HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe
Obsoletes: 2145,2616 (if approved) J. Reschke, Ed.
Updates: 2817 (if approved) greenbytes
Intended status: Standards Track October 4, 2012
Expires: April 7, 2013
Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing
draft-ietf-httpbis-p1-messaging-21
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
.
The current issues list is at
and related
documents (including fancy diffs) can be found at
.
The changes in this draft are summarized in Appendix D.22.
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-
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on April 7, 2013.
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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 . . . . . . . . . . . . . . . . . . . 13
2.7. Uniform Resource Identifiers . . . . . . . . . . . . . . . 15
2.7.1. http URI scheme . . . . . . . . . . . . . . . . . . . 16
2.7.2. https URI scheme . . . . . . . . . . . . . . . . . . . 17
2.7.3. http and https URI Normalization and Comparison . . . 18
3. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 18
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3.1. Start Line . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1.1. Request Line . . . . . . . . . . . . . . . . . . . . . 20
3.1.2. Status Line . . . . . . . . . . . . . . . . . . . . . 21
3.2. Header Fields . . . . . . . . . . . . . . . . . . . . . . 21
3.2.1. Whitespace . . . . . . . . . . . . . . . . . . . . . . 23
3.2.2. Field Parsing . . . . . . . . . . . . . . . . . . . . 23
3.2.3. Field Length . . . . . . . . . . . . . . . . . . . . . 24
3.2.4. Field value components . . . . . . . . . . . . . . . . 24
3.3. Message Body . . . . . . . . . . . . . . . . . . . . . . . 26
3.3.1. Transfer-Encoding . . . . . . . . . . . . . . . . . . 26
3.3.2. Content-Length . . . . . . . . . . . . . . . . . . . . 28
3.3.3. Message Body Length . . . . . . . . . . . . . . . . . 29
3.4. Handling Incomplete Messages . . . . . . . . . . . . . . . 31
3.5. Message Parsing Robustness . . . . . . . . . . . . . . . . 32
4. Transfer Codings . . . . . . . . . . . . . . . . . . . . . . . 32
4.1. Chunked Transfer Coding . . . . . . . . . . . . . . . . . 33
4.1.1. Trailer . . . . . . . . . . . . . . . . . . . . . . . 34
4.1.2. Decoding chunked . . . . . . . . . . . . . . . . . . . 35
4.2. Compression Codings . . . . . . . . . . . . . . . . . . . 35
4.2.1. Compress Coding . . . . . . . . . . . . . . . . . . . 35
4.2.2. Deflate Coding . . . . . . . . . . . . . . . . . . . . 35
4.2.3. Gzip Coding . . . . . . . . . . . . . . . . . . . . . 36
4.3. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5. Message Routing . . . . . . . . . . . . . . . . . . . . . . . 37
5.1. Identifying a Target Resource . . . . . . . . . . . . . . 37
5.2. Connecting Inbound . . . . . . . . . . . . . . . . . . . . 37
5.3. Request Target . . . . . . . . . . . . . . . . . . . . . . 38
5.4. Host . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.5. Effective Request URI . . . . . . . . . . . . . . . . . . 41
5.6. Message Forwarding . . . . . . . . . . . . . . . . . . . . 42
5.7. Via . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.8. Message Transforming . . . . . . . . . . . . . . . . . . . 44
5.9. Associating a Response to a Request . . . . . . . . . . . 46
6. Connection Management . . . . . . . . . . . . . . . . . . . . 46
6.1. Connection . . . . . . . . . . . . . . . . . . . . . . . . 46
6.2. Persistent Connections . . . . . . . . . . . . . . . . . . 48
6.2.1. Establishment . . . . . . . . . . . . . . . . . . . . 49
6.2.2. Reuse . . . . . . . . . . . . . . . . . . . . . . . . 50
6.2.3. Concurrency . . . . . . . . . . . . . . . . . . . . . 51
6.2.4. Failures and Time-outs . . . . . . . . . . . . . . . . 51
6.2.5. Tear-down . . . . . . . . . . . . . . . . . . . . . . 52
6.3. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 53
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 54
7.1. Header Field Registration . . . . . . . . . . . . . . . . 54
7.2. URI Scheme Registration . . . . . . . . . . . . . . . . . 55
7.3. Internet Media Type Registrations . . . . . . . . . . . . 56
7.3.1. Internet Media Type message/http . . . . . . . . . . . 56
7.3.2. Internet Media Type application/http . . . . . . . . . 57
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7.4. Transfer Coding Registry . . . . . . . . . . . . . . . . . 58
7.5. Transfer Coding Registrations . . . . . . . . . . . . . . 58
7.6. Upgrade Token Registry . . . . . . . . . . . . . . . . . . 59
7.7. Upgrade Token Registration . . . . . . . . . . . . . . . . 60
8. Security Considerations . . . . . . . . . . . . . . . . . . . 60
8.1. Personal Information . . . . . . . . . . . . . . . . . . . 60
8.2. Abuse of Server Log Information . . . . . . . . . . . . . 60
8.3. Attacks Based On File and Path Names . . . . . . . . . . . 61
8.4. DNS-related Attacks . . . . . . . . . . . . . . . . . . . 61
8.5. Intermediaries and Caching . . . . . . . . . . . . . . . . 61
8.6. Protocol Element Size Overflows . . . . . . . . . . . . . 62
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 62
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 64
10.1. Normative References . . . . . . . . . . . . . . . . . . . 64
10.2. Informative References . . . . . . . . . . . . . . . . . . 65
Appendix A. HTTP Version History . . . . . . . . . . . . . . . . 67
A.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 67
A.1.1. Multi-homed Web Servers . . . . . . . . . . . . . . . 68
A.1.2. Keep-Alive Connections . . . . . . . . . . . . . . . . 68
A.1.3. Introduction of Transfer-Encoding . . . . . . . . . . 69
A.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 69
Appendix B. ABNF list extension: #rule . . . . . . . . . . . . . 70
Appendix C. Collected ABNF . . . . . . . . . . . . . . . . . . . 71
Appendix D. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 74
D.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 74
D.2. Since draft-ietf-httpbis-p1-messaging-00 . . . . . . . . . 74
D.3. Since draft-ietf-httpbis-p1-messaging-01 . . . . . . . . . 75
D.4. Since draft-ietf-httpbis-p1-messaging-02 . . . . . . . . . 76
D.5. Since draft-ietf-httpbis-p1-messaging-03 . . . . . . . . . 77
D.6. Since draft-ietf-httpbis-p1-messaging-04 . . . . . . . . . 77
D.7. Since draft-ietf-httpbis-p1-messaging-05 . . . . . . . . . 78
D.8. Since draft-ietf-httpbis-p1-messaging-06 . . . . . . . . . 79
D.9. Since draft-ietf-httpbis-p1-messaging-07 . . . . . . . . . 79
D.10. Since draft-ietf-httpbis-p1-messaging-08 . . . . . . . . . 80
D.11. Since draft-ietf-httpbis-p1-messaging-09 . . . . . . . . . 80
D.12. Since draft-ietf-httpbis-p1-messaging-10 . . . . . . . . . 81
D.13. Since draft-ietf-httpbis-p1-messaging-11 . . . . . . . . . 81
D.14. Since draft-ietf-httpbis-p1-messaging-12 . . . . . . . . . 82
D.15. Since draft-ietf-httpbis-p1-messaging-13 . . . . . . . . . 82
D.16. Since draft-ietf-httpbis-p1-messaging-14 . . . . . . . . . 83
D.17. Since draft-ietf-httpbis-p1-messaging-15 . . . . . . . . . 83
D.18. Since draft-ietf-httpbis-p1-messaging-16 . . . . . . . . . 83
D.19. Since draft-ietf-httpbis-p1-messaging-17 . . . . . . . . . 84
D.20. Since draft-ietf-httpbis-p1-messaging-18 . . . . . . . . . 84
D.21. Since draft-ietf-httpbis-p1-messaging-19 . . . . . . . . . 84
D.22. Since draft-ietf-httpbis-p1-messaging-20 . . . . . . . . . 85
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
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1. Introduction
The Hypertext Transfer Protocol (HTTP) is an application-level
request/response protocol that uses extensible semantics and MIME-
like message payloads for flexible interaction with network-based
hypertext information systems. 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, RFC 2145 (on HTTP versioning),
and RFC 2817 (on using CONNECT for TLS upgrades).
HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by
presenting a uniform interface to clients that is independent of the
types of resources provided. Likewise, servers do not need to be
aware of each client's purpose: an HTTP request can be considered in
isolation rather than being associated with a specific type of client
or a predetermined sequence of application steps. The result is a
protocol that can be used effectively in many different contexts and
for which implementations can evolve independently over time.
HTTP is also designed for use as an intermediation protocol for
translating communication to and from non-HTTP information systems.
HTTP proxies and gateways can provide access to alternative
information services by translating their diverse protocols into a
hypertext format that can be viewed and manipulated by clients in the
same way as HTTP services.
One consequence of HTTP flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent of
received communication, and the expected behavior of recipients. If
the communication is considered in isolation, then successful actions
ought to be reflected in corresponding changes to the observable
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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
Appendix B. Appendix C 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.
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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.
The terms client and server refer only to the roles that these
programs perform for a particular connection. The same program might
act as a client on some connections and a server on others. We use
the term ""user agent"" to refer to the program that initiates a
request, such as a WWW browser, editor, or spider (web-traversing
robot), and the term ""origin server"" to refer to the program that
can originate authoritative responses to a request. For general
requirements, we use the term ""sender"" to refer to whichever
component sent a given message and the term ""recipient"" to refer to
any component that receives the message.
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
"response" messages, each beginning with a status line that includes
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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 6.2.
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: 14
Vary: Accept-Encoding
Content-Type: text/plain
Hello World!
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,
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.
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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 can me met via advance
configuration choices, run-time options, or simply not proceeding
with the unsafe action.
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.
We use the terms ""upstream"" and ""downstream"" to describe various
requirements in relation to the directional flow of a message: all
messages flow from upstream to downstream. Likewise, we use the
terms inbound and outbound to refer to directions in relation to the
request path: ""inbound"" means toward the origin server and
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""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 7.3.4 of [Part2] and Section 7.5 of
[Part6] for status and warning codes related to transformations.
A ""gateway"" (a.k.a., ""reverse proxy"") is a receiving agent that
acts as a layer above some other server(s) and translates the
received requests to the underlying server's protocol. Gateways are
often used to encapsulate legacy or untrusted information services,
to improve server performance through ""accelerator"" caching, and to
enable partitioning or load-balancing of HTTP services across
multiple machines.
A gateway behaves as an origin server on its outbound connection and
as a user agent on its inbound connection. All HTTP requirements
applicable to an origin server also apply to the outbound
communication of a gateway. A gateway communicates with inbound
servers using any protocol that it desires, including private
extensions to HTTP that are outside the scope of this specification.
However, an HTTP-to-HTTP gateway that wishes to interoperate with
third-party HTTP servers MUST conform to HTTP user agent requirements
on the gateway's inbound connection and MUST implement the Connection
(Section 6.1) and Via (Section 5.7) header fields for both
connections.
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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,
servers 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.,
[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
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chain if B has a cached copy of an earlier response from O (via C)
for a request which has not been cached by UA or A.
> >
UA =========== A =========== B - - - - - - C - - - - - - O
< <
A response is ""cacheable"" if a cache is allowed to store a copy of
the response message for use in answering subsequent requests. Even
when a response is cacheable, there might be additional constraints
placed by the client or by the origin server on when that cached
response can be used for a particular request. HTTP requirements for
cache behavior and cacheable responses are defined in Section 2 of
[Part6].
There are a wide variety of architectures and configurations of
caches and proxies deployed across the World Wide Web and inside
large organizations. These systems include national hierarchies of
proxy caches to save transoceanic bandwidth, systems that broadcast
or multicast cache entries, organizations that distribute subsets of
cached data via optical media, and so on.
2.5. 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. Note
that SHOULD-level requirements are relevant here, unless one of the
documented exceptions is applicable.
Conformance applies to both the syntax and semantics of HTTP 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 ABNF rules for those protocol elements that are applicable to the
sender's role. If a received protocol element is processed, the
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recipient MUST be able to parse any value that would match the ABNF
rules for that protocol element, excluding only those rules not
applicable to the recipient's role.
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.
2.6. Protocol Versioning
HTTP uses a "." 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 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.
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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 defined such that, when they are understood
by a recipient, they might override or enhance the interpretation of
previously defined header fields. When an implementation receives an
unrecognized header field, the recipient MUST ignore that header
field for local processing regardless of the message's HTTP version.
An unrecognized header field received by a proxy MUST be forwarded
downstream unless the header field's field-name is listed in the
message's Connection header field (see Section 6.1). These
requirements allow HTTP's functionality to be enhanced without
requiring prior update of deployed intermediaries.
Intermediaries that process HTTP messages (i.e., all intermediaries
other than those acting as tunnels) MUST send their own HTTP-version
in forwarded messages. In other words, they MUST NOT blindly forward
the first line of an HTTP message without ensuring that the protocol
version 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.
An HTTP 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. An HTTP client MUST NOT send a version to which it is not
conformant.
An HTTP client MAY send a lower request version if it is known that
the server incorrectly implements the HTTP specification, but only
after the client has attempted at least one normal request and
determined from the response status or header fields (e.g., Server)
that the server improperly handles higher request versions.
An HTTP server SHOULD send a response version equal to the highest
version to which the server is conformant and whose major version is
less than or equal to the one received in the request. An HTTP
server MUST NOT send a version to which it is not conformant. A
server MAY send a 505 (HTTP Version Not Supported) response if it
cannot send a response using the major version used in the client's
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request.
An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
if it is known or suspected that the client incorrectly implements
the HTTP specification and is incapable of correctly processing later
version responses, such as when a client fails to parse the version
number correctly or when an intermediary is known to blindly forward
the HTTP-version even when it doesn't 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 is
specifically avoiding any such changes to the protocol.
2.7. Uniform Resource Identifiers
Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
HTTP as the means for identifying resources (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", "port", "host", "path-abempty",
"path-absolute", "query", and "authority" from the URI generic
syntax. In addition, we define a partial-URI rule for protocol
elements that allow a relative URI but not a fragment.
URI-reference =
absolute-URI =
relative-part =
authority =
path-abempty =
path-absolute =
port =
query =
uri-host =
partial-URI = relative-part [ "?" query ]
Each protocol element in HTTP that allows a URI reference will
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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).
2.7.1. http URI scheme
The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
TCP connections on a given port.
http-URI = "http:" "//" authority path-abempty [ "?" query ]
The HTTP origin server is identified by the generic syntax's
authority component, which includes a host identifier and optional
TCP port ([RFC3986], Section 3.2.2). The remainder of the URI,
consisting of both the hierarchical path component and optional query
component, serves as an identifier for a potential resource within
that origin server's name space.
If the host identifier is provided as an IP literal or IPv4 address,
then the origin server is any listener on the indicated TCP port at
that IP address. If host is a registered name, then that name is
considered an indirect identifier and the recipient might use a name
resolution service, such as DNS, to find the address of a listener
for that host. The host MUST NOT be empty; if an "http" URI is
received with an empty host, then it MUST be rejected as invalid. If
the port subcomponent is empty or not given, then TCP port 80 is
assumed (the default reserved port for WWW services).
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
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HTTP response message, as described in Section 7 of [Part2], then
that response is considered an authoritative answer to the client's
request.
Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority. An HTTP service
based on some other underlying connection protocol would presumably
be identified using a different URI scheme, just as the "https"
scheme (below) is used for 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 used for mapping the namespace that is specific to TCP.
The URI generic syntax for authority also includes a deprecated
userinfo subcomponent ([RFC3986], Section 3.2.1) for including user
authentication information in the URI. Some implementations make use
of the userinfo component for internal configuration of
authentication information, such as within command invocation
options, configuration files, or bookmark lists, even though such
usage might expose a user identifier or password. Senders MUST NOT
include a userinfo subcomponent (and its "@" delimiter) when
transmitting an "http" URI in a message. Recipients of HTTP messages
that contain a URI reference SHOULD parse for the existence of
userinfo and treat its presence as an error, likely indicating that
the deprecated subcomponent is being used to obscure the authority
for the sake of phishing attacks.
2.7.2. https URI scheme
The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening to a
given TCP port for TLS-secured connections [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 TCP connection MUST be secured, end-to-end, through the use of
strong encryption prior to sending the first HTTP request.
https-URI = "https:" "//" authority path-abempty [ "?" query ]
Unlike the "http" scheme, responses to "https" identified requests
are never "public" and thus MUST NOT be reused for shared caching.
They can, however, be reused in a private cache if the message is
cacheable by default in HTTP or specifically indicated as such by the
Cache-Control header field (Section 7.2 of [Part6]).
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Resources made available via the "https" scheme have no shared
identity with the "http" scheme even if their resource identifiers
indicate the same authority (the same host listening to the same TCP
port). They are distinct name spaces and are considered to be
distinct origin servers. However, an extension to HTTP that is
defined to apply to entire host domains, such as the Cookie protocol
[RFC6265], can allow information set by one service to impact
communication with other services within a matching group of host
domains.
The process for authoritative access to an "https" identified
resource is defined in [RFC2818].
2.7.3. http and https URI Normalization and Comparison
Since the "http" and "https" schemes conform to the URI generic
syntax, such URIs are normalized and compared according to the
algorithm defined in [RFC3986], Section 6, using the defaults
described above for each scheme.
If the port is equal to the default port for a scheme, the normal
form is to elide the port subcomponent. Likewise, an empty path
component is equivalent to an absolute path of "/", so the normal
form is to provide a path of "/" instead. The scheme and host are
case-insensitive and normally provided in lowercase; all other
components are compared in a case-sensitive manner. Characters other
than those in the "reserved" set are equivalent to their percent-
encoded octets (see [RFC3986], Section 2.1): the normal form is to
not encode them.
For example, the following three URIs are equivalent:
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 ]
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The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field into a hash table
by field name until the empty line, and then use the parsed data to
determine if a message body is expected. If a message body has been
indicated, then it is read as a stream until an amount of octets
equal to the message body length is read or the connection is closed.
Recipients MUST parse an HTTP message as a sequence of octets in an
encoding that is a superset of US-ASCII [USASCII]. Parsing an HTTP
message as a stream of Unicode characters, without regard for the
specific encoding, creates security vulnerabilities due to the
varying ways that string processing libraries handle invalid
multibyte character sequences that contain the octet LF (%x0A).
String-based parsers can only be safely used within protocol elements
after the element has been extracted from the message, such as within
a header field-value after message parsing has delineated the
individual fields.
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.
3.1. Start Line
An HTTP message can either be a request from client to server or a
response from server to client. Syntactically, the two types of
message differ only in the start-line, which is either a request-line
(for requests) or a status-line (for responses), and in the algorithm
for determining the length of the message body (Section 3.3). In
theory, a client could receive requests and a server could receive
responses, distinguishing them by their different start-line formats,
but in practice servers are implemented to only expect a request (a
response is interpreted as an unknown or invalid request method) and
clients are implemented to only expect a response.
start-line = request-line / status-line
A sender MUST NOT send whitespace between the start-line and the
first header field. The presence of such whitespace in a request
might be an attempt to trick a server into ignoring that field or
processing the line after it as a new request, either of which might
result in a security vulnerability if other implementations within
the request chain interpret the same message differently. Likewise,
the presence of such whitespace in a response might be ignored by
some clients or cause others to cease parsing.
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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
A server MUST be able to parse any received message that begins with
a request-line and matches the ABNF rule for HTTP-message.
The method token indicates the request method to be performed on the
target resource. The request method is case-sensitive.
method = token
The methods defined by this specification can be found in Section 5
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.
No whitespace is allowed inside the method, request-target, and
protocol version. Hence, recipients typically parse the request-line
into its component parts by splitting on the SP characters.
Unfortunately, some user agents fail to properly encode hypertext
references that have embedded whitespace, sending the characters
directly instead of properly percent-encoding the disallowed
characters. 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. Recipients 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 either a 405 (Method Not Allowed), if
it is an origin server, or a 501 (Not Implemented) status code. A
server MUST be prepared to receive URIs of unbounded length and
respond with the 414 (URI Too Long) status code if the received
request-target would be longer than the server wishes to handle (see
Section 7.5.12 of [Part2]).
Various ad-hoc limitations on request-line length are found in
practice. It is RECOMMENDED that all HTTP senders and recipients
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support, at a minimum, request-line lengths of up to 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
A client MUST be able to parse any received message that begins with
a status-line and matches the ABNF rule for HTTP-message.
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 7 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 whitespace, and the field value.
header-field = field-name ":" OWS field-value BWS
field-name = token
field-value = *( field-content / obs-fold )
field-content = *( HTAB / SP / VCHAR / obs-text )
obs-fold = CRLF ( SP / HTAB )
; obsolete line folding
; see Section 3.2.2
The field-name token labels the corresponding field-value as having
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the semantics defined by that header field. For example, the Date
header field is defined in Section 8.1.1.2 of [Part2] as containing
the origination timestamp for the message in which it appears.
HTTP header fields are fully extensible: there is no limit on the
introduction of new field names, each presumably defining new
semantics, or on the number of header fields used in a given message.
Existing fields are defined in each part of this specification and in
many other specifications outside the standards process. New header
fields can be introduced without changing the protocol version if
their defined semantics allow them to be safely ignored by recipients
that do not recognize them.
New HTTP header fields SHOULD be registered with IANA in the Message
Header Field Registry, as described in Section 9.3 of [Part2].
Unrecognized header fields MUST be forwarded by a proxy 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. Unrecognized header fields SHOULD be ignored by other
recipients.
The order in which header fields with differing field names are
received is not significant. However, it is "good practice" to send
header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST
wait until the entire header section is received before interpreting
a request message, since later header fields might include
conditionals, authentication credentials, or deliberately misleading
duplicate header fields that would impact request processing.
Multiple header fields with the same field name MUST NOT be sent in a
message unless the entire field value for that header field is
defined as a comma-separated list [i.e., #(values)]. Multiple header
fields with the same field name can be combined into one "field-name:
field-value" pair, without changing the semantics of the message, by
appending each subsequent field value to the combined field value in
order, separated by a comma. The order in which header fields with
the same field name are received is therefore significant to the
interpretation of the combined field value; a proxy MUST NOT change
the order of these field values when forwarding a message.
Note: The "Set-Cookie" header field as implemented in practice can
occur multiple times, but does not use the list syntax, and thus
cannot be combined into a single line ([RFC6265]). (See Appendix
A.2.3 of [Kri2001] for details.) Also note that the Set-Cookie2
header field specified in [RFC2965] does not share this problem.
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3.2.1. 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. OWS SHOULD either not be produced or be produced as a
single SP. Multiple OWS octets that occur within field-content
SHOULD either be replaced with a single SP or transformed to all SP
octets (each octet other than SP replaced with SP) before
interpreting the field value or forwarding the message downstream.
RWS is used when at least one linear whitespace octet is required to
separate field tokens. RWS SHOULD be produced as a single SP.
Multiple RWS octets that occur within field-content SHOULD either be
replaced with a single SP or transformed to all SP octets before
interpreting the field value or forwarding the message downstream.
BWS is used where the grammar allows optional whitespace, for
historical reasons, but senders SHOULD NOT produce it in messages;
recipients MUST accept such bad optional whitespace and remove it
before interpreting the field value or forwarding the message
downstream.
OWS = *( SP / HTAB )
; "optional" whitespace
RWS = 1*( SP / HTAB )
; "required" whitespace
BWS = OWS
; "bad" whitespace
3.2.2. Field Parsing
No whitespace is allowed between the header field-name and colon. In
the past, differences in the handling of such whitespace have led to
security vulnerabilities in request routing and response handling.
Any received request message that contains whitespace between a
header field-name and colon MUST be rejected with a response code of
400 (Bad Request). A proxy MUST remove any such whitespace from a
response message before forwarding the message downstream.
A field value MAY be preceded by optional whitespace (OWS); a single
SP is preferred. The field value does not include any leading or
trailing white space: OWS occurring before the first non-whitespace
octet of the field value or after the last non-whitespace octet of
the field value is ignored and SHOULD be removed before further
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processing (as this does not change the meaning of the header field).
Historically, HTTP header field values could be extended over
multiple lines by preceding each extra line with at least one space
or horizontal tab (obs-fold). This specification deprecates such
line folding except within the message/http media type
(Section 7.3.1). HTTP senders MUST NOT produce messages that include
line folding (i.e., that contain any field-value that matches the
obs-fold rule) unless the message is intended for packaging within
the message/http media type. HTTP recipients SHOULD accept line
folding and replace any embedded obs-fold whitespace with either a
single SP or a matching number of SP octets (to avoid buffer copying)
prior to interpreting the field value or forwarding the message
downstream.
Historically, HTTP has allowed field content with text in the ISO-
8859-1 [ISO-8859-1] character encoding and supported other character
sets only through use of [RFC2047] encoding. In practice, most HTTP
header field values use only a subset of the US-ASCII character
encoding [USASCII]. Newly defined header fields SHOULD limit their
field values to US-ASCII octets. Recipients SHOULD treat other (obs-
text) octets in field content as opaque data.
3.2.3. Field Length
HTTP does not place a pre-defined limit on the length of header
fields, either in isolation or as a set. A server MUST be prepared
to receive request header fields of unbounded length and respond with
a 4xx (Client Error) status code if the received header field(s)
would be longer than the server wishes to handle.
A client that receives response header fields that are longer than it
wishes to handle can only treat it as a server error.
Various ad-hoc limitations on header field length are found in
practice. It is RECOMMENDED that all HTTP senders and recipients
support messages whose combined header fields have 4000 or more
octets.
3.2.4. Field value components
Many HTTP header field values consist of words (token or quoted-
string) separated by whitespace or special characters. These special
characters MUST be in a quoted string to be used within a parameter
value (as defined in Section 4).
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word = token / quoted-string
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA
; any VCHAR, except special
special = "(" / ")" / "<" / ">" / "@" / ","
/ ";" / ":" / "\" / DQUOTE / "/" / "["
/ "]" / "?" / "=" / "{" / "}"
A string of text is parsed as a single word if it is quoted using
double-quote marks.
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
obs-text = %x80-FF
The backslash octet ("\") can be used as a single-octet quoting
mechanism within quoted-string constructs:
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
Recipients that process the value of the quoted-string MUST handle a
quoted-pair as if it were replaced by the octet following the
backslash.
Senders SHOULD NOT escape octets in quoted-strings that do not
require escaping (i.e., other than DQUOTE and the backslash octet).
Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
comment = "(" *( ctext / quoted-cpair / comment ) ")"
ctext = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
The backslash octet ("\") can be used as a single-octet quoting
mechanism within comment constructs:
quoted-cpair = "\" ( HTAB / SP / VCHAR / obs-text )
Senders SHOULD NOT escape octets in comments that do not require
escaping (i.e., other than the backslash octet "\" and the
parentheses "(" and ")").
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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 a
Content-Length or Transfer-Encoding header field. Request message
framing is independent of method semantics, even if the method does
not define 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 5.3.2 of [Part2]). 2xx (Successful) responses to CONNECT
switch to tunnel mode instead of having a message body (Section 5.3.6
of [Part2]). All 1xx (Informational), 204 (No Content), and 304 (Not
Modified) responses MUST NOT include a message body. All other
responses do include a message body, although the body MAY be of zero
length.
3.3.1. Transfer-Encoding
When one or more transfer codings are applied to a payload body in
order to form the message body, a Transfer-Encoding header field MUST
be sent in the message and MUST contain the list of corresponding
transfer-coding names in the same order that they were applied.
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 target resource.
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The "chunked" transfer-coding (Section 4.1) MUST be implemented by
all HTTP/1.1 recipients because it plays a crucial role in delimiting
messages when the payload body size is not known in advance. When
the "chunked" transfer-coding is used, it MUST be the last transfer-
coding applied to form the message body and MUST NOT be applied more
than once in a message body. If any transfer-coding is applied to a
request payload body, the final transfer-coding applied MUST be
"chunked". If any transfer-coding is applied to a response payload
body, then either the final transfer-coding applied MUST be "chunked"
or the message MUST be terminated by closing the connection.
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.
If more than one Transfer-Encoding header field is present in a
message, the multiple field-values MUST be combined into one field-
value, according to the algorithm defined in Section 3.2, before
determining the message body length.
Unlike Content-Encoding (Section 3.1.2.1 of [Part2]), Transfer-
Encoding is a property of the message, not of the payload, and thus
MAY be added or removed by any implementation along the request/
response chain. 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.
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
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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) and
then close the connection.
3.3.2. Content-Length
When a message is allowed to contain a message body, does not have a
Transfer-Encoding header field, and has a payload body length that is
known to the sender before the message header section has been sent,
the sender SHOULD send a Content-Length header field to indicate the
length of the payload body as a decimal number of octets.
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 server MAY send a Content-Length header field in a response to a
HEAD request (Section 5.3.2 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 SHOULD NOT send a Content-Length header field in any 2xx
(Successful) response to a CONNECT request (Section 5.3.6 of
[Part2]).
Any Content-Length field value greater than or equal to zero is
valid. Since there is no predefined limit to the length of an HTTP
payload, recipients SHOULD anticipate potentially large decimal
numerals and prevent parsing errors due to integer conversion
overflows (Section 8.6).
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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.
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
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
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Content-Length header field, the Transfer-Encoding overrides the
Content-Length. Such a message might indicate an attempt to
perform request or response smuggling (bypass of security-related
checks on message routing or content) and thus ought to be
handled as an error. The provided Content-Length MUST be
removed, prior to forwarding the message downstream, or replaced
with the real message body length after the transfer-coding is
decoded.
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 MUST be
treated as an error to prevent request or response smuggling. If
this is a request message, the server MUST respond with a 400
(Bad Request) status code and then close the connection. If this
is a response message received by a proxy, the proxy MUST discard
the received response, send a 502 (Bad Gateway) status code as
its downstream response, and then close the connection. If this
is a response message received by a user-agent, it MUST be
treated as an error by discarding the message and closing the
connection.
5. If a valid Content-Length header field is present without
Transfer-Encoding, its decimal value defines the message body
length in octets. If the actual number of octets sent in the
message is less than the indicated Content-Length, the recipient
MUST consider the message to be incomplete and treat the
connection as no longer usable. If the actual number of octets
sent in the message is more than the indicated Content-Length,
the recipient MUST only process the message body up to the field
value's number of octets; the remainder of the message MUST
either be discarded or treated as the next message in a pipeline.
For the sake of robustness, a user-agent MAY attempt to detect
and correct such an error in message framing if it is parsing the
response to the last request on a connection and the connection
has been closed by the server.
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.
Since there is no way to distinguish a successfully completed, close-
delimited message from a partially-received message interrupted by
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network failure, a server SHOULD use encoding or length-delimited
messages whenever possible. The close-delimiting feature exists
primarily for backwards compatibility with HTTP/1.0.
A server MAY reject a request that contains a message body but not a
Content-Length by responding with 411 (Length Required).
Unless a transfer-coding other than "chunked" has been applied, a
client that sends a request containing a message body SHOULD use a
valid Content-Length header field if the message body length is known
in advance, rather than the "chunked" encoding, since some existing
services respond to "chunked" with a 411 (Length Required) status
code even though they understand the chunked encoding. This is
typically because such services are implemented via a gateway that
requires a content-length in advance of being called and the server
is unable or unwilling to buffer the entire request before
processing.
A client that sends a request containing a message body MUST include
a valid Content-Length header field if it does not know the server
will handle HTTP/1.1 (or later) requests; such knowledge can be in
the form of specific user configuration or by remembering the version
of a prior received response.
3.4. Handling Incomplete Messages
Request messages that are prematurely terminated, possibly due to a
canceled connection or a server-imposed time-out exception, MUST
result in closure of the connection; sending an error response prior
to closing the connection is OPTIONAL.
Response messages that are prematurely terminated, usually by closure
of the connection prior to receiving the expected number of octets or
by failure to decode a transfer-encoded message body, MUST be
recorded as incomplete. A response that terminates in the middle of
the header block (before the empty line is received) cannot be
assumed to convey the full semantics of the response and MUST be
treated as an error.
A message body that uses the chunked transfer encoding is incomplete
if the zero-sized chunk that terminates the encoding has not been
received. A message that uses a valid Content-Length is incomplete
if the size of the message body received (in octets) is less than the
value given by Content-Length. A response that has neither chunked
transfer encoding nor Content-Length is terminated by closure of the
connection, and thus is considered complete regardless of the number
of message body octets received, provided that the header block was
received intact.
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A user agent MUST NOT render an incomplete response message body as
if it were complete (i.e., some indication needs to be given to the
user that an error occurred). Cache requirements for incomplete
responses are defined in Section 3 of [Part6].
A server MUST read the entire request message body or close the
connection after sending its response, since otherwise the remaining
data on a persistent connection would be misinterpreted as the next
request. Likewise, a client MUST read the entire response message
body if it intends to reuse the same connection for a subsequent
request. Pipelining multiple requests on a connection is described
in Section 6.2.2.1.
3.5. Message Parsing Robustness
Older HTTP/1.0 client implementations might send an extra CRLF after
a POST request as a lame workaround for some early server
applications that failed to read message body content that was not
terminated by a line-ending. An HTTP/1.1 client MUST NOT preface or
follow a request with an extra CRLF. If terminating the request
message body with a line-ending is desired, then the client MUST
include the terminating CRLF octets as part of the message body
length.
In the interest of robustness, servers SHOULD ignore at least one
empty line received where a request-line is expected. In other
words, if the server is reading the protocol stream at the beginning
of a message and receives a CRLF first, it SHOULD ignore the CRLF.
Likewise, although the line terminator for the start-line and header
fields is the sequence CRLF, we recommend that recipients recognize a
single LF as a line terminator and ignore any CR.
When a server listening only for HTTP request messages, or processing
what appears from the start-line to be an HTTP request message,
receives a sequence of octets that does not match the HTTP-message
grammar aside from the robustness exceptions listed above, the server
MUST respond with an HTTP/1.1 400 (Bad Request) response.
4. Transfer Codings
Transfer-coding values are used to indicate an encoding
transformation that has been, can be, or might need to be applied to
a payload body in order to ensure "safe transport" through the
network. This differs from a content coding in that the transfer-
coding is a property of the message rather than a property of the
representation that is being transferred.
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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 values are case-insensitive and SHOULD be
registered within the HTTP Transfer Coding registry, as defined in
Section 7.4. 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 encoding modifies the body of a message in order to
transfer it as a series of chunks, each with its own size indicator,
followed by an OPTIONAL trailer containing header fields. This
allows dynamically produced content to be transferred along with the
information necessary for the recipient to verify that it has
received the full message.
chunked-body = *chunk
last-chunk
trailer-part
CRLF
chunk = chunk-size [ chunk-ext ] CRLF
chunk-data CRLF
chunk-size = 1*HEXDIG
last-chunk = 1*("0") [ chunk-ext ] CRLF
chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token / quoted-str-nf
chunk-data = 1*OCTET ; a sequence of chunk-size octets
trailer-part = *( header-field CRLF )
quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
; like quoted-string, but disallowing line folding
qdtext-nf = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
Chunk extensions within the chucked encoding are deprecated. Senders
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SHOULD NOT send chunk-ext. Definition of new chunk extensions is
discouraged.
The chunk-size field is a string of hex digits indicating the size of
the chunk-data in octets. The chunked encoding is ended by any chunk
whose size is zero, followed by the trailer, which is terminated by
an empty line.
4.1.1. Trailer
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 MUST NOT contain fields that need to be known
before a recipient processes the body, such as Transfer-Encoding,
Content-Length, and 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 send 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
If no Trailer header field is present, the sender of a chunked
message body SHOULD send an empty trailer.
A server MUST send 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
server where the field originated) without receiving that
metadata. In other words, the server that generated the header
field 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
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forwarded to an HTTP/1.0 recipient.
4.1.2. Decoding chunked
A process for decoding the "chunked" transfer-coding can be
represented in pseudo-code as:
length := 0
read chunk-size, chunk-ext (if any) and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to decoded-body
length := length + chunk-size
read chunk-size and CRLF
}
read header-field
while (header-field not empty) {
append header-field to existing header fields
read header-field
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
Remove Trailer from existing header fields
All recipients MUST be able to receive and decode the "chunked"
transfer-coding and MUST ignore chunk-ext extensions they do not
understand.
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" format is produced by the common UNIX file compression
program "compress". This format is an adaptive Lempel-Ziv-Welch
coding (LZW). Recipients SHOULD consider "x-compress" to be
equivalent to "compress".
4.2.2. Deflate Coding
The "deflate" format is defined as the "deflate" compression
mechanism (described in [RFC1951]) used inside the "zlib" data format
([RFC1950]).
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Note: Some incorrect implementations send the "deflate" compressed
data without the zlib wrapper.
4.2.3. Gzip Coding
The "gzip" format is produced by the file compression program "gzip"
(GNU zip), as described in [RFC1952]. This format is a Lempel-Ziv
coding (LZ77) with a 32 bit CRC. Recipients 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
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". Clients 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, on behalf of itself and any downstream
clients. For chained requests, this implies that either: (a) all
downstream clients are willing to accept trailer fields in the
forwarded response; or, (b) the client 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 a client 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
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6.3.1 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.
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 identifier
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 response cache and the request semantics can be
satisfied by a cache ([Part6]), then the request is usually directed
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to the cache first.
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 = path-absolute [ "?" query ]
absolute-form = absolute-URI
authority-form = authority
asterisk-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, containing the target URI's authority component
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(excluding any userinfo).
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.
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 5.6.
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, HTTP/1.1 servers MUST accept the absolute-
form in requests, even though HTTP/1.1 clients will only send them in
requests to proxies.
The authority-form of request-target is only used for CONNECT
requests (Section 5.3.6 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) as
the request-target. For example,
CONNECT www.example.com:80 HTTP/1.1
The asterisk-form of request-target is only used for a server-wide
OPTIONS request (Section 5.3.7 of [Part2]). When a client wishes to
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,
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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. Since the Host field-value is
critical information for handling a request, it SHOULD be sent as the
first header field following the request-line.
Host = uri-host [ ":" port ] ; Section 2.7.1
A client MUST send a Host header field in all HTTP/1.1 request
messages. If the target URI includes an authority component, then
the Host field-value MUST be identical to that authority component
after excluding any userinfo (Section 2.7.1). If the authority
component is missing or undefined for the target URI, then the Host
header field MUST be sent with an empty field-value.
For example, a GET request to the origin server for
would begin with:
GET /pub/WWW/ HTTP/1.1
Host: www.example.org
The Host header field MUST be sent in an HTTP/1.1 request even if the
request-target is in the absolute-form, since this allows the Host
information to be forwarded through ancient HTTP/1.0 proxies that
might not have implemented Host.
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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. If the proxy forwards the request, it 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
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.
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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.
5.6. 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.
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Intermediaries that forward a message MUST implement the Connection
header field, as specified in Section 6.1, to exclude fields that are
only intended for the incoming connection.
In order to avoid request loops, a proxy that forwards requests to
other proxies MUST be able to recognize and exclude all of its own
server names, including any aliases, local variations, or literal IP
addresses.
5.7. Via
The "Via" header field MUST be sent by a proxy or gateway in
forwarded messages to indicate the intermediate protocols and
recipients between the user agent and the server on requests, and
between the origin server and the client on responses. It is
analogous to the "Received" field used by email systems (Section
3.6.7 of [RFC5322]). Via is used in HTTP for tracking message
forwards, avoiding request loops, and identifying the protocol
capabilities of all senders along the request/response chain.
Via = 1#( received-protocol RWS received-by
[ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
received-by = ( uri-host [ ":" port ] ) / pseudonym
pseudonym = token
The received-protocol indicates the protocol version of the message
received by the server or client along each segment of the request/
response chain. The received-protocol version is appended to the Via
field value when the message is forwarded so that information about
the protocol capabilities of upstream applications remains visible to
all recipients.
The protocol-name is excluded if and only if it would be "HTTP". The
received-by field is normally the host and optional port number of a
recipient server or client that subsequently forwarded the message.
However, if the real host is considered to be sensitive information,
it MAY be replaced by a pseudonym. If the port is not given, it MAY
be assumed to be the default port of the received-protocol.
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each recipient MUST append its information
such that the end result is ordered according to the sequence of
forwarding applications.
Comments MAY be used in the Via header field to identify the software
of each recipient, analogous to the User-Agent and Server header
fields. However, all comments in the Via field are optional and MAY
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be removed by any recipient prior to forwarding the message.
For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which
completes the request by forwarding it to the origin server at
www.example.com. The request received by www.example.com would then
have the following Via header field:
Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
A proxy or gateway used as a portal through a network firewall SHOULD
NOT forward the names and ports of hosts within the firewall region
unless it is explicitly enabled to do so. If not enabled, the
received-by host of any host behind the firewall SHOULD be replaced
by an appropriate pseudonym for that host.
A proxy or gateway 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
Senders SHOULD NOT combine multiple entries unless they are all under
the same organizational control and the hosts have already been
replaced by pseudonyms. Senders MUST NOT combine entries which have
different received-protocol values.
5.8. Message Transforming
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 non-transforming proxy MUST NOT modify the "path-absolute" and
"query" parts of the received request-target when forwarding it to
the next inbound server, except as noted above to replace an empty
path with "/" or "*".
A non-transforming proxy MUST preserve the message payload (Section
3.3 of [Part2]), though it MAY change the message body through
application or removal of a transfer-coding (Section 4).
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A non-transforming proxy SHOULD NOT modify header fields that provide
information about the end points of the communication chain, the
resource state, or the selected representation.
A non-transforming proxy MUST NOT modify any of the following fields
in a request or response, and it MUST NOT add any of these fields if
not already present:
o Allow (Section 8.4.1 of [Part2])
o Content-Location (Section 3.1.4.2 of [Part2])
o Content-MD5 (Section 14.15 of [RFC2616])
o ETag (Section 2.3 of [Part4])
o Last-Modified (Section 2.2 of [Part4])
o Server (Section 8.4.2 of [Part2])
A non-transforming proxy MUST NOT modify an Expires header field
(Section 7.3 of [Part6]) if already present in a response, but it MAY
add an Expires header field with a field-value identical to that of
the Date header field.
A proxy MUST NOT modify or add any of the following fields in a
message that contains the no-transform cache-control directive:
o Content-Encoding (Section 3.1.2.2 of [Part2])
o Content-Range (Section 5.2 of [Part5])
o Content-Type (Section 3.1.1.5 of [Part2])
A transforming proxy MAY modify or add these fields to a message that
does not include no-transform, but if it does so, it MUST add a
Warning 214 (Transformation applied) if one does not already appear
in the message (see Section 7.5 of [Part6]).
Warning: Unnecessary modification of header fields might cause
authentication failures if stronger authentication mechanisms are
introduced in later versions of HTTP. Such authentication
mechanisms MAY rely on the values of header fields not listed
here.
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5.9. 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 7.2 of
[Part2]) precede a final response to the same request.
A client that uses persistent connections and sends more than one
request per connection MUST maintain a list of outstanding requests
in the order sent on that connection and MUST associate each received
response message to the highest ordered request that has not yet
received a final (non-1xx) response.
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.
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
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message.
When a header field is used to supply control information for or
about the current connection, the sender SHOULD 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 include field-names in the Connection header field-
value for fields that are defined as expressing constraints for all
recipients in the request or response chain, such as the Cache-
Control header field (Section 7.2 of [Part6]).
The connection options do not have to correspond to a header field
present in the message, since a connection-specific header field
might not be needed if there are no parameters associated with that
connection option. Recipients that trigger certain connection
behavior based on the presence of connection options MUST do so based
on the presence of the connection-option rather than only the
presence of the optional header field. In other words, if the
connection option is received as a header field but not indicated
within the Connection field-value, then the recipient MUST ignore the
connection-specific header field because it has likely been forwarded
by an intermediary that is only partially conformant.
When defining new connection options, specifications ought to
carefully consider existing deployed header fields and ensure that
the new connection option does not share the same name as an
unrelated header field that might already be deployed. Defining a
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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.
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 connection SHOULD be closed after the current request/response is
complete (Section 6.2.5).
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. Persistent Connections
HTTP was originally designed to use a separate connection for each
request/response pair. As the Web evolved and embedded requests
became common for inline images, the connection establishment
overhead was a significant drain on performance and a concern for
Internet congestion. Message framing (via Content-Length) and
optional long-lived connections (via Keep-Alive) were added to
HTTP/1.0 in order to improve performance for some requests. However,
these extensions were insufficient for dynamically generated
responses and difficult to use with intermediaries.
HTTP/1.1 defaults to the use of "persistent connections", which allow
multiple requests and responses to be carried over a single
connection. The "close" connection-option is used to signal that a
connection will close after the current request/response. Persistent
connections have a number of advantages:
o By opening and closing fewer connections, CPU time is saved in
routers and hosts (clients, servers, proxies, gateways, tunnels,
or caches), and memory used for protocol control blocks can be
saved in hosts.
o Most requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single connection to be used
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much more efficiently and with less overall latency.
o For TCP connections, network congestion is reduced by eliminating
the packets associated with the three way handshake and graceful
close procedures, and by allowing sufficient time to determine the
congestion state of the network.
o Latency on subsequent requests is reduced since there is no time
spent in the connection opening handshake.
o HTTP can evolve more gracefully, since most errors can be reported
without the penalty of closing the connection. Clients using
future versions of HTTP might optimistically try a new feature,
but if communicating with an older server, retry with old
semantics after an error is reported.
HTTP implementations SHOULD implement persistent connections.
6.2.1. 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.
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.
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).
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6.2.2. Reuse
In order to remain persistent, all messages on a connection MUST have
a self-defined message length (i.e., one not defined by closure of
the connection), as described in Section 3.3.
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.
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.
6.2.2.1. Pipelining
A client that supports persistent connections MAY "pipeline" its
requests (i.e., send multiple requests without waiting for each
response). A server MUST send its responses to those requests in the
same order that the requests were received.
Clients which assume persistent connections and pipeline immediately
after connection establishment SHOULD be prepared to retry their
connection if the first pipelined attempt fails. If a client does
such a retry, it MUST NOT pipeline before it knows the connection is
persistent. Clients MUST also be prepared to resend their requests
if the server closes the connection before sending all of the
corresponding responses.
Clients SHOULD NOT pipeline requests using non-idempotent request
methods or non-idempotent sequences of request methods (see Section
5.2.2 of [Part2]). Otherwise, a premature termination of the
transport connection could lead to indeterminate results. A client
wishing to send a non-idempotent request SHOULD wait to send that
request until it has received the response status line for the
previous request.
6.2.2.2. Retrying Requests
Senders can close the transport connection at any time. Therefore,
clients, servers, and proxies MUST be able to recover from
asynchronous close events. Client software MAY reopen the transport
connection and retransmit the aborted sequence of requests without
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user interaction so long as the request sequence is idempotent (see
Section 5.2.2 of [Part2]). Non-idempotent request methods or
sequences MUST NOT be automatically retried, although user agents MAY
offer a human operator the choice of retrying the request(s).
Confirmation by user-agent software with semantic understanding of
the application MAY substitute for user confirmation. The automatic
retry SHOULD NOT be repeated if the second sequence of requests
fails.
6.2.3. Concurrency
Clients SHOULD limit the number of simultaneous connections that they
maintain to a given server.
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.
6.2.4. 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.
When a client or server wishes to time-out it SHOULD issue a graceful
close on the transport connection. Clients and servers SHOULD both
constantly watch for the other side of the transport close, and
respond to it as appropriate. If a client or server does not detect
the other side's close promptly it could cause unnecessary resource
drain on the network.
A client, server, or proxy MAY close the transport connection at any
time. For example, a client might have started to send a new request
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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.
Servers SHOULD maintain persistent connections 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 status code while it is transmitting the request. If
the client sees an error status code, it SHOULD immediately cease
transmitting the body and close the connection.
6.2.5. 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
lingering close of the connection after it sends the final response
to the request that contained close. The server SHOULD include 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
lingering close of the connection 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 assume
that they will not 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
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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, a server can perform a lingering
close on a connection by closing only the write side of the read/
write connection (a half-close) and continuing to read from the
connection until the connection is closed by the client or the server
is reasonably certain that its own TCP stack has received the
client's acknowledgement of the packet(s) containing the server's
last response. It is then safe for the server to fully close the
connection.
It is unknown whether the reset problem is exclusive to TCP or might
also be found in other transport connection protocols.
6.3. 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 before sending the final response. A server
MUST send an Upgrade header field in 101 (Switching Protocols)
responses to indicate which protocol(s) are being switched to, and
MUST send it in 426 (Upgrade Required) responses to indicate
acceptable protocols. A server MAY send an Upgrade header field in
any other response to indicate that they might be willing to upgrade
to one of the specified protocols for a future request.
Upgrade = 1#protocol
protocol = protocol-name ["/" protocol-version]
protocol-name = token
protocol-version = token
For example,
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
Upgrade eases the difficult transition between incompatible protocols
by allowing the client to initiate a request in the more commonly
supported protocol while indicating to the server that it would like
to use a "better" protocol if available (where "better" is determined
by the server, possibly according to the nature of the request method
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or target resource).
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 chosen, although the first
action after changing the protocol MUST be a response to the initial
HTTP request that contained the Upgrade header field.
For example, if the Upgrade header field is received in a GET request
and the server decides to switch protocols, then it MUST first
respond with a 101 (Switching Protocols) message in HTTP/1.1 and then
immediately follow 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.
When Upgrade is sent, a sender MUST also send a Connection header
field (Section 6.1) that contains the "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.
The Upgrade header field only applies to switching application-level
protocols on the existing connection; it cannot be used to switch to
a protocol on a different connection. For that purpose, it is more
appropriate to use a 3xx (Redirection) response (Section 7.4 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 can be registered with IANA using
the registration procedure defined in Section 7.6.
7. IANA Considerations
7.1. Header Field Registration
HTTP header fields are registered within the Message Header Field
Registry [RFC3864] maintained by IANA at .
This document defines the following HTTP header fields, so their
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associated registry entries shall be updated according to the
permanent registrations below:
+-------------------+----------+----------+---------------+
| 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 4.1.1 |
| Transfer-Encoding | http | standard | Section 3.3.1 |
| Upgrade | http | standard | Section 6.3 |
| Via | http | standard | Section 5.7 |
+-------------------+----------+----------+---------------+
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).
+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Close | http | reserved | Section 7.1 |
+-------------------+----------+----------+-------------+
The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force".
7.2. URI Scheme Registration
IANA maintains the registry of URI Schemes [RFC4395] at
.
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 |
+------------+------------------------------------+---------------+
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7.3. Internet Media Type Registrations
This document serves as the specification for the Internet media
types "message/http" and "application/http". The following is to be
registered with IANA (see [RFC4288]).
7.3.1. 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
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 7.3.1).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
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Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
7.3.2. Internet Media Type application/http
The application/http type can be used to enclose a pipeline of one or
more HTTP request or response messages (not intermixed).
Type name: application
Subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-version number of the enclosed messages (e.g.,
"1.1"). If not present, the version can be determined from the
first line of the body.
msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first line of the
body.
Encoding considerations: HTTP messages enclosed by this type are in
"binary" format; use of an appropriate Content-Transfer-Encoding
is required when transmitted via E-mail.
Security considerations: none
Interoperability considerations: none
Published specification: This specification (see Section 7.3.2).
Applications that use this media type:
Additional information:
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Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
7.4. Transfer Coding Registry
The HTTP Transfer Coding Registry defines the name space for transfer
coding names.
Registrations MUST include the following fields:
o Name
o Description
o Pointer to specification text
Names of transfer codings MUST NOT overlap with names of content
codings (Section 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 section. Use of program names for
the identification of encoding formats is not desirable and is
discouraged for future encodings.
The registry itself is maintained at
.
7.5. Transfer Coding Registrations
The HTTP Transfer Coding Registry shall be updated with the
registrations below:
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+----------+----------------------------------------+---------------+
| Name | Description | Reference |
+----------+----------------------------------------+---------------+
| chunked | Transfer in a series of chunks | Section 4.1 |
| compress | UNIX "compress" program method | Section 4.2.1 |
| deflate | "deflate" compression mechanism | Section 4.2.2 |
| | ([RFC1951]) used inside the "zlib" | |
| | data format ([RFC1950]) | |
| gzip | Same as GNU zip [RFC1952] | Section 4.2.3 |
+----------+----------------------------------------+---------------+
7.6. 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.
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.
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].
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7.7. Upgrade Token Registration
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".
8. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
8.1. Personal Information
HTTP clients are often privy to large amounts of personal
information, including both information provided by the user to
interact with resources (e.g., the user's name, location, mail
address, passwords, encryption keys, etc.) and information about the
user's browsing activity over time (e.g., history, bookmarks, etc.).
HTTP implementations need to prevent unintentional leakage of this
information.
8.2. Abuse of Server Log Information
A server is in the position to save personal data about a user's
requests which might identify their reading patterns or subjects of
interest. 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
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characteristics. As such, access traces that are keyed to a specific
client should not be published even if the key is pseudonymous.
To minimize the risk of theft or accidental publication, log
information should 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.
8.3. Attacks Based On File and Path Names
Origin servers SHOULD be careful to restrict the documents returned
by HTTP requests to be only those that were intended by the server
administrators. If an HTTP server translates HTTP URIs directly into
file system calls, the server MUST take special care not to serve
files that were not intended to be delivered to HTTP clients. For
example, UNIX, Microsoft Windows, and other operating systems use
".." as a path component to indicate a directory level above the
current one. On such a system, an HTTP server MUST disallow any such
construct in the request-target if it would otherwise allow access to
a resource outside those intended to be accessible via the HTTP
server. Similarly, files intended for reference only internally to
the server (such as access control files, configuration files, and
script code) MUST be protected from inappropriate retrieval, since
they might contain sensitive information.
8.4. DNS-related Attacks
HTTP clients rely heavily on the Domain Name Service (DNS), and are
thus generally prone to security attacks based on the deliberate
misassociation of IP addresses and DNS names not protected by DNSSec.
Clients need to be cautious in assuming the validity of an IP number/
DNS name association unless the response is protected by DNSSec
([RFC4033]).
8.5. 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
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.
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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.
8.6. Protocol Element Size Overflows
Because HTTP uses mostly textual, character-delimited fields,
attackers can overflow buffers in implementations, and/or perform a
Denial of Service against implementations that accept fields with
unlimited lengths.
To promote interoperability, this specification makes specific
recommendations for minimum size limits on request-line
(Section 3.1.1) and blocks of header fields (Section 3.2). These are
minimum recommendations, chosen to be supportable even by
implementations with limited resources; it is expected that most
implementations will choose substantially higher limits.
This specification also provides a way for servers to reject messages
that have request-targets that are too long (Section 7.5.12 of
[Part2]) or request entities that are too large (Section 7.5 of
[Part2]).
Recipients SHOULD 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. Acknowledgments
This edition of HTTP 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, Paul
J. Leach, and Mark Nottingham. See Section 16 of [RFC2616] for
additional acknowledgements from prior revisions.
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:
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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,
Anil Sharma, Anne van Kesteren, Anthony Bryan, Asbjorn Ulsberg,
Balachander Krishnamurthy, Barry Leiba, Ben Laurie, Benjamin Niven-
Jenkins, Bil Corry, Bill Burke, Bjoern Hoehrmann, Bob Scheifler,
Boris Zbarsky, Brett Slatkin, Brian Kell, Brian McBarron, Brian Pane,
Brian Smith, Bryce Nesbitt, Cameron Heavon-Jones, Carl Kugler,
Carsten Bormann, Charles Fry, Chris Newman, Cyrus Daboo, Dale Robert
Anderson, Dan Wing, Dan Winship, Daniel Stenberg, Dave Cridland, Dave
Crocker, Dave Kristol, David Booth, David Singer, David W. Morris,
Diwakar Shetty, Dmitry Kurochkin, Drummond Reed, Duane Wessels,
Edward Lee, Eliot Lear, Eran Hammer-Lahav, Eric D. Williams, Eric J.
Bowman, Eric Lawrence, Eric Rescorla, Erik Aronesty, Evan Prodromou,
Florian Weimer, Frank Ellermann, Fred Bohle, Gabriel Montenegro,
Geoffrey Sneddon, Gervase Markham, Grahame Grieve, Greg Wilkins,
Harald Tveit Alvestrand, Harry Halpin, Helge Hess, Henrik Nordstrom,
Henry S. Thompson, Henry Story, Herbert van de Sompel, Howard Melman,
Hugo Haas, Ian Fette, Ian Hickson, Ido Safruti, Ingo Struck, J. Ross
Nicoll, James H. Manger, James Lacey, James M. Snell, Jamie Lokier,
Jan Algermissen, Jeff Hodges (who came up with the term 'effective
Request-URI'), Jeff Walden, Jim Luther, Joe D. Williams, Joe
Gregorio, Joe Orton, John C. Klensin, John C. Mallery, John Cowan,
John Kemp, John Panzer, John Schneider, John Stracke, John Sullivan,
Jonas Sicking, Jonathan Billington, Jonathan Moore, Jonathan Rees,
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, Koen
Holtman, Konstantin Voronkov, Kris Zyp, Lisa Dusseault, Maciej
Stachowiak, 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, Mike Amundsen,
Mike Belshe, Mike Kelly, Mike Schinkel, Miles Sabin, Murray S.
Kucherawy, Mykyta Yevstifeyev, Nathan Rixham, Nicholas Shanks, Nico
Williams, Nicolas Alvarez, Nicolas Mailhot, Noah Slater, Pablo
Castro, Pat Hayes, Patrick R. McManus, Paul E. Jones, Paul Hoffman,
Paul Marquess, Peter Lepeska, Peter Saint-Andre, Peter Watkins, Phil
Archer, Philippe Mougin, Phillip Hallam-Baker, Poul-Henning Kamp,
Preethi Natarajan, Rajeev Bector, Ray Polk, Reto Bachmann-Gmuer,
Richard Cyganiak, Robert Brewer, Robert Collins, Robert O'Callahan,
Robert Olofsson, Robert Sayre, Robert Siemer, Robert de Wilde,
Roberto Javier Godoy, Roberto Peon, Ronny Widjaja, S. Mike Dierken,
Salvatore Loreto, Sam Johnston, Sam Ruby, Scott Lawrence (who
maintained the original issues list), Sean B. Palmer, Shane McCarron,
Stefan Eissing, Stefan Tilkov, Stefanos Harhalakis, Stephane
Bortzmeyer, Stephen Farrell, Stephen Ludin, Stuart Williams, Subbu
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Allamaraju, Sylvain Hellegouarch, Tapan Divekar, Tatsuya Hayashi, Ted
Hardie, Thomas Broyer, 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, Yutaka
Oiwa, Yves Lafon (long-time member of the editor team), Zed A. Shaw,
and Zhong Yu.
10. References
10.1. Normative References
[Part2] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content",
draft-ietf-httpbis-p2-semantics-21 (work in progress),
October 2012.
[Part4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Conditional Requests",
draft-ietf-httpbis-p4-conditional-21 (work in
progress), October 2012.
[Part5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range
Requests", draft-ietf-httpbis-p5-range-21 (work in
progress), October 2012.
[Part6] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
draft-ietf-httpbis-p6-cache-21 (work in progress),
October 2012.
[Part7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Authentication",
draft-ietf-httpbis-p7-auth-21 (work in progress),
October 2012.
[RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data
Format Specification version 3.3", RFC 1950, May 1996.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format
Specification version 1.3", RFC 1951, May 1996.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and
G. Randers-Pehrson, "GZIP file format specification
version 4.3", RFC 1952, May 1996.
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[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.
10.2. Informative References
[ISO-8859-1] International Organization for Standardization,
"Information technology -- 8-bit single-byte coded
graphic character sets -- Part 1: Latin alphabet No.
1", ISO/IEC 8859-1:1998, 1998.
[Kri2001] Kristol, D., "HTTP Cookies: Standards, Privacy, and
Politics", ACM Transactions on Internet Technology Vol.
1, #2, November 2001,
.
[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",
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RFC 2145, May 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, May 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC2965] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, October 2000.
[RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC 3040,
January 2001.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications
and Registration Procedures", BCP 13, RFC 4288,
December 2005.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines
and Registration Procedures for New URI Schemes",
BCP 115, RFC 4395, February 2006.
[RFC4559] Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based
Kerberos and NTLM HTTP Authentication in Microsoft
Windows", RFC 4559, June 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008.
[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.
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[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
Appendix A. HTTP Version History
HTTP has been in use by the World-Wide Web global information
initiative since 1990. The first version of HTTP, later referred to
as HTTP/0.9, was a simple protocol for hypertext data transfer across
the Internet with only a single request method (GET) and no metadata.
HTTP/1.0, as defined by [RFC1945], added a range of request methods
and MIME-like messaging that could include metadata about the data
transferred and modifiers on the request/response semantics.
However, HTTP/1.0 did not sufficiently take into consideration the
effects of hierarchical proxies, caching, the need for persistent
connections, or name-based virtual hosts. The proliferation of
incompletely-implemented applications calling themselves "HTTP/1.0"
further necessitated a protocol version change in order for two
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.
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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
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 a 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 need will need
to monitor the connection for "hung" requests (which indicate that
the client ought stop sending the header field), and this mechanism
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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). Proxies/gateways MUST remove any transfer-coding
prior to forwarding a message via a MIME-compliant protocol.
A.2. Changes from RFC 2616
Clarify that the string "HTTP" in the HTTP-version ABNF production is
case sensitive. Restrict the version numbers to be single digits due
to the fact that implementations are known to handle multi-digit
version numbers incorrectly. (Section 2.6)
Require that invalid whitespace around field-names be rejected.
Change ABNF productions for header fields to only define 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 3.2.1)
The NUL octet is no longer allowed in comment and quoted-string text.
The quoted-pair rule no longer allows escaping control characters
other than HTAB. Non-ASCII content in header fields and reason
phrase has been obsoleted and made opaque (the TEXT rule was
removed). (Section 3.2.4)
Require recipients to handle bogus "Content-Length" header fields as
errors. (Section 3.3)
Remove reference to non-existent identity transfer-coding value
tokens. (Sections 3.3 and 4)
Clarification that the chunk length does not include the count of the
octets in the chunk header and trailer. Furthermore disallowed line
folding in chunk extensions, and deprecate their use. (Section 4.1)
Update use of abs_path production from RFC 1808 to the path-absolute
+ query components of RFC 3986. State that the asterisk form is
allowed for the OPTIONS request method only. (Section 5.3)
Clarify exactly when "close" connection options have to be sent; drop
notion of header fields being "hop-by-hop" without being listed in
the Connection header field. (Section 6.1)
Remove hard limit of two connections per server. Remove requirement
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to retry a sequence of requests as long it was idempotent. Remove
requirements about when servers are allowed to close connections
prematurely. (Section 6.2)
Remove requirement to retry requests under certain circumstances when
the server prematurely closes the connection. (Section 6.2.2)
Define the semantics of the Upgrade header field in responses other
than 101 (this was incorporated from [RFC2817]). (Section 6.3)
Registration of Transfer Codings now requires IETF Review
(Section 7.4)
Take over the Upgrade Token Registry, previously defined in Section
7.2 of [RFC2817]. (Section 7.6)
Empty list elements in list productions have been deprecated.
(Appendix B)
Appendix B. 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 "#element"
indicating at least and at most elements, each separated by a
single comma (",") and optional whitespace (OWS).
Thus,
1#element => element *( OWS "," OWS element )
and:
#element => [ 1#element ]
and for n >= 1 and m > 1:
#element => element *( OWS "," OWS element )
For compatibility with legacy list rules, recipients SHOULD accept
empty list elements. In other words, consumers would follow the list
productions:
#element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
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Note that empty elements do not contribute to the count of elements
present, though.
For example, given these ABNF productions:
example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 3.2.4
Then these are valid values for example-list (not including the
double quotes, which are present for delimitation only):
"foo,bar"
"foo ,bar,"
"foo , ,bar,charlie "
But these values would be invalid, as at least one non-empty element
is required:
""
","
", ,"
Appendix C shows the collected ABNF, with the list rules expanded as
explained above.
Appendix C. 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 ] )
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URI-reference =
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-form = absolute-URI
asterisk-form = "*"
attribute = token
authority =
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
chunked-body = *chunk last-chunk trailer-part CRLF
comment = "(" *( ctext / quoted-cpair / comment ) ")"
connection-option = token
ctext = OWS / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
field-content = *( HTAB / SP / VCHAR / obs-text )
field-name = token
field-value = *( field-content / obs-fold )
header-field = field-name ":" OWS field-value BWS
http-URI = "http://" authority path-abempty [ "?" query ]
https-URI = "https://" authority path-abempty [ "?" query ]
last-chunk = 1*"0" [ chunk-ext ] CRLF
message-body = *OCTET
method = token
obs-fold = CRLF ( SP / HTAB )
obs-text = %x80-FF
origin-form = path-absolute [ "?" query ]
partial-URI = relative-part [ "?" query ]
path-abempty =
path-absolute =
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port =
protocol = protocol-name [ "/" protocol-version ]
protocol-name = token
protocol-version = token
pseudonym = token
qdtext = OWS / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
qdtext-nf = HTAB / SP / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
query =
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
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 =
request-line = method SP request-target SP HTTP-version CRLF
request-target = origin-form / absolute-form / authority-form /
asterisk-form
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 =
value = word
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word = token / quoted-string
Appendix D. Change Log (to be removed by RFC Editor before publication)
D.1. Since RFC 2616
Extracted relevant partitions from [RFC2616].
D.2. Since draft-ietf-httpbis-p1-messaging-00
Closed issues:
o : "HTTP Version
should be case sensitive"
()
o : "'unsafe'
characters" ()
o : "Chunk Size
Definition" ()
o : "Message Length"
()
o : "Media Type
Registrations" ()
o : "URI includes
query" ()
o : "No close on
1xx responses" ()
o : "Remove
'identity' token references"
()
o : "Import query
BNF"
o : "qdtext BNF"
o : "Normative and
Informative references"
o : "RFC2606
Compliance"
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o : "RFC977
reference"
o : "RFC1700
references"
o : "inconsistency
in date format explanation"
o : "Date reference
typo"
o : "Informative
references"
o : "ISO-8859-1
Reference"
o : "Normative up-
to-date references"
Other changes:
o Update media type registrations to use RFC4288 template.
o Use names of RFC4234 core rules DQUOTE and HTAB, fix broken ABNF
for chunk-data (work in progress on
)
D.3. Since draft-ietf-httpbis-p1-messaging-01
Closed issues:
o : "Bodies on GET
(and other) requests"
o : "Updating to
RFC4288"
o : "Status Code
and Reason Phrase"
o : "rel_path not
used"
Ongoing work on ABNF conversion
():
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o Get rid of duplicate BNF rule names ("host" -> "uri-host",
"trailer" -> "trailer-part").
o Avoid underscore character in rule names ("http_URL" -> "http-
URL", "abs_path" -> "path-absolute").
o Add rules for terms imported from URI spec ("absoluteURI",
"authority", "path-absolute", "port", "query", "relativeURI",
"host) -- these will have to be updated when switching over to
RFC3986.
o Synchronize core rules with RFC5234.
o Get rid of prose rules that span multiple lines.
o Get rid of unused rules LOALPHA and UPALPHA.
o Move "Product Tokens" section (back) into Part 1, as "token" is
used in the definition of the Upgrade header field.
o Add explicit references to BNF syntax and rules imported from
other parts of the specification.
o Rewrite prose rule "token" in terms of "tchar", rewrite prose rule
"TEXT".
D.4. Since draft-ietf-httpbis-p1-messaging-02
Closed issues:
o : "HTTP-date vs.
rfc1123-date"
o : "WS in quoted-
pair"
Ongoing work on IANA Message Header Field Registration
():
o Reference RFC 3984, and update header field registrations for
header fields defined in this document.
Ongoing work on ABNF conversion
():
o Replace string literals when the string really is case-sensitive
(HTTP-version).
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D.5. Since draft-ietf-httpbis-p1-messaging-03
Closed issues:
o : "Connection
closing"
o : "Move
registrations and registry information to IANA Considerations"
o : "need new URL
for PAD1995 reference"
o : "IANA
Considerations: update HTTP URI scheme registration"
o : "Cite HTTPS
URI scheme definition"
o : "List-type
header fields vs Set-Cookie"
Ongoing work on ABNF conversion
():
o Replace string literals when the string really is case-sensitive
(HTTP-Date).
o Replace HEX by HEXDIG for future consistence with RFC 5234's core
rules.
D.6. Since draft-ietf-httpbis-p1-messaging-04
Closed issues:
o : "Out-of-date
reference for URIs"
o : "RFC 2822 is
updated by RFC 5322"
Ongoing work on ABNF conversion
():
o Use "/" instead of "|" for alternatives.
o Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
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o Only reference RFC 5234's core rules.
o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
o Rewrite ABNFs to spell out whitespace rules, factor out header
field value format definitions.
D.7. Since draft-ietf-httpbis-p1-messaging-05
Closed issues:
o : "Header LWS"
o : "Sort 1.3
Terminology"
o : "RFC2047
encoded words"
o : "Character
Encodings in TEXT"
o : "Line Folding"
o : "OPTIONS * and
proxies"
o : "reason-phrase
BNF"
o : "Use of TEXT"
o : "Join
"Differences Between HTTP Entities and RFC 2045 Entities"?"
o : "RFC822
reference left in discussion of date formats"
Final work on ABNF conversion
():
o Rewrite definition of list rules, deprecate empty list elements.
o Add appendix containing collected and expanded ABNF.
Other changes:
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o Rewrite introduction; add mostly new Architecture Section.
o Move definition of quality values from Part 3 into Part 1; make TE
request header field grammar independent of accept-params (defined
in Part 3).
D.8. Since draft-ietf-httpbis-p1-messaging-06
Closed issues:
o : "base for
numeric protocol elements"
o : "comment ABNF"
Partly resolved issues:
o : "205 Bodies"
(took out language that implied that there might be methods for
which a payload body MUST NOT be included)
o : "editorial
improvements around HTTP-date"
D.9. Since draft-ietf-httpbis-p1-messaging-07
Closed issues:
o : "Repeating
single-value header fields"
o : "increase
connection limit"
o : "IP addresses
in URLs"
o : "take over
HTTP Upgrade Token Registry"
o : "CR and LF in
chunk extension values"
o : "HTTP/0.9
support"
o : "pick IANA
policy (RFC5226) for Transfer Coding / Content Coding"
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o : "move
definitions of gzip/deflate/compress to part 1"
o : "disallow
control characters in quoted-pair"
Partly resolved issues:
o : "update IANA
requirements wrt Transfer-Coding values" (add the IANA
Considerations subsection)
D.10. Since draft-ietf-httpbis-p1-messaging-08
Closed issues:
o : "header
parsing, treatment of leading and trailing OWS"
Partly resolved issues:
o : "Placement of
13.5.1 and 13.5.2"
o : "use of term
"word" when talking about header field structure"
D.11. Since draft-ietf-httpbis-p1-messaging-09
Closed issues:
o : "Clarification
of the term 'deflate'"
o : "OPTIONS * and
proxies"
o : "MIME-Version
not listed in P1, general header fields"
o : "IANA registry
for content/transfer encodings"
o : "Case-
sensitivity of HTTP-date"
o : "use of term
"word" when talking about header field structure"
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Partly resolved issues:
o : "Term for the
requested resource's URI"
D.12. Since draft-ietf-httpbis-p1-messaging-10
Closed issues:
o : "Connection
Closing"
o : "Delimiting
messages with multipart/byteranges"
o : "Handling
multiple Content-Length header fields"
o : "Clarify
entity / representation / variant terminology"
o : "consider
removing the 'changes from 2068' sections"
Partly resolved issues:
o : "HTTP(s) URI
scheme definitions"
D.13. Since draft-ietf-httpbis-p1-messaging-11
Closed issues:
o : "Trailer
requirements"
o : "Text about
clock requirement for caches belongs in p6"
o : "effective
request URI: handling of missing host in HTTP/1.0"
o : "confusing
Date requirements for clients"
Partly resolved issues:
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o : "Handling
multiple Content-Length header fields"
D.14. Since draft-ietf-httpbis-p1-messaging-12
Closed issues:
o : "RFC2145
Normative"
o : "HTTP(s) URI
scheme definitions" (tune the requirements on userinfo)
o : "define
'transparent' proxy"
o : "Header Field
Classification"
o : "Is * usable
as a request-uri for new methods?"
o : "Migrate
Upgrade details from RFC2817"
o : "untangle
ABNFs for header fields"
o : "update RFC
2109 reference"
D.15. Since draft-ietf-httpbis-p1-messaging-13
Closed issues:
o : "Allow is not
in 13.5.2"
o : "Handling
multiple Content-Length header fields"
o : "untangle
ABNFs for header fields"
o : "Content-
Length ABNF broken"
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D.16. Since draft-ietf-httpbis-p1-messaging-14
Closed issues:
o : "HTTP-version
should be redefined as fixed length pair of DIGIT . DIGIT"
o : "Recommend
minimum sizes for protocol elements"
o : "Set
expectations around buffering"
o : "Considering
messages in isolation"
D.17. Since draft-ietf-httpbis-p1-messaging-15
Closed issues:
o : "DNS Spoofing
/ DNS Binding advice"
o : "move RFCs
2145, 2616, 2817 to Historic status"
o : "\-escaping in
quoted strings"
o : "'Close'
should be reserved in the HTTP header field registry"
D.18. Since draft-ietf-httpbis-p1-messaging-16
Closed issues:
o : "Document
HTTP's error-handling philosophy"
o : "Explain
header field registration"
o : "Revise
Acknowledgements Sections"
o : "Retrying
Requests"
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o : "Closing the
connection on server error"
D.19. Since draft-ietf-httpbis-p1-messaging-17
Closed issues:
o : "Proxy-
Connection and Keep-Alive"
o : "Clarify 'User
Agent'"
o : "Define non-
final responses"
o : "intended
maturity level vs normative references"
o : "Intermediary
rewriting of queries"
D.20. Since draft-ietf-httpbis-p1-messaging-18
Closed issues:
o : "message-body
in CONNECT response"
o : "Misplaced
text on connection handling in p2"
o : "wording of
line folding rule"
o : "chunk-
extensions"
o : "make IANA
policy definitions consistent"
D.21. Since draft-ietf-httpbis-p1-messaging-19
Closed issues:
o : "make IANA
policy definitions consistent"
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o : "clarify
connection header field values are case-insensitive"
o : "ABNF
requirements for recipients"
o : "note
introduction of new IANA registries as normative changes"
o : "Reference to
ISO-8859-1 is informative"
D.22. Since draft-ietf-httpbis-p1-messaging-20
Closed issues:
o : "is 'q=' case-
sensitive?"
o : "Semantics of
HTTPS"
Other changes:
o Drop notion of header fields being "hop-by-hop" without being
listed in the Connection header field.
o Section about connection management rewritten; dropping some
historic information.
o Move description of "100-continue" into Part 2.
o Rewrite the persistent connection and Upgrade requirements to be
actionable by role and consistent with the rest of HTTP.
Index
A
absolute-form (of request-target) 39
accelerator 10
application/http Media Type 57
asterisk-form (of request-target) 39
authority-form (of request-target) 39
B
browser 7
C
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cache 11
cacheable 12
captive portal 11
chunked (Coding Format) 33
client 7
close 46, 52
compress (Coding Format) 35
connection 7
Connection header field 46, 52
Content-Length header field 28
D
deflate (Coding Format) 35
downstream 9
E
effective request URI 41
G
gateway 10
Grammar
absolute-form 38
absolute-URI 15
ALPHA 6
asterisk-form 38
attribute 33
authority 15
authority-form 38
BWS 23
chunk 33
chunk-data 33
chunk-ext 33
chunk-ext-name 33
chunk-ext-val 33
chunk-size 33
chunked-body 33
comment 25
Connection 47
connection-option 47
Content-Length 28
CR 6
CRLF 6
ctext 25
CTL 6
date2 33
date3 33
DIGIT 6
DQUOTE 6
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field-content 21
field-name 21
field-value 21
header-field 21
HEXDIG 6
Host 40
HTAB 6
HTTP-message 18
HTTP-name 13
http-URI 16
HTTP-version 13
https-URI 17
last-chunk 33
LF 6
message-body 26
method 20
obs-fold 21
obs-text 25
OCTET 6
origin-form 38
OWS 23
partial-URI 15
path-absolute 15
port 15
protocol-name 43
protocol-version 43
pseudonym 43
qdtext 25
qdtext-nf 33
query 15
quoted-cpair 25
quoted-pair 25
quoted-str-nf 33
quoted-string 25
rank 36
reason-phrase 21
received-by 43
received-protocol 43
request-line 20
request-target 38
RWS 23
SP 6
special 25
start-line 19
status-code 21
status-line 21
t-codings 36
t-ranking 36
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tchar 25
TE 36
token 25
Trailer 34
trailer-part 33
transfer-coding 33
Transfer-Encoding 26
transfer-extension 33
transfer-parameter 33
Upgrade 53
uri-host 15
URI-reference 15
value 33
VCHAR 6
Via 43
word 25
gzip (Coding Format) 36
H
header field 18
header section 18
headers 18
Host header field 40
http URI scheme 16
https URI scheme 17
I
inbound 9
interception proxy 11
intermediary 9
M
Media Type
application/http 57
message/http 56
message 7
message/http Media Type 56
method 20
N
non-transforming proxy 10
O
origin server 7
origin-form (of request-target) 38
outbound 9
P
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proxy 10
R
recipient 7
request 7
request-target 20
resource 15
response 7
reverse proxy 10
S
sender 7
server 7
spider 7
T
target resource 37
target URI 37
TE header field 36
Trailer header field 34
Transfer-Encoding header field 26
transforming proxy 10
transparent proxy 11
tunnel 11
U
Upgrade header field 53
upstream 9
URI scheme
http 16
https 17
user agent 7
V
Via header field 43
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/
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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 April 7, 2013 [Page 90]