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RFC 3977 - Network News Transfer Protocol (NNTP)
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RFC3977 - Network News Transfer Protocol (NNTP)
Network Working Group C. Feather
Request for Comments: 3977 THUS plc
Obsoletes: 977 October 2006
Updates: 2980
Category: Standards Track
Network News Transfer Protocol (NNTP)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Author's Note . . . . . . . . . . . . . . . . . . . . . . 4
2. Notation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Commands and Responses . . . . . . . . . . . . . . . . . 6
3.1.1. Multi-line Data Blocks . . . . . . . . . . . . . . . . 8
3.2. Response Codes . . . . . . . . . . . . . . . . . . . . . 9
3.2.1. Generic Response Codes . . . . . . . . . . . . . . . 10
3.2.1.1. Examples . . . . . . . . . . . . . . . . . . . . 12
3.3. Capabilities and Extensions . . . . . . . . . . . . . . . 14
3.3.1. Capability Descriptions . . . . . . . . . . . . . . . 14
3.3.2. Standard Capabilities . . . . . . . . . . . . . . . . 15
3.3.3. Extensions . . . . . . . . . . . . . . . . . . . . . 16
3.3.4. Initial IANA Register . . . . . . . . . . . . . . . . 18
3.4. Mandatory and Optional Commands . . . . . . . . . . . . . 20
3.4.1. Reading and Transit Servers . . . . . . . . . . . . . 21
3.4.2. Mode Switching . . . . . . . . . . . . . . . . . . . 21
3.5. Pipelining . . . . . . . . . . . . . . . . . . . . . . . 22
3.5.1. Examples . . . . . . . . . . . . . . . . . . . . . . 23
3.6. Articles . . . . . . . . . . . . . . . . . . . . . . . . 24
4. The WILDMAT Format . . . . . . . . . . . . . . . . . . . . . 25
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 . . . . . . . . . . . . . . . . . . . . . . . 32
5.4. QUIT . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6. Article Posting and Retrieval . . . . . . . . . . . . . . . . 35
6.1. Group and Article Selection . . . . . . . . . . . . . . . 36
6.1.1. GROUP . . . . . . . . . . . . . . . . . . . . . . . . 36
6.1.2. LISTGROUP . . . . . . . . . . . . . . . . . . . . . . 39
6.1.3. LAST . . . . . . . . . . . . . . . . . . . . . . . . 42
6.1.4. NEXT . . . . . . . . . . . . . . . . . . . . . . . . 44
6.2. Retrieval of Articles and Article Sections . . . . . . . 45
6.2.1. ARTICLE . . . . . . . . . . . . . . . . . . . . . . . 46
6.2.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 49
6.2.3. BODY . . . . . . . . . . . . . . . . . . . . . . . . 51
6.2.4. STAT . . . . . . . . . . . . . . . . . . . . . . . . 53
6.3. Article Posting . . . . . . . . . . . . . . . . . . . . . 56
6.3.1. POST . . . . . . . . . . . . . . . . . . . . . . . . 56
6.3.2. IHAVE . . . . . . . . . . . . . . . . . . . . . . . . 58
7. Information Commands . . . . . . . . . . . . . . . . . . . . 61
7.1. DATE . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.2. HELP . . . . . . . . . . . . . . . . . . . . . . . . . . 62
7.3. NEWGROUPS . . . . . . . . . . . . . . . . . . . . . . . . 63
7.4. NEWNEWS . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.5. Time . . . . . . . . . . . . . . . . . . . . . . . . . . 65
7.5.1. Examples . . . . . . . . . . . . . . . . . . . . . . 66
7.6. The LIST Commands . . . . . . . . . . . . . . . . . . . . 66
7.6.1. LIST . . . . . . . . . . . . . . . . . . . . . . . . 67
7.6.2. Standard LIST Keywords . . . . . . . . . . . . . . . 69
7.6.3. LIST ACTIVE . . . . . . . . . . . . . . . . . . . . . 70
7.6.4. LIST ACTIVE.TIMES . . . . . . . . . . . . . . . . . . 71
7.6.5. LIST DISTRIB.PATS . . . . . . . . . . . . . . . . . . 72
7.6.6. LIST NEWSGROUPS . . . . . . . . . . . . . . . . . . . 73
8. Article Field Access Commands . . . . . . . . . . . . . . . . 73
8.1. Article Metadata . . . . . . . . . . . . . . . . . . . . 74
8.1.1. The :bytes Metadata Item . . . . . . . . . . . . . . 74
8.1.2. The :lines Metadata Item . . . . . . . . . . . . . . 75
8.2. Database Consistency . . . . . . . . . . . . . . . . . . 75
8.3. OVER . . . . . . . . . . . . . . . . . . . . . . . . . . 76
8.4. LIST OVERVIEW.FMT . . . . . . . . . . . . . . . . . . . . 81
8.5. HDR . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
8.6. LIST HEADERS . . . . . . . . . . . . . . . . . . . . . . 87
9. Augmented BNF Syntax for NNTP . . . . . . . . . . . . . . . . 90
9.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 90
9.2. Commands . . . . . . . . . . . . . . . . . . . . . . . . 92
9.3. Command Continuation . . . . . . . . . . . . . . . . . . 93
9.4. Responses . . . . . . . . . . . . . . . . . . . . . . . . 93
9.4.1. Generic Responses . . . . . . . . . . . . . . . . . . 93
9.4.2. Initial Response Line Contents . . . . . . . . . . . 94
9.4.3. Multi-line Response Contents . . . . . . . . . . . . 94
9.5. Capability Lines . . . . . . . . . . . . . . . . . . . . 95
9.6. LIST Variants . . . . . . . . . . . . . . . . . . . . . . 96
9.7. Articles . . . . . . . . . . . . . . . . . . . . . . . . 97
9.8. General Non-terminals . . . . . . . . . . . . . . . . . . 97
9.9. Extensions and Validation . . . . . . . . . . . . . . . . 99
10. Internationalisation Considerations . . . . . . . . . . . . .100
10.1. Introduction and Historical Situation . . . . . . . . . .100
10.2. This Specification . . . . . . . . . . . . . . . . . . .101
10.3. Outstanding Issues . . . . . . . . . . . . . . . . . . .102
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .103
12. Security Considerations . . . . . . . . . . . . . . . . . . .103
12.1. Personal and Proprietary Information . . . . . . . . . .104
12.2. Abuse of Server Log Information . . . . . . . . . . . . .104
12.3. Weak Authentication and Access Control . . . . . . . . .104
12.4. DNS Spoofing . . . . . . . . . . . . . . . . . . . . . .104
12.5. UTF-8 Issues . . . . . . . . . . . . . . . . . . . . . .105
12.6. Caching of Capability Lists . . . . . . . . . . . . . . .106
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .107
14. References . . . . . . . . . . . . . . . . . . . . . . . . .110
14.1. Normative References . . . . . . . . . . . . . . . . . .110
14.2. Informative References . . . . . . . . . . . . . . . . .110
A. Interaction with Other Specifications . . . . . . . . . . . .112
A.1. Header Folding . . . . . . . . . . . . . . . . . . . . .112
A.2. Message-IDs . . . . . . . . . . . . . . . . . . . . . . .112
A.3. Article Posting . . . . . . . . . . . . . . . . . . . . .114
B. Summary of Commands . . . . . . . . . . . . . . . . . . . . .115
C. Summary of Response Codes . . . . . . . . . . . . . . . . . .117
D. Changes from RFC 977 . . . . . . . . . . . . . . . . . . . .121
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.
Although the protocol specification in this document is largely
compatible with the version specified in RFC 977 [RFC977], a number
of changes are summarised in Appendix D. In particular:
o the default character set is changed from US-ASCII [ANSI1986] to
UTF-8 [RFC3629] (note that US-ASCII is a subset of UTF-8);
o a number of commands that were optional in RFC 977 or that have
been taken from RFC 2980 [RFC2980] are now mandatory; and
o a CAPABILITIES command has been added to allow clients to
determine what functionality is available from a server.
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 terms "client" and "client
host" refer to a host making use of the NNTP service, while the terms
"server" and "server host" refer to a host that offers the NNTP
service.
1.1. 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.
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 enclosed material is optional.
elliptical indicates that the argument may be repeated any
... marks 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 in 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 in length.
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 an "[S]" will be used to
represent the server host. Most of the examples do not rely on a
particular server state. In some cases, however, they do assume that
the currently 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 that might be read as specifying details of a client or server
implementation, such as "database", are used simply to ease
description. Provided that implementations conform to the protocol
and format specifications in this document, no specific technique is
mandated.
3. Basic Concepts
3.1. Commands and Responses
NNTP operates over any reliable bi-directional 8-bit-wide data stream
channel. 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. If the connection used is TCP, then 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.
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 each be 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
of 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. Implementations
SHOULD apply these same principles throughout.
The term "character" means a single Unicode code point.
Implementations are not required to carry out Unicode 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; if so, they use 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.
In some cases, a command involves more data than just a single line.
The further data may be sent either immediately after the command
line (there are no instances of this in this specification, but there
are in extensions such as [NNTP-STREAM]) or following a request from
the server (indicated by a 3xx response).
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 initial 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. Single-line responses
consist of an initial line only. Multi-line responses consist of an
initial line followed by a multi-line data block.
An NNTP server MAY have an inactivity autologout timer. Such a timer
SHOULD be of at least three minutes' duration, with the exception
that there MAY be a shorter limit on how long the server is willing
to wait for the first command from the client. The receipt of any
command from the client during the timer interval SHOULD suffice to
reset the autologout timer. Similarly, the receipt of any
significant amount of data from a client that is sending a multi-line
data block (such as during a POST or IHAVE command) SHOULD suffice to
reset the autologout timer. When the timer expires, the server
SHOULD close the connection without sending any response to the
client.
3.1.1. Multi-line Data Blocks
A multi-line data block is used in certain commands and responses.
It MUST adhere to the following rules:
1. The block consists of a sequence of zero 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. In a multi-line response, the block immediately follows the CRLF
at the end of the initial line of the response. When used in any
other context, the specific command will define when the block is
sent.
3. If any line of the data block begins with the "termination octet"
("." or %x2E), that line MUST be "dot-stuffed" by prepending an
additional termination octet to that line of the block.
4. The lines of the block MUST be followed by a terminating line
consisting of a single termination octet followed by a CRLF pair
in the normal way. Thus, unless it is empty, a multi-line block
is always terminated with the five octets CRLF "." CRLF
(%x0D.0A.2E.0D.0A).
5. When a multi-line block is interpreted, the "dot-stuffing" MUST
be undone; i.e., the recipient 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 block; i.e., the recipient
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 of a non-empty block
is, of course, part of the last line of the block.)
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
(subject to that same requirement) it MAY include octets above and
below 128 mixed arbitrarily.
This document does not place any limit on the length of a line in a
multi-line block. However, the standards that define the format of
articles may do so.
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, setup, 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 the code is
single-line or multi-line. 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 single-line or
multi-line 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
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 if 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
variants depending on a second keyword (e.g., LIST ACTIVE and LIST
NEWSGROUPS), 501 MUST be used when the base command is implemented
but the requested variant is not, and 500 MUST be used only when the
base command itself is not implemented.
If an argument is required to be a base64-encoded string [RFC4648]
(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 if it 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 to start a new
one with the appropriate authority before the command can be used.
Historically, some mode-switching servers (see Section 3.4.1) used
this response to indicate that this command will become available
after the MODE READER command (Section 5.3) is used, but this
usage does not conform to this specification and MUST NOT be used.
Note that the server MUST NOT close the 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, it
must 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 that provides the
necessary mechanism (usually an extension, which may be a private
extension). 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 connection. Following a 400 response, 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
[S] NEWNEWS
[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
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
Example of 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 a facility is used:
[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,
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 the
following:
o The capability label, which is a keyword indicating the
capability. A capability label may be defined by this
specification or a successor, or 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 the server is 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 interoperate 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
have a leading zero. Version numbers are assigned only in RFCs
that update or replace this specification; servers MUST NOT create
their own version numbers.
The version number of this specification is 2.
READER
This capability indicates that the server implements the various
commands useful for reading clients.
IHAVE
This capability indicates that the server implements the IHAVE
command.
POST
This capability indicates that the server implements the POST
command.
NEWNEWS
This capability indicates that the server implements the NEWNEWS
command.
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.
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.
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 that the MODE READER command needs to be used
to enable the READER capability.
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 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 the following:
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 that this
extension may have (if any).
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 A specific statement about the circumstances under which the
extension can cause any pre-existing command to produce a 401,
480, or 483 response.
o A description of how the use of MODE READER on a mode-switching
server interacts with the extension.
o A description of 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 9.9.
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 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 that 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 to commands documented in registered
extensions in response to the availability or use of a private
extension.
3.3.4. Initial IANA Register
IANA will maintain a registry of NNTP capability labels. All
capability labels in the registry MUST be keywords and MUST NOT begin
with X.
The initial content of the registry consists of these entries:
+-------------------+--------------------------+--------------------+
| Label | Meaning | Definition |
+-------------------+--------------------------+--------------------+
| AUTHINFO | Authentication | [NNTP-AUTH] |
| | | |
| HDR | Batched header retrieval | Section 3.3.2, |
| | | 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 | |
| | | |
| NEWNEWS | NEWNEWS command | Section 3.3.2 and |
| | available | Section 7.4 |
| | | |
| OVER | Overview support | Section 3.3.2, |
| | | Section 8.3, and |
| | | Section 8.4 |
| | | |
| POST | POST command available | Section 3.3.2 and |
| | | Section 6.3.1 |
| | | |
| READER | Reader commands | Section 3.3.2 |
| | available | |
| | | |
| SASL | Supported SASL | [NNTP-AUTH] |
| | mechanisms | |
| | | |
| STARTTLS | Transport layer security | [NNTP-TLS] |
| | | |
| 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
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 bundles, 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 bundle.
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 bundles have been chosen to provide useful functionality, and
therefore server authors are discouraged from implementing only part
of a bundle.
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 the bundle 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 making this transfer tend to
be peers in a network that transmit articles among one another, and
not end-user systems, this process is called "peering" or "transit".
(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 bundling 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 command (Section 5.3) on a
mode-switching server, once a server advertises either or both of the
IHAVE or READER capabilities, it MUST continue to advertise them for
the entire 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 command (see Section
5.3).
* 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
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
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 it receives 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 it receives 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;
typically, it is 4k octets for TCP. (Since the server only sends
data in response to commands from the client, the converse problem
does not 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, 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
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 that fails to satisfy this requirement has been
received from elsewhere, clients and servers MAY transfer it to each
other without re-folding it.
The content of a header SHOULD be in UTF-8. However, if an
implementation 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
or server without modification. Therefore, implementations MUST be
prepared to receive such headers, and data derived from them (e.g.,
in the responses from the OVER command, Section 8.3), and MUST NOT
assume that they are always UTF-8. Any external processing of 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 "<", 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 that the article be changed as a
result). See also Appendix A.2.
4. The WILDMAT Format
The WILDMAT format described here is based on the version first
developed by Rich Salz [SALZ1992], which was in turn 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 [RFC4234] syntax, which
is an extract of that in Section 9.8.
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x22-29 / %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, whereas 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 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*":
o The string "aaa" matches because the rightmost match is with "a*".
o The string "abb" does not match because the rightmost match is
with "*b".
o The string "ccb" matches because the rightmost match is with
"*c*".
o The string "xxx" does not match because no <wildmat-pattern>
matches.
A <wildmat-pattern> matches a string if the string can be broken into
components, each of which matches the corresponding <wildmat-item> in
the pattern. The matches must be in the same order, and the whole
string must be used in the match. The pattern is "anchored"; that
is, the first and last characters in the string must match the first
and last item, respectively (unless that item is an asterisk matching
zero characters).
A <wildmat-exact> matches the same character (which may be more than
one octet in UTF-8).
"?" matches exactly one character (which may be more than one octet).
"*" matches zero or more characters. It can match an empty string,
but it cannot match a subsequence of a UTF-8 sequence that is not
aligned to the character boundaries.
4.3. Extensions
An NNTP server or extension MAY extend the syntax or semantics of
wildmats provided that all wildmats that meet the requirements of
Section 4.1 have the meaning ascribed to them by Section 4.2. Future
editions of this document may also extend wildmats.
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
5. Session Administration Commands
5.1. Initial Connection
5.1.1. Usage
This command MUST NOT be pipelined.
Responses [1]
200 Service available, posting allowed
201 Service available, posting prohibited
400 Service temporarily unavailable [2]
502 Service permanently unavailable [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 the client 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.
5.1.3. Examples
Example of a normal connection from an authorized client that then
terminates the session (see Section 5.4):
[Initial 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, which also immediately terminates the session:
[Initial 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 connection set-up completed.]
[S] 502 NNTP Service permanently unavailable
[Server closes connection.]
Example of a connection from a client if the server is unable to
provide service:
[Initial 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 (multi-line)
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
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 data block 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 on 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 12.6 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
[S] READER
[S] LIST ACTIVE NEWSGROUPS
[S] .
Example of a response from a server that has a range of facilities
and that also describes itself:
[C] CAPABILITIES
[S] 101 Capability list:
[S] VERSION 2
[S] READER
[S] IHAVE
[S] POST
[S] NEWNEWS
[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
[S] IHAVE
[S] LIST ACTIVE NEWSGROUPS OVERVIEW.FMT HEADERS
[S] OVER MSGID
[S] HDR
[S] NEWNEWS
[S] .
5.3. MODE READER
5.3.1. Usage
Indicating capability: MODE-READER
This command MUST NOT be pipelined.
Syntax
MODE READER
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 this by changing the capability list
accordingly. It MUST then 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 that 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 the following apply:
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
[S] READER
[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 of 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] NEWNEWS
[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 in 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
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 of its transactions with the
NNTP server.
If a client simply disconnects (or if 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.]
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. The first type of key is the message-id
of an article and is globally unique. The second type of key is
composed of a newsgroup name and an article number within that
newsgroup. On a particular server, there MUST only be one article
with a given number within any newsgroup, and an article MUST NOT
have two different numbers in the same newsgroup. An article can be
cross-posted to multiple newsgroups, so there may be multiple keys
that point to the same article on the same server; these MAY have
different numbers in each newsgroup. However, this type of key is
not required to be globally unique, so the same key MAY refer to
different articles on different servers. (Note that the terms
"group" and "newsgroup" are equivalent.)
The final type of 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 2,147,483,647, 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.
Note that it is likely that the article number limit of 2,147,483,647
will be increased by a future revision or extension to this
specification. While servers MUST NOT send article numbers greater
than this current limit, client and server developers are advised to
use internal structures and datatypes capable of handling larger
values in anticipation of such a change.
6.1. Group and Article Selection
The following commands are used to set the "currently 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
6.1.1.2. Description
The GROUP command selects a newsgroup as the currently selected
newsgroup and returns summary information about it.
The required argument is the name of the newsgroup to be selected
(e.g., "news.software.nntp"). 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
it is 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:
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 has
been 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
response for that newsgroup in this session, and it 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
currently selected newsgroup MUST be set to that group, and the
current article number MUST be set to the first article in the group
(this applies even if the group is already the currently selected
newsgroup). If an empty newsgroup is selected, the current article
number is made invalid. If an invalid group is specified, the
currently 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 currently 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
Example reselecting the currently selected newsgroup:
[C] GROUP misc.test
[S] 211 1234 234 567 misc.test
[C] STAT 444
[S] 223 444 <123456@example.net> retrieved
[C] GROUP misc.test
[S] 211 1234 234 567 misc.test
[C] STAT
[S] 223 234 <different@example.net> retrieved
6.1.2. LISTGROUP
6.1.2.1. Usage
Indicating capability: READER
Syntax
LISTGROUP [group [range]]
Responses
211 number low high group Article numbers follow (multi-line)
411 No such newsgroup
412 No newsgroup selected [1]
Parameters
group Name of newsgroup
range Range of articles to report
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 selects a newsgroup in the same manner as the
GROUP command (see Section 6.1.1) but also provides a list of article
numbers in the newsgroup. If no group is specified, the currently
selected newsgroup is used.
On success, a list of article numbers is returned as a multi-line
data block 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 and is in numerical order. It
lists precisely those articles that exist in the group at the moment
of selection (therefore, an empty group produces an empty list). If
the optional range argument is specified, only articles within the
range are included in the list (therefore, the list MAY be empty even
if the group is not).
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.
In the last case, if the second number is less than the first number,
then the range contains no articles. Omitting the range is
equivalent to the range 1- being specified.
If the group specified is not available on the server, a 411 response
MUST be returned. If no group is specified and the currently
selected newsgroup is invalid, a 412 response MUST be returned.
Except that the group argument is optional, that a range argument can
be specified, and that a multi-line data block follows the 211
response code, the LISTGROUP command is identical to the GROUP
command. In particular, when successful, the command sets the
current article number to the first article in the group, if any,
even if this is not within the range specified by the second
argument.
Note that the range argument is a new feature in this specification
and servers that do not support CAPABILITIES (and therefore do not
conform to this specification) are unlikely to support it.
6.1.2.3. Examples
Example of LISTGROUP being used to select a group:
[C] LISTGROUP misc.test
[S] 211 2000 3000234 3002322 misc.test list follows
[S] 3000234
[S] 3000237
[S] 3000238
[S] 3000239
[S] 3002322
[S] .
Example of LISTGROUP on an empty group:
[C] LISTGROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup list follows
[S] .
Example of LISTGROUP on a valid, currently 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 with a range:
[C] LISTGROUP misc.test 3000238-3000248
[S] 211 2000 3000234 3002322 misc.test list follows
[S] 3000238
[S] 3000239
[S] .
Example of LISTGROUP with an empty range:
[C] LISTGROUP misc.test 12345678-
[S] 211 2000 3000234 3002322 misc.test list follows
[S] .
Example of LISTGROUP with an invalid range:
[C] LISTGROUP misc.test 9999-111
[S] 211 2000 3000234 3002322 misc.test list follows
[S] .
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 currently selected newsgroup is valid, the current article
number MUST be set to the previous article in that newsgroup (that
is, the highest existing article number less than the current article
number). If successful, a response indicating the new current
article number and the message-id of that article MUST be returned.
No article text is sent in response to this command.
There MAY be no previous article in the group, although the current
article number is not the reported low water mark. There MUST NOT be
a previous article when the current article number is the reported
low water mark.
Because articles can be removed and added, the results of multiple
LAST and NEXT commands MAY not be consistent over the life of a
particular NNTP session.
If the current article number is already the first article of the
newsgroup, a 422 response MUST be returned. If the current article
number is invalid, a 420 response MUST be returned. If the currently
selected newsgroup is invalid, a 412 response MUST be returned. In
all three cases, the currently 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 currently 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 currently 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
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 currently 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 currently selected newsgroup is invalid.]
[C] NEXT
[S] 412 no newsgroup selected
Example of an attempt to retrieve an article using the NEXT command
when the current article number is that of the last article in the
group:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT 3002322
[S] 223 3002322 <411@example.net> retrieved
[C] NEXT
[S] 421 No next article to retrieve
Example of an attempt to retrieve an article using the NEXT command
when the currently 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 three 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 (multi-line)
430 No article with that message-id
Second form (article number specified)
220 n message-id Article follows (multi-line)
412 No newsgroup selected
423 No article with that number
Third form (current article number used)
220 n message-id Article follows (multi-line)
412 No newsgroup selected
420 Current article number is invalid
Parameters
number Requested article number
n Returned article number
message-id Article message-id
6.2.1.2. Description
The ARTICLE command selects an article according to the arguments and
presents the entire article (that is, the headers, an empty line, and
the body, in that order) to the client. 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 currently 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,
unless there is a currently selected newsgroup and the article is
present in that group, in which case the server MAY use the article's
number in that group. (The server is not required to determine
whether the article is in the currently 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 currently 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 currently 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 this article
number MUST be no less than the reported low water mark for that
group.
The server MUST NOT change the currently selected newsgroup as a
result of this command. The server MUST NOT change the current
article number except when an article number argument was provided
and the article exists; in particular, it MUST NOT change it
following an unsuccessful response.
Since the message-id is unique for each article, it may be used by a
client to skip duplicate displays of articles that have been posted
more than once, or to more than one newsgroup.
The article is returned as a multi-line data block 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 currently selected newsgroup is invalid, a 412 response MUST
be returned. If the argument is a number and that article does not
exist in the currently 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 (explicitly not using
an 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: <45223423@example.com>
[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: <45223423@example.com>
[S]
[S] This is just a test article.
[S] .
Example of an unsuccessful retrieval of an article by message-id:
[C] ARTICLE <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of an article by number:
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 news.groups
[C] ARTICLE 300256
[S] 423 No article with that number
Example of an unsuccessful retrieval of an article by number because
no newsgroup was selected first:
[Assumes currently selected newsgroup is invalid.]
[C] ARTICLE 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve an article when the currently
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 (multi-line)
430 No article with that message-id
Second form (article number specified)
221 n message-id Headers follow (multi-line)
412 No newsgroup selected
423 No article with that number
Third form (current article number used)
221 n message-id Headers follow (multi-line)
412 No newsgroup selected
420 Current article number is invalid
Parameters
number Requested article number
n Returned article number
message-id Article message-id
6.2.2.2. Description
The HEAD command behaves identically to the ARTICLE command except
that, if the article exists, the response code is 221 instead of 220
and only the headers are presented (the empty line separating the
headers and body MUST NOT be included).
6.2.2.3. Examples
Example of a successful retrieval of the headers of an article
(explicitly not using an 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: <45223423@example.com>
[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: <45223423@example.com>
[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
Example of an unsuccessful retrieval of the headers of an article by
number because no newsgroup was selected first:
[Assumes currently 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
currently 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 (multi-line)
430 No article with that message-id
Second form (article number specified)
222 n message-id Body follows (multi-line)
412 No newsgroup selected
423 No article with that number
Third form (current article number used)
222 n message-id Body follows (multi-line)
412 No newsgroup selected
420 Current article number is invalid
Parameters
number Requested article number
n Returned article number
message-id Article message-id
6.2.3.2. Description
The BODY command behaves identically to the ARTICLE command except
that, if the article exists, the response code is 222 instead of 220
and only the body is presented (the empty line separating the headers
and body MUST NOT be included).
6.2.3.3. Examples
Example of a successful retrieval of the body of an article
(explicitly not using an 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 currently 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
currently 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
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 (explicitly not using an
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
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 currently selected newsgroup is invalid.]
[C] STAT 300256
[S] 412 No newsgroup selected
Example of STAT on an article when the currently 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 that 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 currently selected newsgroup. The fifth shows that the
number, if provided, must be that relating to the currently selected
newsgroup. The last one shows that the current article number is
still not changed by the use of STAT with a message-id even if it
returns an article number.
6.3. Article Posting
Article posting is done in one of two 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: 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 as a
multi-line data block (see Section 3.1.1). Thus a single dot (".")
on a line indicates the end of the text, and lines starting with a
dot in the original text have that dot doubled during transmission.
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 while 240 and 441 are returned
after the article is sent.
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, rather than being
accepted and then discarded silently. 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 connection set-up completed.]
[S] 201 NNTP Service Ready, posting prohibited
[C] POST
[S] 440 Posting not permitted
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, to the server as a
multi-line data block (see Section 3.1.1). Thus, a single dot (".")
on a line indicates the end of the text, and lines starting with a
dot in the original text have that dot doubled during transmission.
The server MUST return a 235 response, indicating that the article
was successfully transferred; a 436 response, indicating that the
transfer failed but should be tried again later; or a 437 response,
indicating that the article was rejected.
This function differs from the POST command in that it is intended
for use in transferring already-posted articles between hosts. It
SHOULD NOT be used when the client is a personal news-reading
program, since use of this command indicates that the article has
already been posted at another site and is simply being forwarded
from another host. However, despite this, the server MAY elect not
to post or forward the article if, after further examination of the
article, it deems it inappropriate to do so. Reasons for such
subsequent rejection of an article may include problems such 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 by the NNTP server itself.
The client SHOULD NOT assume that the article has been successfully
transferred unless it receives an affirmative response from the
server. A lack of response (such as a dropped network connection or
a network timeout) SHOULD be treated the same as a 436 response.
Because some news server software may not immediately be able to
determine whether an article is suitable for posting or forwarding,
an NNTP server MAY acknowledge the successful transfer of the article
(with a 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
[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 that the
article be tried again later:
[C] IHAVE <i.am.an.article.you.defer@example.com>
[S] 436 Retry later
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
7.2.1. Usage
This command is mandatory.
Syntax
HELP
Responses
100 Help text follows (multi-line)
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 multi-line data block following the 100 response
code.
This text is not guaranteed to be in any particular format (but must
be UTF-8) 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 (multi-line)
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
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 backward compatibility), the year is to
be taken from the current century if yy is smaller than or equal to
the current year, and the previous century otherwise.
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 of 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: NEWNEWS
Syntax
NEWNEWS wildmat date time [GMT]
Responses
230 List of new articles follows (multi-line)
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, 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.
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 that can, in general, 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.
7.6.1. LIST
7.6.1.1. Usage
Indicating capability: LIST
Syntax
LIST [keyword [wildmat|argument]]
Responses
215 Information follows (multi-line)
Parameters
keyword Information requested [1]
argument Specific to keyword
wildmat Groups of interest
[1] If no keyword is provided, it def