NNTP C. Feather
Internet-Draft Thus plc
Expires: September 19, 2004 March 21, 2004
Network News Transport Protocol
draft-ietf-nntpext-base-22
Status of this Memo
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patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3667.
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This Internet-Draft will expire on September 19, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The Network News Transport Protocol (NNTP) 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 and Ned Freed.
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This is draft 22.
Author's Note
This draft is written in XML using an NNTP-specific DTD. Custom
software is used to convert this to RFC 2629 [RFC2629] 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 Open Group.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . 5
2. Notation . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Basic Concepts . . . . . . . . . . . . . . . . . . . . . 8
3.1 Commands and Responses . . . . . . . . . . . . . . . . . 8
3.2 Response Codes . . . . . . . . . . . . . . . . . . . . . 10
3.2.1 Generic Response Codes . . . . . . . . . . . . . . . . . 11
3.2.1.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . 13
3.3 Pipelining . . . . . . . . . . . . . . . . . . . . . . . 15
3.3.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4 Articles . . . . . . . . . . . . . . . . . . . . . . . . 16
4. The WILDMAT format . . . . . . . . . . . . . . . . . . . 18
4.1 Wildmat syntax . . . . . . . . . . . . . . . . . . . . . 18
4.2 Wildmat semantics . . . . . . . . . . . . . . . . . . . 18
4.3 Extensions . . . . . . . . . . . . . . . . . . . . . . . 19
4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . 20
5. Session administration commands . . . . . . . . . . . . 21
5.1 Initial Connection . . . . . . . . . . . . . . . . . . . 21
5.2 MODE READER . . . . . . . . . . . . . . . . . . . . . . 22
5.3 LIST EXTENSIONS . . . . . . . . . . . . . . . . . . . . 25
5.4 QUIT . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6. Article posting and retrieval . . . . . . . . . . . . . 28
6.1 Group and article selection . . . . . . . . . . . . . . 28
6.1.1 GROUP . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1.2 LAST . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.1.3 NEXT . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.2 Retrieval of articles and article sections . . . . . . . 34
6.2.1 ARTICLE . . . . . . . . . . . . . . . . . . . . . . . . 34
6.2.2 HEAD . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.2.3 BODY . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.2.4 STAT . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.3 Article posting . . . . . . . . . . . . . . . . . . . . 44
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6.3.1 POST . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.3.2 IHAVE . . . . . . . . . . . . . . . . . . . . . . . . . 46
7. Information commands . . . . . . . . . . . . . . . . . . 50
7.1 DATE . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.2 HELP . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.3 NEWGROUPS . . . . . . . . . . . . . . . . . . . . . . . 51
7.4 NEWNEWS . . . . . . . . . . . . . . . . . . . . . . . . 53
7.5 Time . . . . . . . . . . . . . . . . . . . . . . . . . . 54
7.5.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . 54
7.6 The LIST commands . . . . . . . . . . . . . . . . . . . 55
7.6.1 LIST ACTIVE . . . . . . . . . . . . . . . . . . . . . . 55
7.6.2 LIST ACTIVE.TIMES . . . . . . . . . . . . . . . . . . . 57
7.6.3 LIST DISTRIBUTIONS . . . . . . . . . . . . . . . . . . . 59
7.6.4 LIST DISTRIB.PATS . . . . . . . . . . . . . . . . . . . 60
7.6.5 LIST NEWSGROUPS . . . . . . . . . . . . . . . . . . . . 61
8. Framework for NNTP extensions . . . . . . . . . . . . . 63
8.1 Initial IANA registry . . . . . . . . . . . . . . . . . 65
8.2 Standard extensions . . . . . . . . . . . . . . . . . . 65
8.3 The LISTGROUP extension . . . . . . . . . . . . . . . . 65
8.3.1 LISTGROUP . . . . . . . . . . . . . . . . . . . . . . . 66
8.4 Article metadata . . . . . . . . . . . . . . . . . . . . 67
8.4.1 The :bytes metadata item . . . . . . . . . . . . . . . . 68
8.4.2 The :lines metadata item . . . . . . . . . . . . . . . . 68
8.5 The OVER extension . . . . . . . . . . . . . . . . . . . 68
8.5.1 OVER . . . . . . . . . . . . . . . . . . . . . . . . . . 69
8.5.2 LIST OVERVIEW.FMT . . . . . . . . . . . . . . . . . . . 74
8.6 The HDR extension . . . . . . . . . . . . . . . . . . . 76
8.6.1 HDR . . . . . . . . . . . . . . . . . . . . . . . . . . 76
8.6.2 LIST HEADERS . . . . . . . . . . . . . . . . . . . . . . 80
9. Augmented BNF Syntax for NNTP . . . . . . . . . . . . . 84
9.1 Commands . . . . . . . . . . . . . . . . . . . . . . . . 84
9.2 Responses . . . . . . . . . . . . . . . . . . . . . . . 86
9.3 Multi-line response contents . . . . . . . . . . . . . . 86
9.4 Articles . . . . . . . . . . . . . . . . . . . . . . . . 88
9.5 General non-terminals . . . . . . . . . . . . . . . . . 88
10. IANA Considerations . . . . . . . . . . . . . . . . . . 90
11. Security Considerations . . . . . . . . . . . . . . . . 91
11.1 Personal and Proprietary Information . . . . . . . . . . 91
11.2 Abuse of Server Log Information . . . . . . . . . . . . 91
11.3 Weak Authentication and Access Control . . . . . . . . . 91
11.4 DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . 92
11.5 UTF-8 issues . . . . . . . . . . . . . . . . . . . . . . 92
11.6 Caching of LIST EXTENSIONS results . . . . . . . . . . . 93
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . 95
Normative References . . . . . . . . . . . . . . . . . . 97
Informative References . . . . . . . . . . . . . . . . . 98
Author's Address . . . . . . . . . . . . . . . . . . . . 98
A. Future Directions . . . . . . . . . . . . . . . . . . . 99
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B. Interaction with other specifications . . . . . . . . . 100
B.1 Header folding . . . . . . . . . . . . . . . . . . . . . 100
B.2 Message-IDs . . . . . . . . . . . . . . . . . . . . . . 100
B.3 Article posting . . . . . . . . . . . . . . . . . . . . 101
C. Summary of Response Codes . . . . . . . . . . . . . . . 103
D. Formal specification of the standard extensions . . . . 108
D.1 The LISTGROUP extension . . . . . . . . . . . . . . . . 108
D.2 The OVER extension . . . . . . . . . . . . . . . . . . . 108
D.3 The HDR extension . . . . . . . . . . . . . . . . . . . 109
Intellectual Property and Copyright Statements . . . . . 111
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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 Netnews 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 Netnews model provides for indexing, cross-referencing, and
expiration of aged messages. For server-to-server interaction, NNTP
is designed for efficient transmission of Netnews 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
[RFC977]. 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 [RFC3629] instead of US-ASCII [ANSI1986]. It now requires
all articles to have a message-id, eliminating the "<0>" placeholder
used in RFC 977. It also extends the newsgroup name matching
capabilities already documented in RFC 977.
Generally, new functionality is made available using new commands. A
number of such commands (including some commands taken from RFC 2980
[RFC2980]) are now mandatory. Part of the 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 [RFC2119].
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" or "client
host" refers to a host making use of the NNTP service, while the term
"server" or "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 argument is optional;
ellipsis... indicates that the argument may be repeated any
number of times (it must occur at least once);
vertical|bar indicates a choice of two mutually exclusive
arguments (exactly one must be provided).
The name "message-id" for a command or response argument indicates
that it is the message-id of an article as described in Section 3.4,
including the angle brackets.
The name "wildmat" for an argument indicates that it is a wildmat as
defined in Section 4. If the argument 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.
The terms "NUL", "TAB", "LF", "CR, and "space" refer to the octets
with those codes in US-ASCII [ANSI1986] (that is, %x00, %x09, %x0A,
%x0D, and %x20 respectively), as do quoted characters (so "." and "<"
refer to %x2E and %x3C). The term "CRLF" or "CRLF pair" means the
sequence CR immediately followed by LF (that is, %x0D.0A). A
"printable US-ASCII character" is an octet in the range %x21-7E.
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
6.1.1)) is invalid; when so, this is indicated at the start of the
example.
Terms which might be read as specifying details of a client or server
implementation, such as "database", are used simply to ease
description. Providing that implementations conform to the protocol
and format specifications in this document, no specific technique is
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mandated.
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3. Basic Concepts
3.1 Commands and Responses
NNTP operates over any reliable data stream 8-bit-wide channel.
Initially, the server host starts the NNTP service by listening on a
TCP port; when running over TCP/IP, the official port for the NNTP
service is 119. 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. When
the connection is established, the NNTP server host MUST send a
greeting. The client host and server host then exchange commands and
responses (respectively) until the connection is closed or aborted.
The character set for all NNTP commands is UTF-8 [RFC3629]. Commands
in NNTP MUST consist of a keyword, which MAY be followed by one or
more arguments. A 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 by one or
more space or TAB characters. Keywords MUST be at least three
characters and MUST NOT exceed 12 characters. Command lines MUST NOT
exceed 512 octets, which includes the terminating CRLF pair. The
arguments MUST NOT exceed 497 octets. A server MAY relax these limits
for commands defined in an extension.
Where this specification permits UTF-8 characters outside the range
U+0000 to U+007F, implementations MUST NOT use the Byte Order Mark
(U+FEFF, encoding %xEF.BB.BF), and MUST use the Word Joiner (U+2060,
encoding %xE2.91.A0) for the meaning Zero Width No-Break Space, in
command lines and the initial lines of responses, and SHOULD apply
these same principles throughout.
The term "character" means a single Unicode code point and
implementations are not required to carry out normalisation. Thus
U+0084 (A-dieresis) is one character while U+0041 U+0308 (A composed
with dieresis) is two; the two need not be treated as equivalent.
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. Note that such
variants are sometimes referred to as if they were commands in their
own right: "the LIST ACTIVE" command should be read as shorthand for
"the ACTIVE variant of the LIST command".
Keywords are case-insensitive; the case of keywords for commands MUST
be ignored by the server. Command and response arguments are case- or
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language-specific only when stated, either in this document or in
other relevant specifications.
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. The first or only line of the response MUST NOT
exceed 512 octets, which includes the response code and the
terminating CRLF pair; an extension MAY specify a greater maximum for
commands that it defines, but not for any other command.
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 a CRLF pair. Apart from
those line endings, the stream MUST NOT include the octets NUL,
LF, or 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" ("."
or %x2E), that line MUST be "byte-stuffed" by pre-pending an
additional termination octet to that line of the response.
4. The lines of the response MUST be followed by a terminating line
consisting of a single termination octet followed by a CRLF pair
in the normal way. Thus a multi-line response is always
terminated with the five octets CRLF "." CRLF (%x0D.0A.2E.0D.0A).
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 a CRLF pair, that initial termination octet is disregarded.
6. Likewise, the terminating line ("." CRLF or %x2E.0D.0A) 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 a CRLF pair is disregarded; (the first
CRLF pair 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 octets NUL, LF, or CR other than a CRLF pair cannot be
reliably conveyed in the above format. However, except when stated
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otherwise, this specification does not require the content to be
UTF-8 and it is possible for octets above and below 128 to be mixed
arbitrarily.
This document does not place any limit on the length of a subsequent
line in a multi-line response. 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.
3.2 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,
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 syntactically correct but failed for some
reason.
5xx - Command unknown, unsupported, unavailable, or syntax error.
The next digit in the code indicates the function response category:
x0x - Connection, set-up, and miscellaneous messages
x1x - Newsgroup selection
x2x - Article selection
x3x - Distribution functions
x4x - Posting
x8x - Reserved for authentication and privacy extensions
x9x - Reserved for private use (non-standard extensions)
Certain responses contain arguments such as numbers and names in
addition to the status indicator. In those cases, to simplify
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interpretation by the client the number and type of such arguments 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.
Arguments MUST be separated from the numeric status indicator and
from each other by a single space. All numeric arguments MUST be in
base 10 (decimal) format, and MAY have leading zeros. String
arguments MUST contain at least one character and MUST NOT contain
TAB, LF, CR, or space. The server MAY add any text after the response
code or last argument 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 argument by at least one space.
The server MUST respond to any command with the appropriate generic
response (given in Section 3.2.1) 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
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 8) 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.)
3.2.1 Generic Response Codes
The server MUST respond to any command with the appropriate one of
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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 or the command line is longer than the server accepts, the
response code 501 MUST be returned. The line MUST NOT be truncated or
split and then interpreted. 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 base command is implemented but the
requested variant is not, and 500 MUST be used only when the base
command itself is not implemented.
If the server experiences an internal fault or problem that means it
is unable to carry out the command (for example, a necessary file is
missing or a necessary service could not be contacted), the response
code 403 MUST be returned. If the server recognizes the command but
does not provide an optional feature (for example because it does not
store the required information), or only handles a subset of
legitimate cases (see the HDR command (Section 8.6.1) for an
example), the response code 503 MUST be returned. Note that where a
command is optional (e.g. LIST ACTIVE.TIMES) and is not provided by a
server, this MAY be treated as an unimplemented command (response
code 500 or 501 as appropriate) or as a working command where the
information is not available (response code 503).
If the client is not authorized to use the specified facility when
the server is in its current state, then the appropriate one of the
following response codes MUST be used.
502: it is necessary to terminate the connection and start a new one
with the appropriate authority before the command can be used.
Note that the server MUST NOT close the TCP connection immediately
after a 502 response except at the initial connection (Section
5.1) and with the MODE READER (Section 5.2) command. See also the
latter command for historical usage of this response.
480: the client must authenticate itself to the server (that is,
provide information as to the identity of the client) before the
facility can be used. This will involve the use of an
authentication extension.
483: the client must negotiate appropriate privacy protection on the
connection. This will involve the use of a privacy extension.
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401: the client must change the state of the connection in some other
manner. The first argument of the response MUST be the
extension-label (see Section 8) of the extension (which may be a
private extension) that provides the necessary mechanism, or
"MODE-READER" if it is necessary to use the MODE READER (Section
5.2) command.
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.
The client MUST be prepared to receive any of these responses for any
command (except, of course, that the server MUST NOT generate a 500
response code for mandatory commands).
3.2.1.1 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:
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[C] LIST ACTIVE u[ks].*
[S] 501 Syntax error
Example of an attempt to access a facility not available to this
connection:
[C] MODE READER
[S] 200 Reader mode, posting permitted
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 502 Permission denied
Example of an attempt to access a facility requiring authentication:
[C] GROUP secret.group
[S] 480 Permission denied
followed by a successful attempt following such authentication:
[C] XSECRET fred flintstone
[S] 290 Password for fred accepted
[C] GROUP secret.group
[S] 211 5 1 20 secret.group selected
Example of an attempt to access a facility requiring privacy:
[C] GROUP secret.group
[S] 483 Secure connection required
[C] XENCRYPT
[Client and server negotiate encryption on the link]
[S] 283 Encrypted link established
[C] GROUP secret.group
[S] 211 5 1 20 secret.group selected
Example of a need to change mode before using a facility:
[C] GROUP binary.group
[S] 401 XHOST Not on this virtual host
[C] XHOST binary.news.example.org
[S] 290 binary.news.example.org virtual host selected
[C] GROUP binary.group
[S] 211 5 1 77 binary.group selected
Example of a temporary failure:
[C] GROUP archive.local
[S] 403 Archive server temporarily offline
Example of the server needing to close down immediately:
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[C] ARTICLE 123
[S] 400 Power supply failed, running on UPS
[Server closes connection.]
3.3 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 says 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
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. (Since the server only sends data in
response to commands from the client, the converse problem does not
occur.)
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3.3.1 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 MODE READER command may
not be pipelined):
[C] GROUP misc.test
[C] MODE READER
[C] DATE
[C] NEXT
[S] 211 1234 3000234 3002322 misc.test
[S] 200 Server ready, posting allowed
[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.
3.4 Articles
NNTP is intended to transfer articles between clients and servers.
For the purposes of this specification, articles are required to
conform to the rules in this section and clients and servers MUST
correctly process any article received from the other that does so.
Note that this requirement applies only to the contents of
communications over NNTP; it does not prevent the client or server
from subsequently rejecting an article for reasons of local policy.
Also see Appendix B for further restrictions on the format of
articles in some uses of NNTP.
An article consists of two parts: the headers and the body. They are
separated by a single empty line, or in other words by two
consecutive CRLF pairs (if there is more than one empty line, the
second and subsequent ones are part of the body). In order to meet
the general requirements of NNTP, an article MUST NOT include the
octet NUL, MUST NOT contain the octets LF and CR other than as part
of a CRLF pair, and MUST end with a CRLF pair. This specification
puts no further restrictions on the body; in particular, it MAY be
empty.
The headers of an article consist of one or more header lines. Each
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header line consists of a header name, a colon, a space, the header
content, and a CRLF in that order. The name consists of one or more
printable US-ASCII characters other than colon and, for the purposes
of this specification, is not case-sensitive. There MAY be more than
one header line with the same name. The content MUST NOT contain
CRLF; it MAY be empty. A header may be "folded"; that is, a CRLF pair
may be placed before any TAB or space in the line; there MUST still
be some other octet between any two CRLF pairs in a header line.
(Note that folding means that the header line occupies more than one
line when displayed or transmitted; nevertheless it is still referred
to as "a" header line.) The presence or absence of folding does not
affect the meaning of the header line; that is, the CRLF pairs
introduced by folding are not considered part of the header content.
Header lines SHOULD NOT be folded before the space after the colon
that follows the header name, and SHOULD include at least one octet
other than %x09 or %x20 between CRLF pairs. However, if an article
has been received from elsewhere with one of these, clients and
servers MAY transfer it to the other without re-folding it.
The content of a header SHOULD be in UTF-8. However, if a server
receives an article from elsewhere that uses octets in the range 128
to 255 in some other manner, it MAY pass it to a client without
modification. Therefore clients MUST be prepared to receive such
headers and also data derived from them (e.g. in the responses from
the OVER extension (Section 8.5)) and MUST NOT assume that they are
always UTF-8.
Each article MUST have a unique message-id; two articles offered by
an NNTP server MUST NOT have the same message-id. For the purposes of
this specification, message-ids are opaque strings that MUST meet the
following requirements:
o A message-id MUST begin with "<" and end with ">", and MUST NOT
contain the latter except at the end.
o A message-id MUST be between 3 and 250 octets in length.
o A message-id MUST NOT contain octets other than printable US-ASCII
characters.
Two message-ids are the same if and only if they consist of the same
sequence of octets.
This specification does not describe how the message-id of an article
is determined. If the server does not have any way to determine a
message-id from the article itself, it MUST synthesize one (this
specification does not require the article to be changed as a
result). See also Appendix B.2.
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4. The WILDMAT format
The WILDMAT format described here is based on the version first
developed by Rich Salz [SALZ1992], 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 ABNF [RFC2234] 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 /
UTF8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
UTF8-non-ascii is defined in Section 9.
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 suppress the special
meaning of characters while brackets are used to introduce sets.
However, these usages are not universal and interpretation of these
characters in the context of UTF-8 strings is both potentially
complex and differs from existing practice, 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
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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
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 %xC2
and %xA3 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. Session administration commands
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 whether
service is available and whether the client is permitted to post.
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. 400 SHOULD be used if the issue is
only temporary (for example, because of load) and the client can
expect to be able to connect successfully at some point in the future
without making any changes. 502 MUST be used if the client is not
permitted under any circumstances to interact with the server, and
MAY be used if the server has insufficient information to determine
whether the issue is temporary or permanent.
5.1.3 Examples
Example of a normal connection from an authorized client which then
terminates the session (see Section 5.4):
[Initial TCP connection set-up completed.]
[S] 200 NNTP Service Ready, posting permitted
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[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of a normal connection from an authorized client that is not
permitted to post; it also immediately terminates the session:
[Initial TCP connection set-up 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 set-up 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 set-up 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.
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5.2.2 Description
MODE READER SHOULD be sent by any client that intends to use any
command in this specification (including Section 8) other than IHAVE,
HEAD, STAT, LIST ACTIVE, or LIST EXTENSIONS; other extensions MAY
also require MODE READER to be used. Servers MAY require that this
command be issued before any commands other than the above are sent
and MAY reject such commands until after a MODE READER command has
been sent. Such rejections SHOULD use response code 401 with argument
"MODE-READER", but for historical reasons response code 502 MAY be
used, even though this situation does not meet the conditions for
that response.
Once MODE READER is sent, IHAVE (and any related extensions) 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.
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.
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 terminates the session (see Section 5.4):
[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 immediately terminates the
session:
[C] MODE READER
[S] 201 NNTP Service Ready, posting prohibited
[C] QUIT
[S] 205 NNTP Service exits normally
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[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.]
Example of a connection from any client where the server is
temporarily unable to provide news reader service:
[C] MODE READER
[S] 400 NNTP Service temporarily unavailable
[Server closes connection.]
Example of a facility that requires MODE READER before use, using the
preferred response:
[C] GROUP misc.test
[S] 401 MODE-READER currently in peering mode
[C] MODE READER
[S] 200 NNTP Service Ready, posting permitted
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
Example of a facility that requires MODE READER before use, using the
historical but deprecated response:
[C] GROUP misc.test
[S] 502 Not available in peering mode
[C] MODE READER
[S] 200 NNTP Service Ready, posting permitted
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
Example of a facility that cannot be used after MODE READER:
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 435 Duplicate
[C] MODE READER
[S] 200 Reader mode, posting permitted
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 502 Permission denied
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5.3 LIST EXTENSIONS
5.3.1 Usage
This command is optional.
Syntax
LIST EXTENSIONS
Responses
202 Extension list follows (multiline)
402 Server has no extensions
5.3.2 Description
The LIST EXTENSIONS command allows a client to determine which
extensions are supported by the server at any given time. See Section
8 for further discussion of extensions.
This command MUST be implemented by any server that implements any
extensions defined in this document or any other extension in the
IANA registry, and is optional otherwise.
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 (which in
turn may be changed by the effects of other commands). An NNTP client
is only able to get the current and correct information concerning
available extensions at any point during a session by issuing a LIST
EXTENSIONS command at that point of that session and processing the
response, and the server MUST ensure that those extensions currently
listed in the returned information are available. Therefore, if an
extension (including those in Section 8) is only available before or
after a MODE READER command, the LIST EXTENSIONS command MUST only
include the extension in that situation. Similarly, if only some of
the commands in an extension will be available, or if the behaviour
of the extension will change in some other manner, before or after a
MODE READER command, this MUST be indicated by different arguments to
the extension-label in the results of LIST EXTENSIONS in each
situation.
While some extensions are likely to be always available or never
available, others will "appear" and "disappear" depending on server
state changes within the session or external events between sessions.
An NNTP client MAY cache the results of this command, but MUST NOT
rely on the correctness of any cached results, whether from earlier
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in this session or from a previous session, MUST cope gracefully with
the cached status being out of date, and SHOULD (if caching results)
provide a way to force the cached information to be refreshed.
Furthermore, a client MUST NOT use cached results in relation to
security, privacy, and authentication extensions. See Section 11.6
for further discussion of this topic.
The list of extensions is returned as a multi-line response following
the 202 response code. Each extension is listed on a separate line;
the line MUST begin with an extension-label and optionally one or
more arguments (separated by one or more spaces). The extension-label
and the meaning of the arguments are specified as part of the
definition of the extension. The extension-label is a string of 1 to
12 US-ASCII letters and MUST be in uppercase. Arguments are strings
of 1 or more printable UTF-8 characters (that is, either printable
US-ASCII characters or any UTF-8 sequence outside the US-ASCII range,
but not space or TAB).
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, it MUST return an empty list. The 402 response code
is documented for historic reasons only; clients SHOULD handle it
gracefully, but servers MUST NOT generate it.
Following a generic failure response, such as 403, an extension might
still be available, and the client MAY attempt to use it.
5.3.3 Examples
Example of a successful response:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] OVER MSGID
[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:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
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[S] .
Example from a non-conforming server which indicates "no extensions
available" using the 402 response code:
[C] LIST EXTENSIONS
[S] 402 Server has no extensions
5.4 QUIT
5.4.1 Usage
Syntax
QUIT
Responses
205 Connection closing
5.4.2 Description
The client uses the QUIT command to terminate the session. The server
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.
5.4.3 Examples
[C] QUIT
[S] 205 closing connection
[Server closes connection.]
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6. 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.
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 MAY use leading zeroes in specifying article
numbers, but MUST NOT use more than 16 digits. In some situations,
the value zero replaces an article number to show some special
situation.
6.1 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".
6.1.1 GROUP
6.1.1.1 Usage
Syntax
GROUP group
Responses
211 number low high group Group successfully selected
411 No such newsgroup
Parameters
group = name of newsgroup
number = estimated number of articles in the group
low = reported low water mark
high = reported high water mark
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6.1.1.2 Description
The required argument 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 7.6.1).
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 in the group currently available.
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
currently stored. 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
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 and the high water mark adjusted
accordingly, the next new article will not have the number one
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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 in any session, and SHOULD be no less
than that in any previous response for that newsgroup ever sent to
any client. Any failure to meet the latter condition SHOULD be
transient only. 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 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.
6.1.1.3 Examples
Example for a group known to the server:
[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
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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
6.1.2 LAST
6.1.2.1 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
6.1.2.2 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 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
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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.
6.1.2.3 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:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] LAST
[S] 420 No current article selected
6.1.3 NEXT
6.1.3.1 Usage
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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
6.1.3.2 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 6.1.2).
6.1.3.3 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
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:
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[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
6.2 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. As specified in Section 3.4, an article
consists of two parts: the article headers and the article body. When
responding to one of these commands, the server MUST present the
entire article or appropriate part and MUST NOT attempt to alter or
translate it in any way.
6.2.1 ARTICLE
6.2.1.1 Usage
Syntax
ARTICLE message-id
ARTICLE number
ARTICLE
Responses
First form (message-id specified)
220 0|n message-id Article follows (multiline)
430 No article with that message-id
Second form (article number specified)
220 n message-id Article follows (multiline)
412 No newsgroup selected
423 No articles in that range
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Third form (current article number used)
220 n message-id Article follows (multiline)
412 No newsgroup selected
420 Current article number is invalid
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
6.2.1.2 Description
The ARTICLE command selects an article based on the arguments and
presents the entire article (that is, the headers, an empty line, and
the body in that order). The command has three forms.
In the first form, a message-id is specified and the server presents
the article with that message-id. 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 cross-posted to more than
one newsgroup.
In the response, the article number MUST be replaced with zero,
except that if there is a current selected group and the article is
present in that group, the server MAY use that article number. (The
server is not required to determine whether the article is in the
current selected newsgroup or, if so, what article number it has; the
client MUST always be prepared for zero to be specified.) The server
MUST NOT provide an article number unless use of that number in a
second ARTICLE command immediately following this one would return
the same article. Even if the server chooses to return article
numbers in these circumstances, it need not do so consistently; it
MAY return zero to any such command (also see the STAT examples
(Section 6.2.4.3)).
In the second form, an article number is specified. If there is an
article with that number in the current selected newsgroup, the
server MUST set the current article number to that number.
In the third form, the article indicated by the current article
number in the current selected newsgroup is used.
Note that a previously valid article number MAY become invalid if the
article has been removed. A previously invalid article number MAY
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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.
Since the message-id 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 is returned as a multi-line response following the 220
response code.
If the argument is a message-id and no such article exists, a 430
response MUST be returned. If the argument is a number or is omitted
and the current selected newsgroup is invalid, a 412 response MUST be
returned. If the argument is a number and that article does not exist
in the current selected newsgroup, a 423 response MUST be returned.
If the argument is omitted and the current article number is invalid,
a 420 response MUST be returned.
6.2.1.3 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] .
Example of a successful retrieval of an article by message-id:
[C] ARTICLE <45223423@example.com>
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[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
6.2.2 HEAD
6.2.2.1 Usage
Syntax
HEAD message-id
HEAD number
HEAD
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Responses
First form (message-id specified)
221 0|n message-id Headers follow (multiline)
430 No article with that message-id
Second form (article number specified)
221 n message-id Headers follow (multiline)
412 No newsgroup selected
423 No articles in that range
Third form (current article number used)
221 n message-id Headers follow (multiline)
412 No newsgroup selected
420 Current article number is invalid
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
6.2.2.2 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 empty line separating the
headers and body MUST NOT be included).
6.2.2.3 Examples
Example of a successful retrieval of the headers of 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>
[S] .
Example of a successful retrieval of the headers of an article by
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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 headers 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 headers 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 of the headers 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 headers 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
6.2.3 BODY
6.2.3.1 Usage
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Syntax
BODY message-id
BODY number
BODY
Responses
First form (message-id specified)
222 0|n message-id Body follows (multiline)
430 No article with that message-id
Second form (article number specified)
222 n message-id Body follows (multiline)
412 No newsgroup selected
423 No articles in that range
Third form (current article number used)
222 n message-id Body follows (multiline)
412 No newsgroup selected
420 Current article number is invalid
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
6.2.3.2 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 empty line separating the headers
and body MUST NOT be included).
6.2.3.3 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] .
Example of a successful retrieval of the body of an article by
message-id:
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[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
6.2.4 STAT
6.2.4.1 Usage
Syntax
STAT message-id
STAT number
STAT
Responses
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First form (message-id specified)
223 0|n message-id Article exists
430 No article with that message-id
Second form (article number specified)
223 n message-id Article exists
412 No newsgroup selected
423 No articles in that range
Third form (current article number used)
223 n message-id Article exists
412 No newsgroup selected
420 Current article number is invalid
Parameters
number = Requested article number
n = Returned article number
message-id = Article message-id
6.2.4.2 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 and third forms what its message-id is,
without having to process an arbitrary amount of text.
6.2.4.3 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 STAT on an existing article by message-id:
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
Example of STAT on an article not on the server by message-id:
[C] STAT <i.am.not.there@example.com>
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[S] 430 No Such Article Found
Example of STAT on 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 on 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 on 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
Example of STAT by message-id on a server which sometimes reports the
actual article number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT
[S] 223 3000234 <45223423@example.com>
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
[C] STAT <45223423@example.com>
[S] 223 3000234 <45223423@example.com>
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
[C] GROUP alt.crossposts
[S] 211 9999 111111 222222 alt.crossposts
[C] STAT <45223423@example.com>
[S] 223 123456 <45223423@example.com>
[C] STAT
[S] 223 111111 <23894720@example.com>
The first STAT command establishes the identity of an article in the
group. The second and third show that the server may, but need not,
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give the article number when the message-id is specified. The fourth
STAT command shows that zero must be specified if the article isn't
in the current selected group, the fifth shows that the number, if
provided, must be that relating to the current selected group, and
the last one shows that the current selected article is still not
changed by the use of STAT with a message-id even if it returns an
article number.
6.3 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.
6.3.1 POST
6.3.1.1 Usage
This command MUST NOT be pipelined.
Syntax
POST
Responses
Initial responses
340 Send article to be posted
440 Posting not permitted
Subsequent responses
240 Article received OK
441 Posting failed
6.3.1.2 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 in the format specified
in Section 3.4 and MUST be sent by the client to the server in the
manner specified (in Section 3.1) 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.
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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 unforeseen server
errors, the posted article will be made available on the server and/
or transferred to other servers as appropriate, possibly following
further processing. In other words, articles not wanted by the server
SHOULD be rejected with a 441 response and not accepted and silently
discarded. However, the client SHOULD NOT assume that the article has
been successfully transferred unless it receives an affirmative
response from the server, and SHOULD NOT assume that it is being made
available to other clients without explicitly checking (for example
using the STAT command).
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 either check
whether the article was successfully posted before resending or
ensure that the server will allocate the same message-id to the new
attempt (see Appendix B.2) - the latter approach is preferred since
the article might not have been made available for reading yet (for
example, it may have to go through a moderation process).
6.3.1.3 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
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[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
6.3.2 IHAVE
6.3.2.1 Usage
This command MUST NOT be pipelined.
Syntax
IHAVE message-id
Responses
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
6.3.2.2 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
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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 headers and body, in the format defined
above (Section 3.1) 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 use of this command indicates that the article has
already been posted at another site and is simply being forwarded
from another host. However, despite this, the server MAY elect not to
post or forward the article if, after further examination of the
article, it deems it inappropriate to do so. Reasons for such
subsequent rejection of an article may include such problems as
inappropriate newsgroups or distributions, disc space limitations,
article lengths, garbled headers, and the like. These are typically
restrictions enforced by the server host's news software and not
necessarily the NNTP server itself.
The client SHOULD NOT assume that the article has been successfully
transferred unless it receives an affirmative response from the
server. A lack of response (such as a dropped network connection or a
network timeout) SHOULD be treated the same as a 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.
6.3.2.3 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
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[C] Subject: I am just a test article
[C] Date: 6 Oct 1998 04:38:40 -0500
[C] Organization: An Example Com, San Jose, CA
[C] Message-ID: <i.am.an.article.you.will.want@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 235 Article transferred OK
Example of sending an article to another site that rejects it. Note
that the message-id in the IHAVE command is not the same as the one
in the article headers; while this is bad practice and SHOULD NOT be
done, it is not forbidden.
[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.an.article.you.have@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 437 Article rejected; don't send again
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.an.article.you.will.want@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>
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[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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7. 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.
7.1 DATE
7.1.1 Usage
Syntax
DATE
Responses
111 yyyymmddhhmmss server date and time
Parameters
yyyymmddHHmmss = Current UTC date and time on server
7.1.2 Description
This command exists to help clients find out the current Coordinated
Universal Time [TF.686-1] from the server's perspective. This command
SHOULD NOT be used as a substitute for NTP [RFC1305] but to provide
information that might be useful when using the NEWNEWS command (see
Section 7.4). A system providing NNTP service SHOULD keep the system
clock as accurate as possible, either with NTP or by some other
method.
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.
7.1.3 Examples
[C] DATE
[S] 111 19990623135624
7.2 HELP
7.2.1 Usage
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Syntax
HELP
Responses
100 Help text follows (multiline)
7.2.2 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 5.3
7.2.3 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] .
7.3 NEWGROUPS
7.3.1 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
7.3.2 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 7.6.1). However, they MAY
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include groups not available on the server (and so not returned by
LIST ACTIVE) and MAY omit groups for which the creation date is not
available. The results SHOULD be consistent with those of the LIST
ACTIVE.TIMES command (Section 7.6.2), except that if the specified
date and time is earlier than the oldest entry in the latter then the
results of this command may include extra groups.
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). Clients SHOULD specify all four digits
of the year. If the first two digits of the year are not specified
(this is supported only for backwards compatibility), 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 [TF.686-1]; 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" argument) when possible.
7.3.3 Examples
Example where there are new groups:
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] alt.rfc-writers.recovery 4 1 y
[S] tx.natives.recovery 89 56 y
[S] .
Example where there are no new groups:
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] .
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7.4 NEWNEWS
7.4.1 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
7.4.2 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 7.3).
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" argument) when possible.
7.4.3 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
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[S] 230 list of new articles by message-id follows
[S] .
7.5 Time
As described in Section 6, 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
responses.
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.
7.5.1 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):
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[C] DATE
[S] 111 20010204003344
[C] NEWNEWS local.chat 20010203 111933 GMT
[S] 230 list follows
[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.
7.6 The LIST commands
7.6.1 LIST ACTIVE
7.6.1.1 Usage
Syntax
LIST ACTIVE [wildmat]
Responses
215 Information follows (multiline)
Parameters
wildmat = groups of interest
7.6.1.2 Description
The LIST ACTIVE command with no arguments returns a list of valid
newsgroups and associated information. The server MUST include every
group that the client is permitted to select with the GROUP (Section
6.1.1) command. Each newsgroup is sent as a line of text in the
following format:
group high low status
where:
"group" is the name of the newsgroup;
"high" is the reported high water mark for the group;
"low" is the reported low water mark for the group;
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"status" is the current status of the group on this server.
Each field in the line is separated from its neighbouring fields by
one or more spaces.
Note that an empty list is a possible valid response, and indicates
that there are currently no valid newsgroups.
The reported high and low water marks are as described in the GROUP
command (see Section 6.1.1).
The status field is typically one of:
"y" posting is permitted
"n" posting is not permitted
"m" postings will be forwarded to the newsgroup moderator
The server SHOULD use these values when these meanings are required
and MUST NOT use them with any other meaning. Other values for the
status may exist; the definition of these other values and the
circumstances under which they are returned may be specified in an
extension or may be private to the server. A client SHOULD treat an
unrecognized status as giving no information.
The status of a newsgroup only indicates how posts to that newsgroup
are normally processed and is not necessarily customised to the
specific client. For example, if the current client is forbidden from
posting, then this will apply equally to groups with status "y".
Conversely, a client with special privileges (not defined by this
specification) might be able to post to a group with status "n".
If the optional wildmat argument is specified, the response is
limited to only the groups (if any) whose names match the wildmat. If
no wildmat is specified, the keyword ACTIVE MAY be omitted without
altering the effect of the command.
7.6.1.3 Examples
Example of LIST ACTIVE returning a list of newsgroups:
[C] LIST ACTIVE
[S] 215 list of newsgroups follows
[S] misc.test 3002322 3000234 y
[S] comp.risks 442001 441099 m
[S] alt.rfc-writers.recovery 4 1 y
[S] tx.natives.recovery 89 56 y
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[S] tx.natives.recovery.d 11 9 n
[S] .
The same output on an implementation that includes leading zeroes:
[C] LIST ACTIVE
[S] 215 list of newsgroups follows
[S] misc.test 0003002322 0003000234 y
[S] comp.risks 0000442001 0000441099 m
[S] alt.rfc-writers.recovery 0000000004 0000000001 y
[S] tx.natives.recovery 0000000089 0000000056 y
[S] tx.natives.recovery.d 0000000011 0000000009 n
[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:
[C] LIST ACTIVE *.recovery
[S] 215 list of newsgroups follows
[S] alt.rfc-writers.recovery 4 1 y
[S] tx.natives.recovery 89 56 y
[S] .
7.6.2 LIST ACTIVE.TIMES
7.6.2.1 Usage
This command is optional.
Syntax
LIST ACTIVE.TIMES [wildmat]
Responses
215 Information follows (multiline)
Parameters
wildmat = groups of interest
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7.6.2.2 Description
The active.times list is maintained by some news transport systems to
contain information about who created a particular newsgroup and
when. Each line of this list consists of three fields separated from
each other by one or more spaces. 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 plain text intended to describe the entity that created
the newsgroup; it is often a mailbox as defined in RFC 2822
[RFC2822].
The list MAY omit newsgroups for which the information is unavailable
and MAY include groups not available on the server; in particular, it
MAY omit all groups created before the date and time of the oldest
entry. The client MUST NOT assume that the list is complete or that
it matches the list returned by LIST ACTIVE. The NEWGROUPS command
(Section 7.3) may provide a better way to access this information and
the results of the two commands SHOULD be consistent (subject to the
caveats in the description of that command).
If the information is available, it is returned as a multi-line
response following the 215 response code. If the optional wildmat
argument is specified, the response is limited to only the groups (if
any) whose names match the wildmat and for which the information is
available.
Note that an empty list is a possible valid response (whether or not
a wildmat is specified) and indicates that there are no groups
meeting the above criteria.
7.6.2.3 Examples
Example of LIST ACTIVE.TIMES returning a list of newsgroups:
[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
recognized but the software does not maintain this information:
[C] LIST ACTIVE.TIMES
[S] 503 program error, function not performed
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Example of LIST ACTIVE.TIMES sent to a server that does not recognize
this command:
[C] LIST ACTIVE.TIMES
[S] 501 Syntax Error
7.6.3 LIST DISTRIBUTIONS
7.6.3.1 Usage
This command is optional.
Syntax
LIST DISTRIBUTIONS
Responses
215 Information follows (multiline)
7.6.3.2 Description
The distributions list is maintained by some news transport systems
to contain information about valid values for the content of the
Distribution header in a news article and about what the various
values mean. Each line of this list consists of two fields separated
from each other by one or more spaces. 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.
7.6.3.3 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
recognized but the software does not maintain this information:
[C] LIST DISTRIBUTIONS
[S] 503 program error, function not performed
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Example of LIST DISTRIBUTIONS sent to a server that does not
recognize this command:
[C] LIST DISTRIBUTIONS
[S] 501 Syntax Error
7.6.4 LIST DISTRIB.PATS
7.6.4.1 Usage
This command is optional.
Syntax
LIST DISTRIB.PATS
Responses
215 Information follows (multiline)
7.6.4.2 Description
The distrib.pats list is maintained by some news transport systems to
choose a value for the content of the Distribution header of a news
article being posted. Each line of this list consists of three fields
separated from each other by a 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
content.
The client MAY use this information to construct an appropriate
Distribution header given 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.
7.6.4.3 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
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[S] 20:local.here.*:thissite
[S] .
Example of LIST DISTRIB.PATS returning an error where the command is
recognized 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
7.6.5 LIST NEWSGROUPS
7.6.5.1 Usage
This command is optional.
Syntax
LIST NEWSGROUPS [wildmat]
Responses
215 Information follows (multiline)
Parameters
wildmat = groups of interest
7.6.5.2 Description
The newsgroups list 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 list consists of two fields separated from each other by one or
more space or TAB characters (usual practice is a single TAB). The
first field is the name of the newsgroup and the second is a short
description of the group.
The list MAY omit newsgroups for which the information is unavailable
and MAY include groups not available on the server. The client MUST
NOT assume that the list is complete or that it matches the list
returned by LIST ACTIVE.
If the information is available, it is returned as a multi-line
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response following the 215 response code. If the optional wildmat
argument is specified, the response is limited to only the groups (if
any) whose names match the wildmat and for which the information is
available.
Note that an empty list is a possible valid response (whether or not
a wildmat is specified) and indicates that there are no groups
meeting the above criteria.
7.6.5.3 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
recognized 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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8. 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 5.3) and is the mechanism for clients to use to determine
what extensions are available. 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.
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 US-ASCII 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:
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o a descriptive name for the extension;
o the extension-label (which is returned by LIST EXTENSIONS to
indicate to the client that the server supports this particular
extension) - the extension-label of a registered extension MUST
NOT begin with "X";
o the syntax, values, and meanings of any arguments following the
extension-label in the output of LIST EXTENSIONS;
o any new NNTP commands associated with the extension - the names of
commands associated with registered extensions MUST NOT begin with
"X";
o the syntax and possible values of arguments associated with the
new NNTP commands;
o the response codes and possible values of arguments for the
responses of the new NNTP commands;
o any new arguments the extension associates with any other
pre-existing NNTP commands;
o how support for the extension affects the behaviour of a server
and NNTP client;
o any increase in the maximum length of commands and initial
response lines over the value specified in this document;
o a specific statement about the effect on pipelining this extension
may have (if any);
o a specific statement about the circumstances when use of this
extension can alter the output from LIST EXTENSIONS;
o the circumstances under which the extension can cause any
pre-existing command to produce a 401, 480, or 483 response;
o whether the extension can be used before or after the MODE READER
command, and what changes (if any) the latter has on the
extension.
A private extension need not be included in the output of LIST
EXTENSIONS. A server MAY provide additional keywords - either for new
commands or new variants of existing commands - as part of a private
extension. To avoid the risk of a clash with a future registered
extension, the names of private extensions and commands defined by
them SHOULD begin with "X".
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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.
8.1 Initial IANA registry
The IANA's initial registry of NNTP service extensions consists of
these entries:
+-------------------------+--------------+--------------------------+
| Extension | Label | Added behaviour |
+-------------------------+--------------+--------------------------+
| Specific article | LISTGROUP | Defined in this document |
| numbers | | |
| | | |
| Overview support | OVER | Defined in this document |
| | | |
| Batched header | HDR | Defined in this document |
| retrieval | | |
+-------------------------+--------------+--------------------------+
8.2 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.
The formal definitions of these extensions are provided in Appendix
D.
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.
8.3 The LISTGROUP extension
This extension provides one command and has the extension label
LISTGROUP.
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8.3.1 LISTGROUP
8.3.1.1 Usage
Syntax
LISTGROUP [group]
Responses
211 number low high group Article numbers follow (multiline)
411 No such newsgroup
412 No newsgroup selected [1]
Parameters
group = name of newsgroup
number = estimated number of articles in the group
low = reported low water mark
high = reported high water mark
[1] The 412 response can only occur if no group has been specified.
8.3.1.2 Description
The LISTGROUP command is used to get a listing of all the article
numbers in a particular newsgroup.
The optional argument 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.
The list of article numbers is returned as a multi-line response
following the 211 response code (the arguments on the initial
response line are the same as for the GROUP command (see Section
6.1.1). The list 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.
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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.
8.3.1.3 Examples
Example of LISTGROUP on an empty group:
[C] LISTGROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup list follows
[S] .
Example of LISTGROUP on a valid current selected newsgroup:
[C] GROUP misc.test
[S] 211 2000 3000234 3002322 misc.test
[C] LISTGROUP
[S] 211 2000 3000234 3002322 misc.test 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
8.4 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 (and which MUST NOT contain a colon elsewhere within it). As
with header names, metadata item names are not case-sensitive.
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
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article.) If the server has access to several non-identical copies of
an article, the value returned MUST be correct for any copy of that
article retrieved during the same session.
This specification defines two metadata items: ":bytes" and ":lines".
Other metadata items may be defined by extensions. The names of
metadata items defined by registered extensions MUST NOT begin with
":x-". To avoid the risk of a clash with a future registered
extension, the names of metadata items defined by private extensions
SHOULD begin with ":x-".
8.4.1 The :bytes metadata item
The :bytes metadata item for an article is a decimal integer. It
SHOULD equal the number of octets in the entire article - headers,
body, and separating empty line (counting a CRLF pair as two octets,
and excluding both the "." CRLF terminating the response and any "."
added for "byte-stuffing" purposes).
Note to client implementers: some existing servers return a value
different to that above. The commonest reasons for this are:
o counting a CRLF pair as one octet;
o including the "." character used for byte-stuffing in the number;
o including the terminating "." CRLF in the number;
o using one copy of an article for counting the octets but then
returning another one that differs in some (permitted) manner.
Implementations should be prepared for such variation and MUST NOT
rely on the value being accurate.
8.4.2 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 empty
line separating headers and body); equivalently, it is two less than
the number of CRLF pairs that the BODY command would return for that
article (the extra two are those following the response code and the
termination octet).
8.5 The OVER extension
This extension provides two commands, OVER and LIST OVERVIEW.FMT. The
label for this extension is OVER.
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The OVER extension provides access to the "overview database", which
is a database of headers 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. If the
database records the content or absence of a given field (that is, a
header or metadata item) for all articles, it is said to be
"consistent" for that field. If it records the content of a header
for some articles but not for others that nevertheless included that
header, or records a metadata item for some articles but not others
to which that item applies, it is said to be "inconsistent" for that
field.
The LIST OVERVIEW.FMT command SHOULD list all the fields for which
the database is consistent at that moment. It MAY omit such fields
(for example if it is not known whether the database is consistent or
inconsistent). It MUST NOT include fields for which the database is
inconsistent or which are not stored in the database. Therefore if a
header appears in the LIST OVERVIEW.FMT output but not the OVER
output for a given article, that header does not appear in the
article, and similarly for metadata items.
These rules assume the fields being stored in the database remain
constant for long periods of time, with the database therefore being
consistent. When the set of fields to be stored is changed, it will
be inconsistent until either the database is rebuilt or the only
articles remaining are those received since the change. Therefore the
output from LIST OVERVIEW.FMT needs to be altered twice: before any
fields stop being stored, they MUST be removed from the output, then
when the database is once more known to be consistent, the new fields
SHOULD be added to the output.
Support for the message-id form of the OVER command is optional. If
an implementation supports this form, it MUST use the argument
"MSGID" following the extension label in the output of LIST
EXTENSIONS; if not, it MUST NOT use any argument.
This extension is based on the Overview/NOV database [ROBE1995]
developed by Geoff Collyer.
8.5.1 OVER
8.5.1.1 Usage
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Syntax
OVER message-id
OVER range
OVER
Responses
First form (message-id specified)
224 Overview information follows (multiline)
430 No article with that message-id
Second form (range specified)
224 Overview information follows (multiline)
412 No newsgroup selected
423 No articles in that range
Third form (current article number used)
224 Overview information follows (multiline)
412 No newsgroup selected
420 Current article number is invalid
Parameters
range = number(s) of articles
message-id = message-id of article
8.5.1.2 Description
The OVER command returns the contents of the headers and metadata in
the database for an article specified by message-id, or from a
specified article or range of articles in the current selected
newsgroup.
The message-id argument indicates a specific article. The 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 neither is specified, the current article number is used. Support
for the first (message-id) form is optional. If it is not supported,
the generic response code 503 MUST be returned.
If the information is available, it is returned as a multi-line
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response following the 224 response code and contains one line per
article, sorted in numerical order of article number (note that
unless the argument is a range including a dash, there will only be
one line but it will still be in multi-line format). Each line
consists of a number of fields separated by a TAB. A field may be
empty (in which case there will be two adjacent TABs), and a sequence
of trailing TABs may be omitted.
The first 8 fields MUST be the following, in order:
"0" or article number (see below)
Subject header content
From header content
Date header content
Message-ID header content
References header content
:bytes metadata item
:lines metadata item
If the article is specified by message-id (the first form of the
command), the article number MUST be replaced with zero, except that
if there is a current selected group and the article is present in
that group, the server MAY use that article number (see the ARTICLE
command (Section 6.2.1) and STAT examples (Section 6.2.4.3) for more
details). In the other two forms of the command, the article number
MUST be returned.
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 content of the header (that is, with the header name and
following colon and space removed). If the article does not contain
that header, or if the content is empty, 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
the entire header line other than the trailing CRLF. For all
subsequent fields that contain metadata, the field consists of the
metadata name, a single space, and then the value.
For all fields, the value is processed by first removing all CRLF
pairs (that is, undoing any folding and removing the terminating
CRLF) and then replacing each TAB with a single space. 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.
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Note that, after unfolding, the characters NUL, LF, and CR cannot
occur in the header of an article offered by a conformant server.
Nevertheless, servers SHOULD check for these characters and replace
each one by a single space (so that, for example, CR LF LF TAB will
become two spaces, since the CR and first LF will be removed by the
unfolding process). This will encourage robustness in the face of
non-conforming data; it is also possible that future versions of this
specification could permit these characters to appear in articles.
The server SHOULD NOT produce output for articles that no longer
exist.
If the argument is a message-id and no such article exists, a 430
response MUST be returned. If the argument is a range or is omitted
and the current selected newsgroup is invalid, a 412 response MUST be
returned. If the argument is a range and no articles in that number
range exist in the current selected newsgroup, a 423 response MUST be
returned. If the argument is omitted and the current article number
is invalid, a 420 response MUST be returned.
8.5.1.3 Examples
In the first three examples, 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 an
article by message-id:
[C] LIST EXTENSIONS
[S] 202 extensions supported:
[S] OVER MSGID
[S] .
[C] OVER <45223423@example.com>
[S] 224 Overview information follows
[S] 0|I am just a test article|"Demo User"
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<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] .
Note that the article number has been replaced by "0".
Example of the same commands on a system that does not implement
retrieval by message-id:
[C] LIST EXTENSIONS
[S] 202 extensions supported:
[S] OVER
[S] .
[C] OVER <45223423@example.com>
[S] 503 Overview by message-id unsupported
Example of a successful retrieval of overview information for a range
of articles:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[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
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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
8.5.2 LIST OVERVIEW.FMT
8.5.2.1 Usage
This command is optional.
Syntax
LIST OVERVIEW.FMT
Responses
215 Information follows (multiline)
8.5.2.2 Description
The LIST OVERVIEW.FMT command returns a description of the fields in
the database for which it is consistent (as described above).
If the information is available, it is returned as a multi-line
response following the 215 response code. The information contains
one line per field in the order they are returned by the OVER
command; the first 7 lines MUST (except for the case of letters) be
exactly:
Subject:
From:
Date:
Message-ID:
References:
:bytes
:lines
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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
OVER output. The "full" suffix (which may use either uppercase,
lowercase, or a mix) 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.
8.5.2.3 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:
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[S] References:
[S] Bytes:
[S] Lines:
[S] Xref:FULL
[S] Distribution:FULL
[S] .
Example of LIST OVERVIEW.FMT returning an error where the command is
recognized but the software does not maintain this information:
[C] LIST OVERVIEW.FMT
[S] 503 overview.fmt not available
8.6 The HDR extension
This extension provides two new commands: HDR and LIST HEADERS. The
label for this extension is HDR.
The HDR extension provides access to specific headers and metadata
items (collectively "fields") of articles or groups of articles. In
the case of headers, an implementation MAY restrict the use of this
extension to a specific list of headers or MAY allow it to be used
with any header; it may behave differently when the HDR command is
used with a message-id argument and when it is used with a range or
no argument.
The HDR command may take information from a database rather than
directly from the articles. If so, the same issues of consistency and
inconsistency apply as with the OVER extension (Section 8.5) and the
LIST HEADERS command SHOULD take the same approach as the LIST
OVERVIEW.FMT command in resolving them.
8.6.1 HDR
8.6.1.1 Usage
Syntax
HDR header message-id
HDR header range
HDR header
Responses
First form (message-id specified)
225 Headers follow (multiline)
430 No article with that message-id
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Second form (range specified)
225 Headers follow (multiline)
412 No newsgroup selected
423 No articles in that range
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
8.6.1.2 Description
The HDR command retrieves specific headers from an article specified
by message-id, or from a specified article or range of articles in
the current selected newsgroup. It can also return certain metadata
about the article or articles.
The required header argument is the name of a header (e.g. "subject")
in an article, or the name of a metadata item, and is
case-insensitive. Names of metadata items always begin with a colon.
Except where stated otherwise, metadata items are treated as if they
were header contents, and references to headers in this description
apply equally to metadata items.
The message-id argument indicates a specific article. The 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 neither is 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 in the range that exists (note that unless the argument
is a range including a dash, there will be at most one line but it
will still be in multi-line format). The line consists of the article
number, a space, and then the contents of the header or metadata
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item. In the case of a header, the header name, colon, and the first
space after the colon are all omitted.
If the article is specified by message-id (the first form of the
command), the article number MUST be replaced with zero, except that
if there is a current selected group and the article is present in
that group, the server MAY use that article number (see the ARTICLE
command (Section 6.2.1) and STAT examples (Section 6.2.4.3) for more
details). In the other two forms of the command, the article number
MUST be returned.
Header contents are modified as follows: all CRLF pairs are removed,
and then each TAB is replaced with a single space (note that this is
the same transformation as is performed by the OVER extension
(Section 8.5.1.2), and the same comment concerning NUL, CR, and LF
applies).
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 content 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 that
article number is included in the output.
If the second argument is a message-id and no such article exists, a
430 response MUST be returned. If the second argument is a range or
is omitted and the current selected newsgroup is invalid, a 412
response MUST be returned. If the second argument is a range and no
articles in that number range exist in the current selected
newsgroup, a 423 response MUST be returned. If the second argument is
omitted 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; it may behave differently in this respect for the
first (message-id) form than for the other forms. If so, it MUST
respond with the generic 503 response to attempts to request other
headers, rather than returning erroneous results such as a successful
empty response.
If HDR uses a separate database and it is inconsistent for the
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requested header or metadata item, the server MAY return what results
it can or it MAY respond with the generic 503 response; in the latter
case, the field MUST NOT appear in the output from LIST HEADERS.
8.6.1.3 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
[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
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[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
8.6.2 LIST HEADERS
8.6.2.1 Usage
Syntax
LIST HEADERS [MSGID|RANGE]
Responses
215 Header and metadata list follows (multiline)
Parameters
MSGID = requests list for access by message-id
RANGE = requests list for access by range
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8.6.2.2 Description
The LIST HEADERS command returns a list of headers and metadata items
that may be retrieved using the HDR command.
The information is returned as a multi-line response following the
215 response code and contains one line for each header or metadata
item name (excluding the colon in the former case). If the
implementation allows any header to be retrieved, it MUST NOT include
any header names in the list but MUST include the special entry ":"
(a single colon on its own); it MUST still list any metadata items
that are available. The order of items in the list is not
significant; the server need not even consistently return the same
order. The list MAY be empty (though in this circumstance there is
little point in providing the extension).
An implementation that also supports the OVER extension SHOULD at
least permit all the headers and metadata items listed in the output
from the LIST OVERVIEW.FMT command.
If the server treats the first form of the HDR command (message-id
specified) differently to the other two forms (range specified or
current article number used) in respect of which headers or metadata
items are available, then:
o if the MSGID argument is specified, the results MUST be those
available for the first form of the HDR command;
o if the RANGE argument is specified, the results MUST be those
available for the second and third forms of the HDR command;
o if no argument is specified, the results MUST be those available
in all forms of the HDR command (that is, it MUST only list those
items listed in both the previous cases).
If the server does not treat the various forms differently, then it
MUST always produce the same results and ignore any argument.
8.6.2.3 Examples
Example of an implementation providing access to only a few headers:
[C] LIST HEADERS
[S] 215 headers supported:
[S] Subject
[S] Message-ID
[S] Xref
[S] .
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Example of an implementation providing access to the same fields as
the first example in Section 8.5.2.3:
[C] LIST EXTENSIONS
[S] 202 extensions supported:
[S] OVER
[S] HDR
[S] .
[C] LIST HEADERS
[S] 215 headers and metadata items supported:
[S] Date
[S] Distribution
[S] From
[S] Message-ID
[S] References
[S] Subject
[S] Xref
[S] :bytes
[S] :lines
[S] .
Example of an implementation providing access to all headers:
[C] LIST HEADERS
[S] 215 metadata items supported:
[S] :
[S] :lines
[S] :bytes
[S] :x-article-number
[S] .
Example of an implementation distinguishing the first form of the HDR
command from the other two forms:
[C] LIST HEADERS RANGE
[S] 215 metadata items supported:
[S] :
[S] :lines
[S] :bytes
[S] .
[C] LIST HEADERS MSGID
[S] 215 headers and metadata items supported:
[S] Date
[S] Distribution
[S] From
[S] Message-ID
[S] References
[S] Subject
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[S] :lines
[S] :bytes
[S] :x-article-number
[S] .
[C] LIST HEADERS
[S] 215 headers and metadata items supported:
[S] Date
[S] Distribution
[S] From
[S] Message-ID
[S] References
[S] Subject
[S] :lines
[S] :bytes
[S] .
Note how :x-article-number does not appear in the last set of output.
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9. Augmented BNF Syntax for NNTP
Each of the following sections describes the syntax of a major
element of NNTP. This syntax extends and refines the descriptions
elsewhere in this specification, and should be given precedence when
resolving apparent conflicts. Note that ABNF [RFC2234] strings are
case-insensitive. Non-terminals used in several places are defined in
a separate section at the end.
9.1 Commands
This syntax defines the non-terminal "command-line", which represents
what is sent from the client to the server.
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-headers-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]
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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-headers-command = "LIST" WS "HEADERS" WS ["MSGID" / "RANGE"]
list-newsgroups-command = "LIST" WS "NEWSGROUPS" [WS wildmat]
list-overview-fmt-command = "LIST" WS "OVERVIEW.FMT"
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-ref]
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)
date = [2DIGIT] 6DIGIT
date-time = date WS time [WS "GMT"]
header-meta-name = header-name / metadata-name
metadata-name = ":" 1*A-NOTCOLON
newsgroup-name = 1*wildmat-exact
range = article-number ["-" [article-number]]
range-ref = WS (range / message-id)
time = 6DIGIT
x-command-name = 3*12A-CHAR
x-argument = 1*P-CHAR
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 /
UTF8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
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9.2 Responses
This syntax defines the non-terminal "response", which represents
what is sent from the server to the client in response to a command.
response = simple-response / multiline-response
multiline-response = simple-response *content-line termination
termination = "." CRLF
content-line = [content-text] CRLF
content-text = (".." / B-NONDOT) *B-CHAR
simple-response = 3DIGIT arguments [ SP trailing-comment ] CRLF
trailing-comment = *U-CHAR
arguments = *(SP argument) ; How many depends on the response
argument = 1*A-CHAR
9.3 Multi-line response contents
This syntax defines the content of the various multi-line responses,
in each case after any "byte-stuffing" has been undone.
multiline-response-content: article-response /
body-response /
hdr-response /
head-response /
help-response /
list-active-response /
list-active-times-response /
list-distrib-pats-response /
list-distributions-response /
list-extensions-response /
list-headers-response /
list-newsgroups-response /
list-overview-fmt-response /
listgroup-response /
newgroups-response /
newnews-response /
over-response
article-response = article
body-response = body
hdr-response = *(article-number SP hdr-content CRLF)
head-response = 1*header
help-response = *(*B-CHAR CRLF)
list-active-response = *(newsgroup-name SPA article-number
SPA article-number SPA newsgroup-status CRLF)
list-active-times-response =
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*(newsgroup-name SPA 1*DIGIT SPA newsgroup-creator CRLF)
list-distrib-pats-response =
*(1*DIGIT ":" wildmat ":" distribution CRLF)
list-distributions-response =
*(distribution SPA distribution-description CRLF)
list-extensions-response =
*(extension-label *(SPA extension-argument) CRLF)
list-headers-response = *(header-meta-name CRLF) /
*((metadata-name / ":") CRLF)
list-newsgroups-response =
*(newsgroup-name WS newsgroup-description CRLF)
list-overview-fmt-response = list-overview-fmt-text
listgroup-response = *(article-number CRLF)
newgroups-response = list-active-response
newnews-response = *(message-id CRLF)
over-response = *(article-number over-content CRLF)
list-overview-fmt-text =
"Subject:" CRLF
"From:" CRLF
"Date:" CRLF
"Message-ID:" CRLF
"References:" CRLF
( ":bytes" CRLF ":lines" / "Bytes:" CRLF "Lines:") CRLF
*((header-name ":full" / metadata-name) CRLF)
distribution = 1*P-CHAR
distribution-description = U-TEXT
extension-argument = 1*P-CHAR
extension-label = 1*12UPPER
hdr-content = *S-NONTAB
hdr-n-content = [(header-name ":" / metadata-name) SP hdr-content]
newsgroup-creator = U-TEXT
newsgroup-description = S-TEXT
newsgroup-status = %x79 / %x6E / %x6D / private-status
over-content = 1*6(TAB hdr-content) /
7(TAB hdr-content) *(TAB hdr-n-content)
private-status = 1*P-CHAR ; except the values in newsgroup-status
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9.4 Articles
This syntax defines the non-terminal "article", which represents the
format of an article as described in Section 3.4.
article = 1*header CRLF body
header = header-name ":" [CRLF] SP header-content CRLF
header-content = *(S-CHAR / [CRLF] WS)
body = *(*B-CHAR CRLF)
9.5 General non-terminals
article-number = 1*16DIGIT
header-name = 1*A-NOTCOLON
message-id = "<" 1*248A-NOTGT ">"
; Assorted special character sets
; A- means based on ASCII, excluding controls and SP
; P- means based on UTF-8, excluding controls and SP
; U- means based on UTF-8, excluding NUL CR and LF
; B- means based on bytes, excluding NUL CR and LF
A-CHAR = %x21-7E
A-NOTCOLON = %x21-39 / %x3B-7E ; exclude ":"
A-NOTGT = %x21-3D / %x3F-7E ; exclude ">"
P-CHAR = A-CHAR / UTF8-non-ascii
U-CHAR = CTRL / TAB / SP / A-CHAR / UTF8-non-ascii
U-NONTAB = CTRL / SP / A-CHAR / UTF8-non-ascii
U-TEXT = P-CHAR *U-CHAR
B-CHAR = CTRL / TAB / SP / %x21-FF
B-NONDOT = CTRL / TAB / SP / %x21-2D / %x2F-FF ; exclude "."
CR = %x0D
CRLF = CR LF
CTRL = %x01-08 / %x0B-0C / %x0E-1F
DIGIT = %x30-39
EOL = *(SP / TAB) CRLF
LF = %x0A
SP = %x20
SPA = 1*SP
TAB = %x09
UPPER = %41-5A
UTF8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4
UTF8-2 = %xC2-DF UTF8-tail
UTF8-3 = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2UTF8-tail /
%xED %x80-9F UTF8-tail / %xEE-EF 2UTF8-tail
UTF8-4 = %xF0 %x90-BF 2UTF8-tail / %xF1-F3 3UTF8-tail /
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%xF4 %x80-8F 2UTF8-tail
UTF8-tail = %x80-BF
WS = 1*(SP / TAB)
The following non-terminals require special consideration. They
represent situations where material SHOULD be restricted to UTF-8,
but implementations MUST be able to cope with other character
encodings. Therefore there are two sets of definitions for them.
Implementations MUST accept any content that meets this syntax:
S-CHAR = %x21-FF
S-NONTAB = CTRL / SP / S-CHAR
S-TEXT = (CTRL / S-CHAR) *B-CHAR
Implementations SHOULD only generate content that meets this syntax:
S-CHAR = P-CHAR
S-NONTAB = U-NONTAB
S-TEXT = U-TEXT
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10. IANA Considerations
This specification requires IANA to keep a registry of
extension-labels. The initial contents of this registry are specified
in Section 8.1. As described in Section 8, names beginning with X are
reserved for private use while all other names are to be associated
with a specification in an RFC on the standards-track or defining an
IESG-approved experimental protocol.
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11. 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.
11.1 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.
11.2 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.
11.3 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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11.4 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 behaviour 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.
11.5 UTF-8 issues
UTF-8 [RFC3629] 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 generating a 501 response code.
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o replacing such sequences by the sequence %xEF.BF.BD, which encodes
the "replacement character" U+FFFD;
o closing the connection;
o replacing such sequences by a "guessed" valid sequence (based on
properties of the UTF-8 encoding);
In the last case, the implementation MUST ensure that any replacement
cannot be used to bypass validity or security checks. For example,
the illegal sequence %xC0.A0 is an over-long encoding for space
(%x20). If it is replaced by the latter in a command line, this needs
to happen before the command line is parsed into individual
arguments. If the replacement came after parsing, it would be
possible to generate an argument with an embedded space, which is
forbidden. Use of the "replacement character" does not have this
problem, since it is permitted wherever non-US-ASCII characters are.
Implementations SHOULD use one of the first two solutions where the
general structure of the NNTP stream remains intact, and close the
connection if it is no longer possible to parse it sensibly.
11.6 Caching of LIST EXTENSIONS results
The LIST EXTENSIONS command provides information about the extensions
currently available from the server. Whenever there is a relevant
change to the server state, the results of this command are required
to change accordingly.
In most situations the results from this command in a given server
state will not change from session to session; a given extension will
be installed permanently on a server. Some clients may therefore wish
to remember which extensions a server supports to avoid the delay of
an additional command and response, particularly if they open
multiple connections in the same session.
However, information about extensions related to security and privacy
MUST NOT be cached, since this could allow a variety of attacks.
For example, consider a server which permits the use of cleartext
passwords on links that are encrypted but not otherwise:
[Initial TCP connection set-up completed.]
[S] 200 NNTP Service Ready, posting permitted
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] XENCRYPT
[S] .
[C] XENCRYPT
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[Client and server negotiate encryption on the link]
[S] 283 Encrypted link established
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] XSECRET
[S] .
[C] XSECRET fred flintstone
[S] 290 Password for fred accepted
If the client caches the last LIST EXTENSIONS result, then on the
next session it will attempt to use XSECRET on an unencrypted link:
[Initial TCP connection set-up completed.]
[S] 200 NNTP Service Ready, posting permitted
[C] XSECRET fred flintstone
[S] 483 Only permitted on secure links
exposing the password to any eavesdropper. While the primary cause of
this is passing a secret without first checking the security of the
link, caching of LIST EXTENSIONS results can increase the risk.
Any security extension should include requirements to check the
security state of the link in a manner appropriate to that extension.
Caching should normally only be considered for anonymous clients that
do not use any security or privacy extensions and for which the time
required for an additional command and response is a noticeable
issue.
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12. Acknowledgements
The author acknowledges the original authors of NNTP as documented in
RFC 977 [RFC977]: 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 the DRUMS working
group, specifically RFC 1869 [RFC1869], which is the basis of the
NNTP extensions mechanism detailed in this document.
The author gratefully acknowledges the authors of RFC 2616 [RFC2616]
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
Geoff Collyer
Original author of the OVERVIEW database proposal and one of the
original authors of CNEWS
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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
[ANSI1986]
American National Standards Institute, "Coded Character
Set - 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC977] Kantor, B. and P. Lapsley, "Network News Transfer
Protocol", RFC 977, February 1986.
[TF.686-1]
International Telecommunications Union - Radio, "Glossary,
ITU-R Recommendation TF.686-1", ITU-R Recommendation
TF.686-1, October 1997.
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Informative References
[RFC1036] Horton, M. and R. Adams, "Standard for interchange of
USENET messages", RFC 1036, December 1987.
[RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992.
[RFC1869] Klensin, J., Freed, N., Rose, M., Stefferud, E. and D.
Crocker, "SMTP Service Extensions", STD 10, RFC 1869,
November 1995.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
[RFC2980] Barber, S., "Common NNTP Extensions", RFC 2980, October
2000.
[ROBE1995]
Robertson, R., "FAQ: Overview database / NOV General
Information", January 1995.
[SALZ1992]
Salz, R., "Manual Page for wildmat(3) from the INN 1.4
distribution, Revision 1.10", April 1992.
Author's Address
Clive D.W. Feather
Thus plc
322 Regents Park Road
London N3 2QQ
GB
Phone: +44 20 8495 6138
Fax: +44 870 051 9937
EMail: clive@demon.net
URI: http://www.davros.org/
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Appendix A. Future Directions
It has been proposed that the response code range 6xx be used for
multiline responses. While existing commands and extensions do not
use this, it would at least limit the problem clients would face in
dealing with an unknown response.
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Appendix B. Interaction with other specifications
NNTP is most often used for transferring articles that conform to RFC
1036 [RFC1036] (such articles are called "Netnews articles" here). It
is also sometimes used for transferring email messages that conform
to RFC 2822 [RFC2822] (such articles are called "email articles"
here). In this situation, articles must conform both to this
specification and to that other one; this appendix describes some
relevant issues.
B.1 Header folding
NNTP allows a header line to be folded (by inserting a CRLF pair)
before any space or TAB character.
Both email and Netnews articles are required to have at least one
octet other than space or TAB on each header line. Thus folding can
only happen at one point in each sequence of consecutive spaces or
TABs. Netnews articles are further required to have the header name,
colon, and following space all on the first line; folding may only
happen beyond that space. Finally, some non-conforming software will
remove trailing spaces and TABs from a line. Therefore it might be
inadvisable to fold a header after a space or TAB.
For maximum safety, header lines SHOULD conform to the following
syntax rather than that in Section 9.4.
header = header-name ":" SP [header-content] CRLF
header-content = [WS] 1*P-CHAR *( [CRLF] WS 1*P-CHAR )
B.2 Message-IDs
Every article handled by an NNTP server MUST have a unique
message-id. For the purposes of this specification, a message-id is
an arbitrary opaque string that merely needs to meet certain
syntactic requirements and is just a way to refer to the article.
Because there is a significant risk of old articles being reinjected
into the global Usenet system, RFC 1036 [RFC1036] requires that
message-ids are globally unique for all time.
This specification states that message-ids are the same if and only
if they consist of the same sequence of octets. Other specifications
may define two different sequences as being equal because they are
putting an interpretation on particular characters. RFC 2822
[RFC2822] has a concept of "quoted" and "escaped" characters. It
therefore considers the three message-ids:
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<abcd@example.com>
<"abcd"@example.com>
<"ab\cd"@example.com>
as being identical. Therefore an NNTP implementation handing email
articles must ensure that only one of these three appears in the
protocol and the other two are converted to it as and when necessary,
such as when a client checks the results of a NEWNEWS command against
an internal database of message-ids. Note that RFC 1036 [RFC1036]
never treats two different strings as being identical. Its draft
successor restricts the syntax of message-ids so that, whenever RFC
2822 would treat two strings as equivalent, only one of them is valid
(in the above example only the first string is valid).
This specification does not describe how the message-id of an article
is determined; it may be deduced from the contents of the article or
derived from some external source. If the server is also conforming
to another specification that contains a definition of message-id
compatible with this one, the server SHOULD use those message-ids. A
common approach, and one that SHOULD be used for email and Netnews
articles, is to extract the message-id from the contents of a header
with name "Message-ID". This may not be as simple as copying the
entire header contents; it may be necessary to strip off comments and
undo quoting, or to reduce "equivalent" message-ids to a canonical
form.
If an article is obtained through the IHAVE command, there will be a
message-id provided with the command. The server MAY either use it or
determine one from the article contents. However, whichever it does
it SHOULD ensure that, if the IHAVE command is repeated with the same
argument and article, it will be recognized as a duplicate.
If an article does not contain a message-id that the server can
identify, it MUST synthesize one. This could, for example, be a
simple sequence number or based on the date and time that the article
arrived. When handling email or Netnews articles, a Message-ID header
SHOULD be added to ensure global consistency and uniqueness.
B.3 Article posting
As far as NNTP is concerned, the POST and IHAVE commands provide the
same basic facilities in a slightly different way. However they have
rather different intentions.
The IHAVE command is intended for transmitting conforming articles
between a system of NNTP servers, with all articles perhaps also
conforming to another specification (e.g. all articles are Netnews
articles). It is expected that the client will have already done any
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necessary validation (or has in turn obtained the article from a
third party which has done so); therefore the contents SHOULD be left
unchanged.
In contrast, the POST command is intended for use when an end-user is
injecting a newly-created article into a such a system. The article
being transferred might not be a conforming email or Netnews article,
and the server is expected to validate it and, if necessary, convert
it to the right form for onward distribution. It is often the case
that this is done by a separate piece of software on the server
installation. If so, the NNTP server SHOULD pass the incoming article
to that software unaltered, making no attempt to filter characters,
fold or limit lines, or otherwise process the incoming text.
The POST command can fail in various ways and clients should be
prepared to re-send an article. When doing so, however, it is often
important to ensure - as far as possible - that the same message-id
is allocated to both attempts so that the server, or other servers,
can recognize the two articles as being duplicates. In the case of
email or Netnews articles, therefore, the posted article SHOULD
contain a header with name "Message-ID" and the contents of this
header SHOULD be identical on each attempt. The server SHOULD ensure
that two POSTed articles with the same contents for this header are
recognized as identical and the same message-id allocated, whether or
not those contents are suitable for use as the message-id.
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Appendix C. Summary of Response Codes
This section contains a list of every response code defined in this
document, whether it is multi-line, which commands can generate it,
what arguments it has, and what its meaning is.
Response code 100 (multi-line)
Generated by: HELP
Meaning: help text follows.
Response code 111
Generated by: DATE
1 argument: yyyymmddhhmmss
Meaning: server date and time.
Response code 200
Generated by: initial connection, MODE READER
Meaning: service available, posting allowed.
Response code 201
Generated by: initial connection, MODE READER
Meaning: service available, posting prohibited.
Response code 202 (multi-line)
Generated by: LIST EXTENSIONS
Meaning: extension list follows.
Response code 205
Generated by: QUIT
Meaning: connection closing (the server immediately closes the
connection).
Response code 211
The 211 response code has two completely different forms depending
on which command generated it:
Generated by: GROUP
4 arguments: number low high group
Meaning: group selected.
(multi-line)
Generated by: LISTGROUP
Meaning: article numbers follow.
Response code 215 (multi-line)
Generated by: LIST ACTIVE, LIST ACTIVE.TIMES, LIST DISTRIB.PATS,
LIST DISTRIBUTIONS, LIST HEADERS, LIST NEWSGROUPS,
LIST OVERVIEW.FMT
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Meaning: information follows.
Response code 220 (multi-line)
Generated by: ARTICLE
2 arguments: n message-id
Meaning: article follows.
Response code 221 (multi-line)
Generated by: HEAD
2 arguments: n message-id
Meaning: article headers follow.
Response code 222 (multi-line)
Generated by: BODY
2 arguments: n message-id
Meaning: article body follows.
Response code 223
Generated by: LAST, NEXT, STAT
2 arguments: n message-id
Meaning: article exists and selected.
Response code 224 (multi-line)
Generated by: OVER
Meaning: overview information follows.
Response code 225 (multi-line)
Generated by: HDR
Meaning: headers follow.
Response code 230 (multi-line)
Generated by: NEWNEWS
Meaning: list of new articles follows.
Response code 231 (multi-line)
Generated by: NEWGROUPS
Meaning: list of new newsgroups follows.
Response code 235
Generated by: IHAVE (second stage)
Meaning: article transferred OK.
Response code 240
Generated by: POST (second stage)
Meaning: article received OK.
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Response code 335
Generated by: IHAVE (first stage)
Meaning: send article to be transferred.
Response code 340
Generated by: POST (first stage)
Meaning: send article to be posted.
Response code 400
Generic response and generated by initial connection
Meaning: service not available or no longer available (the server
immediately closes the connection).
Response code 401
Generic response
1 argument: extension-label
Meaning: the server is in the wrong mode; the indicated extension
should be used to change the mode.
Response code 402
Generated by: LIST EXTENSIONS
Meaning: server has no extensions.
Response code 403
Generic response
Meaning: internal fault or problem preventing action being taken.
Response code 411
Generated by: GROUP, LISTGROUP
Meaning: no such newsgroup.
Response code 412
Generated by: ARTICLE, BODY, HDR, HEAD, LAST, LISTGROUP, NEXT,
OVER, STAT
Meaning: no newsgroup selected.
Response code 420
Generated by: ARTICLE, BODY, HDR, HEAD, LAST, NEXT, OVER, STAT
Meaning: current article number is invalid.
Response code 421
Generated by: NEXT
Meaning: no next article in this group.
Response code 422
Generated by: LAST
Meaning: no previous article in this group.
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Response code 423
Generated by: ARTICLE, BODY, HDR, HEAD, OVER, STAT
Meaning: no articles in that range.
Response code 430
Generated by: ARTICLE, BODY, HDR, HEAD, OVER, STAT
Meaning: no article with that message-id.
Response code 435
Generated by: IHAVE (first stage)
Meaning: article not wanted.
Response code 436
Generated by: IHAVE (either stage)
Meaning: transfer not possible (first stage) or failed (second
stage); try again later.
Response code 437
Generated by: IHAVE (second stage)
Meaning: transfer rejected; do not retry.
Response code 440
Generated by: POST (first stage)
Meaning: posting not permitted.
Response code 441
Generated by: POST (second stage)
Meaning: posting failed.
Response code 480
Generic response
Meaning: command unavailable until the client has authenticated
itself.
Response code 483
Generic response
Meaning: command unavailable until suitable privacy has been
arranged.
Response code 500
Generic response
Meaning: unknown command.
Response code 501
Generic response
Meaning: syntax error in command.
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Response code 502
Generic response and generated by initial connection
Meaning for the initial connection and the MODE READER command:
service permanently unavailable (the server immediately closes the
connection).
Meaning for all other commands: command not permitted (and there
is no way for the client to change this).
Response code 503
Generic response
Meaning: feature not supported.
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Appendix D. Formal specification of the standard extensions
This section gives a formal definition of each of the extensions in
Section 8.2 as required by Section 8 for the IANA registry.
D.1 The LISTGROUP extension
o This extension provides information about specific article
numbers.
o The extension-label is "LISTGROUP".
o The extension-label has no arguments.
o The extension defines one new command: LISTGROUP, whose behaviour,
arguments, and responses are defined in Section 8.3.
o The extension does not associate any new responses with
pre-existing NNTP commands.
o The extension does not affect the behaviour of a server or client
other than via the new command.
o The extension does not affect the maximum length of commands and
initial response lines.
o The extension does not alter pipelining, and the LISTGROUP command
can be pipelined.
o Use of this extension does not alter the output from LIST
EXTENSIONS.
o The extension does not cause any pre-existing command to produce a
401, 480, or 483 response.
o The LISTGROUP command can only be used after the MODE READER
command.
D.2 The OVER extension
o This extension provides support for an overview of newsgroups.
o The extension-label is "OVER".
o The extension-label has the optional argument "MSGID", indicating
that the message-id variant of the OVER command is supported.
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o The extension defines two new commands: OVER and LIST
OVERVIEW.FMT, whose behaviour, arguments, and responses are
defined in Section 8.5.
o The extension does not associate any new responses with
pre-existing NNTP commands.
o The extension requires the server to maintain an overview database
and article metadata, as described in Section 8.4.
o The extension does not affect the maximum length of commands and
initial response lines.
o The extension does not alter pipelining, and the OVER and LIST
OVERVIEW.FMT commands can be pipelined.
o Use of this extension does not alter the output from LIST
EXTENSIONS.
o The extension does not cause any pre-existing command to produce a
401, 480, or 483 response.
o The OVER and LIST OVERVIEW.FMT commands can only be used after the
MODE READER command.
D.3 The HDR extension
o This extension provides batched header retrieval.
o The extension-label is "HDR".
o The extension-label has no arguments.
o The extension defines two new commands: HDR and LIST HEADERS,
whose behaviour, arguments, and responses are defined in Section
8.6.
o The extension does not associate any new responses with
pre-existing NNTP commands.
o The extension requires the server to maintain article metadata, as
described in Section 8.4.
o The extension does not affect the maximum length of commands and
initial response lines.
o The extension does not alter pipelining, and the HDR and LIST
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HEADERS commands can be pipelined.
o Use of this extension does not alter the output from LIST
EXTENSIONS.
o The extension does not cause any pre-existing command to produce a
401, 480, or 483 response.
o The HDR and LIST HEADERS commands can only be used after the MODE
READER command.
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