Updated by: 8615 PROPOSED STANDARD

Errata Exist

Internet Engineering Task Force (IETF) R. Fielding, Ed. Request for Comments: 7230 Adobe Obsoletes: 2145, 2616 J. Reschke, Ed. Updates: 2817, 2818 greenbytes Category: Standards Track June 2014 ISSN: 2070-1721 Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing Abstract The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7230. Fielding & Reschke Standards Track [Page 1]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction ....................................................5 1.1. Requirements Notation ......................................6 1.2. Syntax Notation ............................................6 2. Architecture ....................................................6 2.1. Client/Server Messaging ....................................7 2.2. Implementation Diversity ...................................8 2.3. Intermediaries .............................................9 2.4. Caches ....................................................11 2.5. Conformance and Error Handling ............................12 2.6. Protocol Versioning .......................................13 2.7. Uniform Resource Identifiers ..............................16 2.7.1. http URI Scheme ....................................17 2.7.2. https URI Scheme ...................................18 2.7.3. http and https URI Normalization and Comparison ....19 3. Message Format .................................................19 3.1. Start Line ................................................20 3.1.1. Request Line .......................................21 3.1.2. Status Line ........................................22 3.2. Header Fields .............................................22 Fielding & Reschke Standards Track [Page 2]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 1 . Introduction RFC7231] 3. "Conditional Requests" [RFC7232] 4. "Range Requests" [RFC7233] 5. "Caching" [RFC7234] 6. "Authentication" [RFC7235] This HTTP/1.1 specification obsoletes RFC 2616 and RFC 2145 (on HTTP versioning). This specification also updates the use of CONNECT to establish a tunnel, previously defined in RFC 2817, and defines the "https" URI scheme that was described informally in RFC 2818. 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 this 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 Fielding & Reschke Standards Track [Page 5]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 2.1 . Client/Server Messaging Section 3) across a reliable transport- or session-layer "connection" (Section 6). 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. 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. The term "user agent" refers to any of the various client programs that initiate a request, including (but not limited to) browsers, spiders (web-based robots), command-line tools, custom applications, and mobile apps. The term "origin server" refers to the program that can originate authoritative responses for a given target resource. The terms "sender" and "recipient" refer to any implementation that sends or receives a given message, respectively. HTTP relies upon the Uniform Resource Identifier (URI) standard [RFC3986] to indicate the target resource (Section 5.1) and relationships between resources. Messages are passed in a format similar to that used by Internet mail [RFC5322] and the Multipurpose Internet Mail Extensions (MIME) [RFC2045] (see Appendix A of [RFC7231] for the differences between HTTP and MIME messages). 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). request > UA ======================================= O < response A client sends an HTTP request to a server in the form of a request message, beginning with a request-line that includes a method, URI, and protocol version (Section 3.1.1), followed by header fields containing request modifiers, client information, and representation metadata (Section 3.2), an empty line to indicate the end of the header section, and finally a message body containing the payload body (if any, Section 3.3). Fielding & Reschke Standards Track [Page 7]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 3.1.2), possibly followed by header fields containing server information, resource metadata, and representation metadata (Section 3.2), an empty line to indicate the end of the header section, and finally a message body containing the payload body (if any, Section 3.3). A connection might be used for multiple request/response exchanges, as defined in Section 6.3. The following example illustrates a typical message exchange for a GET request (Section 4.3.1 of [RFC7231]) on the URI "http://www.example.com/hello.txt": Client request: GET /hello.txt HTTP/1.1 User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3 Host: www.example.com Accept-Language: en, mi Server response: HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT ETag: "34aa387-d-1568eb00" Accept-Ranges: bytes Content-Length: 51 Vary: Accept-Encoding Content-Type: text/plain Hello World! My payload includes a trailing CRLF. 2.2 . Implementation Diversity Fielding & Reschke Standards Track [Page 8]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 2.3 . Intermediaries Fielding & Reschke Standards Track [Page 9]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 5.7.2. A "gateway" (a.k.a. "reverse proxy") is an intermediary that acts as an origin server for the outbound connection but translates received requests and forwards them inbound to another server or servers. 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. 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 ought to conform to user agent requirements on the gateway's inbound connection. 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 (TLS, [RFC5246]) is used to establish confidential communication through a shared firewall proxy. Fielding & Reschke Standards Track [Page 10]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 RFC3040] (also commonly known as a "transparent proxy" [RFC1919] or "captive portal") differs from an HTTP proxy because it is not selected by the client. Instead, an interception proxy filters or redirects outgoing TCP port 80 packets (and occasionally other common port traffic). 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. HTTP is defined as a stateless protocol, meaning that each request message can be understood in isolation. Many implementations depend on HTTP's stateless design in order to reuse proxied connections or dynamically load balance requests across multiple servers. Hence, a server MUST NOT assume that two requests on the same connection are from the same user agent unless the connection is secured and specific to that agent. Some non-standard HTTP extensions (e.g., [RFC4559]) have been known to violate this requirement, resulting in security and interoperability problems. 2.4 . Caches Fielding & Reschke Standards Track [Page 11]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 2 of [RFC7234]. There is a wide variety of architectures and configurations of caches deployed across the World Wide Web and inside large organizations. These include national hierarchies of proxy caches to save transoceanic bandwidth, collaborative systems that broadcast or multicast cache entries, archives of pre-fetched cache entries for use in off-line or high-latency environments, and so on. 2.5 . Conformance and Error Handling Fielding & Reschke Standards Track [Page 12]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 2.6 . Protocol Versioning Fielding & Reschke Standards Track [Page 13]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 RFC1945] or a recipient whose version is unknown, the HTTP/1.1 message is constructed such that it can be interpreted as a valid HTTP/1.0 message if all of the newer features are ignored. This specification places recipient-version requirements on some new features so that a conformant sender will only use compatible features until it has determined, through configuration or the receipt of a message, that the recipient supports HTTP/1.1. The interpretation of a header field does not change between minor versions of the same major HTTP 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 conformance with HTTP/1.1. 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. Header field extensibility is discussed in Section 3.2.1. Intermediaries that process HTTP messages (i.e., all intermediaries other than those acting as tunnels) MUST send their own HTTP-version in forwarded messages. In other words, they are not allowed to blindly forward the first line of an HTTP message without ensuring that the protocol version in that message matches a version to which that intermediary is conformant for both the receiving and sending of messages. Forwarding an HTTP message without rewriting the Fielding & Reschke Standards Track [Page 14]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 RFC2068] and [RFC2616], and this revision has specifically avoided any such changes to the protocol. When an HTTP message is received with a major version number that the recipient implements, but a higher minor version number than what the recipient implements, the recipient SHOULD process the message as if it were in the highest minor version within that major version to which the recipient is conformant. A recipient can assume that a Fielding & Reschke Standards Track [Page 15]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 2.7.1 . http URI Scheme RFC0793]) connections on a given port. http-URI = "http:" "//" authority path-abempty [ "?" query ] [ "#" fragment ] The origin server for an "http" URI is identified by the authority component, which includes a host identifier and optional TCP port ([RFC3986], Section 3.2.2). The hierarchical path component and optional query component serve as an identifier for a potential target resource within that origin server's name space. The optional fragment component allows for indirect identification of a secondary resource, independent of the URI scheme, as defined in Section 3.5 of [RFC3986]. A sender MUST NOT generate an "http" URI with an empty host identifier. A recipient that processes such a URI reference MUST reject it as invalid. If the host identifier is provided as an IP address, the origin server is the listener (if any) on the indicated TCP port at that IP address. If host is a registered name, the registered name is an indirect identifier for use with a name resolution service, such as DNS, to find an address for that origin server. If the port subcomponent is empty or not given, TCP port 80 (the reserved port for WWW services) is the default. Note that the presence of a URI with a given authority component does not imply that there is always an HTTP server listening for connections on that host and port. Anyone can mint a URI. What the authority component determines is who has the right to respond authoritatively to requests that target the identified resource. The delegated nature of registered names and IP addresses creates a federated namespace, based on control over the indicated host and port, whether or not an HTTP server is present. See Section 9.1 for security considerations related to establishing authority. 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 (Section 3) containing the URI's identifying data (Section 5) to the server. If the server responds to that request with a non-interim Fielding & Reschke Standards Track [Page 17]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 6 of [RFC7231], 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 resources that require an end-to-end secured connection. Other protocols might also be used to provide access to "http" identified resources -- it is only the authoritative interface that is specific to TCP. The URI generic syntax for authority also includes a deprecated userinfo subcomponent ([RFC3986], 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. A sender MUST NOT generate the userinfo subcomponent (and its "@" delimiter) when an "http" URI reference is generated within a message as a request target or header field value. Before making use of an "http" URI reference received from an untrusted source, a recipient SHOULD parse for userinfo and treat its presence as an error; it is likely being used to obscure the authority for the sake of phishing attacks. 2.7.2 . https URI Scheme RFC5246]). All of the requirements listed above for the "http" scheme are also requirements for the "https" scheme, except that TCP port 443 is the default if the port subcomponent is empty or not given, and the user agent MUST ensure that its connection to the origin server is secured through the use of strong encryption, end-to-end, prior to sending the first HTTP request. https-URI = "https:" "//" authority path-abempty [ "?" query ] [ "#" fragment ] Note that the "https" URI scheme depends on both TLS and TCP for establishing authority. Resources made available via the "https" scheme have no shared identity with the "http" scheme even if their Fielding & Reschke Standards Track [Page 18]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 RFC6265], 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 [RFC2818]. 2.7.3 . http and https URI Normalization and Comparison Section 6 of [RFC3986], 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 omit the port subcomponent. When not being used in absolute form as the request target of an OPTIONS request, 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: the normal form is to not encode them (see Sections 2.1 and 2.2 of [RFC3986]). For example, the following three URIs are equivalent: http://example.com:80/~smith/home.html http://EXAMPLE.com/%7Esmith/home.html http://EXAMPLE.com:/%7esmith/home.html 3 . Message Format RFC5322]: zero or more header fields (collectively referred to as the "headers" or the "header section"), an empty line indicating the end of the header section, and an optional message body. HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body ] Fielding & Reschke Standards Track [Page 19]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 USASCII]. Parsing an HTTP message as a stream of Unicode characters, without regard for the specific encoding, creates security vulnerabilities due to the varying ways that string processing libraries handle invalid multibyte character sequences that contain the octet LF (%x0A). String-based parsers can only be safely used within protocol elements after the element has been extracted from the message, such as within a header field-value after message parsing has delineated the individual fields. An HTTP message can be parsed as a stream for incremental processing or forwarding downstream. However, recipients cannot rely on incremental delivery of partial messages, since some implementations will buffer or delay message forwarding for the sake of network efficiency, security checks, or payload transformations. A sender MUST NOT send whitespace between the start-line and the first header field. A recipient that receives whitespace between the start-line and the first header field MUST either reject the message as invalid or consume each whitespace-preceded line without further processing of it (i.e., ignore the entire line, along with any subsequent lines preceded by whitespace, until a properly formed header field is received or the header section is terminated). The presence of such whitespace in a request might be an attempt to trick a server into ignoring that field or processing the line after it as a new request, either of which might result in a security vulnerability if other implementations within the request chain interpret the same message differently. Likewise, the presence of such whitespace in a response might be ignored by some clients or cause others to cease parsing. 3.1 . Start Line Section 3.3). Fielding & Reschke Standards Track [Page 20]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 3.1.1 . Request Line Section 4 of [RFC7231], along with information regarding the HTTP method registry and considerations for defining new methods. The request-target identifies the target resource upon which to apply the request, as defined in Section 5.3. Recipients typically parse the request-line into its component parts by splitting on whitespace (see Section 3.5), since no whitespace is allowed in the three components. Unfortunately, some user agents fail to properly encode or exclude whitespace found in hypertext references, resulting in those disallowed characters being sent in a request-target. Recipients of an invalid request-line SHOULD respond with either a 400 (Bad Request) error or a 301 (Moved Permanently) redirect with the request-target properly encoded. A recipient SHOULD NOT attempt to autocorrect and then process the request without a redirect, since the invalid request-line might be deliberately crafted to bypass security filters along the request chain. HTTP does not place a predefined limit on the length of a request-line, as described in Section 2.5. A server that receives a method longer than any that it implements SHOULD respond with a 501 (Not Implemented) status code. A server that receives a Fielding & Reschke Standards Track [Page 21]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 6.5.12 of [RFC7231]). Various ad hoc limitations on request-line length are found in practice. It is RECOMMENDED that all HTTP senders and recipients support, at a minimum, request-line lengths of 8000 octets. 3.1.2 . Status Line Section 6 of [RFC7231] for information about the semantics of status codes, including the classes of status code (indicated by the first digit), the status codes defined by this specification, considerations for the definition of new status codes, and the IANA registry. status-code = 3DIGIT The reason-phrase element exists for the sole purpose of providing a textual description associated with the numeric status code, mostly out of deference to earlier Internet application protocols that were more frequently used with interactive text clients. A client SHOULD ignore the reason-phrase content. reason-phrase = *( HTAB / SP / VCHAR / obs-text ) 3.2 . Header Fields Fielding & Reschke Standards Track [Page 22]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 RFC6265]) often appears multiple times in a response message and does not use the list syntax, violating the above requirements on multiple header fields with the same name. Since it cannot be combined into a single field-value, recipients ought to handle "Set-Cookie" as a special case while processing header fields. (See Appendix A.2.3 of [Kri2001] for details.) 3.2.3 . Whitespace Fielding & Reschke Standards Track [Page 24]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 3.2.4 . Field Parsing Section 8.3.1). A sender MUST NOT generate a message that includes line folding (i.e., that has any field-value that contains a match to the obs-fold rule) unless the message is intended for packaging within the message/http media type. Fielding & Reschke Standards Track [Page 25]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 ISO-8859-1], supporting other charsets only through use of [RFC2047] encoding. In practice, most HTTP header field values use only a subset of the US-ASCII charset [USASCII]. Newly defined header fields SHOULD limit their field values to US-ASCII octets. A recipient SHOULD treat other octets in field content (obs-text) as opaque data. 3.2.5 . Field Limits Section 2.5. Various ad hoc limitations on individual header field length are found in practice, often depending on the specific field semantics. A server that receives a request header field, or set of fields, larger than it wishes to process MUST respond with an appropriate 4xx (Client Error) status code. Ignoring such header fields would increase the server's vulnerability to request smuggling attacks (Section 9.5). A client MAY discard or truncate received header fields that are larger than the client wishes to process if the field semantics are such that the dropped value(s) can be safely ignored without changing the message framing or response semantics. Fielding & Reschke Standards Track [Page 26]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 3.2.6 . Field Value Components Fielding & Reschke Standards Track [Page 27]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 3.3 . Message Body Section 3.3.1. message-body = *OCTET The rules for when a message body is allowed in a message differ for requests and responses. The presence of a message body in a request is signaled by a Content-Length or Transfer-Encoding header field. Request message framing is independent of method semantics, even if the method does not define any use for a message body. The presence of a message body in a response depends on both the request method to which it is responding and the response status code (Section 3.1.2). Responses to the HEAD request method (Section 4.3.2 of [RFC7231]) never include a message body because the associated response header fields (e.g., Transfer-Encoding, Content-Length, etc.), if present, indicate only what their values would have been if the request method had been GET (Section 4.3.1 of [RFC7231]). 2xx (Successful) responses to a CONNECT request method (Section 4.3.6 of [RFC7231]) switch to tunnel mode instead of having a message body. All 1xx (Informational), 204 (No Content), and 304 (Not Modified) responses do not include a message body. All other responses do include a message body, although the body might be of zero length. 3.3.1 . Transfer-Encoding Section 4. Transfer-Encoding = 1#transfer-coding Transfer-Encoding is analogous to the Content-Transfer-Encoding field of MIME, which was designed to enable safe transport of binary data over a 7-bit transport service ([RFC2045], Section 6). However, safe transport has a different focus for an 8bit-clean transfer protocol. In HTTP's case, Transfer-Encoding is primarily intended to accurately delimit a dynamically generated payload and to distinguish payload encodings that are only applied for transport efficiency or security from those that are characteristics of the selected resource. Fielding & Reschke Standards Track [Page 28]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 4.1) because it plays a crucial role in framing messages when the payload body size is not known in advance. A sender MUST NOT apply chunked more than once to a message body (i.e., chunking an already chunked message is not allowed). If any transfer coding other than chunked is applied to a request payload body, the sender MUST apply chunked as the final transfer coding to ensure that the message is properly framed. If any transfer coding other than chunked is applied to a response payload body, the sender MUST either apply chunked as the final transfer coding or terminate the message by closing the connection. For example, Transfer-Encoding: gzip, chunked indicates that the payload body has been compressed using the gzip coding and then chunked using the chunked coding while forming the message body. Unlike Content-Encoding (Section 3.1.2.1 of [RFC7231]), Transfer-Encoding is a property of the message, not of the representation, and any recipient along the request/response chain MAY decode the received transfer coding(s) or apply additional transfer coding(s) to the message body, assuming that corresponding changes are made to the Transfer-Encoding field-value. Additional information about the encoding parameters can be provided by other header fields not defined by this specification. Transfer-Encoding MAY be sent in a response to a HEAD request or in a 304 (Not Modified) response (Section 4.1 of [RFC7232]) to a GET request, neither of which includes a message body, to indicate that the origin server would have applied a transfer coding to the message body if the request had been an unconditional GET. This indication is not required, however, because any recipient on the response chain (including the origin server) can remove transfer codings when they are not needed. A server MUST NOT send a Transfer-Encoding header field in any response with a status code of 1xx (Informational) or 204 (No Content). A server MUST NOT send a Transfer-Encoding header field in any 2xx (Successful) response to a CONNECT request (Section 4.3.6 of [RFC7231]). Transfer-Encoding was added in HTTP/1.1. It is generally assumed that implementations advertising only HTTP/1.0 support will not understand how to process a transfer-encoded payload. A client MUST NOT send a request containing Transfer-Encoding unless it knows the Fielding & Reschke Standards Track [Page 29]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 3.3.2 . Content-Length Section 3 of [RFC7231]). Content-Length = 1*DIGIT An example is Content-Length: 3495 A sender MUST NOT send a Content-Length header field in any message that contains a Transfer-Encoding header field. A user agent SHOULD send a Content-Length in a request message when no Transfer-Encoding is sent and the request method defines a meaning for an enclosed payload body. For example, a Content-Length header field is normally sent in a POST request even when the value is 0 (indicating an empty payload body). A user agent SHOULD NOT send a Content-Length header field when the request message does not contain a payload body and the method semantics do not anticipate such a body. A server MAY send a Content-Length header field in a response to a HEAD request (Section 4.3.2 of [RFC7231]); a server MUST NOT send Content-Length in such a response unless its field-value equals the decimal number of octets that would have been sent in the payload body of a response if the same request had used the GET method. A server MAY send a Content-Length header field in a 304 (Not Modified) response to a conditional GET request (Section 4.1 of [RFC7232]); a server MUST NOT send Content-Length in such a response Fielding & Reschke Standards Track [Page 30]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 4.3.6 of [RFC7231]). Aside from the cases defined above, in the absence of Transfer-Encoding, an origin server SHOULD send a Content-Length header field when the payload body size is known prior to sending the complete header section. This will allow downstream recipients to measure transfer progress, know when a received message is complete, and potentially reuse the connection for additional requests. Any Content-Length field value greater than or equal to zero is valid. Since there is no predefined limit to the length of a payload, a recipient MUST anticipate potentially large decimal numerals and prevent parsing errors due to integer conversion overflows (Section 9.3). 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 or forwarding the message. Note: HTTP's use of Content-Length for message framing differs significantly from the same field's use in MIME, where it is an optional field used only within the "message/external-body" media-type. Fielding & Reschke Standards Track [Page 31]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 3.3.3 . Message Body Length Section 4.1) is the final encoding, the message body length is determined by reading and decoding the chunked data until the transfer coding indicates the data is complete. If a Transfer-Encoding header field is present in a response and the chunked transfer coding is not the final encoding, the message body length is determined by reading the connection until it is closed by the server. If a Transfer-Encoding header field is present in a request and the chunked transfer coding is not the final encoding, the message body length cannot be determined reliably; the server MUST respond with the 400 (Bad Request) status code and then close the connection. If a message is received with both a Transfer-Encoding and a Content-Length header field, the Transfer-Encoding overrides the Content-Length. Such a message might indicate an attempt to perform request smuggling (Section 9.5) or response splitting (Section 9.4) and ought to be handled as an error. A sender MUST remove the received Content-Length field prior to forwarding such a message downstream. 4. If a message is received without Transfer-Encoding and with either multiple Content-Length header fields having differing field-values or a single Content-Length header field having an invalid value, then the message framing is invalid and the recipient MUST treat it as an unrecoverable error. If this is a request message, the server MUST respond with a 400 (Bad Request) status code and then close the connection. If this is a response message received by a proxy, the proxy MUST close the connection to the server, discard the received response, and send a 502 (Bad Fielding & Reschke Standards Track [Page 32]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Fielding & Reschke Standards Track [Page 33]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 3.4 . Handling Incomplete Messages Section 3 of [RFC7234]. If a response terminates in the middle of the header section (before the empty line is received) and the status code might rely on header fields to convey the full meaning of the response, then the client cannot assume that meaning has been conveyed; the client might need to repeat the request in order to determine what action to take next. A message body that uses the chunked transfer coding is incomplete if the zero-sized chunk that terminates the encoding has not been received. A message that uses a valid Content-Length is incomplete if the size of the message body received (in octets) is less than the value given by Content-Length. A response that has neither chunked transfer coding nor Content-Length is terminated by closure of the connection and, thus, is considered complete regardless of the number of message body octets received, provided that the header section was received intact. 3.5 . Message Parsing Robustness Fielding & Reschke Standards Track [Page 34]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 4.1 . Chunked Transfer Coding 4.1.1 . Chunk Extensions Fielding & Reschke Standards Track [Page 36]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 4.1.2 . Chunked Trailer Part Section 5 of [RFC7231]), authentication (e.g., see [RFC7235] and [RFC6265]), response control data (e.g., see Section 7.1 of [RFC7231]), or determining how to process the payload (e.g., Content-Encoding, Content-Type, Content-Range, and Trailer). When a chunked message containing a non-empty trailer is received, the recipient MAY process the fields (aside from those forbidden above) as if they were appended to the message's header section. A recipient MUST ignore (or consider as an error) any fields that are forbidden to be sent in a trailer, since processing them as if they were present in the header section might bypass external security filters. Unless the request includes a TE header field indicating "trailers" is acceptable, as described in Section 4.3, a server SHOULD NOT generate trailer fields that it believes are necessary for the user agent to receive. Without a TE containing "trailers", the server ought to assume that the trailer fields might be silently discarded along the path to the user agent. This requirement allows intermediaries to forward a de-chunked message to an HTTP/1.0 recipient without buffering the entire response. Fielding & Reschke Standards Track [Page 37]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 4.1.3 . Decoding Chunked 4.2 . Compression Codings 4.2.1 . Compress Coding Welch] that is commonly produced by the UNIX file compression program "compress". A recipient SHOULD consider "x-compress" to be equivalent to "compress". 4.2.2 . Deflate Coding RFC1950] containing a "deflate" compressed data stream [RFC1951] that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and Huffman coding. Note: Some non-conformant implementations send the "deflate" compressed data without the zlib wrapper. Fielding & Reschke Standards Track [Page 38]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 4.2.3 . Gzip Coding RFC1952]. A recipient SHOULD consider "x-gzip" to be equivalent to "gzip". 4.3 . TE Section 4), and/or the keyword "trailers". A client MUST NOT send the chunked transfer coding name in TE; chunked is always acceptable for HTTP/1.1 recipients. TE = #t-codings t-codings = "trailers" / ( transfer-coding [ t-ranking ] ) t-ranking = OWS ";" OWS "q=" rank rank = ( "0" [ "." 0*3DIGIT ] ) / ( "1" [ "." 0*3("0") ] ) Three examples of TE use are below. TE: deflate TE: TE: trailers, deflate;q=0.5 The presence of the keyword "trailers" indicates that the client is willing to accept trailer fields in a chunked transfer coding, as defined in Section 4.1.2, on behalf of itself and any downstream clients. For requests from an intermediary, this implies that either: (a) all downstream clients are willing to accept trailer fields in the forwarded response; or, (b) the intermediary will attempt to buffer the response on behalf of downstream recipients. Note that HTTP/1.1 does not define any means to limit the size of a chunked response such that an intermediary can be assured of buffering the entire response. When multiple transfer codings are acceptable, the client MAY rank the codings by preference using a case-insensitive "q" parameter (similar to the qvalues used in content negotiation fields, Section Fielding & Reschke Standards Track [Page 39]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 RFC7231]). The rank value is a real number in the range 0 through 1, where 0.001 is the least preferred and 1 is the most preferred; a value of 0 means "not acceptable". If the TE field-value is empty or if no TE field is present, the only acceptable transfer coding is chunked. A message with no transfer coding is always acceptable. Since the TE header field only applies to the immediate connection, a sender of TE MUST also send a "TE" connection option within the Connection header field (Section 6.1) in order to prevent the TE field from being forwarded by intermediaries that do not support its semantics. 4.4 . Trailer 5 . Message Routing 5.1 . Identifying a Target Resource RFC7231], and a target resource upon which to apply those semantics. A URI reference (Section 2.7) is typically used as an Fielding & Reschke Standards Track [Page 40]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 [RFC3986], Section 3.5). 5.2 . Connecting Inbound RFC7234] and the request can be satisfied by it, then the request is usually directed there first. If the request is not satisfied by a cache, then a typical client will check its configuration to determine whether a proxy is to be used to satisfy the request. Proxy configuration is implementation- dependent, but is often based on URI prefix matching, selective authority matching, or both, and the proxy itself is usually identified by an "http" or "https" URI. If a proxy is applicable, the client connects inbound by establishing (or reusing) a connection to that proxy. If no proxy is applicable, a typical client will invoke a handler routine, usually specific to the target URI's scheme, to connect directly to an authority for the target resource. How that is accomplished is dependent on the target URI scheme and defined by its associated specification, similar to how this specification defines origin server access for resolution of the "http" (Section 2.7.1) and "https" (Section 2.7.2) schemes. HTTP requirements regarding connection management are defined in Section 6. 5.3 . Request Target Section 3) with a request-target derived from the target URI. There are four distinct formats for the request-target, depending on both the method being requested and whether the request is to a proxy. request-target = origin-form / absolute-form / authority-form / asterisk-form Fielding & Reschke Standards Track [Page 41]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 5.3.1 . origin-form Section 5.4. For example, a client wishing to retrieve a representation of the resource identified as http://www.example.org/where?q=now directly from the origin server would open (or reuse) a TCP connection to port 80 of the host "www.example.org" and send the lines: GET /where?q=now HTTP/1.1 Host: www.example.org followed by the remainder of the request message. 5.3.2 . absolute-form Section 5.7. An example absolute-form of request-line would be: GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1 Fielding & Reschke Standards Track [Page 42]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 5.3.3 . authority-form Section 4.3.6 of [RFC7231]). authority-form = authority When making a CONNECT request to establish a tunnel through one or more proxies, a client MUST send only the target URI's authority component (excluding any userinfo and its "@" delimiter) as the request-target. For example, CONNECT www.example.com:80 HTTP/1.1 5.3.4 . asterisk-form Section 4.3.7 of [RFC7231]). asterisk-form = "*" When a client wishes to request OPTIONS for the server as a whole, as opposed to a specific named resource of that server, the client MUST send only "*" (%x2A) as the request-target. For example, OPTIONS * HTTP/1.1 If a proxy receives an OPTIONS request with an absolute-form of request-target in which the URI has an empty path and no query component, then the last proxy on the request chain MUST send a request-target of "*" when it forwards the request to the indicated origin server. For example, the request OPTIONS http://www.example.org:8001 HTTP/1.1 would be forwarded by the final proxy as OPTIONS * HTTP/1.1 Host: www.example.org:8001 after connecting to port 8001 of host "www.example.org". Fielding & Reschke Standards Track [Page 43]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 5.4 . Host Section 2.7.1 A client MUST send a Host header field in all HTTP/1.1 request messages. If the target URI includes an authority component, then a client MUST send a field-value for Host that is identical to that authority component, excluding any userinfo subcomponent and its "@" delimiter (Section 2.7.1). If the authority component is missing or undefined for the target URI, then a client MUST send a Host header field with an empty field-value. Since the Host field-value is critical information for handling a request, a user agent SHOULD generate Host as the first header field following the request-line. For example, a GET request to the origin server for <http://www.example.org/pub/WWW/> would begin with: GET /pub/WWW/ HTTP/1.1 Host: www.example.org A client MUST send a Host header field in an HTTP/1.1 request even if the request-target is in the absolute-form, since this allows the Host information to be forwarded through ancient HTTP/1.0 proxies that might not have implemented Host. When a proxy receives a request with an absolute-form of request-target, the proxy MUST ignore the received Host header field (if any) and instead replace it with the host information of the request-target. A proxy that forwards such a request MUST generate a new Host field-value based on the received request-target rather than forward the received Host field-value. 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 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. Fielding & Reschke Standards Track [Page 44]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 5.5 . Effective Request URI Fielding & Reschke Standards Track [Page 45]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 http://www.example.org:8080/pub/WWW/TheProject.html Example 2: the following message received over a TLS-secured TCP connection OPTIONS * HTTP/1.1 Host: www.example.org has an effective request URI of https://www.example.org Recipients of an HTTP/1.0 request that lacks a Host header field might need to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to guess the effective request URI's authority component. Once the effective request URI has been constructed, an origin server needs to decide whether or not to provide service for that URI via the connection in which the request was received. For example, the request might have been misdirected, deliberately or accidentally, such that the information within a received request-target or Host header field differs from the host or port upon which the connection has been made. If the connection is from a trusted gateway, that inconsistency might be expected; otherwise, it might indicate an attempt to bypass security filters, trick the server into delivering non-public content, or poison a cache. See Section 9 for security considerations regarding message routing. 5.6 . Associating a Response to a Request Section 6.2 of [RFC7231]) precede a final response to the same request. Fielding & Reschke Standards Track [Page 46]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 5.7 . Message Forwarding Section 2.3, intermediaries can serve a variety of roles in the processing of HTTP requests and responses. Some intermediaries are used to improve performance or availability. Others are used for access control or to filter content. Since an HTTP stream has characteristics similar to a pipe-and-filter architecture, there are no inherent limits to the extent an intermediary can enhance (or interfere) with either direction of the stream. An intermediary not acting as a tunnel MUST implement the Connection header field, as specified in Section 6.1, and exclude fields from being forwarded that are only intended for the incoming connection. An intermediary MUST NOT forward a message to itself unless it is protected from an infinite request loop. In general, an intermediary ought to recognize its own server names, including any aliases, local variations, or literal IP addresses, and respond to such requests directly. 5.7.1 . Via Section 3.6.7 of [RFC5322]). Via can be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities of senders along the request/response chain. Via = 1#( received-protocol RWS received-by [ RWS comment ] ) received-protocol = [ protocol-name "/" ] protocol-version ; see Section 6.7 received-by = ( uri-host [ ":" port ] ) / pseudonym pseudonym = token Multiple Via field values represent each proxy or gateway that has forwarded the message. Each intermediary appends its own information about how the message was received, such that the end result is ordered according to the sequence of forwarding recipients. Fielding & Reschke Standards Track [Page 47]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 2.6. For brevity, the protocol-name is omitted when the received protocol is HTTP. The received-by portion of the field value 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, a sender MAY replace it with a pseudonym. If a port is not provided, a recipient MAY interpret that as meaning it was received on the default TCP port, if any, for the received-protocol. A sender MAY generate comments 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 a recipient MAY remove them prior to forwarding the message. For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses HTTP/1.1 to forward the request to a public proxy at p.example.net, which completes the request by forwarding it to the origin server at www.example.com. The request received by www.example.com would then have the following Via header field: Via: 1.0 fred, 1.1 p.example.net An intermediary 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, such an intermediary SHOULD replace each received-by host of any host behind the firewall by an appropriate pseudonym for that host. Fielding & Reschke Standards Track [Page 48]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 5.7.2 . Transformations Fielding & Reschke Standards Track [Page 49]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 6.6). A client that does not support persistent connections MUST send the "close" connection option in every request message. A server that does not support persistent connections MUST send the "close" connection option in every response message that does not have a 1xx (Informational) status code. 6.2 . Establishment 6.3 . Persistence Fielding & Reschke Standards Track [Page 52]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 3.3. 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. A proxy server MUST NOT maintain a persistent connection with an HTTP/1.0 client (see Section 19.7.1 of [RFC2068] for information and discussion of the problems with the Keep-Alive header field implemented by many HTTP/1.0 clients). See Appendix A.1.2 for more information on backwards compatibility with HTTP/1.0 clients. 6.3.1 . Retrying Requests Fielding & Reschke Standards Track [Page 53]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 4.2.2 of [RFC7231]). A proxy MUST NOT automatically retry non-idempotent requests. A user agent MUST NOT automatically retry a request with a non- idempotent method unless it has some means to know that the request semantics are actually idempotent, regardless of the method, or some means to detect that the original request was never applied. For example, a user agent that knows (through design or configuration) that a POST request to a given resource is safe can repeat that request automatically. Likewise, a user agent designed specifically to operate on a version control repository might be able to recover from partial failure conditions by checking the target resource revision(s) after a failed connection, reverting or fixing any changes that were partially applied, and then automatically retrying the requests that failed. A client SHOULD NOT automatically retry a failed automatic retry. 6.3.2 . Pipelining Section 4.2.1 of [RFC7231]), but it MUST send the corresponding responses in the same order that the requests were received. A client that pipelines requests SHOULD retry unanswered requests if the connection closes before it receives all of the corresponding responses. When retrying pipelined requests after a failed connection (a connection not explicitly closed by the server in its last complete response), a client MUST NOT pipeline immediately after connection establishment, since the first remaining request in the prior pipeline might have caused an error response that can be lost again if multiple requests are sent on a prematurely closed connection (see the TCP reset problem described in Section 6.6). Idempotent methods (Section 4.2.2 of [RFC7231]) are significant to pipelining because they can be automatically retried after a connection failure. A user agent SHOULD NOT pipeline requests after a non-idempotent method, until the final response status code for that method has been received, unless the user agent has a means to detect and recover from partial failure conditions involving the pipelined sequence. Fielding & Reschke Standards Track [Page 54]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 6.4 . Concurrency 6.5 . Failures and Timeouts Fielding & Reschke Standards Track [Page 55]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 6.6 . Tear-down Section 6.1) provides a "close" connection option that a sender SHOULD send when it wishes to close the connection after the current request/response pair. A client that sends a "close" connection option MUST NOT send further requests on that connection (after the one containing "close") and MUST close the connection after reading the final response message corresponding to this request. A server that receives a "close" connection option MUST initiate a close of the connection (see below) after it sends the final response to the request that contained "close". The server SHOULD send a "close" connection option in its final response on that connection. The server MUST NOT process any further requests received on that connection. A server that sends a "close" connection option MUST initiate a close of the connection (see below) after it sends the response containing "close". The server MUST NOT process any further requests received on that connection. A client that receives a "close" connection option MUST cease sending requests on that connection and close the connection after reading the response message containing the "close"; if additional pipelined requests had been sent on the connection, the client SHOULD NOT assume that they will be processed by the server. Fielding & Reschke Standards Track [Page 56]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 6.7 . Upgrade Fielding & Reschke Standards Track [Page 57]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Fielding & Reschke Standards Track [Page 58]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 6.1) that contains an "upgrade" connection option, in order to prevent Upgrade from being accidentally forwarded by intermediaries that might not implement the listed protocols. A server MUST ignore an Upgrade header field that is received in an HTTP/1.0 request. A client cannot begin using an upgraded protocol on the connection until it has completely sent the request message (i.e., the client can't change the protocol it is sending in the middle of a message). If a server receives both an Upgrade and an Expect header field with the "100-continue" expectation (Section 5.1.1 of [RFC7231]), the server MUST send a 100 (Continue) response before sending a 101 (Switching Protocols) response. The Upgrade header field only applies to switching protocols on top of the existing connection; it cannot be used to switch the underlying connection (transport) protocol, nor to switch the existing communication to a different connection. For those purposes, it is more appropriate to use a 3xx (Redirection) response (Section 6.4 of [RFC7231]). This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined by the HTTP version rules of Section 2.6 and future updates to this specification. Additional tokens ought to be registered with IANA using the registration procedure defined in Section 8.6. 7 . ABNF List Extension: #rule RFC5234] is used to improve readability in the definitions of some header field values. 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). Fielding & Reschke Standards Track [Page 59]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 3.2.6 Then the following are valid values for example-list (not including the double quotes, which are present for delimitation only): "foo,bar" "foo ,bar," "foo , ,bar,charlie " In contrast, the following values would be invalid, since at least one non-empty element is required by the example-list production: "" "," ", ," Appendix B shows the collected ABNF for recipients after the list constructs have been expanded. Fielding & Reschke Standards Track [Page 60]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 8.2 . URI Scheme Registration BCP115] at <http://www.iana.org/assignments/uri-schemes/>. This document defines the following URI schemes, so the "Permanent URI Schemes" registry has been updated accordingly. +------------+------------------------------------+---------------+ | URI Scheme | Description | Reference | +------------+------------------------------------+---------------+ | http | Hypertext Transfer Protocol | Section 2.7.1 | | https | Hypertext Transfer Protocol Secure | Section 2.7.2 | +------------+------------------------------------+---------------+ 8.3 . Internet Media Type Registration BCP13] at <http://www.iana.org/assignments/media-types>. This document serves as the specification for the Internet media types "message/http" and "application/http". The following has been registered with IANA. 8.3.1 . Internet Media Type message/http Fielding & Reschke Standards Track [Page 62]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 9 Interoperability considerations: N/A Published specification: This specification (see Section 8.3.1). Applications that use this media type: N/A Fragment identifier considerations: N/A Additional information: Magic number(s): N/A Deprecated alias names for this type: N/A File extension(s): N/A Macintosh file type code(s): N/A Person and email address to contact for further information: See Authors' Addresses section. Intended usage: COMMON Restrictions on usage: N/A Author: See Authors' Addresses section. Change controller: IESG 8.3.2 . Internet Media Type application/http Fielding & Reschke Standards Track [Page 63]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 9 Interoperability considerations: N/A Published specification: This specification (see Section 8.3.2). Applications that use this media type: N/A Fragment identifier considerations: N/A Additional information: Deprecated alias names for this type: N/A Magic number(s): N/A File extension(s): N/A Macintosh file type code(s): N/A Person and email address to contact for further information: See Authors' Addresses section. Intended usage: COMMON Restrictions on usage: N/A Author: See Authors' Addresses section. Change controller: IESG 8.4 . Transfer Coding Registry http://www.iana.org/assignments/http-parameters>. Fielding & Reschke Standards Track [Page 64]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Section 2.7.1). User agents can reduce the impact of phishing attacks by enabling users to easily inspect a target URI prior to making an action, by prominently distinguishing (or rejecting) userinfo when present, and by not sending stored credentials and cookies when the referring document is from an unknown or untrusted source. When a registered name is used in the authority component, the "http" URI scheme (Section 2.7.1) relies on the user's local name resolution service to determine where it can find authoritative responses. This means that any attack on a user's network host table, cached names, or name resolution libraries becomes an avenue for attack on establishing authority. Likewise, the user's choice of server for Domain Name Service (DNS), and the hierarchy of servers from which it obtains resolution results, could impact the authenticity of address mappings; DNS Security Extensions (DNSSEC, [RFC4033]) are one way to improve authenticity. Furthermore, after an IP address is obtained, establishing authority for an "http" URI is vulnerable to attacks on Internet Protocol routing. The "https" scheme (Section 2.7.2) is intended to prevent (or at least reveal) many of these potential attacks on establishing authority, provided that the negotiated TLS connection is secured and the client properly verifies that the communicating server's identity matches the target URI's authority component (see [RFC2818]). Correctly implementing such verification can be difficult (see [Georgiev]). 9.2 . Risks of Intermediaries Section 8 of [RFC7234]. Fielding & Reschke Standards Track [Page 68]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 9.3 . Attacks via Protocol Element Length Section 3.1.1) and header fields (Section 3.2). 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. A server can reject a message that has a request-target that is too long (Section 6.5.12 of [RFC7231]) or a request payload that is too large (Section 6.5.11 of [RFC7231]). Additional status codes related to capacity limits have been defined by extensions to HTTP [RFC6585]. Recipients ought to carefully limit the extent to which they process other protocol elements, including (but not limited to) request methods, response status phrases, header field-names, numeric values, and body chunks. Failure to limit such processing can result in buffer overflows, arithmetic overflows, or increased vulnerability to denial-of-service attacks. 9.4 . Response Splitting Klein]. This technique can be particularly damaging when the requests pass through a shared cache. Response splitting exploits a vulnerability in servers (usually within an application server) where an attacker can send encoded data within some parameter of the request that is later decoded and echoed within any of the response header fields of the response. If the decoded data is crafted to look like the response has ended and a Fielding & Reschke Standards Track [Page 69]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 9.5 . Request Smuggling Linhart]) is a technique that exploits differences in protocol parsing among various recipients to hide additional requests (which might otherwise be blocked or disabled by policy) within an apparently harmless request. Like response splitting, request smuggling can lead to a variety of attacks on HTTP usage. This specification has introduced new requirements on request parsing, particularly with regard to message framing in Section 3.3.3, to reduce the effectiveness of request smuggling. 9.6 . Message Integrity Fielding & Reschke Standards Track [Page 70]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 10 . Acknowledgments RFC 1945, RFC 2068, RFC 2145, and RFC 2616, including substantial contributions made by the previous authors, editors, and Working Group Chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding, Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter, and Paul J. Leach. Mark Nottingham oversaw this effort as Working Group Chair. Since 1999, the following contributors have helped improve the HTTP specification by reporting bugs, asking smart questions, drafting or reviewing text, and evaluating open issues: Adam Barth, Adam Roach, Addison Phillips, Adrian Chadd, Adrian Cole, Adrien W. de Croy, Alan Ford, Alan Ruttenberg, Albert Lunde, Alek Storm, Alex Rousskov, Alexandre Morgaut, Alexey Melnikov, Alisha Smith, Amichai Rothman, Amit Klein, Amos Jeffries, Andreas Maier, Andreas Petersson, Andrei Popov, Anil Sharma, Anne van Kesteren, Anthony Bryan, Asbjorn Ulsberg, Ashok Kumar, Balachander Krishnamurthy, Barry Leiba, Ben Laurie, Benjamin Carlyle, Benjamin Niven-Jenkins, Benoit Claise, Bil Corry, Bill Burke, Bjoern Hoehrmann, Bob Scheifler, Boris Zbarsky, Brett Slatkin, Brian Kell, Brian McBarron, Brian Pane, Brian Raymor, Brian Smith, Bruce Perens, Bryce Nesbitt, Cameron Heavon-Jones, Carl Kugler, Carsten Bormann, Charles Fry, Chris Burdess, Chris Newman, Christian Huitema, Cyrus Daboo, Dale Robert Anderson, Dan Wing, Dan Winship, Daniel Stenberg, Darrel Miller, Dave Cridland, Dave Crocker, Dave Kristol, Dave Thaler, David Booth, David Singer, David W. Morris, Diwakar Shetty, Dmitry Kurochkin, Drummond Reed, Duane Wessels, Edward Lee, Eitan Adler, Eliot Lear, Emile Stephan, Eran Hammer-Lahav, Eric D. Williams, Eric J. Bowman, Eric Lawrence, Eric Rescorla, Erik Aronesty, EungJun Yi, Evan Prodromou, Felix Geisendoerfer, Florian Weimer, Frank Ellermann, Fred Akalin, Fred Bohle, Frederic Kayser, Gabor Molnar, Gabriel Montenegro, Geoffrey Sneddon, Gervase Markham, Gili Tzabari, Grahame Grieve, Greg Slepak, Greg Wilkins, Grzegorz Calkowski, Harald Tveit Alvestrand, Harry Halpin, Helge Hess, Henrik Nordstrom, Henry S. Thompson, Henry Story, Herbert van de Sompel, Herve Ruellan, Howard Melman, Hugo Haas, Ian Fette, Ian Hickson, Ido Safruti, Ilari Liusvaara, Ilya Grigorik, Ingo Struck, J. Ross Nicoll, James Cloos, James H. Manger, James Lacey, James M. Snell, Jamie Fielding & Reschke Standards Track [Page 72]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 Appendix A . HTTP Version History RFC1945], added a range of request methods and MIME-like messaging, allowing for metadata to be transferred and modifiers placed on the request/response semantics. However, HTTP/1.0 did not sufficiently take into consideration the effects of hierarchical proxies, caching, the need for persistent connections, or name-based virtual hosts. The proliferation of incompletely implemented applications calling themselves "HTTP/1.0" further necessitated a protocol version change in order for two communicating applications to determine each other's true capabilities. HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent requirements that enable reliable implementations, adding only those features that can either be safely ignored by an HTTP/1.0 recipient or only be sent when communicating with a party advertising conformance with HTTP/1.1. HTTP/1.1 has been designed to make supporting previous versions easy. A general-purpose HTTP/1.1 server ought to be able to understand any valid request in the format of HTTP/1.0, responding appropriately with an HTTP/1.1 message that only uses features understood (or safely ignored) by HTTP/1.0 clients. Likewise, an HTTP/1.1 client can be expected to understand any valid HTTP/1.0 response. Since HTTP/0.9 did not support header fields in a request, there is no mechanism for it to support name-based virtual hosts (selection of resource by inspection of the Host header field). Any server that implements name-based virtual hosts ought to disable support for HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x requests caused by a client failing to properly encode the request-target. A.1 . Changes from HTTP/1.0 A.1.1 . Multihomed Web Servers Section 5.4), report an error if it is missing from an HTTP/1.1 request, and accept absolute URIs (Section 5.3) are among the most important changes defined by HTTP/1.1. Fielding & Reschke Standards Track [Page 78]

RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 A.1.2 . Keep-Alive Connections Section 19.7.1 of [RFC2068]. Some clients and servers might wish to be compatible with these previous approaches to persistent connections, by explicitly negotiating for them with a "Connection: keep-alive" request header field. However, some experimental implementations of HTTP/1.0 persistent connections are faulty; for example, if an HTTP/1.0 proxy server doesn't understand Connection, it will erroneously forward that header field to the next inbound server, which would result in a hung connection. One attempted solution was the introduction of a Proxy-Connection header field, targeted specifically at proxies. In practice, this was also unworkable, because proxies are often deployed in multiple layers, bringing about the same problem discussed above. As a result, clients are encouraged not to send the Proxy-Connection header field in any requests. Clients are also encouraged to consider the use of Connection: keep-alive in requests carefully; while they can enable persistent connections with HTTP/1.0 servers, clients using them will need to monitor the connection for "hung" requests (which indicate that the client ought stop sending the header field), and this mechanism ought not be used by clients at all when a proxy is being used. A.1.3 . Introduction of Transfer-Encoding Section 3.3.1). Transfer codings need to be decoded prior to forwarding an HTTP message over a MIME-compliant protocol. Fielding & Reschke Standards Track [Page 79]

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RFC 7230 HTTP/1.1 Message Syntax and Routing June 2014 http://roy.gbiv.com/ Julian F. Reschke (editor) greenbytes GmbH Hafenweg 16 Muenster, NW 48155 Germany EMail: julian.reschke@greenbytes.de URI: http://greenbytes.de/tech/webdav/ Fielding & Reschke Standards Track [Page 89]