Network Working Group J. Vinocur INTERNET DRAFT Cornell University Document: draft-ietf-nntpext-streaming-01.txt February 2004 NNTP Extension for Streaming Feeds Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.html. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This memo defines an extension to the Network News Transport Protocol [NNTP] to provide asynchronous transfer of articles. This allows servers to transfer articles to other servers with much greater efficiency. Table of Contents 0. Changes from Previous Version ............................ 2 1. Introduction ............................................. 2 1.1. Conventions Used in this Document ................... 3 2. Advertising Capabilities with the Extensions Mechanism ... 3 Vinocur Expires August 2004 [Page 1] Internet Draft NNTP Extension for Streaming Feeds February 2004 3. MODE STREAM Command ...................................... 4 3.1. Usage ............................................... 4 3.2. Description ......................................... 4 3.3. Examples ............................................ 4 4. CHECK Command ............................................ 4 4.1. Usage ............................................... 4 4.2. Description ......................................... 5 4.3. Examples ............................................ 5 5. TAKETHIS Command ......................................... 6 5.1. Usage ............................................... 6 5.2. Description ......................................... 6 5.3. Examples ............................................ 7 6. Augmented BNF Syntax for Streaming ....................... 7 7. IANA Considerations ...................................... 8 8. Security Considerations .................................. 8 9. Acknowledgements ......................................... 8 10. Normative References .................................... 8 11. Informative References .................................. 8 12. Author's Address ........................................ 8 0. Changes from Previous Version New: o Text needed to comply with extensions framework guidelines: - IANA Considerations section o Inclusion of STREAMING in LIST EXTENSIONS output before/after MODE READER o CHECK response codes are advisory; servers must handle client behavior not being what the server has requested Changed: o A freeform message may in fact be sent after the Message-ID in a CHECK or TAKETHIS response o No need to explicitly list 400 and 480 responses for these commands Clarified: o Behavior of LIST EXTENSIONS after MODE STREAM o Articles sent with TAKETHIS are in the same format as with IHAVE Other: o Assorted updates of phrasing and typographical varieties 1. 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 Vinocur Expires August 2004 [Page 2] Internet Draft NNTP Extension for Streaming Feeds February 2004 that can be achieved. The alternative method of server-to-server article transfer described in this document permits a more consistent use of network bandwidth. This document formalizes extensions previously described [NNTP- COMMON] in accordance with the NNTP extension mechanism [NNTP]. 1.1. Conventions Used in this Document 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]. This document assumes you are familiar with NNTP [NNTP]. In general, the connections described below are from one server to another (i.e., feeding articles to a peer), but we will continue to use "client" to mean the initiator of the NNTP connection, and "server" to mean the other endpoint. A variety of response codes are applicable to all NNTP commands (see section 3.2 of [NNTP]). Clients MUST be prepared for the commands defined in this document to return these generic response codes when appropriate, even if they are not explicitly mentioned below. In the examples, commands from the client are indicated with [C], and responses from the server are indicated with [S]. 2. Advertising Capabilities with the Extensions Mechanism The LIST EXTENSIONS command, documented in section 8 of [NNTP], provides a mechanism for clients to discover what extensions are available. A server supporting the streaming commands described in this document will advertise the "STREAMING" capability in response to the LIST EXTENSIONS command. The server MAY continue to advertise this capability after the client has issued the MODE STREAM command. A server MAY advertise this capability before or after (or both) the client has issued the MODE READER command. Example: [C] LIST EXTENSIONS [S] 202 Extensions supported: [S] HDR Vinocur Expires August 2004 [Page 3] Internet Draft NNTP Extension for Streaming Feeds February 2004 [S] STREAMING [S] . 3. MODE STREAM Command 3.1. Usage This command MUST NOT be pipelined. Syntax MODE STREAM Responses 203 Streaming permitted 500 Unknown command [1] 501 Unknown MODE option [1] 501 Command syntax error 502 Permission denied [1] Note the distinction in section 3.2.1 of [NNTP] between the responses for MODE being entirely unimplemented, and MODE being implemented but without the MODE STREAM variant. 3.2. Description A client issues the MODE STREAM command to indicate that it wishes to use the CHECK and TAKETHIS commands instead of, or in addition to, IHAVE. The client MUST NOT send any additional commands on the socket until after it has received the server response to the command; this command MUST NOT be pipelined as per section 3.2 of [NNTP]. 3.3. Examples Example of a client requesting the ability to stream articles from a server which does not support this extension: [C] MODE STREAM [S] 501 Unknown MODE variant Example of a client successfully requesting the ability to stream articles: [C] MODE STREAM [S] 203 Streaming permitted 4. CHECK Command 4.1. Usage Vinocur Expires August 2004 [Page 4] Internet Draft NNTP Extension for Streaming Feeds February 2004 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 The first parameter of the 238, 431, and 438 responses MUST be the message-id provided by the client as the parameter to CHECK. Servers MAY send additional text after the message-id. Parameters message-id = Article message-id 4.2. Description A client issues the CHECK command to discover if the server would like for the article with the specified message-id to be sent using the TAKETHIS command. This command MAY be pipelined; in particular, clients often issue many CHECK commands in sequence and use the responses to construct a list of articles to be sent with the TAKETHIS command. The use of the CHECK command for streaming is OPTIONAL, as described in section 5.2 below. The intent of the 238 response is that the client will send the article with TAKETHIS reasonably soon, the intent of the 431 response is that the client will repeat the CHECK command at some future time, and the intent of the 438 response is that the client will not send the article with TAKETHIS. However, the responses to CHECK are advisory; the server MUST NOT rely on the client to behave as requested by these responses. 4.3. Examples Example of a client checking whether the server would like a number of articles and getting a mixture of responses: [C] CHECK [S] 238 [C] CHECK [S] 438 [C] CHECK [S] 431 The same example, but demonstrating streaming: [C] CHECK Vinocur Expires August 2004 [Page 5] Internet Draft NNTP Extension for Streaming Feeds February 2004 [C] CHECK [C] CHECK [S] 238 [S] 438 [S] 431 5. TAKETHIS Command 5.1. Usage Syntax TAKETHIS message-id Responses 239 message-id Article transferred OK 439 message-id Transfer failed The first parameter of the 239 and 439 responses MUST be the message-id provided by the client as the parameter to CHECK. Servers MAY send additional text after the message-id. Parameters message-id = Article message-id 5.2. Description A client issues the TAKETHIS command to indicate that the article with the specified message-id will be sent immediately following the CRLF at the end of the TAKETHIS command. The client MUST send the entire article, including headers and body, in the format described for IHAVE (see section 6.3.2 of [NNTP]). This command MAY be pipelined; in particular, clients often issue many TAKETHIS command in sequence to reduce the time spent not transferring data. 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 may 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 Expires August 2004 [Page 6] Internet Draft NNTP Extension for Streaming Feeds February 2004 5.3. Examples Example of successfully sending an article to another site: [C] TAKETHIS [C] Path: pathost!demo!somewhere!not-for-mail [C] From: "Demo User" [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: [C] [C] This is just a test article. [C] . [S] 239 Example of sending an article to a site that already has it, or does not want it, or where it does not transfer correctly: [C] TAKETHIS [C] Path: pathost!demo!somewhere!not-for-mail [C] From: "Demo User" [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: [C] [C] This is just a test article. [C] . [S] 439 6. Augmented BNF Syntax for Streaming This amends the formal syntax for NNTP [NNTP] to add the commands described above. The syntax is defined using ABNF [ABNF], including the core rules from section 6 of [ABNF]. command /= mode-stream-command / check-command / takethis-command mode-stream-command = "MODE" WS "STREAM check-command = "CHECK" WS message-id takethis-command = "TAKETHIS" WS message-id ; WS and message-id are defined in section 13 of [NNTP] Vinocur Expires August 2004 [Page 7] Internet Draft NNTP Extension for Streaming Feeds February 2004 7. IANA Considerations This document defines an NNTP extension for "Streaming feeds" with extension-label STREAMING. XXX: Any better ideas for description text above? This extension includes the three new NNTP commands defined above: MODE STREAM, CHECK, and TAKETHIS. It does not affect any pre- existing NNTP commands or their response codes, and does not require any change in maximum command length. 8. Security Considerations No new security considerations are introduced by this extension, beyond those already described in the core specification [NNTP]. 9. Acknowledgements This document is based heavily on the relevant sections of RFC 2980 [NNTP-COMMON], by Stan Barber. 10. Normative References [ABNF] Crocker, D., Overell, P., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997. [NNTP] Feather, C., "Network News Transport Protocol" (draft-ietf-nntpext-base-18.txt). 11. Informative References [NNTP-COMMON] Barber, S., "Common NNTP Extensions", RFC 2980, Academ Consulting Services, October 2000. 12. Author's Address Jeffrey M. Vinocur Department of Computer Science Upson Hall Cornell University Ithaca, NY 14853 EMail: vinocur@cs.cornell.edu Vinocur Expires August 2004 [Page 8] Internet Draft NNTP Extension for Streaming Feeds February 2004 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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