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Network Working Group R. Fielding, Ed.
Internet-Draft Day Software
Obsoletes: 2616 (if approved) J. Gettys
Intended status: Standards Track One Laptop per Child
Expires: December 19, 2008 J. Mogul
HP
H. Frystyk
Microsoft
L. Masinter
Adobe Systems
P. Leach
Microsoft
T. Berners-Lee
W3C/MIT
Y. Lafon, Ed.
W3C
J. Reschke, Ed.
greenbytes
June 17, 2008
HTTP/1.1, part 1: URIs, Connections, and Message Parsing
draft-ietf-httpbis-p1-messaging-03
Status of this Memo
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This Internet-Draft will expire on December 19, 2008.
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Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World Wide Web global
information initiative since 1990. This document is Part 1 of the
seven-part specification that defines the protocol referred to as
"HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 1 provides
an overview of HTTP and its associated terminology, defines the
"http" and "https" Uniform Resource Identifier (URI) schemes, defines
the generic message syntax and parsing requirements for HTTP message
frames, and describes general security concerns for implementations.
Editorial Note (To be removed by RFC Editor)
Discussion of this draft should take place on the HTTPBIS working
group mailing list (ietf-http-wg@w3.org). The current issues list is
at <http://www.tools.ietf.org/wg/httpbis/trac/report/11> and related
documents (including fancy diffs) can be found at
<http://www.tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix E.4.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Overall Operation . . . . . . . . . . . . . . . . . . . . 9
2. Notational Conventions and Generic Grammar . . . . . . . . . . 11
2.1. Augmented BNF . . . . . . . . . . . . . . . . . . . . . . 11
2.2. Basic Rules . . . . . . . . . . . . . . . . . . . . . . . 13
2.3. ABNF Rules defined in other Parts of the Specification . . 16
3. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 16
3.1. HTTP Version . . . . . . . . . . . . . . . . . . . . . . . 16
3.2. Uniform Resource Identifiers . . . . . . . . . . . . . . . 17
3.2.1. General Syntax . . . . . . . . . . . . . . . . . . . . 17
3.2.2. http URL . . . . . . . . . . . . . . . . . . . . . . . 18
3.2.3. URI Comparison . . . . . . . . . . . . . . . . . . . . 18
3.3. Date/Time Formats . . . . . . . . . . . . . . . . . . . . 19
3.3.1. Full Date . . . . . . . . . . . . . . . . . . . . . . 19
3.4. Transfer Codings . . . . . . . . . . . . . . . . . . . . . 20
3.4.1. Chunked Transfer Coding . . . . . . . . . . . . . . . 21
3.5. Product Tokens . . . . . . . . . . . . . . . . . . . . . . 23
4. HTTP Message . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.1. Message Types . . . . . . . . . . . . . . . . . . . . . . 24
4.2. Message Headers . . . . . . . . . . . . . . . . . . . . . 24
4.3. Message Body . . . . . . . . . . . . . . . . . . . . . . . 25
4.4. Message Length . . . . . . . . . . . . . . . . . . . . . . 26
4.5. General Header Fields . . . . . . . . . . . . . . . . . . 28
5. Request . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1. Request-Line . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.1. Method . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1.2. Request-URI . . . . . . . . . . . . . . . . . . . . . 29
5.2. The Resource Identified by a Request . . . . . . . . . . . 30
6. Response . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.1. Status-Line . . . . . . . . . . . . . . . . . . . . . . . 31
6.1.1. Status Code and Reason Phrase . . . . . . . . . . . . 31
7. Connections . . . . . . . . . . . . . . . . . . . . . . . . . 32
7.1. Persistent Connections . . . . . . . . . . . . . . . . . . 32
7.1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 32
7.1.2. Overall Operation . . . . . . . . . . . . . . . . . . 33
7.1.3. Proxy Servers . . . . . . . . . . . . . . . . . . . . 34
7.1.4. Practical Considerations . . . . . . . . . . . . . . . 35
7.2. Message Transmission Requirements . . . . . . . . . . . . 36
7.2.1. Persistent Connections and Flow Control . . . . . . . 36
7.2.2. Monitoring Connections for Error Status Messages . . . 36
7.2.3. Use of the 100 (Continue) Status . . . . . . . . . . . 36
7.2.4. Client Behavior if Server Prematurely Closes
Connection . . . . . . . . . . . . . . . . . . . . . . 38
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8. Header Field Definitions . . . . . . . . . . . . . . . . . . . 39
8.1. Connection . . . . . . . . . . . . . . . . . . . . . . . . 39
8.2. Content-Length . . . . . . . . . . . . . . . . . . . . . . 40
8.3. Date . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
8.3.1. Clockless Origin Server Operation . . . . . . . . . . 42
8.4. Host . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
8.5. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
8.6. Trailer . . . . . . . . . . . . . . . . . . . . . . . . . 44
8.7. Transfer-Encoding . . . . . . . . . . . . . . . . . . . . 44
8.8. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 45
8.9. Via . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 47
9.1. Message Header Registration . . . . . . . . . . . . . . . 47
10. Security Considerations . . . . . . . . . . . . . . . . . . . 48
10.1. Personal Information . . . . . . . . . . . . . . . . . . . 48
10.2. Abuse of Server Log Information . . . . . . . . . . . . . 48
10.3. Attacks Based On File and Path Names . . . . . . . . . . . 49
10.4. DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . . 49
10.5. Proxies and Caching . . . . . . . . . . . . . . . . . . . 50
10.6. Denial of Service Attacks on Proxies . . . . . . . . . . . 50
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 50
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 52
12.1. Normative References . . . . . . . . . . . . . . . . . . . 52
12.2. Informative References . . . . . . . . . . . . . . . . . . 53
Appendix A. Internet Media Types . . . . . . . . . . . . . . . . 55
A.1. Internet Media Type message/http . . . . . . . . . . . . . 55
A.2. Internet Media Type application/http . . . . . . . . . . . 56
Appendix B. Tolerant Applications . . . . . . . . . . . . . . . . 57
Appendix C. Conversion of Date Formats . . . . . . . . . . . . . 58
Appendix D. Compatibility with Previous Versions . . . . . . . . 58
D.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 59
D.1.1. Changes to Simplify Multi-homed Web Servers and
Conserve IP Addresses . . . . . . . . . . . . . . . . 59
D.2. Compatibility with HTTP/1.0 Persistent Connections . . . . 60
D.3. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 60
D.4. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 61
Appendix E. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 61
E.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 61
E.2. Since draft-ietf-httpbis-p1-messaging-00 . . . . . . . . . 61
E.3. Since draft-ietf-httpbis-p1-messaging-01 . . . . . . . . . 63
E.4. Since draft-ietf-httpbis-p1-messaging-02 . . . . . . . . . 64
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 68
Intellectual Property and Copyright Statements . . . . . . . . . . 71
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1. Introduction
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World-Wide Web global
information initiative since 1990. The first version of HTTP,
commonly referred to as HTTP/0.9, was a simple protocol for raw data
transfer across the Internet with only a single method and no
metadata. HTTP/1.0, as defined by [RFC1945], improved the protocol
by allowing messages to be in the format of MIME-like messages,
containing 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. In
addition, the proliferation of incompletely-implemented applications
calling themselves "HTTP/1.0" necessitated a protocol version change
in order for two communicating applications to determine each other's
true capabilities.
This document is Part 1 of the seven-part specification that defines
the protocol referred to as "HTTP/1.1", obsoleting [RFC2616].
HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
requirements that enable reliable implementations and adding only
those new features that will either be safely ignored by an HTTP/1.0
recipient or only sent when communicating with a party advertising
compliance with HTTP/1.1. Part 1 defines those aspects of HTTP/1.1
related to overall network operation, message framing, interaction
with transport protocols, and URI schemes.
This document is currently disorganized in order to minimize the
changes between drafts and enable reviewers to see the smaller errata
changes. The next draft will reorganize the sections to better
reflect the content. In particular, the sections will be organized
according to the typical process of deciding when to use HTTP (URI
schemes), overall network operation, connection management, message
framing, and generic message parsing. The current mess reflects how
widely dispersed these topics and associated requirements had become
in [RFC2616].
1.1. Purpose
Practical information systems require more functionality than simple
retrieval, including search, front-end update, and annotation. HTTP
allows an open-ended set of methods and headers that indicate the
purpose of a request [RFC2324]. It builds on the discipline of
reference provided by the Uniform Resource Identifier (URI)
[RFC1630], as a location (URL) [RFC1738] or name (URN) [RFC1737], for
indicating the resource to which a method is to be applied. Messages
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are passed in a format similar to that used by Internet mail
[RFC2822] as defined by the Multipurpose Internet Mail Extensions
(MIME) [RFC2045].
HTTP is also used as a generic protocol for communication between
user agents and proxies/gateways to other Internet systems, including
those supported by the SMTP [RFC2821], NNTP [RFC3977], FTP [RFC959],
Gopher [RFC1436], and WAIS [WAIS] protocols. In this way, HTTP
allows basic hypermedia access to resources available from diverse
applications.
1.2. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
An implementation is not compliant if it fails to satisfy one or more
of the MUST or REQUIRED level requirements for the protocols it
implements. An implementation that satisfies all the MUST or
REQUIRED level and all the SHOULD level requirements for its
protocols is said to be "unconditionally compliant"; one that
satisfies all the MUST level requirements but not all the SHOULD
level requirements for its protocols is said to be "conditionally
compliant."
1.3. Terminology
This specification uses a number of terms to refer to the roles
played by participants in, and objects of, the HTTP communication.
connection
A transport layer virtual circuit established between two programs
for the purpose of communication.
message
The basic unit of HTTP communication, consisting of a structured
sequence of octets matching the syntax defined in Section 4 and
transmitted via the connection.
request
An HTTP request message, as defined in Section 5.
response
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An HTTP response message, as defined in Section 6.
resource
A network data object or service that can be identified by a URI,
as defined in Section 3.2. Resources may be available in multiple
representations (e.g. multiple languages, data formats, size, and
resolutions) or vary in other ways.
entity
The information transferred as the payload of a request or
response. An entity consists of metainformation in the form of
entity-header fields and content in the form of an entity-body, as
described in Section 4 of [Part3].
representation
An entity included with a response that is subject to content
negotiation, as described in Section 5 of [Part3]. There may
exist multiple representations associated with a particular
response status.
content negotiation
The mechanism for selecting the appropriate representation when
servicing a request, as described in Section 5 of [Part3]. The
representation of entities in any response can be negotiated
(including error responses).
variant
A resource may have one, or more than one, representation(s)
associated with it at any given instant. Each of these
representations is termed a `variant'. Use of the term `variant'
does not necessarily imply that the resource is subject to content
negotiation.
client
A program that establishes connections for the purpose of sending
requests.
user agent
The client which initiates a request. These are often browsers,
editors, spiders (web-traversing robots), or other end user tools.
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server
An application program that accepts connections in order to
service requests by sending back responses. Any given program may
be capable of being both a client and a server; our use of these
terms refers only to the role being performed by the program for a
particular connection, rather than to the program's capabilities
in general. Likewise, any server may act as an origin server,
proxy, gateway, or tunnel, switching behavior based on the nature
of each request.
origin server
The server on which a given resource resides or is to be created.
proxy
An intermediary program which acts as both a server and a client
for the purpose of making requests on behalf of other clients.
Requests are serviced internally or by passing them on, with
possible translation, to other servers. A proxy MUST implement
both the client and server requirements of this specification. A
"transparent proxy" is a proxy that does not modify the request or
response beyond what is required for proxy authentication and
identification. A "non-transparent proxy" is a proxy that
modifies the request or response in order to provide some added
service to the user agent, such as group annotation services,
media type transformation, protocol reduction, or anonymity
filtering. Except where either transparent or non-transparent
behavior is explicitly stated, the HTTP proxy requirements apply
to both types of proxies.
gateway
A server which acts as an intermediary for some other server.
Unlike a proxy, a gateway receives requests as if it were the
origin server for the requested resource; the requesting client
may not be aware that it is communicating with a gateway.
tunnel
An intermediary program which is acting as a blind relay between
two connections. Once active, a tunnel is not considered a party
to the HTTP communication, though the tunnel may have been
initiated by an HTTP request. The tunnel ceases to exist when
both ends of the relayed connections are closed.
cache
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A program's local store of 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 include a cache, though a
cache cannot be used by a server that is acting as a tunnel.
cacheable
A response is cacheable if a cache is allowed to store a copy of
the response message for use in answering subsequent requests.
The rules for determining the cacheability of HTTP responses are
defined in Section 1 of [Part6]. Even if a resource is cacheable,
there may be additional constraints on whether a cache can use the
cached copy for a particular request.
upstream/downstream
Upstream and downstream describe the flow of a message: all
messages flow from upstream to downstream.
inbound/outbound
Inbound and outbound refer to the request and response paths for
messages: "inbound" means "traveling toward the origin server",
and "outbound" means "traveling toward the user agent"
1.4. Overall Operation
HTTP is a request/response protocol. A client sends a request to the
server in the form of a request method, URI, and protocol version,
followed by a MIME-like message containing request modifiers, client
information, and possible body content over a connection with a
server. The server responds with a status line, including the
message's protocol version and a success or error code, followed by a
MIME-like message containing server information, entity
metainformation, and possible entity-body content. The relationship
between HTTP and MIME is described in Appendix A of [Part3].
Most HTTP communication is initiated by a user agent and consists of
a request to be applied to a resource on some origin server. In the
simplest case, this may be accomplished via a single connection (v)
between the user agent (UA) and the origin server (O).
request chain ------------------------>
UA -------------------v------------------- O
<----------------------- response chain
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A more complicated situation occurs when one or more intermediaries
are present in the request/response chain. There are three common
forms of intermediary: proxy, gateway, and tunnel. A proxy is a
forwarding agent, receiving requests for a URI in its absolute form,
rewriting all or part of the message, and forwarding the reformatted
request toward the server identified by the URI. A gateway is a
receiving agent, acting as a layer above some other server(s) and, if
necessary, translating the requests to the underlying server's
protocol. A tunnel acts as a relay point between two connections
without changing the messages; tunnels are used when the
communication needs to pass through an intermediary (such as a
firewall) even when the intermediary cannot understand the contents
of the messages.
request chain -------------------------------------->
UA -----v----- A -----v----- B -----v----- C -----v----- O
<------------------------------------- response chain
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.
This distinction is important because some HTTP communication options
may 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
may be engaged in multiple, simultaneous communications. For
example, B may 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.
Any party to the communication which is not acting as a tunnel may
employ an internal cache for handling requests. The effect of a
cache is that the request/response chain is shortened if one of the
participants along the chain has a cached response applicable to that
request. The following illustrates the resulting chain if B has a
cached copy of an earlier response from O (via C) for a request which
has not been cached by UA or A.
request chain ---------->
UA -----v----- A -----v----- B - - - - - - C - - - - - - O
<--------- response chain
Not all responses are usefully cacheable, and some requests may
contain modifiers which place special requirements on cache behavior.
HTTP requirements for cache behavior and cacheable responses are
defined in Section 1 of [Part6].
In fact, there are a wide variety of architectures and configurations
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of caches and proxies currently being experimented with or deployed
across the World Wide Web. 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 CD-ROM, and so on. HTTP systems are used
in corporate intranets over high-bandwidth links, and for access via
PDAs with low-power radio links and intermittent connectivity. The
goal of HTTP/1.1 is to support the wide diversity of configurations
already deployed while introducing protocol constructs that meet the
needs of those who build web applications that require high
reliability and, failing that, at least reliable indications of
failure.
HTTP communication usually takes place over TCP/IP connections. The
default port is TCP 80
(<http://www.iana.org/assignments/port-numbers>), but other ports can
be used. This does not preclude HTTP from being implemented on top
of any other protocol on the Internet, or on other networks. HTTP
only presumes a reliable transport; any protocol that provides such
guarantees can be used; the mapping of the HTTP/1.1 request and
response structures onto the transport data units of the protocol in
question is outside the scope of this specification.
In HTTP/1.0, most implementations used a new connection for each
request/response exchange. In HTTP/1.1, a connection may be used for
one or more request/response exchanges, although connections may be
closed for a variety of reasons (see Section 7.1).
2. Notational Conventions and Generic Grammar
2.1. Augmented BNF
All of the mechanisms specified in this document are described in
both prose and an augmented Backus-Naur Form (BNF) similar to that
used by [RFC822ABNF]. Implementors will need to be familiar with the
notation in order to understand this specification. The augmented
BNF includes the following constructs:
name = definition
The name of a rule is simply the name itself (without any
enclosing "<" and ">") and is separated from its definition by the
equal "=" character. White space is only significant in that
indentation of continuation lines is used to indicate a rule
definition that spans more than one line. Certain basic rules are
in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, etc.
Angle brackets are used within definitions whenever their presence
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will facilitate discerning the use of rule names.
"literal"
Quotation marks surround literal text. Unless stated otherwise,
the text is case-insensitive.
rule1 | rule2
Elements separated by a bar ("|") are alternatives, e.g., "yes |
no" will accept yes or no.
(rule1 rule2)
Elements enclosed in parentheses are treated as a single element.
Thus, "(elem (foo | bar) elem)" allows the token sequences "elem
foo elem" and "elem bar elem".
*rule
The character "*" preceding an element indicates repetition. The
full form is "<n>*<m>element" indicating at least <n> and at most
<m> occurrences of element. Default values are 0 and infinity so
that "*(element)" allows any number, including zero; "1*element"
requires at least one; and "1*2element" allows one or two.
[rule]
Square brackets enclose optional elements; "[foo bar]" is
equivalent to "*1(foo bar)".
N rule
Specific repetition: "<n>(element)" is equivalent to
"<n>*<n>(element)"; that is, exactly <n> occurrences of (element).
Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
alphabetic characters.
#rule
A construct "#" is defined, similar to "*", for defining lists of
elements. The full form is "<n>#<m>element" indicating at least
<n> and at most <m> elements, each separated by one or more commas
(",") and OPTIONAL linear white space (LWS). This makes the usual
form of lists very easy; a rule such as
( *LWS element *( *LWS "," *LWS element ))
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can be shown as
1#element
Wherever this construct is used, null elements are allowed, but do
not contribute to the count of elements present. That is,
"(element), , (element) " is permitted, but counts as only two
elements. Therefore, where at least one element is required, at
least one non-null element MUST be present. Default values are 0
and infinity so that "#element" allows any number, including zero;
"1#element" requires at least one; and "1#2element" allows one or
two.
; comment
A semi-colon, set off some distance to the right of rule text,
starts a comment that continues to the end of line. This is a
simple way of including useful notes in parallel with the
specifications.
implied *LWS
The grammar described by this specification is word-based. Except
where noted otherwise, linear white space (LWS) can be included
between any two adjacent words (token or quoted-string), and
between adjacent words and separators, without changing the
interpretation of a field. At least one delimiter (LWS and/or
separators) MUST exist between any two tokens (for the definition
of "token" below), since they would otherwise be interpreted as a
single token.
2.2. Basic Rules
The following rules are used throughout this specification to
describe basic parsing constructs. The US-ASCII coded character set
is defined by ANSI X3.4-1986 [USASCII].
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OCTET = %x00-FF
; any 8-bit sequence of data
CHAR = %x01-7F
; any US-ASCII character, excluding NUL
ALPHA = %x41-5A | %x61-7A
; A-Z | a-z
DIGIT = %x30-39
; any US-ASCII digit "0".."9"
CTL = %x00-1F | %x7F
; (octets 0 - 31) and DEL (127)
CR = %x0D
; US-ASCII CR, carriage return (13)
LF = %x0A
; US-ASCII LF, linefeed (10)
SP = %x20
; US-ASCII SP, space (32)
HTAB = %x09
; US-ASCII HT, horizontal-tab (9)
DQUOTE = %x22
; US-ASCII double-quote mark (34)
HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
protocol elements except the entity-body (see Appendix B for tolerant
applications). The end-of-line marker within an entity-body is
defined by its associated media type, as described in Section 3.3 of
[Part3].
CRLF = CR LF
HTTP/1.1 header field values can be folded onto multiple lines if the
continuation line begins with a space or horizontal tab. All linear
white space, including folding, has the same semantics as SP. A
recipient MAY replace any linear white space with a single SP before
interpreting the field value or forwarding the message downstream.
LWS = [CRLF] 1*( SP | HTAB )
The TEXT rule is only used for descriptive field contents and values
that are not intended to be interpreted by the message parser. Words
of *TEXT MAY contain characters from character sets other than ISO-
8859-1 [ISO-8859-1] only when encoded according to the rules of
[RFC2047].
TEXT = %x20-7E | %x80-FF | LWS
; any OCTET except CTLs, but including LWS
A CRLF is allowed in the definition of TEXT only as part of a header
field continuation. It is expected that the folding LWS will be
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replaced with a single SP before interpretation of the TEXT value.
Hexadecimal numeric characters are used in several protocol elements.
HEX = "A" | "B" | "C" | "D" | "E" | "F"
| "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
Many HTTP/1.1 header field values consist of words separated by LWS
or special characters. These special characters MUST be in a quoted
string to be used within a parameter value (as defined in
Section 3.4).
separators = "(" | ")" | "<" | ">" | "@"
| "," | ";" | ":" | "\" | DQUOTE
| "/" | "[" | "]" | "?" | "="
| "{" | "}" | SP | HTAB
tchar = "!" | "#" | "$" | "%" | "&" | "'" | "*"
| "+" | "-" | "." | "^" | "_" | "`" | "|" | "~"
| DIGIT | ALPHA
; any CHAR except CTLs or separators
token = 1*tchar
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.
In all other fields, parentheses are considered part of the field
value.
comment = "(" *( ctext | quoted-pair | comment ) ")"
ctext = <any TEXT excluding "(" and ")">
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 = <any TEXT excluding DQUOTE and "\">
The backslash character ("\") MAY be used as a single-character
quoting mechanism only within quoted-string and comment constructs.
quoted-text = %x01-09 |
%x0B-0C |
%x0E-FF ; Characters excluding NUL, CR and LF
quoted-pair = "\" quoted-text
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2.3. ABNF Rules defined in other Parts of the Specification
The ABNF rules below are defined in other parts:
request-header = <request-header, defined in [Part2], Section 4>
response-header = <response-header, defined in [Part2], Section 6>
accept-params = <accept-params, defined in [Part3], Section 6.1>
entity-body = <entity-body, defined in [Part3], Section 4.2>
entity-header = <entity-header, defined in [Part3], Section 4.1>
Cache-Control = <Cache-Control, defined in [Part6], Section 16.4>
Pragma = <Pragma, defined in [Part6], Section 16.4>
Warning = <Warning, defined in [Part6], Section 16.6>
3. Protocol Parameters
3.1. HTTP Version
HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
of the protocol. The protocol versioning policy is intended to allow
the sender to indicate the format of a message and its capacity for
understanding further HTTP communication, rather than the features
obtained via that communication. No change is made to the version
number for the addition of message components which do not affect
communication behavior or which only add to extensible field values.
The <minor> number is incremented when the changes made to the
protocol add features which do not change the general message parsing
algorithm, but which may add to the message semantics and imply
additional capabilities of the sender. The <major> number is
incremented when the format of a message within the protocol is
changed. See [RFC2145] for a fuller explanation.
The version of an HTTP message is indicated by an HTTP-Version field
in the first line of the message. HTTP-Version is case-sensitive.
HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
Note that the major and minor numbers MUST be treated as separate
integers and that each MAY be incremented higher than a single digit.
Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
lower than HTTP/12.3. Leading zeros MUST be ignored by recipients
and MUST NOT be sent.
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An application that sends a request or response message that includes
HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
with this specification. Applications that are at least
conditionally compliant with this specification SHOULD use an HTTP-
Version of "HTTP/1.1" in their messages, and MUST do so for any
message that is not compatible with HTTP/1.0. For more details on
when to send specific HTTP-Version values, see [RFC2145].
The HTTP version of an application is the highest HTTP version for
which the application is at least conditionally compliant.
Proxy and gateway applications need to be careful when forwarding
messages in protocol versions different from that of the application.
Since the protocol version indicates the protocol capability of the
sender, a proxy/gateway MUST NOT send a message with a version
indicator which is greater than its actual version. If a higher
version request is received, the proxy/gateway MUST either downgrade
the request version, or respond with an error, or switch to tunnel
behavior.
Due to interoperability problems with HTTP/1.0 proxies discovered
since the publication of [RFC2068], caching proxies MUST, gateways
MAY, and tunnels MUST NOT upgrade the request to the highest version
they support. The proxy/gateway's response to that request MUST be
in the same major version as the request.
Note: Converting between versions of HTTP may involve modification
of header fields required or forbidden by the versions involved.
3.2. Uniform Resource Identifiers
URIs have been known by many names: WWW addresses, Universal Document
Identifiers, Universal Resource Identifiers [RFC1630], and finally
the combination of Uniform Resource Locators (URL) [RFC1738] and
Names (URN) [RFC1737]. As far as HTTP is concerned, Uniform Resource
Identifiers are simply formatted strings which identify--via name,
location, or any other characteristic--a resource.
3.2.1. General Syntax
URIs in HTTP can be represented in absolute form or relative to some
known base URI [RFC1808], depending upon the context of their use.
The two forms are differentiated by the fact that absolute URIs
always begin with a scheme name followed by a colon. For definitive
information on URL syntax and semantics, see "Uniform Resource
Identifiers (URI): Generic Syntax and Semantics," [RFC2396] (which
replaces [RFC1738] and [RFC1808]). This specification adopts the
definitions of "URI-reference", "absoluteURI", "fragment",
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"relativeURI", "port", "host", "abs_path", "query", and "authority"
from that specification:
absoluteURI = <absoluteURI, defined in [RFC2396], Section 3>
authority = <authority, defined in [RFC2396], Section 3.2>
fragment = <fragment, defined in [RFC2396], Section 4.1>
path-absolute = <abs_path, defined in [RFC2396], Section 3>
port = <port, defined in [RFC2396], Section 3.2.2>
query = <query, defined in [RFC2396], Section 3.4>
relativeURI = <relativeURI, defined in [RFC2396], Section 5>
uri-host = <host, defined in [RFC2396], Section 3.2.2>
HTTP does not place any a priori limit on the length of a URI.
Servers MUST be able to handle the URI of any resource they serve,
and SHOULD be able to handle URIs of unbounded length if they provide
GET-based forms that could generate such URIs. A server SHOULD
return 414 (Request-URI Too Long) status if a URI is longer than the
server can handle (see Section 9.4.15 of [Part2]).
Note: Servers ought to be cautious about depending on URI lengths
above 255 bytes, because some older client or proxy
implementations might not properly support these lengths.
3.2.2. http URL
The "http" scheme is used to locate network resources via the HTTP
protocol. This section defines the scheme-specific syntax and
semantics for http URLs.
http-URL = "http:" "//" uri-host [ ":" port ]
[ path-absolute [ "?" query ]]
If the port is empty or not given, port 80 is assumed. The semantics
are that the identified resource is located at the server listening
for TCP connections on that port of that host, and the Request-URI
for the resource is path-absolute (Section 5.1.2). The use of IP
addresses in URLs SHOULD be avoided whenever possible (see
[RFC1900]). If the path-absolute is not present in the URL, it MUST
be given as "/" when used as a Request-URI for a resource
(Section 5.1.2). If a proxy receives a host name which is not a
fully qualified domain name, it MAY add its domain to the host name
it received. If a proxy receives a fully qualified domain name, the
proxy MUST NOT change the host name.
3.2.3. URI Comparison
When comparing two URIs to decide if they match or not, a client
SHOULD use a case-sensitive octet-by-octet comparison of the entire
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URIs, with these exceptions:
o A port that is empty or not given is equivalent to the default
port for that URI-reference;
o Comparisons of host names MUST be case-insensitive;
o Comparisons of scheme names MUST be case-insensitive;
o An empty path-absolute is equivalent to an path-absolute of "/".
Characters other than those in the "reserved" set (see [RFC2396]) are
equivalent to their ""%" HEX HEX" encoding.
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
3.3. Date/Time Formats
3.3.1. Full Date
HTTP applications have historically allowed three different formats
for the representation of date/time stamps:
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123
Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
The first format is preferred as an Internet standard and represents
a fixed-length subset of that defined by [RFC1123] (an update to
[RFC822]). The other formats are described here only for
compatibility with obsolete implementations. HTTP/1.1 clients and
servers that parse the date value MUST accept all three formats (for
compatibility with HTTP/1.0), though they MUST only generate the RFC
1123 format for representing HTTP-date values in header fields. See
Appendix B for further information.
Note: Recipients of date values are encouraged to be robust in
accepting date values that may have been sent by non-HTTP
applications, as is sometimes the case when retrieving or posting
messages via proxies/gateways to SMTP or NNTP.
All HTTP date/time stamps MUST be represented in Greenwich Mean Time
(GMT), without exception. For the purposes of HTTP, GMT is exactly
equal to UTC (Coordinated Universal Time). This is indicated in the
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first two formats by the inclusion of "GMT" as the three-letter
abbreviation for time zone, and MUST be assumed when reading the
asctime format. HTTP-date is case sensitive and MUST NOT include
additional LWS beyond that specifically included as SP in the
grammar.
HTTP-date = rfc1123-date | obsolete-date
obsolete-date = rfc850-date | asctime-date
rfc1123-date = wkday "," SP date1 SP time SP "GMT"
rfc850-date = weekday "," SP date2 SP time SP "GMT"
asctime-date = wkday SP date3 SP time SP 4DIGIT
date1 = 2DIGIT SP month SP 4DIGIT
; day month year (e.g., 02 Jun 1982)
date2 = 2DIGIT "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82)
date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
; month day (e.g., Jun 2)
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; 00:00:00 - 23:59:59
wkday = "Mon" | "Tue" | "Wed"
| "Thu" | "Fri" | "Sat" | "Sun"
weekday = "Monday" | "Tuesday" | "Wednesday"
| "Thursday" | "Friday" | "Saturday" | "Sunday"
month = "Jan" | "Feb" | "Mar" | "Apr"
| "May" | "Jun" | "Jul" | "Aug"
| "Sep" | "Oct" | "Nov" | "Dec"
Note: HTTP requirements for the date/time stamp format apply only to
their usage within the protocol stream. Clients and servers are not
required to use these formats for user presentation, request logging,
etc.
3.4. Transfer Codings
Transfer-coding values are used to indicate an encoding
transformation that has been, can be, or may need to be applied to an
entity-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, not of the original entity.
transfer-coding = "chunked" | transfer-extension
transfer-extension = token *( ";" parameter )
Parameters are in the form of attribute/value pairs.
parameter = attribute "=" value
attribute = token
value = token | quoted-string
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All transfer-coding values are case-insensitive. HTTP/1.1 uses
transfer-coding values in the TE header field (Section 8.5) and in
the Transfer-Encoding header field (Section 8.7).
Whenever a transfer-coding is applied to a message-body, the set of
transfer-codings MUST include "chunked", unless the message is
terminated by closing the connection. When the "chunked" transfer-
coding is used, it MUST be the last transfer-coding applied to the
message-body. The "chunked" transfer-coding MUST NOT be applied more
than once to a message-body. These rules allow the recipient to
determine the transfer-length of the message (Section 4.4).
Transfer-codings are analogous to the Content-Transfer-Encoding
values of MIME [RFC2045], which were designed to enable safe
transport of binary data over a 7-bit transport service. However,
safe transport has a different focus for an 8bit-clean transfer
protocol. In HTTP, the only unsafe characteristic of message-bodies
is the difficulty in determining the exact body length (Section 4.4),
or the desire to encrypt data over a shared transport.
The Internet Assigned Numbers Authority (IANA) acts as a registry for
transfer-coding value tokens. Initially, the registry contains the
following tokens: "chunked" (Section 3.4.1), "gzip", "compress", and
"deflate" (Section 3.2 of [Part3]).
New transfer-coding value tokens SHOULD be registered in the same way
as new content-coding value tokens (Section 3.2 of [Part3]).
A server which receives an entity-body with a transfer-coding it does
not understand SHOULD return 501 (Not Implemented), and close the
connection. A server MUST NOT send transfer-codings to an HTTP/1.0
client.
3.4.1. 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 entity-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.
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Chunked-Body = *chunk
last-chunk
trailer-part
CRLF
chunk = chunk-size [ chunk-extension ] CRLF
chunk-data CRLF
chunk-size = 1*HEX
last-chunk = 1*("0") [ chunk-extension ] CRLF
chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token | quoted-string
chunk-data = 1*OCTET ; a sequence of chunk-size octets
trailer-part = *(entity-header CRLF)
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.
The trailer allows the sender to include additional HTTP header
fields at the end of the message. The Trailer header field can be
used to indicate which header fields are included in a trailer (see
Section 8.6).
A server using chunked transfer-coding in a response MUST NOT use the
trailer for any header fields unless at least one of the following is
true:
1. the request included a TE header field that indicates "trailers"
is acceptable in the transfer-coding of the response, as
described in Section 8.5; or,
2. the server is the origin server for the response, the trailer
fields consist entirely of optional metadata, and the recipient
could use the message (in a manner acceptable to the origin
server) without receiving this metadata. In other words, the
origin server is willing to accept the possibility that the
trailer fields might be silently discarded along the path to the
client.
This requirement prevents an interoperability failure when the
message is being received by an HTTP/1.1 (or later) proxy and
forwarded to an HTTP/1.0 recipient. It avoids a situation where
compliance with the protocol would have necessitated a possibly
infinite buffer on the proxy.
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A process for decoding the "chunked" transfer-coding can be
represented in pseudo-code as:
length := 0
read chunk-size, chunk-extension (if any) and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to entity-body
length := length + chunk-size
read chunk-size and CRLF
}
read entity-header
while (entity-header not empty) {
append entity-header to existing header fields
read entity-header
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
All HTTP/1.1 applications MUST be able to receive and decode the
"chunked" transfer-coding, and MUST ignore chunk-extension extensions
they do not understand.
3.5. Product Tokens
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by white space. By
convention, the products are listed in order of their significance
for identifying the application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although
any token character MAY appear in a product-version, this token
SHOULD only be used for a version identifier (i.e., successive
versions of the same product SHOULD only differ in the product-
version portion of the product value).
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4. HTTP Message
4.1. Message Types
HTTP messages consist of requests from client to server and responses
from server to client.
HTTP-message = Request | Response ; HTTP/1.1 messages
Request (Section 5) and Response (Section 6) messages use the generic
message format of [RFC2822] for transferring entities (the payload of
the message). Both types of message consist of a start-line, zero or
more header fields (also known as "headers"), an empty line (i.e., a
line with nothing preceding the CRLF) indicating the end of the
header fields, and possibly a message-body.
generic-message = start-line
*(message-header CRLF)
CRLF
[ message-body ]
start-line = Request-Line | Status-Line
In the interest of robustness, servers SHOULD ignore any empty
line(s) 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.
Certain buggy HTTP/1.0 client implementations generate extra CRLF's
after a POST request. To restate what is explicitly forbidden by the
BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an
extra CRLF.
4.2. Message Headers
HTTP header fields, which include general-header (Section 4.5),
request-header (Section 4 of [Part2]), response-header (Section 6 of
[Part2]), and entity-header (Section 4.1 of [Part3]) fields, follow
the same generic format as that given in Section 2.1 of [RFC2822].
Each header field consists of a name followed by a colon (":") and
the field value. Field names are case-insensitive. The field value
MAY be preceded by any amount of LWS, though a single SP is
preferred. Header fields can be extended over multiple lines by
preceding each extra line with at least one SP or HTAB. Applications
ought to follow "common form", where one is known or indicated, when
generating HTTP constructs, since there might exist some
implementations that fail to accept anything beyond the common forms.
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message-header = field-name ":" [ field-value ]
field-name = token
field-value = *( field-content | LWS )
field-content = <field content>
; the OCTETs making up the field-value
; and consisting of either *TEXT or combinations
; of token, separators, and quoted-string
The field-content does not include any leading or trailing LWS:
linear white space occurring before the first non-whitespace
character of the field-value or after the last non-whitespace
character of the field-value. Such leading or trailing LWS MAY be
removed without changing the semantics of the field value. Any LWS
that occurs between field-content MAY be replaced with a single SP
before interpreting the field value or forwarding the message
downstream.
The order in which header fields with differing field names are
received is not significant. However, it is "good practice" to send
general-header fields first, followed by request-header or response-
header fields, and ending with the entity-header fields.
Multiple message-header fields with the same field-name MAY be
present in a message if and only if the entire field-value for that
header field is defined as a comma-separated list [i.e., #(values)].
It MUST be possible to combine the multiple header fields into one
"field-name: field-value" pair, without changing the semantics of the
message, by appending each subsequent field-value to the first, each
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, and thus a proxy MUST NOT
change the order of these field values when a message is forwarded.
4.3. Message Body
The message-body (if any) of an HTTP message is used to carry the
entity-body associated with the request or response. The message-
body differs from the entity-body only when a transfer-coding has
been applied, as indicated by the Transfer-Encoding header field
(Section 8.7).
message-body = entity-body
| <entity-body encoded as per Transfer-Encoding>
Transfer-Encoding MUST be used to indicate any transfer-codings
applied by an application to ensure safe and proper transfer of the
message. Transfer-Encoding is a property of the message, not of the
entity, and thus MAY be added or removed by any application along the
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request/response chain. (However, Section 3.4 places restrictions on
when certain transfer-codings may be used.)
The rules for when a message-body is allowed in a message differ for
requests and responses.
The presence of a message-body in a request is signaled by the
inclusion of a Content-Length or Transfer-Encoding header field in
the request's message-headers. A message-body MUST NOT be included
in a request if the specification of the request method (Section 3 of
[Part2]) explicitly disallows an entity-body in requests. When a
request message contains both a message-body of non-zero length and a
method that does not define any semantics for that request message-
body, then an origin server SHOULD either ignore the message-body or
respond with an appropriate error message (e.g., 413). A proxy or
gateway, when presented the same request, SHOULD either forward the
request inbound with the message-body or ignore the message-body when
determining a response.
For response messages, whether or not a message-body is included with
a message is dependent on both the request method and the response
status code (Section 6.1.1). All responses to the HEAD request
method MUST NOT include a message-body, even though the presence of
entity-header fields might lead one to believe they do. 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 it MAY be of zero length.
4.4. Message Length
The transfer-length of a message is the length of the message-body as
it appears in the message; that is, after any transfer-codings have
been applied. When a message-body is included with a message, the
transfer-length of that body is determined by one of the following
(in order of precedence):
1. Any response message which "MUST NOT" include a message-body
(such as the 1xx, 204, and 304 responses and any response to a
HEAD request) is always terminated by the first empty line after
the header fields, regardless of the entity-header fields present
in the message.
2. If a Transfer-Encoding header field (Section 8.7) is present,
then the transfer-length is defined by use of the "chunked"
transfer-coding (Section 3.4), unless the message is terminated
by closing the connection.
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3. If a Content-Length header field (Section 8.2) is present, its
decimal value in OCTETs represents both the entity-length and the
transfer-length. The Content-Length header field MUST NOT be
sent if these two lengths are different (i.e., if a Transfer-
Encoding header field is present). If a message is received with
both a Transfer-Encoding header field and a Content-Length header
field, the latter MUST be ignored.
4. If the message uses the media type "multipart/byteranges", and
the transfer-length is not otherwise specified, then this self-
delimiting media type defines the transfer-length. This media
type MUST NOT be used unless the sender knows that the recipient
can parse it; the presence in a request of a Range header with
multiple byte-range specifiers from a 1.1 client implies that the
client can parse multipart/byteranges responses.
A range header might be forwarded by a 1.0 proxy that does not
understand multipart/byteranges; in this case the server MUST
delimit the message using methods defined in items 1, 3 or 5
of this section.
5. By the server closing the connection. (Closing the connection
cannot be used to indicate the end of a request body, since that
would leave no possibility for the server to send back a
response.)
For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
containing a message-body MUST include a valid Content-Length header
field unless the server is known to be HTTP/1.1 compliant. If a
request contains a message-body and a Content-Length is not given,
the server SHOULD respond with 400 (Bad Request) if it cannot
determine the length of the message, or with 411 (Length Required) if
it wishes to insist on receiving a valid Content-Length.
All HTTP/1.1 applications that receive entities MUST accept the
"chunked" transfer-coding (Section 3.4), thus allowing this mechanism
to be used for messages when the message length cannot be determined
in advance.
Messages MUST NOT include both a Content-Length header field and a
transfer-coding. If the message does include a transfer-coding, the
Content-Length MUST be ignored.
When a Content-Length is given in a message where a message-body is
allowed, its field value MUST exactly match the number of OCTETs in
the message-body. HTTP/1.1 user agents MUST notify the user when an
invalid length is received and detected.
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4.5. General Header Fields
There are a few header fields which have general applicability for
both request and response messages, but which do not apply to the
entity being transferred. These header fields apply only to the
message being transmitted.
general-header = Cache-Control ; [Part6], Section 16.2
| Connection ; Section 8.1
| Date ; Section 8.3
| Pragma ; [Part6], Section 16.4
| Trailer ; Section 8.6
| Transfer-Encoding ; Section 8.7
| Upgrade ; Section 8.8
| Via ; Section 8.9
| Warning ; [Part6], Section 16.6
General-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of general
header fields if all parties in the communication recognize them to
be general-header fields. Unrecognized header fields are treated as
entity-header fields.
5. Request
A request message from a client to a server includes, within the
first line of that message, the method to be applied to the resource,
the identifier of the resource, and the protocol version in use.
Request = Request-Line ; Section 5.1
*(( general-header ; Section 4.5
| request-header ; [Part2], Section 4
| entity-header ) CRLF) ; [Part3], Section 4.1
CRLF
[ message-body ] ; Section 4.3
5.1. Request-Line
The Request-Line begins with a method token, followed by the Request-
URI and the protocol version, and ending with CRLF. The elements are
separated by SP characters. No CR or LF is allowed except in the
final CRLF sequence.
Request-Line = Method SP Request-URI SP HTTP-Version CRLF
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5.1.1. Method
The Method token indicates the method to be performed on the resource
identified by the Request-URI. The method is case-sensitive.
Method = token
5.1.2. Request-URI
The Request-URI is a Uniform Resource Identifier (Section 3.2) and
identifies the resource upon which to apply the request.
Request-URI = "*"
| absoluteURI
| ( path-absolute [ "?" query ] )
| authority
The four options for Request-URI are dependent on the nature of the
request. The asterisk "*" means that the request does not apply to a
particular resource, but to the server itself, and is only allowed
when the method used does not necessarily apply to a resource. One
example would be
OPTIONS * HTTP/1.1
The absoluteURI form is REQUIRED when the request is being made to a
proxy. The proxy is requested to forward the request or service it
from a valid cache, and return the response. Note that the proxy MAY
forward the request on to another proxy or directly to the server
specified by the absoluteURI. In order to avoid request loops, a
proxy MUST be able to recognize all of its server names, including
any aliases, local variations, and the numeric IP address. An
example Request-Line would be:
GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
To allow for transition to absoluteURIs in all requests in future
versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI
form in requests, even though HTTP/1.1 clients will only generate
them in requests to proxies.
The authority form is only used by the CONNECT method (Section 8.9 of
[Part2]).
The most common form of Request-URI is that used to identify a
resource on an origin server or gateway. In this case the absolute
path of the URI MUST be transmitted (see Section 3.2.1, path-
absolute) as the Request-URI, and the network location of the URI
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(authority) MUST be transmitted in a Host header field. For example,
a client wishing to retrieve the resource above directly from the
origin server would create a TCP connection to port 80 of the host
"www.example.org" and send the lines:
GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.example.org
followed by the remainder of the Request. Note that the absolute
path cannot be empty; if none is present in the original URI, it MUST
be given as "/" (the server root).
The Request-URI is transmitted in the format specified in
Section 3.2.1. If the Request-URI is encoded using the "% HEX HEX"
encoding [RFC2396], the origin server MUST decode the Request-URI in
order to properly interpret the request. Servers SHOULD respond to
invalid Request-URIs with an appropriate status code.
A transparent proxy MUST NOT rewrite the "path-absolute" part of the
received Request-URI when forwarding it to the next inbound server,
except as noted above to replace a null path-absolute with "/".
Note: The "no rewrite" rule prevents the proxy from changing the
meaning of the request when the origin server is improperly using
a non-reserved URI character for a reserved purpose. Implementors
should be aware that some pre-HTTP/1.1 proxies have been known to
rewrite the Request-URI.
5.2. The Resource Identified by a Request
The exact resource identified by an Internet request is determined by
examining both the Request-URI and the Host header field.
An origin server that does not allow resources to differ by the
requested host MAY ignore the Host header field value when
determining the resource identified by an HTTP/1.1 request. (But see
Appendix D.1.1 for other requirements on Host support in HTTP/1.1.)
An origin server that does differentiate resources based on the host
requested (sometimes referred to as virtual hosts or vanity host
names) MUST use the following rules for determining the requested
resource on an HTTP/1.1 request:
1. If Request-URI is an absoluteURI, the host is part of the
Request-URI. Any Host header field value in the request MUST be
ignored.
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2. If the Request-URI is not an absoluteURI, and the request
includes a Host header field, the host is determined by the Host
header field value.
3. If the host as determined by rule 1 or 2 is not a valid host on
the server, the response MUST be a 400 (Bad Request) error
message.
Recipients of an HTTP/1.0 request that lacks a Host header field MAY
attempt to use heuristics (e.g., examination of the URI path for
something unique to a particular host) in order to determine what
exact resource is being requested.
6. Response
After receiving and interpreting a request message, a server responds
with an HTTP response message.
Response = Status-Line ; Section 6.1
*(( general-header ; Section 4.5
| response-header ; [Part2], Section 6
| entity-header ) CRLF) ; [Part3], Section 4.1
CRLF
[ message-body ] ; Section 4.3
6.1. Status-Line
The first line of a Response message is the Status-Line, consisting
of the protocol version followed by a numeric status code and its
associated textual phrase, with each element separated by SP
characters. No CR or LF is allowed except in the final CRLF
sequence.
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
6.1.1. Status Code and Reason Phrase
The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. These codes are fully
defined in Section 9 of [Part2]. The Reason Phrase exists for the
sole purpose of providing a textual description associated with the
numeric status code, out of deference to earlier Internet application
protocols that were more frequently used with interactive text
clients. A client SHOULD ignore the content of the Reason Phrase.
The first digit of the Status-Code defines the class of response.
The last two digits do not have any categorization role. There are 5
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values for the first digit:
o 1xx: Informational - Request received, continuing process
o 2xx: Success - The action was successfully received, understood,
and accepted
o 3xx: Redirection - Further action must be taken in order to
complete the request
o 4xx: Client Error - The request contains bad syntax or cannot be
fulfilled
o 5xx: Server Error - The server failed to fulfill an apparently
valid request
Status-Code = 3DIGIT
Reason-Phrase = *<TEXT, excluding CR, LF>
7. Connections
7.1. Persistent Connections
7.1.1. Purpose
Prior to persistent connections, a separate TCP connection was
established to fetch each URL, increasing the load on HTTP servers
and causing congestion on the Internet. The use of inline images and
other associated data often require a client to make multiple
requests of the same server in a short amount of time. Analysis of
these performance problems and results from a prototype
implementation are available [Pad1995] [Spe]. Implementation
experience and measurements of actual HTTP/1.1 (RFC 2068)
implementations show good results [Nie1997]. Alternatives have also
been explored, for example, T/TCP [Tou1998].
Persistent HTTP connections have a number of advantages:
o By opening and closing fewer TCP connections, CPU time is saved in
routers and hosts (clients, servers, proxies, gateways, tunnels,
or caches), and memory used for TCP protocol control blocks can be
saved in hosts.
o HTTP requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single TCP connection to be
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used much more efficiently, with much lower elapsed time.
o Network congestion is reduced by reducing the number of packets
caused by TCP opens, and by allowing TCP sufficient time to
determine the congestion state of the network.
o Latency on subsequent requests is reduced since there is no time
spent in TCP's connection opening handshake.
o HTTP can evolve more gracefully, since errors can be reported
without the penalty of closing the TCP connection. Clients using
future versions of HTTP might optimistically try a new feature,
but if communicating with an older server, retry with old
semantics after an error is reported.
HTTP implementations SHOULD implement persistent connections.
7.1.2. Overall Operation
A significant difference between HTTP/1.1 and earlier versions of
HTTP is that persistent connections are the default behavior of any
HTTP connection. That is, unless otherwise indicated, the client
SHOULD assume that the server will maintain a persistent connection,
even after error responses from the server.
Persistent connections provide a mechanism by which a client and a
server can signal the close of a TCP connection. This signaling
takes place using the Connection header field (Section 8.1). Once a
close has been signaled, the client MUST NOT send any more requests
on that connection.
7.1.2.1. Negotiation
An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
maintain a persistent connection unless a Connection header including
the connection-token "close" was sent in the request. If the server
chooses to close the connection immediately after sending the
response, it SHOULD send a Connection header including the
connection-token close.
An HTTP/1.1 client MAY expect a connection to remain open, but would
decide to keep it open based on whether the response from a server
contains a Connection header with the connection-token close. In
case the client does not want to maintain a connection for more than
that request, it SHOULD send a Connection header including the
connection-token close.
If either the client or the server sends the close token in the
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Connection header, that request becomes the last one for the
connection.
Clients and servers SHOULD NOT assume that a persistent connection is
maintained for HTTP versions less than 1.1 unless it is explicitly
signaled. See Appendix D.2 for more information on backward
compatibility with HTTP/1.0 clients.
In order to remain persistent, all messages on the connection MUST
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in Section 4.4.
7.1.2.2. Pipelining
A client that supports persistent connections MAY "pipeline" its
requests (i.e., send multiple requests without waiting for each
response). A server MUST send its responses to those requests in the
same order that the requests were received.
Clients which assume persistent connections and pipeline immediately
after connection establishment SHOULD be prepared to retry their
connection if the first pipelined attempt fails. If a client does
such a retry, it MUST NOT pipeline before it knows the connection is
persistent. Clients MUST also be prepared to resend their requests
if the server closes the connection before sending all of the
corresponding responses.
Clients SHOULD NOT pipeline requests using non-idempotent methods or
non-idempotent sequences of methods (see Section 8.1.2 of [Part2]).
Otherwise, a premature termination of the transport connection could
lead to indeterminate results. A client wishing to send a non-
idempotent request SHOULD wait to send that request until it has
received the response status for the previous request.
7.1.3. Proxy Servers
It is especially important that proxies correctly implement the
properties of the Connection header field as specified in
Section 8.1.
The proxy server MUST signal persistent connections separately with
its clients and the origin servers (or other proxy servers) that it
connects to. Each persistent connection applies to only one
transport link.
A proxy server MUST NOT establish a HTTP/1.1 persistent connection
with an HTTP/1.0 client (but see [RFC2068] for information and
discussion of the problems with the Keep-Alive header implemented by
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many HTTP/1.0 clients).
7.1.4. Practical Considerations
Servers will usually have some time-out value beyond which they will
no longer maintain an inactive connection. Proxy servers might make
this a higher value since it is likely that the client will be making
more connections through the same server. The use of persistent
connections places no requirements on the length (or existence) of
this time-out for either the client or the server.
When a client or server wishes to time-out it SHOULD issue a graceful
close on the transport connection. Clients and servers SHOULD both
constantly watch for the other side of the transport close, and
respond to it as appropriate. If a client or server does not detect
the other side's close promptly it could cause unnecessary resource
drain on the network.
A client, server, or proxy MAY close the transport connection at any
time. For example, a client might have started to send a new request
at the same time that the server has decided to close the "idle"
connection. From the server's point of view, the connection is being
closed while it was idle, but from the client's point of view, a
request is in progress.
This means that clients, servers, and proxies MUST be able to recover
from asynchronous close events. Client software SHOULD reopen the
transport connection and retransmit the aborted sequence of requests
without user interaction so long as the request sequence is
idempotent (see Section 8.1.2 of [Part2]). Non-idempotent 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.
Servers SHOULD always respond to at least one request per connection,
if at all possible. Servers SHOULD NOT close a connection in the
middle of transmitting a response, unless a network or client failure
is suspected.
Clients that use persistent connections SHOULD limit the number of
simultaneous connections that they maintain to a given server. A
single-user client SHOULD NOT maintain more than 2 connections with
any server or proxy. A proxy SHOULD use up to 2*N connections to
another server or proxy, where N is the number of simultaneously
active users. These guidelines are intended to improve HTTP response
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times and avoid congestion.
7.2. Message Transmission Requirements
7.2.1. Persistent Connections and Flow Control
HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
flow control mechanisms to resolve temporary overloads, rather than
terminating connections with the expectation that clients will retry.
The latter technique can exacerbate network congestion.
7.2.2. Monitoring Connections for Error Status Messages
An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
the network connection for an error status while it is transmitting
the request. If the client sees an error status, it SHOULD
immediately cease transmitting the body. If the body is being sent
using a "chunked" encoding (Section 3.4), a zero length chunk and
empty trailer MAY be used to prematurely mark the end of the message.
If the body was preceded by a Content-Length header, the client MUST
close the connection.
7.2.3. Use of the 100 (Continue) Status
The purpose of the 100 (Continue) status (see Section 9.1.1 of
[Part2]) is to allow a client that is sending a request message with
a request body to determine if the origin server is willing to accept
the request (based on the request headers) before the client sends
the request body. In some cases, it might either be inappropriate or
highly inefficient for the client to send the body if the server will
reject the message without looking at the body.
Requirements for HTTP/1.1 clients:
o If a client will wait for a 100 (Continue) response before sending
the request body, it MUST send an Expect request-header field
(Section 10.2 of [Part2]) with the "100-continue" expectation.
o A client MUST NOT send an Expect request-header field (Section
10.2 of [Part2]) with the "100-continue" expectation if it does
not intend to send a request body.
Because of the presence of older implementations, the protocol allows
ambiguous situations in which a client may send "Expect: 100-
continue" without receiving either a 417 (Expectation Failed) status
or a 100 (Continue) status. Therefore, when a client sends this
header field to an origin server (possibly via a proxy) from which it
has never seen a 100 (Continue) status, the client SHOULD NOT wait
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for an indefinite period before sending the request body.
Requirements for HTTP/1.1 origin servers:
o Upon receiving a request which includes an Expect request-header
field with the "100-continue" expectation, an origin server MUST
either respond with 100 (Continue) status and continue to read
from the input stream, or respond with a final status code. The
origin server MUST NOT wait for the request body before sending
the 100 (Continue) response. If it responds with a final status
code, it MAY close the transport connection or it MAY continue to
read and discard the rest of the request. It MUST NOT perform the
requested method if it returns a final status code.
o An origin server SHOULD NOT send a 100 (Continue) response if the
request message does not include an Expect request-header field
with the "100-continue" expectation, and MUST NOT send a 100
(Continue) response if such a request comes from an HTTP/1.0 (or
earlier) client. There is an exception to this rule: for
compatibility with [RFC2068], a server MAY send a 100 (Continue)
status in response to an HTTP/1.1 PUT or POST request that does
not include an Expect request-header field with the "100-continue"
expectation. This exception, the purpose of which is to minimize
any client processing delays associated with an undeclared wait
for 100 (Continue) status, applies only to HTTP/1.1 requests, and
not to requests with any other HTTP-version value.
o An origin server MAY omit a 100 (Continue) response if it has
already received some or all of the request body for the
corresponding request.
o An origin server that sends a 100 (Continue) response MUST
ultimately send a final status code, once the request body is
received and processed, unless it terminates the transport
connection prematurely.
o If an origin server receives a request that does not include an
Expect request-header field with the "100-continue" expectation,
the request includes a request body, and the server responds with
a final status code before reading the entire request body from
the transport connection, then the server SHOULD NOT close the
transport connection until it has read the entire request, or
until the client closes the connection. Otherwise, the client
might not reliably receive the response message. However, this
requirement is not be construed as preventing a server from
defending itself against denial-of-service attacks, or from badly
broken client implementations.
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Requirements for HTTP/1.1 proxies:
o If a proxy receives a request that includes an Expect request-
header field with the "100-continue" expectation, and the proxy
either knows that the next-hop server complies with HTTP/1.1 or
higher, or does not know the HTTP version of the next-hop server,
it MUST forward the request, including the Expect header field.
o If the proxy knows that the version of the next-hop server is
HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
respond with a 417 (Expectation Failed) status.
o Proxies SHOULD maintain a cache recording the HTTP version numbers
received from recently-referenced next-hop servers.
o A proxy MUST NOT forward a 100 (Continue) response if the request
message was received from an HTTP/1.0 (or earlier) client and did
not include an Expect request-header field with the "100-continue"
expectation. This requirement overrides the general rule for
forwarding of 1xx responses (see Section 9.1 of [Part2]).
7.2.4. Client Behavior if Server Prematurely Closes Connection
If an HTTP/1.1 client sends a request which includes a request body,
but which does not include an Expect request-header field with the
"100-continue" expectation, and if the client is not directly
connected to an HTTP/1.1 origin server, and if the client sees the
connection close before receiving any status from the server, the
client SHOULD retry the request. If the client does retry this
request, it MAY use the following "binary exponential backoff"
algorithm to be assured of obtaining a reliable response:
1. Initiate a new connection to the server
2. Transmit the request-headers
3. Initialize a variable R to the estimated round-trip time to the
server (e.g., based on the time it took to establish the
connection), or to a constant value of 5 seconds if the round-
trip time is not available.
4. Compute T = R * (2**N), where N is the number of previous retries
of this request.
5. Wait either for an error response from the server, or for T
seconds (whichever comes first)
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6. If no error response is received, after T seconds transmit the
body of the request.
7. If client sees that the connection is closed prematurely, repeat
from step 1 until the request is accepted, an error response is
received, or the user becomes impatient and terminates the retry
process.
If at any point an error status is received, the client
o SHOULD NOT continue and
o SHOULD close the connection if it has not completed sending the
request message.
8. Header Field Definitions
This section defines the syntax and semantics of HTTP/1.1 header
fields related to message framing and transport protocols.
For entity-header fields, both sender and recipient refer to either
the client or the server, depending on who sends and who receives the
entity.
8.1. Connection
The Connection general-header field allows the sender to specify
options that are desired for that particular connection and MUST NOT
be communicated by proxies over further connections.
The Connection header has the following grammar:
Connection = "Connection" ":" 1#(connection-token)
connection-token = token
HTTP/1.1 proxies MUST parse the Connection header field before a
message is forwarded and, for each connection-token in this field,
remove any header field(s) from the message with the same name as the
connection-token. Connection options are signaled by the presence of
a connection-token in the Connection header field, not by any
corresponding additional header field(s), since the additional header
field may not be sent if there are no parameters associated with that
connection option.
Message headers listed in the Connection header MUST NOT include end-
to-end headers, such as Cache-Control.
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HTTP/1.1 defines the "close" connection option for the sender to
signal that the connection will be closed after completion of the
response. For example,
Connection: close
in either the request or the response header fields indicates that
the connection SHOULD NOT be considered `persistent' (Section 7.1)
after the current request/response is complete.
An HTTP/1.1 client that does not support persistent connections MUST
include the "close" connection option in every request message.
An HTTP/1.1 server that does not support persistent connections MUST
include the "close" connection option in every response message that
does not have a 1xx (informational) status code.
A system receiving an HTTP/1.0 (or lower-version) message that
includes a Connection header MUST, for each connection-token in this
field, remove and ignore any header field(s) from the message with
the same name as the connection-token. This protects against
mistaken forwarding of such header fields by pre-HTTP/1.1 proxies.
See Appendix D.2.
8.2. Content-Length
The Content-Length entity-header field indicates the size of the
entity-body, in decimal number of OCTETs, sent to the recipient or,
in the case of the HEAD method, the size of the entity-body that
would have been sent had the request been a GET.
Content-Length = "Content-Length" ":" 1*DIGIT
An example is
Content-Length: 3495
Applications SHOULD use this field to indicate the transfer-length of
the message-body, unless this is prohibited by the rules in
Section 4.4.
Any Content-Length greater than or equal to zero is a valid value.
Section 4.4 describes how to determine the length of a message-body
if a Content-Length is not given.
Note that the meaning of this field is significantly different from
the corresponding definition in MIME, where it is an optional field
used within the "message/external-body" content-type. In HTTP, it
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SHOULD be sent whenever the message's length can be determined prior
to being transferred, unless this is prohibited by the rules in
Section 4.4.
8.3. Date
The Date general-header field represents the date and time at which
the message was originated, having the same semantics as orig-date in
Section 3.6.1 of [RFC2822]. The field value is an HTTP-date, as
described in Section 3.3.1; it MUST be sent in rfc1123-date format.
Date = "Date" ":" HTTP-date
An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT
Origin servers MUST include a Date header field in all responses,
except in these cases:
1. If the response status code is 100 (Continue) or 101 (Switching
Protocols), the response MAY include a Date header field, at the
server's option.
2. If the response status code conveys a server error, e.g. 500
(Internal Server Error) or 503 (Service Unavailable), and it is
inconvenient or impossible to generate a valid Date.
3. If the server does not have a clock that can provide a reasonable
approximation of the current time, its responses MUST NOT include
a Date header field. In this case, the rules in Section 8.3.1
MUST be followed.
A received message that does not have a Date header field MUST be
assigned one by the recipient if the message will be cached by that
recipient or gatewayed via a protocol which requires a Date. An HTTP
implementation without a clock MUST NOT cache responses without
revalidating them on every use. An HTTP cache, especially a shared
cache, SHOULD use a mechanism, such as NTP [RFC1305], to synchronize
its clock with a reliable external standard.
Clients SHOULD only send a Date header field in messages that include
an entity-body, as in the case of the PUT and POST requests, and even
then it is optional. A client without a clock MUST NOT send a Date
header field in a request.
The HTTP-date sent in a Date header SHOULD NOT represent a date and
time subsequent to the generation of the message. It SHOULD
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represent the best available approximation of the date and time of
message generation, unless the implementation has no means of
generating a reasonably accurate date and time. In theory, the date
ought to represent the moment just before the entity is generated.
In practice, the date can be generated at any time during the message
origination without affecting its semantic value.
8.3.1. Clockless Origin Server Operation
Some origin server implementations might not have a clock available.
An origin server without a clock MUST NOT assign Expires or Last-
Modified values to a response, unless these values were associated
with the resource by a system or user with a reliable clock. It MAY
assign an Expires value that is known, at or before server
configuration time, to be in the past (this allows "pre-expiration"
of responses without storing separate Expires values for each
resource).
8.4. Host
The Host request-header field specifies the Internet host and port
number of the resource being requested, as obtained from the original
URI given by the user or referring resource (generally an HTTP URL,
as described in Section 3.2.2). The Host field value MUST represent
the naming authority of the origin server or gateway given by the
original URL. This allows the origin server or gateway to
differentiate between internally-ambiguous URLs, such as the root "/"
URL of a server for multiple host names on a single IP address.
Host = "Host" ":" uri-host [ ":" port ] ; Section 3.2.2
A "host" without any trailing port information implies the default
port for the service requested (e.g., "80" for an HTTP URL). For
example, a request on the origin server for
<http://www.example.org/pub/WWW/> would properly include:
GET /pub/WWW/ HTTP/1.1
Host: www.example.org
A client MUST include a Host header field in all HTTP/1.1 request
messages. If the requested URI does not include an Internet host
name for the service being requested, then the Host header field MUST
be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
request message it forwards does contain an appropriate Host header
field that identifies the service being requested by the proxy. All
Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
status code to any HTTP/1.1 request message which lacks a Host header
field.
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See Sections 5.2 and D.1.1 for other requirements relating to Host.
8.5. TE
The TE request-header field indicates what extension transfer-codings
it is willing to accept in the response and whether or not it is
willing to accept trailer fields in a chunked transfer-coding. Its
value may consist of the keyword "trailers" and/or a comma-separated
list of extension transfer-coding names with optional accept
parameters (as described in Section 3.4).
TE = "TE" ":" #( t-codings )
t-codings = "trailers" | ( transfer-extension [ accept-params ] )
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 3.4.1. This keyword is reserved for use with
transfer-coding values even though it does not itself represent a
transfer-coding.
Examples of its use are:
TE: deflate
TE:
TE: trailers, deflate;q=0.5
The TE header field only applies to the immediate connection.
Therefore, the keyword MUST be supplied within a Connection header
field (Section 8.1) whenever TE is present in an HTTP/1.1 message.
A server tests whether a transfer-coding is acceptable, according to
a TE field, using these rules:
1. The "chunked" transfer-coding is always acceptable. If the
keyword "trailers" is listed, the client indicates that it is
willing to accept trailer fields in the chunked response on
behalf of itself and any downstream clients. The implication is
that, if given, the client is stating that either all downstream
clients are willing to accept trailer fields in the forwarded
response, or that it will attempt to buffer the response on
behalf of downstream recipients.
Note: HTTP/1.1 does not define any means to limit the size of a
chunked response such that a client can be assured of buffering
the entire response.
2. If the transfer-coding being tested is one of the transfer-
codings listed in the TE field, then it is acceptable unless it
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is accompanied by a qvalue of 0. (As defined in Section 3.4 of
[Part3], a qvalue of 0 means "not acceptable.")
3. If multiple transfer-codings are acceptable, then the acceptable
transfer-coding with the highest non-zero qvalue is preferred.
The "chunked" transfer-coding always has a qvalue of 1.
If the TE field-value is empty or if no TE field is present, the only
transfer-coding is "chunked". A message with no transfer-coding is
always acceptable.
8.6. Trailer
The Trailer general field value indicates that the given set of
header fields is present in the trailer of a message encoded with
chunked transfer-coding.
Trailer = "Trailer" ":" 1#field-name
An HTTP/1.1 message SHOULD include a Trailer header field in a
message using chunked transfer-coding with a non-empty trailer.
Doing so allows the recipient to know which header fields to expect
in the trailer.
If no Trailer header field is present, the trailer SHOULD NOT include
any header fields. See Section 3.4.1 for restrictions on the use of
trailer fields in a "chunked" transfer-coding.
Message header fields listed in the Trailer header field MUST NOT
include the following header fields:
o Transfer-Encoding
o Content-Length
o Trailer
8.7. Transfer-Encoding
The Transfer-Encoding general-header field indicates what (if any)
type of transformation has been applied to the message body in order
to safely transfer it between the sender and the recipient. This
differs from the content-coding in that the transfer-coding is a
property of the message, not of the entity.
Transfer-Encoding = "Transfer-Encoding" ":" 1#transfer-coding
Transfer-codings are defined in Section 3.4. An example is:
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Transfer-Encoding: chunked
If multiple encodings have been applied to an entity, the transfer-
codings MUST be listed in the order in which they were applied.
Additional information about the encoding parameters MAY be provided
by other entity-header fields not defined by this specification.
Many older HTTP/1.0 applications do not understand the Transfer-
Encoding header.
8.8. Upgrade
The Upgrade general-header allows the client to specify what
additional communication protocols it supports and would like to use
if the server finds it appropriate to switch protocols. The server
MUST use the Upgrade header field within a 101 (Switching Protocols)
response to indicate which protocol(s) are being switched.
Upgrade = "Upgrade" ":" 1#product
For example,
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
The Upgrade header field is intended to provide a simple mechanism
for transition from HTTP/1.1 to some other, incompatible protocol.
It does so by allowing the client to advertise its desire to use
another protocol, such as a later version of HTTP with a higher major
version number, even though the current request has been made using
HTTP/1.1. This eases the difficult transition between incompatible
protocols by allowing the client to initiate a request in the more
commonly supported protocol while indicating to the server that it
would like to use a "better" protocol if available (where "better" is
determined by the server, possibly according to the nature of the
method and/or resource being requested).
The Upgrade header field only applies to switching application-layer
protocols upon the existing transport-layer connection. Upgrade
cannot be used to insist on a protocol change; its acceptance and use
by the server is optional. The capabilities and nature of the
application-layer communication after the protocol change is entirely
dependent upon the new protocol chosen, although the first action
after changing the protocol MUST be a response to the initial HTTP
request containing the Upgrade header field.
The Upgrade header field only applies to the immediate connection.
Therefore, the upgrade keyword MUST be supplied within a Connection
header field (Section 8.1) whenever Upgrade is present in an HTTP/1.1
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message.
The Upgrade header field cannot be used to indicate a switch to a
protocol on a different connection. For that purpose, it is more
appropriate to use a 301, 302, 303, or 305 redirection response.
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 3.1 and future updates to this
specification. Any token can be used as a protocol name; however, it
will only be useful if both the client and server associate the name
with the same protocol.
8.9. Via
The Via general-header field MUST be used by gateways and proxies 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
defined in Section 3.6.7 of [RFC2822] and is intended to be used for
tracking message forwards, avoiding request loops, and identifying
the protocol capabilities of all senders along the request/response
chain.
Via = "Via" ":" 1#( received-protocol received-by [ comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
protocol-name = token
protocol-version = token
received-by = ( uri-host [ ":" port ] ) | pseudonym
pseudonym = token
The received-protocol indicates the protocol version of the message
received by the server or client along each segment of the request/
response chain. The received-protocol version is appended to the Via
field value when the message is forwarded so that information about
the protocol capabilities of upstream applications remains visible to
all recipients.
The protocol-name is optional 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 represents 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
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forwarding applications.
Comments MAY be used in the Via header field to identify the software
of the recipient proxy or gateway, analogous to the User-Agent and
Server header fields. However, all comments in the Via field are
optional and MAY be removed by any recipient prior to forwarding the
message.
For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which
completes the request by forwarding it to the origin server at
www.example.com. The request received by www.example.com would then
have the following Via header field:
Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
Proxies and gateways used as a portal through a network firewall
SHOULD NOT, by default, forward the names and ports of hosts within
the firewall region. This information SHOULD only be propagated if
explicitly enabled. If not enabled, the received-by host of any host
behind the firewall SHOULD be replaced by an appropriate pseudonym
for that host.
For organizations that have strong privacy requirements for hiding
internal structures, a proxy MAY combine an ordered subsequence of
Via header field entries with identical received-protocol values into
a single such entry. For example,
Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
could be collapsed to
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
Applications SHOULD NOT combine multiple entries unless they are all
under the same organizational control and the hosts have already been
replaced by pseudonyms. Applications MUST NOT combine entries which
have different received-protocol values.
9. IANA Considerations
9.1. Message Header Registration
The Message Header Registry located at <http://www.iana.org/
assignments/message-headers/message-header-index.html> should be
updated with the permanent registrations below (see [RFC3864]):
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+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Connection | http | standard | Section 8.1 |
| Content-Length | http | standard | Section 8.2 |
| Date | http | standard | Section 8.3 |
| Host | http | standard | Section 8.4 |
| TE | http | standard | Section 8.5 |
| Trailer | http | standard | Section 8.6 |
| Transfer-Encoding | http | standard | Section 8.7 |
| Upgrade | http | standard | Section 8.8 |
| Via | http | standard | Section 8.9 |
+-------------------+----------+----------+-------------+
The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force".
10. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
10.1. Personal Information
HTTP clients are often privy to large amounts of personal information
(e.g. the user's name, location, mail address, passwords, encryption
keys, etc.), and SHOULD be very careful to prevent unintentional
leakage of this information. We very strongly recommend that a
convenient interface be provided for the user to control
dissemination of such information, and that designers and
implementors be particularly careful in this area. History shows
that errors in this area often create serious security and/or privacy
problems and generate highly adverse publicity for the implementor's
company.
10.2. Abuse of Server Log Information
A server is in the position to save personal data about a user's
requests which might identify their reading patterns or subjects of
interest. This information is clearly confidential in nature and its
handling can be constrained by law in certain countries. People
using HTTP to provide data are responsible for ensuring that such
material is not distributed without the permission of any individuals
that are identifiable by the published results.
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10.3. Attacks Based On File and Path Names
Implementations of HTTP origin servers SHOULD be careful to restrict
the documents returned by HTTP requests to be only those that were
intended by the server administrators. If an HTTP server translates
HTTP URIs directly into file system calls, the server MUST take
special care not to serve files that were not intended to be
delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
other operating systems use ".." as a path component to indicate a
directory level above the current one. On such a system, an HTTP
server MUST disallow any such construct in the Request-URI if it
would otherwise allow access to a resource outside those intended to
be accessible via the HTTP server. Similarly, files intended for
reference only internally to the server (such as access control
files, configuration files, and script code) MUST be protected from
inappropriate retrieval, since they might contain sensitive
information. Experience has shown that minor bugs in such HTTP
server implementations have turned into security risks.
10.4. DNS Spoofing
Clients using HTTP rely heavily on the Domain Name Service, and are
thus generally prone to security attacks based on the deliberate mis-
association of IP addresses and DNS names. Clients need to be
cautious in assuming the continuing validity of an IP number/DNS name
association.
In particular, HTTP clients SHOULD rely on their name resolver for
confirmation of an IP number/DNS name association, rather than
caching the result of previous host name lookups. Many platforms
already can cache host name lookups locally when appropriate, and
they SHOULD be configured to do so. It is proper for these lookups
to be cached, however, only when the TTL (Time To Live) information
reported by the name server makes it likely that the cached
information will remain useful.
If HTTP clients cache the results of host name lookups in order to
achieve a performance improvement, they MUST observe the TTL
information reported by DNS.
If HTTP clients do not observe this rule, they could be spoofed when
a previously-accessed server's IP address changes. As network
renumbering is expected to become increasingly common [RFC1900], the
possibility of this form of attack will grow. Observing this
requirement thus reduces this potential security vulnerability.
This requirement also improves the load-balancing behavior of clients
for replicated servers using the same DNS name and reduces the
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likelihood of a user's experiencing failure in accessing sites which
use that strategy.
10.5. Proxies and Caching
By their very nature, HTTP proxies are men-in-the-middle, and
represent an opportunity for man-in-the-middle attacks. Compromise
of the systems on which the proxies run can result in serious
security and privacy problems. Proxies have access to security-
related information, personal information about individual users and
organizations, and proprietary information belonging to users and
content providers. A compromised proxy, or a proxy implemented or
configured without regard to security and privacy considerations,
might be used in the commission of a wide range of potential attacks.
Proxy operators should protect the systems on which proxies run as
they would protect any system that contains or transports sensitive
information. In particular, log information gathered at proxies
often contains highly sensitive personal information, and/or
information about organizations. Log information should be carefully
guarded, and appropriate guidelines for use developed and followed.
(Section 10.2).
Proxy implementors should consider the privacy and security
implications of their design and coding decisions, and of the
configuration options they provide to proxy operators (especially the
default configuration).
Users of a proxy need to be aware that they are no trustworthier than
the people who run the proxy; HTTP itself cannot solve this problem.
The judicious use of cryptography, when appropriate, may suffice to
protect against a broad range of security and privacy attacks. Such
cryptography is beyond the scope of the HTTP/1.1 specification.
10.6. Denial of Service Attacks on Proxies
They exist. They are hard to defend against. Research continues.
Beware.
11. Acknowledgments
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for [RFC822ABNF]. Similarly,
it reuses many of the definitions provided by Nathaniel Borenstein
and Ned Freed for MIME [RFC2045]. We hope that their inclusion in
this specification will help reduce past confusion over the
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relationship between HTTP and Internet mail message formats.
HTTP has evolved considerably over the years. It has benefited from
a large and active developer community--the many people who have
participated on the www-talk mailing list--and it is that community
which has been most responsible for the success of HTTP and of the
World-Wide Web in general. Marc Andreessen, Robert Cailliau, Daniel
W. Connolly, Bob Denny, John Franks, Jean-Francois Groff, Phillip M.
Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli,
Dave Raggett, Tony Sanders, and Marc VanHeyningen deserve special
recognition for their efforts in defining early aspects of the
protocol.
This document has benefited greatly from the comments of all those
participating in the HTTP-WG. In addition to those already
mentioned, the following individuals have contributed to this
specification:
Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc
Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann, Bob Jernigan, Shel
Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut,
David M. Kristol, Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert
Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David
Morris, Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott
Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich
Salz, Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart)
Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen.
Thanks to the "cave men" of Palo Alto. You know who you are.
Jim Gettys (the editor of [RFC2616]) wishes particularly to thank Roy
Fielding, the editor of [RFC2068], along with John Klensin, Jeff
Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh
Cohen, Alex Hopmann, Scott Lawrence, and Larry Masinter for their
help. And thanks go particularly to Jeff Mogul and Scott Lawrence
for performing the "MUST/MAY/SHOULD" audit.
The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
Frystyk implemented RFC 2068 early, and we wish to thank them for the
discovery of many of the problems that this document attempts to
rectify.
12. References
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12.1. Normative References
[ISO-8859-1]
International Organization for Standardization,
"Information technology -- 8-bit single-byte coded graphic
character sets -- Part 1: Latin alphabet No. 1", ISO/
IEC 8859-1:1998, 1998.
[Part2] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 2: Message
Semantics", draft-ietf-httpbis-p2-semantics-03 (work in
progress), June 2008.
[Part3] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload
and Content Negotiation", draft-ietf-httpbis-p3-payload-03
(work in progress), June 2008.
[Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
Partial Responses", draft-ietf-httpbis-p5-range-03 (work
in progress), June 2008.
[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
and J. Reschke, Ed., "HTTP/1.1, part 6: Caching",
draft-ietf-httpbis-p6-cache-03 (work in progress),
June 2008.
[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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC822ABNF]
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Internet-Draft HTTP/1.1, Part 1 June 2008
Crocker, D., "Standard for the format of ARPA Internet
text messages", STD 11, RFC 822, August 1982.
[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
12.2. Informative References
[Nie1997] Nielsen, H., Gettys, J., Prud'hommeaux, E., Lie, H., and
C. Lilley, "Network Performance Effects of HTTP/1.1, CSS1,
and PNG", ACM Proceedings of the ACM SIGCOMM '97
conference on Applications, technologies, architectures,
and protocols for computer communication SIGCOMM '97,
September 1997,
<http://doi.acm.org/10.1145/263105.263157>.
[Pad1995] Padmanabhan, V. and J. Mogul, "Improving HTTP Latency",
Computer Networks and ISDN Systems v. 28, pp. 25-35,
December 1995.
Slightly revised version of paper in Proc. 2nd
International WWW Conference '94: Mosaic and the Web, Oct.
1994, which is available at <http://www.ncsa.uiuc.edu/SDG/
IT94/Proceedings/DDay/mogul/HTTPLatency.html>.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992.
[RFC1436] Anklesaria, F., McCahill, M., Lindner, P., Johnson, D.,
Torrey, D., and B. Alberti, "The Internet Gopher Protocol
(a distributed document search and retrieval protocol)",
RFC 1436, March 1993.
[RFC1630] Berners-Lee, T., "Universal Resource Identifiers in WWW: A
Unifying Syntax for the Expression of Names and Addresses
of Objects on the Network as used in the World-Wide Web",
RFC 1630, June 1994.
[RFC1737] Masinter, L. and K. Sollins, "Functional Requirements for
Uniform Resource Names", RFC 1737, December 1994.
[RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, December 1994.
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[RFC1808] Fielding, R., "Relative Uniform Resource Locators",
RFC 1808, June 1995.
[RFC1900] Carpenter, B. and Y. Rekhter, "Renumbering Needs Work",
RFC 1900, February 1996.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2068, January 1997.
[RFC2145] Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, "Use
and Interpretation of HTTP Version Numbers", RFC 2145,
May 1997.
[RFC2324] Masinter, L., "Hyper Text Coffee Pot Control Protocol
(HTCPCP/1.0)", RFC 2324, April 1998.
[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.
[RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC3977] Feather, C., "Network News Transfer Protocol (NNTP)",
RFC 3977, October 2006.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[RFC822] Crocker, D., "Standard for the format of ARPA Internet
text messages", STD 11, RFC 822, August 1982.
[RFC959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[Spe] Spero, S., "Analysis of HTTP Performance Problems",
<http://sunsite.unc.edu/mdma-release/http-prob.html>.
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[Tou1998] Touch, J., Heidemann, J., and K. Obraczka, "Analysis of
HTTP Performance", ISI Research Report ISI/RR-98-463,
Aug 1998, <http://www.isi.edu/touch/pubs/http-perf96/>.
(original report dated Aug. 1996)
[WAIS] Davis, F., Kahle, B., Morris, H., Salem, J., Shen, T.,
Wang, R., Sui, J., and M. Grinbaum, "WAIS Interface
Protocol Prototype Functional Specification (v1.5)",
Thinking Machines Corporation , April 1990.
Appendix A. Internet Media Types
In addition to defining HTTP/1.1, this document serves as the
specification for the Internet media type "message/http" and
"application/http". The following is to be registered with IANA
[RFC4288].
A.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
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Interoperability considerations: none
Published specification: This specification (see Appendix A.1).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
A.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.
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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 Appendix A.2).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
Appendix B. Tolerant Applications
Although this document specifies the requirements for the generation
of HTTP/1.1 messages, not all applications will be correct in their
implementation. We therefore recommend that operational applications
be tolerant of deviations whenever those deviations can be
interpreted unambiguously.
Clients SHOULD be tolerant in parsing the Status-Line and servers
tolerant when parsing the Request-Line. In particular, they SHOULD
accept any amount of SP or HTAB characters between fields, even
though only a single SP is required.
The line terminator for message-header fields is the sequence CRLF.
However, we recommend that applications, when parsing such headers,
recognize a single LF as a line terminator and ignore the leading CR.
The character set of an entity-body SHOULD be labeled as the lowest
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common denominator of the character codes used within that body, with
the exception that not labeling the entity is preferred over labeling
the entity with the labels US-ASCII or ISO-8859-1. See [Part3].
Additional rules for requirements on parsing and encoding of dates
and other potential problems with date encodings include:
o HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
which appears to be more than 50 years in the future is in fact in
the past (this helps solve the "year 2000" problem).
o An HTTP/1.1 implementation MAY internally represent a parsed
Expires date as earlier than the proper value, but MUST NOT
internally represent a parsed Expires date as later than the
proper value.
o All expiration-related calculations MUST be done in GMT. The
local time zone MUST NOT influence the calculation or comparison
of an age or expiration time.
o If an HTTP header incorrectly carries a date value with a time
zone other than GMT, it MUST be converted into GMT using the most
conservative possible conversion.
Appendix C. Conversion of Date Formats
HTTP/1.1 uses a restricted set of date formats (Section 3.3.1) to
simplify the process of date comparison. Proxies and gateways from
other protocols SHOULD ensure that any Date header field present in a
message conforms to one of the HTTP/1.1 formats and rewrite the date
if necessary.
Appendix D. Compatibility with Previous Versions
It is beyond the scope of a protocol specification to mandate
compliance with previous versions. HTTP/1.1 was deliberately
designed, however, to make supporting previous versions easy. It is
worth noting that, at the time of composing this specification
(1996), we would expect commercial HTTP/1.1 servers to:
o recognize the format of the Request-Line for HTTP/0.9, 1.0, and
1.1 requests;
o understand any valid request in the format of HTTP/0.9, 1.0, or
1.1;
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o respond appropriately with a message in the same major version
used by the client.
And we would expect HTTP/1.1 clients to:
o recognize the format of the Status-Line for HTTP/1.0 and 1.1
responses;
o understand any valid response in the format of HTTP/0.9, 1.0, or
1.1.
For most implementations of HTTP/1.0, each connection is established
by the client prior to the request and closed by the server after
sending the response. Some implementations implement the Keep-Alive
version of persistent connections described in Section 19.7.1 of
[RFC2068].
D.1. Changes from HTTP/1.0
This section summarizes major differences between versions HTTP/1.0
and HTTP/1.1.
D.1.1. Changes to Simplify Multi-homed Web Servers and Conserve IP
Addresses
The requirements that clients and servers support the Host request-
header, report an error if the Host request-header (Section 8.4) is
missing from an HTTP/1.1 request, and accept absolute URIs
(Section 5.1.2) are among the most important changes defined by this
specification.
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 changes outlined above will
allow the Internet, once older HTTP clients are no longer common, to
support multiple Web sites from a single IP address, greatly
simplifying large operational Web servers, where allocation of many
IP addresses to a single host has created serious problems. The
Internet will also be able to recover the IP addresses that have been
allocated for the sole purpose of allowing special-purpose domain
names to be used in root-level HTTP URLs. Given the rate of growth
of the Web, and the number of servers already deployed, it is
extremely important that all implementations of HTTP (including
updates to existing HTTP/1.0 applications) correctly implement these
requirements:
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o Both clients and servers MUST support the Host request-header.
o A client that sends an HTTP/1.1 request MUST send a Host header.
o Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
request does not include a Host request-header.
o Servers MUST accept absolute URIs.
D.2. Compatibility with HTTP/1.0 Persistent Connections
Some clients and servers might wish to be compatible with some
previous implementations of persistent connections in HTTP/1.0
clients and servers. Persistent connections in HTTP/1.0 are
explicitly negotiated as they are not the default behavior. HTTP/1.0
experimental implementations of persistent connections are faulty,
and the new facilities in HTTP/1.1 are designed to rectify these
problems. The problem was that some existing 1.0 clients may be
sending Keep-Alive to a proxy server that doesn't understand
Connection, which would then erroneously forward it to the next
inbound server, which would establish the Keep-Alive connection and
result in a hung HTTP/1.0 proxy waiting for the close on the
response. The result is that HTTP/1.0 clients must be prevented from
using Keep-Alive when talking to proxies.
However, talking to proxies is the most important use of persistent
connections, so that prohibition is clearly unacceptable. Therefore,
we need some other mechanism for indicating a persistent connection
is desired, which is safe to use even when talking to an old proxy
that ignores Connection. Persistent connections are the default for
HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
declaring non-persistence. See Section 8.1.
The original HTTP/1.0 form of persistent connections (the Connection:
Keep-Alive and Keep-Alive header) is documented in [RFC2068].
D.3. Changes from RFC 2068
This specification has been carefully audited to correct and
disambiguate key word usage; RFC 2068 had many problems in respect to
the conventions laid out in [RFC2119].
Transfer-coding and message lengths all interact in ways that
required fixing exactly when chunked encoding is used (to allow for
transfer encoding that may not be self delimiting); it was important
to straighten out exactly how message lengths are computed.
(Sections 3.4, 4.4, 8.2, see also [Part3], [Part5] and [Part6])
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The use and interpretation of HTTP version numbers has been clarified
by [RFC2145]. Require proxies to upgrade requests to highest
protocol version they support to deal with problems discovered in
HTTP/1.0 implementations (Section 3.1)
Transfer-coding had significant problems, particularly with
interactions with chunked encoding. The solution is that transfer-
codings become as full fledged as content-codings. This involves
adding an IANA registry for transfer-codings (separate from content
codings), a new header field (TE) and enabling trailer headers in the
future. Transfer encoding is a major performance benefit, so it was
worth fixing [Nie1997]. TE also solves another, obscure, downward
interoperability problem that could have occurred due to interactions
between authentication trailers, chunked encoding and HTTP/1.0
clients.(Section 3.4, 3.4.1, and 8.5)
D.4. Changes from RFC 2616
The CHAR rule does not allow the NUL character anymore (this affects
the comment and quoted-string rules). Furthermore, the quoted-pair
rule does not allow escaping NUL, CR or LF anymore. (Section 2.2)
Clarify that HTTP-Version is case sensitive. (Section 3.1)
Remove reference to non-existant identity transfer-coding value
tokens. (Sections 3.4 and 4.4)
Clarification that the chunk length does not include the count of the
octets in the chunk header and trailer. (Section 3.4.1)
Fix BNF to add query, as the abs_path production in Section 3 of
[RFC2396] doesn't define it. (Section 5.1.2)
Clarify exactly when close connection options must be sent.
(Section 8.1)
Appendix E. Change Log (to be removed by RFC Editor before publication)
E.1. Since RFC2616
Extracted relevant partitions from [RFC2616].
E.2. Since draft-ietf-httpbis-p1-messaging-00
Closed issues:
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o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/1>: "HTTP
Version should be case sensitive"
(<http://purl.org/NET/http-errata#verscase>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/2>: "'unsafe'
characters" (<http://purl.org/NET/http-errata#unsafe-uri>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/3>: "Chunk Size
Definition" (<http://purl.org/NET/http-errata#chunk-size>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/4>: "Message
Length" (<http://purl.org/NET/http-errata#msg-len-chars>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/8>: "Media Type
Registrations" (<http://purl.org/NET/http-errata#media-reg>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/11>: "URI
includes query" (<http://purl.org/NET/http-errata#uriquery>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/15>: "No close
on 1xx responses" (<http://purl.org/NET/http-errata#noclose1xx>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/16>: "Remove
'identity' token references"
(<http://purl.org/NET/http-errata#identity>)
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/26>: "Import
query BNF"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/31>: "qdtext
BNF"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative
and Informative references"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42>: "RFC2606
Compliance"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/45>: "RFC977
reference"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700
references"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/47>:
"inconsistency in date format explanation"
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o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/48>: "Date
reference typo"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65>:
"Informative references"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/66>:
"ISO-8859-1 Reference"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86>: "Normative
up-to-date references"
Other changes:
o Update media type registrations to use RFC4288 template.
o Use names of RFC4234 core rules DQUOTE and HTAB, fix broken ABNF
for chunk-data (work in progress on
<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>)
E.3. Since draft-ietf-httpbis-p1-messaging-01
Closed issues:
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/19>: "Bodies on
GET (and other) requests"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating
to RFC4288"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/57>: "Status
Code and Reason Phrase"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/82>: "rel_path
not used"
Ongoing work on ABNF conversion
(<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Get rid of duplicate BNF rule names ("host" -> "uri-host",
"trailer" -> "trailer-part").
o Avoid underscore character in rule names ("http_URL" -> "http-
URL", "abs_path" -> "path-absolute").
o Add rules for terms imported from URI spec ("absoluteURI",
"authority", "path-absolute", "port", "query", "relativeURI",
"host) -- these will have to be updated when switching over to
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RFC3986.
o Synchronize core rules with RFC5234 (this includes a change to
CHAR which now excludes NUL).
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.
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".
E.4. Since draft-ietf-httpbis-p1-messaging-02
Closed issues:
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/51>: "HTTP-date
vs. rfc1123-date"
o <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/64>: "WS in
quoted-pair"
Ongoing work on IANA Message Header Registration
(<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40>):
o Reference RFC 3984, and update header registrations for headers
defined in this document.
Ongoing work on ABNF conversion
(<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Replace string literals when the string really is case-sensitive
(HTTP-Version).
Index
A
application/http Media Type 56
C
cache 8
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cacheable 9
client 7
connection 6
Connection header 39
content negotiation 7
Content-Length header 40
D
Date header 41
downstream 9
E
entity 7
G
gateway 8
Grammar
absoluteURI 18
ALPHA 14
asctime-date 20
attribute 20
authority 18
CHAR 14
chunk 22
chunk-data 22
chunk-ext-name 22
chunk-ext-val 22
chunk-extension 22
chunk-size 22
Chunked-Body 22
comment 15
Connection 39
connection-token 39
Content-Length 40
CR 14
CRLF 14
ctext 15
CTL 14
Date 41
date1 20
date2 20
date3 20
DIGIT 14
DQUOTE 14
extension-code 32
extension-method 29
field-content 25
field-name 25
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field-value 25
general-header 28
generic-message 24
HEX 15
Host 42
HTAB 14
HTTP-date 20
HTTP-message 24
HTTP-Prot-Name 16
http-URL 18
HTTP-Version 16
last-chunk 22
LF 14
LWS 14
message-body 25
message-header 25
Method 29
month 20
obsolete-date 20
OCTET 14
parameter 20
path-absolute 18
port 18
product 23
product-version 23
protocol-name 46
protocol-version 46
pseudonym 46
qdtext 15
query 18
quoted-pair 15
quoted-string 15
quoted-text 15
Reason-Phrase 32
received-by 46
received-protocol 46
relativeURI 18
Request 28
Request-Line 28
Request-URI 29
Response 31
rfc850-date 20
rfc1123-date 20
separators 15
SP 14
start-line 24
Status-Code 32
Status-Line 31
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t-codings 43
tchar 15
TE 43
TEXT 14
time 20
token 15
Trailer 44
trailer-part 22
transfer-coding 20
Transfer-Encoding 44
transfer-extension 20
Upgrade 45
uri-host 18
value 20
Via 46
weekday 20
wkday 20
H
Headers
Connection 39
Content-Length 40
Date 41
Host 42
TE 43
Trailer 44
Transfer-Encoding 44
Upgrade 45
Via 46
Host header 42
I
implied *LWS 13
inbound 9
M
Media Type
application/http 56
message/http 55
message 6
message/http Media Type 55
O
origin server 8
outbound 9
P
proxy 8
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R
representation 7
request 6
resource 7
response 6
S
server 8
T
TE header 43
Trailer header 44
Transfer-Encoding header 44
tunnel 8
U
Upgrade header 45
upstream 9
user agent 7
V
variant 7
Via header 46
Authors' Addresses
Roy T. Fielding (editor)
Day Software
23 Corporate Plaza DR, Suite 280
Newport Beach, CA 92660
USA
Phone: +1-949-706-5300
Fax: +1-949-706-5305
Email: fielding@gbiv.com
URI: http://roy.gbiv.com/
Jim Gettys
One Laptop per Child
21 Oak Knoll Road
Carlisle, MA 01741
USA
Email: jg@laptop.org
URI: http://www.laptop.org/
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Jeffrey C. Mogul
Hewlett-Packard Company
HP Labs, Large Scale Systems Group
1501 Page Mill Road, MS 1177
Palo Alto, CA 94304
USA
Email: JeffMogul@acm.org
Henrik Frystyk Nielsen
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
USA
Email: henrikn@microsoft.com
Larry Masinter
Adobe Systems, Incorporated
345 Park Ave
San Jose, CA 95110
USA
Email: LMM@acm.org
URI: http://larry.masinter.net/
Paul J. Leach
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
Email: paulle@microsoft.com
Tim Berners-Lee
World Wide Web Consortium
MIT Computer Science and Artificial Intelligence Laboratory
The Stata Center, Building 32
32 Vassar Street
Cambridge, MA 02139
USA
Email: timbl@w3.org
URI: http://www.w3.org/People/Berners-Lee/
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Yves Lafon (editor)
World Wide Web Consortium
W3C / ERCIM
2004, rte des Lucioles
Sophia-Antipolis, AM 06902
France
Email: ylafon@w3.org
URI: http://www.raubacapeu.net/people/yves/
Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
Email: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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Fielding, et al. Expires December 19, 2008 [Page 71]
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