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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: April 2005                                   Oceana Matrix Ltd.
                                                            October 2004


                   NNTP Extension for Streaming Feeds
                    draft-ietf-nntpext-streaming-02


Status of this memo

     By submitting this Internet-Draft, I certify that any applicable
     patent or other IPR claims of which I am aware have been disclosed,
     and any of which I become aware will be disclosed, in accordance
     with RFC 3668.

     Internet-Drafts are working documents of the Internet Engineering
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     Internet-Drafts are draft documents valid for a maximum of six
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     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
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Copyright Notice

     Copyright (C) The Internet Society (2004).

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.

     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 ..................................  4
        2.1. Advertising the STREAMING Extension .................  4
        2.2. Asynschronous 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. LIST EXTENSIONS responses ........................... 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. Author's Address ......................................... 12
     9. Acknowledgements ......................................... 12
     10. Intellectual Property Rights ............................ 13
     11. Copyright ............................................... 13

0. Changes from Previous Version

     New:
     o  Added Ken as co-author.
     o  Added 432 response code as a temporary failure for TAKETHIS (with
        example).
     o  "Summary of Response Codes" section.
     o  "Intellectual Property Rights" section (as required).

     Changed:
     o  Updated boilerplate to conform to new requirements.



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     o  Changed layout to be more consistent with the base, AUTHINFO, and
        STARTTLS documents.
     o  Updated Abstract, referencing NNTP-COMMON.
     o  Split pipelining discussion into separate section.
     o  Updated CHECK and TAKETHIS description, utilizing text from
        [NNTP].
     o  Merged two TAKETHIS examples to illustrate pipelining.
     o  Updated IANA section to be more complete.
     o  Updated acknowledgments.

     Clarified:
     o  Behavior of LIST EXTENSIONS after MODE STREAM (with extended
        example).
     o  MODE STREAM is deprecated and only used for compatibility with
        legacy implementations.
     o  439 response code is a rejection (permanent failure).

     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
     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.

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 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.

     In the examples, commands from the client are indicated with [C],



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     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 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" extension label in response
     to the LIST EXTENSIONS command.  The server MUST continue to
     advertise this extension label after a client has issued the MODE
     STREAM command.  This extension label MAY be advertised both before
     and after any use of MODE READER, with the same semantics.

     Example:
        [C] LIST EXTENSIONS
        [S] 202 Extensions supported:
        [S] NNTPv2
        [S] STREAMING
        [S] .
        [C] MODE STREAM
        [S] 203 Streaming permitted
        [C] LIST EXTENSIONS
        [S] 202 Extensions supported:
        [S] NNTPv2
        [S] STREAMING
        [S] .
        [C] MODE READER
        [S] 200 Posting allowed
        [C] LIST EXTENSIONS
        [S] 202 Extensions supported:
        [S] NNTPv2
        [S] HDR
        [S] .

2.2. Asynschronous 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 asynschronous 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



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     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 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

     This command is deprecated and is only documented for compatibility
     with legacy implementations of the STREAMING extension.  New client
     and server implementations are not required to support this command
     but they are encouraged to do so.

2.3.1. Usage

     This command MUST NOT be pipelined.

     Syntax
        MODE STREAM

     Responses
        203   Streaming permitted

2.3.2. 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.  If the server supports the CHECK and TAKETHIS commands
     a 203 response MUST be returned.

     If a server advertises the STREAMING extension label in the LIST
     EXTENSIONS response, the MODE STREAM command is not required and a
     client SHOULD NOT issue it.  If a legacy server does not support
     the LIST EXTENSIONS command or does not advertise the NNTPv2
     extension label, a client SHOULD issue the MODE STREAM command
     prior to using the CHECK or TAKETHIS commands.



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     A server MUST NOT require that the MODE STREAM command be issued by
     the client before accepting the CHECK or TAKETHIS commands.  A
     server SHOULD accept the MODE STREAM command for compatibility with
     legacy clients which don't use the LIST EXTENSIONS discovery
     mechanism.

2.3.3. 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

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 is in the process of
     sending the same article to the server), a 431 response MUST be



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     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.

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

     Syntax
        TAKETHIS message-id

     Responses
        239 message-id   Article transferred OK
        432 message-id   Transfer failed; try again later
        439 message-id   Transfer rejected; do not retry

     Parameters
        message-id = Article message-id

     The first parameter of the 239, 432, and 439 responses MUST be the
     message-id provided by the client as the parameter to TAKETHIS.

2.5.2. Description

     The TAKETHIS command informs the server that the client has an
     article with the specified message-id that will be sent immediately
     following the CRLF at the end of the TAKETHIS command.  The client



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     MUST send the entire article, including headers and body, in the
     format defined in Section 3.1 of [NNTP] for multi-line responses
     (except that there is no initial line containing a response code).
     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,
     a 432 response, indicating that the transfer failed but should be
     tried again later, or a 439 response, indicating that the article
     was rejected.

     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, disc 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) SHOULD be treated the same as a 432 response.

     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 sending two pipelined 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>



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        [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] 432 <i.am.an.article.you.will.want@example.com>

3. Augmented BNF Syntax for the STREAMING Extension

     This section describes the syntax of the STREAMING extension.  It
     extends the syntax in [NNTP], and non-terminals not defined in this
     document are defined there.

3.1. Commands

     This syntax extends the non-terminal "command", which represents an
     NNTP command.

     command =/ mode-stream-command /
                check-command /
                takethis-command

     mode-stream-command = "MODE" WS "STREAM



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     check-command       = "CHECK" WS message-id
     takethis-command    = "TAKETHIS" WS message-id

3.2. LIST EXTENSIONS responses

     This syntax defines the specific LIST EXTENSIONS responses for the
     STREAMING extension.

     extension-descriptor =/ streaming-extension
     streaming-extension = %x53.54.52.45.41.4D.49.4E,47  ; "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
     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
        Meaning: send article to be transferred.

     Response code 239
        Generated by: TAKETHIS
        Meaning: article transferred OK.

     Response code 431
        Generated by: CHECK
        Meaning: transfer not possible; try again later.

     Response code 432
        Generated by: TAKETHIS
        Meaning: transfer failed; try again later.

     Response code 438
        Generated by: CHECK
        Meaning: article not wanted.

     Response code 439
        Generated by: TAKETHIS
        Meaning: transfer rejected; do not retry.







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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 8 of [NNTP] for the IANA registry.

     o  The STREAMING extension provides for asynchronous transfer of
        articles.

     o  The extension-label is "STREAMING".

     o  The extension-label has no arguments.

     o  The extension defines three new commands, MODE STREAM, CHECK,
        and TAKETHIS, whose behaviour, 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 behaviour of a server or
        client other than via the new commands.

     o  The extension does not affect the maximum length of commands and
        initial response lines.

     o  The extension does not alter pipelining, and the CHECK and
        TAKETHIS command can be pipelined, but the MODE STREAM command
        cannot be pipelined.

     o  Use of this extension does not alter the output from LIST
        EXTENSIONS.

     o  The extension does not cause any pre-existing command to produce
        a 401, 480, or 483 response.

     o  A server MAY choose to disallow the MODE STREAM, CHECK, TAKETHIS
        commands after the MODE READER command.

     o  Published Specification: This document.

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




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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", 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,
     Academ Consulting Services, October 2000.

8. Author's Address

     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. Acknowledgements

     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.






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10. Intellectual Property Rights

     The IETF takes no position regarding the validity or scope of any
     intellectual property 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; neither does it represent that it
     has made any effort to identify any such rights.  Information on
     the IETF's procedures with respect to rights in standards-track and
     standards-related documentation can be found in BCP-11.  Copies of
     claims of rights made available for publication 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 Secretariat.

     The IETF invites any interested party to bring to its attention any
     copyrights, patents or patent applications, or other proprietary
     rights which may cover technology that may be required to practice
     this standard.  Please address the information to the IETF
     Executive Director.

11. Copyright

     Copyright (C) The Internet Society (2004).  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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