HTTP Working Group R. Fielding, Ed.
Internet-Draft Adobe
Obsoletes: 7230 (if approved) M. Nottingham, Ed.
Intended status: Standards Track Fastly
Expires: January 3, 2019 J. Reschke, Ed.
greenbytes
July 2, 2018
HTTP/1.1 Messaging
draft-ietf-httpbis-messaging-02
Abstract
The Hypertext Transfer Protocol (HTTP) is a stateless application-
level protocol for distributed, collaborative, hypertext information
systems. This document specifies the HTTP/1.1 message syntax,
message parsing, connection management, and related security
concerns.
This document obsoletes portions of RFC 7230.
Editorial Note
This note is to be removed before publishing as an RFC.
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
.
Working Group information can be found at ;
source code and issues list for this draft can be found at
.
The changes in this draft are summarized in Appendix D.3.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on January 3, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5
2. Message . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Message Format . . . . . . . . . . . . . . . . . . . . . 6
2.2. HTTP Version . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Message Parsing . . . . . . . . . . . . . . . . . . . . . 7
3. Request Line . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2. Request Target . . . . . . . . . . . . . . . . . . . . . 9
3.2.1. origin-form . . . . . . . . . . . . . . . . . . . . . 10
3.2.2. absolute-form . . . . . . . . . . . . . . . . . . . . 10
3.2.3. authority-form . . . . . . . . . . . . . . . . . . . 11
3.2.4. asterisk-form . . . . . . . . . . . . . . . . . . . . 11
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3.3. Effective Request URI . . . . . . . . . . . . . . . . . . 12
4. Status Line . . . . . . . . . . . . . . . . . . . . . . . . . 13
5. Header Fields . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1. Field Parsing . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Obsolete Line Folding . . . . . . . . . . . . . . . . . . 15
6. Message Body . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Transfer-Encoding . . . . . . . . . . . . . . . . . . . . 17
6.2. Content-Length . . . . . . . . . . . . . . . . . . . . . 18
6.3. Message Body Length . . . . . . . . . . . . . . . . . . . 19
7. Transfer Codings . . . . . . . . . . . . . . . . . . . . . . 21
7.1. Chunked Transfer Coding . . . . . . . . . . . . . . . . . 22
7.1.1. Chunk Extensions . . . . . . . . . . . . . . . . . . 23
7.1.2. Chunked Trailer Part . . . . . . . . . . . . . . . . 23
7.1.3. Decoding Chunked . . . . . . . . . . . . . . . . . . 24
7.2. Transfer Codings for Compression . . . . . . . . . . . . 25
7.3. Transfer Coding Registry . . . . . . . . . . . . . . . . 25
7.4. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8. Handling Incomplete Messages . . . . . . . . . . . . . . . . 27
9. Connection Management . . . . . . . . . . . . . . . . . . . . 28
9.1. Connection . . . . . . . . . . . . . . . . . . . . . . . 28
9.2. Establishment . . . . . . . . . . . . . . . . . . . . . . 30
9.3. Persistence . . . . . . . . . . . . . . . . . . . . . . . 30
9.3.1. Retrying Requests . . . . . . . . . . . . . . . . . . 31
9.3.2. Pipelining . . . . . . . . . . . . . . . . . . . . . 31
9.4. Concurrency . . . . . . . . . . . . . . . . . . . . . . . 32
9.5. Failures and Timeouts . . . . . . . . . . . . . . . . . . 33
9.6. Tear-down . . . . . . . . . . . . . . . . . . . . . . . . 33
9.7. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.7.1. Upgrade Protocol Names . . . . . . . . . . . . . . . 36
9.7.2. Upgrade Token Registry . . . . . . . . . . . . . . . 37
10. Enclosing Messages as Data . . . . . . . . . . . . . . . . . 37
10.1. Media Type message/http . . . . . . . . . . . . . . . . 38
10.2. Media Type application/http . . . . . . . . . . . . . . 39
11. Security Considerations . . . . . . . . . . . . . . . . . . . 40
11.1. Response Splitting . . . . . . . . . . . . . . . . . . . 40
11.2. Request Smuggling . . . . . . . . . . . . . . . . . . . 41
11.3. Message Integrity . . . . . . . . . . . . . . . . . . . 41
11.4. Message Confidentiality . . . . . . . . . . . . . . . . 42
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
12.1. Header Field Registration . . . . . . . . . . . . . . . 42
12.2. Media Type Registration . . . . . . . . . . . . . . . . 42
12.3. Transfer Coding Registration . . . . . . . . . . . . . . 42
12.4. Upgrade Token Registration . . . . . . . . . . . . . . . 43
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
13.1. Normative References . . . . . . . . . . . . . . . . . . 43
13.2. Informative References . . . . . . . . . . . . . . . . . 44
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 46
Appendix B. Differences between HTTP and MIME . . . . . . . . . 47
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B.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . 48
B.2. Conversion to Canonical Form . . . . . . . . . . . . . . 48
B.3. Conversion of Date Formats . . . . . . . . . . . . . . . 48
B.4. Conversion of Content-Encoding . . . . . . . . . . . . . 49
B.5. Conversion of Content-Transfer-Encoding . . . . . . . . . 49
B.6. MHTML and Line Length Limitations . . . . . . . . . . . . 49
Appendix C. HTTP Version History . . . . . . . . . . . . . . . . 49
C.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 50
C.1.1. Multihomed Web Servers . . . . . . . . . . . . . . . 50
C.1.2. Keep-Alive Connections . . . . . . . . . . . . . . . 51
C.1.3. Introduction of Transfer-Encoding . . . . . . . . . . 51
C.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 52
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 52
D.1. Between RFC7230 and draft 00 . . . . . . . . . . . . . . 52
D.2. Since draft-ietf-httpbis-messaging-00 . . . . . . . . . . 52
D.3. Since draft-ietf-httpbis-messaging-01 . . . . . . . . . . 53
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 56
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56
1. Introduction
The Hypertext Transfer Protocol (HTTP) is a stateless application-
level request/response protocol that uses extensible semantics and
self-descriptive messages for flexible interaction with network-based
hypertext information systems. HTTP is defined by a series of
documents that collectively form the HTTP/1.1 specification:
o "HTTP Semantics" [Semantics]
o "HTTP Caching" [Caching]
o "HTTP/1.1 Messaging" (this document)
This document defines HTTP/1.1 message syntax and framing
requirements and their associated connection management. Our goal is
to define all of the mechanisms necessary for HTTP/1.1 message
handling that are independent of message semantics, thereby defining
the complete set of requirements for message parsers and message-
forwarding intermediaries.
This document obsoletes the portions of RFC 7230 related to HTTP/1.1
messaging and connection management, with the changes being
summarized in Appendix C.2. The other parts of RFC 7230 are
obsoleted by "HTTP Semantics" [Semantics].
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1.1. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Conformance criteria and considerations regarding error handling are
defined in Section 3 of [Semantics].
1.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with a list extension, defined in Section 11 of
[Semantics], that allows for compact definition of comma-separated
lists using a '#' operator (similar to how the '*' operator indicates
repetition). Appendix A shows the collected grammar with all list
operators expanded to standard ABNF notation.
As a convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons.
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line
feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any
visible [USASCII] character).
The rules below are defined in [Semantics]:
BWS =
OWS =
RWS =
absolute-URI =
absolute-path =
authority =
comment =
field-name =
field-value =
obs-text =
port =
query =
quoted-string =
token =
uri-host =
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2. Message
2.1. Message Format
All HTTP/1.1 messages consist of a start-line followed by a sequence
of octets in a format similar to the Internet Message Format
[RFC5322]: zero or more header fields (collectively referred to as
the "headers" or the "header section"), an empty line indicating the
end of the header section, and an optional message body.
HTTP-message = start-line
*( header-field CRLF )
CRLF
[ message-body ]
An HTTP message can be either 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 6).
start-line = request-line / status-line
In theory, a client could receive requests and a server could receive
responses, distinguishing them by their different start-line formats.
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.
Although HTTP makes use of some protocol elements similar to the
Multipurpose Internet Mail Extensions (MIME) [RFC2045], see
Appendix B for the differences between HTTP and MIME messages.
2.2. HTTP Version
HTTP uses a "." numbering scheme to indicate versions
of the protocol. This specification defines version "1.1".
Section 3.5 of [Semantics] specifies the semantics of HTTP version
numbers.
The version of an HTTP/1.x message is indicated by an HTTP-version
field in the start-line. HTTP-version is case-sensitive.
HTTP-version = HTTP-name "/" DIGIT "." DIGIT
HTTP-name = %x48.54.54.50 ; "HTTP", case-sensitive
When an HTTP/1.1 message is sent to an HTTP/1.0 recipient [RFC1945]
or a recipient whose version is unknown, the HTTP/1.1 message is
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constructed such that it can be interpreted as a valid HTTP/1.0
message if all of the newer features are ignored. This specification
places recipient-version requirements on some new features so that a
conformant sender will only use compatible features until it has
determined, through configuration or the receipt of a message, that
the recipient supports HTTP/1.1.
Intermediaries that process HTTP messages (i.e., all intermediaries
other than those acting as tunnels) MUST send their own HTTP-version
in forwarded messages. In other words, they are not allowed to
blindly forward the start-line without ensuring that the protocol
version in that message matches a version to which that intermediary
is conformant for both the receiving and sending of messages.
Forwarding an HTTP message without rewriting the HTTP-version might
result in communication errors when downstream recipients use the
message sender's version to determine what features are safe to use
for later communication with that sender.
A server MAY send an HTTP/1.0 response to an HTTP/1.1 request if it
is known or suspected that the client incorrectly implements the HTTP
specification and is incapable of correctly processing later version
responses, such as when a client fails to parse the version number
correctly or when an intermediary is known to blindly forward the
HTTP-version even when it doesn't conform to the given minor version
of the protocol. Such protocol downgrades SHOULD NOT be performed
unless triggered by specific client attributes, such as when one or
more of the request header fields (e.g., User-Agent) uniquely match
the values sent by a client known to be in error.
2.3. Message Parsing
The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field into a hash table
by field name until the empty line, and then use the parsed data to
determine if a message body is expected. If a message body has been
indicated, then it is read as a stream until an amount of octets
equal to the message body length is read or the connection is closed.
A recipient MUST parse an HTTP message as a sequence of octets in an
encoding that is a superset of US-ASCII [USASCII]. Parsing an HTTP
message as a stream of Unicode characters, without regard for the
specific encoding, creates security vulnerabilities due to the
varying ways that string processing libraries handle invalid
multibyte character sequences that contain the octet LF (%x0A).
String-based parsers can only be safely used within protocol elements
after the element has been extracted from the message, such as within
a header field-value after message parsing has delineated the
individual fields.
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Although the line terminator for the start-line and header fields is
the sequence CRLF, a recipient MAY recognize a single LF as a line
terminator and ignore any preceding CR.
Older HTTP/1.0 user agent implementations might send an extra CRLF
after a POST request as a workaround for some early server
applications that failed to read message body content that was not
terminated by a line-ending. An HTTP/1.1 user agent MUST NOT preface
or follow a request with an extra CRLF. If terminating the request
message body with a line-ending is desired, then the user agent MUST
count the terminating CRLF octets as part of the message body length.
In the interest of robustness, a server that is expecting to receive
and parse a request-line SHOULD ignore at least one empty line (CRLF)
received prior to the request-line.
A sender MUST NOT send whitespace between the start-line and the
first header field. A recipient that receives whitespace between the
start-line and the first header field MUST either reject the message
as invalid or consume each whitespace-preceded line without further
processing of it (i.e., ignore the entire line, along with any
subsequent lines preceded by whitespace, until a properly formed
header field is received or the header section is terminated).
The presence of such whitespace in a request might be an attempt to
trick a server into ignoring that field or processing the line after
it as a new request, either of which might result in a security
vulnerability if other implementations within the request chain
interpret the same message differently. Likewise, the presence of
such whitespace in a response might be ignored by some clients or
cause others to cease parsing.
When a server listening only for HTTP request messages, or processing
what appears from the start-line to be an HTTP request message,
receives a sequence of octets that does not match the HTTP-message
grammar aside from the robustness exceptions listed above, the server
SHOULD respond with a 400 (Bad Request) response.
3. Request Line
A request-line begins with a method token, followed by a single space
(SP), the request-target, another single space (SP), the protocol
version, and ends with CRLF.
request-line = method SP request-target SP HTTP-version CRLF
Although the request-line grammar rule requires that each of the
component elements be separated by a single SP octet, recipients MAY
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instead parse on whitespace-delimited word boundaries and, aside from
the CRLF terminator, treat any form of whitespace as the SP separator
while ignoring preceding or trailing whitespace; such whitespace
includes one or more of the following octets: SP, HTAB, VT (%x0B), FF
(%x0C), or bare CR. However, lenient parsing can result in request
smuggling security vulnerabilities if there are multiple recipients
of the message and each has its own unique interpretation of
robustness (see Section 11.2).
HTTP does not place a predefined limit on the length of a request-
line, as described in Section 3 of [Semantics]. A server that
receives a method longer than any that it implements SHOULD respond
with a 501 (Not Implemented) status code. A server that receives a
request-target longer than any URI it wishes to parse MUST respond
with a 414 (URI Too Long) status code (see Section 9.5.15 of
[Semantics]).
Various ad hoc limitations on request-line length are found in
practice. It is RECOMMENDED that all HTTP senders and recipients
support, at a minimum, request-line lengths of 8000 octets.
3.1. Method
The method token indicates the request method to be performed on the
target resource. The request method is case-sensitive.
method = token
The request methods defined by this specification can be found in
Section 7 of [Semantics], along with information regarding the HTTP
method registry and considerations for defining new methods.
3.2. Request Target
The request-target identifies the target resource upon which to apply
the request. The client derives a request-target from its desired
target URI. There are four distinct formats for the request-target,
depending on both the method being requested and whether the request
is to a proxy.
request-target = origin-form
/ absolute-form
/ authority-form
/ asterisk-form
No whitespace is allowed in the request-target. Unfortunately, some
user agents fail to properly encode or exclude whitespace found in
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hypertext references, resulting in those disallowed characters being
sent as the request-target in a malformed request-line.
Recipients of an invalid request-line SHOULD respond with either a
400 (Bad Request) error or a 301 (Moved Permanently) redirect with
the request-target properly encoded. A recipient SHOULD NOT attempt
to autocorrect and then process the request without a redirect, since
the invalid request-line might be deliberately crafted to bypass
security filters along the request chain.
3.2.1. origin-form
The most common form of request-target is the "origin-form".
origin-form = absolute-path [ "?" query ]
When making a request directly to an origin server, other than a
CONNECT or server-wide OPTIONS request (as detailed below), a client
MUST send only the absolute path and query components of the target
URI as the request-target. If the target URI's path component is
empty, the client MUST send "/" as the path within the origin-form of
request-target. A Host header field is also sent, as defined in
Section 5.4 of [Semantics].
For example, a client wishing to retrieve a representation of the
resource identified as
http://www.example.org/where?q=now
directly from the origin server would open (or reuse) a TCP
connection to port 80 of the host "www.example.org" and send the
lines:
GET /where?q=now HTTP/1.1
Host: www.example.org
followed by the remainder of the request message.
3.2.2. absolute-form
When making a request to a proxy, other than a CONNECT or server-wide
OPTIONS request (as detailed below), a client MUST send the target
URI in "absolute-form" as the request-target.
absolute-form = absolute-URI
The proxy is requested to either service that request from a valid
cache, if possible, or make the same request on the client's behalf
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to either the next inbound proxy server or directly to the origin
server indicated by the request-target. Requirements on such
"forwarding" of messages are defined in Section 5.6 of [Semantics].
An example absolute-form of request-line would be:
GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
To allow for transition to the absolute-form for all requests in some
future version of HTTP, a server MUST accept the absolute-form in
requests, even though HTTP/1.1 clients will only send them in
requests to proxies.
3.2.3. authority-form
The "authority-form" of request-target is only used for CONNECT
requests (Section 7.3.6 of [Semantics]).
authority-form = authority
When making a CONNECT request to establish a tunnel through one or
more proxies, a client MUST send only the target URI's authority
component (excluding any userinfo and its "@" delimiter) as the
request-target. For example,
CONNECT www.example.com:80 HTTP/1.1
3.2.4. asterisk-form
The "asterisk-form" of request-target is only used for a server-wide
OPTIONS request (Section 7.3.7 of [Semantics]).
asterisk-form = "*"
When a client wishes to request OPTIONS for the server as a whole, as
opposed to a specific named resource of that server, the client MUST
send only "*" (%x2A) as the request-target. For example,
OPTIONS * HTTP/1.1
If a proxy receives an OPTIONS request with an absolute-form of
request-target in which the URI has an empty path and no query
component, then the last proxy on the request chain MUST send a
request-target of "*" when it forwards the request to the indicated
origin server.
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For example, the request
OPTIONS http://www.example.org:8001 HTTP/1.1
would be forwarded by the final proxy as
OPTIONS * HTTP/1.1
Host: www.example.org:8001
after connecting to port 8001 of host "www.example.org".
3.3. Effective Request URI
Since the request-target often contains only part of the user agent's
target URI, a server reconstructs the intended target as an effective
request URI to properly service the request (Section 5.3 of
[Semantics]).
If the request-target is in absolute-form, the effective request URI
is the same as the request-target. Otherwise, the effective request
URI is constructed as follows:
If the server's configuration (or outbound gateway) provides a
fixed URI scheme, that scheme is used for the effective request
URI. Otherwise, if the request is received over a TLS-secured TCP
connection, the effective request URI's scheme is "https"; if not,
the scheme is "http".
If the server's configuration (or outbound gateway) provides a
fixed URI authority component, that authority is used for the
effective request URI. If not, then if the request-target is in
authority-form, the effective request URI's authority component is
the same as the request-target. If not, then if a Host header
field is supplied with a non-empty field-value, the authority
component is the same as the Host field-value. Otherwise, the
authority component is assigned the default name configured for
the server and, if the connection's incoming TCP port number
differs from the default port for the effective request URI's
scheme, then a colon (":") and the incoming port number (in
decimal form) are appended to the authority component.
If the request-target is in authority-form or asterisk-form, the
effective request URI's combined path and query component is
empty. Otherwise, the combined path and query component is the
same as the request-target.
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The components of the effective request URI, once determined as
above, can be combined into absolute-URI form by concatenating the
scheme, "://", authority, and combined path and query component.
Example 1: the following message received over an insecure TCP
connection
GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.example.org:8080
has an effective request URI of
http://www.example.org:8080/pub/WWW/TheProject.html
Example 2: the following message received over a TLS-secured TCP
connection
OPTIONS * HTTP/1.1
Host: www.example.org
has an effective request URI of
https://www.example.org
Recipients of an HTTP/1.0 request that lacks a Host header field
might need to use heuristics (e.g., examination of the URI path for
something unique to a particular host) in order to guess the
effective request URI's authority component.
4. Status Line
The first line of a response message is the status-line, consisting
of the protocol version, a space (SP), the status code, another
space, a possibly empty textual phrase describing the status code,
and ending with CRLF.
status-line = HTTP-version SP status-code SP reason-phrase CRLF
Although the status-line grammar rule requires that each of the
component elements be separated by a single SP octet, recipients MAY
instead parse on whitespace-delimited word boundaries and, aside from
the line terminator, treat any form of whitespace as the SP separator
while ignoring preceding or trailing whitespace; such whitespace
includes one or more of the following octets: SP, HTAB, VT (%x0B), FF
(%x0C), or bare CR. However, lenient parsing can result in response
splitting security vulnerabilities if there are multiple recipients
of the message and each has its own unique interpretation of
robustness (see Section 11.1).
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The status-code element is a 3-digit integer code describing the
result of the server's attempt to understand and satisfy the client's
corresponding request. The rest of the response message is to be
interpreted in light of the semantics defined for that status code.
See Section 9 of [Semantics] for information about the semantics of
status codes, including the classes of status code (indicated by the
first digit), the status codes defined by this specification,
considerations for the definition of new status codes, and the IANA
registry.
status-code = 3DIGIT
The reason-phrase element exists for the sole purpose of providing a
textual description associated with the numeric status code, mostly
out of deference to earlier Internet application protocols that were
more frequently used with interactive text clients. A client SHOULD
ignore the reason-phrase content.
reason-phrase = *( HTAB / SP / VCHAR / obs-text )
5. Header Fields
Each header field consists of a case-insensitive field name followed
by a colon (":"), optional leading whitespace, the field value, and
optional trailing whitespace.
header-field = field-name ":" OWS field-value OWS
Most HTTP field names and the rules for parsing within field values
are defined in Section 4 of [Semantics]. This section covers the
generic syntax for header field inclusion within, and extraction
from, HTTP/1.1 messages. In addition, the following header fields
are defined by this document because they are specific to HTTP/1.1
message processing:
+-------------------+----------+----------+---------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+---------------+
| Connection | http | standard | Section 9.1 |
| MIME-Version | http | standard | Appendix B.1 |
| TE | http | standard | Section 7.4 |
| Transfer-Encoding | http | standard | Section 6.1 |
| Upgrade | http | standard | Section 9.7 |
+-------------------+----------+----------+---------------+
Furthermore, the field name "Close" is reserved, since using that
name as an HTTP header field might conflict with the "close"
connection option of the Connection header field (Section 9.1).
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+-------------------+----------+----------+------------+
| Header Field Name | Protocol | Status | Reference |
+-------------------+----------+----------+------------+
| Close | http | reserved | Section 5 |
+-------------------+----------+----------+------------+
5.1. Field Parsing
Messages are parsed using a generic algorithm, independent of the
individual header field names. The contents within a given field
value are not parsed until a later stage of message interpretation
(usually after the message's entire header section has been
processed).
No whitespace is allowed between the header field-name and colon. In
the past, differences in the handling of such whitespace have led to
security vulnerabilities in request routing and response handling. A
server MUST reject any received request message that contains
whitespace between a header field-name and colon with a response
status code of 400 (Bad Request). A proxy MUST remove any such
whitespace from a response message before forwarding the message
downstream.
A field value might be preceded and/or followed by optional
whitespace (OWS); a single SP preceding the field-value is preferred
for consistent readability by humans. The field value does not
include any leading or trailing whitespace: OWS occurring before the
first non-whitespace octet of the field value or after the last non-
whitespace octet of the field value ought to be excluded by parsers
when extracting the field value from a header field.
5.2. Obsolete Line Folding
Historically, HTTP header field values could be extended over
multiple lines by preceding each extra line with at least one space
or horizontal tab (obs-fold). This specification deprecates such
line folding except within the message/http media type
(Section 10.1).
obs-fold = CRLF 1*( SP / HTAB )
; obsolete line folding
A sender MUST NOT generate a message that includes line folding
(i.e., that has any field-value that contains a match to the obs-fold
rule) unless the message is intended for packaging within the
message/http media type.
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A server that receives an obs-fold in a request message that is not
within a message/http container MUST either reject the message by
sending a 400 (Bad Request), preferably with a representation
explaining that obsolete line folding is unacceptable, or replace
each received obs-fold with one or more SP octets prior to
interpreting the field value or forwarding the message downstream.
A proxy or gateway that receives an obs-fold in a response message
that is not within a message/http container MUST either discard the
message and replace it with a 502 (Bad Gateway) response, preferably
with a representation explaining that unacceptable line folding was
received, or replace each received obs-fold with one or more SP
octets prior to interpreting the field value or forwarding the
message downstream.
A user agent that receives an obs-fold in a response message that is
not within a message/http container MUST replace each received obs-
fold with one or more SP octets prior to interpreting the field
value.
6. Message Body
The message body (if any) of an HTTP message is used to carry the
payload body of that request or response. The message body is
identical to the payload body unless a transfer coding has been
applied, as described in Section 6.1.
message-body = *OCTET
The rules for when a message body is allowed in a message differ for
requests and responses.
The presence of a message body in a request is signaled by a Content-
Length or Transfer-Encoding header field. Request message framing is
independent of method semantics, even if the method does not define
any use for a message body.
The presence of a message body in a response depends on both the
request method to which it is responding and the response status code
(Section 4). Responses to the HEAD request method (Section 7.3.2 of
[Semantics]) never include a message body because the associated
response header fields (e.g., Transfer-Encoding, Content-Length,
etc.), if present, indicate only what their values would have been if
the request method had been GET (Section 7.3.1 of [Semantics]). 2xx
(Successful) responses to a CONNECT request method (Section 7.3.6 of
[Semantics]) switch to tunnel mode instead of having a message body.
All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
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responses do not include a message body. All other responses do
include a message body, although the body might be of zero length.
6.1. Transfer-Encoding
The Transfer-Encoding header field lists the transfer coding names
corresponding to the sequence of transfer codings that have been (or
will be) applied to the payload body in order to form the message
body. Transfer codings are defined in Section 7.
Transfer-Encoding = 1#transfer-coding
Transfer-Encoding is analogous to the Content-Transfer-Encoding field
of MIME, which was designed to enable safe transport of binary data
over a 7-bit transport service ([RFC2045], Section 6). However, safe
transport has a different focus for an 8bit-clean transfer protocol.
In HTTP's case, Transfer-Encoding is primarily intended to accurately
delimit a dynamically generated payload and to distinguish payload
encodings that are only applied for transport efficiency or security
from those that are characteristics of the selected resource.
A recipient MUST be able to parse the chunked transfer coding
(Section 7.1) because it plays a crucial role in framing messages
when the payload body size is not known in advance. A sender MUST
NOT apply chunked more than once to a message body (i.e., chunking an
already chunked message is not allowed). If any transfer coding
other than chunked is applied to a request payload body, the sender
MUST apply chunked as the final transfer coding to ensure that the
message is properly framed. If any transfer coding other than
chunked is applied to a response payload body, the sender MUST either
apply chunked as the final transfer coding or terminate the message
by closing the connection.
For example,
Transfer-Encoding: gzip, chunked
indicates that the payload body has been compressed using the gzip
coding and then chunked using the chunked coding while forming the
message body.
Unlike Content-Encoding (Section 6.1.2 of [Semantics]), Transfer-
Encoding is a property of the message, not of the representation, and
any recipient along the request/response chain MAY decode the
received transfer coding(s) or apply additional transfer coding(s) to
the message body, assuming that corresponding changes are made to the
Transfer-Encoding field-value. Additional information about the
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encoding parameters can be provided by other header fields not
defined by this specification.
Transfer-Encoding MAY be sent in a response to a HEAD request or in a
304 (Not Modified) response (Section 9.4.5 of [Semantics]) to a GET
request, neither of which includes a message body, to indicate that
the origin server would have applied a transfer coding to the message
body if the request had been an unconditional GET. This indication
is not required, however, because any recipient on the response chain
(including the origin server) can remove transfer codings when they
are not needed.
A server MUST NOT send a Transfer-Encoding header field in any
response with a status code of 1xx (Informational) or 204 (No
Content). A server MUST NOT send a Transfer-Encoding header field in
any 2xx (Successful) response to a CONNECT request (Section 7.3.6 of
[Semantics]).
Transfer-Encoding was added in HTTP/1.1. It is generally assumed
that implementations advertising only HTTP/1.0 support will not
understand how to process a transfer-encoded payload. A client MUST
NOT send a request containing Transfer-Encoding unless it knows the
server will handle HTTP/1.1 (or later) requests; such knowledge might
be in the form of specific user configuration or by remembering the
version of a prior received response. A server MUST NOT send a
response containing Transfer-Encoding unless the corresponding
request indicates HTTP/1.1 (or later).
A server that receives a request message with a transfer coding it
does not understand SHOULD respond with 501 (Not Implemented).
6.2. Content-Length
When a message does not have a Transfer-Encoding header field, a
Content-Length header field can provide the anticipated size, as a
decimal number of octets, for a potential payload body. For messages
that do include a payload body, the Content-Length field-value
provides the framing information necessary for determining where the
body (and message) ends. For messages that do not include a payload
body, the Content-Length indicates the size of the selected
representation (Section 6.2.4 of [Semantics]).
Note: HTTP's use of Content-Length for message framing differs
significantly from the same field's use in MIME, where it is an
optional field used only within the "message/external-body" media-
type.
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6.3. Message Body Length
The length of a message body is determined by one of the following
(in order of precedence):
1. Any response to a HEAD request and any response with a 1xx
(Informational), 204 (No Content), or 304 (Not Modified) status
code is always terminated by the first empty line after the
header fields, regardless of the header fields present in the
message, and thus cannot contain a message body.
2. Any 2xx (Successful) response to a CONNECT request implies that
the connection will become a tunnel immediately after the empty
line that concludes the header fields. A client MUST ignore any
Content-Length or Transfer-Encoding header fields received in
such a message.
3. If a Transfer-Encoding header field is present and the chunked
transfer coding (Section 7.1) is the final encoding, the message
body length is determined by reading and decoding the chunked
data until the transfer coding indicates the data is complete.
If a Transfer-Encoding header field is present in a response and
the chunked transfer coding is not the final encoding, the
message body length is determined by reading the connection until
it is closed by the server. If a Transfer-Encoding header field
is present in a request and the chunked transfer coding is not
the final encoding, the message body length cannot be determined
reliably; the server MUST respond with the 400 (Bad Request)
status code and then close the connection.
If a message is received with both a Transfer-Encoding and a
Content-Length header field, the Transfer-Encoding overrides the
Content-Length. Such a message might indicate an attempt to
perform request smuggling (Section 11.2) or response splitting
(Section 11.1) and ought to be handled as an error. A sender
MUST remove the received Content-Length field prior to forwarding
such a message downstream.
4. If a message is received without Transfer-Encoding and with
either multiple Content-Length header fields having differing
field-values or a single Content-Length header field having an
invalid value, then the message framing is invalid and the
recipient MUST treat it as an unrecoverable error. If this is a
request message, the server MUST respond with a 400 (Bad Request)
status code and then close the connection. If this is a response
message received by a proxy, the proxy MUST close the connection
to the server, discard the received response, and send a 502 (Bad
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Gateway) response to the client. If this is a response message
received by a user agent, the user agent MUST close the
connection to the server and discard the received response.
5. If a valid Content-Length header field is present without
Transfer-Encoding, its decimal value defines the expected message
body length in octets. If the sender closes the connection or
the recipient times out before the indicated number of octets are
received, the recipient MUST consider the message to be
incomplete and close the connection.
6. If this is a request message and none of the above are true, then
the message body length is zero (no message body is present).
7. Otherwise, this is a response message without a declared message
body length, so the message body length is determined by the
number of octets received prior to the server closing the
connection.
Since there is no way to distinguish a successfully completed, close-
delimited message from a partially received message interrupted by
network failure, a server SHOULD generate encoding or length-
delimited messages whenever possible. The close-delimiting feature
exists primarily for backwards compatibility with HTTP/1.0.
A server MAY reject a request that contains a message body but not a
Content-Length by responding with 411 (Length Required).
Unless a transfer coding other than chunked has been applied, a
client that sends a request containing a message body SHOULD use a
valid Content-Length header field if the message body length is known
in advance, rather than the chunked transfer coding, since some
existing services respond to chunked with a 411 (Length Required)
status code even though they understand the chunked transfer coding.
This is typically because such services are implemented via a gateway
that requires a content-length in advance of being called and the
server is unable or unwilling to buffer the entire request before
processing.
A user agent that sends a request containing a message body MUST send
a valid Content-Length header field if it does not know the server
will handle HTTP/1.1 (or later) requests; such knowledge can be in
the form of specific user configuration or by remembering the version
of a prior received response.
If the final response to the last request on a connection has been
completely received and there remains additional data to read, a user
agent MAY discard the remaining data or attempt to determine if that
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data belongs as part of the prior response body, which might be the
case if the prior message's Content-Length value is incorrect. A
client MUST NOT process, cache, or forward such extra data as a
separate response, since such behavior would be vulnerable to cache
poisoning.
7. Transfer Codings
Transfer coding names are used to indicate an encoding transformation
that has been, can be, or might need to be applied to a payload body
in order to ensure "safe transport" through the network. This
differs from a content coding in that the transfer coding is a
property of the message rather than a property of the representation
that is being transferred.
transfer-coding = "chunked" ; Section 7.1
/ "compress" ; [Semantics], Section 6.1.2.1
/ "deflate" ; [Semantics], Section 6.1.2.2
/ "gzip" ; [Semantics], Section 6.1.2.3
/ transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
Parameters are in the form of a name=value pair.
transfer-parameter = token BWS "=" BWS ( token / quoted-string )
All transfer-coding names are case-insensitive and ought to be
registered within the HTTP Transfer Coding registry, as defined in
Section 7.3. They are used in the TE (Section 7.4) and Transfer-
Encoding (Section 6.1) header fields.
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+------------+------------------------------------------+-----------+
| Name | Description | Reference |
+------------+------------------------------------------+-----------+
| chunked | Transfer in a series of chunks | Section 7 |
| | | .1 |
| compress | UNIX "compress" data format [Welch] | Section 7 |
| | | .2 |
| deflate | "deflate" compressed data ([RFC1951]) | Section 7 |
| | inside the "zlib" data format | .2 |
| | ([RFC1950]) | |
| gzip | GZIP file format [RFC1952] | Section 7 |
| | | .2 |
| trailers | (reserved) | Section 7 |
| x-compress | Deprecated (alias for compress) | Section 7 |
| | | .2 |
| x-gzip | Deprecated (alias for gzip) | Section 7 |
| | | .2 |
+------------+------------------------------------------+-----------+
Note: the coding name "trailers" is reserved because it would
clash with the use of the keyword "trailers" in the TE header
field (Section 7.4).
7.1. Chunked Transfer Coding
The chunked transfer coding wraps the payload body in order to
transfer it as a series of chunks, each with its own size indicator,
followed by an OPTIONAL trailer containing header fields. Chunked
enables content streams of unknown size to be transferred as a
sequence of length-delimited buffers, which enables the sender to
retain connection persistence and the recipient to know when it has
received the entire message.
chunked-body = *chunk
last-chunk
trailer-part
CRLF
chunk = chunk-size [ chunk-ext ] CRLF
chunk-data CRLF
chunk-size = 1*HEXDIG
last-chunk = 1*("0") [ chunk-ext ] CRLF
chunk-data = 1*OCTET ; a sequence of chunk-size octets
The chunk-size field is a string of hex digits indicating the size of
the chunk-data in octets. The chunked transfer coding is complete
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when a chunk with a chunk-size of zero is received, possibly followed
by a trailer, and finally terminated by an empty line.
A recipient MUST be able to parse and decode the chunked transfer
coding.
7.1.1. Chunk Extensions
The chunked encoding allows each chunk to include zero or more chunk
extensions, immediately following the chunk-size, for the sake of
supplying per-chunk metadata (such as a signature or hash), mid-
message control information, or randomization of message body size.
chunk-ext = *( BWS ";" BWS chunk-ext-name
[ BWS "=" BWS chunk-ext-val ] )
chunk-ext-name = token
chunk-ext-val = token / quoted-string
The chunked encoding is specific to each connection and is likely to
be removed or recoded by each recipient (including intermediaries)
before any higher-level application would have a chance to inspect
the extensions. Hence, use of chunk extensions is generally limited
to specialized HTTP services such as "long polling" (where client and
server can have shared expectations regarding the use of chunk
extensions) or for padding within an end-to-end secured connection.
A recipient MUST ignore unrecognized chunk extensions. A server
ought to limit the total length of chunk extensions received in a
request to an amount reasonable for the services provided, in the
same way that it applies length limitations and timeouts for other
parts of a message, and generate an appropriate 4xx (Client Error)
response if that amount is exceeded.
7.1.2. Chunked Trailer Part
A trailer allows the sender to include additional fields at the end
of a chunked message in order to supply metadata that might be
dynamically generated while the message body is sent, such as a
message integrity check, digital signature, or post-processing
status. The trailer fields are identical to header fields, except
they are sent in a chunked trailer instead of the message's header
section.
trailer-part = *( header-field CRLF )
A sender MUST NOT generate a trailer that contains a field necessary
for message framing (e.g., Transfer-Encoding and Content-Length),
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routing (e.g., Host), request modifiers (e.g., controls and
conditionals in Section 8 of [Semantics]), authentication (e.g., see
Section 8.5 of [Semantics] and [RFC6265]), response control data
(e.g., see Section 10.1 of [Semantics]), or determining how to
process the payload (e.g., Content-Encoding, Content-Type, Content-
Range, and Trailer).
When a chunked message containing a non-empty trailer is received,
the recipient MAY process the fields (aside from those forbidden
above) as if they were appended to the message's header section. A
recipient MUST ignore (or consider as an error) any fields that are
forbidden to be sent in a trailer, since processing them as if they
were present in the header section might bypass external security
filters.
Unless the request includes a TE header field indicating "trailers"
is acceptable, as described in Section 7.4, a server SHOULD NOT
generate trailer fields that it believes are necessary for the user
agent to receive. Without a TE containing "trailers", the server
ought to assume that the trailer fields might be silently discarded
along the path to the user agent. This requirement allows
intermediaries to forward a de-chunked message to an HTTP/1.0
recipient without buffering the entire response.
When a message includes a message body encoded with the chunked
transfer coding and the sender desires to send metadata in the form
of trailer fields at the end of the message, the sender SHOULD
generate a Trailer header field before the message body to indicate
which fields will be present in the trailers. This allows the
recipient to prepare for receipt of that metadata before it starts
processing the body, which is useful if the message is being streamed
and the recipient wishes to confirm an integrity check on the fly.
7.1.3. Decoding Chunked
A process for decoding the chunked transfer coding can be represented
in pseudo-code as:
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length := 0
read chunk-size, chunk-ext (if any), and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to decoded-body
length := length + chunk-size
read chunk-size, chunk-ext (if any), and CRLF
}
read trailer field
while (trailer field is not empty) {
if (trailer field is allowed to be sent in a trailer) {
append trailer field to existing header fields
}
read trailer-field
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
Remove Trailer from existing header fields
7.2. Transfer Codings for Compression
The following transfer coding names for compression are defined by
the same algorithm as their corresponding content coding:
compress (and x-compress) See Section 6.1.2.1 of [Semantics].
deflate See Section 6.1.2.2 of [Semantics].
gzip (and x-gzip) See Section 6.1.2.3 of [Semantics].
7.3. Transfer Coding Registry
The "HTTP Transfer Coding Registry" defines the namespace for
transfer coding names. It is maintained at
.
Registrations MUST include the following fields:
o Name
o Description
o Pointer to specification text
Names of transfer codings MUST NOT overlap with names of content
codings (Section 6.1.2 of [Semantics]) unless the encoding
transformation is identical, as is the case for the compression
codings defined in Section 7.2.
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The TE header field (Section 7.4) uses a pseudo parameter named "q"
as rank value when multiple transfer codings are acceptable. Future
registrations of transfer codings SHOULD NOT define parameters called
"q" (case-insensitively) in order to avoid ambiguities.
Values to be added to this namespace require IETF Review (see
Section 4.8 of [RFC8126]), and MUST conform to the purpose of
transfer coding defined in this specification.
Use of program names for the identification of encoding formats is
not desirable and is discouraged for future encodings.
7.4. TE
The "TE" header field in a request indicates what transfer codings,
besides chunked, the client is willing to accept in response, and
whether or not the client is willing to accept trailer fields in a
chunked transfer coding.
The TE field-value consists of a comma-separated list of transfer
coding names, each allowing for optional parameters (as described in
Section 7), and/or the keyword "trailers". A client MUST NOT send
the chunked transfer coding name in TE; chunked is always acceptable
for HTTP/1.1 recipients.
TE = #t-codings
t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
t-ranking = OWS ";" OWS "q=" rank
rank = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] )
Three examples of TE use are below.
TE: deflate
TE:
TE: trailers, deflate;q=0.5
The presence of the keyword "trailers" indicates that the client is
willing to accept trailer fields in a chunked transfer coding, as
defined in Section 7.1.2, on behalf of itself and any downstream
clients. For requests from an intermediary, this implies that
either: (a) all downstream clients are willing to accept trailer
fields in the forwarded response; or, (b) the intermediary will
attempt to buffer the response on behalf of downstream recipients.
Note that HTTP/1.1 does not define any means to limit the size of a
chunked response such that an intermediary can be assured of
buffering the entire response.
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When multiple transfer codings are acceptable, the client MAY rank
the codings by preference using a case-insensitive "q" parameter
(similar to the qvalues used in content negotiation fields,
Section 8.4.1 of [Semantics]). The rank value is a real number in
the range 0 through 1, where 0.001 is the least preferred and 1 is
the most preferred; a value of 0 means "not acceptable".
If the TE field-value is empty or if no TE field is present, the only
acceptable transfer coding is chunked. A message with no transfer
coding is always acceptable.
Since the TE header field only applies to the immediate connection, a
sender of TE MUST also send a "TE" connection option within the
Connection header field (Section 9.1) in order to prevent the TE
field from being forwarded by intermediaries that do not support its
semantics.
8. Handling Incomplete Messages
A server that receives an incomplete request message, usually due to
a canceled request or a triggered timeout exception, MAY send an
error response prior to closing the connection.
A client that receives an incomplete response message, which can
occur when a connection is closed prematurely or when decoding a
supposedly chunked transfer coding fails, MUST record the message as
incomplete. Cache requirements for incomplete responses are defined
in Section 3 of [Caching].
If a response terminates in the middle of the header section (before
the empty line is received) and the status code might rely on header
fields to convey the full meaning of the response, then the client
cannot assume that meaning has been conveyed; the client might need
to repeat the request in order to determine what action to take next.
A message body that uses the chunked transfer coding is incomplete if
the zero-sized chunk that terminates the encoding has not been
received. A message that uses a valid Content-Length is incomplete
if the size of the message body received (in octets) is less than the
value given by Content-Length. A response that has neither chunked
transfer coding nor Content-Length is terminated by closure of the
connection and, thus, is considered complete regardless of the number
of message body octets received, provided that the header section was
received intact.
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9. Connection Management
HTTP messaging is independent of the underlying transport- or
session-layer connection protocol(s). HTTP only presumes a reliable
transport with in-order delivery of requests and the corresponding
in-order delivery of responses. The mapping of HTTP request and
response structures onto the data units of an underlying transport
protocol is outside the scope of this specification.
As described in Section 5.2 of [Semantics], the specific connection
protocols to be used for an HTTP interaction are determined by client
configuration and the target URI. For example, the "http" URI scheme
(Section 2.5.1 of [Semantics]) indicates a default connection of TCP
over IP, with a default TCP port of 80, but the client might be
configured to use a proxy via some other connection, port, or
protocol.
HTTP implementations are expected to engage in connection management,
which includes maintaining the state of current connections,
establishing a new connection or reusing an existing connection,
processing messages received on a connection, detecting connection
failures, and closing each connection. Most clients maintain
multiple connections in parallel, including more than one connection
per server endpoint. Most servers are designed to maintain thousands
of concurrent connections, while controlling request queues to enable
fair use and detect denial-of-service attacks.
9.1. Connection
The "Connection" header field allows the sender to indicate desired
control options for the current connection. In order to avoid
confusing downstream recipients, a proxy or gateway MUST remove or
replace any received connection options before forwarding the
message.
When a header field aside from Connection is used to supply control
information for or about the current connection, the sender MUST list
the corresponding field-name within the Connection header field. A
proxy or gateway MUST parse a received Connection header field before
a message is forwarded and, for each connection-option in this field,
remove any header field(s) from the message with the same name as the
connection-option, and then remove the Connection header field itself
(or replace it with the intermediary's own connection options for the
forwarded message).
Hence, the Connection header field provides a declarative way of
distinguishing header fields that are only intended for the immediate
recipient ("hop-by-hop") from those fields that are intended for all
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recipients on the chain ("end-to-end"), enabling the message to be
self-descriptive and allowing future connection-specific extensions
to be deployed without fear that they will be blindly forwarded by
older intermediaries.
The Connection header field's value has the following grammar:
Connection = 1#connection-option
connection-option = token
Connection options are case-insensitive.
A sender MUST NOT send a connection option corresponding to a header
field that is intended for all recipients of the payload. For
example, Cache-Control is never appropriate as a connection option
(Section 5.2 of [Caching]).
The connection options do not always correspond to a header field
present in the message, since a connection-specific header field
might not be needed if there are no parameters associated with a
connection option. In contrast, a connection-specific header field
that is received without a corresponding connection option usually
indicates that the field has been improperly forwarded by an
intermediary and ought to be ignored by the recipient.
When defining new connection options, specification authors ought to
survey existing header field names and ensure that the new connection
option does not share the same name as an already deployed header
field. Defining a new connection option essentially reserves that
potential field-name for carrying additional information related to
the connection option, since it would be unwise for senders to use
that field-name for anything else.
The ""close"" connection option is defined for a sender to signal
that this connection will be closed after completion of the response.
For example,
Connection: close
in either the request or the response header fields indicates that
the sender is going to close the connection after the current
request/response is complete (Section 9.6).
A client that does not support persistent connections MUST send the
"close" connection option in every request message.
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A server that does not support persistent connections MUST send the
"close" connection option in every response message that does not
have a 1xx (Informational) status code.
9.2. Establishment
It is beyond the scope of this specification to describe how
connections are established via various transport- or session-layer
protocols. Each connection applies to only one transport link.
9.3. Persistence
HTTP/1.1 defaults to the use of ""persistent connections"", allowing
multiple requests and responses to be carried over a single
connection. The "close" connection option is used to signal that a
connection will not persist after the current request/response. HTTP
implementations SHOULD support persistent connections.
A recipient determines whether a connection is persistent or not
based on the most recently received message's protocol version and
Connection header field (if any):
o If the "close" connection option is present, the connection will
not persist after the current response; else,
o If the received protocol is HTTP/1.1 (or later), the connection
will persist after the current response; else,
o If the received protocol is HTTP/1.0, the "keep-alive" connection
option is present, either the recipient is not a proxy or the
message is a response, and the recipient wishes to honor the
HTTP/1.0 "keep-alive" mechanism, the connection will persist after
the current response; otherwise,
o The connection will close after the current response.
A client MAY send additional requests on a persistent connection
until it sends or receives a "close" connection option or receives an
HTTP/1.0 response without a "keep-alive" connection option.
In order to remain persistent, all messages on a connection need to
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in Section 6. A server MUST read
the entire request message body or close the connection after sending
its response, since otherwise the remaining data on a persistent
connection would be misinterpreted as the next request. Likewise, a
client MUST read the entire response message body if it intends to
reuse the same connection for a subsequent request.
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A proxy server MUST NOT maintain a persistent connection with an
HTTP/1.0 client (see Section 19.7.1 of [RFC2068] for information and
discussion of the problems with the Keep-Alive header field
implemented by many HTTP/1.0 clients).
See Appendix C.1.2 for more information on backwards compatibility
with HTTP/1.0 clients.
9.3.1. Retrying Requests
Connections can be closed at any time, with or without intention.
Implementations ought to anticipate the need to recover from
asynchronous close events.
When an inbound connection is closed prematurely, a client MAY open a
new connection and automatically retransmit an aborted sequence of
requests if all of those requests have idempotent methods
(Section 7.2.2 of [Semantics]). A proxy MUST NOT automatically retry
non-idempotent requests.
A user agent MUST NOT automatically retry a request with a non-
idempotent method unless it has some means to know that the request
semantics are actually idempotent, regardless of the method, or some
means to detect that the original request was never applied. For
example, a user agent that knows (through design or configuration)
that a POST request to a given resource is safe can repeat that
request automatically. Likewise, a user agent designed specifically
to operate on a version control repository might be able to recover
from partial failure conditions by checking the target resource
revision(s) after a failed connection, reverting or fixing any
changes that were partially applied, and then automatically retrying
the requests that failed.
A client SHOULD NOT automatically retry a failed automatic retry.
9.3.2. Pipelining
A client that supports persistent connections MAY ""pipeline"" its
requests (i.e., send multiple requests without waiting for each
response). A server MAY process a sequence of pipelined requests in
parallel if they all have safe methods (Section 7.2.1 of
[Semantics]), but it MUST send the corresponding responses in the
same order that the requests were received.
A client that pipelines requests SHOULD retry unanswered requests if
the connection closes before it receives all of the corresponding
responses. When retrying pipelined requests after a failed
connection (a connection not explicitly closed by the server in its
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last complete response), a client MUST NOT pipeline immediately after
connection establishment, since the first remaining request in the
prior pipeline might have caused an error response that can be lost
again if multiple requests are sent on a prematurely closed
connection (see the TCP reset problem described in Section 9.6).
Idempotent methods (Section 7.2.2 of [Semantics]) are significant to
pipelining because they can be automatically retried after a
connection failure. A user agent SHOULD NOT pipeline requests after
a non-idempotent method, until the final response status code for
that method has been received, unless the user agent has a means to
detect and recover from partial failure conditions involving the
pipelined sequence.
An intermediary that receives pipelined requests MAY pipeline those
requests when forwarding them inbound, since it can rely on the
outbound user agent(s) to determine what requests can be safely
pipelined. If the inbound connection fails before receiving a
response, the pipelining intermediary MAY attempt to retry a sequence
of requests that have yet to receive a response if the requests all
have idempotent methods; otherwise, the pipelining intermediary
SHOULD forward any received responses and then close the
corresponding outbound connection(s) so that the outbound user
agent(s) can recover accordingly.
9.4. Concurrency
A client ought to limit the number of simultaneous open connections
that it maintains to a given server.
Previous revisions of HTTP gave a specific number of connections as a
ceiling, but this was found to be impractical for many applications.
As a result, this specification does not mandate a particular maximum
number of connections but, instead, encourages clients to be
conservative when opening multiple connections.
Multiple connections are typically used to avoid the "head-of-line
blocking" problem, wherein a request that takes significant server-
side processing and/or has a large payload blocks subsequent requests
on the same connection. However, each connection consumes server
resources. Furthermore, using multiple connections can cause
undesirable side effects in congested networks.
Note that a server might reject traffic that it deems abusive or
characteristic of a denial-of-service attack, such as an excessive
number of open connections from a single client.
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9.5. Failures and Timeouts
Servers will usually have some timeout 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 proxy server. The use of
persistent connections places no requirements on the length (or
existence) of this timeout for either the client or the server.
A client or server that wishes to time out SHOULD issue a graceful
close on the connection. Implementations SHOULD constantly monitor
open connections for a received closure signal and respond to it as
appropriate, since prompt closure of both sides of a connection
enables allocated system resources to be reclaimed.
A client, server, or proxy MAY close the transport connection at any
time. For example, a client might have started to send a new request
at the same time that the server has decided to close the "idle"
connection. From the server's point of view, the connection is being
closed while it was idle, but from the client's point of view, a
request is in progress.
A server SHOULD sustain persistent connections, when possible, and
allow the underlying transport's flow-control mechanisms to resolve
temporary overloads, rather than terminate connections with the
expectation that clients will retry. The latter technique can
exacerbate network congestion.
A client sending a message body SHOULD monitor the network connection
for an error response while it is transmitting the request. If the
client sees a response that indicates the server does not wish to
receive the message body and is closing the connection, the client
SHOULD immediately cease transmitting the body and close its side of
the connection.
9.6. Tear-down
The Connection header field (Section 9.1) provides a "close"
connection option that a sender SHOULD send when it wishes to close
the connection after the current request/response pair.
A client that sends a "close" connection option MUST NOT send further
requests on that connection (after the one containing "close") and
MUST close the connection after reading the final response message
corresponding to this request.
A server that receives a "close" connection option MUST initiate a
close of the connection (see below) after it sends the final response
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to the request that contained "close". The server SHOULD send a
"close" connection option in its final response on that connection.
The server MUST NOT process any further requests received on that
connection.
A server that sends a "close" connection option MUST initiate a close
of the connection (see below) after it sends the response containing
"close". The server MUST NOT process any further requests received
on that connection.
A client that receives a "close" connection option MUST cease sending
requests on that connection and close the connection after reading
the response message containing the "close"; if additional pipelined
requests had been sent on the connection, the client SHOULD NOT
assume that they will be processed by the server.
If a server performs an immediate close of a TCP connection, there is
a significant risk that the client will not be able to read the last
HTTP response. If the server receives additional data from the
client on a fully closed connection, such as another request that was
sent by the client before receiving the server's response, the
server's TCP stack will send a reset packet to the client;
unfortunately, the reset packet might erase the client's
unacknowledged input buffers before they can be read and interpreted
by the client's HTTP parser.
To avoid the TCP reset problem, servers typically close a connection
in stages. First, the server performs a half-close by closing only
the write side of the read/write connection. The server then
continues to read from the connection until it receives a
corresponding close by the client, or until the server is reasonably
certain that its own TCP stack has received the client's
acknowledgement of the packet(s) containing the server's last
response. Finally, the server fully closes the connection.
It is unknown whether the reset problem is exclusive to TCP or might
also be found in other transport connection protocols.
9.7. Upgrade
The "Upgrade" header field is intended to provide a simple mechanism
for transitioning from HTTP/1.1 to some other protocol on the same
connection. A client MAY send a list of protocols in the Upgrade
header field of a request to invite the server to switch to one or
more of those protocols, in order of descending preference, before
sending the final response. A server MAY ignore a received Upgrade
header field if it wishes to continue using the current protocol on
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that connection. Upgrade cannot be used to insist on a protocol
change.
Upgrade = 1#protocol
protocol = protocol-name ["/" protocol-version]
protocol-name = token
protocol-version = token
A server that sends a 101 (Switching Protocols) response MUST send an
Upgrade header field to indicate the new protocol(s) to which the
connection is being switched; if multiple protocol layers are being
switched, the sender MUST list the protocols in layer-ascending
order. A server MUST NOT switch to a protocol that was not indicated
by the client in the corresponding request's Upgrade header field. A
server MAY choose to ignore the order of preference indicated by the
client and select the new protocol(s) based on other factors, such as
the nature of the request or the current load on the server.
A server that sends a 426 (Upgrade Required) response MUST send an
Upgrade header field to indicate the acceptable protocols, in order
of descending preference.
A server MAY send an Upgrade header field in any other response to
advertise that it implements support for upgrading to the listed
protocols, in order of descending preference, when appropriate for a
future request.
The following is a hypothetical example sent by a client:
GET /hello.txt HTTP/1.1
Host: www.example.com
Connection: upgrade
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
The capabilities and nature of the application-level communication
after the protocol change is entirely dependent upon the new
protocol(s) chosen. However, immediately after sending the 101
(Switching Protocols) response, the server is expected to continue
responding to the original request as if it had received its
equivalent within the new protocol (i.e., the server still has an
outstanding request to satisfy after the protocol has been changed,
and is expected to do so without requiring the request to be
repeated).
For example, if the Upgrade header field is received in a GET request
and the server decides to switch protocols, it first responds with a
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101 (Switching Protocols) message in HTTP/1.1 and then immediately
follows that with the new protocol's equivalent of a response to a
GET on the target resource. This allows a connection to be upgraded
to protocols with the same semantics as HTTP without the latency cost
of an additional round trip. A server MUST NOT switch protocols
unless the received message semantics can be honored by the new
protocol; an OPTIONS request can be honored by any protocol.
The following is an example response to the above hypothetical
request:
HTTP/1.1 101 Switching Protocols
Connection: upgrade
Upgrade: HTTP/2.0
[... data stream switches to HTTP/2.0 with an appropriate response
(as defined by new protocol) to the "GET /hello.txt" request ...]
When Upgrade is sent, the sender MUST also send a Connection header
field (Section 9.1) that contains an "upgrade" connection option, in
order to prevent Upgrade from being accidentally forwarded by
intermediaries that might not implement the listed protocols. A
server MUST ignore an Upgrade header field that is received in an
HTTP/1.0 request.
A client cannot begin using an upgraded protocol on the connection
until it has completely sent the request message (i.e., the client
can't change the protocol it is sending in the middle of a message).
If a server receives both an Upgrade and an Expect header field with
the "100-continue" expectation (Section 8.1.1 of [Semantics]), the
server MUST send a 100 (Continue) response before sending a 101
(Switching Protocols) response.
The Upgrade header field only applies to switching protocols on top
of the existing connection; it cannot be used to switch the
underlying connection (transport) protocol, nor to switch the
existing communication to a different connection. For those
purposes, it is more appropriate to use a 3xx (Redirection) response
(Section 9.4 of [Semantics]).
9.7.1. Upgrade Protocol Names
This specification only defines the protocol name "HTTP" for use by
the family of Hypertext Transfer Protocols, as defined by the HTTP
version rules of Section 3.5 of [Semantics] and future updates to
this specification. Additional protocol names ought to be registered
using the registration procedure defined in Section 9.7.2.
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+------+-------------------+--------------------+-------------------+
| Name | Description | Expected Version | Reference |
| | | Tokens | |
+------+-------------------+--------------------+-------------------+
| HTTP | Hypertext | any DIGIT.DIGIT | Section 3.5 of |
| | Transfer Protocol | (e.g, "2.0") | [Semantics] |
+------+-------------------+--------------------+-------------------+
9.7.2. Upgrade Token Registry
The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry"
defines the namespace for protocol-name tokens used to identify
protocols in the Upgrade header field. The registry is maintained at
.
Each registered protocol name is associated with contact information
and an optional set of specifications that details how the connection
will be processed after it has been upgraded.
Registrations happen on a "First Come First Served" basis (see
Section 4.4 of [RFC8126]) and are subject to the following rules:
1. A protocol-name token, once registered, stays registered forever.
2. The registration MUST name a responsible party for the
registration.
3. The registration MUST name a point of contact.
4. The registration MAY name a set of specifications associated with
that token. Such specifications need not be publicly available.
5. The registration SHOULD name a set of expected "protocol-version"
tokens associated with that token at the time of registration.
6. The responsible party MAY change the registration at any time.
The IANA will keep a record of all such changes, and make them
available upon request.
7. The IESG MAY reassign responsibility for a protocol token. This
will normally only be used in the case when a responsible party
cannot be contacted.
10. Enclosing Messages as Data
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10.1. Media Type message/http
The message/http media type can be used to enclose a single HTTP
request or response message, provided that it obeys the MIME
restrictions for all "message" types regarding line length and
encodings.
Type name: message
Subtype name: http
Required parameters: N/A
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: see Section 11
Interoperability considerations: N/A
Published specification: This specification (see Section 10.1).
Applications that use this media type: N/A
Fragment identifier considerations: N/A
Additional information:
Magic number(s): N/A
Deprecated alias names for this type: N/A
File extension(s): N/A
Macintosh file type code(s): N/A
Person and email address to contact for further information:
See Authors' Addresses section.
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Intended usage: COMMON
Restrictions on usage: N/A
Author: See Authors' Addresses section.
Change controller: IESG
10.2. Media Type application/http
The application/http media 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: N/A
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 email.
Security considerations: see Section 11
Interoperability considerations: N/A
Published specification: This specification (see Section 10.2).
Applications that use this media type: N/A
Fragment identifier considerations: N/A
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
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File extension(s): N/A
Macintosh file type code(s): N/A
Person and email address to contact for further information:
See Authors' Addresses section.
Intended usage: COMMON
Restrictions on usage: N/A
Author: See Authors' Addresses section.
Change controller: IESG
11. Security Considerations
This section is meant to inform developers, information providers,
and users of known security considerations relevant to HTTP message
syntax, parsing, and routing. Security considerations about HTTP
semantics and payloads are addressed in [Semantics].
11.1. Response Splitting
Response splitting (a.k.a, CRLF injection) is a common technique,
used in various attacks on Web usage, that exploits the line-based
nature of HTTP message framing and the ordered association of
requests to responses on persistent connections [Klein]. This
technique can be particularly damaging when the requests pass through
a shared cache.
Response splitting exploits a vulnerability in servers (usually
within an application server) where an attacker can send encoded data
within some parameter of the request that is later decoded and echoed
within any of the response header fields of the response. If the
decoded data is crafted to look like the response has ended and a
subsequent response has begun, the response has been split and the
content within the apparent second response is controlled by the
attacker. The attacker can then make any other request on the same
persistent connection and trick the recipients (including
intermediaries) into believing that the second half of the split is
an authoritative answer to the second request.
For example, a parameter within the request-target might be read by
an application server and reused within a redirect, resulting in the
same parameter being echoed in the Location header field of the
response. If the parameter is decoded by the application and not
properly encoded when placed in the response field, the attacker can
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send encoded CRLF octets and other content that will make the
application's single response look like two or more responses.
A common defense against response splitting is to filter requests for
data that looks like encoded CR and LF (e.g., "%0D" and "%0A").
However, that assumes the application server is only performing URI
decoding, rather than more obscure data transformations like charset
transcoding, XML entity translation, base64 decoding, sprintf
reformatting, etc. A more effective mitigation is to prevent
anything other than the server's core protocol libraries from sending
a CR or LF within the header section, which means restricting the
output of header fields to APIs that filter for bad octets and not
allowing application servers to write directly to the protocol
stream.
11.2. Request Smuggling
Request smuggling ([Linhart]) is a technique that exploits
differences in protocol parsing among various recipients to hide
additional requests (which might otherwise be blocked or disabled by
policy) within an apparently harmless request. Like response
splitting, request smuggling can lead to a variety of attacks on HTTP
usage.
This specification has introduced new requirements on request
parsing, particularly with regard to message framing in Section 6.3,
to reduce the effectiveness of request smuggling.
11.3. Message Integrity
HTTP does not define a specific mechanism for ensuring message
integrity, instead relying on the error-detection ability of
underlying transport protocols and the use of length or chunk-
delimited framing to detect completeness. Additional integrity
mechanisms, such as hash functions or digital signatures applied to
the content, can be selectively added to messages via extensible
metadata header fields. Historically, the lack of a single integrity
mechanism has been justified by the informal nature of most HTTP
communication. However, the prevalence of HTTP as an information
access mechanism has resulted in its increasing use within
environments where verification of message integrity is crucial.
User agents are encouraged to implement configurable means for
detecting and reporting failures of message integrity such that those
means can be enabled within environments for which integrity is
necessary. For example, a browser being used to view medical history
or drug interaction information needs to indicate to the user when
such information is detected by the protocol to be incomplete,
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expired, or corrupted during transfer. Such mechanisms might be
selectively enabled via user agent extensions or the presence of
message integrity metadata in a response. At a minimum, user agents
ought to provide some indication that allows a user to distinguish
between a complete and incomplete response message (Section 8) when
such verification is desired.
11.4. Message Confidentiality
HTTP relies on underlying transport protocols to provide message
confidentiality when that is desired. HTTP has been specifically
designed to be independent of the transport protocol, such that it
can be used over many different forms of encrypted connection, with
the selection of such transports being identified by the choice of
URI scheme or within user agent configuration.
The "https" scheme can be used to identify resources that require a
confidential connection, as described in Section 2.5.2 of
[Semantics].
12. IANA Considerations
The change controller for the following registrations is: "IETF
(iesg@ietf.org) - Internet Engineering Task Force".
12.1. Header Field Registration
Please update the "Message Headers" registry of "Permanent Message
Header Field Names" at with the header field names listed in the two tables of
Section 5.
12.2. Media Type Registration
Please update the "Media Types" registry at
with the registration
information in Section 10.1 and Section 10.2 for the media types
"message/http" and "application/http", respectively.
12.3. Transfer Coding Registration
Please update the "HTTP Transfer Coding Registry" at
with the
registration procedure of Section 7.3 and the content coding names
summarized in the table of Section 7.
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12.4. Upgrade Token Registration
Please update the "Hypertext Transfer Protocol (HTTP) Upgrade Token
Registry" at
with the registration procedure of Section 9.7.2 and the upgrade
token names summarized in the table of Section 9.7.1.
13. References
13.1. Normative References
[Caching] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", draft-ietf-httpbis-cache-02 (work in
progress), July 2018.
[RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format
Specification version 3.3", RFC 1950,
DOI 10.17487/RFC1950, May 1996,
.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, DOI 10.17487/RFC1951, May 1996,
.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
Randers-Pehrson, "GZIP file format specification version
4.3", RFC 1952, DOI 10.17487/RFC1952, May 1996,
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
.
[Semantics]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", draft-ietf-httpbis-semantics-02
(work in progress), July 2018.
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[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
[Welch] Welch, T., "A Technique for High-Performance Data
Compression", IEEE Computer 17(6), June 1984.
13.2. Informative References
[Err4667] RFC Errata, Erratum ID 4667, RFC 7230,
.
[Klein] Klein, A., "Divide and Conquer - HTTP Response Splitting,
Web Cache Poisoning Attacks, and Related Topics", March
2004, .
[Linhart] Linhart, C., Klein, A., Heled, R., and S. Orrin, "HTTP
Request Smuggling", June 2005,
.
[RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945,
DOI 10.17487/RFC1945, May 1996,
.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
.
[RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Five: Conformance Criteria and
Examples", RFC 2049, DOI 10.17487/RFC2049, November 1996,
.
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2068, DOI 10.17487/RFC2068, January 1997,
.
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[RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud,
"MIME Encapsulation of Aggregate Documents, such as HTML
(MHTML)", RFC 2557, DOI 10.17487/RFC2557, March 1999,
.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
.
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Appendix A. Collected ABNF
In the collected ABNF below, list rules are expanded as per
Section 11 of [Semantics].
BWS =
Connection = *( "," OWS ) connection-option *( OWS "," [ OWS
connection-option ] )
HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
]
HTTP-name = %x48.54.54.50 ; HTTP
HTTP-version = HTTP-name "/" DIGIT "." DIGIT
OWS =
RWS =
TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
transfer-coding ] )
Upgrade = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
absolute-URI =
absolute-form = absolute-URI
absolute-path =
asterisk-form = "*"
authority =
authority-form = authority
chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
chunk-data = 1*OCTET
chunk-ext = *( BWS ";" BWS chunk-ext-name [ BWS "=" BWS chunk-ext-val
] )
chunk-ext-name = token
chunk-ext-val = token / quoted-string
chunk-size = 1*HEXDIG
chunked-body = *chunk last-chunk trailer-part CRLF
comment =
connection-option = token
field-name =
field-value =
header-field = field-name ":" OWS field-value OWS
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last-chunk = 1*"0" [ chunk-ext ] CRLF
message-body = *OCTET
method = token
obs-fold = CRLF 1*( SP / HTAB )
obs-text =
origin-form = absolute-path [ "?" query ]
port =
protocol = protocol-name [ "/" protocol-version ]
protocol-name = token
protocol-version = token
query =
quoted-string =
rank = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
reason-phrase = *( HTAB / SP / VCHAR / obs-text )
request-line = method SP request-target SP HTTP-version CRLF
request-target = origin-form / absolute-form / authority-form /
asterisk-form
start-line = request-line / status-line
status-code = 3DIGIT
status-line = HTTP-version SP status-code SP reason-phrase CRLF
t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
t-ranking = OWS ";" OWS "q=" rank
token =
trailer-part = *( header-field CRLF )
transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
transfer-extension
transfer-extension = token *( OWS ";" OWS transfer-parameter )
transfer-parameter = token BWS "=" BWS ( token / quoted-string )
uri-host =
Appendix B. Differences between HTTP and MIME
HTTP/1.1 uses many of the constructs defined for the Internet Message
Format [RFC5322] and the Multipurpose Internet Mail Extensions (MIME)
[RFC2045] to allow a message body to be transmitted in an open
variety of representations and with extensible header fields.
However, RFC 2045 is focused only on email; applications of HTTP have
many characteristics that differ from email; hence, HTTP has features
that differ from MIME. These differences were carefully chosen to
optimize performance over binary connections, to allow greater
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freedom in the use of new media types, to make date comparisons
easier, and to acknowledge the practice of some early HTTP servers
and clients.
This appendix describes specific areas where HTTP differs from MIME.
Proxies and gateways to and from strict MIME environments need to be
aware of these differences and provide the appropriate conversions
where necessary.
B.1. MIME-Version
HTTP is not a MIME-compliant protocol. However, messages can include
a single MIME-Version header field to indicate what version of the
MIME protocol was used to construct the message. Use of the MIME-
Version header field indicates that the message is in full
conformance with the MIME protocol (as defined in [RFC2045]).
Senders are responsible for ensuring full conformance (where
possible) when exporting HTTP messages to strict MIME environments.
B.2. Conversion to Canonical Form
MIME requires that an Internet mail body part be converted to
canonical form prior to being transferred, as described in Section 4
of [RFC2049]. Section 6.1.1.2 of [Semantics] describes the forms
allowed for subtypes of the "text" media type when transmitted over
HTTP. [RFC2046] requires that content with a type of "text"
represent line breaks as CRLF and forbids the use of CR or LF outside
of line break sequences. HTTP allows CRLF, bare CR, and bare LF to
indicate a line break within text content.
A proxy or gateway from HTTP to a strict MIME environment ought to
translate all line breaks within text media types to the RFC 2049
canonical form of CRLF. Note, however, this might be complicated by
the presence of a Content-Encoding and by the fact that HTTP allows
the use of some charsets that do not use octets 13 and 10 to
represent CR and LF, respectively.
Conversion will break any cryptographic checksums applied to the
original content unless the original content is already in canonical
form. Therefore, the canonical form is recommended for any content
that uses such checksums in HTTP.
B.3. Conversion of Date Formats
HTTP/1.1 uses a restricted set of date formats (Section 10.1.1.1 of
[Semantics]) to simplify the process of date comparison. Proxies and
gateways from other protocols ought to ensure that any Date header
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field present in a message conforms to one of the HTTP/1.1 formats
and rewrite the date if necessary.
B.4. Conversion of Content-Encoding
MIME does not include any concept equivalent to HTTP/1.1's Content-
Encoding header field. Since this acts as a modifier on the media
type, proxies and gateways from HTTP to MIME-compliant protocols
ought to either change the value of the Content-Type header field or
decode the representation before forwarding the message. (Some
experimental applications of Content-Type for Internet mail have used
a media-type parameter of ";conversions=" to perform
a function equivalent to Content-Encoding. However, this parameter
is not part of the MIME standards).
B.5. Conversion of Content-Transfer-Encoding
HTTP does not use the Content-Transfer-Encoding field of MIME.
Proxies and gateways from MIME-compliant protocols to HTTP need to
remove any Content-Transfer-Encoding prior to delivering the response
message to an HTTP client.
Proxies and gateways from HTTP to MIME-compliant protocols are
responsible for ensuring that the message is in the correct format
and encoding for safe transport on that protocol, where "safe
transport" is defined by the limitations of the protocol being used.
Such a proxy or gateway ought to transform and label the data with an
appropriate Content-Transfer-Encoding if doing so will improve the
likelihood of safe transport over the destination protocol.
B.6. MHTML and Line Length Limitations
HTTP implementations that share code with MHTML [RFC2557]
implementations need to be aware of MIME line length limitations.
Since HTTP does not have this limitation, HTTP does not fold long
lines. MHTML messages being transported by HTTP follow all
conventions of MHTML, including line length limitations and folding,
canonicalization, etc., since HTTP transfers message-bodies as
payload and, aside from the "multipart/byteranges" type
(Section 6.3.4 of [Semantics]), does not interpret the content or any
MIME header lines that might be contained therein.
Appendix C. HTTP Version History
HTTP has been in use since 1990. The first version, later referred
to as HTTP/0.9, was a simple protocol for hypertext data transfer
across the Internet, using only a single request method (GET) and no
metadata. HTTP/1.0, as defined by [RFC1945], added a range of
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request methods and MIME-like messaging, allowing for metadata to be
transferred and modifiers placed 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
features that can either be safely ignored by an HTTP/1.0 recipient
or only be sent when communicating with a party advertising
conformance with HTTP/1.1.
HTTP/1.1 has been designed to make supporting previous versions easy.
A general-purpose HTTP/1.1 server ought to be able to understand any
valid request in the format of HTTP/1.0, responding appropriately
with an HTTP/1.1 message that only uses features understood (or
safely ignored) by HTTP/1.0 clients. Likewise, an HTTP/1.1 client
can be expected to understand any valid HTTP/1.0 response.
Since HTTP/0.9 did not support header fields in a request, there is
no mechanism for it to support name-based virtual hosts (selection of
resource by inspection of the Host header field). Any server that
implements name-based virtual hosts ought to disable support for
HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in fact,
badly constructed HTTP/1.x requests caused by a client failing to
properly encode the request-target.
C.1. Changes from HTTP/1.0
This section summarizes major differences between versions HTTP/1.0
and HTTP/1.1.
C.1.1. Multihomed Web Servers
The requirements that clients and servers support the Host header
field (Section 5.4 of [Semantics]), report an error if it is missing
from an HTTP/1.1 request, and accept absolute URIs (Section 3.2) are
among the most important changes defined by HTTP/1.1.
Older HTTP/1.0 clients assumed a one-to-one relationship of IP
addresses and servers; there was no other established mechanism for
distinguishing the intended server of a request than the IP address
to which that request was directed. The Host header field was
introduced during the development of HTTP/1.1 and, though it was
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quickly implemented by most HTTP/1.0 browsers, additional
requirements were placed on all HTTP/1.1 requests in order to ensure
complete adoption. At the time of this writing, most HTTP-based
services are dependent upon the Host header field for targeting
requests.
C.1.2. Keep-Alive Connections
In HTTP/1.0, each connection is established by the client prior to
the request and closed by the server after sending the response.
However, some implementations implement the explicitly negotiated
("Keep-Alive") version of persistent connections described in
Section 19.7.1 of [RFC2068].
Some clients and servers might wish to be compatible with these
previous approaches to persistent connections, by explicitly
negotiating for them with a "Connection: keep-alive" request header
field. However, some experimental implementations of HTTP/1.0
persistent connections are faulty; for example, if an HTTP/1.0 proxy
server doesn't understand Connection, it will erroneously forward
that header field to the next inbound server, which would result in a
hung connection.
One attempted solution was the introduction of a Proxy-Connection
header field, targeted specifically at proxies. In practice, this
was also unworkable, because proxies are often deployed in multiple
layers, bringing about the same problem discussed above.
As a result, clients are encouraged not to send the Proxy-Connection
header field in any requests.
Clients are also encouraged to consider the use of Connection: keep-
alive in requests carefully; while they can enable persistent
connections with HTTP/1.0 servers, clients using them will need to
monitor the connection for "hung" requests (which indicate that the
client ought stop sending the header field), and this mechanism ought
not be used by clients at all when a proxy is being used.
C.1.3. Introduction of Transfer-Encoding
HTTP/1.1 introduces the Transfer-Encoding header field (Section 6.1).
Transfer codings need to be decoded prior to forwarding an HTTP
message over a MIME-compliant protocol.
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C.2. Changes from RFC 7230
Most of the sections introducing HTTP's design goals, history,
architecture, conformance criteria, protocol versioning, URIs,
message routing, and header field values have been moved to
[Semantics]. This document has been reduced to just the messaging
syntax and connection management requirements specific to HTTP/1.1.
Furthermore:
In the ABNF for chunked extensions, re-introduce (bad) whitespace
around ";" and "=". Whitespace was removed in [RFC7230], but later
this change was found to break existing implementations (see
[Err4667]). (Section 7.1.1)
Disallow transfer coding parameters called "q" in order to avoid
conflicts with the use of ranks in the TE header field.
(Section 7.3)
Appendix D. Change Log
This section is to be removed before publishing as an RFC.
D.1. Between RFC7230 and draft 00
The changes were purely editorial:
o Change boilerplate and abstract to indicate the "draft" status,
and update references to ancestor specifications.
o Adjust historical notes.
o Update links to sibling specifications.
o Replace sections listing changes from RFC 2616 by new empty
sections referring to RFC 723x.
o Remove acknowledgements specific to RFC 723x.
o Move "Acknowledgements" to the very end and make them unnumbered.
D.2. Since draft-ietf-httpbis-messaging-00
The changes in this draft are editorial, with respect to HTTP as a
whole, to move all core HTTP semantics into [Semantics]:
o Moved introduction, architecture, conformance, and ABNF extensions
from RFC 7230 (Messaging) to semantics [Semantics].
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o Moved discussion of MIME differences from RFC 7231 (Semantics) to
Appendix B since they mostly cover transforming 1.1 messages.
o Moved all extensibility tips, registration procedures, and
registry tables from the IANA considerations to normative
sections, reducing the IANA considerations to just instructions
that will be removed prior to publication as an RFC.
D.3. Since draft-ietf-httpbis-messaging-01
o Cite RFC 8126 instead of RFC 5226 ()
o Resolved erratum 4779, no change needed here
(,
)
o In Section 7, fixed prose claiming transfer parameters allow bare
names (,
)
o Resolved erratum 4225, no change needed here
(,
)
o Replace "response code" with "response status code"
(,
)
o In Section 9.3, clarify statement about HTTP/1.0 keep-alive
(,
)
o In Section 7.1.1, re-introduce (bad) whitespace around ";" and "="
(,
, )
o In Section 7.3, state that transfer codings should not use
parameters named "q" (, )
o In Section 7, mark coding name "trailers" as reserved in the IANA
registry ()
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Index
A
absolute-form (of request-target) 10
application/http Media Type 39
asterisk-form (of request-target) 11
authority-form (of request-target) 11
C
Connection header field 28, 33
Content-Length header field 18
Content-Transfer-Encoding header field 49
chunked (Coding Format) 17, 19
chunked (transfer coding) 22
close 28, 33
compress (transfer coding) 25
D
deflate (transfer coding) 25
E
effective request URI 12
G
Grammar
absolute-form 9-10
ALPHA 5
asterisk-form 9, 11
authority-form 9, 11
chunk 22
chunk-data 22
chunk-ext 22-23
chunk-ext-name 23
chunk-ext-val 23
chunk-size 22
chunked-body 22-23
Connection 29
connection-option 29
CR 5
CRLF 5
CTL 5
DIGIT 5
DQUOTE 5
field-name 14
field-value 14
header-field 14, 23
HEXDIG 5
HTAB 5
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HTTP-message 6
HTTP-name 6
HTTP-version 6
last-chunk 22
LF 5
message-body 16
method 9
obs-fold 15
OCTET 5
origin-form 9-10
rank 26
reason-phrase 14
request-line 8
request-target 9
SP 5
start-line 6
status-code 14
status-line 13
t-codings 26
t-ranking 26
TE 26
trailer-part 22-23
transfer-coding 21
Transfer-Encoding 17
transfer-extension 21
transfer-parameter 21
Upgrade 35
VCHAR 5
gzip (transfer coding) 25
H
header field 6
header section 6
headers 6
M
MIME-Version header field 48
Media Type
application/http 39
message/http 38
message/http Media Type 38
method 9
O
origin-form (of request-target) 10
R
request-target 9
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T
TE header field 26
Transfer-Encoding header field 17
U
Upgrade header field 34
X
x-compress (transfer coding) 25
x-gzip (transfer coding) 25
Acknowledgments
See Appendix "Acknowledgments" of [Semantics].
Authors' Addresses
Roy T. Fielding (editor)
Adobe
345 Park Ave
San Jose, CA 95110
USA
EMail: fielding@gbiv.com
URI: https://roy.gbiv.com/
Mark Nottingham (editor)
Fastly
EMail: mnot@mnot.net
URI: https://www.mnot.net/
Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: https://greenbytes.de/tech/webdav/
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