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Network Working Group                                         J. Vinocur
INTERNET DRAFT                                        Cornell University
Document: draft-ietf-nntpext-streaming-00.txt
                                                               June 2003


                   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
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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 (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

     1. Introduction .............................................  2
        1.1. Conventions Used in this Document ...................  2
     2. Advertising Capabilities with the Extensions Mechanism ...  3
     3. MODE STREAM Command ......................................  3



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        3.1. Usage ...............................................  3
        3.2. Description .........................................  3
        3.3. Examples ............................................  4
     4. CHECK Command ............................................  4
        4.1. Usage ...............................................  4
        4.2. Description .........................................  4
        4.3. Examples ............................................  5
     5. TAKETHIS Command .........................................  5
        5.1. Usage ...............................................  5
        5.2. Description .........................................  5
        5.3. Examples ............................................  6
     6. Augmented BNF Syntax for Streaming .......................  7
     7. Security Considerations ..................................  7
     8. Acknowledgements .........................................  7
     9. Normative References .....................................  7
     10. Informative References ..................................  7
     11. Author's Address ........................................  7

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.

     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



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     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.

     Example:
        [C] LIST EXTENSIONS
        [S] 202 Extensions supported:
        [S]  HDR
        [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



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     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

     Syntax
        CHECK message-id

     Responses
        238 message-id   Send article to be transferred
        400              Service temporarily unavailable
        431 message-id   Transfer not possible; try again later
        438 message-id   Article not wanted
        480              Permission denied

        The 238, 431, and 438 responses MUST contain only the response
        code followed by the message-id of the article in question;
        free-form text is not permitted.

     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.




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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 <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>

     The same example, but demonstrating streaming:
        [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>

5. TAKETHIS Command

5.1. Usage

     Syntax
        TAKETHIS message-id
        [the entire article MUST be sent at this point, without prompting]

     Responses
        239 message-id   Article transferred OK
        400              Service temporarily unavailable
        439 message-id   Transfer failed
        480              Permission denied

        XXX:  Are those all the responses used in current practice?

        The 239 and 439 responses MUST contain only the response code
        followed by the message-id of the article in question; free-form
        text is not permitted.

     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 entire article,
     headers and body, is sent just as with IHAVE; articles sent using



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     this command MUST obey 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.

5.3. Examples

     Example of successfully sending an article to another site:
        [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] 239 <i.am.an.article.you.will.want@example.com>

     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 <i.am.an.article@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@example.com>
        [C]
        [C] This is just a test article.
        [C] .
        [S] 439 <i.am.an.article@example.com>




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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]

7. Security Considerations

     No new security considerations are introduced by this extension,
     beyond those already described in the core specification [NNTP].

8. Acknowledgements

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

9. 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).

10. Informative References

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

11. Author's Address

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




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     EMail: vinocur@cs.cornell.edu

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