HTTP/1.1, part 1: URIs, Connections, and Message Parsing

Practical information systems require more functionality than simple retrieval, including search, front-end update, and annotation. HTTP allows an open-ended set of methods and headers that indicate the purpose of a request [RFC2324]. It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) [RFC1630], as a location (URL) [RFC1738] or name (URN) [RFC1737], for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by Internet mail [RFC2822] as defined by the Multipurpose Internet Mail Extensions (MIME) [RFC2045].¶

HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems, including those supported by the SMTP [RFC2821], NNTP [RFC3977], FTP [RFC959], Gopher [RFC1436], and WAIS [WAIS] protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications.¶

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶

An implementation is not compliant if it fails to satisfy one or more of the MUST or REQUIRED level requirements for the protocols it implements. An implementation that satisfies all the MUST or REQUIRED level and all the SHOULD level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the MUST level requirements but not all the SHOULD level requirements for its protocols is said to be "conditionally compliant."¶

This specification uses a number of terms to refer to the roles played by participants in, and objects of, the HTTP communication.¶

connection ¶

• A transport layer virtual circuit established between two programs for the purpose of communication.

message ¶

• The basic unit of HTTP communication, consisting of a structured sequence of octets matching the syntax defined in Section 4 and transmitted via the connection.

request ¶

• An HTTP request message, as defined in Section 5.

response ¶

• An HTTP response message, as defined in Section 6.

resource ¶

• A network data object or service that can be identified by a URI, as defined in Section 3.2. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or vary in other ways.

entity ¶

• The information transferred as the payload of a request or response. An entity consists of metainformation in the form of entity-header fields and content in the form of an entity-body, as described in Section 4 of [Part3].

representation ¶

• An entity included with a response that is subject to content negotiation, as described in Section 5 of [Part3]. There may exist multiple representations associated with a particular response status.

content negotiation ¶

• The mechanism for selecting the appropriate representation when servicing a request, as described in Section 5 of [Part3]. The representation of entities in any response can be negotiated (including error responses).

variant ¶

• A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations is termed a `variant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation.

client ¶

• A program that establishes connections for the purpose of sending requests.

user agent ¶

• The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user tools.

server ¶

• An application program that accepts connections in order to service requests by sending back responses. Any given program may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request.

origin server ¶

• The server on which a given resource resides or is to be created.

proxy ¶

• An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients. Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy MUST implement both the client and server requirements of this specification. A "transparent proxy" is a proxy that does not modify the request or response beyond what is required for proxy authentication and identification. A "non-transparent proxy" is a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation services, media type transformation, protocol reduction, or anonymity filtering. Except where either transparent or non-transparent behavior is explicitly stated, the HTTP proxy requirements apply to both types of proxies.

gateway ¶

• A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the origin server for the requested resource; the requesting client may not be aware that it is communicating with a gateway.

tunnel ¶

• An intermediary program which is acting as a blind relay between two connections. Once active, a tunnel is not considered a party to the HTTP communication, though the tunnel may have been initiated by an HTTP request. The tunnel ceases to exist when both ends of the relayed connections are closed.

cache ¶

• A program's local store of response messages and the subsystem that controls its message storage, retrieval, and deletion. A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent requests. Any client or server may include a cache, though a cache cannot be used by a server that is acting as a tunnel.

cacheable ¶

• A response is cacheable if a cache is allowed to store a copy of the response message for use in answering subsequent requests. The rules for determining the cacheability of HTTP responses are defined in Section 1 of [Part6]. Even if a resource is cacheable, there may be additional constraints on whether a cache can use the cached copy for a particular request.

upstream/downstream ¶

• Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream.

inbound/outbound ¶

• Inbound and outbound refer to the request and response paths for messages: "inbound" means "traveling toward the origin server", and "outbound" means "traveling toward the user agent"

HTTP is a request/response protocol. A client sends a request to the server in the form of a request method, URI, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible body content over a connection with a server. The server responds with a status line, including the message's protocol version and a success or error code, followed by a MIME-like message containing server information, entity metainformation, and possible entity-body content. The relationship between HTTP and MIME is described in Appendix A of [Part3].¶

Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin server (O).¶

A more complicated situation occurs when one or more intermediaries are present in the request/response chain. There are three common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages; tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary cannot understand the contents of the messages.¶

The figure above shows three intermediaries (A, B, and C) between the user agent and origin server. A request or response message that travels the whole chain will pass through four separate connections. This distinction is important because some HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple, simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests to servers other than C, at the same time that it is handling A's request.¶

Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from O (via C) for a request which has not been cached by UA or A.¶

Not all responses are usefully cacheable, and some requests may contain modifiers which place special requirements on cache behavior. HTTP requirements for cache behavior and cacheable responses are defined in Section 1 of [Part6].¶

In fact, there are a wide variety of architectures and configurations of caches and proxies currently being experimented with or deployed across the World Wide Web. These systems include national hierarchies of proxy caches to save transoceanic bandwidth, systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so on. HTTP systems are used in corporate intranets over high-bandwidth links, and for access via PDAs with low-power radio links and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while introducing protocol constructs that meet the needs of those who build web applications that require high reliability and, failing that, at least reliable indications of failure.¶

HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 (<http://www.iana.org/assignments/port-numbers>), but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet, or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside the scope of this specification.¶

In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection may be used for one or more request/response exchanges, although connections may be closed for a variety of reasons (see Section 7.1).¶

name = definition ¶

• The name of a rule is simply the name itself (without any enclosing "<" and ">") and is separated from its definition by the equal "=" character. White space is only significant in that indentation of continuation lines is used to indicate a rule definition that spans more than one line. Certain basic rules are in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, etc. Angle brackets are used within definitions whenever their presence will facilitate discerning the use of rule names.

"literal" ¶

• Quotation marks surround literal text. Unless stated otherwise, the text is case-insensitive.

rule1 | rule2 ¶

• Elements separated by a bar ("|") are alternatives, e.g., "yes | no" will accept yes or no.

(rule1 rule2) ¶

• Elements enclosed in parentheses are treated as a single element. Thus, "(elem (foo | bar) elem)" allows the token sequences "elem foo elem" and "elem bar elem".

*rule ¶

• The character "*" preceding an element indicates repetition. The full form is "<n>*<m>element" indicating at least <n> and at most <m> occurrences of element. Default values are 0 and infinity so that "*(element)" allows any number, including zero; "1*element" requires at least one; and "1*2element" allows one or two.

[rule] ¶

• Square brackets enclose optional elements; "[foo bar]" is equivalent to "*1(foo bar)".

N rule ¶

• Specific repetition: "<n>(element)" is equivalent to "<n>*<n>(element)"; that is, exactly <n> occurrences of (element). Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters.

#rule ¶

• A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "<n>#<m>element" indicating at least <n> and at most <m> elements, each separated by one or more commas (",") and OPTIONAL linear white space (LWS). This makes the usual form of lists very easy; a rule such as

     ( *LWS element *( *LWS "," *LWS element ))

• can be shown as

     1#element

• Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is, "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required, at least one non-null element MUST be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at least one; and "1#2element" allows one or two.

; comment ¶

• A semi-colon, set off some distance to the right of rule text, starts a comment that continues to the end of line. This is a simple way of including useful notes in parallel with the specifications.

implied *LWS ¶

• The grammar described by this specification is word-based. Except where noted otherwise, linear white space (LWS) can be included between any two adjacent words (token or quoted-string), and between adjacent words and separators, without changing the interpretation of a field. At least one delimiter (LWS and/or separators) MUST exist between any two tokens (for the definition of "token" below), since they would otherwise be interpreted as a single token.

The following rules are used throughout this specification to describe basic parsing constructs. The US-ASCII coded character set is defined by ANSI X3.4-1986 [USASCII].¶

HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see Appendix A for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described in Section 3.3 of [Part3].¶

HTTP/1.1 header field values can be folded onto multiple lines if the continuation line begins with a space or horizontal tab. All linear white space, including folding, has the same semantics as SP. A recipient MAY replace any linear white space with a single SP before interpreting the field value or forwarding the message downstream.¶

The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message parser. Words of *TEXT MAY contain characters from character sets other than ISO-8859-1 [ISO-8859-1] only when encoded according to the rules of [RFC2047].¶

A CRLF is allowed in the definition of TEXT only as part of a header field continuation. It is expected that the folding LWS will be replaced with a single SP before interpretation of the TEXT value.¶

Hexadecimal numeric characters are used in several protocol elements.¶

Many HTTP/1.1 header field values consist of words separated by LWS or special characters. These special characters MUST be in a quoted string to be used within a parameter value (as defined in Section 3.4).¶

Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part of the field value.¶

A string of text is parsed as a single word if it is quoted using double-quote marks.¶

The backslash character ("\") MAY be used as a single-character quoting mechanism only within quoted-string and comment constructs.¶

HTTP uses a "<major>.<minor>" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather than the features obtained via that communication. No change is made to the version number for the addition of message components which do not affect communication behavior or which only add to extensible field values. The <minor> number is incremented when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may add to the message semantics and imply additional capabilities of the sender. The <major> number is incremented when the format of a message within the protocol is changed. See [RFC2145] for a fuller explanation.¶

The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message. HTTP-Version is case-sensitive.¶

Note that the major and minor numbers MUST be treated as separate integers and that each MAY be incremented higher than a single digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and MUST NOT be sent.¶

An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this specification SHOULD use an HTTP-Version of "HTTP/1.1" in their messages, and MUST do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values, see [RFC2145].¶

The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.¶

Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway MUST NOT send a message with a version indicator which is greater than its actual version. If a higher version request is received, the proxy/gateway MUST either downgrade the request version, or respond with an error, or switch to tunnel behavior.¶

Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of [RFC2068], caching proxies MUST, gateways MAY, and tunnels MUST NOT upgrade the request to the highest version they support. The proxy/gateway's response to that request MUST be in the same major version as the request.¶

• Note: Converting between versions of HTTP may involve modification of header fields required or forbidden by the versions involved.

URIs have been known by many names: WWW addresses, Universal Document Identifiers, Universal Resource Identifiers [RFC1630], and finally the combination of Uniform Resource Locators (URL) [RFC1738] and Names (URN) [RFC1737]. As far as HTTP is concerned, Uniform Resource Identifiers are simply formatted strings which identify--via name, location, or any other characteristic--a resource.¶

Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding is a property of the message, not of the original entity.¶

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 (Section 8.5) and in the Transfer-Encoding header field (Section 8.7).¶

Whenever a transfer-coding is applied to a message-body, the set of transfer-codings MUST include "chunked", unless the message indicates it is terminated by closing the connection. When the "chunked" transfer-coding is used, it MUST be the last transfer-coding applied to the message-body. The "chunked" transfer-coding MUST NOT be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message (Section 4.4).¶

Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME [RFC2045], which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty in determining the exact body length (Section 4.4), or the desire to encrypt data over a shared transport.¶

The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry contains the following tokens: "chunked" (Section 3.4.1), "gzip", "compress", and "deflate" (Section 3.2 of [Part3]).¶

New transfer-coding value tokens SHOULD be registered in the same way as new content-coding value tokens (Section 3.2 of [Part3]).¶

A server which receives an entity-body with a transfer-coding it does not understand SHOULD return 501 (Not Implemented), and close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0 client.¶

Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white space. By convention, the products are listed in order of their significance for identifying the application.¶

Product tokens SHOULD be short and to the point. They MUST NOT be used for advertising or other non-essential information. Although any token character MAY appear in a product-version, this token SHOULD only be used for a version identifier (i.e., successive versions of the same product SHOULD only differ in the product-version portion of the product value).¶

HTTP messages consist of requests from client to server and responses from server to client.¶

Request (Section 5) and Response (Section 6) messages use the generic message format of [RFC2822] for transferring entities (the payload of the message). Both types of message consist of a start-line, zero or more header fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header fields, and possibly a message-body.¶

In the interest of robustness, servers SHOULD ignore any empty line(s) received where a Request-Line is expected. In other words, if the server is reading the protocol stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF.¶

Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST request. To restate what is explicitly forbidden by the BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an extra CRLF.¶

HTTP header fields, which include general-header (Section 4.5), request-header (Section 4 of [Part2]), response-header (Section 6 of [Part2]), and entity-header (Section 4.1 of [Part3]) fields, follow the same generic format as that given in Section 2.1 of [RFC2822]. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The field value MAY be preceded by any amount of LWS, though a single SP is preferred. Header fields can be extended over multiple lines by preceding each extra line with at least one SP or HTAB. Applications ought to follow "common form", where one is known or indicated, when generating HTTP constructs, since there might exist some implementations that fail to accept anything beyond the common forms.¶

The field-content does not include any leading or trailing LWS: linear white space occurring before the first non-whitespace character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS MAY be removed without changing the semantics of the field value. Any LWS that occurs between field-content MAY be replaced with a single SP before interpreting the field value or forwarding the message downstream.¶

The order in which header fields with differing field names are received is not significant. However, it is "good practice" to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header fields.¶

Multiple message-header fields with the same field-name MAY be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e., #(values)]. It MUST be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which header fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and thus a proxy MUST NOT change the order of these field values when a message is forwarded.¶

• Note: the "Set-Cookie" header as implemented in practice (as opposed to how it is specified in [RFC2109]) can occur multiple times, but does not use the list syntax, and thus cannot be combined into a single line. (See Appendix A.2.3 of [Kri2001] for details.) Also note that the Set-Cookie2 header specified in [RFC2965] does not share this problem.

The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding header field (Section 8.7).¶

Transfer-Encoding MUST be used to indicate any transfer-codings applied by an application to ensure safe and proper transfer of the message. Transfer-Encoding is a property of the message, not of the entity, and thus MAY be added or removed by any application along the request/response chain. (However, Section 3.4 places restrictions on when certain transfer-codings may be used.)¶

The rules for when a message-body is allowed in a message differ for requests and responses.¶

The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field in the request's message-headers. A message-body MUST NOT be included in a request if the specification of the request method (Section 3 of [Part2]) explicitly disallows an entity-body in requests. When a request message contains both a message-body of non-zero length and a method that does not define any semantics for that request message-body, then an origin server SHOULD either ignore the message-body or respond with an appropriate error message (e.g., 413). A proxy or gateway, when presented the same request, SHOULD either forward the request inbound with the message-body or ignore the message-body when determining a response.¶

For response messages, whether or not a message-body is included with a message is dependent on both the request method and the response status code (Section 6.1.1). All responses to the HEAD request method MUST NOT include a message-body, even though the presence of entity-header fields might lead one to believe they do. All 1xx (informational), 204 (No Content), and 304 (Not Modified) responses MUST NOT include a message-body. All other responses do include a message-body, although it MAY be of zero length.¶

1. Any response message which "MUST NOT" include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD request) is always terminated by the first empty line after the header fields, regardless of the entity-header fields present in the message.

2. If a Transfer-Encoding header field (Section 8.7) is present and the "chunked" transfer-coding (Section 3.4) is used, the transfer-length is defined by the use of this transfer-coding. If a Transfer-Encoding header field is present and the "chunked" transfer-coding is not present, the transfer-length is defined by the sender closing the connection.

3. If a Content-Length header field (Section 8.2) is present, its decimal value in OCTETs represents both the entity-length and the transfer-length. The Content-Length header field MUST NOT be sent if these two lengths are different (i.e., if a Transfer-Encoding header field is present). If a message is received with both a Transfer-Encoding header field and a Content-Length header field, the latter MUST be ignored.

4. If the message uses the media type "multipart/byteranges", and the transfer-length is not otherwise specified, then this self-delimiting media type defines the transfer-length. This media type MUST NOT be used unless the sender knows that the recipient can parse it; the presence in a request of a Range header with multiple byte-range specifiers from a 1.1 client implies that the client can parse multipart/byteranges responses.

   • A range header might be forwarded by a 1.0 proxy that does not understand multipart/byteranges; in this case the server MUST delimit the message using methods defined in items 1, 3 or 5 of this section.

5. By the server closing the connection. (Closing the connection cannot be used to indicate the end of a request body, since that would leave no possibility for the server to send back a response.)

For compatibility with HTTP/1.0 applications, HTTP/1.1 requests containing a message-body MUST include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a request contains a message-body and a Content-Length is not given, the server SHOULD respond with 400 (Bad Request) if it cannot determine the length of the message, or with 411 (Length Required) if it wishes to insist on receiving a valid Content-Length.¶

All HTTP/1.1 applications that receive entities MUST accept the "chunked" transfer-coding (Section 3.4), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance.¶

Messages MUST NOT include both a Content-Length header field and a transfer-coding. If the message does include a transfer-coding, the Content-Length MUST be ignored.¶

When a Content-Length is given in a message where a message-body is allowed, its field value MUST exactly match the number of OCTETs in the message-body. HTTP/1.1 user agents MUST notify the user when an invalid length is received and detected.¶

There are a few header fields which have general applicability for both request and response messages, but which do not apply to the entity being transferred. These header fields apply only to the message being transmitted.¶

General-header field names can be extended reliably only in combination with a change in the protocol version. However, new or experimental header fields may be given the semantics of general header fields if all parties in the communication recognize them to be general-header fields. Unrecognized header fields are treated as entity-header fields.¶

The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.¶

The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.¶

An origin server that does not allow resources to differ by the requested host MAY ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see Appendix C.1.1 for other requirements on Host support in HTTP/1.1.)¶

An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or vanity host names) MUST use the following rules for determining the requested resource on an HTTP/1.1 request: ¶

1. If Request-URI is an absoluteURI, the host is part of the Request-URI. Any Host header field value in the request MUST be ignored.
2. If the Request-URI is not an absoluteURI, and the request includes a Host header field, the host is determined by the Host header field value.
3. If the host as determined by rule 1 or 2 is not a valid host on the server, the response MUST be a 400 (Bad Request) error message.

Recipients of an HTTP/1.0 request that lacks a Host header field MAY attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine what exact resource is being requested.¶

The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.¶

The Connection general-header field allows the sender to specify options that are desired for that particular connection and MUST NOT be communicated by proxies over further connections.¶

HTTP/1.1 proxies MUST parse the Connection header field before a message is forwarded and, for each connection-token in this field, remove any header field(s) from the message with the same name as the connection-token. Connection options are signaled by the presence of a connection-token in the Connection header field, not by any corresponding additional header field(s), since the additional header field may not be sent if there are no parameters associated with that connection option.¶

Message headers listed in the Connection header MUST NOT include end-to-end headers, such as Cache-Control.¶

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' (Section 7.1) after the current request/response is complete.¶

An HTTP/1.1 client that does not support persistent connections MUST include the "close" connection option in every request message.¶

An HTTP/1.1 server that does not support persistent connections MUST include the "close" connection option in every response message that does not have a 1xx (informational) status code.¶

A system receiving an HTTP/1.0 (or lower-version) message that includes a Connection header MUST, for each connection-token in this field, remove and ignore any header field(s) from the message with the same name as the connection-token. This protects against mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. See Appendix C.2.¶

The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.¶

An example is¶

Applications SHOULD use this field to indicate the transfer-length of the message-body, unless this is prohibited by the rules in Section 4.4.¶

Any Content-Length greater than or equal to zero is a valid value. Section 4.4 describes how to determine the length of a message-body if a Content-Length is not given.¶

Note that the meaning of this field is significantly different from the corresponding definition in MIME, where it is an optional field used within the "message/external-body" content-type. In HTTP, it SHOULD be sent whenever the message's length can be determined prior to being transferred, unless this is prohibited by the rules in Section 4.4.¶

The Date general-header field represents the date and time at which the message was originated, having the same semantics as orig-date in Section 3.6.1 of [RFC2822]. The field value is an HTTP-date, as described in Section 3.3.1; it MUST be sent in rfc1123-date format.¶

An example is¶

Origin servers MUST include a Date header field in all responses, except in these cases: ¶

1. If the response status code is 100 (Continue) or 101 (Switching Protocols), the response MAY include a Date header field, at the server's option.
2. If the response status code conveys a server error, e.g. 500 (Internal Server Error) or 503 (Service Unavailable), and it is inconvenient or impossible to generate a valid Date.
3. If the server does not have a clock that can provide a reasonable approximation of the current time, its responses MUST NOT include a Date header field. In this case, the rules in Section 8.3.1 MUST be followed.

A received message that does not have a Date header field MUST be assigned one by the recipient if the message will be cached by that recipient or gatewayed via a protocol which requires a Date. An HTTP implementation without a clock MUST NOT cache responses without revalidating them on every use. An HTTP cache, especially a shared cache, SHOULD use a mechanism, such as NTP [RFC1305], to synchronize its clock with a reliable external standard.¶

Clients SHOULD only send a Date header field in messages that include an entity-body, as in the case of the PUT and POST requests, and even then it is optional. A client without a clock MUST NOT send a Date header field in a request.¶

The HTTP-date sent in a Date header SHOULD NOT represent a date and time subsequent to the generation of the message. It SHOULD represent the best available approximation of the date and time of message generation, unless the implementation has no means of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the entity is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic value.¶

The Host request-header field specifies the Internet host and port number of the resource being requested, as obtained from the original URI given by the user or referring resource (generally an HTTP URL, as described in Section 3.2.2). The Host field value MUST represent the naming authority of the origin server or gateway given by the original URL. This allows the origin server or gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL of a server for multiple host names on a single IP address.¶

A client MUST include a Host header field in all HTTP/1.1 request messages. If the requested URI does not include an Internet host name for the service being requested, then the Host header field MUST be given with an empty value. An HTTP/1.1 proxy MUST ensure that any request message it forwards does contain an appropriate Host header field that identifies the service being requested by the proxy. All Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request) status code to any HTTP/1.1 request message which lacks a Host header field.¶

See Sections 5.2 and C.1.1 for other requirements relating to Host.¶

The TE request-header field indicates what extension transfer-codings it is willing to accept in the response and whether or not it is willing to accept trailer fields in a chunked transfer-coding. Its value may consist of the keyword "trailers" and/or a comma-separated list of extension transfer-coding names with optional accept parameters (as described in Section 3.4).¶

The presence of the keyword "trailers" indicates that the client is willing to accept trailer fields in a chunked transfer-coding, as defined in Section 3.4.1. This keyword is reserved for use with transfer-coding values even though it does not itself represent a transfer-coding.¶

The TE header field only applies to the immediate connection. Therefore, the keyword MUST be supplied within a Connection header field (Section 8.1) whenever TE is present in an HTTP/1.1 message.¶

A server tests whether a transfer-coding is acceptable, according to a TE field, using these rules: ¶

1. The "chunked" transfer-coding is always acceptable. If the keyword "trailers" is listed, the client indicates that it is willing to accept trailer fields in the chunked response on behalf of itself and any downstream clients. The implication is that, if given, the client is stating that either all downstream clients are willing to accept trailer fields in the forwarded response, or that it will attempt to buffer the response on behalf of downstream recipients.

   Note: HTTP/1.1 does not define any means to limit the size of a chunked response such that a client can be assured of buffering the entire response.

2. If the transfer-coding being tested is one of the transfer-codings listed in the TE field, then it is acceptable unless it is accompanied by a qvalue of 0. (As defined in Section 3.4 of [Part3], a qvalue of 0 means "not acceptable.")

3. If multiple transfer-codings are acceptable, then the acceptable transfer-coding with the highest non-zero qvalue is preferred. The "chunked" transfer-coding always has a qvalue of 1.

If the TE field-value is empty or if no TE field is present, the only transfer-coding is "chunked". A message with no transfer-coding is always acceptable.¶

The Trailer general field value indicates that the given set of header fields is present in the trailer of a message encoded with chunked transfer-coding.¶

An HTTP/1.1 message SHOULD include a Trailer header field in a message using chunked transfer-coding with a non-empty trailer. Doing so allows the recipient to know which header fields to expect in the trailer.¶

If no Trailer header field is present, the trailer SHOULD NOT include any header fields. See Section 3.4.1 for restrictions on the use of trailer fields in a "chunked" transfer-coding.¶

Message header fields listed in the Trailer header field MUST NOT include the following header fields: ¶

• Transfer-Encoding
• Content-Length
• Trailer

The Transfer-Encoding general-header field indicates what (if any) type of transformation has been applied to the message body in order to safely transfer it between the sender and the recipient. This differs from the content-coding in that the transfer-coding is a property of the message, not of the entity.¶

If multiple encodings have been applied to an entity, the transfer-codings MUST be listed in the order in which they were applied. Additional information about the encoding parameters MAY be provided by other entity-header fields not defined by this specification.¶

Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.¶

The Upgrade general-header allows the client to specify what additional communication protocols it supports and would like to use if the server finds it appropriate to switch protocols. The server MUST use the Upgrade header field within a 101 (Switching Protocols) response to indicate which protocol(s) are being switched.¶

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 method and/or resource being requested).¶

The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer connection. Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. The capabilities and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen, although the first action after changing the protocol MUST be a response to the initial HTTP request containing the Upgrade header field.¶

The Upgrade header field only applies to the immediate connection. Therefore, the upgrade keyword MUST be supplied within a Connection header field (Section 8.1) whenever Upgrade is present in an HTTP/1.1 message.¶

The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it is more appropriate to use a 301, 302, 303, or 305 redirection response.¶

This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined by the HTTP version rules of Section 3.1 and future updates to this specification. Any token can be used as a protocol name; however, it will only be useful if both the client and server associate the name with the same protocol.¶

The Via general-header field MUST be used by gateways and proxies to indicate the intermediate protocols and recipients between the user agent and the server on requests, and between the origin server and the client on responses. It is analogous to the "Received" field defined in Section 3.6.7 of [RFC2822] and is intended to be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities of all senders along the request/response chain.¶

The received-protocol indicates the protocol version of the message received by the server or client along each segment of the request/response chain. The received-protocol version is appended to the Via field value when the message is forwarded so that information about the protocol capabilities of upstream applications remains visible to all recipients.¶

The protocol-name is optional if and only if it would be "HTTP". The received-by field is normally the host and optional port number of a recipient server or client that subsequently forwarded the message. However, if the real host is considered to be sensitive information, it MAY be replaced by a pseudonym. If the port is not given, it MAY be assumed to be the default port of the received-protocol.¶

Multiple Via field values represents each proxy or gateway that has forwarded the message. Each recipient MUST append its information such that the end result is ordered according to the sequence of forwarding applications.¶

Comments MAY be used in the Via header field to identify the software of the recipient proxy or gateway, analogous to the User-Agent and Server header fields. However, all comments in the Via field are optional and MAY be removed by any recipient prior to forwarding the message.¶

Proxies and gateways used as a portal through a network firewall SHOULD NOT, by default, forward the names and ports of hosts within the firewall region. This information SHOULD only be propagated if explicitly enabled. If not enabled, the received-by host of any host behind the firewall SHOULD be replaced by an appropriate pseudonym for that host.¶

For organizations that have strong privacy requirements for hiding internal structures, a proxy MAY combine an ordered subsequence of Via header field entries with identical received-protocol values into a single such entry. For example,¶

could be collapsed to¶

Applications SHOULD NOT combine multiple entries unless they are all under the same organizational control and the hosts have already been replaced by pseudonyms. Applications MUST NOT combine entries which have different received-protocol values.¶

The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".¶

The entry for the "http" URI Scheme in the registry located at <http://www.iana.org/assignments/uri-schemes.html> should be updated to point to Section 3.2.2 of this document (see [RFC4395]).¶

This document serves as the specification for the Internet media types "message/http" and "application/http". The following is to be registered with IANA (see [RFC4288]).¶

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-URI if it would otherwise allow access to a resource outside those intended to be accessible via the HTTP server. Similarly, files intended for reference only internally to the server (such as access control files, configuration files, and script code) MUST be protected from inappropriate retrieval, since they might contain sensitive information. Experience has shown that minor bugs in such HTTP server implementations have turned into security risks.¶

Clients using HTTP rely heavily on the Domain Name Service, and are thus generally prone to security attacks based on the deliberate mis-association of IP addresses and DNS names. Clients need to be cautious in assuming the continuing validity of an IP number/DNS name association.¶

In particular, HTTP clients SHOULD rely on their name resolver for confirmation of an IP number/DNS name association, rather than caching the result of previous host name lookups. Many platforms already can cache host name lookups locally when appropriate, and they SHOULD be configured to do so. It is proper for these lookups to be cached, however, only when the TTL (Time To Live) information reported by the name server makes it likely that the cached information will remain useful.¶

If HTTP clients cache the results of host name lookups in order to achieve a performance improvement, they MUST observe the TTL information reported by DNS.¶

If HTTP clients do not observe this rule, they could be spoofed when a previously-accessed server's IP address changes. As network renumbering is expected to become increasingly common [RFC1900], the possibility of this form of attack will grow. Observing this requirement thus reduces this potential security vulnerability.¶

This requirement also improves the load-balancing behavior of clients for replicated servers using the same DNS name and reduces the likelihood of a user's experiencing failure in accessing sites which use that strategy.¶

By their very nature, HTTP proxies are men-in-the-middle, and represent an opportunity for man-in-the-middle attacks. Compromise of the systems on which the proxies run can result in serious security and privacy problems. Proxies have access to security-related information, personal information about individual users and organizations, and proprietary information belonging to users and content providers. A compromised proxy, or a proxy implemented or configured without regard to security and privacy considerations, might be used in the commission of a wide range of potential attacks.¶

Proxy operators should protect the systems on which proxies run as they would protect any system that contains or transports sensitive information. In particular, log information gathered at proxies often contains highly sensitive personal information, and/or information about organizations. Log information should be carefully guarded, and appropriate guidelines for use developed and followed. (Section 10.2).¶

Proxy implementors should consider the privacy and security implications of their design and coding decisions, and of the configuration options they provide to proxy operators (especially the default configuration).¶

Users of a proxy need to be aware that they are no trustworthier than the people who run the proxy; HTTP itself cannot solve this problem.¶

The judicious use of cryptography, when appropriate, may suffice to protect against a broad range of security and privacy attacks. Such cryptography is beyond the scope of the HTTP/1.1 specification.¶

They exist. They are hard to defend against. Research continues. Beware.¶

12.1. Normative References

[ISO-8859-1]

International Organization for Standardization, “Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1”, ISO/IEC 8859-1:1998, 1998.

[Part2]

Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed., “HTTP/1.1, part 2: Message Semantics”, Internet-Draft draft-ietf-httpbis-p2-semantics-04 (work in progress), August 2008.

[Part3]

Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed., “HTTP/1.1, part 3: Message Payload and Content Negotiation”, Internet-Draft draft-ietf-httpbis-p3-payload-04 (work in progress), August 2008.

[Part5]

Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed., “HTTP/1.1, part 5: Range Requests and Partial Responses”, Internet-Draft draft-ietf-httpbis-p5-range-04 (work in progress), August 2008.

[Part6]

Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., and J. Reschke, Ed., “HTTP/1.1, part 6: Caching”, Internet-Draft draft-ietf-httpbis-p6-cache-04 (work in progress), August 2008.

[RFC2045]

Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies”, RFC 2045, November 1996.

[RFC2047]

Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text”, RFC 2047, November 1996.

[RFC2119]

Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, March 1997.

[RFC2396]

Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifiers (URI): Generic Syntax”, RFC 2396, August 1998.

[RFC822ABNF]

Crocker, D., “Standard for the format of ARPA Internet text messages”, STD 11, RFC 822, August 1982.

[USASCII]

American National Standards Institute, “Coded Character Set -- 7-bit American Standard Code for Information Interchange”, ANSI X3.4, 1986.

12.2. Informative References

[Kri2001]

Kristol, D., “HTTP Cookies: Standards, Privacy, and Politics”, ACM Transactions on Internet Technology Vol. 1, #2, November 2001, <http://arxiv.org/abs/cs.SE/0105018>.

[Nie1997]

Nielsen, H., Gettys, J., Prud'hommeaux, E., Lie, H., and C. Lilley, “Network Performance Effects of HTTP/1.1, CSS1, and PNG”, ACM Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97, September 1997, <http://doi.acm.org/10.1145/263105.263157>.

[Pad1995]

Padmanabhan, V. and J. Mogul, “Improving HTTP Latency”, Computer Networks and ISDN Systems v. 28, pp. 25-35, December 1995, <http://portal.acm.org/citation.cfm?id=219094>.

[RFC1123]

Braden, R., “Requirements for Internet Hosts - Application and Support”, STD 3, RFC 1123, October 1989.

[RFC1305]

Mills, D., “Network Time Protocol (Version 3) Specification, Implementation”, RFC 1305, March 1992.

[RFC1436]

Anklesaria, F., McCahill, M., Lindner, P., Johnson, D., Torrey, D., and B. Alberti, “The Internet Gopher Protocol (a distributed document search and retrieval protocol)”, RFC 1436, March 1993.

[RFC1630]

Berners-Lee, T., “Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web”, RFC 1630, June 1994.

[RFC1737]

Masinter, L. and K. Sollins, “Functional Requirements for Uniform Resource Names”, RFC 1737, December 1994.

[RFC1738]

Berners-Lee, T., Masinter, L., and M. McCahill, “Uniform Resource Locators (URL)”, RFC 1738, December 1994.

[RFC1808]

Fielding, R., “Relative Uniform Resource Locators”, RFC 1808, June 1995.

[RFC1900]

Carpenter, B. and Y. Rekhter, “Renumbering Needs Work”, RFC 1900, February 1996.

[RFC1945]

Berners-Lee, T., Fielding, R., and H. Nielsen, “Hypertext Transfer Protocol -- HTTP/1.0”, RFC 1945, May 1996.

[RFC2068]

Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1”, RFC 2068, January 1997.

[RFC2109]

Kristol, D. and L. Montulli, “HTTP State Management Mechanism”, RFC 2109, February 1997.

[RFC2145]

Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, “Use and Interpretation of HTTP Version Numbers”, RFC 2145, May 1997.

[RFC2324]

Masinter, L., “Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)”, RFC 2324, April 1998.

[RFC2616]

Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1”, RFC 2616, June 1999.

[RFC2818]

Rescorla, E., “HTTP Over TLS”, RFC 2818, May 2000.

[RFC2821]

Klensin, J., “Simple Mail Transfer Protocol”, RFC 2821, April 2001.

[RFC2822]

Resnick, P., “Internet Message Format”, RFC 2822, April 2001.

[RFC2965]

Kristol, D. and L. Montulli, “HTTP State Management Mechanism”, RFC 2965, October 2000.

[RFC3864]

Klyne, G., Nottingham, M., and J. Mogul, “Registration Procedures for Message Header Fields”, BCP 90, RFC 3864, September 2004.

[RFC3977]

Feather, C., “Network News Transfer Protocol (NNTP)”, RFC 3977, October 2006.

[RFC4288]

Freed, N. and J. Klensin, “Media Type Specifications and Registration Procedures”, BCP 13, RFC 4288, December 2005.

[RFC4395]

Hansen, T., Hardie, T., and L. Masinter, “Guidelines and Registration Procedures for New URI Schemes”, BCP 115, RFC 4395, February 2006.

[RFC822]

Crocker, D., “Standard for the format of ARPA Internet text messages”, STD 11, RFC 822, August 1982.

[RFC959]

Postel, J. and J. Reynolds, “File Transfer Protocol”, STD 9, RFC 959, October 1985.

[Spe]

Spero, S., “Analysis of HTTP Performance Problems”, <http://sunsite.unc.edu/mdma-release/http-prob.html>.

[Tou1998]

Touch, J., Heidemann, J., and K. Obraczka, “Analysis of HTTP Performance”, ISI Research Report ISI/RR-98-463, Aug 1998, <http://www.isi.edu/touch/pubs/http-perf96/>.
(original report dated Aug. 1996)

[WAIS]

Davis, F., Kahle, B., Morris, H., Salem, J., Shen, T., Wang, R., Sui, J., and M. Grinbaum, “WAIS Interface Protocol Prototype Functional Specification (v1.5)”, Thinking Machines Corporation, April 1990.

This section summarizes major differences between versions HTTP/1.0 and HTTP/1.1.¶

Some clients and servers might wish to be compatible with some previous implementations of persistent connections in HTTP/1.0 clients and servers. Persistent connections in HTTP/1.0 are explicitly negotiated as they are not the default behavior. HTTP/1.0 experimental implementations of persistent connections are faulty, and the new facilities in HTTP/1.1 are designed to rectify these problems. The problem was that some existing 1.0 clients may be sending Keep-Alive to a proxy server that doesn't understand Connection, which would then erroneously forward it to the next inbound server, which would establish the Keep-Alive connection and result in a hung HTTP/1.0 proxy waiting for the close on the response. The result is that HTTP/1.0 clients must be prevented from using Keep-Alive when talking to proxies.¶

However, talking to proxies is the most important use of persistent connections, so that prohibition is clearly unacceptable. Therefore, we need some other mechanism for indicating a persistent connection is desired, which is safe to use even when talking to an old proxy that ignores Connection. Persistent connections are the default for HTTP/1.1 messages; we introduce a new keyword (Connection: close) for declaring non-persistence. See Section 8.1.¶

The original HTTP/1.0 form of persistent connections (the Connection: Keep-Alive and Keep-Alive header) is documented in [RFC2068].¶

This specification has been carefully audited to correct and disambiguate key word usage; RFC 2068 had many problems in respect to the conventions laid out in [RFC2119].¶

Transfer-coding and message lengths all interact in ways that required fixing exactly when chunked encoding is used (to allow for transfer encoding that may not be self delimiting); it was important to straighten out exactly how message lengths are computed. (Sections 3.4, 4.4, 8.2, see also [Part3], [Part5] and [Part6])¶

The use and interpretation of HTTP version numbers has been clarified by [RFC2145]. Require proxies to upgrade requests to highest protocol version they support to deal with problems discovered in HTTP/1.0 implementations (Section 3.1)¶

Transfer-coding had significant problems, particularly with interactions with chunked encoding. The solution is that transfer-codings become as full fledged as content-codings. This involves adding an IANA registry for transfer-codings (separate from content codings), a new header field (TE) and enabling trailer headers in the future. Transfer encoding is a major performance benefit, so it was worth fixing [Nie1997]. TE also solves another, obscure, downward interoperability problem that could have occurred due to interactions between authentication trailers, chunked encoding and HTTP/1.0 clients.(Section 3.4, 3.4.1, and 8.5)¶

The CHAR rule does not allow the NUL character anymore (this affects the comment and quoted-string rules). Furthermore, the quoted-pair rule does not allow escaping NUL, CR or LF anymore. (Section 2.2)¶

Clarify that HTTP-Version is case sensitive. (Section 3.1)¶

Remove reference to non-existant identity transfer-coding value tokens. (Sections 3.4 and 4.4)¶

Clarification that the chunk length does not include the count of the octets in the chunk header and trailer. (Section 3.4.1)¶

Fix BNF to add query, as the abs_path production in Section 3 of [RFC2396] doesn't define it. (Section 5.1.2)¶

Clarify exactly when close connection options must be sent. (Section 8.1)¶

Extracted relevant partitions from [RFC2616].¶

Closed issues: ¶

• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/1>: "HTTP Version should be case sensitive" (<http://purl.org/NET/http-errata#verscase>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/2>: "'unsafe' characters" (<http://purl.org/NET/http-errata#unsafe-uri>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/3>: "Chunk Size Definition" (<http://purl.org/NET/http-errata#chunk-size>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/4>: "Message Length" (<http://purl.org/NET/http-errata#msg-len-chars>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/8>: "Media Type Registrations" (<http://purl.org/NET/http-errata#media-reg>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/11>: "URI includes query" (<http://purl.org/NET/http-errata#uriquery>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/15>: "No close on 1xx responses" (<http://purl.org/NET/http-errata#noclose1xx>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/16>: "Remove 'identity' token references" (<http://purl.org/NET/http-errata#identity>)
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/26>: "Import query BNF"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/31>: "qdtext BNF"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and Informative references"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42>: "RFC2606 Compliance"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/45>: "RFC977 reference"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/46>: "RFC1700 references"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/47>: "inconsistency in date format explanation"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/48>: "Date reference typo"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65>: "Informative references"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/66>: "ISO-8859-1 Reference"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86>: "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 <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>)

Closed issues: ¶

• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/19>: "Bodies on GET (and other) requests"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/55>: "Updating to RFC4288"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/57>: "Status Code and Reason Phrase"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/82>: "rel_path not used"

Ongoing work on ABNF conversion (<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>): ¶

• 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 (this includes a change to CHAR which now excludes NUL).
• 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.
• 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://www3.tools.ietf.org/wg/httpbis/trac/ticket/51>: "HTTP-date vs. rfc1123-date"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/64>: "WS in quoted-pair"

Ongoing work on IANA Message Header Registration (<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40>): ¶

• Reference RFC 3984, and update header registrations for headers defined in this document.

Ongoing work on ABNF conversion (<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>): ¶

• Replace string literals when the string really is case-sensitive (HTTP-Version).

Closed issues: ¶

• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/28>: "Connection closing"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/97>: "Move registrations and registry information to IANA Considerations"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/120>: "need new URL for PAD1995 reference"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/127>: "IANA Considerations: update HTTP URI scheme registration"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/128>: "Cite HTTPS URI scheme definition"
• <http://www3.tools.ietf.org/wg/httpbis/trac/ticket/129>: "List-type headers vs Set-Cookie"

Ongoing work on ABNF conversion (<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36>): ¶

• 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.