draft-reschke-http-jfv-14.txt   draft-reschke-http-jfv-latest.txt 
Network Working Group J. F. Reschke Network Working Group J. F. Reschke
Internet-Draft greenbytes Internet-Draft greenbytes
Intended status: Informational April 22, 2021 Intended status: Informational July 6, 2024
Expires: October 24, 2021 Expires: January 7, 2025
A JSON Encoding for HTTP Field Values A JSON Encoding for HTTP Field Values
draft-reschke-http-jfv-14 draft-reschke-http-jfv-latest
Abstract Abstract
This document establishes a convention for use of JSON-encoded field This document establishes a convention for use of JSON-encoded field
values in new HTTP fields. values in new HTTP fields.
Editorial Note Editorial Note
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
skipping to change at page 1, line 34 skipping to change at page 1, line 34
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request@w3.org (mailto:ietf-http-wg- request@w3.org (mailto:ietf-http-wg-
request@w3.org?subject=subscribe). request@w3.org?subject=subscribe).
Discussions of the HTTPbis Working Group are archived at Discussions of the HTTPbis Working Group are archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>. <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
XML versions and latest edits for this document are available from XML versions and latest edits for this document are available from
<http://greenbytes.de/tech/webdav/#draft-reschke-http-jfv>. <http://greenbytes.de/tech/webdav/#draft-reschke-http-jfv>.
The changes in this draft are summarized in Appendix D.17. The changes in this draft are summarized in Appendix D.18.
Status of This Memo Status of This Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Relation to "Structured Field Values for HTTP" 1.1. Relation to "Structured Field Values for HTTP"
(RFC8941) . . . . . . . . . . . . . . . . . . . . . . . . 4 (RFC8941bis) . . . . . . . . . . . . . . . . . . . . . . 4
2. Data Model and Format . . . . . . . . . . . . . . . . . . . . 4 2. Data Model and Format . . . . . . . . . . . . . . . . . . . . 4
3. Sender Requirements . . . . . . . . . . . . . . . . . . . . . 5 3. Sender Requirements . . . . . . . . . . . . . . . . . . . . . 5
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Recipient Requirements . . . . . . . . . . . . . . . . . . . 6 4. Recipient Requirements . . . . . . . . . . . . . . . . . . . 6
4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Using this Format in Field Definitions . . . . . . . . . . . 7 5. Using this Format in Field Definitions . . . . . . . . . . . 7
6. Deployment Considerations . . . . . . . . . . . . . . . . . . 7 6. Deployment Considerations . . . . . . . . . . . . . . . . . . 7
7. Interoperability Considerations . . . . . . . . . . . . . . . 7 7. Interoperability Considerations . . . . . . . . . . . . . . . 7
7.1. Encoding and Characters . . . . . . . . . . . . . . . . . 7 7.1. Encoding and Characters . . . . . . . . . . . . . . . . . 7
7.2. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.2. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.3. Object Constraints . . . . . . . . . . . . . . . . . . . 8 7.3. Object Constraints . . . . . . . . . . . . . . . . . . . 8
8. Internationalization Considerations . . . . . . . . . . . . . 8 8. Internationalization Considerations . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 9
10.3. Specifications Using This Syntax (at some point of 10.3. Specifications Using This Syntax (at some point of
time) . . . . . . . . . . . . . . . . . . . . . . . . . 10 time) . . . . . . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Comparison with Structured Fields . . . . . . . . . 10 Appendix A. Comparison with Structured Fields . . . . . . . . . 10
A.1. Base Types . . . . . . . . . . . . . . . . . . . . . . . 10 A.1. Base Types . . . . . . . . . . . . . . . . . . . . . . . 11
A.2. Structures . . . . . . . . . . . . . . . . . . . . . . . 11 A.2. Structures . . . . . . . . . . . . . . . . . . . . . . . 11
Appendix B. Use of JSON Field Value Encoding in the Wild . . . . 11 Appendix B. Use of JSON Field Value Encoding in the Wild . . . . 12
B.1. W3C Reporting API Specification . . . . . . . . . . . . . 12 B.1. W3C Reporting API Specification . . . . . . . . . . . . . 12
B.2. W3C Clear Site Data Specification . . . . . . . . . . . . 12 B.2. W3C Clear Site Data Specification . . . . . . . . . . . . 12
B.3. W3C Feature Policy Specification . . . . . . . . . . . . 12 B.3. W3C Feature Policy Specification . . . . . . . . . . . . 12
Appendix C. Implementations . . . . . . . . . . . . . . . . . . 12 Appendix C. Implementations . . . . . . . . . . . . . . . . . . 12
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 12 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 13
D.1. Since draft-reschke-http-jfv-00 . . . . . . . . . . . . . 12 D.1. Since draft-reschke-http-jfv-00 . . . . . . . . . . . . . 13
D.2. Since draft-reschke-http-jfv-01 . . . . . . . . . . . . . 12 D.2. Since draft-reschke-http-jfv-01 . . . . . . . . . . . . . 13
D.3. Since draft-reschke-http-jfv-02 . . . . . . . . . . . . . 12 D.3. Since draft-reschke-http-jfv-02 . . . . . . . . . . . . . 13
D.4. Since draft-reschke-http-jfv-03 . . . . . . . . . . . . . 13 D.4. Since draft-reschke-http-jfv-03 . . . . . . . . . . . . . 13
D.5. Since draft-reschke-http-jfv-04 . . . . . . . . . . . . . 13 D.5. Since draft-reschke-http-jfv-04 . . . . . . . . . . . . . 13
D.6. Since draft-ietf-httpbis-jfv-00 . . . . . . . . . . . . . 13 D.6. Since draft-ietf-httpbis-jfv-00 . . . . . . . . . . . . . 13
D.7. Since draft-ietf-httpbis-jfv-01 . . . . . . . . . . . . . 13 D.7. Since draft-ietf-httpbis-jfv-01 . . . . . . . . . . . . . 13
D.8. Since draft-ietf-httpbis-jfv-02 . . . . . . . . . . . . . 13 D.8. Since draft-ietf-httpbis-jfv-02 . . . . . . . . . . . . . 14
D.9. Since draft-reschke-http-jfv-05 . . . . . . . . . . . . . 13 D.9. Since draft-reschke-http-jfv-05 . . . . . . . . . . . . . 14
D.10. Since draft-reschke-http-jfv-06 . . . . . . . . . . . . . 13 D.10. Since draft-reschke-http-jfv-06 . . . . . . . . . . . . . 14
D.11. Since draft-reschke-http-jfv-07 . . . . . . . . . . . . . 13 D.11. Since draft-reschke-http-jfv-07 . . . . . . . . . . . . . 14
D.12. Since draft-reschke-http-jfv-08 . . . . . . . . . . . . . 14 D.12. Since draft-reschke-http-jfv-08 . . . . . . . . . . . . . 14
D.13. Since draft-reschke-http-jfv-09 . . . . . . . . . . . . . 14 D.13. Since draft-reschke-http-jfv-09 . . . . . . . . . . . . . 14
D.14. Since draft-reschke-http-jfv-10 . . . . . . . . . . . . . 14 D.14. Since draft-reschke-http-jfv-10 . . . . . . . . . . . . . 14
D.15. Since draft-reschke-http-jfv-11 . . . . . . . . . . . . . 14 D.15. Since draft-reschke-http-jfv-11 . . . . . . . . . . . . . 14
D.16. Since draft-reschke-http-jfv-12 . . . . . . . . . . . . . 14 D.16. Since draft-reschke-http-jfv-12 . . . . . . . . . . . . . 15
D.17. Since draft-reschke-http-jfv-13 . . . . . . . . . . . . . 14 D.17. Since draft-reschke-http-jfv-13 . . . . . . . . . . . . . 15
D.18. Since draft-reschke-http-jfv-14 . . . . . . . . . . . . . 15
D.19. Since draft-reschke-http-jfv-15 . . . . . . . . . . . . . 15
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
Defining syntax for new HTTP fields ([HTTP], Section 5) is non- Defining syntax for new HTTP fields ([HTTP], Section 5) is non-
trivial. Among the commonly encountered problems are: trivial. Among the commonly encountered problems are:
o There is no common syntax for complex field values. Several well- o There is no common syntax for complex field values. Several well-
known fields do use a similarly looking syntax, but it is hard to known fields do use a similarly looking syntax, but it is hard to
write generic parsing code that will both correctly handle valid write generic parsing code that will both correctly handle valid
field values but also reject invalid ones. field values but also reject invalid ones.
skipping to change at page 4, line 15 skipping to change at page 4, line 15
a generic JSON-based ([RFC8259]) data model and a concrete wire a generic JSON-based ([RFC8259]) data model and a concrete wire
format that can be used in definitions of new fields, where the goals format that can be used in definitions of new fields, where the goals
were: were:
o to be compatible with field recombination when field lines occur o to be compatible with field recombination when field lines occur
multiple times in a single message (Section 5.3 of [HTTP]), and multiple times in a single message (Section 5.3 of [HTTP]), and
o not to use any problematic characters in the field value (non- o not to use any problematic characters in the field value (non-
ASCII characters and certain whitespace characters). ASCII characters and certain whitespace characters).
1.1. Relation to "Structured Field Values for HTTP" ([RFC8941]) 1.1. Relation to "Structured Field Values for HTTP" ([RFC8941bis])
"Structured Field Values for HTTP", an IETF RFC on the Standards "Structured Field Values for HTTP", an IETF RFC on the Standards
Track, is a different approach to this set of problems. It uses a Track, is a different approach to this set of problems. It uses a
more compact notation, similar to what is used in existing header more compact notation, similar to what is used in existing header
fields, and avoids several potential interoperability problems fields, and avoids several potential interoperability problems
inherent to the use of JSON. inherent to the use of JSON.
In general, that format is preferred for newly defined fields. The In general, that format is preferred for newly defined fields. The
JSON-based format defined by this document might however be useful in JSON-based format defined by this document might however be useful in
case the data that needs to be transferred is already in JSON format, case the data that needs to be transferred is already in JSON format,
skipping to change at page 9, line 15 skipping to change at page 9, line 15
Other than that, any syntax that makes extensions easy can be used to Other than that, any syntax that makes extensions easy can be used to
smuggle information through field values; however, this concern is smuggle information through field values; however, this concern is
shared with other widely used formats, such as those using parameters shared with other widely used formats, such as those using parameters
in the form of name/value pairs. in the form of name/value pairs.
10. References 10. References
10.1. Normative References 10.1. Normative References
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", Work in Progress, Internet-Draft, Ed., "HTTP Semantics", RFC 9110, DOI 10.17487/RFC9110,
draft-ietf-httpbis-semantics-15, March 30, 2021, June 2022, <https://www.rfc-editor.org/info/rfc9110>.
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-15>.
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80, [RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969, RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>. <https://www.rfc-editor.org/info/rfc20>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
skipping to change at page 10, line 10 skipping to change at page 10, line 10
International Organization for Standardization, International Organization for Standardization,
"Information technology -- 8-bit single-byte coded graphic "Information technology -- 8-bit single-byte coded graphic
character sets -- Part 1: Latin alphabet No. 1", ISO/ character sets -- Part 1: Latin alphabet No. 1", ISO/
IEC 8859-1:1998, 1998. IEC 8859-1:1998, 1998.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365, Internationalization in the IETF", BCP 166, RFC 6365,
DOI 10.17487/RFC6365, September 2011, DOI 10.17487/RFC6365, September 2011,
<https://www.rfc-editor.org/info/rfc6365>. <https://www.rfc-editor.org/info/rfc6365>.
[RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for [RFC8941bis]
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021, Nottingham, M. and P.-H. Kamp, "Structured Field Values
<https://www.rfc-editor.org/info/rfc8941>. for HTTP", Work in Progress, Internet-Draft, draft-ietf-
httpbis-sfbis-05, January 23, 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
sfbis-05>.
[XMLHttpRequest] [XMLHttpRequest]
WhatWG, "XMLHttpRequest", <https://xhr.spec.whatwg.org/>. WhatWG, "XMLHttpRequest", <https://xhr.spec.whatwg.org/>.
10.3. Specifications Using This Syntax (at some point of time) 10.3. Specifications Using This Syntax (at some point of time)
[CLEARSITE] [CLEARSITE]
West, M., "Clear Site Data", W3C Working Draft WD-clear- West, M., "Clear Site Data", W3C Working Draft WD-clear-
site-data-20171130, November 30, 2017, site-data-20171130, November 30, 2017,
<https://www.w3.org/TR/2017/WD-clear-site-data-20171130/>. <https://www.w3.org/TR/2017/WD-clear-site-data-20171130/>.
skipping to change at page 10, line 38 skipping to change at page 10, line 41
<https://w3c.github.io/webappsec-feature-policy/>. <https://w3c.github.io/webappsec-feature-policy/>.
[REPORTING] [REPORTING]
Creager, D., Grigorik, I., Meyer, P., and M. West, Creager, D., Grigorik, I., Meyer, P., and M. West,
"Reporting API", W3C Working Draft WD-reporting- "Reporting API", W3C Working Draft WD-reporting-
1-20180925, September 25, 2018, 1-20180925, September 25, 2018,
<https://www.w3.org/TR/2018/WD-reporting-1-20180925/>. <https://www.w3.org/TR/2018/WD-reporting-1-20180925/>.
Latest version available at Latest version available at
<https://www.w3.org/TR/reporting-1/>. <https://www.w3.org/TR/reporting-1/>.
Appendix A. Comparison with Structured Fields [UNICHARS] Bray, T. and P. E. Hoffman, "Unicode Character Repertoire
Subsets", Work in Progress, Internet-Draft, draft-bray-
unichars-07, October 12, 2023,
<https://datatracker.ietf.org/doc/html/draft-bray-
unichars-07>.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
Appendix A. Comparison with Structured Fields
A.1. Base Types A.1. Base Types
+----------+----------------------------------+------------------+ +----------+------------------------------------+------------------+
| Type | in Structured Fields | in JSON-based | | Type | in Structured Fields | in JSON-based |
| | | Fields | | | | Fields |
+----------+----------------------------------+------------------+ +----------+------------------------------------+------------------+
| Integer | | Section 6 | | Integer | | Section 6 |
| Integer | (restricted to 15 digits) | | | Integer | (restricted to 15 digits) | |
+----------+ [RFC8941], Section 3.3.2 | [RFC8259], | +----------+ [RFC8941bis], Section 3.3.2 | [RFC8259], |
| Decimal | | Section 6 | | Decimal | | Section 6 |
| Decimal | (a fixed point decimal | | | Decimal | (a fixed point decimal restricted | |
| | restricted to 12 + 3 digits) | | | | to 12 + 3 digits) | |
+----------+ [RFC8941], Section 3.3.3 | [RFC8259], | +----------+ [RFC8941bis], Section 3.3.3 and | [RFC8259], |
| String | | Section 7 | | String | [RFC8941bis], Section 3.3.8 | Section 7 |
| String | (only ASCII supported, non-ASCII | | | String | Strings only support ASCII | JSON strings can |
| | requires using Byte Sequences) | | | | ([RFC0020]), but "Display Strings" | transport any |
+----------+ [RFC8941], Section 3.3.5 | not available | | | cover anything encodable as | Unicode code |
+----------+ | (usually mapped | | | [UTF-8] (that excludes surrogates | point, due to |
| Byte | | to strings using | | | (Section 2.2.1 of [UNICHARS])). | the "\uxxxx" |
| Sequence | | base64 encoding) | | | | escape notation. |
+----------+ [RFC8941], Section 3.3.6 | [RFC8259], | +----------+ [RFC8941bis], Section 3.3.4 | not available, |
| Boolean | | Section 3 | | Token | | but can be |
| +----------------------------------+------------------+ | | | mapped to |
+ + | strings |
| Byte | | usually mapped |
| Sequence | | to strings using |
+ + | base64 encoding |
+ Boolean + | Section 3 |
| Date | | usually mapped |
| | | to Strings or |
| | | Numbers |
| +------------------------------------+------------------+
Table 1 Table 1
Structured Fields provide more data types (such as "token" or "byte Structured Fields provide more data types (such as "token" or "byte
sequence"). Numbers are restricted, avoiding the JSON interop sequence"). Numbers are restricted, avoiding the JSON interop
problems described in Section 7.2. Strings are limited to ASCII, problems described in Section 7.2.
requiring the use of byte sequences should non-ASCII characters be
needed.
A.2. Structures A.2. Structures
Structured Fields define Lists ([RFC8941], Section 3.1), similar to Structured Fields define Lists ([RFC8941bis], Section 3.1), similar
JSON arrays ([RFC8259], Section 5), and Dictionaries ([RFC8941], to JSON arrays ([RFC8259], Section 5), and Dictionaries
Section 3.2), similar to JSON objects ([RFC8259], Section 4). ([RFC8941bis], Section 3.2), similar to JSON objects ([RFC8259],
Section 4).
In addition, most items in Structured Fields can be parametrized In addition, most items in Structured Fields can be parametrized
([RFC8941], Section 3.1.2), attaching a dictionary-like structure to ([RFC8941bis], Section 3.1.2), attaching a dictionary-like structure
the value. To emulate this in JSON based field, an additional to the value. To emulate this in JSON based field, an additional
nesting of objects would be needed. nesting of objects would be needed.
Finally, nesting of data structures is intentionally limited to two Finally, nesting of data structures is intentionally limited to two
levels (see Appendix A.1 of [RFC8941] for the motivation). levels (see Appendix A.1 of [RFC8941bis] for the motivation).
Appendix B. Use of JSON Field Value Encoding in the Wild Appendix B. Use of JSON Field Value Encoding in the Wild
This section is to be removed before publishing as an RFC. This section is to be removed before publishing as an RFC.
Since work started on this document, various specifications have Since work started on this document, various specifications have
adopted this format. At least one of these moved away after the HTTP adopted this format. At least one of these moved away after the HTTP
Working Group decided to focus on [RFC8941] (see thread starting at Working Group decided to focus on [RFC8941bis] (see thread starting
<https://lists.w3.org/Archives/Public/ietf-http- at <https://lists.w3.org/Archives/Public/ietf-http-
wg/2016OctDec/0505.html>). wg/2016OctDec/0505.html>).
The sections below summarize the current usage of this format. The sections below summarize the current usage of this format.
B.1. W3C Reporting API Specification B.1. W3C Reporting API Specification
Defined in W3C Working Draft "Reporting API" (Section 3.1 of Defined in W3C Working Draft "Reporting API" (Section 3.1 of
[REPORTING]). Still in use in latest working draft dated September [REPORTING]). Still in use in latest working draft dated September
2018. 2018.
skipping to change at page 12, line 22 skipping to change at page 12, line 42
Used in earlier versions of "Clear Site Data". The current version Used in earlier versions of "Clear Site Data". The current version
replaces the use of JSON with a custom syntax that happens to be replaces the use of JSON with a custom syntax that happens to be
somewhat compatible with an array of JSON strings (see Section 3.1 of somewhat compatible with an array of JSON strings (see Section 3.1 of
[CLEARSITE] and <https://lists.w3.org/Archives/Public/ietf-http- [CLEARSITE] and <https://lists.w3.org/Archives/Public/ietf-http-
wg/2017AprJun/0214.html> for feedback). wg/2017AprJun/0214.html> for feedback).
B.3. W3C Feature Policy Specification B.3. W3C Feature Policy Specification
Originally defined in W3C document "Feature Policy" ([FEATUREPOL]), Originally defined in W3C document "Feature Policy" ([FEATUREPOL]),
but switched to use of Structured Header Fields ([RFC8941]). but switched to use of Structured Header Fields ([RFC8941bis]).
Appendix C. Implementations Appendix C. Implementations
This section is to be removed before publishing as an RFC. This section is to be removed before publishing as an RFC.
See <https://github.com/reschke/json-fields> for a proof-of-concept See <https://github.com/reschke/json-fields> for a proof-of-concept
(in development). (in development).
Appendix D. Change Log Appendix D. Change Log
skipping to change at page 15, line 8 skipping to change at page 15, line 33
D.17. Since draft-reschke-http-jfv-13 D.17. Since draft-reschke-http-jfv-13
Update HTTP reference. Update HTTP reference.
Mention test implementation. Mention test implementation.
Clarify that Unicode unpaired surrogates or Noncharacters must not be Clarify that Unicode unpaired surrogates or Noncharacters must not be
sent. sent.
Rewrite text about [RFC8941], add appendix comparing both formats. Rewrite text about [RFC8941bis], add appendix comparing both formats.
And send/receive examples. And send/receive examples.
D.18. Since draft-reschke-http-jfv-14
Update HTTP reference.
Mention [RFC8941bis].
D.19. Since draft-reschke-http-jfv-15
Cite [RFC8941bis] (in WGLC) instead RFC 8941. Cite [UTF-8] and
[UNICHARS], and rework comparison chart for strings.
Acknowledgements Acknowledgements
Thanks go to the Hypertext Transfer Protocol Working Group Thanks go to the Hypertext Transfer Protocol Working Group
participants. participants.
Author's Address Author's Address
Julian F. Reschke Julian F. Reschke
greenbytes GmbH greenbytes GmbH
Hafenweg 16 Hafenweg 16
 End of changes. 26 change blocks. 
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