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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 HTTPbis Working Group R. Fielding, Ed. 3 Internet-Draft Day Software 4 Obsoletes: 2616 (if approved) J. Gettys 5 Updates: 2817 (if approved) One Laptop per Child 6 Intended status: Standards Track J. Mogul 7 Expires: April 29, 2010 HP 8 H. Frystyk 9 Microsoft 10 L. Masinter 11 Adobe Systems 12 P. Leach 13 Microsoft 14 T. Berners-Lee 15 W3C/MIT 16 Y. Lafon, Ed. 17 W3C 18 J. Reschke, Ed. 19 greenbytes 20 October 26, 2009 22 HTTP/1.1, part 2: Message Semantics 23 draft-ietf-httpbis-p2-semantics-08 25 Status of this Memo 27 This Internet-Draft is submitted to IETF in full conformance with the 28 provisions of BCP 78 and BCP 79. This document may contain material 29 from IETF Documents or IETF Contributions published or made publicly 30 available before November 10, 2008. The person(s) controlling the 31 copyright in some of this material may not have granted the IETF 32 Trust the right to allow modifications of such material outside the 33 IETF Standards Process. Without obtaining an adequate license from 34 the person(s) controlling the copyright in such materials, this 35 document may not be modified outside the IETF Standards Process, and 36 derivative works of it may not be created outside the IETF Standards 37 Process, except to format it for publication as an RFC or to 38 translate it into languages other than English. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF), its areas, and its working groups. Note that 42 other groups may also distribute working documents as Internet- 43 Drafts. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 The list of current Internet-Drafts can be accessed at 50 http://www.ietf.org/ietf/1id-abstracts.txt. 52 The list of Internet-Draft Shadow Directories can be accessed at 53 http://www.ietf.org/shadow.html. 55 This Internet-Draft will expire on April 29, 2010. 57 Copyright Notice 59 Copyright (c) 2009 IETF Trust and the persons identified as the 60 document authors. All rights reserved. 62 This document is subject to BCP 78 and the IETF Trust's Legal 63 Provisions Relating to IETF Documents in effect on the date of 64 publication of this document (http://trustee.ietf.org/license-info). 65 Please review these documents carefully, as they describe your rights 66 and restrictions with respect to this document. 68 Abstract 70 The Hypertext Transfer Protocol (HTTP) is an application-level 71 protocol for distributed, collaborative, hypermedia information 72 systems. HTTP has been in use by the World Wide Web global 73 information initiative since 1990. This document is Part 2 of the 74 seven-part specification that defines the protocol referred to as 75 "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 2 defines 76 the semantics of HTTP messages as expressed by request methods, 77 request-header fields, response status codes, and response-header 78 fields. 80 Editorial Note (To be removed by RFC Editor) 82 Discussion of this draft should take place on the HTTPBIS working 83 group mailing list (ietf-http-wg@w3.org). The current issues list is 84 at and related 85 documents (including fancy diffs) can be found at 86 . 88 The changes in this draft are summarized in Appendix C.9. 90 Table of Contents 92 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 93 1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 6 94 1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6 95 1.2.1. Core Rules . . . . . . . . . . . . . . . . . . . . . . 7 96 1.2.2. ABNF Rules defined in other Parts of the 97 Specification . . . . . . . . . . . . . . . . . . . . 7 98 2. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 99 2.1. Method Registry . . . . . . . . . . . . . . . . . . . . . 8 100 3. Request Header Fields . . . . . . . . . . . . . . . . . . . . 9 101 4. Status Code and Reason Phrase . . . . . . . . . . . . . . . . 10 102 4.1. Status Code Registry . . . . . . . . . . . . . . . . . . . 12 103 5. Response Header Fields . . . . . . . . . . . . . . . . . . . . 12 104 6. Entity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 105 6.1. Identifying the Resource Associated with a 106 Representation . . . . . . . . . . . . . . . . . . . . . . 13 107 7. Method Definitions . . . . . . . . . . . . . . . . . . . . . . 14 108 7.1. Safe and Idempotent Methods . . . . . . . . . . . . . . . 14 109 7.1.1. Safe Methods . . . . . . . . . . . . . . . . . . . . . 14 110 7.1.2. Idempotent Methods . . . . . . . . . . . . . . . . . . 14 111 7.2. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . 15 112 7.3. GET . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 113 7.4. HEAD . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 114 7.5. POST . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 115 7.6. PUT . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 116 7.7. DELETE . . . . . . . . . . . . . . . . . . . . . . . . . . 19 117 7.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . . . 19 118 7.9. CONNECT . . . . . . . . . . . . . . . . . . . . . . . . . 20 119 8. Status Code Definitions . . . . . . . . . . . . . . . . . . . 20 120 8.1. Informational 1xx . . . . . . . . . . . . . . . . . . . . 20 121 8.1.1. 100 Continue . . . . . . . . . . . . . . . . . . . . . 20 122 8.1.2. 101 Switching Protocols . . . . . . . . . . . . . . . 20 123 8.2. Successful 2xx . . . . . . . . . . . . . . . . . . . . . . 21 124 8.2.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . . 21 125 8.2.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 21 126 8.2.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . . 22 127 8.2.4. 203 Non-Authoritative Information . . . . . . . . . . 22 128 8.2.5. 204 No Content . . . . . . . . . . . . . . . . . . . . 22 129 8.2.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 23 130 8.2.7. 206 Partial Content . . . . . . . . . . . . . . . . . 23 131 8.3. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 23 132 8.3.1. 300 Multiple Choices . . . . . . . . . . . . . . . . . 23 133 8.3.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 24 134 8.3.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 24 135 8.3.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 25 136 8.3.5. 304 Not Modified . . . . . . . . . . . . . . . . . . . 25 137 8.3.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 26 138 8.3.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . . 26 139 8.3.8. 307 Temporary Redirect . . . . . . . . . . . . . . . . 26 140 8.4. Client Error 4xx . . . . . . . . . . . . . . . . . . . . . 26 141 8.4.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 27 142 8.4.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . . 27 143 8.4.3. 402 Payment Required . . . . . . . . . . . . . . . . . 27 144 8.4.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 27 145 8.4.5. 404 Not Found . . . . . . . . . . . . . . . . . . . . 27 146 8.4.6. 405 Method Not Allowed . . . . . . . . . . . . . . . . 27 147 8.4.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . . 28 148 8.4.8. 407 Proxy Authentication Required . . . . . . . . . . 28 149 8.4.9. 408 Request Timeout . . . . . . . . . . . . . . . . . 28 150 8.4.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . . 28 151 8.4.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . . 29 152 8.4.12. 411 Length Required . . . . . . . . . . . . . . . . . 29 153 8.4.13. 412 Precondition Failed . . . . . . . . . . . . . . . 29 154 8.4.14. 413 Request Entity Too Large . . . . . . . . . . . . . 29 155 8.4.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . . 30 156 8.4.16. 415 Unsupported Media Type . . . . . . . . . . . . . . 30 157 8.4.17. 416 Requested Range Not Satisfiable . . . . . . . . . 30 158 8.4.18. 417 Expectation Failed . . . . . . . . . . . . . . . . 30 159 8.5. Server Error 5xx . . . . . . . . . . . . . . . . . . . . . 30 160 8.5.1. 500 Internal Server Error . . . . . . . . . . . . . . 31 161 8.5.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 31 162 8.5.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 31 163 8.5.4. 503 Service Unavailable . . . . . . . . . . . . . . . 31 164 8.5.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 31 165 8.5.6. 505 HTTP Version Not Supported . . . . . . . . . . . . 31 166 9. Header Field Definitions . . . . . . . . . . . . . . . . . . . 32 167 9.1. Allow . . . . . . . . . . . . . . . . . . . . . . . . . . 32 168 9.2. Expect . . . . . . . . . . . . . . . . . . . . . . . . . . 32 169 9.3. From . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 170 9.4. Location . . . . . . . . . . . . . . . . . . . . . . . . . 34 171 9.5. Max-Forwards . . . . . . . . . . . . . . . . . . . . . . . 35 172 9.6. Referer . . . . . . . . . . . . . . . . . . . . . . . . . 35 173 9.7. Retry-After . . . . . . . . . . . . . . . . . . . . . . . 36 174 9.8. Server . . . . . . . . . . . . . . . . . . . . . . . . . . 36 175 9.9. User-Agent . . . . . . . . . . . . . . . . . . . . . . . . 37 176 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 177 10.1. Method Registry . . . . . . . . . . . . . . . . . . . . . 37 178 10.2. Status Code Registry . . . . . . . . . . . . . . . . . . . 38 179 10.3. Message Header Registration . . . . . . . . . . . . . . . 39 180 11. Security Considerations . . . . . . . . . . . . . . . . . . . 40 181 11.1. Transfer of Sensitive Information . . . . . . . . . . . . 40 182 11.2. Encoding Sensitive Information in URIs . . . . . . . . . . 41 183 11.3. Location Headers and Spoofing . . . . . . . . . . . . . . 42 184 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 42 185 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42 186 13.1. Normative References . . . . . . . . . . . . . . . . . . . 42 187 13.2. Informative References . . . . . . . . . . . . . . . . . . 43 188 Appendix A. Compatibility with Previous Versions . . . . . . . . 43 189 A.1. Changes from RFC 2068 . . . . . . . . . . . . . . . . . . 43 190 A.2. Changes from RFC 2616 . . . . . . . . . . . . . . . . . . 44 191 Appendix B. Collected ABNF . . . . . . . . . . . . . . . . . . . 45 192 Appendix C. Change Log (to be removed by RFC Editor before 193 publication) . . . . . . . . . . . . . . . . . . . . 48 194 C.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . . 48 195 C.2. Since draft-ietf-httpbis-p2-semantics-00 . . . . . . . . . 48 196 C.3. Since draft-ietf-httpbis-p2-semantics-01 . . . . . . . . . 49 197 C.4. Since draft-ietf-httpbis-p2-semantics-02 . . . . . . . . . 49 198 C.5. Since draft-ietf-httpbis-p2-semantics-03 . . . . . . . . . 50 199 C.6. Since draft-ietf-httpbis-p2-semantics-04 . . . . . . . . . 50 200 C.7. Since draft-ietf-httpbis-p2-semantics-05 . . . . . . . . . 51 201 C.8. Since draft-ietf-httpbis-p2-semantics-06 . . . . . . . . . 51 202 C.9. Since draft-ietf-httpbis-p2-semantics-07 . . . . . . . . . 51 203 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 204 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 56 206 1. Introduction 208 This document defines HTTP/1.1 request and response semantics. Each 209 HTTP message, as defined in [Part1], is in the form of either a 210 request or a response. An HTTP server listens on a connection for 211 HTTP requests and responds to each request, in the order received on 212 that connection, with one or more HTTP response messages. This 213 document defines the commonly agreed upon semantics of the HTTP 214 uniform interface, the intentions defined by each request method, and 215 the various response messages that might be expected as a result of 216 applying that method for the requested resource. 218 This document is currently disorganized in order to minimize the 219 changes between drafts and enable reviewers to see the smaller errata 220 changes. The next draft will reorganize the sections to better 221 reflect the content. In particular, the sections will be ordered 222 according to the typical processing of an HTTP request message (after 223 message parsing): resource mapping, general header fields, methods, 224 request modifiers, response status, and resource metadata. The 225 current mess reflects how widely dispersed these topics and 226 associated requirements had become in [RFC2616]. 228 1.1. Requirements 230 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 231 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 232 document are to be interpreted as described in [RFC2119]. 234 An implementation is not compliant if it fails to satisfy one or more 235 of the MUST or REQUIRED level requirements for the protocols it 236 implements. An implementation that satisfies all the MUST or 237 REQUIRED level and all the SHOULD level requirements for its 238 protocols is said to be "unconditionally compliant"; one that 239 satisfies all the MUST level requirements but not all the SHOULD 240 level requirements for its protocols is said to be "conditionally 241 compliant." 243 1.2. Syntax Notation 245 This specification uses the ABNF syntax defined in Section 1.2 of 246 [Part1] (which extends the syntax defined in [RFC5234] with a list 247 rule). Appendix B shows the collected ABNF, with the list rule 248 expanded. 250 The following core rules are included by reference, as defined in 251 [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF 252 (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), 253 HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit 254 sequence of data), SP (space), VCHAR (any visible USASCII character), 255 and WSP (whitespace). 257 1.2.1. Core Rules 259 The core rules below are defined in Section 1.2.2 of [Part1]: 261 quoted-string = 262 token = 263 OWS = 264 RWS = 265 obs-text = 267 1.2.2. ABNF Rules defined in other Parts of the Specification 269 The ABNF rules below are defined in other parts: 271 absolute-URI = 272 comment = 273 Host = 274 HTTP-date = 275 partial-URI = 276 product = 277 TE = 278 URI = 280 Accept = 281 Accept-Charset = 282 283 Accept-Encoding = 284 285 Accept-Language = 286 288 ETag = 289 If-Match = 290 If-Modified-Since = 291 292 If-None-Match = 293 If-Unmodified-Since = 294 296 Accept-Ranges = 297 If-Range = 298 Range = 299 Age = 300 Vary = 302 Authorization = 303 Proxy-Authenticate = 304 305 Proxy-Authorization = 306 307 WWW-Authenticate = 308 310 2. Method 312 The Method token indicates the method to be performed on the resource 313 identified by the request-target. The method is case-sensitive. 315 Method = %x4F.50.54.49.4F.4E.53 ; "OPTIONS", Section 7.2 316 / %x47.45.54 ; "GET", Section 7.3 317 / %x48.45.41.44 ; "HEAD", Section 7.4 318 / %x50.4F.53.54 ; "POST", Section 7.5 319 / %x50.55.54 ; "PUT", Section 7.6 320 / %x44.45.4C.45.54.45 ; "DELETE", Section 7.7 321 / %x54.52.41.43.45 ; "TRACE", Section 7.8 322 / %x43.4F.4E.4E.45.43.54 ; "CONNECT", Section 7.9 323 / extension-method 324 extension-method = token 326 The list of methods allowed by a resource can be specified in an 327 Allow header field (Section 9.1). The return code of the response 328 always notifies the client whether a method is currently allowed on a 329 resource, since the set of allowed methods can change dynamically. 330 An origin server SHOULD return the status code 405 (Method Not 331 Allowed) if the method is known by the origin server but not allowed 332 for the requested resource, and 501 (Not Implemented) if the method 333 is unrecognized or not implemented by the origin server. The methods 334 GET and HEAD MUST be supported by all general-purpose servers. All 335 other methods are OPTIONAL; however, if the above methods are 336 implemented, they MUST be implemented with the same semantics as 337 those specified in Section 7. 339 2.1. Method Registry 341 The HTTP Method Registry defines the name space for the Method token 342 in the Request line of an HTTP request. 344 Registrations MUST include the following fields: 346 o Method Name (see Section 2) 348 o Safe ("yes" or "no", see Section 7.1.1) 350 o Pointer to specification text 352 Values to be added to this name space are subject to IETF review 353 ([RFC5226], Section 4.1). 355 The registry itself is maintained at 356 . 358 3. Request Header Fields 360 The request-header fields allow the client to pass additional 361 information about the request, and about the client itself, to the 362 server. These fields act as request modifiers, with semantics 363 equivalent to the parameters on a programming language method 364 invocation. 366 request-header = Accept ; [Part3], Section 5.1 367 / Accept-Charset ; [Part3], Section 5.2 368 / Accept-Encoding ; [Part3], Section 5.3 369 / Accept-Language ; [Part3], Section 5.4 370 / Authorization ; [Part7], Section 3.1 371 / Expect ; Section 9.2 372 / From ; Section 9.3 373 / Host ; [Part1], Section 9.4 374 / If-Match ; [Part4], Section 6.2 375 / If-Modified-Since ; [Part4], Section 6.3 376 / If-None-Match ; [Part4], Section 6.4 377 / If-Range ; [Part5], Section 5.3 378 / If-Unmodified-Since ; [Part4], Section 6.5 379 / Max-Forwards ; Section 9.5 380 / Proxy-Authorization ; [Part7], Section 3.3 381 / Range ; [Part5], Section 5.4 382 / Referer ; Section 9.6 383 / TE ; [Part1], Section 9.8 384 / User-Agent ; Section 9.9 386 Request-header field names can be extended reliably only in 387 combination with a change in the protocol version. However, new or 388 experimental header fields MAY be given the semantics of request- 389 header fields if all parties in the communication recognize them to 390 be request-header fields. Unrecognized header fields are treated as 391 entity-header fields. 393 4. Status Code and Reason Phrase 395 The Status-Code element is a 3-digit integer result code of the 396 attempt to understand and satisfy the request. The status codes 397 listed below are defined in Section 8. The Reason-Phrase is intended 398 to give a short textual description of the Status-Code. The Status- 399 Code is intended for use by automata and the Reason-Phrase is 400 intended for the human user. The client is not required to examine 401 or display the Reason-Phrase. 403 The individual values of the numeric status codes defined for 404 HTTP/1.1, and an example set of corresponding Reason-Phrase's, are 405 presented below. The reason phrases listed here are only 406 recommendations -- they MAY be replaced by local equivalents without 407 affecting the protocol. 409 Status-Code = 410 "100" ; Section 8.1.1: Continue 411 / "101" ; Section 8.1.2: Switching Protocols 412 / "200" ; Section 8.2.1: OK 413 / "201" ; Section 8.2.2: Created 414 / "202" ; Section 8.2.3: Accepted 415 / "203" ; Section 8.2.4: Non-Authoritative Information 416 / "204" ; Section 8.2.5: No Content 417 / "205" ; Section 8.2.6: Reset Content 418 / "206" ; [Part5], Section 3.1: Partial Content 419 / "300" ; Section 8.3.1: Multiple Choices 420 / "301" ; Section 8.3.2: Moved Permanently 421 / "302" ; Section 8.3.3: Found 422 / "303" ; Section 8.3.4: See Other 423 / "304" ; [Part4], Section 3.1: Not Modified 424 / "305" ; Section 8.3.6: Use Proxy 425 / "307" ; Section 8.3.8: Temporary Redirect 426 / "400" ; Section 8.4.1: Bad Request 427 / "401" ; [Part7], Section 2.1: Unauthorized 428 / "402" ; Section 8.4.3: Payment Required 429 / "403" ; Section 8.4.4: Forbidden 430 / "404" ; Section 8.4.5: Not Found 431 / "405" ; Section 8.4.6: Method Not Allowed 432 / "406" ; Section 8.4.7: Not Acceptable 433 / "407" ; [Part7], Section 2.2: Proxy Authentication Required 434 / "408" ; Section 8.4.9: Request Time-out 435 / "409" ; Section 8.4.10: Conflict 436 / "410" ; Section 8.4.11: Gone 437 / "411" ; Section 8.4.12: Length Required 438 / "412" ; [Part4], Section 3.2: Precondition Failed 439 / "413" ; Section 8.4.14: Request Entity Too Large 440 / "414" ; Section 8.4.15: URI Too Long 441 / "415" ; Section 8.4.16: Unsupported Media Type 442 / "416" ; status-416;: Requested range not satisfiable 443 / "417" ; Section 8.4.18: Expectation Failed 444 / "500" ; Section 8.5.1: Internal Server Error 445 / "501" ; Section 8.5.2: Not Implemented 446 / "502" ; Section 8.5.3: Bad Gateway 447 / "503" ; Section 8.5.4: Service Unavailable 448 / "504" ; Section 8.5.5: Gateway Time-out 449 / "505" ; Section 8.5.6: HTTP Version not supported 450 / extension-code 452 extension-code = 3DIGIT 453 Reason-Phrase = *( WSP / VCHAR / obs-text ) 455 HTTP status codes are extensible. HTTP applications are not required 456 to understand the meaning of all registered status codes, though such 457 understanding is obviously desirable. However, applications MUST 458 understand the class of any status code, as indicated by the first 459 digit, and treat any unrecognized response as being equivalent to the 460 x00 status code of that class, with the exception that an 461 unrecognized response MUST NOT be cached. For example, if an 462 unrecognized status code of 431 is received by the client, it can 463 safely assume that there was something wrong with its request and 464 treat the response as if it had received a 400 status code. In such 465 cases, user agents SHOULD present to the user the entity returned 466 with the response, since that entity is likely to include human- 467 readable information which will explain the unusual status. 469 4.1. Status Code Registry 471 The HTTP Status Code Registry defines the name space for the Status- 472 Code token in the Status line of an HTTP response. 474 Values to be added to this name space are subject to IETF review 475 ([RFC5226], Section 4.1). 477 The registry itself is maintained at 478 . 480 5. Response Header Fields 482 The response-header fields allow the server to pass additional 483 information about the response which cannot be placed in the Status- 484 Line. These header fields give information about the server and 485 about further access to the resource identified by the request- 486 target. 488 response-header = Accept-Ranges ; [Part5], Section 5.1 489 / Age ; [Part6], Section 3.1 490 / Allow ; Section 9.1 491 / ETag ; [Part4], Section 6.1 492 / Location ; Section 9.4 493 / Proxy-Authenticate ; [Part7], Section 3.2 494 / Retry-After ; Section 9.7 495 / Server ; Section 9.8 496 / Vary ; [Part6], Section 3.5 497 / WWW-Authenticate ; [Part7], Section 3.4 499 Response-header field names can be extended reliably only in 500 combination with a change in the protocol version. However, new or 501 experimental header fields MAY be given the semantics of response- 502 header fields if all parties in the communication recognize them to 503 be response-header fields. Unrecognized header fields are treated as 504 entity-header fields. 506 6. Entity 508 Request and Response messages MAY transfer an entity if not otherwise 509 restricted by the request method or response status code. An entity 510 consists of entity-header fields and an entity-body, although some 511 responses will only include the entity-headers. HTTP entity-body and 512 entity-header fields are defined in [Part3]. 514 An entity-body is only present in a message when a message-body is 515 present, as described in Section 3.3 of [Part1]. The entity-body is 516 obtained from the message-body by decoding any Transfer-Encoding that 517 might have been applied to ensure safe and proper transfer of the 518 message. 520 6.1. Identifying the Resource Associated with a Representation 522 It is sometimes necessary to determine the identity of the resource 523 associated with a representation. 525 An HTTP request representation, when present, is always associated 526 with an anonymous (i.e., unidentified) resource. 528 In the common case, an HTTP response is a representation of the 529 resource located at the request-URI. However, this is not always the 530 case. To determine the URI of the resource a response is associated 531 with, the following rules are used (first match winning): 533 1. If the response status code is 200 or 203 and the request method 534 was GET, the response is a representation of the resource at the 535 request-URI. 537 2. If the response status is 204, 206, or 304 and the request method 538 was GET or HEAD, the response is a partial representation of the 539 resource at the request-URI (see Section 2.7 of [Part6]). 541 3. If the response has a Content-Location header, and that URI is 542 the same as the request-URI [[anchor1: (see [ref])]], the 543 response is a representation of the resource at the request-URI. 545 4. If the response has a Content-Location header, and that URI is 546 not the same as the request-URI, the response asserts that it is 547 a representation of the resource at the Content-Location URI (but 548 it may not be). 550 5. Otherwise, the response is a representation of an anonymous 551 (i.e., unidentified) resource. 553 [[TODO-req-uri: Note that 'request-URI' is used here; however, we 554 need to come up with a term to denote "the URI that can be inferred 555 from examining the request-target and the Host header." (see 556 ). Also, the 557 comparison function is going to have to be defined somewhere, because 558 we already need to compare URIs for things like cache invalidation.]] 560 7. Method Definitions 562 The set of common methods for HTTP/1.1 is defined below. Although 563 this set can be expanded, additional methods cannot be assumed to 564 share the same semantics for separately extended clients and servers. 566 7.1. Safe and Idempotent Methods 568 7.1.1. Safe Methods 570 Implementors should be aware that the software represents the user in 571 their interactions over the Internet, and should be careful to allow 572 the user to be aware of any actions they might take which may have an 573 unexpected significance to themselves or others. 575 In particular, the convention has been established that the GET, 576 HEAD, OPTIONS, and TRACE methods SHOULD NOT have the significance of 577 taking an action other than retrieval. These methods ought to be 578 considered "safe". This allows user agents to represent other 579 methods, such as POST, PUT and DELETE, in a special way, so that the 580 user is made aware of the fact that a possibly unsafe action is being 581 requested. 583 Naturally, it is not possible to ensure that the server does not 584 generate side-effects as a result of performing a GET request; in 585 fact, some dynamic resources consider that a feature. The important 586 distinction here is that the user did not request the side-effects, 587 so therefore cannot be held accountable for them. 589 7.1.2. Idempotent Methods 591 Methods can also have the property of "idempotence" in that, aside 592 from error or expiration issues, the intended effect of multiple 593 identical requests is the same as for a single request. The methods 594 PUT, DELETE, and all safe methods are idempotent. It is important to 595 note that idempotence refers only to changes requested by the client: 596 a server is free to change its state due to multiple requests for the 597 purpose of tracking those requests, versioning of results, etc. 599 7.2. OPTIONS 601 The OPTIONS method represents a request for information about the 602 communication options available on the request/response chain 603 identified by the request-target. This method allows the client to 604 determine the options and/or requirements associated with a resource, 605 or the capabilities of a server, without implying a resource action 606 or initiating a resource retrieval. 608 Responses to this method are not cacheable. 610 If the OPTIONS request includes an entity-body (as indicated by the 611 presence of Content-Length or Transfer-Encoding), then the media type 612 MUST be indicated by a Content-Type field. Although this 613 specification does not define any use for such a body, future 614 extensions to HTTP might use the OPTIONS body to make more detailed 615 queries on the server. 617 If the request-target is an asterisk ("*"), the OPTIONS request is 618 intended to apply to the server in general rather than to a specific 619 resource. Since a server's communication options typically depend on 620 the resource, the "*" request is only useful as a "ping" or "no-op" 621 type of method; it does nothing beyond allowing the client to test 622 the capabilities of the server. For example, this can be used to 623 test a proxy for HTTP/1.1 compliance (or lack thereof). 625 If the request-target is not an asterisk, the OPTIONS request applies 626 only to the options that are available when communicating with that 627 resource. 629 A 200 response SHOULD include any header fields that indicate 630 optional features implemented by the server and applicable to that 631 resource (e.g., Allow), possibly including extensions not defined by 632 this specification. The response body, if any, SHOULD also include 633 information about the communication options. The format for such a 634 body is not defined by this specification, but might be defined by 635 future extensions to HTTP. Content negotiation MAY be used to select 636 the appropriate response format. If no response body is included, 637 the response MUST include a Content-Length field with a field-value 638 of "0". 640 The Max-Forwards request-header field MAY be used to target a 641 specific proxy in the request chain. When a proxy receives an 642 OPTIONS request on an absolute-URI for which request forwarding is 643 permitted, the proxy MUST check for a Max-Forwards field. If the 644 Max-Forwards field-value is zero ("0"), the proxy MUST NOT forward 645 the message; instead, the proxy SHOULD respond with its own 646 communication options. If the Max-Forwards field-value is an integer 647 greater than zero, the proxy MUST decrement the field-value when it 648 forwards the request. If no Max-Forwards field is present in the 649 request, then the forwarded request MUST NOT include a Max-Forwards 650 field. 652 7.3. GET 654 The GET method means retrieve whatever information (in the form of an 655 entity) is identified by the request-target. If the request-target 656 refers to a data-producing process, it is the produced data which 657 shall be returned as the entity in the response and not the source 658 text of the process, unless that text happens to be the output of the 659 process. 661 The semantics of the GET method change to a "conditional GET" if the 662 request message includes an If-Modified-Since, If-Unmodified-Since, 663 If-Match, If-None-Match, or If-Range header field. A conditional GET 664 method requests that the entity be transferred only under the 665 circumstances described by the conditional header field(s). The 666 conditional GET method is intended to reduce unnecessary network 667 usage by allowing cached entities to be refreshed without requiring 668 multiple requests or transferring data already held by the client. 670 The semantics of the GET method change to a "partial GET" if the 671 request message includes a Range header field. A partial GET 672 requests that only part of the entity be transferred, as described in 673 Section 5.4 of [Part5]. The partial GET method is intended to reduce 674 unnecessary network usage by allowing partially-retrieved entities to 675 be completed without transferring data already held by the client. 677 The response to a GET request is cacheable if and only if it meets 678 the requirements for HTTP caching described in [Part6]. 680 See Section 11.2 for security considerations when used for forms. 682 7.4. HEAD 684 The HEAD method is identical to GET except that the server MUST NOT 685 return a message-body in the response. The metainformation contained 686 in the HTTP headers in response to a HEAD request SHOULD be identical 687 to the information sent in response to a GET request. This method 688 can be used for obtaining metainformation about the entity implied by 689 the request without transferring the entity-body itself. This method 690 is often used for testing hypertext links for validity, 691 accessibility, and recent modification. 693 The response to a HEAD request MAY be cacheable in the sense that the 694 information contained in the response MAY be used to update a 695 previously cached entity from that resource. If the new field values 696 indicate that the cached entity differs from the current entity (as 697 would be indicated by a change in Content-Length, Content-MD5, ETag 698 or Last-Modified), then the cache MUST treat the cache entry as 699 stale. 701 7.5. POST 703 The POST method is used to request that the origin server accept the 704 entity enclosed in the request as data to be processed by the 705 resource identified by the request-target in the Request-Line. POST 706 is designed to allow a uniform method to cover the following 707 functions: 709 o Annotation of existing resources; 711 o Posting a message to a bulletin board, newsgroup, mailing list, or 712 similar group of articles; 714 o Providing a block of data, such as the result of submitting a 715 form, to a data-handling process; 717 o Extending a database through an append operation. 719 The actual function performed by the POST method is determined by the 720 server and is usually dependent on the request-target. 722 The action performed by the POST method might not result in a 723 resource that can be identified by a URI. In this case, either 200 724 (OK) or 204 (No Content) is the appropriate response status, 725 depending on whether or not the response includes an entity that 726 describes the result. 728 If a resource has been created on the origin server, the response 729 SHOULD be 201 (Created) and contain an entity which describes the 730 status of the request and refers to the new resource, and a Location 731 header (see Section 9.4). 733 Responses to this method are not cacheable, unless the response 734 includes appropriate Cache-Control or Expires header fields. 735 However, the 303 (See Other) response can be used to direct the user 736 agent to retrieve a cacheable resource. 738 7.6. PUT 740 The PUT method requests that the enclosed entity be stored at the 741 supplied request-target. If the request-target refers to an already 742 existing resource, the enclosed entity SHOULD be considered as a 743 modified version of the one residing on the origin server. If the 744 request-target does not point to an existing resource, and that URI 745 is capable of being defined as a new resource by the requesting user 746 agent, the origin server can create the resource with that URI. If a 747 new resource is created at the request-target, the origin server MUST 748 inform the user agent via the 201 (Created) response. If an existing 749 resource is modified, either the 200 (OK) or 204 (No Content) 750 response codes SHOULD be sent to indicate successful completion of 751 the request. If the resource could not be created or modified with 752 the request-target, an appropriate error response SHOULD be given 753 that reflects the nature of the problem. The recipient of the entity 754 MUST NOT ignore any Content-* headers (headers starting with the 755 prefix 'Content-') that it does not understand or implement and MUST 756 return a 501 (Not Implemented) response in such cases. 758 If the request passes through a cache and the request-target 759 identifies one or more currently cached entities, those entries 760 SHOULD be treated as stale. Responses to this method are not 761 cacheable. 763 The fundamental difference between the POST and PUT requests is 764 reflected in the different meaning of the request-target. The URI in 765 a POST request identifies the resource that will handle the enclosed 766 entity. That resource might be a data-accepting process, a gateway 767 to some other protocol, or a separate entity that accepts 768 annotations. In contrast, the URI in a PUT request identifies the 769 entity enclosed with the request -- the user agent knows what URI is 770 intended and the server MUST NOT attempt to apply the request to some 771 other resource. If the server desires that the request be applied to 772 a different URI, it MUST send a 301 (Moved Permanently) response; the 773 user agent MAY then make its own decision regarding whether or not to 774 redirect the request. 776 A single resource MAY be identified by many different URIs. For 777 example, an article might have a URI for identifying "the current 778 version" which is separate from the URI identifying each particular 779 version. In this case, a PUT request on a general URI might result 780 in several other URIs being defined by the origin server. 782 HTTP/1.1 does not define how a PUT method affects the state of an 783 origin server. 785 Unless otherwise specified for a particular entity-header, the 786 entity-headers in the PUT request SHOULD be applied to the resource 787 created or modified by the PUT. 789 7.7. DELETE 791 The DELETE method requests that the origin server delete the resource 792 identified by the request-target. This method MAY be overridden by 793 human intervention (or other means) on the origin server. The client 794 cannot be guaranteed that the operation has been carried out, even if 795 the status code returned from the origin server indicates that the 796 action has been completed successfully. However, the server SHOULD 797 NOT indicate success unless, at the time the response is given, it 798 intends to delete the resource or move it to an inaccessible 799 location. 801 A successful response SHOULD be 200 (OK) if the response includes an 802 entity describing the status, 202 (Accepted) if the action has not 803 yet been enacted, or 204 (No Content) if the action has been enacted 804 but the response does not include an entity. 806 If the request passes through a cache and the request-target 807 identifies one or more currently cached entities, those entries 808 SHOULD be treated as stale. Responses to this method are not 809 cacheable. 811 7.8. TRACE 813 The TRACE method is used to invoke a remote, application-layer loop- 814 back of the request message. The final recipient of the request 815 SHOULD reflect the message received back to the client as the entity- 816 body of a 200 (OK) response. The final recipient is either the 817 origin server or the first proxy or gateway to receive a Max-Forwards 818 value of zero (0) in the request (see Section 9.5). A TRACE request 819 MUST NOT include an entity. 821 TRACE allows the client to see what is being received at the other 822 end of the request chain and use that data for testing or diagnostic 823 information. The value of the Via header field (Section 9.9 of 824 [Part1]) is of particular interest, since it acts as a trace of the 825 request chain. Use of the Max-Forwards header field allows the 826 client to limit the length of the request chain, which is useful for 827 testing a chain of proxies forwarding messages in an infinite loop. 829 If the request is valid, the response SHOULD contain the entire 830 request message in the entity-body, with a Content-Type of "message/ 831 http" (see Section 10.3.1 of [Part1]). Responses to this method MUST 832 NOT be cached. 834 7.9. CONNECT 836 This specification reserves the method name CONNECT for use with a 837 proxy that can dynamically switch to being a tunnel (e.g. SSL 838 tunneling [RFC2817]). 840 8. Status Code Definitions 842 Each Status-Code is described below, including any metainformation 843 required in the response. 845 8.1. Informational 1xx 847 This class of status code indicates a provisional response, 848 consisting only of the Status-Line and optional headers, and is 849 terminated by an empty line. There are no required headers for this 850 class of status code. Since HTTP/1.0 did not define any 1xx status 851 codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client 852 except under experimental conditions. 854 A client MUST be prepared to accept one or more 1xx status responses 855 prior to a regular response, even if the client does not expect a 100 856 (Continue) status message. Unexpected 1xx status responses MAY be 857 ignored by a user agent. 859 Proxies MUST forward 1xx responses, unless the connection between the 860 proxy and its client has been closed, or unless the proxy itself 861 requested the generation of the 1xx response. (For example, if a 862 proxy adds a "Expect: 100-continue" field when it forwards a request, 863 then it need not forward the corresponding 100 (Continue) 864 response(s).) 866 8.1.1. 100 Continue 868 The client SHOULD continue with its request. This interim response 869 is used to inform the client that the initial part of the request has 870 been received and has not yet been rejected by the server. The 871 client SHOULD continue by sending the remainder of the request or, if 872 the request has already been completed, ignore this response. The 873 server MUST send a final response after the request has been 874 completed. See Section 7.2.3 of [Part1] for detailed discussion of 875 the use and handling of this status code. 877 8.1.2. 101 Switching Protocols 879 The server understands and is willing to comply with the client's 880 request, via the Upgrade message header field (Section 5.4 of 882 [Part5]), for a change in the application protocol being used on this 883 connection. The server will switch protocols to those defined by the 884 response's Upgrade header field immediately after the empty line 885 which terminates the 101 response. 887 The protocol SHOULD be switched only when it is advantageous to do 888 so. For example, switching to a newer version of HTTP is 889 advantageous over older versions, and switching to a real-time, 890 synchronous protocol might be advantageous when delivering resources 891 that use such features. 893 8.2. Successful 2xx 895 This class of status code indicates that the client's request was 896 successfully received, understood, and accepted. 898 8.2.1. 200 OK 900 The request has succeeded. The information returned with the 901 response is dependent on the method used in the request, for example: 903 GET an entity corresponding to the requested resource is sent in the 904 response; 906 HEAD the entity-header fields corresponding to the requested 907 resource are sent in the response without any message-body; 909 POST an entity describing or containing the result of the action; 911 TRACE an entity containing the request message as received by the 912 end server. 914 8.2.2. 201 Created 916 The request has been fulfilled and resulted in a new resource being 917 created. The newly created resource can be referenced by the URI(s) 918 returned in the entity of the response, with the most specific URI 919 for the resource given by a Location header field. The response 920 SHOULD include an entity containing a list of resource 921 characteristics and location(s) from which the user or user agent can 922 choose the one most appropriate. The entity format is specified by 923 the media type given in the Content-Type header field. The origin 924 server MUST create the resource before returning the 201 status code. 925 If the action cannot be carried out immediately, the server SHOULD 926 respond with 202 (Accepted) response instead. 928 A 201 response MAY contain an ETag response header field indicating 929 the current value of the entity tag for the requested variant just 930 created, see Section 6.1 of [Part4]. 932 8.2.3. 202 Accepted 934 The request has been accepted for processing, but the processing has 935 not been completed. The request might or might not eventually be 936 acted upon, as it might be disallowed when processing actually takes 937 place. There is no facility for re-sending a status code from an 938 asynchronous operation such as this. 940 The 202 response is intentionally non-committal. Its purpose is to 941 allow a server to accept a request for some other process (perhaps a 942 batch-oriented process that is only run once per day) without 943 requiring that the user agent's connection to the server persist 944 until the process is completed. The entity returned with this 945 response SHOULD include an indication of the request's current status 946 and either a pointer to a status monitor or some estimate of when the 947 user can expect the request to be fulfilled. 949 8.2.4. 203 Non-Authoritative Information 951 The returned metainformation in the entity-header is not the 952 definitive set as available from the origin server, but is gathered 953 from a local or a third-party copy. The set presented MAY be a 954 subset or superset of the original version. For example, including 955 local annotation information about the resource might result in a 956 superset of the metainformation known by the origin server. Use of 957 this response code is not required and is only appropriate when the 958 response would otherwise be 200 (OK). 960 8.2.5. 204 No Content 962 The server has fulfilled the request but does not need to return an 963 entity-body, and might want to return updated metainformation. The 964 response MAY include new or updated metainformation in the form of 965 entity-headers, which if present SHOULD be associated with the 966 requested variant. 968 If the client is a user agent, it SHOULD NOT change its document view 969 from that which caused the request to be sent. This response is 970 primarily intended to allow input for actions to take place without 971 causing a change to the user agent's active document view, although 972 any new or updated metainformation SHOULD be applied to the document 973 currently in the user agent's active view. 975 The 204 response MUST NOT include a message-body, and thus is always 976 terminated by the first empty line after the header fields. 978 8.2.6. 205 Reset Content 980 The server has fulfilled the request and the user agent SHOULD reset 981 the document view which caused the request to be sent. This response 982 is primarily intended to allow input for actions to take place via 983 user input, followed by a clearing of the form in which the input is 984 given so that the user can easily initiate another input action. The 985 response MUST NOT include an entity. 987 8.2.7. 206 Partial Content 989 The server has fulfilled the partial GET request for the resource and 990 the enclosed entity is a partial representation as defined in Section 991 3.1 of [Part5]. 993 8.3. Redirection 3xx 995 This class of status code indicates that further action needs to be 996 taken by the user agent in order to fulfill the request. The action 997 required MAY be carried out by the user agent without interaction 998 with the user if and only if the method used in the second request is 999 GET or HEAD. A client SHOULD detect infinite redirection loops, 1000 since such loops generate network traffic for each redirection. 1002 Note: an earlier version of this specification recommended a 1003 maximum of five redirections ([RFC2068], Section 10.3). Content 1004 developers should be aware that there might be clients that 1005 implement such a fixed limitation. 1007 8.3.1. 300 Multiple Choices 1009 The requested resource corresponds to any one of a set of 1010 representations, each with its own specific location, and agent- 1011 driven negotiation information (Section 4 of [Part3]) is being 1012 provided so that the user (or user agent) can select a preferred 1013 representation and redirect its request to that location. 1015 Unless it was a HEAD request, the response SHOULD include an entity 1016 containing a list of resource characteristics and location(s) from 1017 which the user or user agent can choose the one most appropriate. 1018 The entity format is specified by the media type given in the 1019 Content-Type header field. Depending upon the format and the 1020 capabilities of the user agent, selection of the most appropriate 1021 choice MAY be performed automatically. However, this specification 1022 does not define any standard for such automatic selection. 1024 If the server has a preferred choice of representation, it SHOULD 1025 include the specific URI for that representation in the Location 1026 field; user agents MAY use the Location field value for automatic 1027 redirection. This response is cacheable unless indicated otherwise. 1029 8.3.2. 301 Moved Permanently 1031 The requested resource has been assigned a new permanent URI and any 1032 future references to this resource SHOULD use one of the returned 1033 URIs. Clients with link editing capabilities ought to automatically 1034 re-link references to the request-target to one or more of the new 1035 references returned by the server, where possible. This response is 1036 cacheable unless indicated otherwise. 1038 The new permanent URI SHOULD be given by the Location field in the 1039 response. Unless the request method was HEAD, the entity of the 1040 response SHOULD contain a short hypertext note with a hyperlink to 1041 the new URI(s). 1043 If the 301 status code is received in response to a request method 1044 that is known to be "safe", as defined in Section 7.1.1, then the 1045 request MAY be automatically redirected by the user agent without 1046 confirmation. Otherwise, the user agent MUST NOT automatically 1047 redirect the request unless it can be confirmed by the user, since 1048 this might change the conditions under which the request was issued. 1050 Note: When automatically redirecting a POST request after 1051 receiving a 301 status code, some existing HTTP/1.0 user agents 1052 will erroneously change it into a GET request. 1054 8.3.3. 302 Found 1056 The requested resource resides temporarily under a different URI. 1057 Since the redirection might be altered on occasion, the client SHOULD 1058 continue to use the request-target for future requests. This 1059 response is only cacheable if indicated by a Cache-Control or Expires 1060 header field. 1062 The temporary URI SHOULD be given by the Location field in the 1063 response. Unless the request method was HEAD, the entity of the 1064 response SHOULD contain a short hypertext note with a hyperlink to 1065 the new URI(s). 1067 If the 302 status code is received in response to a request method 1068 that is known to be "safe", as defined in Section 7.1.1, then the 1069 request MAY be automatically redirected by the user agent without 1070 confirmation. Otherwise, the user agent MUST NOT automatically 1071 redirect the request unless it can be confirmed by the user, since 1072 this might change the conditions under which the request was issued. 1074 Note: HTTP/1.0 ([RFC1945], Section 9.3) and the first version of 1075 HTTP/1.1 ([RFC2068], Section 10.3.3) specify that the client is 1076 not allowed to change the method on the redirected request. 1077 However, most existing user agent implementations treat 302 as if 1078 it were a 303 response, performing a GET on the Location field- 1079 value regardless of the original request method. Therefore, a 1080 previous version of this specification ([RFC2616], Section 10.3.3) 1081 has added the status codes 303 and 307 for servers that wish to 1082 make unambiguously clear which kind of reaction is expected of the 1083 client. 1085 8.3.4. 303 See Other 1087 The server directs the user agent to a different resource, indicated 1088 by a URI in the Location header field, that provides an indirect 1089 response to the original request. The user agent MAY perform a GET 1090 request on the URI in the Location field in order to obtain a 1091 representation corresponding to the response, be redirected again, or 1092 end with an error status. The Location URI is not a substitute 1093 reference for the originally requested resource. 1095 The 303 status is generally applicable to any HTTP method. It is 1096 primarily used to allow the output of a POST action to redirect the 1097 user agent to a selected resource, since doing so provides the 1098 information corresponding to the POST response in a form that can be 1099 separately identified, bookmarked, and cached independent of the 1100 original request. 1102 A 303 response to a GET request indicates that the requested resource 1103 does not have a representation of its own that can be transferred by 1104 the server over HTTP. The Location URI indicates a resource that is 1105 descriptive of the requested resource such that the follow-on 1106 representation may be useful without implying that it adequately 1107 represents the previously requested resource. Note that answers to 1108 the questions of what can be represented, what representations are 1109 adequate, and what might be a useful description are outside the 1110 scope of HTTP and thus entirely determined by the URI owner(s). 1112 A 303 response SHOULD NOT be cached unless it is indicated as 1113 cacheable by Cache-Control or Expires header fields. Except for 1114 responses to a HEAD request, the entity of a 303 response SHOULD 1115 contain a short hypertext note with a hyperlink to the Location URI. 1117 8.3.5. 304 Not Modified 1119 The response to the request has not been modified since the 1120 conditions indicated by the client's conditional GET request, as 1121 defined in Section 3.1 of [Part4]. 1123 8.3.6. 305 Use Proxy 1125 The 305 status was defined in a previous version of this 1126 specification (see Appendix A.2), and is now deprecated. 1128 8.3.7. 306 (Unused) 1130 The 306 status code was used in a previous version of the 1131 specification, is no longer used, and the code is reserved. 1133 8.3.8. 307 Temporary Redirect 1135 The requested resource resides temporarily under a different URI. 1136 Since the redirection MAY be altered on occasion, the client SHOULD 1137 continue to use the request-target for future requests. This 1138 response is only cacheable if indicated by a Cache-Control or Expires 1139 header field. 1141 The temporary URI SHOULD be given by the Location field in the 1142 response. Unless the request method was HEAD, the entity of the 1143 response SHOULD contain a short hypertext note with a hyperlink to 1144 the new URI(s) , since many pre-HTTP/1.1 user agents do not 1145 understand the 307 status. Therefore, the note SHOULD contain the 1146 information necessary for a user to repeat the original request on 1147 the new URI. 1149 If the 307 status code is received in response to a request method 1150 that is known to be "safe", as defined in Section 7.1.1, then the 1151 request MAY be automatically redirected by the user agent without 1152 confirmation. Otherwise, the user agent MUST NOT automatically 1153 redirect the request unless it can be confirmed by the user, since 1154 this might change the conditions under which the request was issued. 1156 8.4. Client Error 4xx 1158 The 4xx class of status code is intended for cases in which the 1159 client seems to have erred. Except when responding to a HEAD 1160 request, the server SHOULD include an entity containing an 1161 explanation of the error situation, and whether it is a temporary or 1162 permanent condition. These status codes are applicable to any 1163 request method. User agents SHOULD display any included entity to 1164 the user. 1166 If the client is sending data, a server implementation using TCP 1167 SHOULD be careful to ensure that the client acknowledges receipt of 1168 the packet(s) containing the response, before the server closes the 1169 input connection. If the client continues sending data to the server 1170 after the close, the server's TCP stack will send a reset packet to 1171 the client, which may erase the client's unacknowledged input buffers 1172 before they can be read and interpreted by the HTTP application. 1174 8.4.1. 400 Bad Request 1176 The request could not be understood by the server due to malformed 1177 syntax. The client SHOULD NOT repeat the request without 1178 modifications. 1180 8.4.2. 401 Unauthorized 1182 The request requires user authentication (see Section 2.1 of 1183 [Part7]). 1185 8.4.3. 402 Payment Required 1187 This code is reserved for future use. 1189 8.4.4. 403 Forbidden 1191 The server understood the request, but is refusing to fulfill it. 1192 Authorization will not help and the request SHOULD NOT be repeated. 1193 If the request method was not HEAD and the server wishes to make 1194 public why the request has not been fulfilled, it SHOULD describe the 1195 reason for the refusal in the entity. If the server does not wish to 1196 make this information available to the client, the status code 404 1197 (Not Found) can be used instead. 1199 8.4.5. 404 Not Found 1201 The server has not found anything matching the request-target. No 1202 indication is given of whether the condition is temporary or 1203 permanent. The 410 (Gone) status code SHOULD be used if the server 1204 knows, through some internally configurable mechanism, that an old 1205 resource is permanently unavailable and has no forwarding address. 1206 This status code is commonly used when the server does not wish to 1207 reveal exactly why the request has been refused, or when no other 1208 response is applicable. 1210 8.4.6. 405 Method Not Allowed 1212 The method specified in the Request-Line is not allowed for the 1213 resource identified by the request-target. The response MUST include 1214 an Allow header containing a list of valid methods for the requested 1215 resource. 1217 8.4.7. 406 Not Acceptable 1219 The resource identified by the request is only capable of generating 1220 response entities which have content characteristics not acceptable 1221 according to the accept headers sent in the request. 1223 Unless it was a HEAD request, the response SHOULD include an entity 1224 containing a list of available entity characteristics and location(s) 1225 from which the user or user agent can choose the one most 1226 appropriate. The entity format is specified by the media type given 1227 in the Content-Type header field. Depending upon the format and the 1228 capabilities of the user agent, selection of the most appropriate 1229 choice MAY be performed automatically. However, this specification 1230 does not define any standard for such automatic selection. 1232 Note: HTTP/1.1 servers are allowed to return responses which are 1233 not acceptable according to the accept headers sent in the 1234 request. In some cases, this may even be preferable to sending a 1235 406 response. User agents are encouraged to inspect the headers 1236 of an incoming response to determine if it is acceptable. 1238 If the response could be unacceptable, a user agent SHOULD 1239 temporarily stop receipt of more data and query the user for a 1240 decision on further actions. 1242 8.4.8. 407 Proxy Authentication Required 1244 This code is similar to 401 (Unauthorized), but indicates that the 1245 client must first authenticate itself with the proxy (see Section 2.2 1246 of [Part7]). 1248 8.4.9. 408 Request Timeout 1250 The client did not produce a request within the time that the server 1251 was prepared to wait. The client MAY repeat the request without 1252 modifications at any later time. 1254 8.4.10. 409 Conflict 1256 The request could not be completed due to a conflict with the current 1257 state of the resource. This code is only allowed in situations where 1258 it is expected that the user might be able to resolve the conflict 1259 and resubmit the request. The response body SHOULD include enough 1260 information for the user to recognize the source of the conflict. 1261 Ideally, the response entity would include enough information for the 1262 user or user agent to fix the problem; however, that might not be 1263 possible and is not required. 1265 Conflicts are most likely to occur in response to a PUT request. For 1266 example, if versioning were being used and the entity being PUT 1267 included changes to a resource which conflict with those made by an 1268 earlier (third-party) request, the server might use the 409 response 1269 to indicate that it can't complete the request. In this case, the 1270 response entity would likely contain a list of the differences 1271 between the two versions in a format defined by the response Content- 1272 Type. 1274 8.4.11. 410 Gone 1276 The requested resource is no longer available at the server and no 1277 forwarding address is known. This condition is expected to be 1278 considered permanent. Clients with link editing capabilities SHOULD 1279 delete references to the request-target after user approval. If the 1280 server does not know, or has no facility to determine, whether or not 1281 the condition is permanent, the status code 404 (Not Found) SHOULD be 1282 used instead. This response is cacheable unless indicated otherwise. 1284 The 410 response is primarily intended to assist the task of web 1285 maintenance by notifying the recipient that the resource is 1286 intentionally unavailable and that the server owners desire that 1287 remote links to that resource be removed. Such an event is common 1288 for limited-time, promotional services and for resources belonging to 1289 individuals no longer working at the server's site. It is not 1290 necessary to mark all permanently unavailable resources as "gone" or 1291 to keep the mark for any length of time -- that is left to the 1292 discretion of the server owner. 1294 8.4.12. 411 Length Required 1296 The server refuses to accept the request without a defined Content- 1297 Length. The client MAY repeat the request if it adds a valid 1298 Content-Length header field containing the length of the message-body 1299 in the request message. 1301 8.4.13. 412 Precondition Failed 1303 The precondition given in one or more of the request-header fields 1304 evaluated to false when it was tested on the server, as defined in 1305 Section 3.2 of [Part4]. 1307 8.4.14. 413 Request Entity Too Large 1309 The server is refusing to process a request because the request 1310 entity is larger than the server is willing or able to process. The 1311 server MAY close the connection to prevent the client from continuing 1312 the request. 1314 If the condition is temporary, the server SHOULD include a Retry- 1315 After header field to indicate that it is temporary and after what 1316 time the client MAY try again. 1318 8.4.15. 414 URI Too Long 1320 The server is refusing to service the request because the request- 1321 target is longer than the server is willing to interpret. This rare 1322 condition is only likely to occur when a client has improperly 1323 converted a POST request to a GET request with long query 1324 information, when the client has descended into a URI "black hole" of 1325 redirection (e.g., a redirected URI prefix that points to a suffix of 1326 itself), or when the server is under attack by a client attempting to 1327 exploit security holes present in some servers using fixed-length 1328 buffers for reading or manipulating the request-target. 1330 8.4.16. 415 Unsupported Media Type 1332 The server is refusing to service the request because the entity of 1333 the request is in a format not supported by the requested resource 1334 for the requested method. 1336 8.4.17. 416 Requested Range Not Satisfiable 1338 The request included a Range request-header field (Section 5.4 of 1339 [Part5]) and none of the range-specifier values in this field overlap 1340 the current extent of the selected resource. See Section 3.2 of 1341 [Part5] 1343 8.4.18. 417 Expectation Failed 1345 The expectation given in an Expect request-header field (see 1346 Section 9.2) could not be met by this server, or, if the server is a 1347 proxy, the server has unambiguous evidence that the request could not 1348 be met by the next-hop server. 1350 8.5. Server Error 5xx 1352 Response status codes beginning with the digit "5" indicate cases in 1353 which the server is aware that it has erred or is incapable of 1354 performing the request. Except when responding to a HEAD request, 1355 the server SHOULD include an entity containing an explanation of the 1356 error situation, and whether it is a temporary or permanent 1357 condition. User agents SHOULD display any included entity to the 1358 user. These response codes are applicable to any request method. 1360 8.5.1. 500 Internal Server Error 1362 The server encountered an unexpected condition which prevented it 1363 from fulfilling the request. 1365 8.5.2. 501 Not Implemented 1367 The server does not support the functionality required to fulfill the 1368 request. This is the appropriate response when the server does not 1369 recognize the request method and is not capable of supporting it for 1370 any resource. 1372 8.5.3. 502 Bad Gateway 1374 The server, while acting as a gateway or proxy, received an invalid 1375 response from the upstream server it accessed in attempting to 1376 fulfill the request. 1378 8.5.4. 503 Service Unavailable 1380 The server is currently unable to handle the request due to a 1381 temporary overloading or maintenance of the server. The implication 1382 is that this is a temporary condition which will be alleviated after 1383 some delay. If known, the length of the delay MAY be indicated in a 1384 Retry-After header. If no Retry-After is given, the client SHOULD 1385 handle the response as it would for a 500 response. 1387 Note: The existence of the 503 status code does not imply that a 1388 server must use it when becoming overloaded. Some servers may 1389 wish to simply refuse the connection. 1391 8.5.5. 504 Gateway Timeout 1393 The server, while acting as a gateway or proxy, did not receive a 1394 timely response from the upstream server specified by the URI (e.g. 1395 HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed 1396 to access in attempting to complete the request. 1398 Note: Note to implementors: some deployed proxies are known to 1399 return 400 or 500 when DNS lookups time out. 1401 8.5.6. 505 HTTP Version Not Supported 1403 The server does not support, or refuses to support, the protocol 1404 version that was used in the request message. The server is 1405 indicating that it is unable or unwilling to complete the request 1406 using the same major version as the client, as described in Section 1407 2.5 of [Part1], other than with this error message. The response 1408 SHOULD contain an entity describing why that version is not supported 1409 and what other protocols are supported by that server. 1411 9. Header Field Definitions 1413 This section defines the syntax and semantics of HTTP/1.1 header 1414 fields related to request and response semantics. 1416 For entity-header fields, both sender and recipient refer to either 1417 the client or the server, depending on who sends and who receives the 1418 entity. 1420 9.1. Allow 1422 The "Allow" response-header field lists the set of methods advertised 1423 as supported by the resource identified by the request-target. The 1424 purpose of this field is strictly to inform the recipient of valid 1425 methods associated with the resource. 1427 Allow = "Allow" ":" OWS Allow-v 1428 Allow-v = #Method 1430 Example of use: 1432 Allow: GET, HEAD, PUT 1434 The actual set of allowed methods is defined by the origin server at 1435 the time of each request. 1437 A proxy MUST NOT modify the Allow header field even if it does not 1438 understand all the methods specified, since the user agent might have 1439 other means of communicating with the origin server. 1441 9.2. Expect 1443 The "Expect" request-header field is used to indicate that particular 1444 server behaviors are required by the client. 1446 Expect = "Expect" ":" OWS Expect-v 1447 Expect-v = 1#expectation 1449 expectation = "100-continue" / expectation-extension 1450 expectation-extension = token [ "=" ( token / quoted-string ) 1451 *expect-params ] 1452 expect-params = ";" token [ "=" ( token / quoted-string ) ] 1454 A server that does not understand or is unable to comply with any of 1455 the expectation values in the Expect field of a request MUST respond 1456 with appropriate error status. The server MUST respond with a 417 1457 (Expectation Failed) status if any of the expectations cannot be met 1458 or, if there are other problems with the request, some other 4xx 1459 status. 1461 This header field is defined with extensible syntax to allow for 1462 future extensions. If a server receives a request containing an 1463 Expect field that includes an expectation-extension that it does not 1464 support, it MUST respond with a 417 (Expectation Failed) status. 1466 Comparison of expectation values is case-insensitive for unquoted 1467 tokens (including the 100-continue token), and is case-sensitive for 1468 quoted-string expectation-extensions. 1470 The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST 1471 return a 417 (Expectation Failed) status if it receives a request 1472 with an expectation that it cannot meet. However, the Expect 1473 request-header itself is end-to-end; it MUST be forwarded if the 1474 request is forwarded. 1476 Many older HTTP/1.0 and HTTP/1.1 applications do not understand the 1477 Expect header. 1479 See Section 7.2.3 of [Part1] for the use of the 100 (Continue) 1480 status. 1482 9.3. From 1484 The "From" request-header field, if given, SHOULD contain an Internet 1485 e-mail address for the human user who controls the requesting user 1486 agent. The address SHOULD be machine-usable, as defined by "mailbox" 1487 in Section 3.4 of [RFC5322]: 1489 From = "From" ":" OWS From-v 1490 From-v = mailbox 1492 mailbox = 1494 An example is: 1496 From: webmaster@example.org 1498 This header field MAY be used for logging purposes and as a means for 1499 identifying the source of invalid or unwanted requests. It SHOULD 1500 NOT be used as an insecure form of access protection. The 1501 interpretation of this field is that the request is being performed 1502 on behalf of the person given, who accepts responsibility for the 1503 method performed. In particular, robot agents SHOULD include this 1504 header so that the person responsible for running the robot can be 1505 contacted if problems occur on the receiving end. 1507 The Internet e-mail address in this field MAY be separate from the 1508 Internet host which issued the request. For example, when a request 1509 is passed through a proxy the original issuer's address SHOULD be 1510 used. 1512 The client SHOULD NOT send the From header field without the user's 1513 approval, as it might conflict with the user's privacy interests or 1514 their site's security policy. It is strongly recommended that the 1515 user be able to disable, enable, and modify the value of this field 1516 at any time prior to a request. 1518 9.4. Location 1520 The "Location" response-header field is used to identify a newly 1521 created resource, or to redirect the recipient to a different 1522 location for completion of the request. 1524 For 201 (Created) responses, the Location is the URI of the new 1525 resource which was created by the request. For 3xx responses, the 1526 location SHOULD indicate the server's preferred URI for automatic 1527 redirection to the resource. 1529 The field value consists of a single URI. 1531 Location = "Location" ":" OWS Location-v 1532 Location-v = URI 1534 An example is: 1536 Location: http://www.example.org/pub/WWW/People.html 1538 There are circumstances in which a fragment identifier in a Location 1539 URI would not be appropriate: 1541 o With a 201 Created response, because in this usage the Location 1542 header specifies the URI for the entire created resource. 1544 o With 305 Use Proxy. 1546 Note: The Content-Location header field (Section 5.7 of [Part3]) 1547 differs from Location in that the Content-Location identifies the 1548 original location of the entity enclosed in the response. It is 1549 therefore possible for a response to contain header fields for 1550 both Location and Content-Location. 1552 9.5. Max-Forwards 1554 The "Max-Forwards" request-header field provides a mechanism with the 1555 TRACE (Section 7.8) and OPTIONS (Section 7.2) methods to limit the 1556 number of times that the request is forwarded by proxies or gateways. 1557 This can be useful when the client is attempting to trace a request 1558 which appears to be failing or looping in mid-chain. 1560 Max-Forwards = "Max-Forwards" ":" OWS Max-Forwards-v 1561 Max-Forwards-v = 1*DIGIT 1563 The Max-Forwards value is a decimal integer indicating the remaining 1564 number of times this request message may be forwarded. 1566 Each proxy or gateway recipient of a TRACE or OPTIONS request 1567 containing a Max-Forwards header field MUST check and update its 1568 value prior to forwarding the request. If the received value is zero 1569 (0), the recipient MUST NOT forward the request; instead, it MUST 1570 respond as the final recipient. If the received Max-Forwards value 1571 is greater than zero, then the forwarded message MUST contain an 1572 updated Max-Forwards field with a value decremented by one (1). 1574 The Max-Forwards header field MAY be ignored for all other methods 1575 defined by this specification and for any extension methods for which 1576 it is not explicitly referred to as part of that method definition. 1578 9.6. Referer 1580 The "Referer" [sic] request-header field allows the client to specify 1581 the URI of the resource from which the request-target was obtained 1582 (the "referrer", although the header field is misspelled.). 1584 The Referer header allows servers to generate lists of back-links to 1585 resources for interest, logging, optimized caching, etc. It also 1586 allows obsolete or mistyped links to be traced for maintenance. Some 1587 servers use Referer as a means of controlling where they allow links 1588 from (so-called "deep linking"), but it should be noted that 1589 legitimate requests are not required to contain a Referer header 1590 field. 1592 If the request-target was obtained from a source that does not have 1593 its own URI (e.g., input from the user keyboard), the Referer field 1594 MUST either be sent with the value "about:blank", or not be sent at 1595 all. Note that this requirement does not apply to sources with non- 1596 HTTP URIs (e.g., FTP). 1598 Referer = "Referer" ":" OWS Referer-v 1599 Referer-v = absolute-URI / partial-URI 1601 Example: 1603 Referer: http://www.example.org/hypertext/Overview.html 1605 If the field value is a relative URI, it SHOULD be interpreted 1606 relative to the request-target. The URI MUST NOT include a fragment. 1607 See Section 11.2 for security considerations. 1609 9.7. Retry-After 1611 The response-header "Retry-After" field can be used with a 503 1612 (Service Unavailable) response to indicate how long the service is 1613 expected to be unavailable to the requesting client. This field MAY 1614 also be used with any 3xx (Redirection) response to indicate the 1615 minimum time the user-agent is asked wait before issuing the 1616 redirected request. 1618 The value of this field can be either an HTTP-date or an integer 1619 number of seconds (in decimal) after the time of the response. 1621 Retry-After = "Retry-After" ":" OWS Retry-After-v 1622 Retry-After-v = HTTP-date / delta-seconds 1624 Time spans are non-negative decimal integers, representing time in 1625 seconds. 1627 delta-seconds = 1*DIGIT 1629 Two examples of its use are 1631 Retry-After: Fri, 31 Dec 1999 23:59:59 GMT 1632 Retry-After: 120 1634 In the latter example, the delay is 2 minutes. 1636 9.8. Server 1638 The "Server" response-header field contains information about the 1639 software used by the origin server to handle the request. 1641 The field can contain multiple product tokens (Section 6.3 of 1642 [Part1]) and comments (Section 3.2 of [Part1]) identifying the server 1643 and any significant subproducts. The product tokens are listed in 1644 order of their significance for identifying the application. 1646 Server = "Server" ":" OWS Server-v 1647 Server-v = product 1648 *( RWS ( product / comment ) ) 1650 Example: 1652 Server: CERN/3.0 libwww/2.17 1654 If the response is being forwarded through a proxy, the proxy 1655 application MUST NOT modify the Server response-header. Instead, it 1656 MUST include a Via field (as described in Section 9.9 of [Part1]). 1658 Note: Revealing the specific software version of the server might 1659 allow the server machine to become more vulnerable to attacks 1660 against software that is known to contain security holes. Server 1661 implementors are encouraged to make this field a configurable 1662 option. 1664 9.9. User-Agent 1666 The "User-Agent" request-header field contains information about the 1667 user agent originating the request. This is for statistical 1668 purposes, the tracing of protocol violations, and automated 1669 recognition of user agents for the sake of tailoring responses to 1670 avoid particular user agent limitations. 1672 User agents SHOULD include this field with requests. The field can 1673 contain multiple product tokens (Section 6.3 of [Part1]) and comments 1674 (Section 3.2 of [Part1]) identifying the agent and any subproducts 1675 which form a significant part of the user agent. By convention, the 1676 product tokens are listed in order of their significance for 1677 identifying the application. 1679 User-Agent = "User-Agent" ":" OWS User-Agent-v 1680 User-Agent-v = product 1681 *( RWS ( product / comment ) ) 1683 Example: 1685 User-Agent: CERN-LineMode/2.15 libwww/2.17b3 1687 10. IANA Considerations 1689 10.1. Method Registry 1691 The registration procedure for HTTP Methods is defined by Section 2.1 1692 of this document. 1694 The HTTP Method Registry located at 1695 should be populated 1696 with the registrations below: 1698 +---------+------+-------------+ 1699 | Method | Safe | Reference | 1700 +---------+------+-------------+ 1701 | CONNECT | no | Section 7.9 | 1702 | DELETE | no | Section 7.7 | 1703 | GET | yes | Section 7.3 | 1704 | HEAD | yes | Section 7.4 | 1705 | OPTIONS | yes | Section 7.2 | 1706 | POST | no | Section 7.5 | 1707 | PUT | no | Section 7.6 | 1708 | TRACE | yes | Section 7.8 | 1709 +---------+------+-------------+ 1711 10.2. Status Code Registry 1713 The registration procedure for HTTP Status Codes -- previously 1714 defined in Section 7.1 of [RFC2817] -- is now defined by Section 4.1 1715 of this document. 1717 The HTTP Status Code Registry located at 1718 should be updated 1719 with the registrations below: 1721 +-------+-------------------------------+----------------+ 1722 | Value | Description | Reference | 1723 +-------+-------------------------------+----------------+ 1724 | 100 | Continue | Section 8.1.1 | 1725 | 101 | Switching Protocols | Section 8.1.2 | 1726 | 200 | OK | Section 8.2.1 | 1727 | 201 | Created | Section 8.2.2 | 1728 | 202 | Accepted | Section 8.2.3 | 1729 | 203 | Non-Authoritative Information | Section 8.2.4 | 1730 | 204 | No Content | Section 8.2.5 | 1731 | 205 | Reset Content | Section 8.2.6 | 1732 | 300 | Multiple Choices | Section 8.3.1 | 1733 | 301 | Moved Permanently | Section 8.3.2 | 1734 | 302 | Found | Section 8.3.3 | 1735 | 303 | See Other | Section 8.3.4 | 1736 | 305 | Use Proxy | Section 8.3.6 | 1737 | 306 | (Unused) | Section 8.3.7 | 1738 | 307 | Temporary Redirect | Section 8.3.8 | 1739 | 400 | Bad Request | Section 8.4.1 | 1740 | 402 | Payment Required | Section 8.4.3 | 1741 | 403 | Forbidden | Section 8.4.4 | 1742 | 404 | Not Found | Section 8.4.5 | 1743 | 405 | Method Not Allowed | Section 8.4.6 | 1744 | 406 | Not Acceptable | Section 8.4.7 | 1745 | 407 | Proxy Authentication Required | Section 8.4.8 | 1746 | 408 | Request Timeout | Section 8.4.9 | 1747 | 409 | Conflict | Section 8.4.10 | 1748 | 410 | Gone | Section 8.4.11 | 1749 | 411 | Length Required | Section 8.4.12 | 1750 | 413 | Request Entity Too Large | Section 8.4.14 | 1751 | 414 | URI Too Long | Section 8.4.15 | 1752 | 415 | Unsupported Media Type | Section 8.4.16 | 1753 | 417 | Expectation Failed | Section 8.4.18 | 1754 | 500 | Internal Server Error | Section 8.5.1 | 1755 | 501 | Not Implemented | Section 8.5.2 | 1756 | 502 | Bad Gateway | Section 8.5.3 | 1757 | 503 | Service Unavailable | Section 8.5.4 | 1758 | 504 | Gateway Timeout | Section 8.5.5 | 1759 | 505 | HTTP Version Not Supported | Section 8.5.6 | 1760 +-------+-------------------------------+----------------+ 1762 10.3. Message Header Registration 1764 The Message Header Registry located at should be 1766 updated with the permanent registrations below (see [RFC3864]): 1768 +-------------------+----------+----------+-------------+ 1769 | Header Field Name | Protocol | Status | Reference | 1770 +-------------------+----------+----------+-------------+ 1771 | Allow | http | standard | Section 9.1 | 1772 | Expect | http | standard | Section 9.2 | 1773 | From | http | standard | Section 9.3 | 1774 | Location | http | standard | Section 9.4 | 1775 | Max-Forwards | http | standard | Section 9.5 | 1776 | Referer | http | standard | Section 9.6 | 1777 | Retry-After | http | standard | Section 9.7 | 1778 | Server | http | standard | Section 9.8 | 1779 | User-Agent | http | standard | Section 9.9 | 1780 +-------------------+----------+----------+-------------+ 1782 The change controller is: "IETF (iesg@ietf.org) - Internet 1783 Engineering Task Force". 1785 11. Security Considerations 1787 This section is meant to inform application developers, information 1788 providers, and users of the security limitations in HTTP/1.1 as 1789 described by this document. The discussion does not include 1790 definitive solutions to the problems revealed, though it does make 1791 some suggestions for reducing security risks. 1793 11.1. Transfer of Sensitive Information 1795 Like any generic data transfer protocol, HTTP cannot regulate the 1796 content of the data that is transferred, nor is there any a priori 1797 method of determining the sensitivity of any particular piece of 1798 information within the context of any given request. Therefore, 1799 applications SHOULD supply as much control over this information as 1800 possible to the provider of that information. Four header fields are 1801 worth special mention in this context: Server, Via, Referer and From. 1803 Revealing the specific software version of the server might allow the 1804 server machine to become more vulnerable to attacks against software 1805 that is known to contain security holes. Implementors SHOULD make 1806 the Server header field a configurable option. 1808 Proxies which serve as a portal through a network firewall SHOULD 1809 take special precautions regarding the transfer of header information 1810 that identifies the hosts behind the firewall. In particular, they 1811 SHOULD remove, or replace with sanitized versions, any Via fields 1812 generated behind the firewall. 1814 The Referer header allows reading patterns to be studied and reverse 1815 links drawn. Although it can be very useful, its power can be abused 1816 if user details are not separated from the information contained in 1817 the Referer. Even when the personal information has been removed, 1818 the Referer header might indicate a private document's URI whose 1819 publication would be inappropriate. 1821 The information sent in the From field might conflict with the user's 1822 privacy interests or their site's security policy, and hence it 1823 SHOULD NOT be transmitted without the user being able to disable, 1824 enable, and modify the contents of the field. The user MUST be able 1825 to set the contents of this field within a user preference or 1826 application defaults configuration. 1828 We suggest, though do not require, that a convenient toggle interface 1829 be provided for the user to enable or disable the sending of From and 1830 Referer information. 1832 The User-Agent (Section 9.9) or Server (Section 9.8) header fields 1833 can sometimes be used to determine that a specific client or server 1834 have a particular security hole which might be exploited. 1835 Unfortunately, this same information is often used for other valuable 1836 purposes for which HTTP currently has no better mechanism. 1838 Some methods, like TRACE (Section 7.8) may expose information sent in 1839 request headers in the response entity. Clients SHOULD be careful 1840 with sensitive information, like Cookies, Authorization credentials 1841 and other headers that might be used to collect data from the client. 1843 11.2. Encoding Sensitive Information in URIs 1845 Because the source of a link might be private information or might 1846 reveal an otherwise private information source, it is strongly 1847 recommended that the user be able to select whether or not the 1848 Referer field is sent. For example, a browser client could have a 1849 toggle switch for browsing openly/anonymously, which would 1850 respectively enable/disable the sending of Referer and From 1851 information. 1853 Clients SHOULD NOT include a Referer header field in a (non-secure) 1854 HTTP request if the referring page was transferred with a secure 1855 protocol. 1857 Authors of services should not use GET-based forms for the submission 1858 of sensitive data because that data will be encoded in the Request- 1859 target. Many existing servers, proxies, and user agents log or 1860 display the Request-target in places where it might be visible to 1861 third parties. Such services can use POST-based form submission 1862 instead. 1864 11.3. Location Headers and Spoofing 1866 If a single server supports multiple organizations that do not trust 1867 one another, then it MUST check the values of Location and Content- 1868 Location headers in responses that are generated under control of 1869 said organizations to make sure that they do not attempt to 1870 invalidate resources over which they have no authority. 1872 12. Acknowledgments 1874 13. References 1876 13.1. Normative References 1878 [Part1] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1879 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1880 and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections, 1881 and Message Parsing", draft-ietf-httpbis-p1-messaging-08 1882 (work in progress), October 2009. 1884 [Part3] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1885 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1886 and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload 1887 and Content Negotiation", draft-ietf-httpbis-p3-payload-08 1888 (work in progress), October 2009. 1890 [Part4] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1891 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1892 and J. Reschke, Ed., "HTTP/1.1, part 4: Conditional 1893 Requests", draft-ietf-httpbis-p4-conditional-08 (work in 1894 progress), October 2009. 1896 [Part5] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1897 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1898 and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and 1899 Partial Responses", draft-ietf-httpbis-p5-range-08 (work 1900 in progress), October 2009. 1902 [Part6] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1903 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1904 Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part 1905 6: Caching", draft-ietf-httpbis-p6-cache-08 (work in 1906 progress), October 2009. 1908 [Part7] Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H., 1909 Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed., 1910 and J. Reschke, Ed., "HTTP/1.1, part 7: Authentication", 1911 draft-ietf-httpbis-p7-auth-08 (work in progress), 1912 October 2009. 1914 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1915 Requirement Levels", BCP 14, RFC 2119, March 1997. 1917 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1918 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1920 13.2. Informative References 1922 [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext 1923 Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. 1925 [RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. 1926 Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", 1927 RFC 2068, January 1997. 1929 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 1930 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 1931 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 1933 [RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within 1934 HTTP/1.1", RFC 2817, May 2000. 1936 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 1937 Procedures for Message Header Fields", BCP 90, RFC 3864, 1938 September 2004. 1940 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1941 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1942 May 2008. 1944 [RFC5322] Resnick, P., "Internet Message Format", RFC 5322, 1945 October 2008. 1947 Appendix A. Compatibility with Previous Versions 1949 A.1. Changes from RFC 2068 1951 Clarified which error code should be used for inbound server failures 1952 (e.g. DNS failures). (Section 8.5.5). 1954 201 (Created) had a race that required an Etag be sent when a 1955 resource is first created. (Section 8.2.2). 1957 303 (See Also) and 307 (Temporary Redirect) added to address user 1958 agent failure to implement status code 302 properly. (Section 8.3.4 1959 and 8.3.8) 1961 Rewrite of message transmission requirements to make it much harder 1962 for implementors to get it wrong, as the consequences of errors here 1963 can have significant impact on the Internet, and to deal with the 1964 following problems: 1966 1. Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where 1967 this was incorrectly placing a requirement on the behavior of an 1968 implementation of a future version of HTTP/1.x 1970 2. Made it clear that user-agents should retry requests, not 1971 "clients" in general. 1973 3. Converted requirements for clients to ignore unexpected 100 1974 (Continue) responses, and for proxies to forward 100 responses, 1975 into a general requirement for 1xx responses. 1977 4. Modified some TCP-specific language, to make it clearer that non- 1978 TCP transports are possible for HTTP. 1980 5. Require that the origin server MUST NOT wait for the request body 1981 before it sends a required 100 (Continue) response. 1983 6. Allow, rather than require, a server to omit 100 (Continue) if it 1984 has already seen some of the request body. 1986 7. Allow servers to defend against denial-of-service attacks and 1987 broken clients. 1989 This change adds the Expect header and 417 status code. 1991 Clean up confusion between 403 and 404 responses. (Section 8.4.4, 1992 8.4.5, and 8.4.11) 1994 The PATCH, LINK, UNLINK methods were defined but not commonly 1995 implemented in previous versions of this specification. See Section 1996 19.6.1 of [RFC2068]. 1998 A.2. Changes from RFC 2616 2000 This document takes over the Status Code Registry, previously defined 2001 in Section 7.1 of [RFC2817]. (Section 4.1) 2003 Clarify definition of POST. (Section 7.5) 2004 Failed to consider that there are many other request methods that are 2005 safe to automatically redirect, and further that the user agent is 2006 able to make that determination based on the request method 2007 semantics. (Sections 8.3.2, 8.3.3 and 8.3.8) 2009 Deprecate 305 Use Proxy status code, because user agents did not 2010 implement it. It used to indicate that the requested resource must 2011 be accessed through the proxy given by the Location field. The 2012 Location field gave the URI of the proxy. The recipient was expected 2013 to repeat this single request via the proxy. (Section 8.3.6) 2015 Reclassify Allow header as response header, removing the option to 2016 specify it in a PUT request. Relax the server requirement on the 2017 contents of the Allow header and remove requirement on clients to 2018 always trust the header value. (Section 9.1) 2020 Correct syntax of Location header to allow fragment, as referred 2021 symbol wasn't what was expected, and add some clarifications as to 2022 when it would not be appropriate. (Section 9.4) 2024 Allow Referer value of "about:blank" as alternative to not specifying 2025 it. (Section 9.6) 2027 In the description of the Server header, the Via field was described 2028 as a SHOULD. The requirement was and is stated correctly in the 2029 description of the Via header in Section 9.9 of [Part1]. 2030 (Section 9.8) 2032 Appendix B. Collected ABNF 2034 Accept = 2035 Accept-Charset = 2036 Accept-Encoding = 2037 Accept-Language = 2038 Accept-Ranges = 2039 Age = 2040 Allow = "Allow:" OWS Allow-v 2041 Allow-v = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ] 2042 Authorization = 2044 ETag = 2045 Expect = "Expect:" OWS Expect-v 2046 Expect-v = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] ) 2048 From = "From:" OWS From-v 2049 From-v = mailbox 2050 HTTP-date = 2051 Host = 2053 If-Match = 2054 If-Modified-Since = 2055 2056 If-None-Match = 2057 If-Range = 2058 If-Unmodified-Since = 2059 2061 Location = "Location:" OWS Location-v 2062 Location-v = URI 2064 Max-Forwards = "Max-Forwards:" OWS Max-Forwards-v 2065 Max-Forwards-v = 1*DIGIT 2066 Method = %x4F.50.54.49.4F.4E.53 ; OPTIONS 2067 / %x47.45.54 ; GET 2068 / %x48.45.41.44 ; HEAD 2069 / %x50.4F.53.54 ; POST 2070 / %x50.55.54 ; PUT 2071 / %x44.45.4C.45.54.45 ; DELETE 2072 / %x54.52.41.43.45 ; TRACE 2073 / %x43.4F.4E.4E.45.43.54 ; CONNECT 2074 / extension-method 2076 OWS = 2078 Proxy-Authenticate = 2079 2080 Proxy-Authorization = 2081 2083 RWS = 2084 Range = 2085 Reason-Phrase = *( WSP / VCHAR / obs-text ) 2086 Referer = "Referer:" OWS Referer-v 2087 Referer-v = absolute-URI / partial-URI 2088 Retry-After = "Retry-After:" OWS Retry-After-v 2089 Retry-After-v = HTTP-date / delta-seconds 2091 Server = "Server:" OWS Server-v 2092 Server-v = product *( RWS ( product / comment ) ) 2093 Status-Code = "100" / "101" / "200" / "201" / "202" / "203" / "204" / 2094 "205" / "206" / "300" / "301" / "302" / "303" / "304" / "305" / 2095 "307" / "400" / "401" / "402" / "403" / "404" / "405" / "406" / 2096 "407" / "408" / "409" / "410" / "411" / "412" / "413" / "414" / 2097 "415" / "416" / "417" / "500" / "501" / "502" / "503" / "504" / 2098 "505" / extension-code 2100 TE = 2102 URI = 2103 User-Agent = "User-Agent:" OWS User-Agent-v 2104 User-Agent-v = product *( RWS ( product / comment ) ) 2106 Vary = 2108 WWW-Authenticate = 2109 2111 absolute-URI = 2113 comment = 2115 delta-seconds = 1*DIGIT 2117 expect-params = ";" token [ "=" ( token / quoted-string ) ] 2118 expectation = "100-continue" / expectation-extension 2119 expectation-extension = token [ "=" ( token / quoted-string ) 2120 *expect-params ] 2121 extension-code = 3DIGIT 2122 extension-method = token 2124 mailbox = 2126 obs-text = 2128 partial-URI = 2129 product = 2131 quoted-string = 2133 request-header = Accept / Accept-Charset / Accept-Encoding / 2134 Accept-Language / Authorization / Expect / From / Host / If-Match / 2135 If-Modified-Since / If-None-Match / If-Range / If-Unmodified-Since / 2136 Max-Forwards / Proxy-Authorization / Range / Referer / TE / 2137 User-Agent 2138 response-header = Accept-Ranges / Age / Allow / ETag / Location / 2139 Proxy-Authenticate / Retry-After / Server / Vary / WWW-Authenticate 2141 token = 2143 ABNF diagnostics: 2145 ; Reason-Phrase defined but not used 2146 ; Status-Code defined but not used 2147 ; request-header defined but not used 2148 ; response-header defined but not used 2150 Appendix C. Change Log (to be removed by RFC Editor before publication) 2152 C.1. Since RFC2616 2154 Extracted relevant partitions from [RFC2616]. 2156 C.2. Since draft-ietf-httpbis-p2-semantics-00 2158 Closed issues: 2160 o : "Via is a MUST" 2161 () 2163 o : "Fragments 2164 allowed in Location" 2165 () 2167 o : "Safe Methods 2168 vs Redirection" () 2170 o : "Revise 2171 description of the POST method" 2172 () 2174 o : "Normative and 2175 Informative references" 2177 o : "RFC2606 2178 Compliance" 2180 o : "Informative 2181 references" 2183 o : "Redundant 2184 cross-references" 2186 Other changes: 2188 o Move definitions of 304 and 412 condition codes to [Part4] 2190 C.3. Since draft-ietf-httpbis-p2-semantics-01 2192 Closed issues: 2194 o : "PUT side 2195 effects" 2197 o : "Duplicate Host 2198 header requirements" 2200 Ongoing work on ABNF conversion 2201 (): 2203 o Move "Product Tokens" section (back) into Part 1, as "token" is 2204 used in the definition of the Upgrade header. 2206 o Add explicit references to BNF syntax and rules imported from 2207 other parts of the specification. 2209 o Copy definition of delta-seconds from Part6 instead of referencing 2210 it. 2212 C.4. Since draft-ietf-httpbis-p2-semantics-02 2214 Closed issues: 2216 o : "Requiring 2217 Allow in 405 responses" 2219 o : "Status Code 2220 Registry" 2222 o : "Redirection 2223 vs. Location" 2225 o : "Cacheability 2226 of 303 response" 2228 o : "305 Use Proxy" 2230 o : 2231 "Classification for Allow header" 2233 o : "PUT - 'store 2234 under' vs 'store at'" 2236 Ongoing work on IANA Message Header Registration 2237 (): 2239 o Reference RFC 3984, and update header registrations for headers 2240 defined in this document. 2242 Ongoing work on ABNF conversion 2243 (): 2245 o Replace string literals when the string really is case-sensitive 2246 (method). 2248 C.5. Since draft-ietf-httpbis-p2-semantics-03 2250 Closed issues: 2252 o : "OPTIONS 2253 request bodies" 2255 o : "Description 2256 of CONNECT should refer to RFC2817" 2258 o : "Location 2259 Content-Location reference request/response mixup" 2261 Ongoing work on Method Registry 2262 (): 2264 o Added initial proposal for registration process, plus initial 2265 content (non-HTTP/1.1 methods to be added by a separate 2266 specification). 2268 C.6. Since draft-ietf-httpbis-p2-semantics-04 2270 Closed issues: 2272 o : "Content-*" 2274 o : "RFC 2822 is 2275 updated by RFC 5322" 2277 Ongoing work on ABNF conversion 2278 (): 2280 o Use "/" instead of "|" for alternatives. 2282 o Introduce new ABNF rules for "bad" whitespace ("BWS"), optional 2283 whitespace ("OWS") and required whitespace ("RWS"). 2285 o Rewrite ABNFs to spell out whitespace rules, factor out header 2286 value format definitions. 2288 C.7. Since draft-ietf-httpbis-p2-semantics-05 2290 Closed issues: 2292 o : "Reason-Phrase 2293 BNF" 2295 Final work on ABNF conversion 2296 (): 2298 o Add appendix containing collected and expanded ABNF, reorganize 2299 ABNF introduction. 2301 C.8. Since draft-ietf-httpbis-p2-semantics-06 2303 Closed issues: 2305 o : "Clarify when 2306 Referer is sent" 2308 o : "status codes 2309 vs methods" 2311 o : "Do not 2312 require "updates" relation for specs that register status codes or 2313 method names" 2315 C.9. Since draft-ietf-httpbis-p2-semantics-07 2317 Closed issues: 2319 o : "Idempotency" 2321 o : "TRACE security 2322 considerations" 2324 o : "Clarify rules 2325 for determining what entities a response carries" 2327 o : "update note 2328 citing RFC 1945 and 2068" 2330 o : "update note 2331 about redirect limit" 2333 o : "Location 2334 header ABNF should use 'URI'" 2336 o : "fragments in 2337 Location vs status 303" 2339 o : "move IANA 2340 registrations for optional status codes" 2342 Partly resolved issues: 2344 o : "Are OPTIONS 2345 and TRACE safe?" 2347 Index 2349 1 2350 100 Continue (status code) 20 2351 101 Switching Protocols (status code) 20 2353 2 2354 200 OK (status code) 21 2355 201 Created (status code) 21 2356 202 Accepted (status code) 22 2357 203 Non-Authoritative Information (status code) 22 2358 204 No Content (status code) 22 2359 205 Reset Content (status code) 23 2360 206 Partial Content (status code) 23 2362 3 2363 300 Multiple Choices (status code) 23 2364 301 Moved Permanently (status code) 24 2365 302 Found (status code) 24 2366 303 See Other (status code) 25 2367 304 Not Modified (status code) 25 2368 305 Use Proxy (status code) 26 2369 306 (Unused) (status code) 26 2370 307 Temporary Redirect (status code) 26 2372 4 2373 400 Bad Request (status code) 27 2374 401 Unauthorized (status code) 27 2375 402 Payment Required (status code) 27 2376 403 Forbidden (status code) 27 2377 404 Not Found (status code) 27 2378 405 Method Not Allowed (status code) 27 2379 406 Not Acceptable (status code) 28 2380 407 Proxy Authentication Required (status code) 28 2381 408 Request Timeout (status code) 28 2382 409 Conflict (status code) 28 2383 410 Gone (status code) 29 2384 411 Length Required (status code) 29 2385 412 Precondition Failed (status code) 29 2386 413 Request Entity Too Large (status code) 29 2387 414 URI Too Long (status code) 30 2388 415 Unsupported Media Type (status code) 30 2389 416 Requested Range Not Satisfiable (status code) 30 2390 417 Expectation Failed (status code) 30 2392 5 2393 500 Internal Server Error (status code) 31 2394 501 Not Implemented (status code) 31 2395 502 Bad Gateway (status code) 31 2396 503 Service Unavailable (status code) 31 2397 504 Gateway Timeout (status code) 31 2398 505 HTTP Version Not Supported (status code) 31 2400 A 2401 Allow header 32 2403 C 2404 CONNECT method 20 2406 D 2407 DELETE method 19 2409 E 2410 Expect header 32 2412 F 2413 From header 33 2415 G 2416 GET method 16 2417 Grammar 2418 Allow 32 2419 Allow-v 32 2420 delta-seconds 36 2421 Expect 32 2422 expect-params 32 2423 Expect-v 32 2424 expectation 32 2425 expectation-extension 32 2426 extension-code 11 2427 extension-method 8 2428 From 33 2429 From-v 33 2430 Location 34 2431 Location-v 34 2432 Max-Forwards 35 2433 Max-Forwards-v 35 2434 Method 8 2435 Reason-Phrase 11 2436 Referer 35 2437 Referer-v 35 2438 request-header 9 2439 response-header 12 2440 Retry-After 36 2441 Retry-After-v 36 2442 Server 36 2443 Server-v 36 2444 Status-Code 11 2445 User-Agent 37 2446 User-Agent-v 37 2448 H 2449 HEAD method 16 2450 Headers 2451 Allow 32 2452 Expect 32 2453 From 33 2454 Location 34 2455 Max-Forwards 35 2456 Referer 35 2457 Retry-After 36 2458 Server 36 2459 User-Agent 37 2461 I 2462 Idempotent Methods 14 2464 L 2465 LINK method 44 2466 Location header 34 2468 M 2469 Max-Forwards header 35 2470 Methods 2471 CONNECT 20 2472 DELETE 19 2473 GET 16 2474 HEAD 16 2475 LINK 44 2476 OPTIONS 15 2477 PATCH 44 2478 POST 17 2479 PUT 18 2480 TRACE 19 2481 UNLINK 44 2483 O 2484 OPTIONS method 15 2486 P 2487 PATCH method 44 2488 POST method 17 2489 PUT method 18 2491 R 2492 Referer header 35 2493 Retry-After header 36 2495 S 2496 Safe Methods 14 2497 Server header 36 2498 Status Codes 2499 100 Continue 20 2500 101 Switching Protocols 20 2501 200 OK 21 2502 201 Created 21 2503 202 Accepted 22 2504 203 Non-Authoritative Information 22 2505 204 No Content 22 2506 205 Reset Content 23 2507 206 Partial Content 23 2508 300 Multiple Choices 23 2509 301 Moved Permanently 24 2510 302 Found 24 2511 303 See Other 25 2512 304 Not Modified 25 2513 305 Use Proxy 26 2514 306 (Unused) 26 2515 307 Temporary Redirect 26 2516 400 Bad Request 27 2517 401 Unauthorized 27 2518 402 Payment Required 27 2519 403 Forbidden 27 2520 404 Not Found 27 2521 405 Method Not Allowed 27 2522 406 Not Acceptable 28 2523 407 Proxy Authentication Required 28 2524 408 Request Timeout 28 2525 409 Conflict 28 2526 410 Gone 29 2527 411 Length Required 29 2528 412 Precondition Failed 29 2529 413 Request Entity Too Large 29 2530 414 URI Too Long 30 2531 415 Unsupported Media Type 30 2532 416 Requested Range Not Satisfiable 30 2533 417 Expectation Failed 30 2534 500 Internal Server Error 31 2535 501 Not Implemented 31 2536 502 Bad Gateway 31 2537 503 Service Unavailable 31 2538 504 Gateway Timeout 31 2539 505 HTTP Version Not Supported 31 2541 T 2542 TRACE method 19 2544 U 2545 UNLINK method 44 2546 User-Agent header 37 2548 Authors' Addresses 2550 Roy T. Fielding (editor) 2551 Day Software 2552 23 Corporate Plaza DR, Suite 280 2553 Newport Beach, CA 92660 2554 USA 2556 Phone: +1-949-706-5300 2557 Fax: +1-949-706-5305 2558 Email: fielding@gbiv.com 2559 URI: http://roy.gbiv.com/ 2561 Jim Gettys 2562 One Laptop per Child 2563 21 Oak Knoll Road 2564 Carlisle, MA 01741 2565 USA 2567 Email: jg@laptop.org 2568 URI: http://www.laptop.org/ 2569 Jeffrey C. Mogul 2570 Hewlett-Packard Company 2571 HP Labs, Large Scale Systems Group 2572 1501 Page Mill Road, MS 1177 2573 Palo Alto, CA 94304 2574 USA 2576 Email: JeffMogul@acm.org 2578 Henrik Frystyk Nielsen 2579 Microsoft Corporation 2580 1 Microsoft Way 2581 Redmond, WA 98052 2582 USA 2584 Email: henrikn@microsoft.com 2586 Larry Masinter 2587 Adobe Systems, Incorporated 2588 345 Park Ave 2589 San Jose, CA 95110 2590 USA 2592 Email: LMM@acm.org 2593 URI: http://larry.masinter.net/ 2595 Paul J. Leach 2596 Microsoft Corporation 2597 1 Microsoft Way 2598 Redmond, WA 98052 2600 Email: paulle@microsoft.com 2602 Tim Berners-Lee 2603 World Wide Web Consortium 2604 MIT Computer Science and Artificial Intelligence Laboratory 2605 The Stata Center, Building 32 2606 32 Vassar Street 2607 Cambridge, MA 02139 2608 USA 2610 Email: timbl@w3.org 2611 URI: http://www.w3.org/People/Berners-Lee/ 2612 Yves Lafon (editor) 2613 World Wide Web Consortium 2614 W3C / ERCIM 2615 2004, rte des Lucioles 2616 Sophia-Antipolis, AM 06902 2617 France 2619 Email: ylafon@w3.org 2620 URI: http://www.raubacapeu.net/people/yves/ 2622 Julian F. Reschke (editor) 2623 greenbytes GmbH 2624 Hafenweg 16 2625 Muenster, NW 48155 2626 Germany 2628 Phone: +49 251 2807760 2629 Fax: +49 251 2807761 2630 Email: julian.reschke@greenbytes.de 2631 URI: http://greenbytes.de/tech/webdav/