NNTP C. Feather
Internet-Draft Thus plc
Expires: August 14, 2005 February 10, 2005
Network News Transfer Protocol
draft-ietf-nntpext-base-25
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The Network News Transfer 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.
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Administration
This document is a product of the NNTP Working Group, chaired by Russ
Allbery and Ned Freed.
This is draft 25.
Author's Note
This document 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 document.
Rights
UNIX is a registered trademark of The Open Group.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Commands and Responses . . . . . . . . . . . . . . . . . 9
3.2 Response Codes . . . . . . . . . . . . . . . . . . . . . 11
3.2.1 Generic Response Codes . . . . . . . . . . . . . . . 12
3.2.1.1 Examples . . . . . . . . . . . . . . . . . . . . 14
3.3 Capabilities and Extensions . . . . . . . . . . . . . . 15
3.3.1 Capability descriptions . . . . . . . . . . . . . . 16
3.3.2 Standard capabilities . . . . . . . . . . . . . . . 16
3.3.3 Extensions . . . . . . . . . . . . . . . . . . . . . 18
3.3.4 Initial IANA register . . . . . . . . . . . . . . . 19
3.4 Mandatory and Optional Commands . . . . . . . . . . . . 20
3.4.1 Reading and Transit Servers . . . . . . . . . . . . 21
3.4.2 Mode switching . . . . . . . . . . . . . . . . . . . 22
3.5 Pipelining . . . . . . . . . . . . . . . . . . . . . . . 23
3.5.1 Examples . . . . . . . . . . . . . . . . . . . . . . 24
3.6 Articles . . . . . . . . . . . . . . . . . . . . . . . . 24
4. The WILDMAT format . . . . . . . . . . . . . . . . . . . . . 26
4.1 Wildmat syntax . . . . . . . . . . . . . . . . . . . . . 26
4.2 Wildmat semantics . . . . . . . . . . . . . . . . . . . 26
4.3 Extensions . . . . . . . . . . . . . . . . . . . . . . . 27
4.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . 27
5. Session administration commands . . . . . . . . . . . . . . 28
5.1 Initial Connection . . . . . . . . . . . . . . . . . . . 28
5.2 CAPABILITIES . . . . . . . . . . . . . . . . . . . . . . 29
5.3 MODE READER . . . . . . . . . . . . . . . . . . . . . . 31
5.4 QUIT . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6. Article posting and retrieval . . . . . . . . . . . . . . . 35
6.1 Group and article selection . . . . . . . . . . . . . . 35
6.1.1 GROUP . . . . . . . . . . . . . . . . . . . . . . . 35
6.1.2 LISTGROUP . . . . . . . . . . . . . . . . . . . . . 38
6.1.3 LAST . . . . . . . . . . . . . . . . . . . . . . . . 39
6.1.4 NEXT . . . . . . . . . . . . . . . . . . . . . . . . 40
6.2 Retrieval of articles and article sections . . . . . . . 42
6.2.1 ARTICLE . . . . . . . . . . . . . . . . . . . . . . 42
6.2.2 HEAD . . . . . . . . . . . . . . . . . . . . . . . . 45
6.2.3 BODY . . . . . . . . . . . . . . . . . . . . . . . . 47
6.2.4 STAT . . . . . . . . . . . . . . . . . . . . . . . . 48
6.3 Article posting . . . . . . . . . . . . . . . . . . . . 51
6.3.1 POST . . . . . . . . . . . . . . . . . . . . . . . . 51
6.3.2 IHAVE . . . . . . . . . . . . . . . . . . . . . . . 53
7. Information commands . . . . . . . . . . . . . . . . . . . . 56
7.1 DATE . . . . . . . . . . . . . . . . . . . . . . . . . . 56
7.2 HELP . . . . . . . . . . . . . . . . . . . . . . . . . . 56
7.3 NEWGROUPS . . . . . . . . . . . . . . . . . . . . . . . 57
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7.4 NEWNEWS . . . . . . . . . . . . . . . . . . . . . . . . 58
7.5 Time . . . . . . . . . . . . . . . . . . . . . . . . . . 59
7.5.1 Examples . . . . . . . . . . . . . . . . . . . . . . 60
7.6 The LIST commands . . . . . . . . . . . . . . . . . . . 60
7.6.1 LIST . . . . . . . . . . . . . . . . . . . . . . . . 61
7.6.2 Standard LIST keywords . . . . . . . . . . . . . . . 63
7.6.3 LIST ACTIVE . . . . . . . . . . . . . . . . . . . . 63
7.6.4 LIST ACTIVE.TIMES . . . . . . . . . . . . . . . . . 65
7.6.5 LIST DISTRIB.PATS . . . . . . . . . . . . . . . . . 66
7.6.6 LIST NEWSGROUPS . . . . . . . . . . . . . . . . . . 66
8. Article field access commands . . . . . . . . . . . . . . . 68
8.1 Article metadata . . . . . . . . . . . . . . . . . . . . 68
8.1.1 The :bytes metadata item . . . . . . . . . . . . . . 68
8.1.2 The :lines metadata item . . . . . . . . . . . . . . 69
8.2 Database consistency . . . . . . . . . . . . . . . . . . 69
8.3 OVER . . . . . . . . . . . . . . . . . . . . . . . . . . 70
8.4 LIST OVERVIEW.FMT . . . . . . . . . . . . . . . . . . . 74
8.5 HDR . . . . . . . . . . . . . . . . . . . . . . . . . . 75
8.6 LIST HEADERS . . . . . . . . . . . . . . . . . . . . . . 79
9. Augmented BNF Syntax for NNTP . . . . . . . . . . . . . . . 83
9.1 Commands . . . . . . . . . . . . . . . . . . . . . . . . 83
9.2 Command continuation . . . . . . . . . . . . . . . . . . 85
9.3 Responses . . . . . . . . . . . . . . . . . . . . . . . 85
9.3.1 Generic responses . . . . . . . . . . . . . . . . . 85
9.3.2 Initial response line contents . . . . . . . . . . . 86
9.3.3 Multi-line response contents . . . . . . . . . . . . 87
9.4 Capability lines . . . . . . . . . . . . . . . . . . . . 88
9.5 LIST variants . . . . . . . . . . . . . . . . . . . . . 88
9.6 Articles . . . . . . . . . . . . . . . . . . . . . . . . 89
9.7 General non-terminals . . . . . . . . . . . . . . . . . 90
9.8 Extensions and Validation . . . . . . . . . . . . . . . 91
10. IANA Considerations . . . . . . . . . . . . . . . . . . . 93
11. Security Considerations . . . . . . . . . . . . . . . . . 94
11.1 Personal and Proprietary Information . . . . . . . . . . 94
11.2 Abuse of Server Log Information . . . . . . . . . . . . 94
11.3 Weak Authentication and Access Control . . . . . . . . . 94
11.4 DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . 95
11.5 UTF-8 issues . . . . . . . . . . . . . . . . . . . . . . 95
11.6 Caching of capability lists . . . . . . . . . . . . . . 96
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 98
13. References . . . . . . . . . . . . . . . . . . . . . . . . 100
13.1 Normative References . . . . . . . . . . . . . . . . . . 100
13.2 Informative References . . . . . . . . . . . . . . . . . 100
Author's Address . . . . . . . . . . . . . . . . . . . . . . 101
A. Interaction with other specifications . . . . . . . . . . . 102
A.1 Header folding . . . . . . . . . . . . . . . . . . . . . 102
A.2 Message-IDs . . . . . . . . . . . . . . . . . . . . . . 102
A.3 Article posting . . . . . . . . . . . . . . . . . . . . 103
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B. Summary of Commands . . . . . . . . . . . . . . . . . . . . 105
C. Summary of Response Codes . . . . . . . . . . . . . . . . . 108
Intellectual Property and Copyright Statements . . . . . . . 112
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1. Introduction
This document specifies the Network News Transfer 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. 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] (note that US-ASCII
is a subset of UTF-8). It now requires all articles to have a
message-id, eliminating the "<0>" placeholder used in RFC 977 in some
responses. 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 3.6,
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
%x00, %x09, %x0A, %x0D, and %x20 respectively (that is, the octets
with those codes in US-ASCII [ANSI1986] and thus UTF-8 [RFC3629]).
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. Quoted characters refer to the
octets with those codes in US-ASCII (so "." and "<" refer to %x2E and
%x3C) and will always be printable US-ASCII characters; similarly,
"digit" refers to the octets %x30-39.
A "keyword" MUST consist only of US-ASCII letters, digits, and the
characters dot (".") and dash ("-"), and must begin with a letter.
Keywords MUST be at least three characters and MUST NOT exceed 12
characters.
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
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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. Examples may use commands or other keywords not
defined in this specification (such as an XENCRYPT command). These
will be used to illustrate some point and do not imply that any such
command is defined elsewhere or needs to exist in any particular
implementation.
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
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 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. 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. 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 language-specific only when stated, either in this document or in
other relevant specifications.
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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 (that is, they violate the MUST
requirement above). However, except when stated otherwise, this
specification does not require the content to be UTF-8 and therefore
it MAY include octets above and below 128 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
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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
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. Note that, for historical reasons, the 211
response code is an exception to this in that the response may be
multi-line or not depending on the command (GROUP or LISTGROUP) that
generated it. 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
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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 registered extension (see
Section 3.3.3) 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
the following generic responses if it represents the situation.
If the command is not recognized, or it is an optional command 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
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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.
As a special case, if an argument is required to be a base64-encoded
string [RFC3548] (there are no such arguments in this specification,
but there may be in extensions) and is not validly encoded, the
response code 504 MUST be returned.
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 8.5) for an example),
the response code 503 MUST be returned.
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.
Historically, some mode-switching servers (see Section 3.4.1) have
used this response to indicate that this command will become
available after the MODE READER (Section 5.3) command is used, but
this usage is not conforming to this specification and MUST NOT 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 command.
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 on this connection. This will involve the
use of an authentication extension such as [NNTP-AUTH].
483: the client must negotiate appropriate privacy protection on the
connection. This will involve the use of a privacy extension such
as [NNTP-TLS].
401: the client must change the state of the connection in some other
manner. The first argument of the response MUST be the capability
label (see Section 5.2) of the facility (usually an extension,
which may be a private extension) that provides the necessary
mechanism. The server MUST NOT use this response code except as
specified by the definition of the capability in question.
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. Following a 400 response,
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clients SHOULD NOT simply reconnect immediately and retry the same
actions. Rather, a client SHOULD either use an exponentially
increasing delay between retries (e.g. double the waiting time after
each 400 response) or present any associated text to the user for
them to decide whether and when to retry.
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 command:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER LISTGROUP
[S] LIST ACTIVE NEWSGROUPS
[S] .
[C] OVER
[S] 500 Unknown command
Example of an unsupported variant:
[C] MODE POSTER
[S] 501 Unknown MODE option
Example of a syntax error:
[C] ARTICLE a.message.id@no.angle.brackets
[S] 501 Syntax error
Example of an overlong command line:
[C] HEAD 53 54 55
[S] 501 Too many arguments
Example of a bad wildmat:
[C] LIST ACTIVE u[ks].*
[S] 501 Syntax error
Example of a base64-encoding error (the second argument is meant to
be base64-encoded):
[C] XENCRYPT RSA abcd=efg
[S] 504 Base64 encoding error
Example of an attempt to access a facility not available to this
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connection:
[C] MODE READER
[S] 200 Reader mode, posting permitted
[C] IHAVE <i.am.an.article.you.will.want@example.com>
[S] 500 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:
[C] ARTICLE 123
[S] 400 Power supply failed, running on UPS
[Server closes connection.]
3.3 Capabilities and Extensions
Not all NNTP servers provide exactly the same facilities, both
because this specification allows variation and because servers may
provide extensions. A set of facilities that are related are called
a "capability". This specification provides a way to determine what
capabilities are available, includes a list of standard capabilities,
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and includes a mechanism (the extension mechanism) for defining new
capabilities.
3.3.1 Capability descriptions
A client can determine the available capabilities of the server by
using the CAPABILITIES command (Section 5.2). This returns a
capability list, which is a list of capability lines. Each line
describes one available capability.
Each capability line consists of one or more tokens, which MUST be
separated by one or more space or TAB characters. A token is a
string 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). Unless stated otherwise,
tokens are case-insensitive. Each capability line consists of:
o The capability label, which is a keyword indicating the
capability. A capability label may be defined by this
specification or a successor, or may be defined by an extension.
o The label is then followed by zero or more tokens, which are
arguments of the capability. The form and meaning of these tokens
is specific to each capability.
The server MUST ensure that the capability list accurately reflects
the capabilities (including extensions) currently available. If a
capability is only available with the server in a certain state (for
example, only after authentication), the list MUST only include the
capability label when in that state. 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, according to the
state of the server, this MUST be indicated by different arguments in
the capability line.
Note that a capability line can only begin with a letter. Lines
beginning with other characters are reserved for future versions of
this specification. In order to inter-work with such versions,
clients MUST be prepared to receive lines beginning with other
characters and MUST ignore any they do not understand.
3.3.2 Standard capabilities
The following capabilities are defined by this specification.
VERSION
This capability MUST be advertised by all servers and MUST be the
first capability in the capability list; it indicates the
version(s) of NNTP that the server supports. There must be at
least one argument; each argument is a decimal number and MUST NOT
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have a leading zero. Version numbers are assigned only in RFCs
which update or replace this specification; servers MUST NOT
create their own version numbers.
The version number of this specification is 2.
IHAVE
This capability indicates that the server implements the IHAVE
command.
READER
This capability indicates that the server implements the various
commands useful for reading clients. If and only if the LISTGROUP
command is implemented, there MUST be a single argument LISTGROUP.
If and only if posting is permitted using the POST command, there
MUST be a single argument POST. (These arguments may appear in
either order.)
LIST
This capability indicates that the server implements at least one
variant of the LIST command. There MUST be one argument for each
variant of the LIST command supported by the server, giving the
keyword for that variant.
HDR
This capability indicates that the server implements the header
access commands (HDR and LIST HEADERS).
OVER
This capability indicates that the server implements the overview
access commands (OVER and LIST OVERVIEW.FMT). If and only if the
server supports the message-id form of the OVER command, there
must be a single argument MSGID.
IMPLEMENTATION
This capability MAY be provided by a server. If so, the arguments
SHOULD be used to provide information such as the server software
name and version number. The client MUST NOT use this line to
determine capabilities of the server. (While servers often
provide this information in the initial greeting, clients need to
guess whether this is the case; this capability makes it clear
what the information is.)
MODE-READER
This capability indicates that the server is mode-switching
(Section 3.4.2) and the MODE READER command needs to be used to
enable the READER capability.
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3.3.3 Extensions
Although NNTP is widely and robustly deployed, some parts of the
Internet community might wish to extend the NNTP service. It must be
emphasized that any extension to NNTP 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.
An extension is a package of associated facilities, often but not
always including one or more new commands. Each extension MUST
define at least one new capability label (this will often, but need
not, be the name of one of these new commands). While any additional
capability information can normally be specified using arguments to
that label, an extension MAY define more than one capability label.
However, this SHOULD be limited to exceptional circumstances.
An extension is either a private extension or else its capabilities
are included in the IANA registry of capabilities (see Section 3.3.4)
and it is defined in an RFC (in which case it is a "registered
extension"). Such RFCs either must be on the standards track or must
define an IESG-approved experimental protocol.
The definition of an extension must include:
o a descriptive name for the extension;
o the capability label or labels defined by the extension; the
capability label of a registered extension MUST NOT begin with
"X";
o the syntax, values, and meanings of any arguments for each
capability label defined by the extension;
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 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);
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o a specific statement about the circumstances when use of this
extension can alter the contents of the capabilities list (other
than the new capability labels it defines);
o the circumstances under which the extension can cause any
pre-existing command to produce a 401, 480, or 483 response;
o how the use of MODE READER on a mode-switching server interacts
with the extension;
o how support for the extension affects the behaviour of a server
and NNTP client in any other manner not outlined above;
o formal syntax as described in Section 9.8.
A private extension MAY or MAY NOT be included in the capabilities
list. If it is, the capability label MUST begin with "X". A server
MAY provide additional keywords - for new commands and also for new
variants of existing commands - as part of a private extension. To
avoid the risk of a clash with a future registered extension, these
keywords SHOULD begin with "X".
If the server advertises a capability defined by a registered
extension, it MUST implement the extension so as to fully conform
with the specification (for example, it MUST implement all of the
commands that the extension describes as mandatory). If it does not
implement the extension as specified, it MUST NOT list the extension
in the capabilities list under its registered name; in this case it
MAY, but SHOULD NOT, provide a private extension (not listed, or
listed with a different name) that implements part of the extension
or implements the commands of the extension with a different meaning.
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.
3.3.4 Initial IANA register
IANA is requested to maintain a registry of NNTP capability labels.
All capability labels in the registry MUST be keywords and MUST NOT
begin with X.
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The initial contents of the registry consists of these entries:
+--------------------+-------------------------+--------------------+
| Label | Meaning | Definition |
+--------------------+-------------------------+--------------------+
| AUTHINFO | Authentication | [NNTP-AUTH] |
| | | |
| HDR | Batched header | Section 3.3.2, |
| | retrieval | Section 8.5, and |
| | | Section 8.6 |
| | | |
| IHAVE | IHAVE command available | Section 3.3.2 and |
| | | Section 6.3.2 |
| | | |
| IMPLEMENTATION | Server | Section 3.3.2 |
| | implementation-specific | |
| | information | |
| | | |
| LIST | LIST command variants | Section 3.3.2 and |
| | | Section 7.6.1 |
| | | |
| MODE-READER | Mode-switching server | Section 3.4.2 |
| | and MODE READER command | |
| | available | |
| | | |
| OVER | Overview support | Section 3.3.2, |
| | | Section 8.3, and |
| | | Section 8.4 |
| | | |
| READER | Reader commands | Section 3.3.2 |
| | available | |
| | | |
| SASL | Supported SASL | [NNTP-AUTH] |
| | mechanisms | |
| | | |
| STARTTLS | Transport layer | [NNTP-TLS] |
| | security | |
| | | |
| STREAMING | Streaming feeds | [NNTP-STREAM] |
| | | |
| VERSION | Supported NNTP versions | Section 3.3.2 |
+--------------------+-------------------------+--------------------+
3.4 Mandatory and Optional Commands
For a number of reasons, not all the commands in this specification
are mandatory. However, it is equally undesirable for every command
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to be optional, since this means that a client will have no idea what
facilities are available. Therefore, as a compromise, some of the
commands in this specification are mandatory - they must be supported
by all servers - while the remainder are not. The latter are then
subdivided into groups, each indicated by a single capability label.
o If the label is included in the capability list returned by the
server, the server MUST support all commands in that group.
o If the label is not included, the server MAY support none or some
of the commands, but SHOULD NOT support all of them. In general,
there will be no way for a client to determine which commands are
supported without trying them.
The groups have been chosen to provide useful functionality, and
therefore server authors are discouraged from implementing only part
of a group.
The description of each command will either indicate that it is
mandatory, or will give, using the term "indicating capability", the
capability label indicating whether or not the group including this
command is available.
Where a server does not implement a command, it MUST always generate
a 500 generic response code (or a 501 generic response code in the
case of a variant of a command depending on a second keyword where
the base command is recognised). Otherwise the command MUST be fully
implemented as specified; a server MUST NOT only partially implement
any of the commands in this specification. (Client authors should
note that some servers, not conforming to this specification, will
return a 502 generic response code to some commands that are not
implemented.)
Note: some commands have cases that require other commands to be used
first. If the former command is implemented but the latter is not,
the former MUST still generate the relevant specific response code.
For example, if ARTICLE (Section 6.2.1) is implemented but GROUP
(Section 6.1.1) is not, the correct response to "ARTICLE 1234"
remains 412.
3.4.1 Reading and Transit Servers
NNTP is traditionally used in two different ways. The first use is
"reading", where the client fetches articles from a large store
maintained by the server for immediate or later presentation to a
user, and sends articles created by that user back to the server (an
action called "posting") to be stored and distributed to other stores
and users. The second use is for the bulk transfer of articles from
one store to another. Since the hosts doing this transfer tend to be
peers in a network that transmit articles among one another, rather
than end-user systems, this process is called "peering" or "transit"
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(even so, one host is still the client and the other is the server).
In practice these two uses are so different that some server
implementations are optimised for reading or for transit and, as a
result, do not offer the other facility or only offer limited
features. Other implementations are more general and offer both.
This specification allows for this by grouping the relevant commands
accordingly: the IHAVE command is designed for transit, while the
commands indicated by the READER capability are designed for reading
clients.
Except as an effect of the MODE READER (Section 5.3) command on a
mode-switching server, once a server advertises either or both of the
IHAVE or READER capabilities, it MUST NOT cease to advertise them
later in the session.
A server MAY provide different modes of behaviour (transit, reader,
or a combination) to different client connections and MAY use
external information, such as the IP address of the client, to
determine which mode to provide to any given connection.
The official TCP port for the NNTP service is 119. However, if a
host wishes to offer separate servers for transit and reading
clients, port 433 SHOULD be used for the transit server and 119 for
the reading server.
3.4.2 Mode switching
An implementation MAY, but SHOULD NOT, provide both transit and
reader facilities on the same server but require the client to select
which it wishes to use. Such an arrangement is called a
"mode-switching" server.
A mode-switching server has two modes:
o Transit mode, which applies after the initial connection:
* it MUST advertise the MODE-READER capability;
* it MUST NOT advertise the READER capability.
However, the server MAY cease to advertise the MODE-READER
capability after the client uses any command except CAPABILITIES.
o Reading mode, after a successful MODE READER (Section 5.3)
command:
* it MUST not advertise the MODE-READER capability;
* it MUST advertise the READER capability;
* it MAY NOT advertise the IHAVE capability even if it was
advertising it in transit mode.
A client SHOULD only issue a MODE READER command to a server if it is
advertising the MODE-READER capability. If the server does not
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support CAPABILITIES (and therefore does not conform to this
specification), the client MAY use the following heuristic:
o if the client wishes to use any "reader" commands, it SHOULD use
the MODE READER command immediately after the initial connection;
o otherwise it SHOULD NOT use the MODE READER command.
In each case it should be prepared for some commands to be
unavailable that would have been available if it had made the other
choice.
3.5 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
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occur.)
3.5.1 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] MODE READER
[C] DATE
[C] NEXT
[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.
3.6 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 A 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
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
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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 (Section 8.3) command) and MUST NOT assume that they are
always UTF-8. How the client will then process those headers,
including identifying the encoding used, is outside the scope of this
document.
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 A.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, which
is an extract of that in Section 9.7.
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
; must not begin with "!" if not immediately preceded by "!"
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E /
UTF8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
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
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
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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.
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
This command MUST NOT be pipelined.
Responses
200 Service available, posting allowed [1]
201 Service available, posting prohibited [1]
400 Service temporarily unavailable [1][2]
502 Service permanently unavailable [1][2]
[1] These are the only valid response codes for the initial greeting;
the server MUST not return any other generic response code.
[2] 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.
Note: the distinction between the 200 and 201 response codes has
turned out in practice to be insufficient; for example, some servers
do not allow posting until the client has authenticated, while other
clients assume that a 201 response means that posting will never be
possible even after authentication. Therefore clients SHOULD use the
CAPABILITIES command (Section 5.2) rather than rely on this response.
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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
[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 CAPABILITIES
5.2.1 Usage
This command is mandatory.
Syntax
CAPABILITIES [keyword]
Responses
101 Capability list follows (multiline)
Parameters
keyword = additional feature, see description
5.2.2 Description
The CAPABILITIES command allows a client to determine the
capabilities of the server at any given time.
This command MAY be issued at any time; the server MUST NOT require
it to be issued in order to make use of any capability. The response
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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 or by external events). An NNTP client is only
able to get the current and correct information concerning available
capabilities at any point during a session by issuing a CAPABILITIES
command at that point of that session and processing the response.
The capability list is returned as a multi-line response following
the 101 response code. Each capability is described by a separate
capability line. The server MUST NOT list the same capability twice
in the response, even with different arguments. Except that the
VERSION capability MUST be the first line, the order in which the
capability lines appears is not significant; the server need not even
consistently return the same order.
While some capabilities are likely to be always available or never
available, others - notably extensions - 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 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 keyword argument is not used by this specification. It is
provided so that extensions or revisions to this specification can
include extra features for this command without requiring the
CAPABILITIES command to be used twice (once to determine if the extra
features are available and a second time to make use of them). If
the server does not recognise the argument (and it is a keyword), it
MUST respond with the 101 response code as if the argument had been
omitted. If an argument is provided that the server does recognise,
it MAY use the 101 response code or MAY use some other response code
(which will be defined in the specification of that feature). If the
argument is not a keyword, the 501 generic response code MUST be
returned. The server MUST NOT generate any other response code to
the CAPABILITIES command.
5.2.3 Examples
Example of a minimal response (a read-only server):
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
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[S] READER
[S] LIST ACTIVE NEWSGROUPS
[S] .
Example of a response from a server that has a range of facilities
and also describes itself:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] IHAVE
[S] LIST ACTIVE NEWSGROUPS ACTIVE.TIMES OVERVIEW.FMT
[S] IMPLEMENTATION INN 4.2 2004-12-25
[S] OVER MSGID
[S] STREAMING
[S] XSECRET
[S] .
Example of a server that supports more than one version of NNTP:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2 3
[S] READER
[S] LIST ACTIVE NEWSGROUPS
[S] .
Example of a client attempting to use a feature of the CAPABILITIES
command that the server does not support:
[C] CAPABILITIES AUTOUPDATE
[S] 101 Capability list:
[S] VERSION 2
[S] READER LISTGROUP
[S] IHAVE
[S] LIST ACTIVE NEWSGROUPS OVERVIEW.FMT HEADERS
[S] OVER MSGID
[S] HDR
[S] .
5.3 MODE READER
5.3.1 Usage
Indicating capability: MODE-READER
This command MUST NOT be pipelined.
Syntax
MODE READER
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Responses
200 Posting allowed
201 Posting prohibited
502 Reading service permanently unavailable [1]
[1] Following a 502 response the server MUST immediately close the
connection.
5.3.2 Description
The MODE READER command instructs a mode-switching server to switch
modes, as described in Section 3.4.2.
If the server is mode-switching, it switches from its transit mode to
its reader mode, indicating the fact by changing the capability list
accordingly, and then MUST return a 200 or 201 response with the same
meaning as for the initial greeting (as described in Section 5.1.1);
note that the response need not be the same as the one presented
during the initial greeting. The client MUST NOT issue MODE READER
more than once in a session or after any security or privacy commands
are issued. When the MODE READER command is issued, the server MAY
reset its state to that immediately after the initial connection
before switching mode.
If the server is not mode-switching, then:
o If it advertises the READER capability, it MUST return a 200 or
201 response with the same meaning as for the initial greeting; in
this case the command MUST NOT affect the server state in any way.
o If it does not advertise the READER capability, it MUST return a
502 response and then immediately close the connection.
5.3.3 Examples
Example of use of the MODE READER command on a transit-only server
(which therefore does not providing reading facilities):
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] .
[C] MODE READER
[S] 502 Transit service only
[Server closes connection.]
Example of use of the MODE READER command on a server that provides
reading facilities:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
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[S] READER LISTGROUP
[S] LIST ACTIVE NEWSGROUPS
[S] .
[C] MODE READER
[S] 200 Reader mode, posting permitted
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 500 Permission denied
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
Note that in both these situations the client SHOULD NOT use MODE
READER.
Example of use of the MODE READER command on a mode-switching server:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] IHAVE
[S] MODE-READER
[S] .
[C] MODE READER
[S] 200 Reader mode, posting permitted
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] LIST ACTIVE NEWSGROUPS
[S] STARTTLS
[S] .
In this case the server offers (but does not require) TLS privacy in
its reading mode but not its transit mode.
Example of use of the MODE READER command where the client is not
permitted to post:
[C] MODE READER
[S] 201 NNTP Service Ready, posting prohibited
5.4 QUIT
5.4.1 Usage
This command is mandatory.
Syntax
QUIT
Responses
205 Connection closing
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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.
The server MUST NOT generate any response code to the QUIT command
other than 205 or, if any arguments are provided, 501.
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
Indicating capability: READER
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 7.6.3).
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
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
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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 or LISTGROUP command (see Section 6.1.2) 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
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
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6.1.2 LISTGROUP
6.1.2.1 Usage
Indicating capability: READER with argument LISTGROUP
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.
6.1.2.2 Description
The LISTGROUP command is used to get a listing of all the article
numbers in a particular newsgroup. As a side effect, it also selects
the group in the same way as the GROUP command (see Section 6.1.1).
The optional argument is the name of the newsgroup to be selected
(e.g. "news.software.misc"). If no group is specified, the current
selected newsgroup is used.
On success, 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). The
list contains one number per line, is in numerical order, and lists
precisely those articles that exist in the group at the moment of
selection.
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.
In all other aspects the LISTGROUP command behaves identically to the
GROUP command.
6.1.2.3 Examples
Example of LISTGROUP on an empty group:
[C] LISTGROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup list follows
[S] .
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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
6.1.3 LAST
6.1.3.1 Usage
Indicating capability: READER
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
6.1.3.2 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
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a previous article when the current article number is the reported
low water mark.
Because articles can be removed and added, the results of multiple
LAST and NEXT commands MAY not be consistent over the life of a
particular NNTP session.
If the current article number is already the first article of the
newsgroup, a 422 response MUST be returned. If the current article
number is invalid, a 420 response MUST be returned. If the current
selected newsgroup is invalid, a 412 response MUST be returned. In
all three cases the current selected newsgroup and current article
number MUST NOT be altered.
6.1.3.3 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
6.1.4 NEXT
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6.1.4.1 Usage
Indicating capability: READER
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
6.1.4.2 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 6.1.3).
6.1.4.3 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:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT 3002322
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[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 3.6, 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
Indicating capability: READER
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 article with that number
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
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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
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
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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>
[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:
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[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 article with that number
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
This command is mandatory.
Syntax
HEAD message-id
HEAD number
HEAD
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 article with that number
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
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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
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 article with that number
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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
Indicating capability: READER
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 article with that number
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).
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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:
[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 article with that number
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
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This command is mandatory.
Syntax
STAT message-id
STAT number
STAT
Responses
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 article with that number
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>
[S] 430 No Such Article Found
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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 article with that number
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,
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.
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6.3 Article posting
Article posting is done in one of two ways: 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
Indicating capability: READER with argument POST
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 3.6 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.
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
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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 A.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
[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:
[Initial TCP connection set-up completed.]
[S] 201 NNTP Service Ready, posting prohibited
[C] POST
[S] 440 Posting not permitted
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6.3.2 IHAVE
6.3.2.1 Usage
Indicating capability: IHAVE
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 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
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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
[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
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[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>
[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
Indicating capability: READER
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).
The DATE command MUST return a timestamp from the same clock as is
used for determining article arrival and group creation times (see
Section 6). 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. 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
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7.2.1 Usage
This command is mandatory.
Syntax
HELP
Responses
100 Help text follows (multiline)
7.2.2 Description
This command provides a short summary of the 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 CAPABILITIES command
described in Section 5.2
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
Indicating capability: READER
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 7.6.3). However, they MAY
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
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available.
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] .
7.4 NEWNEWS
7.4.1 Usage
Indicating capability: READER
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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
[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.
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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):
[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
The LIST family of commands all return information that is multi-line
and, in general, can be expected not to change during the session.
Often the information is related to newsgroups, in which case the
response has one line per newsgroup and a wildmat MAY be provided to
restrict the groups for which information is returned.
The set of available keywords (including those provided by
extensions) is given in the capability list with capability label
LIST.
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7.6.1 LIST
7.6.1.1 Usage
Indicating capability: LIST
Syntax
LIST [keyword [wildmat|argument]]
Responses
215 Information follows (multiline)
Parameters
keyword = information requested [1]
argument = specific to keyword
wildmat = groups of interest
[1] If no keyword is provided, it defaults to ACTIVE.
7.6.1.2 Description
The LIST command allows the server to provide blocks of information
to the client. This information may be global or may be related to
newsgroups; in the latter case, the information may be returned
either for all groups or only for those matching a wildmat. Each
block of information is represented by a different keyword. The
command returns the specific information identified by the keyword.
If the information is available, it is returned as a multi-line
response following the 215 response code. The format of the
information depends on the keyword. The information MAY be affected
by the additional argument, but the format MUST NOT be.
If the information is based on newsgroups and 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; for a
newsgroup-based keyword, it indicates that there are no groups
meeting the above criteria.
If the keyword is not recognised, or if an argument is specified and
the keyword does not expect one, a 501 response code MUST BE
returned. If the keyword is recognised but the server does not
maintain the information, a 503 response code MUST BE returned.
The LIST command MUST NOT change the visible state of the server in
any way; that is, the behaviour of subsequent commands MUST NOT be
affected by whether the LIST command was issued or not. For example,
it MUST NOT make groups available that otherwise would not have been.
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7.6.1.3 Examples
Example of LIST with the ACTIVE keyword:
[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
[S] tx.natives.recovery.d 11 9 n
[S] .
Example of LIST with no keyword:
[C] LIST
[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
[S] tx.natives.recovery.d 11 9 n
[S] .
The output is identical to that of the previous example.
Example of LIST on a newsgroup-based keyword with and without
wildmat:
[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] .
[C] LIST ACTIVE.TIMES tx.*
[S] 215 information follows
[S] tx.natives.recovery 930678923 <sob@academ.com>
[S] .
Example of LIST returning an error where the keyword is recognized
but the software does not maintain this information:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] LIST ACTIVE NEWSGROUPS ACTIVE.TIMES XTRA.DATA
[S] .
[C] LIST XTRA.DATA
[S] 503 Data item not stored
Example of LIST where the keyword is not recognised:
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[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] LIST ACTIVE NEWSGROUPS ACTIVE.TIMES XTRA.DATA
[S] .
[C] LIST DISTRIB.PATS
[S] 501 Syntax Error
7.6.2 Standard LIST keywords
This specification defines the following LIST keywords:
+----------------------+----------------------+---------------------+
| Keyword | Definition | Status |
+----------------------+----------------------+---------------------+
| ACTIVE | Section 7.6.3 | Mandatory if the |
| | | READER capability |
| | | is advertised |
| | | |
| ACTIVE.TIMES | Section 7.6.4 | Optional |
| | | |
| DISTRIB.PATS | Section 7.6.5 | Optional |
| | | |
| HEADERS | Section 8.6 | Mandatory if the |
| | | HDR capability is |
| | | advertised |
| | | |
| NEWSGROUPS | Section 7.6.6 | Mandatory if the |
| | | READER capability |
| | | is advertised |
| | | |
| OVERVIEW.FMT | Section 8.4 | Mandatory if the |
| | | OVER capability is |
| | | advertised |
+----------------------+----------------------+---------------------+
Where one of these LIST keywords is supported by a server, it MUST
have the meaning given in the following sub-sections.
7.6.3 LIST ACTIVE
This keyword MUST be supported by servers advertising the READER
capability.
LIST ACTIVE returns a list of valid newsgroups and associated
information. If no wildmat is specified, the server MUST include
every group that the client is permitted to select with the GROUP
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(Section 6.1.1) command. Each line of this list consists of four
fields separated from each other by one or more spaces:
o the name of the newsgroup;
o the reported high water mark for the group;
o the reported low water mark for the group;
o the current status of the group on this server.
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".
For example:
[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
[S] tx.natives.recovery.d 11 9 n
[S] .
or, 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
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[S] .
The information is newsgroup-based and a wildmat MAY be specified, in
which case the response is limited to only the groups (if any) whose
names match the wildmat. For example:
[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] .
7.6.4 LIST ACTIVE.TIMES
This keyword is optional.
The active.times list is maintained by some NNTP servers 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].
For example:
[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] .
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 the LIST ACTIVE (Section 7.6.3)
command. 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 except that, if the latter is invoked with a
date and time earlier than the oldest entry in active.times list, its
result may include extra groups.
The information is newsgroup-based and a wildmat MAY be specified, in
which case the response is limited to only the groups (if any) whose
names match the wildmat.
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7.6.5 LIST DISTRIB.PATS
This keyword is optional.
The distrib.pats list is maintained by some NNTP servers to assist
clients 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. For example:
[C] LIST DISTRIB.PATS
[S] 215 information follows
[S] 10:local.*:local
[S] 5:*:world
[S] 20:local.here.*:thissite
[S] .
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.
The information is not newsgroup-based and an argument MUST NOT be
specified.
7.6.6 LIST NEWSGROUPS
This keyword MUST be supported by servers advertising the READER
capability.
The newsgroups list is maintained by NNTP servers 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 (the 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. For example:
[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] .
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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.
The information is newsgroup-based and a wildmat MAY be specified, in
which case the response is limited to only the groups (if any) whose
names match the wildmat.
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8. Article field access commands
This section lists commands that may be used to access specific
article fields; that is, headers of articles and metadata about
articles. These commands typically fetch data from an "overview
database", which is a database of headers extracted from incoming
articles plus metadata determined as the article arrives. Only
certain fields are included in the database.
This section is based on the Overview/NOV database [ROBE1995]
developed by Geoff Collyer.
8.1 Article metadata
Article "metadata" 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
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-".
8.1.1 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;
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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.
8.1.2 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).
8.2 Database consistency
The information stored in the overview 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.
If the HDR command uses the overview database rather than taking
information directly from the articles, the same issues of
consistency and inconsistency apply and the and the LIST HEADERS
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command SHOULD take the same approach as the LIST OVERVIEW.FMT
command in resolving them.
8.3 OVER
8.3.1 Usage
Indicating capability: OVER
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
8.3.2 Description
The OVER command returns the contents of all the fields 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 is is
supported, the OVER capability line MUST include the argument
"MSGID". Otherwise, the capability line MUST NOT include this
argument, and the OVER command MUST return the the generic response
code 503 when this form is used.
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If the information is available, it is returned as a multi-line
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.
8.3.3 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] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] OVER MSGID
[S] LIST ACTIVE NEWSGROUPS OVERVIEW.FMT
[S] .
[C] OVER <45223423@example.com>
[S] 224 Overview information follows
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[S] 0|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] .
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] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] OVER
[S] LIST ACTIVE NEWSGROUPS OVERVIEW.FMT
[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] 423 No such article in this group
Example of an unsuccessful retrieval of overview information by
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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
8.4 LIST OVERVIEW.FMT
8.4.1 Usage
Indicating capability: OVER
Syntax
LIST OVERVIEW.FMT
Responses
215 Information follows (multiline)
8.4.2 Description
See Section 7.6.1 for general requirements of the LIST command.
The LIST OVERVIEW.FMT command returns a description of the fields in
the database for which it is consistent (as described above). The
information 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
except that, for compatibility with existing implementations, the
last two lines MAY instead be:
Bytes:
Lines:
even though they refer to metadata, not headers.
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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.
8.4.3 Examples
Example of LIST OVERVIEW.FMT output corresponding to the example OVER
output above, using the preferred format:
[C] LIST OVERVIEW.FMT
[S] 215 Order of fields in overview database.
[S] Subject:
[S] From:
[S] Date:
[S] Message-ID:
[S] References:
[S] :bytes
[S] :lines
[S] Xref:full
[S] Distribution:full
[S] .
Example of LIST OVERVIEW.FMT output corresponding to the example OVER
output above, using the alternative format:
[C] LIST OVERVIEW.FMT
[S] 215 Order of fields in overview database.
[S] Subject:
[S] From:
[S] Date:
[S] Message-ID:
[S] References:
[S] Bytes:
[S] Lines:
[S] Xref:FULL
[S] Distribution:FULL
[S] .
8.5 HDR
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8.5.1 Usage
Indicating capability: HDR
Syntax
HDR field message-id
HDR field range
HDR field
Responses
First form (message-id specified)
225 Headers follow (multiline)
430 No article with that message-id
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
field = name of field
range = number(s) of articles
message-id = message-id of article
8.5.2 Description
The HDR command provides access to specific fields from an article
specified by message-id, or from a specified article or range of
articles in the current selected newsgroup. It MAY take the
information directly from the articles or from the overview database.
In the case of headers, an implementation MAY restrict the use of
this command to a specific list of headers or MAY allow it to be used
with any header; it may behave differently when it is used with a
message-id argument and when it is used with a range or no argument.
The required field argument is the name of a header with the colon
omitted (e.g. "subject"), or the name of a metadata item including
the leading colon (e.g. ":bytes"), and is case-insensitive.
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
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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 field. 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 command
(Section 8.3.2), and the same comment concerning NUL, CR, and LF
applies).
Note the distinction between headers and metadata appearing to have
the same meaning. Headers are always taken unchanged from the
article; metadata are always calculated. For example, a request for
"Lines" returns the contents of the "Lines" header of the specified
articles, if any, no matter whether or not they accurately state the
number of lines, while a request for ":lines" returns the line count
metadata, which is always the actual number of lines irrespective of
what any header may state.
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 the header occurs
in a given article more than once, only the content of the first
occurrence is returned by HDR. 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.
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A server MAY only allow HDR commands for a limited set of fields; 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 fields, rather than
returning erroneous results such as a successful empty response.
If HDR uses the overview database and it is inconsistent for the
requested field, 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.
8.5.3 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:
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[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR subject
[S] 225 Header information follows
[S] 3000234 I am just a test article
[S] .
Example of an unsuccessful retrieval of a header from an article by
message-id:
[C] HDR subject <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of headers from articles by
number because no newsgroup was selected first:
[Assumes current selected newsgroup is invalid.]
[C] HDR subject 300256-
[S] 412 No newsgroup selected
Example of an unsuccessful retrieval of headers because the current
selected newsgroup is empty:
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] HDR subject 1-
[S] 423 No articles in that range
Example of an unsuccessful retrieval of headers because the server
does not allow HDR commands for that header:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR Content-Type 3000234-300238
[S] 503 HDR not permitted on Content-Type
8.6 LIST HEADERS
8.6.1 Usage
Indicating capability: HDR
Syntax
LIST HEADERS [MSGID|RANGE]
Responses
215 Field list follows (multiline)
Parameters
MSGID = requests list for access by message-id
RANGE = requests list for access by range
8.6.2 Description
See Section 7.6.1 for general requirements of the LIST command.
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The LIST HEADERS command returns a list of fields 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 field name
(excluding the trailing colon for headers and including the leading
colon for metadata items). 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 explicitly 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
HDR command).
An implementation that also supports the OVER command 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.
8.6.3 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] .
Example of an implementation providing access to the same fields as
the first example in Section 8.4.3:
[C] CAPABILITIES
[S] 101 Capability list:
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[S] VERSION 2
[S] READER
[S] OVER
[S] HDR
[S] LIST ACTIVE NEWSGROUPS HEADERS OVERVIEW.FMT
[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
[S] :lines
[S] :bytes
[S] :x-article-number
[S] .
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[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.
The non-terminals <command-line>, <command-continuation>, and
<response> between them specify the text that flows between client
and server. For each command, the sequence is:
o the client sends an instance of <command-line>;
o if the client is one that immediately streams data [1], it sends
an instance of <command-datastream>;
o the server sends an instance of <response>;
o while the latest response is one that indicates more data is
required (in general, a 3xx response):
* the client sends an instance of <command-continuation>;
* the server sends an instance of <response>.
[1] There are no commands in this specification that immediately
stream data, but this non-terminal is defined for the convenience of
extensions.
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 = X-command
X-command = keyword *(WS token)
command =/ article-command /
body-command /
capabilities-command /
date-command /
group-command /
hdr-command /
head-command /
help-command /
ihave-command /
last-command /
list-command /
listgroup-command /
mode-reader-command /
newgroups-command /
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newnews-command /
next-command /
over-command /
post-command /
quit-command /
stat-command
article-command = "ARTICLE" [WS article-ref]
body-command = "BODY" [WS article-ref]
capabilities-command = "CAPABILITIES" [WS keyword]
date-command = "DATE"
group-command = "GROUP" WS newsgroup-name
hdr-command = "HDR" WS header-meta-name [WS range-ref]
head-command = "HEAD" [WS article-ref]
help-command = "HELP"
ihave-command = "IHAVE" WS message-id
last-command = "LAST"
list-command = "LIST" [WS list-arguments]
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" [WS article-ref]
article-ref = article-number / message-id
date = date2y / date4y
date4y = 4DIGIT 2DIGIT 2DIGIT
date2y = 2DIGIT 2DIGIT 2DIGIT
date-time = date WS time [WS "GMT"]
header-meta-name = header-name / metadata-name
list-arguments = keyword [WS token]
metadata-name = ":" 1*A-NOTCOLON
range = article-number ["-" [article-number]]
range-ref = range / message-id
time = 2DIGIT 2DIGIT 2DIGIT
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9.2 Command continuation
This syntax defines the further material sent by the client in the
case of multi-stage commands and those that stream data.
command-datastream = UNDEFINED
; not used, provided as a hook for extensions
command-continuation = ihave-continuation /
post-continuation
ihave-continuation = encoded-article
post-continuation = encoded-article
encoded-article = content-lines termination
; after undoing the "byte-stuffing", this MUST match <article>
9.3 Responses
9.3.1 Generic responses
This syntax defines the non-terminal <response>, which represents the
generic form of responses - that is, what is sent from the server to
the client in response to a <command> or a<command-continuation>.
response = simple-response / multiline-response
multiline-response = simple-response content-lines termination
simple-response =
simple-response-content [SP trailing-comment] CRLF
simple-response-content = X-simple-response-content
X-simple-response-content = 3DIGIT *(SP response-argument)
response-argument = 1*A-CHAR
trailing-comment = *U-CHAR
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9.3.2 Initial response line contents
This syntax defines the specific initial response lines for the
various commands in this specification. Only those response codes
with arguments are listed.
simple-response-content =/ response-111-content
response-211-content
response-22x-content
response-401-content
response-111-content = "111" SP date4y time
response-211-content = "211" 3(SP article-number) SP newsgroup-name
response-22x-content = ("220" / "221" / "222" / "223")
SP article-number SP message-id
response-401-content = "401" SP capability-label
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9.3.3 Multi-line response contents
This syntax defines the content of the various multi-line responses
(more precisely, the part of the response in <content-lines>), in
each case after any "byte-stuffing" has been undone.
multiline-response-content = article-response /
body-response /
capabilities-response /
hdr-response /
head-response /
help-response /
list-response /
listgroup-response /
newgroups-response /
newnews-response /
over-response
article-response = article
body-response = body
capabilities-response = 1*(capability-line CRLF)
hdr-response = *(article-number SP hdr-content CRLF)
head-response = 1*header
help-response = *(*B-CHAR CRLF)
list-response = body
listgroup-response = *(article-number CRLF)
newgroups-response = *(newsgroup-name SPA article-number
SPA article-number SPA newsgroup-status CRLF)
newnews-response = *(message-id CRLF)
over-response = *(article-number over-content CRLF)
hdr-content = *S-NONTAB
hdr-n-content = [(header-name ":" / metadata-name) SP hdr-content]
newsgroup-status = %x79 / %x6E / %x6D / private-status
over-content = 1*6(TAB hdr-content) /
7(TAB hdr-content) *(TAB hdr-n-content)
private-status = token ; except the values in newsgroup-status
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9.4 Capability lines
This syntax defines the generic form of a capability line in the
capabilities list (see Section 3.3.1).
capability-line = capability-entry
capability-entry = X-capability-entry
X-capability-entry = capability-label *(WS capability-argument)
capability-label = keyword
capability-argument = token
This syntax defines the specific capability entries for the
capabilities in this specification.
capability-entry =/
hdr-capability /
ihave-capability /
implementation-capability /
list-capability /
mode-reader-capability /
over-capability /
reader-capability /
version-capability
hdr-capability = "HDR"
ihave-capability = "IHAVE"
implementation-capability = "IMPLEMENTATION" *(WS token)
list-capability = "LIST" 1*(WS keyword)
mode-reader-capability = "MODE-READER"
over-capability = "OVER" [WS "MSGID"]
reader-capability = "READER" *(WS reader-option)
reader-option = "POST" / "LISTGROUP" ; each to appear at most once
version-capability = "VERSION" 1*(WS version-number)
version-number = nzDIGIT *5DIGIT
9.5 LIST variants
This section defines more specifically the keywords for the LIST
command and the syntax of the corresponding responses.
; active
list-arguments =/ "ACTIVE" [WS wildmat]
list-response =/ list-active-response
list-active-response = newgroups-response
; active.times
list-arguments =/ "ACTIVE.TIMES" [WS wildmat]
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list-response =/ list-active-times-response
list-active-times-response =
*(newsgroup-name SPA 1*DIGIT SPA newsgroup-creator CRLF)
newsgroup-creator = U-TEXT
; distrib.pats
list-arguments =/ "DISTRIB.PATS"
list-response =/ list-distrib-pats-response
list-distrib-pats-response =
*(1*DIGIT ":" wildmat ":" distribution CRLF)
distribution = token
; headers
list-arguments =/ "HEADERS" [WS ("MSGID" / "RANGE")]
list-response =/ list-headers-response
list-headers-response = *(header-meta-name CRLF) /
*((metadata-name / ":") CRLF)
; newsgroups
list-arguments =/ "NEWSGROUPS" [WS wildmat]
list-response =/ list-newsgroups-response
list-newsgroups-response =
*(newsgroup-name WS newsgroup-description CRLF)
newsgroup-description = S-TEXT
; overview.fmt
list-arguments =/ "OVERVIEW.FMT"
list-response =/ list-overview-fmt-response
list-overview-fmt-response = "Subject:" CRLF
"From:" CRLF
"Date:" CRLF
"Message-ID:" CRLF
"References:" CRLF
( ":bytes" CRLF ":lines" / "Bytes:" CRLF "Lines:") CRLF
*((header-name ":full" / metadata-name) CRLF)
9.6 Articles
This syntax defines the non-terminal <article>, which represents the
format of an article as described in Section 3.6.
article = 1*header CRLF body
header = header-name ":" [CRLF] SP header-content CRLF
header-content = *(S-CHAR / [CRLF] WS)
body = *(*B-CHAR CRLF)
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9.7 General non-terminals
These non-terminals are used at various places in the syntax and are
collected here for convenience. A few of these non-terminals are not
used in this specification but are provided for the consistency and
convenience of extension authors.
article-number = 1*16DIGIT
content-lines = *([content-text] CRLF)
content-text = (".." / B-NONDOT) *B-CHAR
header-name = 1*A-NOTCOLON
keyword = ALPHA 2*11(ALPHA / DIGIT / "." / "-")
message-id = "<" 1*248A-NOTGT ">"
newsgroup-name = 1*wildmat-exact
termination = "." CRLF
token = 1*P-CHAR
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
; must not begin with "!" if not immediately preceded by "!"
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E /
UTF8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
base64 = *(4base64-char) [base64-terminal]
base64-char = UPPER / LOWER / DIGIT / "+" / "/"
base64-terminal = 2base64-char "==" / 3base64-char "="
; Assorted special character sets
; A- means based on US-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 "."
ALPHA = UPPER / LOWER ; use only when case-insensitive
CR = %x0D
CRLF = CR LF
CTRL = %x01-08 / %x0B-0C / %x0E-1F
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DIGIT = %x30-39
nzDIGIT = %x31-39
EOL = *(SP / TAB) CRLF
LF = %x0A
LOWER = %x61-7A
SP = %x20
SPA = 1*SP
TAB = %x09
UPPER = %x41-5A
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 /
%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
9.8 Extensions and Validation
The specification of a registered extension MUST include formal
syntax that defines additional forms for the following non-terminals:
command
for each new command other than a variant of the LIST command -
the syntax of each command MUST be compatible with the definition
of <X-command>;
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command-datastream
for each new command that immediately streams data;
command-continuation
for each new command that sends further material after the initial
command line - the syntax of each continuation MUST be exactly
what is sent to the server, including any escape mechanisms such
as "byte-stuffing";
simple-response-content
for each new response code that has arguments - the syntax of each
response MUST be compatible with the definition of
<X-simple-response-content>;
multiline-response-content
for each new response code that has a multi-line response - the
syntax MUST show the response after the lines containing the
response code and the terminating octet have been removed and any
"byte-stuffing" undone;
capability-entry
for each new capability label - the syntax of each entry MUST be
compatible with the definition of <X-capability-entry>;
list-arguments
for each new variant of the LIST command - the syntax of each
entry MUST be compatible with the definition of <X-command>;
list-response
for each new variant of the LIST command - the syntax MUST show
the response after the lines containing the 215 response code and
the terminating octet have been removed and any "byte-stuffing"
undone.
The =/ notation of ABNF [RFC2234] SHOULD be used for this.
When validating the syntax in this specification, or syntax based on
it, it should be noted that:
o the non-terminals <command-line>, <command-datastream>,
<command-continuation>, <response>, and
<multiline-response-content> describe basic concepts of the
protocol and are not referred to by any other rule;
o the non-terminal <base64> is provided for the convenience of
extension authors and is not referred to by any rule in this
specification;
o for the reasons given above, the non-terminals <S-CHAR>,
<S-NONTAB>, and <S-TEXT> each have two definitions;
o the non-terminal <UNDEFINED> is deliberately not defined.
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10. IANA Considerations
This specification requires IANA to keep a registry of capability
labels. The initial contents of this registry are specified in
Section 3.3.4. As described in Section 3.3.3, labels beginning with
X are reserved for private use while all other names are expected to
be associated with a specification in an RFC on the standards-track
or defining an IESG-approved experimental protocol.
Different entries in the registry MUST use different capability
labels.
Different entries in the registry MUST NOT use the same command name.
For this purpose, variants distinguished by a second or subsequent
keyword (e.g. "LIST HEADERS" and "LIST OVERVIEW.FMT") count as
different commands. If there is a need for two extensions to use the
same command, a single harmonised specification MUST be registered.
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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;
one such extension is [NNTP-AUTH]. 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 capability lists
The CAPABILITIES command provides a capability list, which is
information about the current capabilities of 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 capabilities list in a given server state will
not change from session to session; for example, 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] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER POST
[S] XENCRYPT
[S] LIST ACTIVE NEWSGROUPS
[S] .
[C] XENCRYPT
[Client and server negotiate encryption on the link]
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[S] 283 Encrypted link established
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER POST
[S] XSECRET
[S] LIST ACTIVE NEWSGROUPS
[S] .
[C] XSECRET fred flintstone
[S] 290 Password for fred accepted
If the client caches the last capabilities list, 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 capability lists 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
This document is the result of much effort by the present and past
members of the NNTP Working Group, chaired by Russ Allbery and Ned
Freed. It could not have been produced without them.
The author acknowledges the original authors of NNTP as documented in
RFC 977 [RFC977]: Brian Kantor and Phil Lapsey.
The author gratefully acknowledges:
o 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.
o The work of the DRUMS working group, specifically RFC 1869
[RFC1869], which drove the original thinking which led to the
CAPABILITIES command and the extensions mechanism detailed in this
document.
o 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.
o 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
Other people who contributed to this document include:
Matthias Andree
Greg Andruk
Maurizio Codogno
Mark Crispin
Andrew Gierth
Juergen Helbing
Scott Hollenbeck
Charles Lindsey
Ade Lovett
Ken Murchison
Francois Petillon
Peter Robinson
Rob Siemborski
Howard Swinehart
Ruud van Tol
Jeffrey Vinocur
The author thanks them all and apologises to anyone omitted.
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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13. References
13.1 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.
[RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 2003.
[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.
13.2 Informative References
[NNTP-AUTH]
Vinocur, J., Murchison, K. and C. Newman, "NNTP
Authentication",
Internet-draft draft-ietf-nntpext-authinfo-06, December
2004.
[NNTP-STREAM]
Vinocur, J. and K. Murchison, "NNTP Authentication",
Internet-draft draft-ietf-nntpext-streaming-03, December
2004.
[NNTP-TLS]
Vinocur, J., Murchison, K. and C. Newman, "Using TLS with
NNTP", Internet-draft draft-ietf-nntpext-tls-nntp-04,
December 2004.
[RFC1036] Horton, M. and R. Adams, "Standard for interchange of
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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.
There is no definitive copy of this document known to the
author. It was previously posted as the Usenet article
<news:nov-faq-1-930909720@agate.Berkeley.EDU>
[SALZ1992]
Salz, R., "Manual Page for wildmat(3) from the INN 1.4
distribution, Revision 1.10", April 1992.
There is no definitive copy of this document known to the
author.
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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. 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.
A.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 9.6.
header = header-name ":" SP [header-content] CRLF
header-content = [WS] token *( [CRLF] WS token )
A.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.
A.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
necessary validation (or has in turn obtained the article from a
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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. This is often 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 B. Summary of Commands
This section contains a list of every command defined in this
document, ordered by command name and by indicating capability.
Ordered by command name:
+-------------------+-----------------------+---------------+
| Command | Indicating capability | Definition |
+-------------------+-----------------------+---------------+
| ARTICLE | READER | Section 6.2.1 |
| | | |
| BODY | READER | Section 6.2.3 |
| | | |
| CAPABILITIES | mandatory | Section 5.2 |
| | | |
| DATE | READER | Section 7.1 |
| | | |
| GROUP | READER | Section 6.1.1 |
| | | |
| HDR | HDR | Section 8.5 |
| | | |
| HEAD | mandatory | Section 6.2.2 |
| | | |
| HELP | mandatory | Section 7.2 |
| | | |
| IHAVE | IHAVE | Section 6.3.2 |
| | | |
| LAST | READER | Section 6.1.3 |
| | | |
| LIST | LIST | Section 7.6.1 |
| | | |
| LIST ACTIVE.TIMES | LIST | Section 7.6.4 |
| | | |
| LIST ACTIVE | LIST | Section 7.6.3 |
| | | |
| LIST DISTRIB.PATS | LIST | Section 7.6.5 |
| | | |
| LIST HEADERS | HDR | Section 8.6 |
| | | |
| LIST NEWSGROUPS | LIST | Section 7.6.6 |
| | | |
| LIST OVERVIEW.FMT | OVER | Section 8.4 |
| | | |
| LISTGROUP | READER LISTGROUP | Section 6.1.2 |
| | | |
| MODE READER | MODE-READER | Section 5.3 |
| | | |
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| NEWGROUPS | READER | Section 7.3 |
| | | |
| NEWNEWS | READER | Section 7.4 |
| | | |
| NEXT | READER | Section 6.1.4 |
| | | |
| OVER | OVER | Section 8.3 |
| | | |
| POST | READER POST | Section 6.3.1 |
| | | |
| QUIT | mandatory | Section 5.4 |
| | | |
| STAT | mandatory | Section 6.2.4 |
+-------------------+-----------------------+---------------+
Ordered by indicating capability:
+-------------------+-----------------------+---------------+
| Command | Indicating capability | Definition |
+-------------------+-----------------------+---------------+
| CAPABILITIES | mandatory | Section 5.2 |
| | | |
| HEAD | mandatory | Section 6.2.2 |
| | | |
| HELP | mandatory | Section 7.2 |
| | | |
| QUIT | mandatory | Section 5.4 |
| | | |
| STAT | mandatory | Section 6.2.4 |
| | | |
| HDR | HDR | Section 8.5 |
| | | |
| LIST HEADERS | HDR | Section 8.6 |
| | | |
| IHAVE | IHAVE | Section 6.3.2 |
| | | |
| LIST | LIST | Section 7.6.1 |
| | | |
| LIST ACTIVE | LIST | Section 7.6.3 |
| | | |
| LIST ACTIVE.TIMES | LIST | Section 7.6.4 |
| | | |
| LIST DISTRIB.PATS | LIST | Section 7.6.5 |
| | | |
| LIST NEWSGROUPS | LIST | Section 7.6.6 |
| | | |
| MODE READER | MODE-READER | Section 5.3 |
| | | |
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| OVER | OVER | Section 8.3 |
| | | |
| LIST OVERVIEW.FMT | OVER | Section 8.4 |
| | | |
| ARTICLE | READER | Section 6.2.1 |
| | | |
| BODY | READER | Section 6.2.3 |
| | | |
| DATE | READER | Section 7.1 |
| | | |
| GROUP | READER | Section 6.1.1 |
| | | |
| LAST | READER | Section 6.1.3 |
| | | |
| NEWGROUPS | READER | Section 7.3 |
| | | |
| NEWNEWS | READER | Section 7.4 |
| | | |
| NEXT | READER | Section 6.1.4 |
| | | |
| LISTGROUP | READER LISTGROUP | Section 6.1.2 |
| | | |
| POST | READER POST | Section 6.3.1 |
+-------------------+-----------------------+---------------+
Where two keywords are given in the capability column, the second is
an argument to the first.
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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 101 (multi-line)
Generated by: CAPABILITIES
Meaning: capabilities list 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 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
4 arguments: number low high group
Meaning: article numbers follow.
Response code 215 (multi-line)
Generated by: LIST
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.
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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.
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: capability-label
Meaning: the server is in the wrong mode; the indicated capability
should be used to change the mode.
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.
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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.
Response code 423
Generated by: ARTICLE, BODY, HDR, HEAD, OVER, STAT
Meaning: no article with that number or 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.
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Response code 501
Generic response
Meaning: syntax error in command.
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.
Response code 504
Generic response
Meaning: error in base64-encoding [RFC3548] of an argument
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Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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