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Network News Transport Protocol
draft-ietf-nntpext-base-16.txt
1 Status of this memo
This memo is an Internet-Draft and is in full conformance
with Section 10 of RFC 2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may
also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of
six months and may be updated, replaced, or made obsolete by
other documents at any time. It is inappropriate to use
Internet-Drafts as reference material or to cite them other
than as "work in progress."
The list of current Internet-Drafts can be accesses at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft shadow directories can be accessed
at http://www.ietf.org/shadow.html.
This section will be updated with the appropriate verbiage
from RFC 2223 should this memo have been found ready for
publication as an RFC. This update will include its standards
track status.
This memo is a product of the NNTP Working Group, chaired by
Russ Allbery.
2 Abstract
The Network News Transport Protocol has been in use in the
Internet for a decade and remains one of the most popular
protocols (by volume) in use today. This memo is a
replacement for RFC 977 and officially updates the protocol
specification. It clarifies some vagueness in RFC 977,
includes some new base functionality and provides a specific
mechanism to add standardized extensions to NNTP.
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3 Introduction
This memo specifies the Network News Transport Protocol
(NNTP), which is used for the distribution, inquiry,
retrieval, and posting of net news articles using a reliable
stream-based mechanism. For news reading clients, NNTP
enables retrieval of news articles that are stored in a
central database, giving subscribers the ability to select
only those articles they wish to read.
The netnews model provides for indexing, cross-referencing,
and expiration of aged messages. For server-to-server
interaction, NNTP is designed for efficient transmission of
net news articles over a reliable full duplex communication
channel.
Every attempt is made to ensure that the protocol
specification in this memo is compatible with the version
specified in RFC 977[1]. However, this version does not
support the ill-defined SLAVE command and permits four digit
years to be specified in the NEWNEWS and NEWGROUPS commands.
It changes the default character set to UTF-8[2] instead of
US-ASCII[3]. It also extends the newsgroup name matching
capabilities already documented in RFC 977.
Generally, new functionality is available using new keywords.
Part of that new functionality involves a mechanism to
discover what new functionality is available to clients from
a server.
This mechanism can also be used to add more functionality as
needs merit such additions.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this memo are to be interpreted as described in
RFC 2119[4].
An implementation is not compliant if it fails to satisfy one
or more of the MUST requirements for this protocol. An
implementation that satisfies all the MUST and all the SHOULD
requirements for its protocols is said to be "unconditionally
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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 memo, the term "client host" refers
to a host making use of the NNTP service, while the term
"server host" refers to a host that offers the NNTP service.
In addition, where examples of interactions between a client
host and a server host are provided a "[C]" will be used to
represent the client host and a "[S]" will be used to
represent the server host.
For the remainder of this memo, responses will be described
in tables listing the required format of a response followed
by the meaning that should be ascribed to that response.
4 Basic Operation.
Every NNTP session MUST involve the following in this order:
CONNECTION
GREETING
DISCONNECTION
Other steps may occur between the GREETING and DISCONNECTION
step. They are:
CAPABILITIES DISCOVERY
NEWS EXCHANGE
CONCLUSION
NNTP operates over any reliable data stream 8-bit-wide
channel. When running over TCP/IP, the official port for the
NNTP service is 119. Initially, the server host starts the
NNTP service by listening on a TCP port. When a client host
wishes to make use of the service, it MUST establish a TCP
connection with the server host by connecting to that host on
the same port on which the server is listening. This is the
CONNECTION step. When the connection is established, the
NNTP server host MUST send a greeting. This is the GREETING
step. The client host and server host SHOULD then exchange
commands and responses (respectively) until the connection is
closed or aborted. This final step is called the
DISCONNECTION step.
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If there is a CONCLUSION step, it MUST immediately precede
the DISCONNECTION step. There MUST be only one CONNECTION,
CONCLUSION and DISCONNECTION step for each NNTP session. All
other steps MAY be repeated as needed. For example, the
GREETING step may be repeated if the client makes use of the
MODE READER command (See Section 7.2 for more on the MODE
READER command).
The character set for all NNTP commands is UTF-8. Commands in
the NNTP MUST consist of an US-ASCII case-insensitive
keyword, which MAY be followed by one or more arguments. An
US-ASCII CRLF pair MUST terminate all commands. Multiple
commands MUST NOT be on the same line. Keywords MUST consist
of printable US-ASCII characters. Unless otherwise noted
elsewhere in this memo, arguments SHOULD consist of printable
US-ASCII characters. Keywords and arguments MUST be each
separated by one or more US-ASCII SPACE or US-ASCII TAB
characters. Keywords MUST be at least three US-ASCII
characters and MUST NOT exceed 12 US-ASCII characters.
Command lines MUST NOT exceed 512 octets, which includes the
terminating US-ASCII CRLF pair. Arguments MUST NOT exceed 497
octets.
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. All multi-line
responses MUST adhere to the following format:
The response consists of a sequence of one or more "lines",
each being a stream of octets ending with 0x0D 0x0A (US-ASCII
CRLF). Apart from those line endings, the stream MUST NOT
include the octets 0x00, 0x0A, or 0x0D (US-ASCII NUL, LF, and
CR).
The first such line contains the response code as with a
single line response.
If any subsequent line begins with the "termination octet"
(0x2E or US_ASCII "."), that line MUST be "byte-stuffed" by
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pre-pending an additional termination octet (0x2E) to that
line of the response.
The lines of the response MUST be followed by a terminating
line consisting of a single termination octet (0x2E or
US_ASCII ".")followed by CRLF in the normal way. Thus a
multi-line response is always terminated with the five octets
"CRLF.CRLF" (in US-ASCII).
There is NO limit on the length of a line.
When interpreting a multi-line response, the "byte stuffing"
MUST be undone; i.e. the client MUST ensure that, in any line
beginning with the termination octet followed by octets other
than US-ASCII CRLF, that initial termination octet is
disregarded.
Likewise, the terminating line ".CRLF" (in US-ASCII) MUST NOT
be considered part of the multi-line response; i.e. the
client MUST ensure that any line beginning with the
termination octet followed immediately by US-ASCII CRLF is
disregarded; (the first CRLF of the terminating "CRLF.CRLF"
is, of course, part of the last line of the response).
NOTE: Texts using an encoding (such as UTF-16 or UTF-32) that
may contain the NUL octet or the CR or LF octets in contexts
other than the CRLF line ending cannot be reliably conveyed
in the above format.
Note also that, although this memo does not limit the length
of a line in any way, the standards that define the format of
articles may do so.
An NNTP server MAY have an inactivity autologout timer. Such
a timer SHOULD be of at least three minutes duration, with
the exception that there MAY be a shorter limit on how long
the server is willing to wait for the first command from the
client. The receipt of any command from the client during
the timer interval SHOULD suffice to reset the autologout
timer. Similarly, the receipt of any significant amount of
data from the client while in the midst of sending a multi-
line message to the server (such as during a POST or IHAVE
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command) SHOULD suffice to reset the autologout timer. When
the timer expires, the server SHOULD close the TCP connection
without sending any response to the client, including when
the client is in the middle of sending a multi-line message
to the server.
4.1 Response Codes
Each response MUST begin with a three-digit status indicator.
These are status reports from the server and indicate the
response to the last command received from the client.
The first digit of the response broadly indicates the
success, failure, or progress of the previous command.
1xx - Informative message
2xx - Command ok
3xx - Command ok so far, send the rest of it.
4xx - Command was correct, but couldn't be performed for
some reason.
5xx - Command unimplemented, or incorrect, or a serious
program error occurred.
The next digit in the code indicates the function response
category.
x0x - Connection, setup, and miscellaneous messages
x1x - Newsgroup selection
x2x - Article selection
x3x - Distribution functions
x4x - Posting
x8x - Reserved for authentication and authorization
extensions
x9x - Reserved for private use (non-standard extensions)
Certain responses contain parameters such as numbers and
names in addition to the status indicator. In those cases,
the number and type of such parameters is fixed for each
response code to simplify interpretation by the client (any
extension MUST follow this principle as well). In all other
cases, the client MUST only use the status indicator itself
to determine the nature of the response. The exact response
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codes that can be returned in response to a given command are
detailed in the description of the keyword that is the first
part of the command.
Parameters MUST be separated from the numeric status
indicator and from each other by a single US-ASCII space. All
numeric parameters MUST be in base 10 (decimal) format, and
MAY have leading zeros. String parameters MUST contain at
least one character and MUST NOT contain US-ASCII spaces, CR,
LF, or tab). The server MAY add any text after the response
code or last parameter as appropriate, and the client MUST
NOT make decisions based on this text. Such text MUST be
separated from the numeric status indicator or the last
parameter by at least one US-ASCII space.
The server MUST respond to any command with the appropriate
generic response (given in section 4.1.1) if it represents
the situation. Otherwise, each recognized command MUST return
one of the response codes specifically listed in its
description or in an extension. A server MAY provide
extensions to this memo, including new commands, new 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 memo 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 memo 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 memo nor any extension registered with IANA (see
section 12) will specify any response codes of the x9x
pattern. (Implementers of extensions are accordingly
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cautioned not to use such responses for extensions that may
subsequently be submitted for registration.)
4.1.1 Generic Response Codes
The server MUST respond to any command with the appropriate
one of the following generic responses if it represents the
situation.
If the command is not recognized, or it is an optional
command or extension that is not implemented by the server,
the response code 500 MUST be returned.
If there is a syntax error in the arguments of a recognized
command, the response code 501 MUST be returned. Note that
where a command has variants depending on a keyword (e.g.
LIST ACTIVE and LIST NEWSGROUPS), then 501 MUST be used when
the requested variant is not implemented but the base command
is.
If the client is not authorized to use the specified facility
when the server is in its current state, the response code
502 MUST be returned. A different command might change the
server state and permit the command if it is retried.
If the server does not provide an optional feature, then the
response code 403 MUST be returned if the omission is
temporary (e.g. because a necessary facility is unavailable)
and the code 503 if it is permanent (e.g. because the server
does not store the required information).
If the server has to terminate the connection for some
reason, it MUST give a 400 response code to the next command
and then immediately close the TCP connection. It MAY give a
401 response code to any command to indicate that termination
is imminent (following a 401 response, it MUST NOT close the
TCP connection immediately).
4.2 Streaming
NNTP is designed to operate over a reliable bi-directional
connection such as TCP. Therefore, if a command does not
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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 "streaming". However, certain server
implementations throw away all text received from the client
following certain commands before sending their response. If
this happens, streaming 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 streaming, but also
circumstances where it is reasonable or common for servers to
behave in the above manner, this memo puts certain
requirements on both clients and servers.
Except where stated otherwise, a client MAY use streaming.
That is, it may send a command before receiving the response
for the previous command. The server MUST allow streaming and
MUST NOT throw away any text received after a command.
Finally, the server MUST process commands in the order they
are sent.
If the specific description of a command describes it as "not
streamable", that command MUST end any stream of commands.
That is, the client MUST NOT send any following command until
receiving the CRLF at the end of the response from the
command. The server MAY ignore any data received after the
command and before the CRLF at the end of the response is
sent to the client.
The initial connection must not be part of a stream; that is,
the client MUST NOT send any command until receiving the CRLF
at the end of the greeting.
If the client uses blocking system calls to send commands, it
MUST ensure that the amount of text sent in streaming does
not cause a deadlock between transmission and reception. The
amount of text involved will depend on window sizes in the
transmission layer, and is typically 4k bytes for TCP.
5 The WILDMAT format
The WILDMAT format described here is based on the version
first developed by Rich Salz [5], which in turn was derived
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from the format used in the UNIX "find" command to articulate
file names. It was developed to provide a uniform mechanism
for matching newsgroup names in the same manner that the UNIX
shell matches filenames.
5.1 Wildmat syntax
A wildmat is described by the following augmented BNF[6]
syntax (note that this syntax contains ambiguities and
special cases described at the end):
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-
7F /UTF-8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
UTF-8-non-ascii is defined in section 13.
This syntax must be interpreted subject to the following
rule:
Where a wildmat-pattern is not immediately preceded by "!",
it shall not begin with a "!".
NOTE: the characters \ , [ and ] are not allowed in wildmats,
while * and ? are always wildcards. This should not be a
problem since these characters cannot occur in newsgroup
names, which is the only current use of wildmats. Backslash
is commonly used to supress the special meaning of characters
and brackets to introduce sets, but there is no existing
standard practice for these in wildmats and so they were
omitted from this memo. A future extension to this memo may
provide semantics for these characters.
5.2 Wildmat semantics
A wildmat is tested against a string, and either matches or
does not match. To do this, each constituent wildmat-pattern
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is matched against the string and the rightmost pattern that
matches is identified. If that wildmat-pattern is not
preceded with "!", the whole wildmat matches. If it is
preceded by "!", or if no wildmat-pattern matches, the whole
wildmat does not match.
For example, consider the wildmat "a*,!*b,*c*":
the string "aaa" matches because the rightmost match is
with "a*"
the string "abb" does not match because the rightmost
match is with "*b"
the string "ccb" matches because the rightmost match is
with "*c*"
the string "xxx" does not match because no wildmat-pattern
matches
A wildmat-pattern matches a string if the string can be
broken into components, each of which matches the
corresponding wildmat-item in the pattern; the matches must
be in the same order, and the whole string must be used in
the match. The pattern is "anchored"; that is, the first and
last characters in the string must match the first and last
item respectively (unless that item is an asterisk matching
zero characters).
A wildmat-exact matches the same character (which may be more
than one octet in UTF-8).
"?" matches exactly one character (which may be more than one
octet).
"*" matches zero or more characters. It can match an empty
string, but it cannot match a subsequence of a UTF-8 sequence
that is not aligned to the character boundaries.
5.3 Extensions
An NNTP server or extension MAY extend the syntax or
semantics of wildmats provided that all wildmats that meet
the requirements of section 5.1 have the meaning ascribed to
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them by section 5.2. Future editions of this memo may also
extend wildmats.
5.4 Examples
In these examples, $ and @ are used to represent the two
octets 0xC2 and 0xA3 respectively; $@ is thus the UTF-8
encoding for the pound sterling symbol, shown as # in the
descriptions.
Wildmat Description of strings that match
abc the one string "abc"
abc,def the two strings "abc" and "def"
$@ the one character string "#"
a* any string that begins with "a"
a*b any string that begins with "a" and ends with "b"
a*,*b any string that begins with "a" or ends with "b"
a*,!*b any string that begins with "a" and does not end with
"b"
any string that begins with "a" and does not end with
a*,!*b,c* "b", and any string that begins with "c" no matter
what it ends with
any string that begins with "a" or "c" and does not
a*,c*,!*b 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
6 Format for Keyword Descriptions
On the following pages are descriptions of each keyword
recognized by the NNTP server and the responses that will be
returned by those commands. These keywords are grouped by the
functional step in which they are used.
Each keyword is shown in upper case for clarity, although the
NNTP server ignores case in the interpretation of commands.
Parameters are shown as follows:
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UPPERCASE indicates literal text to be included in the
command;
lowercase indicates a token described elsewhere;
[brackets] indicate that the parameter is optional;
ellipsis... indicates that the parameter may be repeated
any number of times (it must occur at least
once);
vertical|bar indicates a choice of two mutually exclusive
parameters (exactly one must be provided).
Parameters are case or language specific only when specified
(either in this memo or in RFC 1036[7]).
The name "wildmat" for a parameter indicates that it is a
wildmat format pattern as defined in section 5. If the
parameter does not meet the requirements of that section (for
example, if it does not fit the grammar of 5.1) the NNTP
server MAY place some interpretation on it (not specified by
this memo) or otherwise MUST generate a 501 response.
7 The GREETING Step
7.1 Initial Connection
There is no keyword presented by the client upon initial
connection to the server. The server MUST present an
appropriate response code as a greeting to the client. This
response informs the client about what steps the client
should take to reach the news exchange step.
If the server will accept further commands from the client
including POST, the server MUST present a 200 greeting code.
If the server will accept further commands from the client,
but it is not authorized to post articles using the POST
command, the server MUST present a 201 greeting code.
Otherwise the server MUST present a 400 or 502 greeting code
and then immediately close the connection. 502 MUST be used
if the client is not permitted under any circumstances to
interact with the server and 400 otherwise.
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7.1.1 Responses
200 Service available, posting allowed
201 Service available, posting prohibited
400 Service temporarily unavailable
502 Service unavailable
Following a 400 or 502 response the server MUST immediately
close the connection.
7.1.2 Initial Connection Example
Example of a normal connection from an authorized client
[Initial TCP connection setup completed.]
[C] Initial TCP connection completed
[S] 200 NNTP Service Ready, posting permitted
Client can send commands at this point. In this example, the
client jumps directly to the conclusion step (See section
10).
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of a normal connection from an unauthorized client
[C] Initial TCP connection completed
[S] 502 NNTP Service Unavailable
[Server closes connection.]
Example of a normal connection from an authorized client that
is not permitted to post
[Initial TCP connection setup completed.]
[S] 201 NNTP Service Ready, posting prohibited
Client can send commands at this point. In this example, the
client jumps directly to the conclusion step (See section
10).
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of a connection from any client where the server is
unable to provide service
[Initial TCP connection setup completed.]
[S] 400 NNTP Service temporarily unavailable
[Server closes connection.]
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7.2 MODE READER
MODE READER
MODE READER SHOULD be sent by any client that intends to use
any command other than IHAVE, HEAD, STAT, LIST, LIST
EXTENSIONS, or commands advertised by the server as available
via LIST EXTENSIONS. This command is not streamable.
Servers MAY require that this command be issued before any
other commands are sent and MAY reject any other commands
until after a MODE READER command has been sent.
The server MUST present a response using the same codes as
the initial greeting (as described in section 7.1) to
indicate its ability to provide reading service to the
client.
Clients SHOULD wait for a response to MODE READER after
sending this command and SHOULD NOT send any additional
commands until that response has been received from the
server.
Once MODE READER is sent, IHAVE (and any extensions intended
for peer-to-peer article transfer) MAY no longer be
permitted, even if it were permitted before the MODE READER
command. The results of LIST EXTENSIONS MAY be different
following a MODE READER command than prior to the issuing of
that command.
Servers are encouraged to not require this command even
though clients SHOULD send it when appropriate. It is present
to support some news architectures that switch between modes
based on whether a given connection is a peer-to-peer
connection with another server or a news reading client.
7.2.1 Responses
200 Posting permitted
201 Posting prohibited
400 Service temporarily unavailable
502 Service unavailable
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Following a 400 or 502 response the server MUST immediately
close the connection.
Note that the response need not be the same as the one
presented during the initial greeting.
7.2.2 MODE READER Examples
Example of use of the MODE READER command by an authorized
client
[C] MODE READER
[S] 200 NNTP Service Ready, posting permitted
Client can send commands at this point. In this example, the
client jumps directly to the conclusion step (See section
10).
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of use of MODE READER by a client not authorized to
receive service from the server as a news reader
[C] MODE READER
[S] 502 Service Unavailable
[Server closes connection.]
Example of a normal connection from an authorized client that
is not permitted to post
[C] MODE READER
[S] 201 NNTP Service Ready, posting prohibited
Client can send commands at this point. In this example, the
client jumps directly to the conclusion step (See section
10).
[C] QUIT
[S] 205 NNTP Service exits normally
[Server closes connection.]
Example of a connection from any client where the server is
unable to provide news reader service
[C] MODE READER
[S] 400 NNTP Service temporarily unavailable
[Server closes connection.]
8 The CAPABILITIES DISCOVERY Step
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To discover what extensions are available, an NNTP client can
query the server with the LIST EXTENSIONS command.
If a particular extension is unavailable, the client can
attempt to work around it or it may wish to terminate the
session.
See section 12 for further discussion of extensions.
8.1 LIST EXTENSIONS
The LIST EXTENSIONS command allows a client to determine
which extensions are supported by the server. This command
MUST be implemented by any server that implements any
extensions defined in this memo. This command is not
streamable.
To discover what extensions are available, an NNTP client
SHOULD query the server early in the session for extensions
information by issuing the LIST EXTENSIONS command. This
command MAY be issued at anytime during a session. It is not
required that the client issues this command before
attempting to make use of any extension. The response
generated by this command MAY change during a session because
of other state information. However, an NNTP client MUST NOT
cache (for use in another session) any information returned
if the LIST EXTENSIONS command succeeds. That is, an NNTP
client is only able to get the current and correct
information concerning available extensions during a session
by issuing a LIST EXTENSIONS command during that session and
processing that response.
A successful response starts with a 202 code and is followed
by a list of extensions, one per line. Each line MUST begin
with an extension-label and optionally one or more parameters
(separated by single spaces). The extension-label and the
meaning of the parameters are specified as part of the
definition of the extension. The extension-label MUST be in
uppercase.
The server MUST NOT list the same extension twice in the
response, and MUST list all supported extensions. The order
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in which the extensions are listed is not significant. The
server need not even consistently return the same order.
If the server does not support any extensions, it SHOULD
return a 402 failure response but MAY return an empty list
instead.
8.1.1 Responses
202 Extension list follows (multi-line response)
400 Service temporarily unavailable
402 Server has no extensions
500 Unknown Command
501 Syntax Error
502 Program error, function not performed
Following a 502 response an extension might still be
available, and the client MAY attempt to use it
The LIST EXTENSIONS command is optional, and a server MAY
issue a 500 (unknown command) or 501 (syntax error) response
to it.
8.1.1.1 LIST EXTENSIONS Examples
Example of a successful response:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] OVER
[S] HDR
[S] LISTGROUP
[S] .
The particular extensions shown here are simply examples of
what might be defined in other places, and no particular
meaning should be attributed to them.
Example where no extensions are available, using preferred
format:
[C] LIST EXTENSIONS
[S] 402 Server has no extensions
Example where no extensions are available, using an empty
list:
[C] LIST EXTENSIONS
[S] 202 Extensions supported:
[S] .
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9 The NEWS EXCHANGE Step
During this step, two basic types of transactions occur:
* article retrieval from the server
* article posting to the server
9.1 Article Retrieval
News reading clients have available a variety of mechanisms
to retrieve articles via NNTP. The news articles are stored
and indexed using three types of keys. One key is the message
id of an article. According to RFC 1036, this identifier
should be globally unique. Another key is composed of the
newsgroup name and the article number within that newsgroup.
That key MUST be unique to a particular server (there will be
only one article with that number within a particular
newsgroup), but is not required to be globally unique.
Additionally, because the same article can be cross-posted to
multiple newsgroups, there may be multiple keys that point to
the same article on the same server. The final key is the
arrival timestamp, giving the time that the article arrived
at the server.
The server MUST ensure that article numbers are issued in
order of arrival timestamp; that is, articles arriving later
MUST have higher numbers than those that arrive earlier. The
server SHOULD allocate the next sequential unused number to
each new article.
Article numbers MUST lie between 1 and 4,294,967,295
inclusive. The client and server SHOULD NOT use leading
zeroes in specifying article numbers, and MUST NOT use more
than 16 digits. In some situations, the value zero replaces
an article number to show some special situation.
Message ids are defined in RFC 2822 with the following
modifications:
* A message id MUST NOT contain a US-ASCII space within any
quoted-pair.
* A message id MUST NOT be longer than 250 octets.
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* RFC 2822 obsolete syntax for message ids are not supported
by the protocol specified in this memo.
9.1.1 Article Retrieval by Newsgroup Name and Article Number
The following commands are used to set the current newsgroup
name and the "current article pointer" which is used by other
commands for article retrieval. At the start of an NNTP
session, both of these values are undefined.
9.1.1.1 GROUP
GROUP ggg
The required parameter ggg is the name of the newsgroup to be
selected (e.g. "news.software.b"). A list of valid newsgroups
may be obtained by using the LIST keyword. See section 9.4
for more information on the LIST keyword.
The successful selection response will return the article
numbers of the first and last articles in the group at the
moment of selection (these numbers are referred to as the
"reported low water mark" and the "reported high water
mark"), and an estimate of the number of articles on file in
the group.
If the group is not empty, the estimate MUST be at least the
actual number of articles available, and MUST be no greater
than one more than the difference between the reported low
and high water marks. (Some implementations will actually
count the number of articles on file. Others will just
subtract the low water mark from the high water mark and add
one to get an estimate.)
If the group is empty, one of the following three situations
will occur. Clients MUST accept all three cases; servers MUST
NOT represent an empty group in any other way.
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.
All three numbers will be zero.
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The high water mark is greater than or equal to the low water
mark; the estimated article count might be zero or non-zero;
if non-zero, the same requirements apply as for a non-empty
group.
The set of articles in a group may change after the GROUP
command is carried out. That is:
* articles may be removed from the group
* 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)
* new articles may be added with article numbers greater
than the reported high water mark (if an article that was
the one with the highest number has been removed, the next
new article will not have the number one greater than the
reported high water mark)
Except when the group is empty and all three numbers are
zero, whenever a subsequent GROUP command for the same
newsgroup is issued, either by the same client or a different
client, the reported low water mark in the response MUST be
no less than that in any previous response for that newsgroup
sent to any client. The client may make use of the low water
mark to remove all remembered information about articles with
lower numbers, as these will never recur. This includes the
situation when the high water mark is one less than the low
water mark.
No similar assumption can be made about the high water mark,
as this can decrease if an article is removed, and then
increase again if it is reinstated or if new articles arrive.
When a valid group is selected by means of this command, the
internally maintained "current article pointer" MUST be set
to the first article in the group and the name of the current
newsgroup MUST be set to the selected newsgroup name. If an
invalid group is specified, the previously selected group, if
any, and article MUST remain selected. If an empty newsgroup
is selected, the "current article pointer" is in an
indeterminate state and MUST NOT be used.
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The GROUP keyword (or the LISTGROUP keyword, if implemented)
MUST be used by a client and a successful response received
before the any other command is used that depends on having
the "current article pointer" be valid.
If the group specified is not available on the server, it
MUST return a 411 error code.
9.1.1.1.1 Responses
211 n l h ggg Group successfully selected (n =
estimated number of articles in the
group, l = low water mark, h = high
water mark, ggg = name of the group
411 No such newsgroup
9.1.1.1.2 GROUP 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
9.1.1.2 LAST
LAST
If the current newsgroup is valid, the internally maintained
"current article pointer" MUST be set to the previous article
in the current newsgroup. If already positioned at the first
article of the newsgroup, an error message MUST be returned
and the current article MUST remain selected.
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.
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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 successful, a response indicating the current article
number and a message-id string MUST be returned. No article
text is sent in response to this command.
9.1.1.2.1 Responses
223 n a Article found (n = number, a = message-id)
412 No newsgroup selected
420 Current article pointer is invalid
422 No previous article in this group
9.1.1.2.2 LAST Examples
Example of a successful article retrieval using LAST
[S] 200 NNTP Service Ready
[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
[S] 200 NNTP Service ready
[C] LAST
[S] 412 no newsgroup selected
Example of an attempt to retrieve an article using the LAST
command when the current article pointer is pointing at the
first article in the group
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] LAST
[S] 422 No previous article to retrieve
Example of an attempt to retrieve an article using the LAST
command when the current group selected is empty
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[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] LAST
[S] 420 No current article selected
9.1.1.3 NEXT
NEXT
If the current newsgroup is valid, the internally maintained
"current article pointer" MUST be advanced to the next
article in the current newsgroup. If no more articles remain
in the current group, an error message MUST be returned and
the current article MUST remain selected.
If successful, a response indicating the current article
number and the message-id string MUST be returned. No
article text is sent in response to this command.
9.1.1.3.1 Responses
223 n a Article found (n = number, a = message-id)
412 No newsgroup selected
420 Current article pointer is invalid
421 No next article in this group
9.1.1.3.2 NEXT Examples
Example of a successful article retrieval using NEXT
[S] 200 NNTP Service Ready
[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
[S] 200 NNTP Service ready
[C] NEXT
[S] 412 no newsgroup selected
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Example of an attempt to retrieve an article using the NEXT
command when the current article pointer is pointing at the
last article in the group
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] ARTICLE 3002322
[S] 220 3002322 <411@example.net> retrieved
[S] Path: pathost!demo!whitehouse!not-for-mail
[S] From: ôDemo Userö <nobody@example.net>
[S] Newsgroups: misc.test
[S] Subject: I am just a test article
[S] Date: 6 Oct 1998 04:38:40 -0500
[S] Organization: An Example Net, Uncertain, Texas
[S] Message-ID: <411@example.net>
[S]
[S] This is just a test article.
[S] .
[C] NEXT
[S] 421 No next article to retrieve
Example of an attempt to retrieve an article using the NEXT
command when the current group selected is empty
[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] NEXT
[S] 420 No current article selected
9.2 Retrieval of Articles and Article Sections
The ARTICLE, BODY, HEAD, and STAT commands are very similar.
They differ only in the parts of the article that are
presented to the client and in the successful response code.
The ARTICLE command is described here in full, while the
other commands are described in terms of the differences.
An article, as defined by RFC 1036, consists of two parts:
the article headers and the article body. When responding to
one of these commands, the server presents the entire article
or appropriate part and does not attempt to alter or
translate it in any way.
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9.2.1 ARTICLE
ARTICLE <message-id>
ARTICLE [number]
The ARTICLE command selects an article based on the arguments
and presents the header, a blank line, and the body of that
article. The command has two forms.
In the first form, a message-id is specified (including the
angle brackets), and the server presents the article with
that message-id in its headers. In this case, the server MUST
NOT alter the "current article pointer". This is both to
facilitate the presentation of articles that may be
referenced within another article being read, and because of
the semantic difficulties of determining the proper sequence
and membership of an article that may have been crossposted
to more than one newsgroup.
In the second form, an article number may be specified. If
so, and if there is an article with that number in the
currently selected group, the server MUST set the current
article pointer to that number.
Then, whether or not a number was specified, the article
indicated by the current article pointer is presented to the
client.
Note that a previously valid article number MAY become
invalid if the article has been removed. A previously invalid
article number MAY become valid if the article has been
reinstated, but such an article number MUST be no less than
the reported low water mark for that group.
The server MUST NOT change the currently selected group as a
result of this command. The server MUST NOT change the
current selected article except when an article number
argument was provided and the article exists; in particular,
it MUST NOT change it following an unsuccessful response.
9.2.1.1 Responses
First form (message-id specified):
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220 0 a Article follows (multi-line response, a =
message-id)
430 No article found with that message-id
502 Program error, function not performed
Second form (optional article number specified):
220 n a Article follows (multi-line response, n =
article number, a = message-id)
412 No newsgroup selected
420 No current article selected
423 No such article in this newsgroup
502 Program error, function not performed
The 420 response only occurs if no article number has been
specified.
In the 220 response, the first parameter is 0 for the first
form and the article number (within the current group) for
the second form. The second parameter is the message-id of
the article (within angle brackets). This is taken from the
message-id header line of the article (required by RFC 1036).
If there is no such line, the message-id "<0>" MUST be used
instead (without the double quotes).
Since the message-id field is unique for each article, it may
be used by a client to skip duplicate displays of articles
that have been posted more than once, or to more than one
newsgroup.
The article headers and body are returned as a multi-line
response following the initial response line.
9.2.1.2 Examples
Example of a successful retrieval of an article (using no
article number)
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] ARTICLE
[S] 220 3000234 <45223423@example.com>
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[S] Path: pathost!demo!somewhere!not-for-mail
[S] From: ôDemo Userö <nobody@example.com>
[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 Com, San Jose, CA
[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
[S] 200 NNTP Service Ready
[C] ARTICLE <45223423@example.com>
[S] 220 0 <45223423@example.com>
[S] Path: pathost!demo!somewhere!not-for-mail
[S] From: ôDemo Userö <nobody@example.com>
[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 Com, San Jose, CA
[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
[S] 200 NNTP Service Ready
[C] ARTICLE <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of an article by number
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 news.groups
[C] ARTICLE 300256
[S] 423 No such article number in this group
Example of an unsuccessful retrieval of an article by number
because no newsgroup was selected first
[S] 200 NNTP Service Ready
[C] ARTICLE 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve an article when the current
group selected is empty
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[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] ARTICLE
[S] 420 No current article selected
Example of a failure due to the service being unavailable
[S] 200 NNTP Service Ready
[C] ARTICLE <i.am.a.test.article@example.com>
[S] 502 Service unavailable
9.2.2 HEAD
HEAD <message-id>
HEAD [number]
The HEAD command behaves identically to the ARTICLE command
except that, if the article exists, only the headers are
presented (the blank line separating the headers and body
MUST NOT be included).
9.2.2.1 Responses
First form (message-id specified):
221 0 a Article follows (multi-line response, a =
message-id)
430 No article found with that message-id
502 Program error, function not performed
Second form (optional article number specified):
221 n a Article follows (multi-line response, n =
article number, a = message-id)
412 No newsgroup selected
420 No current article selected
423 No such article in this newsgroup
502 Program error, function not performed
Except that only the headers are included in the response,
the 221 response behaves identically to the 220 response of
the ARTICLE command.
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9.2.2.2 Examples
Example of a successful retrieval of the headers in an
article (using no article number)
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HEAD
[S] 221 3000234 <45223423@example.com>
[S] Path: pathost!demo!somewhere!not-for-mail
[S] From: ôDemo Userö <nobody@example.com>
[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 Com, San Jose, CA
[S] Message-ID: <45223423@example.com>
[S] .
Example of a successful retrieval of the headers in an
article by message-id
[S] 200 NNTP Service Ready
[C] HEAD <45223423@example.com>
[S] 221 0 <45223423@example.com>
[S] Path: pathost!demo!somewhere!not-for-mail
[S] From: ôDemo Userö <nobody@example.com>
[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 Com, San Jose, CA
[S] Message-ID: <45223423@example.com>
[S] .
Example of an unsuccessful retrieval of the header of an
article by message-id
[S] 200 NNTP Service Ready
[C] HEAD <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of the header of an
article by number
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HEAD 300256
[S] 423 No such article number in this group
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Example of an unsuccessful retrieval the header of an article
by number because no newsgroup was selected first
[S] 200 NNTP Service Ready
[C] HEAD 300256
[S] 412 No newsgroup selected
Example of an attempt to retrieve the header of an article
when the current group selected is empty
[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] HEAD
[S] 420 No current article selected
Example of a failure due to the service being unavailable
[S] 200 NNTP Service Ready
[C] HEAD <i.am.a.test.article@example.com>
[S] 502 Service unavailable
9.2.3 BODY
BODY <message-id>
BODY [number]
The BODY command behaves identically to the ARTICLE command
except that, if the article exists, only the body is
presented (the blank line separating the headers and body
MUST NOT be included).
9.2.3.1 Responses
First form (message-id specified):
222 0 a Article follows (multi-line response, a =
message-id)
430 No article found with that message-id
502 Program error, function not performed
Second form (optional article number specified):
222 n a Article follows (multi-line response, n =
article number, a = message-id)
412 No newsgroup selected
420 No current article selected
423 No such article in this newsgroup
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502 Program error, function not performed
Except that only the body is included in the response, the
222 response behaves identically to the 220 response of the
ARTICLE command.
9.2.3.2 Examples
Example of a successful retrieval of the body of an article
(using no article number)
[S] 200 NNTP Service Ready
[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
[S] 200 NNTP Service Ready
[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
[S] 200 NNTP Service Ready
[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
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] BODY 300256
[S] 423 No such article number in this group
Example of an unsuccessful retrieval of the body of an
article by number because no newsgroup was selected first
[S] 200 NNTP Service Ready
[C] BODY 300256
[S] 412 No newsgroup selected
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Example of an attempt to retrieve the body of an article when
the current group selected is empty
[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] BODY
[S] 420 No current article selected
Example of a failure due to the service being unavailable
[S] 200 NNTP Service Ready
[C] BODY <i.am.a.test.article@example.com>
[S] 502 Service unavailable
9.2.4 STAT
STAT <message-id>
STAT [number]
The STAT command behaves identically to the ARTICLE command
except that, if the article exists, it is NOT presented to
the client.
This command allows the client to determine whether an
article exists, and in the second form what its message-id
is, without having to process an arbitrary amount of text.
9.2.4.1 Responses
First form (message-id specified):
223 0 a Article exists (a = message-id)
430 No article found with that message-id
502 Program error, function not performed
Second form (optional article number specified):
223 n a Article exists (n = article number, a =
message-id)
412 No newsgroup selected
420 No current article selected
423 No such article in this newsgroup
502 Program error, function not performed
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The parameters of the 223 response are identical to those
that would have been given in a 220 response to the
equivalent ARTICLE command. However, the response is NOT
multi-line.
9.2.4.2 Examples
Example of STAT on an existing article (using no article
number)
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT
[S] 223 3000234 <45223423@example.com>
Example of a STAT of an existing article by message-id
[S] 200 NNTP Service Ready
[C] STAT <45223423@example.com>
[S] 223 0 <45223423@example.com>
Example of an STAT of an article not on the server by
message-id
[S] 200 NNTP Service Ready
[C] STAT <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of STAT of an article not in the server by number
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] STAT 300256
[S] 423 No such article number in this group
Example of STAT of an article by number when no newsgroup was
selected first
[S] 200 NNTP Service Ready
[C] STAT 300256
[S] 412 No newsgroup selected
Example of STAT of an article when the current group selected
is empty
[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] STAT
[S] 420 No current article selected
Example of a failure due to the service being unavailable
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[S] 200 NNTP Service Ready
[C] STAT <i.am.a.test.article@example.com>
[S] 502 Service unavailable
9.3 Article Posting
Article posting is done in one of two modes: individual
article posting from news reading clients and article
transfer from other news servers.
9.3.1 POST
POST
If posting is allowed, response code 340 MUST be returned to
indicate that the article to be posted should be sent.
Response code 440 MUST be sent if that posting is prohibited
for some installation-dependent reason.
If posting is permitted, the article MUST be presented to the
server by the client in the format specified by RFC 1036 (or
by any of its successors or extensions). The text forming the
header and body of the message to be posted MUST be sent by
the client in the format defined above (section 0) for multi-
line responses (except that there is no initial line
containing a response code). Thus a single period (".") on a
line indicates the end of the text, and lines starting with a
period in the original text have that period doubled during
transmission.
Following the presentation of the termination sequence by the
client, the server MUST return a response code indicating
success or failure of the article transfer. Note that
response codes 340 and 440 are used in direct response to the
POST command. Others are returned following the sending of
the article.
No attempt shall be made by the server to filter characters,
fold or limit lines, or otherwise process incoming text. The
intent is that the server just passes the incoming message to
be posted to the server installation's news posting software,
which is not defined by this memo.
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The client SHOULD NOT assume that the article has been
successfully transferred unless it receives an affirmative
response from the server. Since, however, the affirmative
response may have been sent and lost, the client SHOULD use
the same message-id in the article when resending it or check
whether the article was successfully posted before resending
it to ensure that the resend will not result in a duplicate
article.
This command is not streamable.
9.3.1.1 Responses
240 Article received ok
340 Send article to be posted
440 Posting not permitted
441 Posting failed
9.3.1.2 Examples
Example of a successful posting
[S] 200 NNTP Service Ready
[C] POST
[S] 340 Input article. End with <CR-LF>.<CR-LF>
[C] From: ôDemo Userö <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
[S] 200 NNTP Service Ready
[C] POST
[S] 340 Input article. End with <CR-LF>.<CR-LF>
[C] From: ôDemo Userö <nobody@example.net>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Organization: An Example Net
[C]
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[C] This is just a test article.
[C] .
[S] 441 Posting failed
Example of an attempt to post when posting is not allowed
[S] 201 NNTP Service Ready, read-only
[C] POST
[S] 440 Posting not permitted
9.3.2 IHAVE
IHAVE <message-id>
The IHAVE command informs the server that the client has an
article whose id is <message-id>. If the server desires a
copy of that article, it MUST return response code 335
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), response code 435 indicating that
the article is not wanted MUST be returned. 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), response
code 436 MUST be returned.
If transmission of the article is requested, the client MUST
send the entire article, including header and body, in the
format defined above (section 4) for multi-line responses
(except that there is no initial line containing a response
code). Thus a single period (".") on a line indicates the end
of the text, and lines starting with a period in the original
text have that period doubled during transmission. The server
MUST return either response code 235, indicating that the
article was successfully transferred, response code 436,
indicating that the transfer failed but should be tried again
later, or response code 437, indicating that the article was
rejected.
This function differs from the POST command in that it is
intended for use in transferring already-posted articles
between hosts. It SHOULD NOT be used when the client is a
personal news reading program, since this command indicates
that the forthcoming article has already been posted at
another site and is being forwarded from another host.
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However, the server MAY elect not to post or forward the
article if after further examination of the article it deems
it inappropriate to do so. Reasons for such subsequent
rejection of an article may include such problems as
inappropriate newsgroups or distributions, disk space
limitations, article lengths, garbled headers, and the like.
These are typically restrictions enforced by the server
host's news software and not necessarily the NNTP server
itself.
The client SHOULD NOT assume that the article has been
successfully transferred unless it receives an affirmative
response from the server. A lack of response (such as a
dropped network connection or a network timeout) SHOULD be
treated the same as a 436 error response.
Because some news server software may not be able immediately
to determine whether or not an article is suitable for
posting or forwarding, an NNTP server MAY acknowledge the
successful transfer of the article (with a 235 response) but
later silently discard it.
9.3.2.1 Responses
235 Article transferred ok
335 Send article to be transferred
435 Article not wanted, please donÆt send it.
436 Transfer failed, try again later.
437 Article rejected, please donÆt sent it again.
9.3.2.2 Examples
Example of successfully sending an article to another site
[S] 200 NNTP Service Ready
[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: ôDemo Userö <nobody@example.com>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Date: 6 Oct 1998 04:38:40 -0500
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[C] Organization: An Example Com, San Jose, CA
[C] Message-ID: <i.am.a.test.article@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 235 Article transferred ok
Example of sending an article to another site that rejects it
[S] 200 NNTP Service Ready
[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: ôDemo Userö <nobody@example.com>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Date: 6 Oct 1998 04:38:40 -0500
[C] Organization: An Example Com, San Jose, CA
[C] Message-ID: <i.am.a.test.article@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 437 Article rejected. Don't send again
Example of sending an article to another site where the
transfer fails
[S] 200 NNTP Service Ready
[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: ôDemo Userö <nobody@example.com>
[C] Newsgroups: misc.test
[C] Subject: I am just a test article
[C] Date: 6 Oct 1998 04:38:40 -0500
[C] Organization: An Example Com, San Jose, CA
[C] Message-ID: <i.am.a.test.article@example.com>
[C]
[C] This is just a test article.
[C] .
[S] 436 Transfer failed
Example of sending an article to a site that already has it
[S] 200 NNTP Service Ready
[C] IHAVE <i.am.an.article.you.have@example.com>
[S] 435 Duplicate
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Example of sending an article to a site that requests the
article be tried again later
[S] 200 NNTP Service Ready
[C] IHAVE <i.am.an.article.you.defer@example.com>
[S] 436 Retry later
9.4 The LIST Keyword
9.4.1 LIST
LIST [ACTIVE [wildmat]]
The response to the LIST keyword with no parameters returns a
list of valid newsgroups and associated information. Each
newsgroup is sent as a line of text in the following format:
group first last status
where <group> is the name of the newsgroup, <last> is the
number of the last known article currently in that newsgroup,
<first> is the number of the first article currently in the
newsgroup, and <status> indicates the current status of the
group on this server. Typically, the <status> will consist of
the US-ASCII character 'y' where posting is permitted, 'n'
where posting is not permitted and 'm' where postings will be
forwarded to the newsgroup moderator by the news server.
Other status strings may exist. The definition of these other
values and the circumstances under which they are returned is
covered in other specifications. Each field in the line is
separated from its neighboring fields by one or more US-ASCII
spaces.
The <first> and <last> fields will always be numeric. They
may have leading zeros. The <first> field corresponds to the
"reported low water mark" and the <last> field corresponds to
the "reported high water mark" described in the GROUP command
(see Section 9.1.1.1).
The status of a newsgroup only indicates how posts to that
newsgroup are processed. It does not indicate if the current
client is permitted to post. That is indicated by the status
code returned as part of the greeting.
Please note that an empty list (i.e., the text body returned
by this command consists only of the terminating period) is a
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possible valid response, and indicates that there are
currently no valid newsgroups.
If the optional wildmat parameter is specified, the list is
limited to only the groups that match the pattern.
9.4.1.1 Responses
215 Information Follows (multi-line response)
9.4.1.2 Examples
Example of LIST returning a list of newsgroups
[S] 200 NNTP Service Ready
[C] LIST
[S] 215 list of newsgroups follows
[S] misc.test 3000234 3002322 y
[S] alt.fc-writers.recovery 1 4 y
[S] tx.natives.recovery 56 89 y
[S] .
Example of LIST returning no newsgroups
[S] 200 NNTP Service Ready
[C] LIST
[S] 215 list of newsgroups follows
[S] .
9.4.2 LIST ACTIVE.TIMES
LIST ACTIVE.TIMES [wildmat]
The active.times file is maintained by some news transport
systems to contain information about who created a particular
newsgroup and when. The format of this file includes three
fields separated from each other by one or more US-ASCII
space characters. The first field is the name of the
newsgroup. The second is the time when this group was created
on this news server measured in seconds since the start of
January 1, 1970. The third is the email address of the
entity that created the newsgroup and must be a mailbox as
defined in RFC 28228. When executed, the information is
displayed following the 215 response. When display is
completed, the server will send a period on a line by itself.
If the information is not available, the server will return
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the 503 error response. If the server does not recognize the
command, it SHOULD return the 501 error response.
If the optional wildmat parameter is specified, the list is
limited to only the groups that match the pattern.
9.4.2.1 Responses
215 Information Follows (multi-line response)
501 Syntax error
503 Program error, function not performed
9.4.2.2 Examples
Example of LIST ACTIVE.TIMES returning a list of newsgroups
[S] 200 NNTP Service Ready
[C] LIST ACTIVE.TIMES
[S] 215 information follows
[S] misc.test 930445408 <creatme@isc.org>
[S] alt.rfc-writers.recovery 930562309 <m@example.com>
[S] tx.natives.recovery 930678923 <sob@academ.com>
[S] .
Example of LIST ACTIVE.TIMES returning an error (The server
software is not configured to maintain this information, but
does recognize the command as valid.)
[S] 200 NNTP Service Ready
[C] LIST ACTIVE.TIMES
[S] 503 program error, function not performed
Example of LIST ACTIVE.TIMES sent to a server that does not
recognize this argument (e.g. The software does not maintain
this information.)
[S] 200 NNTP Service Ready
[C] LIST ACTIVE.TIMES
[S] 501 Syntax Error
9.4.3 LIST DISTRIBUTIONS
LIST DISTRIBUTIONS
The distributions file is maintained by some news transport
systems to contain information about valid values for the
Distribution: line in a news article header and about what
the values mean. Each line contains two fields, the value and
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a short explanation on the meaning of the value. The first
field is separated from the second field by one or more US-
ASCII spaces. When executed, the information is displayed
following the 215 response. When display is completed, the
server will send a period on a line by itself. If the
information is not available, the server will return the 503
error response. If the server does not recognize this
command, it SHOULD return the 501 error response.
9.4.3.1 Responses
215 Information Follows (multi-line response)
501 Syntax error
503 Program error, function not performed
9.4.3.2 Examples
Example of LIST DISTRIBUTIONS returning a list of newsgroups
[S] 200 NNTP Service Ready
[C] LIST DISTRIBUTIONS
[S] 215 information follows
[S] usa United States of America
[S] na North America
[S] world All over the World
[S] .
Example of LIST DISTRIBUTIONS returning an error (e.g. The
server software is not configured to maintain this
information, but does recognize the command as valid.)
[S] 200 NNTP Service Ready
[C] LIST DISTRIBUTIONS
[S] 503 program error, function not performed
Example of LIST DISTRIBUTIONS sent to a server that does not
recognize the command (e.g. The server does not maintain this
information regardless of configuration.)
[S] 200 NNTP Service Ready
[C] LIST DISTRIBUTIONS
[S] 501 Syntax Error
9.4.4 LIST DISTRIB.PATS
LIST DISTRIB.PATS
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The distrib.pats file is maintained by some news transport
systems to allow clients to choose a value for the
Distribution: line in the header of a news article being
posted. The information returned consists of lines, in no
particular order, each of which contains three fields
separated by colons. These fields are a weight, a wildmat
(which may be a simple group name), and a Distribution:
value, in that order.
The client MAY use this information to select a Distribution:
value based on the name of a newsgroup. To do so, it should
determine the lines whose second field matches the newsgroup
name, select that line with the highest weight (with 0 being
the lowest), and use the Distribution: field from that line.
When executed, the information is displayed following the 215
response. When display is completed, the server will send a
period on a line by itself. If the information is not
available, the server will return the 503 error response. If
this command is not recognized, the server SHOULD return the
501 error response.
9.4.4.1 Responses
215 Information Follows (multi-line response)
501 Syntax error
503 Program error, function not performed
9.4.4.2 Examples
Example of LIST DISTRIB.PATS returning a list of newsgroups
[S] 200 NNTP Service Ready
[C] LIST DISTRIB.PATS
[S] 215 information follows
[S] 10:local.*:local
[S] .
Example of LIST DISTRIB.PATS returning an error (e.g. The
server software is not configured to maintain this
information, but does recognize the command as valid.)
[S] 200 NNTP Service Ready
[C] LIST DISTRIB.PATS
[S] 503 program error, function not performed
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Example of LIST DISTRIB.PATS sent to a server that does not
recognize the command (e.g. The software does not maintain
this information regardless of configuration.)
[S] 200 NNTP Service Ready
[C] LIST DISTRIB.PATS
[S] 501 Syntax Error
9.4.5 LIST NEWSGROUPS
LIST NEWSGROUPS [wildmat]
The newsgroups file is maintained by some news transport
systems to contain the name of each newsgroup that is active
on the server and a short description about the purpose of
each newsgroup. Each line in the file contains two fields,
the newsgroup name and a short explanation of the purpose of
that newsgroup. The first field is separated from the second
field by one or more US-ASCII spaces. When executed, the
information is displayed following the 215 response. When
display is completed, the server will send a period on a line
by itself. If the information is not available, the server
will return the 503 response. If the server does not
recognize the command it should return a 501 response. If the
optional wildmat parameter is specified, the list is limited
to only those groups that match the wildmat (no matching is
done on the group descriptions). If nothing is matched an
empty list is returned, not an error.
9.4.5.1 Responses
215 Information Follows (multi-line response)
501 Syntax error
503 Program error, function not performed
9.4.5.2 Examples
Example of LIST NEWSGROUPS returning a list of newsgroups
[S] 200 NNTP Service Ready
[C] LIST NEWSGROUPS
[S] 215 information follows
[S] misc.test General Usenet testing
[S] alt.rfc-writers.recovery RFC Writers Recovery
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[S] tx.natives.recovery Texas Natives Recovery
[S] .
Example of LIST NEWSGROUPS returning an error (e.g. The
server software recognizes the command as valid, but the
information is not available.)
[S] 200 NNTP Service Ready
[C] LIST NEWSGROUPS
[S] 503 program error, function not performed
9.5 Standard extensions
Each of the following sections describes an extension that a
server MAY provide. If the server provides the extension, it
MUST include the appropriate extension label in the response
to LIST EXTENSIONS. If it does not provide it, it MUST NOT
include the appropriate extension label. The descriptions of
facilities in each section are written as if the extension is
provided. If it is not provided, the entire section should be
ignored.
9.5.1 LISTGROUP extension
This extension provides one command and has the extension
label LISTGROUP.
9.5.1.1 The LISTGROUP Command
LISTGROUP [ggg]
The LISTGROUP command is used to get a listing of all the
article numbers in a particular newsgroup.
The optional parameter ggg is the name of the newsgroup to be
selected (e.g. "news.software.misc"). A list of valid
newsgroups may be obtained from the LIST command. If no group
is specified, the current group is used as the default
argument.
The successful selection response will be a list of the
article numbers in the group followed by a period on a line
by itself. The list starts on the next line following the 211
response code.
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When a valid group is selected by means of this command, the
internally maintained "current article pointer" MUST be set
to the first article in the group and the name of the current
newsgroup MUST be set to the selected newsgroup name. If an
invalid group is specified, the previously selected group and
article remain selected. If an empty newsgroup is selected,
the "current article pointer" may be in an indeterminate
state and should not be used.
The LISTGROUP keyword MAY be used by a client as a
replacement for the GROUP command in establishing a valid
"current article pointer." After a successful response is
received, any other command may be used that depends on
having the "current article pointer" be valid.
If a group name is specified and that group is not available
on that server, the server MUST respond with the 411 error
code.
A server that does not implement this command SHOULD return a
500 error response.
9.5.1.1.1 Responses
211 List of article numbers follow (multi-line
response)
411 No such group
412 No newsgroup currently selected
500 Command not recognized
9.5.1.1.2 Examples
Example of LISTGROUP on an empty group:
[S] 200 NNTP Service Ready
[C] LISTGROUP example.empty.newsgroup
[S] 211 list of article numbers follows
[S] .
Example of LISTGROUP on a valid current group:
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 2000 3000234 3002322 misc.test selected
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[C] LISTGROUP
[S] 211 list follows
[S] 3000234
[S] 3000237
[S] 3000238
[S] 3000239
[S] 3002322
[S] .
Example of LISTGROUP failing because no group has been
selected:
[S] 200 NNTP Service Ready
[C] LISTGROUP
[S] 412 no current group
[C] GROUP example.is.sob.bradner.or.barber
[S] 411 no such group
[C] LISTGROUP
[S] 412 no current group
9.5.2 The OVER Extension
This extension provides two commands, OVER and LIST
OVERVIEW.FMT. The label for this extension is OVER.
9.5.2.1 LIST OVERVIEW.FMT
LIST OVERVIEW.FMT
The overview.fmt file is maintained by some news transport
systems to contain the order in which header information is
stored in the overview databases for each newsgroup. When
executed, news article header fields are displayed one line
at a time in the order in which they are stored in the
overview database[9] following the 215 response. When
display is completed, the server will send a period on a line
by itself. If the information is not available, the server
will return the 503 response.
If the header has the word "full" (without quotes) after the
colon, the header's name is prepended to its field in the
output returned by the server.
This is command is part of the optional OVER extension which
includes the OVER command defined in section . If the OVER
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extension is not implemented, then this command MUST NOT be
implemented. If that case, the server MUST return a 501 error
response when this command is presented by the client.
9.5.2.1.1 Responses
215 Information follows (multi-line response)
501 Syntax Error
503 Program error, function not performed
9.5.2.1.2 Examples
Example of LIST OVERVIEW.FMT returning a list of newsgroups
[S] 200 NNTP Service Ready
[C] LIST OVERVIEW.FMT
[S] 215 Order of fields in overview database.
[S] Subject:
[S] From:
[S] Date:
[S] Message-ID:
[S] .
Example of LIST OVERVIEW.FMT returning an error
[S] 200 NNTP Service Ready
[C] LIST OVERVIEW.FMT
[S] 503 program error, function not performed
9.5.2.2 OVER
OVER [range]
The OVER command returns specific header information for the
article(s) specified from the current selected group. The
information returned in the response to this command can be
used by clients to follow discussion threads.
The optional range argument may be any of the following:
* an article number
* an article number followed by a dash to indicate all
following
* an article number followed by a dash followed by another
article number
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If no argument is specified, then information from the
current article is displayed. Successful responses start with
a 224 response followed by the overview information for all
matched messages. Once the output is complete, a period is
sent on a line by itself. A newsgroup must have been selected
earlier, else a 412 error response is returned. If no
articles are in the range specified, the server returns a 420
error response. A 502 response will be returned if the client
only has permission to transfer articles. A 500 response
SHOULD be returned by servers that do not implement this
command.
The output consists of one line per article, sorted in
numerical order of article number. Each line consists of a
number of fields separated by an US-ASCII TAB character. The
first 8 fields MUST be the following, in order: article
number, subject, author, date, message-ID, references, byte
count, line count.
The article number field should contain the article number
(within the group). The line count and byte count are
calculated by the server based on the actual size and number
of lines in the article. The content of the rest of the
fields is formed by taking the original header content (such
as the raw subject line from the article), removing all US-
ASCII CRLF pairs, and then replacing each remaining US-ASCII
NUL, TAB, CR, or LF character with a single US-ASCII space.
The content of any subsequent field is given by the response
to the LIST OVERVIEW.FMT command. A field may be empty (in
which case there will be two adjacent US-ASCII tabs, and a
sequence of trailing US-ASCII tabs may be omitted).
The server SHOULD not produce output for articles that no
longer exist.
9.5.2.2.1 Responses
224 Overview information follows (multi-line
response)
412 No newsgroup currently selected
420 No article(s) selected
500 Command not recognized
502 Program error, functions no performed
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9.5.2.2.2 Examples
Example of a successful retrieval of overview information for
an article (using no article number)
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] OVER
[S] 224 Overview information follows
300234|I am just a test article|öDemo Userö
<nobody@example.com>|6 Oct 1998 04:38:40 -0500|
<45223423@example.com>|<45454@example.net>|1234|
17|Xref: news.example.com misc.test:3000363
[S] .
[Please note that the line that begins with 300234 is all one
line that has been wrapped for readability. A vertical bar
has been inserted to show where the US-ASCII TAB should
actually be.]
Example of an unsuccessful retrieval of overview information
on an article by number
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] OVER 300256
[S] 420 No such article in this group
Example of an unsuccessful retrieval of overview information
by number because no newsgroup was selected first
[S] 200 NNTP Service Ready
[C] OVER
[S] 412 No newsgroup selected
Example of an attempt to retrieve an article when the current
group selected is empty
[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] OVER
[S] 420 No current article selected
9.5.3 The HDR Extension
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This extension provides one new command, HDR. The label for
this extension is HDR
9.5.3.1 HDR
HDR header range|<message-id>
The HDR command is used to retrieve specific headers from
specific articles in the currently selected group.
The required header parameter is the name of a header line
(e.g. "subject") in a newsgroup article. See RFC-1036 for a
list of valid header lines. The required range argument may
be any of the following:
* an article number
* an article number followed by a dash to indicate all
following
* an article number followed by a dash followed by another
article number.
The required message-id argument indicates a specific
article. The range and message-id arguments are mutually
exclusive.
A successful response consists of a 221 code followed by the
output from the command. The output consists of one line for
each article where the relevant header line exists. The line
consists of the article number, a US-ASCII space, and then
the contents of the header (without the header name). A valid
response includes an empty list (indicating that there were
no matches). Once the output is complete, a period is sent on
a line by itself. If the optional argument is a message-id
and no such article exists, a 430 error response shall be
returned. A 502 response shall be returned if the client only
has permission to transfer articles. A 500 response SHOULD be
issued by all servers that do not recognize this command.
9.5.3.1.1 Responses
221 Header follows (multi-line response)
412 No newsgroup selected
430 No such article
500 Command not recognized
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502 Program error, function not performed
9.5.3.1.2 Examples
Example of a successful retrieval of subject lines from a
range of articles
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR Subject 3000234-300238
[S] 221 Header Follows
[S] 3000234 I am just a test article
[S] 3000237 Re: I am just a test article
[S] 3000238 Ditto
[S] .
Example of a successful retrieval of header from an article
by message-id
[S] 200 NNTP Service Ready
[C] GROUP misc.test
[S] 211 1234 3000234 3002322 misc.test
[C] HDR subject <i.am.a.test.article@example.com>
[S] 221 Header information follows
[S] 3000345 I am just a test article
[S] .
Example of an unsuccessful retrieval of a header from an
article by message-id
[S] 200 NNTP Service Ready
[C] HDR subject <i.am.not.there@example.com>
[S] 430 No Such Article Found
Example of an unsuccessful retrieval of headers from articles
by number because no newsgroup was selected first
[S] 200 NNTP Service Ready
[C] HDR subject 300256-
[S] 412 No newsgroup selected
Example of an unsuccessful retrieval of headers from articles
by message-id because no newsgroup was selected first
[S] 200 NNTP Service Ready
[C] HDR subject <i.am.a.test.article@example.com>
[S] 412 No newsgroup selected
Example of retrieving header information when the current
group selected is empty
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[S] 200 NNTP Service Ready
[C] GROUP example.empty.newsgroup
[S] 211 0 0 0 example.empty.newsgroup
[C] HDR subject 0-
[S] 221 Headers follow
.
Example of a failure due to restrictions configured into the
server
[S] 200 NNTP Service Ready
[C] GROUP news.group
[S] 211 1234 3000234 3002322 misc.test
[C] HDR Subject 3000234-300238
[S] 502 Service Unavailable
10 The CONCLUSION Step
10.1 QUIT
QUIT
The server process MUST acknowledge the QUIT command and then
close the connection to the client. This is the preferred
method for a client to indicate that it has finished all its
transactions with the NNTP server.
If a client simply disconnects (or the connection times out
or some other fault occurs), the server MUST gracefully cease
its attempts to service the client, disconnecting from its
end if necessary.
10.1.1 Responses
250 Connection closing
10.1.2 Example
[S] 200 NNTP Service Ready
[C] QUIT
[S] 205 closing connection
[Server closes connection.]
11 Other Keywords
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There are other keywords that may be used at any time between
the beginning of a session and its termination. Using these
keywords does not alter any state information, but the
response generated from the use of these keywords may provide
useful information to clients that use them.
11.1 DATE
DATE
This command exists to help clients find out the current
Coordinated Universal Time[10] from the server's perspective.
This command MUST NOT be used as a substitute for NTP[11],
but to provide information that might be useful when using
the NEWNEWS command (see section 11.4). A system providing
NNTP service SHOULD implement NTP for the purposes of keeping
the system clock as accurate as possible.
This command returns a one-line response code of 111 followed
by the date and time on the server in the form
YYYYMMDDhhmmss. This date and time is presented in
Coordinated Universal Time.
11.1.1 Response
111 YYYYMMDDhhmmss Current date and time on server
presented in Coordinated
Universal Time
11.1.2 Example
[S] 200 NNTP Service Ready
[C] DATE
[S] 111 19990623135624
11.2 The HELP Command
HELP
This command provides a short summary of commands that are
understood by this implementation of the server. The help
text will be presented as a textual response terminated by a
single period on a line by itself.
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This text is not guaranteed to be in any particular format
and SHALL NOT be used by clients as a replacement for the
LIST EXTENSIONS command described in section 8.1.
11.2.1 Responses
100 Help text follows (multi-line response)
11.2.2 Example
[S] 200 NNTP Service Ready
[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] .
11.3 NEWGROUPS
NEWGROUPS date time [GMT]
A list of newsgroups created since <date and time> MUST be
listed in the same format as the LIST command.
The date is sent as 6 or 8 digits in the format [XX]YYMMDD,
where XX is the first two digits of the year, YY is the last
two digits of the year, MM is the two digits of the month
(with leading zero, if appropriate), and DD is the day of the
month (with leading zero, if appropriate). If the first two
digits of the year are not specified, the year is to be taken
from the current century if YY is smaller than or equal to
the current year, otherwise the year is from the previous
century.
Time must also be specified. It must be as 6 digits HHMMSS
with HH being hours in the 24-hour clock 00-23, MM minutes
00-59, and SS seconds 00-60, which allows for leap seconds.
The token "GMT" specifies that the date and time are given in
Coordinated Universal Time. If the token "GMT" is omitted
then the date and time are specified in the server's local
timezone. Note that there is no way using the protocol
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specified in this memo to establish the server's local
timezone.
Note that an empty list (i.e., the text body returned by this
command consists only of the terminating period) is a
possible valid response, and indicates that there are
currently no new newsgroups.
Clients SHOULD make all queries using Coordinated Universal
Time (i.e. by including the ôGMTö parameter) when possible.
11.3.1 Responses
231 List of new newsgroups follows (multi-line
response)
11.3.2 Examples
Example where there are new groups
[S] 200 NNTP Service Ready
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] alt.rfc-writers.recovery
[S] tx.natives.recovery
[S] .
Example where there are no new groups
[S] 200 NNTP Service Ready
[C] NEWGROUPS 19990624 000000 GMT
[S] 231 list of new newsgroups follows
[S] .
11.4 NEWNEWS
NEWNEWS wildmat date time [GMT]
A list of message-ids of articles posted or received on the
server to the list of newsgroups that match the wildmat since
"date" will be listed. The format of the listing will be one
message-id per line, as though text were being sent. The
order of the response has no specific significance and may
vary from response to response in the same session. If a
message-id appears more than once it has the same meaning as
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if it appears only once. A single line consisting solely of
one period followed by CR-LF will terminate the list.
Date and time are in the same format as the NEWGROUPS
command.
Note that an empty list (i.e., the text body returned by this
command consists only of the terminating period) is a
possible valid response, and indicates that there is
currently no new news.
Clients SHOULD make all queries in Coordinated Universal Time
(i.e. by using the ôGMTö parameter) when possible.
11.4.1 Responses
230 List of new articles by message-id follows (may be a
multi-line response)
11.4.2 Examples
Example where there are new articles
[S] 200 NNTP Service Ready
[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>
Example where there are no new articles
[S] 200 NNTP Service Ready
[C] NEWNEWS alt.* 19990624 000000 GMT
[S] 230 list of new articles by message-id follows
[S] .
12 Framework for NNTP Extensions
Although NNTP is widely and robustly deployed, some parts of
the Internet community might wish to extend the NNTP service.
This memo defines a means whereby an extended NNTP client may
query the server to determine the service extensions that it
supports.
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It must be emphasized that any extension to the NNTP service
should not be considered lightly. NNTP's strength comes
primarily from its simplicity. Experience with many
protocols has shown that:
Protocols with few options tend towards ubiquity, whilst
protocols with many options tend towards obscurity.
This means that each and every extension, regardless of its
benefits, must be carefully scrutinized with respect to its
implementation, deployment, and interoperability costs. In
many cases, the cost of extending the NNTP service will
likely outweigh the benefit.
Given this environment, the framework for the extensions
described in this memo consists of:
* a mechanism for clients to determine a server's available
extensions
* a registry of NNTP service extensions
The LIST EXTENSIONS command is described in section 8.1 of
this memo and is the mechanism for clients to use to
determine what extensions are available for client use.
The IANA shall maintain a registry of NNTP service
extensions.
An extension is identified by a unique extension-label, which
is a string of 1 to 12 uppercase letters. The extension-label
will often be the name of a new command that the extension
adds. However this is not a requirement: an extension might
not add any new commands or keywords.
An extension is either a private extension or else it is
included in the IANA registry and is defined in an RFC. Such
RFCs either must be on the standards-track or must define an
IESG-approved experimental protocol.
The definition of an extension must include:
* a descriptive name for the extension
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* the extension-label (which is returned by LIST EXTENSIONS
to indicate to the client that the server supports this
particular extension)
* the syntax, values, and meanings of any parameters
following the extension-label in the output of LIST
EXTENSIONS
* any new NNTP keywords associated with the extension
* the syntax and possible values of parameters associated
with the new NNTP keywords
* any new parameters the extension associates with any other
pre-existing NNTP keywords
* how support for the extension affects the behavior of a
server and NNTP client
* any increase in the maximum length of commands over the
value specified in this memo
* a specific statement about the effect on streaming this
extension may have (if any)
The extension-label of private extensions MUST begin with
"X". The extension-label of registered extensions MUST NOT
begin with "X".
Any keyword values presented in the NNTP response that do not
begin with "X" MUST correspond to a standard, standards-
track, or IESG-approved experimental NNTP service extension
registered with IANA. A conforming server MUST NOT offer non
"X" prefixed keyword values that are not described in a
registered extension.
Except where stated otherwise, the commands in this memo are
understood (even if not supported) by all servers and are not
described in the list of features returned by the LIST
EXTENSIONS command.
A server MAY provide additional keywords - either new
commands or new parameters to existing commands - as part of
a private extension. These new keywords MUST begin with "X".
A server MUST NOT send different response codes to basic NNTP
commands documented here or commands documented in registered
extensions in response to the availability or use of a
private extension.
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12.1 Initial IANA Registry
The IANA's initial registry of NNTP service extensions
consists of these entries:
Service Extension NNTP Extension Label Added Behavior
Overview Support OVER Defined in this memo
Specific Article
LISTGROUP Defined in this memo
Numbers
Header Pattern
HDR Defined in this memo
Matching
13 Augmented BNF Syntax for NNTP Commands
This syntax defines the non-terminal "command". The non-
terminal "parameter" is used for command parameters whose
syntax is specified elsewhere. The syntax is in alphabetical
order. Note that ABNF strings are case insensitive.
article-command = "ARTICLE" [1*WSP (msg-id / article-
number)] *WSP CRLF
article-number = 1*16DIGIT
argument = parameter ; excluding sequence ".."
body-command = "BODY" [1*WSP (msg-id / article-number)]
*WSP CRLF
command = article-command /
body-command /
date-command /
group-command /
head-command /
help-command /
ihave-command /
last-command /
list-active-times-command /
list-distrib-pats-command /
list-distributions-command /
list-extensions-command /
list-newsgroups-command /
list-overview-fmt-command /
list-command /
listgroup-command /
mode-reader-command /
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newgroups-command /
newnews-command /
next-command /
over-command /
hdr-command /
post-command /
quit-command /
stat-command
CR = %x0D
CRLF = CR LF
date-command = "DATE" *WSP CRLF
date = 6*8DIGIT
DIGIT = %x30-39
group-command = "GROUP" 1*WSP wildmat *WSP CRLF
hdr-command = "HDR" 1*WSP header 1*WSP (range / msg-id)
*WSP CRLF
head-command = "HEAD" [1*WSP (msg-id / article-number)]
*WSP CRLF
header = parameter
help-command = "HELP" *WSP CRLF
HT = %x09
ihave-command = "IHAVE" 1*WSP msg-id *WSP CRLF
last-command = "LAST" *WSP CRLF
LF = %x0A
list-active-times-command = "LIST" 1*WSP "ACTIVE.TIMES"
[1*WSP wildmat] *WSP CRLF
list-command = "LIST" [1*WSP "ACTIVE" [1*WSP wildmat]]
*WSP CRLF
list-distrib-pats-command = "LIST" 1*WSP "DISTRIB.PATS"
*WSP CRLF
list-distributions-command = "LIST" 1*WSP "DISTRIBUTIONS"
*WSP CRLF
list-extensions-command = "LIST" 1*WSP "EXTENSIONS" *WSP
CRLF
list-newsgroups-command = "LIST" 1*WSP "NEWSGROUPS" [1*WSP
wildmat] *WSP CRLF
list-overview-fmt-command = "LIST" 1*WSP "OVERVIEW.FMT"
*WSP CRLF
listgroup-command = "LISTGROUP" [1*WSP wildmat] *WSP CRLF
mode-reader-command = "MODE" 1*WSP "READER" *WSP CRLF
msg-id = <defined in section 9.1 of this memo>
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newgroups-command = "NEWGROUPS" 1*WSP date 1*WSP time
1*WSP "GMT"] *WSP CRLF
newnews-command = "NEWNEWS" 1*WSP wildmat 1*WSP date
1*WSP time [1*WSP "GMTö]*WSP CRLF
next-command = "NEXT" *WSP CRLF
over-command = "OVER" [1*WSP range] *WSP CRLF
parameter = 1*(%x21-FF) ; generic command parameter
post-command = "POST" *WSP CRLF
quit-command = "QUIT" *WSP CRLF
range = article-number ["-" [article-number]]
SP = %x20
stat-command = "STAT" [1*WSP (msg-id / article-number)]
*WSP CRLF
time = 6DIGIT
UTF-8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4 / UTF8-5 /
UTF8-6
UTF8-1 = %x80-BF
UTF8-2 = %xC0-DF UTF8-1
UTF8-3 = %xE0-EF 2UTF8-1
UTF8-4 = %xF0-F7 3UTF8-1
UTF8-5 = %xF8-FB 4UTF8-1
UTF8-6 = %xFC-FD 5UTF8-1
wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
wildmat-pattern = 1*wildmat-item
wildmat-item = wildmat-exact / wildmat-wild
wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-
7F /UTF-8-non-ascii ; exclude * , ? [ \ ]
wildmat-wild = "*" / "?"
WSP = SP / HT
14 Security Considerations
This section is meant to inform application developers,
information providers, and users of the security limitations
in NNTP as described by this memo. The discussion does not
include definitive solutions to the problems revealed, though
it does make some suggestions for reducing security risks.
14.1 Personal and Proprietary Information
NNTP, because it was created to distribute network news
articles, will forward whatever information is stored in
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those articles. Specification of that information is outside
this scope of this memo, but it is likely that some personal
and/or proprietary information is available in some of those
articles. It is very important that designers and
implementers provide informative warnings to users so
personal and/or proprietary information is not disclosed
inadvertently. Additionally, effective and easily understood
mechanisms to manage the distribution of news articles must
be provided to NNTP Server administrators, so that they are
able to report with confidence what information is and is not
being forwarded in news articles passing though their
servers.
14.2 Abuse of Server Log Information
A server is in the position to save session data about a
user's requests that might identify their reading patterns or
subjects of interest. This information is clearly
confidential in nature and its handling can be constrained by
law in certain countries. People using the NNTP protocol to
provide data are responsible for ensuring that such material
is not distributed without the permission of any individuals
that are identifiable by the published results.
14.3 Weak Authentication and Access Control
There is no user-based or token-based authentication in the
basic NNTP specification. Access is normally controlled by
server configuration files. Those files specify access by
using domain names or IP addresses. However, this memo does
permit the creation of extensions to the NNTP protocol itself
for such purposes. While including such mechanisms is
optional, doing so is strongly encouraged.
Other mechanisms are also available. For example, a proxy
server could be put in place that requires authentication
before connecting via the proxy to the NNTP server.
14.4 DNS Spoofing
Many existing NNTP implementations authorize incoming
connections by checking the IP address of that connection
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against the IP addresses obtained via DNS lookups of lists of
domain names given in local configuration files. Servers
that use this type of authentication, and clients that find a
server by doing a DNS lookup of the server name, rely very
heavily on the Domain Name Service, and are thus generally
prone to security attacks based on the deliberate
misassociation of IP addresses and DNS names. Clients and
servers need to be cautious in assuming the continuing
validity of an IP number/DNS name association.
In particular, NNTP clients and servers SHOULD rely on their
name resolver for confirmation of an IP number/DNS name
association, rather than caching the result of previous host
name lookups. Many platforms already can cache host name
lookups locally when appropriate, and they SHOULD be
configured to do so. It is proper for these lookups to be
cached, however, only when the TTL (Time To Live) information
reported by the name server makes it likely that the cached
information will remain useful.
If NNTP clients or servers cache the results of host name
lookups in order to achieve a performance improvement, they
MUST observe the TTL information reported by DNS.
If NNTP clients or servers do not observe this rule, they
could be spoofed when a previously accessed server's IP
address changes. As network renumbering is expected to become
increasingly common, the possibility of this form of attack
will grow. Observing this requirement thus reduces this
potential security vulnerability.
This requirement also improves the load-balancing behavior of
clients for replicated servers using the same DNS name and
reduces the likelihood of a user's experiencing failure in
accessing sites that use that strategy.
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15 References
1 Kantor, B and P. Lapsley, "Network News Transfer Protocol",
RFC-977, U.C. San Diego and U.C. Berkeley, February, 1986.
2 Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 2279, Alis Technologies, January, 1998.
3 Coded Character Set-7-bit American Standard Code for
Information Interchange, ANSI x3.4-1986.
4 Bradner, Scott, "Keywords for use in RFCs to Indicate
Requirement Levels", RFC-2119, Harvard University, March,
1997.
5 Salz, Rich, Manual Page for wildmat(3) from the INN 1.4
distribution, UUNET Technologies, Revision 1.10, April,
1992.
6 Crocker, D. and Overell, P., "Augmented BNF for Syntax
Specifications: ABNF", RFC-2234, Internet Mail Consortium
and Demon Internet, Ltd., November, 1997.
7 Horton, M. and Adams, R., "Standard for the Interchange of
USENET messages", RFC 1036, AT&T Bell Laboratories and The
Center for Seismic Studies, December, 1987.
8 Resnick, P., Editor, "Internet Message Format", RFC 2822,
QUALCOMM Incorporated, April 2001.
9 Robertson, Rob, "FAQ: Overview database / NOV General
Information",
ftp://ftp.uu.net/networking/news/nntp/inn/faq-nov.Z,
January, 1995.
10 International Telecommunications Union-Radio, "Glossary",
ITU-R Recommendation TF.686-1, October, 1997.
11 Mills, David L., "Network Time Protocol (Version 3),
Specification, Implementation and Analysis", RFC-1305,
University of Delaware, March 1992.
16 Notes
UNIX is a registered trademark of the X/Open Company Ltd.
17 Acknowledgments
The author acknowledges the original authors of NNTP as
documented in RFC 977: Brian Kantor and Phil Lapsey.
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The author gratefully acknowledges the work of the NNTP
committee chaired by Eliot Lear. The organization of this
memo was influenced by the last available draft from this
working group. A special thanks to Eliot for generously
providing the original machine-readable sources for that
document.
The author gratefully acknowledges the work of the Marshall
Rose & John G. Meyers in RFC 1939 and the work of the DRUMS
working group, specifically RFC 1869, which is the basis of
the NNTP extensions mechanism detailed in this memo.
The author gratefully acknowledges the authors of RFC 2616
for providing specific and relevant examples of security
issues that should be considered for HTTP. Since many of the
same considerations exist for NNTP, those examples that are
relevant have been included here with some minor rewrites.
The author gratefully acknowledges the comments and
additional information provided by the following individuals
in preparing one or more of the progenitors of this memo:
Russ Allbery <rra@stanford.edu>
Wayne Davison <davison@armory.com>
Chris Lewis <clewis@bnr.ca>
Tom Limoncelli <tal@mars.superlink.net>
Eric Schnoebelen <eric@egsner.cirr.com>
Rich Salz <rsalz@osf.org>
This work was motivated by the work of various news reader
authors and news server authors, which includes those listed
below:
Rick Adams-Original author of the NNTP extensions to the
RN news reader and last maintainer of Bnews
Stan Barber-Original author of the NNTP extensions to the
news readers that are part of Bnews.
Geoff Collyer-Original author of the OVERVIEW database
proposal and one of the original authors of CNEWS
Dan Curry-Original author of the xvnews news reader
Wayne Davison-Author of the first threading extensions to
the RN news reader (commonly called TRN).
Geoff Huston-Original author of ANU NEWS
Phil Lapsey-Original author of the UNIX reference
implementation for NNTP
Iain Lea-Original maintainer of the TIN news reader
Chris Lewis-First known implementer of the AUTHINFO
GENERIC extension
Rich Salz-Original author of INN
Henry Spencer-One of the original authors of CNEWS
Kim Storm-Original author of the NN news reader
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The present author gratefully acknowledges the vast amount of
work put into previous drafts by the original author:
Stan Barber <sob@academ.com>
18 Author's Address
Clive Feather
Thus plc
322 Regents Park Road
London
N3 2QQ
United Kingdom
Email: clive@demon.net
or: clive@davros.org
Tel: +44 20 8371 1138
This memo expires July 31, 2003.
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