📄 rfc2616.ps
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( age) s5 517 M( The age of a response is the time since it was sent by, or) s5 504 M( successfully validated with, the origin server.) s5 478 M( freshness lifetime) s5 465 M( The length of time between the generation of a response and its) s5 452 M( expiration time.) s5 426 M( fresh) s5 413 M( A response is fresh if its age has not yet exceeded its freshness) s5 400 M( lifetime.) s5 374 M( stale) s5 361 M( A response is stale if its age has passed its freshness lifetime.) s5 335 M( semantically transparent) s5 322 M( A cache behaves in a "semantically transparent" manner, with) s5 309 M( respect to a particular response, when its use affects neither the) s5 296 M( requesting client nor the origin server, except to improve) s5 283 M( performance. When a cache is semantically transparent, the client) s5 270 M( receives exactly the same response \(except for hop-by-hop headers\)) s5 257 M( that it would have received had its request been handled directly) s5 244 M( by the origin server.) s5 218 M( validator) s5 205 M( A protocol element \(e.g., an entity tag or a Last-Modified time\)) s5 192 M( that is used to find out whether a cache entry is an equivalent) s5 179 M( copy of an entity.) s5 153 M( upstream/downstream) s5 140 M( Upstream and downstream describe the flow of a message: all) s5 127 M( messages flow from upstream to downstream.) s5 49 M(Fielding, et al. Standards Track [Page 11]) s_RS%%Page: (12) 12%%BeginPageSetup_S24 24 translate/pagenum 12 def/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc2616.txt) def/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def/ftail (rfc2616.txt) def% User defined strings:/fmodstr (Fri Jun 11 11:46:00 1999) def/pagenumstr (12) def/user_header_p true def/user_header_left_str (RFC2616) def/user_header_center_str (RFC.net) def/user_header_right_str (Page 12 of 177) def%%EndPageSetupdo_header5 751 M(RFC 2616 HTTP/1.1 June 1999) s5 712 M( inbound/outbound) s5 699 M( Inbound and outbound refer to the request and response paths for) s5 686 M( messages: "inbound" means "traveling toward the origin server",) s5 673 M( and "outbound" means "traveling toward the user agent") s5 647 M(1.4 Overall Operation) s5 621 M( The HTTP protocol is a request/response protocol. A client sends a) s5 608 M( request to the server in the form of a request method, URI, and) s5 595 M( protocol version, followed by a MIME-like message containing request) s5 582 M( modifiers, client information, and possible body content over a) s5 569 M( connection with a server. The server responds with a status line,) s5 556 M( including the message's protocol version and a success or error code,) s5 543 M( followed by a MIME-like message containing server information, entity) s5 530 M( metainformation, and possible entity-body content. The relationship) s5 517 M( between HTTP and MIME is described in appendix 19.4.) s5 491 M( Most HTTP communication is initiated by a user agent and consists of) s5 478 M( a request to be applied to a resource on some origin server. In the) s5 465 M( simplest case, this may be accomplished via a single connection \(v\)) s5 452 M( between the user agent \(UA\) and the origin server \(O\).) s5 426 M( request chain ------------------------>) s5 413 M( UA -------------------v------------------- O) s5 400 M( <----------------------- response chain) s5 374 M( A more complicated situation occurs when one or more intermediaries) s5 361 M( are present in the request/response chain. There are three common) s5 348 M( forms of intermediary: proxy, gateway, and tunnel. A proxy is a) s5 335 M( forwarding agent, receiving requests for a URI in its absolute form,) s5 322 M( rewriting all or part of the message, and forwarding the reformatted) s5 309 M( request toward the server identified by the URI. A gateway is a) s5 296 M( receiving agent, acting as a layer above some other server\(s\) and, if) s5 283 M( necessary, translating the requests to the underlying server's) s5 270 M( protocol. A tunnel acts as a relay point between two connections) s5 257 M( without changing the messages; tunnels are used when the) s5 244 M( communication needs to pass through an intermediary \(such as a) s5 231 M( firewall\) even when the intermediary cannot understand the contents) s5 218 M( of the messages.) s5 192 M( request chain -------------------------------------->) s5 179 M( UA -----v----- A -----v----- B -----v----- C -----v----- O) s5 166 M( <------------------------------------- response chain) s5 140 M( The figure above shows three intermediaries \(A, B, and C\) between the) s5 127 M( user agent and origin server. A request or response message that) s5 114 M( travels the whole chain will pass through four separate connections.) s5 101 M( This distinction is important because some HTTP communication options) s5 49 M(Fielding, et al. Standards Track [Page 12]) s_RS%%Page: (13) 13%%BeginPageSetup_S24 24 translate/pagenum 13 def/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc2616.txt) def/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def/ftail (rfc2616.txt) def% User defined strings:/fmodstr (Fri Jun 11 11:46:00 1999) def/pagenumstr (13) def/user_header_p true def/user_header_left_str (RFC2616) def/user_header_center_str (RFC.net) def/user_header_right_str (Page 13 of 177) def%%EndPageSetupdo_header5 751 M(RFC 2616 HTTP/1.1 June 1999) s5 712 M( may apply only to the connection with the nearest, non-tunnel) s5 699 M( neighbor, only to the end-points of the chain, or to all connections) s5 686 M( along the chain. Although the diagram is linear, each participant may) s5 673 M( be engaged in multiple, simultaneous communications. For example, B) s5 660 M( may be receiving requests from many clients other than A, and/or) s5 647 M( forwarding requests to servers other than C, at the same time that it) s5 634 M( is handling A's request.) s5 608 M( Any party to the communication which is not acting as a tunnel may) s5 595 M( employ an internal cache for handling requests. The effect of a cache) s5 582 M( is that the request/response chain is shortened if one of the) s5 569 M( participants along the chain has a cached response applicable to that) s5 556 M( request. The following illustrates the resulting chain if B has a) s5 543 M( cached copy of an earlier response from O \(via C\) for a request which) s5 530 M( has not been cached by UA or A.) s5 504 M( request chain ---------->) s5 491 M( UA -----v----- A -----v----- B - - - - - - C - - - - - - O) s5 478 M( <--------- response chain) s5 452 M( Not all responses are usefully cacheable, and some requests may) s5 439 M( contain modifiers which place special requirements on cache behavior.) s5 426 M( HTTP requirements for cache behavior and cacheable responses are) s5 413 M( defined in section 13.) s5 387 M( In fact, there are a wide variety of architectures and configurations) s5 374 M( of caches and proxies currently being experimented with or deployed) s5 361 M( across the World Wide Web. These systems include national hierarchies) s5 348 M( of proxy caches to save transoceanic bandwidth, systems that) s5 335 M( broadcast or multicast cache entries, organizations that distribute) s5 322 M( subsets of cached data via CD-ROM, and so on. HTTP systems are used) s5 309 M( in corporate intranets over high-bandwidth links, and for access via) s5 296 M( PDAs with low-power radio links and intermittent connectivity. The) s5 283 M( goal of HTTP/1.1 is to support the wide diversity of configurations) s5 270 M( already deployed while introducing protocol constructs that meet the) s5 257 M( needs of those who build web applications that require high) s5 244 M( reliability and, failing that, at least reliable indications of) s5 231 M( failure.) s5 205 M( HTTP communication usually takes place over TCP/IP connections. The) s5 192 M( default port is TCP 80 [19], but other ports can be used. This does) s5 179 M( not preclude HTTP from being implemented on top of any other protocol) s5 166 M( on the Internet, or on other networks. HTTP only presumes a reliable) s5 153 M( transport; any protocol that provides such guarantees can be used;) s5 140 M( the mapping of the HTTP/1.1 request and response structures onto the) s5 127 M( transport data units of the protocol in question is outside the scope) s5 114 M( of this specification.) s5 49 M(Fielding, et al. Standards Track [Page 13]) s_RS%%Page: (14) 14%%BeginPageSetup_S24 24 translate/pagenum 14 def/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc2616.txt) def/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def/ftail (rfc2616.txt) def% User defined strings:/fmodstr (Fri Jun 11 11:46:00 1999) def/pagenumstr (14) def/user_header_p true def/user_header_left_str (RFC2616) def/user_header_center_str (RFC.net) def/user_header_right_str (Page 14 of 177) def%%EndPageSetupdo_header5 751 M(RFC 2616 HTTP/1.1 June 1999) s5 712 M( In HTTP/1.0, most implementations used a new connection for each) s5 699 M( request/response exchange. In HTTP/1.1, a connection may be used for) s5 686 M( one or more request/response exchanges, although connections may be) s5 673 M( closed for a variety of reasons \(see section 8.1\).) s5 647 M(2 Notational Conventions and Generic Grammar) s5 621 M(2.1 Augmented BNF) s5 595 M( All of the mechanisms specified in this document are described in) s5 582 M( both prose and an augmented Backus-Naur Form \(BNF\) similar to that) s5 569 M( used by RFC 822 [9]. Implementors will need to be familiar with the) s5 556 M( notation in order to understand this specification. The augmented BNF) s5 543 M( includes the following constructs:) s5 517 M( name = definition) s5 504 M( The name of a rule is simply the name itself \(without any) s5 491 M( enclosing "<" and ">"\) and is separated from its definition by the) s5 478 M( equal "=" character. White space is only significant in that) s5 465 M( indentation of continuation lines is used to indicate a rule) s5 452 M( definition that spans more than one line. Certain basic rules are) s5 439 M( in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc. Angle) s5 426 M( brackets are used within definitions whenever their presence will) s5 413 M( facilitate discerning the use of rule names.) s5 387 M( "literal") s5 374 M( Quotation marks surround literal text. Unless stated otherwise,) s5 361 M( the text is case-insensitive.) s5 335 M( rule1 | rule2) s5 322 M( Elements separated by a bar \("|"\) are alternatives, e.g., "yes |) s5 309 M( no" will accept yes or no.) s5 283 M( \(rule1 rule2\)) s5 270 M( Elements enclosed in parentheses are treated as a single element.) s5 257 M( Thus, "\(elem \(foo | bar\) elem\)" allows the token sequences "elem) s5 244 M( foo elem" and "elem bar elem".) s5 218 M( *rule) s5 205 M( The character "*" preceding an element indicates repetition. The) s5 192 M( full form is "<n>*<m>element" indicating at least <n> and at most) s5 179 M( <m> occurrences of element. Default values are 0 and infinity so) s5 166 M( that "*\(element\)" allows any number, including zero; "1*element") s5 153 M( requires at least one; and "1*2element" allows one or two.) s5 127 M( [rule]) s5 114 M( Square brackets enclose optional elements; "[foo bar]" is) s5 101 M( equivalent to "*1\(foo bar\)".) s5 49 M(Fielding, et al. Standards Track [Page 14]) s_RS%%Page: (15) 15%%BeginPageSetup_S24 24 translate/pagenum 15 def/fname (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/rfc2616.txt) def/fdir (/usr/local/share/doc/rfc/Mirrors/ftp.isi.edu/in-notes/) def/ftail (rfc2616.txt) def% User defined strings:/fmodstr (Fri Jun 11 11:46:00 1999) def/pagenumstr (15) def/user_header_p true def/user_header_left_str (RFC2616) def/user_header_center_str (RFC.net) def/user_header_right_str (Page 15 of ⌨️ 快捷键说明
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