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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: November 27, 2020 J. Reschke, Ed.
7 greenbytes
8 May 26, 2020
10 HTTP/1.1 Messaging
11 draft-ietf-httpbis-messaging-08
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.9.
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 November 27, 2020.
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
61 (https://trustee.ietf.org/license-info) in effect on the date of
62 publication of this document. Please review these documents
63 carefully, as they describe your rights and restrictions with respect
64 to this document. Code Components extracted from this document must
65 include Simplified BSD License text as described in Section 4.e of
66 the Trust Legal Provisions and are provided without warranty as
67 described in the Simplified BSD License.
69 This document may contain material from IETF Documents or IETF
70 Contributions published or made publicly available before November
71 10, 2008. The person(s) controlling the copyright in some of this
72 material may not have granted the IETF Trust the right to allow
73 modifications of such material outside the IETF Standards Process.
74 Without obtaining an adequate license from the person(s) controlling
75 the copyright in such materials, this document may not be modified
76 outside the IETF Standards Process, and derivative works of it may
77 not be created outside the IETF Standards Process, except to format
78 it for publication as an RFC or to translate it into languages other
79 than English.
81 Table of Contents
83 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
84 1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5
85 1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5
86 2. Message . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
87 2.1. Message Format . . . . . . . . . . . . . . . . . . . . . 6
88 2.2. Message Parsing . . . . . . . . . . . . . . . . . . . . . 7
89 2.3. HTTP Version . . . . . . . . . . . . . . . . . . . . . . 8
90 3. Request Line . . . . . . . . . . . . . . . . . . . . . . . . 9
91 3.1. Method . . . . . . . . . . . . . . . . . . . . . . . . . 9
92 3.2. Request Target . . . . . . . . . . . . . . . . . . . . . 10
93 3.2.1. origin-form . . . . . . . . . . . . . . . . . . . . . 10
94 3.2.2. absolute-form . . . . . . . . . . . . . . . . . . . . 11
95 3.2.3. authority-form . . . . . . . . . . . . . . . . . . . 12
96 3.2.4. asterisk-form . . . . . . . . . . . . . . . . . . . . 12
98 3.3. Reconstructing the Target URI . . . . . . . . . . . . . . 13
99 4. Status Line . . . . . . . . . . . . . . . . . . . . . . . . . 14
100 5. Field Syntax . . . . . . . . . . . . . . . . . . . . . . . . 15
101 5.1. Field Line Parsing . . . . . . . . . . . . . . . . . . . 16
102 5.2. Obsolete Line Folding . . . . . . . . . . . . . . . . . . 16
103 6. Message Body . . . . . . . . . . . . . . . . . . . . . . . . 17
104 6.1. Transfer-Encoding . . . . . . . . . . . . . . . . . . . . 17
105 6.2. Content-Length . . . . . . . . . . . . . . . . . . . . . 19
106 6.3. Message Body Length . . . . . . . . . . . . . . . . . . . 19
107 7. Transfer Codings . . . . . . . . . . . . . . . . . . . . . . 21
108 7.1. Chunked Transfer Coding . . . . . . . . . . . . . . . . . 22
109 7.1.1. Chunk Extensions . . . . . . . . . . . . . . . . . . 23
110 7.1.2. Chunked Trailer Section . . . . . . . . . . . . . . . 24
111 7.1.3. Decoding Chunked . . . . . . . . . . . . . . . . . . 24
112 7.2. Transfer Codings for Compression . . . . . . . . . . . . 25
113 7.3. Transfer Coding Registry . . . . . . . . . . . . . . . . 25
114 7.4. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
115 8. Handling Incomplete Messages . . . . . . . . . . . . . . . . 27
116 9. Connection Management . . . . . . . . . . . . . . . . . . . . 28
117 9.1. Connection . . . . . . . . . . . . . . . . . . . . . . . 28
118 9.2. Establishment . . . . . . . . . . . . . . . . . . . . . . 30
119 9.3. Associating a Response to a Request . . . . . . . . . . . 30
120 9.4. Persistence . . . . . . . . . . . . . . . . . . . . . . . 31
121 9.4.1. Retrying Requests . . . . . . . . . . . . . . . . . . 32
122 9.4.2. Pipelining . . . . . . . . . . . . . . . . . . . . . 32
123 9.5. Concurrency . . . . . . . . . . . . . . . . . . . . . . . 33
124 9.6. Failures and Timeouts . . . . . . . . . . . . . . . . . . 33
125 9.7. Tear-down . . . . . . . . . . . . . . . . . . . . . . . . 34
126 9.8. TLS Connection Closure . . . . . . . . . . . . . . . . . 35
127 9.9. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . . 36
128 9.9.1. Upgrade Protocol Names . . . . . . . . . . . . . . . 38
129 9.9.2. Upgrade Token Registry . . . . . . . . . . . . . . . 38
130 10. Enclosing Messages as Data . . . . . . . . . . . . . . . . . 39
131 10.1. Media Type message/http . . . . . . . . . . . . . . . . 39
132 10.2. Media Type application/http . . . . . . . . . . . . . . 40
133 11. Security Considerations . . . . . . . . . . . . . . . . . . . 42
134 11.1. Response Splitting . . . . . . . . . . . . . . . . . . . 42
135 11.2. Request Smuggling . . . . . . . . . . . . . . . . . . . 43
136 11.3. Message Integrity . . . . . . . . . . . . . . . . . . . 43
137 11.4. Message Confidentiality . . . . . . . . . . . . . . . . 43
138 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
139 12.1. Field Name Registration . . . . . . . . . . . . . . . . 44
140 12.2. Media Type Registration . . . . . . . . . . . . . . . . 44
141 12.3. Transfer Coding Registration . . . . . . . . . . . . . . 44
142 12.4. Upgrade Token Registration . . . . . . . . . . . . . . . 44
143 12.5. ALPN Protocol ID Registration . . . . . . . . . . . . . 44
144 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
145 13.1. Normative References . . . . . . . . . . . . . . . . . . 45
146 13.2. Informative References . . . . . . . . . . . . . . . . . 46
147 Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 48
148 Appendix B. Differences between HTTP and MIME . . . . . . . . . 49
149 B.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . 50
150 B.2. Conversion to Canonical Form . . . . . . . . . . . . . . 50
151 B.3. Conversion of Date Formats . . . . . . . . . . . . . . . 50
152 B.4. Conversion of Content-Encoding . . . . . . . . . . . . . 51
153 B.5. Conversion of Content-Transfer-Encoding . . . . . . . . . 51
154 B.6. MHTML and Line Length Limitations . . . . . . . . . . . . 51
155 Appendix C. HTTP Version History . . . . . . . . . . . . . . . . 51
156 C.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . . 52
157 C.1.1. Multihomed Web Servers . . . . . . . . . . . . . . . 52
158 C.1.2. Keep-Alive Connections . . . . . . . . . . . . . . . 53
159 C.1.3. Introduction of Transfer-Encoding . . . . . . . . . . 53
160 C.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 53
161 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 54
162 D.1. Between RFC7230 and draft 00 . . . . . . . . . . . . . . 54
163 D.2. Since draft-ietf-httpbis-messaging-00 . . . . . . . . . . 54
164 D.3. Since draft-ietf-httpbis-messaging-01 . . . . . . . . . . 55
165 D.4. Since draft-ietf-httpbis-messaging-02 . . . . . . . . . . 56
166 D.5. Since draft-ietf-httpbis-messaging-03 . . . . . . . . . . 56
167 D.6. Since draft-ietf-httpbis-messaging-04 . . . . . . . . . . 56
168 D.7. Since draft-ietf-httpbis-messaging-05 . . . . . . . . . . 56
169 D.8. Since draft-ietf-httpbis-messaging-06 . . . . . . . . . . 57
170 D.9. Since draft-ietf-httpbis-messaging-07 . . . . . . . . . . 57
171 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
172 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 60
173 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60
175 1. Introduction
177 The Hypertext Transfer Protocol (HTTP) is a stateless application-
178 level request/response protocol that uses extensible semantics and
179 self-descriptive messages for flexible interaction with network-based
180 hypertext information systems. HTTP is defined by a series of
181 documents that collectively form the HTTP/1.1 specification:
183 o "HTTP Semantics" [Semantics]
185 o "HTTP Caching" [Caching]
187 o "HTTP/1.1 Messaging" (this document)
189 This document defines HTTP/1.1 message syntax and framing
190 requirements and their associated connection management. Our goal is
191 to define all of the mechanisms necessary for HTTP/1.1 message
192 handling that are independent of message semantics, thereby defining
193 the complete set of requirements for message parsers and message-
194 forwarding intermediaries.
196 This document obsoletes the portions of RFC 7230 related to HTTP/1.1
197 messaging and connection management, with the changes being
198 summarized in Appendix C.2. The other parts of RFC 7230 are
199 obsoleted by "HTTP Semantics" [Semantics].
201 1.1. Requirements Notation
203 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
204 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
205 "OPTIONAL" in this document are to be interpreted as described in BCP
206 14 [RFC2119] [RFC8174] when, and only when, they appear in all
207 capitals, as shown here.
209 Conformance criteria and considerations regarding error handling are
210 defined in Section 3 of [Semantics].
212 1.2. Syntax Notation
214 This specification uses the Augmented Backus-Naur Form (ABNF)
215 notation of [RFC5234], extended with the notation for case-
216 sensitivity in strings defined in [RFC7405].
218 It also uses a list extension, defined in Section 4.5 of [Semantics],
219 that allows for compact definition of comma-separated lists using a
220 '#' operator (similar to how the '*' operator indicates repetition).
221 Appendix A shows the collected grammar with all list operators
222 expanded to standard ABNF notation.
224 As a convention, ABNF rule names prefixed with "obs-" denote
225 "obsolete" grammar rules that appear for historical reasons.
227 The following core rules are included by reference, as defined in
228 [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
229 (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
230 HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line
231 feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any
232 visible [USASCII] character).
234 The rules below are defined in [Semantics]:
236 BWS =
237 OWS =
238 RWS =
239 absolute-URI =
240 absolute-path =
241 authority =
242 comment =
243 field-name =
244 field-value =
245 obs-text =
246 port =
247 query =
248 quoted-string =
249 token =
250 uri-host =
252 2. Message
254 2.1. Message Format
256 An HTTP/1.1 message consists of a start-line followed by a CRLF and a
257 sequence of octets in a format similar to the Internet Message Format
258 [RFC5322]: zero or more header field lines (collectively referred to
259 as the "headers" or the "header section"), an empty line indicating
260 the end of the header section, and an optional message body.
262 HTTP-message = start-line CRLF
263 *( field-line CRLF )
264 CRLF
265 [ message-body ]
267 A message can be either a request from client to server or a response
268 from server to client. Syntactically, the two types of message
269 differ only in the start-line, which is either a request-line (for
270 requests) or a status-line (for responses), and in the algorithm for
271 determining the length of the message body (Section 6).
273 start-line = request-line / status-line
275 In theory, a client could receive requests and a server could receive
276 responses, distinguishing them by their different start-line formats.
277 In practice, servers are implemented to only expect a request (a
278 response is interpreted as an unknown or invalid request method) and
279 clients are implemented to only expect a response.
281 Although HTTP makes use of some protocol elements similar to the
282 Multipurpose Internet Mail Extensions (MIME) [RFC2045], see
283 Appendix B for the differences between HTTP and MIME messages.
285 2.2. Message Parsing
287 The normal procedure for parsing an HTTP message is to read the
288 start-line into a structure, read each header field line into a hash
289 table by field name until the empty line, and then use the parsed
290 data to determine if a message body is expected. If a message body
291 has been indicated, then it is read as a stream until an amount of
292 octets equal to the message body length is read or the connection is
293 closed.
295 A recipient MUST parse an HTTP message as a sequence of octets in an
296 encoding that is a superset of US-ASCII [USASCII]. Parsing an HTTP
297 message as a stream of Unicode characters, without regard for the
298 specific encoding, creates security vulnerabilities due to the
299 varying ways that string processing libraries handle invalid
300 multibyte character sequences that contain the octet LF (%x0A).
301 String-based parsers can only be safely used within protocol elements
302 after the element has been extracted from the message, such as within
303 a header field line value after message parsing has delineated the
304 individual field lines.
306 Although the line terminator for the start-line and header fields is
307 the sequence CRLF, a recipient MAY recognize a single LF as a line
308 terminator and ignore any preceding CR.
310 Older HTTP/1.0 user agent implementations might send an extra CRLF
311 after a POST request as a workaround for some early server
312 applications that failed to read message body content that was not
313 terminated by a line-ending. An HTTP/1.1 user agent MUST NOT preface
314 or follow a request with an extra CRLF. If terminating the request
315 message body with a line-ending is desired, then the user agent MUST
316 count the terminating CRLF octets as part of the message body length.
318 In the interest of robustness, a server that is expecting to receive
319 and parse a request-line SHOULD ignore at least one empty line (CRLF)
320 received prior to the request-line.
322 A sender MUST NOT send whitespace between the start-line and the
323 first header field. A recipient that receives whitespace between the
324 start-line and the first header field MUST either reject the message
325 as invalid or consume each whitespace-preceded line without further
326 processing of it (i.e., ignore the entire line, along with any
327 subsequent lines preceded by whitespace, until a properly formed
328 header field is received or the header section is terminated).
330 The presence of such whitespace in a request might be an attempt to
331 trick a server into ignoring that field line or processing the line
332 after it as a new request, either of which might result in a security
333 vulnerability if other implementations within the request chain
334 interpret the same message differently. Likewise, the presence of
335 such whitespace in a response might be ignored by some clients or
336 cause others to cease parsing.
338 When a server listening only for HTTP request messages, or processing
339 what appears from the start-line to be an HTTP request message,
340 receives a sequence of octets that does not match the HTTP-message
341 grammar aside from the robustness exceptions listed above, the server
342 SHOULD respond with a 400 (Bad Request) response.
344 2.3. HTTP Version
346 HTTP uses a "." numbering scheme to indicate versions
347 of the protocol. This specification defines version "1.1".
348 Section 3.5 of [Semantics] specifies the semantics of HTTP version
349 numbers.
351 The version of an HTTP/1.x message is indicated by an HTTP-version
352 field in the start-line. HTTP-version is case-sensitive.
354 HTTP-version = HTTP-name "/" DIGIT "." DIGIT
355 HTTP-name = %s"HTTP"
357 When an HTTP/1.1 message is sent to an HTTP/1.0 recipient [RFC1945]
358 or a recipient whose version is unknown, the HTTP/1.1 message is
359 constructed such that it can be interpreted as a valid HTTP/1.0
360 message if all of the newer features are ignored. This specification
361 places recipient-version requirements on some new features so that a
362 conformant sender will only use compatible features until it has
363 determined, through configuration or the receipt of a message, that
364 the recipient supports HTTP/1.1.
366 Intermediaries that process HTTP messages (i.e., all intermediaries
367 other than those acting as tunnels) MUST send their own HTTP-version
368 in forwarded messages. In other words, they are not allowed to
369 blindly forward the start-line without ensuring that the protocol
370 version in that message matches a version to which that intermediary
371 is conformant for both the receiving and sending of messages.
372 Forwarding an HTTP message without rewriting the HTTP-version might
373 result in communication errors when downstream recipients use the
374 message sender's version to determine what features are safe to use
375 for later communication with that sender.
377 A server MAY send an HTTP/1.0 response to an HTTP/1.1 request if it
378 is known or suspected that the client incorrectly implements the HTTP
379 specification and is incapable of correctly processing later version
380 responses, such as when a client fails to parse the version number
381 correctly or when an intermediary is known to blindly forward the
382 HTTP-version even when it doesn't conform to the given minor version
383 of the protocol. Such protocol downgrades SHOULD NOT be performed
384 unless triggered by specific client attributes, such as when one or
385 more of the request header fields (e.g., User-Agent) uniquely match
386 the values sent by a client known to be in error.
388 3. Request Line
390 A request-line begins with a method token, followed by a single space
391 (SP), the request-target, another single space (SP), and ends with
392 the protocol version.
394 request-line = method SP request-target SP HTTP-version
396 Although the request-line grammar rule requires that each of the
397 component elements be separated by a single SP octet, recipients MAY
398 instead parse on whitespace-delimited word boundaries and, aside from
399 the CRLF terminator, treat any form of whitespace as the SP separator
400 while ignoring preceding or trailing whitespace; such whitespace
401 includes one or more of the following octets: SP, HTAB, VT (%x0B), FF
402 (%x0C), or bare CR. However, lenient parsing can result in request
403 smuggling security vulnerabilities if there are multiple recipients
404 of the message and each has its own unique interpretation of
405 robustness (see Section 11.2).
407 HTTP does not place a predefined limit on the length of a request-
408 line, as described in Section 3 of [Semantics]. A server that
409 receives a method longer than any that it implements SHOULD respond
410 with a 501 (Not Implemented) status code. A server that receives a
411 request-target longer than any URI it wishes to parse MUST respond
412 with a 414 (URI Too Long) status code (see Section 9.5.15 of
413 [Semantics]).
415 Various ad hoc limitations on request-line length are found in
416 practice. It is RECOMMENDED that all HTTP senders and recipients
417 support, at a minimum, request-line lengths of 8000 octets.
419 3.1. Method
421 The method token indicates the request method to be performed on the
422 target resource. The request method is case-sensitive.
424 method = token
426 The request methods defined by this specification can be found in
427 Section 7 of [Semantics], along with information regarding the HTTP
428 method registry and considerations for defining new methods.
430 3.2. Request Target
432 The request-target identifies the target resource upon which to apply
433 the request. The client derives a request-target from its desired
434 target URI. There are four distinct formats for the request-target,
435 depending on both the method being requested and whether the request
436 is to a proxy.
438 request-target = origin-form
439 / absolute-form
440 / authority-form
441 / asterisk-form
443 No whitespace is allowed in the request-target. Unfortunately, some
444 user agents fail to properly encode or exclude whitespace found in
445 hypertext references, resulting in those disallowed characters being
446 sent as the request-target in a malformed request-line.
448 Recipients of an invalid request-line SHOULD respond with either a
449 400 (Bad Request) error or a 301 (Moved Permanently) redirect with
450 the request-target properly encoded. A recipient SHOULD NOT attempt
451 to autocorrect and then process the request without a redirect, since
452 the invalid request-line might be deliberately crafted to bypass
453 security filters along the request chain.
455 3.2.1. origin-form
457 The most common form of request-target is the origin-form.
459 origin-form = absolute-path [ "?" query ]
461 When making a request directly to an origin server, other than a
462 CONNECT or server-wide OPTIONS request (as detailed below), a client
463 MUST send only the absolute path and query components of the target
464 URI as the request-target. If the target URI's path component is
465 empty, the client MUST send "/" as the path within the origin-form of
466 request-target. A Host header field is also sent, as defined in
467 Section 5.6 of [Semantics].
469 For example, a client wishing to retrieve a representation of the
470 resource identified as
472 http://www.example.org/where?q=now
474 directly from the origin server would open (or reuse) a TCP
475 connection to port 80 of the host "www.example.org" and send the
476 lines:
478 GET /where?q=now HTTP/1.1
479 Host: www.example.org
481 followed by the remainder of the request message.
483 3.2.2. absolute-form
485 When making a request to a proxy, other than a CONNECT or server-wide
486 OPTIONS request (as detailed below), a client MUST send the target
487 URI in absolute-form as the request-target.
489 absolute-form = absolute-URI
491 The proxy is requested to either service that request from a valid
492 cache, if possible, or make the same request on the client's behalf
493 to either the next inbound proxy server or directly to the origin
494 server indicated by the request-target. Requirements on such
495 "forwarding" of messages are defined in Section 5.7 of [Semantics].
497 An example absolute-form of request-line would be:
499 GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
501 A client MUST send a Host header field in an HTTP/1.1 request even if
502 the request-target is in the absolute-form, since this allows the
503 Host information to be forwarded through ancient HTTP/1.0 proxies
504 that might not have implemented Host.
506 When a proxy receives a request with an absolute-form of request-
507 target, the proxy MUST ignore the received Host header field (if any)
508 and instead replace it with the host information of the request-
509 target. A proxy that forwards such a request MUST generate a new
510 Host field value based on the received request-target rather than
511 forward the received Host field value.
513 When an origin server receives a request with an absolute-form of
514 request-target, the origin server MUST ignore the received Host
515 header field (if any) and instead use the host information of the
516 request-target. Note that if the request-target does not have an
517 authority component, an empty Host header field will be sent in this
518 case.
520 To allow for transition to the absolute-form for all requests in some
521 future version of HTTP, a server MUST accept the absolute-form in
522 requests, even though HTTP/1.1 clients will only send them in
523 requests to proxies.
525 3.2.3. authority-form
527 The authority-form of request-target is only used for CONNECT
528 requests (Section 7.3.6 of [Semantics]).
530 authority-form = authority
532 When making a CONNECT request to establish a tunnel through one or
533 more proxies, a client MUST send only the target URI's authority
534 component (excluding any userinfo and its "@" delimiter) as the
535 request-target. For example,
537 CONNECT www.example.com:80 HTTP/1.1
539 3.2.4. asterisk-form
541 The asterisk-form of request-target is only used for a server-wide
542 OPTIONS request (Section 7.3.7 of [Semantics]).
544 asterisk-form = "*"
546 When a client wishes to request OPTIONS for the server as a whole, as
547 opposed to a specific named resource of that server, the client MUST
548 send only "*" (%x2A) as the request-target. For example,
550 OPTIONS * HTTP/1.1
552 If a proxy receives an OPTIONS request with an absolute-form of
553 request-target in which the URI has an empty path and no query
554 component, then the last proxy on the request chain MUST send a
555 request-target of "*" when it forwards the request to the indicated
556 origin server.
558 For example, the request
560 OPTIONS http://www.example.org:8001 HTTP/1.1
562 would be forwarded by the final proxy as
564 OPTIONS * HTTP/1.1
565 Host: www.example.org:8001
567 after connecting to port 8001 of host "www.example.org".
569 3.3. Reconstructing the Target URI
571 Since the request-target often contains only part of the user agent's
572 target URI, a server constructs its value to properly service the
573 request (Section 5.1 of [Semantics]).
575 If the request-target is in absolute-form, the target URI is the same
576 as the request-target. Otherwise, the target URI is constructed as
577 follows:
579 If the server's configuration (or outbound gateway) provides a
580 fixed URI scheme, that scheme is used for the target URI.
581 Otherwise, if the request is received over a TLS-secured TCP
582 connection, the target URI's scheme is "https"; if not, the scheme
583 is "http".
585 If the server's configuration (or outbound gateway) provides a
586 fixed URI authority component, that authority is used for the
587 target URI. If not, then if the request-target is in authority-
588 form, the target URI's authority component is the same as the
589 request-target. If not, then if a Host header field is supplied
590 with a non-empty field-value, the authority component is the same
591 as the Host field-value. Otherwise, the authority component is
592 assigned the default name configured for the server and, if the
593 connection's incoming TCP port number differs from the default
594 port for the target URI's scheme, then a colon (":") and the
595 incoming port number (in decimal form) are appended to the
596 authority component.
598 If the request-target is in authority-form or asterisk-form, the
599 target URI's combined path and query component is empty.
600 Otherwise, the combined path and query component is the same as
601 the request-target.
603 The components of the target URI, once determined as above, can be
604 combined into absolute-URI form by concatenating the scheme,
605 "://", authority, and combined path and query component.
607 Example 1: the following message received over an insecure TCP
608 connection
610 GET /pub/WWW/TheProject.html HTTP/1.1
611 Host: www.example.org:8080
613 has a target URI of
615 http://www.example.org:8080/pub/WWW/TheProject.html
617 Example 2: the following message received over a TLS-secured TCP
618 connection
620 OPTIONS * HTTP/1.1
621 Host: www.example.org
623 has a target URI of
625 https://www.example.org
627 Recipients of an HTTP/1.0 request that lacks a Host header field
628 might need to use heuristics (e.g., examination of the URI path for
629 something unique to a particular host) in order to guess the target
630 URI's authority component.
632 4. Status Line
634 The first line of a response message is the status-line, consisting
635 of the protocol version, a space (SP), the status code, another
636 space, and ending with an OPTIONAL textual phrase describing the
637 status code.
639 status-line = HTTP-version SP status-code SP [reason-phrase]
641 Although the status-line grammar rule requires that each of the
642 component elements be separated by a single SP octet, recipients MAY
643 instead parse on whitespace-delimited word boundaries and, aside from
644 the line terminator, treat any form of whitespace as the SP separator
645 while ignoring preceding or trailing whitespace; such whitespace
646 includes one or more of the following octets: SP, HTAB, VT (%x0B), FF
647 (%x0C), or bare CR. However, lenient parsing can result in response
648 splitting security vulnerabilities if there are multiple recipients
649 of the message and each has its own unique interpretation of
650 robustness (see Section 11.1).
652 The status-code element is a 3-digit integer code describing the
653 result of the server's attempt to understand and satisfy the client's
654 corresponding request. The rest of the response message is to be
655 interpreted in light of the semantics defined for that status code.
656 See Section 9 of [Semantics] for information about the semantics of
657 status codes, including the classes of status code (indicated by the
658 first digit), the status codes defined by this specification,
659 considerations for the definition of new status codes, and the IANA
660 registry.
662 status-code = 3DIGIT
664 The reason-phrase element exists for the sole purpose of providing a
665 textual description associated with the numeric status code, mostly
666 out of deference to earlier Internet application protocols that were
667 more frequently used with interactive text clients.
669 reason-phrase = 1*( HTAB / SP / VCHAR / obs-text )
671 A client SHOULD ignore the reason-phrase content because it is not a
672 reliable channel for information (it might be translated for a given
673 locale, overwritten by intermediaries, or discarded when the message
674 is forwarded via other versions of HTTP). A server MUST send the
675 space that separates status-code from the reason-phrase even when the
676 reason-phrase is absent (i.e., the status-line would end with the
677 three octets SP CR LF).
679 5. Field Syntax
681 Each field line consists of a case-insensitive field name followed by
682 a colon (":"), optional leading whitespace, the field line value, and
683 optional trailing whitespace.
685 field-line = field-name ":" OWS field-value OWS
687 Most HTTP field names and the rules for parsing within field values
688 are defined in Section 4 of [Semantics]. This section covers the
689 generic syntax for header field inclusion within, and extraction
690 from, HTTP/1.1 messages. In addition, the following header fields
691 are defined by this document because they are specific to HTTP/1.1
692 message processing:
694 +-------------------+----------+---------------+
695 | Field Name | Status | Reference |
696 +-------------------+----------+---------------+
697 | Connection | standard | Section 9.1 |
698 | MIME-Version | standard | Appendix B.1 |
699 | TE | standard | Section 7.4 |
700 | Transfer-Encoding | standard | Section 6.1 |
701 | Upgrade | standard | Section 9.9 |
702 +-------------------+----------+---------------+
704 Table 1
706 Furthermore, the field name "Close" is reserved, since using that
707 name as an HTTP header field might conflict with the "close"
708 connection option of the Connection header field (Section 9.1).
710 +-------------------+----------+----------+------------+
711 | Header Field Name | Protocol | Status | Reference |
712 +-------------------+----------+----------+------------+
713 | Close | http | reserved | Section 5 |
714 +-------------------+----------+----------+------------+
716 5.1. Field Line Parsing
718 Messages are parsed using a generic algorithm, independent of the
719 individual field names. The contents within a given field line value
720 are not parsed until a later stage of message interpretation (usually
721 after the message's entire header section has been processed).
723 No whitespace is allowed between the field name and colon. In the
724 past, differences in the handling of such whitespace have led to
725 security vulnerabilities in request routing and response handling. A
726 server MUST reject any received request message that contains
727 whitespace between a header field name and colon with a response
728 status code of 400 (Bad Request). A proxy MUST remove any such
729 whitespace from a response message before forwarding the message
730 downstream.
732 A field line value might be preceded and/or followed by optional
733 whitespace (OWS); a single SP preceding the field line value is
734 preferred for consistent readability by humans. The field line value
735 does not include any leading or trailing whitespace: OWS occurring
736 before the first non-whitespace octet of the field line value or
737 after the last non-whitespace octet of the field line value ought to
738 be excluded by parsers when extracting the field line value from a
739 header field line.
741 5.2. Obsolete Line Folding
743 Historically, HTTP header field line values could be extended over
744 multiple lines by preceding each extra line with at least one space
745 or horizontal tab (obs-fold). This specification deprecates such
746 line folding except within the message/http media type
747 (Section 10.1).
749 obs-fold = OWS CRLF RWS
750 ; obsolete line folding
752 A sender MUST NOT generate a message that includes line folding
753 (i.e., that has any field line value that contains a match to the
754 obs-fold rule) unless the message is intended for packaging within
755 the message/http media type.
757 A server that receives an obs-fold in a request message that is not
758 within a message/http container MUST either reject the message by
759 sending a 400 (Bad Request), preferably with a representation
760 explaining that obsolete line folding is unacceptable, or replace
761 each received obs-fold with one or more SP octets prior to
762 interpreting the field value or forwarding the message downstream.
764 A proxy or gateway that receives an obs-fold in a response message
765 that is not within a message/http container MUST either discard the
766 message and replace it with a 502 (Bad Gateway) response, preferably
767 with a representation explaining that unacceptable line folding was
768 received, or replace each received obs-fold with one or more SP
769 octets prior to interpreting the field value or forwarding the
770 message downstream.
772 A user agent that receives an obs-fold in a response message that is
773 not within a message/http container MUST replace each received obs-
774 fold with one or more SP octets prior to interpreting the field
775 value.
777 6. Message Body
779 The message body (if any) of an HTTP message is used to carry the
780 payload body (Section 6.3.3 of [Semantics]) of that request or
781 response. The message body is identical to the payload body unless a
782 transfer coding has been applied, as described in Section 6.1.
784 message-body = *OCTET
786 The rules for determining when a message body is present in an
787 HTTP/1.1 message differ for requests and responses.
789 The presence of a message body in a request is signaled by a Content-
790 Length or Transfer-Encoding header field. Request message framing is
791 independent of method semantics, even if the method does not define
792 any use for a message body.
794 The presence of a message body in a response depends on both the
795 request method to which it is responding and the response status code
796 (Section 4), and corresponds to when a payload body is allowed; see
797 Section 6.3.3 of [Semantics].
799 6.1. Transfer-Encoding
801 The Transfer-Encoding header field lists the transfer coding names
802 corresponding to the sequence of transfer codings that have been (or
803 will be) applied to the payload body in order to form the message
804 body. Transfer codings are defined in Section 7.
806 Transfer-Encoding = 1#transfer-coding
808 Transfer-Encoding is analogous to the Content-Transfer-Encoding field
809 of MIME, which was designed to enable safe transport of binary data
810 over a 7-bit transport service ([RFC2045], Section 6). However, safe
811 transport has a different focus for an 8bit-clean transfer protocol.
812 In HTTP's case, Transfer-Encoding is primarily intended to accurately
813 delimit a dynamically generated payload and to distinguish payload
814 encodings that are only applied for transport efficiency or security
815 from those that are characteristics of the selected resource.
817 A recipient MUST be able to parse the chunked transfer coding
818 (Section 7.1) because it plays a crucial role in framing messages
819 when the payload body size is not known in advance. A sender MUST
820 NOT apply chunked more than once to a message body (i.e., chunking an
821 already chunked message is not allowed). If any transfer coding
822 other than chunked is applied to a request payload body, the sender
823 MUST apply chunked as the final transfer coding to ensure that the
824 message is properly framed. If any transfer coding other than
825 chunked is applied to a response payload body, the sender MUST either
826 apply chunked as the final transfer coding or terminate the message
827 by closing the connection.
829 For example,
831 Transfer-Encoding: gzip, chunked
833 indicates that the payload body has been compressed using the gzip
834 coding and then chunked using the chunked coding while forming the
835 message body.
837 Unlike Content-Encoding (Section 6.1.2 of [Semantics]), Transfer-
838 Encoding is a property of the message, not of the representation, and
839 any recipient along the request/response chain MAY decode the
840 received transfer coding(s) or apply additional transfer coding(s) to
841 the message body, assuming that corresponding changes are made to the
842 Transfer-Encoding field value. Additional information about the
843 encoding parameters can be provided by other header fields not
844 defined by this specification.
846 Transfer-Encoding MAY be sent in a response to a HEAD request or in a
847 304 (Not Modified) response (Section 9.4.5 of [Semantics]) to a GET
848 request, neither of which includes a message body, to indicate that
849 the origin server would have applied a transfer coding to the message
850 body if the request had been an unconditional GET. This indication
851 is not required, however, because any recipient on the response chain
852 (including the origin server) can remove transfer codings when they
853 are not needed.
855 A server MUST NOT send a Transfer-Encoding header field in any
856 response with a status code of 1xx (Informational) or 204 (No
857 Content). A server MUST NOT send a Transfer-Encoding header field in
858 any 2xx (Successful) response to a CONNECT request (Section 7.3.6 of
859 [Semantics]).
861 Transfer-Encoding was added in HTTP/1.1. It is generally assumed
862 that implementations advertising only HTTP/1.0 support will not
863 understand how to process a transfer-encoded payload. A client MUST
864 NOT send a request containing Transfer-Encoding unless it knows the
865 server will handle HTTP/1.1 requests (or later minor revisions); such
866 knowledge might be in the form of specific user configuration or by
867 remembering the version of a prior received response. A server MUST
868 NOT send a response containing Transfer-Encoding unless the
869 corresponding request indicates HTTP/1.1 (or later minor revisions).
871 A server that receives a request message with a transfer coding it
872 does not understand SHOULD respond with 501 (Not Implemented).
874 6.2. Content-Length
876 When a message does not have a Transfer-Encoding header field, a
877 Content-Length header field can provide the anticipated size, as a
878 decimal number of octets, for a potential payload body. For messages
879 that do include a payload body, the Content-Length field value
880 provides the framing information necessary for determining where the
881 body (and message) ends. For messages that do not include a payload
882 body, the Content-Length indicates the size of the selected
883 representation (Section 6.2.4 of [Semantics]).
885 Note: HTTP's use of Content-Length for message framing differs
886 significantly from the same field's use in MIME, where it is an
887 optional field used only within the "message/external-body" media-
888 type.
890 6.3. Message Body Length
892 The length of a message body is determined by one of the following
893 (in order of precedence):
895 1. Any response to a HEAD request and any response with a 1xx
896 (Informational), 204 (No Content), or 304 (Not Modified) status
897 code is always terminated by the first empty line after the
898 header fields, regardless of the header fields present in the
899 message, and thus cannot contain a message body.
901 2. Any 2xx (Successful) response to a CONNECT request implies that
902 the connection will become a tunnel immediately after the empty
903 line that concludes the header fields. A client MUST ignore any
904 Content-Length or Transfer-Encoding header fields received in
905 such a message.
907 3. If a Transfer-Encoding header field is present and the chunked
908 transfer coding (Section 7.1) is the final encoding, the message
909 body length is determined by reading and decoding the chunked
910 data until the transfer coding indicates the data is complete.
912 If a Transfer-Encoding header field is present in a response and
913 the chunked transfer coding is not the final encoding, the
914 message body length is determined by reading the connection until
915 it is closed by the server. If a Transfer-Encoding header field
916 is present in a request and the chunked transfer coding is not
917 the final encoding, the message body length cannot be determined
918 reliably; the server MUST respond with the 400 (Bad Request)
919 status code and then close the connection.
921 If a message is received with both a Transfer-Encoding and a
922 Content-Length header field, the Transfer-Encoding overrides the
923 Content-Length. Such a message might indicate an attempt to
924 perform request smuggling (Section 11.2) or response splitting
925 (Section 11.1) and ought to be handled as an error. A sender
926 MUST remove the received Content-Length field prior to forwarding
927 such a message downstream.
929 4. If a message is received without Transfer-Encoding and with an
930 invalid Content-Length header field, then the message framing is
931 invalid and the recipient MUST treat it as an unrecoverable
932 error, unless the field value can be successfully parsed as a
933 comma-separated list (Section 4.5 of [Semantics]), all values in
934 the list are valid, and all values in the list are the same. If
935 this is a request message, the server MUST respond with a 400
936 (Bad Request) status code and then close the connection. If this
937 is a response message received by a proxy, the proxy MUST close
938 the connection to the server, discard the received response, and
939 send a 502 (Bad Gateway) response to the client. If this is a
940 response message received by a user agent, the user agent MUST
941 close the connection to the server and discard the received
942 response.
944 5. If a valid Content-Length header field is present without
945 Transfer-Encoding, its decimal value defines the expected message
946 body length in octets. If the sender closes the connection or
947 the recipient times out before the indicated number of octets are
948 received, the recipient MUST consider the message to be
949 incomplete and close the connection.
951 6. If this is a request message and none of the above are true, then
952 the message body length is zero (no message body is present).
954 7. Otherwise, this is a response message without a declared message
955 body length, so the message body length is determined by the
956 number of octets received prior to the server closing the
957 connection.
959 Since there is no way to distinguish a successfully completed, close-
960 delimited message from a partially received message interrupted by
961 network failure, a server SHOULD generate encoding or length-
962 delimited messages whenever possible. The close-delimiting feature
963 exists primarily for backwards compatibility with HTTP/1.0.
965 A server MAY reject a request that contains a message body but not a
966 Content-Length by responding with 411 (Length Required).
968 Unless a transfer coding other than chunked has been applied, a
969 client that sends a request containing a message body SHOULD use a
970 valid Content-Length header field if the message body length is known
971 in advance, rather than the chunked transfer coding, since some
972 existing services respond to chunked with a 411 (Length Required)
973 status code even though they understand the chunked transfer coding.
974 This is typically because such services are implemented via a gateway
975 that requires a content-length in advance of being called and the
976 server is unable or unwilling to buffer the entire request before
977 processing.
979 A user agent that sends a request containing a message body MUST send
980 a valid Content-Length header field if it does not know the server
981 will handle HTTP/1.1 (or later) requests; such knowledge can be in
982 the form of specific user configuration or by remembering the version
983 of a prior received response.
985 If the final response to the last request on a connection has been
986 completely received and there remains additional data to read, a user
987 agent MAY discard the remaining data or attempt to determine if that
988 data belongs as part of the prior response body, which might be the
989 case if the prior message's Content-Length value is incorrect. A
990 client MUST NOT process, cache, or forward such extra data as a
991 separate response, since such behavior would be vulnerable to cache
992 poisoning.
994 7. Transfer Codings
996 Transfer coding names are used to indicate an encoding transformation
997 that has been, can be, or might need to be applied to a payload body
998 in order to ensure "safe transport" through the network. This
999 differs from a content coding in that the transfer coding is a
1000 property of the message rather than a property of the representation
1001 that is being transferred.
1003 transfer-coding = token *( OWS ";" OWS transfer-parameter )
1005 Parameters are in the form of a name=value pair.
1007 transfer-parameter = token BWS "=" BWS ( token / quoted-string )
1009 All transfer-coding names are case-insensitive and ought to be
1010 registered within the HTTP Transfer Coding registry, as defined in
1011 Section 7.3. They are used in the TE (Section 7.4) and Transfer-
1012 Encoding (Section 6.1) header fields.
1014 +------------+------------------------------------------+-----------+
1015 | Name | Description | Reference |
1016 +------------+------------------------------------------+-----------+
1017 | chunked | Transfer in a series of chunks | Section 7 |
1018 | | | .1 |
1019 | compress | UNIX "compress" data format [Welch] | Section 7 |
1020 | | | .2 |
1021 | deflate | "deflate" compressed data ([RFC1951]) | Section 7 |
1022 | | inside the "zlib" data format | .2 |
1023 | | ([RFC1950]) | |
1024 | gzip | GZIP file format [RFC1952] | Section 7 |
1025 | | | .2 |
1026 | trailers | (reserved) | Section 7 |
1027 | x-compress | Deprecated (alias for compress) | Section 7 |
1028 | | | .2 |
1029 | x-gzip | Deprecated (alias for gzip) | Section 7 |
1030 | | | .2 |
1031 +------------+------------------------------------------+-----------+
1033 Table 2
1035 Note: the coding name "trailers" is reserved because its use would
1036 conflict with the keyword "trailers" in the TE header field
1037 (Section 7.4).
1039 7.1. Chunked Transfer Coding
1041 The chunked transfer coding wraps the payload body in order to
1042 transfer it as a series of chunks, each with its own size indicator,
1043 followed by an OPTIONAL trailer section containing trailer fields.
1044 Chunked enables content streams of unknown size to be transferred as
1045 a sequence of length-delimited buffers, which enables the sender to
1046 retain connection persistence and the recipient to know when it has
1047 received the entire message.
1049 chunked-body = *chunk
1050 last-chunk
1051 trailer-section
1052 CRLF
1054 chunk = chunk-size [ chunk-ext ] CRLF
1055 chunk-data CRLF
1056 chunk-size = 1*HEXDIG
1057 last-chunk = 1*("0") [ chunk-ext ] CRLF
1059 chunk-data = 1*OCTET ; a sequence of chunk-size octets
1061 The chunk-size field is a string of hex digits indicating the size of
1062 the chunk-data in octets. The chunked transfer coding is complete
1063 when a chunk with a chunk-size of zero is received, possibly followed
1064 by a trailer section, and finally terminated by an empty line.
1066 A recipient MUST be able to parse and decode the chunked transfer
1067 coding.
1069 Note that HTTP/1.1 does not define any means to limit the size of a
1070 chunked response such that an intermediary can be assured of
1071 buffering the entire response.
1073 The chunked encoding does not define any parameters. Their presence
1074 SHOULD be treated as an error.
1076 7.1.1. Chunk Extensions
1078 The chunked encoding allows each chunk to include zero or more chunk
1079 extensions, immediately following the chunk-size, for the sake of
1080 supplying per-chunk metadata (such as a signature or hash), mid-
1081 message control information, or randomization of message body size.
1083 chunk-ext = *( BWS ";" BWS chunk-ext-name
1084 [ BWS "=" BWS chunk-ext-val ] )
1086 chunk-ext-name = token
1087 chunk-ext-val = token / quoted-string
1089 The chunked encoding is specific to each connection and is likely to
1090 be removed or recoded by each recipient (including intermediaries)
1091 before any higher-level application would have a chance to inspect
1092 the extensions. Hence, use of chunk extensions is generally limited
1093 to specialized HTTP services such as "long polling" (where client and
1094 server can have shared expectations regarding the use of chunk
1095 extensions) or for padding within an end-to-end secured connection.
1097 A recipient MUST ignore unrecognized chunk extensions. A server
1098 ought to limit the total length of chunk extensions received in a
1099 request to an amount reasonable for the services provided, in the
1100 same way that it applies length limitations and timeouts for other
1101 parts of a message, and generate an appropriate 4xx (Client Error)
1102 response if that amount is exceeded.
1104 7.1.2. Chunked Trailer Section
1106 A trailer section allows the sender to include additional fields at
1107 the end of a chunked message in order to supply metadata that might
1108 be dynamically generated while the message body is sent, such as a
1109 message integrity check, digital signature, or post-processing
1110 status. The proper use and limitations of trailer fields are defined
1111 in Section 4.6 of [Semantics].
1113 trailer-section = *( field-line CRLF )
1115 A recipient that decodes and removes the chunked encoding from a
1116 message (e.g., for storage or forwarding to a non-HTTP/1.1 peer) MUST
1117 discard any received trailer fields, store/forward them separately
1118 from the header fields, or selectively merge into the header section
1119 only those trailer fields corresponding to header field definitions
1120 that are understood by the recipient to explicitly permit and define
1121 how their corresponding trailer field value can be safely merged.
1123 7.1.3. Decoding Chunked
1125 A process for decoding the chunked transfer coding can be represented
1126 in pseudo-code as:
1128 length := 0
1129 read chunk-size, chunk-ext (if any), and CRLF
1130 while (chunk-size > 0) {
1131 read chunk-data and CRLF
1132 append chunk-data to decoded-body
1133 length := length + chunk-size
1134 read chunk-size, chunk-ext (if any), and CRLF
1135 }
1136 read trailer field
1137 while (trailer field is not empty) {
1138 if (trailer fields are stored/forwarded separately) {
1139 append trailer field to existing trailer fields
1140 }
1141 else if (trailer field is understood and defined as mergeable) {
1142 merge trailer field with existing header fields
1143 }
1144 else {
1145 discard trailer field
1146 }
1147 read trailer field
1148 }
1149 Content-Length := length
1150 Remove "chunked" from Transfer-Encoding
1151 Remove Trailer from existing header fields
1153 7.2. Transfer Codings for Compression
1155 The following transfer coding names for compression are defined by
1156 the same algorithm as their corresponding content coding:
1158 compress (and x-compress)
1159 See Section 6.1.2.1 of [Semantics].
1161 deflate
1162 See Section 6.1.2.2 of [Semantics].
1164 gzip (and x-gzip)
1165 See Section 6.1.2.3 of [Semantics].
1167 The compression codings do not define any parameters. Their presence
1168 SHOULD be treated as an error.
1170 7.3. Transfer Coding Registry
1172 The "HTTP Transfer Coding Registry" defines the namespace for
1173 transfer coding names. It is maintained at
1174 .
1176 Registrations MUST include the following fields:
1178 o Name
1180 o Description
1182 o Pointer to specification text
1184 Names of transfer codings MUST NOT overlap with names of content
1185 codings (Section 6.1.2 of [Semantics]) unless the encoding
1186 transformation is identical, as is the case for the compression
1187 codings defined in Section 7.2.
1189 The TE header field (Section 7.4) uses a pseudo parameter named "q"
1190 as rank value when multiple transfer codings are acceptable. Future
1191 registrations of transfer codings SHOULD NOT define parameters called
1192 "q" (case-insensitively) in order to avoid ambiguities.
1194 Values to be added to this namespace require IETF Review (see
1195 Section 4.8 of [RFC8126]), and MUST conform to the purpose of
1196 transfer coding defined in this specification.
1198 Use of program names for the identification of encoding formats is
1199 not desirable and is discouraged for future encodings.
1201 7.4. TE
1203 The "TE" header field in a request indicates what transfer codings,
1204 besides chunked, the client is willing to accept in response, and
1205 whether or not the client is willing to accept trailer fields in a
1206 chunked transfer coding.
1208 The TE field-value consists of a list of transfer coding names, each
1209 allowing for optional parameters (as described in Section 7), and/or
1210 the keyword "trailers". A client MUST NOT send the chunked transfer
1211 coding name in TE; chunked is always acceptable for HTTP/1.1
1212 recipients.
1214 TE = #t-codings
1215 t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
1216 t-ranking = OWS ";" OWS "q=" rank
1217 rank = ( "0" [ "." 0*3DIGIT ] )
1218 / ( "1" [ "." 0*3("0") ] )
1220 Three examples of TE use are below.
1222 TE: deflate
1223 TE:
1224 TE: trailers, deflate;q=0.5
1226 When multiple transfer codings are acceptable, the client MAY rank
1227 the codings by preference using a case-insensitive "q" parameter
1228 (similar to the qvalues used in content negotiation fields,
1229 Section 6.4.4 of [Semantics]). The rank value is a real number in
1230 the range 0 through 1, where 0.001 is the least preferred and 1 is
1231 the most preferred; a value of 0 means "not acceptable".
1233 If the TE field value is empty or if no TE field is present, the only
1234 acceptable transfer coding is chunked. A message with no transfer
1235 coding is always acceptable.
1237 The keyword "trailers" indicates that the sender will not discard
1238 trailer fields, as described in Section 4.6 of [Semantics].
1240 Since the TE header field only applies to the immediate connection, a
1241 sender of TE MUST also send a "TE" connection option within the
1242 Connection header field (Section 9.1) in order to prevent the TE
1243 field from being forwarded by intermediaries that do not support its
1244 semantics.
1246 8. Handling Incomplete Messages
1248 A server that receives an incomplete request message, usually due to
1249 a canceled request or a triggered timeout exception, MAY send an
1250 error response prior to closing the connection.
1252 A client that receives an incomplete response message, which can
1253 occur when a connection is closed prematurely or when decoding a
1254 supposedly chunked transfer coding fails, MUST record the message as
1255 incomplete. Cache requirements for incomplete responses are defined
1256 in Section 3 of [Caching].
1258 If a response terminates in the middle of the header section (before
1259 the empty line is received) and the status code might rely on header
1260 fields to convey the full meaning of the response, then the client
1261 cannot assume that meaning has been conveyed; the client might need
1262 to repeat the request in order to determine what action to take next.
1264 A message body that uses the chunked transfer coding is incomplete if
1265 the zero-sized chunk that terminates the encoding has not been
1266 received. A message that uses a valid Content-Length is incomplete
1267 if the size of the message body received (in octets) is less than the
1268 value given by Content-Length. A response that has neither chunked
1269 transfer coding nor Content-Length is terminated by closure of the
1270 connection and, thus, is considered complete regardless of the number
1271 of message body octets received, provided that the header section was
1272 received intact.
1274 9. Connection Management
1276 HTTP messaging is independent of the underlying transport- or
1277 session-layer connection protocol(s). HTTP only presumes a reliable
1278 transport with in-order delivery of requests and the corresponding
1279 in-order delivery of responses. The mapping of HTTP request and
1280 response structures onto the data units of an underlying transport
1281 protocol is outside the scope of this specification.
1283 As described in Section 5.3 of [Semantics], the specific connection
1284 protocols to be used for an HTTP interaction are determined by client
1285 configuration and the target URI. For example, the "http" URI scheme
1286 (Section 2.5.1 of [Semantics]) indicates a default connection of TCP
1287 over IP, with a default TCP port of 80, but the client might be
1288 configured to use a proxy via some other connection, port, or
1289 protocol.
1291 HTTP implementations are expected to engage in connection management,
1292 which includes maintaining the state of current connections,
1293 establishing a new connection or reusing an existing connection,
1294 processing messages received on a connection, detecting connection
1295 failures, and closing each connection. Most clients maintain
1296 multiple connections in parallel, including more than one connection
1297 per server endpoint. Most servers are designed to maintain thousands
1298 of concurrent connections, while controlling request queues to enable
1299 fair use and detect denial-of-service attacks.
1301 9.1. Connection
1303 The "Connection" header field allows the sender to list desired
1304 control options for the current connection.
1306 When a field aside from Connection is used to supply control
1307 information for or about the current connection, the sender MUST list
1308 the corresponding field name within the Connection header field.
1310 Intermediaries MUST parse a received Connection header field before a
1311 message is forwarded and, for each connection-option in this field,
1312 remove any header or trailer field(s) from the message with the same
1313 name as the connection-option, and then remove the Connection header
1314 field itself (or replace it with the intermediary's own connection
1315 options for the forwarded message).
1317 Hence, the Connection header field provides a declarative way of
1318 distinguishing fields that are only intended for the immediate
1319 recipient ("hop-by-hop") from those fields that are intended for all
1320 recipients on the chain ("end-to-end"), enabling the message to be
1321 self-descriptive and allowing future connection-specific extensions
1322 to be deployed without fear that they will be blindly forwarded by
1323 older intermediaries.
1325 Furthermore, intermediaries SHOULD remove or replace field(s) whose
1326 semantics are known to require removal before forwarding, whether or
1327 not they appear as a Connection option, after applying those fields'
1328 semantics. This includes but is not limited to:
1330 o Proxy-Connection Appendix C.1.2
1332 o Keep-Alive Section 19.7.1 of [RFC2068]
1334 o TE Section 7.4
1336 o Trailer Section 4.6.3 of [Semantics]
1338 o Transfer-Encoding Section 6.1
1340 o Upgrade Section 9.9
1342 The Connection header field's value has the following grammar:
1344 Connection = 1#connection-option
1345 connection-option = token
1347 Connection options are case-insensitive.
1349 A sender MUST NOT send a connection option corresponding to a field
1350 that is intended for all recipients of the payload. For example,
1351 Cache-Control is never appropriate as a connection option
1352 (Section 5.2 of [Caching]).
1354 The connection options do not always correspond to a field present in
1355 the message, since a connection-specific field might not be needed if
1356 there are no parameters associated with a connection option. In
1357 contrast, a connection-specific field that is received without a
1358 corresponding connection option usually indicates that the field has
1359 been improperly forwarded by an intermediary and ought to be ignored
1360 by the recipient.
1362 When defining new connection options, specification authors ought to
1363 document it as reserved field name and register that definition in
1364 the Hypertext Transfer Protocol (HTTP) Field Name Registry
1365 (Section 4.3.2 of [Semantics]), to avoid collisions.
1367 The "close" connection option is defined for a sender to signal that
1368 this connection will be closed after completion of the response. For
1369 example,
1371 Connection: close
1373 in either the request or the response header fields indicates that
1374 the sender is going to close the connection after the current
1375 request/response is complete (Section 9.7).
1377 A client that does not support persistent connections MUST send the
1378 "close" connection option in every request message.
1380 A server that does not support persistent connections MUST send the
1381 "close" connection option in every response message that does not
1382 have a 1xx (Informational) status code.
1384 9.2. Establishment
1386 It is beyond the scope of this specification to describe how
1387 connections are established via various transport- or session-layer
1388 protocols. Each connection applies to only one transport link.
1390 9.3. Associating a Response to a Request
1392 HTTP/1.1 does not include a request identifier for associating a
1393 given request message with its corresponding one or more response
1394 messages. Hence, it relies on the order of response arrival to
1395 correspond exactly to the order in which requests are made on the
1396 same connection. More than one response message per request only
1397 occurs when one or more informational responses (1xx, see Section 9.2
1398 of [Semantics]) precede a final response to the same request.
1400 A client that has more than one outstanding request on a connection
1401 MUST maintain a list of outstanding requests in the order sent and
1402 MUST associate each received response message on that connection to
1403 the highest ordered request that has not yet received a final (non-
1404 1xx) response.
1406 If an HTTP/1.1 client receives data on a connection that doesn't have
1407 any outstanding requests, it MUST NOT consider them to be a response
1408 to a not-yet-issued request; it SHOULD close the connection, since
1409 message delimitation is now ambiguous, unless the data consists only
1410 of one or more CRLF (which can be discarded, as per Section 2.2).
1412 9.4. Persistence
1414 HTTP/1.1 defaults to the use of "persistent connections", allowing
1415 multiple requests and responses to be carried over a single
1416 connection. The "close" connection option is used to signal that a
1417 connection will not persist after the current request/response. HTTP
1418 implementations SHOULD support persistent connections.
1420 A recipient determines whether a connection is persistent or not
1421 based on the most recently received message's protocol version and
1422 Connection header field (if any):
1424 o If the "close" connection option is present, the connection will
1425 not persist after the current response; else,
1427 o If the received protocol is HTTP/1.1 (or later), the connection
1428 will persist after the current response; else,
1430 o If the received protocol is HTTP/1.0, the "keep-alive" connection
1431 option is present, either the recipient is not a proxy or the
1432 message is a response, and the recipient wishes to honor the
1433 HTTP/1.0 "keep-alive" mechanism, the connection will persist after
1434 the current response; otherwise,
1436 o The connection will close after the current response.
1438 A client MAY send additional requests on a persistent connection
1439 until it sends or receives a "close" connection option or receives an
1440 HTTP/1.0 response without a "keep-alive" connection option.
1442 In order to remain persistent, all messages on a connection need to
1443 have a self-defined message length (i.e., one not defined by closure
1444 of the connection), as described in Section 6. A server MUST read
1445 the entire request message body or close the connection after sending
1446 its response, since otherwise the remaining data on a persistent
1447 connection would be misinterpreted as the next request. Likewise, a
1448 client MUST read the entire response message body if it intends to
1449 reuse the same connection for a subsequent request.
1451 A proxy server MUST NOT maintain a persistent connection with an
1452 HTTP/1.0 client (see Section 19.7.1 of [RFC2068] for information and
1453 discussion of the problems with the Keep-Alive header field
1454 implemented by many HTTP/1.0 clients).
1456 See Appendix C.1.2 for more information on backwards compatibility
1457 with HTTP/1.0 clients.
1459 9.4.1. Retrying Requests
1461 Connections can be closed at any time, with or without intention.
1462 Implementations ought to anticipate the need to recover from
1463 asynchronous close events. The conditions under which a client can
1464 automatically retry a sequence of outstanding requests are defined in
1465 Section 7.2.2 of [Semantics].
1467 9.4.2. Pipelining
1469 A client that supports persistent connections MAY "pipeline" its
1470 requests (i.e., send multiple requests without waiting for each
1471 response). A server MAY process a sequence of pipelined requests in
1472 parallel if they all have safe methods (Section 7.2.1 of
1473 [Semantics]), but it MUST send the corresponding responses in the
1474 same order that the requests were received.
1476 A client that pipelines requests SHOULD retry unanswered requests if
1477 the connection closes before it receives all of the corresponding
1478 responses. When retrying pipelined requests after a failed
1479 connection (a connection not explicitly closed by the server in its
1480 last complete response), a client MUST NOT pipeline immediately after
1481 connection establishment, since the first remaining request in the
1482 prior pipeline might have caused an error response that can be lost
1483 again if multiple requests are sent on a prematurely closed
1484 connection (see the TCP reset problem described in Section 9.7).
1486 Idempotent methods (Section 7.2.2 of [Semantics]) are significant to
1487 pipelining because they can be automatically retried after a
1488 connection failure. A user agent SHOULD NOT pipeline requests after
1489 a non-idempotent method, until the final response status code for
1490 that method has been received, unless the user agent has a means to
1491 detect and recover from partial failure conditions involving the
1492 pipelined sequence.
1494 An intermediary that receives pipelined requests MAY pipeline those
1495 requests when forwarding them inbound, since it can rely on the
1496 outbound user agent(s) to determine what requests can be safely
1497 pipelined. If the inbound connection fails before receiving a
1498 response, the pipelining intermediary MAY attempt to retry a sequence
1499 of requests that have yet to receive a response if the requests all
1500 have idempotent methods; otherwise, the pipelining intermediary
1501 SHOULD forward any received responses and then close the
1502 corresponding outbound connection(s) so that the outbound user
1503 agent(s) can recover accordingly.
1505 9.5. Concurrency
1507 A client ought to limit the number of simultaneous open connections
1508 that it maintains to a given server.
1510 Previous revisions of HTTP gave a specific number of connections as a
1511 ceiling, but this was found to be impractical for many applications.
1512 As a result, this specification does not mandate a particular maximum
1513 number of connections but, instead, encourages clients to be
1514 conservative when opening multiple connections.
1516 Multiple connections are typically used to avoid the "head-of-line
1517 blocking" problem, wherein a request that takes significant server-
1518 side processing and/or has a large payload blocks subsequent requests
1519 on the same connection. However, each connection consumes server
1520 resources. Furthermore, using multiple connections can cause
1521 undesirable side effects in congested networks.
1523 Note that a server might reject traffic that it deems abusive or
1524 characteristic of a denial-of-service attack, such as an excessive
1525 number of open connections from a single client.
1527 9.6. Failures and Timeouts
1529 Servers will usually have some timeout value beyond which they will
1530 no longer maintain an inactive connection. Proxy servers might make
1531 this a higher value since it is likely that the client will be making
1532 more connections through the same proxy server. The use of
1533 persistent connections places no requirements on the length (or
1534 existence) of this timeout for either the client or the server.
1536 A client or server that wishes to time out SHOULD issue a graceful
1537 close on the connection. Implementations SHOULD constantly monitor
1538 open connections for a received closure signal and respond to it as
1539 appropriate, since prompt closure of both sides of a connection
1540 enables allocated system resources to be reclaimed.
1542 A client, server, or proxy MAY close the transport connection at any
1543 time. For example, a client might have started to send a new request
1544 at the same time that the server has decided to close the "idle"
1545 connection. From the server's point of view, the connection is being
1546 closed while it was idle, but from the client's point of view, a
1547 request is in progress.
1549 A server SHOULD sustain persistent connections, when possible, and
1550 allow the underlying transport's flow-control mechanisms to resolve
1551 temporary overloads, rather than terminate connections with the
1552 expectation that clients will retry. The latter technique can
1553 exacerbate network congestion.
1555 A client sending a message body SHOULD monitor the network connection
1556 for an error response while it is transmitting the request. If the
1557 client sees a response that indicates the server does not wish to
1558 receive the message body and is closing the connection, the client
1559 SHOULD immediately cease transmitting the body and close its side of
1560 the connection.
1562 9.7. Tear-down
1564 The Connection header field (Section 9.1) provides a "close"
1565 connection option that a sender SHOULD send when it wishes to close
1566 the connection after the current request/response pair.
1568 A client that sends a "close" connection option MUST NOT send further
1569 requests on that connection (after the one containing "close") and
1570 MUST close the connection after reading the final response message
1571 corresponding to this request.
1573 A server that receives a "close" connection option MUST initiate a
1574 close of the connection (see below) after it sends the final response
1575 to the request that contained "close". The server SHOULD send a
1576 "close" connection option in its final response on that connection.
1577 The server MUST NOT process any further requests received on that
1578 connection.
1580 A server that sends a "close" connection option MUST initiate a close
1581 of the connection (see below) after it sends the response containing
1582 "close". The server MUST NOT process any further requests received
1583 on that connection.
1585 A client that receives a "close" connection option MUST cease sending
1586 requests on that connection and close the connection after reading
1587 the response message containing the "close"; if additional pipelined
1588 requests had been sent on the connection, the client SHOULD NOT
1589 assume that they will be processed by the server.
1591 If a server performs an immediate close of a TCP connection, there is
1592 a significant risk that the client will not be able to read the last
1593 HTTP response. If the server receives additional data from the
1594 client on a fully closed connection, such as another request that was
1595 sent by the client before receiving the server's response, the
1596 server's TCP stack will send a reset packet to the client;
1597 unfortunately, the reset packet might erase the client's
1598 unacknowledged input buffers before they can be read and interpreted
1599 by the client's HTTP parser.
1601 To avoid the TCP reset problem, servers typically close a connection
1602 in stages. First, the server performs a half-close by closing only
1603 the write side of the read/write connection. The server then
1604 continues to read from the connection until it receives a
1605 corresponding close by the client, or until the server is reasonably
1606 certain that its own TCP stack has received the client's
1607 acknowledgement of the packet(s) containing the server's last
1608 response. Finally, the server fully closes the connection.
1610 It is unknown whether the reset problem is exclusive to TCP or might
1611 also be found in other transport connection protocols.
1613 9.8. TLS Connection Closure
1615 TLS provides a facility for secure connection closure. When a valid
1616 closure alert is received, an implementation can be assured that no
1617 further data will be received on that connection. TLS
1618 implementations MUST initiate an exchange of closure alerts before
1619 closing a connection. A TLS implementation MAY, after sending a
1620 closure alert, close the connection without waiting for the peer to
1621 send its closure alert, generating an "incomplete close". Note that
1622 an implementation which does this MAY choose to reuse the session.
1623 This SHOULD only be done when the application knows (typically
1624 through detecting HTTP message boundaries) that it has received all
1625 the message data that it cares about.
1627 As specified in [RFC8446], any implementation which receives a
1628 connection close without first receiving a valid closure alert (a
1629 "premature close") MUST NOT reuse that session. Note that a
1630 premature close does not call into question the security of the data
1631 already received, but simply indicates that subsequent data might
1632 have been truncated. Because TLS is oblivious to HTTP request/
1633 response boundaries, it is necessary to examine the HTTP data itself
1634 (specifically the Content-Length header) to determine whether the
1635 truncation occurred inside a message or between messages.
1637 When encountering a premature close, a client SHOULD treat as
1638 completed all requests for which it has received as much data as
1639 specified in the Content-Length header.
1641 A client detecting an incomplete close SHOULD recover gracefully. It
1642 MAY resume a TLS session closed in this fashion.
1644 Clients MUST send a closure alert before closing the connection.
1645 Clients which are unprepared to receive any more data MAY choose not
1646 to wait for the server's closure alert and simply close the
1647 connection, thus generating an incomplete close on the server side.
1649 Servers SHOULD be prepared to receive an incomplete close from the
1650 client, since the client can often determine when the end of server
1651 data is. Servers SHOULD be willing to resume TLS sessions closed in
1652 this fashion.
1654 Servers MUST attempt to initiate an exchange of closure alerts with
1655 the client before closing the connection. Servers MAY close the
1656 connection after sending the closure alert, thus generating an
1657 incomplete close on the client side.
1659 9.9. Upgrade
1661 The "Upgrade" header field is intended to provide a simple mechanism
1662 for transitioning from HTTP/1.1 to some other protocol on the same
1663 connection.
1665 A client MAY send a list of protocol names in the Upgrade header
1666 field of a request to invite the server to switch to one or more of
1667 the named protocols, in order of descending preference, before
1668 sending the final response. A server MAY ignore a received Upgrade
1669 header field if it wishes to continue using the current protocol on
1670 that connection. Upgrade cannot be used to insist on a protocol
1671 change.
1673 Upgrade = 1#protocol
1675 protocol = protocol-name ["/" protocol-version]
1676 protocol-name = token
1677 protocol-version = token
1679 Although protocol names are registered with a preferred case,
1680 recipients SHOULD use case-insensitive comparison when matching each
1681 protocol-name to supported protocols.
1683 A server that sends a 101 (Switching Protocols) response MUST send an
1684 Upgrade header field to indicate the new protocol(s) to which the
1685 connection is being switched; if multiple protocol layers are being
1686 switched, the sender MUST list the protocols in layer-ascending
1687 order. A server MUST NOT switch to a protocol that was not indicated
1688 by the client in the corresponding request's Upgrade header field. A
1689 server MAY choose to ignore the order of preference indicated by the
1690 client and select the new protocol(s) based on other factors, such as
1691 the nature of the request or the current load on the server.
1693 A server that sends a 426 (Upgrade Required) response MUST send an
1694 Upgrade header field to indicate the acceptable protocols, in order
1695 of descending preference.
1697 A server MAY send an Upgrade header field in any other response to
1698 advertise that it implements support for upgrading to the listed
1699 protocols, in order of descending preference, when appropriate for a
1700 future request.
1702 The following is a hypothetical example sent by a client:
1704 GET /hello HTTP/1.1
1705 Host: www.example.com
1706 Connection: upgrade
1707 Upgrade: websocket, IRC/6.9, RTA/x11
1709 The capabilities and nature of the application-level communication
1710 after the protocol change is entirely dependent upon the new
1711 protocol(s) chosen. However, immediately after sending the 101
1712 (Switching Protocols) response, the server is expected to continue
1713 responding to the original request as if it had received its
1714 equivalent within the new protocol (i.e., the server still has an
1715 outstanding request to satisfy after the protocol has been changed,
1716 and is expected to do so without requiring the request to be
1717 repeated).
1719 For example, if the Upgrade header field is received in a GET request
1720 and the server decides to switch protocols, it first responds with a
1721 101 (Switching Protocols) message in HTTP/1.1 and then immediately
1722 follows that with the new protocol's equivalent of a response to a
1723 GET on the target resource. This allows a connection to be upgraded
1724 to protocols with the same semantics as HTTP without the latency cost
1725 of an additional round trip. A server MUST NOT switch protocols
1726 unless the received message semantics can be honored by the new
1727 protocol; an OPTIONS request can be honored by any protocol.
1729 The following is an example response to the above hypothetical
1730 request:
1732 HTTP/1.1 101 Switching Protocols
1733 Connection: upgrade
1734 Upgrade: websocket
1736 [... data stream switches to websocket with an appropriate response
1737 (as defined by new protocol) to the "GET /hello" request ...]
1739 When Upgrade is sent, the sender MUST also send a Connection header
1740 field (Section 9.1) that contains an "upgrade" connection option, in
1741 order to prevent Upgrade from being accidentally forwarded by
1742 intermediaries that might not implement the listed protocols. A
1743 server MUST ignore an Upgrade header field that is received in an
1744 HTTP/1.0 request.
1746 A client cannot begin using an upgraded protocol on the connection
1747 until it has completely sent the request message (i.e., the client
1748 can't change the protocol it is sending in the middle of a message).
1749 If a server receives both an Upgrade and an Expect header field with
1750 the "100-continue" expectation (Section 8.1.1 of [Semantics]), the
1751 server MUST send a 100 (Continue) response before sending a 101
1752 (Switching Protocols) response.
1754 The Upgrade header field only applies to switching protocols on top
1755 of the existing connection; it cannot be used to switch the
1756 underlying connection (transport) protocol, nor to switch the
1757 existing communication to a different connection. For those
1758 purposes, it is more appropriate to use a 3xx (Redirection) response
1759 (Section 9.4 of [Semantics]).
1761 9.9.1. Upgrade Protocol Names
1763 This specification only defines the protocol name "HTTP" for use by
1764 the family of Hypertext Transfer Protocols, as defined by the HTTP
1765 version rules of Section 3.5 of [Semantics] and future updates to
1766 this specification. Additional protocol names ought to be registered
1767 using the registration procedure defined in Section 9.9.2.
1769 +------+-------------------+--------------------+-------------------+
1770 | Name | Description | Expected Version | Reference |
1771 | | | Tokens | |
1772 +------+-------------------+--------------------+-------------------+
1773 | HTTP | Hypertext | any DIGIT.DIGIT | Section 3.5 of |
1774 | | Transfer Protocol | (e.g, "2.0") | [Semantics] |
1775 +------+-------------------+--------------------+-------------------+
1777 9.9.2. Upgrade Token Registry
1779 The "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry"
1780 defines the namespace for protocol-name tokens used to identify
1781 protocols in the Upgrade header field. The registry is maintained at
1782 .
1784 Each registered protocol name is associated with contact information
1785 and an optional set of specifications that details how the connection
1786 will be processed after it has been upgraded.
1788 Registrations happen on a "First Come First Served" basis (see
1789 Section 4.4 of [RFC8126]) and are subject to the following rules:
1791 1. A protocol-name token, once registered, stays registered forever.
1793 2. A protocol-name token is case-insensitive and registered with the
1794 preferred case to be generated by senders.
1796 3. The registration MUST name a responsible party for the
1797 registration.
1799 4. The registration MUST name a point of contact.
1801 5. The registration MAY name a set of specifications associated with
1802 that token. Such specifications need not be publicly available.
1804 6. The registration SHOULD name a set of expected "protocol-version"
1805 tokens associated with that token at the time of registration.
1807 7. The responsible party MAY change the registration at any time.
1808 The IANA will keep a record of all such changes, and make them
1809 available upon request.
1811 8. The IESG MAY reassign responsibility for a protocol token. This
1812 will normally only be used in the case when a responsible party
1813 cannot be contacted.
1815 10. Enclosing Messages as Data
1817 10.1. Media Type message/http
1819 The message/http media type can be used to enclose a single HTTP
1820 request or response message, provided that it obeys the MIME
1821 restrictions for all "message" types regarding line length and
1822 encodings.
1824 Type name: message
1826 Subtype name: http
1828 Required parameters: N/A
1830 Optional parameters: version, msgtype
1832 version: The HTTP-version number of the enclosed message (e.g.,
1833 "1.1"). If not present, the version can be determined from the
1834 first line of the body.
1836 msgtype: The message type -- "request" or "response". If not
1837 present, the type can be determined from the first line of the
1838 body.
1840 Encoding considerations: only "7bit", "8bit", or "binary" are
1841 permitted
1843 Security considerations: see Section 11
1845 Interoperability considerations: N/A
1847 Published specification: This specification (see Section 10.1).
1849 Applications that use this media type: N/A
1851 Fragment identifier considerations: N/A
1853 Additional information:
1855 Magic number(s): N/A
1857 Deprecated alias names for this type: N/A
1859 File extension(s): N/A
1861 Macintosh file type code(s): N/A
1863 Person and email address to contact for further information:
1864 See Authors' Addresses section.
1866 Intended usage: COMMON
1868 Restrictions on usage: N/A
1870 Author: See Authors' Addresses section.
1872 Change controller: IESG
1874 10.2. Media Type application/http
1876 The application/http media type can be used to enclose a pipeline of
1877 one or more HTTP request or response messages (not intermixed).
1879 Type name: application
1881 Subtype name: http
1883 Required parameters: N/A
1884 Optional parameters: version, msgtype
1886 version: The HTTP-version number of the enclosed messages (e.g.,
1887 "1.1"). If not present, the version can be determined from the
1888 first line of the body.
1890 msgtype: The message type -- "request" or "response". If not
1891 present, the type can be determined from the first line of the
1892 body.
1894 Encoding considerations: HTTP messages enclosed by this type are in
1895 "binary" format; use of an appropriate Content-Transfer-Encoding
1896 is required when transmitted via email.
1898 Security considerations: see Section 11
1900 Interoperability considerations: N/A
1902 Published specification: This specification (see Section 10.2).
1904 Applications that use this media type: N/A
1906 Fragment identifier considerations: N/A
1908 Additional information:
1910 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:
1919 See Authors' 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 +----------+--------------------------------------+-----------------+
2072 | HTTP/1.1 | 0x68 0x74 0x74 0x70 0x2f 0x31 0x2e | (this |
2073 | | 0x31 ("http/1.1") | specification) |
2074 +----------+--------------------------------------+-----------------+
2076 13. References
2078 13.1. Normative References
2080 [Caching] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
2081 Ed., "HTTP Caching", draft-ietf-httpbis-cache-08 (work in
2082 progress), May 2020.
2084 [RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format
2085 Specification version 3.3", RFC 1950,
2086 DOI 10.17487/RFC1950, May 1996,
2087 .
2089 [RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
2090 version 1.3", RFC 1951, DOI 10.17487/RFC1951, May 1996,
2091 .
2093 [RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
2094 Randers-Pehrson, "GZIP file format specification version
2095 4.3", RFC 1952, DOI 10.17487/RFC1952, May 1996,
2096 .
2098 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
2099 Requirement Levels", BCP 14, RFC 2119,
2100 DOI 10.17487/RFC2119, March 1997,
2101 .
2103 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
2104 Resource Identifier (URI): Generic Syntax", STD 66,
2105 RFC 3986, DOI 10.17487/RFC3986, January 2005,
2106 .
2108 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
2109 Specifications: ABNF", STD 68, RFC 5234,
2110 DOI 10.17487/RFC5234, January 2008,
2111 .
2113 [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
2114 RFC 7405, DOI 10.17487/RFC7405, December 2014,
2115 .
2117 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2118 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
2119 May 2017, .
2121 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
2122 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
2123 .
2125 [Semantics]
2126 Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
2127 Ed., "HTTP Semantics", draft-ietf-httpbis-semantics-08
2128 (work in progress), May 2020.
2130 [USASCII] American National Standards Institute, "Coded Character
2131 Set -- 7-bit American Standard Code for Information
2132 Interchange", ANSI X3.4, 1986.
2134 [Welch] Welch, T., "A Technique for High-Performance Data
2135 Compression", IEEE Computer 17(6), June 1984.
2137 13.2. Informative References
2139 [Err4667] RFC Errata, Erratum ID 4667, RFC 7230,
2140 .
2142 [Klein] Klein, A., "Divide and Conquer - HTTP Response Splitting,
2143 Web Cache Poisoning Attacks, and Related Topics", March
2144 2004, .
2147 [Linhart] Linhart, C., Klein, A., Heled, R., and S. Orrin, "HTTP
2148 Request Smuggling", June 2005,
2149 .
2151 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
2152 Transfer Protocol -- HTTP/1.0", RFC 1945,
2153 DOI 10.17487/RFC1945, May 1996,
2154 .
2156 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
2157 Extensions (MIME) Part One: Format of Internet Message
2158 Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
2159 .
2161 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
2162 Extensions (MIME) Part Two: Media Types", RFC 2046,
2163 DOI 10.17487/RFC2046, November 1996,
2164 .
2166 [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
2167 Extensions (MIME) Part Five: Conformance Criteria and
2168 Examples", RFC 2049, DOI 10.17487/RFC2049, November 1996,
2169 .
2171 [RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
2172 Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
2173 RFC 2068, DOI 10.17487/RFC2068, January 1997,
2174 .
2176 [RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud,
2177 "MIME Encapsulation of Aggregate Documents, such as HTML
2178 (MHTML)", RFC 2557, DOI 10.17487/RFC2557, March 1999,
2179 .
2181 [RFC5322] Resnick, P., "Internet Message Format", RFC 5322,
2182 DOI 10.17487/RFC5322, October 2008,
2183 .
2185 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
2186 Protocol (HTTP/1.1): Message Syntax and Routing",
2187 RFC 7230, DOI 10.17487/RFC7230, June 2014,
2188 .
2190 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
2191 Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
2192 DOI 10.17487/RFC7231, June 2014,
2193 .
2195 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
2196 Writing an IANA Considerations Section in RFCs", BCP 26,
2197 RFC 8126, DOI 10.17487/RFC8126, June 2017,
2198 .
2200 Appendix A. Collected ABNF
2202 In the collected ABNF below, list rules are expanded as per
2203 Section 4.5 of [Semantics].
2205 BWS =
2207 Connection = [ connection-option ] *( OWS "," OWS [ connection-option
2208 ] )
2210 HTTP-message = start-line CRLF *( field-line CRLF ) CRLF [
2211 message-body ]
2212 HTTP-name = %x48.54.54.50 ; HTTP
2213 HTTP-version = HTTP-name "/" DIGIT "." DIGIT
2215 OWS =
2217 RWS =
2219 TE = [ t-codings ] *( OWS "," OWS [ t-codings ] )
2220 Transfer-Encoding = [ transfer-coding ] *( OWS "," OWS [
2221 transfer-coding ] )
2223 Upgrade = [ protocol ] *( OWS "," OWS [ protocol ] )
2225 absolute-URI =
2226 absolute-form = absolute-URI
2227 absolute-path =
2228 asterisk-form = "*"
2229 authority =
2230 authority-form = authority
2232 chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
2233 chunk-data = 1*OCTET
2234 chunk-ext = *( BWS ";" BWS chunk-ext-name [ BWS "=" BWS chunk-ext-val
2235 ] )
2236 chunk-ext-name = token
2237 chunk-ext-val = token / quoted-string
2238 chunk-size = 1*HEXDIG
2239 chunked-body = *chunk last-chunk trailer-section CRLF
2240 comment =
2241 connection-option = token
2243 field-line = field-name ":" OWS field-value OWS
2244 field-name =
2245 field-value =
2247 last-chunk = 1*"0" [ chunk-ext ] CRLF
2248 message-body = *OCTET
2249 method = token
2251 obs-fold = OWS CRLF RWS
2252 obs-text =
2253 origin-form = absolute-path [ "?" query ]
2255 port =
2256 protocol = protocol-name [ "/" protocol-version ]
2257 protocol-name = token
2258 protocol-version = token
2260 query =
2261 quoted-string =
2263 rank = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
2264 reason-phrase = 1*( HTAB / SP / VCHAR / obs-text )
2265 request-line = method SP request-target SP HTTP-version
2266 request-target = origin-form / absolute-form / authority-form /
2267 asterisk-form
2269 start-line = request-line / status-line
2270 status-code = 3DIGIT
2271 status-line = HTTP-version SP status-code SP [ reason-phrase ]
2273 t-codings = "trailers" / ( transfer-coding [ t-ranking ] )
2274 t-ranking = OWS ";" OWS "q=" rank
2275 token =
2276 trailer-section = *( field-line CRLF )
2277 transfer-coding = token *( OWS ";" OWS transfer-parameter )
2278 transfer-parameter = token BWS "=" BWS ( token / quoted-string )
2280 uri-host =
2282 Appendix B. Differences between HTTP and MIME
2284 HTTP/1.1 uses many of the constructs defined for the Internet Message
2285 Format [RFC5322] and the Multipurpose Internet Mail Extensions (MIME)
2286 [RFC2045] to allow a message body to be transmitted in an open
2287 variety of representations and with extensible fields. However, RFC
2288 2045 is focused only on email; applications of HTTP have many
2289 characteristics that differ from email; hence, HTTP has features that
2290 differ from MIME. These differences were carefully chosen to
2291 optimize performance over binary connections, to allow greater
2292 freedom in the use of new media types, to make date comparisons
2293 easier, and to acknowledge the practice of some early HTTP servers
2294 and clients.
2296 This appendix describes specific areas where HTTP differs from MIME.
2297 Proxies and gateways to and from strict MIME environments need to be
2298 aware of these differences and provide the appropriate conversions
2299 where necessary.
2301 B.1. MIME-Version
2303 HTTP is not a MIME-compliant protocol. However, messages can include
2304 a single MIME-Version header field to indicate what version of the
2305 MIME protocol was used to construct the message. Use of the MIME-
2306 Version header field indicates that the message is in full
2307 conformance with the MIME protocol (as defined in [RFC2045]).
2308 Senders are responsible for ensuring full conformance (where
2309 possible) when exporting HTTP messages to strict MIME environments.
2311 B.2. Conversion to Canonical Form
2313 MIME requires that an Internet mail body part be converted to
2314 canonical form prior to being transferred, as described in Section 4
2315 of [RFC2049]. Section 6.1.1.2 of [Semantics] describes the forms
2316 allowed for subtypes of the "text" media type when transmitted over
2317 HTTP. [RFC2046] requires that content with a type of "text"
2318 represent line breaks as CRLF and forbids the use of CR or LF outside
2319 of line break sequences. HTTP allows CRLF, bare CR, and bare LF to
2320 indicate a line break within text content.
2322 A proxy or gateway from HTTP to a strict MIME environment ought to
2323 translate all line breaks within text media types to the RFC 2049
2324 canonical form of CRLF. Note, however, this might be complicated by
2325 the presence of a Content-Encoding and by the fact that HTTP allows
2326 the use of some charsets that do not use octets 13 and 10 to
2327 represent CR and LF, respectively.
2329 Conversion will break any cryptographic checksums applied to the
2330 original content unless the original content is already in canonical
2331 form. Therefore, the canonical form is recommended for any content
2332 that uses such checksums in HTTP.
2334 B.3. Conversion of Date Formats
2336 HTTP/1.1 uses a restricted set of date formats (Section 10.1.1.1 of
2337 [Semantics]) to simplify the process of date comparison. Proxies and
2338 gateways from other protocols ought to ensure that any Date header
2339 field present in a message conforms to one of the HTTP/1.1 formats
2340 and rewrite the date if necessary.
2342 B.4. Conversion of Content-Encoding
2344 MIME does not include any concept equivalent to HTTP/1.1's Content-
2345 Encoding header field. Since this acts as a modifier on the media
2346 type, proxies and gateways from HTTP to MIME-compliant protocols
2347 ought to either change the value of the Content-Type header field or
2348 decode the representation before forwarding the message. (Some
2349 experimental applications of Content-Type for Internet mail have used
2350 a media-type parameter of ";conversions=" to perform
2351 a function equivalent to Content-Encoding. However, this parameter
2352 is not part of the MIME standards).
2354 B.5. Conversion of Content-Transfer-Encoding
2356 HTTP does not use the Content-Transfer-Encoding field of MIME.
2357 Proxies and gateways from MIME-compliant protocols to HTTP need to
2358 remove any Content-Transfer-Encoding prior to delivering the response
2359 message to an HTTP client.
2361 Proxies and gateways from HTTP to MIME-compliant protocols are
2362 responsible for ensuring that the message is in the correct format
2363 and encoding for safe transport on that protocol, where "safe
2364 transport" is defined by the limitations of the protocol being used.
2365 Such a proxy or gateway ought to transform and label the data with an
2366 appropriate Content-Transfer-Encoding if doing so will improve the
2367 likelihood of safe transport over the destination protocol.
2369 B.6. MHTML and Line Length Limitations
2371 HTTP implementations that share code with MHTML [RFC2557]
2372 implementations need to be aware of MIME line length limitations.
2373 Since HTTP does not have this limitation, HTTP does not fold long
2374 lines. MHTML messages being transported by HTTP follow all
2375 conventions of MHTML, including line length limitations and folding,
2376 canonicalization, etc., since HTTP transfers message-bodies as
2377 payload and, aside from the "multipart/byteranges" type
2378 (Section 6.3.5 of [Semantics]), does not interpret the content or any
2379 MIME header lines that might be contained therein.
2381 Appendix C. HTTP Version History
2383 HTTP has been in use since 1990. The first version, later referred
2384 to as HTTP/0.9, was a simple protocol for hypertext data transfer
2385 across the Internet, using only a single request method (GET) and no
2386 metadata. HTTP/1.0, as defined by [RFC1945], added a range of
2387 request methods and MIME-like messaging, allowing for metadata to be
2388 transferred and modifiers placed on the request/response semantics.
2389 However, HTTP/1.0 did not sufficiently take into consideration the
2390 effects of hierarchical proxies, caching, the need for persistent
2391 connections, or name-based virtual hosts. The proliferation of
2392 incompletely implemented applications calling themselves "HTTP/1.0"
2393 further necessitated a protocol version change in order for two
2394 communicating applications to determine each other's true
2395 capabilities.
2397 HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
2398 requirements that enable reliable implementations, adding only those
2399 features that can either be safely ignored by an HTTP/1.0 recipient
2400 or only be sent when communicating with a party advertising
2401 conformance with HTTP/1.1.
2403 HTTP/1.1 has been designed to make supporting previous versions easy.
2404 A general-purpose HTTP/1.1 server ought to be able to understand any
2405 valid request in the format of HTTP/1.0, responding appropriately
2406 with an HTTP/1.1 message that only uses features understood (or
2407 safely ignored) by HTTP/1.0 clients. Likewise, an HTTP/1.1 client
2408 can be expected to understand any valid HTTP/1.0 response.
2410 Since HTTP/0.9 did not support header fields in a request, there is
2411 no mechanism for it to support name-based virtual hosts (selection of
2412 resource by inspection of the Host header field). Any server that
2413 implements name-based virtual hosts ought to disable support for
2414 HTTP/0.9. Most requests that appear to be HTTP/0.9 are, in fact,
2415 badly constructed HTTP/1.x requests caused by a client failing to
2416 properly encode the request-target.
2418 C.1. Changes from HTTP/1.0
2420 This section summarizes major differences between versions HTTP/1.0
2421 and HTTP/1.1.
2423 C.1.1. Multihomed Web Servers
2425 The requirements that clients and servers support the Host header
2426 field (Section 5.6 of [Semantics]), report an error if it is missing
2427 from an HTTP/1.1 request, and accept absolute URIs (Section 3.2) are
2428 among the most important changes defined by HTTP/1.1.
2430 Older HTTP/1.0 clients assumed a one-to-one relationship of IP
2431 addresses and servers; there was no other established mechanism for
2432 distinguishing the intended server of a request than the IP address
2433 to which that request was directed. The Host header field was
2434 introduced during the development of HTTP/1.1 and, though it was
2435 quickly implemented by most HTTP/1.0 browsers, additional
2436 requirements were placed on all HTTP/1.1 requests in order to ensure
2437 complete adoption. At the time of this writing, most HTTP-based
2438 services are dependent upon the Host header field for targeting
2439 requests.
2441 C.1.2. Keep-Alive Connections
2443 In HTTP/1.0, each connection is established by the client prior to
2444 the request and closed by the server after sending the response.
2445 However, some implementations implement the explicitly negotiated
2446 ("Keep-Alive") version of persistent connections described in
2447 Section 19.7.1 of [RFC2068].
2449 Some clients and servers might wish to be compatible with these
2450 previous approaches to persistent connections, by explicitly
2451 negotiating for them with a "Connection: keep-alive" request header
2452 field. However, some experimental implementations of HTTP/1.0
2453 persistent connections are faulty; for example, if an HTTP/1.0 proxy
2454 server doesn't understand Connection, it will erroneously forward
2455 that header field to the next inbound server, which would result in a
2456 hung connection.
2458 One attempted solution was the introduction of a Proxy-Connection
2459 header field, targeted specifically at proxies. In practice, this
2460 was also unworkable, because proxies are often deployed in multiple
2461 layers, bringing about the same problem discussed above.
2463 As a result, clients are encouraged not to send the Proxy-Connection
2464 header field in any requests.
2466 Clients are also encouraged to consider the use of Connection: keep-
2467 alive in requests carefully; while they can enable persistent
2468 connections with HTTP/1.0 servers, clients using them will need to
2469 monitor the connection for "hung" requests (which indicate that the
2470 client ought stop sending the header field), and this mechanism ought
2471 not be used by clients at all when a proxy is being used.
2473 C.1.3. Introduction of Transfer-Encoding
2475 HTTP/1.1 introduces the Transfer-Encoding header field (Section 6.1).
2476 Transfer codings need to be decoded prior to forwarding an HTTP
2477 message over a MIME-compliant protocol.
2479 C.2. Changes from RFC 7230
2481 Most of the sections introducing HTTP's design goals, history,
2482 architecture, conformance criteria, protocol versioning, URIs,
2483 message routing, and header fields have been moved to [Semantics].
2484 This document has been reduced to just the messaging syntax and
2485 connection management requirements specific to HTTP/1.1.
2487 In the ABNF for chunked extensions, re-introduced (bad) whitespace
2488 around ";" and "=". Whitespace was removed in [RFC7230], but that
2489 change was found to break existing implementations (see [Err4667]).
2490 (Section 7.1.1)
2492 Trailer field semantics now transcend the specifics of chunked
2493 encoding. The decoding algorithm for chunked (Section 7.1.3) has
2494 been updated to encourage storage/forwarding of trailer fields
2495 separately from the header section, to only allow merging into the
2496 header section if the recipient knows the corresponding field
2497 definition permits and defines how to merge, and otherwise to discard
2498 the trailer fields instead of merging. The trailer part is now
2499 called the trailer section to be more consistent with the header
2500 section and more distinct from a body part. (Section 7.1.2)
2502 Disallowed transfer coding parameters called "q" in order to avoid
2503 conflicts with the use of ranks in the TE header field.
2504 (Section 7.3)
2506 Appendix D. Change Log
2508 This section is to be removed before publishing as an RFC.
2510 D.1. Between RFC7230 and draft 00
2512 The changes were purely editorial:
2514 o Change boilerplate and abstract to indicate the "draft" status,
2515 and update references to ancestor specifications.
2517 o Adjust historical notes.
2519 o Update links to sibling specifications.
2521 o Replace sections listing changes from RFC 2616 by new empty
2522 sections referring to RFC 723x.
2524 o Remove acknowledgements specific to RFC 723x.
2526 o Move "Acknowledgements" to the very end and make them unnumbered.
2528 D.2. Since draft-ietf-httpbis-messaging-00
2530 The changes in this draft are editorial, with respect to HTTP as a
2531 whole, to move all core HTTP semantics into [Semantics]:
2533 o Moved introduction, architecture, conformance, and ABNF extensions
2534 from RFC 7230 (Messaging) to semantics [Semantics].
2536 o Moved discussion of MIME differences from RFC 7231 (Semantics) to
2537 Appendix B since they mostly cover transforming 1.1 messages.
2539 o Moved all extensibility tips, registration procedures, and
2540 registry tables from the IANA considerations to normative
2541 sections, reducing the IANA considerations to just instructions
2542 that will be removed prior to publication as an RFC.
2544 D.3. Since draft-ietf-httpbis-messaging-01
2546 o Cite RFC 8126 instead of RFC 5226 ()
2549 o Resolved erratum 4779, no change needed here
2550 (,
2551 )
2553 o In Section 7, fixed prose claiming transfer parameters allow bare
2554 names (,
2555 )
2557 o Resolved erratum 4225, no change needed here
2558 (,
2559 )
2561 o Replace "response code" with "response status code"
2562 (,
2563 )
2565 o In Section 9.4, clarify statement about HTTP/1.0 keep-alive
2566 (,
2567 )
2569 o In Section 7.1.1, re-introduce (bad) whitespace around ";" and "="
2570 (,
2571 , )
2574 o In Section 7.3, state that transfer codings should not use
2575 parameters named "q" (, )
2578 o In Section 7, mark coding name "trailers" as reserved in the IANA
2579 registry ()
2581 D.4. Since draft-ietf-httpbis-messaging-02
2583 o In Section 4, explain why the reason phrase should be ignored by
2584 clients ().
2586 o Add Section 9.3 to explain how request/response correlation is
2587 performed ()
2589 D.5. Since draft-ietf-httpbis-messaging-03
2591 o In Section 9.3, caution against treating data on a connection as
2592 part of a not-yet-issued request ()
2595 o In Section 7, remove the predefined codings from the ABNF and make
2596 it generic instead ()
2599 o Use RFC 7405 ABNF notation for case-sensitive string constants
2600 ()
2602 D.6. Since draft-ietf-httpbis-messaging-04
2604 o In Section 9.9, clarify that protocol-name is to be matched case-
2605 insensitively ()
2607 o In Section 5.2, add leading optional whitespace to obs-fold ABNF
2608 (,
2609 )
2611 o In Section 4, add clarifications about empty reason phrases
2612 ()
2614 o Move discussion of retries from Section 9.4.1 into [Semantics]
2615 ()
2617 D.7. Since draft-ietf-httpbis-messaging-05
2619 o In Section 7.1.2, the trailer part has been renamed the trailer
2620 section (for consistency with the header section) and trailers are
2621 no longer merged as header fields by default, but rather can be
2622 discarded, kept separate from header fields, or merged with header
2623 fields only if understood and defined as being mergeable
2624 ()
2626 o In Section 2.1 and related Sections, move the trailing CRLF from
2627 the line grammars into the message format
2628 ()
2630 o Moved Section 2.3 down ()
2633 o In Section 9.9, use 'websocket' instead of 'HTTP/2.0' in examples
2634 ()
2636 o Move version non-specific text from Section 6 into semantics as
2637 "payload body" ()
2639 o In Section 9.8, add text from RFC 2818
2640 ()
2642 D.8. Since draft-ietf-httpbis-messaging-06
2644 o In Section 12.5, update the APLN protocol id for HTTP/1.1
2645 ()
2647 o In Section 5, align with updates to field terminology in semantics
2648 ()
2650 o In Section 9.1, clarify that new connection options indeed need to
2651 be registered ()
2653 o In Section 1.1, reference RFC 8174 as well
2654 ()
2656 D.9. Since draft-ietf-httpbis-messaging-07
2658 o Move TE: trailers into [Semantics] ()
2661 o In Section 6.3, adjust requirements for handling multiple content-
2662 length values ()
2664 o Throughout, replace "effective request URI" with "target URI"
2665 ()
2667 o In Section 6.1, don't claim Transfer-Encoding is supported by
2668 HTTP/2 or later ()
2670 Index
2672 A
2673 absolute-form (of request-target) 11
2674 application/http Media Type 40
2675 asterisk-form (of request-target) 12
2676 authority-form (of request-target) 12
2678 C
2679 Connection header field 28, 34
2680 Content-Length header field 19
2681 Content-Transfer-Encoding header field 51
2682 chunked (Coding Format) 17, 19
2683 chunked (transfer coding) 22
2684 close 28, 34
2685 compress (transfer coding) 25
2687 D
2688 deflate (transfer coding) 25
2690 F
2691 Fields
2692 Connection 28
2693 MIME-Version 50
2694 TE 26
2695 Transfer-Encoding 17
2696 Upgrade 36
2698 G
2699 Grammar
2700 absolute-form 10-11
2701 ALPHA 5
2702 asterisk-form 10, 12
2703 authority-form 10, 12
2704 chunk 23
2705 chunk-data 23
2706 chunk-ext 23
2707 chunk-ext-name 23
2708 chunk-ext-val 23
2709 chunk-size 23
2710 chunked-body 23
2711 Connection 29
2712 connection-option 29
2713 CR 5
2714 CRLF 5
2715 CTL 5
2716 DIGIT 5
2717 DQUOTE 5
2718 field-line 15, 24
2719 field-name 15
2720 field-value 15
2721 HEXDIG 5
2722 HTAB 5
2723 HTTP-message 6
2724 HTTP-name 8
2725 HTTP-version 8
2726 last-chunk 23
2727 LF 5
2728 message-body 17
2729 method 9
2730 obs-fold 16
2731 OCTET 5
2732 origin-form 10
2733 rank 26
2734 reason-phrase 15
2735 request-line 9
2736 request-target 10
2737 SP 5
2738 start-line 6
2739 status-code 14
2740 status-line 14
2741 t-codings 26
2742 t-ranking 26
2743 TE 26
2744 trailer-section 23-24
2745 transfer-coding 22
2746 Transfer-Encoding 18
2747 transfer-parameter 22
2748 Upgrade 36
2749 VCHAR 5
2750 gzip (transfer coding) 25
2752 H
2753 Header Fields
2754 Connection 28
2755 MIME-Version 50
2756 TE 26
2757 Transfer-Encoding 17
2758 Upgrade 36
2759 header line 6
2760 header section 6
2761 headers 6
2763 M
2764 MIME-Version header field 50
2765 Media Type
2766 application/http 40
2767 message/http 39
2768 message/http Media Type 39
2769 method 9
2771 O
2772 origin-form (of request-target) 10
2774 R
2775 request-target 10
2777 T
2778 TE header field 26
2779 Transfer-Encoding header field 17
2781 U
2782 Upgrade header field 36
2784 X
2785 x-compress (transfer coding) 25
2786 x-gzip (transfer coding) 25
2788 Acknowledgments
2790 See Appendix "Acknowledgments" of [Semantics].
2792 Authors' Addresses
2794 Roy T. Fielding (editor)
2795 Adobe
2796 345 Park Ave
2797 San Jose, CA 95110
2798 United States of America
2800 EMail: fielding@gbiv.com
2801 URI: https://roy.gbiv.com/
2803 Mark Nottingham (editor)
2804 Fastly
2806 EMail: mnot@mnot.net
2807 URI: https://www.mnot.net/
2809 Julian F. Reschke (editor)
2810 greenbytes GmbH
2811 Hafenweg 16
2812 Muenster 48155
2813 Germany
2815 EMail: julian.reschke@greenbytes.de
2816 URI: https://greenbytes.de/tech/webdav/