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Network Working Group                                         J. VinocurRequest for Comments: 4644                            Cornell UniversityUpdates:2980                                               K. MurchisonCategory: Standards Track                     Carnegie Mellon University                                                            October 2006Network News Transfer Protocol (NNTP) Extension for Streaming FeedsStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   This memo defines an extension to the Network News Transfer Protocol   (NNTP) to provide asynchronous (otherwise known as "streaming")   transfer of articles.  This allows servers to transfer articles to   other servers with much greater efficiency.   This document updates and formalizes the CHECK and TAKETHIS commands   specified inRFC 2980 and deprecates the MODE STREAM command.Table of Contents1. Introduction ....................................................21.1. Conventions Used in this Document ..........................22. The STREAMING Extension .........................................32.1. Streaming Article Transfer .................................32.2. Advertising the STREAMING Extension ........................42.3. MODE STREAM Command ........................................52.3.1. Usage ...............................................52.3.2. Description .........................................52.3.3. Examples ............................................52.4. CHECK Command ..............................................62.4.1. Usage ...............................................62.4.2. Description .........................................62.4.3. Examples ............................................62.5. TAKETHIS Command ...........................................7Vinocur & Murchison         Standards Track                     [Page 1]

RFC 4644           NNTP Extension for Streaming Feeds       October 20062.5.1. Usage ...............................................72.5.2. Description .........................................72.5.3. Examples ............................................83. Augmented BNF Syntax for the STREAMING Extension ................93.1. Commands ...................................................93.2. Command Datastream .........................................93.3. Responses .................................................103.4. Capability Entries ........................................104. Summary of Response Codes ......................................105. Security Considerations ........................................116. IANA Considerations ............................................117. Acknowledgements ...............................................128. References .....................................................128.1. Normative References ......................................128.2. Informative References ....................................121.  Introduction   According to the NNTP specification [NNTP], a peer uses the IHAVE   command to query whether a server wants a particular article.   Because the IHAVE command cannot be pipelined, the need to stop and   wait for the remote end's response greatly restricts the throughput   that can be achieved.   The ad-hoc CHECK and TAKETHIS commands, originally documented in   [NNTP-COMMON], provide an alternative method of peer-to-peer article   transfer that permits a more effective use of network bandwidth.  Due   to their proven usefulness and wide deployment, they are formalized   in this specification.   The ad-hoc MODE STREAM command, also documented in [NNTP-COMMON], is   deprecated by this specification, but due to its ubiquity is   documented here for backwards compatibility.1.1.  Conventions Used in this Document   The notational conventions used in this document are the same as   those in [NNTP] and any term not defined in this document has the   same meaning as in that one.   The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT",   "MAY", and "OPTIONAL" in this document are to be interpreted as   described in "Key words for use in RFCs to Indicate Requirement   Levels" [KEYWORDS].Vinocur & Murchison         Standards Track                     [Page 2]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006   This document assumes you familiarity with NNTP [NNTP].  In general,   the connections described below are from one peer to another, but we   will continue to use "client" to mean the initiator of the NNTP   connection, and "server" to mean the other endpoint.   In the examples, commands from the client are indicated with [C], and   responses from the server are indicated with [S].2.  The STREAMING Extension   This extension provides three new commands: MODE STREAM, CHECK, and   TAKETHIS.  The capability label for this extension is STREAMING.2.1.  Streaming Article Transfer   The STREAMING extension provides the same functionality as the IHAVE   command ([NNTP]section 6.3.2) but splits the query and transfer   functionality into the CHECK and TAKETHIS commands respectively.   This allows the CHECK and TAKETHIS commands to be pipelined ([NNTP]section 3.5) and provides for "streaming" article transfer.   A streaming client will often pipeline many CHECK commands and use   the responses to construct a list of articles to be sent by a   pipelined sequence of TAKETHIS commands, thus increasing the fraction   of time spent transferring articles.  The CHECK and TAKETHIS commands   utilize distinct response codes so that these commands can be   intermingled in a pipeline and the response to any single command can   be definitively identified by the client.   The client MAY send articles via TAKETHIS without first querying the   server with CHECK.  The client SHOULD NOT send every article in this   fashion unless explicitly configured to do so by the site   administrator based on out-of-band information.  However, the client   MAY use an adaptive strategy where it initially sends CHECK commands   for all articles, but switches to using TAKETHIS without CHECK if   most articles are being accepted (over 95% acceptance might be a   reasonable metric in some configurations).  If the client uses such a   strategy, it SHOULD also switch back to using CHECK on all articles   if the acceptance rate ever falls much below the threshold.Vinocur & Murchison         Standards Track                     [Page 3]

RFC 4644           NNTP Extension for Streaming Feeds       October 20062.2.  Advertising the STREAMING Extension   A server supporting the streaming commands described in this document   will advertise the "STREAMING" capability label in response to the   CAPABILITIES command ([NNTP]section 5.2).  The server MUST continue   to advertise this capability after a client has issued the MODE   STREAM command.  This capability MAY be advertised both before and   after any use of the MODE READER command ([NNTP]section 5.3), with   the same semantics.   Example of a client using CAPABILITIES and MODE STREAM on a mode-   switching server:      [C] CAPABILITIES      [S] 101 Capability list:      [S] VERSION 2      [S] MODE-READER      [S] IHAVE      [S] LIST ACTIVE      [S] STREAMING      [S] .      [C] MODE STREAM      [S] 203 Streaming permitted      [C] CAPABILITIES      [S] 101 Capability list:      [S] VERSION 2      [S] MODE-READER      [S] IHAVE      [S] LIST ACTIVE      [S] STREAMING      [S] .      [C] MODE READER      [S] 200 Posting allowed      [C] CAPABILITIES      [S] 101 Capability list:      [S] VERSION 2      [S] READER      [S] POST      [S] LIST ACTIVE NEWSGROUPS HEADERS      [S] HDR      [S] .Vinocur & Murchison         Standards Track                     [Page 4]

RFC 4644           NNTP Extension for Streaming Feeds       October 20062.3.  MODE STREAM Command   Historically this command was used by a client to discover if a   server supported the CHECK and TAKETHIS commands.  This command is   deprecated in favor of the CAPABILITIES discovery command and is only   provided here for compatibility with legacy implementations   [NNTP-COMMON] of these transport commands.   New clients SHOULD use the CAPABILITIES command to check a server for   support of the STREAMING extension but MAY use the MODE STREAM   command for backwards compatibility with legacy servers that don't   support the CAPABILITIES discovery command.  Servers MUST accept the   MODE STREAM command for backwards compatibility with legacy clients   that don't use the CAPABILITIES discovery command.   NOTE: This command may be removed from a future version of this   specification, therefore clients are urged to transition to the   CAPABILITIES command wherever possible.2.3.1.  Usage   Syntax      MODE STREAM   Responses      203   Streaming permitted2.3.2.  Description   If a server supports this extension, it MUST return a 203 response to   the MODE STREAM command (or 501 if an argument is given).  The MODE   STREAM command MUST NOT affect the server state in any way (that is,   it is not a mode change despite the name), therefore this command MAY   be pipelined.  A server MUST NOT require that the MODE STREAM command   be issued by the client before accepting the CHECK or TAKETHIS   commands.2.3.3.  Examples   Example of a client checking the ability to stream articles on a   server which does not support this extension:      [C] MODE STREAM      [S] 501 Unknown MODE variant   Example of a client checking the ability to stream articles on a   server which supports this extension:Vinocur & Murchison         Standards Track                     [Page 5]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006      [C] MODE STREAM      [S] 203 Streaming permitted2.4.  CHECK Command2.4.1.  Usage   Syntax      CHECK message-id   Responses      238 message-id   Send article to be transferred      431 message-id   Transfer not possible; try again later      438 message-id   Article not wanted   Parameters      message-id = Article message-id   The first parameter of the 238, 431, and 438 responses MUST be the   message-id provided by the client as the parameter to CHECK.2.4.2.  Description   The CHECK command informs the server that the client has an article   with the specified message-id.  If the server desires a copy of that   article, a 238 response MUST be returned, indicating that the client   may send the article using the TAKETHIS command.  If the server does   not want the article (if, for example, the server already has a copy   of it), a 438 response MUST be returned, indicating that the article   is not wanted.  Finally, if the article isn't wanted immediately but   the client should retry later if possible (if, for example, another   client has offered to send the same article to the server), a 431   response MUST be returned.   NOTE: The responses to CHECK are advisory; the server MUST NOT rely   on the client to behave as requested by these responses.2.4.3.  Examples   Example of a client checking whether the server would like a set of   articles and getting a mixture of responses:      [C] CHECK <i.am.an.article.you.will.want@example.com>      [S] 238 <i.am.an.article.you.will.want@example.com>      [C] CHECK <i.am.an.article.you.have@example.com>      [S] 438 <i.am.an.article.you.have@example.com>      [C] CHECK <i.am.an.article.you.defer@example.com>      [S] 431 <i.am.an.article.you.defer@example.com>Vinocur & Murchison         Standards Track                     [Page 6]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006   Example of pipelining the CHECK commands in the previous example:      [C] CHECK <i.am.an.article.you.will.want@example.com>      [C] CHECK <i.am.an.article.you.have@example.com>      [C] CHECK <i.am.an.article.you.defer@example.com>      [S] 238 <i.am.an.article.you.will.want@example.com>      [S] 438 <i.am.an.article.you.have@example.com>      [S] 431 <i.am.an.article.you.defer@example.com>2.5.  TAKETHIS Command2.5.1.  Usage   A client MUST NOT use this command unless the server advertises the   STREAMING capability or returns a 203 response to the MODE STREAM   command.   Syntax      TAKETHIS message-id   Responses      239 message-id   Article transferred OK      439 message-id   Transfer rejected; do not retry   Parameters      message-id = Article message-id   The first parameter of the 239 and 439 responses MUST be the   message-id provided by the client as the parameter to TAKETHIS.2.5.2.  Description   The TAKETHIS command is used to send an article with the specified   message-id to the server.  The article is sent immediately following   the CRLF at the end of the TAKETHIS command line.  The client MUST   send the entire article, including headers and body, to the server as   a multi-line data block ([NNTP]section 3.1.1).  Thus, a single dot   (".") on a line indicates the end of the text, and lines starting   with a dot in the original text have that dot doubled during   transmission.  The server MUST return either a 239 response,   indicating that the article was successfully transferred, or a 439   response, indicating that the article was rejected.  If the server   encounters a temporary error that prevents it from processing the   article but does not want to reject the article, it MUST reply with a   400 response to the client and close the connection.   This function differs from the POST command in that it is intended   for use in transferring already-posted articles between hosts.  ItVinocur & Murchison         Standards Track                     [Page 7]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006   SHOULD NOT be used when the client is a personal news-reading   program, since use of this command indicates that the article has   already been posted at another site and is simply being forwarded   from another host.  However, despite this, the server MAY elect not   to post or forward the article if, after further examination of the   article, it deems it inappropriate to do so.  Reasons for such   subsequent rejection of an article may include problems such as   inappropriate newsgroups or distributions, disk space limitations,   article lengths, garbled headers, and the like.  These are typically   restrictions enforced by the server host's news software and not   necessarily by the NNTP server itself.   The client SHOULD NOT assume that the article has been successfully   transferred unless it receives an affirmative response from the   server.  A lack of response (such as a dropped network connection or   a network timeout) or a 400 response SHOULD be treated as a temporary   failure and cause the transfer to be tried again later if possible.   Because some news server software may not immediately be able to   determine whether an article is suitable for posting or forwarding,   an NNTP server MAY acknowledge the successful transfer of the article   (with a 239 response) but later silently discard it.2.5.3.  Examples   Example of streaming two articles to another site (the first article   is accepted and the second is rejected):      [C] TAKETHIS <i.am.an.article.you.will.want@example.com>      [C] Path: pathost!demo!somewhere!not-for-mail      [C] From: "Demo User" <nobody@example.com>      [C] Newsgroups: misc.test      [C] Subject: I am just a test article      [C] Date: 6 Oct 1998 04:38:40 -0500      [C] Organization: An Example Com, San Jose, CA      [C] Message-ID: <i.am.an.article.you.will.want@example.com>      [C]      [C] This is just a test article.      [C] .      [C] TAKETHIS <i.am.an.article.you.have@example.com>      [C] Path: pathost!demo!somewhere!not-for-mail      [C] From: "Demo User" <nobody@example.com>      [C] Newsgroups: misc.test      [C] Subject: I am just a test article      [C] Date: 6 Oct 1998 04:38:40 -0500      [C] Organization: An Example Com, San Jose, CA      [C] Message-ID: <i.am.an.article.you.have@example.com>      [C]Vinocur & Murchison         Standards Track                     [Page 8]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006      [C] This is just a test article.      [C] .      [S] 239 <i.am.an.article.you.will.want@example.com>      [S] 439 <i.am.an.article.you.have@example.com>   Example of sending an article to a site where the transfer fails:      [C] TAKETHIS <i.am.an.article.you.will.want@example.com>      [C] Path: pathost!demo!somewhere!not-for-mail      [C] From: "Demo User" <nobody@example.com>      [C] Newsgroups: misc.test      [C] Subject: I am just a test article      [C] Date: 6 Oct 1998 04:38:40 -0500      [C] Organization: An Example Com, San Jose, CA      [C] Message-ID: <i.am.an.article.you.will.want@example.com>      [C]      [C] This is just a test article.      [C] .      [S] 400 Service temporarily unavailable      [Server closes connection.]3.  Augmented BNF Syntax for the STREAMING Extension   This section describes the formal syntax of the STREAMING extension   using ABNF [ABNF].  It extends the syntax in section 9 of [NNTP], and   non-terminals not defined in this document are defined there.  The   [NNTP] ABNF should be imported first before attempting to validate   these rules.3.1.  Commands   This syntax extends the non-terminal "command", which represents an   NNTP command.   command =/ check-command /        mode-stream-command /        takethis-command   check-command       = "CHECK" WS message-id   mode-stream-command = "MODE" WS "STREAM"   takethis-command    = "TAKETHIS" WS message-id3.2.  Command Datastream   This syntax extends the non-terminal "command-datastream", which   represents the further material sent by the client in the case of   streaming commands.Vinocur & Murchison         Standards Track                     [Page 9]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006   command-datastream =/ takethis-datastream   takethis-datastream = encoded-article3.3.  Responses   This syntax extends the non-terminal "initial-response-content",   which represents an initial response line sent by the server.   initial-response-content =/ response-238-content /        response-239-content /        response-431-content /        response-438-content /        response-439-content   response-238-content = "238" SP message-id   response-239-content = "239" SP message-id   response-431-content = "431" SP message-id   response-438-content = "438" SP message-id   response-439-content = "439" SP message-id3.4.  Capability Entries   This syntax extends the non-terminal "capability-entry", which   represents a capability that may be advertised by the server.   capability-entry =/ streaming-capability   streaming-capability = "STREAMING"4.  Summary of Response Codes   This section contains a list of each new response code defined in   this document and indicates whether it is multi-line, which commands   can generate it, what arguments it has, and what its meaning is.   Response code 203      Generated by: MODE STREAM      Meaning: streaming permitted.   Response code 238      Generated by: CHECK      1 argument: message-id      Meaning: send article to be transferred.Vinocur & Murchison         Standards Track                    [Page 10]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006   Response code 239      Generated by: TAKETHIS      1 argument: message-id      Meaning: article transferred OK.   Response code 431      Generated by: CHECK      1 argument: message-id      Meaning: transfer not possible; try again later.   Response code 438      Generated by: CHECK      1 argument: message-id      Meaning: article not wanted.   Response code 439      Generated by: TAKETHIS      1 argument: message-id      Meaning: transfer rejected; do not retry.5.  Security Considerations   No new security considerations are introduced by this extension,   beyond those already described in the core specification [NNTP].6.  IANA Considerations   This section gives a formal definition of the STREAMING extension as   required by Section 3.3.3 of [NNTP] for the IANA registry.   o  The STREAMING extension provides for streaming transfer of      articles.   o  The capability label for this extension is "STREAMING".   o  The capability label has no arguments.   o  The extension defines three new commands, MODE STREAM, CHECK, and      TAKETHIS, whose behavior, arguments, and responses are defined in      Sections2.3,2.4, and2.5 respectively.   o  The extension does not associate any new responses with pre-      existing NNTP commands.   o  The extension does not affect the behavior of a server or client      other than via the new commands.Vinocur & Murchison         Standards Track                    [Page 11]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006   o  The extension does not affect the maximum length of commands or      initial response lines.   o  The extension does not alter pipelining, and the MODE STREAM,      CHECK, and TAKETHIS commands can be pipelined.   o  Use of this extension does not alter the capabilities list.   o  The extension does not cause any pre-existing command to produce a      401, 480, or 483 response.   o  Use of the MODE READER command on a mode-switching server may      disable this extension.   o  Published Specification: This document.   o  Contact for Further Information: Authors of this document.   o  Change Controller: IESG <iesg@ietf.org>.7.  Acknowledgements   This document is based heavily on the relevant sections ofRFC 2980   [NNTP-COMMON], by Stan Barber.   Special acknowledgement also goes to Russ Allbery, Clive Feather,   Andrew Gierth, and others who commented privately on intermediate   revisions of this document, as well as the members of the IETF NNTP   Working Group for continual (yet sporadic) insight in discussion.8.  References8.1.  Normative References   [ABNF]        Crocker, D., Ed. and P. Overell, "Augmented BNF for                 Syntax Specifications: ABNF",RFC 4234, October 2005.   [KEYWORDS]    Bradner, S., "Key words for use in RFCs to Indicate                 Requirement Levels",BCP 14,RFC 2119, March 1997.   [NNTP]        Feather, C., "Network News Transfer Protocol (NNTP)",RFC 3977, October 2006.8.2.  Informative References   [NNTP-COMMON] Barber, S., "Common NNTP Extensions",RFC 2980, October                 2000.Vinocur & Murchison         Standards Track                    [Page 12]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006Authors' Addresses   Jeffrey M. Vinocur   Department of Computer Science   Upson Hall   Cornell University   Ithaca, NY  14853   EMail: vinocur@cs.cornell.edu   Kenneth Murchison   Carnegie Mellon University   5000 Forbes Avenue   Cyert Hall 285   Pittsburgh, PA  15213 USA   EMail: murch@andrew.cmu.eduVinocur & Murchison         Standards Track                    [Page 13]

RFC 4644           NNTP Extension for Streaming Feeds       October 2006Full Copyright StatementCopyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Vinocur & Murchison         Standards Track                    [Page 14]