NNTP C. Feather
Internet-Draft Thus plc
Expires: August 30, 2003 March 1, 2003
Network News Transport Protocol
draft-ietf-nntpext-base-17
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on August 30, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The Network News Transport Protocol has been in use in the Internet
for a decade and remains one of the most popular protocols (by
volume) in use today. This document is a replacement for RFC 977 and
officially updates the protocol specification. It clarifies some
vagueness in RFC 977, includes some new base functionality and
provides a specific mechanism to add standardized extensions to NNTP.
Administration
This document is a product of the NNTP Working Group, chaired by Russ
Allbery.
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This is draft 17 pre-publication version 2.
Outstanding issues
Outstanding substantive (as opposed to editorial) issues in the text
are shown as in the following case.
OUTSTANDING ISSUE
Reference consistency: should every RFC that is mentioned be
included in the references? Where the same document is referred to
in more than one place, should every occasion have a reference
number (that is, "RFC 977 [3]" or similar), or only the first one,
or only the first one in each section?
Author's Note
This draft is the first produced using a new formatting process. It
therefore may contain unintentional layout or formatting changes
compared with previous drafts. The author would appreciate being
informed of any problems this has caused.
This draft is written in XML using an NNTP-specific DTD. Custom
software is used to convert this to RFC 2629 [12] format, and then
the public "xml2rfc" package to further reduce this to text, nroff
source, and HTML.
No perl was used in producing this draft.
Rights
UNIX is a registered trademark of the X/Open Company Ltd.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . 7
2. Notation . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Basic Operation . . . . . . . . . . . . . . . . . . . . 9
3.1 Response Codes . . . . . . . . . . . . . . . . . . . . . 11
3.1.1 Generic Response Codes . . . . . . . . . . . . . . . . . 13
3.1.1.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 Pipelining . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . 17
4. The WILDMAT format . . . . . . . . . . . . . . . . . . . 18
4.1 Wildmat syntax . . . . . . . . . . . . . . . . . . . . . 18
4.2 Wildmat semantics . . . . . . . . . . . . . . . . . . . 18
4.3 Extensions . . . . . . . . . . . . . . . . . . . . . . . 19
4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . 20
5. The GREETING Step . . . . . . . . . . . . . . . . . . . 21
5.1 Initial Connection . . . . . . . . . . . . . . . . . . . 21
5.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 21
5.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2 MODE READER . . . . . . . . . . . . . . . . . . . . . . 22
5.2.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2.2 Description . . . . . . . . . . . . . . . . . . . . . . 22
5.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 23
6. The CAPABILITIES DISCOVERY step . . . . . . . . . . . . 25
6.1 LIST EXTENSIONS . . . . . . . . . . . . . . . . . . . . 25
6.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 25
6.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 26
7. Article posting and retrieval . . . . . . . . . . . . . 27
7.1 Group and article selection . . . . . . . . . . . . . . 27
7.1.1 GROUP . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.1.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 28
7.1.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1.2 LAST . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.1.2.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.1.2.2 Description . . . . . . . . . . . . . . . . . . . . . . 30
7.1.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1.3 NEXT . . . . . . . . . . . . . . . . . . . . . . . . . . 32
7.1.3.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 32
7.1.3.2 Description . . . . . . . . . . . . . . . . . . . . . . 32
7.1.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 32
7.2 Retrieval of articles and article sections . . . . . . . 33
7.2.1 ARTICLE . . . . . . . . . . . . . . . . . . . . . . . . 33
7.2.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.2.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 34
7.2.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 35
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7.2.2 HEAD . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.2.2.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.2.2.2 Description . . . . . . . . . . . . . . . . . . . . . . 37
7.2.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 37
7.2.3 BODY . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.2.3.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.2.3.2 Description . . . . . . . . . . . . . . . . . . . . . . 39
7.2.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 39
7.2.4 STAT . . . . . . . . . . . . . . . . . . . . . . . . . . 40
7.2.4.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 40
7.2.4.2 Description . . . . . . . . . . . . . . . . . . . . . . 41
7.2.4.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 41
7.3 Article posting . . . . . . . . . . . . . . . . . . . . 42
7.3.1 POST . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.3.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.3.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 43
7.3.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 44
7.3.2 IHAVE . . . . . . . . . . . . . . . . . . . . . . . . . 44
7.3.2.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 44
7.3.2.2 Description . . . . . . . . . . . . . . . . . . . . . . 45
7.3.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 46
8. Information commands . . . . . . . . . . . . . . . . . . 48
8.1 DATE . . . . . . . . . . . . . . . . . . . . . . . . . . 48
8.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 48
8.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 48
8.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 48
8.2 HELP . . . . . . . . . . . . . . . . . . . . . . . . . . 48
8.2.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 48
8.2.2 Description . . . . . . . . . . . . . . . . . . . . . . 49
8.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 49
8.3 NEWGROUPS . . . . . . . . . . . . . . . . . . . . . . . 49
8.3.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 49
8.3.2 Description . . . . . . . . . . . . . . . . . . . . . . 49
8.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 50
8.4 NEWNEWS . . . . . . . . . . . . . . . . . . . . . . . . 50
8.4.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 51
8.4.2 Description . . . . . . . . . . . . . . . . . . . . . . 51
8.4.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 51
8.5 Time . . . . . . . . . . . . . . . . . . . . . . . . . . 52
8.5.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . 52
8.6 The LIST commands . . . . . . . . . . . . . . . . . . . 53
8.6.1 LIST ACTIVE . . . . . . . . . . . . . . . . . . . . . . 53
8.6.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 53
8.6.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 53
8.6.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 54
8.6.2 LIST ACTIVE.TIMES . . . . . . . . . . . . . . . . . . . 55
8.6.2.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 55
8.6.2.2 Description . . . . . . . . . . . . . . . . . . . . . . 55
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8.6.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 55
8.6.3 LIST DISTRIBUTIONS . . . . . . . . . . . . . . . . . . . 56
8.6.3.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 56
8.6.3.2 Description . . . . . . . . . . . . . . . . . . . . . . 56
8.6.3.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 57
8.6.4 LIST DISTRIB.PATS . . . . . . . . . . . . . . . . . . . 57
8.6.4.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 57
8.6.4.2 Description . . . . . . . . . . . . . . . . . . . . . . 57
8.6.4.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 58
8.6.5 LIST NEWSGROUPS . . . . . . . . . . . . . . . . . . . . 58
8.6.5.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 58
8.6.5.2 Description . . . . . . . . . . . . . . . . . . . . . . 59
8.6.5.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 59
9. The CONCLUSION step . . . . . . . . . . . . . . . . . . 60
9.1 QUIT . . . . . . . . . . . . . . . . . . . . . . . . . . 60
9.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 60
9.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 60
9.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 60
10. Framework for NNTP extensions . . . . . . . . . . . . . 61
10.1 Initial IANA registry . . . . . . . . . . . . . . . . . 63
10.2 Standard extensions . . . . . . . . . . . . . . . . . . 63
10.3 The LISTGROUP extension . . . . . . . . . . . . . . . . 63
10.3.1 LISTGROUP . . . . . . . . . . . . . . . . . . . . . . . 63
10.3.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 63
10.3.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 64
10.3.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 64
10.4 Article metadata . . . . . . . . . . . . . . . . . . . . 65
10.4.1 The :bytes metadata item . . . . . . . . . . . . . . . . 65
10.4.2 The :lines metadata item . . . . . . . . . . . . . . . . 66
10.5 The OVER extension . . . . . . . . . . . . . . . . . . . 66
10.5.1 OVER . . . . . . . . . . . . . . . . . . . . . . . . . . 66
10.5.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 66
10.5.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 67
10.5.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 68
10.5.2 LIST OVERVIEW.FMT . . . . . . . . . . . . . . . . . . . 69
10.5.2.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 69
10.5.2.2 Description . . . . . . . . . . . . . . . . . . . . . . 70
10.5.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 71
10.6 The HDR extension . . . . . . . . . . . . . . . . . . . 72
10.6.1 HDR . . . . . . . . . . . . . . . . . . . . . . . . . . 72
10.6.1.1 Usage . . . . . . . . . . . . . . . . . . . . . . . . . 72
10.6.1.2 Description . . . . . . . . . . . . . . . . . . . . . . 72
10.6.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . 74
11. Augmented BNF Syntax for NNTP Commands . . . . . . . . . 76
12. Security Considerations . . . . . . . . . . . . . . . . 79
12.1 Personal and Proprietary Information . . . . . . . . . . 79
12.2 Abuse of Server Log Information . . . . . . . . . . . . 79
12.3 Weak Authentication and Access Control . . . . . . . . . 79
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12.4 DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . 80
12.5 UTF-8 issues . . . . . . . . . . . . . . . . . . . . . . 80
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . 82
Normative References . . . . . . . . . . . . . . . . . . 84
Informative References . . . . . . . . . . . . . . . . . 85
Author's Address . . . . . . . . . . . . . . . . . . . . 85
Intellectual Property and Copyright Statements . . . . . 86
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1. Introduction
This document specifies the Network News Transport Protocol (NNTP),
which is used for the distribution, inquiry, retrieval, and posting
of net news articles using a reliable stream-based mechanism. For
news reading clients, NNTP enables retrieval of news articles that
are stored in a central database, giving subscribers the ability to
select only those articles they wish to read.
The net news model provides for indexing, cross-referencing, and
expiration of aged messages. For server-to-server interaction, NNTP
is designed for efficient transmission of net news articles over a
reliable full duplex communication channel.
Every attempt is made to ensure that the protocol specification in
this document is compatible with the version specified in RFC 977
[1]. However, this version does not support the ill-defined SLAVE
command and permits four digit years to be specified in the NEWNEWS
and NEWGROUPS commands. It changes the default character set to
UTF-8 [2] instead of US-ASCII [3]. It also extends the newsgroup
name matching capabilities already documented in RFC 977.
Generally, new functionality is made available using new commands.
Part of that new functionality involves a mechanism to discover what
new functionality is available to clients from a server.
This mechanism can also be used to add more functionality as needs
merit such additions.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [4].
An implementation is not compliant if it fails to satisfy one or more
of the MUST requirements for this protocol. An implementation that
satisfies all the MUST and all the SHOULD requirements for its
protocols is said to be "unconditionally compliant"; one that
satisfies all the MUST requirements but not all the SHOULD
requirements for NNTP is said to be "conditionally compliant".
For the remainder of this document, the term "client host" refers to
a host making use of the NNTP service, while the term "server host"
refers to a host that offers the NNTP service.
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2. Notation
The following notational conventions are used in this document.
UPPERCASE indicates literal text to be included in the
command;
lowercase indicates a token described elsewhere;
[brackets] indicate that the parameter is optional;
ellipsis... indicates that the parameter may be repeated any
number of times (it must occur at least once);
vertical|bar indicates a choice of two mutually exclusive
parameters (exactly one must be provided).
The name "message-id" for a command or response parameter indicates
that it is the message-id of an article as described in Section 7.
The actual parameter MUST include the angle brackets.
The name "wildmat" for a parameter indicates that it is a wildmat as
defined in Section 4. If the parameter does not meet the
requirements of that section (for example, if it does not fit the
grammar of Section 4.1) the NNTP server MAY place some interpretation
on it (not specified by this document) or otherwise MUST treat it as
a syntax error.
Responses for each command will be described in tables listing the
required format of a response followed by the meaning that should be
ascribed to that response.
Examples in this document are not normative but serve to illustrate
usages, arguments, and responses. In the examples, a "[C]" will be
used to represent the client host and a "[S]" will be used to
represent the server host. Most of the examples do not rely on a
particular server state. In some cases, however, they do assume that
the current selected newsgroup (see the GROUP command (Section
7.1.1)) is invalid; when so, this is indicated at the start of the
example.
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3. Basic Operation
Every NNTP session MUST involve the following in this order:
CONNECTION
GREETING
DISCONNECTION
Other steps may occur between the GREETING and DISCONNECTION step.
They are:
CAPABILITIES DISCOVERY
NEWS EXCHANGE
CONCLUSION
NNTP operates over any reliable data stream 8-bit-wide channel. When
running over TCP/IP, the official port for the NNTP service is 119.
Initially, the server host starts the NNTP service by listening on a
TCP port. When a client host wishes to make use of the service, it
MUST establish a TCP connection with the server host by connecting to
that host on the same port on which the server is listening. This is
the CONNECTION step. When the connection is established, the NNTP
server host MUST send a greeting. This is the GREETING step. The
client host and server host SHOULD then exchange commands and
responses (respectively) until the connection is closed or aborted.
This final step is called the DISCONNECTION step.
If there is a CONCLUSION step, it MUST immediately precede the
DISCONNECTION step. There MUST be only one CONNECTION, CONCLUSION
and DISCONNECTION step for each NNTP session. All other steps MAY be
repeated as needed. For example, the GREETING step may be repeated
if the client makes use of the MODE READER command (see Section 5.2
for more on the MODE READER command).
OUTSTANDING ISSUE
Do we actually need this GREETING / NEWS EXCHANGE / DISCONNECTION
type stuff? I don't see that it buys us anything compared with
simply saying that there's the initial greeting and a set of
commands.
The character set for all NNTP commands is UTF-8. Commands in the
NNTP MUST consist of a keyword, which MAY be followed by one or more
arguments. An US-ASCII CRLF pair MUST terminate all commands.
Multiple commands MUST NOT be on the same line. Keywords MUST
consist of printable US-ASCII characters. Unless otherwise noted
elsewhere in this document, arguments SHOULD consist of printable
US-ASCII characters. Keywords and arguments MUST be each separated
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by one or more US-ASCII SPACE or US-ASCII TAB characters. Keywords
MUST be at least three US-ASCII characters and MUST NOT exceed 12
US-ASCII characters. Command lines MUST NOT exceed 512 octets, which
includes the terminating US-ASCII CRLF pair. The arguments MUST NOT
exceed 497 octets.
Commands may have variants, using a second keyword immediately after
the first to indicate which variant is required. The only such
commands in this specification are LIST and MODE.
Keywords are case-insensitive; the case of keywords for commands MUST
be ignored by the server. Command and response parameters are case
or language specific only when specified (either in this document or
in RFC 1036 [6]).
An NNTP server MUST implement all the commands in this specification
except for those marked as optional and those in extensions.
Each response MUST start with a three-digit response code that is
sufficient to distinguish all responses. Certain valid responses are
defined to be multi-line; for all others, the response is contained
in a single line.
OUTSTANDING ISSUE
Should the initial response line be limited to 512 octets as well?
Possible text:
The first or only line of the response MUST NOT exceed 512 octets,
which includes the response code and the terminating US-ASCII CRLF
pair.
The text further down about "does not place any limit on the
length" would need equivalent edits.
All multi-line responses MUST adhere to the following format:
1. The response consists of a sequence of one or more "lines", each
being a stream of octets ending with 0x0D 0x0A (US-ASCII CRLF).
Apart from those line endings, the stream MUST NOT include the
octets 0x00, 0x0A, or 0x0D (US-ASCII NUL, LF, and CR).
2. The first such line contains the response code as with a single
line response.
3. If any subsequent line begins with the "termination octet" (0x2E
or US_ASCII "."), that line MUST be "byte-stuffed" by pre-pending
an additional termination octet (0x2E) to that line of the
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response.
4. The lines of the response MUST be followed by a terminating line
consisting of a single termination octet (0x2E or US_ASCII ".")
followed by CRLF in the normal way. Thus a multi-line response
is always terminated with the five octets CRLF "." CRLF (in
US-ASCII).
5. When interpreting a multi-line response, the "byte stuffing" MUST
be undone; i.e. the client MUST ensure that, in any line
beginning with the termination octet followed by octets other
than US-ASCII CRLF, that initial termination octet is
disregarded.
6. Likewise, the terminating line "." CRLF (in US-ASCII) MUST NOT be
considered part of the multi-line response; i.e. the client MUST
ensure that any line beginning with the termination octet
followed immediately by US-ASCII CRLF is disregarded; (the first
CRLF of the terminating CRLF "." CRLF is, of course, part of the
last line of the response).
Note that texts using an encoding (such as UTF-16 or UTF-32) that may
contain the NUL octet or the CR or LF octets in contexts other than
the CRLF line ending cannot be reliably conveyed in the above format.
This document does not place any limit on the length of a line.
However, the standards that define the format of articles may do so.
An NNTP server MAY have an inactivity autologout timer. Such a timer
SHOULD be of at least three minutes duration, with the exception that
there MAY be a shorter limit on how long the server is willing to
wait for the first command from the client. The receipt of any
command from the client during the timer interval SHOULD suffice to
reset the autologout timer. Similarly, the receipt of any
significant amount of data from the client while in the midst of
sending a multi-line message to the server (such as during a POST or
IHAVE command) SHOULD suffice to reset the autologout timer. When
the timer expires, the server SHOULD close the TCP connection without
sending any response to the client, including when the client is in
the middle of sending a multi-line message to the server.
3.1 Response Codes
Each response MUST begin with a three-digit status indicator. These
are status reports from the server and indicate the response to the
last command received from the client.
The first digit of the response broadly indicates the success,
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failure, or progress of the previous command.
1xx - Informative message.
2xx - Command completed OK.
3xx - Command OK so far; send the rest of it.
4xx - Command was correct, but couldn't be performed for some
reason.
5xx - Command unimplemented, or incorrect, or a serious program
error occurred.
The next digit in the code indicates the function response category.
x0x - Connection, setup, and miscellaneous messages
x1x - Newsgroup selection
x2x - Article selection
x3x - Distribution functions
x4x - Posting
x8x - Reserved for authentication and authorization extensions
x9x - Reserved for private use (non-standard extensions)
Certain responses contain parameters such as numbers and names in
addition to the status indicator. In those cases, to simplify
interpretation by the client the number and type of such parameters
is fixed for each response code, as is whether or not the code
introduces a multi-line response. Any extension MUST follow this
principle as well, but note that, for historical reasons, the 211
response code is an exception to this. In all other cases, the
client MUST only use the status indicator itself to determine the
nature of the response. The exact response codes that can be
returned by any given command are detailed in the description of that
command.
Parameters MUST be separated from the numeric status indicator and
from each other by a single US-ASCII space. All numeric parameters
MUST be in base 10 (decimal) format, and MAY have leading zeros.
String parameters MUST contain at least one character and MUST NOT
contain US-ASCII spaces, CR, LF, or tab. The server MAY add any text
after the response code or last parameter as appropriate, and the
client MUST NOT make decisions based on this text. Such text MUST be
separated from the numeric status indicator or the last parameter by
at least one US-ASCII space.
The server MUST respond to any command with the appropriate generic
response (given in Section 3.1.1) if it represents the situation.
Otherwise, each recognized command MUST return one of the response
codes specifically listed in its description or in an extension. A
server MAY provide extensions to this specification, including new
commands, new variants or features of existing commands, and other
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ways of changing the internal state of the server. However, the
server MUST NOT produce any other responses to a client that does not
invoke any of the additional features. (Therefore a client that
restricts itself to this specification will only receive the
responses that are listed.)
If a client receives an unexpected response, it SHOULD use the first
digit of the response to determine the result. For example, an
unexpected 2xx should be taken as success and an unexpected 4xx or
5xx as failure.
Response codes not specified in this document MAY be used for any
installation-specific additional commands also not specified. These
SHOULD be chosen to fit the pattern of x9x specified above.
Neither this document nor any extension registered with IANA (see
Section 10) will specify any response codes of the x9x pattern.
(Implementers of extensions are accordingly cautioned not to use such
responses for extensions that may subsequently be submitted for
registration.)
3.1.1 Generic Response Codes
The server MUST respond to any command with the appropriate one of
the following generic responses if it represents the situation.
If the command is not recognized, or it is an optional command or
extension that is not implemented by the server, the response code
500 MUST be returned.
If there is a syntax error in the arguments of a recognized command,
including the case where more arguments are provided than the command
specifies, the response code 501 MUST be returned. Note that where a
command has variants depending on a second keyword (e.g. LIST ACTIVE
and LIST NEWSGROUPS), then 501 MUST be used when the requested
variant is not implemented but the base command is.
If the client is not authorized to use the specified facility when
the server is in its current state, the response code 502 MUST be
returned. A different command might change the server state and
permit the command if it is retried.
If the server does not provide an optional feature, then the response
code 403 MUST be returned if the omission is temporary (e.g. because
a necessary facility is unavailable) and the code 503 if it is
permanent (e.g. because the server does not store the required
information).
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OUTSTANDING ISSUE
Is anyone aware of a server that implements 403, or is it an
invention of our own? If the latter, do we want to keep it? INN
apparently uses 503 for temporary errors; someone suggested adding
the text:
If the server encounters an unexpected internal error that
prevents it from completing a command, the response code 503
MAY be returned.
Some servers return 503 for things like "can't contact a posting
server" or "can't execute external authenticator".
OUTSTANDING ISSUE
The 503 response seems to have three separate meanings:
1. LIST ACTIVE.TIMES etc. use it for "this data isn't stored".
HDR uses it for "this header can't be requested", which is
consistent. Are there other commands that can reasonably
return such a thing? If not, is this kind of 503 really a
generic response?
2. Temporary errors, the kind that 403 is supposed to represent.
3. It's apparently returned by LIST EXTENSIONS, but what does it
mean in this case? Not "there are no extensions", because
that's 402. Is this also an invention of our own? Again,
would a different code be better?
If the server has to terminate the connection for some reason, it
MUST give a 400 response code to the next command and then
immediately close the TCP connection. It MAY give a 401 response
code to any command to indicate that termination is imminent
(following a 401 response, it MUST NOT close the TCP connection
immediately).
OUTSTANDING ISSUE
Since the 401 doesn't terminate the session, what about commands
that change the status? For example, if GROUP returns 401 what
happens to the current selected newsgroup.
With the exception of mandatory commands and the 500 response, the
client MUST be prepared to receive any of these responses for any
command.
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3.1.1.1 Examples
Example of an unknown command:
[C] MAIL
[S] 500 Unknown command
Example of an unsupported extension:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] LISTGROUP
[S] .
[C] OVER
[S] 500 Unknown command
Example of an unsupported variant:
[C] MODE POSTER
[S] 501 Unknown MODE option
Example of a syntax error:
[C] ARTICLE a.message.id@no.angle.brackets
[S] 501 Syntax error
Example of an overlong command line:
[C] HEAD 53 54 55
[S] 501 Too many arguments
Example of a bad wildmat:
[C] LIST ACTIVE u[ks].*
[S] 501 Syntax error
Example of an attempt to access a restricted facility:
[C] GROUP secret.group
[S] 502 Permission denied
followed by a successful attempt following authentication:
[C] XSECRET fred flintstone
[S] 290 Password for fred accepted.
[C] GROUP secret.group
[S] 211 5 1 20 secret.group selected
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Example of a temporary failure:
[C] GROUP archive.local
[S] 403 Archive server temporarily offline
Example of the server needing to close down immediately:
[C] ARTICLE 123
[S] 400 Power supply failed, running on UPS
[Server closes connection.]
Example of imminent termination of the server:
[C] STAT 123
[S] 401 Pre-payment expired, you have 10 seconds
[C] STAT 123
[S] 423 No such article number in this group
[C] NEXT
[S] 400 Time expired
[Server closes connection.]
3.2 Pipelining
NNTP is designed to operate over a reliable bi-directional connection
such as TCP. Therefore, if a command does not depend on the response
to the previous one, it should not matter if it is sent before that
response is received. Doing this is called "pipelining". However,
certain server implementations throw away all text received from the
client following certain commands before sending their response. If
this happens, pipelining will be affected because one or more
commands will have been ignored or misinterpreted, and the client
will be matching the wrong responses to each command. Since there
are significant benefits to pipelining, but also circumstances where
it is reasonable or common for servers to behave in the above manner,
this document puts certain requirements on both clients and servers.
Except where stated otherwise, a client MAY use pipelining. That is,
it may send a command before receiving the response for the previous
command. The server MUST allow pipelining and MUST NOT throw away
any text received after a command. Irrespective of whether or not
pipelining is used, the server MUST process commands in the order
they are sent.
If the specific description of a command say it "MUST NOT be
pipelined", that command MUST end any pipeline of commands. That is,
the client MUST NOT send any following command until receiving the
CRLF at the end of the response from the command. The server MAY
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ignore any data received after the command and before the CRLF at the
end of the response is sent to the client.
The initial connection must not be part of a pipeline; that is, the
client MUST NOT send any command until receiving the CRLF at the end
of the greeting.
If the client uses blocking system calls to send commands, it MUST
ensure that the amount of text sent in pipelining does not cause a
deadlock between transmission and reception. The amount of text
involved will depend on window sizes in the transmission layer, and
is typically 4k octets for TCP.
3.2.1 Examples
Example of correct use of pipelining:
[C] GROUP misc.test
[C] STAT
[C] NEXT
[S] 211 1234 3000234 3002322 misc.test
[S] 223 3000234 <45223423@example.com> retrieved
[S] 223 3000237 <668929@example.org> retrieved
Example of incorrect use of pipelining (the LIST EXTENSIONS command
may not be pipelined):
[C] GROUP misc.test
[C] LIST EXTENSIONS
[C] DATE
[C] NEXT
[S] 211 1234 3000234 3002322 misc.test
[S] 402 server has no extensions
[S] 223 3000237 <668929@example.org> retrieved
The DATE command has been thrown away by the server and so there is
no 111 response to match it.
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4. The WILDMAT format
The WILDMAT format described here is based on the version first
developed by Rich Salz [11], which in turn was derived from the
format used in the UNIX "find" command to articulate file names. It
was developed to provide a uniform mechanism for matching patterns in
the same manner that the UNIX shell matches filenames.
4.1 Wildmat syntax
A wildmat is described by the following augmented BNF [5] syntax
(note that this syntax contains ambiguities and special cases
described at the end):
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E /
UTF-8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
UTF-8-non-ascii is defined in Section 11
This syntax must be interpreted subject to the following rule:
Where a wildmat-pattern is not immediately preceded by "!", it shall
not begin with a "!".
Note: the characters \ , [ and ] are not allowed in wildmats, while *
and ? are always wildcards. This should not be a problem since these
characters cannot occur in newsgroup names, which is the only current
use of wildmats. Backslash is commonly used to supress the special
meaning of characters and brackets to introduce sets, but there is no
existing standard practice for these in wildmats and so they were
omitted from this specification. A future extension to this
specification may provide semantics for these characters.
4.2 Wildmat semantics
A wildmat is tested against a string, and either matches or does not
match. To do this, each constituent wildmat-pattern is matched
against the string and the rightmost pattern that matches is
identified. If that wildmat-pattern is not preceded with "!", the
whole wildmat matches. If it is preceded by "!", or if no
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wildmat-pattern matches, the whole wildmat does not match.
For example, consider the wildmat "a*,!*b,*c*":
the string "aaa" matches because the rightmost match is with "a*"
the string "abb" does not match because the rightmost match is
with "*b"
the string "ccb" matches because the rightmost match is with "*c*"
the string "xxx" does not match because no wildmat-pattern matches
A wildmat-pattern matches a string if the string can be broken into
components, each of which matches the corresponding wildmat-item in
the pattern; the matches must be in the same order, and the whole
string must be used in the match. The pattern is "anchored"; that
is, the first and last characters in the string must match the first
and last item respectively (unless that item is an asterisk matching
zero characters).
A wildmat-exact matches the same character (which may be more than
one octet in UTF-8).
"?" matches exactly one character (which may be more than one octet).
"*" matches zero or more characters. It can match an empty string,
but it cannot match a subsequence of a UTF-8 sequence that is not
aligned to the character boundaries.
4.3 Extensions
An NNTP server or extension MAY extend the syntax or semantics of
wildmats provided that all wildmats that meet the requirements of
Section 4.1 have the meaning ascribed to them by Section 4.2. Future
editions of this document may also extend wildmats.
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4.4 Examples
In these examples, $ and @ are used to represent the two octets 0xC2
and 0xA3 respectively; $@ is thus the UTF-8 encoding for the pound
sterling symbol, shown as # in the descriptions.
Wildmat Description of strings that match
abc the one string "abc"
abc,def the two strings "abc" and "def"
$@ the one character string "#"
a* any string that begins with "a"
a*b any string that begins with "a" and ends with "b"
a*,*b any string that begins with "a" or ends with "b"
a*,!*b any string that begins with "a" and does not end with
"b"
a*,!*b,c* any string that begins with "a" and does not end with
"b", and any string that begins with "c" no matter
what it ends with
a*,c*,!*b any string that begins with "a" or "c" and does not
end with "b"
?a* any string with "a" as its second character
??a* any string with "a" as its third character
*a? any string with "a" as its penultimate character
*a?? any string with "a" as its antepenultimate character
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5. The GREETING Step
5.1 Initial Connection
5.1.1 Usage
Responses
200 Service available, posting allowed
201 Service available, posting prohibited
400 Service temporarily unavailable [1]
502 Service permanently unavailable [1]
These are the only valid response codes for the initial greeting;
the server MUST not return any other generic response code.
[1] Following a 400 or 502 response the server MUST immediately close
the connection.
5.1.2 Description
There is no command presented by the client upon initial connection
to the server. The server MUST present an appropriate response code
as a greeting to the client. This response informs the client about
what steps the client should take to reach the news exchange step.
If the server will accept further commands from the client including
POST, the server MUST present a 200 greeting code. If the server
will accept further commands from the client, but it is not
authorized to post articles using the POST command, the server MUST
present a 201 greeting code.
Otherwise the server MUST present a 400 or 502 greeting code and then
immediately close the connection. 502 MUST be used if the client is
not permitted under any circumstances to interact with the server and
400 otherwise.
5.1.3 Examples
Example of a normal connection from an authorized client which then
jumps directly to the conclusion step (see Section 9):
[Initial TCP connection setup completed.]
[S] 200 NNTP Service Ready, posting permitted
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
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Example of a normal connection from an authorized client that is not
permitted to post; it also jumps directly to the conclusion step:
[Initial TCP connection setup completed.]
[S] 201 NNTP Service Ready, posting prohibited
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of a normal connection from an unauthorized client:
[Initial TCP connection setup completed.]
[S] 502 NNTP Service permanently unavailable
[Server closes connection.]
Example of a connection from a client where the server is unable to
provide service:
[Initial TCP connection setup completed.]
[S] 400 NNTP Service temporarily unavailable
[Server closes connection.]
5.2 MODE READER
5.2.1 Usage
This command MUST NOT be pipelined.
Syntax
MODE READER
Responses
200 Posting allowed
201 Posting prohibited
400 Service temporarily unavailable [1]
502 Service permanently unavailable [1]
[1] Following a 400 or 502 response the server MUST immediately close
the connection.
5.2.2 Description
MODE READER SHOULD be sent by any client that intends to use any
command other than IHAVE, HEAD, STAT, LIST ACTIVE, LIST EXTENSIONS,
or commands advertised by the server as available via LIST
EXTENSIONS.
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Servers MAY require that this command be issued before any other
commands are sent and MAY reject any other commands until after a
MODE READER command has been sent.
The server MUST return a response using the same codes as the initial
greeting (as described in Section 5.1.1) to indicate its ability to
provide reading service to the client. Note that the response need
not be the same as the one presented during the initial greeting.
Once MODE READER is sent, IHAVE (and any extensions intended for
peer-to-peer article transfer) MAY no longer be permitted, even if it
were permitted before the MODE READER command. The results of LIST
EXTENSIONS MAY be different following a MODE READER command than
prior to the issuing of that command.
Servers are encouraged to not require this command even though
clients SHOULD send it when appropriate. It is present to support
some news architectures that switch between modes based on whether a
given connection is a peer-to-peer connection with another server or
a news reading client.
5.2.3 Examples
Example of use of the MODE READER command by an authorized client
which then jumps directly to the conclusion step (see Section 9):
[C] MODE READER
[S] 200 NNTP Service Ready, posting permitted
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of use of the MODE READER command by an authorized client
that is not permitted to post; it also jumps directly to the
conclusion step:
[C] MODE READER
[S] 201 NNTP Service Ready, posting prohibited
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of use of MODE READER by a client not authorized to receive
service from the server as a news reader:
[C] MODE READER
[S] 502 NNTP Service permanently unavailable
[Server closes connection.]
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Example of a connection from any client where the server is unable to
provide news reader service:
[C] QUIT
[S] 400 NNTP Service temporarily unavailable
[Server closes connection.]
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6. The CAPABILITIES DISCOVERY step
To discover what extensions are available, an NNTP client can query
the server with the LIST EXTENSIONS command. If a particular
extension is unavailable, the client can attempt to work around it or
it may wish to terminate the session.
See Section 10 for further discussion of extensions.
6.1 LIST EXTENSIONS
6.1.1 Usage
This command is optional.
This command MUST NOT be pipelined.
Syntax
LIST EXTENSIONS
Responses
202 Extension list follows (multiline)
402 Server has no extensions
503 Extension information not available
6.1.2 Description
The LIST EXTENSIONS command allows a client to determine which
extensions are supported by the server. This command MUST be
implemented by any server that implements any extensions defined in
this document.
To discover what extensions are available, an NNTP client SHOULD
query the server early in the session for extensions information by
issuing the LIST EXTENSIONS command. This command MAY be issued at
anytime during a session. It is not required that the client issues
this command before attempting to make use of any extension. The
response generated by this command MAY change during a session
because of other state information. However, an NNTP client MUST NOT
cache (for use in another session) any information returned if the
LIST EXTENSIONS command succeeds. That is, an NNTP client is only
able to get the current and correct information concerning available
extensions during a session by issuing a LIST EXTENSIONS command
during that session and processing that response.
The list of extensions is returned as a multi-line response following
the 202 response code. Each extension is listed on a separate line;
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the line MUST begin with an extension-label and optionally one or
more parameters (separated by single spaces). The extension-label
and the meaning of the parameters are specified as part of the
definition of the extension. The extension-label MUST be in
uppercase.
The server MUST NOT list the same extension twice in the response,
and MUST list all supported extensions. The order in which the
extensions are listed is not significant. The server need not even
consistently return the same order. If the server does not support
any extensions, a 402 response SHOULD be returned, but it MAY instead
return an empty list.
Following a 503 response an extension might still be available, and
the client MAY attempt to use it.
6.1.3 Examples
Example of a successful response:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] OVER
[S] HDR
[S] LISTGROUP
[S] .
The particular extensions shown here are simply examples of what
might be defined in other places, and no particular meaning should be
attributed to them.
Example where no extensions are available, using preferred format:
[C] LIST EXTENSIONS
[S] 402 Server has no extensions
Example where no extensions are available, using an empty list:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] .
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7. Article posting and retrieval
News reading clients have available a variety of mechanisms to
retrieve articles via NNTP. The news articles are stored and indexed
using three types of keys. One key is the message-id of an article.
According to RFC 1036, this identifier should be globally unique.
Another key is composed of the newsgroup name and the article number
within that newsgroup. That key MUST be unique to a particular
server (there will be only one article with that number within a
particular newsgroup), but is not required to be globally unique.
Additionally, because the same article can be cross-posted to
multiple newsgroups, there may be multiple keys that point to the
same article on the same server. The final key is the arrival
timestamp, giving the time that the article arrived at the server.
The server MUST ensure that article numbers are issued in order of
arrival timestamp; that is, articles arriving later MUST have higher
numbers than those that arrive earlier. The server SHOULD allocate
the next sequential unused number to each new article.
Article numbers MUST lie between 1 and 4,294,967,295 inclusive. The
client and server SHOULD NOT use leading zeroes in specifying article
numbers, and MUST NOT use more than 16 digits. In some situations,
the value zero replaces an article number to show some special
situation.
Message-ids are as defined in RFC 2822 [7] with the following
modifications:
o A message-id MUST NOT contain a US-ASCII space within any
quoted-pair.
o A message-id MUST NOT be longer than 250 octets.
o RFC 2822 obsolete syntax for message-ids is not supported by the
protocol specified in this document.
7.1 Group and article selection
The following commands are used to set the "current selected
newsgroup" and the "current article number", which are used by
various commands. At the start of an NNTP session, both of these
values are set to the special value "invalid".
7.1.1 GROUP
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7.1.1.1 Usage
Syntax
GROUP ggg
Responses
211 n l h ggg Group successfully selected
411 No such newsgroup
Parameters
ggg = name of newsgroup
n = estimated number of articles in the group
l = reported low water mark
h = reported high water mark
7.1.1.2 Description
The required parameter ggg is the name of the newsgroup to be
selected (e.g. "news.software.b"). A list of valid newsgroups may
be obtained by using the LIST ACTIVE command (see Section 8.6.1).
The successful selection response will return the article numbers of
the first and last articles in the group at the moment of selection
(these numbers are referred to as the "reported low water mark" and
the "reported high water mark"), and an estimate of the number of
articles on file in the group.
If the group is not empty, the estimate MUST be at least the actual
number of articles available, and MUST be no greater than one more
than the difference between the reported low and high water marks.
(Some implementations will actually count the number of articles on
file. Others will just subtract the low water mark from the high
water mark and add one to get an estimate.)
If the group is empty, one of the following three situations will
occur. Clients MUST accept all three cases; servers MUST NOT
represent an empty group in any other way.
o The high water mark will be one less than the low water mark, and
the estimated article count will be zero. Servers SHOULD use this
method to show an empty group. This is the only time that the
high water mark can be less than the low water mark.
o All three numbers will be zero.
o The high water mark is greater than or equal to the low water
mark. The estimated article count might be zero or non-zero; if
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non-zero, the same requirements apply as for a non-empty group.
The set of articles in a group may change after the GROUP command is
carried out. That is:
o articles may be removed from the group
o articles may be reinstated in the group with the same article
number, but those articles MUST have numbers no less than the
reported low water mark (note that this is a reinstatement of the
previous article, not a new article reusing the number)
o new articles may be added with article numbers greater than the
reported high water mark (if an article that was the one with the
highest number has been removed, the next new article will not
have the number one greater than the reported high water mark)
Except when the group is empty and all three numbers are zero,
whenever a subsequent GROUP command for the same newsgroup is issued,
either by the same client or a different client, the reported low
water mark in the response MUST be no less than that in any previous
response for that newsgroup sent to any client. The client may make
use of the low water mark to remove all remembered information about
articles with lower numbers, as these will never recur. This
includes the situation when the high water mark is one less than the
low water mark.
No similar assumption can be made about the high water mark, as this
can decrease if an article is removed, and then increase again if it
is reinstated or if new articles arrive. When a valid group is
selected by means of this command, the current selected newsgroup
MUST be set to that group and the current article number MUST be set
to the first article in the group. If an empty newsgroup is
selected, the current article pointer is made invalid. If an invalid
group is specified, the current selected newsgroup and current
article number MUST NOT be changed.
The GROUP command (or the LISTGROUP command, if implemented) MUST be
used by a client and a successful response received before the any
other command is used that depends on the value of the current
selected newsgroup or current article number.
If the group specified is not available on the server, a 411 response
MUST be returned.
7.1.1.3 Examples
Example for a group known to the server:
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[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
Example for a group unknown to the server:
[C] GROUP example.is.sob.bradner.or.barber
[S] 411 example.is.sob.bradner.or.barber is unknown
Example of an empty group using the preferred response:
[C] GROUP example.currently.empty.newsgroup
[S] 211 0 4000 3999 example.currently.empty.newsgroup
Example of an empty group using an alternative response:
[C] GROUP example.currently.empty.newsgroup
[S] 211 0 0 0 example.currently.empty.newsgroup
Example of an empty group using a different alternative response:
[C] GROUP example.currently.empty.newsgroup
[S] 211 0 4000 4321 example.currently.empty.newsgroup
7.1.2 LAST
7.1.2.1 Usage
Syntax
LAST
Responses
223 n message-id Article found
412 No newsgroup selected
420 Current article number is invalid
422 No previous article in this group
Parameters
n = article number
message-id = article message-id
7.1.2.2 Description
If the current selected newsgroup is valid, the current article
number MUST be set to the previous article in that newsgroup (that
is, the highest existing article number less than the current article
number). If successful, a response indicating the new current
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article number and the message-id of that article MUST be returned.
No article text is sent in response to this command.
There MAY be no previous article in the group, although the current
article number is not the reported low water mark. There MUST NOT be
a previous article when the current article number is the reported
low water mark.
Because articles can be removed and added, the results of multiple
LAST and NEXT commands MAY not be consistent over the life of a
particular NNTP session.
If the current article number is already the first article of the
newsgroup, a 422 response MUST be returned. If the current article
number is invalid, a 420 response MUST be returned. If the current
selected newsgroup is invalid, a 412 response MUST be returned. In
all three cases the current selected newsgroup and current article
number MUST NOT be altered.
7.1.2.3 Examples
Example of a successful article retrieval using LAST:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] NEXT
[S] 223 3000237 <668929@example.org> retrieved
[C] LAST
[S] 223 3000234 <45223423@example.com> retrieved
Example of an attempt to retrieve an article without having selected
a group (via the GROUP command) first:
[Assumes current selected newsgroup is invalid.]
[C] LAST
[S] 412 no newsgroup selected
Example of an attempt to retrieve an article using the LAST command
when the current article number is that of the first article in the
group:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] LAST
[S] 422 No previous article to retrieve
Example of an attempt to retrieve an article using the LAST command
when the current selected newsgroup is empty:
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[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] LAST
[S] 420 No current article selected
7.1.3 NEXT
7.1.3.1 Usage
Syntax
NEXT
Responses
223 n message-id Article found
412 No newsgroup selected
420 Current article number is invalid
421 No next article in this group
Parameters
n = article number
message-id = article message-id
7.1.3.2 Description
If the current selected newsgroup is valid, the current article
number MUST be set to the next article in that newsgroup (that is,
the lowest existing article number greater than the current article
number). If successful, a response indicating the new current
article number and the message-id of that article MUST be returned.
No article text is sent in response to this command.
If the current article number is already the last article of the
newsgroup, a 421 response MUST be returned. In all other aspects
(apart, of course, from the lack of 422 response) this command is
identical to the LAST command (Section 7.1.2).
7.1.3.3 Examples
Example of a successful article retrieval using NEXT:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] NEXT
[S] 223 3000237 <668929@example.org> retrieved
Example of an attempt to retrieve an article without having selected
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a group (via the GROUP command) first:
[Assumes current selected newsgroup is invalid.]
[C] NEXT
[S] 412 no newsgroup selected
Example of an attempt to retrieve an article using the NEXT command
when the current article number is that of the last article in the
group:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT 3002322
[S] 223 3002322 <411@example.net> retrieved
[C] NEXT
[S] 421 No next article to retrieve
Example of an attempt to retrieve an article using the NEXT command
when the current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] NEXT
[S] 420 No current article selected
7.2 Retrieval of articles and article sections
The ARTICLE, BODY, HEAD, and STAT commands are very similar. They
differ only in the parts of the article that are presented to the
client and in the successful response code. The ARTICLE command is
described here in full, while the other commands are described in
terms of the differences. An article, as defined by RFC 1036,
consists of two parts: the article headers and the article body.
When responding to one of these commands, the server presents the
entire article or appropriate part and does not attempt to alter or
translate it in any way.
7.2.1 ARTICLE
7.2.1.1 Usage
Syntax
ARTICLE message-id
ARTICLE [number]
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Responses
First form (message-id specified)
220 0 message-id Article follows (multiline)
430 No article found with that message-id
Second form (optional article number specified)
220 n message-id Article follows (multiline)
412 No newsgroup selected
420 Current article number is invalid [1]
423 No such article in this newsgroup
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
[1] The 420 response can only occur if no article number has been
specified.
7.2.1.2 Description
The ARTICLE command selects an article based on the arguments and
presents the header, a blank line, and the body of that article. The
command has two forms.
In the first form, a message-id is specified (including the angle
brackets), and the server presents the article with that message-id
in its headers. In this case, the server MUST NOT alter the current
selected newsgroup or current article number. This is both to
facilitate the presentation of articles that may be referenced within
another article being read, and because of the semantic difficulties
of determining the proper sequence and membership of an article that
may have been crossposted to more than one newsgroup.
In the response, the article number is replaced with zero (that is,
the server is not required to determine whether the article is in the
current group or what article number(s) it has).
In the second form, an article number may be specified. If so, and
if there is an article with that number in the currently selected
newsgroup, the server MUST set the current article number to that
number.
Then, whether or not a number was specified, the article indicated by
the current article number is presented to the client.
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Note that a previously valid article number MAY become invalid if the
article has been removed. A previously invalid article number MAY
become valid if the article has been reinstated, but such an article
number MUST be no less than the reported low water mark for that
group.
The server MUST NOT change the current selected newsgroup as a result
of this command. The server MUST NOT change the current article
number except when an article number argument was provided and the
article exists; in particular, it MUST NOT change it following an
unsuccessful response.
The message-id of the article is taken from the message-id header
line of the article (required by RFC 1036). If there is no such
line, the message-id "<0>" MUST be used instead (without the double
quotes).
Since the message-id field is unique for each article, it may be used
by a client to skip duplicate displays of articles that have been
posted more than once, or to more than one newsgroup.
The article headers and body are returned as a multi-line response
following the 220 response code.
If the current article number is invalid, a 420 response MUST be
returned. If there is no article with the specified number, a 423
response MUST be returned. If the current selected newsgroup is
invalid, a 412 response MUST be returned.
7.2.1.3 Examples
Example of a successful retrieval of an article (using no article
number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] ARTICLE
[S] 220 3000234 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S]
[S] This is just a test article.
[S] .
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Example of a successful retrieval of an article by message-id:
[C] ARTICLE <45223423@example.com>
[S] 220 0 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S]
[S] This is just a test article.
[S] .
Example of an unsuccessful retrieval of an article by message-id:
[C] ARTICLE <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of an article by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 news.groups
[C] ARTICLE 300256
[S] 423 No such article number in this group
Example of an unsuccessful retrieval of an article by number because
no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] ARTICLE 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve an article when the current
selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] ARTICLE
[S] 420 No current article selected
7.2.2 HEAD
7.2.2.1 Usage
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Syntax
HEAD message-id
HEAD [number]
Responses
First form (message-id specified)
221 0 message-id Headers follow (multiline)
430 No article found with that message-id
Second form (optional article number specified)
221 n message-id Headers follow (multiline)
412 No newsgroup selected
420 Current article number is invalid [1]
423 No such article in this newsgroup
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
[1] The 420 response can only occur if no article number has been
specified.
7.2.2.2 Description
The HEAD command behaves identically to the ARTICLE command except
that, if the article exists, the response code is 221 instead of 220
and only the headers are presented (the blank line separating the
headers and body MUST NOT be included).
7.2.2.3 Examples
Example of a successful retrieval of the headers in an article (using
no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HEAD
[S] 221 3000234 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
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[S] .
Example of a successful retrieval of the headers in an article by
message-id:
[C] HEAD <45223423@example.com>
[S] 221 0 <45223423@example.com>
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: "Demo User" <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S] .
Example of an unsuccessful retrieval of the header of an article by
message-id:
[C] HEAD <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of the header of an article by
number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HEAD 300256
[S] 423 No such article number in this group
Example of an unsuccessful retrieval the header of an article by
number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] HEAD 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve the header of an article when the
current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] HEAD
[S] 420 No current article selected
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7.2.3 BODY
7.2.3.1 Usage
Syntax
BODY message-id
BODY [number]
Responses
First form (message-id specified)
222 0 message-id Body follows (multiline)
430 No article found with that message-id
Second form (optional article number specified)
222 n message-id Body follows (multiline)
412 No newsgroup selected
420 Current article number is invalid [1]
423 No such article in this newsgroup
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
[1] The 420 response can only occur if no article number has been
specified.
7.2.3.2 Description
The BODY command behaves identically to the ARTICLE command except
that, if the article exists, the response code is 222 instead of 220
and only the body is presented (the blank line separating the headers
and body MUST NOT be included).
7.2.3.3 Examples
Example of a successful retrieval of the body of an article (using no
article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] BODY
[S] 222 3000234 <45223423@example.com>
[S] This is just a test article.
[S] .
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Example of a successful retrieval of the body of an article by
message-id:
[C] BODY <45223423@example.com>
[S] 222 0 <45223423@example.com>
[S] This is just a test article.
[S] .
Example of an unsuccessful retrieval of the body of an article by
message-id:
[C] BODY <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of the body of an article by
number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] BODY 300256
[S] 423 No such article number in this group
Example of an unsuccessful retrieval of the body of an article by
number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] BODY 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve the body of an article when the
current selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] BODY
[S] 420 No current article selected
7.2.4 STAT
7.2.4.1 Usage
Syntax
STAT message-id
STAT [number]
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Responses
First form (message-id specified)
223 0 message-id Article exists
430 No article found with that message-id
Second form (optional article number specified)
223 n message-id Article exists
412 No newsgroup selected
420 Current article number is invalid [1]
423 No such article in this newsgroup
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
[1] The 420 response can only occur if no article number has been
specified.
7.2.4.2 Description
The STAT command behaves identically to the ARTICLE command except
that, if the article exists, it is NOT presented to the client and
the response code is 223 instead of 220. Note that the response is
NOT multi-line.
This command allows the client to determine whether an article
exists, and in the second form what its message-id is, without having
to process an arbitrary amount of text.
7.2.4.3 Examples
Example of STAT on an existing article (using no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT
[S] 223 3000234 <45223423@example.com>
Example of a STAT of an existing article by message-id:
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
Example of an STAT of an article not on the server by message-id:
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[C] STAT <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of STAT of an article not in the server by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT 300256
[S] 423 No such article number in this group
Example of STAT of an article by number when no newsgroup was
selected first:
[Assumes current selected newsgroup is invalid.]
[C] STAT 300256
[S] 412 No newsgroup selected
Example of STAT of an article when the current selected newsgroup is
empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] STAT
[S] 420 No current article selected
7.3 Article posting
Article posting is done in one of two modes: individual article
posting from news reading clients using POST, and article transfer
from other news servers using IHAVE.
7.3.1 POST
7.3.1.1 Usage
This command MUST NOT be pipelined.
Syntax
POST
Responses
Initial responses
340 Send article to be posted
440 Posting not permitted
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Subsequent responses
240 Article received OK
441 Posting failed
7.3.1.2 Description
If posting is allowed, a 340 response MUST be returned to indicate
that the article to be posted should be sent. If posting is
prohibited for some installation-dependent reason, a 440 response
MUST be returned.
If posting is permitted, the article MUST be presented to the server
by the client in the format specified by RFC 1036 (or by any of its
successors or extensions). The text forming the header and body of
the message to be posted MUST be sent by the client in the format
defined above (Section 3) 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.
Following the presentation of the termination sequence by the client,
the server MUST return a response indicating success or failure of
the article transfer. Note that response codes 340 and 440 are used
in direct response to the POST command. Others are returned
following the sending of the article.
A response of 240 SHOULD indicate that, barring unforseen server
errors, the posted article will be made available on the server and/
or transferred to other servers as appropriate. In other words,
articles not wanted by the server SHOULD be rejected with a 411
response and not accepted and silently discarded.
No attempt shall be made by the server to filter characters, fold or
limit lines, or otherwise process incoming text. The intent is that
the server just passes the incoming message to be posted to the
server installation's news posting software, which is not defined by
this document.
The client SHOULD NOT assume that the article has been successfully
transferred unless it receives an affirmative response from the
server. If the session is interrupted before the response is
received, it is possible that an affirmative response was sent but
has been lost. Therefore, in any subsequent session the client
SHOULD use the same message-id in the article when resending it or
check whether the article was successfully posted before resending it
to ensure that the resend will not result in a duplicate article.
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7.3.1.3 Examples
Example of a successful posting:
[C] POST
[S] 340 Input article; end with <CR-LF>.<CR-LF>
[C] From: "Demo User" <nobody@example.net>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Organization: An Example Net
[C]
[C] This is just a test article.
[C] .
[S] 240 Article received OK
Example of an unsuccessful posting:
[C] POST
[S] 340 Input article; end with <CR-LF>.<CR-LF>
[C] From: "Demo User" <nobody@example.net>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Organization: An Example Net
[C]
[C] This is just a test article.
[C] .
[S] 441 Posting failed
Example of an attempt to post when posting is not allowed:
[C] MODE READER
[S] 201 NNTP Service Ready, posting prohibited
[C] POST
[S] 440 Posting not permitted
7.3.2 IHAVE
7.3.2.1 Usage
This command MUST NOT be pipelined.
Syntax
IHAVE message-id
Responses
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Initial responses
335 Send article to be transferred
435 Article not wanted
436 Transfer not possible; try again later
Subsequent responses
235 Article transferred OK
436 Transfer failed; try again later
437 Transfer rejected; do not retry
Parameters
message-id = Article message-id
7.3.2.2 Description
The IHAVE 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 335 response MUST be returned, instructing the client to
send the entire article. If the server does not want the article
(if, for example, the server already has a copy of it), a 435
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 436
response MUST be returned.
If transmission of the article is requested, the client MUST send the
entire article, including header and body, in the format defined
above (Section 3) 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 235 response, indicating that the article
was successfully transferred, a 436 response, indicating that the
transfer failed but should be tried again later, or a 437 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 this command indicates that the forthcoming article
has already been posted at another site and is being forwarded from
another host. However, 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
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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 436 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 235 response) but later silently discard it.
7.3.2.3 Examples
Example of successfully sending an article to another site:
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 335 Send it; end with <CR-LF>.<CR-LF>
[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.a.test.article@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 235 Article transferred OK
Example of sending an article to another site that rejects it:
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 335 Send it; end with <CR-LF>.<CR-LF>
[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.a.test.article@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 437 Article rejected; don't send again
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Example of sending an article to another site where the transfer
fails:
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 335 Send it; end with <CR-LF>.<CR-LF>
[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.a.test.article@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 436 Transfer failed
Example of sending an article to a site that already has it:
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 435 Duplicate
Example of sending an article to a site that requests the article be
tried again later:
[C] IHAVE <i.am.an.article.you.defer@example.com>
[S] 436 Retry later
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8. Information commands
This section lists other commands that may be used at any time
between the beginning of a session and its termination. Using these
commands does not alter any state information, but the response
generated from their use may provide useful information to clients.
All servers MUST implement these commands.
8.1 DATE
8.1.1 Usage
Syntax
DATE
Responses
111 yyyymmddhhmmss server date and time
Parameters
yyyymmddHHmmss = Current UTC date and time on server
8.1.2 Description
This command exists to help clients find out the current Coordinated
Universal Time [9] from the server's perspective. This command MUST
NOT be used as a substitute for NTP [10], but to provide information
that might be useful when using the NEWNEWS command (see Section
8.4). A system providing NNTP service SHOULD implement NTP for the
purposes of keeping the system clock as accurate as possible.
The server MUST return a 111 response specifying the date and time on
the server in the form yyyymmddhhmmss. This date and time is in
Coordinated Universal Time.
8.1.3 Examples
[C] DATE
[S] 111 19990623135624
8.2 HELP
8.2.1 Usage
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Syntax
HELP
Responses
100 Help text follows (multiline)
8.2.2 Description
This command provides a short summary of commands that are understood
by this implementation of the server. The help text will be
presented as a multiline response following the 100 response code.
This text is not guaranteed to be in any particular format and MUST
NOT be used by clients as a replacement for the LIST EXTENSIONS
command described in Section 6.1
8.2.3 Examples
[C] HELP
[S] 100 Help text follows
[S] This is some help text. There is no specific
[S] formatting requirement for this test, though
[S] it is customary for it to list the valid commands
[S] and give a brief definition of what they do
[S] .
8.3 NEWGROUPS
8.3.1 Usage
Syntax
NEWGROUPS date time [GMT]
Responses
231 List of new newsgroups follows (multiline)
Parameters
date = Date in yymmdd or yyyymmdd format
time = Time in hhmmss format
8.3.2 Description
This command returns a list of newsgroups created on the server since
the specified date and time. The results are in the same format as
the LIST ACTIVE command (see Section 8.6.1).
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OUTSTANDING ISSUE
Does the output include high/low/status or not? If so, the
examples are wrong. If not, the above text is wrong.
The date is specified as 6 or 8 digits in the format [xx]yymmdd,
where xx is the first two digits of the year (19-99), yy is the last
two digits of the year (00-99), mm is the month (01-12), and dd is
the day of the month (01-31). If the first two digits of the year
are not specified, the year is to be taken from the current century
if yy is smaller than or equal to the current year, otherwise the
year is from the previous century.
The time is specified as 6 digits in the format hhmmss, where hh is
the hours in the 24-hour clock (00-23), mm is the minutes (00-59),
and ss is the seconds (00-60, to allow for leap seconds). The token
"GMT" specifies that the date and time are given in Coordinated
Universal Time; if it is omitted then the date and time are specified
in the server's local timezone. Note that there is no way using the
protocol specified in this document to establish the server's local
timezone.
Note that an empty list is a possible valid response and indicates
that there are no new newsgroups since that date-time.
Clients SHOULD make all queries using Coordinated Universal Time
(i.e. by including the "GMT" parameter) when possible.
8.3.3 Examples
Example where there are new groups:
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] alt.rfc-writers.recovery
[S] tx.natives.recovery
[S] .
Example where there are no new groups:
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] .
8.4 NEWNEWS
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8.4.1 Usage
Syntax
NEWNEWS wildmat date time [GMT]
Responses
230 List of new articles follows (multiline)
Parameters
wildmat = Newsgroups of interest
date = Date in yymmdd or yyyymmdd format
time = Time in hhmmss format
8.4.2 Description
This command returns a list of message-ids of articles posted or
received on the server, in the newsgroups whose names match the
wildmat, since the specified date and time. One message-id is sent
on each line; the order of the response has no specific significance
and may vary from response to response in the same session. A
message-id MAY appear more than once; if it does so, it has the same
meaning as if it appeared only once.
Date and time are in the same format as the NEWGROUPS command (see
Section 8.3).
Note that an empty list is a possible valid response and indicates
that there is currently no new news in the relevant groups.
Clients SHOULD make all queries in Coordinated Universal Time (i.e.
by using the "GMT" parameter) when possible.
8.4.3 Examples
Example where there are new articles:
[C] NEWNEWS news.*,sci.* 19990624 000000 GMT
[S] 230 list of new articles by message-id follows
[S] <i.am.a.new.article@example.com>
[S] <i.am.another.new.article@example.com>
[S] .
Example where there are no new articles:
[C] NEWNEWS alt.* 19990624 000000 GMT
[S] 230 list of new articles by message-id follows
[S] .
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8.5 Time
As described in Section 7, each article has an arrival timestamp.
Each newsgroup also has a creation timestamp. These timestamps are
used by the NEWNEWS and NEWGROUP commands to construct their
reponses.
The DATE command MUST return a timestamp from the same clock as is
used for determining article arrival and group creation times. This
clock SHOULD be monotonic, and adjustments SHOULD be made by running
it fast or slow compared to "real" time rather than by making sudden
jumps.
Clients can ensure that they do not have gaps in lists of articles or
groups by using the DATE command in the following manner:
First session:
Issue DATE command and record result
Issue NEWNEWS command using a previously chosen timestamp
Subsequent sessions:
Issue DATE command and hold result in temporary storage
Issue NEWNEWS command using timestamp saved from previous session
Overwrite saved timestamp with that currently in temporary storage
In order to allow for minor errors, clients MAY want to adjust the
timestamp back by two or three minutes before using it in NEWNEWS.
8.5.1 Examples
First session:
[C] DATE
[S] 111 20010203112233
[C] NEWNEWS local.chat 20001231 235959 GMT
[S] 230 list follows
[S] <article.1@local.service>
[S] <article.2@local.service>
[S] <article.3@local.service>
[S] .
Second session (the client has subtracted 3 minutes from the
timestamp returned previously):
[C] DATE
[S] 111 20010204003344
[C] NEWNEWS local.chat 20010203 111933 GMT
[S] 230 list follows
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[S] <article.3@local.service>
[S] <article.4@local.service>
[S] <article.5@local.service>
[S] .
Note how <article.3@local.service> arrived in the 3 minute gap and so
is listed in both responses.
8.6 The LIST commands
8.6.1 LIST ACTIVE
8.6.1.1 Usage
Syntax
LIST ACTIVE [wildmat]
Responses
215 Information follows (multiline)
Parameters
wildmat = groups of interest
8.6.1.2 Description
The LIST ACTIVE command with no parameters returns a list of valid
newsgroups and associated information. Each newsgroup is sent as a
line of text in the following format:
group first last status
where:
"group" is the name of the newsgroup;
"first" is the current low water mark for the group;
"last" is the current high water mark for the group;
"status" is the current status of the group on this server; typically
this is one of:
"y" posting is permitted
"n" posting is not permitted
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"m" postings will be forwarded to the newsgroup moderator
Other status strings may exist. The definition of these other
values and the circumstances under which they are returned is
covered in other specifications.
OUTSTANDING ISSUE
Is the order "group first last status" or "group last first
status"? The examples match the description above, but they
don't match the news server I have tested.
Each field in the line is separated from its neighboring fields by
one or more US-ASCII spaces.
The "first" and "last" fields correspond to the high and low water
marks described in the GROUP command (see Section 7.1.1).
The status of a newsgroup only indicates how posts to that newsgroup
are processed. It does not indicate if the current client is
permitted to post. That is indicated by the status code returned as
part of the greeting. Note that an empty list is a possible valid
response, and indicates that there are currently no valid newsgroups.
If the optional wildmat parameter is specified, the list is limited
to only the groups whose names match the wildmat. If no wildmat is
specified, the keyword ACTIVE MAY be omitted without altering the
effect of the command.
8.6.1.3 Examples
Example of LIST ACTIVE returning a list of newsgroups:
[C] LIST ACTIVE
[S] 215 list of newsgroups follows
[S] misc.test 3000234 3002322 y
[S] alt.fc-writers.recovery 1 4 y
[S] tx.natives.recovery 56 89 y
[S] .
Example of LIST ACTIVE omitting the second keyword and returning no
newsgroups:
[C] LIST
[S] 215 list of newsgroups follows
[S] .
Example of LIST ACTIVE with a wildmat:
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[C] LIST ACTIVE *.recovery
[S] 215 list of newsgroups follows
[S] alt.fc-writers.recovery 1 4 y
[S] tx.natives.recovery 56 89 y
[S] .
8.6.2 LIST ACTIVE.TIMES
8.6.2.1 Usage
This command is optional.
Syntax
LIST ACTIVE.TIMES [wildmat]
Responses
215 Information follows (multiline)
503 Facility not available
Parameters
wildmat = groups of interest
8.6.2.2 Description
The active.times file is maintained by some news transport systems to
contain information about who created a particular newsgroup and
when. Each line of this file consists of three fields separated from
each other by one or more US-ASCII space characters. The first field
is the name of the newsgroup. The second is the time when this group
was created on this news server, measured in seconds since the start
of January 1, 1970. The third is the email address of the entity
that created the newsgroup, and must be a mailbox as defined in RFC
2822 [7].
If the information is available, it is returned as a multi-line
response following the 215 response code. If the information is not
available, a 503 response MUST be returned. If the server does not
recognize the command, a 501 response MUST be returned.
If the optional wildmat parameter is specified, the list is limited
to only the groups whose names match the wildmat (and therefore may
be empty).
8.6.2.3 Examples
Example of LIST ACTIVE.TIMES returning a list of newsgroups:
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[C] LIST ACTIVE.TIMES
[S] 215 information follows
[S] misc.test 930445408 <creatme@isc.org>
[S] alt.rfc-writers.recovery 930562309 <m@example.com>
[S] tx.natives.recovery 930678923 <sob@academ.com>
[S] .
Example of LIST ACTIVE.TIMES returning an error where the command is
recognised but the software does not maintain this information:
[C] LIST ACTIVE.TIMES
[S] 503 program error, function not performed
Example of LIST ACTIVE.TIMES sent to a server that does not recognize
this command:
[C] LIST ACTIVE.TIMES
[S] 501 Syntax Error
8.6.3 LIST DISTRIBUTIONS
8.6.3.1 Usage
This command is optional.
Syntax
LIST DISTRIBUTIONS
Responses
215 Information follows (multiline)
503 Facility not available
8.6.3.2 Description
The distributions file is maintained by some news transport systems
to contain information about valid values for the Distribution: line
in a news article header and about what the values mean. Each line
of this file consists of two fields separated from each other by one
or more US-ASCII space characters. The first field is a value and
the second is a short explanation of the meaning of that value.
If the information is available, it is returned as a multi-line
response following the 215 response code. If the information is not
available, a 503 response MUST be returned. If the server does not
recognize the command, a 501 response MUST be returned.
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8.6.3.3 Examples
Example of LIST DISTRIBUTIONS returning a list of distributions:
[C] LIST DISTRIBUTIONS
[S] 215 information follows
[S] usa United States of America
[S] na North America
[S] world All over the World
[S] .
Example of LIST DISTRIBUTIONS returning an error where the command is
recognised but the software does not maintain this information:
[C] LIST DISTRIBUTIONS
[S] 503 program error, function not performed
Example of LIST DISTRIBUTIONS sent to a server that does not
recognize this command:
[C] LIST DISTRIBUTIONS
[S] 501 Syntax Error
8.6.4 LIST DISTRIB.PATS
8.6.4.1 Usage
This command is optional.
Syntax
LIST DISTRIB.PATS
Responses
215 Information follows (multiline)
503 Facility not available
8.6.4.2 Description
The distrib.pats file is maintained by some news transport systems to
choose a value for the Distribution: line in the header of a news
article being posted. Each line of this file consists of three
fields separated from each other by a US-ASCII colon. The first
field is a weight, the second field is a wildmat (which may be a
simple group name), and the third field is a value for the
Distribution: header.
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The client MAY use this information to select a Distribution: value
based on the name of a newsgroup. To do so, it should determine the
lines whose second field matches the newsgroup name, select from
among them the line with the highest weight (with 0 being the
lowest), and use the value of the third field to construct the
Distribution: header.
If the information is available, it is returned as a multi-line
response following the 215 response code. If the information is not
available, a 503 response MUST be returned. If the server does not
recognize the command, a 501 response MUST be returned.
8.6.4.3 Examples
Example of LIST DISTRIB.PATS returning a list of newsgroups:
[C] LIST DISTRIB.PATS
[S] 215 information follows
[S] 10:local.*:local
[S] 5:*:world
[S] 20:local.here.*:thissite
[S] .
Example of LIST DISTRIB.PATS returning an error where the command is
recognised but the software does not maintain this information:
[C] LIST DISTRIB.PATS
[S] 503 program error, function not performed
Example of LIST DISTRIB.PATS sent to a server that does not recognize
this command:
[C] LIST DISTRIB.PATS
[S] 501 Syntax Error
8.6.5 LIST NEWSGROUPS
8.6.5.1 Usage
This command is optional.
Syntax
LIST NEWSGROUPS [wildmat]
Responses
215 Information follows (multiline)
503 Facility not available
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Parameters
wildmat = groups of interest
8.6.5.2 Description
The newsgroups file is maintained by some news transport systems to
contain the name of each newsgroup that is available on the server
and a short description about the purpose of the group. Each line of
this file consists of two fields separated from each other by one or
more US-ASCII space characters. The first field is the name of the
newsgroup and the second is a short description of the group. Note
that an empty list is a possible valid response, and indicates that
there are currently no valid newsgroups.
If the information is available, it is returned as a multi-line
response following the 215 response code. If the information is not
available, a 503 response MUST be returned. If the server does not
recognize the command, a 501 response MUST be returned.
If the optional wildmat parameter is specified, the list is limited
to only the groups whose names match the wildmat.
8.6.5.3 Examples
Example of LIST NEWSGROUPS returning a list of newsgroups:
[C] LIST NEWSGROUPS
[S] 215 information follows
[S] misc.test General Usenet testing
[S] alt.rfc-writers.recovery RFC Writers Recovery
[S] tx.natives.recovery Texas Natives Recovery
[S] .
Example of LIST NEWSGROUPS returning an error where the command is
recognised but the software does not maintain this information:
[C] LIST NEWSGROUPS
[S] 503 program error, function not performed
Example of LIST NEWSGROUPS sent to a server that does not recognize
this command:
[C] LIST NEWSGROUPS
[S] 501 Syntax error
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9. The CONCLUSION step
9.1 QUIT
9.1.1 Usage
Syntax
QUIT
Responses
205 Connection closing
9.1.2 Description
The server process MUST acknowledge the QUIT command and then close
the connection to the client. This is the preferred method for a
client to indicate that it has finished all its transactions with the
NNTP server.
If a client simply disconnects (or the connection times out or some
other fault occurs), the server MUST gracefully cease its attempts to
service the client, disconnecting from its end if necessary.
9.1.3 Examples
[C] QUIT
[S] 205 closing connection
[Server closes connection.]
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10. Framework for NNTP extensions
Although NNTP is widely and robustly deployed, some parts of the
Internet community might wish to extend the NNTP service. This
document defines a means whereby an extended NNTP client can query
the server to determine the service extensions that it supports.
It must be emphasized that any extension to the NNTP service should
not be considered lightly. NNTP's strength comes primarily from its
simplicity. Experience with many protocols has shown that:
Protocols with few options tend towards ubiquity, whilst protocols
with many options tend towards obscurity.
This means that each and every extension, regardless of its benefits,
must be carefully scrutinized with respect to its implementation,
deployment, and interoperability costs. In many cases, the cost of
extending the NNTP service will likely outweigh the benefit.
Given this environment, the framework for extensions described in
this document consists of:
o a mechanism for clients to determine a server's available
extensions
o a registry of NNTP service extensions
The LIST EXTENSIONS command is described in this document (see
Section 6.1) and is the mechanism for clients to use to determine
what extensions are available.
The IANA shall maintain a registry of NNTP service extensions.
An extension is identified by a unique extension-label, which is a
string of 1 to 12 uppercase letters. The extension-label will often
be the name of a new command that the extension adds. However this
is not a requirement: an extension might not add any new commands or
keywords.
An extension is either a private extension or else it is included in
the IANA registry and is defined in an RFC. Such RFCs either must be
on the standards-track or must define an IESG-approved experimental
protocol.
The definition of an extension must include:
o a descriptive name for the extension
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o the extension-label (which is returned by LIST EXTENSIONS to
indicate to the client that the server supports this particular
extension)
o the syntax, values, and meanings of any parameters following the
extension-label in the output of LIST EXTENSIONS
o any new NNTP commands associated with the extension
o the syntax and possible values of parameters associated with the
new NNTP commands
o any new parameters the extension associates with any other
pre-existing NNTP commands
o how support for the extension affects the behavior of a server and
NNTP client
o any increase in the maximum length of commands over the value
specified in this document
o a specific statement about the effect on pipelining this extension
may have (if any)
The extension-label of private extensions MUST begin with "X". The
extension-label of registered extensions MUST NOT begin with "X".
A server MUST NOT provide any extension, whether or not listed in the
output from LIST EXTENSIONS, unless it is either a registered
extension or a private extension.
Except where stated otherwise, the commands in this document are
understood (even if not supported) by all servers and are not
described in the list of features returned by the LIST EXTENSIONS
command.
A server MAY provide additional keywords - either for new commands or
new variants of existing commands - as part of a private extension.
These new keywords MUST begin with "X".
A server MUST NOT send different response codes to basic NNTP
commands documented here or commands documented in registered
extensions in response to the availability or use of a private
extension.
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10.1 Initial IANA registry
The IANA's initial registry of NNTP service extensions consists of
these entries:
Extension Label Added behavior
Specific article numbers LISTGROUP Defined in this document
Overview support OVER Defined in this document
Header pattern matching HDR Defined in this document
10.2 Standard extensions
Each of the following sections describes an extension that a server
MAY provide. If the server provides the extension, it MUST include
the appropriate extension label in the response to LIST EXTENSIONS.
If it does not provide it, it MUST NOT include the appropriate
extension label. The descriptions of facilities in each section are
written as if the extension is provided. If it is not provided, the
entire section should be ignored.
If the server provides an extension, it MUST implement all of the
commands in the specification of the extension except for those
marked as optional. If it does not provide an extension, it MUST NOT
implement any of the commands in the specification of that extension.
10.3 The LISTGROUP extension
This extension provides one command and has the extension label
LISTGROUP.
10.3.1 LISTGROUP
10.3.1.1 Usage
Syntax
LISTGROUP [ggg]
Responses
211 Article numbers follow (multiline)
411 No such newsgroup
412 No newsgroup selected [1]
Parameters
ggg = name of newsgroup
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[1] The 412 response can only occur if no group has been specified.
10.3.1.2 Description
The LISTGROUP command is used to get a listing of all the article
numbers in a particular newsgroup.
The optional parameter ggg is the name of the newsgroup to be
selected (e.g. "news.software.misc"). A list of valid newsgroups
may be obtained from the LIST ACTIVE command. If no group is
specified, the current selected newsgroup is used.
OUTSTANDING ISSUE
On at least some servers the 211 response line is the same as with
GROUP. Should this be a requirement?
The list of article numbers is returned as a multi-line response
following the 211 response code. It contains one number per line, is
in numerical order, and lists precisely those articles that exist in
the group.
When a valid group is selected by means of this command, the current
selected newsgroup MUST be set to that group and the current article
number MUST be set to the first article in the group. If an empty
newsgroup is selected, the current article pointer is made invalid.
If an invalid group is specified, the current selected newsgroup and
current article number MUST NOT be changed.
The LISTGROUP command MAY be used by a client as a replacement for
the GROUP command in establishing a valid current selected newsgroup
and current article number.
If the group specified is not available on the server, a 411 response
MUST be returned. If no group is specified and the current selected
newsgroup is invalid, a 412 response MUST be returned.
10.3.1.3 Examples
Example of LISTGROUP on an empty group:
[C] LISTGROUP example.empty.newsgroup
[S] 211 list of article numbers follows
[S] .
Example of LISTGROUP on a valid current selected newsgroup:
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[C] GROUP misc.test
[S] 211 2000 3000234 3002322 misc.test selected
[C] LISTGROUP
[S] 211 list follows
[S] 3000234
[S] 3000237
[S] 3000238
[S] 3000239
[S] 3002322
[S] .
Example of LISTGROUP failing because no group has been selected:
[Assumes current selected newsgroup is invalid.]
[C] LISTGROUP
[S] 412 no current group
[C] GROUP example.is.sob.bradner.or.barber
[S] 411 no such group
[C] LISTGROUP
[S] 412 no current group
10.4 Article metadata
The OVER and HDR extensions refer to the concept of "article
metadata". This is data about articles that does not occur within
the article itself. Each metadata item has a name which MUST begin
with a colon. Note that a historical feature of the LIST
OVERVIEW.FMT command means that metadata names SHOULD NOT end with
":full".
When generating a metadata item, the server MUST compute it for
itself and MUST NOT trust any related value provided in the article.
(In particular, a Lines: or Bytes: header in the article MUST NOT be
assumed to specify the correct number of lines or bytes in the
article.)
This specification defines two metadata items: ":bytes" and ":lines".
Implementations and other extensions may define other metadata items.
10.4.1 The :bytes metadata item
The :bytes metadata item for an article is a decimal integer. It
MUST equal the number of octets in the entire article - headers,
body, and separating blank line - except that the US-ASCII CRLF at
the end of each line MAY (but SHOULD NOT) be counted as a single
octet.
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OUTSTANDING ISSUE
Should this be called ":octets" instead? Or should it be a count
of UTF characters rather than octets?
10.4.2 The :lines metadata item
The :lines metadata item for an article is a decimal integer. It
MUST equal the number of lines in the article body (excluding the
blank line separating headers and body); equivalently, it is two less
than the number of US-ASCII CRLF pairs that the BODY command would
return for that article (the extra two are those following the
response code and the termination octet).
10.5 The OVER extension
This extension provides two commands, OVER and LIST OVERVIEW.FMT.
The label for this extension is OVER.
The OVER extension provides access to the overview database [8],
which is a database of header lines extracted from incoming articles.
Only certain headers are included in the database. The database also
includes some article metadata.
The information stored in the database may change over time. The
LIST OVERVIEW.FMT command describes the information that would be
stored for an article arriving at the same time as the command was
executed.
10.5.1 OVER
10.5.1.1 Usage
Syntax
OVER [range]
Responses
224 Overview information follows (multiline)
412 No newsgroup selected
420 Current article number is invalid
423 No articles in that range
Parameters
range = Article(s) to return information for
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10.5.1.2 Description
The OVER command returns the contents of the headers and metadata in
the database for the article(s) specified from the current selected
newsgroup.
The optional range argument may be any of the following:
o an article number
o an article number followed by a dash to indicate all following
o an article number followed by a dash followed by another article
number
If no argument is specified, then the current article number is used.
If the information is available, it is returned as a multi-line
response following the 224 response code. If the current selected
newsgroup is invalid, a 412 response MUST be returned. If there are
no articles in the range specified, a 423 response MUST be returned.
If OVER is sent without any arguments and the current article number
is invalid, a 420 response MUST be returned. If the client does not
have permission to access the overview database, a 502 response MUST
be returned.
OUTSTANDING ISSUE
Should this be 502 ("not permitted") or 503 ("there is no overview
database")? In which case, why provide the command?
For a successful response, the output consists of one line per
article, sorted in numerical order of article number. Each line
consists of a number of fields separated by an US-ASCII TAB
character. A field may be empty (in which case there will be two
adjacent US-ASCII TABs), and a sequence of trailing US-ASCII TABs may
be omitted.
The first 8 fields MUST be the following, in order:
article number
"Subject" header
"From" header
"Date" header
"Message-ID" header
"References" header
:bytes metadata item
:lines metadata item
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Any subsequent fields are the contents of the other headers and
metadata held in the database.
For the five mandatory headers, the content of each field MUST be
based on the original header with the header name and following colon
and space removed. If the article does not contain that header, or
if there is nothing following the colon and space, the field MUST be
empty. For the two mandatory metadata items, the content of the
field MUST be just the value, with no other text.
For all subsequent fields that contain headers, the content MUST be
based on the entire header including the name. For all subsequent
fields that contain metadata, the field consists of the metadata
name, a single US-ASCII space, and then the value.
For all fields, the value is processed by first removing all US-ASCII
CRLF pairs and then replacing each remaining US-ASCII NUL, TAB, CR,
or LF character with a single US-ASCII space (for example, CR LF LF
TAB will become two spaces). If there is no such header in the
article, or no such metadata item, or no header or item stored in the
database for that article, the corresponding field MUST be empty.
The server SHOULD NOT produce output for articles that no longer
exist.
10.5.1.3 Examples
In the first two examples, US-ASCII tab has been replaced by vertical
bar and some lines have been folded for readability.
Example of a successful retrieval of overview information for an
article (using no article number):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] OVER
[S] 224 Overview information follows
[S] 300234|I am just a test article|"Demo User"
<nobody@example.com>|6 Oct 1998 04:38:40 -0500|
<45223423@example.com>|<45454@example.net>|1234|
17|Xref: news.example.com misc.test:3000363
[S] .
Example of a successful retrieval of overview information for a range
of articles:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
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[C] OVER 3000234-3000240
[S] 224 Overview information follows
[S] 300234|I am just a test article|"Demo User"
<nobody@example.com>|6 Oct 1998 04:38:40 -0500|
<45223423@example.com>|<45454@example.net>|1234|
17|Xref: news.example.com misc.test:3000363
[S] 3000235|Another test article|nobody@nowhere.to
(Demo User)|6 Oct 1998 04:38:45 -0500|<45223425@to.to>||
4818|37||Distribution: fi
[S] 3000238|Re: I am just a test article|somebody@elsewhere.to|
7 Oct 1998 11:38:40 +1200|<kfwer3v@elsewhere.to>|
<45223423@to.to>|9234|51
[S] .
Note the missing "References" and Xref headers in the second line,
the missing trailing field(s) in the first and last lines, and that
there are only results for those articles that still exist.
Example of an unsuccessful retrieval of overview information on an
article by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] OVER 300256
[S] 420 No such article in this group
Example of an unsuccessful retrieval of overview information by
number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] OVER
[S] 412 No newsgroup selected
Example of an attempt to retrieve information when the current
selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] OVER
[S] 420 No current article selected
10.5.2 LIST OVERVIEW.FMT
10.5.2.1 Usage
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Syntax
LIST OVERVIEW.FMT
Responses
215 Information follows (multiline)
503 Facility not available
10.5.2.2 Description
OUTSTANDING ISSUE
Should this be optional even when the OVER extension is provided?
If so, is there a point in the 503 response?
The LIST OVERVIEW.FMT command returns a description of the fields in
the database. The fields MUST be listed in the order that they will
be returned by the OVER command for a newly-received article (the
information stored for articles may change over time).
If the information is available, it is returned as a multi-line
response following the 215 response code. If the information is not
available, a 503 response MUST be returned. The information contains
one line per field in the order they are returned by the OVER
command; he first 7 lines MUST be exactly:
Subject:
From:
Date:
Message-ID:
References:
:bytes
:lines
except that, for compatibility with existing implementations, the
last two lines MAY instead be:
Bytes:
Lines:
even though they refer to metadata, not headers.
All subsequent lines MUST consist of either a header name followed by
":full", or the name of a piece of metadata.
There are no leading or trailing spaces in the output.
Note that the 7 fixed lines describe the 2nd to 8th fields of the
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OVER output. The "full" suffix is a reminder that the corresponding
fields include the header name.
This command MAY generate different results if used more than once in
a session.
10.5.2.3 Examples
Example of LIST OVERVIEW.FMT output corresponding to the example OVER
output above, using the preferred format:
[C] LIST OVERVIEW.FMT
[S] 215 Order of fields in overview database.
[S] Subject:
[S] From:
[S] Date:
[S] Message-ID:
[S] References:
[S] :bytes
[S] :lines
[S] Xref:full
[S] Distribution:full
[S] .
Example of LIST OVERVIEW.FMT output corresponding to the example OVER
output above, using the alternative format:
[C] LIST OVERVIEW.FMT
[S] 215 Order of fields in overview database.
[S] Subject:
[S] From:
[S] Date:
[S] Message-ID:
[S] References:
[S] Bytes:
[S] Lines:
[S] Xref:full
[S] Distribution:full
[S] .
Example of LIST OVERVIEW.FMT returning an error:
[C] LIST OVERVIEW.FMT
[S] 503 overview.fmt not available
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10.6 The HDR extension
This extension provides one new command: HDR. The label for this
extension is HDR.
10.6.1 HDR
10.6.1.1 Usage
Syntax
HDR header range
HDR header message-id
HDR header
Responses
First form (range specified)
225 Headers follow (multiline)
412 No newsgroup selected
423 No articles in that range
Second form (message-id specified)
225 Headers follow (multiline)
430 No article with that message-id
Third form (current article number used)
225 Headers follow (multiline)
412 No newsgroup selected
420 Current article number is invalid
Parameters
header = name of header, without the colon
range = number(s) of articles
message-id = message-id of article
10.6.1.2 Description
The HDR command retrieves specific headers from an article or
specified range of articles in the current selected newsgroup, or
from an article specified by message-id. It can also return certain
metadata about the article or articles.
The required header parameter is the name of a header (e.g.
"subject") in an article, or the name of a metadata item, and is
case-insensitive. See RFC 1036 [6] for a list of valid header lines.
Names of metadata items always include a colon. Except where stated
otherwise, metadata items are treated as if they were header values,
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and references to headers in this description apply equally to
metadata items.
OUTSTANDING ISSUE
Should this be changed to require the name to *begin* with a
colon?
The range parameter may be any of the following:
o an article number
o an article number followed by a dash to indicate all following
o an article number followed by a dash followed by another article
number
The message-id argument indicates a specific article. As shown by
the syntax, the range and message-id arguments are mutually
exclusive; if neither are specified, the current article number is
used.
If the information is available, it is returned as a multi-line
response following the 225 response code and contains one line for
each article where the relevant header line exists. The line
consists of the article number, a US-ASCII space, and then the
contents of the header (without the header name or the colon and
space that follow it) or metadata item. If the article is specified
by message-id rather than by article range, the article number is
given as "0".
Header contents are modified as follows: all US-ASCII CRLF pairs are
removed, and then each remaining US-ASCII NUL, TAB, CR, or LF
character is replaced with a single US-ASCII space. (Note that this
is the same transformation as is performed by the OVER extension.)
The header content is in all cases taken from the article. This
means that, for example, a request for the header "Lines" returns the
contents of the "Lines" header of the specified articles, if any, not
the line count metadata or any other server-generated value. If the
header occurs in a given article multiple times, only the value of
the first occurrence is returned by HDR.
If the requested header is not present in the article or if it is
present but empty, a line for that article is included in the output
but the header content portion of the line is empty (the space after
the article number MAY be retained or omitted). If any article
number in the provided range does not exist in the group, no line for
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that article number is included in the output.
If the optional argument is a message-id and no such article exists,
a 430 response MUST be returned. If the optional argument is not a
message-id and the current selected newsgroup is invalid, a 412
response MUST be returned. If the optional argument is an article
number or number range and no article with that number or in that
number range exists in the current selected newsgroup, a 423 response
MUST be returned. If HDR is sent without any arguments and the
current article number is invalid, a 420 response MUST be returned.
A server MAY only allow HDR commands for a limited set of headers and
metadata items (such as those present in the overview database). If
so, it MUST respond with a 503 response to attempts to request other
headers, rather than returning erroneous results such as a successful
empty response.
10.6.1.3 Examples
Example of a successful retrieval of subject lines from a range of
articles (3000235 has no Subject header, and 3000236 is missing):
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR Subject 3000234-300238
[S] 225 Headers follow
[S] 3000234 I am just a test article
[S] 3000235
[S] 3000237 Re: I am just a test article
[S] 3000238 Ditto
[S] .
Example of a successful retrieval of line counts from a range of
articles:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR :lines 3000234-300238
[S] 225 Headers follow
[S] 3000234 42
[S] 3000235 5
[S] 3000237 11
[S] 3000238 2378
[S] .
Example of a successful retrieval of the subject line from an article
by message-id:
[C] GROUP misc.test
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[S] 211 1234 3000234 3002322 misc.test
[C] HDR subject <i.am.a.test.article@example.com>
[S] 225 Header information follows
[S] 0 I am just a test article
[S] .
Example of a successful retrieval of the subject line from the
current article:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR subject
[S] 225 Header information follows
[S] 3000234 I am just a test article
[S] .
Example of an unsuccessful retrieval of a header from an article by
message-id:
[C] HDR subject <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of headers from articles by
number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] HDR subject 300256-
[S] 412 No newsgroup selected
Example of an unsuccessful retrieval of headers because the current
selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] HDR subject 1-
[S] 423 No articles in that range
Example of an unsuccessful retrieval of headers because the server
does not allow HDR commands for that header:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR Content-Type 3000234-300238
[S] 503 HDR not permitted on Content-Type
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11. Augmented BNF Syntax for NNTP Commands
This syntax defines the non-terminal "command-line". Note that ABNF
strings are case insensitive.
command-line = command EOL
command = article-command /
body-command /
date-command /
group-command /
hdr-command /
head-command /
help-command /
ihave-command /
last-command /
list-active-command /
list-active-times-command /
list-distrib-pats-command /
list-distributions-command /
list-extensions-command /
list-newsgroups-command /
list-overview-fmt-command /
listgroup-command /
mode-reader-command /
newgroups-command /
newnews-command /
next-command /
over-command /
post-command /
quit-command /
stat-command /
x-command
article-command = "ARTICLE" [article-ref]
body-command = "BODY" [article-ref]
date-command = "DATE"
group-command = "GROUP" WS newsgroup-name
hdr-command = "HDR" WS header-meta-name [range-ref]
head-command = "HEAD" [article-ref]
help-command = "HELP"
ihave-command = "IHAVE" WS message-id
last-command = "LAST"
list-active-command = "LIST" [WS "ACTIVE" [WS wildmat]]
list-active-times-command = "LIST" WS "ACTIVE.TIMES" [WS wildmat]
list-distrib-pats-command = "LIST" WS "DISTRIB.PATS"
list-distributions-command = "LIST" WS "DISTRIBUTIONS"
list-extensions-command = "LIST" WS "EXTENSIONS"
list-newsgroups-command = "LIST" WS "NEWSGROUPS" [WS wildmat]
list-overview-fmt-command = "LIST" WS "OVERVIEW.FMT"
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listgroup-command = "LISTGROUP" [WS newsgroup-name]
mode-reader-command = "MODE" WS "READER"
newgroups-command = "NEWGROUPS" WS date-time
newnews-command = "NEWNEWS" WS wildmat WS date-time
next-command = "NEXT"
over-command = "OVER" [WS range]
post-command = "POST"
quit-command = "QUIT"
stat-command = "STAT" [article-ref]
x-command = x-command-name *(WS x-argument)
; Each extension command is specified fully elsewhere
article-ref = WS (article-number / message-id)
article-number = 1*16DIGIT
date = [2DIGIT] 6DIGIT
date-time = date WS time [WS "GMT"]
header-meta-name = header-name / metadata-name
header-name = 1*header-name-char
header-name-char = %x21-39 / %x3B-7E ; exclude SP and :
message-id = "<" 1*248message-id-char ">"
; subject to requirements in
Section 7
>
message-id-char = %x21-3B / %x3C / %x3E-7E ; exclude SP < >
metadata-name = ":" 1*header-name-char
newsgroup-name = 1*wildmat-exact
range = article-number ["-" [article-number]]
range-ref = WS (range / message-id)
time = 6DIGIT
x-command-name = 3*12%x21-7E
x-argument = 1*(%x21-7E / UTF-8-non-ascii)
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E /
UTF-8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
CR = %x0D
CRLF = CR LF
DIGIT = %x30-39
EOL = *(SP / HT) CRLF
HT = %x09
LF = %x0A
SP = %x20
UTF-8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4 / UTF8-5 / UTF8-6
UTF8-1 = %x80-BF
UTF8-2 = %xC2-DF UTF8-1
UTF8-3 = %xE0 %A0-BF UTF8-1 / %xE1-EC 2UTF8-1 /
%xED %80-9F UTF8-1 / %xEE-EF 2UTF8-1
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UTF8-4 = %xF0 %90-BF 2UTF8-1 / %xF1-F7 3UTF8-1
UTF8-5 = %xF8 %88-BF 3UTF8-1 / %xF9-FB 4UTF8-1
UTF8-6 = %xFC %84-BF 4UTF8-1 / %xFD 5UTF8-1
WS = 1*(SP / HT)
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12. Security Considerations
This section is meant to inform application developers, information
providers, and users of the security limitations in NNTP as described
by this document. The discussion does not include definitive
solutions to the problems revealed, though it does make some
suggestions for reducing security risks.
12.1 Personal and Proprietary Information
NNTP, because it was created to distribute network news articles,
will forward whatever information is stored in those articles.
Specification of that information is outside this scope of this
document, but it is likely that some personal and/or proprietary
information is available in some of those articles. It is very
important that designers and implementers provide informative
warnings to users so personal and/or proprietary information in
material that is added automatically to articles (e.g. in headers)
is not disclosed inadvertently. Additionally, effective and easily
understood mechanisms to manage the distribution of news articles
SHOULD be provided to NNTP Server administrators, so that they are
able to report with confidence the likely spread of any particular
set of news articles.
12.2 Abuse of Server Log Information
A server is in the position to save session data about a user's
requests that might identify their reading patterns or subjects of
interest. This information is clearly confidential in nature and its
handling can be constrained by law in certain countries. People
using the NNTP protocol to provide data are responsible for ensuring
that such material is not distributed without the permission of any
individuals that are identifiable by the published results.
12.3 Weak Authentication and Access Control
There is no user-based or token-based authentication in the basic
NNTP specification. Access is normally controlled by server
configuration files. Those files specify access by using domain
names or IP addresses. However, this specification does permit the
creation of extensions to the NNTP protocol itself for such purposes.
While including such mechanisms is optional, doing so is strongly
encouraged.
Other mechanisms are also available. For example, a proxy server
could be put in place that requires authentication before connecting
via the proxy to the NNTP server.
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12.4 DNS Spoofing
Many existing NNTP implementations authorize incoming connections by
checking the IP address of that connection against the IP addresses
obtained via DNS lookups of lists of domain names given in local
configuration files. Servers that use this type of authentication,
and clients that find a server by doing a DNS lookup of the server
name, rely very heavily on the Domain Name Service, and are thus
generally prone to security attacks based on the deliberate
misassociation of IP addresses and DNS names. Clients and servers
need to be cautious in assuming the continuing validity of an IP
number/DNS name association.
In particular, NNTP clients and servers SHOULD rely on their name
resolver for confirmation of an IP number/DNS name association,
rather than caching the result of previous host name lookups. Many
platforms already can cache host name lookups locally when
appropriate, and they SHOULD be configured to do so. It is proper
for these lookups to be cached, however, only when the TTL (Time To
Live) information reported by the name server makes it likely that
the cached information will remain useful.
If NNTP clients or servers cache the results of host name lookups in
order to achieve a performance improvement, they MUST observe the TTL
information reported by DNS. If NNTP clients or servers do not
observe this rule, they could be spoofed when a previously accessed
server's IP address changes. As network renumbering is expected to
become increasingly common, the possibility of this form of attack
will grow. Observing this requirement thus reduces this potential
security vulnerability.
This requirement also improves the load-balancing behavior of clients
for replicated servers using the same DNS name and reduces the
likelihood of a user's experiencing failure in accessing sites that
use that strategy.
12.5 UTF-8 issues
The UTF-8 specification [2] permits only certain sequences of octets
and designates others as either malformed or "illegal". The Unicode
standard identifies a number of security issues related to illegal
sequences and forbids their generation by conforming implementations.
Implementations of this specification MUST NOT generate malformed or
illegal sequences and SHOULD detect them and take some appropriate
action. This could include:
o replacing such sequences by a "guessed" valid sequence (based on
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properties of the UTF-8 encoding);
o replacing such sequences by the sequence %xEF.BF.BD, which encodes
the "replacement character";
o closing the connection;
o generating a 501 response code.
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13. Acknowledgments
The author acknowledges the original authors of NNTP as documented in
RFC 977: Brian Kantor and Phil Lapsey.
The author gratefully acknowledges the work of the NNTP committee
chaired by Eliot Lear. The organization of this document was
influenced by the last available draft from this working group. A
special thanks to Eliot for generously providing the original
machine-readable sources for that document.
The author gratefully acknowledges the work of Marshall Rose & John
G. Meyers in RFC 1939 and the work of the DRUMS working group,
specifically RFC 1869, which is the basis of the NNTP extensions
mechanism detailed in this document.
OUTSTANDING ISSUE
Why RFC 1939?
The author gratefully acknowledges the authors of RFC 2616 for
providing specific and relevant examples of security issues that
should be considered for HTTP. Since many of the same considerations
exist for NNTP, those examples that are relevant have been included
here with some minor rewrites.
The author gratefully acknowledges the comments and additional
information provided by the following individuals in preparing one or
more of the progenitors of this document:
Russ Allbery <rra@stanford.edu>
Wayne Davison <davison@armory.com>
Chris Lewis <clewis@bnr.ca>
Tom Limoncelli <tal@mars.superlink.net>
Eric Schnoebelen <eric@egsner.cirr.com>
Rich Salz <rsalz@osf.org>
This work was motivated by the work of various news reader authors
and news server authors, which includes those listed below:
Rick Adams
Original author of the NNTP extensions to the RN news reader and
last maintainer of Bnews
Stan Barber
Original author of the NNTP extensions to the news readers that
are part of Bnews
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Geoff Collyer
Original author of the OVERVIEW database proposal and one of the
original authors of CNEWS
Dan Curry
Original author of the xvnews news reader
Wayne Davison
Author of the first threading extensions to the RN news reader
(commonly called TRN)
Geoff Huston
Original author of ANU NEWS
Phil Lapsey
Original author of the UNIX reference implementation for NNTP
Iain Lea
Original maintainer of the TIN news reader
Chris Lewis
First known implementer of the AUTHINFO GENERIC extension
Rich Salz
Original author of INN
Henry Spencer
One of the original authors of CNEWS
Kim Storm
Original author of the NN news reader
Finally, the present author gratefully acknowledges the vast amount
of work put into previous drafts by the previous author:
Stan Barber <sob@academ.com>
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Normative References
[1] Kantor, B. and P. Lapsley, "Network News Transfer Protocol",
RFC 977, February 1986.
[2] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[3] American National Standards Institute, "Coded Character Set -
7-bit American Standard Code for Information Interchange", ANSI
X3.4, 1986.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[6] Horton, M. and R. Adams, "Standard for interchange of USENET
messages", RFC 1036, December 1987.
[7] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[8] Robertson, R., "FAQ: Overview database / NOV General
Information", January 1995.
[9] International Telecommunications Union - Radio, "Glossary,
ITU-R Recommendation TF.686-1", ITU-R Recommendation TF.686-1,
October 1997.
[10] Mills, D., "Network Time Protocol (Version 3) Specification,
Implementation", RFC 1305, March 1992.
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Informative References
[11] Salz, R., "Manual Page for wildmat(3) from the INN 1.4
distribution, Revision 1.10", April 1992.
[12] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June
1999.
Author's Address
Clive D.W. Feather
Thus plc
322 Regents Park Road
London N3 2QQ
GB
Phone: +44 20 8371 1138
Fax: +44 870 051 9937
URI: http://www.davros.org/
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Intellectual Property Statement
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
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Feather Expires August 30, 2003 [Page 87]
