If the target URI's path component is empty,
then the client MUST send "/" as the path within the origin-form of
request-target. A Host header field is also sent, as defined in
Section 5.4.
Fielding & Reschke Expires May 21, 2014 [Page 41]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
For example, a client wishing to retrieve a representation of the
resource identified as
http://www.example.org/where?q=now
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 /where?q=now HTTP/1.1
Host: www.example.org
followed by the remainder of the request message.
absolute-form
When making a request to a proxy, other than a CONNECT or server-wide
OPTIONS request (as detailed below), a client MUST send the target
URI in absolute-form as the request-target. The proxy is requested
to either service that request from a valid cache, if possible, or
make the same request on the client's behalf to either the next
inbound proxy server or directly to the origin server indicated by
the request-target. Requirements on such "forwarding" of messages
are defined in Section 5.7.
An example absolute-form of request-line would be:
GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
To allow for transition to the absolute-form for all requests in some
future version of HTTP, a server MUST accept the absolute-form in
requests, even though HTTP/1.1 clients will only send them in
requests to proxies.
authority-form
The authority-form of request-target is only used for CONNECT
requests (Section 4.3.6 of [Part2]). When making a CONNECT request
to establish a tunnel through one or more proxies, a client MUST send
only the target URI's authority component (excluding any userinfo and
its "@" delimiter) as the request-target. For example,
CONNECT www.example.com:80 HTTP/1.1
asterisk-form
The asterisk-form of request-target is only used for a server-wide
OPTIONS request (Section 4.3.7 of [Part2]). When a client wishes to
Fielding & Reschke Expires May 21, 2014 [Page 42]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
request OPTIONS for the server as a whole, as opposed to a specific
named resource of that server, the client MUST send only "*" (%x2A)
as the request-target. For example,
OPTIONS * HTTP/1.1
If a proxy receives an OPTIONS request with an absolute-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 send a
request-target of "*" when it forwards the request to the indicated
origin server.
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".
5.4. Host
The "Host" header field in a request provides the host and port
information from the target URI, enabling the origin server to
distinguish among resources while servicing requests for multiple
host names on a single IP address.
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 URI includes an authority component, then a
client MUST send a field-value for Host that is identical to that
authority component, excluding any userinfo subcomponent and its "@"
delimiter (Section 2.7.1). If the authority component is missing or
undefined for the target URI, then a client MUST send a Host header
field with an empty field-value.
Since the Host field-value is critical information for handling a
request, a user agent SHOULD generate Host as the first header field
following the request-line.
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
Fielding & Reschke Expires May 21, 2014 [Page 43]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Host: www.example.org
A client MUST send a Host header field in an HTTP/1.1 request even if
the request-target is in the absolute-form, since this allows the
Host information to be forwarded through ancient HTTP/1.0 proxies
that might not have implemented Host.
When a proxy receives a request with an absolute-form of request-
target, the proxy MUST ignore the received Host header field (if any)
and instead replace it with the host information of the request-
target. A proxy that forwards such a request MUST generate a new
Host field-value based on the received request-target rather than
forward the received Host field-value.
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 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.
5.5. Effective Request URI
A server that receives an HTTP request message MUST reconstruct the
user agent's original target URI, based on the pieces of information
learned from the request-target, Host header field, and connection
context, in order to identify the intended target resource and
properly service the request. The URI derived from this
reconstruction process is referred to as the "effective request URI".
For a user agent, the effective request URI is the target URI.
If the request-target is in absolute-form, then the effective request
URI is the same as the request-target. Otherwise, the effective
request URI is constructed as follows.
If the request is received over a TLS-secured TCP connection, then
the effective request URI's scheme is "https"; otherwise, the scheme
is "http".
If the request-target is in authority-form, then the effective
Fielding & Reschke Expires May 21, 2014 [Page 44]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
request URI's authority component is the same as the request-target.
Otherwise, if a Host header field is supplied with a non-empty field-
value, then the authority component is the same as the Host field-
value. Otherwise, the authority component is the concatenation of
the default host name configured for the server, a colon (":"), and
the connection's incoming TCP port number in decimal form.
If the request-target is in authority-form or asterisk-form, then the
effective request URI's combined path and query component is empty.
Otherwise, the combined path and query component is the same as the
request-target.
The components of the effective request URI, once determined as
above, can be combined into absolute-URI form by concatenating the
scheme, "://", authority, and combined path and query component.
Example 1: the following message received over an insecure TCP
connection
GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.example.org:8080
has an effective request URI of
http://www.example.org:8080/pub/WWW/TheProject.html
Example 2: the following message received over a TLS-secured TCP
connection
OPTIONS * HTTP/1.1
Host: www.example.org
has an effective request URI of
https://www.example.org
An origin server that does not allow resources to differ by requested
host MAY ignore the Host field-value and instead replace it with a
configured server name when constructing the effective request URI.
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 guess the
effective request URI's authority component.
Fielding & Reschke Expires May 21, 2014 [Page 45]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
5.6. Associating a Response to a Request
HTTP does not include a request identifier for associating a given
request message with its corresponding one or more response messages.
Hence, it relies on the order of response arrival to correspond
exactly to the order in which requests are made on the same
connection. More than one response message per request only occurs
when one or more informational responses (1xx, see Section 6.2 of
[Part2]) precede a final response to the same request.
A client that has more than one outstanding request on a connection
MUST maintain a list of outstanding requests in the order sent and
MUST associate each received response message on that connection to
the highest ordered request that has not yet received a final (non-
1xx) response.
5.7. Message Forwarding
As described in Section 2.3, intermediaries can serve a variety of
roles in the processing of HTTP requests and responses. Some
intermediaries are used to improve performance or availability.
Others are used for access control or to filter content. Since an
HTTP stream has characteristics similar to a pipe-and-filter
architecture, there are no inherent limits to the extent an
intermediary can enhance (or interfere) with either direction of the
stream.
An intermediary not acting as a tunnel MUST implement the Connection
header field, as specified in Section 6.1, and exclude fields from
being forwarded that are only intended for the incoming connection.
An intermediary MUST NOT forward a message to itself unless it is
protected from an infinite request loop. In general, an intermediary
ought to recognize its own server names, including any aliases, local
variations, or literal IP addresses, and respond to such requests
directly.
5.7.1. Via
The "Via" header field indicates the presence of intermediate
protocols and recipients between the user agent and the server (on
requests) or between the origin server and the client (on responses),
similar to the "Received" header field in email (Section 3.6.7 of
[RFC5322]). Via can be used for tracking message forwards, avoiding
request loops, and identifying the protocol capabilities of senders
along the request/response chain.
Fielding & Reschke Expires May 21, 2014 [Page 46]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Via = 1#( received-protocol RWS received-by [ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
; see Section 6.7
received-by = ( uri-host [ ":" port ] ) / pseudonym
pseudonym = token
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each intermediary appends its own information
about how the message was received, such that the end result is
ordered according to the sequence of forwarding recipients.
A proxy MUST send an appropriate Via header field, as described
below, in each message that it forwards. An HTTP-to-HTTP gateway
MUST send an appropriate Via header field in each inbound request
message and MAY send a Via header field in forwarded response
messages.
For each intermediary, the received-protocol indicates the protocol
and protocol version used by the upstream sender of the message.
Hence, the Via field value records the advertised protocol
capabilities of the request/response chain such that they remain
visible to downstream recipients; this can be useful for determining
what backwards-incompatible features might be safe to use in
response, or within a later request, as described in Section 2.6.
For brevity, the protocol-name is omitted when the received protocol
is 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, a sender MAY replace it with a pseudonym. If a port is
not provided, a recipient MAY interpret that as meaning it was
received on the default TCP port, if any, for the received-protocol.
A sender MAY generate comments in the Via header field to identify
the software of each recipient, analogous to the User-Agent and
Server header fields. However, all comments in the Via field are
optional and a recipient MAY remove them 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:
Fielding & Reschke Expires May 21, 2014 [Page 47]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Via: 1.0 fred, 1.1 p.example.net
An intermediary 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, such an
intermediary SHOULD replace each received-by host of any host behind
the firewall by an appropriate pseudonym for that host.
An intermediary MAY combine an ordered subsequence of Via header
field entries into a single such entry if the entries have identical
received-protocol values. 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
A sender SHOULD NOT combine multiple entries unless they are all
under the same organizational control and the hosts have already been
replaced by pseudonyms. A sender MUST NOT combine entries that have
different received-protocol values.
5.7.2. Transformations
Some intermediaries include features for transforming messages and
their payloads. A transforming proxy might, for example, convert
between image formats in order to save cache space or to reduce the
amount of traffic on a slow link. However, operational problems
might occur when these transformations are applied to payloads
intended for critical applications, such as medical imaging or
scientific data analysis, particularly when integrity checks or
digital signatures are used to ensure that the payload received is
identical to the original.
If a proxy receives a request-target with a host name that is not a
fully qualified domain name, it MAY add its own domain to the host
name it received when forwarding the request. A proxy MUST NOT
change the host name if it is a fully qualified domain name.
A proxy MUST NOT modify the "absolute-path" and "query" parts of the
received request-target when forwarding it to the next inbound
server, except as noted above to replace an empty path with "/" or
"*".
A proxy MUST NOT modify header fields that provide information about
the end points of the communication chain, the resource state, or the
selected representation. A proxy MAY change the message body through
Fielding & Reschke Expires May 21, 2014 [Page 48]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
application or removal of a transfer coding (Section 4).
A non-transforming proxy MUST NOT modify the message payload (Section
3.3 of [Part2]). A transforming proxy MUST NOT modify the payload of
a message that contains the no-transform cache-control directive.
A transforming proxy MAY transform the payload of a message that does
not contain the no-transform cache-control directive; if the payload
is transformed, the transforming proxy MUST add a Warning header
field with the warn-code of 214 ("Transformation Applied") if one
does not already appear in the message (see Section 5.5 of [Part6]).
If the payload of a 200 (OK) response is transformed, the
transforming proxy can also inform downstream recipients that a
transformation has been applied by changing the response status code
to 203 (Non-Authoritative Information) (Section 6.3.4 of [Part2]).
6. Connection Management
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 an underlying transport
protocol is outside the scope of this specification.
As described in Section 5.2, the specific connection protocols to be
used for an HTTP interaction are determined by client configuration
and the target 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.
HTTP implementations are expected to engage in connection management,
which includes maintaining the state of current connections,
establishing a new connection or reusing an existing connection,
processing messages received on a connection, detecting connection
failures, and closing each connection. Most clients maintain
multiple connections in parallel, including more than one connection
per server endpoint. Most servers are designed to maintain thousands
of concurrent connections, while controlling request queues to enable
fair use and detect denial of service attacks.
TOM: Do you want to refer to the security section for the DoS Attack?
6.1. Connection
The "Connection" header field allows the sender to indicate desired
control options for the current connection. In order to avoid
confusing downstream recipients, a proxy or gateway MUST remove or
replace any received connection options before forwarding the
Fielding & Reschke Expires May 21, 2014 [Page 49]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
message.
When a header field aside from Connection is used to supply control
information for or about the current connection, the sender MUST list
the corresponding field-name within the "Connection" header field. A
proxy or gateway MUST parse a received Connection header field before
a message is forwarded and, for each connection-option in this field,
remove any header field(s) from the message with the same name as the
connection-option, and then remove the Connection header field itself
(or replace it with the intermediary's own connection options for the
forwarded message).
Hence, the Connection header field provides a declarative way of
distinguishing header fields that are only intended for the immediate
recipient ("hop-by-hop") from those fields that are intended for all
recipients on the chain ("end-to-end"), enabling the message to be
self-descriptive and allowing future connection-specific extensions
to be deployed without fear that they will be blindly forwarded by
older intermediaries.
The Connection header field's value has the following grammar:
Connection = 1#connection-option
connection-option = token
Connection options are case-insensitive.
A sender MUST NOT send a connection option corresponding to a header
field that is intended for all recipients of the payload. For
example, Cache-Control is never appropriate as a connection option
(Section 5.2 of [Part6]).
The connection options do not always 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 a
connection option. In contrast, a connection-specific header field
that is received without a corresponding connection option usually
indicates that the field has been improperly forwarded by an
intermediary and ought to be ignored by the recipient.
When defining new connection options, specification authors ought to
survey existing header field names and ensure that the new connection
option does not share the same name as an already deployed header
field. Defining a new connection option 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.
Fielding & Reschke Expires May 21, 2014 [Page 50]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
The "close" connection option is defined for a sender to signal that
this connection will be closed after completion of the response. For
example,
Connection: close
in either the request or the response header fields indicates that
the sender is going to close the connection after the current
request/response is complete (Section 6.6).
A client that does not support persistent connections MUST send the
"close" connection option in every request message.
A server that does not support persistent connections MUST send the
"close" connection option in every response message that does not
have a 1xx (Informational) status code.
6.2. Establishment
It is beyond the scope of this specification to describe how
connections are established via various transport or session-layer
protocols. Each connection applies to only one transport link.
6.3. Persistence
HTTP/1.1 defaults to the use of "persistent connections", allowing
multiple requests and responses to be carried over a single
connection. The "close" connection-option is used to signal that a
connection will not persist after the current request/response. HTTP
implementations SHOULD support persistent connections.
A recipient determines whether a connection is persistent or not
based on the most recently received message's protocol version and
Connection header field (if any):
o If the close connection option is present, the connection will not
persist after the current response; else,
o If the received protocol is HTTP/1.1 (or later), the connection
will persist after the current response; else,
o If the received protocol is HTTP/1.0, the "keep-alive" connection
option is present, the recipient is not a proxy, and the recipient
wishes to honor the HTTP/1.0 "keep-alive" mechanism, the
connection will persist after the current response; otherwise,
o The connection will close after the current response.
Fielding & Reschke Expires May 21, 2014 [Page 51]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
A server MAY assume that an HTTP/1.1 client intends to maintain a
persistent connection until a close connection option is received in
a request.
A client MAY reuse a persistent connection until it sends or receives
a close connection option or receives an HTTP/1.0 response without a
"keep-alive" connection option.
In order to remain persistent, all messages on a connection need to
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in Section 3.3. 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 request. Likewise, a
client MUST read the entire response message body if it intends to
reuse the same connection for a subsequent request.
A proxy server MUST NOT maintain a persistent connection with an
HTTP/1.0 client (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).
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.
6.3.1. Retrying Requests
Connections can be closed at any time, with or without intention.
Implementations ought to anticipate the need to recover from
asynchronous close events.
When an inbound connection is closed prematurely, a client MAY open a
new connection and automatically retransmit an aborted sequence of
requests if all of those requests have idempotent methods (Section
4.2.2 of [Part2]). A proxy MUST NOT automatically retry non-
idempotent requests.
A user agent MUST NOT automatically retry a request with a non-
idempotent method unless it has some means to know that the request
semantics are actually idempotent, regardless of the method, or some
means to detect that the original request was never applied. For
example, a user agent that knows (through design or configuration)
that a POST request to a given resource is safe can repeat that
request automatically. Likewise, a user agent designed specifically
to operate on a version control repository might be able to recover
from partial failure conditions by checking the target resource
Fielding & Reschke Expires May 21, 2014 [Page 52]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
revision(s) after a failed connection, reverting or fixing any
changes that were partially applied, and then automatically retrying
the requests that failed.
A client SHOULD NOT automatically retry a failed automatic retry.
6.3.2. Pipelining
A client that supports persistent connections MAY "pipeline" its
requests (i.e., send multiple requests without waiting for each
response). A server MAY process a sequence of pipelined requests in
parallel if they all have safe methods (Section 4.2.1 of [Part2]),
but MUST send the corresponding responses in the same order that the
requests were received.
TOM: Have you considered that packets may be delivered out-of-order?
While not ideal, this is a very real possibility especially with
multi-path TCP and other load-balancing techniques. In these cases, I
think the statement of requiring the server to return responses in the
same order of receiving requests is fine, but it might be useful to
mention this point so that clients are not confused if respones come
back in a different order than they were sent (in reality).
A client that pipelines requests SHOULD retry unanswered requests if
the connection closes before it receives all of the corresponding
responses. When retrying pipelined requests after a failed
connection (a connection not explicitly closed by the server in its
last complete response), a client MUST NOT pipeline immediately after
connection establishment, since the first remaining request in the
prior pipeline might have caused an error response that can be lost
again if multiple requests are sent on a prematurely closed
connection (see the TCP reset problem described in Section 6.6).
Idempotent methods (Section 4.2.2 of [Part2]) are significant to
pipelining because they can be automatically retried after a
connection failure. A user agent SHOULD NOT pipeline requests after
a non-idempotent method, until the final response status code for
that method has been received, unless the user agent has a means to
detect and recover from partial failure conditions involving the
pipelined sequence.
An intermediary that receives pipelined requests MAY pipeline those
requests when forwarding them inbound, since it can rely on the
outbound user agent(s) to determine what requests can be safely
pipelined. If the inbound connection fails before receiving a
response, the pipelining intermediary MAY attempt to retry a sequence
of requests that have yet to receive a response if the requests all
have idempotent methods; otherwise, the pipelining intermediary
SHOULD forward any received responses and then close the
corresponding outbound connection(s) so that the outbound user
agent(s) can recover accordingly.
6.4. Concurrency
A client SHOULD limit the number of simultaneous open connections
that it maintains to a given server.
Fielding & Reschke Expires May 21, 2014 [Page 53]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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.
Multiple connections are typically used to avoid the "head-of-line
blocking" problem, wherein a request that takes significant server-
side processing and/or has a large payload blocks subsequent requests
on the same connection. However, each connection consumes server
resources. Furthermore, using multiple connections can cause
undesirable side effects in congested networks.
Note that servers might reject traffic that they deem abusive,
including an excessive number of connections from a client.
6.5. Failures and Time-outs
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.
A client or server that wishes to time-out SHOULD issue a graceful
close on the connection. Implementations SHOULD constantly monitor
open connections for a received closure signal and respond to it as
appropriate, since prompt closure of both sides of a connection
enables allocated system resources to be reclaimed.
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.
A server SHOULD sustain persistent connections, when possible, and
allow the underlying transport's flow control mechanisms to resolve
temporary overloads, rather than terminate connections with the
expectation that clients will retry. The latter technique can
exacerbate network congestion.
A client sending a message body SHOULD monitor the network connection
for an error response while it is transmitting the request. If the
client sees a response that indicates the server does not wish to
receive the message body and is closing the connection, the client
Fielding & Reschke Expires May 21, 2014 [Page 54]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
SHOULD immediately cease transmitting the body and close its side of
the connection.
6.6. Tear-down
The Connection header field (Section 6.1) provides a "close"
connection option that a sender SHOULD send when it wishes to close
the connection after the current request/response pair.
A client that sends a close connection option MUST NOT send further
requests on that connection (after the one containing close) and MUST
close the connection after reading the final response message
corresponding to this request.
A server that receives a close connection option MUST initiate a
close of the connection (see below) after it sends the final response
to the request that contained close. The server SHOULD send a close
connection option in its final response on that connection. The
server MUST NOT process any further requests received on that
connection.
A server that sends a close connection option MUST initiate a close
of the connection (see below) after it sends the response containing
close. The server MUST NOT process any further requests received on
that connection.
A client that receives a close connection option MUST cease sending
requests on that connection and close the connection after reading
the response message containing the close; if additional pipelined
requests had been sent on the connection, the client SHOULD NOT
assume that they will be processed by the server.
If a server performs an immediate close of a TCP connection, there is
a significant risk that the client will not be able to read the last
HTTP response. If the server receives additional data from the
client on a fully-closed connection, such as another request that was
sent by the client before receiving the server's response, the
server's TCP stack will send a reset packet to the client;
unfortunately, the reset packet might erase the client's
unacknowledged input buffers before they can be read and interpreted
by the client's HTTP parser.
To avoid the TCP reset problem, servers typically close a connection
in stages. First, the server performs a half-close by closing only
the write side of the read/write connection. The server then
continues to read from the connection until it receives a
corresponding close by the client, or until the server is reasonably
certain that its own TCP stack has received the client's
Fielding & Reschke Expires May 21, 2014 [Page 55]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
acknowledgement of the packet(s) containing the server's last
response. Finally, the server fully closes the connection.
It is unknown whether the reset problem is exclusive to TCP or might
also be found in other transport connection protocols.
6.7. Upgrade
The "Upgrade" header field is intended to provide a simple mechanism
for transitioning from HTTP/1.1 to some other protocol on the same
connection. A client MAY send a list of protocols in the Upgrade
header field of a request to invite the server to switch to one or
more of those protocols, in order of descending preference, before
sending the final response. A server MAY ignore a received Upgrade
header field if it wishes to continue using the current protocol on
that connection.
Upgrade = 1#protocol
protocol = protocol-name ["/" protocol-version]
protocol-name = token
protocol-version = token
A server that sends a 101 (Switching Protocols) response MUST send an
Upgrade header field to indicate the new protocol(s) to which the
connection is being switched; if multiple protocol layers are being
switched, the sender MUST list the protocols in layer-ascending
order. A server MUST NOT switch to a protocol that was not indicated
by the client in the corresponding request's Upgrade header field. A
server MAY choose to ignore the order of preference indicated by the
client and select the new protocol(s) based on other factors, such as
the nature of the request or the current load on the server.
A server that sends a 426 (Upgrade Required) response MUST send an
Upgrade header field to indicate the acceptable protocols, in order
of descending preference.
A server MAY send an Upgrade header field in any other response to
advertise that it implements support for upgrading to the listed
protocols, in order of descending preference, when appropriate for a
future request.
The following is a hypothetical example sent by a client:
GET /hello.txt HTTP/1.1
Host: www.example.com
Connection: upgrade
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
Fielding & Reschke Expires May 21, 2014 [Page 56]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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-level communication after the protocol change is
entirely dependent upon the new protocol(s) chosen. However,
immediately after sending the 101 response, the server is expected to
continue responding to the original request as if it had received its
equivalent within the new protocol (i.e., the server still has an
outstanding request to satisfy after the protocol has been changed,
and is expected to do so without requiring the request to be
repeated).
For example, if the Upgrade header field is received in a GET request
and the server decides to switch protocols, it first responds with a
101 (Switching Protocols) message in HTTP/1.1 and then immediately
follows that with the new protocol's equivalent of a response to a
GET on the target resource. This allows a connection to be upgraded
to protocols with the same semantics as HTTP without the latency cost
of an additional round-trip. A server MUST NOT switch protocols
unless the received message semantics can be honored by the new
protocol; an OPTIONS request can be honored by any protocol.
The following is an example response to the above hypothetical
request:
HTTP/1.1 101 Switching Protocols
Connection: upgrade
Upgrade: HTTP/2.0
[... data stream switches to HTTP/2.0 with an appropriate response
(as defined by new protocol) to the "GET /hello.txt" request ...]
When Upgrade is sent, the sender MUST also send a Connection header
field (Section 6.1) that contains an "upgrade" connection option, in
order to prevent Upgrade from being accidentally forwarded by
intermediaries that might not implement the listed protocols. A
server MUST ignore an Upgrade header field that is received in an
HTTP/1.0 request.
A client cannot begin using an upgraded protocol on the connection
until it has completely sent the request message (i.e., the client
can't change the protocol it is sending in the middle of a message).
If a server receives both Upgrade and an Expect header field with the
"100-continue" expectation (Section 5.1.1 of [Part2]), the server
MUST send a 100 (Continue) response before sending a 101 (Switching
Protocols) response.
The Upgrade header field only applies to switching protocols on top
of the existing connection; it cannot be used to switch the
Fielding & Reschke Expires May 21, 2014 [Page 57]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
underlying connection (transport) protocol, nor to switch the
existing communication to a different connection. For those
purposes, it is more appropriate to use a 3xx (Redirection) response
(Section 6.4 of [Part2]).
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 ought to be registered with IANA
using the registration procedure defined in Section 8.6.
7. ABNF list extension: #rule
A #rule extension to the ABNF rules of [RFC5234] is used to improve
readability in the definitions of some header field values.
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).
Thus, a sender MUST expand the list construct as follows:
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, a recipient MUST parse and
ignore a reasonable number of empty list elements: enough to handle
common mistakes by senders that merge values, but not so much that
they could be used as a denial of service mechanism. In other words,
a recipient MUST expand the list construct as follows:
#element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
Empty elements do not contribute to the count of elements present.
For example, given these ABNF productions:
example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 3.2.6
Fielding & Reschke Expires May 21, 2014 [Page 58]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Then the following are valid values for example-list (not including
the double quotes, which are present for delimitation only):
"foo,bar"
"foo ,bar,"
"foo , ,bar,charlie "
In contrast, the following values would be invalid, since at least
one non-empty element is required by the example-list production:
""
","
", ,"
Appendix B shows the collected ABNF after the list constructs have
been expanded, as described above, for recipients.
8. IANA Considerations
8.1. Header Field Registration
HTTP header fields are registered within the Message Header Field
Registry maintained at
<http://www.iana.org/assignments/message-headers/>.
This document defines the following HTTP header fields, so their
associated registry entries shall be updated according to the
permanent registrations below (see [BCP90]):
+-------------------+----------+----------+---------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+---------------+
| Connection | http | standard | Section 6.1 |
| Content-Length | http | standard | Section 3.3.2 |
| Host | http | standard | Section 5.4 |
| TE | http | standard | Section 4.3 |
| Trailer | http | standard | Section 4.4 |
| Transfer-Encoding | http | standard | Section 3.3.1 |
| Upgrade | http | standard | Section 6.7 |
| Via | http | standard | Section 5.7.1 |
+-------------------+----------+----------+---------------+
Furthermore, the header field-name "Close" shall be registered as
"reserved", since using that name as an HTTP header field might
conflict with the "close" connection option of the "Connection"
header field (Section 6.1).
Fielding & Reschke Expires May 21, 2014 [Page 59]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Close | http | reserved | Section 8.1 |
+-------------------+----------+----------+-------------+
The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force".
8.2. URI Scheme Registration
IANA maintains the registry of URI Schemes [BCP115] at
<http://www.iana.org/assignments/uri-schemes/>.
This document defines the following URI schemes, so their associated
registry entries shall be updated according to the permanent
registrations below:
+------------+------------------------------------+---------------+
| URI Scheme | Description | Reference |
+------------+------------------------------------+---------------+
| http | Hypertext Transfer Protocol | Section 2.7.1 |
| https | Hypertext Transfer Protocol Secure | Section 2.7.2 |
+------------+------------------------------------+---------------+
8.3. Internet Media Type Registration
IANA maintains the registry of Internet media types [BCP13] at
<http://www.iana.org/assignments/media-types>.
This document serves as the specification for the Internet media
types "message/http" and "application/http". The following is to be
registered with IANA.
8.3.1. 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.
Type name: message
Subtype name: http
Required parameters: none
Fielding & Reschke Expires May 21, 2014 [Page 60]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 8.3.1).
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: See Authors Section.
Change controller: IESG
8.3.2. 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).
Fielding & Reschke Expires May 21, 2014 [Page 61]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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 8.3.2).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author: See Authors Section.
Fielding & Reschke Expires May 21, 2014 [Page 62]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Change controller: IESG
8.4. Transfer Coding Registry
The HTTP Transfer Coding Registry defines the name space for transfer
coding names. It is maintained at
<http://www.iana.org/assignments/http-parameters>.
8.4.1. Procedure
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 3.1.2.1 of [Part2]) unless the encoding
transformation is identical, as is the case for the compression
codings defined in Section 4.2.
Values to be added to this name space require IETF Review (see
Section 4.1 of [RFC5226]), and MUST conform to the purpose of
transfer coding defined in this specification.
Use of program names for the identification of encoding formats is
not desirable and is discouraged for future encodings.
8.4.2. Registration
The HTTP Transfer Coding Registry shall be updated with the
registrations below:
+------------+--------------------------------------+---------------+
| Name | Description | Reference |
+------------+--------------------------------------+---------------+
| chunked | Transfer in a series of chunks | Section 4.1 |
| compress | UNIX "compress" data format [Welch] | Section 4.2.1 |
| deflate | "deflate" compressed data | Section 4.2.2 |
| | ([RFC1951]) inside the "zlib" data | |
| | format ([RFC1950]) | |
| gzip | GZIP file format [RFC1952] | Section 4.2.3 |
| x-compress | Deprecated (alias for compress) | Section 4.2.1 |
| x-gzip | Deprecated (alias for gzip) | Section 4.2.3 |
+------------+--------------------------------------+---------------+
Fielding & Reschke Expires May 21, 2014 [Page 63]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
8.5. Content Coding Registration
IANA maintains the registry of HTTP Content Codings at
<http://www.iana.org/assignments/http-parameters>.
The HTTP Content Codings Registry shall be updated with the
registrations below:
+------------+--------------------------------------+---------------+
| Name | Description | Reference |
+------------+--------------------------------------+---------------+
| compress | UNIX "compress" data format [Welch] | Section 4.2.1 |
| deflate | "deflate" compressed data | Section 4.2.2 |
| | ([RFC1951]) inside the "zlib" data | |
| | format ([RFC1950]) | |
| gzip | GZIP file format [RFC1952] | Section 4.2.3 |
| x-compress | Deprecated (alias for compress) | Section 4.2.1 |
| x-gzip | Deprecated (alias for gzip) | Section 4.2.3 |
+------------+--------------------------------------+---------------+
8.6. Upgrade Token Registry
The HTTP Upgrade Token Registry defines the name space for protocol-
name tokens used to identify protocols in the Upgrade header field.
The registry is maintained at
<http://www.iana.org/assignments/http-upgrade-tokens>.
8.6.1. Procedure
Each registered protocol name 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 happen on a "First Come First Served" basis (see
Section 4.1 of [RFC5226]) and are subject to the following rules:
1. A protocol-name 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 registration SHOULD name a set of expected "protocol-version"
tokens associated with that token at the time of registration.
Fielding & Reschke Expires May 21, 2014 [Page 64]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
6. 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.
7. The IESG MAY reassign responsibility for a protocol token. This
will normally only be used in the case when a responsible party
cannot be contacted.
This registration procedure for HTTP Upgrade Tokens replaces that
previously defined in Section 7.2 of [RFC2817].
8.6.2. Upgrade Token Registration
The "HTTP" entry in the HTTP Upgrade Token Registry shall be updated
with the registration below:
+-------+----------------------+----------------------+-------------+
| Value | Description | Expected Version | Reference |
| | | Tokens | |
+-------+----------------------+----------------------+-------------+
| HTTP | Hypertext Transfer | any DIGIT.DIGIT | Section 2.6 |
| | Protocol | (e.g, "2.0") | |
+-------+----------------------+----------------------+-------------+
The responsible party is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force".
9. Security Considerations
This section is meant to inform developers, information providers,
and users of known security concerns relevant to HTTP/1.1 message
syntax, parsing, and routing.
9.1. 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/
DNS name association unless the response is protected by DNSSEC
([RFC4033]).
9.2. Intermediaries and Caching
By their very nature, HTTP intermediaries are men-in-the-middle, and
represent an opportunity for man-in-the-middle attacks. Compromise
of the systems on which the intermediaries run can result in serious
security and privacy problems. Intermediaries have access to
Fielding & Reschke Expires May 21, 2014 [Page 65]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
security-related information, personal information about individual
users and organizations, and proprietary information belonging to
users and content providers. A compromised intermediary, or an
intermediary implemented or configured without regard to security and
privacy considerations, might be used in the commission of a wide
range of potential attacks.
Intermediaries that contain a shared cache are especially vulnerable
to cache poisoning attacks.
Implementers need to consider the privacy and security implications
of their design and coding decisions, and of the configuration
options they provide to operators (especially the default
configuration).
Users need to be aware that intermediaries are no more trustworthy
than the people who run them; HTTP itself cannot solve this problem.
9.3. Buffer 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 minimum size limits on request-line
(Section 3.1.1) and 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.
This specification also provides a way for servers to reject messages
that have request-targets that are too long (Section 6.5.12 of
[Part2]) or request entities that are too large (Section 6.5 of
[Part2]). Additional status codes related to capacity limits have
been defined by extensions to HTTP [RFC6585].
Recipients ought to carefully limit the extent to which they read
other fields, including (but not limited to) request methods,
response status phrases, header field-names, and body chunks, so as
to avoid denial of service attacks without impeding interoperability.
9.4. Message Integrity
HTTP does not define a specific mechanism for ensuring message
integrity, instead relying on the error-detection ability of
underlying transport protocols and the use of length or chunk-
Fielding & Reschke Expires May 21, 2014 [Page 66]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
delimited framing to detect completeness. Additional integrity
mechanisms, such as hash functions or digital signatures applied to
the content, can be selectively added to messages via extensible
metadata header fields. Historically, the lack of a single integrity
mechanism has been justified by the informal nature of most HTTP
communication. However, the prevalence of HTTP as an information
access mechanism has resulted in its increasing use within
environments where verification of message integrity is crucial.
User agents are encouraged to implement configurable means for
detecting and reporting failures of message integrity such that those
means can be enabled within environments for which integrity is
necessary. For example, a browser being used to view medical history
or drug interaction information needs to indicate to the user when
such information is detected by the protocol to be incomplete,
expired, or corrupted during transfer. Such mechanisms might be
selectively enabled via user agent extensions or the presence of
message integrity metadata in a response. At a minimum, user agents
ought to provide some indication that allows a user to distinguish
between a complete and incomplete response message (Section 3.4) when
such verification is desired.
9.5. Server Log Information
A server is in the position to save personal data about a user's
requests over time, which might identify their reading patterns or
subjects of interest. In particular, log information gathered at an
intermediary often contains a history of user agent interaction,
across a multitude of sites, that can be traced to individual users.
HTTP log information is confidential in nature; its handling is often
constrained by laws and regulations. Log information needs to be
securely stored and appropriate guidelines followed for its analysis.
Anonymization of personal information within individual entries
helps, but is generally not sufficient to prevent real log traces
from being re-identified based on correlation with other access
characteristics. As such, access traces that are keyed to a specific
client are unsafe to publish even if the key is pseudonymous.
To minimize the risk of theft or accidental publication, log
information ought to be purged of personally identifiable
information, including user identifiers, IP addresses, and user-
provided query parameters, as soon as that information is no longer
necessary to support operational needs for security, auditing, or
fraud control.
Fielding & Reschke Expires May 21, 2014 [Page 67]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
10. Acknowledgments
This edition of HTTP/1.1 builds on the many contributions that went
into RFC 1945, RFC 2068, RFC 2145, and RFC 2616, including
substantial contributions made by the previous authors, editors, and
working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
and Paul J. Leach. Mark Nottingham oversaw this effort as working
group chair.
Since 1999, the following contributors have helped improve the HTTP
specification by reporting bugs, asking smart questions, drafting or
reviewing text, and evaluating open issues:
Adam Barth, Adam Roach, Addison Phillips, Adrian Chadd, Adrien W. de
Croy, Alan Ford, Alan Ruttenberg, Albert Lunde, Alek Storm, Alex
Rousskov, Alexandre Morgaut, Alexey Melnikov, Alisha Smith, Amichai
Rothman, Amit Klein, Amos Jeffries, Andreas Maier, Andreas Petersson,
Andrei Popov, Anil Sharma, Anne van Kesteren, Anthony Bryan, Asbjorn
Ulsberg, Ashok Kumar, Balachander Krishnamurthy, Barry Leiba, Ben
Laurie, Benjamin Carlyle, Benjamin Niven-Jenkins, Bil Corry, Bill
Burke, Bjoern Hoehrmann, Bob Scheifler, Boris Zbarsky, Brett Slatkin,
Brian Kell, Brian McBarron, Brian Pane, Brian Raymor, Brian Smith,
Bryce Nesbitt, Cameron Heavon-Jones, Carl Kugler, Carsten Bormann,
Charles Fry, Chris Newman, Cyrus Daboo, Dale Robert Anderson, Dan
Wing, Dan Winship, Daniel Stenberg, Darrel Miller, Dave Cridland,
Dave Crocker, Dave Kristol, Dave Thaler, David Booth, David Singer,
David W. Morris, Diwakar Shetty, Dmitry Kurochkin, Drummond Reed,
Duane Wessels, Edward Lee, Eitan Adler, Eliot Lear, Emile Stephan,
Eran Hammer-Lahav, Eric D. Williams, Eric J. Bowman, Eric Lawrence,
Eric Rescorla, Erik Aronesty, EungJun Yi, Evan Prodromou, Felix
Geisendoerfer, Florian Weimer, Frank Ellermann, Fred Akalin, Fred
Bohle, Frederic Kayser, Gabor Molnar, Gabriel Montenegro, Geoffrey
Sneddon, Gervase Markham, Gili Tzabari, Grahame Grieve, Greg Wilkins,
Grzegorz Calkowski, Harald Tveit Alvestrand, Harry Halpin, Helge
Hess, Henrik Nordstrom, Henry S. Thompson, Henry Story, Herbert van
de Sompel, Herve Ruellan, Howard Melman, Hugo Haas, Ian Fette, Ian
Hickson, Ido Safruti, Ilari Liusvaara, Ilya Grigorik, Ingo Struck, J.
Ross Nicoll, James Cloos, James H. Manger, James Lacey, James M.
Snell, Jamie Lokier, Jan Algermissen, Jeff Hodges (who came up with
the term 'effective Request-URI'), Jeff Pinner, Jeff Walden, Jim
Luther, Jitu Padhye, Joe D. Williams, Joe Gregorio, Joe Orton, John
C. Klensin, John C. Mallery, John Cowan, John Kemp, John Panzer, John
Schneider, John Stracke, John Sullivan, Jonas Sicking, Jonathan A.
Rees, Jonathan Billington, Jonathan Moore, Jonathan Silvera, Jordi
Ros, Joris Dobbelsteen, Josh Cohen, Julien Pierre, Jungshik Shin,
Justin Chapweske, Justin Erenkrantz, Justin James, Kalvinder Singh,
Karl Dubost, Keith Hoffman, Keith Moore, Ken Murchison, Koen Holtman,
Fielding & Reschke Expires May 21, 2014 [Page 68]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Konstantin Voronkov, Kris Zyp, Leif Hedstrom, Lisa Dusseault, Maciej
Stachowiak, Manu Sporny, Marc Schneider, Marc Slemko, Mark Baker,
Mark Pauley, Mark Watson, Markus Isomaki, Markus Lanthaler, Martin J.
Duerst, Martin Musatov, Martin Nilsson, Martin Thomson, Matt Lynch,
Matthew Cox, Max Clark, Michael Burrows, Michael Hausenblas, Michael
Scharf, Michael Sweet, Michael Tuexen, Michael Welzl, Mike Amundsen,
Mike Belshe, Mike Bishop, Mike Kelly, Mike Schinkel, Miles Sabin,
Murray S. Kucherawy, Mykyta Yevstifeyev, Nathan Rixham, Nicholas
Shanks, Nico Williams, Nicolas Alvarez, Nicolas Mailhot, Noah Slater,
Osama Mazahir, Pablo Castro, Pat Hayes, Patrick R. McManus, Paul E.
Jones, Paul Hoffman, Paul Marquess, Peter Lepeska, Peter Occil, Peter
Saint-Andre, Peter Watkins, Phil Archer, Philippe Mougin, Phillip
Hallam-Baker, Piotr Dobrogost, Poul-Henning Kamp, Preethi Natarajan,
Rajeev Bector, Ray Polk, Reto Bachmann-Gmuer, Richard Cyganiak, Robby
Simpson, Robert Brewer, Robert Collins, Robert Mattson, Robert
O'Callahan, Robert Olofsson, Robert Sayre, Robert Siemer, Robert de
Wilde, Roberto Javier Godoy, Roberto Peon, Roland Zink, Ronny
Widjaja, Ryan Hamilton, S. Mike Dierken, Salvatore Loreto, Sam
Johnston, Sam Pullara, Sam Ruby, Saurabh Kulkarni, Scott Lawrence
(who maintained the original issues list), Sean B. Palmer, Sebastien
Barnoud, Shane McCarron, Shigeki Ohtsu, Stefan Eissing, Stefan
Tilkov, Stefanos Harhalakis, Stephane Bortzmeyer, Stephen Farrell,
Stephen Ludin, Stuart Williams, Subbu Allamaraju, Subramanian
Moonesamy, Sylvain Hellegouarch, Tapan Divekar, Tatsuhiro Tsujikawa,
Tatsuya Hayashi, Ted Hardie, Thomas Broyer, Thomas Fossati, Thomas
Maslen, Thomas Nordin, Thomas Roessler, Tim Bray, Tim Morgan, Tim
Olsen, Tom Zhou, 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, Yoav Nir, Yogesh Bang, Yuchung Cheng,
Yutaka Oiwa, Yves Lafon (long-time member of the editor team), Zed A.
Shaw, and Zhong Yu.
See Section 16 of [RFC2616] for additional acknowledgements from
prior revisions.
11. References
11.1. Normative References
[Part2] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content",
draft-ietf-httpbis-p2-semantics-25 (work in progress),
November 2013.
[Part4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Conditional Requests",
draft-ietf-httpbis-p4-conditional-25 (work in
Fielding & Reschke Expires May 21, 2014 [Page 69]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
progress), November 2013.
[Part5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range
Requests", draft-ietf-httpbis-p5-range-25 (work in
progress), November 2013.
[Part6] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
draft-ietf-httpbis-p6-cache-25 (work in progress),
November 2013.
[Part7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Authentication",
draft-ietf-httpbis-p7-auth-25 (work in progress),
November 2013.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[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.
[Welch] Welch, T., "A Technique for High Performance Data
Compression", IEEE Computer 17(6), June 1984.
Fielding & Reschke Expires May 21, 2014 [Page 70]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
11.2. Informative References
[BCP115] Hansen, T., Hardie, T., and L. Masinter, "Guidelines
and Registration Procedures for New URI Schemes",
BCP 115, RFC 4395, February 2006.
[BCP13] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, January 2013.
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.
[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.
[Kri2001] Kristol, D., "HTTP Cookies: Standards, Privacy, and
Politics", ACM Transactions on Internet
Technology 1(2), November 2001,
<http://arxiv.org/abs/cs.SE/0105018>.
[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.,
Fielding & Reschke Expires May 21, 2014 [Page 71]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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.
[RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC 3040,
January 2001.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[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.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, April 2012.
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
Fielding & Reschke Expires May 21, 2014 [Page 72]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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
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
conformance with HTTP/1.1.
It is beyond the scope of a protocol specification to mandate
conformance 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, we 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 5.4), report an error if it is missing from an
HTTP/1.1 request, and accept absolute URIs (Section 5.3) 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
Fielding & Reschke Expires May 21, 2014 [Page 73]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
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
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 an HTTP/1.0 proxy
server doesn't understand Connection, it will erroneously forward
that header field to the next inbound server, which would result in a
hung connection.
One attempted solution was the introduction of a Proxy-Connection
header field, 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 field 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 will need to
monitor the connection for "hung" requests (which indicate that the
client ought stop sending the header field), and this mechanism ought
not be used by clients at all when a proxy is being used.
A.1.3. Introduction of Transfer-Encoding
HTTP/1.1 introduces the Transfer-Encoding header field
(Section 3.3.1). Transfer codings need to be decoded prior to
forwarding an HTTP message over a MIME-compliant protocol.
A.2. Changes from RFC 2616
HTTP's approach to error handling has been explained. (Section 2.5)
The HTTP-version ABNF production has been clarified to be case-
Fielding & Reschke Expires May 21, 2014 [Page 74]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
sensitive. Additionally, version numbers has been restricted to
single digits, due to the fact that implementations are known to
handle multi-digit version numbers incorrectly. (Section 2.6)
Userinfo (i.e., username and password) are now disallowed in HTTP and
HTTPS URIs, because of security issues related to their transmission
on the wire. (Section 2.7.1)
The HTTPS URI scheme is now defined by this specification;
previously, it was done in Section 2.4 of [RFC2818]. Furthermore, it
implies end-to-end security. (Section 2.7.2)
HTTP messages can be (and often are) buffered by implementations;
despite it sometimes being available as a stream, HTTP is
fundamentally a message-oriented protocol. Minimum supported sizes
for various protocol elements have been suggested, to improve
interoperability. (Section 3)
Invalid whitespace around field-names is now required to be rejected,
because accepting it represents a security vulnerability. The ABNF
productions defining header fields now only list the field value.
(Section 3.2)
Rules about implicit linear whitespace between certain grammar
productions have been removed; now whitespace is only allowed where
specifically defined in the ABNF. (Section 3.2.3)
Header fields that span multiple lines ("line folding") are
deprecated. (Section 3.2.4)
The NUL octet is no longer allowed in comment and quoted-string text,
and handling of backslash-escaping in them has been clarified. The
quoted-pair rule no longer allows escaping control characters other
than HTAB. Non-ASCII content in header fields and the reason phrase
has been obsoleted and made opaque (the TEXT rule was removed).
(Section 3.2.6)
Bogus "Content-Length" header fields are now required to be handled
as errors by recipients. (Section 3.3.2)
The algorithm for determining the message body length has been
clarified to indicate all of the special cases (e.g., driven by
methods or status codes) that affect it, and that new protocol
elements cannot define such special cases. CONNECT is a new, special
case in determining message body length. "multipart/byteranges" is no
longer a way of determining message body length detection.
(Section 3.3.3)
Fielding & Reschke Expires May 21, 2014 [Page 75]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
The "identity" transfer coding token has been removed. (Sections 3.3
and 4)
Chunk length does not include the count of the octets in the chunk
header and trailer. Line folding in chunk extensions is disallowed.
(Section 4.1)
The meaning of the "deflate" content coding has been clarified.
(Section 4.2.2)
The segment + query components of RFC 3986 have been used to define
the request-target, instead of abs_path from RFC 1808. The asterisk-
form of the request-target is only allowed with the OPTIONS method.
(Section 5.3)
The term "Effective Request URI" has been introduced. (Section 5.5)
Gateways do not need to generate Via header fields anymore.
(Section 5.7.1)
Exactly when "close" connection options have to be sent has been
clarified. Also, "hop-by-hop" header fields are required to appear
in the Connection header field; just because they're defined as hop-
by-hop in this specification doesn't exempt them. (Section 6.1)
The limit of two connections per server has been removed. An
idempotent sequence of requests is no longer required to be retried.
The requirement to retry requests under certain circumstances when
the server prematurely closes the connection has been removed. Also,
some extraneous requirements about when servers are allowed to close
connections prematurely have been removed. (Section 6.3)
The semantics of the Upgrade header field is now defined in responses
other than 101 (this was incorporated from [RFC2817]). Furthermore,
the ordering in the field value is now significant. (Section 6.7)
Empty list elements in list productions (e.g., a list header field
containing ", ,") have been deprecated. (Section 7)
Registration of Transfer Codings now requires IETF Review
(Section 8.4)
This specification now defines the Upgrade Token Registry, previously
defined in Section 7.2 of [RFC2817]. (Section 8.6)
The expectation to support HTTP/0.9 requests has been removed.
(Appendix A)
Fielding & Reschke Expires May 21, 2014 [Page 76]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
Issues with the Keep-Alive and Proxy-Connection header fields in
requests are pointed out, with use of the latter being discouraged
altogether. (Appendix A.1.2)
Appendix B. Collected ABNF
BWS = OWS
Connection = *( "," OWS ) connection-option *( OWS "," [ OWS
connection-option ] )
Content-Length = 1*DIGIT
HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
]
HTTP-name = %x48.54.54.50 ; HTTP
HTTP-version = HTTP-name "/" DIGIT "." DIGIT
Host = uri-host [ ":" port ]
OWS = *( SP / HTAB )
RWS = 1*( SP / HTAB )
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 ) protocol *( OWS "," [ OWS protocol ] )
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>
absolute-form = absolute-URI
absolute-path = 1*( "/" segment )
asterisk-form = "*"
attribute = token
authority = <authority, defined in [RFC3986], Section 3.2>
authority-form = authority
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
Fielding & Reschke Expires May 21, 2014 [Page 77]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
chunked-body = *chunk last-chunk trailer-part CRLF
comment = "(" *( ctext / quoted-cpair / comment ) ")"
connection-option = token
ctext = HTAB / SP / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
field-content = *( HTAB / SP / VCHAR / obs-text )
field-name = token
field-value = *( field-content / obs-fold )
fragment = <fragment, defined in [RFC3986], Section 3.5>
header-field = field-name ":" OWS field-value OWS
http-URI = "http://" authority path-abempty [ "?" query ] [ "#"
fragment ]
https-URI = "https://" authority path-abempty [ "?" query ] [ "#"
fragment ]
last-chunk = 1*"0" [ chunk-ext ] CRLF
message-body = *OCTET
method = token
obs-fold = CRLF ( SP / HTAB )
obs-text = %x80-FF
origin-form = absolute-path [ "?" query ]
partial-URI = relative-part [ "?" query ]
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
port = <port, defined in [RFC3986], Section 3.2.3>
protocol = protocol-name [ "/" protocol-version ]
protocol-name = token
protocol-version = token
pseudonym = token
qdtext = HTAB / SP / "!" / %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
Fielding & Reschke Expires May 21, 2014 [Page 78]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
rank = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
reason-phrase = *( HTAB / SP / VCHAR / obs-text )
received-by = ( uri-host [ ":" port ] ) / pseudonym
received-protocol = [ protocol-name "/" ] protocol-version
relative-part = <relative-part, defined in [RFC3986], Section 4.2>
request-line = method SP request-target SP HTTP-version CRLF
request-target = origin-form / absolute-form / authority-form /
asterisk-form
segment = <segment, defined in [RFC3986], Section 3.3>
special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
start-line = request-line / status-line
status-code = 3DIGIT
status-line = HTTP-version SP status-code SP reason-phrase CRLF
t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
t-ranking = OWS ";" OWS "q=" rank
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
"^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
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
Appendix C. Change Log (to be removed by RFC Editor before publication)
C.1. Since RFC 2616
Changes up to the IETF Last Call draft are summarized in <http://
trac.tools.ietf.org/html/
draft-ietf-httpbis-p1-messaging-24#appendix-C>.
C.2. Since draft-ietf-httpbis-p1-messaging-24
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/502>: "APPSDIR
review of draft-ietf-httpbis-p1-messaging-24"
Fielding & Reschke Expires May 21, 2014 [Page 79]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
o <http://tools.ietf.org/wg/httpbis/trac/ticket/507>: "integer value
parsing"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/517>: "move IANA
registrations to correct draft"
Index
A
absolute-form (of request-target) 42
accelerator 10
application/http Media Type 61
asterisk-form (of request-target) 42
authority-form (of request-target) 42
B
browser 7
C
cache 11
cacheable 12
captive portal 11
chunked (Coding Format) 28, 31, 35
client 7
close 49, 55
compress (Coding Format) 38
connection 7
Connection header field 49, 55
Content-Length header field 30
D
deflate (Coding Format) 38
downstream 9
E
effective request URI 44
G
gateway 10
Grammar
absolute-form 41
absolute-path 16
absolute-URI 16
ALPHA 6
asterisk-form 41
attribute 35
authority 16
authority-form 41
Fielding & Reschke Expires May 21, 2014 [Page 80]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
BWS 24
chunk 35-36
chunk-data 35-36
chunk-ext 35-36
chunk-ext-name 35-36
chunk-ext-val 35-36
chunk-size 35-36
chunked-body 35-36
comment 27
Connection 50
connection-option 50
Content-Length 30
CR 6
CRLF 6
ctext 27
CTL 6
date2 35
date3 35
DIGIT 6
DQUOTE 6
field-content 22
field-name 22
field-value 22
fragment 16
header-field 22
HEXDIG 6
Host 43
HTAB 6
HTTP-message 19
HTTP-name 14
http-URI 17
HTTP-version 14
https-URI 18
last-chunk 35-36
LF 6
message-body 27
method 21
obs-fold 22
obs-text 27
OCTET 6
origin-form 41
OWS 24
partial-URI 16
port 16
protocol-name 47
protocol-version 47
pseudonym 47
qdtext 27
Fielding & Reschke Expires May 21, 2014 [Page 81]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
qdtext-nf 35-36
query 16
quoted-cpair 27
quoted-pair 27
quoted-str-nf 35-36
quoted-string 27
rank 39
reason-phrase 22
received-by 47
received-protocol 47
request-line 21
request-target 41
RWS 24
segment 16
SP 6
special 26
start-line 21
status-code 22
status-line 22
t-codings 39
t-ranking 39
tchar 26
TE 39
token 26
Trailer 40
trailer-part 35-37
transfer-coding 35
Transfer-Encoding 28
transfer-extension 35
transfer-parameter 35
Upgrade 56
uri-host 16
URI-reference 16
value 35
VCHAR 6
Via 47
word 26
gzip (Coding Format) 38
H
header field 19
header section 19
headers 19
Host header field 43
http URI scheme 17
https URI scheme 18
I
Fielding & Reschke Expires May 21, 2014 [Page 82]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
inbound 9
interception proxy 11
intermediary 9
M
Media Type
application/http 61
message/http 60
message 7
message/http Media Type 60
method 21
N
non-transforming proxy 10
O
origin server 7
origin-form (of request-target) 41
outbound 9
P
proxy 10
R
recipient 7
request 7
request-target 21
resource 16
response 7
reverse proxy 10
S
sender 7
server 7
spider 7
T
target resource 40
target URI 40
TE header field 38
Trailer header field 40
Transfer-Encoding header field 28
transforming proxy 10
transparent proxy 11
tunnel 11
U
Upgrade header field 56
Fielding & Reschke Expires May 21, 2014 [Page 83]
Internet-Draft HTTP/1.1 Message Syntax and Routing November 2013
upstream 9
URI scheme
http 17
https 18
user agent 7
V
Via header field 46
Authors' Addresses
Roy T. Fielding (editor)
Adobe Systems Incorporated
345 Park Ave
San Jose, CA 95110
USA
EMail: fielding@gbiv.com
URI: http://roy.gbiv.com/
Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
Fielding & Reschke Expires May 21, 2014 [Page 84]
Received on Monday, 16 December 2013 16:11:00 UTC