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



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          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].







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  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.












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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] .










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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:




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     [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 <[email protected]>
     [S] 238 <[email protected]>
     [C] CHECK <[email protected]>
     [S] 438 <[email protected]>
     [C] CHECK <[email protected]>
     [S] 431 <[email protected]>



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  Example of pipelining the CHECK commands in the previous example:

     [C] CHECK <[email protected]>
     [C] CHECK <[email protected]>
     [C] CHECK <[email protected]>
     [S] 238 <[email protected]>
     [S] 438 <[email protected]>
     [S] 431 <[email protected]>

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



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  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 <[email protected]>
     [C] Path: pathost!demo!somewhere!not-for-mail
     [C] From: "Demo User" <[email protected]>
     [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: <[email protected]>
     [C]
     [C] This is just a test article.
     [C] .
     [C] TAKETHIS <[email protected]>
     [C] Path: pathost!demo!somewhere!not-for-mail
     [C] From: "Demo User" <[email protected]>
     [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: <[email protected]>
     [C]



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     [C] This is just a test article.
     [C] .
     [S] 239 <[email protected]>
     [S] 439 <[email protected]>

  Example of sending an article to a site where the transfer fails:

     [C] TAKETHIS <[email protected]>
     [C] Path: pathost!demo!somewhere!not-for-mail
     [C] From: "Demo User" <[email protected]>
     [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: <[email protected]>
     [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.




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  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.







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  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.





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  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 <[email protected]>.

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.




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Authors' Addresses

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

  EMail: [email protected]


  Kenneth Murchison
  Carnegie Mellon University
  5000 Forbes Avenue
  Cyert Hall 285
  Pittsburgh, PA  15213 USA

  EMail: [email protected]

































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Full Copyright Statement

Copyright (C) The Internet Society (2006).

  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.

Intellectual Property

  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
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  http://www.ietf.org/ipr.

  The IETF invites any interested party to bring to its attention any
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  this standard.  Please address the information to the IETF at ietf-
  [email protected].

Acknowledgement

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







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