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Versions: 00 01 02 03 04 05 06 RFC 4644

NNTP Extensions Working Group                                 J. Vinocur
Internet Draft                                        Cornell University
Updates: 2970 (if approved)                                 K. Murchison
Expires: November 2005                                Oceana Matrix Ltd.
                                                                May 2005


                   NNTP Extension for Streaming Feeds
                    draft-ietf-nntpext-streaming-05


Status of this memo

     By submitting this Internet-Draft, each author represents that any
     applicable patent or other IPR claims of which he or she is aware
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Copyright Notice

     Copyright (C) The Internet Society (2005).

Abstract

     This memo defines an extension to the Network News Transport
     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.

     Section 1 of [NNTP-COMMON] summarizes some ad-hoc transport
     extensions currently used in the NNTP protocol.  This document



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     updates and formalizes the CHECK and TAKETHIS commands and
     deprecates the MODE STREAM command.

Table of Contents

     0. Changes from Previous Version ............................  2
     1. Introduction .............................................  3
        1.1. Conventions Used in this Document ...................  3
     2. The STREAMING Extension ..................................  3
        2.1. Advertising the STREAMING Extension .................  3
        2.2. Streaming Article Transfer ..........................  4
        2.3. MODE STREAM Command .................................  5
           2.3.1. Usage ..........................................  5
           2.3.2. Description ....................................  5
           2.3.3. Examples .......................................  6
        2.4. CHECK Command .......................................  6
           2.4.1. Usage ..........................................  6
           2.4.2. Description ....................................  6
           2.4.3. Examples .......................................  7
        2.5. TAKETHIS Command ....................................  7
           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 .................................. 10
        3.3. Responses ........................................... 10
        3.4. Capability entries .................................. 10
     4. Summary of Response Codes ................................ 10
     5. Security Considerations .................................. 11
     6. IANA Considerations ...................................... 11
     7. References ............................................... 12
        7.1. Normative References ................................ 12
        7.2. Informative References .............................. 12
     8. Authors' Addresses ....................................... 13
     9. Acknowledgments .......................................... 13
     10. Intellectual Property Rights ............................ 13
     11. Copyright ............................................... 14

0. Changes from Previous Version

     Changed:
     o  Updated to RFC 3978/3979 boilerplate.
     o  Uses new ABNF tokens from [NNTP].
     o  Uses new "multi-line data block" term from [NNTP].
     o  POST has its own capability.

     Clarified:



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     o  Section 3: This document extends the ABNF in [NNTP], and the
        [NNTP] ABNF must be imported first before validating the
        STREAMING ABNF (based on recommendations of AD regarding
        IMAPEXT I-Ds).

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 alternative method of peer-to-peer
     article transfer described in this document permits a more
     consistent use of network bandwidth.

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].

     This document assumes you are familiar 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. 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.  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 MODE READER, with the same semantics.




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     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] .

2.2. 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 (unlike IHAVE) 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.



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     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.

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 which 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.  A
     server MUST NOT require that the MODE STREAM command be issued by
     the client before accepting the CHECK or TAKETHIS commands.





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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:

        [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
     however, that the responses to CHECK are advisory; the server MUST
     NOT rely on the client to behave as requested by these responses.





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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>

     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



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     the server as a multi-line data block (see Section 3.1.1 of
     [NNTP]).  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
     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 such problems 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 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 be able immediately to
     determine whether or not 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



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        [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]
        [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.




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     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.

     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 every new response code defined in
     this document, whether it is multi-line, which commands can



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     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.

     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.




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     o  The extension defines three new commands, MODE STREAM, CHECK,
        and TAKETHIS, whose behavior, arguments, and responses are
        defined in Sections 2.2, 2.3, and 2.4 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.

     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 command 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  Author, Change Controller, and Contact for Further Information:
        Author of this document.

7. References

7.1. 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", BCP 14, RFC 2119, March 1997.

     [NNTP] Feather, C., "Network News Transport Protocol",
     draft-ietf-nntpext-base-*.txt, Work in Progress.

7.2. Informative References

     [NNTP-COMMON] Barber, S., "Common NNTP Extensions", RFC 2980,
     October 2000.





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8. Authors' Addresses

     Jeffrey M. Vinocur
     Department of Computer Science
     Upson Hall
     Cornell University
     Ithaca, NY  14853

     EMail: vinocur@cs.cornell.edu


     Kenneth Murchison
     Oceana Matrix Ltd.
     21 Princeton Place
     Orchard Park, NY 14127 USA

     Email: ken@oceana.com

9. Acknowledgments

     This document is based heavily on the relevant sections of RFC 2980
     [NNTP-COMMON], by Stan Barber.

     Special acknowledgment also goes to Russ Allbery, Clive Feather,
     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.

10. Intellectual Property Rights

     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 in BCP 78 and BCP 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
     at http://www.ietf.org/ipr.

     The IETF invites any interested party to bring to its attention any
     copyrights, patents or patent applications, or other proprietary



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     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.

11. Copyright

     Copyright (C) The Internet Society (2005).

     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.

     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.































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