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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. F. Reschke 3 Internet-Draft greenbytes 4 Intended status: Informational 22 April 2021 5 Expires: 24 October 2021 7 A JSON Encoding for HTTP Field Values 8 draft-reschke-http-jfv-14 10 Abstract 12 This document establishes a convention for use of JSON-encoded field 13 values in new HTTP fields. 15 Editorial Note 17 This note is to be removed before publishing as an RFC. 19 Distribution of this document is unlimited. Although this is not a 20 work item of the HTTPbis Working Group, comments should be sent to 21 the Hypertext Transfer Protocol (HTTP) mailing list at ietf-http- 22 wg@w3.org (mailto:ietf-http-wg@w3.org), which may be joined by 23 sending a message with subject "subscribe" to ietf-http-wg- 24 request@w3.org (mailto:ietf-http-wg- 25 request@w3.org?subject=subscribe). 27 Discussions of the HTTPbis Working Group are archived at 28 . 30 XML versions and latest edits for this document are available from 31 . 33 The changes in this draft are summarized in Appendix D.17. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at https://datatracker.ietf.org/drafts/current/. 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 This Internet-Draft will expire on 24 October 2021. 51 Copyright Notice 53 Copyright (c) 2021 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 58 license-info) in effect on the date of publication of this document. 59 Please review these documents carefully, as they describe your rights 60 and restrictions with respect to this document. Code Components 61 extracted from this document must include Simplified BSD License text 62 as described in Section 4.e of the Trust Legal Provisions and are 63 provided without warranty as described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 68 1.1. Relation to "Structured Field Values for HTTP" 69 (RFC8941) . . . . . . . . . . . . . . . . . . . . . . . . 4 70 2. Data Model and Format . . . . . . . . . . . . . . . . . . . . 4 71 3. Sender Requirements . . . . . . . . . . . . . . . . . . . . . 5 72 3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5 73 4. Recipient Requirements . . . . . . . . . . . . . . . . . . . 6 74 4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6 75 5. Using this Format in Field Definitions . . . . . . . . . . . 7 76 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 7 77 7. Interoperability Considerations . . . . . . . . . . . . . . . 7 78 7.1. Encoding and Characters . . . . . . . . . . . . . . . . . 7 79 7.2. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 8 80 7.3. Object Constraints . . . . . . . . . . . . . . . . . . . 8 81 8. Internationalization Considerations . . . . . . . . . . . . . 8 82 9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 83 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 84 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 85 10.2. Informative References . . . . . . . . . . . . . . . . . 9 86 10.3. Specifications Using This Syntax (at some point of 87 time) . . . . . . . . . . . . . . . . . . . . . . . . . 10 88 Appendix A. Comparison with Structured Fields . . . . . . . . . 10 89 A.1. Base Types . . . . . . . . . . . . . . . . . . . . . . . 10 90 A.2. Structures . . . . . . . . . . . . . . . . . . . . . . . 11 91 Appendix B. Use of JSON Field Value Encoding in the Wild . . . . 11 92 B.1. W3C Reporting API Specification . . . . . . . . . . . . . 12 93 B.2. W3C Clear Site Data Specification . . . . . . . . . . . . 12 94 B.3. W3C Feature Policy Specification . . . . . . . . . . . . 12 95 Appendix C. Implementations . . . . . . . . . . . . . . . . . . 12 96 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 12 97 D.1. Since draft-reschke-http-jfv-00 . . . . . . . . . . . . . 12 98 D.2. Since draft-reschke-http-jfv-01 . . . . . . . . . . . . . 12 99 D.3. Since draft-reschke-http-jfv-02 . . . . . . . . . . . . . 13 100 D.4. Since draft-reschke-http-jfv-03 . . . . . . . . . . . . . 13 101 D.5. Since draft-reschke-http-jfv-04 . . . . . . . . . . . . . 13 102 D.6. Since draft-ietf-httpbis-jfv-00 . . . . . . . . . . . . . 13 103 D.7. Since draft-ietf-httpbis-jfv-01 . . . . . . . . . . . . . 13 104 D.8. Since draft-ietf-httpbis-jfv-02 . . . . . . . . . . . . . 13 105 D.9. Since draft-reschke-http-jfv-05 . . . . . . . . . . . . . 13 106 D.10. Since draft-reschke-http-jfv-06 . . . . . . . . . . . . . 14 107 D.11. Since draft-reschke-http-jfv-07 . . . . . . . . . . . . . 14 108 D.12. Since draft-reschke-http-jfv-08 . . . . . . . . . . . . . 14 109 D.13. Since draft-reschke-http-jfv-09 . . . . . . . . . . . . . 14 110 D.14. Since draft-reschke-http-jfv-10 . . . . . . . . . . . . . 14 111 D.15. Since draft-reschke-http-jfv-11 . . . . . . . . . . . . . 14 112 D.16. Since draft-reschke-http-jfv-12 . . . . . . . . . . . . . 15 113 D.17. Since draft-reschke-http-jfv-13 . . . . . . . . . . . . . 15 114 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15 115 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15 117 1. Introduction 119 Defining syntax for new HTTP fields ([HTTP], Section 5) is non- 120 trivial. Among the commonly encountered problems are: 122 * There is no common syntax for complex field values. Several well- 123 known fields do use a similarly looking syntax, but it is hard to 124 write generic parsing code that will both correctly handle valid 125 field values but also reject invalid ones. 127 * The HTTP message format allows field lines to repeat, so field 128 syntax needs to be designed in a way that these cases are either 129 meaningful, or can be unambiguously detected and rejected. 131 * HTTP does not define a character encoding scheme ([RFC6365], 132 Section 2), so fields are either stuck with US-ASCII ([RFC0020]), 133 or need out-of-band information to decide what encoding scheme is 134 used. Furthermore, APIs usually assume a default encoding scheme 135 in order to map from octet sequences to strings (for instance, 136 [XMLHttpRequest] uses the IDL type "ByteString", effectively 137 resulting in the ISO-8859-1 character encoding scheme [ISO-8859-1] 138 being used). 140 (See Section 16.3 of [HTTP] for a summary of considerations for new 141 fields.) 142 This specification addresses the issues listed above by defining both 143 a generic JSON-based ([RFC8259]) data model and a concrete wire 144 format that can be used in definitions of new fields, where the goals 145 were: 147 * to be compatible with field recombination when field lines occur 148 multiple times in a single message (Section 5.3 of [HTTP]), and 150 * not to use any problematic characters in the field value (non- 151 ASCII characters and certain whitespace characters). 153 1.1. Relation to "Structured Field Values for HTTP" ([RFC8941]) 155 "Structured Field Values for HTTP", an IETF RFC on the Standards 156 Track, is a different approach to this set of problems. It uses a 157 more compact notation, similar to what is used in existing header 158 fields, and avoids several potential interoperability problems 159 inherent to the use of JSON. 161 In general, that format is preferred for newly defined fields. The 162 JSON-based format defined by this document might however be useful in 163 case the data that needs to be transferred is already in JSON format, 164 or features not covered by "Structured Field Values" are needed. 166 See Appendix A for more details. 168 2. Data Model and Format 170 In HTTP, field lines with the same field name can occur multiple 171 times within a single message (Section 5.3 of [HTTP]). When this 172 happens, recipients are allowed to combine the field line values 173 using commas as delimiter, forming a combined "field value". This 174 rule matches nicely JSON's array format (Section 5 of [RFC8259]). 175 Thus, the basic data model used here is the JSON array. 177 Field definitions that need only a single value can restrict 178 themselves to arrays of length 1, and are encouraged to define error 179 handling in case more values are received (such as "first wins", 180 "last wins", or "abort with fatal error message"). 182 JSON arrays are mapped to field values by creating a sequence of 183 serialized member elements, separated by commas and optionally 184 whitespace. This is equivalent to using the full JSON array format, 185 while leaving out the "begin-array" ('[') and "end-array" (']') 186 delimiters. 188 The ABNF character names and classes below are used (copied from 189 [RFC5234], Appendix B.1): 191 CR = %x0D ; carriage return 192 HTAB = %x09 ; horizontal tab 193 LF = %x0A ; line feed 194 SP = %x20 ; space 195 VCHAR = %x21-7E ; visible (printing) characters 197 Characters in JSON strings that are not allowed or discouraged in 198 HTTP field values - that is, not in the "VCHAR" definition - need to 199 be represented using JSON's "backslash" escaping mechanism 200 ([RFC8259], Section 7). 202 The control characters CR, LF, and HTAB do not appear inside JSON 203 strings, but can be used outside (line breaks, indentation etc.). 204 These characters need to be either stripped or replaced by space 205 characters (ABNF "SP"). 207 Formally, using the HTTP specification's ABNF extensions defined in 208 Section 5.6.1 of [HTTP]: 210 json-field-value = #json-field-item 211 json-field-item = JSON-Text 212 ; see [RFC8259], Section 2, 213 ; post-processed so that only VCHAR characters 214 ; are used 216 3. Sender Requirements 218 To map a JSON array to an HTTP field value, process each array 219 element separately by: 221 1. generating the JSON representation, 223 2. stripping all JSON control characters (CR, HTAB, LF), or 224 replacing them by space ("SP") characters, 226 3. replacing all remaining non-VSPACE characters by the equivalent 227 backslash-escape sequence ([RFC8259], Section 7). 229 The resulting list of strings is transformed into an HTTP field value 230 by combining them using comma (%x2C) plus optional SP as delimiter, 231 and encoding the resulting string into an octet sequence using the 232 US-ASCII character encoding scheme ([RFC0020]). 234 3.1. Example 236 With the JSON data below, containing the non-ASCII characters "ü" 237 (LATIN SMALL LETTER U WITH DIAERESIS, U+00FC) and "€" (EURO SIGN, 238 U+20AC): 240 [ 241 { 242 "destination": "Münster", 243 "price": 123, 244 "currency": "€" 245 } 246 ] 248 The generated field value would be: 250 { "destination": "M\u00FCnster", "price": 123, "currency": "\u20AC" } 252 4. Recipient Requirements 254 To map a set of HTTP field line values to a JSON array: 256 1. combine all field line values into a single field value as per 257 Section 5.3 of [HTTP], 259 2. add a leading begin-array ("[") octet and a trailing end-array 260 ("]") octet, then 262 3. run the resulting octet sequence through a JSON parser. 264 The result of the parsing operation is either an error (in which case 265 the field values needs to be considered invalid), or a JSON array. 267 4.1. Example 269 An HTTP message containing the field lines: 271 Example: "\u221E" 272 Example: {"date":"2012-08-25"} 273 Example: [17,42] 275 would be parsed into the JSON array below: 277 [ 278 "∞", 279 { 280 "date": "2012-08-25" 281 }, 282 [ 283 17, 284 42 285 ] 286 ] 288 5. Using this Format in Field Definitions 290 Specifications defining new HTTP fields need to take the 291 considerations listed in Section 16.3 of [HTTP] into account. Many 292 of these will already be accounted for by using the format defined in 293 this specification. 295 Readers of HTTP-related specifications frequently expect an ABNF 296 definition of the field value syntax. This is not really needed 297 here, as the actual syntax is JSON text, as defined in Section 2 of 298 [RFC8259]. 300 A very simple way to use this JSON encoding thus is just to cite this 301 specification - specifically the "json-field-value" ABNF production 302 defined in Section 2 - and otherwise not to talk about the details of 303 the field syntax at all. 305 An alternative approach is just to repeat the ABNF-related parts from 306 Section 2. 308 This frees the specification from defining the concrete on-the-wire 309 syntax. What's left is defining the field value in terms of a JSON 310 array. An important aspect is the question of extensibility, e.g. 311 how recipients ought to treat unknown field names. In general, a 312 "must ignore" approach will allow protocols to evolve without 313 versioning or even using entire new field names. 315 6. Deployment Considerations 317 This JSON-based syntax will only apply to newly introduced fields, 318 thus backwards compatibility is not a problem. That being said, it 319 is conceivable that there is existing code that might trip over 320 double quotes not being used for HTTP's quoted-string syntax 321 (Section 5.6.4 of [HTTP]). 323 7. Interoperability Considerations 325 The "I-JSON Message Format" specification ([RFC7493]) addresses known 326 JSON interoperability pain points. This specification borrows from 327 the requirements made over there: 329 7.1. Encoding and Characters 331 This specification requires that field values use only US-ASCII 332 characters, and thus by definition uses a subset of UTF-8 333 (Section 2.1 of [RFC7493]). 335 Furthermore, escape sequences in JSON strings (Section 7 of 336 [RFC8259]) - both in object member names and string values - are not 337 allowed to represent non-Unicode code points such as unpaired 338 surrogates or Noncharacters (see "General Structure" in [UNICODE]). 340 7.2. Numbers 342 Be aware of the issues around number precision, as discussed in 343 Section 2.2 of [RFC7493]. 345 7.3. Object Constraints 347 As described in Section 4 of [RFC8259], JSON parser implementations 348 differ in the handling of duplicate object names. Therefore, senders 349 are not allowed to use duplicate object names, and recipients are 350 advised to either treat field values with duplicate names as invalid 351 (consistent with [RFC7493], Section 2.3) or use the lexically last 352 value (consistent with [ECMA-262], Section 24.3.1.1). 354 Furthermore, ordering of object members is not significant and can 355 not be relied upon. 357 8. Internationalization Considerations 359 In current versions of HTTP, field values are represented by octet 360 sequences, usually used to transmit ASCII characters, with 361 restrictions on the use of certain control characters, and no 362 associated default character encoding, nor a way to describe it 363 ([HTTP], Section 5). 365 This specification maps all characters which can cause problems to 366 JSON escape sequences, thereby solving the HTTP field 367 internationalization problem. 369 Future specifications of HTTP might change to allow non-ASCII 370 characters natively. In that case, fields using the syntax defined 371 by this specification would have a simple migration path (by just 372 stopping to require escaping of non-ASCII characters). 374 9. Security Considerations 376 Using JSON-shaped field values is believed to not introduce any new 377 threads beyond those described in Section 12 of [RFC8259], namely the 378 risk of recipients using the wrong tools to parse them. 380 Other than that, any syntax that makes extensions easy can be used to 381 smuggle information through field values; however, this concern is 382 shared with other widely used formats, such as those using parameters 383 in the form of name/value pairs. 385 10. References 387 10.1. Normative References 389 [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, 390 Ed., "HTTP Semantics", Work in Progress, Internet-Draft, 391 draft-ietf-httpbis-semantics-15, 30 March 2021, 392 . 395 [RFC0020] Cerf, V., "ASCII format for network interchange", STD 80, 396 RFC 20, DOI 10.17487/RFC0020, October 1969, 397 . 399 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 400 Specifications: ABNF", STD 68, RFC 5234, 401 DOI 10.17487/RFC5234, January 2008, 402 . 404 [RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493, 405 DOI 10.17487/RFC7493, March 2015, 406 . 408 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 409 Interchange Format", RFC 8259, DOI 10.17487/RFC8259, 410 December 2017, . 412 [UNICODE] The Unicode Consortium, "The Unicode Standard", 413 . 415 10.2. Informative References 417 [ECMA-262] Ecma International, "ECMA-262 6th Edition, The ECMAScript 418 2015 Language Specification", Standard ECMA-262, June 419 2015, . 421 [ISO-8859-1] 422 International Organization for Standardization, 423 "Information technology -- 8-bit single-byte coded graphic 424 character sets -- Part 1: Latin alphabet No. 1", ISO/ 425 IEC 8859-1:1998, 1998. 427 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 428 Internationalization in the IETF", BCP 166, RFC 6365, 429 DOI 10.17487/RFC6365, September 2011, 430 . 432 [RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for 433 HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, 434 . 436 [XMLHttpRequest] 437 WhatWG, "XMLHttpRequest", . 439 10.3. Specifications Using This Syntax (at some point of time) 441 [CLEARSITE] 442 West, M., "Clear Site Data", W3C Working Draft WD-clear- 443 site-data-20171130, 30 November 2017, 444 . 445 Latest version available at . 448 [FEATUREPOL] 449 Clelland, I., "Feature Policy", W3C Editor's Draft , 450 . 452 [REPORTING] 453 Creager, D., Grigorik, I., Meyer, P., and M. West, 454 "Reporting API", W3C Working Draft WD-reporting- 455 1-20180925, 25 September 2018, 456 . 457 Latest version available at . 460 Appendix A. Comparison with Structured Fields 462 A.1. Base Types 464 +==========+==================================+==================+ 465 | Type | in Structured Fields | in JSON-based | 466 | | | Fields | 467 +==========+==================================+==================+ 468 | Integer | [RFC8941], Section 3.3.1 | [RFC8259], | 469 | | | Section 6 | 470 | +----------------------------------+------------------+ 471 | | (restricted to 15 digits) | | 472 +==========+----------------------------------+------------------+ 473 | Decimal | [RFC8941], Section 3.3.2 | [RFC8259], | 474 | | | Section 6 | 475 | +----------------------------------+------------------+ 476 | | (a fixed point decimal | | 477 | | restricted to 12 + 3 digits) | | 478 +==========+----------------------------------+------------------+ 479 | String | [RFC8941], Section 3.3.3 | [RFC8259], | 480 | | | Section 7 | 481 | +----------------------------------+------------------+ 482 | | (only ASCII supported, non-ASCII | | 483 | | requires using Byte Sequences) | | 484 +==========+----------------------------------+------------------+ 485 | Token | [RFC8941], Section 3.3.4 | not available | 486 +==========+----------------------------------+------------------+ 487 | Byte | [RFC8941], Section 3.3.5 | not available | 488 | Sequence +----------------------------------+------------------+ 489 | | | (usually mapped | 490 | | | to strings using | 491 | | | base64 encoding) | 492 +==========+----------------------------------+------------------+ 493 | Boolean | [RFC8941], Section 3.3.6 | [RFC8259], | 494 | | | Section 3 | 495 +==========+----------------------------------+------------------+ 497 Table 1 499 Structured Fields provide more data types (such as "token" or "byte 500 sequence"). Numbers are restricted, avoiding the JSON interop 501 problems described in Section 7.2. Strings are limited to ASCII, 502 requiring the use of byte sequences should non-ASCII characters be 503 needed. 505 A.2. Structures 507 Structured Fields define Lists ([RFC8941], Section 3.1), similar to 508 JSON arrays ([RFC8259], Section 5), and Dictionaries ([RFC8941], 509 Section 3.2), similar to JSON objects ([RFC8259], Section 4). 511 In addition, most items in Structured Fields can be parametrized 512 ([RFC8941], Section 3.1.2), attaching a dictionary-like structure to 513 the value. To emulate this in JSON based field, an additional 514 nesting of objects would be needed. 516 Finally, nesting of data structures is intentionally limited to two 517 levels (see Appendix A.1 of [RFC8941] for the motivation). 519 Appendix B. Use of JSON Field Value Encoding in the Wild 521 This section is to be removed before publishing as an RFC. 523 Since work started on this document, various specifications have 524 adopted this format. At least one of these moved away after the HTTP 525 Working Group decided to focus on [RFC8941] (see thread starting at 526 ). 529 The sections below summarize the current usage of this format. 531 B.1. W3C Reporting API Specification 533 Defined in W3C Working Draft "Reporting API" (Section 3.1 of 534 [REPORTING]). Still in use in latest working draft dated September 535 2018. 537 B.2. W3C Clear Site Data Specification 539 Used in earlier versions of "Clear Site Data". The current version 540 replaces the use of JSON with a custom syntax that happens to be 541 somewhat compatible with an array of JSON strings (see Section 3.1 of 542 [CLEARSITE] and for feedback). 545 B.3. W3C Feature Policy Specification 547 Originally defined in W3C document "Feature Policy" ([FEATUREPOL]), 548 but switched to use of Structured Header Fields ([RFC8941]). 550 Appendix C. Implementations 552 This section is to be removed before publishing as an RFC. 554 See for a proof-of-concept 555 (in development). 557 Appendix D. Change Log 559 This section is to be removed before publishing as an RFC. 561 D.1. Since draft-reschke-http-jfv-00 563 Editorial fixes + working on the TODOs. 565 D.2. Since draft-reschke-http-jfv-01 567 Mention slightly increased risk of smuggling information in header 568 field values. 570 D.3. Since draft-reschke-http-jfv-02 572 Mention Kazuho Oku's proposal for abbreviated forms. 574 Added a bit of text about the motivation for a concrete JSON subset 575 (ack Cory Benfield). 577 Expand I18N section. 579 D.4. Since draft-reschke-http-jfv-03 581 Mention relation to KEY header field. 583 D.5. Since draft-reschke-http-jfv-04 585 Between June and December 2016, this was a work item of the HTTP 586 working group (see ). Work (if any) continues now on 588 . 590 Changes made while this was a work item of the HTTP Working Group: 592 D.6. Since draft-ietf-httpbis-jfv-00 594 Added example for "Accept-Encoding" (inspired by Kazuho's feedback), 595 showing a potential way to optimize the format when default values 596 apply. 598 D.7. Since draft-ietf-httpbis-jfv-01 600 Add interop discussion, building on I-JSON and ECMA-262 (see 601 ). 603 D.8. Since draft-ietf-httpbis-jfv-02 605 Move non-essential parts into appendix. 607 Updated XHR reference. 609 D.9. Since draft-reschke-http-jfv-05 611 Add meat to "Using this Format in Header Field Definitions". 613 Add a few lines on the relation to "Key". 615 Summarize current use of the format. 617 D.10. Since draft-reschke-http-jfv-06 619 RFC 5987 is obsoleted by RFC 8187. 621 Update CLEARSITE comment. 623 D.11. Since draft-reschke-http-jfv-07 625 Update JSON and HSTRUCT references. 627 FEATUREPOL doesn't use JSON syntax anymore. 629 D.12. Since draft-reschke-http-jfv-08 631 Update HSTRUCT reference. 633 Update notes about CLEARSITE and FEATUREPOL. 635 D.13. Since draft-reschke-http-jfv-09 637 Update HSTRUCT and FEATUREPOL references. 639 Update note about REPORTING. 641 Changed category to "informational". 643 D.14. Since draft-reschke-http-jfv-10 645 Update HSTRUCT reference. 647 D.15. Since draft-reschke-http-jfv-11 649 Update HSTRUCT reference. 651 Update note about FEATUREPOL (now using Structured Fields). 653 Reference [HTTP] instead if RFC723* and adjust (header) field 654 terminology accordingly. 656 Remove discussion about the relation to KEY (as that spec is dormant: 657 ). 659 Remove appendices "Examples" and "Discussion". 661 Mark "Use of JSON Field Value Encoding in the Wild" for removal in 662 RFC. 664 D.16. Since draft-reschke-http-jfv-12 666 Update HTTP reference and update terminology some more. 668 Update HSTRUCT reference (now RFC 8941). 670 D.17. Since draft-reschke-http-jfv-13 672 Update HTTP reference. 674 Mention test implementation. 676 Clarify that Unicode unpaired surrogates or Noncharacters must not be 677 sent. 679 Rewrite text about [RFC8941], add appendix comparing both formats. 681 And send/receive examples. 683 Acknowledgements 685 Thanks go to the Hypertext Transfer Protocol Working Group 686 participants. 688 Author's Address 690 Julian F. Reschke 691 greenbytes GmbH 692 Hafenweg 16 693 48155 Münster 694 Germany 696 Email: julian.reschke@greenbytes.de 697 URI: http://greenbytes.de/tech/webdav/