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HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Day Software
Obsoletes: 2616 (if approved) J. Gettys
Updates: 2817 (if approved) One Laptop per Child
Intended status: Standards Track J. Mogul
Expires: September 9, 2010 HP
H. Frystyk
Microsoft
L. Masinter
Adobe Systems
P. Leach
Microsoft
T. Berners-Lee
W3C/MIT
Y. Lafon, Ed.
W3C
J. Reschke, Ed.
greenbytes
March 8, 2010
HTTP/1.1, part 1: URIs, Connections, and Message Parsing
draft-ietf-httpbis-p1-messaging-09
Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypertext information
systems. HTTP has been in use by the World Wide Web global
information initiative since 1990. This document is Part 1 of the
seven-part specification that defines the protocol referred to as
"HTTP/1.1" and, taken together, obsoletes RFC 2616. 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://tools.ietf.org/wg/httpbis/trac/report/11> and related
documents (including fancy diffs) can be found at
<http://tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix D.10.
Status of this Memo
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This Internet-Draft is submitted to IETF in full conformance with the
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This Internet-Draft will expire on September 9, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
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it for publication as an RFC or to translate it into languages other
than English.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 7
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7
1.2.1. ABNF Extension: #rule . . . . . . . . . . . . . . . . 7
1.2.2. Basic Rules . . . . . . . . . . . . . . . . . . . . . 8
1.2.3. ABNF Rules defined in other Parts of the
Specification . . . . . . . . . . . . . . . . . . . . 10
2. HTTP architecture . . . . . . . . . . . . . . . . . . . . . . 10
2.1. Client/Server Operation . . . . . . . . . . . . . . . . . 10
2.2. Intermediaries . . . . . . . . . . . . . . . . . . . . . . 12
2.3. Caches . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4. Transport Independence . . . . . . . . . . . . . . . . . . 14
2.5. HTTP Version . . . . . . . . . . . . . . . . . . . . . . . 14
2.6. Uniform Resource Identifiers . . . . . . . . . . . . . . . 16
2.6.1. http URI scheme . . . . . . . . . . . . . . . . . . . 16
2.6.2. https URI scheme . . . . . . . . . . . . . . . . . . . 17
2.6.3. http and https URI Normalization and Comparison . . . 18
3. HTTP Message . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1. Message Parsing Robustness . . . . . . . . . . . . . . . . 19
3.2. Header Fields . . . . . . . . . . . . . . . . . . . . . . 20
3.3. Message Body . . . . . . . . . . . . . . . . . . . . . . . 22
3.4. Message Length . . . . . . . . . . . . . . . . . . . . . . 23
3.5. General Header Fields . . . . . . . . . . . . . . . . . . 24
4. Request . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1. Request-Line . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.1. Method . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.2. request-target . . . . . . . . . . . . . . . . . . . . 25
4.2. The Resource Identified by a Request . . . . . . . . . . . 27
5. Response . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1. Status-Line . . . . . . . . . . . . . . . . . . . . . . . 28
5.1.1. Status Code and Reason Phrase . . . . . . . . . . . . 28
6. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 29
6.1. Date/Time Formats: Full Date . . . . . . . . . . . . . . . 29
6.2. Transfer Codings . . . . . . . . . . . . . . . . . . . . . 31
6.2.1. Chunked Transfer Coding . . . . . . . . . . . . . . . 32
6.2.2. Compression Codings . . . . . . . . . . . . . . . . . 34
6.2.3. Transfer Coding Registry . . . . . . . . . . . . . . . 35
6.3. Product Tokens . . . . . . . . . . . . . . . . . . . . . . 35
6.4. Quality Values . . . . . . . . . . . . . . . . . . . . . . 36
7. Connections . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1. Persistent Connections . . . . . . . . . . . . . . . . . . 36
7.1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 36
7.1.2. Overall Operation . . . . . . . . . . . . . . . . . . 37
7.1.3. Proxy Servers . . . . . . . . . . . . . . . . . . . . 38
7.1.4. Practical Considerations . . . . . . . . . . . . . . . 41
7.2. Message Transmission Requirements . . . . . . . . . . . . 42
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7.2.1. Persistent Connections and Flow Control . . . . . . . 42
7.2.2. Monitoring Connections for Error Status Messages . . . 42
7.2.3. Use of the 100 (Continue) Status . . . . . . . . . . . 42
7.2.4. Client Behavior if Server Prematurely Closes
Connection . . . . . . . . . . . . . . . . . . . . . . 44
8. Miscellaneous notes that may disappear . . . . . . . . . . . . 45
8.1. Scheme aliases considered harmful . . . . . . . . . . . . 45
8.2. Use of HTTP for proxy communication . . . . . . . . . . . 45
8.3. Interception of HTTP for access control . . . . . . . . . 46
8.4. Use of HTTP by other protocols . . . . . . . . . . . . . . 46
8.5. Use of HTTP by media type specification . . . . . . . . . 46
9. Header Field Definitions . . . . . . . . . . . . . . . . . . . 46
9.1. Connection . . . . . . . . . . . . . . . . . . . . . . . . 46
9.2. Content-Length . . . . . . . . . . . . . . . . . . . . . . 47
9.3. Date . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
9.3.1. Clockless Origin Server Operation . . . . . . . . . . 49
9.4. Host . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
9.5. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9.6. Trailer . . . . . . . . . . . . . . . . . . . . . . . . . 51
9.7. Transfer-Encoding . . . . . . . . . . . . . . . . . . . . 52
9.8. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 52
9.8.1. Upgrade Token Registry . . . . . . . . . . . . . . . . 53
9.9. Via . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 56
10.1. Message Header Registration . . . . . . . . . . . . . . . 56
10.2. URI Scheme Registration . . . . . . . . . . . . . . . . . 56
10.3. Internet Media Type Registrations . . . . . . . . . . . . 56
10.3.1. Internet Media Type message/http . . . . . . . . . . . 56
10.3.2. Internet Media Type application/http . . . . . . . . . 58
10.4. Transfer Coding Registry . . . . . . . . . . . . . . . . . 59
10.5. Upgrade Token Registration . . . . . . . . . . . . . . . . 59
11. Security Considerations . . . . . . . . . . . . . . . . . . . 59
11.1. Personal Information . . . . . . . . . . . . . . . . . . . 60
11.2. Abuse of Server Log Information . . . . . . . . . . . . . 60
11.3. Attacks Based On File and Path Names . . . . . . . . . . . 60
11.4. DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . . 60
11.5. Proxies and Caching . . . . . . . . . . . . . . . . . . . 61
11.6. Denial of Service Attacks on Proxies . . . . . . . . . . . 62
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 62
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 63
13.1. Normative References . . . . . . . . . . . . . . . . . . . 63
13.2. Informative References . . . . . . . . . . . . . . . . . . 65
Appendix A. Tolerant Applications . . . . . . . . . . . . . . . . 67
Appendix B. Compatibility with Previous Versions . . . . . . . . 67
B.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 68
B.1.1. Changes to Simplify Multi-homed Web Servers and
Conserve IP Addresses . . . . . . . . . . . . . . . . 68
B.2. Compatibility with HTTP/1.0 Persistent Connections . . . . 69
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B.3. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 70
B.4. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 70
Appendix C. Collected ABNF . . . . . . . . . . . . . . . . . . . 71
Appendix D. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 76
D.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 76
D.2. Since draft-ietf-httpbis-p1-messaging-00 . . . . . . . . . 76
D.3. Since draft-ietf-httpbis-p1-messaging-01 . . . . . . . . . 77
D.4. Since draft-ietf-httpbis-p1-messaging-02 . . . . . . . . . 78
D.5. Since draft-ietf-httpbis-p1-messaging-03 . . . . . . . . . 79
D.6. Since draft-ietf-httpbis-p1-messaging-04 . . . . . . . . . 79
D.7. Since draft-ietf-httpbis-p1-messaging-05 . . . . . . . . . 80
D.8. Since draft-ietf-httpbis-p1-messaging-06 . . . . . . . . . 81
D.9. Since draft-ietf-httpbis-p1-messaging-07 . . . . . . . . . 81
D.10. Since draft-ietf-httpbis-p1-messaging-08 . . . . . . . . . 82
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 86
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1. Introduction
The Hypertext Transfer Protocol (HTTP) is an application-level
request/response protocol that uses extensible semantics and MIME-
like message payloads for flexible interaction with network-based
hypertext information systems. HTTP relies upon the Uniform Resource
Identifier (URI) standard [RFC3986] to indicate request targets and
relationships between resources. Messages are passed in a format
similar to that used by Internet mail [RFC5322] and the Multipurpose
Internet Mail Extensions (MIME) [RFC2045] (see Appendix A of [Part3]
for the differences between HTTP and MIME messages).
HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by
presenting a uniform interface to clients that is independent of the
types of resources provided. Likewise, servers do not need to be
aware of each client's purpose: an HTTP request can be considered in
isolation rather than being associated with a specific type of client
or a predetermined sequence of application steps. The result is a
protocol that can be used effectively in many different contexts and
for which implementations can evolve independently over time.
HTTP is also designed for use as a generic protocol for translating
communication to and from other Internet information systems. HTTP
proxies and gateways provide access to alternative information
services by translating their diverse protocols into a hypertext
format that can be viewed and manipulated by clients in the same way
as HTTP services.
One consequence of HTTP flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent of
received communication, and the expected behavior of recipients. If
the communication is considered in isolation, then successful actions
should be reflected in corresponding changes to the observable
interface provided by servers. However, since multiple clients may
act in parallel and perhaps at cross-purposes, we cannot require that
such changes be observable beyond the scope of a single response.
This document is Part 1 of the seven-part specification of HTTP,
defining the protocol referred to as "HTTP/1.1" and obsoleting
[RFC2616]. Part 1 describes the architectural elements that are used
or referred to in HTTP, defines the "http" and "https" URI schemes,
describes overall network operation and connection management, and
defines HTTP message framing and forwarding requirements. Our goal
is to define all of the mechanisms necessary for HTTP message
handling that are independent of message semantics, thereby defining
the complete set of requirements for message parsers and message-
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forwarding intermediaries.
1.1. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
An implementation is not compliant if it fails to satisfy one or more
of the MUST or REQUIRED level requirements for the protocols it
implements. An implementation that satisfies all the MUST or
REQUIRED level and all the SHOULD level requirements for its
protocols is said to be "unconditionally compliant"; one that
satisfies all the MUST level requirements but not all the SHOULD
level requirements for its protocols is said to be "conditionally
compliant."
1.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234].
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
sequence of data), SP (space), VCHAR (any visible [USASCII]
character), and WSP (whitespace).
As a syntactical convention, ABNF rule names prefixed with "obs-"
denote "obsolete" grammar rules that appear for historical reasons.
1.2.1. ABNF Extension: #rule
The #rule extension to the ABNF rules of [RFC5234] is used to improve
readability.
A construct "#" is defined, similar to "*", for defining comma-
delimited lists of elements. The full form is "<n>#<m>element"
indicating at least <n> and at most <m> elements, each separated by a
single comma (",") and optional whitespace (OWS, Section 1.2.2).
Thus,
1#element => element *( OWS "," OWS element )
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and:
#element => [ 1#element ]
and for n >= 1 and m > 1:
<n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
For compatibility with legacy list rules, recipients SHOULD accept
empty list elements. In other words, consumers would follow the list
productions:
#element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
Note that empty elements do not contribute to the count of elements
present, though.
For example, given these ABNF productions:
example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 1.2.2
Then these are valid values for example-list (not including the
double quotes, which are present for delimitation only):
"foo,bar"
" foo ,bar,"
" foo , ,bar,charlie "
"foo ,bar, charlie "
But these values would be invalid, as at least one non-empty element
is required:
""
","
", ,"
Appendix C shows the collected ABNF, with the list rules expanded as
explained above.
1.2.2. Basic Rules
HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
protocol elements except the entity-body (see Appendix A for tolerant
applications). The end-of-line marker within an entity-body is
defined by its associated media type, as described in Section 2.3 of
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[Part3].
This specification uses three rules to denote the use of linear
whitespace: OWS (optional whitespace), RWS (required whitespace), and
BWS ("bad" whitespace).
The OWS rule is used where zero or more linear whitespace characters
may appear. OWS SHOULD either not be produced or be produced as a
single SP character. Multiple OWS characters that occur within
field-content SHOULD be replaced with a single SP before interpreting
the field value or forwarding the message downstream.
RWS is used when at least one linear whitespace character is required
to separate field tokens. RWS SHOULD be produced as a single SP
character. Multiple RWS characters that occur within field-content
SHOULD be replaced with a single SP before interpreting the field
value or forwarding the message downstream.
BWS is used where the grammar allows optional whitespace for
historical reasons but senders SHOULD NOT produce it in messages.
HTTP/1.1 recipients MUST accept such bad optional whitespace and
remove it before interpreting the field value or forwarding the
message downstream.
OWS = *( [ obs-fold ] WSP )
; "optional" whitespace
RWS = 1*( [ obs-fold ] WSP )
; "required" whitespace
BWS = OWS
; "bad" whitespace
obs-fold = CRLF
; see Section 3.2
Many HTTP/1.1 header field values consist of words (token or quoted-
string) separated by whitespace or special characters. These special
characters MUST be in a quoted string to be used within a parameter
value (as defined in Section 6.2).
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA
; any VCHAR, except special
special = "(" / ")" / "<" / ">" / "@" / ","
/ ";" / ":" / "\" / DQUOTE / "/" / "["
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/ "]" / "?" / "=" / "{" / "}"
A string of text is parsed as a single word if it is quoted using
double-quote marks.
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
; OWS / <VCHAR except DQUOTE and "\"> / obs-text
obs-text = %x80-FF
The backslash character ("\") can be used as a single-character
quoting mechanism within quoted-string constructs:
quoted-pair = "\" ( WSP / VCHAR / obs-text )
Producers SHOULD NOT escape characters that do not require escaping
(i.e., other than DQUOTE and the backslash character).
1.2.3. 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 3>
response-header = <response-header, defined in [Part2], Section 5>
entity-body = <entity-body, defined in [Part3], Section 3.2>
entity-header = <entity-header, defined in [Part3], Section 3.1>
Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
Pragma = <Pragma, defined in [Part6], Section 3.4>
Warning = <Warning, defined in [Part6], Section 3.6>
2. HTTP architecture
HTTP was created for the World Wide Web architecture and has evolved
over time to support the scalability needs of a worldwide hypertext
system. Much of that architecture is reflected in the terminology
and syntax productions used to define HTTP.
2.1. Client/Server Operation
HTTP is a request/response protocol that operates by exchanging
messages across a reliable transport or session-layer connection. An
HTTP client is a program that establishes a connection to a server
for the purpose of sending one or more HTTP requests. An HTTP server
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is a program that accepts connections in order to service HTTP
requests by sending HTTP responses.
Note that the terms "client" and "server" refer only to the roles
that these programs perform for a particular connection. The same
program may act as a client on some connections and a server on
others. We use the term "user agent" to refer to the program that
initiates a request, such as a WWW browser, editor, or spider (web-
traversing robot), and the term "origin server" to refer to the
program that can originate authoritative responses to a request.
Most HTTP communication consists of a retrieval request (GET) for a
representation of some resource identified by a URI. 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
A client sends an HTTP request to the server in the form of a request
message (Section 4), beginning with a method, URI, and protocol
version, followed by MIME-like header fields containing request
modifiers, client information, and payload metadata, an empty line to
indicate the end of the header section, and finally the payload body
(if any).
A server responds to the client's request by sending an HTTP response
message (Section 5), beginning with a status line that includes the
protocol version, a success or error code, and textual reason phrase,
followed by MIME-like header fields containing server information,
resource metadata, and payload metadata, an empty line to indicate
the end of the header section, and finally the payload body (if any).
The following example illustrates a typical message exchange for a
GET request on the URI "http://www.example.com/hello.txt":
client request:
GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept: */*
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server response:
HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 14
Vary: Accept-Encoding
Content-Type: text/plain
Hello World!
2.2. Intermediaries
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. In some cases, a
single intermediary may act as an origin server, proxy, gateway, or
tunnel, switching behavior based on the nature of each request.
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.
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.
We use the terms "upstream" and "downstream" to describe various
requirements in relation to the directional flow of a message: all
messages flow from upstream to downstream. Likewise, we use the
terms "inbound" and "outbound" to refer to directions in relation to
the request path: "inbound" means toward the origin server and
"outbound" means toward the user agent.
A proxy is a message forwarding agent that is selected by the client,
usually via local configuration rules, to receive requests for some
type(s) of absolute URI and attempt to satisfy those requests via
translation through the HTTP interface. Some translations are
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minimal, such as for proxy requests for "http" URIs, whereas other
requests may require translation to and from entirely different
application-layer protocols. Proxies are often used to group an
organization's HTTP requests through a common intermediary for the
sake of security, annotation services, or shared caching.
A gateway (a.k.a., reverse proxy) is a receiving agent that acts as a
layer above some other server(s) and translates the received requests
to the underlying server's protocol. Gateways are often used for
load balancing or partitioning HTTP services across multiple
machines. Unlike a proxy, a gateway receives requests as if it were
the origin server for the requested resource; the requesting client
will not be aware that it is communicating with a gateway. A gateway
communicates with the client as if the gateway is the origin server
and thus is subject to all of the requirements on origin servers for
that connection. A gateway communicates with inbound servers using
any protocol it desires, including private extensions to HTTP that
are outside the scope of this specification.
A tunnel acts as a blind relay between two connections without
changing the messages. Once active, a tunnel is not considered a
party to the HTTP communication, though the tunnel may have been
initiated by an HTTP request. A tunnel ceases to exist when both
ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when
transport-layer security is used to establish private communication
through a shared firewall proxy.
2.3. Caches
Any party to HTTP communication that is not acting as a tunnel may
employ an internal cache for handling requests. A cache is a local
store of previous response messages and the subsystem that controls
its message storage, retrieval, and deletion. A cache stores
cacheable responses in order to reduce the response time and network
bandwidth consumption on future, equivalent requests. Any client or
server may include a cache, though a cache cannot be used by a server
while it is acting as a tunnel.
The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting
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
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A response is cacheable if a cache is allowed to store a copy of the
response message for use in answering subsequent requests. Even when
a response is cacheable, there may be additional constraints placed
by the client or by the origin server on when that cached response
can be used for a particular request. HTTP requirements for cache
behavior and cacheable responses are defined in Section 2 of [Part6].
There are a wide variety of architectures and configurations of
caches and proxies deployed across the World Wide Web and inside
large organizations. These systems include national hierarchies of
proxy caches to save transoceanic bandwidth, systems that broadcast
or multicast cache entries, organizations that distribute subsets of
cached data via optical media, and so on.
2.4. Transport Independence
HTTP systems are used in a wide variety of environments, from
corporate intranets with high-bandwidth links to long-distance
communication over low-power radio links and intermittent
connectivity.
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).
2.5. 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
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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.
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.
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2.6. Uniform Resource Identifiers
Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
HTTP as the means for identifying resources. URI references are used
to target requests, indicate redirects, and define relationships.
HTTP does not limit what a resource may be; it merely defines an
interface that can be used to interact with a resource via HTTP.
More information on the scope of URIs and resources can be found in
[RFC3986].
This specification adopts the definitions of "URI-reference",
"absolute-URI", "relative-part", "port", "host", "path-abempty",
"path-absolute", "query", and "authority" from [RFC3986]. In
addition, we define a partial-URI rule for protocol elements that
allow a relative URI without a fragment.
URI = <URI, defined in [RFC3986], Section 3>
URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
relative-part = <relative-part, defined in [RFC3986], Section 4.2>
authority = <authority, defined in [RFC3986], Section 3.2>
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
port = <port, defined in [RFC3986], Section 3.2.3>
query = <query, defined in [RFC3986], Section 3.4>
uri-host = <host, defined in [RFC3986], Section 3.2.2>
partial-URI = relative-part [ "?" query ]
Each protocol element in HTTP that allows a URI reference will
indicate in its ABNF production whether the element allows only a URI
in absolute form (absolute-URI), any relative reference (relative-
ref), or some other subset of the URI-reference grammar. Unless
otherwise indicated, URI references are parsed relative to the
request target (the default base URI for both the request and its
corresponding response).
2.6.1. http URI scheme
The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
TCP connections on a given port. The HTTP server is identified via
the generic syntax's authority component, which includes a host
identifier and optional TCP port, and the remainder of the URI is
considered to be identifying data corresponding to a resource for
which that server might provide an HTTP interface.
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http-URI = "http:" "//" authority path-abempty [ "?" query ]
The host identifier within an authority component is defined in
[RFC3986], Section 3.2.2. If host is provided as an IP literal or
IPv4 address, then the HTTP server is any listener on the indicated
TCP port at that IP address. If host is a registered name, then that
name is considered an indirect identifier and the recipient might use
a name resolution service, such as DNS, to find the address of a
listener for that host. The host MUST NOT be empty; if an "http" URI
is received with an empty host, then it MUST be rejected as invalid.
If the port subcomponent is empty or not given, then TCP port 80 is
assumed (the default reserved port for WWW services).
Regardless of the form of host identifier, access to that host is not
implied by the mere presence of its name or address. The host may or
may not exist and, even when it does exist, may or may not be running
an HTTP server or listening to the indicated port. The "http" URI
scheme makes use of the delegated nature of Internet names and
addresses to establish a naming authority (whatever entity has the
ability to place an HTTP server at that Internet name or address) and
allows that authority to determine which names are valid and how they
might be used.
When an "http" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the
host to an IP address, establishing a TCP connection to that address
on the indicated port, and sending an HTTP request message to the
server containing the URI's identifying data as described in
Section 4. If the server responds to that request with a non-interim
HTTP response message, as described in Section 5, then that response
is considered an authoritative answer to the client's request.
Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority. An HTTP service
based on some other underlying connection protocol would presumably
be identified using a different URI scheme, just as the "https"
scheme (below) is used for servers that require an SSL/TLS transport
layer on a connection. Other protocols may also be used to provide
access to "http" identified resources --- it is only the
authoritative interface used for mapping the namespace that is
specific to TCP.
2.6.2. https URI scheme
The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
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SSL/TLS-secured connections on a given TCP port. The host and port
are determined in the same way as for the "http" scheme, except that
a default TCP port of 443 is assumed if the port subcomponent is
empty or not given.
https-URI = "https:" "//" authority path-abempty [ "?" query ]
The primary difference between the "http" and "https" schemes is that
interaction with the latter is required to be secured for privacy
through the use of strong encryption. The URI cannot be sent in a
request until the connection is secure. Likewise, the default for
caching is that each response that would be considered "public" under
the "http" scheme is instead treated as "private" and thus not
eligible for shared caching.
The process for authoritative access to an "https" identified
resource is defined in [RFC2818].
2.6.3. http and https URI Normalization and Comparison
Since the "http" and "https" schemes conform to the URI generic
syntax, such URIs are normalized and compared according to the
algorithm defined in [RFC3986], Section 6, using the defaults
described above for each scheme.
If the port is equal to the default port for a scheme, the normal
form is to elide the port subcomponent. Likewise, an empty path
component is equivalent to an absolute path of "/", so the normal
form is to provide a path of "/" instead. The scheme and host are
case-insensitive and normally provided in lowercase; all other
components are compared in a case-sensitive manner. Characters other
than those in the "reserved" set are equivalent to their percent-
encoded octets (see [RFC3986], Section 2.1): the normal form is to
not encode them.
For example, the following three URIs are equivalent:
http://example.com:80/~smith/home.html
http://EXAMPLE.com/%7Esmith/home.html
http://EXAMPLE.com:/%7esmith/home.html
[[TODO-not-here: This paragraph does not belong here. --roy]] If
path-abempty is the empty string (i.e., there is no slash "/" path
separator following the authority), then the "http" URI MUST be given
as "/" when used as a request-target (Section 4.1.2). 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
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name.
3. HTTP Message
All HTTP/1.1 messages consist of a start-line followed by a sequence
of characters in a format similar to the Internet Message Format
[RFC5322]: zero or more header fields (collectively referred to as
the "headers" or the "header section"), an empty line indicating the
end of the header section, and an optional message-body.
An HTTP message can either be a request from client to server or a
response from server to client. Syntactically, the two types of
message differ only in the start-line, which is either a Request-Line
(for requests) or a Status-Line (for responses), and in the algorithm
for determining the length of the message-body (Section 3.4). In
theory, a client could receive requests and a server could receive
responses, distinguishing them by their different start-line formats,
but in practice servers are implemented to only expect a request (a
response is interpreted as an unknown or invalid request method) and
clients are implemented to only expect a response.
HTTP-message = start-line
*( header-field CRLF )
CRLF
[ message-body ]
start-line = Request-Line / Status-Line
Whitespace (WSP) MUST NOT be sent between the start-line and the
first header field. The presence of whitespace might be an attempt
to trick a noncompliant implementation of HTTP into ignoring that
field or processing the next line as a new request, either of which
may result in security issues when implementations within the request
chain interpret the same message differently. HTTP/1.1 servers MUST
reject such a message with a 400 (Bad Request) response.
3.1. Message Parsing Robustness
In the interest of robustness, servers SHOULD ignore at least one
empty line received where a Request-Line is expected. In other
words, if the server is reading the protocol stream at the beginning
of a message and receives a CRLF first, it should ignore the CRLF.
Some old HTTP/1.0 client implementations generate an extra CRLF after
a POST request as a lame workaround for some early server
applications that failed to read message-body content that was not
terminated by a line-ending. An HTTP/1.1 client MUST NOT preface or
follow a request with an extra CRLF. If terminating the request
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message-body with a line-ending is desired, then the client MUST
include the terminating CRLF octets as part of the message-body
length.
The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field into a hash table
by field name until the empty line, and then use the parsed data to
determine if a message-body is expected. If a message-body has been
indicated, then it is read as a stream until an amount of OCTETs
equal to the message-length is read or the connection is closed.
Care must be taken to parse an HTTP message as a sequence of OCTETs
in an encoding that is a superset of US-ASCII. Attempting to parse
HTTP as a stream of Unicode characters in a character encoding like
UTF-16 may introduce security flaws due to the differing ways that
such parsers interpret invalid characters.
3.2. Header Fields
Each HTTP header field consists of a case-insensitive field name
followed by a colon (":"), optional whitespace, and the field value.
header-field = field-name ":" OWS [ field-value ] OWS
field-name = token
field-value = *( field-content / OWS )
field-content = *( WSP / VCHAR / obs-text )
No whitespace is allowed between the header field name and colon.
For security reasons, any request message received containing such
whitespace MUST be rejected with a response code of 400 (Bad
Request). A proxy MUST remove any such whitespace from a response
message before forwarding the message downstream.
A field value MAY be preceded by optional whitespace (OWS); a single
SP is preferred. The field value does not include any leading or
trailing white space: OWS occurring before the first non-whitespace
character of the field value or after the last non-whitespace
character of the field value is ignored and SHOULD be removed before
further processing (as this does not change the meaning of the header
field).
The order in which header fields with differing field names are
received is not significant. However, it is "good practice" to send
header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST
wait until the entire header section is received before interpreting
a request message, since later header fields might include
conditionals, authentication credentials, or deliberately misleading
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duplicate header fields that would impact request processing.
Multiple header fields with the same field name MUST NOT be sent in a
message unless the entire field value for that header field is
defined as a comma-separated list [i.e., #(values)]. Multiple header
fields with the same field name can be combined into one "field-name:
field-value" pair, without changing the semantics of the message, by
appending each subsequent field value to the combined field value in
order, separated by a comma. The order in which header fields with
the same field name are received is therefore significant to the
interpretation of the combined field value; a proxy MUST NOT change
the order of these field values when forwarding a message.
Note: The "Set-Cookie" header as implemented in practice (as
opposed to how it is specified in [RFC2109]) can occur multiple
times, but does not use the list syntax, and thus cannot be
combined into a single line. (See Appendix A.2.3 of [Kri2001] for
details.) Also note that the Set-Cookie2 header specified in
[RFC2965] does not share this problem.
Historically, HTTP header field values could be extended over
multiple lines by preceding each extra line with at least one space
or horizontal tab character (line folding). This specification
deprecates such line folding except within the message/http media
type (Section 10.3.1). HTTP/1.1 senders MUST NOT produce messages
that include line folding (i.e., that contain any field-content that
matches the obs-fold rule) unless the message is intended for
packaging within the message/http media type. HTTP/1.1 recipients
SHOULD accept line folding and replace any embedded obs-fold
whitespace with a single SP prior to interpreting the field value or
forwarding the message downstream.
Historically, HTTP has allowed field content with text in the ISO-
8859-1 [ISO-8859-1] character encoding and supported other character
sets only through use of [RFC2047] encoding. In practice, most HTTP
header field values use only a subset of the US-ASCII character
encoding [USASCII]. Newly defined header fields SHOULD limit their
field values to US-ASCII characters. Recipients SHOULD treat other
(obs-text) octets in field content as opaque data.
Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
comment = "(" *( ctext / quoted-cpair / comment ) ")"
ctext = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
; OWS / <VCHAR except "(", ")", and "\"> / obs-text
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The backslash character ("\") can be used as a single-character
quoting mechanism within comment constructs:
quoted-cpair = "\" ( WSP / VCHAR / obs-text )
Producers SHOULD NOT escape characters that do not require escaping
(i.e., other than the backslash character "\" and the parentheses "("
and ")").
3.3. 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 9.7).
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
request/response chain. (However, Section 6.2 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 header fields. 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 5.1.1). 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.
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3.4. 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 9.7) is present and
the "chunked" transfer-coding (Section 6.2) is used, the
transfer-length is defined by the use of this transfer-coding.
If a Transfer-Encoding header field is present and the "chunked"
transfer-coding is not present, the transfer-length is defined by
the sender closing the connection.
3. If a Content-Length header field (Section 9.2) is present, its
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 HTTP/1.1 client implies
that the client can parse multipart/byteranges responses.
A range header might be forwarded by a HTTP/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
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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 6.2), 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.
3.5. 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 3.2
/ Connection ; Section 9.1
/ Date ; Section 9.3
/ Pragma ; [Part6], Section 3.4
/ Trailer ; Section 9.6
/ Transfer-Encoding ; Section 9.7
/ Upgrade ; Section 9.8
/ Via ; Section 9.9
/ Warning ; [Part6], Section 3.6
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.
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4. 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 4.1
*(( general-header ; Section 3.5
/ request-header ; [Part2], Section 3
/ entity-header ) CRLF ) ; [Part3], Section 3.1
CRLF
[ message-body ] ; Section 3.3
4.1. Request-Line
The Request-Line begins with a method token, followed by the request-
target 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-target SP HTTP-Version CRLF
4.1.1. Method
The Method token indicates the method to be performed on the resource
identified by the request-target. The method is case-sensitive.
Method = token
4.1.2. request-target
The request-target identifies the resource upon which to apply the
request.
request-target = "*"
/ absolute-URI
/ ( path-absolute [ "?" query ] )
/ authority
The four options for request-target 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 absolute-URI form is REQUIRED when the request is being made to a
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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 absolute-URI. 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 absolute-URIs in all requests in future
versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
form in requests, even though HTTP/1.1 clients will only generate
them in requests to proxies.
The authority form is only used by the CONNECT method (Section 7.9 of
[Part2]).
The most common form of request-target 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 2.6.1, path-
absolute) as the request-target, and the network location of the URI
(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).
If a proxy receives a request without any path in the request-target
and the method specified is capable of supporting the asterisk form
of request-target, then the last proxy on the request chain MUST
forward the request with "*" as the final request-target.
For example, the request
OPTIONS http://www.example.org:8001 HTTP/1.1
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would be forwarded by the proxy as
OPTIONS * HTTP/1.1
Host: www.example.org:8001
after connecting to port 8001 of host "www.example.org".
The request-target is transmitted in the format specified in
Section 2.6.1. If the request-target is percent-encoded ([RFC3986],
Section 2.1), the origin server MUST decode the request-target in
order to properly interpret the request. Servers SHOULD respond to
invalid request-targets with an appropriate status code.
A transparent proxy MUST NOT rewrite the "path-absolute" part of the
received request-target 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-target.
HTTP does not place a pre-defined limit on the length of a request-
target. A server MUST be prepared to receive URIs of unbounded
length and respond with the 414 (URI Too Long) status if the received
request-target would be longer than the server wishes to handle (see
Section 8.4.15 of [Part2]).
Various ad-hoc limitations on request-target length are found in
practice. It is RECOMMENDED that all HTTP senders and recipients
support request-target lengths of 8000 or more OCTETs.
4.2. The Resource Identified by a Request
The exact resource identified by an Internet request is determined by
examining both the request-target and the Host header field.
An origin server that does not allow resources to differ by the
requested host MAY ignore the Host header field value when
determining the resource identified by an HTTP/1.1 request. (But see
Appendix B.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:
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1. If request-target is an absolute-URI, the host is part of the
request-target. Any Host header field value in the request MUST
be ignored.
2. If the request-target is not an absolute-URI, and the request
includes a Host header field, the host is determined by the Host
header field value.
3. If the host as determined by rule 1 or 2 is not a valid host on
the server, the response MUST be a 400 (Bad Request) error
message.
Recipients of an HTTP/1.0 request that lacks a Host header field MAY
attempt to use heuristics (e.g., examination of the URI path for
something unique to a particular host) in order to determine what
exact resource is being requested.
5. Response
After receiving and interpreting a request message, a server responds
with an HTTP response message.
Response = Status-Line ; Section 5.1
*(( general-header ; Section 3.5
/ response-header ; [Part2], Section 5
/ entity-header ) CRLF ) ; [Part3], Section 3.1
CRLF
[ message-body ] ; Section 3.3
5.1. 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
5.1.1. 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 8 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
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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
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 = *( WSP / VCHAR / obs-text )
6. Protocol Parameters
6.1. Date/Time Formats: 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 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]. 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 A for
further information.
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 whitespace beyond that specifically included as SP in the
grammar.
HTTP-date = rfc1123-date / obs-date
Preferred format:
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
day-name = %x4D.6F.6E ; "Mon", case-sensitive
/ %x54.75.65 ; "Tue", case-sensitive
/ %x57.65.64 ; "Wed", case-sensitive
/ %x54.68.75 ; "Thu", case-sensitive
/ %x46.72.69 ; "Fri", case-sensitive
/ %x53.61.74 ; "Sat", case-sensitive
/ %x53.75.6E ; "Sun", case-sensitive
date1 = day SP month SP year
; e.g., 02 Jun 1982
day = 2DIGIT
month = %x4A.61.6E ; "Jan", case-sensitive
/ %x46.65.62 ; "Feb", case-sensitive
/ %x4D.61.72 ; "Mar", case-sensitive
/ %x41.70.72 ; "Apr", case-sensitive
/ %x4D.61.79 ; "May", case-sensitive
/ %x4A.75.6E ; "Jun", case-sensitive
/ %x4A.75.6C ; "Jul", case-sensitive
/ %x41.75.67 ; "Aug", case-sensitive
/ %x53.65.70 ; "Sep", case-sensitive
/ %x4F.63.74 ; "Oct", case-sensitive
/ %x4E.6F.76 ; "Nov", case-sensitive
/ %x44.65.63 ; "Dec", case-sensitive
year = 4DIGIT
GMT = %x47.4D.54 ; "GMT", case-sensitive
time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:59
hour = 2DIGIT
minute = 2DIGIT
second = 2DIGIT
The semantics of day-name, day, month, year, and time-of-day are the
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same as those defined for the RFC 5322 constructs with the
corresponding name ([RFC5322], Section 3.3).
Obsolete formats:
obs-date = rfc850-date / asctime-date
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
date2 = day "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82)
day-name-l = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
/ %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
/ %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
/ %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
/ %x46.72.69.64.61.79 ; "Friday", case-sensitive
/ %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
/ %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; month day (e.g., Jun 2)
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.
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.
6.2. 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" ; Section 6.2.1
/ "compress" ; Section 6.2.2.1
/ "deflate" ; Section 6.2.2.2
/ "gzip" ; Section 6.2.2.3
/ transfer-extension
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transfer-extension = token *( OWS ";" OWS transfer-parameter )
Parameters are in the form of attribute/value pairs.
transfer-parameter = attribute BWS "=" BWS value
attribute = token
value = token / quoted-string
All transfer-coding values are case-insensitive. HTTP/1.1 uses
transfer-coding values in the TE header field (Section 9.5) and in
the Transfer-Encoding header field (Section 9.7).
Whenever a transfer-coding is applied to a message-body, the set of
transfer-codings MUST include "chunked", unless the message indicates
it 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 3.4).
Transfer-codings are analogous to the Content-Transfer-Encoding
values of MIME, which were designed to enable safe transport of
binary data over a 7-bit transport service ([RFC2045], Section 6).
However, safe transport has a different focus for an 8bit-clean
transfer protocol. In HTTP, the only unsafe characteristic of
message-bodies is the difficulty in determining the exact body length
(Section 3.4), or the desire to encrypt data over a shared transport.
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.
6.2.1. 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 *WSP [ chunk-ext ] CRLF
chunk-data CRLF
chunk-size = 1*HEXDIG
last-chunk = 1*("0") *WSP [ chunk-ext ] CRLF
chunk-ext = *( ";" *WSP chunk-ext-name
[ "=" chunk-ext-val ] *WSP )
chunk-ext-name = token
chunk-ext-val = token / quoted-str-nf
chunk-data = 1*OCTET ; a sequence of chunk-size octets
trailer-part = *( entity-header CRLF )
quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
; like quoted-string, but disallowing line folding
qdtext-nf = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
; WSP / <VCHAR except DQUOTE and "\"> / obs-text
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 9.6).
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 9.5; 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.
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This requirement prevents an interoperability failure when the
message is being received by an HTTP/1.1 (or later) proxy and
forwarded to an HTTP/1.0 recipient. It avoids a situation where
compliance with the protocol would have necessitated a possibly
infinite buffer on the proxy.
A process for decoding the "chunked" transfer-coding can be
represented in pseudo-code as:
length := 0
read chunk-size, chunk-ext (if any) and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to 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-ext extensions they
do not understand.
6.2.2. Compression Codings
The codings defined below can be used to compress the payload of a
message.
Note: Use of program names for the identification of encoding
formats is not desirable and is discouraged for future encodings.
Their use here is representative of historical practice, not good
design.
Note: For compatibility with previous implementations of HTTP,
applications SHOULD consider "x-gzip" and "x-compress" to be
equivalent to "gzip" and "compress" respectively.
6.2.2.1. Compress Coding
The "compress" format is produced by the common UNIX file compression
program "compress". This format is an adaptive Lempel-Ziv-Welch
coding (LZW).
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6.2.2.2. Deflate Coding
The "zlib" format is defined in [RFC1950] in combination with the
"deflate" compression mechanism described in [RFC1951].
6.2.2.3. Gzip Coding
The "gzip" format is produced by the file compression program "gzip"
(GNU zip), as described in [RFC1952]. This format is a Lempel-Ziv
coding (LZ77) with a 32 bit CRC.
6.2.3. Transfer Coding Registry
The HTTP Transfer Coding Registry defines the name space for the
transfer coding names.
Registrations MUST include the following fields:
o Name
o Description
o Pointer to specification text
Values to be added to this name space require expert review and a
specification (see "Expert Review" and "Specification Required" in
Section 4.1 of [RFC5226]), and MUST conform to the purpose of
transfer coding defined in this section.
The registry itself is maintained at
<http://www.iana.org/assignments/http-parameters>.
6.3. Product Tokens
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by whitespace. By
convention, the products are listed in order of their significance
for identifying the application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
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Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although
any token 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).
6.4. Quality Values
Both transfer codings (TE request header, Section 9.5) and content
negotiation (Section 4 of [Part3]) use short "floating point" numbers
to indicate the relative importance ("weight") of various negotiable
parameters. A weight is normalized to a real number in the range 0
through 1, where 0 is the minimum and 1 the maximum value. If a
parameter has a quality value of 0, then content with this parameter
is "not acceptable" for the client. HTTP/1.1 applications MUST NOT
generate more than three digits after the decimal point. User
configuration of these values SHOULD also be limited in this fashion.
qvalue = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] )
Note: "Quality values" is a misnomer, since these values merely
represent relative degradation in desired quality.
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 requires a client to make multiple
requests of the same server in a short amount of time. Analysis of
these performance problems and results from a prototype
implementation are available [Pad1995] [Spe]. Implementation
experience and measurements of actual HTTP/1.1 implementations show
good results [Nie1997]. Alternatives have also been explored, for
example, T/TCP [Tou1998].
Persistent HTTP connections have a number of advantages:
o By opening and closing fewer TCP connections, CPU time is saved in
routers and hosts (clients, servers, proxies, gateways, tunnels,
or caches), and memory used for TCP protocol control blocks can be
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saved in hosts.
o HTTP requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single TCP connection to be
used much more efficiently, with much lower elapsed time.
o Network congestion is reduced by reducing the number of packets
caused by TCP opens, and by allowing TCP sufficient time to
determine the congestion state of the network.
o Latency on subsequent requests is reduced since there is no time
spent in TCP's connection opening handshake.
o HTTP can evolve more gracefully, since errors can be reported
without the penalty of closing the TCP connection. Clients using
future versions of HTTP might optimistically try a new feature,
but if communicating with an older server, retry with old
semantics after an error is reported.
HTTP implementations SHOULD implement persistent connections.
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 9.1). 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
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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
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 B.2 for more information on backward
compatibility with HTTP/1.0 clients.
In order to remain persistent, all messages on the connection MUST
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in Section 3.4.
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 7.1.2 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 9.1.
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
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transport link.
A proxy server MUST NOT establish a HTTP/1.1 persistent connection
with an HTTP/1.0 client (but see Section 19.7.1 of [RFC2068] for
information and discussion of the problems with the Keep-Alive header
implemented by many HTTP/1.0 clients).
7.1.3.1. End-to-end and Hop-by-hop Headers
[[TODO-end-to-end: Restored from <http://tools.ietf.org/html/
draft-ietf-httpbis-p6-cache-05#section-7.1>. See also
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60>. --jre]]
For the purpose of defining the behavior of caches and non-caching
proxies, we divide HTTP headers into two categories:
o End-to-end headers, which are transmitted to the ultimate
recipient of a request or response. End-to-end headers in
responses MUST be stored as part of a cache entry and MUST be
transmitted in any response formed from a cache entry.
o Hop-by-hop headers, which are meaningful only for a single
transport-level connection, and are not stored by caches or
forwarded by proxies.
The following HTTP/1.1 headers are hop-by-hop headers:
o Connection
o Keep-Alive
o Proxy-Authenticate
o Proxy-Authorization
o TE
o Trailer
o Transfer-Encoding
o Upgrade
All other headers defined by HTTP/1.1 are end-to-end headers.
Other hop-by-hop headers MUST be listed in a Connection header
(Section 9.1).
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7.1.3.2. Non-modifiable Headers
[[TODO-non-mod-headers: Restored from <http://tools.ietf.org/html/
draft-ietf-httpbis-p6-cache-05#section-7.2>. See also
<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60>. --jre]]
Some features of HTTP/1.1, such as Digest Authentication, depend on
the value of certain end-to-end headers. A transparent proxy SHOULD
NOT modify an end-to-end header unless the definition of that header
requires or specifically allows that.
A transparent proxy MUST NOT modify any of the following fields in a
request or response, and it MUST NOT add any of these fields if not
already present:
o Content-Location
o Content-MD5
o ETag
o Last-Modified
A transparent proxy MUST NOT modify any of the following fields in a
response:
o Expires
but it MAY add any of these fields if not already present. If an
Expires header is added, it MUST be given a field-value identical to
that of the Date header in that response.
A proxy MUST NOT modify or add any of the following fields in a
message that contains the no-transform cache-control directive, or in
any request:
o Content-Encoding
o Content-Range
o Content-Type
A non-transparent proxy MAY modify or add these fields to a message
that does not include no-transform, but if it does so, it MUST add a
Warning 214 (Transformation applied) if one does not already appear
in the message (see Section 3.6 of [Part6]).
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Warning: Unnecessary modification of end-to-end headers might
cause authentication failures if stronger authentication
mechanisms are introduced in later versions of HTTP. Such
authentication mechanisms MAY rely on the values of header fields
not listed here.
The Content-Length field of a request or response is added or deleted
according to the rules in Section 3.4. A transparent proxy MUST
preserve the entity-length (Section 3.2.2 of [Part3]) of the entity-
body, although it MAY change the transfer-length (Section 3.4).
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 7.1.2 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
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middle of transmitting a response, unless a network or client failure
is suspected.
Clients (including proxies) SHOULD limit the number of simultaneous
connections that they maintain to a given server (including proxies).
Previous revisions of HTTP gave a specific number of connections as a
ceiling, but this was found to be impractical for many applications.
As a result, this specification does not mandate a particular maximum
number of connections, but instead encourages clients to be
conservative when opening multiple connections.
In particular, while using multiple connections avoids the "head-of-
line blocking" problem (whereby a request that takes significant
server-side processing and/or has a large payload can block
subsequent requests on the same connection), each connection used
consumes server resources (sometimes significantly), and furthermore
using multiple connections can cause undesirable side effects in
congested networks.
Note that servers might reject traffic that they deem abusive,
including an excessive number of connections from a client.
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 6.2), 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 8.1.1 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
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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 9.2 of [Part2]) with the "100-continue" expectation.
o A client MUST NOT send an Expect request-header field (Section 9.2
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
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.
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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.
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 8.1 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
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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)
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. Miscellaneous notes that may disappear
8.1. Scheme aliases considered harmful
[[TBD-aliases-harmful: describe why aliases like webcal are
harmful.]]
8.2. Use of HTTP for proxy communication
[[TBD-proxy-other: Configured to use HTTP to proxy HTTP or other
protocols.]]
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8.3. Interception of HTTP for access control
[[TBD-intercept: Interception of HTTP traffic for initiating access
control.]]
8.4. Use of HTTP by other protocols
[[TBD-profiles: Profiles of HTTP defined by other protocol.
Extensions of HTTP like WebDAV.]]
8.5. Use of HTTP by media type specification
[[TBD-hypertext: Instructions on composing HTTP requests via
hypertext formats.]]
9. 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.
9.1. 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's value has the following grammar:
Connection = "Connection" ":" OWS Connection-v
Connection-v = 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 B.2.
9.2. Content-Length
The "Content-Length" entity-header field indicates the size of the
entity-body, in number of OCTETs. In the case of responses to the
HEAD method, it indicates the size of the entity-body that would have
been sent had the request been a GET.
Content-Length = "Content-Length" ":" OWS 1*Content-Length-v
Content-Length-v = 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 3.4.
Any Content-Length greater than or equal to zero is a valid value.
Section 3.4 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
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used within the "message/external-body" content-type. In HTTP, it
SHOULD be sent whenever the message's length can be determined prior
to being transferred, unless this is prohibited by the rules in
Section 3.4.
9.3. Date
The "Date" general-header field represents the date and time at which
the message was originated, having the same semantics as the
Origination Date Field (orig-date) defined in Section 3.6.1 of
[RFC5322]. The field value is an HTTP-date, as described in
Section 6.1; it MUST be sent in rfc1123-date format.
Date = "Date" ":" OWS Date-v
Date-v = 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 9.3.1
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.
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The HTTP-date sent in a Date header SHOULD NOT represent a date and
time subsequent to the generation of the message. It SHOULD
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.
9.3.1. 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).
9.4. Host
The "Host" request-header field specifies the Internet host and port
number of the resource being requested, allowing 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.
The Host field value MUST represent the naming authority of the
origin server or gateway given by the original URL obtained from the
user or referring resource (generally an http URI, as described in
Section 2.6.1).
Host = "Host" ":" OWS Host-v
Host-v = uri-host [ ":" port ] ; Section 2.6.1
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
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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.
See Sections 4.2 and B.1.1 for other requirements relating to Host.
9.5. 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 6.2).
TE = "TE" ":" OWS TE-v
TE-v = #t-codings
t-codings = "trailers" / ( transfer-extension [ te-params ] )
te-params = OWS ";" OWS "q=" qvalue *( te-ext )
te-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
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 6.2.1. 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 9.1) 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
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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
is accompanied by a qvalue of 0. (As defined in Section 6.4, 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.
9.6. Trailer
The "Trailer" general-header field indicates that the given set of
header fields is present in the trailer of a message encoded with
chunked transfer-coding.
Trailer = "Trailer" ":" OWS Trailer-v
Trailer-v = 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 6.2.1 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
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9.7. Transfer-Encoding
The "Transfer-Encoding" general-header field indicates what transfer-
codings (if any) have been applied to the message body. It differs
from Content-Encoding (Section 2.2 of [Part3]) in that transfer-
codings are a property of the message (and therefore are removed by
intermediaries), whereas content-codings are not.
Transfer-Encoding = "Transfer-Encoding" ":" OWS
Transfer-Encoding-v
Transfer-Encoding-v = 1#transfer-coding
Transfer-codings are defined in Section 6.2. An example is:
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.
9.8. Upgrade
The "Upgrade" general-header field allows the client to specify what
additional communication protocols it would like to use, if the
server chooses to switch protocols. Additionally, the server MUST
use the Upgrade header field within a 101 (Switching Protocols)
response to indicate which protocol(s) are being switched to.
Upgrade = "Upgrade" ":" OWS Upgrade-v
Upgrade-v = 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
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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 9.1) whenever Upgrade is present in an HTTP/1.1
message.
The Upgrade header field cannot be used to indicate a switch to a
protocol on a different connection. For that purpose, it is more
appropriate to use a 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 2.5 and future updates to this
specification. Additional tokens can be registered with IANA using
the registration procedure defined below.
9.8.1. Upgrade Token Registry
The HTTP Upgrade Token Registry defines the name space for product
tokens used to identify protocols in the Upgrade header field. Each
registered token should be associated with one or a set of
specifications, and with contact information.
Registrations should be allowed on a First Come First Served basis as
described in Section 4.1 of [RFC5226]. These specifications need not
be IETF documents or be subject to IESG review, but should obey the
following rules:
1. A token, once registered, stays registered forever.
2. The registration MUST name a responsible party for the
registration.
3. The registration MUST name a point of contact.
4. The registration MAY name the documentation required for the
token.
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5. The responsible party MAY change the registration at any time.
The IANA will keep a record of all such changes, and make them
available upon request.
6. The responsible party for the first registration of a "product"
token MUST approve later registrations of a "version" token
together with that "product" token before they can be registered.
7. If absolutely required, the IESG MAY reassign the responsibility
for a token. This will normally only be used in the case when a
responsible party cannot be contacted.
It is not required that specifications for upgrade tokens be made
publicly available, but the contact information for the registration
should be.
9.9. 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 [RFC5322] and is intended to be used for
tracking message forwards, avoiding request loops, and identifying
the protocol capabilities of all senders along the request/response
chain.
Via = "Via" ":" OWS Via-v
Via-v = 1#( received-protocol RWS received-by
[ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
protocol-name = token
protocol-version = token
received-by = ( uri-host [ ":" port ] ) / pseudonym
pseudonym = token
The received-protocol indicates the protocol version of the message
received by the server or client along each segment of the request/
response chain. The received-protocol version is appended to the Via
field value when the message is forwarded so that information about
the protocol capabilities of upstream applications remains visible to
all recipients.
The protocol-name is 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
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be assumed to be the default port of the received-protocol.
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each recipient MUST append its information
such that the end result is ordered according to the sequence of
forwarding applications.
Comments MAY be used in the Via header field to identify the software
of 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.
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10. IANA Considerations
10.1. 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]):
+-------------------+----------+----------+-------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+-------------+
| Connection | http | standard | Section 9.1 |
| Content-Length | http | standard | Section 9.2 |
| Date | http | standard | Section 9.3 |
| Host | http | standard | Section 9.4 |
| TE | http | standard | Section 9.5 |
| Trailer | http | standard | Section 9.6 |
| Transfer-Encoding | http | standard | Section 9.7 |
| Upgrade | http | standard | Section 9.8 |
| Via | http | standard | Section 9.9 |
+-------------------+----------+----------+-------------+
The change controller is: "IETF (iesg@ietf.org) - Internet
Engineering Task Force".
10.2. URI Scheme Registration
The entries for the "http" and "https" URI Schemes in the registry
located at <http://www.iana.org/assignments/uri-schemes.html> should
be updated to point to Sections 2.6.1 and 2.6.2 of this document (see
[RFC4395]).
10.3. Internet Media Type Registrations
This document serves as the specification for the Internet media
types "message/http" and "application/http". The following is to be
registered with IANA (see [RFC4288]).
10.3.1. Internet Media Type message/http
The message/http type can be used to enclose a single HTTP request or
response message, provided that it obeys the MIME restrictions for
all "message" types regarding line length and encodings.
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Type name: message
Subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed message (e.g.,
"1.1"). If not present, the version can be determined from the
first line of the body.
msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first line of the
body.
Encoding considerations: only "7bit", "8bit", or "binary" are
permitted
Security considerations: none
Interoperability considerations: none
Published specification: This specification (see Section 10.3.1).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
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10.3.2. Internet Media Type application/http
The application/http type can be used to enclose a pipeline of one or
more HTTP request or response messages (not intermixed).
Type name: application
Subtype name: http
Required parameters: none
Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed messages (e.g.,
"1.1"). If not present, the version can be determined from the
first line of the body.
msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first line of the
body.
Encoding considerations: HTTP messages enclosed by this type are in
"binary" format; use of an appropriate Content-Transfer-Encoding
is required when transmitted via E-mail.
Security considerations: none
Interoperability considerations: none
Published specification: This specification (see Section 10.3.2).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
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Restrictions on usage: none
Author/Change controller: IESG
10.4. Transfer Coding Registry
The registration procedure for HTTP Transfer Codings is now defined
by Section 6.2.3 of this document.
The HTTP Transfer Codings Registry located at
<http://www.iana.org/assignments/http-parameters> should be updated
with the registrations below:
+----------+--------------------------------------+-----------------+
| Name | Description | Reference |
+----------+--------------------------------------+-----------------+
| chunked | Transfer in a series of chunks | Section 6.2.1 |
| compress | UNIX "compress" program method | Section 6.2.2.1 |
| deflate | "zlib" format [RFC1950] with | Section 6.2.2.2 |
| | "deflate" compression | |
| gzip | Same as GNU zip [RFC1952] | Section 6.2.2.3 |
+----------+--------------------------------------+-----------------+
10.5. Upgrade Token Registration
The registration procedure for HTTP Upgrade Tokens -- previously
defined in Section 7.2 of [RFC2817] -- is now defined by
Section 9.8.1 of this document.
The HTTP Status Code Registry located at
<http://www.iana.org/assignments/http-upgrade-tokens/> should be
updated with the registration below:
+-------+---------------------------+-------------------------------+
| Value | Description | Reference |
+-------+---------------------------+-------------------------------+
| HTTP | Hypertext Transfer | Section 2.5 of this |
| | Protocol | specification |
+-------+---------------------------+-------------------------------+
11. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
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11.1. 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.
11.2. 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.
11.3. Attacks Based On File and Path Names
Implementations of HTTP origin servers SHOULD be careful to restrict
the documents returned by HTTP requests to be only those that were
intended by the server administrators. If an HTTP server translates
HTTP URIs directly into file system calls, the server MUST take
special care not to serve files that were not intended to be
delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
other operating systems use ".." as a path component to indicate a
directory level above the current one. On such a system, an HTTP
server MUST disallow any such construct in the request-target if it
would otherwise allow access to a resource outside those intended to
be accessible via the HTTP server. Similarly, files intended for
reference only internally to the server (such as access control
files, configuration files, and script code) MUST be protected from
inappropriate retrieval, since they might contain sensitive
information. Experience has shown that minor bugs in such HTTP
server implementations have turned into security risks.
11.4. 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
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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
likelihood of a user's experiencing failure in accessing sites which
use that strategy.
11.5. 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 should be developed and
followed. (Section 11.2).
Proxy implementors should consider the privacy and security
implications of their design and coding decisions, and of the
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configuration options they provide to proxy operators (especially the
default configuration).
Users of a proxy need to be aware that proxies are no trustworthier
than the people who run them; HTTP itself cannot solve this problem.
The judicious use of cryptography, when appropriate, 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.
11.6. Denial of Service Attacks on Proxies
They exist. They are hard to defend against. Research continues.
Beware.
12. Acknowledgments
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.
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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.
This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for [RFC5234]. 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 relationship
between HTTP and Internet mail message formats.
13. References
13.1. 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-09 (work in
progress), March 2010.
[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-09
(work in progress), March 2010.
[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-09 (work
in progress), March 2010.
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[Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part
6: Caching", draft-ietf-httpbis-p6-cache-09 (work in
progress), March 2010.
[RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format
Specification version 3.3", RFC 1950, May 1996.
RFC 1950 is an Informational RFC, thus it may be less
stable than this specification. On the other hand, this
downward reference was present since the publication of
RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to
cause problems in practice. See also [BCP97].
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, May 1996.
RFC 1951 is an Informational RFC, thus it may be less
stable than this specification. On the other hand, this
downward reference was present since the publication of
RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to
cause problems in practice. See also [BCP97].
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
Randers-Pehrson, "GZIP file format specification version
4.3", RFC 1952, May 1996.
RFC 1952 is an Informational RFC, thus it may be less
stable than this specification. On the other hand, this
downward reference was present since the publication of
RFC 2068 in 1997 ([RFC2068]), therefore it is unlikely to
cause problems in practice. See also [BCP97].
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", RFC 3986,
STD 66, January 2005.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
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13.2. Informative References
[BCP97] Klensin, J. and S. Hartman, "Handling Normative References
to Standards-Track Documents", BCP 97, RFC 4897,
June 2007.
[Kri2001] Kristol, D., "HTTP Cookies: Standards, Privacy, and
Politics", ACM Transactions on Internet Technology Vol. 1,
#2, November 2001, <http://arxiv.org/abs/cs.SE/0105018>.
[Nie1997] 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,
<http://portal.acm.org/citation.cfm?id=219094>.
[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.
[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.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996.
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2068, January 1997.
[RFC2109] Kristol, D. and L. Montulli, "HTTP State Management
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Mechanism", RFC 2109, February 1997.
[RFC2145] Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, "Use
and Interpretation of HTTP Version Numbers", RFC 2145,
May 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, May 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC2965] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, October 2000.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", BCP 115,
RFC 4395, February 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
October 2008.
[Spe] Spero, S., "Analysis of HTTP Performance Problems",
<http://sunsite.unc.edu/mdma-release/http-prob.html>.
[Tou1998] Touch, J., Heidemann, J., and K. Obraczka, "Analysis of
HTTP Performance", ISI Research Report ISI/RR-98-463,
Aug 1998, <http://www.isi.edu/touch/pubs/http-perf96/>.
(original report dated Aug. 1996)
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Appendix A. 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
SHOULD be tolerant when parsing the Request-Line. In particular,
they SHOULD accept any amount of WSP characters between fields, even
though only a single SP is required.
The line terminator for 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
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 B. Compatibility with Previous Versions
HTTP has been in use by the World-Wide Web global information
initiative since 1990. The first version of HTTP, later referred to
as HTTP/0.9, was a simple protocol for hypertext data transfer across
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the Internet with only a single method and no metadata. HTTP/1.0, as
defined by [RFC1945], added a range of request methods and MIME-like
messaging that could include metadata about the data transferred and
modifiers on the request/response semantics. However, HTTP/1.0 did
not sufficiently take into consideration the effects of hierarchical
proxies, caching, the need for persistent connections, or name-based
virtual hosts. The proliferation of incompletely-implemented
applications calling themselves "HTTP/1.0" further necessitated a
protocol version change in order for two communicating applications
to determine each other's true capabilities.
HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
requirements that enable reliable implementations, adding only those
new features that will either be safely ignored by an HTTP/1.0
recipient or only sent when communicating with a party advertising
compliance with HTTP/1.1.
It is beyond the scope of a protocol specification to mandate
compliance with previous versions. HTTP/1.1 was deliberately
designed, however, to make supporting previous versions easy. It is
worth noting that, at the time of composing this specification, we
would expect general-purpose HTTP/1.1 servers to:
o understand any valid request in the format of HTTP/1.0 and 1.1;
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 understand any valid response in the format of HTTP/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].
B.1. Changes from HTTP/1.0
This section summarizes major differences between versions HTTP/1.0
and HTTP/1.1.
B.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 9.4) is
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missing from an HTTP/1.1 request, and accept absolute URIs
(Section 4.1.2) 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:
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.
B.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 HTTP/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
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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 9.1.
The original HTTP/1.0 form of persistent connections (the Connection:
Keep-Alive and Keep-Alive header) is documented in Section 19.7.1 of
[RFC2068].
B.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 6.2, 3.4, 9.2, see also [Part3], [Part5] and [Part6])
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 2.5)
Quality Values of zero should indicate that "I don't want something"
to allow clients to refuse a representation. (Section 6.4)
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 6.2, 6.2.1, 7.1.3.2, and 9.5)
Proxies should be able to add Content-Length when appropriate.
(Section 7.1.3.2)
B.4. Changes from RFC 2616
Empty list elements in list productions have been deprecated.
(Section 1.2.1)
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Rules about implicit linear whitespace between certain grammar
productions have been removed; now it's only allowed when
specifically pointed out in the ABNF. The NUL character is no longer
allowed in comment and quoted-string text. The quoted-pair rule no
longer allows escaping control characters other than HTAB. Non-ASCII
content in header fields and reason phrase has been obsoleted and
made opaque (the TEXT rule was removed) (Section 1.2.2)
Clarify that HTTP-Version is case sensitive. (Section 2.5)
Remove reference to non-existent identity transfer-coding value
tokens. (Sections 6.2 and 3.4)
Require that invalid whitespace around field-names be rejected.
(Section 3.2)
Update use of abs_path production from RFC1808 to the path-absolute +
query components of RFC3986. (Section 4.1.2)
Clarification that the chunk length does not include the count of the
octets in the chunk header and trailer. Furthermore disallowed line
folding in chunk extensions. (Section 6.2.1)
Remove hard limit of two connections per server. (Section 7.1.4)
Clarify exactly when close connection options must be sent.
(Section 9.1)
Appendix C. Collected ABNF
BWS = OWS
Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
Chunked-Body = *chunk last-chunk trailer-part CRLF
Connection = "Connection:" OWS Connection-v
Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
connection-token ] )
Content-Length = "Content-Length:" OWS 1*Content-Length-v
Content-Length-v = 1*DIGIT
Date = "Date:" OWS Date-v
Date-v = HTTP-date
GMT = %x47.4D.54 ; GMT
HTTP-Prot-Name = %x48.54.54.50 ; HTTP
HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
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HTTP-date = rfc1123-date / obs-date
HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
]
Host = "Host:" OWS Host-v
Host-v = uri-host [ ":" port ]
Method = token
OWS = *( [ obs-fold ] WSP )
Pragma = <Pragma, defined in [Part6], Section 3.4>
RWS = 1*( [ obs-fold ] WSP )
Reason-Phrase = *( WSP / VCHAR / obs-text )
Request = Request-Line *( ( general-header / request-header /
entity-header ) CRLF ) CRLF [ message-body ]
Request-Line = Method SP request-target SP HTTP-Version CRLF
Response = Status-Line *( ( general-header / response-header /
entity-header ) CRLF ) CRLF [ message-body ]
Status-Code = 3DIGIT
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
TE = "TE:" OWS TE-v
TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
Trailer = "Trailer:" OWS Trailer-v
Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
transfer-coding ] )
URI = <URI, defined in [RFC3986], Section 3>
URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
Upgrade = "Upgrade:" OWS Upgrade-v
Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
Via = "Via:" OWS Via-v
Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
] )
Warning = <Warning, defined in [Part6], Section 3.6>
absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
asctime-date = day-name SP date3 SP time-of-day SP year
attribute = token
authority = <authority, defined in [RFC3986], Section 3.2>
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chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
chunk-data = 1*OCTET
chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
chunk-ext-name = token
chunk-ext-val = token / quoted-str-nf
chunk-size = 1*HEXDIG
comment = "(" *( ctext / quoted-cpair / comment ) ")"
connection-token = token
ctext = OWS / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
date1 = day SP month SP year
date2 = day "-" month "-" 2DIGIT
date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
day = 2DIGIT
day-name = %x4D.6F.6E ; Mon
/ %x54.75.65 ; Tue
/ %x57.65.64 ; Wed
/ %x54.68.75 ; Thu
/ %x46.72.69 ; Fri
/ %x53.61.74 ; Sat
/ %x53.75.6E ; Sun
day-name-l = %x4D.6F.6E.64.61.79 ; Monday
/ %x54.75.65.73.64.61.79 ; Tuesday
/ %x57.65.64.6E.65.73.64.61.79 ; Wednesday
/ %x54.68.75.72.73.64.61.79 ; Thursday
/ %x46.72.69.64.61.79 ; Friday
/ %x53.61.74.75.72.64.61.79 ; Saturday
/ %x53.75.6E.64.61.79 ; Sunday
entity-body = <entity-body, defined in [Part3], Section 3.2>
entity-header = <entity-header, defined in [Part3], Section 3.1>
field-content = *( WSP / VCHAR / obs-text )
field-name = token
field-value = *( field-content / OWS )
general-header = Cache-Control / Connection / Date / Pragma / Trailer
/ Transfer-Encoding / Upgrade / Via / Warning
header-field = field-name ":" OWS [ field-value ] OWS
hour = 2DIGIT
http-URI = "http://" authority path-abempty [ "?" query ]
https-URI = "https://" authority path-abempty [ "?" query ]
last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
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message-body = entity-body /
<entity-body encoded as per Transfer-Encoding>
minute = 2DIGIT
month = %x4A.61.6E ; Jan
/ %x46.65.62 ; Feb
/ %x4D.61.72 ; Mar
/ %x41.70.72 ; Apr
/ %x4D.61.79 ; May
/ %x4A.75.6E ; Jun
/ %x4A.75.6C ; Jul
/ %x41.75.67 ; Aug
/ %x53.65.70 ; Sep
/ %x4F.63.74 ; Oct
/ %x4E.6F.76 ; Nov
/ %x44.65.63 ; Dec
obs-date = rfc850-date / asctime-date
obs-fold = CRLF
obs-text = %x80-FF
partial-URI = relative-part [ "?" query ]
path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
port = <port, defined in [RFC3986], Section 3.2.3>
product = token [ "/" product-version ]
product-version = token
protocol-name = token
protocol-version = token
pseudonym = token
qdtext = OWS / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~'
/ obs-text
query = <query, defined in [RFC3986], Section 3.4>
quoted-cpair = "\" ( WSP / VCHAR / obs-text )
quoted-pair = "\" ( WSP / VCHAR / obs-text )
quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
received-by = ( uri-host [ ":" port ] ) / pseudonym
received-protocol = [ protocol-name "/" ] protocol-version
relative-part = <relative-part, defined in [RFC3986], Section 4.2>
request-header = <request-header, defined in [Part2], Section 3>
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request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
/ authority
response-header = <response-header, defined in [Part2], Section 5>
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
second = 2DIGIT
special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
start-line = Request-Line / Status-Line
t-codings = "trailers" / ( transfer-extension [ te-params ] )
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
"^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
te-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
te-params = OWS ";" OWS "q=" qvalue *te-ext
time-of-day = hour ":" minute ":" second
token = 1*tchar
trailer-part = *( entity-header CRLF )
transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
transfer-parameter = attribute BWS "=" BWS value
uri-host = <host, defined in [RFC3986], Section 3.2.2>
value = token / quoted-string
year = 4DIGIT
ABNF diagnostics:
; Chunked-Body defined but not used
; Content-Length defined but not used
; HTTP-message defined but not used
; Host defined but not used
; Request defined but not used
; Response defined but not used
; TE defined but not used
; URI defined but not used
; URI-reference defined but not used
; http-URI defined but not used
; https-URI defined but not used
; partial-URI defined but not used
; special defined but not used
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Appendix D. Change Log (to be removed by RFC Editor before publication)
D.1. Since RFC2616
Extracted relevant partitions from [RFC2616].
D.2. Since draft-ietf-httpbis-p1-messaging-00
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/1>: "HTTP Version
should be case sensitive"
(<http://purl.org/NET/http-errata#verscase>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/2>: "'unsafe'
characters" (<http://purl.org/NET/http-errata#unsafe-uri>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/3>: "Chunk Size
Definition" (<http://purl.org/NET/http-errata#chunk-size>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/4>: "Message Length"
(<http://purl.org/NET/http-errata#msg-len-chars>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/8>: "Media Type
Registrations" (<http://purl.org/NET/http-errata#media-reg>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/11>: "URI includes
query" (<http://purl.org/NET/http-errata#uriquery>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/15>: "No close on
1xx responses" (<http://purl.org/NET/http-errata#noclose1xx>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/16>: "Remove
'identity' token references"
(<http://purl.org/NET/http-errata#identity>)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/26>: "Import query
BNF"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/31>: "qdtext BNF"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
Informative references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/42>: "RFC2606
Compliance"
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/45>: "RFC977
reference"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700
references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/47>: "inconsistency
in date format explanation"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/48>: "Date reference
typo"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/65>: "Informative
references"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/66>: "ISO-8859-1
Reference"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/86>: "Normative up-
to-date references"
Other changes:
o Update media type registrations to use RFC4288 template.
o Use names of RFC4234 core rules DQUOTE and WSP, fix broken ABNF
for chunk-data (work in progress on
<http://tools.ietf.org/wg/httpbis/trac/ticket/36>)
D.3. Since draft-ietf-httpbis-p1-messaging-01
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/19>: "Bodies on GET
(and other) requests"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating to
RFC4288"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/57>: "Status Code
and Reason Phrase"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/82>: "rel_path not
used"
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
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o Get rid of duplicate BNF rule names ("host" -> "uri-host",
"trailer" -> "trailer-part").
o Avoid underscore character in rule names ("http_URL" -> "http-
URL", "abs_path" -> "path-absolute").
o Add rules for terms imported from URI spec ("absoluteURI",
"authority", "path-absolute", "port", "query", "relativeURI",
"host) -- these will have to be updated when switching over to
RFC3986.
o Synchronize core rules with RFC5234.
o Get rid of prose rules that span multiple lines.
o Get rid of unused rules LOALPHA and UPALPHA.
o Move "Product Tokens" section (back) into Part 1, as "token" is
used in the definition of the Upgrade header.
o Add explicit references to BNF syntax and rules imported from
other parts of the specification.
o Rewrite prose rule "token" in terms of "tchar", rewrite prose rule
"TEXT".
D.4. Since draft-ietf-httpbis-p1-messaging-02
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/51>: "HTTP-date vs.
rfc1123-date"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/64>: "WS in quoted-
pair"
Ongoing work on IANA Message Header Registration
(<http://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://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Replace string literals when the string really is case-sensitive
(HTTP-Version).
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D.5. Since draft-ietf-httpbis-p1-messaging-03
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/28>: "Connection
closing"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/97>: "Move
registrations and registry information to IANA Considerations"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/120>: "need new URL
for PAD1995 reference"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/127>: "IANA
Considerations: update HTTP URI scheme registration"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/128>: "Cite HTTPS
URI scheme definition"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/129>: "List-type
headers vs Set-Cookie"
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Replace string literals when the string really is case-sensitive
(HTTP-Date).
o Replace HEX by HEXDIG for future consistence with RFC 5234's core
rules.
D.6. Since draft-ietf-httpbis-p1-messaging-04
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/34>: "Out-of-date
reference for URIs"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/132>: "RFC 2822 is
updated by RFC 5322"
Ongoing work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Use "/" instead of "|" for alternatives.
o Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
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o Only reference RFC 5234's core rules.
o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
o Rewrite ABNFs to spell out whitespace rules, factor out header
value format definitions.
D.7. Since draft-ietf-httpbis-p1-messaging-05
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/30>: "Header LWS"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/52>: "Sort 1.3
Terminology"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/63>: "RFC2047
encoded words"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/74>: "Character
Encodings in TEXT"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/77>: "Line Folding"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/83>: "OPTIONS * and
proxies"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/94>: "Reason-Phrase
BNF"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/111>: "Use of TEXT"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/118>: "Join
"Differences Between HTTP Entities and RFC 2045 Entities"?"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/134>: "RFC822
reference left in discussion of date formats"
Final work on ABNF conversion
(<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
o Rewrite definition of list rules, deprecate empty list elements.
o Add appendix containing collected and expanded ABNF.
Other changes:
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o Rewrite introduction; add mostly new Architecture Section.
o Move definition of quality values from Part 3 into Part 1; make TE
request header grammar independent of accept-params (defined in
Part 3).
D.8. Since draft-ietf-httpbis-p1-messaging-06
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/161>: "base for
numeric protocol elements"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/162>: "comment ABNF"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/88>: "205 Bodies"
(took out language that implied that there may be methods for
which a request body MUST NOT be included)
o <http://tools.ietf.org/wg/httpbis/trac/ticket/163>: "editorial
improvements around HTTP-date"
D.9. Since draft-ietf-httpbis-p1-messaging-07
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/93>: "Repeating
single-value headers"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/131>: "increase
connection limit"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/157>: "IP addresses
in URLs"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/172>: "take over
HTTP Upgrade Token Registry"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/173>: "CR and LF in
chunk extension values"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/184>: "HTTP/0.9
support"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/188>: "pick IANA
policy (RFC5226) for Transfer Coding / Content Coding"
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o <http://tools.ietf.org/wg/httpbis/trac/ticket/189>: "move
definitions of gzip/deflate/compress to part 1"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/194>: "disallow
control characters in quoted-pair"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/148>: "update IANA
requirements wrt Transfer-Coding values" (add the IANA
Considerations subsection)
D.10. Since draft-ietf-httpbis-p1-messaging-08
Closed issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/201>: "header
parsing, treatment of leading and trailing OWS"
Partly resolved issues:
o <http://tools.ietf.org/wg/httpbis/trac/ticket/60>: "Placement of
13.5.1 and 13.5.2"
o <http://tools.ietf.org/wg/httpbis/trac/ticket/200>: "use of term
"word" when talking about header structure"
Index
A
application/http Media Type 58
C
cache 13
cacheable 14
chunked (Coding Format) 32
client 10
Coding Format
chunked 32
compress 34
deflate 35
gzip 35
compress (Coding Format) 34
connection 10
Connection header 46
Content-Length header 47
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D
Date header 48
deflate (Coding Format) 35
downstream 12
G
gateway 13
Grammar
absolute-URI 16
ALPHA 7
asctime-date 31
attribute 32
authority 16
BWS 9
chunk 33
chunk-data 33
chunk-ext 33
chunk-ext-name 33
chunk-ext-val 33
chunk-size 33
Chunked-Body 33
comment 21
Connection 46
connection-token 46
Connection-v 46
Content-Length 47
Content-Length-v 47
CR 7
CRLF 7
ctext 21
CTL 7
Date 48
Date-v 48
date1 30
date2 32
date3 32
day 30
day-name 30
day-name-l 30
DIGIT 7
DQUOTE 7
extension-code 29
extension-method 25
field-content 20
field-name 20
field-value 20
general-header 24
GMT 30
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header-field 20
HEXDIG 7
Host 49
Host-v 49
hour 30
HTTP-date 30
HTTP-message 19
HTTP-Prot-Name 15
http-URI 16
HTTP-Version 15
https-URI 18
last-chunk 33
LF 7
message-body 22
Method 25
minute 30
month 30
obs-date 31
obs-text 10
OCTET 7
OWS 9
path-absolute 16
port 16
product 35
product-version 35
protocol-name 54
protocol-version 54
pseudonym 54
qdtext 10
qdtext-nf 33
query 16
quoted-cpair 22
quoted-pair 10
quoted-str-nf 33
quoted-string 10
qvalue 36
Reason-Phrase 29
received-by 54
received-protocol 54
Request 25
Request-Line 25
request-target 25
Response 28
rfc850-date 31
rfc1123-date 30
RWS 9
second 30
SP 7
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special 9
Status-Code 29
Status-Line 28
t-codings 50
tchar 9
TE 50
te-ext 50
te-params 50
TE-v 50
time-of-day 30
token 9
Trailer 51
trailer-part 33
Trailer-v 51
transfer-coding 31
Transfer-Encoding 52
Transfer-Encoding-v 52
transfer-extension 31
transfer-parameter 32
Upgrade 52
Upgrade-v 52
uri-host 16
URI-reference 16
value 32
VCHAR 7
Via 54
Via-v 54
WSP 7
year 30
gzip (Coding Format) 35
H
header field 19
header section 19
Headers
Connection 46
Content-Length 47
Date 48
Host 49
TE 50
Trailer 51
Transfer-Encoding 52
Upgrade 52
Via 54
headers 19
Host header 49
http URI scheme 16
https URI scheme 17
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I
inbound 12
M
Media Type
application/http 58
message/http 56
message 11
message/http Media Type 56
O
origin server 11
outbound 12
P
proxy 12
R
request 11
resource 16
response 11
reverse proxy 13
S
server 10
T
TE header 50
Trailer header 51
Transfer-Encoding header 52
tunnel 13
U
Upgrade header 52
upstream 12
URI scheme
http 16
https 17
user agent 11
V
Via header 54
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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/
Jeffrey C. Mogul
Hewlett-Packard Company
HP Labs, Large Scale Systems Group
1501 Page Mill Road, MS 1177
Palo Alto, CA 94304
USA
Email: JeffMogul@acm.org
Henrik Frystyk Nielsen
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
USA
Email: henrikn@microsoft.com
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Larry Masinter
Adobe Systems, Incorporated
345 Park Ave
San Jose, CA 95110
USA
Email: LMM@acm.org
URI: http://larry.masinter.net/
Paul J. Leach
Microsoft Corporation
1 Microsoft Way
Redmond, WA 98052
Email: paulle@microsoft.com
Tim Berners-Lee
World Wide Web Consortium
MIT Computer Science and Artificial Intelligence Laboratory
The Stata Center, Building 32
32 Vassar Street
Cambridge, MA 02139
USA
Email: timbl@w3.org
URI: http://www.w3.org/People/Berners-Lee/
Yves Lafon (editor)
World Wide Web Consortium
W3C / ERCIM
2004, rte des Lucioles
Sophia-Antipolis, AM 06902
France
Email: ylafon@w3.org
URI: http://www.raubacapeu.net/people/yves/
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Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
Phone: +49 251 2807760
Fax: +49 251 2807761
Email: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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