HTTP参考手册

RFC 7230: Message Syntax and Routing

摘要

超文本传输协议（HTTP）是一种用于分布式协作超文本信息系统的无状态应用级协议。本文档提供了HTTP体系结构及其相关术语的概述，定义了“http”和“https”统一资源标识符（URI）方案，定义了HTTP / 1.1消息语法和分析要求，并描述了实现的相关安全性问题。本备忘录的状态这是一个Internet标准跟踪文档。

1.介绍

The Hypertext Transfer Protocol (HTTP) is a stateless application-    level request/response protocol that uses extensible semantics and    self-descriptive message payloads for flexible interaction with    network-based hypertext information systems.  This document is the    first in a series of documents that collectively form the HTTP/1.1    specification:     1.  "Message Syntax and Routing" (this document)     2.  "Semantics and Content" [[RFC7231](https://tools.ietf.org/html/rfc7231)]     3.  "Conditional Requests" [[RFC7232](https://tools.ietf.org/html/rfc7232)]     4.  "Range Requests" [[RFC7233](https://tools.ietf.org/html/rfc7233)]     5.  "Caching" [[RFC7234](https://tools.ietf.org/html/rfc7234)]     6.  "Authentication" [[RFC7235](https://tools.ietf.org/html/rfc7235)]     This HTTP/1.1 specification obsoletes [RFC 2616](https://tools.ietf.org/html/rfc2616) and [RFC 2145](https://tools.ietf.org/html/rfc2145) (on HTTP    versioning).  This specification also updates the use of CONNECT to    establish a tunnel, previously defined in [RFC 2817](https://tools.ietf.org/html/rfc2817), and defines the    "https" URI scheme that was described informally in [RFC 2818](https://tools.ietf.org/html/rfc2818).     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      ought to be reflected in corresponding changes to the observable    interface provided by servers.  However, since multiple clients might    act in parallel and perhaps at cross-purposes, we cannot require that    such changes be observable beyond the scope of a single response.     This document describes the architectural elements that are used or    referred to in HTTP, defines the "http" and "https" URI schemes,    describes overall network operation and connection management, and    defines HTTP message framing and forwarding requirements.  Our goal    is to define all of the mechanisms necessary for HTTP message    handling that are independent of message semantics, thereby defining    the complete set of requirements for message parsers and message-    forwarding intermediaries.

1.1 要求符号

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](https://tools.ietf.org/html/rfc2119)].     Conformance criteria and considerations regarding error handling are    defined in [Section 2.5](about:blank#section-2.5).

1.2 语法表示法

This specification uses the Augmented Backus-Naur Form (ABNF)    notation of [[RFC5234](https://tools.ietf.org/html/rfc5234)] with a list extension, defined in [Section 7](about:blank#section-7),    that allows for compact definition of comma-separated lists using a    '#' operator (similar to how the '\*' operator indicates repetition).    [Appendix B](about:blank#appendix-B) shows the collected grammar with all list operators    expanded to standard ABNF notation.     The following core rules are included by reference, as defined in    [[RFC5234], Appendix B.1](https://tools.ietf.org/html/rfc5234#appendix-B.1): ALPHA (letters), CR (carriage return), CRLF    (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),    HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line    feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any    visible [[USASCII](about:blank#ref-USASCII)] character).     As a convention, ABNF rule names prefixed with "obs-" denote    "obsolete" grammar rules that appear for historical reasons.

2.架构

HTTP was created for the World Wide Web (WWW) architecture and has    evolved over time to support the scalability needs of a worldwide    hypertext system.  Much of that architecture is reflected in the    terminology and syntax productions used to define HTTP.

2.1 客户端/服务器消息传递

HTTP is a stateless request/response protocol that operates by    exchanging messages ([Section 3](about:blank#section-3)) across a reliable transport- or    session-layer "connection" ([Section 6](about:blank#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](https://tools.ietf.org/html/rfc3986)] to indicate the target resource ([Section 5.1](about:blank#section-5.1)) and    relationships between resources.  Messages are passed in a format    similar to that used by Internet mail [[RFC5322](https://tools.ietf.org/html/rfc5322)] and the Multipurpose    Internet Mail Extensions (MIME) [[RFC2045](https://tools.ietf.org/html/rfc2045)] (see [Appendix A of    [RFC7231]](https://tools.ietf.org/html/rfc7231#appendix-A) 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](about:blank#section-3.1.1)), followed by header fields    containing request modifiers, client information, and representation    metadata ([Section 3.2](about:blank#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](about:blank#section-3.3)).      A server responds to a client's request by sending one or more HTTP    response messages, each beginning with a status line that includes    the protocol version, a success or error code, and textual reason    phrase ([Section 3.1.2](about:blank#section-3.1.2)), possibly followed by header fields containing    server information, resource metadata, and representation metadata    ([Section 3.2](about:blank#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](about:blank#section-3.3)).     A connection might be used for multiple request/response exchanges,    as defined in [Section 6.3](about:blank#section-6.3).     The following example illustrates a typical message exchange for a    GET request ([Section 4.3.1 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.3.1)) 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 实施多样性

When considering the design of HTTP, it is easy to fall into a trap    of thinking that all user agents are general-purpose browsers and all    origin servers are large public websites.  That is not the case in    practice.  Common HTTP user agents include household appliances,    stereos, scales, firmware update scripts, command-line programs,    mobile apps, and communication devices in a multitude of shapes and    sizes.  Likewise, common HTTP origin servers include home automation      units, configurable networking components, office machines,    autonomous robots, news feeds, traffic cameras, ad selectors, and    video-delivery platforms.     The term "user agent" does not imply that there is a human user    directly interacting with the software agent at the time of a    request.  In many cases, a user agent is installed or configured to    run in the background and save its results for later inspection (or    save only a subset of those results that might be interesting or    erroneous).  Spiders, for example, are typically given a start URI    and configured to follow certain behavior while crawling the Web as a    hypertext graph.     The implementation diversity of HTTP means that not all user agents    can make interactive suggestions to their user or provide adequate    warning for security or privacy concerns.  In the few cases where    this specification requires reporting of errors to the user, it is    acceptable for such reporting to only be observable in an error    console or log file.  Likewise, requirements that an automated action    be confirmed by the user before proceeding might be met via advance    configuration choices, run-time options, or simple avoidance of the    unsafe action; confirmation does not imply any specific user    interface or interruption of normal processing if the user has    already made that choice.

2.3 中介

HTTP enables the use of intermediaries to satisfy requests through a    chain of connections.  There are three common forms of HTTP    intermediary: proxy, gateway, and tunnel.  In some cases, a single    intermediary might act as an origin server, proxy, gateway, or    tunnel, switching behavior based on the nature of each request.              >             >             >             >        UA =========== A =========== B =========== C =========== O                   <             <             <             <     The figure above shows three intermediaries (A, B, and C) between the    user agent and origin server.  A request or response message that    travels the whole chain will pass through four separate connections.    Some HTTP communication options might apply only to the connection    with the nearest, non-tunnel neighbor, only to the endpoints of the    chain, or to all connections along the chain.  Although the diagram    is linear, each participant might be engaged in multiple,    simultaneous communications.  For example, B might be receiving    requests from many clients other than A, and/or forwarding requests    to servers other than C, at the same time that it is handling A's      request.  Likewise, later requests might be sent through a different    path of connections, often based on dynamic configuration for load    balancing.     The terms "upstream" and "downstream" are used to describe    directional requirements in relation to the message flow: all    messages flow from upstream to downstream.  The terms "inbound" and    "outbound" are used to describe directional requirements in relation    to the request route: "inbound" means toward the origin server and    "outbound" means toward the user agent.     A "proxy" is a message-forwarding agent that is selected by the    client, usually via local configuration rules, to receive requests    for some type(s) of absolute URI and attempt to satisfy those    requests via translation through the HTTP interface.  Some    translations are minimal, such as for proxy requests for "http" URIs,    whereas other requests might require translation to and from entirely    different application-level protocols.  Proxies are often used to    group an organization's HTTP requests through a common intermediary    for the sake of security, annotation services, or shared caching.    Some proxies are designed to apply transformations to selected    messages or payloads while they are being forwarded, as described in    [Section 5.7.2](about:blank#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](https://tools.ietf.org/html/rfc5246)]) is used to establish    confidential communication through a shared firewall proxy.      The above categories for intermediary only consider those acting as    participants in the HTTP communication.  There are also    intermediaries that can act on lower layers of the network protocol    stack, filtering or redirecting HTTP traffic without the knowledge or    permission of message senders.  Network intermediaries are    indistinguishable (at a protocol level) from a man-in-the-middle    attack, often introducing security flaws or interoperability problems    due to mistakenly violating HTTP semantics.     For example, an "interception proxy" [[RFC3040](https://tools.ietf.org/html/rfc3040)] (also commonly known    as a "transparent proxy" [[RFC1919](https://tools.ietf.org/html/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](https://tools.ietf.org/html/rfc4559)]) have been known to violate this requirement, resulting in    security and interoperability problems.

2.4 高速缓存

A "cache" is a local store of previous response messages and the    subsystem that controls its message storage, retrieval, and deletion.    A cache stores cacheable responses in order to reduce the response    time and network bandwidth consumption on future, equivalent    requests.  Any client or server MAY employ a cache, though a cache    cannot be used by a server while it is acting as a tunnel.     The effect of a cache is that the request/response chain is shortened    if one of the participants along the chain has a cached response    applicable to that request.  The following illustrates the resulting    chain if B has a cached copy of an earlier response from O (via C)    for a request that has not been cached by UA or A.                 >             >           UA =========== A =========== B - - - - - - C - - - - - - O                      <             <      A response is "cacheable" if a cache is allowed to store a copy of    the response message for use in answering subsequent requests.  Even    when a response is cacheable, there might be additional constraints    placed by the client or by the origin server on when that cached    response can be used for a particular request.  HTTP requirements for    cache behavior and cacheable responses are defined in [Section 2 of    [RFC7234]](https://tools.ietf.org/html/rfc7234#section-2).     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 一致性和错误处理

This specification targets conformance criteria according to the role    of a participant in HTTP communication.  Hence, HTTP requirements are    placed on senders, recipients, clients, servers, user agents,    intermediaries, origin servers, proxies, gateways, or caches,    depending on what behavior is being constrained by the requirement.    Additional (social) requirements are placed on implementations,    resource owners, and protocol element registrations when they apply    beyond the scope of a single communication.     The verb "generate" is used instead of "send" where a requirement    differentiates between creating a protocol element and merely    forwarding a received element downstream.     An implementation is considered conformant if it complies with all of    the requirements associated with the roles it partakes in HTTP.     Conformance includes both the syntax and semantics of protocol    elements.  A sender MUST NOT generate protocol elements that convey a    meaning that is known by that sender to be false.  A sender MUST NOT    generate protocol elements that do not match the grammar defined by    the corresponding ABNF rules.  Within a given message, a sender MUST    NOT generate protocol elements or syntax alternatives that are only    allowed to be generated by participants in other roles (i.e., a role    that the sender does not have for that message).     When a received protocol element is parsed, the recipient MUST be    able to parse any value of reasonable length that is applicable to    the recipient's role and that matches the grammar defined by the    corresponding ABNF rules.  Note, however, that some received protocol    elements might not be parsed.  For example, an intermediary      forwarding a message might parse a header-field into generic    field-name and field-value components, but then forward the header    field without further parsing inside the field-value.     HTTP does not have specific length limitations for many of its    protocol elements because the lengths that might be appropriate will    vary widely, depending on the deployment context and purpose of the    implementation.  Hence, interoperability between senders and    recipients depends on shared expectations regarding what is a    reasonable length for each protocol element.  Furthermore, what is    commonly understood to be a reasonable length for some protocol    elements has changed over the course of the past two decades of HTTP    use and is expected to continue changing in the future.     At a minimum, a recipient MUST be able to parse and process protocol    element lengths that are at least as long as the values that it    generates for those same protocol elements in other messages.  For    example, an origin server that publishes very long URI references to    its own resources needs to be able to parse and process those same    references when received as a request target.     A recipient MUST interpret a received protocol element according to    the semantics defined for it by this specification, including    extensions to this specification, unless the recipient has determined    (through experience or configuration) that the sender incorrectly    implements what is implied by those semantics.  For example, an    origin server might disregard the contents of a received    Accept-Encoding header field if inspection of the User-Agent header    field indicates a specific implementation version that is known to    fail on receipt of certain content codings.     Unless noted otherwise, a recipient MAY attempt to recover a usable    protocol element from an invalid construct.  HTTP does not define    specific error handling mechanisms except when they have a direct    impact on security, since different applications of the protocol    require different error handling strategies.  For example, a Web    browser might wish to transparently recover from a response where the    Location header field doesn't parse according to the ABNF, whereas a    systems control client might consider any form of error recovery to    be dangerous.

2.6 协议版本控制

HTTP uses a "<major>.<minor>" numbering scheme to indicate versions    of the protocol.  This specification defines version "1.1".  The    protocol version as a whole indicates the sender's conformance with    the set of requirements laid out in that version's corresponding    specification of HTTP.      The version of an HTTP message is indicated by an HTTP-version field    in the first line of the message.  HTTP-version is case-sensitive.       HTTP-version  = HTTP-name "/" DIGIT "." DIGIT      HTTP-name     = %x48.54.54.50 ; "HTTP", case-sensitive     The HTTP version number consists of two decimal digits separated by a    "." (period or decimal point).  The first digit ("major version")    indicates the HTTP messaging syntax, whereas the second digit ("minor    version") indicates the highest minor version within that major    version to which the sender is conformant and able to understand for    future communication.  The minor version advertises the sender's    communication capabilities even when the sender is only using a    backwards-compatible subset of the protocol, thereby letting the    recipient know that more advanced features can be used in response    (by servers) or in future requests (by clients).     When an HTTP/1.1 message is sent to an HTTP/1.0 recipient [[RFC1945](https://tools.ietf.org/html/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](about:blank#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      HTTP-version might result in communication errors when downstream    recipients use the message sender's version to determine what    features are safe to use for later communication with that sender.     A client SHOULD send a request version equal to the highest version    to which the client is conformant and whose major version is no    higher than the highest version supported by the server, if this is    known.  A client MUST NOT send a version to which it is not    conformant.     A client MAY send a lower request version if it is known that the    server incorrectly implements the HTTP specification, but only after    the client has attempted at least one normal request and determined    from the response status code or header fields (e.g., Server) that    the server improperly handles higher request versions.     A server SHOULD send a response version equal to the highest version    to which the server is conformant that has a major version less than    or equal to the one received in the request.  A server MUST NOT send    a version to which it is not conformant.  A server can send a 505    (HTTP Version Not Supported) response if it wishes, for any reason,    to refuse service of the client's major protocol version.     A server MAY send an HTTP/1.0 response to a request if it is known or    suspected that the client incorrectly implements the HTTP    specification and is incapable of correctly processing later version    responses, such as when a client fails to parse the version number    correctly or when an intermediary is known to blindly forward the    HTTP-version even when it doesn't conform to the given minor version    of the protocol.  Such protocol downgrades SHOULD NOT be performed    unless triggered by specific client attributes, such as when one or    more of the request header fields (e.g., User-Agent) uniquely match    the values sent by a client known to be in error.     The intention of HTTP's versioning design is that the major number    will only be incremented if an incompatible message syntax is    introduced, and that the minor number will only be incremented when    changes made to the protocol have the effect of adding to the message    semantics or implying additional capabilities of the sender.    However, the minor version was not incremented for the changes    introduced between [[RFC2068](https://tools.ietf.org/html/rfc2068)] and [[RFC2616](https://tools.ietf.org/html/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      message with a higher minor version, when sent to a recipient that    has not yet indicated support for that higher version, is    sufficiently backwards-compatible to be safely processed by any    implementation of the same major version.

2.7 统一资源标识符

Uniform Resource Identifiers (URIs) [[RFC3986](https://tools.ietf.org/html/rfc3986)] are used throughout    HTTP as the means for identifying resources ([Section 2 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-2)).    URI references are used to target requests, indicate redirects, and    define relationships.     The definitions of "URI-reference", "absolute-URI", "relative-part",    "scheme", "authority", "port", "host", "path-abempty", "segment",    "query", and "fragment" are adopted from the URI generic syntax.  An    "absolute-path" rule is defined for protocol elements that can    contain a non-empty path component.  (This rule differs slightly from    the path-abempty rule of [RFC 3986](https://tools.ietf.org/html/rfc3986), which allows for an empty path to    be used in references, and path-absolute rule, which does not allow    paths that begin with "//".)  A "partial-URI" rule is defined for    protocol elements that can contain a relative URI but not a fragment    component.       URI-reference = <URI-reference, see [[RFC3986], Section 4.1](https://tools.ietf.org/html/rfc3986#section-4.1)>      absolute-URI  = <absolute-URI, see [[RFC3986], Section 4.3](https://tools.ietf.org/html/rfc3986#section-4.3)>      relative-part = <relative-part, see [[RFC3986], Section 4.2](https://tools.ietf.org/html/rfc3986#section-4.2)>      scheme        = <scheme, see [[RFC3986], Section 3.1](https://tools.ietf.org/html/rfc3986#section-3.1)>      authority     = <authority, see [[RFC3986], Section 3.2](https://tools.ietf.org/html/rfc3986#section-3.2)>      uri-host      = <host, see [[RFC3986], Section 3.2.2](https://tools.ietf.org/html/rfc3986#section-3.2.2)>      port          = <port, see [[RFC3986], Section 3.2.3](https://tools.ietf.org/html/rfc3986#section-3.2.3)>      path-abempty  = <path-abempty, see [[RFC3986], Section 3.3](https://tools.ietf.org/html/rfc3986#section-3.3)>      segment       = <segment, see [[RFC3986], Section 3.3](https://tools.ietf.org/html/rfc3986#section-3.3)>      query         = <query, see [[RFC3986], Section 3.4](https://tools.ietf.org/html/rfc3986#section-3.4)>      fragment      = <fragment, see [[RFC3986], Section 3.5](https://tools.ietf.org/html/rfc3986#section-3.5)>       absolute-path = 1\*( "/" segment )      partial-URI   = relative-part [ "?" query ]     Each protocol element in HTTP that allows a URI reference will    indicate in its ABNF production whether the element allows any form    of reference (URI-reference), only a URI in absolute form    (absolute-URI), only the path and optional query components, or some    combination of the above.  Unless otherwise indicated, URI references    are parsed relative to the effective request URI ([Section 5.5](about:blank#section-5.5)).

2.7.1 http URI方案

The "http" URI scheme is hereby defined for the purpose of minting    identifiers according to their association with the hierarchical    namespace governed by a potential HTTP origin server listening for    TCP ([[RFC0793](https://tools.ietf.org/html/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](https://tools.ietf.org/html/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]](https://tools.ietf.org/html/rfc3986#section-3.5).     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](about:blank#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](about:blank#section-3)) containing the URI's identifying data ([Section 5](about:blank#section-5)) to the    server.  If the server responds to that request with a non-interim      HTTP response message, as described in [Section 6 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-6), 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](https://tools.ietf.org/html/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方案

The "https" URI scheme is hereby defined for the purpose of minting    identifiers according to their association with the hierarchical    namespace governed by a potential HTTP origin server listening to a    given TCP port for TLS-secured connections ([[RFC5246](https://tools.ietf.org/html/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      resource identifiers indicate the same authority (the same host    listening to the same TCP port).  They are distinct namespaces and    are considered to be distinct origin servers.  However, an extension    to HTTP that is defined to apply to entire host domains, such as the    Cookie protocol [[RFC6265](https://tools.ietf.org/html/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](https://tools.ietf.org/html/rfc2818)].

2.7.3 http和https URI标准化和比较

Since the "http" and "https" schemes conform to the URI generic    syntax, such URIs are normalized and compared according to the    algorithm defined in [Section 6 of [RFC3986]](https://tools.ietf.org/html/rfc3986#section-6), using the defaults    described above for each scheme.     If the port is equal to the default port for a scheme, the normal    form is to 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](about:blank#section-2.1) and [2.2](about:blank#section-2.2) of [[RFC3986](https://tools.ietf.org/html/rfc3986)]).     For example, the following three URIs are equivalent:        [http://example.com:80/~smith/home.html](http://example.com/~smith/home.html)       http://EXAMPLE.com/%7Esmith/home.html       [http://EXAMPLE.com:/%7esmith/home.html](http://example.com/%7esmith/home.html)

3.消息格式

All HTTP/1.1 messages consist of a start-line followed by a sequence    of octets in a format similar to the Internet Message Format    [[RFC5322](https://tools.ietf.org/html/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 ]      The normal procedure for parsing an HTTP message is to read the    start-line into a structure, read each header field into a hash table    by field name until the empty line, and then use the parsed data to    determine if a message body is expected.  If a message body has been    indicated, then it is read as a stream until an amount of octets    equal to the message body length is read or the connection is closed.     A recipient MUST parse an HTTP message as a sequence of octets in an    encoding that is a superset of US-ASCII [[USASCII](about:blank#ref-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 起始行

An HTTP message can be either a request from client to server or a    response from server to client.  Syntactically, the two types of    message differ only in the start-line, which is either a request-line    (for requests) or a status-line (for responses), and in the algorithm    for determining the length of the message body ([Section 3.3](about:blank#section-3.3)).      In theory, a client could receive requests and a server could receive    responses, distinguishing them by their different start-line formats,    but, in practice, servers are implemented to only expect a request (a    response is interpreted as an unknown or invalid request method) and    clients are implemented to only expect a response.       start-line     = request-line / status-line

3.1.1 请求线

A request-line begins with a method token, followed by a single space    (SP), the request-target, another single space (SP), the protocol    version, and ends with CRLF.       request-line   = method SP request-target SP HTTP-version CRLF     The method token indicates the request method to be performed on the    target resource.  The request method is case-sensitive.       method         = token     The request methods defined by this specification can be found in    [Section 4 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4), 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](about:blank#section-5.3).     Recipients typically parse the request-line into its component parts    by splitting on whitespace (see [Section 3.5](about:blank#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](about:blank#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      request-target longer than any URI it wishes to parse MUST respond    with a 414 (URI Too Long) status code (see [Section 6.5.12 of    [RFC7231]](https://tools.ietf.org/html/rfc7231#section-6.5.12)).     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 状态行

The first line of a response message is the status-line, consisting    of the protocol version, a space (SP), the status code, another    space, a possibly empty textual phrase describing the status code,    and ending with CRLF.       status-line = HTTP-version SP status-code SP reason-phrase CRLF     The status-code element is a 3-digit integer code describing the    result of the server's attempt to understand and satisfy the client's    corresponding request.  The rest of the response message is to be    interpreted in light of the semantics defined for that status code.    See [Section 6 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-6) 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 标题字段

Each header field consists of a case-insensitive field name followed    by a colon (":"), optional leading whitespace, the field value, and    optional trailing whitespace.        header-field   = field-name ":" OWS field-value OWS       field-name     = token      field-value    = \*( field-content / obs-fold )      field-content  = field-vchar [ 1\*( SP / HTAB ) field-vchar ]      field-vchar    = VCHAR / obs-text       obs-fold       = CRLF 1\*( SP / HTAB )                     ; obsolete line folding                     ; see [Section 3.2.4](about:blank#section-3.2.4)     The field-name token labels the corresponding field-value as having    the semantics defined by that header field.  For example, the Date    header field is defined in [Section 7.1.1.2 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-7.1.1.2) as containing    the origination timestamp for the message in which it appears.

3.2.1 领域可扩展性

Header fields are fully extensible: there is no limit on the    introduction of new field names, each presumably defining new    semantics, nor on the number of header fields used in a given    message.  Existing fields are defined in each part of this    specification and in many other specifications outside this document    set.     New header fields can be defined such that, when they are understood    by a recipient, they might override or enhance the interpretation of    previously defined header fields, define preconditions on request    evaluation, or refine the meaning of responses.     A proxy MUST forward unrecognized header fields unless the field-name    is listed in the Connection header field ([Section 6.1](about:blank#section-6.1)) or the proxy    is specifically configured to block, or otherwise transform, such    fields.  Other recipients SHOULD ignore unrecognized header fields.    These requirements allow HTTP's functionality to be enhanced without    requiring prior update of deployed intermediaries.     All defined header fields ought to be registered with IANA in the    "Message Headers" registry, as described in [Section 8.3 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-8.3).

3.2.2 领域秩序

The order in which header fields with differing field names are    received is not significant.  However, it is good practice to send    header fields that contain control data first, such as Host on    requests and Date on responses, so that implementations can decide    when not to handle a message as early as possible.  A server MUST NOT    apply a request to the target resource until the entire request      header section is received, since later header fields might include    conditionals, authentication credentials, or deliberately misleading    duplicate header fields that would impact request processing.     A sender MUST NOT generate multiple header fields with the same field    name in a message unless either the entire field value for that    header field is defined as a comma-separated list [i.e., #(values)]    or the header field is a well-known exception (as noted below).     A recipient MAY combine multiple header fields with the same field    name into one "field-name: field-value" pair, without changing the    semantics of the message, by appending each subsequent field value to    the combined field value in order, separated by a comma.  The order    in which header fields with the same field name are received is    therefore significant to the interpretation of the combined field    value; a proxy MUST NOT change the order of these field values when    forwarding a message.        Note: In practice, the "Set-Cookie" header field ([[RFC6265](https://tools.ietf.org/html/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](about:blank#appendix-A.2.3)       of [[Kri2001](about:blank#ref-Kri2001)] for details.)

3.2.3 空白

This specification uses three rules to denote the use of linear    whitespace: OWS (optional whitespace), RWS (required whitespace), and    BWS ("bad" whitespace).     The OWS rule is used where zero or more linear whitespace octets    might appear.  For protocol elements where optional whitespace is    preferred to improve readability, a sender SHOULD generate the    optional whitespace as a single SP; otherwise, a sender SHOULD NOT    generate optional whitespace except as needed to white out invalid or    unwanted protocol elements during in-place message filtering.     The RWS rule is used when at least one linear whitespace octet is    required to separate field tokens.  A sender SHOULD generate RWS as a    single SP.     The BWS rule is used where the grammar allows optional whitespace    only for historical reasons.  A sender MUST NOT generate BWS in    messages.  A recipient MUST parse for such bad whitespace and remove    it before interpreting the protocol element.        OWS            = \*( SP / HTAB )                     ; optional whitespace      RWS            = 1\*( SP / HTAB )                     ; required whitespace      BWS            = OWS                     ; "bad" whitespace

3.2.4 字段解析

Messages are parsed using a generic algorithm, independent of the    individual header field names.  The contents within a given field    value are not parsed until a later stage of message interpretation    (usually after the message's entire header section has been    processed).  Consequently, this specification does not use ABNF rules    to define each "Field-Name: Field Value" pair, as was done in    previous editions.  Instead, this specification uses ABNF rules that    are named according to each registered field name, wherein the rule    defines the valid grammar for that field's corresponding field values    (i.e., after the field-value has been extracted from the header    section by a generic field parser).     No whitespace is allowed between the header field-name and colon.  In    the past, differences in the handling of such whitespace have led to    security vulnerabilities in request routing and response handling.  A    server MUST reject any received request message that contains    whitespace between a header field-name and colon with a response code    of 400 (Bad Request).  A proxy MUST remove any such whitespace from a    response message before forwarding the message downstream.     A field value might be preceded and/or followed by optional    whitespace (OWS); a single SP preceding the field-value is preferred    for consistent readability by humans.  The field value does not    include any leading or trailing whitespace: OWS occurring before the    first non-whitespace octet of the field value or after the last    non-whitespace octet of the field value ought to be excluded by    parsers when extracting the field value from a header field.     Historically, HTTP header field values could be extended over    multiple lines by preceding each extra line with at least one space    or horizontal tab (obs-fold).  This specification deprecates such    line folding except within the message/http media type    ([Section 8.3.1](about:blank#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.      A server that receives an obs-fold in a request message that is not    within a message/http container MUST either reject the message by    sending a 400 (Bad Request), preferably with a representation    explaining that obsolete line folding is unacceptable, or replace    each received obs-fold with one or more SP octets prior to    interpreting the field value or forwarding the message downstream.     A proxy or gateway that receives an obs-fold in a response message    that is not within a message/http container MUST either discard the    message and replace it with a 502 (Bad Gateway) response, preferably    with a representation explaining that unacceptable line folding was    received, or replace each received obs-fold with one or more SP    octets prior to interpreting the field value or forwarding the    message downstream.     A user agent that receives an obs-fold in a response message that is    not within a message/http container MUST replace each received    obs-fold with one or more SP octets prior to interpreting the field    value.     Historically, HTTP has allowed field content with text in the    ISO-8859-1 charset [[ISO-8859-1](about:blank#ref-ISO-8859-1)], supporting other charsets only    through use of [[RFC2047](https://tools.ietf.org/html/rfc2047)] encoding.  In practice, most HTTP header    field values use only a subset of the US-ASCII charset [[USASCII](about:blank#ref-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 字段限制

HTTP does not place a predefined limit on the length of each header    field or on the length of the header section as a whole, as described    in [Section 2.5](about:blank#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](about:blank#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.

3.2.6 字段值组件

Most HTTP header field values are defined using common syntax    components (token, quoted-string, and comment) separated by    whitespace or specific delimiting characters.  Delimiters are chosen    from the set of US-ASCII visual characters not allowed in a token    (DQUOTE and "(),/:;<=>?@[\]{}").       token          = 1\*tchar       tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "\*"                     / "+" / "-" / "." / "^" / "\_" / "`" / "|" / "~"                     / DIGIT / ALPHA                     ; any VCHAR, except delimiters     A string of text is parsed as a single value if it is quoted using    double-quote marks.       quoted-string  = DQUOTE \*( qdtext / quoted-pair ) DQUOTE      qdtext         = HTAB / SP /%x21 / %x23-5B / %x5D-7E / obs-text      obs-text       = %x80-FF     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.       comment        = "(" \*( ctext / quoted-pair / comment ) ")"      ctext          = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text     The backslash octet ("\") can be used as a single-octet quoting    mechanism within quoted-string and comment constructs.  Recipients    that process the value of a quoted-string MUST handle a quoted-pair    as if it were replaced by the octet following the backslash.       quoted-pair    = "\" ( HTAB / SP / VCHAR / obs-text )     A sender SHOULD NOT generate a quoted-pair in a quoted-string except    where necessary to quote DQUOTE and backslash octets occurring within    that string.  A sender SHOULD NOT generate a quoted-pair in a comment    except where necessary to quote parentheses ["(" and ")"] and    backslash octets occurring within that comment.

3.3 邮件正文

The message body (if any) of an HTTP message is used to carry the    payload body of that request or response.  The message body is    identical to the payload body unless a transfer coding has been    applied, as described in [Section 3.3.1](about:blank#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](about:blank#section-3.1.2)).  Responses to the HEAD request method ([Section 4.3.2    of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.3.2)) 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]](https://tools.ietf.org/html/rfc7231#section-4.3.1)). 2xx    (Successful) responses to a CONNECT request method ([Section 4.3.6 of    [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.3.6)) 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 传输编码

The Transfer-Encoding header field lists the transfer coding names    corresponding to the sequence of transfer codings that have been (or    will be) applied to the payload body in order to form the message    body.  Transfer codings are defined in [Section 4](about:blank#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](https://tools.ietf.org/html/rfc2045#section-6)).  However, safe    transport has a different focus for an 8bit-clean transfer protocol.    In HTTP's case, Transfer-Encoding is primarily intended to accurately    delimit a dynamically generated payload and to distinguish payload    encodings that are only applied for transport efficiency or security    from those that are characteristics of the selected resource.      A recipient MUST be able to parse the chunked transfer coding    ([Section 4.1](about:blank#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]](https://tools.ietf.org/html/rfc7231#section-3.1.2.1)),    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]](https://tools.ietf.org/html/rfc7232#section-4.1)) 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]](https://tools.ietf.org/html/rfc7231#section-4.3.6)).     Transfer-Encoding was added in HTTP/1.1.  It is generally assumed    that implementations advertising only HTTP/1.0 support will not    understand how to process a transfer-encoded payload.  A client MUST    NOT send a request containing Transfer-Encoding unless it knows the      server will handle HTTP/1.1 (or later) requests; such knowledge might    be in the form of specific user configuration or by remembering the    version of a prior received response.  A server MUST NOT send a    response containing Transfer-Encoding unless the corresponding    request indicates HTTP/1.1 (or later).     A server that receives a request message with a transfer coding it    does not understand SHOULD respond with 501 (Not Implemented).

3.3.2 内容长度

When a message does not have a Transfer-Encoding header field, a    Content-Length header field can provide the anticipated size, as a    decimal number of octets, for a potential payload body.  For messages    that do include a payload body, the Content-Length field-value    provides the framing information necessary for determining where the    body (and message) ends.  For messages that do not include a payload    body, the Content-Length indicates the size of the selected    representation ([Section 3 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-3)).       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]](https://tools.ietf.org/html/rfc7231#section-4.3.2)); 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]](https://tools.ietf.org/html/rfc7232#section-4.1)); 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 200 (OK) response to the same    request.     A server MUST NOT send a Content-Length header field in any response    with a status code of 1xx (Informational) or 204 (No Content).  A    server MUST NOT send a Content-Length header field in any 2xx    (Successful) response to a CONNECT request ([Section 4.3.6 of    [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.3.6)).     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](about:blank#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.

3.3.3 消息体长度

The length of a message body is determined by one of the following    (in order of precedence):     1.  Any response to a HEAD request and any response with a 1xx        (Informational), 204 (No Content), or 304 (Not Modified) status        code is always terminated by the first empty line after the        header fields, regardless of the header fields present in the        message, and thus cannot contain a message body.     2.  Any 2xx (Successful) response to a CONNECT request implies that        the connection will become a tunnel immediately after the empty        line that concludes the header fields.  A client MUST ignore any        Content-Length or Transfer-Encoding header fields received in        such a message.     3.  If a Transfer-Encoding header field is present and the chunked        transfer coding ([Section 4.1](about:blank#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](about:blank#section-9.5)) or response splitting        ([Section 9.4](about:blank#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          Gateway) response to the client.  If this is a response message        received by a user agent, the user agent MUST close the        connection to the server and discard the received response.     5.  If a valid Content-Length header field is present without        Transfer-Encoding, its decimal value defines the expected message        body length in octets.  If the sender closes the connection or        the recipient times out before the indicated number of octets are        received, the recipient MUST consider the message to be        incomplete and close the connection.     6.  If this is a request message and none of the above are true, then        the message body length is zero (no message body is present).     7.  Otherwise, this is a response message without a declared message        body length, so the message body length is determined by the        number of octets received prior to the server closing the        connection.     Since there is no way to distinguish a successfully completed,    close-delimited message from a partially received message interrupted    by network failure, a server SHOULD generate encoding or    length-delimited messages whenever possible.  The close-delimiting    feature exists primarily for backwards compatibility with HTTP/1.0.     A server MAY reject a request that contains a message body but not a    Content-Length by responding with 411 (Length Required).     Unless a transfer coding other than chunked has been applied, a    client that sends a request containing a message body SHOULD use a    valid Content-Length header field if the message body length is known    in advance, rather than the chunked transfer coding, since some    existing services respond to chunked with a 411 (Length Required)    status code even though they understand the chunked transfer coding.    This is typically because such services are implemented via a gateway    that requires a content-length in advance of being called and the    server is unable or unwilling to buffer the entire request before    processing.     A user agent that sends a request containing a message body MUST send    a valid Content-Length header field if it does not know the server    will handle HTTP/1.1 (or later) requests; such knowledge can be in    the form of specific user configuration or by remembering the version    of a prior received response.     If the final response to the last request on a connection has been    completely received and there remains additional data to read, a user    agent MAY discard the remaining data or attempt to determine if that      data belongs as part of the prior response body, which might be the    case if the prior message's Content-Length value is incorrect.  A    client MUST NOT process, cache, or forward such extra data as a    separate response, since such behavior would be vulnerable to cache    poisoning.

3.4 处理不完整的消息

A server that receives an incomplete request message, usually due to    a canceled request or a triggered timeout exception, MAY send an    error response prior to closing the connection.     A client that receives an incomplete response message, which can    occur when a connection is closed prematurely or when decoding a    supposedly chunked transfer coding fails, MUST record the message as    incomplete.  Cache requirements for incomplete responses are defined    in [Section 3 of [RFC7234]](https://tools.ietf.org/html/rfc7234#section-3).     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 消息解析稳健性

Older HTTP/1.0 user agent implementations might send an extra CRLF    after a POST request as a workaround for some early server    applications that failed to read message body content that was not    terminated by a line-ending.  An HTTP/1.1 user agent MUST NOT preface    or follow a request with an extra CRLF.  If terminating the request    message body with a line-ending is desired, then the user agent MUST    count the terminating CRLF octets as part of the message body length.     In the interest of robustness, a server that is expecting to receive    and parse a request-line SHOULD ignore at least one empty line (CRLF)    received prior to the request-line.      Although the line terminator for the start-line and header fields is    the sequence CRLF, a recipient MAY recognize a single LF as a line    terminator and ignore any preceding CR.     Although the request-line and status-line grammar rules require that    each of the component elements be separated by a single SP octet,    recipients MAY instead parse on whitespace-delimited word boundaries    and, aside from the CRLF terminator, treat any form of whitespace as    the SP separator while ignoring preceding or trailing whitespace;    such whitespace includes one or more of the following octets: SP,    HTAB, VT (%x0B), FF (%x0C), or bare CR.  However, lenient parsing can    result in security vulnerabilities if there are multiple recipients    of the message and each has its own unique interpretation of    robustness (see [Section 9.5](about:blank#section-9.5)).     When a server listening only for HTTP request messages, or processing    what appears from the start-line to be an HTTP request message,    receives a sequence of octets that does not match the HTTP-message    grammar aside from the robustness exceptions listed above, the server    SHOULD respond with a 400 (Bad Request) response.

4.转移编码

Transfer coding names are used to indicate an encoding transformation    that has been, can be, or might need to be applied to a payload body    in order to ensure "safe transport" through the network.  This    differs from a content coding in that the transfer coding is a    property of the message rather than a property of the representation    that is being transferred.       transfer-coding    = "chunked" ; [Section 4.1](about:blank#section-4.1)                         / "compress" ; [Section 4.2.1](about:blank#section-4.2.1)                         / "deflate" ; [Section 4.2.2](about:blank#section-4.2.2)                         / "gzip" ; [Section 4.2.3](about:blank#section-4.2.3)                         / transfer-extension      transfer-extension = token \*( OWS ";" OWS transfer-parameter )     Parameters are in the form of a name or name=value pair.       transfer-parameter = token BWS "=" BWS ( token / quoted-string )     All transfer-coding names are case-insensitive and ought to be    registered within the HTTP Transfer Coding registry, as defined in    [Section 8.4](about:blank#section-8.4).  They are used in the TE ([Section 4.3](about:blank#section-4.3)) and    Transfer-Encoding ([Section 3.3.1](about:blank#section-3.3.1)) header fields.

4.1 分块传输编码

The chunked transfer coding wraps the payload body in order to    transfer it as a series of chunks, each with its own size indicator,    followed by an OPTIONAL trailer containing header fields.  Chunked    enables content streams of unknown size to be transferred as a    sequence of length-delimited buffers, which enables the sender to    retain connection persistence and the recipient to know when it has    received the entire message.       chunked-body   = \*chunk                       last-chunk                       trailer-part                       CRLF       chunk          = chunk-size [ chunk-ext ] CRLF                       chunk-data CRLF      chunk-size     = 1\*HEXDIG      last-chunk     = 1\*("0") [ chunk-ext ] CRLF       chunk-data     = 1\*OCTET ; a sequence of chunk-size octets     The chunk-size field is a string of hex digits indicating the size of    the chunk-data in octets.  The chunked transfer coding is complete    when a chunk with a chunk-size of zero is received, possibly followed    by a trailer, and finally terminated by an empty line.     A recipient MUST be able to parse and decode the chunked transfer    coding.

4.1.1 块扩展

The chunked encoding allows each chunk to include zero or more chunk    extensions, immediately following the chunk-size, for the sake of    supplying per-chunk metadata (such as a signature or hash),    mid-message control information, or randomization of message body    size.       chunk-ext      = \*( ";" chunk-ext-name [ "=" chunk-ext-val ] )       chunk-ext-name = token      chunk-ext-val  = token / quoted-string     The chunked encoding is specific to each connection and is likely to    be removed or recoded by each recipient (including intermediaries)    before any higher-level application would have a chance to inspect    the extensions.  Hence, use of chunk extensions is generally limited      to specialized HTTP services such as "long polling" (where client and    server can have shared expectations regarding the use of chunk    extensions) or for padding within an end-to-end secured connection.     A recipient MUST ignore unrecognized chunk extensions.  A server    ought to limit the total length of chunk extensions received in a    request to an amount reasonable for the services provided, in the    same way that it applies length limitations and timeouts for other    parts of a message, and generate an appropriate 4xx (Client Error)    response if that amount is exceeded.

4.1.2 块状的未来式零件

A trailer allows the sender to include additional fields at the end    of a chunked message in order to supply metadata that might be    dynamically generated while the message body is sent, such as a    message integrity check, digital signature, or post-processing    status.  The trailer fields are identical to header fields, except    they are sent in a chunked trailer instead of the message's header    section.       trailer-part   = \*( header-field CRLF )     A sender MUST NOT generate a trailer that contains a field necessary    for message framing (e.g., Transfer-Encoding and Content-Length),    routing (e.g., Host), request modifiers (e.g., controls and    conditionals in [Section 5 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-5)), authentication (e.g., see    [[RFC7235](https://tools.ietf.org/html/rfc7235)] and [[RFC6265](https://tools.ietf.org/html/rfc6265)]), response control data (e.g., see [Section](https://tools.ietf.org/html/rfc7231#section-7.1) [7.1 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-7.1)), 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](about:blank#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.

4.1.3 解码分块

A process for decoding the chunked transfer coding can be represented    in pseudo-code as:       length := 0      read chunk-size, chunk-ext (if any), and CRLF      while (chunk-size > 0) {         read chunk-data and CRLF         append chunk-data to decoded-body         length := length + chunk-size         read chunk-size, chunk-ext (if any), and CRLF      }      read trailer field      while (trailer field is not empty) {         if (trailer field is allowed to be sent in a trailer) {             append trailer field to existing header fields         }         read trailer-field      }      Content-Length := length      Remove "chunked" from Transfer-Encoding      Remove Trailer from existing header fields

4.2 压缩编码

The codings defined below can be used to compress the payload of a    message.

4.2.1 压缩编码

The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding    [[Welch](about:blank#ref-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编码

The "deflate" coding is a "zlib" data format [[RFC1950](https://tools.ietf.org/html/rfc1950)] containing a    "deflate" compressed data stream [[RFC1951](https://tools.ietf.org/html/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.

4.2.3 Gzip编码

The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy    Check (CRC) that is commonly produced by the gzip file compression    program [[RFC1952](https://tools.ietf.org/html/rfc1952)].  A recipient SHOULD consider "x-gzip" to be    equivalent to "gzip".

4.3. TE

The "TE" header field in a request indicates what transfer codings,    besides chunked, the client is willing to accept in response, and    whether or not the client is willing to accept trailer fields in a    chunked transfer coding.     The TE field-value consists of a comma-separated list of transfer    coding names, each allowing for optional parameters (as described in    [Section 4](about:blank#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](about:blank#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      5.3.1 of [[RFC7231](https://tools.ietf.org/html/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](about:blank#section-6.1)) in order to prevent the TE    field from being forwarded by intermediaries that do not support its    semantics.

4.4 预告

When a message includes a message body encoded with the chunked    transfer coding and the sender desires to send metadata in the form    of trailer fields at the end of the message, the sender SHOULD    generate a Trailer header field before the message body to indicate    which fields will be present in the trailers.  This allows the    recipient to prepare for receipt of that metadata before it starts    processing the body, which is useful if the message is being streamed    and the recipient wishes to confirm an integrity check on the fly.       Trailer = 1#field-name

5.消息路由

HTTP request message routing is determined by each client based on    the target resource, the client's proxy configuration, and    establishment or reuse of an inbound connection.  The corresponding    response routing follows the same connection chain back to the    client.

5.1 识别目标资源

HTTP is used in a wide variety of applications, ranging from    general-purpose computers to home appliances.  In some cases,    communication options are hard-coded in a client's configuration.    However, most HTTP clients rely on the same resource identification    mechanism and configuration techniques as general-purpose Web    browsers.     HTTP communication is initiated by a user agent for some purpose.    The purpose is a combination of request semantics, which are defined    in [[RFC7231](https://tools.ietf.org/html/rfc7231)], and a target resource upon which to apply those    semantics.  A URI reference ([Section 2.7](about:blank#section-2.7)) is typically used as an      identifier for the "target resource", which a user agent would    resolve to its absolute form in order to obtain the "target URI".    The target URI excludes the reference's fragment component, if any,    since fragment identifiers are reserved for client-side processing    ([[RFC3986], Section 3.5](https://tools.ietf.org/html/rfc3986#section-3.5)).

5.2 连接入站

Once the target URI is determined, a client needs to decide whether a    network request is necessary to accomplish the desired semantics and,    if so, where that request is to be directed.     If the client has a cache [[RFC7234](https://tools.ietf.org/html/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](about:blank#section-2.7.1)) and    "https" ([Section 2.7.2](about:blank#section-2.7.2)) schemes.     HTTP requirements regarding connection management are defined in    [Section 6](about:blank#section-6).

5.3 请求目标

Once an inbound connection is obtained, the client sends an HTTP    request message ([Section 3](about:blank#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

5.3.1 起源形式

The most common form of request-target is the origin-form.       origin-form    = absolute-path [ "?" query ]     When making a request directly to an origin server, other than a    CONNECT or server-wide OPTIONS request (as detailed below), a client    MUST send only the absolute path and query components of the target    URI as the request-target.  If the target URI's path component is    empty, the client MUST send "/" as the path within the origin-form of    request-target.  A Host header field is also sent, as defined in    [Section 5.4](about:blank#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 绝对形式

When making a request to a proxy, other than a CONNECT or server-wide    OPTIONS request (as detailed below), a client MUST send the target    URI in absolute-form as the request-target.       absolute-form  = absolute-URI     The proxy is requested to either service that request from a valid    cache, if possible, or make the same request on the client's behalf    to either the next inbound proxy server or directly to the origin    server indicated by the request-target.  Requirements on such    "forwarding" of messages are defined in [Section 5.7](about:blank#section-5.7).     An example absolute-form of request-line would be:       GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1      To allow for transition to the absolute-form for all requests in some    future version of HTTP, a server MUST accept the absolute-form in    requests, even though HTTP/1.1 clients will only send them in    requests to proxies.

5.3.3 授权形式

The authority-form of request-target is only used for CONNECT    requests ([Section 4.3.6 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.3.6)).       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 星号形式

The asterisk-form of request-target is only used for a server-wide    OPTIONS request ([Section 4.3.7 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.3.7)).       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://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".

5.4 主办

The "Host" header field in a request provides the host and port    information from the target URI, enabling the origin server to    distinguish among resources while servicing requests for multiple    host names on a single IP address.       Host = uri-host [ ":" port ] ; [Section 2.7.1](about:blank#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](about:blank#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.      A server MUST respond with a 400 (Bad Request) status code to any    HTTP/1.1 request message that lacks a Host header field and to any    request message that contains more than one Host header field or a    Host header field with an invalid field-value.

5.5 有效的请求URI

Since the request-target often contains only part of the user agent's    target URI, a server reconstructs the intended target as an    "effective request URI" to properly service the request.  This    reconstruction involves both the server's local configuration and    information communicated in the request-target, Host header field,    and connection context.     For a user agent, the effective request URI is the target URI.     If the request-target is in absolute-form, the effective request URI    is the same as the request-target.  Otherwise, the effective request    URI is constructed as follows:        If the server's configuration (or outbound gateway) provides a       fixed URI scheme, that scheme is used for the effective request       URI.  Otherwise, if the request is received over a TLS-secured TCP       connection, the effective request URI's scheme is "https"; if not,       the scheme is "http".        If the server's configuration (or outbound gateway) provides a       fixed URI authority component, that authority is used for the       effective request URI.  If not, then if the request-target is in       authority-form, the effective request URI's authority component is       the same as the request-target.  If not, then if a Host header       field is supplied with a non-empty field-value, the authority       component is the same as the Host field-value.  Otherwise, the       authority component is assigned the default name configured for       the server and, if the connection's incoming TCP port number       differs from the default port for the effective request URI's       scheme, then a colon (":") and the incoming port number (in       decimal form) are appended to the authority component.        If the request-target is in authority-form or asterisk-form, the       effective request URI's combined path and query component is       empty.  Otherwise, the combined path and query component is the       same as the request-target.        The components of the effective request URI, once determined as       above, can be combined into absolute-URI form by concatenating the       scheme, "://", authority, and combined path and query component.      Example 1: the following message received over an insecure TCP    connection       GET /pub/WWW/TheProject.html HTTP/1.1      Host: www.example.org:8080     has an effective request URI of       [http://www.example.org:8080/pub/WWW/TheProject.html](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](about:blank#section-9) for security    considerations regarding message routing.

5.6 将响应与请求关联

HTTP does not include a request identifier for associating a given    request message with its corresponding one or more response messages.    Hence, it relies on the order of response arrival to correspond    exactly to the order in which requests are made on the same    connection.  More than one response message per request only occurs    when one or more informational responses (1xx, see [Section 6.2 of    [RFC7231]](https://tools.ietf.org/html/rfc7231#section-6.2)) precede a final response to the same request.      A client that has more than one outstanding request on a connection    MUST maintain a list of outstanding requests in the order sent and    MUST associate each received response message on that connection to    the highest ordered request that has not yet received a final    (non-1xx) response.

5.7 消息转发

As described in [Section 2.3](about:blank#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](about:blank#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 通过

The "Via" header field indicates the presence of intermediate    protocols and recipients between the user agent and the server (on    requests) or between the origin server and the client (on responses),    similar to the "Received" header field in email ([Section 3.6.7 of    [RFC5322]](https://tools.ietf.org/html/rfc5322#section-3.6.7)).  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](about:blank#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.      A proxy MUST send an appropriate Via header field, as described    below, in each message that it forwards.  An HTTP-to-HTTP gateway    MUST send an appropriate Via header field in each inbound request    message and MAY send a Via header field in forwarded response    messages.     For each intermediary, the received-protocol indicates the protocol    and protocol version used by the upstream sender of the message.    Hence, the Via field value records the advertised protocol    capabilities of the request/response chain such that they remain    visible to downstream recipients; this can be useful for determining    what backwards-incompatible features might be safe to use in    response, or within a later request, as described in [Section 2.6](about:blank#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.      An intermediary MAY combine an ordered subsequence of Via header    field entries into a single such entry if the entries have identical    received-protocol values.  For example,       Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy     could be collapsed to       Via: 1.0 ricky, 1.1 mertz, 1.0 lucy     A sender SHOULD NOT combine multiple entries unless they are all    under the same organizational control and the hosts have already been    replaced by pseudonyms.  A sender MUST NOT combine entries that have    different received-protocol values.

5.7.2 转换

Some intermediaries include features for transforming messages and    their payloads.  A proxy might, for example, convert between image    formats in order to save cache space or to reduce the amount of    traffic on a slow link.  However, operational problems might occur    when these transformations are applied to payloads intended for    critical applications, such as medical imaging or scientific data    analysis, particularly when integrity checks or digital signatures    are used to ensure that the payload received is identical to the    original.     An HTTP-to-HTTP proxy is called a "transforming proxy" if it is    designed or configured to modify messages in a semantically    meaningful way (i.e., modifications, beyond those required by normal    HTTP processing, that change the message in a way that would be    significant to the original sender or potentially significant to    downstream recipients).  For example, a transforming proxy might be    acting as a shared annotation server (modifying responses to include    references to a local annotation database), a malware filter, a    format transcoder, or a privacy filter.  Such transformations are    presumed to be desired by whichever client (or client organization)    selected the proxy.     If a proxy receives a request-target with a host name that is not a    fully qualified domain name, it MAY add its own domain to the host    name it received when forwarding the request.  A proxy MUST NOT    change the host name if the request-target contains a fully qualified    domain name.      A proxy MUST NOT modify the "absolute-path" and "query" parts of the    received request-target when forwarding it to the next inbound    server, except as noted above to replace an empty path with "/" or    "\*".     A proxy MAY modify the message body through application or removal of    a transfer coding ([Section 4](about:blank#section-4)).     A proxy MUST NOT transform the payload ([Section 3.3 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-3.3)) of    a message that contains a no-transform cache-control directive    ([Section 5.2 of [RFC7234]](https://tools.ietf.org/html/rfc7234#section-5.2)).     A proxy MAY transform the payload of a message that does not contain    a no-transform cache-control directive.  A proxy that transforms a    payload MUST add a Warning header field with the warn-code of 214    ("Transformation Applied") if one is not already in the message (see    [Section 5.5 of [RFC7234]](https://tools.ietf.org/html/rfc7234#section-5.5)).  A proxy that transforms the payload of a    200 (OK) response can further inform downstream recipients that a    transformation has been applied by changing the response status code    to 203 (Non-Authoritative Information) ([Section 6.3.4 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-6.3.4)).     A proxy SHOULD NOT modify header fields that provide information    about the endpoints of the communication chain, the resource state,    or the selected representation (other than the payload) unless the    field's definition specifically allows such modification or the    modification is deemed necessary for privacy or security.

6.连接管理

HTTP messaging is independent of the underlying transport- or    session-layer connection protocol(s).  HTTP only presumes a reliable    transport with in-order delivery of requests and the corresponding    in-order delivery of responses.  The mapping of HTTP request and    response structures onto the data units of an underlying transport    protocol is outside the scope of this specification.     As described in [Section 5.2](about:blank#section-5.2), the specific connection protocols to be    used for an HTTP interaction are determined by client configuration    and the target URI.  For example, the "http" URI scheme    ([Section 2.7.1](about:blank#section-2.7.1)) indicates a default connection of TCP over IP, with a    default TCP port of 80, but the client might be configured to use a    proxy via some other connection, port, or protocol.      HTTP implementations are expected to engage in connection management,    which includes maintaining the state of current connections,    establishing a new connection or reusing an existing connection,    processing messages received on a connection, detecting connection    failures, and closing each connection.  Most clients maintain    multiple connections in parallel, including more than one connection    per server endpoint.  Most servers are designed to maintain thousands    of concurrent connections, while controlling request queues to enable    fair use and detect denial-of-service attacks.

6.1 连接

The "Connection" header field allows the sender to indicate desired    control options for the current connection.  In order to avoid    confusing downstream recipients, a proxy or gateway MUST remove or    replace any received connection options before forwarding the    message.     When a header field aside from Connection is used to supply control    information for or about the current connection, the sender MUST list    the corresponding field-name within the Connection header field.  A    proxy or gateway MUST parse a received Connection header field before    a message is forwarded and, for each connection-option in this field,    remove any header field(s) from the message with the same name as the    connection-option, and then remove the Connection header field itself    (or replace it with the intermediary's own connection options for the    forwarded message).     Hence, the Connection header field provides a declarative way of    distinguishing header fields that are only intended for the immediate    recipient ("hop-by-hop") from those fields that are intended for all    recipients on the chain ("end-to-end"), enabling the message to be    self-descriptive and allowing future connection-specific extensions    to be deployed without fear that they will be blindly forwarded by    older intermediaries.     The Connection header field's value has the following grammar:       Connection        = 1#connection-option      connection-option = token     Connection options are case-insensitive.     A sender MUST NOT send a connection option corresponding to a header    field that is intended for all recipients of the payload.  For    example, Cache-Control is never appropriate as a connection option    ([Section 5.2 of [RFC7234]](https://tools.ietf.org/html/rfc7234#section-5.2)).      The connection options do not always correspond to a header field    present in the message, since a connection-specific header field    might not be needed if there are no parameters associated with a    connection option.  In contrast, a connection-specific header field    that is received without a corresponding connection option usually    indicates that the field has been improperly forwarded by an    intermediary and ought to be ignored by the recipient.     When defining new connection options, specification authors ought to    survey existing header field names and ensure that the new connection    option does not share the same name as an already deployed header    field.  Defining a new connection option essentially reserves that    potential field-name for carrying additional information related to    the connection option, since it would be unwise for senders to use    that field-name for anything else.     The "close" connection option is defined for a sender to signal that    this connection will be closed after completion of the response.  For    example,       Connection: close     in either the request or the response header fields indicates that    the sender is going to close the connection after the current    request/response is complete ([Section 6.6](about:blank#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 编制

It is beyond the scope of this specification to describe how    connections are established via various transport- or session-layer    protocols.  Each connection applies to only one transport link.

6.3 坚持

HTTP/1.1 defaults to the use of "persistent connections", allowing    multiple requests and responses to be carried over a single    connection.  The "close" connection option is used to signal that a    connection will not persist after the current request/response.  HTTP    implementations SHOULD support persistent connections.      A recipient determines whether a connection is persistent or not    based on the most recently received message's protocol version and    Connection header field (if any):     o  If the "close" connection option is present, the connection will       not persist after the current response; else,     o  If the received protocol is HTTP/1.1 (or later), the connection       will persist after the current response; else,     o  If the received protocol is HTTP/1.0, the "keep-alive" connection       option is present, the recipient is not a proxy, and the recipient       wishes to honor the HTTP/1.0 "keep-alive" mechanism, the       connection will persist after the current response; otherwise,     o  The connection will close after the current response.     A client MAY send additional requests on a persistent connection    until it sends or receives a "close" connection option or receives an    HTTP/1.0 response without a "keep-alive" connection option.     In order to remain persistent, all messages on a connection need to    have a self-defined message length (i.e., one not defined by closure    of the connection), as described in [Section 3.3](about:blank#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]](https://tools.ietf.org/html/rfc2068#section-19.7.1) 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](about:blank#appendix-A.1.2) for more information on backwards compatibility    with HTTP/1.0 clients.

6.3.1 重试请求

Connections can be closed at any time, with or without intention.    Implementations ought to anticipate the need to recover from    asynchronous close events.      When an inbound connection is closed prematurely, a client MAY open a    new connection and automatically retransmit an aborted sequence of    requests if all of those requests have idempotent methods ([Section](https://tools.ietf.org/html/rfc7231#section-4.2.2) [4.2.2 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.2.2)).  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 流水线

A client that supports persistent connections MAY "pipeline" its    requests (i.e., send multiple requests without waiting for each    response).  A server MAY process a sequence of pipelined requests in    parallel if they all have safe methods ([Section 4.2.1 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.2.1)),    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](about:blank#section-6.6)).     Idempotent methods ([Section 4.2.2 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-4.2.2)) are significant to    pipelining because they can be automatically retried after a    connection failure.  A user agent SHOULD NOT pipeline requests after    a non-idempotent method, until the final response status code for    that method has been received, unless the user agent has a means to    detect and recover from partial failure conditions involving the    pipelined sequence.      An intermediary that receives pipelined requests MAY pipeline those    requests when forwarding them inbound, since it can rely on the    outbound user agent(s) to determine what requests can be safely    pipelined.  If the inbound connection fails before receiving a    response, the pipelining intermediary MAY attempt to retry a sequence    of requests that have yet to receive a response if the requests all    have idempotent methods; otherwise, the pipelining intermediary    SHOULD forward any received responses and then close the    corresponding outbound connection(s) so that the outbound user    agent(s) can recover accordingly.

6.4 并发

A client ought to limit the number of simultaneous open connections    that it maintains to a given server.     Previous revisions of HTTP gave a specific number of connections as a    ceiling, but this was found to be impractical for many applications.    As a result, this specification does not mandate a particular maximum    number of connections but, instead, encourages clients to be    conservative when opening multiple connections.     Multiple connections are typically used to avoid the "head-of-line    blocking" problem, wherein a request that takes significant    server-side processing and/or has a large payload blocks subsequent    requests on the same connection.  However, each connection consumes    server resources.  Furthermore, using multiple connections can cause    undesirable side effects in congested networks.     Note that a server might reject traffic that it deems abusive or    characteristic of a denial-of-service attack, such as an excessive    number of open connections from a single client.

6.5 失败和超时

Servers will usually have some timeout value beyond which they will    no longer maintain an inactive connection.  Proxy servers might make    this a higher value since it is likely that the client will be making    more connections through the same proxy server.  The use of    persistent connections places no requirements on the length (or    existence) of this timeout for either the client or the server.     A client or server that wishes to time out SHOULD issue a graceful    close on the connection.  Implementations SHOULD constantly monitor    open connections for a received closure signal and respond to it as    appropriate, since prompt closure of both sides of a connection    enables allocated system resources to be reclaimed.      A client, server, or proxy MAY close the transport connection at any    time.  For example, a client might have started to send a new request    at the same time that the server has decided to close the "idle"    connection.  From the server's point of view, the connection is being    closed while it was idle, but from the client's point of view, a    request is in progress.     A server SHOULD sustain persistent connections, when possible, and    allow the underlying transport's flow-control mechanisms to resolve    temporary overloads, rather than terminate connections with the    expectation that clients will retry.  The latter technique can    exacerbate network congestion.     A client sending a message body SHOULD monitor the network connection    for an error response while it is transmitting the request.  If the    client sees a response that indicates the server does not wish to    receive the message body and is closing the connection, the client    SHOULD immediately cease transmitting the body and close its side of    the connection.

6.6 拆除

The Connection header field ([Section 6.1](about:blank#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.      If a server performs an immediate close of a TCP connection, there is    a significant risk that the client will not be able to read the last    HTTP response.  If the server receives additional data from the    client on a fully closed connection, such as another request that was    sent by the client before receiving the server's response, the    server's TCP stack will send a reset packet to the client;    unfortunately, the reset packet might erase the client's    unacknowledged input buffers before they can be read and interpreted    by the client's HTTP parser.     To avoid the TCP reset problem, servers typically close a connection    in stages.  First, the server performs a half-close by closing only    the write side of the read/write connection.  The server then    continues to read from the connection until it receives a    corresponding close by the client, or until the server is reasonably    certain that its own TCP stack has received the client's    acknowledgement of the packet(s) containing the server's last    response.  Finally, the server fully closes the connection.     It is unknown whether the reset problem is exclusive to TCP or might    also be found in other transport connection protocols.

6.7 升级

The "Upgrade" header field is intended to provide a simple mechanism    for transitioning from HTTP/1.1 to some other protocol on the same    connection.  A client MAY send a list of protocols in the Upgrade    header field of a request to invite the server to switch to one or    more of those protocols, in order of descending preference, before    sending the final response.  A server MAY ignore a received Upgrade    header field if it wishes to continue using the current protocol on    that connection.  Upgrade cannot be used to insist on a protocol    change.       Upgrade          = 1#protocol       protocol         = protocol-name ["/" protocol-version]      protocol-name    = token      protocol-version = token     A server that sends a 101 (Switching Protocols) response MUST send an    Upgrade header field to indicate the new protocol(s) to which the    connection is being switched; if multiple protocol layers are being    switched, the sender MUST list the protocols in layer-ascending    order.  A server MUST NOT switch to a protocol that was not indicated    by the client in the corresponding request's Upgrade header field.  A      server MAY choose to ignore the order of preference indicated by the    client and select the new protocol(s) based on other factors, such as    the nature of the request or the current load on the server.     A server that sends a 426 (Upgrade Required) response MUST send an    Upgrade header field to indicate the acceptable protocols, in order    of descending preference.     A server MAY send an Upgrade header field in any other response to    advertise that it implements support for upgrading to the listed    protocols, in order of descending preference, when appropriate for a    future request.     The following is a hypothetical example sent by a client:       GET /hello.txt HTTP/1.1      Host: www.example.com      Connection: upgrade      Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11      The capabilities and nature of the application-level communication    after the protocol change is entirely dependent upon the new    protocol(s) chosen.  However, immediately after sending the 101    (Switching Protocols) response, the server is expected to continue    responding to the original request as if it had received its    equivalent within the new protocol (i.e., the server still has an    outstanding request to satisfy after the protocol has been changed,    and is expected to do so without requiring the request to be    repeated).     For example, if the Upgrade header field is received in a GET request    and the server decides to switch protocols, it first responds with a    101 (Switching Protocols) message in HTTP/1.1 and then immediately    follows that with the new protocol's equivalent of a response to a    GET on the target resource.  This allows a connection to be upgraded    to protocols with the same semantics as HTTP without the latency cost    of an additional round trip.  A server MUST NOT switch protocols    unless the received message semantics can be honored by the new    protocol; an OPTIONS request can be honored by any protocol.      The following is an example response to the above hypothetical    request:       HTTP/1.1 101 Switching Protocols      Connection: upgrade      Upgrade: HTTP/2.0       [... data stream switches to HTTP/2.0 with an appropriate response      (as defined by new protocol) to the "GET /hello.txt" request ...]     When Upgrade is sent, the sender MUST also send a Connection header    field ([Section 6.1](about:blank#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]](https://tools.ietf.org/html/rfc7231#section-5.1.1)), 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]](https://tools.ietf.org/html/rfc7231#section-6.4)).     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](about:blank#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](about:blank#section-8.6).

7. ABNF名单扩展：＃规则

A #rule extension to the ABNF rules of [[RFC5234](https://tools.ietf.org/html/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).      In any production that uses the list construct, a sender MUST NOT    generate empty list elements.  In other words, a sender MUST generate    lists that satisfy the following syntax:       1#element => element \*( OWS "," OWS element )     and:       #element => [ 1#element ]     and for n >= 1 and m > 1:       <n>#<m>element => element <n-1>\*<m-1>( OWS "," OWS element )     For compatibility with legacy list rules, a recipient MUST parse and    ignore a reasonable number of empty list elements: enough to handle    common mistakes by senders that merge values, but not so much that    they could be used as a denial-of-service mechanism.  In other words,    a recipient MUST accept lists that satisfy the following syntax:       #element => [ ( "," / element ) \*( OWS "," [ OWS element ] ) ]       1#element => \*( "," OWS ) element \*( OWS "," [ OWS element ] )     Empty elements do not contribute to the count of elements present.    For example, given these ABNF productions:       example-list      = 1#example-list-elmt      example-list-elmt = token ; see [Section 3.2.6](about:blank#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](about:blank#appendix-B) shows the collected ABNF for recipients after the list    constructs have been expanded.

8. IANA考虑事项

8.1 标题字段注册

HTTP header fields are registered within the "Message Headers"    registry maintained at    <[http://www.iana.org/assignments/message-headers/](http://www.iana.org/assignments/message-headers/)>.     This document defines the following HTTP header fields, so the    "Permanent Message Header Field Names" registry has been updated    accordingly (see [[BCP90](about:blank#ref-BCP90)]).     +-------------------+----------+----------+---------------+    | Header Field Name | Protocol | Status   | Reference     |    +-------------------+----------+----------+---------------+    | Connection        | http     | standard | [Section 6.1](about:blank#section-6.1)   |    | Content-Length    | http     | standard | [Section 3.3.2](about:blank#section-3.3.2) |    | Host              | http     | standard | [Section 5.4](about:blank#section-5.4)   |    | TE                | http     | standard | [Section 4.3](about:blank#section-4.3)   |    | Trailer           | http     | standard | [Section 4.4](about:blank#section-4.4)   |    | Transfer-Encoding | http     | standard | [Section 3.3.1](about:blank#section-3.3.1) |    | Upgrade           | http     | standard | [Section 6.7](about:blank#section-6.7)   |    | Via               | http     | standard | [Section 5.7.1](about:blank#section-5.7.1) |    +-------------------+----------+----------+---------------+     Furthermore, the header field-name "Close" has been registered as    "reserved", since using that name as an HTTP header field might    conflict with the "close" connection option of the Connection header    field ([Section 6.1](about:blank#section-6.1)).     +-------------------+----------+----------+-------------+    | Header Field Name | Protocol | Status   | Reference   |    +-------------------+----------+----------+-------------+    | Close             | http     | reserved | [Section 8.1](about:blank#section-8.1) |    +-------------------+----------+----------+-------------+     The change controller is: "IETF (iesg@ietf.org) - Internet    Engineering Task Force".

8.2 URI方案注册

IANA maintains the registry of URI Schemes [[BCP115](about:blank#ref-BCP115)] at    <[http://www.iana.org/assignments/uri-schemes/](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](about:blank#section-2.7.1) |    | https      | Hypertext Transfer Protocol Secure | [Section 2.7.2](about:blank#section-2.7.2) |    +------------+------------------------------------+---------------+

8.3 互联网媒体类型注册

IANA maintains the registry of Internet media types [[BCP13](about:blank#ref-BCP13)] at    <[http://www.iana.org/assignments/media-types](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 互联网媒体类型消息/ http

The message/http type can be used to enclose a single HTTP request or    response message, provided that it obeys the MIME restrictions for    all "message" types regarding line length and encodings.     Type name:  message     Subtype name:  http     Required parameters:  N/A     Optional parameters:  version, msgtype        version:  The HTTP-version number of the enclosed message (e.g.,          "1.1").  If not present, the version can be determined from the          first line of the body.        msgtype:  The message type -- "request" or "response".  If not          present, the type can be determined from the first line of the          body.     Encoding considerations:  only "7bit", "8bit", or "binary" are       permitted      Security considerations:  see [Section 9](about:blank#section-9)     Interoperability considerations:  N/A     Published specification:  This specification (see [Section 8.3.1](about:blank#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媒体类型应用程序/ http

The application/http type can be used to enclose a pipeline of one or    more HTTP request or response messages (not intermixed).     Type name:  application     Subtype name:  http     Required parameters:  N/A     Optional parameters:  version, msgtype        version:  The HTTP-version number of the enclosed messages (e.g.,          "1.1").  If not present, the version can be determined from the          first line of the body.         msgtype:  The message type -- "request" or "response".  If not          present, the type can be determined from the first line of the          body.     Encoding considerations:  HTTP messages enclosed by this type are in       "binary" format; use of an appropriate Content-Transfer-Encoding       is required when transmitted via email.     Security considerations:  see [Section 9](about:blank#section-9)     Interoperability considerations:  N/A     Published specification:  This specification (see [Section 8.3.2](about:blank#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 传输编码注册表

The "HTTP Transfer Coding Registry" defines the namespace for    transfer coding names.  It is maintained at    <[http://www.iana.org/assignments/http-parameters](http://www.iana.org/assignments/http-parameters)>.

8.4.1 程序

Registrations MUST include the following fields:     o  Name     o  Description     o  Pointer to specification text     Names of transfer codings MUST NOT overlap with names of content    codings ([Section 3.1.2.1 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-3.1.2.1)) unless the encoding    transformation is identical, as is the case for the compression    codings defined in [Section 4.2](about:blank#section-4.2).     Values to be added to this namespace require IETF Review (see [Section](https://tools.ietf.org/html/rfc5226#section-4.1) [4.1 of [RFC5226]](https://tools.ietf.org/html/rfc5226#section-4.1)), and MUST conform to the purpose of transfer coding    defined in this specification.     Use of program names for the identification of encoding formats is    not desirable and is discouraged for future encodings.

8.4.2 注册

The "HTTP Transfer Coding Registry" has been updated with the    registrations below:     +------------+--------------------------------------+---------------+    | Name       | Description                          | Reference     |    +------------+--------------------------------------+---------------+    | chunked    | Transfer in a series of chunks       | [Section 4.1](about:blank#section-4.1)   |    | compress   | UNIX "compress" data format [[Welch](about:blank#ref-Welch)]  | [Section 4.2.1](about:blank#section-4.2.1) |    | deflate    | "deflate" compressed data            | [Section 4.2.2](about:blank#section-4.2.2) |    |            | ([[RFC1951](https://tools.ietf.org/html/rfc1951)]) inside the "zlib" data   |               |    |            | format ([[RFC1950](https://tools.ietf.org/html/rfc1950)])                   |               |    | gzip       | GZIP file format [[RFC1952](https://tools.ietf.org/html/rfc1952)]           | [Section 4.2.3](about:blank#section-4.2.3) |    | x-compress | Deprecated (alias for compress)      | [Section 4.2.1](about:blank#section-4.2.1) |    | x-gzip     | Deprecated (alias for gzip)          | [Section 4.2.3](about:blank#section-4.2.3) |    +------------+--------------------------------------+---------------+

8.5 内容编码注册

IANA maintains the "HTTP Content Coding Registry" at    <[http://www.iana.org/assignments/http-parameters](http://www.iana.org/assignments/http-parameters)>.     The "HTTP Content Coding Registry" has been updated with the    registrations below:     +------------+--------------------------------------+---------------+    | Name       | Description                          | Reference     |    +------------+--------------------------------------+---------------+    | compress   | UNIX "compress" data format [[Welch](about:blank#ref-Welch)]  | [Section 4.2.1](about:blank#section-4.2.1) |    | deflate    | "deflate" compressed data            | [Section 4.2.2](about:blank#section-4.2.2) |    |            | ([[RFC1951](https://tools.ietf.org/html/rfc1951)]) inside the "zlib" data   |               |    |            | format ([[RFC1950](https://tools.ietf.org/html/rfc1950)])                   |               |    | gzip       | GZIP file format [[RFC1952](https://tools.ietf.org/html/rfc1952)]           | [Section 4.2.3](about:blank#section-4.2.3) |    | x-compress | Deprecated (alias for compress)      | [Section 4.2.1](about:blank#section-4.2.1) |    | x-gzip     | Deprecated (alias for gzip)          | [Section 4.2.3](about:blank#section-4.2.3) |    +------------+--------------------------------------+---------------+

8.6 升级令牌注册表

The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry"    defines the namespace for protocol-name tokens used to identify    protocols in the Upgrade header field.  The registry is maintained at    <[http://www.iana.org/assignments/http-upgrade-tokens](http://www.iana.org/assignments/http-upgrade-tokens)>.

8.6.1 程序

Each registered protocol name is associated with contact information    and an optional set of specifications that details how the connection    will be processed after it has been upgraded.     Registrations happen on a "First Come First Served" basis (see    [Section 4.1 of [RFC5226]](https://tools.ietf.org/html/rfc5226#section-4.1)) and are subject to the following rules:     1.  A protocol-name token, once registered, stays registered forever.     2.  The registration MUST name a responsible party for the        registration.     3.  The registration MUST name a point of contact.     4.  The registration MAY name a set of specifications associated with        that token.  Such specifications need not be publicly available.     5.  The registration SHOULD name a set of expected "protocol-version"        tokens associated with that token at the time of registration.      6.  The responsible party MAY change the registration at any time.        The IANA will keep a record of all such changes, and make them        available upon request.     7.  The IESG MAY reassign responsibility for a protocol token.  This        will normally only be used in the case when a responsible party        cannot be contacted.     This registration procedure for HTTP Upgrade Tokens replaces that    previously defined in [Section 7.2 of [RFC2817]](https://tools.ietf.org/html/rfc2817#section-7.2).

8.6.2 升级令牌注册

The "HTTP" entry in the upgrade token registry has been updated with    the registration below:     +-------+----------------------+----------------------+-------------+    | Value | Description          | Expected Version     | Reference   |    |       |                      | Tokens               |             |    +-------+----------------------+----------------------+-------------+    | HTTP  | Hypertext Transfer   | any DIGIT.DIGIT      | [Section 2.6](about:blank#section-2.6) |    |       | Protocol             | (e.g, "2.0")         |             |    +-------+----------------------+----------------------+-------------+     The responsible party is: "IETF (iesg@ietf.org) - Internet    Engineering Task Force".

9.安全考虑

This section is meant to inform developers, information providers,    and users of known security considerations relevant to HTTP message    syntax, parsing, and routing.  Security considerations about HTTP    semantics and payloads are addressed in [[RFC7231](https://tools.ietf.org/html/rfc7231)].

9.1 建立管理局

HTTP relies on the notion of an authoritative response: a response    that has been determined by (or at the direction of) the authority    identified within the target URI to be the most appropriate response    for that request given the state of the target resource at the time    of response message origination.  Providing a response from a    non-authoritative source, such as a shared cache, is often useful to    improve performance and availability, but only to the extent that the    source can be trusted or the distrusted response can be safely used.     Unfortunately, establishing authority can be difficult.  For example,    phishing is an attack on the user's perception of authority, where    that perception can be misled by presenting similar branding in      hypertext, possibly aided by userinfo obfuscating the authority    component (see [Section 2.7.1](about:blank#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](about:blank#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](https://tools.ietf.org/html/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](about:blank#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](https://tools.ietf.org/html/rfc2818)]).    Correctly implementing such verification can be difficult (see    [[Georgiev](about:blank#ref-Georgiev)]).

9.2 中介机构的风险

By their very nature, HTTP intermediaries are men-in-the-middle and,    thus, represent an opportunity for man-in-the-middle attacks.    Compromise of the systems on which the intermediaries run can result    in serious security and privacy problems.  Intermediaries might have    access to security-related information, personal information about    individual users and organizations, and proprietary information    belonging to users and content providers.  A compromised    intermediary, or an intermediary implemented or configured without    regard to security and privacy considerations, might be used in the    commission of a wide range of potential attacks.     Intermediaries that contain a shared cache are especially vulnerable    to cache poisoning attacks, as described in [Section 8 of [RFC7234]](https://tools.ietf.org/html/rfc7234#section-8).      Implementers need to consider the privacy and security implications    of their design and coding decisions, and of the configuration    options they provide to operators (especially the default    configuration).     Users need to be aware that intermediaries are no more trustworthy    than the people who run them; HTTP itself cannot solve this problem.

9.3 通过协议元素长度进行攻击

Because HTTP uses mostly textual, character-delimited fields, parsers    are often vulnerable to attacks based on sending very long (or very    slow) streams of data, particularly where an implementation is    expecting a protocol element with no predefined length.     To promote interoperability, specific recommendations are made for    minimum size limits on request-line ([Section 3.1.1](about:blank#section-3.1.1)) and header fields    ([Section 3.2](about:blank#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]](https://tools.ietf.org/html/rfc7231#section-6.5.12)) or a request payload that is too    large ([Section 6.5.11 of [RFC7231]](https://tools.ietf.org/html/rfc7231#section-6.5.11)).  Additional status codes related    to capacity limits have been defined by extensions to HTTP [[RFC6585](https://tools.ietf.org/html/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 响应分裂

Response splitting (a.k.a, CRLF injection) is a common technique,    used in various attacks on Web usage, that exploits the line-based    nature of HTTP message framing and the ordered association of    requests to responses on persistent connections [[Klein](about:blank#ref-Klein)].  This    technique can be particularly damaging when the requests pass through    a shared cache.     Response splitting exploits a vulnerability in servers (usually    within an application server) where an attacker can send encoded data    within some parameter of the request that is later decoded and echoed    within any of the response header fields of the response.  If the    decoded data is crafted to look like the response has ended and a      subsequent response has begun, the response has been split and the    content within the apparent second response is controlled by the    attacker.  The attacker can then make any other request on the same    persistent connection and trick the recipients (including    intermediaries) into believing that the second half of the split is    an authoritative answer to the second request.     For example, a parameter within the request-target might be read by    an application server and reused within a redirect, resulting in the    same parameter being echoed in the Location header field of the    response.  If the parameter is decoded by the application and not    properly encoded when placed in the response field, the attacker can    send encoded CRLF octets and other content that will make the    application's single response look like two or more responses.     A common defense against response splitting is to filter requests for    data that looks like encoded CR and LF (e.g., "%0D" and "%0A").    However, that assumes the application server is only performing URI    decoding, rather than more obscure data transformations like charset    transcoding, XML entity translation, base64 decoding, sprintf    reformatting, etc.  A more effective mitigation is to prevent    anything other than the server's core protocol libraries from sending    a CR or LF within the header section, which means restricting the    output of header fields to APIs that filter for bad octets and not    allowing application servers to write directly to the protocol    stream.

9.5 请求走私

Request smuggling ([[Linhart](about:blank#ref-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](about:blank#section-3.3.3), to reduce the effectiveness of request smuggling.

9.6 消息完整性

HTTP does not define a specific mechanism for ensuring message    integrity, instead relying on the error-detection ability of    underlying transport protocols and the use of length or    chunk-delimited framing to detect completeness.  Additional integrity    mechanisms, such as hash functions or digital signatures applied to    the content, can be selectively added to messages via extensible      metadata header fields.  Historically, the lack of a single integrity    mechanism has been justified by the informal nature of most HTTP    communication.  However, the prevalence of HTTP as an information    access mechanism has resulted in its increasing use within    environments where verification of message integrity is crucial.     User agents are encouraged to implement configurable means for    detecting and reporting failures of message integrity such that those    means can be enabled within environments for which integrity is    necessary.  For example, a browser being used to view medical history    or drug interaction information needs to indicate to the user when    such information is detected by the protocol to be incomplete,    expired, or corrupted during transfer.  Such mechanisms might be    selectively enabled via user agent extensions or the presence of    message integrity metadata in a response.  At a minimum, user agents    ought to provide some indication that allows a user to distinguish    between a complete and incomplete response message ([Section 3.4](about:blank#section-3.4)) when    such verification is desired.

9.7 消息机密性

HTTP relies on underlying transport protocols to provide message    confidentiality when that is desired.  HTTP has been specifically    designed to be independent of the transport protocol, such that it    can be used over many different forms of encrypted connection, with    the selection of such transports being identified by the choice of    URI scheme or within user agent configuration.     The "https" scheme can be used to identify resources that require a    confidential connection, as described in [Section 2.7.2](about:blank#section-2.7.2).

9.8 服务器日志信息的隐私

A server is in the position to save personal data about a user's    requests over time, which might identify their reading patterns or    subjects of interest.  In particular, log information gathered at an    intermediary often contains a history of user agent interaction,    across a multitude of sites, that can be traced to individual users.     HTTP log information is confidential in nature; its handling is often    constrained by laws and regulations.  Log information needs to be    securely stored and appropriate guidelines followed for its analysis.    Anonymization of personal information within individual entries    helps, but it is generally not sufficient to prevent real log traces    from being re-identified based on correlation with other access    characteristics.  As such, access traces that are keyed to a specific    client are unsafe to publish even if the key is pseudonymous.      To minimize the risk of theft or accidental publication, log    information ought to be purged of personally identifiable    information, including user identifiers, IP addresses, and    user-provided query parameters, as soon as that information is no    longer necessary to support operational needs for security, auditing,    or fraud control.

10.致谢

This edition of HTTP/1.1 builds on the many contributions that went    into [RFC 1945](https://tools.ietf.org/html/rfc1945), [RFC 2068](https://tools.ietf.org/html/rfc2068), [RFC 2145](https://tools.ietf.org/html/rfc2145), and [RFC 2616](https://tools.ietf.org/html/rfc2616), 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      Lokier, Jan Algermissen, Jari Arkko, Jeff Hodges (who came up with    the term 'effective Request-URI'), Jeff Pinner, Jeff Walden, Jim    Luther, Jitu Padhye, Joe D. Williams, Joe Gregorio, Joe Orton, Joel    Jaeggli, John C. Klensin, John C. Mallery, John Cowan, John Kemp,    John Panzer, John Schneider, John Stracke, John Sullivan, Jonas    Sicking, Jonathan A. Rees, Jonathan Billington, Jonathan Moore,    Jonathan Silvera, Jordi Ros, Joris Dobbelsteen, Josh Cohen, Julien    Pierre, Jungshik Shin, Justin Chapweske, Justin Erenkrantz, Justin    James, Kalvinder Singh, Karl Dubost, Kathleen Moriarty, Keith    Hoffman, Keith Moore, Ken Murchison, Koen Holtman, Konstantin    Voronkov, Kris Zyp, Leif Hedstrom, Lionel Morand, Lisa Dusseault,    Maciej Stachowiak, Manu Sporny, Marc Schneider, Marc Slemko, Mark    Baker, Mark Pauley, Mark Watson, Markus Isomaki, Markus Lanthaler,    Martin J. Duerst, Martin Musatov, Martin Nilsson, Martin Thomson,    Matt Lynch, Matthew Cox, Matthew Kerwin, Max Clark, Menachem Dodge,    Meral Shirazipour, Michael Burrows, Michael Hausenblas, Michael    Scharf, Michael Sweet, Michael Tuexen, Michael Welzl, Mike Amundsen,    Mike Belshe, Mike Bishop, Mike Kelly, Mike Schinkel, Miles Sabin,    Murray S. Kucherawy, Mykyta Yevstifeyev, Nathan Rixham, Nicholas    Shanks, Nico Williams, Nicolas Alvarez, Nicolas Mailhot, Noah Slater,    Osama Mazahir, Pablo Castro, Pat Hayes, Patrick R. McManus, Paul E.    Jones, Paul Hoffman, Paul Marquess, Pete Resnick, Peter Lepeska,    Peter Occil, Peter Saint-Andre, Peter Watkins, Phil Archer, Phil    Hunt, Philippe Mougin, Phillip Hallam-Baker, Piotr Dobrogost, Poul-    Henning Kamp, Preethi Natarajan, Rajeev Bector, Ray Polk, Reto    Bachmann-Gmuer, Richard Barnes, Richard Cyganiak, Rob Trace, Robby    Simpson, Robert Brewer, Robert Collins, Robert Mattson, Robert    O'Callahan, Robert Olofsson, Robert Sayre, Robert Siemer, Robert de    Wilde, Roberto Javier Godoy, Roberto Peon, Roland Zink, Ronny    Widjaja, Ryan Hamilton, S. Mike Dierken, Salvatore Loreto, Sam    Johnston, Sam Pullara, Sam Ruby, Saurabh Kulkarni, Scott Lawrence    (who maintained the original issues list), Sean B. Palmer, Sean    Turner, Sebastien Barnoud, Shane McCarron, Shigeki Ohtsu, Simon    Yarde, Stefan Eissing, Stefan Tilkov, Stefanos Harhalakis, Stephane    Bortzmeyer, Stephen Farrell, Stephen Kent, Stephen Ludin, Stuart    Williams, Subbu Allamaraju, Subramanian Moonesamy, Susan Hares,    Sylvain Hellegouarch, Tapan Divekar, Tatsuhiro Tsujikawa, Tatsuya    Hayashi, Ted Hardie, Ted Lemon, Thomas Broyer, Thomas Fossati, Thomas    Maslen, Thomas Nadeau, Thomas Nordin, Thomas Roessler, Tim Bray, Tim    Morgan, Tim Olsen, Tom Zhou, Travis Snoozy, Tyler Close, Vincent    Murphy, Wenbo Zhu, Werner Baumann, Wilbur Streett, Wilfredo Sanchez    Vega, William A. Rowe Jr., William Chan, Willy Tarreau, Xiaoshu Wang,    Yaron Goland, Yngve Nysaeter Pettersen, Yoav Nir, Yogesh Bang,    Yuchung Cheng, Yutaka Oiwa, Yves Lafon (long-time member of the    editor team), Zed A. Shaw, and Zhong Yu.     See [Section 16 of [RFC2616]](https://tools.ietf.org/html/rfc2616#section-16) for additional acknowledgements from    prior revisions.

11.参考文献

11.1 规范性参考文献

[[RFC0793]()]     Postel, J., "Transmission Control Protocol", STD 7,                  [RFC 793](https://tools.ietf.org/html/rfc793), September 1981.     [[RFC1950]()]     Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data                  Format Specification version 3.3", [RFC 1950](https://tools.ietf.org/html/rfc1950), May 1996.     [[RFC1951]()]     Deutsch, P., "DEFLATE Compressed Data Format                  Specification version 1.3", [RFC 1951](https://tools.ietf.org/html/rfc1951), May 1996.     [[RFC1952]()]     Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and                  G. Randers-Pehrson, "GZIP file format specification                  version 4.3", [RFC 1952](https://tools.ietf.org/html/rfc1952), May 1996.     [[RFC2119]()]     Bradner, S., "Key words for use in RFCs to Indicate                  Requirement Levels", [BCP 14](https://tools.ietf.org/html/bcp14), [RFC 2119](https://tools.ietf.org/html/rfc2119), March 1997.     [[RFC3986]()]     Berners-Lee, T., Fielding, R., and L. Masinter,                  "Uniform Resource Identifier (URI): Generic Syntax",                  STD 66, [RFC 3986](https://tools.ietf.org/html/rfc3986), January 2005.     [[RFC5234]()]     Crocker, D., Ed. and P. Overell, "Augmented BNF for                  Syntax Specifications: ABNF", STD 68, [RFC 5234](https://tools.ietf.org/html/rfc5234),                  January 2008.     [[RFC7231]()]     Fielding, R., Ed. and J. Reschke, Ed., "Hypertext                  Transfer Protocol (HTTP/1.1): Semantics and Content",                  [RFC 7231](https://tools.ietf.org/html/rfc7231), June 2014.     [[RFC7232]()]     Fielding, R., Ed. and J. Reschke, Ed., "Hypertext                  Transfer Protocol (HTTP/1.1): Conditional Requests",                  [RFC 7232](https://tools.ietf.org/html/rfc7232), June 2014.     [[RFC7233]()]     Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,                  "Hypertext Transfer Protocol (HTTP/1.1): Range                  Requests", [RFC 7233](https://tools.ietf.org/html/rfc7233), June 2014.     [[RFC7234]()]     Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,                  Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",                  [RFC 7234](https://tools.ietf.org/html/rfc7234), June 2014.     [[RFC7235]()]     Fielding, R., Ed. and J. Reschke, Ed., "Hypertext                  Transfer Protocol (HTTP/1.1): Authentication",                  [RFC 7235](https://tools.ietf.org/html/rfc7235), June 2014.      [[USASCII]()]     American National Standards Institute, "Coded Character                  Set -- 7-bit American Standard Code for Information                  Interchange", ANSI X3.4, 1986.     [[Welch]()]       Welch, T., "A Technique for High-Performance Data                  Compression", IEEE Computer 17(6), June 1984.

11.2 信息性参考

[[BCP115]()]      Hansen, T., Hardie, T., and L. Masinter, "Guidelines                  and Registration Procedures for New URI Schemes",                  [BCP 115](https://tools.ietf.org/html/bcp115), [RFC 4395](https://tools.ietf.org/html/rfc4395), February 2006.     [[BCP13]()]       Freed, N., Klensin, J., and T. Hansen, "Media Type                  Specifications and Registration Procedures", [BCP 13](https://tools.ietf.org/html/bcp13),                  [RFC 6838](https://tools.ietf.org/html/rfc6838), January 2013.     [[BCP90]()]       Klyne, G., Nottingham, M., and J. Mogul, "Registration                  Procedures for Message Header Fields", [BCP 90](https://tools.ietf.org/html/bcp90),                  [RFC 3864](https://tools.ietf.org/html/rfc3864), September 2004.     [[Georgiev]()]    Georgiev, M., Iyengar, S., Jana, S., Anubhai, R.,                  Boneh, D., and V. Shmatikov, "The Most Dangerous Code                  in the World: Validating SSL Certificates in Non-                  browser Software", In Proceedings of the 2012 ACM                  Conference on Computer and Communications Security (CCS                  '12), pp. 38-49, October 2012,                  <[http://doi.acm.org/10.1145/2382196.2382204](http://doi.acm.org/10.1145/2382196.2382204)>.     [[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.     [[Klein]()]       Klein, A., "Divide and Conquer - HTTP Response                  Splitting, Web Cache Poisoning Attacks, and Related                  Topics", March 2004, <[http://packetstormsecurity.com/](http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf) [papers/general/whitepaper\_httpresponse.pdf](http://packetstormsecurity.com/papers/general/whitepaper_httpresponse.pdf)>.     [[Kri2001]()]     Kristol, D., "HTTP Cookies: Standards, Privacy, and                  Politics", ACM Transactions on Internet                  Technology 1(2), November 2001,                  <[http://arxiv.org/abs/cs.SE/0105018](http://arxiv.org/abs/cs.SE/0105018)>.     [[Linhart]()]     Linhart, C., Klein, A., Heled, R., and S. Orrin, "HTTP                  Request Smuggling", June 2005,                  <[http://www.watchfire.com/news/whitepapers.aspx](http://www.watchfire.com/news/whitepapers.aspx)>.      [[RFC1919]()]     Chatel, M., "Classical versus Transparent IP Proxies",                  [RFC 1919](https://tools.ietf.org/html/rfc1919), March 1996.     [[RFC1945]()]     Berners-Lee, T., Fielding, R., and H. Nielsen,                  "Hypertext Transfer Protocol -- HTTP/1.0", [RFC 1945](https://tools.ietf.org/html/rfc1945),                  May 1996.     [[RFC2045]()]     Freed, N. and N. Borenstein, "Multipurpose Internet                  Mail Extensions (MIME) Part One: Format of Internet                  Message Bodies", [RFC 2045](https://tools.ietf.org/html/rfc2045), November 1996.     [[RFC2047]()]     Moore, K., "MIME (Multipurpose Internet Mail                  Extensions) Part Three: Message Header Extensions for                  Non-ASCII Text", [RFC 2047](https://tools.ietf.org/html/rfc2047), November 1996.     [[RFC2068]()]     Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and                  T. Berners-Lee, "Hypertext Transfer Protocol --                  HTTP/1.1", [RFC 2068](https://tools.ietf.org/html/rfc2068), January 1997.     [[RFC2145]()]     Mogul, J., Fielding, R., Gettys, J., and H. Nielsen,                  "Use and Interpretation of HTTP Version Numbers",                  [RFC 2145](https://tools.ietf.org/html/rfc2145), May 1997.     [[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](https://tools.ietf.org/html/rfc2616), June 1999.     [[RFC2817]()]     Khare, R. and S. Lawrence, "Upgrading to TLS Within                  HTTP/1.1", [RFC 2817](https://tools.ietf.org/html/rfc2817), May 2000.     [[RFC2818]()]     Rescorla, E., "HTTP Over TLS", [RFC 2818](https://tools.ietf.org/html/rfc2818), May 2000.     [[RFC3040]()]     Cooper, I., Melve, I., and G. Tomlinson, "Internet Web                  Replication and Caching Taxonomy", [RFC 3040](https://tools.ietf.org/html/rfc3040),                  January 2001.     [[RFC4033]()]     Arends, R., Austein, R., Larson, M., Massey, D., and S.                  Rose, "DNS Security Introduction and Requirements",                  [RFC 4033](https://tools.ietf.org/html/rfc4033), March 2005.     [[RFC4559]()]     Jaganathan, K., Zhu, L., and J. Brezak, "SPNEGO-based                  Kerberos and NTLM HTTP Authentication in Microsoft                  Windows", [RFC 4559](https://tools.ietf.org/html/rfc4559), June 2006.     [[RFC5226]()]     Narten, T. and H. Alvestrand, "Guidelines for Writing                  an IANA Considerations Section in RFCs", [BCP 26](https://tools.ietf.org/html/bcp26),                  [RFC 5226](https://tools.ietf.org/html/rfc5226), May 2008.      [[RFC5246]()]     Dierks, T. and E. Rescorla, "The Transport Layer                  Security (TLS) Protocol Version 1.2", [RFC 5246](https://tools.ietf.org/html/rfc5246),                  August 2008.     [[RFC5322]()]     Resnick, P., "Internet Message Format", [RFC 5322](https://tools.ietf.org/html/rfc5322),                  October 2008.     [[RFC6265]()]     Barth, A., "HTTP State Management Mechanism", [RFC 6265](https://tools.ietf.org/html/rfc6265),                  April 2011.     [[RFC6585]()]     Nottingham, M. and R. Fielding, "Additional HTTP Status                  Codes", [RFC 6585](https://tools.ietf.org/html/rfc6585), April 2012.

附录A. HTTP版本历史

HTTP has been in use since 1990.  The first version, later referred    to as HTTP/0.9, was a simple protocol for hypertext data transfer    across the Internet, using only a single request method (GET) and no    metadata.  HTTP/1.0, as defined by [[RFC1945](https://tools.ietf.org/html/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 来自HTTP / 1.0的更改

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

A.1.1 多宿主Web服务器

The requirements that clients and servers support the Host header    field ([Section 5.4](about:blank#section-5.4)), report an error if it is missing from an    HTTP/1.1 request, and accept absolute URIs ([Section 5.3](about:blank#section-5.3)) are among    the most important changes defined by HTTP/1.1.      Older HTTP/1.0 clients assumed a one-to-one relationship of IP    addresses and servers; there was no other established mechanism for    distinguishing the intended server of a request than the IP address    to which that request was directed.  The Host header field was    introduced during the development of HTTP/1.1 and, though it was    quickly implemented by most HTTP/1.0 browsers, additional    requirements were placed on all HTTP/1.1 requests in order to ensure    complete adoption.  At the time of this writing, most HTTP-based    services are dependent upon the Host header field for targeting    requests.

A.1.2 保持连接

In HTTP/1.0, each connection is established by the client prior to    the request and closed by the server after sending the response.    However, some implementations implement the explicitly negotiated    ("Keep-Alive") version of persistent connections described in [Section](https://tools.ietf.org/html/rfc2068#section-19.7.1) [19.7.1 of [RFC2068]](https://tools.ietf.org/html/rfc2068#section-19.7.1).     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 传输编码介绍

HTTP/1.1 introduces the Transfer-Encoding header field    ([Section 3.3.1](about:blank#section-3.3.1)).  Transfer codings need to be decoded prior to    forwarding an HTTP message over a MIME-compliant protocol.

A2 RFC 2616的变化

HTTP's approach to error handling has been explained.  ([Section 2.5](about:blank#section-2.5))     The HTTP-version ABNF production has been clarified to be case-    sensitive.  Additionally, version numbers have been restricted to    single digits, due to the fact that implementations are known to    handle multi-digit version numbers incorrectly.  ([Section 2.6](about:blank#section-2.6))     Userinfo (i.e., username and password) are now disallowed in HTTP and    HTTPS URIs, because of security issues related to their transmission    on the wire.  ([Section 2.7.1](about:blank#section-2.7.1))     The HTTPS URI scheme is now defined by this specification;    previously, it was done in [Section 2.4 of [RFC2818]](https://tools.ietf.org/html/rfc2818#section-2.4).  Furthermore, it    implies end-to-end security.  ([Section 2.7.2](about:blank#section-2.7.2))     HTTP messages can be (and often are) buffered by implementations;    despite it sometimes being available as a stream, HTTP is    fundamentally a message-oriented protocol.  Minimum supported sizes    for various protocol elements have been suggested, to improve    interoperability.  ([Section 3](about:blank#section-3))     Invalid whitespace around field-names is now required to be rejected,    because accepting it represents a security vulnerability.  The ABNF    productions defining header fields now only list the field value.    ([Section 3.2](about:blank#section-3.2))     Rules about implicit linear whitespace between certain grammar    productions have been removed; now whitespace is only allowed where    specifically defined in the ABNF.  ([Section 3.2.3](about:blank#section-3.2.3))     Header fields that span multiple lines ("line folding") are    deprecated.  ([Section 3.2.4](about:blank#section-3.2.4))     The NUL octet is no longer allowed in comment and quoted-string text,    and handling of backslash-escaping in them has been clarified.  The    quoted-pair rule no longer allows escaping control characters other    than HTAB.  Non-US-ASCII content in header fields and the reason    phrase has been obsoleted and made opaque (the TEXT rule was    removed).  ([Section 3.2.6](about:blank#section-3.2.6))     Bogus Content-Length header fields are now required to be handled as    errors by recipients.  ([Section 3.3.2](about:blank#section-3.3.2))     The algorithm for determining the message body length has been    clarified to indicate all of the special cases (e.g., driven by    methods or status codes) that affect it, and that new protocol      elements cannot define such special cases.  CONNECT is a new, special    case in determining message body length. "multipart/byteranges" is no    longer a way of determining message body length detection.    ([Section 3.3.3](about:blank#section-3.3.3))     The "identity" transfer coding token has been removed.  (Sections [3.3](about:blank#section-3.3)    and 4)     Chunk length does not include the count of the octets in the chunk    header and trailer.  Line folding in chunk extensions is disallowed.    ([Section 4.1](about:blank#section-4.1))     The meaning of the "deflate" content coding has been clarified.    ([Section 4.2.2](about:blank#section-4.2.2))     The segment + query components of [RFC 3986](https://tools.ietf.org/html/rfc3986) have been used to define    the request-target, instead of abs\_path from [RFC 1808](https://tools.ietf.org/html/rfc1808).  The    asterisk-form of the request-target is only allowed with the OPTIONS    method.  ([Section 5.3](about:blank#section-5.3))     The term "Effective Request URI" has been introduced.  ([Section 5.5](about:blank#section-5.5))     Gateways do not need to generate Via header fields anymore.    ([Section 5.7.1](about:blank#section-5.7.1))     Exactly when "close" connection options have to be sent has been    clarified.  Also, "hop-by-hop" header fields are required to appear    in the Connection header field; just because they're defined as hop-    by-hop in this specification doesn't exempt them.  ([Section 6.1](about:blank#section-6.1))     The limit of two connections per server has been removed.  An    idempotent sequence of requests is no longer required to be retried.    The requirement to retry requests under certain circumstances when    the server prematurely closes the connection has been removed.  Also,    some extraneous requirements about when servers are allowed to close    connections prematurely have been removed.  ([Section 6.3](about:blank#section-6.3))     The semantics of the Upgrade header field is now defined in responses    other than 101 (this was incorporated from [[RFC2817](https://tools.ietf.org/html/rfc2817)]).  Furthermore,    the ordering in the field value is now significant.  ([Section 6.7](about:blank#section-6.7))     Empty list elements in list productions (e.g., a list header field    containing ", ,") have been deprecated.  ([Section 7](about:blank#section-7))     Registration of Transfer Codings now requires IETF Review    ([Section 8.4](about:blank#section-8.4))      This specification now defines the Upgrade Token Registry, previously    defined in [Section 7.2 of [RFC2817]](https://tools.ietf.org/html/rfc2817#section-7.2).  ([Section 8.6](about:blank#section-8.6))     The expectation to support HTTP/0.9 requests has been removed.    (Appendix A)     Issues with the Keep-Alive and Proxy-Connection header fields in    requests are pointed out, with use of the latter being discouraged    altogether.  (Appendix A.1.2)

附录B.收集的ABNF

BWS = OWS     Connection = \*( "," OWS ) connection-option \*( OWS "," [ OWS     connection-option ] )     Content-Length = 1\*DIGIT     HTTP-message = start-line \*( header-field CRLF ) CRLF [ message-body     ]    HTTP-name = %x48.54.54.50 ; HTTP    HTTP-version = HTTP-name "/" DIGIT "." DIGIT    Host = uri-host [ ":" port ]     OWS = \*( SP / HTAB )     RWS = 1\*( SP / HTAB )     TE = [ ( "," / t-codings ) \*( OWS "," [ OWS t-codings ] ) ]    Trailer = \*( "," OWS ) field-name \*( OWS "," [ OWS field-name ] )    Transfer-Encoding = \*( "," OWS ) transfer-coding \*( OWS "," [ OWS     transfer-coding ] )     URI-reference = <URI-reference, see [[RFC3986], Section 4.1](https://tools.ietf.org/html/rfc3986#section-4.1)>    Upgrade = \*( "," OWS ) protocol \*( OWS "," [ OWS protocol ] )     Via = \*( "," OWS ) ( received-protocol RWS received-by [ RWS comment     ] ) \*( OWS "," [ OWS ( received-protocol RWS received-by [ RWS     comment ] ) ] )     absolute-URI = <absolute-URI, see [[RFC3986], Section 4.3](https://tools.ietf.org/html/rfc3986#section-4.3)>    absolute-form = absolute-URI    absolute-path = 1\*( "/" segment )    asterisk-form = "\*"    authority = <authority, see [[RFC3986], Section 3.2](https://tools.ietf.org/html/rfc3986#section-3.2)>    authority-form = authority      chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF    chunk-data = 1\*OCTET    chunk-ext = \*( ";" chunk-ext-name [ "=" chunk-ext-val ] )    chunk-ext-name = token    chunk-ext-val = token / quoted-string    chunk-size = 1\*HEXDIG    chunked-body = \*chunk last-chunk trailer-part CRLF    comment = "(" \*( ctext / quoted-pair / comment ) ")"    connection-option = token    ctext = HTAB / SP / %x21-27 ; '!'-'''     / %x2A-5B ; '\*'-'['     / %x5D-7E ; ']'-'~'     / obs-text     field-content = field-vchar [ 1\*( SP / HTAB ) field-vchar ]    field-name = token    field-value = \*( field-content / obs-fold )    field-vchar = VCHAR / obs-text    fragment = <fragment, see [[RFC3986], Section 3.5](https://tools.ietf.org/html/rfc3986#section-3.5)>     header-field = field-name ":" OWS field-value OWS    http-URI = "http://" authority path-abempty [ "?" query ] [ "#"     fragment ]    https-URI = "https://" authority path-abempty [ "?" query ] [ "#"     fragment ]     last-chunk = 1\*"0" [ chunk-ext ] CRLF     message-body = \*OCTET    method = token     obs-fold = CRLF 1\*( SP / HTAB )    obs-text = %x80-FF    origin-form = absolute-path [ "?" query ]     partial-URI = relative-part [ "?" query ]    path-abempty = <path-abempty, see [[RFC3986], Section 3.3](https://tools.ietf.org/html/rfc3986#section-3.3)>    port = <port, see [[RFC3986], Section 3.2.3](https://tools.ietf.org/html/rfc3986#section-3.2.3)>    protocol = protocol-name [ "/" protocol-version ]    protocol-name = token    protocol-version = token    pseudonym = token     qdtext = HTAB / SP / "!" / %x23-5B ; '#'-'['     / %x5D-7E ; ']'-'~'     / obs-text    query = <query, see [[RFC3986], Section 3.4](https://tools.ietf.org/html/rfc3986#section-3.4)>    quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )      quoted-string = DQUOTE \*( qdtext / quoted-pair ) DQUOTE     rank = ( "0" [ "." \*3DIGIT ] ) / ( "1" [ "." \*3"0" ] )    reason-phrase = \*( HTAB / SP / VCHAR / obs-text )    received-by = ( uri-host [ ":" port ] ) / pseudonym    received-protocol = [ protocol-name "/" ] protocol-version    relative-part = <relative-part, see [[RFC3986], Section 4.2](https://tools.ietf.org/html/rfc3986#section-4.2)>    request-line = method SP request-target SP HTTP-version CRLF    request-target = origin-form / absolute-form / authority-form /     asterisk-form     scheme = <scheme, see [[RFC3986], Section 3.1](https://tools.ietf.org/html/rfc3986#section-3.1)>    segment = <segment, see [[RFC3986], Section 3.3](https://tools.ietf.org/html/rfc3986#section-3.3)>    start-line = request-line / status-line    status-code = 3DIGIT    status-line = HTTP-version SP status-code SP reason-phrase CRLF     t-codings = "trailers" / ( transfer-coding [ t-ranking ] )    t-ranking = OWS ";" OWS "q=" rank    tchar = "!" / "#" / "$" / "%" / "&" / "'" / "\*" / "+" / "-" / "." /     "^" / "\_" / "`" / "|" / "~" / DIGIT / ALPHA    token = 1\*tchar    trailer-part = \*( header-field CRLF )    transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /     transfer-extension    transfer-extension = token \*( OWS ";" OWS transfer-parameter )    transfer-parameter = token BWS "=" BWS ( token / quoted-string )     uri-host = <host, see [[RFC3986], Section 3.2.2](https://tools.ietf.org/html/rfc3986#section-3.2.2)>   Index     A       absolute-form (of request-target)  42       accelerator  10       application/http Media Type  63       asterisk-form (of request-target)  43       authoritative response  67       authority-form (of request-target)  42-43     B       browser  7     C       cache  11       cacheable  12       captive portal  11       chunked (Coding Format)  28, 32, 36       client  7       close  51, 56       compress (Coding Format)  38       connection  7       Connection header field  51, 56       Content-Length header field  30     D       deflate (Coding Format)  38       Delimiters  27       downstream  10     E       effective request URI  45     G       gateway  10       Grammar          absolute-form  42          absolute-path  16          absolute-URI  16          ALPHA  6          asterisk-form  41, 43          authority  16          authority-form  42-43          BWS  25          chunk  36          chunk-data  36          chunk-ext  36          chunk-ext-name  36            chunk-ext-val  36          chunk-size  36          chunked-body  36          comment  27          Connection  51          connection-option  51          Content-Length  30          CR  6          CRLF  6          ctext  27          CTL  6          DIGIT  6          DQUOTE  6          field-content  23          field-name  23, 40          field-value  23          field-vchar  23          fragment  16          header-field  23, 37          HEXDIG  6          Host  44          HTAB  6          HTTP-message  19          HTTP-name  14          http-URI  17          HTTP-version  14          https-URI  18          last-chunk  36          LF  6          message-body  28          method  21          obs-fold  23          obs-text  27          OCTET  6          origin-form  42          OWS  25          partial-URI  16          port  16          protocol-name  47          protocol-version  47          pseudonym  47          qdtext  27          query  16          quoted-pair  27          quoted-string  27          rank  39          reason-phrase  22          received-by  47            received-protocol  47          request-line  21          request-target  41          RWS  25          scheme  16          segment  16          SP  6          start-line  21          status-code  22          status-line  22          t-codings  39          t-ranking  39          tchar  27          TE  39          token  27          Trailer  40          trailer-part  37          transfer-coding  35          Transfer-Encoding  28          transfer-extension  35          transfer-parameter  35          Upgrade  57          uri-host  16          URI-reference  16          VCHAR  6          Via  47       gzip (Coding Format)  39     H       header field  19       header section  19       headers  19       Host header field  44       http URI scheme  17       https URI scheme  17    I       inbound  9       interception proxy  11       intermediary  9     M       Media Type          application/http  63          message/http  62       message  7       message/http Media Type  62       method  21      N       non-transforming proxy  49     O       origin server  7       origin-form (of request-target)  42       outbound  10     P       phishing  67       proxy  10     R       recipient  7       request  7       request-target  21       resource  16       response  7       reverse proxy  10     S       sender  7       server  7       spider  7     T       target resource  40       target URI  40       TE header field  39       Trailer header field  40       Transfer-Encoding header field  28       transforming proxy  49       transparent proxy  11       tunnel  10     U       Upgrade header field  57       upstream  9       URI scheme          http  17          https  17       user agent  7     V       Via header field  47   Authors' Addresses     Roy T. Fielding (editor)    Adobe Systems Incorporated    345 Park Ave    San Jose, CA  95110    USA     EMail: fielding@gbiv.com    URI:   [http://roy.gbiv.com/](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/](http://greenbytes.de/tech/webdav/)   Fielding & Reschke           Standards Track                   [Page 89]

	RFC 7230: Message Syntax and Routing
	RFC 7230: Message Syntax and Routing	详细

HTTP

超文本传输协议（ HTTP，HyperText Transfer Protocol ) 是互联网上应用最为广泛的一种网络协议。所有的 WWW 文件都必须遵守这个标准。

HTTP目录

1.指南 \| Guides
2.指南：基础 \| Guides: Basics
3.CSP
4.标题 \| Headers
5.方法 \| Methods
6.RFC 2616: HTTP/1.1
7.RFC 4918: WebDAV
8.RFC 5023: The Atom Publishing Protocol
9.RFC 7230: Message Syntax and Routing
10.RFC 7231: Semantics and Content
11.RFC 7232: Conditional Requests
12.RFC 7233: Range Requests
13.RFC 7234: Caching
14.RFC 7235: Authentication
15.状态 \| Status
16.HTTP 请求方法
17.HTTP状态码
18.HTTP 响应头信息
19.HTTP 教程