RFC 9112: HTTP/1.1

RFC 9112: HTTP/1.1
RFC 9112
HTTP/1.1
June 2022
Fielding, et al.
Standards Track
[Page]
Stream:
Internet Engineering Task Force (IETF)
RFC:
9112
STD:
99
Obsoletes:
7230
Category:
Standards Track
Published:
June 2022
ISSN:
2070-1721
Authors:
R. Fielding,
Ed.
Adobe
M. Nottingham,
Ed.
Fastly
J. Reschke,
Ed.
greenbytes
RFC 9112
HTTP/1.1
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.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by
the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 7841.
Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Revised BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Revised BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s)
controlling the copyright in such materials, this document may not
be modified outside the IETF Standards Process, and derivative
works of it may not be created outside the IETF Standards Process,
except to format it for publication as an RFC or to translate it
into languages other than English.
Table of Contents
1.
Introduction
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/1.1 is defined by:
This document
"HTTP Semantics"
HTTP
"HTTP Caching"
CACHING
This document specifies how HTTP semantics are conveyed using the
HTTP/1.1 message syntax, framing, and connection management mechanisms.
Its goal is to define the complete set of requirements for HTTP/1.1
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.3
. The other parts of
RFC 7230
are obsoleted by
"HTTP Semantics"
HTTP
1.1.
Requirements Notation
The key words "
MUST
", "
MUST NOT
", "
REQUIRED
", "
SHALL
", "
SHALL NOT
", "
SHOULD
", "
SHOULD NOT
", "
RECOMMENDED
", "
NOT RECOMMENDED
",
MAY
", and "
OPTIONAL
" in this document are to be interpreted as
described in BCP 14
RFC2119
RFC8174
when, and only when, they appear in all capitals, as shown here.
Conformance criteria and considerations regarding error handling
are defined in
Section 2
of [
HTTP
1.2.
Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF) notation of
RFC5234
, extended with the notation for case-sensitivity
in strings defined in
RFC7405
It also uses a list extension, defined in
Section 5.6.1
of [
HTTP
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
HTTP
BWS =
OWS =
RWS =
absolute-path =
field-name =
field-value =
obs-text =
quoted-string =
token =
transfer-coding =

The rules below are defined in
URI
absolute-URI =
authority =
uri-host =
port =
query =
2.
Message
HTTP/1.1 clients and servers communicate by sending messages.
See
Section 3
of [
HTTP
for
the general terminology and core concepts of HTTP.
2.1.
Message Format
An HTTP/1.1 message consists of a start-line followed by a CRLF and a
sequence of
octets in a format similar to the Internet Message Format
RFC5322
: zero or more header field lines (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 CRLF
*( field-line CRLF )
CRLF
[ message-body ]
A message can be either a request from client to server or a
response from server to client. Syntactically, the two types of messages
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.
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.
Message Parsing
The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field line 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 line value
after message parsing has delineated the individual field lines.
Although the line terminator for the start-line and
fields is the sequence CRLF, a recipient
MAY
recognize a
single LF as a line terminator and ignore any preceding CR.
A sender
MUST NOT
generate a bare CR (a CR character not immediately
followed by LF) within any protocol elements other than the content.
A recipient of such a bare CR
MUST
consider that element to be invalid or
replace each bare CR with SP before processing the element or forwarding
the message.
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).
Rejection or removal of invalid whitespace-preceded lines is necessary
to prevent their misinterpretation by downstream recipients that might
be vulnerable to request smuggling (
Section 11.2
or response splitting (
Section 11.1
) attacks.
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
and close the connection.
2.3.
HTTP Version
HTTP uses a "." numbering scheme to indicate
versions of the protocol. This specification defines version "1.1".
Section 2.5
of [
HTTP
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 = %s"HTTP"
When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
HTTP/1.0
or a recipient whose version is unknown,
the HTTP/1.1 message is constructed such that it can be interpreted
as a valid HTTP/1.0 message if all of the newer features are ignored.
This specification places recipient-version requirements on some
new features so that a conformant sender will only use compatible
features until it has determined, through configuration or the
receipt of a message, that the recipient supports HTTP/1.1.
Intermediaries that process HTTP messages (i.e., all intermediaries
other than those acting as tunnels)
MUST
send their own HTTP-version
in forwarded messages, unless it is purposefully downgraded as a workaround
for an upstream issue. In other words, an intermediary is 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.
3.
Request Line
A request-line begins with a method token, followed by a single
space (SP), the request-target, and another single space (SP), and ends
with the protocol version.
request-line = method SP request-target SP HTTP-version
Although the request-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 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 2.3
of [
HTTP
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 15.5.15
of [
HTTP
).
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 9
of [
HTTP
, 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 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.
A client
MUST
send a Host header field (
Section 7.2
of [
HTTP
in all HTTP/1.1 request messages. If the target URI includes an authority component, then a client
MUST
send a field value for Host that is identical to that authority
component, excluding any userinfo subcomponent and its "@" delimiter
Section 4.2
of [
HTTP
).
If the authority component is missing or undefined for the target URI,
then a client
MUST
send a Host header field with an empty field value.
A server
MUST
respond with a 400 (Bad Request) status code
to any HTTP/1.1 request message that lacks a Host header field and
to any request message that contains more than one Host header field line
or a Host header field with an invalid field value.
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 7.2
of [
HTTP
For example, a client wishing to retrieve a representation of the resource
identified as
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 either to
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 7.6
of [
HTTP
An example absolute-form of request-line would be:
GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
A client
MUST
send a Host header field in an HTTP/1.1 request even
if the request-target is in the absolute-form, since this
allows the Host information to be forwarded through ancient HTTP/1.0
proxies that might not have implemented Host.
When a proxy receives a request with an absolute-form of
request-target, the proxy
MUST
ignore the received
Host header field (if any) and instead replace it with the host
information of the request-target. A proxy that forwards such a request
MUST
generate a new Host field value based on the received
request-target rather than forward the received Host field value.
When an origin server receives a request with an absolute-form of
request-target, the origin server
MUST
ignore the received Host header
field (if any) and instead use the host information of the request-target.
Note that if the request-target does not have an authority component, an
empty Host header field will be sent in this case.
A server
MUST
accept the absolute-form in requests even though most
HTTP/1.1 clients will only send the absolute-form to a proxy.
3.2.3.
authority-form
The "authority-form" of request-target is only used for
CONNECT requests (
Section 9.3.6
of [
HTTP
). It consists of only the
uri-host and port number of the tunnel
destination, separated by a colon (":").
authority-form = uri-host ":" port
When making a CONNECT request to establish a tunnel through one or more
proxies, a client
MUST
send only the host and port of the tunnel
destination as the request-target. The client obtains the host and port
from the target URI's
authority
component, except that it
sends the scheme's default port if the target URI elides the port.
For example, a CONNECT request to "http://www.example.com" looks like the following:
CONNECT www.example.com:80 HTTP/1.1
Host: www.example.com
3.2.4.
asterisk-form
The "asterisk-form" of request-target is only used for a server-wide
OPTIONS request (
Section 9.3.7
of [
HTTP
).
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.
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.
Reconstructing the Target URI
The target URI is the
request-target
when the
request-target is in
absolute-form
. In that case,
a server will parse the URI into its generic components for further
evaluation.
Otherwise, the server reconstructs the target URI from the connection
context and various parts of the request message in order to identify the
target resource (
Section 7.1
of [
HTTP
):
If the server's configuration provides for a fixed URI scheme, or a scheme
is provided by a trusted outbound gateway, that scheme is used for the
target URI. This is common in large-scale deployments because a gateway
server will receive the client's connection context and replace that with
their own connection to the inbound server.
Otherwise, if the request is received over a secured connection,
the target URI's scheme is "https"; if not, the scheme is "http".
If the request-target is in
authority-form
the target URI's authority component is the request-target.
Otherwise, the target URI's authority component is the field value of the
Host header field. If there is no Host
header field or if its field value is empty or invalid,
the target URI's authority component is empty.
If the request-target is in
authority-form
or
asterisk-form
, the target URI's combined
path and
query
component is empty.
Otherwise, the target URI's combined path and
query
component is the request-target.
The components of a reconstructed target URI, once determined as above,
can be recombined into
absolute-URI
form by concatenating
the scheme, "://", authority, and combined path and query component.
Example 1: The following message received over a secure connection
GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.example.org
has a target URI of
Example 2: The following message received over an insecure connection
OPTIONS * HTTP/1.1
Host: www.example.org:8080
has a target URI of
If the target URI's authority component is empty and its URI scheme
requires a non-empty authority (as is the case for "http" and "https"),
the server can reject the request or determine whether a configured
default applies that is consistent with the incoming connection's context.
Context might include connection details like address and port, what
security has been applied, and locally defined information specific to
that server's configuration. An empty authority is replaced with the
configured default before further processing of the request.
Supplying a default name for authority within the context of a secured
connection is inherently unsafe if there is any chance that the user
agent's intended authority might differ from the default.
A server that can uniquely identify an authority from the request
context
MAY
use that identity as a default without this risk.
Alternatively, it might be better to redirect the request to a safe
resource that explains how to obtain a new client.
Note that reconstructing the client's target URI is only half of the
process for identifying a target resource. The other half is determining
whether that target URI identifies a resource for which the server is
willing and able to send a response, as defined in
Section 7.4
of [
HTTP
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, and another space
and ending with an
OPTIONAL
textual phrase describing the status code.
status-line = HTTP-version SP status-code SP [ reason-phrase ]
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
).
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. A recipient parses and interprets the remainder
of the response message in light of the semantics defined for that
status code, if the status code is recognized by that recipient,
or in accordance with the class of that status code when the specific
code is unrecognized.
status-code = 3DIGIT
HTTP's core status codes are defined in
Section 15
of [
HTTP
along with the classes of status codes, considerations for the
definition of new status codes, and the IANA registry for collecting
such definitions.
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.
reason-phrase = 1*( HTAB / SP / VCHAR / obs-text )
A client
SHOULD
ignore the reason-phrase content because it is not a
reliable channel for information (it might be translated for a given locale,
overwritten by intermediaries, or discarded when the message is forwarded
via other versions of HTTP).
A server
MUST
send the space that separates the status-code from the
reason-phrase even when the reason-phrase is absent (i.e., the status-line
would end with the space).
5.
Field Syntax
Each field line consists of a case-insensitive field name
followed by a colon (":"), optional leading whitespace, the field line value,
and optional trailing whitespace.
field-line = field-name ":" OWS field-value OWS
Rules for parsing within field values are
defined in
Section 5.5
of [
HTTP
. This section covers the
generic syntax for header field inclusion within, and extraction from,
HTTP/1.1 messages.
5.1.
Field Line Parsing
Messages are parsed using a generic algorithm, independent of the
individual field names. The contents within a given field line value are
not parsed until a later stage of message interpretation (usually after the
message's entire field section has been processed).
No whitespace is allowed between the 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, with a response status code of
400 (Bad Request), any received request message that contains
whitespace between a header field name and colon.
A proxy
MUST
remove any such whitespace
from a response message before forwarding the message downstream.
A field line value might be preceded and/or followed by optional whitespace
(OWS); a single SP preceding the field line value is preferred for consistent
readability by humans.
The field line value does not include that leading or trailing whitespace: OWS
occurring before the first non-whitespace octet of the field line value,
or after the last non-whitespace octet of the field line value, is excluded by
parsers when extracting the field line value from a field line.
5.2.
Obsolete Line Folding
Historically, HTTP/1.x 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 = OWS CRLF RWS
; obsolete line folding
A sender
MUST NOT
generate a message that includes line folding
(i.e., that has any field line value that contains a match to the
obs-fold
rule) unless the message is intended for packaging
within the "message/http" media type.
A server that receives an
obs-fold
in a request message that
is not within a "message/http" container
MUST
either reject the message by
sending a 400 (Bad Request), preferably with a
representation explaining that obsolete line folding is unacceptable, or
replace each received
obs-fold
with one or more
SP
octets prior to interpreting the field value or
forwarding the message downstream.
A proxy or gateway that receives an
obs-fold
in a response
message that is not within a "message/http" container
MUST
either discard
the message and replace it with a 502 (Bad Gateway)
response, preferably with a representation explaining that unacceptable
line folding was received, or replace each received
obs-fold
with one or more
SP
octets prior to interpreting the field
value or forwarding the message downstream.
A user agent that receives an
obs-fold
in a response message
that is not within a "message/http" container
MUST
replace each received
obs-fold
with one or more
SP
octets prior to
interpreting the field value.
6.
Message Body
The message body (if any) of an HTTP/1.1 message is used to carry content
Section 6.4
of [
HTTP
) for the request or response. The
message body is identical to the content unless a transfer coding has
been applied, as described in
Section 6.1
message-body = *OCTET
The rules for determining when a message body is present in an HTTP/1.1
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.
The presence of a message body in a response, as detailed in
Section 6.3
, depends on both the request
method to which it is responding and the response status code.
This corresponds to when response content is
allowed by HTTP semantics (
Section 6.4.1
of [
HTTP
).
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 content in order to form the message body.
Transfer codings are defined in
Section 7
Transfer-Encoding = #transfer-coding
; defined in [HTTP], Section 10.1.4
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 dynamically generated content. It also serves to
distinguish encodings that are only applied in transit from the encodings
that are a characteristic of the selected representation.
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 content size is not known in advance.
A sender
MUST NOT
apply the chunked transfer coding 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's content,
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's content,
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 content has been compressed using the gzip
coding and then chunked using the chunked coding while forming the
message body.
Unlike Content-Encoding (
Section 8.4.1
of [
HTTP
),
Transfer-Encoding is a property of the message, not of the representation.
Any recipient along the request/response chain
MAY
decode the received
transfer coding(s) or apply additional transfer coding(s) to the message
body, assuming that corresponding changes are made to the Transfer-Encoding
field value. Additional information about the encoding parameters 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 15.4.5
of [
HTTP
) 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 9.3.6
of [
HTTP
).
A server that receives a request message with a transfer coding it does
not understand
SHOULD
respond with 501 (Not Implemented).
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 transfer-encoded content, and that an HTTP/1.0 message
received with a Transfer-Encoding is likely to have been forwarded
without proper handling of the chunked transfer coding in transit.
A client
MUST NOT
send a request containing Transfer-Encoding unless it
knows the server will handle HTTP/1.1 requests (or later minor revisions);
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 minor revisions).
Early implementations of Transfer-Encoding would occasionally send both
a chunked transfer coding for message framing and an estimated Content-Length
header field for use by progress bars. This is why Transfer-Encoding is
defined as overriding Content-Length, as opposed to them being mutually
incompatible. Unfortunately, forwarding such a message can lead to
vulnerabilities regarding
request smuggling (
Section 11.2
) or
response splitting (
Section 11.1
) attacks
if any downstream recipient fails to parse the message according to this
specification, particularly when a downstream recipient only implements
HTTP/1.0.
A server
MAY
reject a request that contains both Content-Length and
Transfer-Encoding or process such a request in accordance with the
Transfer-Encoding alone. Regardless, the server
MUST
close the connection
after responding to such a request to avoid the potential attacks.
A server or client that receives an HTTP/1.0 message containing a
Transfer-Encoding header field
MUST
treat the message as if the framing
is faulty, even if a Content-Length is present, and close the connection
after processing the message. The message sender might have retained a
portion of the message, in buffer, that could be misinterpreted by further
use of the connection.
6.2.
Content-Length
When a message does not have a
Transfer-Encoding
header
field, a Content-Length header field (
Section 8.6
of [
HTTP
) can provide the anticipated size,
as a decimal number of octets, for potential content.
For messages that do include content, the Content-Length field value
provides the framing information necessary for determining where the data
(and message) ends. For messages that do not include content, the
Content-Length indicates the size of the selected representation
Section 8.6
of [
HTTP
).
A sender
MUST NOT
send a Content-Length header field in any message that
contains a
Transfer-Encoding
header field.
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.
6.3.
Message Body Length
The length of a message body is determined by one of the following
(in order of precedence):
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 or trailer section.
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.
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.
An intermediary that chooses to forward the message
MUST
first remove the
received Content-Length field and process the Transfer-Encoding
(as described below) prior to forwarding the message downstream.
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 without
Transfer-Encoding
and with
an invalid
Content-Length
header field, then the message
framing is invalid and the recipient
MUST
treat it as an unrecoverable
error, unless the field value can be successfully parsed as a
comma-separated list (
Section 5.6.1
of [
HTTP
), all values in the
list are valid, and all values in the list are the same (in which case, the
message is processed with that single value used as the Content-Length field
value).
If the unrecoverable error is in a request message,
the server
MUST
respond with
a 400 (Bad Request) status code and then close the connection.
If it is in a response message received by a proxy,
the proxy
MUST
close the connection to the server, discard the received
response, and send a 502 (Bad Gateway) response to the
client.
If it is in a response message received by a user agent,
the user agent
MUST
close the connection to the server and discard the
received response.
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.
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).
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 response 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.
Note:
Request messages are never close-delimited because they are always
explicitly framed by length or transfer coding, with the absence of both implying
the request ends immediately after the header section.
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 that contains a message body
MUST
send
either a valid
Content-Length
header field or use the
chunked transfer coding. A client
MUST NOT
use the chunked transfer
coding unless it knows the server will handle HTTP/1.1 (or later)
requests; such knowledge can be in the form of specific user configuration
or by remembering the version of a prior received response.
If the final response to the last request on a connection has been
completely received and there remains additional data to read, a user agent
MAY
discard the remaining data or attempt to determine if that data
belongs as part of the prior message 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
message's content 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.
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
Transfer-Encoding
Section 6.1
) and TE
Section 10.1.4
of [
HTTP
) header fields (the latter also
defining the "transfer-coding" grammar).
7.1.
Chunked Transfer Coding
The chunked transfer coding wraps content in order to transfer it
as a series of chunks, each with its own size indicator, followed by an
OPTIONAL
trailer section containing trailer 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-section
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 when a
chunk with a chunk-size of zero is received, possibly followed by a
trailer section, and finally terminated by an empty line.
A recipient
MUST
be able to parse and decode the chunked transfer coding.
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. Additionally, very large chunk sizes may cause overflows
or loss of precision if their values are not represented accurately in a
receiving implementation. Therefore, recipients
MUST
anticipate
potentially large hexadecimal numerals and prevent parsing errors due to
integer conversion overflows or precision loss due to integer
representation.
The chunked coding does not define any parameters. Their presence
SHOULD
be treated as an error.
7.1.1.
Chunk Extensions
The chunked coding 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 coding 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, the 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 Section
A trailer section 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 content is sent, such as a message integrity
check, digital signature, or post-processing status. The proper use and
limitations of trailer fields are defined in
Section 6.5
of [
HTTP
trailer-section = *( field-line CRLF )
A recipient that removes the chunked coding from a message
MAY
selectively retain or discard the received trailer fields. A recipient
that retains a received trailer field
MUST
either store/forward the
trailer field separately from the received header fields or merge the
received trailer field into the header section.
A recipient
MUST NOT
merge a received trailer field into the
header section unless its corresponding header field definition
explicitly permits and instructs how the trailer field value can be
safely merged.
7.1.3.
Decoding Chunked
A process for decoding the chunked transfer coding
can be represented in pseudo-code as:
length := 0
read chunk-size, chunk-ext (if any), and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to content
length := length + chunk-size
read chunk-size, chunk-ext (if any), and CRLF
read trailer field
while (trailer field is not empty) {
if (trailer fields are stored/forwarded separately) {
append trailer field to existing trailer fields
else if (trailer field is understood and defined as mergeable) {
merge trailer field with existing header fields
else {
discard trailer field
read trailer field
Content-Length := length
Remove "chunked" from Transfer-Encoding
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 8.4.1.1
of [
HTTP
deflate
See
Section 8.4.1.2
of [
HTTP
gzip (and x-gzip)
See
Section 8.4.1.3
of [
HTTP
The compression codings do not define any parameters. The presence
of parameters with any of these compression codings
SHOULD
be treated
as an error.
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:
Name
Description
Pointer to specification text
Names of transfer codings
MUST NOT
overlap with names of content codings
Section 8.4.1
of [
HTTP
) unless the encoding transformation is identical, as
is the case for the compression codings defined in
Section 7.2
The TE header field (
Section 10.1.4
of [
HTTP
) uses a
pseudo-parameter named "q" as the 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.
Negotiating Transfer Codings
The TE field (
Section 10.1.4
of [
HTTP
) is used in HTTP/1.1 to indicate
what transfer codings, besides chunked, the client is willing to accept
in the response and whether the client is willing to preserve
trailer fields in a chunked transfer coding.
A client
MUST NOT
send the chunked transfer coding name in TE;
chunked is always acceptable for HTTP/1.1 recipients.
Three examples of TE use are below.
TE: deflate
TE:
TE: trailers, deflate;q=0.5
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; see
Section 12.4.2
of [
HTTP
). 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.
The keyword "trailers" indicates that the sender will not discard trailer
fields, as described in
Section 6.5
of [
HTTP
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 7.6.1
of [
HTTP
in order to prevent the TE header 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 3.3
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, if the header section was received intact, is considered
complete unless an error was indicated by the underlying connection
(e.g., an "incomplete close" in TLS would leave the response incomplete,
as described in
Section 9.8
).
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 7.3
of [
HTTP
, 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 4.2.1
of [
HTTP
) 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.
Establishment
It is beyond the scope of this specification to describe how connections
are established via various transport- or session-layer protocols.
Each HTTP connection maps to one underlying transport connection.
9.2.
Associating a Response to a Request
HTTP/1.1 does not include a request identifier for associating a given
request message with its corresponding one or more response messages.
Hence, it relies on the order of response arrival to correspond exactly
to the order in which requests are made on the same connection.
More than one response message per request only occurs when one or more
informational responses (1xx; see
Section 15.2
of [
HTTP
) precede a
final response to the same request.
A client that has more than one outstanding request on a connection
MUST
maintain a list of outstanding requests in the order sent and
MUST
associate each received response message on that connection to the
first outstanding request that has not yet received a final
(non-1xx) response.
If a client receives data on a connection that doesn't have
outstanding requests, the client
MUST NOT
consider that data to be a
valid response; the client
SHOULD
close the connection, since message
delimitation is now ambiguous, unless the data consists only of one or
more CRLF (which can be discarded per
Section 2.2
).
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. HTTP implementations
SHOULD
support persistent connections.
A recipient determines whether a connection is persistent or not based on
the protocol version and Connection header field
Section 7.6.1
of [
HTTP
) in the
most recently received message, if any:
If the "
close
" connection option is present
Section 9.6
), the
connection will not persist after the current response; else,
If the received protocol is HTTP/1.1 (or later), the connection will
persist after the current response; else,
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,
The connection will close after the current response.
A client that does not support
persistent connections
MUST
send the "
close
" connection option in every request message.
A server that does not support
persistent connections
MUST
send the "
close
" connection option in every response message
that does not have a 1xx (Informational) status code.
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; otherwise, the
remaining data on a persistent connection would be misinterpreted
as the next request. Likewise,
a client
MUST
read the entire response message body if it intends
to reuse the same connection for a subsequent request.
A proxy server
MUST NOT
maintain a persistent connection with an
HTTP/1.0 client (see
Appendix C.2.2
for
information and discussion of the problems with the Keep-Alive header field
implemented by many HTTP/1.0 clients).
See
Appendix C.2.2
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. The conditions under which a client can
automatically retry a sequence of outstanding requests are defined in
Section 9.2.2
of [
HTTP
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 9.2.1
of [
HTTP
), 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 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 9.2.2
of [
HTTP
) 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 transfers very large content would block subsequent
requests on the
same connection. However, each connection consumes server resources.
Furthermore, using multiple connections can cause undesirable side effects
in congested networks.
Using larger numbers of connections can also cause side effects in
otherwise uncongested networks, because their aggregate and initially
synchronized sending behavior can cause congestion that would not have
been present if fewer parallel connections had been used.
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.
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 or server load.
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 "close" connection option is defined as a signal that the sender
will close this connection after completion of the response.
A sender
SHOULD
send a Connection header field
Section 7.6.1
of [
HTTP
) containing the "close" connection option
when it intends to close a connection. For example,
Connection: close
as a request header field indicates that this is the last request that
the client will send on this connection, while in a response, the same
field indicates that the server is going to close this connection after
the response message is complete.
Note that the field name "Close" is reserved, since using that name as a
header field might conflict with the "close" connection option.
A client that sends a "close" connection option
MUST NOT
send further requests on that connection (after the one containing the
"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 closure of the connection (see below) after it sends the
final response to the request that contained the "close" connection option.
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 closure of the connection (see below) after it sends the
response containing the "close" connection option. 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" connection option;
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 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.
Note that a TCP connection that is half-closed by the client does not
delimit a request message, nor does it imply that the client is no longer
interested in a response. In general, transport signals cannot be relied
upon to signal edge cases, since HTTP/1.1 is independent of transport.
9.7.
TLS Connection Initiation
Conceptually, HTTP/TLS is simply sending HTTP messages over a connection
secured via TLS
TLS13
The HTTP client also acts as the TLS client. It initiates a connection to
the server on the appropriate port and sends the TLS ClientHello to begin
the TLS handshake. When the TLS handshake has finished, the client may then
initiate the first HTTP request. All HTTP data
MUST
be sent as TLS
"application data" but is otherwise treated like a normal connection for
HTTP (including potential reuse as a persistent connection).
9.8.
TLS Connection Closure
TLS uses an exchange of closure alerts prior to (non-error) connection
closure to provide secure connection closure; see
Section 6.1
of [
TLS13
. When a
valid closure alert is received, an implementation can be assured that no
further data will be received on that connection.
When an implementation knows that it has sent or received all the
message data that it cares about, typically by detecting HTTP message
boundaries, it might generate an "incomplete close" by sending a
closure alert and then closing the connection without waiting to
receive the corresponding closure alert from its peer.
An incomplete close does not call into question the security of the data
already received, but it could indicate that subsequent data might have been
truncated. As TLS is not directly aware of HTTP message framing, it is
necessary to examine the HTTP data itself to determine whether messages are
complete. Handling of incomplete messages is defined in
Section 8
When encountering an incomplete close, a client
SHOULD
treat as completed
all requests for which it has received either
as much data as specified in the
Content-Length
header
field or
the terminal zero-length chunk (when
Transfer-Encoding
of chunked is used).
A response that has neither chunked
transfer coding nor Content-Length is complete only if a valid closure alert
has been received. Treating an incomplete message as complete could expose
implementations to attack.
A client detecting an incomplete close
SHOULD
recover gracefully.
Clients
MUST
send a closure alert before closing the connection.
Clients that do not expect to receive any more data
MAY
choose not
to wait for the server's closure alert and simply close the
connection, thus generating an incomplete close on the server side.
Servers
SHOULD
be prepared to receive an incomplete close from the client,
since the client can often locate the end of server data.
Servers
MUST
attempt to initiate an exchange of closure alerts with
the client before closing the connection. Servers
MAY
close the
connection after sending the closure alert, thus generating an
incomplete close on the client side.
10.
Enclosing Messages as Data
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. Because of the line length
limitations, field values within "message/http" are allowed to use
line folding (
obs-fold
), as described in
Section 5.2
, to convey the field value over multiple
lines. A recipient of "message/http" data
MUST
replace any obsolete line
folding with one or more SP characters when the message is consumed.
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:
RFC 9112 (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.
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:
RFC 9112 (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
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 about known security considerations relevant to HTTP message syntax
and parsing. Security considerations about HTTP semantics,
content, and routing are addressed in
HTTP
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 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. 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.
The mechanisms provided with the "https" scheme, such as authenticated
encryption, provide protection against modification of messages. Care
is needed, however, to ensure that connection closure cannot be used to
truncate messages (see
Section 9.8
). User agents
might refuse to accept incomplete messages or treat them specially. For
example, a browser being used to view medical history or drug interaction
information needs to indicate to the user when such information is detected
by the protocol to be incomplete, expired, or corrupted during transfer.
Such mechanisms might be selectively enabled via user agent extensions or
the presence of message integrity metadata in a response.
The "http" scheme provides no protection against accidental or malicious
modification of messages.
Extensions to the protocol might be used to mitigate the risk of unwanted
modification of messages by intermediaries, even when the "https" scheme is
used. Integrity might be assured by using message authentication codes
or digital
signatures that are selectively added to messages via extensible metadata
fields.
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 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 4.2.2
of [
HTTP
12.
IANA Considerations
The change controller for the following registrations is:
"IETF (iesg@ietf.org) - Internet Engineering Task Force".
12.1.
Field Name Registration
IANA has added the following field names to the "Hypertext Transfer Protocol (HTTP) Field
Name Registry" at
as described in
Section 18.4
of [
HTTP
Table 1
Field Name
Status
Section
Comments
Close
permanent
9.6
(reserved)
MIME-Version
permanent
B.1
Transfer-Encoding
permanent
6.1
12.2.
Media Type Registration
IANA has updated the "Media Types" registry at
with the registration information in Sections
10.1
and
10.2
for the media types
"message/http" and "application/http", respectively.
12.3.
Transfer Coding Registration
IANA has updated the "HTTP Transfer Coding Registry" at
with the registration procedure of
Section 7.3
and the content coding names summarized in the table below.
Table 2
Name
Description
Section
chunked
Transfer in a series of chunks
7.1
compress
UNIX "compress" data format
Welch
7.2
deflate
"deflate" compressed data (
RFC1951
) inside
the "zlib" data format (
RFC1950
7.2
gzip
GZIP file format
RFC1952
7.2
trailers
(reserved)
12.3
x-compress
Deprecated (alias for compress)
7.2
x-gzip
Deprecated (alias for gzip)
7.2
Note:
the coding name "trailers" is reserved because its use would
conflict with the keyword "trailers" in the TE
header field (
Section 10.1.4
of [
HTTP
).
12.4.
ALPN Protocol ID Registration
IANA has updated the
"TLS Application-Layer Protocol Negotiation (ALPN) Protocol IDs" registry at
with the registration below:
Table 3
Protocol
Identification Sequence
Reference
HTTP/1.1
0x68 0x74 0x74 0x70 0x2f 0x31 0x2e 0x31 ("http/1.1")
RFC 9112
13.
References
13.1.
Normative References
[CACHING]
Fielding, R., Ed.
Nottingham, M., Ed.
, and
J. Reschke, Ed.
"HTTP Caching"
STD 98
RFC 9111
DOI 10.17487/RFC9111
June 2022
[HTTP]
Fielding, R., Ed.
Nottingham, M., Ed.
, and
J. Reschke, Ed.
"HTTP Semantics"
STD 97
RFC 9110
DOI 10.17487/RFC9110
June 2022
[RFC1950]
Deutsch, P.
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.
"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
[RFC5234]
Crocker, D., Ed.
and
P. Overell
"Augmented BNF for Syntax Specifications: ABNF"
STD 68
RFC 5234
DOI 10.17487/RFC5234
January 2008
[RFC7405]
Kyzivat, P.
"Case-Sensitive String Support in ABNF"
RFC 7405
DOI 10.17487/RFC7405
December 2014
[RFC8174]
Leiba, B.
"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"
BCP 14
RFC 8174
DOI 10.17487/RFC8174
May 2017
[TLS13]
Rescorla, E.
"The Transport Layer Security (TLS) Protocol Version 1.3"
RFC 8446
DOI 10.17487/RFC8446
August 2018
[URI]
Berners-Lee, T.
Fielding, R.
, and
L. Masinter
"Uniform Resource Identifier (URI): Generic Syntax"
STD 66
RFC 3986
DOI 10.17487/RFC3986
January 2005
[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)
DOI 10.1109/MC.1984.1659158
June 1984
13.2.
Informative References
[HTTP/1.0]
Berners-Lee, T.
Fielding, R.
, and
H. Frystyk
"Hypertext Transfer Protocol -- HTTP/1.0"
RFC 1945
DOI 10.17487/RFC1945
May 1996
[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
[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.
Frystyk, H.
, and
T. Berners-Lee
"Hypertext Transfer Protocol -- HTTP/1.1"
RFC 2068
DOI 10.17487/RFC2068
January 1997
[RFC2557]
Palme, J.
Hopmann, A.
, and
N. Shelness
"MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)"
RFC 2557
DOI 10.17487/RFC2557
March 1999
[RFC5322]
Resnick, P., Ed.
"Internet Message Format"
RFC 5322
DOI 10.17487/RFC5322
October 2008
[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
[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
Appendix A.
Collected ABNF
In the collected ABNF below, list rules are expanded per
Section 5.6.1
of [
HTTP
BWS =

HTTP-message = start-line CRLF *( field-line CRLF ) CRLF [
message-body ]
HTTP-name = %x48.54.54.50 ; HTTP
HTTP-version = HTTP-name "/" DIGIT "." DIGIT

OWS =

RWS =

Transfer-Encoding = [ transfer-coding *( OWS "," OWS transfer-coding
) ]

absolute-URI =
absolute-form = absolute-URI
absolute-path =
asterisk-form = "*"
authority =
authority-form = uri-host ":" port

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-section CRLF

field-line = field-name ":" OWS field-value OWS
field-name =
field-value =

last-chunk = 1*"0" [ chunk-ext ] CRLF

message-body = *OCTET
method = token

obs-fold = OWS CRLF RWS
obs-text =
origin-form = absolute-path [ "?" query ]

port =

query =
quoted-string =

reason-phrase = 1*( HTAB / SP / VCHAR / obs-text )
request-line = method SP request-target SP HTTP-version
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 ]

token =
trailer-section = *( field-line CRLF )
transfer-coding =

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 Multipurpose
Internet Mail Extensions (MIME)
RFC2045
to
allow a message body to be transmitted in an open variety of
representations and with extensible fields. However, some
of these constructs have been reinterpreted to better fit the needs
of interactive communication, leading to some differences in how MIME
constructs are used within HTTP. These differences were carefully
chosen to optimize performance over binary connections, allow
greater freedom in the use of new media types, ease date comparisons,
and accommodate common implementations.
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
, and that content with a type of "text" represents
line breaks as CRLF, forbidding the use of CR or LF outside of line break
sequences
RFC2046
. In contrast, HTTP does not care whether
CRLF, bare CR, or bare LF are used to indicate a line break within 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 5.6.7
of [
HTTP
) to
simplify the process of date comparison. Proxies and gateways from
other protocols ought to ensure that any Date header field
present in a message conforms to one of the HTTP/1.1 formats and rewrite
the date if necessary.
B.4.
Conversion of Content-Encoding
MIME does not include any concept equivalent to HTTP'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 without modification and, aside from the
"multipart/byteranges" type (
Section 14.6
of [
HTTP
),
does not interpret
the content or any MIME header lines that might be contained therein.
Appendix C.
Changes from Previous RFCs
C.1.
Changes from HTTP/0.9
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.2.
Changes from HTTP/1.0
C.2.1.
Multihomed Web Servers
The requirements that clients and servers support the Host
header field (
Section 7.2
of [
HTTP
), 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 established mechanism for
distinguishing the intended server of a request other than the IP address
to which that request was directed. The Host header field was
introduced during the development of HTTP/1.1 and, though it was
quickly implemented by most HTTP/1.0 browsers, additional requirements
were placed on all HTTP/1.1 requests in order to ensure complete
adoption. At the time of this writing, most HTTP-based services
are dependent upon the Host header field for targeting requests.
C.2.2.
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 to stop
sending the header field), and this mechanism ought not be used by clients
at all when a proxy is being used.
C.2.3.
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.
C.3.
Changes from RFC 7230
Most of the sections introducing HTTP's design goals, history, architecture,
conformance criteria, protocol versioning, URIs, message routing, and
header fields have been moved to
HTTP
This document has been reduced to just the messaging syntax and
connection management requirements specific to HTTP/1.1.
Bare CRs have been prohibited outside of content.
Section 2.2
The ABNF definition of
authority-form
has changed from the
more general authority component of a URI (in which port is optional) to
the specific host:port format that is required by CONNECT.
Section 3.2.3
Recipients are required to avoid smuggling/splitting attacks when processing an
ambiguous message framing.
Section 6.1
In the ABNF for chunked extensions, (bad) whitespace around
";" and "=" has been reintroduced. Whitespace was removed
in
RFC7230
, but that change was found to break existing
implementations. (
Section 7.1.1
Trailer field semantics now transcend the specifics of chunked transfer coding.
The decoding algorithm for chunked (
Section 7.1.3
) has
been updated to encourage storage/forwarding of trailer fields separately
from the header section, to only allow merging into the header section if
the recipient knows the corresponding field definition permits and defines
how to merge, and otherwise to discard the trailer fields instead of
merging. The trailer part is now called the trailer section to be more
consistent with the header section and more distinct from a body part.
Section 7.1.2
Transfer coding parameters called "q" are disallowed in order to avoid
conflicts with the use of ranks in the TE header field.
Section 7.3
Acknowledgements
See Appendix "Acknowledgements" of
HTTP
, which applies to this document as well.
Index
absolute-form (of request-target)
Section 3.2.2
application/http Media Type
Section 10.2
asterisk-form (of request-target)
Section 3.2.4
authority-form (of request-target)
Section 3.2.3
chunked (Coding Format)
Section 6.1
Section 6.3
chunked (transfer coding)
Section 7.1
close
Section 9.3
Section 9.6
compress (transfer coding)
Section 7.2
Connection header field
Section 9.6
Content-Length header field
Section 6.2
Content-Transfer-Encoding header field
Appendix B.5
deflate (transfer coding)
Section 7.2
Fields
Close
Section 9.6, Paragraph 4
MIME-Version
Appendix B.1
Transfer-Encoding
Section 6.1
Grammar
ALPHA
Section 1.2
CR
Section 1.2
CRLF
Section 1.2
CTL
Section 1.2
DIGIT
Section 1.2
DQUOTE
Section 1.2
HEXDIG
Section 1.2
HTAB
Section 1.2
HTTP-message
Section 2.1
HTTP-name
Section 2.3
HTTP-version
Section 2.3
LF
Section 1.2
OCTET
Section 1.2
SP
Section 1.2
Transfer-Encoding
Section 6.1
VCHAR
Section 1.2
absolute-form
Section 3.2
Section 3.2.2
asterisk-form
Section 3.2
Section 3.2.4
authority-form
Section 3.2
Section 3.2.3
chunk
Section 7.1
chunk-data
Section 7.1
chunk-ext
Section 7.1
Section 7.1.1
chunk-ext-name
Section 7.1.1
chunk-ext-val
Section 7.1.1
chunk-size
Section 7.1
chunked-body
Section 7.1
field-line
Section 5
Section 7.1.2
field-name
Section 5
field-value
Section 5
last-chunk
Section 7.1
message-body
Section 6
method
Section 3.1
obs-fold
Section 5.2
origin-form
Section 3.2
Section 3.2.1
reason-phrase
Section 4
request-line
Section 3
request-target
Section 3.2
start-line
Section 2.1
status-code
Section 4
status-line
Section 4
trailer-section
Section 7.1
Section 7.1.2
gzip (transfer coding)
Section 7.2
Header Fields
MIME-Version
Appendix B.1
Transfer-Encoding
Section 6.1
header line
Section 2.1
header section
Section 2.1
headers
Section 2.1
Media Type
application/http
Section 10.2
message/http
Section 10.1
message/http Media Type
Section 10.1
method
Section 3.1
MIME-Version header field
Appendix B.1
origin-form (of request-target)
Section 3.2.1
request-target
Section 3.2
Transfer-Encoding header field
Section 6.1
x-compress (transfer coding)
Section 7.2
x-gzip (transfer coding)
Section 7.2
Authors' Addresses
Roy T. Fielding (
editor
Adobe
345 Park Ave
San Jose, CA 95110
United States of America
Email:
fielding@gbiv.com
URI:
Mark Nottingham (
editor
Fastly
Prahran
Australia
Email:
mnot@mnot.net
URI:
Julian Reschke (
editor
greenbytes GmbH
Hafenweg 16
48155 Münster
Germany
Email:
julian.reschke@greenbytes.de
URI: