Network Working Group J. Vinocur
INTERNET DRAFT Cornell University
Document: draft-ietf-nntpext-streaming-01.txt
February 2004
NNTP Extension for Streaming Feeds
Status of this memo
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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
0. Changes from Previous Version ............................ 2
1. Introduction ............................................. 2
1.1. Conventions Used in this Document ................... 3
2. Advertising Capabilities with the Extensions Mechanism ... 3
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3. MODE STREAM Command ...................................... 4
3.1. Usage ............................................... 4
3.2. Description ......................................... 4
3.3. Examples ............................................ 4
4. CHECK Command ............................................ 4
4.1. Usage ............................................... 4
4.2. Description ......................................... 5
4.3. Examples ............................................ 5
5. TAKETHIS Command ......................................... 6
5.1. Usage ............................................... 6
5.2. Description ......................................... 6
5.3. Examples ............................................ 7
6. Augmented BNF Syntax for Streaming ....................... 7
7. IANA Considerations ...................................... 8
8. Security Considerations .................................. 8
9. Acknowledgements ......................................... 8
10. Normative References .................................... 8
11. Informative References .................................. 8
12. Author's Address ........................................ 8
0. Changes from Previous Version
New:
o Text needed to comply with extensions framework guidelines:
- IANA Considerations section
o Inclusion of STREAMING in LIST EXTENSIONS output before/after MODE
READER
o CHECK response codes are advisory; servers must handle client
behavior not being what the server has requested
Changed:
o A freeform message may in fact be sent after the Message-ID in a
CHECK or TAKETHIS response
o No need to explicitly list 400 and 480 responses for these commands
Clarified:
o Behavior of LIST EXTENSIONS after MODE STREAM
o Articles sent with TAKETHIS are in the same format as with IHAVE
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
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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
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. The server MAY continue to advertise
this capability after the client has issued the MODE STREAM
command.
A server MAY advertise this capability before or after (or both)
the client has issued the MODE READER command.
Example:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] HDR
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[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
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
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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
The first parameter of the 238, 431, and 438 responses MUST be
the message-id provided by the client as the parameter to CHECK.
Servers MAY send additional text after the message-id.
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.
The intent of the 238 response is that the client will send the
article with TAKETHIS reasonably soon, the intent of the 431
response is that the client will repeat the CHECK command at some
future time, and the intent of the 438 response is that the client
will not send the article with TAKETHIS. However, the responses to
CHECK are advisory; the server MUST NOT rely on the client to
behave as requested by these responses.
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>
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[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
Responses
239 message-id Article transferred OK
439 message-id Transfer failed
The first parameter of the 239 and 439 responses MUST be the
message-id provided by the client as the parameter to CHECK.
Servers MAY send additional text after the message-id.
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 client MUST send
the entire article, including headers and body, in 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.
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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>
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]
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7. IANA Considerations
This document defines an NNTP extension for "Streaming feeds" with
extension-label STREAMING.
XXX: Any better ideas for description text above?
This extension includes the three new NNTP commands defined above:
MODE STREAM, CHECK, and TAKETHIS. It does not affect any pre-
existing NNTP commands or their response codes, and does not
require any change in maximum command length.
8. Security Considerations
No new security considerations are introduced by this extension,
beyond those already described in the core specification [NNTP].
9. Acknowledgements
This document is based heavily on the relevant sections of RFC 2980
[NNTP-COMMON], by Stan Barber.
10. 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).
11. Informative References
[NNTP-COMMON] Barber, S., "Common NNTP Extensions", RFC 2980,
Academ Consulting Services, October 2000.
12. Author's Address
Jeffrey M. Vinocur
Department of Computer Science
Upson Hall
Cornell University
Ithaca, NY 14853
EMail: vinocur@cs.cornell.edu
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