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rfc:rfc4644

Network Working Group J. Vinocur Request for Comments: 4644 Cornell University Updates: 2980 K. Murchison Category: Standards Track Carnegie Mellon University

                                                          October 2006
Network News Transfer Protocol (NNTP) Extension for Streaming Feeds

Status 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 in RFC 2980 and deprecates the MODE STREAM command.

Table of Contents

 1. Introduction ....................................................2
    1.1. Conventions Used in this Document ..........................2
 2. The STREAMING Extension .........................................3
    2.1. Streaming Article Transfer .................................3
    2.2. Advertising the STREAMING Extension ........................4
    2.3. MODE STREAM Command ........................................5
         2.3.1. Usage ...............................................5
         2.3.2. Description .........................................5
         2.3.3. Examples ............................................5
    2.4. CHECK Command ..............................................6
         2.4.1. Usage ...............................................6
         2.4.2. Description .........................................6
         2.4.3. Examples ............................................6
    2.5. TAKETHIS Command ...........................................7

Vinocur & Murchison Standards Track [Page 1] RFC 4644 NNTP Extension for Streaming Feeds October 2006

         2.5.1. Usage ...............................................7
         2.5.2. Description .........................................7
         2.5.3. Examples ............................................8
 3. Augmented BNF Syntax for the STREAMING Extension ................9
    3.1. Commands ...................................................9
    3.2. Command Datastream .........................................9
    3.3. Responses .................................................10
    3.4. Capability Entries ........................................10
 4. Summary of Response Codes ......................................10
 5. Security Considerations ........................................11
 6. IANA Considerations ............................................11
 7. Acknowledgements ...............................................12
 8. References .....................................................12
    8.1. Normative References ......................................12
    8.2. Informative References ....................................12

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
 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 2006

2.2. 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 2006

2.3. 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 permitted

2.3.2. 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 permitted

2.4. CHECK Command

2.4.1. 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 Command

2.5.1. 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.  It

Vinocur & 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-id

3.2. 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-article

3.3. 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-id

3.4. 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
    Sections 2.3, 2.4, and 2.5 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 of RFC 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. References

8.1. 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 2006

Authors' 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.edu

Vinocur & Murchison Standards Track [Page 13] RFC 4644 NNTP Extension for Streaming Feeds October 2006

Full Copyright Statement

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 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Vinocur & Murchison Standards Track [Page 14]

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