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2 HTTP Working Group R. Fielding, Ed.
3 Internet-Draft Adobe
4 Obsoletes: 7230 (if approved) M. Nottingham, Ed.
5 Intended status: Standards Track Fastly
6 Expires: January 13, 2021 J. F. Reschke, Ed.
7 greenbytes
8 July 12, 2020
10 HTTP/1.1 Messaging
11 draft-ietf-httpbis-messaging-10
13 Abstract
15 The Hypertext Transfer Protocol (HTTP) is a stateless application-
16 level protocol for distributed, collaborative, hypertext information
17 systems. This document specifies the HTTP/1.1 message syntax,
18 message parsing, connection management, and related security
19 concerns.
21 This document obsoletes portions of RFC 7230.
23 Editorial Note
25 This note is to be removed before publishing as an RFC.
27 Discussion of this draft takes place on the HTTP working group
28 mailing list (ietf-http-wg@w3.org), which is archived at
29 .
31 Working Group information can be found at ;
32 source code and issues list for this draft can be found at
33 .
35 The changes in this draft are summarized in Appendix D.11.
37 Status of This Memo
39 This Internet-Draft is submitted in full conformance with the
40 provisions of BCP 78 and BCP 79.
42 Internet-Drafts are working documents of the Internet Engineering
43 Task Force (IETF). Note that other groups may also distribute
44 working documents as Internet-Drafts. The list of current Internet-
45 Drafts is at https://datatracker.ietf.org/drafts/current/.
47 Internet-Drafts are draft documents valid for a maximum of six months
48 and may be updated, replaced, or obsoleted by other documents at any
49 time. It is inappropriate to use Internet-Drafts as reference
50 material or to cite them other than as "work in progress."
52 This Internet-Draft will expire on January 13, 2021.
54 Copyright Notice
56 Copyright (c) 2020 IETF Trust and the persons identified as the
57 document authors. All rights reserved.
59 This document is subject to BCP 78 and the IETF Trust's Legal
60 Provisions Relating to IETF Documents (https://trustee.ietf.org/
61 license-info) in effect on the date of publication of this document.
62 Please review these documents carefully, as they describe your rights
63 and restrictions with respect to this document. Code Components
64 extracted from this document must include Simplified BSD License text
65 as described in Section 4.e of the Trust Legal Provisions and are
66 provided without warranty as described in the Simplified BSD License.
68 This document may contain material from IETF Documents or IETF
69 Contributions published or made publicly available before November
70 10, 2008. The person(s) controlling the copyright in some of this
71 material may not have granted the IETF Trust the right to allow
72 modifications of such material outside the IETF Standards Process.
73 Without obtaining an adequate license from the person(s) controlling
74 the copyright in such materials, this document may not be modified
75 outside the IETF Standards Process, and derivative works of it may
76 not be created outside the IETF Standards Process, except to format
77 it for publication as an RFC or to translate it into languages other
78 than English.
80 Table of Contents
82 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
83 1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
84 1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5
85 2. Message . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
86 2.1. Message Format . . . . . . . . . . . . . . . . . . . . . 6
87 2.2. Message Parsing . . . . . . . . . . . . . . . . . . . . . 7
88 2.3. HTTP Version . . . . . . . . . . . . . . . . . . . . . . 8
89 3. Request Line . . . . . . . . . . . . . . . . . . . . . . . . 9
90 3.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . 10
91 3.2. Request Target . . . . . . . . . . . . . . . . . . . . . 10
92 3.2.1. origin-form . . . . . . . . . . . . . . . . . . . . . 10
93 3.2.2. absolute-form . . . . . . . . . . . . . . . . . . . . 11
94 3.2.3. authority-form . . . . . . . . . . . . . . . . . . . 12
95 3.2.4. asterisk-form . . . . . . . . . . . . . . . . . . . . 12
96 3.3. Reconstructing the Target URI . . . . . . . . . . . . . . 13
97 4. Status Line . . . . . . . . . . . . . . . . . . . . . . . . . 14
98 5. Field Syntax . . . . . . . . . . . . . . . . . . . . . . . . 15
99 5.1. Field Line Parsing . . . . . . . . . . . . . . . . . . . 16
100 5.2. Obsolete Line Folding . . . . . . . . . . . . . . . . . . 17
101 6. Message Body . . . . . . . . . . . . . . . . . . . . . . . . 17
102 6.1. Transfer-Encoding . . . . . . . . . . . . . . . . . . . . 18
103 6.2. Content-Length . . . . . . . . . . . . . . . . . . . . . 19
104 6.3. Message Body Length . . . . . . . . . . . . . . . . . . . 20
105 7. Transfer Codings . . . . . . . . . . . . . . . . . . . . . . 22
106 7.1. Chunked Transfer Coding . . . . . . . . . . . . . . . . . 23
107 7.1.1. Chunk Extensions . . . . . . . . . . . . . . . . . . 24
108 7.1.2. Chunked Trailer Section . . . . . . . . . . . . . . . 25
109 7.1.3. Decoding Chunked . . . . . . . . . . . . . . . . . . 25
110 7.2. Transfer Codings for Compression . . . . . . . . . . . . 26
111 7.3. Transfer Coding Registry . . . . . . . . . . . . . . . . 26
112 7.4. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
113 8. Handling Incomplete Messages . . . . . . . . . . . . . . . . 28
114 9. Connection Management . . . . . . . . . . . . . . . . . . . . 28
115 9.1. Connection . . . . . . . . . . . . . . . . . . . . . . . 29
116 9.2. Establishment . . . . . . . . . . . . . . . . . . . . . . 30
117 9.3. Associating a Response to a Request . . . . . . . . . . . 31
118 9.4. Persistence . . . . . . . . . . . . . . . . . . . . . . . 31
119 9.4.1. Retrying Requests . . . . . . . . . . . . . . . . . . 32
120 9.4.2. Pipelining . . . . . . . . . . . . . . . . . . . . . 32
121 9.5. Concurrency . . . . . . . . . . . . . . . . . . . . . . . 33
122 9.6. Failures and Timeouts . . . . . . . . . . . . . . . . . . 34
123 9.7. Tear-down . . . . . . . . . . . . . . . . . . . . . . . . 34
124 9.8. TLS Connection Closure . . . . . . . . . . . . . . . . . 35
125 9.9. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 36
126 9.9.1. Upgrade Protocol Names . . . . . . . . . . . . . . . 39
127 9.9.2. Upgrade Token Registry . . . . . . . . . . . . . . . 39
128 10. Enclosing Messages as Data . . . . . . . . . . . . . . . . . 40
129 10.1. Media Type message/http . . . . . . . . . . . . . . . . 40
130 10.2. Media Type application/http . . . . . . . . . . . . . . 41
131 11. Security Considerations . . . . . . . . . . . . . . . . . . . 42
132 11.1. Response Splitting . . . . . . . . . . . . . . . . . . . 42
133 11.2. Request Smuggling . . . . . . . . . . . . . . . . . . . 43
134 11.3. Message Integrity . . . . . . . . . . . . . . . . . . . 43
135 11.4. Message Confidentiality . . . . . . . . . . . . . . . . 44
136 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
137 12.1. Field Name Registration . . . . . . . . . . . . . . . . 44
138 12.2. Media Type Registration . . . . . . . . . . . . . . . . 44
139 12.3. Transfer Coding Registration . . . . . . . . . . . . . . 45
140 12.4. Upgrade Token Registration . . . . . . . . . . . . . . . 45
141 12.5. ALPN Protocol ID Registration . . . . . . . . . . . . . 45
142 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
143 13.1. Normative References . . . . . . . . . . . . . . . . . . 45
144 13.2. Informative References . . . . . . . . . . . . . . . . . 46
145 Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 48
146 Appendix B. Differences between HTTP and MIME . . . . . . . . . 50
147 B.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . 50
148 B.2. Conversion to Canonical Form . . . . . . . . . . . . . . 50
149 B.3. Conversion of Date Formats . . . . . . . . . . . . . . . 51
150 B.4. Conversion of Content-Encoding . . . . . . . . . . . . . 51
151 B.5. Conversion of Content-Transfer-Encoding . . . . . . . . . 51
152 B.6. MHTML and Line Length Limitations . . . . . . . . . . . . 51
153 Appendix C. HTTP Version History . . . . . . . . . . . . . . . . 52
154 C.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 52
155 C.1.1. Multihomed Web Servers . . . . . . . . . . . . . . . 53
156 C.1.2. Keep-Alive Connections . . . . . . . . . . . . . . . 53
157 C.1.3. Introduction of Transfer-Encoding . . . . . . . . . . 54
158 C.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 54
159 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 54
160 D.1. Between RFC7230 and draft 00 . . . . . . . . . . . . . . 55
161 D.2. Since draft-ietf-httpbis-messaging-00 . . . . . . . . . . 55
162 D.3. Since draft-ietf-httpbis-messaging-01 . . . . . . . . . . 55
163 D.4. Since draft-ietf-httpbis-messaging-02 . . . . . . . . . . 56
164 D.5. Since draft-ietf-httpbis-messaging-03 . . . . . . . . . . 56
165 D.6. Since draft-ietf-httpbis-messaging-04 . . . . . . . . . . 56
166 D.7. Since draft-ietf-httpbis-messaging-05 . . . . . . . . . . 57
167 D.8. Since draft-ietf-httpbis-messaging-06 . . . . . . . . . . 57
168 D.9. Since draft-ietf-httpbis-messaging-07 . . . . . . . . . . 58
169 D.10. Since draft-ietf-httpbis-messaging-08 . . . . . . . . . . 58
170 D.11. Since draft-ietf-httpbis-messaging-09 . . . . . . . . . . 58
171 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 58
172 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 58
174 1. Introduction
176 The Hypertext Transfer Protocol (HTTP) is a stateless application-
177 level request/response protocol that uses extensible semantics and
178 self-descriptive messages for flexible interaction with network-based
179 hypertext information systems. HTTP is defined by a series of
180 documents that collectively form the HTTP/1.1 specification:
182 o "HTTP Semantics" [Semantics]
184 o "HTTP Caching" [Caching]
186 o "HTTP/1.1 Messaging" (this document)
188 This document defines HTTP/1.1 message syntax and framing
189 requirements and their associated connection management. Our goal is
190 to define all of the mechanisms necessary for HTTP/1.1 message
191 handling that are independent of message semantics, thereby defining
192 the complete set of requirements for message parsers and message-
193 forwarding intermediaries.
195 This document obsoletes the portions of RFC 7230 related to HTTP/1.1
196 messaging and connection management, with the changes being
197 summarized in Appendix C.2. The other parts of RFC 7230 are
198 obsoleted by "HTTP Semantics" [Semantics].
200 1.1. Requirements Notation
202 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
203 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
204 "OPTIONAL" in this document are to be interpreted as described in BCP
205 14 [RFC2119] [RFC8174] when, and only when, they appear in all
206 capitals, as shown here.
208 Conformance criteria and considerations regarding error handling are
209 defined in Section 3 of [Semantics].
211 1.2. Syntax Notation
213 This specification uses the Augmented Backus-Naur Form (ABNF)
214 notation of [RFC5234], extended with the notation for case-
215 sensitivity in strings defined in [RFC7405].
217 It also uses a list extension, defined in Section 5.5 of [Semantics],
218 that allows for compact definition of comma-separated lists using a
219 '#' operator (similar to how the '*' operator indicates repetition).
220 Appendix A shows the collected grammar with all list operators
221 expanded to standard ABNF notation.
223 As a convention, ABNF rule names prefixed with "obs-" denote
224 "obsolete" grammar rules that appear for historical reasons.
226 The following core rules are included by reference, as defined in
227 [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
228 (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
229 HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line
230 feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any
231 visible [USASCII] character).
233 The rules below are defined in [Semantics]:
235 BWS =
236 OWS =
237 RWS =
238 absolute-URI =
239 absolute-path =
240 authority =
241 comment =
242 field-name =
243 field-value =
244 obs-text =
245 port =
246 query =
247 quoted-string =
248 token =
249 uri-host =
251 2. Message
253 2.1. Message Format
255 An HTTP/1.1 message consists of a start-line followed by a CRLF and a
256 sequence of octets in a format similar to the Internet Message Format
257 [RFC5322]: zero or more header field lines (collectively referred to
258 as the "headers" or the "header section"), an empty line indicating
259 the end of the header section, and an optional message body.
261 HTTP-message = start-line CRLF
262 *( field-line CRLF )
263 CRLF
264 [ message-body ]
266 A message can be either a request from client to server or a response
267 from server to client. Syntactically, the two types of message
268 differ only in the start-line, which is either a request-line (for
269 requests) or a status-line (for responses), and in the algorithm for
270 determining the length of the message body (Section 6).
272 start-line = request-line / status-line
274 In theory, a client could receive requests and a server could receive
275 responses, distinguishing them by their different start-line formats.
276 In practice, servers are implemented to only expect a request (a
277 response is interpreted as an unknown or invalid request method) and
278 clients are implemented to only expect a response.
280 Although HTTP makes use of some protocol elements similar to the
281 Multipurpose Internet Mail Extensions (MIME) [RFC2045], see
282 Appendix B for the differences between HTTP and MIME messages.
284 2.2. Message Parsing
286 The normal procedure for parsing an HTTP message is to read the
287 start-line into a structure, read each header field line into a hash
288 table by field name until the empty line, and then use the parsed
289 data to determine if a message body is expected. If a message body
290 has been indicated, then it is read as a stream until an amount of
291 octets equal to the message body length is read or the connection is
292 closed.
294 A recipient MUST parse an HTTP message as a sequence of octets in an
295 encoding that is a superset of US-ASCII [USASCII]. Parsing an HTTP
296 message as a stream of Unicode characters, without regard for the
297 specific encoding, creates security vulnerabilities due to the
298 varying ways that string processing libraries handle invalid
299 multibyte character sequences that contain the octet LF (%x0A).
300 String-based parsers can only be safely used within protocol elements
301 after the element has been extracted from the message, such as within
302 a header field line value after message parsing has delineated the
303 individual field lines.
305 Although the line terminator for the start-line and header fields is
306 the sequence CRLF, a recipient MAY recognize a single LF as a line
307 terminator and ignore any preceding CR.
309 A sender MUST NOT generate a bare CR (a CR character not immediately
310 followed by LF) within any protocol elements other than the payload
311 body. A recipient of such a bare CR MUST consider that element to be
312 invalid or replace each bare CR with SP before processing the element
313 or forwarding the message.
315 Older HTTP/1.0 user agent implementations might send an extra CRLF
316 after a POST request as a workaround for some early server
317 applications that failed to read message body content that was not
318 terminated by a line-ending. An HTTP/1.1 user agent MUST NOT preface
319 or follow a request with an extra CRLF. If terminating the request
320 message body with a line-ending is desired, then the user agent MUST
321 count the terminating CRLF octets as part of the message body length.
323 In the interest of robustness, a server that is expecting to receive
324 and parse a request-line SHOULD ignore at least one empty line (CRLF)
325 received prior to the request-line.
327 A sender MUST NOT send whitespace between the start-line and the
328 first header field. A recipient that receives whitespace between the
329 start-line and the first header field MUST either reject the message
330 as invalid or consume each whitespace-preceded line without further
331 processing of it (i.e., ignore the entire line, along with any
332 subsequent lines preceded by whitespace, until a properly formed
333 header field is received or the header section is terminated).
335 The presence of such whitespace in a request might be an attempt to
336 trick a server into ignoring that field line or processing the line
337 after it as a new request, either of which might result in a security
338 vulnerability if other implementations within the request chain
339 interpret the same message differently. Likewise, the presence of
340 such whitespace in a response might be ignored by some clients or
341 cause others to cease parsing.
343 When a server listening only for HTTP request messages, or processing
344 what appears from the start-line to be an HTTP request message,
345 receives a sequence of octets that does not match the HTTP-message
346 grammar aside from the robustness exceptions listed above, the server
347 SHOULD respond with a 400 (Bad Request) response.
349 2.3. HTTP Version
351 HTTP uses a "." numbering scheme to indicate versions
352 of the protocol. This specification defines version "1.1".
353 Section 4.2 of [Semantics] specifies the semantics of HTTP version
354 numbers.
356 The version of an HTTP/1.x message is indicated by an HTTP-version
357 field in the start-line. HTTP-version is case-sensitive.
359 HTTP-version = HTTP-name "/" DIGIT "." DIGIT
360 HTTP-name = %s"HTTP"
362 When an HTTP/1.1 message is sent to an HTTP/1.0 recipient [RFC1945]
363 or a recipient whose version is unknown, the HTTP/1.1 message is
364 constructed such that it can be interpreted as a valid HTTP/1.0
365 message if all of the newer features are ignored. This specification
366 places recipient-version requirements on some new features so that a
367 conformant sender will only use compatible features until it has
368 determined, through configuration or the receipt of a message, that
369 the recipient supports HTTP/1.1.
371 Intermediaries that process HTTP messages (i.e., all intermediaries
372 other than those acting as tunnels) MUST send their own HTTP-version
373 in forwarded messages. In other words, they are not allowed to
374 blindly forward the start-line without ensuring that the protocol
375 version in that message matches a version to which that intermediary
376 is conformant for both the receiving and sending of messages.
377 Forwarding an HTTP message without rewriting the HTTP-version might
378 result in communication errors when downstream recipients use the
379 message sender's version to determine what features are safe to use
380 for later communication with that sender.
382 A server MAY send an HTTP/1.0 response to an HTTP/1.1 request if it
383 is known or suspected that the client incorrectly implements the HTTP
384 specification and is incapable of correctly processing later version
385 responses, such as when a client fails to parse the version number
386 correctly or when an intermediary is known to blindly forward the
387 HTTP-version even when it doesn't conform to the given minor version
388 of the protocol. Such protocol downgrades SHOULD NOT be performed
389 unless triggered by specific client attributes, such as when one or
390 more of the request header fields (e.g., User-Agent) uniquely match
391 the values sent by a client known to be in error.
393 3. Request Line
395 A request-line begins with a method token, followed by a single space
396 (SP), the request-target, another single space (SP), and ends with
397 the protocol version.
399 request-line = method SP request-target SP HTTP-version
401 Although the request-line grammar rule requires that each of the
402 component elements be separated by a single SP octet, recipients MAY
403 instead parse on whitespace-delimited word boundaries and, aside from
404 the CRLF terminator, treat any form of whitespace as the SP separator
405 while ignoring preceding or trailing whitespace; such whitespace
406 includes one or more of the following octets: SP, HTAB, VT (%x0B), FF
407 (%x0C), or bare CR. However, lenient parsing can result in request
408 smuggling security vulnerabilities if there are multiple recipients
409 of the message and each has its own unique interpretation of
410 robustness (see Section 11.2).
412 HTTP does not place a predefined limit on the length of a request-
413 line, as described in Section 3 of [Semantics]. A server that
414 receives a method longer than any that it implements SHOULD respond
415 with a 501 (Not Implemented) status code. A server that receives a
416 request-target longer than any URI it wishes to parse MUST respond
417 with a 414 (URI Too Long) status code (see Section 10.5.15 of
418 [Semantics]).
420 Various ad hoc limitations on request-line length are found in
421 practice. It is RECOMMENDED that all HTTP senders and recipients
422 support, at a minimum, request-line lengths of 8000 octets.
424 3.1. Method
426 The method token indicates the request method to be performed on the
427 target resource. The request method is case-sensitive.
429 method = token
431 The request methods defined by this specification can be found in
432 Section 8 of [Semantics], along with information regarding the HTTP
433 method registry and considerations for defining new methods.
435 3.2. Request Target
437 The request-target identifies the target resource upon which to apply
438 the request. The client derives a request-target from its desired
439 target URI. There are four distinct formats for the request-target,
440 depending on both the method being requested and whether the request
441 is to a proxy.
443 request-target = origin-form
444 / absolute-form
445 / authority-form
446 / asterisk-form
448 No whitespace is allowed in the request-target. Unfortunately, some
449 user agents fail to properly encode or exclude whitespace found in
450 hypertext references, resulting in those disallowed characters being
451 sent as the request-target in a malformed request-line.
453 Recipients of an invalid request-line SHOULD respond with either a
454 400 (Bad Request) error or a 301 (Moved Permanently) redirect with
455 the request-target properly encoded. A recipient SHOULD NOT attempt
456 to autocorrect and then process the request without a redirect, since
457 the invalid request-line might be deliberately crafted to bypass
458 security filters along the request chain.
460 3.2.1. origin-form
462 The most common form of request-target is the origin-form.
464 origin-form = absolute-path [ "?" query ]
466 When making a request directly to an origin server, other than a
467 CONNECT or server-wide OPTIONS request (as detailed below), a client
468 MUST send only the absolute path and query components of the target
469 URI as the request-target. If the target URI's path component is
470 empty, the client MUST send "/" as the path within the origin-form of
471 request-target. A Host header field is also sent, as defined in
472 Section 6.6 of [Semantics].
474 For example, a client wishing to retrieve a representation of the
475 resource identified as
477 http://www.example.org/where?q=now
479 directly from the origin server would open (or reuse) a TCP
480 connection to port 80 of the host "www.example.org" and send the
481 lines:
483 GET /where?q=now HTTP/1.1
484 Host: www.example.org
486 followed by the remainder of the request message.
488 3.2.2. absolute-form
490 When making a request to a proxy, other than a CONNECT or server-wide
491 OPTIONS request (as detailed below), a client MUST send the target
492 URI in absolute-form as the request-target.
494 absolute-form = absolute-URI
496 The proxy is requested to either service that request from a valid
497 cache, if possible, or make the same request on the client's behalf
498 to either the next inbound proxy server or directly to the origin
499 server indicated by the request-target. Requirements on such
500 "forwarding" of messages are defined in Section 6.7 of [Semantics].
502 An example absolute-form of request-line would be:
504 GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
506 A client MUST send a Host header field in an HTTP/1.1 request even if
507 the request-target is in the absolute-form, since this allows the
508 Host information to be forwarded through ancient HTTP/1.0 proxies
509 that might not have implemented Host.
511 When a proxy receives a request with an absolute-form of request-
512 target, the proxy MUST ignore the received Host header field (if any)
513 and instead replace it with the host information of the request-
514 target. A proxy that forwards such a request MUST generate a new
515 Host field value based on the received request-target rather than
516 forward the received Host field value.
518 When an origin server receives a request with an absolute-form of
519 request-target, the origin server MUST ignore the received Host
520 header field (if any) and instead use the host information of the
521 request-target. Note that if the request-target does not have an
522 authority component, an empty Host header field will be sent in this
523 case.
525 To allow for transition to the absolute-form for all requests in some
526 future version of HTTP, a server MUST accept the absolute-form in
527 requests, even though HTTP/1.1 clients will only send them in
528 requests to proxies.
530 3.2.3. authority-form
532 The authority-form of request-target is only used for CONNECT
533 requests (Section 8.3.6 of [Semantics]).
535 authority-form = authority
537 When making a CONNECT request to establish a tunnel through one or
538 more proxies, a client MUST send only the target URI's authority
539 component (excluding any userinfo and its "@" delimiter) as the
540 request-target. For example,
542 CONNECT www.example.com:80 HTTP/1.1
544 3.2.4. asterisk-form
546 The asterisk-form of request-target is only used for a server-wide
547 OPTIONS request (Section 8.3.7 of [Semantics]).
549 asterisk-form = "*"
551 When a client wishes to request OPTIONS for the server as a whole, as
552 opposed to a specific named resource of that server, the client MUST
553 send only "*" (%x2A) as the request-target. For example,
555 OPTIONS * HTTP/1.1
557 If a proxy receives an OPTIONS request with an absolute-form of
558 request-target in which the URI has an empty path and no query
559 component, then the last proxy on the request chain MUST send a
560 request-target of "*" when it forwards the request to the indicated
561 origin server.
563 For example, the request
565 OPTIONS http://www.example.org:8001 HTTP/1.1
567 would be forwarded by the final proxy as
569 OPTIONS * HTTP/1.1
570 Host: www.example.org:8001
572 after connecting to port 8001 of host "www.example.org".
574 3.3. Reconstructing the Target URI
576 Since the request-target often contains only part of the user agent's
577 target URI, a server constructs its value to properly service the
578 request (Section 6.1 of [Semantics]).
580 If the request-target is in absolute-form, the target URI is the same
581 as the request-target. Otherwise, the target URI is constructed as
582 follows:
584 If the server's configuration (or outbound gateway) provides a
585 fixed URI scheme, that scheme is used for the target URI.
586 Otherwise, if the request is received over a TLS-secured TCP
587 connection, the target URI's scheme is "https"; if not, the scheme
588 is "http".
590 If the server's configuration (or outbound gateway) provides a
591 fixed URI authority component, that authority is used for the
592 target URI. If not, then if the request-target is in
593 authority-form, the target URI's authority component is the same
594 as the request-target. If not, then if a Host header field is
595 supplied with a non-empty field-value, the authority component is
596 the same as the Host field-value. Otherwise, the authority
597 component is assigned the default name configured for the server
598 and, if the connection's incoming TCP port number differs from the
599 default port for the target URI's scheme, then a colon (":") and
600 the incoming port number (in decimal form) are appended to the
601 authority component.
603 If the request-target is in authority-form or asterisk-form, the
604 target URI's combined path and query component is empty.
605 Otherwise, the combined path and query component is the same as
606 the request-target.
608 The components of the target URI, once determined as above, can be
609 combined into absolute-URI form by concatenating the scheme,
610 "://", authority, and combined path and query component.
612 Example 1: the following message received over an insecure TCP
613 connection
615 GET /pub/WWW/TheProject.html HTTP/1.1
616 Host: www.example.org:8080
618 has a target URI of
620 http://www.example.org:8080/pub/WWW/TheProject.html
622 Example 2: the following message received over a TLS-secured TCP
623 connection
625 OPTIONS * HTTP/1.1
626 Host: www.example.org
628 has a target URI of
630 https://www.example.org
632 Recipients of an HTTP/1.0 request that lacks a Host header field
633 might need to use heuristics (e.g., examination of the URI path for
634 something unique to a particular host) in order to guess the target
635 URI's authority component.
637 4. Status Line
639 The first line of a response message is the status-line, consisting
640 of the protocol version, a space (SP), the status code, another
641 space, and ending with an OPTIONAL textual phrase describing the
642 status code.
644 status-line = HTTP-version SP status-code SP [reason-phrase]
646 Although the status-line grammar rule requires that each of the
647 component elements be separated by a single SP octet, recipients MAY
648 instead parse on whitespace-delimited word boundaries and, aside from
649 the line terminator, treat any form of whitespace as the SP separator
650 while ignoring preceding or trailing whitespace; such whitespace
651 includes one or more of the following octets: SP, HTAB, VT (%x0B), FF
652 (%x0C), or bare CR. However, lenient parsing can result in response
653 splitting security vulnerabilities if there are multiple recipients
654 of the message and each has its own unique interpretation of
655 robustness (see Section 11.1).
657 The status-code element is a 3-digit integer code describing the
658 result of the server's attempt to understand and satisfy the client's
659 corresponding request. The rest of the response message is to be
660 interpreted in light of the semantics defined for that status code.
661 See Section 10 of [Semantics] for information about the semantics of
662 status codes, including the classes of status code (indicated by the
663 first digit), the status codes defined by this specification,
664 considerations for the definition of new status codes, and the IANA
665 registry.
667 status-code = 3DIGIT
669 The reason-phrase element exists for the sole purpose of providing a
670 textual description associated with the numeric status code, mostly
671 out of deference to earlier Internet application protocols that were
672 more frequently used with interactive text clients.
674 reason-phrase = 1*( HTAB / SP / VCHAR / obs-text )
676 A client SHOULD ignore the reason-phrase content because it is not a
677 reliable channel for information (it might be translated for a given
678 locale, overwritten by intermediaries, or discarded when the message
679 is forwarded via other versions of HTTP). A server MUST send the
680 space that separates status-code from the reason-phrase even when the
681 reason-phrase is absent (i.e., the status-line would end with the
682 three octets SP CR LF).
684 5. Field Syntax
686 Each field line consists of a case-insensitive field name followed by
687 a colon (":"), optional leading whitespace, the field line value, and
688 optional trailing whitespace.
690 field-line = field-name ":" OWS field-value OWS
692 Most HTTP field names and the rules for parsing within field values
693 are defined in Section 5 of [Semantics]. This section covers the
694 generic syntax for header field inclusion within, and extraction
695 from, HTTP/1.1 messages. In addition, the following header fields
696 are defined by this document because they are specific to HTTP/1.1
697 message processing:
699 +-------------------+----------+--------------+
700 | Field Name | Status | Reference |
701 | Connection | standard | Section 9.1 |
702 | MIME-Version | standard | Appendix B.1 |
703 | TE | standard | Section 7.4 |
704 | Transfer-Encoding | standard | Section 6.1 |
705 | Upgrade | standard | Section 9.9 |
706 +-------------------+----------+--------------+
708 Table 1
710 Furthermore, the field name "Close" is reserved, since using that
711 name as an HTTP header field might conflict with the "close"
712 connection option of the Connection header field (Section 9.1).
714 +------------+----------+-----------+------------+
715 | Field Name | Status | Reference | Comments |
716 | Close | standard | Section 5 | (reserved) |
717 +------------+----------+-----------+------------+
719 Table 2
721 5.1. Field Line Parsing
723 Messages are parsed using a generic algorithm, independent of the
724 individual field names. The contents within a given field line value
725 are not parsed until a later stage of message interpretation (usually
726 after the message's entire header section has been processed).
728 No whitespace is allowed between the field name and colon. In the
729 past, differences in the handling of such whitespace have led to
730 security vulnerabilities in request routing and response handling. A
731 server MUST reject any received request message that contains
732 whitespace between a header field name and colon with a response
733 status code of 400 (Bad Request). A proxy MUST remove any such
734 whitespace from a response message before forwarding the message
735 downstream.
737 A field line value might be preceded and/or followed by optional
738 whitespace (OWS); a single SP preceding the field line value is
739 preferred for consistent readability by humans. The field line value
740 does not include any leading or trailing whitespace: OWS occurring
741 before the first non-whitespace octet of the field line value or
742 after the last non-whitespace octet of the field line value ought to
743 be excluded by parsers when extracting the field line value from a
744 header field line.
746 5.2. Obsolete Line Folding
748 Historically, HTTP header field line values could be extended over
749 multiple lines by preceding each extra line with at least one space
750 or horizontal tab (obs-fold). This specification deprecates such
751 line folding except within the message/http media type
752 (Section 10.1).
754 obs-fold = OWS CRLF RWS
755 ; obsolete line folding
757 A sender MUST NOT generate a message that includes line folding
758 (i.e., that has any field line value that contains a match to the
759 obs-fold rule) unless the message is intended for packaging within
760 the message/http media type.
762 A server that receives an obs-fold in a request message that is not
763 within a message/http container MUST either reject the message by
764 sending a 400 (Bad Request), preferably with a representation
765 explaining that obsolete line folding is unacceptable, or replace
766 each received obs-fold with one or more SP octets prior to
767 interpreting the field value or forwarding the message downstream.
769 A proxy or gateway that receives an obs-fold in a response message
770 that is not within a message/http container MUST either discard the
771 message and replace it with a 502 (Bad Gateway) response, preferably
772 with a representation explaining that unacceptable line folding was
773 received, or replace each received obs-fold with one or more SP
774 octets prior to interpreting the field value or forwarding the
775 message downstream.
777 A user agent that receives an obs-fold in a response message that is
778 not within a message/http container MUST replace each received
779 obs-fold with one or more SP octets prior to interpreting the field
780 value.
782 6. Message Body
784 The message body (if any) of an HTTP message is used to carry the
785 payload body (Section 7.3.3 of [Semantics]) of that request or
786 response. The message body is identical to the payload body unless a
787 transfer coding has been applied, as described in Section 6.1.
789 message-body = *OCTET
791 The rules for determining when a message body is present in an
792 HTTP/1.1 message differ for requests and responses.
794 The presence of a message body in a request is signaled by a
795 Content-Length or Transfer-Encoding header field. Request message
796 framing is independent of method semantics, even if the method does
797 not define any use for a message body.
799 The presence of a message body in a response depends on both the
800 request method to which it is responding and the response status code
801 (Section 4), and corresponds to when a payload body is allowed; see
802 Section 7.3.3 of [Semantics].
804 6.1. Transfer-Encoding
806 The Transfer-Encoding header field lists the transfer coding names
807 corresponding to the sequence of transfer codings that have been (or
808 will be) applied to the payload body in order to form the message
809 body. Transfer codings are defined in Section 7.
811 Transfer-Encoding = 1#transfer-coding
813 Transfer-Encoding is analogous to the Content-Transfer-Encoding field
814 of MIME, which was designed to enable safe transport of binary data
815 over a 7-bit transport service ([RFC2045], Section 6). However, safe
816 transport has a different focus for an 8bit-clean transfer protocol.
817 In HTTP's case, Transfer-Encoding is primarily intended to accurately
818 delimit a dynamically generated payload and to distinguish payload
819 encodings that are only applied for transport efficiency or security
820 from those that are characteristics of the selected resource.
822 A recipient MUST be able to parse the chunked transfer coding
823 (Section 7.1) because it plays a crucial role in framing messages
824 when the payload body size is not known in advance. A sender MUST
825 NOT apply chunked more than once to a message body (i.e., chunking an
826 already chunked message is not allowed). If any transfer coding
827 other than chunked is applied to a request payload body, the sender
828 MUST apply chunked as the final transfer coding to ensure that the
829 message is properly framed. If any transfer coding other than
830 chunked is applied to a response payload body, the sender MUST either
831 apply chunked as the final transfer coding or terminate the message
832 by closing the connection.
834 For example,
836 Transfer-Encoding: gzip, chunked
838 indicates that the payload body has been compressed using the gzip
839 coding and then chunked using the chunked coding while forming the
840 message body.
842 Unlike Content-Encoding (Section 7.1.2 of [Semantics]), Transfer-
843 Encoding is a property of the message, not of the representation, and
844 any recipient along the request/response chain MAY decode the
845 received transfer coding(s) or apply additional transfer coding(s) to
846 the message body, assuming that corresponding changes are made to the
847 Transfer-Encoding field value. Additional information about the
848 encoding parameters can be provided by other header fields not
849 defined by this specification.
851 Transfer-Encoding MAY be sent in a response to a HEAD request or in a
852 304 (Not Modified) response (Section 10.4.5 of [Semantics]) to a GET
853 request, neither of which includes a message body, to indicate that
854 the origin server would have applied a transfer coding to the message
855 body if the request had been an unconditional GET. This indication
856 is not required, however, because any recipient on the response chain
857 (including the origin server) can remove transfer codings when they
858 are not needed.
860 A server MUST NOT send a Transfer-Encoding header field in any
861 response with a status code of 1xx (Informational) or 204 (No
862 Content). A server MUST NOT send a Transfer-Encoding header field in
863 any 2xx (Successful) response to a CONNECT request (Section 8.3.6 of
864 [Semantics]).
866 Transfer-Encoding was added in HTTP/1.1. It is generally assumed
867 that implementations advertising only HTTP/1.0 support will not
868 understand how to process a transfer-encoded payload. A client MUST
869 NOT send a request containing Transfer-Encoding unless it knows the
870 server will handle HTTP/1.1 requests (or later minor revisions); such
871 knowledge might be in the form of specific user configuration or by
872 remembering the version of a prior received response. A server MUST
873 NOT send a response containing Transfer-Encoding unless the
874 corresponding request indicates HTTP/1.1 (or later minor revisions).
876 A server that receives a request message with a transfer coding it
877 does not understand SHOULD respond with 501 (Not Implemented).
879 6.2. Content-Length
881 When a message does not have a Transfer-Encoding header field, a
882 Content-Length header field can provide the anticipated size, as a
883 decimal number of octets, for a potential payload body. For messages
884 that do include a payload body, the Content-Length field value
885 provides the framing information necessary for determining where the
886 body (and message) ends. For messages that do not include a payload
887 body, the Content-Length indicates the size of the selected
888 representation (Section 7.2.4 of [Semantics]).
890 | *Note:* HTTP's use of Content-Length for message framing
891 | differs significantly from the same field's use in MIME, where
892 | it is an optional field used only within the "message/external-
893 | body" media-type.
895 6.3. Message Body Length
897 The length of a message body is determined by one of the following
898 (in order of precedence):
900 1. Any response to a HEAD request and any response with a 1xx
901 (Informational), 204 (No Content), or 304 (Not Modified) status
902 code is always terminated by the first empty line after the
903 header fields, regardless of the header fields present in the
904 message, and thus cannot contain a message body.
906 2. Any 2xx (Successful) response to a CONNECT request implies that
907 the connection will become a tunnel immediately after the empty
908 line that concludes the header fields. A client MUST ignore any
909 Content-Length or Transfer-Encoding header fields received in
910 such a message.
912 3. If a Transfer-Encoding header field is present and the chunked
913 transfer coding (Section 7.1) is the final encoding, the message
914 body length is determined by reading and decoding the chunked
915 data until the transfer coding indicates the data is complete.
917 If a Transfer-Encoding header field is present in a response and
918 the chunked transfer coding is not the final encoding, the
919 message body length is determined by reading the connection until
920 it is closed by the server. If a Transfer-Encoding header field
921 is present in a request and the chunked transfer coding is not
922 the final encoding, the message body length cannot be determined
923 reliably; the server MUST respond with the 400 (Bad Request)
924 status code and then close the connection.
926 If a message is received with both a Transfer-Encoding and a
927 Content-Length header field, the Transfer-Encoding overrides the
928 Content-Length. Such a message might indicate an attempt to
929 perform request smuggling (Section 11.2) or response splitting
930 (Section 11.1) and ought to be handled as an error. A sender
931 MUST remove the received Content-Length field prior to forwarding
932 such a message downstream.
934 4. If a message is received without Transfer-Encoding and with an
935 invalid Content-Length header field, then the message framing is
936 invalid and the recipient MUST treat it as an unrecoverable
937 error, unless the field value can be successfully parsed as a
938 comma-separated list (Section 5.5 of [Semantics]), all values in
939 the list are valid, and all values in the list are the same. If
940 this is a request message, the server MUST respond with a 400
941 (Bad Request) status code and then close the connection. If this
942 is a response message received by a proxy, the proxy MUST close
943 the connection to the server, discard the received response, and
944 send a 502 (Bad Gateway) response to the client. If this is a
945 response message received by a user agent, the user agent MUST
946 close the connection to the server and discard the received
947 response.
949 5. If a valid Content-Length header field is present without
950 Transfer-Encoding, its decimal value defines the expected message
951 body length in octets. If the sender closes the connection or
952 the recipient times out before the indicated number of octets are
953 received, the recipient MUST consider the message to be
954 incomplete and close the connection.
956 6. If this is a request message and none of the above are true, then
957 the message body length is zero (no message body is present).
959 7. Otherwise, this is a response message without a declared message
960 body length, so the message body length is determined by the
961 number of octets received prior to the server closing the
962 connection.
964 Since there is no way to distinguish a successfully completed, close-
965 delimited message from a partially received message interrupted by
966 network failure, a server SHOULD generate encoding or length-
967 delimited messages whenever possible. The close-delimiting feature
968 exists primarily for backwards compatibility with HTTP/1.0.
970 A server MAY reject a request that contains a message body but not a
971 Content-Length by responding with 411 (Length Required).
973 Unless a transfer coding other than chunked has been applied, a
974 client that sends a request containing a message body SHOULD use a
975 valid Content-Length header field if the message body length is known
976 in advance, rather than the chunked transfer coding, since some
977 existing services respond to chunked with a 411 (Length Required)
978 status code even though they understand the chunked transfer coding.
979 This is typically because such services are implemented via a gateway
980 that requires a content-length in advance of being called and the
981 server is unable or unwilling to buffer the entire request before
982 processing.
984 A user agent that sends a request containing a message body MUST send
985 a valid Content-Length header field if it does not know the server
986 will handle HTTP/1.1 (or later) requests; such knowledge can be in
987 the form of specific user configuration or by remembering the version
988 of a prior received response.
990 If the final response to the last request on a connection has been
991 completely received and there remains additional data to read, a user
992 agent MAY discard the remaining data or attempt to determine if that
993 data belongs as part of the prior response body, which might be the
994 case if the prior message's Content-Length value is incorrect. A
995 client MUST NOT process, cache, or forward such extra data as a
996 separate response, since such behavior would be vulnerable to cache
997 poisoning.
999 7. Transfer Codings
1001 Transfer coding names are used to indicate an encoding transformation
1002 that has been, can be, or might need to be applied to a payload body
1003 in order to ensure "safe transport" through the network. This
1004 differs from a content coding in that the transfer coding is a
1005 property of the message rather than a property of the representation
1006 that is being transferred.
1008 transfer-coding = token *( OWS ";" OWS transfer-parameter )
1010 Parameters are in the form of a name=value pair.
1012 transfer-parameter = token BWS "=" BWS ( token / quoted-string )
1014 All transfer-coding names are case-insensitive and ought to be
1015 registered within the HTTP Transfer Coding registry, as defined in
1016 Section 7.3. They are used in the TE (Section 7.4) and
1017 Transfer-Encoding (Section 6.1) header fields.
1019 +------------+-------------------------------+-----------+
1020 | Name | Description | Reference |
1021 | chunked | Transfer in a series of | Section |
1022 | | chunks | 7.1 |
1023 | compress | UNIX "compress" data format | Section |
1024 | | [Welch] | 7.2 |
1025 | deflate | "deflate" compressed data | Section |
1026 | | ([RFC1951]) inside the "zlib" | 7.2 |
1027 | | data format ([RFC1950]) | |
1028 | gzip | GZIP file format [RFC1952] | Section |
1029 | | | 7.2 |
1030 | trailers | (reserved) | Section 7 |
1031 | x-compress | Deprecated (alias for | Section |
1032 | | compress) | 7.2 |
1033 | x-gzip | Deprecated (alias for gzip) | Section |
1034 | | | 7.2 |
1035 +------------+-------------------------------+-----------+
1037 Table 3
1039 | *Note:* the coding name "trailers" is reserved because its use
1040 | would conflict with the keyword "trailers" in the TE header
1041 | field (Section 7.4).
1043 7.1. Chunked Transfer Coding
1045 The chunked transfer coding wraps the payload body in order to
1046 transfer it as a series of chunks, each with its own size indicator,
1047 followed by an OPTIONAL trailer section containing trailer fields.
1048 Chunked enables content streams of unknown size to be transferred as
1049 a sequence of length-delimited buffers, which enables the sender to
1050 retain connection persistence and the recipient to know when it has
1051 received the entire message.
1053 chunked-body = *chunk
1054 last-chunk
1055 trailer-section
1056 CRLF
1058 chunk = chunk-size [ chunk-ext ] CRLF
1059 chunk-data CRLF
1060 chunk-size = 1*HEXDIG
1061 last-chunk = 1*("0") [ chunk-ext ] CRLF
1063 chunk-data = 1*OCTET ; a sequence of chunk-size octets
1065 The chunk-size field is a string of hex digits indicating the size of
1066 the chunk-data in octets. The chunked transfer coding is complete
1067 when a chunk with a chunk-size of zero is received, possibly followed
1068 by a trailer section, and finally terminated by an empty line.
1070 A recipient MUST be able to parse and decode the chunked transfer
1071 coding.
1073 Note that HTTP/1.1 does not define any means to limit the size of a
1074 chunked response such that an intermediary can be assured of
1075 buffering the entire response.
1077 The chunked encoding does not define any parameters. Their presence
1078 SHOULD be treated as an error.
1080 7.1.1. Chunk Extensions
1082 The chunked encoding allows each chunk to include zero or more chunk
1083 extensions, immediately following the chunk-size, for the sake of
1084 supplying per-chunk metadata (such as a signature or hash), mid-
1085 message control information, or randomization of message body size.
1087 chunk-ext = *( BWS ";" BWS chunk-ext-name
1088 [ BWS "=" BWS chunk-ext-val ] )
1090 chunk-ext-name = token
1091 chunk-ext-val = token / quoted-string
1093 The chunked encoding is specific to each connection and is likely to
1094 be removed or recoded by each recipient (including intermediaries)
1095 before any higher-level application would have a chance to inspect
1096 the extensions. Hence, use of chunk extensions is generally limited
1097 to specialized HTTP services such as "long polling" (where client and
1098 server can have shared expectations regarding the use of chunk
1099 extensions) or for padding within an end-to-end secured connection.
1101 A recipient MUST ignore unrecognized chunk extensions. A server
1102 ought to limit the total length of chunk extensions received in a
1103 request to an amount reasonable for the services provided, in the
1104 same way that it applies length limitations and timeouts for other
1105 parts of a message, and generate an appropriate 4xx (Client Error)
1106 response if that amount is exceeded.
1108 7.1.2. Chunked Trailer Section
1110 A trailer section allows the sender to include additional fields at
1111 the end of a chunked message in order to supply metadata that might
1112 be dynamically generated while the message body is sent, such as a
1113 message integrity check, digital signature, or post-processing
1114 status. The proper use and limitations of trailer fields are defined
1115 in Section 5.6 of [Semantics].
1117 trailer-section = *( field-line CRLF )
1119 A recipient that decodes and removes the chunked encoding from a
1120 message (e.g., for storage or forwarding to a non-HTTP/1.1 peer) MUST
1121 discard any received trailer fields, store/forward them separately
1122 from the header fields, or selectively merge into the header section
1123 only those trailer fields corresponding to header field definitions
1124 that are understood by the recipient to explicitly permit and define
1125 how their corresponding trailer field value can be safely merged.
1127 7.1.3. Decoding Chunked
1129 A process for decoding the chunked transfer coding can be represented
1130 in pseudo-code as:
1132 length := 0
1133 read chunk-size, chunk-ext (if any), and CRLF
1134 while (chunk-size > 0) {
1135 read chunk-data and CRLF
1136 append chunk-data to decoded-body
1137 length := length + chunk-size
1138 read chunk-size, chunk-ext (if any), and CRLF
1139 }
1140 read trailer field
1141 while (trailer field is not empty) {
1142 if (trailer fields are stored/forwarded separately) {
1143 append trailer field to existing trailer fields
1144 }
1145 else if (trailer field is understood and defined as mergeable) {
1146 merge trailer field with existing header fields
1147 }
1148 else {
1149 discard trailer field
1150 }
1151 read trailer field
1152 }
1153 Content-Length := length
1154 Remove "chunked" from Transfer-Encoding
1155 Remove Trailer from existing header fields
1157 7.2. Transfer Codings for Compression
1159 The following transfer coding names for compression are defined by
1160 the same algorithm as their corresponding content coding:
1162 compress (and x-compress)
1163 See Section 7.1.2.1 of [Semantics].
1165 deflate
1166 See Section 7.1.2.2 of [Semantics].
1168 gzip (and x-gzip)
1169 See Section 7.1.2.3 of [Semantics].
1171 The compression codings do not define any parameters. Their presence
1172 SHOULD be treated as an error.
1174 7.3. Transfer Coding Registry
1176 The "HTTP Transfer Coding Registry" defines the namespace for
1177 transfer coding names. It is maintained at
1178 .
1180 Registrations MUST include the following fields:
1182 o Name
1184 o Description
1186 o Pointer to specification text
1188 Names of transfer codings MUST NOT overlap with names of content
1189 codings (Section 7.1.2 of [Semantics]) unless the encoding
1190 transformation is identical, as is the case for the compression
1191 codings defined in Section 7.2.
1193 The TE header field (Section 7.4) uses a pseudo parameter named "q"
1194 as rank value when multiple transfer codings are acceptable. Future
1195 registrations of transfer codings SHOULD NOT define parameters called
1196 "q" (case-insensitively) in order to avoid ambiguities.
1198 Values to be added to this namespace require IETF Review (see
1199 Section 4.8 of [RFC8126]), and MUST conform to the purpose of
1200 transfer coding defined in this specification.
1202 Use of program names for the identification of encoding formats is
1203 not desirable and is discouraged for future encodings.
1205 7.4. TE
1207 The "TE" header field in a request indicates what transfer codings,
1208 besides chunked, the client is willing to accept in response, and
1209 whether or not the client is willing to accept trailer fields in a
1210 chunked transfer coding.
1212 The TE field-value consists of a list of transfer coding names, each
1213 allowing for optional parameters (as described in Section 7), and/or
1214 the keyword "trailers". A client MUST NOT send the chunked transfer
1215 coding name in TE; chunked is always acceptable for HTTP/1.1
1216 recipients.
1218 TE = #t-codings
1219 t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
1220 t-ranking = OWS ";" OWS "q=" rank
1221 rank = ( "0" [ "." 0*3DIGIT ] )
1222 / ( "1" [ "." 0*3("0") ] )
1224 Three examples of TE use are below.
1226 TE: deflate
1227 TE:
1228 TE: trailers, deflate;q=0.5
1230 When multiple transfer codings are acceptable, the client MAY rank
1231 the codings by preference using a case-insensitive "q" parameter
1232 (similar to the qvalues used in content negotiation fields,
1233 Section 7.4.4 of [Semantics]). The rank value is a real number in
1234 the range 0 through 1, where 0.001 is the least preferred and 1 is
1235 the most preferred; a value of 0 means "not acceptable".
1237 If the TE field value is empty or if no TE field is present, the only
1238 acceptable transfer coding is chunked. A message with no transfer
1239 coding is always acceptable.
1241 The keyword "trailers" indicates that the sender will not discard
1242 trailer fields, as described in Section 5.6 of [Semantics].
1244 Since the TE header field only applies to the immediate connection, a
1245 sender of TE MUST also send a "TE" connection option within the
1246 Connection header field (Section 9.1) in order to prevent the TE
1247 field from being forwarded by intermediaries that do not support its
1248 semantics.
1250 8. Handling Incomplete Messages
1252 A server that receives an incomplete request message, usually due to
1253 a canceled request or a triggered timeout exception, MAY send an
1254 error response prior to closing the connection.
1256 A client that receives an incomplete response message, which can
1257 occur when a connection is closed prematurely or when decoding a
1258 supposedly chunked transfer coding fails, MUST record the message as
1259 incomplete. Cache requirements for incomplete responses are defined
1260 in Section 3 of [Caching].
1262 If a response terminates in the middle of the header section (before
1263 the empty line is received) and the status code might rely on header
1264 fields to convey the full meaning of the response, then the client
1265 cannot assume that meaning has been conveyed; the client might need
1266 to repeat the request in order to determine what action to take next.
1268 A message body that uses the chunked transfer coding is incomplete if
1269 the zero-sized chunk that terminates the encoding has not been
1270 received. A message that uses a valid Content-Length is incomplete
1271 if the size of the message body received (in octets) is less than the
1272 value given by Content-Length. A response that has neither chunked
1273 transfer coding nor Content-Length is terminated by closure of the
1274 connection and, thus, is considered complete regardless of the number
1275 of message body octets received, provided that the header section was
1276 received intact.
1278 9. Connection Management
1280 HTTP messaging is independent of the underlying transport- or
1281 session-layer connection protocol(s). HTTP only presumes a reliable
1282 transport with in-order delivery of requests and the corresponding
1283 in-order delivery of responses. The mapping of HTTP request and
1284 response structures onto the data units of an underlying transport
1285 protocol is outside the scope of this specification.
1287 As described in Section 6.3 of [Semantics], the specific connection
1288 protocols to be used for an HTTP interaction are determined by client
1289 configuration and the target URI. For example, the "http" URI scheme
1290 (Section 2.5.1 of [Semantics]) indicates a default connection of TCP
1291 over IP, with a default TCP port of 80, but the client might be
1292 configured to use a proxy via some other connection, port, or
1293 protocol.
1295 HTTP implementations are expected to engage in connection management,
1296 which includes maintaining the state of current connections,
1297 establishing a new connection or reusing an existing connection,
1298 processing messages received on a connection, detecting connection
1299 failures, and closing each connection. Most clients maintain
1300 multiple connections in parallel, including more than one connection
1301 per server endpoint. Most servers are designed to maintain thousands
1302 of concurrent connections, while controlling request queues to enable
1303 fair use and detect denial-of-service attacks.
1305 9.1. Connection
1307 The "Connection" header field allows the sender to list desired
1308 control options for the current connection.
1310 When a field aside from Connection is used to supply control
1311 information for or about the current connection, the sender MUST list
1312 the corresponding field name within the Connection header field.
1314 Intermediaries MUST parse a received Connection header field before a
1315 message is forwarded and, for each connection-option in this field,
1316 remove any header or trailer field(s) from the message with the same
1317 name as the connection-option, and then remove the Connection header
1318 field itself (or replace it with the intermediary's own connection
1319 options for the forwarded message).
1321 Hence, the Connection header field provides a declarative way of
1322 distinguishing fields that are only intended for the immediate
1323 recipient ("hop-by-hop") from those fields that are intended for all
1324 recipients on the chain ("end-to-end"), enabling the message to be
1325 self-descriptive and allowing future connection-specific extensions
1326 to be deployed without fear that they will be blindly forwarded by
1327 older intermediaries.
1329 Furthermore, intermediaries SHOULD remove or replace field(s) whose
1330 semantics are known to require removal before forwarding, whether or
1331 not they appear as a Connection option, after applying those fields'
1332 semantics. This includes but is not limited to:
1334 o Proxy-Connection (Appendix C.1.2)
1336 o Keep-Alive (Section 19.7.1 of [RFC2068])
1338 o TE (Section 7.4)
1340 o Trailer (Section 5.6.3 of [Semantics])
1342 o Transfer-Encoding (Section 6.1)
1344 o Upgrade (Section 9.9)
1345 The Connection header field's value has the following grammar:
1347 Connection = 1#connection-option
1348 connection-option = token
1350 Connection options are case-insensitive.
1352 A sender MUST NOT send a connection option corresponding to a field
1353 that is intended for all recipients of the payload. For example,
1354 Cache-Control is never appropriate as a connection option
1355 (Section 5.2 of [Caching]).
1357 The connection options do not always correspond to a field present in
1358 the message, since a connection-specific field might not be needed if
1359 there are no parameters associated with a connection option. In
1360 contrast, a connection-specific field that is received without a
1361 corresponding connection option usually indicates that the field has
1362 been improperly forwarded by an intermediary and ought to be ignored
1363 by the recipient.
1365 When defining new connection options, specification authors ought to
1366 document it as reserved field name and register that definition in
1367 the Hypertext Transfer Protocol (HTTP) Field Name Registry
1368 (Section 5.3.2 of [Semantics]), to avoid collisions.
1370 The "close" connection option is defined for a sender to signal that
1371 this connection will be closed after completion of the response. For
1372 example,
1374 Connection: close
1376 in either the request or the response header fields indicates that
1377 the sender is going to close the connection after the current
1378 request/response is complete (Section 9.7).
1380 A client that does not support persistent connections MUST send the
1381 "close" connection option in every request message.
1383 A server that does not support persistent connections MUST send the
1384 "close" connection option in every response message that does not
1385 have a 1xx (Informational) status code.
1387 9.2. Establishment
1389 It is beyond the scope of this specification to describe how
1390 connections are established via various transport- or session-layer
1391 protocols. Each connection applies to only one transport link.
1393 9.3. Associating a Response to a Request
1395 HTTP/1.1 does not include a request identifier for associating a
1396 given request message with its corresponding one or more response
1397 messages. Hence, it relies on the order of response arrival to
1398 correspond exactly to the order in which requests are made on the
1399 same connection. More than one response message per request only
1400 occurs when one or more informational responses (1xx, see
1401 Section 10.2 of [Semantics]) precede a final response to the same
1402 request.
1404 A client that has more than one outstanding request on a connection
1405 MUST maintain a list of outstanding requests in the order sent and
1406 MUST associate each received response message on that connection to
1407 the highest ordered request that has not yet received a final (non-
1408 1xx) response.
1410 If an HTTP/1.1 client receives data on a connection that doesn't have
1411 any outstanding requests, it MUST NOT consider them to be a response
1412 to a not-yet-issued request; it SHOULD close the connection, since
1413 message delimitation is now ambiguous, unless the data consists only
1414 of one or more CRLF (which can be discarded, as per Section 2.2).
1416 9.4. Persistence
1418 HTTP/1.1 defaults to the use of "persistent connections", allowing
1419 multiple requests and responses to be carried over a single
1420 connection. The "close" connection option is used to signal that a
1421 connection will not persist after the current request/response. HTTP
1422 implementations SHOULD support persistent connections.
1424 A recipient determines whether a connection is persistent or not
1425 based on the most recently received message's protocol version and
1426 Connection header field (if any):
1428 o If the "close" connection option is present, the connection will
1429 not persist after the current response; else,
1431 o If the received protocol is HTTP/1.1 (or later), the connection
1432 will persist after the current response; else,
1434 o If the received protocol is HTTP/1.0, the "keep-alive" connection
1435 option is present, either the recipient is not a proxy or the
1436 message is a response, and the recipient wishes to honor the
1437 HTTP/1.0 "keep-alive" mechanism, the connection will persist after
1438 the current response; otherwise,
1440 o The connection will close after the current response.
1442 A client MAY send additional requests on a persistent connection
1443 until it sends or receives a "close" connection option or receives an
1444 HTTP/1.0 response without a "keep-alive" connection option.
1446 In order to remain persistent, all messages on a connection need to
1447 have a self-defined message length (i.e., one not defined by closure
1448 of the connection), as described in Section 6. A server MUST read
1449 the entire request message body or close the connection after sending
1450 its response, since otherwise the remaining data on a persistent
1451 connection would be misinterpreted as the next request. Likewise, a
1452 client MUST read the entire response message body if it intends to
1453 reuse the same connection for a subsequent request.
1455 A proxy server MUST NOT maintain a persistent connection with an
1456 HTTP/1.0 client (see Section 19.7.1 of [RFC2068] for information and
1457 discussion of the problems with the Keep-Alive header field
1458 implemented by many HTTP/1.0 clients).
1460 See Appendix C.1.2 for more information on backwards compatibility
1461 with HTTP/1.0 clients.
1463 9.4.1. Retrying Requests
1465 Connections can be closed at any time, with or without intention.
1466 Implementations ought to anticipate the need to recover from
1467 asynchronous close events. The conditions under which a client can
1468 automatically retry a sequence of outstanding requests are defined in
1469 Section 8.2.2 of [Semantics].
1471 9.4.2. Pipelining
1473 A client that supports persistent connections MAY "pipeline" its
1474 requests (i.e., send multiple requests without waiting for each
1475 response). A server MAY process a sequence of pipelined requests in
1476 parallel if they all have safe methods (Section 8.2.1 of
1477 [Semantics]), but it MUST send the corresponding responses in the
1478 same order that the requests were received.
1480 A client that pipelines requests SHOULD retry unanswered requests if
1481 the connection closes before it receives all of the corresponding
1482 responses. When retrying pipelined requests after a failed
1483 connection (a connection not explicitly closed by the server in its
1484 last complete response), a client MUST NOT pipeline immediately after
1485 connection establishment, since the first remaining request in the
1486 prior pipeline might have caused an error response that can be lost
1487 again if multiple requests are sent on a prematurely closed
1488 connection (see the TCP reset problem described in Section 9.7).
1490 Idempotent methods (Section 8.2.2 of [Semantics]) are significant to
1491 pipelining because they can be automatically retried after a
1492 connection failure. A user agent SHOULD NOT pipeline requests after
1493 a non-idempotent method, until the final response status code for
1494 that method has been received, unless the user agent has a means to
1495 detect and recover from partial failure conditions involving the
1496 pipelined sequence.
1498 An intermediary that receives pipelined requests MAY pipeline those
1499 requests when forwarding them inbound, since it can rely on the
1500 outbound user agent(s) to determine what requests can be safely
1501 pipelined. If the inbound connection fails before receiving a
1502 response, the pipelining intermediary MAY attempt to retry a sequence
1503 of requests that have yet to receive a response if the requests all
1504 have idempotent methods; otherwise, the pipelining intermediary
1505 SHOULD forward any received responses and then close the
1506 corresponding outbound connection(s) so that the outbound user
1507 agent(s) can recover accordingly.
1509 9.5. Concurrency
1511 A client ought to limit the number of simultaneous open connections
1512 that it maintains to a given server.
1514 Previous revisions of HTTP gave a specific number of connections as a
1515 ceiling, but this was found to be impractical for many applications.
1516 As a result, this specification does not mandate a particular maximum
1517 number of connections but, instead, encourages clients to be
1518 conservative when opening multiple connections.
1520 Multiple connections are typically used to avoid the "head-of-line
1521 blocking" problem, wherein a request that takes significant server-
1522 side processing and/or has a large payload blocks subsequent requests
1523 on the same connection. However, each connection consumes server
1524 resources. Furthermore, using multiple connections can cause
1525 undesirable side effects in congested networks.
1527 Note that a server might reject traffic that it deems abusive or
1528 characteristic of a denial-of-service attack, such as an excessive
1529 number of open connections from a single client.
1531 9.6. Failures and Timeouts
1533 Servers will usually have some timeout value beyond which they will
1534 no longer maintain an inactive connection. Proxy servers might make
1535 this a higher value since it is likely that the client will be making
1536 more connections through the same proxy server. The use of
1537 persistent connections places no requirements on the length (or
1538 existence) of this timeout for either the client or the server.
1540 A client or server that wishes to time out SHOULD issue a graceful
1541 close on the connection. Implementations SHOULD constantly monitor
1542 open connections for a received closure signal and respond to it as
1543 appropriate, since prompt closure of both sides of a connection
1544 enables allocated system resources to be reclaimed.
1546 A client, server, or proxy MAY close the transport connection at any
1547 time. For example, a client might have started to send a new request
1548 at the same time that the server has decided to close the "idle"
1549 connection. From the server's point of view, the connection is being
1550 closed while it was idle, but from the client's point of view, a
1551 request is in progress.
1553 A server SHOULD sustain persistent connections, when possible, and
1554 allow the underlying transport's flow-control mechanisms to resolve
1555 temporary overloads, rather than terminate connections with the
1556 expectation that clients will retry. The latter technique can
1557 exacerbate network congestion.
1559 A client sending a message body SHOULD monitor the network connection
1560 for an error response while it is transmitting the request. If the
1561 client sees a response that indicates the server does not wish to
1562 receive the message body and is closing the connection, the client
1563 SHOULD immediately cease transmitting the body and close its side of
1564 the connection.
1566 9.7. Tear-down
1568 The Connection header field (Section 9.1) provides a "close"
1569 connection option that a sender SHOULD send when it wishes to close
1570 the connection after the current request/response pair.
1572 A client that sends a "close" connection option MUST NOT send further
1573 requests on that connection (after the one containing "close") and
1574 MUST close the connection after reading the final response message
1575 corresponding to this request.
1577 A server that receives a "close" connection option MUST initiate a
1578 close of the connection (see below) after it sends the final response
1579 to the request that contained "close". The server SHOULD send a
1580 "close" connection option in its final response on that connection.
1581 The server MUST NOT process any further requests received on that
1582 connection.
1584 A server that sends a "close" connection option MUST initiate a close
1585 of the connection (see below) after it sends the response containing
1586 "close". The server MUST NOT process any further requests received
1587 on that connection.
1589 A client that receives a "close" connection option MUST cease sending
1590 requests on that connection and close the connection after reading
1591 the response message containing the "close"; if additional pipelined
1592 requests had been sent on the connection, the client SHOULD NOT
1593 assume that they will be processed by the server.
1595 If a server performs an immediate close of a TCP connection, there is
1596 a significant risk that the client will not be able to read the last
1597 HTTP response. If the server receives additional data from the
1598 client on a fully closed connection, such as another request that was
1599 sent by the client before receiving the server's response, the
1600 server's TCP stack will send a reset packet to the client;
1601 unfortunately, the reset packet might erase the client's
1602 unacknowledged input buffers before they can be read and interpreted
1603 by the client's HTTP parser.
1605 To avoid the TCP reset problem, servers typically close a connection
1606 in stages. First, the server performs a half-close by closing only
1607 the write side of the read/write connection. The server then
1608 continues to read from the connection until it receives a
1609 corresponding close by the client, or until the server is reasonably
1610 certain that its own TCP stack has received the client's
1611 acknowledgement of the packet(s) containing the server's last
1612 response. Finally, the server fully closes the connection.
1614 It is unknown whether the reset problem is exclusive to TCP or might
1615 also be found in other transport connection protocols.
1617 9.8. TLS Connection Closure
1619 TLS provides a facility for secure connection closure. When a valid
1620 closure alert is received, an implementation can be assured that no
1621 further data will be received on that connection. TLS
1622 implementations MUST initiate an exchange of closure alerts before
1623 closing a connection. A TLS implementation MAY, after sending a
1624 closure alert, close the connection without waiting for the peer to
1625 send its closure alert, generating an "incomplete close". Note that
1626 an implementation which does this MAY choose to reuse the session.
1627 This SHOULD only be done when the application knows (typically
1628 through detecting HTTP message boundaries) that it has received all
1629 the message data that it cares about.
1631 As specified in [RFC8446], any implementation which receives a
1632 connection close without first receiving a valid closure alert (a
1633 "premature close") MUST NOT reuse that session. Note that a
1634 premature close does not call into question the security of the data
1635 already received, but simply indicates that subsequent data might
1636 have been truncated. Because TLS is oblivious to HTTP request/
1637 response boundaries, it is necessary to examine the HTTP data itself
1638 (specifically the Content-Length header) to determine whether the
1639 truncation occurred inside a message or between messages.
1641 When encountering a premature close, a client SHOULD treat as
1642 completed all requests for which it has received as much data as
1643 specified in the Content-Length header.
1645 A client detecting an incomplete close SHOULD recover gracefully. It
1646 MAY resume a TLS session closed in this fashion.
1648 Clients MUST send a closure alert before closing the connection.
1649 Clients which are unprepared to receive any more data MAY choose not
1650 to wait for the server's closure alert and simply close the
1651 connection, thus generating an incomplete close on the server side.
1653 Servers SHOULD be prepared to receive an incomplete close from the
1654 client, since the client can often determine when the end of server
1655 data is. Servers SHOULD be willing to resume TLS sessions closed in
1656 this fashion.
1658 Servers MUST attempt to initiate an exchange of closure alerts with
1659 the client before closing the connection. Servers MAY close the
1660 connection after sending the closure alert, thus generating an
1661 incomplete close on the client side.
1663 9.9. Upgrade
1665 The "Upgrade" header field is intended to provide a simple mechanism
1666 for transitioning from HTTP/1.1 to some other protocol on the same
1667 connection.
1669 A client MAY send a list of protocol names in the Upgrade header
1670 field of a request to invite the server to switch to one or more of
1671 the named protocols, in order of descending preference, before
1672 sending the final response. A server MAY ignore a received Upgrade
1673 header field if it wishes to continue using the current protocol on
1674 that connection. Upgrade cannot be used to insist on a protocol
1675 change.
1677 Upgrade = 1#protocol
1679 protocol = protocol-name ["/" protocol-version]
1680 protocol-name = token
1681 protocol-version = token
1683 Although protocol names are registered with a preferred case,
1684 recipients SHOULD use case-insensitive comparison when matching each
1685 protocol-name to supported protocols.
1687 A server that sends a 101 (Switching Protocols) response MUST send an
1688 Upgrade header field to indicate the new protocol(s) to which the
1689 connection is being switched; if multiple protocol layers are being
1690 switched, the sender MUST list the protocols in layer-ascending
1691 order. A server MUST NOT switch to a protocol that was not indicated
1692 by the client in the corresponding request's Upgrade header field. A
1693 server MAY choose to ignore the order of preference indicated by the
1694 client and select the new protocol(s) based on other factors, such as
1695 the nature of the request or the current load on the server.
1697 A server that sends a 426 (Upgrade Required) response MUST send an
1698 Upgrade header field to indicate the acceptable protocols, in order
1699 of descending preference.
1701 A server MAY send an Upgrade header field in any other response to
1702 advertise that it implements support for upgrading to the listed
1703 protocols, in order of descending preference, when appropriate for a
1704 future request.
1706 The following is a hypothetical example sent by a client:
1708 GET /hello HTTP/1.1
1709 Host: www.example.com
1710 Connection: upgrade
1711 Upgrade: websocket, IRC/6.9, RTA/x11
1713 The capabilities and nature of the application-level communication
1714 after the protocol change is entirely dependent upon the new
1715 protocol(s) chosen. However, immediately after sending the 101
1716 (Switching Protocols) response, the server is expected to continue
1717 responding to the original request as if it had received its
1718 equivalent within the new protocol (i.e., the server still has an
1719 outstanding request to satisfy after the protocol has been changed,
1720 and is expected to do so without requiring the request to be
1721 repeated).
1723 For example, if the Upgrade header field is received in a GET request
1724 and the server decides to switch protocols, it first responds with a
1725 101 (Switching Protocols) message in HTTP/1.1 and then immediately
1726 follows that with the new protocol's equivalent of a response to a
1727 GET on the target resource. This allows a connection to be upgraded
1728 to protocols with the same semantics as HTTP without the latency cost
1729 of an additional round trip. A server MUST NOT switch protocols
1730 unless the received message semantics can be honored by the new
1731 protocol; an OPTIONS request can be honored by any protocol.
1733 The following is an example response to the above hypothetical
1734 request:
1736 HTTP/1.1 101 Switching Protocols
1737 Connection: upgrade
1738 Upgrade: websocket
1740 [... data stream switches to websocket with an appropriate response
1741 (as defined by new protocol) to the "GET /hello" request ...]
1743 When Upgrade is sent, the sender MUST also send a Connection header
1744 field (Section 9.1) that contains an "upgrade" connection option, in
1745 order to prevent Upgrade from being accidentally forwarded by
1746 intermediaries that might not implement the listed protocols. A
1747 server MUST ignore an Upgrade header field that is received in an
1748 HTTP/1.0 request.
1750 A client cannot begin using an upgraded protocol on the connection
1751 until it has completely sent the request message (i.e., the client
1752 can't change the protocol it is sending in the middle of a message).
1753 If a server receives both an Upgrade and an Expect header field with
1754 the "100-continue" expectation (Section 9.1.1 of [Semantics]), the
1755 server MUST send a 100 (Continue) response before sending a 101
1756 (Switching Protocols) response.
1758 The Upgrade header field only applies to switching protocols on top
1759 of the existing connection; it cannot be used to switch the
1760 underlying connection (transport) protocol, nor to switch the
1761 existing communication to a different connection. For those
1762 purposes, it is more appropriate to use a 3xx (Redirection) response
1763 (Section 10.4 of [Semantics]).
1765 9.9.1. Upgrade Protocol Names
1767 This specification only defines the protocol name "HTTP" for use by
1768 the family of Hypertext Transfer Protocols, as defined by the HTTP
1769 version rules of Section 4.2 of [Semantics] and future updates to
1770 this specification. Additional protocol names ought to be registered
1771 using the registration procedure defined in Section 9.9.2.
1773 +------+-------------------+-----------------+----------------+
1774 | Name | Description | Expected | Reference |
1775 | | | Version Tokens | |
1776 | HTTP | Hypertext | any DIGIT.DIGIT | Section 4.2 of |
1777 | | Transfer Protocol | (e.g, "2.0") | [Semantics] |
1778 +------+-------------------+-----------------+----------------+
1780 Table 4
1782 9.9.2. Upgrade Token Registry
1784 The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry"
1785 defines the namespace for protocol-name tokens used to identify
1786 protocols in the Upgrade header field. The registry is maintained at
1787 .
1789 Each registered protocol name is associated with contact information
1790 and an optional set of specifications that details how the connection
1791 will be processed after it has been upgraded.
1793 Registrations happen on a "First Come First Served" basis (see
1794 Section 4.4 of [RFC8126]) and are subject to the following rules:
1796 1. A protocol-name token, once registered, stays registered forever.
1798 2. A protocol-name token is case-insensitive and registered with the
1799 preferred case to be generated by senders.
1801 3. The registration MUST name a responsible party for the
1802 registration.
1804 4. The registration MUST name a point of contact.
1806 5. The registration MAY name a set of specifications associated with
1807 that token. Such specifications need not be publicly available.
1809 6. The registration SHOULD name a set of expected "protocol-version"
1810 tokens associated with that token at the time of registration.
1812 7. The responsible party MAY change the registration at any time.
1813 The IANA will keep a record of all such changes, and make them
1814 available upon request.
1816 8. The IESG MAY reassign responsibility for a protocol token. This
1817 will normally only be used in the case when a responsible party
1818 cannot be contacted.
1820 10. Enclosing Messages as Data
1822 10.1. Media Type message/http
1824 The message/http media type can be used to enclose a single HTTP
1825 request or response message, provided that it obeys the MIME
1826 restrictions for all "message" types regarding line length and
1827 encodings.
1829 Type name: message
1831 Subtype name: http
1833 Required parameters: N/A
1835 Optional parameters: version, msgtype
1837 version: The HTTP-version number of the enclosed message (e.g.,
1838 "1.1"). If not present, the version can be determined from the
1839 first line of the body.
1841 msgtype: The message type - "request" or "response". If not
1842 present, the type can be determined from the first line of the
1843 body.
1845 Encoding considerations: only "7bit", "8bit", or "binary" are
1846 permitted
1848 Security considerations: see Section 11
1850 Interoperability considerations: N/A
1852 Published specification: This specification (see Section 10.1).
1854 Applications that use this media type: N/A
1856 Fragment identifier considerations: N/A
1857 Additional information: Magic number(s): N/A
1859 Deprecated alias names for this type: N/A
1861 File extension(s): N/A
1863 Macintosh file type code(s): N/A
1865 Person and email address to contact for further information: See Aut
1866 hors' Addresses section.
1868 Intended usage: COMMON
1870 Restrictions on usage: N/A
1872 Author: See Authors' Addresses section.
1874 Change controller: IESG
1876 10.2. Media Type application/http
1878 The application/http media type can be used to enclose a pipeline of
1879 one or more HTTP request or response messages (not intermixed).
1881 Type name: application
1883 Subtype name: http
1885 Required parameters: N/A
1887 Optional parameters: version, msgtype
1889 version: The HTTP-version number of the enclosed messages (e.g.,
1890 "1.1"). If not present, the version can be determined from the
1891 first line of the body.
1893 msgtype: The message type - "request" or "response". If not
1894 present, the type can be determined from the first line of the
1895 body.
1897 Encoding considerations: HTTP messages enclosed by this type are in
1898 "binary" format; use of an appropriate Content-Transfer-Encoding
1899 is required when transmitted via email.
1901 Security considerations: see Section 11
1903 Interoperability considerations: N/A
1904 Published specification: This specification (see Section 10.2).
1906 Applications that use this media type: N/A
1908 Fragment identifier considerations: N/A
1910 Additional information: Deprecated alias names for this type: N/A
1912 Magic number(s): N/A
1914 File extension(s): N/A
1916 Macintosh file type code(s): N/A
1918 Person and email address to contact for further information: See Aut
1919 hors' Addresses section.
1921 Intended usage: COMMON
1923 Restrictions on usage: N/A
1925 Author: See Authors' Addresses section.
1927 Change controller: IESG
1929 11. Security Considerations
1931 This section is meant to inform developers, information providers,
1932 and users of known security considerations relevant to HTTP message
1933 syntax, parsing, and routing. Security considerations about HTTP
1934 semantics and payloads are addressed in [Semantics].
1936 11.1. Response Splitting
1938 Response splitting (a.k.a, CRLF injection) is a common technique,
1939 used in various attacks on Web usage, that exploits the line-based
1940 nature of HTTP message framing and the ordered association of
1941 requests to responses on persistent connections [Klein]. This
1942 technique can be particularly damaging when the requests pass through
1943 a shared cache.
1945 Response splitting exploits a vulnerability in servers (usually
1946 within an application server) where an attacker can send encoded data
1947 within some parameter of the request that is later decoded and echoed
1948 within any of the response header fields of the response. If the
1949 decoded data is crafted to look like the response has ended and a
1950 subsequent response has begun, the response has been split and the
1951 content within the apparent second response is controlled by the
1952 attacker. The attacker can then make any other request on the same
1953 persistent connection and trick the recipients (including
1954 intermediaries) into believing that the second half of the split is
1955 an authoritative answer to the second request.
1957 For example, a parameter within the request-target might be read by
1958 an application server and reused within a redirect, resulting in the
1959 same parameter being echoed in the Location header field of the
1960 response. If the parameter is decoded by the application and not
1961 properly encoded when placed in the response field, the attacker can
1962 send encoded CRLF octets and other content that will make the
1963 application's single response look like two or more responses.
1965 A common defense against response splitting is to filter requests for
1966 data that looks like encoded CR and LF (e.g., "%0D" and "%0A").
1967 However, that assumes the application server is only performing URI
1968 decoding, rather than more obscure data transformations like charset
1969 transcoding, XML entity translation, base64 decoding, sprintf
1970 reformatting, etc. A more effective mitigation is to prevent
1971 anything other than the server's core protocol libraries from sending
1972 a CR or LF within the header section, which means restricting the
1973 output of header fields to APIs that filter for bad octets and not
1974 allowing application servers to write directly to the protocol
1975 stream.
1977 11.2. Request Smuggling
1979 Request smuggling ([Linhart]) is a technique that exploits
1980 differences in protocol parsing among various recipients to hide
1981 additional requests (which might otherwise be blocked or disabled by
1982 policy) within an apparently harmless request. Like response
1983 splitting, request smuggling can lead to a variety of attacks on HTTP
1984 usage.
1986 This specification has introduced new requirements on request
1987 parsing, particularly with regard to message framing in Section 6.3,
1988 to reduce the effectiveness of request smuggling.
1990 11.3. Message Integrity
1992 HTTP does not define a specific mechanism for ensuring message
1993 integrity, instead relying on the error-detection ability of
1994 underlying transport protocols and the use of length or chunk-
1995 delimited framing to detect completeness. Additional integrity
1996 mechanisms, such as hash functions or digital signatures applied to
1997 the content, can be selectively added to messages via extensible
1998 metadata fields. Historically, the lack of a single integrity
1999 mechanism has been justified by the informal nature of most HTTP
2000 communication. However, the prevalence of HTTP as an information
2001 access mechanism has resulted in its increasing use within
2002 environments where verification of message integrity is crucial.
2004 User agents are encouraged to implement configurable means for
2005 detecting and reporting failures of message integrity such that those
2006 means can be enabled within environments for which integrity is
2007 necessary. For example, a browser being used to view medical history
2008 or drug interaction information needs to indicate to the user when
2009 such information is detected by the protocol to be incomplete,
2010 expired, or corrupted during transfer. Such mechanisms might be
2011 selectively enabled via user agent extensions or the presence of
2012 message integrity metadata in a response. At a minimum, user agents
2013 ought to provide some indication that allows a user to distinguish
2014 between a complete and incomplete response message (Section 8) when
2015 such verification is desired.
2017 11.4. Message Confidentiality
2019 HTTP relies on underlying transport protocols to provide message
2020 confidentiality when that is desired. HTTP has been specifically
2021 designed to be independent of the transport protocol, such that it
2022 can be used over many different forms of encrypted connection, with
2023 the selection of such transports being identified by the choice of
2024 URI scheme or within user agent configuration.
2026 The "https" scheme can be used to identify resources that require a
2027 confidential connection, as described in Section 2.5.2 of
2028 [Semantics].
2030 12. IANA Considerations
2032 The change controller for the following registrations is: "IETF
2033 (iesg@ietf.org) - Internet Engineering Task Force".
2035 12.1. Field Name Registration
2037 Please update the "Hypertext Transfer Protocol (HTTP) Field Name
2038 Registry" at with the
2039 field names listed in the two tables of Section 5.
2041 12.2. Media Type Registration
2043 Please update the "Media Types" registry at
2044 with the registration
2045 information in Section 10.1 and Section 10.2 for the media types
2046 "message/http" and "application/http", respectively.
2048 12.3. Transfer Coding Registration
2050 Please update the "HTTP Transfer Coding Registry" at
2051 with the
2052 registration procedure of Section 7.3 and the content coding names
2053 summarized in the table of Section 7.
2055 12.4. Upgrade Token Registration
2057 Please update the "Hypertext Transfer Protocol (HTTP) Upgrade Token
2058 Registry" at
2059 with the registration procedure of Section 9.9.2 and the upgrade
2060 token names summarized in the table of Section 9.9.1.
2062 12.5. ALPN Protocol ID Registration
2064 Please update the "TLS Application-Layer Protocol Negotiation (ALPN)
2065 Protocol IDs" registry at with the
2067 registration below:
2069 +----------+-----------------------------+----------------+
2070 | Protocol | Identification Sequence | Reference |
2071 | HTTP/1.1 | 0x68 0x74 0x74 0x70 0x2f | (this |
2072 | | 0x31 0x2e 0x31 ("http/1.1") | specification) |
2073 +----------+-----------------------------+----------------+
2075 Table 5
2077 13. References
2079 13.1. Normative References
2081 [Caching] Fielding, R., Ed., Nottingham, M., Ed., and J. F. Reschke,
2082 Ed., "HTTP Caching", Work in Progress, Internet-Draft,
2083 draft-ietf-httpbis-cache-10, July 12, 2020,
2084 .
2086 [RFC1950] Deutsch, L.P. and J-L. Gailly, "ZLIB Compressed Data
2087 Format Specification version 3.3", RFC 1950,
2088 DOI 10.17487/RFC1950, May 1996,
2089 .
2091 [RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
2092 version 1.3", RFC 1951, DOI 10.17487/RFC1951, May 1996,
2093 .
2095 [RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L.P., and
2096 G. Randers-Pehrson, "GZIP file format specification
2097 version 4.3", RFC 1952, DOI 10.17487/RFC1952, May 1996,
2098 .
2100 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
2101 Requirement Levels", BCP 14, RFC 2119,
2102 DOI 10.17487/RFC2119, March 1997,
2103 .
2105 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
2106 Resource Identifier (URI): Generic Syntax", STD 66,
2107 RFC 3986, DOI 10.17487/RFC3986, January 2005,
2108 .
2110 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
2111 Specifications: ABNF", STD 68, RFC 5234,
2112 DOI 10.17487/RFC5234, January 2008,
2113 .
2115 [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
2116 RFC 7405, DOI 10.17487/RFC7405, December 2014,
2117 .
2119 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2120 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
2121 May 2017, .
2123 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
2124 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
2125 .
2127 [Semantics]
2128 Fielding, R., Ed., Nottingham, M., Ed., and J. F. Reschke,
2129 Ed., "HTTP Semantics", Work in Progress, Internet-Draft,
2130 draft-ietf-httpbis-semantics-10, July 12, 2020,
2131 .
2134 [USASCII] American National Standards Institute, "Coded Character
2135 Set -- 7-bit American Standard Code for Information
2136 Interchange", ANSI X3.4, 1986.
2138 [Welch] Welch, T. A., "A Technique for High-Performance Data
2139 Compression", IEEE Computer 17(6), June 1984.
2141 13.2. Informative References
2143 [Err4667] RFC Errata, Erratum ID 4667, RFC 7230,
2144 .
2146 [Klein] Klein, A., "Divide and Conquer - HTTP Response Splitting,
2147 Web Cache Poisoning Attacks, and Related Topics", March
2148 2004, .
2151 [Linhart] Linhart, C., Klein, A., Heled, R., and S. Orrin, "HTTP
2152 Request Smuggling", June 2005,
2153 .
2155 [RFC1945] Berners-Lee, T., Fielding, R.T., and H.F. Nielsen,
2156 "Hypertext Transfer Protocol -- HTTP/1.0", RFC 1945,
2157 DOI 10.17487/RFC1945, May 1996,
2158 .
2160 [RFC2045] Freed, N. and N.S. Borenstein, "Multipurpose Internet Mail
2161 Extensions (MIME) Part One: Format of Internet Message
2162 Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
2163 .
2165 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
2166 Extensions (MIME) Part Two: Media Types", RFC 2046,
2167 DOI 10.17487/RFC2046, November 1996,
2168 .
2170 [RFC2049] Freed, N. and N.S. Borenstein, "Multipurpose Internet Mail
2171 Extensions (MIME) Part Five: Conformance Criteria and
2172 Examples", RFC 2049, DOI 10.17487/RFC2049, November 1996,
2173 .
2175 [RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
2176 Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
2177 RFC 2068, DOI 10.17487/RFC2068, January 1997,
2178 .
2180 [RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud,
2181 "MIME Encapsulation of Aggregate Documents, such as HTML
2182 (MHTML)", RFC 2557, DOI 10.17487/RFC2557, March 1999,
2183 .
2185 [RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
2186 DOI 10.17487/RFC5322, October 2008,
2187 .
2189 [RFC7230] Fielding, R., Ed. and J. F. Reschke, Ed., "Hypertext
2190 Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
2191 RFC 7230, DOI 10.17487/RFC7230, June 2014,
2192 .
2194 [RFC7231] Fielding, R., Ed. and J. F. Reschke, Ed., "Hypertext
2195 Transfer Protocol (HTTP/1.1): Semantics and Content",
2196 RFC 7231, DOI 10.17487/RFC7231, June 2014,
2197 .
2199 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
2200 Writing an IANA Considerations Section in RFCs", BCP 26,
2201 RFC 8126, DOI 10.17487/RFC8126, June 2017,
2202 .
2204 Appendix A. Collected ABNF
2206 In the collected ABNF below, list rules are expanded as per
2207 Section 5.5.1 of [Semantics].
2209 BWS =
2211 Connection = connection-option *( OWS "," OWS connection-option )
2213 HTTP-message = start-line CRLF *( field-line CRLF ) CRLF [
2214 message-body ]
2215 HTTP-name = %x48.54.54.50 ; HTTP
2216 HTTP-version = HTTP-name "/" DIGIT "." DIGIT
2218 OWS =
2220 RWS =
2222 TE = [ t-codings *( OWS "," OWS t-codings ) ]
2223 Transfer-Encoding = transfer-coding *( OWS "," OWS transfer-coding )
2225 Upgrade = protocol *( OWS "," OWS protocol )
2227 absolute-URI =
2228 absolute-form = absolute-URI
2229 absolute-path =
2230 asterisk-form = "*"
2231 authority =
2232 authority-form = authority
2234 chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
2235 chunk-data = 1*OCTET
2236 chunk-ext = *( BWS ";" BWS chunk-ext-name [ BWS "=" BWS chunk-ext-val
2237 ] )
2238 chunk-ext-name = token
2239 chunk-ext-val = token / quoted-string
2240 chunk-size = 1*HEXDIG
2241 chunked-body = *chunk last-chunk trailer-section CRLF
2242 comment =
2243 connection-option = token
2245 field-line = field-name ":" OWS field-value OWS
2246 field-name =
2247 field-value =
2249 last-chunk = 1*"0" [ chunk-ext ] CRLF
2251 message-body = *OCTET
2252 method = token
2254 obs-fold = OWS CRLF RWS
2255 obs-text =
2256 origin-form = absolute-path [ "?" query ]
2258 port =
2259 protocol = protocol-name [ "/" protocol-version ]
2260 protocol-name = token
2261 protocol-version = token
2263 query =
2264 quoted-string =
2266 rank = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
2267 reason-phrase = 1*( HTAB / SP / VCHAR / obs-text )
2268 request-line = method SP request-target SP HTTP-version
2269 request-target = origin-form / absolute-form / authority-form /
2270 asterisk-form
2272 start-line = request-line / status-line
2273 status-code = 3DIGIT
2274 status-line = HTTP-version SP status-code SP [ reason-phrase ]
2276 t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
2277 t-ranking = OWS ";" OWS "q=" rank
2278 token =
2279 trailer-section = *( field-line CRLF )
2280 transfer-coding = token *( OWS ";" OWS transfer-parameter )
2281 transfer-parameter = token BWS "=" BWS ( token / quoted-string )
2283 uri-host =
2285 Appendix B. Differences between HTTP and MIME
2287 HTTP/1.1 uses many of the constructs defined for the Internet Message
2288 Format [RFC5322] and the Multipurpose Internet Mail Extensions (MIME)
2289 [RFC2045] to allow a message body to be transmitted in an open
2290 variety of representations and with extensible fields. However, RFC
2291 2045 is focused only on email; applications of HTTP have many
2292 characteristics that differ from email; hence, HTTP has features that
2293 differ from MIME. These differences were carefully chosen to
2294 optimize performance over binary connections, to allow greater
2295 freedom in the use of new media types, to make date comparisons
2296 easier, and to acknowledge the practice of some early HTTP servers
2297 and clients.
2299 This appendix describes specific areas where HTTP differs from MIME.
2300 Proxies and gateways to and from strict MIME environments need to be
2301 aware of these differences and provide the appropriate conversions
2302 where necessary.
2304 B.1. MIME-Version
2306 HTTP is not a MIME-compliant protocol. However, messages can include
2307 a single MIME-Version header field to indicate what version of the
2308 MIME protocol was used to construct the message. Use of the MIME-
2309 Version header field indicates that the message is in full
2310 conformance with the MIME protocol (as defined in [RFC2045]).
2311 Senders are responsible for ensuring full conformance (where
2312 possible) when exporting HTTP messages to strict MIME environments.
2314 B.2. Conversion to Canonical Form
2316 MIME requires that an Internet mail body part be converted to
2317 canonical form prior to being transferred, as described in Section 4
2318 of [RFC2049]. Section 7.1.1.2 of [Semantics] describes the forms
2319 allowed for subtypes of the "text" media type when transmitted over
2320 HTTP. [RFC2046] requires that content with a type of "text"
2321 represent line breaks as CRLF and forbids the use of CR or LF outside
2322 of line break sequences. HTTP allows CRLF, bare CR, and bare LF to
2323 indicate a line break within text content.
2325 A proxy or gateway from HTTP to a strict MIME environment ought to
2326 translate all line breaks within text media types to the RFC 2049
2327 canonical form of CRLF. Note, however, this might be complicated by
2328 the presence of a Content-Encoding and by the fact that HTTP allows
2329 the use of some charsets that do not use octets 13 and 10 to
2330 represent CR and LF, respectively.
2332 Conversion will break any cryptographic checksums applied to the
2333 original content unless the original content is already in canonical
2334 form. Therefore, the canonical form is recommended for any content
2335 that uses such checksums in HTTP.
2337 B.3. Conversion of Date Formats
2339 HTTP/1.1 uses a restricted set of date formats (Section 5.4.1.5 of
2340 [Semantics]) to simplify the process of date comparison. Proxies and
2341 gateways from other protocols ought to ensure that any Date header
2342 field present in a message conforms to one of the HTTP/1.1 formats
2343 and rewrite the date if necessary.
2345 B.4. Conversion of Content-Encoding
2347 MIME does not include any concept equivalent to HTTP/1.1's Content-
2348 Encoding header field. Since this acts as a modifier on the media
2349 type, proxies and gateways from HTTP to MIME-compliant protocols
2350 ought to either change the value of the Content-Type header field or
2351 decode the representation before forwarding the message. (Some
2352 experimental applications of Content-Type for Internet mail have used
2353 a media-type parameter of ";conversions=" to perform
2354 a function equivalent to Content-Encoding. However, this parameter
2355 is not part of the MIME standards).
2357 B.5. Conversion of Content-Transfer-Encoding
2359 HTTP does not use the Content-Transfer-Encoding field of MIME.
2360 Proxies and gateways from MIME-compliant protocols to HTTP need to
2361 remove any Content-Transfer-Encoding prior to delivering the response
2362 message to an HTTP client.
2364 Proxies and gateways from HTTP to MIME-compliant protocols are
2365 responsible for ensuring that the message is in the correct format
2366 and encoding for safe transport on that protocol, where "safe
2367 transport" is defined by the limitations of the protocol being used.
2368 Such a proxy or gateway ought to transform and label the data with an
2369 appropriate Content-Transfer-Encoding if doing so will improve the
2370 likelihood of safe transport over the destination protocol.
2372 B.6. MHTML and Line Length Limitations
2374 HTTP implementations that share code with MHTML [RFC2557]
2375 implementations need to be aware of MIME line length limitations.
2376 Since HTTP does not have this limitation, HTTP does not fold long
2377 lines. MHTML messages being transported by HTTP follow all
2378 conventions of MHTML, including line length limitations and folding,
2379 canonicalization, etc., since HTTP transfers message-bodies as
2380 payload and, aside from the "multipart/byteranges" type
2381 (Section 7.3.5 of [Semantics]), does not interpret the content or any
2382 MIME header lines that might be contained therein.
2384 Appendix C. HTTP Version History
2386 HTTP has been in use since 1990. The first version, later referred
2387 to as HTTP/0.9, was a simple protocol for hypertext data transfer
2388 across the Internet, using only a single request method (GET) and no
2389 metadata. HTTP/1.0, as defined by [RFC1945], added a range of
2390 request methods and MIME-like messaging, allowing for metadata to be
2391 transferred and modifiers placed on the request/response semantics.
2392 However, HTTP/1.0 did not sufficiently take into consideration the
2393 effects of hierarchical proxies, caching, the need for persistent
2394 connections, or name-based virtual hosts. The proliferation of
2395 incompletely implemented applications calling themselves "HTTP/1.0"
2396 further necessitated a protocol version change in order for two
2397 communicating applications to determine each other's true
2398 capabilities.
2400 HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
2401 requirements that enable reliable implementations, adding only those
2402 features that can either be safely ignored by an HTTP/1.0 recipient
2403 or only be sent when communicating with a party advertising
2404 conformance with HTTP/1.1.
2406 HTTP/1.1 has been designed to make supporting previous versions easy.
2407 A general-purpose HTTP/1.1 server ought to be able to understand any
2408 valid request in the format of HTTP/1.0, responding appropriately
2409 with an HTTP/1.1 message that only uses features understood (or
2410 safely ignored) by HTTP/1.0 clients. Likewise, an HTTP/1.1 client
2411 can be expected to understand any valid HTTP/1.0 response.
2413 Since HTTP/0.9 did not support header fields in a request, there is
2414 no mechanism for it to support name-based virtual hosts (selection of
2415 resource by inspection of the Host header field). Any server that
2416 implements name-based virtual hosts ought to disable support for
2417 HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in fact,
2418 badly constructed HTTP/1.x requests caused by a client failing to
2419 properly encode the request-target.
2421 C.1. Changes from HTTP/1.0
2423 This section summarizes major differences between versions HTTP/1.0
2424 and HTTP/1.1.
2426 C.1.1. Multihomed Web Servers
2428 The requirements that clients and servers support the Host header
2429 field (Section 6.6 of [Semantics]), report an error if it is missing
2430 from an HTTP/1.1 request, and accept absolute URIs (Section 3.2) are
2431 among the most important changes defined by HTTP/1.1.
2433 Older HTTP/1.0 clients assumed a one-to-one relationship of IP
2434 addresses and servers; there was no other established mechanism for
2435 distinguishing the intended server of a request than the IP address
2436 to which that request was directed. The Host header field was
2437 introduced during the development of HTTP/1.1 and, though it was
2438 quickly implemented by most HTTP/1.0 browsers, additional
2439 requirements were placed on all HTTP/1.1 requests in order to ensure
2440 complete adoption. At the time of this writing, most HTTP-based
2441 services are dependent upon the Host header field for targeting
2442 requests.
2444 C.1.2. Keep-Alive Connections
2446 In HTTP/1.0, each connection is established by the client prior to
2447 the request and closed by the server after sending the response.
2448 However, some implementations implement the explicitly negotiated
2449 ("Keep-Alive") version of persistent connections described in
2450 Section 19.7.1 of [RFC2068].
2452 Some clients and servers might wish to be compatible with these
2453 previous approaches to persistent connections, by explicitly
2454 negotiating for them with a "Connection: keep-alive" request header
2455 field. However, some experimental implementations of HTTP/1.0
2456 persistent connections are faulty; for example, if an HTTP/1.0 proxy
2457 server doesn't understand Connection, it will erroneously forward
2458 that header field to the next inbound server, which would result in a
2459 hung connection.
2461 One attempted solution was the introduction of a Proxy-Connection
2462 header field, targeted specifically at proxies. In practice, this
2463 was also unworkable, because proxies are often deployed in multiple
2464 layers, bringing about the same problem discussed above.
2466 As a result, clients are encouraged not to send the Proxy-Connection
2467 header field in any requests.
2469 Clients are also encouraged to consider the use of Connection: keep-
2470 alive in requests carefully; while they can enable persistent
2471 connections with HTTP/1.0 servers, clients using them will need to
2472 monitor the connection for "hung" requests (which indicate that the
2473 client ought stop sending the header field), and this mechanism ought
2474 not be used by clients at all when a proxy is being used.
2476 C.1.3. Introduction of Transfer-Encoding
2478 HTTP/1.1 introduces the Transfer-Encoding header field (Section 6.1).
2479 Transfer codings need to be decoded prior to forwarding an HTTP
2480 message over a MIME-compliant protocol.
2482 C.2. Changes from RFC 7230
2484 Most of the sections introducing HTTP's design goals, history,
2485 architecture, conformance criteria, protocol versioning, URIs,
2486 message routing, and header fields have been moved to [Semantics].
2487 This document has been reduced to just the messaging syntax and
2488 connection management requirements specific to HTTP/1.1.
2490 Prohibited generation of bare CRs outside of payload body.
2491 (Section 2.2)
2493 In the ABNF for chunked extensions, re-introduced (bad) whitespace
2494 around ";" and "=". Whitespace was removed in [RFC7230], but that
2495 change was found to break existing implementations (see [Err4667]).
2496 (Section 7.1.1)
2498 Trailer field semantics now transcend the specifics of chunked
2499 encoding. The decoding algorithm for chunked (Section 7.1.3) has
2500 been updated to encourage storage/forwarding of trailer fields
2501 separately from the header section, to only allow merging into the
2502 header section if the recipient knows the corresponding field
2503 definition permits and defines how to merge, and otherwise to discard
2504 the trailer fields instead of merging. The trailer part is now
2505 called the trailer section to be more consistent with the header
2506 section and more distinct from a body part. (Section 7.1.2)
2508 Disallowed transfer coding parameters called "q" in order to avoid
2509 conflicts with the use of ranks in the TE header field.
2510 (Section 7.3)
2512 Appendix D. Change Log
2514 This section is to be removed before publishing as an RFC.
2516 D.1. Between RFC7230 and draft 00
2518 The changes were purely editorial:
2520 o Change boilerplate and abstract to indicate the "draft" status,
2521 and update references to ancestor specifications.
2523 o Adjust historical notes.
2525 o Update links to sibling specifications.
2527 o Replace sections listing changes from RFC 2616 by new empty
2528 sections referring to RFC 723x.
2530 o Remove acknowledgements specific to RFC 723x.
2532 o Move "Acknowledgements" to the very end and make them unnumbered.
2534 D.2. Since draft-ietf-httpbis-messaging-00
2536 The changes in this draft are editorial, with respect to HTTP as a
2537 whole, to move all core HTTP semantics into [Semantics]:
2539 o Moved introduction, architecture, conformance, and ABNF extensions
2540 from RFC 7230 (Messaging) to semantics [Semantics].
2542 o Moved discussion of MIME differences from RFC 7231 (Semantics) to
2543 Appendix B since they mostly cover transforming 1.1 messages.
2545 o Moved all extensibility tips, registration procedures, and
2546 registry tables from the IANA considerations to normative
2547 sections, reducing the IANA considerations to just instructions
2548 that will be removed prior to publication as an RFC.
2550 D.3. Since draft-ietf-httpbis-messaging-01
2552 o Cite RFC 8126 instead of RFC 5226 ()
2555 o Resolved erratum 4779, no change needed here
2556 (,
2557 )
2559 o In Section 7, fixed prose claiming transfer parameters allow bare
2560 names (,
2561 )
2563 o Resolved erratum 4225, no change needed here
2564 (,
2565 )
2567 o Replace "response code" with "response status code"
2568 (,
2569 )
2571 o In Section 9.4, clarify statement about HTTP/1.0 keep-alive
2572 (,
2573 )
2575 o In Section 7.1.1, re-introduce (bad) whitespace around ";" and "="
2576 (,
2577 , )
2580 o In Section 7.3, state that transfer codings should not use
2581 parameters named "q" (, )
2584 o In Section 7, mark coding name "trailers" as reserved in the IANA
2585 registry ()
2587 D.4. Since draft-ietf-httpbis-messaging-02
2589 o In Section 4, explain why the reason phrase should be ignored by
2590 clients ().
2592 o Add Section 9.3 to explain how request/response correlation is
2593 performed ()
2595 D.5. Since draft-ietf-httpbis-messaging-03
2597 o In Section 9.3, caution against treating data on a connection as
2598 part of a not-yet-issued request ()
2601 o In Section 7, remove the predefined codings from the ABNF and make
2602 it generic instead ()
2605 o Use RFC 7405 ABNF notation for case-sensitive string constants
2606 ()
2608 D.6. Since draft-ietf-httpbis-messaging-04
2609 o In Section 9.9, clarify that protocol-name is to be matched case-
2610 insensitively ()
2612 o In Section 5.2, add leading optional whitespace to obs-fold ABNF
2613 (,
2614 )
2616 o In Section 4, add clarifications about empty reason phrases
2617 ()
2619 o Move discussion of retries from Section 9.4.1 into [Semantics]
2620 ()
2622 D.7. Since draft-ietf-httpbis-messaging-05
2624 o In Section 7.1.2, the trailer part has been renamed the trailer
2625 section (for consistency with the header section) and trailers are
2626 no longer merged as header fields by default, but rather can be
2627 discarded, kept separate from header fields, or merged with header
2628 fields only if understood and defined as being mergeable
2629 ()
2631 o In Section 2.1 and related Sections, move the trailing CRLF from
2632 the line grammars into the message format
2633 ()
2635 o Moved Section 2.3 down ()
2638 o In Section 9.9, use 'websocket' instead of 'HTTP/2.0' in examples
2639 ()
2641 o Move version non-specific text from Section 6 into semantics as
2642 "payload body" ()
2644 o In Section 9.8, add text from RFC 2818
2645 ()
2647 D.8. Since draft-ietf-httpbis-messaging-06
2649 o In Section 12.5, update the APLN protocol id for HTTP/1.1
2650 ()
2652 o In Section 5, align with updates to field terminology in semantics
2653 ()
2655 o In Section 9.1, clarify that new connection options indeed need to
2656 be registered ()
2658 o In Section 1.1, reference RFC 8174 as well
2659 ()
2661 D.9. Since draft-ietf-httpbis-messaging-07
2663 o Move TE: trailers into [Semantics] ()
2666 o In Section 6.3, adjust requirements for handling multiple content-
2667 length values ()
2669 o Throughout, replace "effective request URI" with "target URI"
2670 ()
2672 o In Section 6.1, don't claim Transfer-Encoding is supported by
2673 HTTP/2 or later ()
2675 D.10. Since draft-ietf-httpbis-messaging-08
2677 o In Section 2.2, disallow bare CRs ()
2680 o Appendix A now uses the sender variant of the "#" list expansion
2681 ()
2683 o In Section 5, adjust IANA "Close" entry for new registry format
2684 ()
2686 D.11. Since draft-ietf-httpbis-messaging-09
2688 o Switch to xml2rfc v3 mode for draft generation
2689 ()
2691 Acknowledgments
2693 See Appendix "Acknowledgments" of [Semantics].
2695 Authors' Addresses
2697 Roy T. Fielding (editor)
2698 Adobe
2699 345 Park Ave
2700 San Jose, CA 95110
2701 United States of America
2703 Email: fielding@gbiv.com
2704 URI: https://roy.gbiv.com/
2705 Mark Nottingham (editor)
2706 Fastly
2708 Email: mnot@mnot.net
2709 URI: https://www.mnot.net/
2711 Julian F. Reschke (editor)
2712 greenbytes GmbH
2713 Hafenweg 16
2714 48155 Münster
2715 Germany
2717 Email: julian.reschke@greenbytes.de
2718 URI: https://greenbytes.de/tech/webdav/