HTTP/1.1, part 1: URIs, Connections, and Message ParsingAdobe Systems Incorporated345 Park AveSan JoseCA95110USAfielding@gbiv.comhttp://roy.gbiv.com/Alcatel-Lucent Bell Labs21 Oak Knoll RoadCarlisleMA01741USAjg@freedesktop.orghttp://gettys.wordpress.com/Hewlett-Packard CompanyHP Labs, Large Scale Systems Group1501 Page Mill Road, MS 1177Palo AltoCA94304USAJeffMogul@acm.orgMicrosoft Corporation1 Microsoft WayRedmondWA98052USAhenrikn@microsoft.comAdobe Systems Incorporated345 Park AveSan JoseCA95110USALMM@acm.orghttp://larry.masinter.net/Microsoft Corporation1 Microsoft WayRedmondWA98052paulle@microsoft.comWorld Wide Web ConsortiumMIT Computer Science and Artificial Intelligence LaboratoryThe Stata Center, Building 3232 Vassar StreetCambridgeMA02139USAtimbl@w3.orghttp://www.w3.org/People/Berners-Lee/World Wide Web ConsortiumW3C / ERCIM2004, rte des LuciolesSophia-AntipolisAM06902Franceylafon@w3.orghttp://www.raubacapeu.net/people/yves/greenbytes GmbHHafenweg 16MuensterNW48155Germany+49 251 2807760+49 251 2807761julian.reschke@greenbytes.dehttp://greenbytes.de/tech/webdav/HTTPbis Working Group
The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
distributed, collaborative, hypertext information systems. HTTP has been in
use by the World Wide Web global information initiative since 1990. This
document is Part 1 of the seven-part specification that defines the protocol
referred to as "HTTP/1.1" and, taken together, obsoletes
RFC 2616 and moves it to historic
status, along with its predecessor RFC
2068.
Part 1 provides an overview of HTTP and its associated terminology, defines
the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
the generic message syntax and parsing requirements for HTTP message frames,
and describes general security concerns for implementations.
This part also obsoletes RFCs 2145
(on HTTP version numbers) and 2817
(on using CONNECT for TLS upgrades) and moves them to historic status.
Discussion of this draft should take place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
.
The current issues list is at
and related
documents (including fancy diffs) can be found at
.
The changes in this draft are summarized in .
The Hypertext Transfer Protocol (HTTP) is an application-level
request/response protocol that uses extensible semantics and MIME-like
message payloads for flexible interaction with network-based hypertext
information systems. HTTP relies upon the Uniform Resource Identifier (URI)
standard to indicate the target resource and
relationships between resources.
Messages are passed in a format similar to that used by Internet mail
and the Multipurpose Internet Mail Extensions
(MIME) (see Appendix A of for the differences
between HTTP and MIME messages).
HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by presenting
a uniform interface to clients that is independent of the types of
resources provided. Likewise, servers do not need to be aware of each
client's purpose: an HTTP request can be considered in isolation rather
than being associated with a specific type of client or a predetermined
sequence of application steps. The result is a protocol that can be used
effectively in many different contexts and for which implementations can
evolve independently over time.
HTTP is also designed for use as an intermediation protocol for translating
communication to and from non-HTTP information systems.
HTTP proxies and gateways can provide access to alternative information
services by translating their diverse protocols into a hypertext
format that can be viewed and manipulated by clients in the same way
as HTTP services.
One consequence of HTTP flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent
of received communication, and the expected behavior of recipients.
If the communication is considered in isolation, then successful
actions ought to be reflected in corresponding changes to the
observable interface provided by servers. However, since multiple
clients might act in parallel and perhaps at cross-purposes, we
cannot require that such changes be observable beyond the scope
of a single response.
This document is Part 1 of the seven-part specification of HTTP,
defining the protocol referred to as "HTTP/1.1", obsoleting
and .
Part 1 describes the architectural elements that are used or
referred to in HTTP, defines the "http" and "https" URI schemes,
describes overall network operation and connection management,
and defines HTTP message framing and forwarding requirements.
Our goal is to define all of the mechanisms necessary for HTTP message
handling that are independent of message semantics, thereby defining the
complete set of requirements for message parsers and
message-forwarding intermediaries.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in .
This document defines conformance criteria for several roles in HTTP
communication, including Senders, Recipients, Clients, Servers, User-Agents,
Origin Servers, Intermediaries, Proxies and Gateways. See
for definitions of these terms.
An implementation is considered conformant if it complies with all of the
requirements associated with its role(s). Note that SHOULD-level requirements
are relevant here, unless one of the documented exceptions is applicable.
This document also uses ABNF to define valid protocol elements
(). In addition to the prose requirements placed
upon them, Senders MUST NOT generate protocol elements that are invalid.
Unless noted otherwise, Recipients MAY take steps to recover a usable
protocol element from an invalid construct. However, HTTP does not define
specific error handling mechanisms, except in cases where it has direct
impact on security. This is because different uses of the protocol require
different error handling strategies; for example, a Web browser may wish to
transparently recover from a response where the Location header field
doesn't parse according to the ABNF, whereby in a systems control protocol
using HTTP, this type of error recovery could lead to dangerous consequences.
This specification uses the Augmented Backus-Naur Form (ABNF) notation
of .
The following core rules are included by
reference, as defined in , 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 character).
As a syntactic convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons.
The #rule extension to the ABNF rules of is used to
improve readability.
A construct "#" is defined, similar to "*", for defining comma-delimited
lists of elements. The full form is "<n>#<m>element" indicating
at least <n> and at most <m> elements, each separated by a single
comma (",") and optional whitespace (OWS, ).
For compatibility with legacy list rules, recipients SHOULD accept empty
list elements. In other words, consumers would follow the list productions:
Note that empty elements do not contribute to the count of elements present,
though.
For example, given these ABNF productions:
Then these are valid values for example-list (not including the double
quotes, which are present for delimitation only):
But these values would be invalid, as at least one non-empty element is
required:
shows the collected ABNF, with the list rules
expanded as explained above.
This specification uses three rules to denote the use of linear
whitespace: OWS (optional whitespace), RWS (required whitespace), and
BWS ("bad" whitespace).
The OWS rule is used where zero or more linear whitespace octets might
appear. OWS SHOULD either not be produced or be produced as a single
SP. Multiple OWS octets that occur within field-content SHOULD either
be replaced with a single SP or transformed to all SP octets (each
octet other than SP replaced with SP) before interpreting the field value
or forwarding the message downstream.
RWS is used when at least one linear whitespace octet is required to
separate field tokens. RWS SHOULD be produced as a single SP.
Multiple RWS octets that occur within field-content SHOULD either
be replaced with a single SP or transformed to all SP octets before
interpreting the field value or forwarding the message downstream.
BWS is used where the grammar allows optional whitespace for historical
reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
recipients MUST accept such bad optional whitespace and remove it before
interpreting the field value or forwarding the message downstream.
HTTP was created for the World Wide Web architecture
and has evolved over time to support the scalability needs of a worldwide
hypertext system. Much of that architecture is reflected in the terminology
and syntax productions used to define HTTP.
HTTP is a stateless request/response protocol that operates by exchanging
messages () across a reliable
transport or session-layer
"connection". An HTTP "client" is a
program that establishes a connection to a server for the purpose of
sending one or more HTTP requests. An HTTP "server" is a
program that accepts connections in order to service HTTP requests by
sending HTTP responses.
Note that the terms client and server refer only to the roles that
these programs perform for a particular connection. The same program
might act as a client on some connections and a server on others. We use
the term "user agent" to refer to the program that initiates a request,
such as a WWW browser, editor, or spider (web-traversing robot), and
the term "origin server" to refer to the program that can originate
authoritative responses to a request. For general requirements, we use
the term "sender" to refer to whichever component sent a given message
and the term "recipient" to refer to any component that receives the
message.
Note: The term 'user agent' covers both those situations where
there is a user (human) interacting with the software agent (and for which
user interface or interactive suggestions might be made, e.g., warning the
user or given the user an option in the case of security or privacy
options) and also those where the software agent may act autonomously.
Most HTTP communication consists of a retrieval request (GET) for
a representation of some resource identified by a URI. In the
simplest case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin server (O).
A client sends an HTTP request to the server in the form of a request
message, beginning with a request-line that includes a method, URI, and
protocol version (),
followed by MIME-like header fields containing
request modifiers, client information, and payload metadata
(),
an empty line to indicate the end of the header section, and finally
a message body containing the payload body (if any,
).
A server responds to the client's request by sending an HTTP response
message, beginning with a status line that
includes the protocol version, a success or error code, and textual
reason phrase (),
followed by MIME-like header fields containing server
information, resource metadata, and payload metadata
(),
an empty line to indicate the end of the header section, and finally
a message body containing the payload body (if any,
).
Note that 1xx responses (Section 7.1 of ) are not final; therefore, a server
can send zero or more 1xx responses, followed by exactly one final response
(with any other status code).
The following example illustrates a typical message exchange for a
GET request on the URI "http://www.example.com/hello.txt":
Fundamentally, HTTP is a message-based protocol. Although message bodies can
be chunked () and implementations often
make parts of a message available progressively, this is not required, and
some widely-used implementations only make a message available when it is
complete. Furthermore, while most proxies will progressively stream messages,
some amount of buffering will take place, and some proxies might buffer
messages to perform transformations, check content or provide other services.
Therefore, extensions to and uses of HTTP cannot rely on the availability of
a partial message, or assume that messages will not be buffered. There are
strategies that can be used to test for buffering in a given connection, but
it should be understood that behaviors can differ across connections, and
between requests and responses.
Recipients MUST consider every message in a connection in isolation;
because HTTP is a stateless protocol, it cannot be assumed that two requests
on the same connection are from the same client or share any other common
attributes. In particular, intermediaries might mix requests from different
clients into a single server connection. Note that some existing HTTP
extensions (e.g., ) violate this requirement, thereby
potentially causing interoperability and security problems.
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 the underlying transport
protocol is outside the scope of this specification.
The specific connection protocols to be used for an interaction
are determined by client configuration and the target resource's URI.
For example, the "http" URI scheme
() 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
instead of using the defaults.
A connection might be used for multiple HTTP request/response exchanges,
as defined in .
HTTP enables the use of intermediaries to satisfy requests through
a chain of connections. There are three common forms of HTTP
intermediary: proxy, gateway, and tunnel. In some cases,
a single intermediary might act as an origin server, proxy, gateway,
or tunnel, switching behavior based on the nature of each request.
The figure above shows three intermediaries (A, B, and C) between the
user agent and origin server. A request or response message that
travels the whole chain will pass through four separate connections.
Some HTTP communication options
might apply only to the connection with the nearest, non-tunnel
neighbor, only to the end-points of the chain, or to all connections
along the chain. Although the diagram is linear, each participant might
be engaged in multiple, simultaneous communications. For example, B
might be receiving requests from many clients other than A, and/or
forwarding requests to servers other than C, at the same time that it
is handling A's request.
We use the terms "upstream" and "downstream"
to describe various requirements in relation to the directional flow of a
message: all messages flow from upstream to downstream.
Likewise, we use the terms inbound and outbound to refer to
directions in relation to the request path:
"inbound" means toward the origin server and
"outbound" means toward the user agent.
A "proxy" is a message forwarding agent that is selected by the
client, usually via local configuration rules, to receive requests
for some type(s) of absolute URI and attempt to satisfy those
requests via translation through the HTTP interface. Some translations
are minimal, such as for proxy requests for "http" URIs, whereas
other requests might require translation to and from entirely different
application-layer protocols. Proxies are often used to group an
organization's HTTP requests through a common intermediary for the
sake of security, annotation services, or shared caching.
An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
or configured to modify request or response messages in a semantically
meaningful way (i.e., modifications, beyond those required by normal
HTTP processing, that change the message in a way that would be
significant to the original sender or potentially significant to
downstream recipients). For example, a transforming proxy might be
acting as a shared annotation server (modifying responses to include
references to a local annotation database), a malware filter, a
format transcoder, or an intranet-to-Internet privacy filter. Such
transformations are presumed to be desired by the client (or client
organization) that selected the proxy and are beyond the scope of
this specification. However, when a proxy is not intended to transform
a given message, we use the term "non-transforming proxy" to target
requirements that preserve HTTP message semantics. See Section 7.2.4 of and
Section 3.6 of for status and warning codes related to transformations.
A "gateway" (a.k.a., "reverse proxy")
is a receiving agent that acts
as a layer above some other server(s) and translates the received
requests to the underlying server's protocol. Gateways are often
used to encapsulate legacy or untrusted information services, to
improve server performance through "accelerator" caching, and to
enable partitioning or load-balancing of HTTP services across
multiple machines.
A gateway behaves as an origin server on its outbound connection and
as a user agent on its inbound connection.
All HTTP requirements applicable to an origin server
also apply to the outbound communication of a gateway.
A gateway communicates with inbound servers using any protocol that
it desires, including private extensions to HTTP that are outside
the scope of this specification. However, an HTTP-to-HTTP gateway
that wishes to interoperate with third-party HTTP servers MUST
comply with HTTP user agent requirements on the gateway's inbound
connection and MUST implement the Connection
() and Via ()
header fields for both connections.
A "tunnel" acts as a blind relay between two connections
without changing the messages. Once active, a tunnel is not
considered a party to the HTTP communication, though the tunnel might
have been initiated by an HTTP request. A tunnel ceases to exist when
both ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when
transport-layer security is used to establish private communication
through a shared firewall proxy.
In addition, there may exist network intermediaries that are not
considered part of the HTTP communication but nevertheless act as
filters or redirecting agents (usually violating HTTP semantics,
causing security problems, and otherwise making a mess of things).
Such a network intermediary, often referred to as an "interception proxy"
, "transparent proxy" ,
or "captive portal",
differs from an HTTP proxy because it has not been selected by the client.
Instead, the network intermediary redirects outgoing TCP port 80 packets
(and occasionally other common port traffic) to an internal HTTP server.
Interception proxies are commonly found on public network access points,
as a means of enforcing account subscription prior to allowing use of
non-local Internet services, and within corporate firewalls to enforce
network usage policies.
They are indistinguishable from a man-in-the-middle attack.
A "cache" is a local store of previous response messages and the
subsystem that controls its message storage, retrieval, and deletion.
A cache stores cacheable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent
requests. Any client or server MAY employ a cache, though a cache
cannot be used by a server while it is acting as a tunnel.
The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting
chain if B has a cached copy of an earlier response from O (via C)
for a request which has not been cached by UA or A.
A response is "cacheable" if a cache is allowed to store a copy of
the response message for use in answering subsequent requests.
Even when a response is cacheable, there might be additional
constraints placed by the client or by the origin server on when
that cached response can be used for a particular request. HTTP
requirements for cache behavior and cacheable responses are
defined in Section 2 of .
There are a wide variety of architectures and configurations
of caches and proxies deployed across the World Wide Web and
inside large organizations. These systems include national hierarchies
of proxy caches to save transoceanic bandwidth, systems that
broadcast or multicast cache entries, organizations that distribute
subsets of cached data via optical media, and so on.
HTTP uses a "<major>.<minor>" numbering scheme to indicate
versions of the protocol. This specification defines version "1.1".
The protocol version as a whole indicates the sender's compliance
with the set of requirements laid out in that version's corresponding
specification of HTTP.
The version of an HTTP message is indicated by an HTTP-Version field
in the first line of the message. HTTP-Version is case-sensitive.
The HTTP version number consists of two decimal digits separated by a "."
(period or decimal point). The first digit ("major version") indicates the
HTTP messaging syntax, whereas the second digit ("minor version") indicates
the highest minor version to which the sender is at least conditionally
compliant and able to understand for future communication. The minor
version advertises the sender's communication capabilities even when the
sender is only using a backwards-compatible subset of the protocol,
thereby letting the recipient know that more advanced features can
be used in response (by servers) or in future requests (by clients).
When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
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 compliant 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.
The interpretation of an HTTP header field does not change
between minor versions of the same major version, though the default
behavior of a recipient in the absence of such a field can change.
Unless specified otherwise, header fields defined in HTTP/1.1 are
defined for all versions of HTTP/1.x. In particular, the Host and
Connection header fields ought to be implemented by all HTTP/1.x
implementations whether or not they advertise compliance with HTTP/1.1.
New header fields can be defined such that, when they are
understood by a recipient, they might override or enhance the
interpretation of previously defined header fields. When an
implementation receives an unrecognized header field, the recipient
MUST ignore that header field for local processing regardless of
the message's HTTP version. An unrecognized header field received
by a proxy MUST be forwarded downstream unless the header field's
field-name is listed in the message's Connection header-field
(see ).
These requirements allow HTTP's functionality to be enhanced without
requiring prior update of all compliant intermediaries.
Intermediaries that process HTTP messages (i.e., all intermediaries
other than those acting as a tunnel) MUST send their own HTTP-Version
in forwarded messages. In other words, they MUST NOT blindly
forward the first line of an HTTP message without ensuring that the
protocol version matches what the intermediary understands, and
is at least conditionally compliant to, for both the receiving and
sending of messages. Forwarding an HTTP message without rewriting
the HTTP-Version might result in communication errors when downstream
recipients use the message sender's version to determine what features
are safe to use for later communication with that sender.
An HTTP client SHOULD send a request version equal to the highest
version for which the client is at least conditionally compliant and
whose major version is no higher than the highest version supported
by the server, if this is known. An HTTP client MUST NOT send a
version for which it is not at least conditionally compliant.
An HTTP client MAY send a lower request version if it is known that
the server incorrectly implements the HTTP specification, but only
after the client has attempted at least one normal request and determined
from the response status or header fields (e.g., Server) that the
server improperly handles higher request versions.
An HTTP server SHOULD send a response version equal to the highest
version for which the server is at least conditionally compliant and
whose major version is less than or equal to the one received in the
request. An HTTP server MUST NOT send a version for which it is not
at least conditionally compliant. A server MAY send a 505 (HTTP
Version Not Supported) response if it cannot send a response using the
major version used in the client's request.
An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
if it is known or suspected that the client incorrectly implements the
HTTP specification and is incapable of correctly processing later
version responses, such as when a client fails to parse the version
number correctly or when an intermediary is known to blindly forward
the HTTP-Version even when it doesn't comply with the given minor
version of the protocol. Such protocol downgrades SHOULD NOT be
performed unless triggered by specific client attributes, such as when
one or more of the request header fields (e.g., User-Agent) uniquely
match the values sent by a client known to be in error.
The intention of HTTP's versioning design is that the major number
will only be incremented if an incompatible message syntax is
introduced, and that the minor number will only be incremented when
changes made to the protocol have the effect of adding to the message
semantics or implying additional capabilities of the sender. However,
the minor version was not incremented for the changes introduced between
and , and this revision
is specifically avoiding any such changes to the protocol.
Uniform Resource Identifiers (URIs) are used
throughout HTTP as the means for identifying resources. URI references
are used to target requests, indicate redirects, and define relationships.
HTTP does not limit what a resource might be; it merely defines an interface
that can be used to interact with a resource via HTTP. More information on
the scope of URIs and resources can be found in .
This specification adopts the definitions of "URI-reference",
"absolute-URI", "relative-part", "port", "host",
"path-abempty", "path-absolute", "query", and "authority" from the
URI generic syntax .
In addition, we define a partial-URI rule for protocol elements
that allow a relative URI but not a fragment.
Each protocol element in HTTP that allows a URI reference will indicate
in its ABNF production whether the element allows any form of reference
(URI-reference), only a URI in absolute form (absolute-URI), only the
path and optional query components, or some combination of the above.
Unless otherwise indicated, URI references are parsed relative to the
effective request URI, which defines the default base URI for references
in both the request and its corresponding response.
The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
TCP connections on a given port.
The HTTP origin server is identified by the generic syntax's
authority component, which includes a host identifier
and optional TCP port (, Section 3.2.2).
The remainder of the URI, consisting of both the hierarchical path
component and optional query component, serves as an identifier for
a potential resource within that origin server's name space.
If the host identifier is provided as an IP literal or IPv4 address,
then the origin server is any listener on the indicated TCP port at
that IP address. If host is a registered name, then that name is
considered an indirect identifier and the recipient might use a name
resolution service, such as DNS, to find the address of a listener
for that host.
The host MUST NOT be empty; if an "http" URI is received with an
empty host, then it MUST be rejected as invalid.
If the port subcomponent is empty or not given, then TCP port 80 is
assumed (the default reserved port for WWW services).
Regardless of the form of host identifier, access to that host is not
implied by the mere presence of its name or address. The host might or might
not exist and, even when it does exist, might or might not be running an
HTTP server or listening to the indicated port. The "http" URI scheme
makes use of the delegated nature of Internet names and addresses to
establish a naming authority (whatever entity has the ability to place
an HTTP server at that Internet name or address) and allows that
authority to determine which names are valid and how they might be used.
When an "http" URI is used within a context that calls for access to the
indicated resource, a client MAY attempt access by resolving
the host to an IP address, establishing a TCP connection to that address
on the indicated port, and sending an HTTP request message
() containing the URI's identifying data
() to the server.
If the server responds to that request with a non-interim HTTP response
message, as described in Section 4 of , then that response
is considered an authoritative answer to the client's request.
Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority.
An HTTP service based on some other underlying connection protocol
would presumably be identified using a different URI scheme, just as
the "https" scheme (below) is used for servers that require an SSL/TLS
transport layer on a connection. Other protocols might also be used to
provide access to "http" identified resources — it is only the
authoritative interface used for mapping the namespace that is
specific to TCP.
The URI generic syntax for authority also includes a deprecated
userinfo subcomponent (, Section 3.2.1)
for including user authentication information in the URI. Some
implementations make use of the userinfo component for internal
configuration of authentication information, such as within command
invocation options, configuration files, or bookmark lists, even
though such usage might expose a user identifier or password.
Senders MUST NOT include a userinfo subcomponent (and its "@"
delimiter) when transmitting an "http" URI in a message. Recipients
of HTTP messages that contain a URI reference SHOULD parse for the
existence of userinfo and treat its presence as an error, likely
indicating that the deprecated subcomponent is being used to obscure
the authority for the sake of phishing attacks.
The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
SSL/TLS-secured connections on a given TCP port.
All of the requirements listed above for the "http" scheme are also
requirements for the "https" scheme, except that a default TCP port
of 443 is assumed if the port subcomponent is empty or not given,
and the TCP connection MUST be secured for privacy through the
use of strong encryption prior to sending the first HTTP request.
Unlike the "http" scheme, responses to "https" identified requests
are never "public" and thus MUST NOT be reused for shared caching.
They can, however, be reused in a private cache if the message is
cacheable by default in HTTP or specifically indicated as such by
the Cache-Control header field (Section 3.2 of ).
Resources made available via the "https" scheme have no shared
identity with the "http" scheme even if their resource identifiers
indicate the same authority (the same host listening to the same
TCP port). They are distinct name spaces and are considered to be
distinct origin servers. However, an extension to HTTP that is
defined to apply to entire host domains, such as the Cookie protocol
, can allow information
set by one service to impact communication with other services
within a matching group of host domains.
The process for authoritative access to an "https" identified
resource is defined in .
Since the "http" and "https" schemes conform to the URI generic syntax,
such URIs are normalized and compared according to the algorithm defined
in , Section 6, using the defaults
described above for each scheme.
If the port is equal to the default port for a scheme, the normal
form is to elide the port subcomponent. Likewise, an empty path
component is equivalent to an absolute path of "/", so the normal
form is to provide a path of "/" instead. The scheme and host
are case-insensitive and normally provided in lowercase; all
other components are compared in a case-sensitive manner.
Characters other than those in the "reserved" set are equivalent
to their percent-encoded octets (see , Section 2.1): the normal form is to not encode them.
For example, the following three URIs are equivalent:
All HTTP/1.1 messages consist of a start-line followed by a sequence of
octets in a format similar to the Internet Message Format
: zero or more header fields (collectively
referred to as the "headers" or the "header section"), an empty line
indicating the end of the header section, and an optional message-body.
The normal procedure for parsing an HTTP message is to read the
start-line into a structure, read each header field into a hash
table by field name until the empty line, and then use the parsed
data to determine if a message-body is expected. If a message-body
has been indicated, then it is read as a stream until an amount
of octets equal to the message-body length is read or the connection
is closed.
Recipients MUST parse an HTTP message as a sequence of octets in an
encoding that is a superset of US-ASCII .
Parsing an HTTP message as a stream of Unicode characters, without regard
for the specific encoding, creates security vulnerabilities due to the
varying ways that string processing libraries handle invalid multibyte
character sequences that contain the octet LF (%x0A). String-based
parsers can only be safely used within protocol elements after the element
has been extracted from the message, such as within a header field-value
after message parsing has delineated the individual fields.
An HTTP message can either be a request from client to server or a
response from server to client. Syntactically, the two types of message
differ only in the start-line, which is either a Request-Line (for requests)
or a Status-Line (for responses), and in the algorithm for determining
the length of the message-body ().
In theory, a client could receive requests and a server could receive
responses, distinguishing them by their different start-line formats,
but in practice servers are implemented to only expect a request
(a response is interpreted as an unknown or invalid request method)
and clients are implemented to only expect a response.
Implementations MUST NOT send whitespace between the start-line and
the first header field. The presence of such whitespace in a request
might be an attempt to trick a server into ignoring that field or
processing the line after it as a new request, either of which might
result in a security vulnerability if other implementations within
the request chain interpret the same message differently.
Likewise, the presence of such whitespace in a response might be
ignored by some clients or cause others to cease parsing.
The Request-Line begins with a method token, followed by a single
space (SP), the request-target, another single space (SP), the
protocol version, and ending with CRLF.
The Method token indicates the request method to be performed on the
target resource. The request method is case-sensitive.
See Section 2 of for further information, such as the list of methods defined
by this specification, the IANA registry, and considerations for new methods.
The request-target identifies the target resource upon which to apply
the request. The four options for request-target are described in
.
HTTP does not place a pre-defined limit on the length of a request-target.
A server MUST be prepared to receive URIs of unbounded length and
respond with the 414 (URI Too Long) status code if the received
request-target would be longer than the server wishes to handle
(see Section 7.4.15 of ).
Various ad-hoc limitations on request-target length are found in practice.
It is RECOMMENDED that all HTTP senders and recipients support
request-target lengths of 8000 or more octets.
Note: Fragments (, Section 3.5)
are not part of the request-target and thus will not be transmitted
in an HTTP request.
The first line of a Response message is the Status-Line, consisting
of the protocol version, a space (SP), the status code, another space,
a possibly-empty textual phrase describing the status code, and
ending with CRLF.
The Status-Code element is a 3-digit integer result code of the attempt to
understand and satisfy the request. See Section 4 of for
further information, such as the list of status codes defined by this
specification, the IANA registry, and considerations for new status codes.
The Reason Phrase exists for the sole purpose of providing a textual
description associated with the numeric status code, out of deference to
earlier Internet application protocols that were more frequently used with
interactive text clients. A client SHOULD ignore the content of the Reason
Phrase.
Each HTTP header field consists of a case-insensitive field name
followed by a colon (":"), optional whitespace, and the field value.
The field-name token labels the corresponding field-value as having the
semantics defined by that header field. For example, the Date header field
is defined in Section 9.2 of as containing the origination
timestamp for the message in which it appears.
HTTP header fields are fully extensible: there is no limit on the
introduction of new field names, each presumably defining new semantics,
or on the number of header fields used in a given message. Existing
fields are defined in each part of this specification and in many other
specifications outside the standards process.
New header fields can be introduced without changing the protocol version
if their defined semantics allow them to be safely ignored by recipients
that do not recognize them.
New HTTP header fields SHOULD be registered with IANA according
to the procedures in Section 3.1 of .
Unrecognized header fields MUST be forwarded by a proxy unless the
field-name is listed in the Connection header field
() or the proxy is specifically
configured to block or otherwise transform such fields.
Unrecognized header fields SHOULD be ignored by other recipients.
The order in which header fields with differing field names are
received is not significant. However, it is "good practice" to send
header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST
wait until the entire header section is received before interpreting
a request message, since later header fields might include conditionals,
authentication credentials, or deliberately misleading duplicate
header fields that would impact request processing.
Multiple header fields with the same field name MUST NOT be
sent in a message unless the entire field value for that
header field is defined as a comma-separated list [i.e., #(values)].
Multiple header fields with the same field name can be combined into
one "field-name: field-value" pair, without changing the semantics of the
message, by appending each subsequent field value to the combined
field value in order, separated by a comma. The order in which
header fields with the same field name are received is therefore
significant to the interpretation of the combined field value;
a proxy MUST NOT change the order of these field values when
forwarding a message.
Note: The "Set-Cookie" header field as implemented in
practice can occur multiple times, but does not use the list syntax, and
thus cannot be combined into a single line (). (See Appendix A.2.3 of
for details.) Also note that the Set-Cookie2 header field specified in
does not share this problem.
No whitespace is allowed between the header field-name and colon.
In the past, differences in the handling of such whitespace have led to
security vulnerabilities in request routing and response handling.
Any received request message that contains whitespace between a header
field-name and colon MUST be rejected with a response code of 400
(Bad Request). A proxy MUST remove any such whitespace from a response
message before forwarding the message downstream.
A field value MAY be preceded by optional whitespace (OWS); a single SP is
preferred. The field value does not include any leading or trailing white
space: OWS occurring before the first non-whitespace octet of the
field value or after the last non-whitespace octet of the field value
is ignored and SHOULD be removed before further processing (as this does
not change the meaning of the header field).
Historically, HTTP header field values could be extended over multiple
lines by preceding each extra line with at least one space or horizontal
tab (obs-fold). This specification deprecates such line
folding except within the message/http media type
().
HTTP senders MUST NOT produce messages that include line folding
(i.e., that contain any field-content that matches the obs-fold rule) unless
the message is intended for packaging within the message/http media type.
HTTP recipients SHOULD accept line folding and replace any embedded
obs-fold whitespace with either a single SP or a matching number of SP
octets (to avoid buffer copying) prior to interpreting the field value or
forwarding the message downstream.
Historically, HTTP has allowed field content with text in the ISO-8859-1
character encoding and supported other
character sets only through use of encoding.
In practice, most HTTP header field values use only a subset of the
US-ASCII character encoding . Newly defined
header fields SHOULD limit their field values to US-ASCII octets.
Recipients SHOULD treat other (obs-text) octets in field content as
opaque data.
HTTP does not place a pre-defined limit on the length of header fields,
either in isolation or as a set. A server MUST be prepared to receive
request header fields of unbounded length and respond with a 4xx status
code if the received header field(s) would be longer than the server wishes
to handle.
A client that receives response headers that are longer than it wishes to
handle can only treat it as a server error.
Various ad-hoc limitations on header length are found in practice. It is
RECOMMENDED that all HTTP senders and recipients support messages whose
combined header fields have 4000 or more octets.
Many HTTP/1.1 header field values consist of words (token or quoted-string)
separated by whitespace or special characters. These special characters
MUST be in a quoted string to be used within a parameter value (as defined
in ).
A string of text is parsed as a single word if it is quoted using
double-quote marks.
The backslash octet ("\") can be used as a single-octet
quoting mechanism within quoted-string constructs:
Recipients that process the value of the quoted-string MUST handle a
quoted-pair as if it were replaced by the octet following the backslash.
Senders SHOULD NOT escape octets in quoted-strings that do not require
escaping (i.e., other than DQUOTE and the backslash octet).
Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
The backslash octet ("\") can be used as a single-octet
quoting mechanism within comment constructs:
Senders SHOULD NOT escape octets in comments that do not require escaping
(i.e., other than the backslash octet "\" and the parentheses "(" and ")").
The message-body (if any) of an HTTP message is used to carry the
payload body associated with the request or response.
The message-body differs from the payload body only when a transfer-coding
has been applied, as indicated by the Transfer-Encoding header field
(). If more than one
Transfer-Encoding header field is present in a message, the multiple
field-values MUST be combined into one field-value, according to the
algorithm defined in , before determining
the message-body length.
When one or more transfer-codings are applied to a payload in order to
form the message-body, the Transfer-Encoding header field MUST contain
the list of transfer-codings applied. Transfer-Encoding is a property of
the message, not of the payload, and thus MAY be added or removed by
any implementation along the request/response chain under the constraints
found in .
If a message is received that has multiple Content-Length header fields
() with field-values consisting
of the same decimal value, or a single Content-Length header field with
a field value containing a list of identical decimal values (e.g.,
"Content-Length: 42, 42"), indicating that duplicate Content-Length
header fields have been generated or combined by an upstream message
processor, then the recipient MUST either reject the message as invalid
or replace the duplicated field-values with a single valid Content-Length
field containing that decimal value prior to determining the message-body
length.
The rules for when a message-body is allowed in a message differ for
requests and responses.
The presence of a message-body in a request is signaled by the
inclusion of a Content-Length or Transfer-Encoding header field in
the request's header fields, even if the request method does not
define any use for a message-body. This allows the request
message framing algorithm to be independent of method semantics.
For response messages, whether or not a message-body is included with
a message is dependent on both the request method and the response
status code ().
Responses to the HEAD request method never include a message-body
because the associated response header fields (e.g., Transfer-Encoding,
Content-Length, etc.) only indicate what their values would have been
if the request method had been GET. All 1xx (Informational), 204 (No Content),
and 304 (Not Modified) responses MUST NOT include a message-body.
All other responses do include a message-body, although the body
MAY be of zero length.
The length of the message-body is determined by one of the following
(in order of precedence):
Any response to a HEAD request and any response with a status
code of 100-199, 204, or 304 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.
If a Transfer-Encoding header field is present
and the "chunked" transfer-coding ()
is the final encoding, the message-body length is determined by reading
and decoding the chunked data until the transfer-coding indicates the
data is complete.
If a Transfer-Encoding header field is present in a response and the
"chunked" transfer-coding is not the final encoding, the message-body
length is determined by reading the connection until it is closed by
the server.
If a Transfer-Encoding header field is present in a request and the
"chunked" transfer-coding is not the final encoding, the message-body
length cannot be determined reliably; the server MUST respond with
the 400 (Bad Request) status code and then close the connection.
If a message is received with both a Transfer-Encoding header field
and a Content-Length header field, the Transfer-Encoding overrides
the Content-Length.
Such a message might indicate an attempt to perform request or response
smuggling (bypass of security-related checks on message routing or content)
and thus ought to be handled as an error. The provided Content-Length MUST
be removed, prior to forwarding the message downstream, or replaced with
the real message-body length after the transfer-coding is decoded.
If a message is received without Transfer-Encoding and with either
multiple Content-Length header fields having differing field-values or
a single Content-Length header field having an invalid value, then the
message framing is invalid and MUST be treated as an error to
prevent request or response smuggling.
If this is a request message, the server MUST respond with
a 400 (Bad Request) status code and then close the connection.
If this is a response message received by a proxy, the proxy
MUST discard the received response, send a 502 (Bad Gateway)
status code as its downstream response, and then close the connection.
If this is a response message received by a user-agent, it MUST be
treated as an error by discarding the message and closing the connection.
If a valid Content-Length header field
is present without Transfer-Encoding, its decimal value defines the
message-body length in octets. If the actual number of octets sent in
the message is less than the indicated Content-Length, the recipient
MUST consider the message to be incomplete and treat the connection
as no longer usable.
If the actual number of octets sent in the message is more than the indicated
Content-Length, the recipient MUST only process the message-body up to the
field value's number of octets; the remainder of the message MUST either
be discarded or treated as the next message in a pipeline. For the sake of
robustness, a user-agent MAY attempt to detect and correct such an error
in message framing if it is parsing the response to the last request on
a connection and the connection has been closed by the server.
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 message from a partially-received message interrupted
by network failure, implementations SHOULD use encoding or
length-delimited messages whenever possible. The close-delimiting
feature exists primarily for backwards compatibility with HTTP/1.0.
A server MAY reject a request that contains a message-body but
not a Content-Length by responding with 411 (Length Required).
Unless a transfer-coding other than "chunked" has been applied,
a client that sends a request containing a message-body SHOULD
use a valid Content-Length header field if the message-body length
is known in advance, rather than the "chunked" encoding, since some
existing services respond to "chunked" with a 411 (Length Required)
status code even though they understand the chunked encoding. This
is typically because such services are implemented via a gateway that
requires a content-length in advance of being called and the server
is unable or unwilling to buffer the entire request before processing.
A client that sends a request containing a message-body MUST include a
valid Content-Length header field if it does not know the server will
handle HTTP/1.1 (or later) requests; such knowledge can be in the form
of specific user configuration or by remembering the version of a prior
received response.
Request messages that are prematurely terminated, possibly due to a
cancelled connection or a server-imposed time-out exception, MUST
result in closure of the connection; sending an HTTP/1.1 error response
prior to closing the connection is OPTIONAL.
Response messages that are prematurely terminated, usually by closure
of the connection prior to receiving the expected number of octets or by
failure to decode a transfer-encoded message-body, MUST be recorded
as incomplete. A response that terminates in the middle of the header
block (before the empty line is received) cannot be assumed to convey the
full semantics of the response and MUST be treated as an error.
A message-body that uses the chunked transfer encoding is
incomplete if the zero-sized chunk that terminates the encoding has not
been received. A message that uses a valid Content-Length is incomplete
if the size of the message-body received (in octets) is less than the
value given by Content-Length. A response that has neither chunked
transfer encoding nor Content-Length is terminated by closure of the
connection, and thus is considered complete regardless of the number of
message-body octets received, provided that the header block was received
intact.
A user agent MUST NOT render an incomplete response message-body as if
it were complete (i.e., some indication must be given to the user that an
error occurred). Cache requirements for incomplete responses are defined
in Section 2.1 of .
A server MUST read the entire request message-body or close
the connection after sending its response, since otherwise the
remaining data on a persistent connection would be misinterpreted
as the next request. Likewise,
a client MUST read the entire response message-body if it intends
to reuse the same connection for a subsequent request. Pipelining
multiple requests on a connection is described in .
Older HTTP/1.0 client implementations might send an extra CRLF
after a POST request as a lame workaround for some early server
applications that failed to read message-body content that was
not terminated by a line-ending. An HTTP/1.1 client MUST NOT
preface or follow a request with an extra CRLF. If terminating
the request message-body with a line-ending is desired, then the
client MUST include the terminating CRLF octets as part of the
message-body length.
In the interest of robustness, servers SHOULD ignore at least one
empty line received where a Request-Line is expected. In other words, if
the server is reading the protocol stream at the beginning of a
message and receives a CRLF first, it SHOULD ignore the CRLF.
Likewise, although the line terminator for the start-line and header
fields is the sequence CRLF, we recommend that recipients recognize a
single LF as a line terminator and ignore any CR.
When a server listening only for HTTP request messages, or processing
what appears from the start-line to be an HTTP request message,
receives a sequence of octets that does not match the HTTP-message
grammar aside from the robustness exceptions listed above, the
server MUST respond with an HTTP/1.1 400 (Bad Request) response.
In most cases, the user agent is provided a URI reference
from which it determines an absolute URI for identifying the target
resource. When a request to the resource is initiated, all or part
of that URI is used to construct the HTTP request-target.
The four options for request-target are dependent on the nature of the
request.
The asterisk "*" form of request-target, which MUST NOT be used
with any request method other than OPTIONS, means that the request
applies to the server as a whole (the listening process) rather than
to a specific named resource at that server. For example,
The "absolute-URI" form is REQUIRED when the request is being made to a
proxy. The proxy is requested to either forward the request or service it
from a valid cache, and then return the response. Note that the proxy MAY
forward the request on to another proxy or directly to the server
specified by the absolute-URI. In order to avoid request loops, a
proxy that forwards requests to other proxies MUST be able to
recognize and exclude all of its own server names, including
any aliases, local variations, and the numeric IP address. An example
Request-Line would be:
To allow for transition to absolute-URIs in all requests in future
versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
form in requests, even though HTTP/1.1 clients will only generate
them in requests to proxies.
If a proxy receives a host name that is not a fully qualified domain
name, it MAY add its domain to the host name it received. If a proxy
receives a fully qualified domain name, the proxy MUST NOT change
the host name.
The "authority form" is only used by the CONNECT request method (Section 6.9 of ).
The most common form of request-target is that used when making
a request to an origin server ("origin form").
In this case, the absolute path and query components of the URI
MUST be transmitted as the request-target, and the authority component
MUST be transmitted in a Host header field. For example, a client wishing
to retrieve a representation of the resource, as identified above,
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:
followed by the remainder of the Request. Note that the origin form
of request-target always starts with an absolute path; if the target
resource's URI path is empty, then an absolute path of "/" MUST be
provided in the request-target.
If a proxy receives an OPTIONS request with an absolute-URI 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 use a request-target
of "*" when it forwards the request to the indicated origin server.
The request-target is transmitted in the format specified in
. If the request-target is percent-encoded
(, Section 2.1), the origin server
MUST decode the request-target in order to
properly interpret the request. Servers SHOULD respond to invalid
request-targets with an appropriate status code.
A non-transforming proxy MUST NOT rewrite the "path-absolute" and "query"
parts of the received request-target when forwarding it to the next inbound
server, except as noted above to replace a null path-absolute with "/" or
"*".
Note: The "no rewrite" rule prevents the proxy from changing the
meaning of the request when the origin server is improperly using
a non-reserved URI character for a reserved purpose. Implementors
need to be aware that some pre-HTTP/1.1 proxies have been known to
rewrite the request-target.
The exact resource identified by an Internet request is determined by
examining both the request-target and the Host header field.
An origin server that does not allow resources to differ by the
requested host MAY ignore the Host header field value when
determining the resource identified by an HTTP/1.1 request. (But see
for other requirements on Host support in HTTP/1.1.)
An origin server that does differentiate resources based on the host
requested (sometimes referred to as virtual hosts or vanity host
names) MUST use the following rules for determining the requested
resource on an HTTP/1.1 request:
If request-target is an absolute-URI, the host is part of the
request-target. Any Host header field value in the request MUST be
ignored.If the request-target is not an absolute-URI, and the request includes
a Host header field, the host is determined by the Host header
field value.If the host as determined by rule 1 or 2 is not a valid host on
the server, the response MUST be a 400 (Bad Request) error message.
Recipients of an HTTP/1.0 request that lacks a Host header field MAY
attempt to use heuristics (e.g., examination of the URI path for
something unique to a particular host) in order to determine what
exact resource is being requested.
HTTP requests often do not carry the absolute URI (, Section 4.3)
for the target resource; instead, the URI needs to be inferred from the
request-target, Host header field, and connection context. The result of
this process is called the "effective request URI". The "target resource"
is the resource identified by the effective request URI.
If the request-target is an absolute-URI, then the effective request URI is
the request-target.
If the request-target uses the origin form or the asterisk form,
and the Host header field is present, then the effective request URI is
constructed by concatenating
the scheme name: "http" if the request was received over an insecure
TCP connection, or "https" when received over a SSL/TLS-secured TCP
connection,
the octet sequence "://",
the authority component, as specified in the Host header field
(), and
the request-target obtained from the Request-Line, unless the
request-target is just the asterisk "*".
If the request-target uses the origin form or the asterisk form,
and the Host header field is not present, then the effective request URI is
undefined.
Otherwise, when request-target uses the authority form, the effective
request URI is undefined.
Effective request URIs are compared using the rules described in
, except that empty path components MUST NOT
be treated as equivalent to an absolute path of "/".
Transfer-coding values are used to indicate an encoding
transformation that has been, can be, or might need to be applied to a
payload body in order to ensure "safe transport" through the network.
This differs from a content coding in that the transfer-coding is a
property of the message rather than a property of the representation
that is being transferred.
Parameters are in the form of attribute/value pairs.
All transfer-coding values are case-insensitive. HTTP/1.1 uses
transfer-coding values in the TE header field () and in
the Transfer-Encoding header field ().
Transfer-codings are analogous to the Content-Transfer-Encoding values of
MIME, which were designed to enable safe transport of binary data over a
7-bit transport service (, Section 6).
However, safe transport
has a different focus for an 8bit-clean transfer protocol. In HTTP,
the only unsafe characteristic of message-bodies is the difficulty in
determining the exact message body length (),
or the desire to encrypt data over a shared transport.
A server that receives a request message with a transfer-coding it does
not understand SHOULD respond with 501 (Not Implemented) and then
close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
client.
The chunked encoding modifies the body of a message in order to
transfer it as a series of chunks, each with its own size indicator,
followed by an OPTIONAL trailer containing header fields. This
allows dynamically produced content to be transferred along with the
information necessary for the recipient to verify that it has
received the full message.
The chunk-size field is a string of hex digits indicating the size of
the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
zero, followed by the trailer, which is terminated by an empty line.
The trailer allows the sender to include additional HTTP header
fields at the end of the message. The Trailer header field can be
used to indicate which header fields are included in a trailer (see
).
A server using chunked transfer-coding in a response MUST NOT use the
trailer for any header fields unless at least one of the following is
true:
the request included a TE header field that indicates "trailers" is
acceptable in the transfer-coding of the response, as described in
; or,the trailer fields consist entirely of optional metadata, and the
recipient could use the message (in a manner acceptable to the server where
the field originated) without receiving it. In other words, the server that
generated the header (often but not always the origin server) is willing to
accept the possibility that the trailer fields might be silently discarded
along the path to the client.
This requirement prevents an interoperability failure when the
message is being received by an HTTP/1.1 (or later) proxy and
forwarded to an HTTP/1.0 recipient. It avoids a situation where
compliance with the protocol would have necessitated a possibly
infinite buffer on the proxy.
A process for decoding the "chunked" transfer-coding
can be represented in pseudo-code as:
All HTTP/1.1 applications MUST be able to receive and decode the
"chunked" transfer-coding and MUST ignore chunk-ext extensions
they do not understand.
Since "chunked" is the only transfer-coding required to be understood
by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
on a persistent connection. Whenever a transfer-coding is applied to
a payload body in a request, the final transfer-coding applied MUST
be "chunked". If a transfer-coding is applied to a response payload
body, then either the final transfer-coding applied MUST be "chunked"
or the message MUST be terminated by closing the connection. When the
"chunked" transfer-coding is used, it MUST be the last transfer-coding
applied to form the message-body. The "chunked" transfer-coding MUST NOT
be applied more than once in a message-body.
The codings defined below can be used to compress the payload of a
message.
Note: Use of program names for the identification of encoding formats
is not desirable and is discouraged for future encodings. Their
use here is representative of historical practice, not good
design.
Note: For compatibility with previous implementations of HTTP,
applications SHOULD consider "x-gzip" and "x-compress" to be
equivalent to "gzip" and "compress" respectively.
The "compress" format is produced by the common UNIX file compression
program "compress". This format is an adaptive Lempel-Ziv-Welch
coding (LZW).
The "deflate" format is defined as the "deflate" compression mechanism
(described in ) used inside the "zlib"
data format ().
Note: Some incorrect implementations send the "deflate"
compressed data without the zlib wrapper.
The "gzip" format is produced by the file compression program
"gzip" (GNU zip), as described in . This format is a
Lempel-Ziv coding (LZ77) with a 32 bit CRC.
The HTTP Transfer Coding Registry defines the name space for the transfer
coding names.
Registrations MUST include the following fields:
NameDescriptionPointer to specification text
Names of transfer codings MUST NOT overlap with names of content codings
(Section 2.2 of ), unless the encoding transformation is identical (as it
is the case for the compression codings defined in
).
Values to be added to this name space require a specification
(see "Specification Required" in Section 4.1 of ), and MUST
conform to the purpose of transfer coding defined in this section.
The registry itself is maintained at
.
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by whitespace. By
convention, the products are listed in order of their significance
for identifying the application.
Examples:
Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although any
token octet MAY appear in a product-version, this token SHOULD
only be used for a version identifier (i.e., successive versions of
the same product SHOULD only differ in the product-version portion of
the product value).
Both transfer codings (TE request header field, )
and content negotiation (Section 5 of ) use short "floating point"
numbers to indicate the relative importance ("weight") of various
negotiable parameters. A weight is normalized to a real number in
the range 0 through 1, where 0 is the minimum and 1 the maximum
value. If a parameter has a quality value of 0, then content with
this parameter is "not acceptable" for the client. HTTP/1.1
applications MUST NOT generate more than three digits after the
decimal point. User configuration of these values SHOULD also be
limited in this fashion.
Note: "Quality values" is a misnomer, since these values merely represent
relative degradation in desired quality.
Prior to persistent connections, a separate TCP connection was
established for each request, increasing the load on HTTP servers
and causing congestion on the Internet. The use of inline images and
other associated data often requires a client to make multiple
requests of the same server in a short amount of time. Analysis of
these performance problems and results from a prototype
implementation are available . Implementation experience and
measurements of actual HTTP/1.1 implementations show good
results . Alternatives have also been explored, for example,
T/TCP .
Persistent HTTP connections have a number of advantages:
By opening and closing fewer TCP connections, CPU time is saved
in routers and hosts (clients, servers, proxies, gateways,
tunnels, or caches), and memory used for TCP protocol control
blocks can be saved in hosts.
HTTP requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single TCP connection to
be used much more efficiently, with much lower elapsed time.
Network congestion is reduced by reducing the number of packets
caused by TCP opens, and by allowing TCP sufficient time to
determine the congestion state of the network.
Latency on subsequent requests is reduced since there is no time
spent in TCP's connection opening handshake.
HTTP can evolve more gracefully, since errors can be reported
without the penalty of closing the TCP connection. Clients using
future versions of HTTP might optimistically try a new feature,
but if communicating with an older server, retry with old
semantics after an error is reported.
HTTP implementations SHOULD implement persistent connections.
A significant difference between HTTP/1.1 and earlier versions of
HTTP is that persistent connections are the default behavior of any
HTTP connection. That is, unless otherwise indicated, the client
SHOULD assume that the server will maintain a persistent connection,
even after error responses from the server.
Persistent connections provide a mechanism by which a client and a
server can signal the close of a TCP connection. This signaling takes
place using the Connection header field (). Once a close
has been signaled, the client MUST NOT send any more requests on that
connection.
An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
maintain a persistent connection unless a Connection header field including
the connection-token "close" was sent in the request. If the server
chooses to close the connection immediately after sending the
response, it SHOULD send a Connection header field including the
connection-token "close".
An HTTP/1.1 client MAY expect a connection to remain open, but would
decide to keep it open based on whether the response from a server
contains a Connection header field with the connection-token close. In case
the client does not want to maintain a connection for more than that
request, it SHOULD send a Connection header field including the
connection-token close.
If either the client or the server sends the close token in the
Connection header field, that request becomes the last one for the
connection.
Clients and servers SHOULD NOT assume that a persistent connection is
maintained for HTTP versions less than 1.1 unless it is explicitly
signaled. See for more information on backward
compatibility with HTTP/1.0 clients.
In order to remain persistent, all messages on the connection MUST
have a self-defined message length (i.e., one not defined by closure
of the connection), as described in .
A client that supports persistent connections MAY "pipeline" its
requests (i.e., send multiple requests without waiting for each
response). A server MUST send its responses to those requests in the
same order that the requests were received.
Clients which assume persistent connections and pipeline immediately
after connection establishment SHOULD be prepared to retry their
connection if the first pipelined attempt fails. If a client does
such a retry, it MUST NOT pipeline before it knows the connection is
persistent. Clients MUST also be prepared to resend their requests if
the server closes the connection before sending all of the
corresponding responses.
Clients SHOULD NOT pipeline requests using non-idempotent request methods or
non-idempotent sequences of request methods (see Section 6.1.2 of ). Otherwise, a
premature termination of the transport connection could lead to
indeterminate results. A client wishing to send a non-idempotent
request SHOULD wait to send that request until it has received the
response status line for the previous request.
It is especially important that proxies correctly implement the
properties of the Connection header field as specified in .
The proxy server MUST signal persistent connections separately with
its clients and the origin servers (or other proxy servers) that it
connects to. Each persistent connection applies to only one transport
link.
A proxy server MUST NOT establish a HTTP/1.1 persistent connection
with an HTTP/1.0 client (but see Section 19.7.1 of
for information and discussion of the problems with the Keep-Alive header field
implemented by many HTTP/1.0 clients).
For the purpose of defining the behavior of caches and non-caching
proxies, we divide HTTP header fields into two categories:
End-to-end header fields, which are transmitted to the ultimate
recipient of a request or response. End-to-end header fields in
responses MUST be stored as part of a cache entry and MUST be
transmitted in any response formed from a cache entry.Hop-by-hop header fields, which are meaningful only for a single
transport-level connection, and are not stored by caches or
forwarded by proxies.
The following HTTP/1.1 header fields are hop-by-hop header fields:
ConnectionKeep-AliveProxy-AuthenticateProxy-AuthorizationTETrailerTransfer-EncodingUpgrade
All other header fields defined by HTTP/1.1 are end-to-end header fields.
Other hop-by-hop header fields MUST be listed in a Connection header field
().
Some features of HTTP/1.1, such as Digest Authentication, depend on the
value of certain end-to-end header fields. A non-transforming proxy SHOULD NOT
modify an end-to-end header field unless the definition of that header field requires
or specifically allows that.
A non-transforming proxy MUST NOT modify any of the following fields in a
request or response, and it MUST NOT add any of these fields if not
already present:
AllowContent-LocationContent-MD5ETagLast-ModifiedServer
A non-transforming proxy MUST NOT modify any of the following fields in a
response:
Expires
but it MAY add any of these fields if not already present. If an
Expires header field is added, it MUST be given a field-value identical to
that of the Date header field in that response.
A proxy MUST NOT modify or add any of the following fields in a
message that contains the no-transform cache-control directive, or in
any request:
Content-EncodingContent-RangeContent-Type
A transforming proxy MAY modify or add these fields to a message
that does not include no-transform, but if it does so, it MUST add a
Warning 214 (Transformation applied) if one does not already appear
in the message (see Section 3.6 of ).
Warning: Unnecessary modification of end-to-end header fields might
cause authentication failures if stronger authentication
mechanisms are introduced in later versions of HTTP. Such
authentication mechanisms MAY rely on the values of header fields
not listed here.
A non-transforming proxy MUST preserve the message payload (),
though it MAY change the message-body through application or removal
of a transfer-coding ().
Servers will usually have some time-out value beyond which they will
no longer maintain an inactive connection. Proxy servers might make
this a higher value since it is likely that the client will be making
more connections through the same server. The use of persistent
connections places no requirements on the length (or existence) of
this time-out for either the client or the server.
When a client or server wishes to time-out it SHOULD issue a graceful
close on the transport connection. Clients and servers SHOULD both
constantly watch for the other side of the transport close, and
respond to it as appropriate. If a client or server does not detect
the other side's close promptly it could cause unnecessary resource
drain on the network.
A client, server, or proxy MAY close the transport connection at any
time. For example, a client might have started to send a new request
at the same time that the server has decided to close the "idle"
connection. From the server's point of view, the connection is being
closed while it was idle, but from the client's point of view, a
request is in progress.
Clients (including proxies) SHOULD limit the number of simultaneous
connections that they maintain to a given server (including proxies).
Previous revisions of HTTP gave a specific number of connections as a
ceiling, but this was found to be impractical for many applications. As a
result, this specification does not mandate a particular maximum number of
connections, but instead encourages clients to be conservative when opening
multiple connections.
In particular, while using multiple connections avoids the "head-of-line
blocking" problem (whereby a request that takes significant server-side
processing and/or has a large payload can block subsequent requests on the
same connection), each connection used consumes server resources (sometimes
significantly), and furthermore using multiple connections can cause
undesirable side effects in congested networks.
Note that servers might reject traffic that they deem abusive, including an
excessive number of connections from a client.
Senders can close the transport connection at any time. Therefore,
clients, servers, and proxies MUST be able to recover
from asynchronous close events. Client software MAY reopen the
transport connection and retransmit the aborted sequence of requests
without user interaction so long as the request sequence is
idempotent (see Section 6.1.2 of ). Non-idempotent request methods or sequences
MUST NOT be automatically retried, although user agents MAY offer a
human operator the choice of retrying the request(s). Confirmation by
user-agent software with semantic understanding of the application
MAY substitute for user confirmation. The automatic retry SHOULD NOT
be repeated if the second sequence of requests fails.
HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
flow control mechanisms to resolve temporary overloads, rather than
terminating connections with the expectation that clients will retry.
The latter technique can exacerbate network congestion.
An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
the network connection for an error status code while it is transmitting
the request. If the client sees an error status code, it SHOULD
immediately cease transmitting the body. If the body is being sent
using a "chunked" encoding (), a zero length chunk and
empty trailer MAY be used to prematurely mark the end of the message.
If the body was preceded by a Content-Length header field, the client MUST
close the connection.
The purpose of the 100 (Continue) status code (see Section 7.1.1 of ) is to
allow a client that is sending a request message with a request body
to determine if the origin server is willing to accept the request
(based on the request header fields) before the client sends the request
body. In some cases, it might either be inappropriate or highly
inefficient for the client to send the body if the server will reject
the message without looking at the body.
Requirements for HTTP/1.1 clients:
If a client will wait for a 100 (Continue) response before
sending the request body, it MUST send an Expect header
field (Section 9.3 of ) with the "100-continue" expectation.
A client MUST NOT send an Expect header field (Section 9.3 of )
with the "100-continue" expectation if it does not intend
to send a request body.
Because of the presence of older implementations, the protocol allows
ambiguous situations in which a client might send "Expect: 100-continue"
without receiving either a 417 (Expectation Failed)
or a 100 (Continue) status code. Therefore, when a client sends this
header field to an origin server (possibly via a proxy) from which it
has never seen a 100 (Continue) status code, the client SHOULD NOT
wait for an indefinite period before sending the request body.
Requirements for HTTP/1.1 origin servers:
Upon receiving a request which includes an Expect header
field with the "100-continue" expectation, an origin server MUST
either respond with 100 (Continue) status code and continue to read
from the input stream, or respond with a final status code. The
origin server MUST NOT wait for the request body before sending
the 100 (Continue) response. If it responds with a final status
code, it MAY close the transport connection or it MAY continue
to read and discard the rest of the request. It MUST NOT
perform the request method if it returns a final status code.
An origin server SHOULD NOT send a 100 (Continue) response if
the request message does not include an Expect header
field with the "100-continue" expectation, and MUST NOT send a
100 (Continue) response if such a request comes from an HTTP/1.0
(or earlier) client. There is an exception to this rule: for
compatibility with , a server MAY send a 100 (Continue)
status code in response to an HTTP/1.1 PUT or POST request that does
not include an Expect header field with the "100-continue"
expectation. This exception, the purpose of which is
to minimize any client processing delays associated with an
undeclared wait for 100 (Continue) status code, applies only to
HTTP/1.1 requests, and not to requests with any other HTTP-version
value.
An origin server MAY omit a 100 (Continue) response if it has
already received some or all of the request body for the
corresponding request.
An origin server that sends a 100 (Continue) response MUST
ultimately send a final status code, once the request body is
received and processed, unless it terminates the transport
connection prematurely.
If an origin server receives a request that does not include an
Expect header field with the "100-continue" expectation,
the request includes a request body, and the server responds
with a final status code before reading the entire request body
from the transport connection, then the server SHOULD NOT close
the transport connection until it has read the entire request,
or until the client closes the connection. Otherwise, the client
might not reliably receive the response message. However, this
requirement is not be construed as preventing a server from
defending itself against denial-of-service attacks, or from
badly broken client implementations.
Requirements for HTTP/1.1 proxies:
If a proxy receives a request that includes an Expect header
field with the "100-continue" expectation, and the proxy
either knows that the next-hop server complies with HTTP/1.1 or
higher, or does not know the HTTP version of the next-hop
server, it MUST forward the request, including the Expect header
field.
If the proxy knows that the version of the next-hop server is
HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
respond with a 417 (Expectation Failed) status code.
Proxies SHOULD maintain a record of the HTTP version
numbers received from recently-referenced next-hop servers.
A proxy MUST NOT forward a 100 (Continue) response if the
request message was received from an HTTP/1.0 (or earlier)
client and did not include an Expect header field with
the "100-continue" expectation. This requirement overrides the
general rule for forwarding of 1xx responses (see Section 7.1 of ).
describe why aliases like webcal are harmful.Configured to use HTTP to proxy HTTP or other protocols.Interception of HTTP traffic for initiating access control.Profiles of HTTP defined by other protocol.
Extensions of HTTP like WebDAV.Instructions on composing HTTP requests via hypertext formats.
This section defines the syntax and semantics of HTTP header fields
related to message origination, framing, and routing.
Header Field NameDefined in...ConnectionContent-LengthHostTETrailerTransfer-EncodingUpgradeVia
The "Connection" header field allows the sender to specify
options that are desired only for that particular connection.
Such connection options MUST be removed or replaced before the
message can be forwarded downstream by a proxy or gateway.
This mechanism also allows the sender to indicate which HTTP
header fields used in the message are only intended for the
immediate recipient ("hop-by-hop"), as opposed to all recipients
on the chain ("end-to-end"), enabling the message to be
self-descriptive and allowing future connection-specific extensions
to be deployed in HTTP without fear that they will be blindly
forwarded by previously deployed intermediaries.
The Connection header field's value has the following grammar:
A proxy or gateway MUST parse a received Connection
header field before a message is forwarded and, for each
connection-token in this field, remove any header field(s) from
the message with the same name as the connection-token, and then
remove the Connection header field itself or replace it with the
sender's own connection options for the forwarded message.
A sender MUST NOT include field-names in the Connection header
field-value for fields that are defined as expressing constraints
for all recipients in the request or response chain, such as the
Cache-Control header field (Section 3.2 of ).
The connection options do not have to correspond to a header field
present in the message, since a connection-specific header field
might not be needed if there are no parameters associated with that
connection option. Recipients that trigger certain connection
behavior based on the presence of connection options MUST do so
based on the presence of the connection-token rather than only the
presence of the optional header field. In other words, if the
connection option is received as a header field but not indicated
within the Connection field-value, then the recipient MUST ignore
the connection-specific header field because it has likely been
forwarded by an intermediary that is only partially compliant.
When defining new connection options, specifications ought to
carefully consider existing deployed header fields and ensure
that the new connection-token does not share the same name as
an unrelated header field that might already be deployed.
Defining a new connection-token essentially reserves that potential
field-name for carrying additional information related to the
connection option, since it would be unwise for senders to use
that field-name for anything else.
HTTP/1.1 defines the "close" connection option for the sender to
signal that the connection will be closed after completion of the
response. For example,
in either the request or the response header fields indicates that
the connection SHOULD NOT be considered "persistent" ()
after the current request/response is complete.
An HTTP/1.1 client that does not support persistent connections MUST
include the "close" connection option in every request message.
An HTTP/1.1 server that does not support persistent connections MUST
include the "close" connection option in every response message that
does not have a 1xx (Informational) status code.
The "Content-Length" header field indicates the size of the
message-body, in decimal number of octets, for any message other than
a response to a HEAD request or a response with a status code of 304.
In the case of a response to a HEAD request, Content-Length indicates
the size of the payload body (not including any potential transfer-coding)
that would have been sent had the request been a GET.
In the case of a 304 (Not Modified) response to a GET request,
Content-Length indicates the size of the payload body (not including
any potential transfer-coding) that would have been sent in a 200 (OK)
response.
An example is
Implementations SHOULD use this field to indicate the message-body
length when no transfer-coding is being applied and the
payload's body length can be determined prior to being transferred.
describes how recipients determine the length
of a message-body.
Any Content-Length greater than or equal to zero is a valid value.
Note that the use of this field in HTTP is significantly different from
the corresponding definition in MIME, where it is an optional field
used within the "message/external-body" content-type.
The "Host" header field in a request provides the host and port
information from the target resource's URI, enabling the origin
server to distinguish between resources while servicing requests
for multiple host names on a single IP address. Since the Host
field-value is critical information for handling a request, it
SHOULD be sent as the first header field following the Request-Line.
A client MUST send a Host header field in all HTTP/1.1 request
messages. If the target resource's URI includes an authority
component, then the Host field-value MUST be identical to that
authority component after excluding any userinfo ().
If the authority component is missing or undefined for the target
resource's URI, then the Host header field MUST be sent with an
empty field-value.
For example, a GET request to the origin server for
<http://www.example.org/pub/WWW/> would begin with:
The Host header field MUST be sent in an HTTP/1.1 request even
if the request-target is in the form of an absolute-URI, since this
allows the Host information to be forwarded through ancient HTTP/1.0
proxies that might not have implemented Host.
When an HTTP/1.1 proxy receives a request with a request-target in
the form of an absolute-URI, the proxy MUST ignore the received
Host header field (if any) and instead replace it with the host
information of the request-target. When a proxy forwards a request,
it MUST generate the Host header field based on the received
absolute-URI rather than the received Host.
Since the Host header field acts as an application-level routing
mechanism, it is a frequent target for malware seeking to poison
a shared cache or redirect a request to an unintended server.
An interception proxy is particularly vulnerable if it relies on
the Host header field value for redirecting requests to internal
servers, or for use as a cache key in a shared cache, without
first verifying that the intercepted connection is targeting a
valid IP address for that host.
A server MUST respond with a 400 (Bad Request) status code to
any HTTP/1.1 request message that lacks a Host header field and
to any request message that contains more than one Host header field
or a Host header field with an invalid field-value.
See Sections
and
for other requirements relating to Host.
The "TE" header field indicates what extension transfer-codings
it is willing to accept in the response, and whether or not it is
willing to accept trailer fields in a chunked transfer-coding.
Its value consists of the keyword "trailers" and/or a comma-separated
list of extension transfer-coding names with optional accept
parameters (as described in ).
The presence of the keyword "trailers" indicates that the client is
willing to accept trailer fields in a chunked transfer-coding, as
defined in . This keyword is reserved for use with
transfer-coding values even though it does not itself represent a
transfer-coding.
Examples of its use are:
The TE header field only applies to the immediate connection.
Therefore, the keyword MUST be supplied within a Connection header
field () whenever TE is present in an HTTP/1.1 message.
A server tests whether a transfer-coding is acceptable, according to
a TE field, using these rules:
The "chunked" transfer-coding is always acceptable. If the
keyword "trailers" is listed, the client indicates that it is
willing to accept trailer fields in the chunked response on
behalf of itself and any downstream clients. The implication is
that, if given, the client is stating that either all
downstream clients are willing to accept trailer fields in the
forwarded response, or that it will attempt to buffer the
response on behalf of downstream recipients.
Note: HTTP/1.1 does not define any means to limit the size of a
chunked response such that a client can be assured of buffering
the entire response.If the transfer-coding being tested is one of the transfer-codings
listed in the TE field, then it is acceptable unless it
is accompanied by a qvalue of 0. (As defined in , a
qvalue of 0 means "not acceptable".)If multiple transfer-codings are acceptable, then the
acceptable transfer-coding with the highest non-zero qvalue is
preferred. The "chunked" transfer-coding always has a qvalue
of 1.
If the TE field-value is empty or if no TE field is present, the only
transfer-coding is "chunked". A message with no transfer-coding is
always acceptable.
The "Trailer" header field indicates that the given set of
header fields is present in the trailer of a message encoded with
chunked transfer-coding.
An HTTP/1.1 message SHOULD include a Trailer header field in a
message using chunked transfer-coding with a non-empty trailer. Doing
so allows the recipient to know which header fields to expect in the
trailer.
If no Trailer header field is present, the trailer SHOULD NOT include
any header fields. See for restrictions on the use of
trailer fields in a "chunked" transfer-coding.
Message header fields listed in the Trailer header field MUST NOT
include the following header fields:
Transfer-EncodingContent-LengthTrailer
The "Transfer-Encoding" header field indicates what transfer-codings
(if any) have been applied to the message body. It differs from
Content-Encoding (Section 2.2 of ) in that transfer-codings are a property
of the message (and therefore are removed by intermediaries), whereas
content-codings are not.
Transfer-codings are defined in . An example is:
If multiple encodings have been applied to a representation, the transfer-codings
MUST be listed in the order in which they were applied.
Additional information about the encoding parameters MAY be provided
by other header fields not defined by this specification.
Many older HTTP/1.0 applications do not understand the Transfer-Encoding
header field.
The "Upgrade" header field allows the client to specify what
additional communication protocols it would like to use, if the server
chooses to switch protocols. Servers can use it to indicate what protocols
they are willing to switch to.
For example,
The Upgrade header field is intended to provide a simple mechanism
for transition from HTTP/1.1 to some other, incompatible protocol. It
does so by allowing the client to advertise its desire to use another
protocol, such as a later version of HTTP with a higher major version
number, even though the current request has been made using HTTP/1.1.
This eases the difficult transition between incompatible protocols by
allowing the client to initiate a request in the more commonly
supported protocol while indicating to the server that it would like
to use a "better" protocol if available (where "better" is determined
by the server, possibly according to the nature of the request method
or target resource).
The Upgrade header field only applies to switching application-layer
protocols upon the existing transport-layer connection. Upgrade
cannot be used to insist on a protocol change; its acceptance and use
by the server is optional. The capabilities and nature of the
application-layer communication after the protocol change is entirely
dependent upon the new protocol chosen, although the first action
after changing the protocol MUST be a response to the initial HTTP
request containing the Upgrade header field.
The Upgrade header field only applies to the immediate connection.
Therefore, the upgrade keyword MUST be supplied within a Connection
header field () whenever Upgrade is present in an
HTTP/1.1 message.
The Upgrade header field cannot be used to indicate a switch to a
protocol on a different connection. For that purpose, it is more
appropriate to use a 3xx redirection response (Section 7.3 of ).
Servers MUST include the "Upgrade" header field in 101 (Switching
Protocols) responses to indicate which protocol(s) are being switched to,
and MUST include it in 426 (Upgrade Required) responses to indicate
acceptable protocols to upgrade to. Servers MAY include it in any other
response to indicate that they are willing to upgrade to one of the
specified protocols.
This specification only defines the protocol name "HTTP" for use by
the family of Hypertext Transfer Protocols, as defined by the HTTP
version rules of and future updates to this
specification. Additional tokens can be registered with IANA using the
registration procedure defined below.
The HTTP Upgrade Token Registry defines the name space for product
tokens used to identify protocols in the Upgrade header field.
Each registered token is associated with contact information and
an optional set of specifications that details how the connection
will be processed after it has been upgraded.
Registrations are allowed on a First Come First Served basis as
described in Section 4.1 of . The
specifications need not be IETF documents or be subject to IESG review.
Registrations are subject to the following rules:
A token, once registered, stays registered forever.The registration MUST name a responsible party for the
registration.The registration MUST name a point of contact.The registration MAY name a set of specifications associated with that
token. Such specifications need not be publicly available.The responsible party MAY change the registration at any time.
The IANA will keep a record of all such changes, and make them
available upon request.The responsible party for the first registration of a "product"
token MUST approve later registrations of a "version" token
together with that "product" token before they can be registered.If absolutely required, the IESG MAY reassign the responsibility
for a token. This will normally only be used in the case when a
responsible party cannot be contacted.
The "Via" header field MUST be sent by a proxy or gateway to
indicate the intermediate protocols and recipients between the user
agent and the server on requests, and between the origin server and
the client on responses. It is analogous to the "Received" field
used by email systems (Section 3.6.7 of )
and is intended to be used for tracking message forwards,
avoiding request loops, and identifying the protocol capabilities of
all senders along the request/response chain.
The received-protocol indicates the protocol version of the message
received by the server or client along each segment of the
request/response chain. The received-protocol version is appended to
the Via field value when the message is forwarded so that information
about the protocol capabilities of upstream applications remains
visible to all recipients.
The protocol-name is excluded if and only if it would be "HTTP". The
received-by field is normally the host and optional port number of a
recipient server or client that subsequently forwarded the message.
However, if the real host is considered to be sensitive information,
it MAY be replaced by a pseudonym. If the port is not given, it MAY
be assumed to be the default port of the received-protocol.
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each recipient MUST append its information
such that the end result is ordered according to the sequence of
forwarding applications.
Comments MAY be used in the Via header field to identify the software
of each recipient, analogous to the User-Agent and Server header fields.
However, all comments in the Via field are optional and MAY be removed
by any recipient prior to forwarding the message.
For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which completes
the request by forwarding it to the origin server at www.example.com.
The request received by www.example.com would then have the following
Via header field:
A proxy or gateway used as a portal through a network firewall
SHOULD NOT forward the names and ports of hosts within the firewall
region unless it is explicitly enabled to do so. If not enabled, the
received-by host of any host behind the firewall SHOULD be replaced
by an appropriate pseudonym for that host.
For organizations that have strong privacy requirements for hiding
internal structures, a proxy or gateway MAY combine an ordered
subsequence of Via header field entries with identical received-protocol
values into a single such entry. For example,
could be collapsed to
Senders SHOULD NOT combine multiple entries unless they are all
under the same organizational control and the hosts have already been
replaced by pseudonyms. Senders MUST NOT combine entries which
have different received-protocol values.
The Message Header Field Registry located at shall be updated
with the permanent registrations below (see ):
Header Field NameProtocolStatusReferenceConnectionhttpstandardContent-LengthhttpstandardHosthttpstandardTEhttpstandardTrailerhttpstandardTransfer-EncodinghttpstandardUpgradehttpstandardViahttpstandard
Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
HTTP header field would be in conflict with the use of the "close" connection
option for the "Connection" header field ().
Header Field NameProtocolStatusReferenceClosehttpreserved
The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
The entries for the "http" and "https" URI Schemes in the registry located at
shall be updated to point to Sections
and of this document
(see ).
This document serves as the specification for the Internet media types
"message/http" and "application/http". The following is to be registered with
IANA (see ).
The message/http type can be used to enclose a single HTTP request or
response message, provided that it obeys the MIME restrictions for all
"message" types regarding line length and encodings.
message
http
none
version, msgtype
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.
The message type — "request" or "response". If not
present, the type can be determined from the first
line of the body.
only "7bit", "8bit", or "binary" are permitted
none
none
This specification (see ).
nonenonenone
See Authors Section.
COMMON
none
IESG
The application/http type can be used to enclose a pipeline of one or more
HTTP request or response messages (not intermixed).
application
http
none
version, msgtype
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.
The message type — "request" or "response". If not
present, the type can be determined from the first
line of the body.
HTTP messages enclosed by this type
are in "binary" format; use of an appropriate
Content-Transfer-Encoding is required when
transmitted via E-mail.
none
none
This specification (see ).
nonenonenone
See Authors Section.
COMMON
none
IESG
The registration procedure for HTTP Transfer Codings is now defined by
of this document.
The HTTP Transfer Codings Registry located at
shall be updated with the registrations below:
NameDescriptionReferencechunkedTransfer in a series of chunkscompressUNIX "compress" program methoddeflate"deflate" compression mechanism () used inside
the "zlib" data format ()
gzipSame as GNU zip
The registration procedure for HTTP Upgrade Tokens — previously defined
in Section 7.2 of — is now defined
by of this document.
The HTTP Status Code Registry located at
shall be updated with the registration below:
ValueDescriptionReferenceHTTPHypertext Transfer Protocol of this specification
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
HTTP clients are often privy to large amounts of personal information
(e.g., the user's name, location, mail address, passwords, encryption
keys, etc.), and SHOULD be very careful to prevent unintentional
leakage of this information.
We very strongly recommend that a convenient interface be provided
for the user to control dissemination of such information, and that
designers and implementors be particularly careful in this area.
History shows that errors in this area often create serious security
and/or privacy problems and generate highly adverse publicity for the
implementor's company.
A server is in the position to save personal data about a user's
requests which might identify their reading patterns or subjects of
interest. This information is clearly confidential in nature and its
handling can be constrained by law in certain countries. People using
HTTP to provide data are responsible for ensuring that
such material is not distributed without the permission of any
individuals that are identifiable by the published results.
Implementations of HTTP origin servers SHOULD be careful to restrict
the documents returned by HTTP requests to be only those that were
intended by the server administrators. If an HTTP server translates
HTTP URIs directly into file system calls, the server MUST take
special care not to serve files that were not intended to be
delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
other operating systems use ".." as a path component to indicate a
directory level above the current one. On such a system, an HTTP
server MUST disallow any such construct in the request-target if it
would otherwise allow access to a resource outside those intended to
be accessible via the HTTP server. Similarly, files intended for
reference only internally to the server (such as access control
files, configuration files, and script code) MUST be protected from
inappropriate retrieval, since they might contain sensitive
information. Experience has shown that minor bugs in such HTTP server
implementations have turned into security risks.
HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
generally prone to security attacks based on the deliberate misassociation
of IP addresses and DNS names not protected by DNSSec. Clients need to be
cautious in assuming the validity of an IP number/DNS name association unless
the response is protected by DNSSec ().
By their very nature, HTTP proxies are men-in-the-middle, and
represent an opportunity for man-in-the-middle attacks. Compromise of
the systems on which the proxies run can result in serious security
and privacy problems. Proxies have access to security-related
information, personal information about individual users and
organizations, and proprietary information belonging to users and
content providers. A compromised proxy, or a proxy implemented or
configured without regard to security and privacy considerations,
might be used in the commission of a wide range of potential attacks.
Proxy operators need to protect the systems on which proxies run as
they would protect any system that contains or transports sensitive
information. In particular, log information gathered at proxies often
contains highly sensitive personal information, and/or information
about organizations. Log information needs to be carefully guarded, and
appropriate guidelines for use need to be developed and followed.
().
Proxy implementors need to consider the privacy and security
implications of their design and coding decisions, and of the
configuration options they provide to proxy operators (especially the
default configuration).
Users of a proxy need to be aware that proxies are no trustworthier than
the people who run them; HTTP itself cannot solve this problem.
The judicious use of cryptography, when appropriate, might suffice to
protect against a broad range of security and privacy attacks. Such
cryptography is beyond the scope of the HTTP/1.1 specification.
Because HTTP uses mostly textual, character-delimited fields, attackers can
overflow buffers in implementations, and/or perform a Denial of Service
against implementations that accept fields with unlimited lengths.
To promote interoperability, this specification makes specific
recommendations for size limits on request-targets ()
and blocks of header fields (). These are
minimum recommendations, chosen to be supportable even by implementations
with limited resources; it is expected that most implementations will choose
substantially higher limits.
This specification also provides a way for servers to reject messages that
have request-targets that are too long (Section 7.4.15 of ) or request entities
that are too large (Section 7.4 of ).
Other fields (including but not limited to request methods, response status
phrases, header field-names, and body chunks) SHOULD be limited by
implementations carefully, so as to not impede interoperability.
They exist. They are hard to defend against. Research continues.
Beware.
This document revision builds on the work that went into
RFC 2616 and its predecessors.
See Section 16 of for detailed
acknowledgements.
Since 1999, many contributors have helped by reporting bugs, asking
smart questions, drafting and reviewing text, and discussing open issues:
Adam Barth,
Adam Roach,
Addison Phillips,
Adrian Chadd,
Adrien de Croy,
Alan Ford,
Alan Ruttenberg,
Albert Lunde,
Alex Rousskov,
Alexey Melnikov,
Alisha Smith,
Amichai Rothman,
Amit Klein,
Amos Jeffries,
Andreas Maier,
Andreas Petersson,
Anne van Kesteren,
Anthony Bryan,
Asbjorn Ulsberg,
Balachander Krishnamurthy,
Barry Leiba,
Ben Laurie,
Benjamin Niven-Jenkins,
Bil Corry,
Bill Burke,
Bjoern Hoehrmann,
Bob Scheifler,
Boris Zbarsky,
Brett Slatkin,
Brian Kell,
Brian McBarron,
Brian Pane,
Brian Smith,
Bryce Nesbitt,
Cameron Heavon-Jones,
Carl Kugler,
Charles Fry,
Chris Newman,
Cyrus Daboo,
Dale Robert Anderson,
Dan Winship,
Daniel Stenberg,
Dave Cridland,
Dave Crocker,
Dave Kristol,
David Booth,
David Singer,
David W. Morris,
Diwakar Shetty,
Dmitry Kurochkin,
Drummond Reed,
Duane Wessels,
Edward Lee,
Eliot Lear,
Eran Hammer-Lahav,
Eric D. Williams,
Eric J. Bowman,
Eric Lawrence,
Erik Aronesty,
Florian Weimer,
Frank Ellermann,
Fred Bohle,
Geoffrey Sneddon,
Gervase Markham,
Greg Wilkins,
Harald Tveit Alvestrand,
Harry Halpin,
Helge Hess,
Henrik Nordstrom,
Henry S. Thompson,
Henry Story,
Herbert van de Sompel,
Howard Melman,
Hugo Haas,
Ian Hickson,
Ingo Struck,
J. Ross Nicoll,
James H. Manger,
James Lacey,
James M. Snell,
Jamie Lokier,
Jan Algermissen,
Jeff Hodges (for coming up with the term 'effective Request-URI'),
Jeff Walden,
Jim Luther,
Joe D. Williams,
Joe Gregorio,
Joe Orton,
John C. Klensin,
John C. Mallery,
John Cowan,
John Kemp,
John Panzer,
John Schneider,
John Stracke,
Jonas Sicking,
Jonathan Moore,
Jonathan Rees,
Jordi Ros,
Joris Dobbelsteen,
Josh Cohen,
Julien Pierre,
Jungshik Shin,
Justin Chapweske,
Justin Erenkrantz,
Justin James,
Kalvinder Singh,
Karl Dubost,
Keith Hoffman,
Keith Moore,
Koen Holtman,
Konstantin Voronkov,
Kris Zyp,
Lisa Dusseault,
Maciej Stachowiak,
Marc Schneider,
Marc Slemko,
Mark Baker,
Mark Nottingham (Working Group chair),
Mark Pauley,
Martin J. Duerst,
Martin Thomson,
Matt Lynch,
Matthew Cox,
Max Clark,
Michael Burrows,
Michael Hausenblas,
Mike Amundsen,
Mike Kelly,
Mike Schinkel,
Miles Sabin,
Mykyta Yevstifeyev,
Nathan Rixham,
Nicholas Shanks,
Nico Williams,
Nicolas Alvarez,
Noah Slater,
Pablo Castro,
Pat Hayes,
Patrick R. McManus,
Paul E. Jones,
Paul Hoffman,
Paul Marquess,
Peter Saint-Andre,
Peter Watkins,
Phil Archer,
Phillip Hallam-Baker,
Poul-Henning Kamp,
Preethi Natarajan,
Reto Bachmann-Gmuer,
Richard Cyganiak,
Robert Brewer,
Robert Collins,
Robert O'Callahan,
Robert Olofsson,
Robert Sayre,
Robert Siemer,
Robert de Wilde,
Roberto Javier Godoy,
Ronny Widjaja,
S. Mike Dierken,
Salvatore Loreto,
Sam Johnston,
Sam Ruby,
Scott Lawrence (for maintaining the original issues list),
Sean B. Palmer,
Shane McCarron,
Stefan Eissing,
Stefan Tilkov,
Stefanos Harhalakis,
Stephane Bortzmeyer,
Stuart Williams,
Subbu Allamaraju,
Sylvain Hellegouarch,
Tapan Divekar,
Thomas Broyer,
Thomas Nordin,
Thomas Roessler,
Tim Morgan,
Tim Olsen,
Travis Snoozy,
Tyler Close,
Vincent Murphy,
Wenbo Zhu,
Werner Baumann,
Wilbur Streett,
Wilfredo Sanchez Vega,
William A. Rowe Jr.,
William Chan,
Willy Tarreau,
Xiaoshu Wang,
Yaron Goland,
Yngve Nysaeter Pettersen,
Yogesh Bang,
Yutaka Oiwa, and
Zed A. Shaw.
Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
International Organization for StandardizationHTTP/1.1, part 2: Message SemanticsAdobe Systems Incorporatedfielding@gbiv.comAlcatel-Lucent Bell Labsjg@freedesktop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 3: Message Payload and Content NegotiationAdobe Systems Incorporatedfielding@gbiv.comAlcatel-Lucent Bell Labsjg@freedesktop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 6: CachingAdobe Systems Incorporatedfielding@gbiv.comAlcatel-Lucent Bell Labsjg@freedesktop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orgRackspacemnot@mnot.netgreenbytes GmbHjulian.reschke@greenbytes.deAugmented BNF for Syntax Specifications: ABNFBrandenburg InternetWorkingdcrocker@bbiw.netTHUS plc.paul.overell@thus.netKey words for use in RFCs to Indicate Requirement LevelsHarvard Universitysob@harvard.eduUniform Resource Identifier (URI): Generic SyntaxWorld Wide Web Consortiumtimbl@w3.orghttp://www.w3.org/People/Berners-Lee/Day Softwarefielding@gbiv.comhttp://roy.gbiv.com/Adobe Systems IncorporatedLMM@acm.orghttp://larry.masinter.net/Coded Character Set -- 7-bit American Standard Code for Information InterchangeAmerican National Standards InstituteZLIB Compressed Data Format Specification version 3.3Aladdin Enterprisesghost@aladdin.comDEFLATE Compressed Data Format Specification version 1.3Aladdin Enterprisesghost@aladdin.comGZIP file format specification version 4.3Aladdin Enterprisesghost@aladdin.comgzip@prep.ai.mit.edumadler@alumni.caltech.edughost@aladdin.comrandeg@alumni.rpi.eduNetwork Performance Effects of HTTP/1.1, CSS1, and PNGImproving HTTP LatencyClassical versus Transparent IP Proxiesmchatel@pax.eunet.chHypertext Transfer Protocol -- HTTP/1.0MIT, Laboratory for Computer Sciencetimbl@w3.orgUniversity of California, Irvine, Department of Information and Computer Sciencefielding@ics.uci.eduW3 Consortium, MIT Laboratory for Computer Sciencefrystyk@w3.orgMultipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message BodiesInnosoft International, Inc.ned@innosoft.comFirst Virtual Holdingsnsb@nsb.fv.comMIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII TextUniversity of Tennesseemoore@cs.utk.eduHypertext Transfer Protocol -- HTTP/1.1University of California, Irvine, Department of Information and Computer Sciencefielding@ics.uci.eduMIT Laboratory for Computer Sciencejg@w3.orgDigital Equipment Corporation, Western Research Laboratorymogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgMIT Laboratory for Computer Sciencetimbl@w3.orgUse and Interpretation of HTTP Version NumbersWestern Research Laboratorymogul@wrl.dec.comDepartment of Information and Computer Sciencefielding@ics.uci.eduMIT Laboratory for Computer Sciencejg@w3.orgW3 Consortiumfrystyk@w3.orgHypertext Transfer Protocol -- HTTP/1.1University of California, Irvinefielding@ics.uci.eduW3Cjg@w3.orgCompaq Computer Corporationmogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgXerox Corporationmasinter@parc.xerox.comMicrosoft Corporationpaulle@microsoft.comW3Ctimbl@w3.orgUpgrading to TLS Within HTTP/1.14K Associates / UC Irvinerohit@4K-associates.comAgranat Systems, Inc.lawrence@agranat.comHTTP Over TLSRTFM, Inc.ekr@rtfm.comHTTP State Management MechanismBell Laboratories, Lucent Technologiesdmk@bell-labs.comEpinions.com, Inc.lou@montulli.orgInternet Web Replication and Caching TaxonomyEquinix, Inc.UNINETTCacheFlow Inc.Registration Procedures for Message Header FieldsNine by NineGK-IETF@ninebynine.orgBEA Systemsmnot@pobox.comHP LabsJeffMogul@acm.orgDNS Security Introduction and RequirementsMedia Type Specifications and Registration ProceduresSun Microsystemsned.freed@mrochek.comklensin+ietf@jck.comGuidelines and Registration Procedures for New URI SchemesAT&T Laboratoriestony+urireg@maillennium.att.comQualcomm, Inc.hardie@qualcomm.comAdobe SystemsLMM@acm.orgSPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft WindowsGuidelines for Writing an IANA Considerations Section in RFCsIBMnarten@us.ibm.comGoogleHarald@Alvestrand.noInternet Message FormatQualcomm IncorporatedHTTP State Management Mechanism
University of California, Berkeley
abarth@eecs.berkeley.eduHTTP Cookies: Standards, Privacy, and PoliticsAnalysis of HTTP Performance ProblemsAnalysis of HTTP PerformanceUSC/Information Sciences Institutetouch@isi.eduUSC/Information Sciences Institutejohnh@isi.eduUSC/Information Sciences Institutekatia@isi.edu(original report dated Aug. 1996)
HTTP has been in use by the World-Wide Web global information initiative
since 1990. The first version of HTTP, later referred to as HTTP/0.9,
was a simple protocol for hypertext data transfer across the Internet
with only a single request method (GET) and no metadata.
HTTP/1.0, as defined by , added a range of request
methods and MIME-like messaging that could include metadata about the data
transferred and modifiers on the request/response semantics. However,
HTTP/1.0 did not sufficiently take into consideration the effects of
hierarchical proxies, caching, the need for persistent connections, or
name-based virtual hosts. The proliferation of incompletely-implemented
applications calling themselves "HTTP/1.0" further necessitated a
protocol version change in order for two communicating applications
to determine each other's true capabilities.
HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
requirements that enable reliable implementations, adding only
those new features that will either be safely ignored by an HTTP/1.0
recipient or only sent when communicating with a party advertising
compliance with HTTP/1.1.
It is beyond the scope of a protocol specification to mandate
compliance with previous versions. HTTP/1.1 was deliberately
designed, however, to make supporting previous versions easy.
We would expect a general-purpose HTTP/1.1 server to understand
any valid request in the format of HTTP/1.0 and respond appropriately
with an HTTP/1.1 message that only uses features understood (or
safely ignored) by HTTP/1.0 clients. Likewise, would expect
an HTTP/1.1 client to understand any valid HTTP/1.0 response.
Since HTTP/0.9 did not support header fields in a request,
there is no mechanism for it to support name-based virtual
hosts (selection of resource by inspection of the Host header
field). Any server that implements name-based virtual hosts
ought to disable support for HTTP/0.9. Most requests that
appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
requests wherein a buggy client failed to properly encode
linear whitespace found in a URI reference and placed in
the request-target.
This section summarizes major differences between versions HTTP/1.0
and HTTP/1.1.
The requirements that clients and servers support the Host header
field (), report an error if it is
missing from an HTTP/1.1 request, and accept absolute URIs ()
are among the most important changes defined by HTTP/1.1.
Older HTTP/1.0 clients assumed a one-to-one relationship of IP
addresses and servers; there was no other established mechanism for
distinguishing the intended server of a request than the IP address
to which that request was directed. The Host header field was
introduced during the development of HTTP/1.1 and, though it was
quickly implemented by most HTTP/1.0 browsers, additional requirements
were placed on all HTTP/1.1 requests in order to ensure complete
adoption. At the time of this writing, most HTTP-based services
are dependent upon the Host header field for targeting requests.
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 .
Some clients and servers might wish to be compatible with these previous
approaches to persistent connections, by explicitly negotiating for them
with a "Connection: keep-alive" request header field. However, some
experimental implementations of HTTP/1.0 persistent connections are faulty;
for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
will erroneously forward that header to the next inbound server, which
would result in a hung connection.
One attempted solution was the introduction of a Proxy-Connection header,
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
in any requests.
Clients are also encouraged to consider the use of Connection: keep-alive
in requests carefully; while they can enable persistent connections with
HTTP/1.0 servers, clients using them need will need to monitor the
connection for "hung" requests (which indicate that the client ought stop
sending the header), and this mechanism ought not be used by clients at all
when a proxy is being used.
Empty list elements in list productions have been deprecated.
()
Rules about implicit linear whitespace between certain grammar productions
have been removed; now it's only allowed when specifically pointed out
in the ABNF.
()
Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
sensitive. Restrict the version numbers to be single digits due to the fact
that implementations are known to handle multi-digit version numbers
incorrectly.
()
Require that invalid whitespace around field-names be rejected.
()
The NUL octet is no longer allowed in comment and quoted-string
text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
Non-ASCII content in header fields and reason phrase has been obsoleted and
made opaque (the TEXT rule was removed).
()
Require recipients to handle bogus Content-Length header fields as errors.
()
Remove reference to non-existent identity transfer-coding value tokens.
(Sections and
)
Update use of abs_path production from RFC 1808 to the path-absolute + query
components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
request method only.
()
Clarification that the chunk length does not include the count of the octets
in the chunk header and trailer. Furthermore disallowed line folding
in chunk extensions.
()
Remove hard limit of two connections per server.
Remove requirement to retry a sequence of requests as long it was idempotent.
Remove requirements about when servers are allowed to close connections
prematurely.
()
Remove requirement to retry requests under certain cirumstances when the
server prematurely closes the connection.
()
Change ABNF productions for header fields to only define the field value.
()
Clarify exactly when close connection options must be sent.
()
Define the semantics of the "Upgrade" header field in responses other than
101 (this was incorporated from ).
()
Extracted relevant partitions from .
Closed issues:
:
"HTTP Version should be case sensitive"
()
:
"'unsafe' characters"
()
:
"Chunk Size Definition"
()
:
"Message Length"
()
:
"Media Type Registrations"
()
:
"URI includes query"
()
:
"No close on 1xx responses"
()
:
"Remove 'identity' token references"
()
:
"Import query BNF"
:
"qdtext BNF"
:
"Normative and Informative references"
:
"RFC2606 Compliance"
:
"RFC977 reference"
:
"RFC1700 references"
:
"inconsistency in date format explanation"
:
"Date reference typo"
:
"Informative references"
:
"ISO-8859-1 Reference"
:
"Normative up-to-date references"
Other changes:
Update media type registrations to use RFC4288 template.
Use names of RFC4234 core rules DQUOTE and HTAB,
fix broken ABNF for chunk-data
(work in progress on )
Closed issues:
:
"Bodies on GET (and other) requests"
:
"Updating to RFC4288"
:
"Status Code and Reason Phrase"
:
"rel_path not used"
Ongoing work on ABNF conversion ():
Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
"trailer-part").
Avoid underscore character in rule names ("http_URL" ->
"http-URL", "abs_path" -> "path-absolute").
Add rules for terms imported from URI spec ("absoluteURI", "authority",
"path-absolute", "port", "query", "relativeURI", "host) — these will
have to be updated when switching over to RFC3986.
Synchronize core rules with RFC5234.
Get rid of prose rules that span multiple lines.
Get rid of unused rules LOALPHA and UPALPHA.
Move "Product Tokens" section (back) into Part 1, as "token" is used
in the definition of the Upgrade header field.
Add explicit references to BNF syntax and rules imported from other parts of the specification.
Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
Closed issues:
:
"HTTP-date vs. rfc1123-date"
:
"WS in quoted-pair"
Ongoing work on IANA Message Header Field Registration ():
Reference RFC 3984, and update header field registrations for headers defined
in this document.
Ongoing work on ABNF conversion ():
Replace string literals when the string really is case-sensitive (HTTP-Version).
Closed issues:
:
"Connection closing"
:
"Move registrations and registry information to IANA Considerations"
:
"need new URL for PAD1995 reference"
:
"IANA Considerations: update HTTP URI scheme registration"
:
"Cite HTTPS URI scheme definition"
:
"List-type headers vs Set-Cookie"
Ongoing work on ABNF conversion ():
Replace string literals when the string really is case-sensitive (HTTP-Date).
Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
Closed issues:
:
"Out-of-date reference for URIs"
:
"RFC 2822 is updated by RFC 5322"
Ongoing work on ABNF conversion ():
Use "/" instead of "|" for alternatives.
Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
Only reference RFC 5234's core rules.
Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
whitespace ("OWS") and required whitespace ("RWS").
Rewrite ABNFs to spell out whitespace rules, factor out
header field value format definitions.
Closed issues:
:
"Header LWS"
:
"Sort 1.3 Terminology"
:
"RFC2047 encoded words"
:
"Character Encodings in TEXT"
:
"Line Folding"
:
"OPTIONS * and proxies"
:
"Reason-Phrase BNF"
:
"Use of TEXT"
:
"Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
:
"RFC822 reference left in discussion of date formats"
Final work on ABNF conversion ():
Rewrite definition of list rules, deprecate empty list elements.
Add appendix containing collected and expanded ABNF.
Other changes:
Rewrite introduction; add mostly new Architecture Section.
Move definition of quality values from Part 3 into Part 1;
make TE request header field grammar independent of accept-params (defined in Part 3).
Closed issues:
:
"base for numeric protocol elements"
:
"comment ABNF"
Partly resolved issues:
:
"205 Bodies" (took out language that implied that there might be
methods for which a request body MUST NOT be included)
:
"editorial improvements around HTTP-date"
Closed issues:
:
"Repeating single-value headers"
:
"increase connection limit"
:
"IP addresses in URLs"
:
"take over HTTP Upgrade Token Registry"
:
"CR and LF in chunk extension values"
:
"HTTP/0.9 support"
:
"pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
:
"move definitions of gzip/deflate/compress to part 1"
:
"disallow control characters in quoted-pair"
Partly resolved issues:
:
"update IANA requirements wrt Transfer-Coding values" (add the
IANA Considerations subsection)
Closed issues:
:
"header parsing, treatment of leading and trailing OWS"
Partly resolved issues:
:
"Placement of 13.5.1 and 13.5.2"
:
"use of term "word" when talking about header structure"
Closed issues:
:
"Clarification of the term 'deflate'"
:
"OPTIONS * and proxies"
:
"MIME-Version not listed in P1, general header fields"
:
"IANA registry for content/transfer encodings"
:
"Case-sensitivity of HTTP-date"
:
"use of term "word" when talking about header structure"
Partly resolved issues:
:
"Term for the requested resource's URI"
Closed issues:
:
"Connection Closing"
:
"Delimiting messages with multipart/byteranges"
:
"Handling multiple Content-Length headers"
:
"Clarify entity / representation / variant terminology"
:
"consider removing the 'changes from 2068' sections"
Partly resolved issues:
:
"HTTP(s) URI scheme definitions"
Closed issues:
:
"Trailer requirements"
:
"Text about clock requirement for caches belongs in p6"
:
"effective request URI: handling of missing host in HTTP/1.0"
:
"confusing Date requirements for clients"
Partly resolved issues:
:
"Handling multiple Content-Length headers"
Closed issues:
:
"RFC2145 Normative"
:
"HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
:
"define 'transparent' proxy"
:
"Header Classification"
:
"Is * usable as a request-uri for new methods?"
:
"Migrate Upgrade details from RFC2817"
:
"untangle ABNFs for header fields"
:
"update RFC 2109 reference"
Closed issues:
:
"Allow is not in 13.5.2"
:
"Handling multiple Content-Length headers"
:
"untangle ABNFs for header fields"
:
"Content-Length ABNF broken"
Closed issues:
:
"HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
:
"Recommend minimum sizes for protocol elements"
:
"Set expectations around buffering"
:
"Considering messages in isolation"
Closed issues:
:
"DNS Spoofing / DNS Binding advice"
:
"move RFCs 2145, 2616, 2817 to Historic status"
:
"\-escaping in quoted strings"
:
"'Close' should be reserved in the HTTP header field registry"
Closed issues:
:
"Document HTTP's error-handling philosophy"
:
"Explain header registration"
:
"Revise Acknowledgements Sections"
:
"Retrying Requests"
:
"Closing the connection on server error"
Closed issues:
:
"Clarify 'User Agent'"
:
"Define non-final responses"
:
"intended maturity level vs normative references"
:
"Intermediary rewriting of queries"
:
"Proxy-Connection and Keep-Alive"