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draft-ietf-nntpext-base-02.txt
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INTERNET DRAFT S. Barber
Expires: February 5, 1998 Academ Consulting Services
September 1997
Network News Transport Protocol
draft-ietf-nntpext-base-02.txt
1. Status of this Document
This document is an Internet-Draft. 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."
To learn the current status of any Internet-Draft, please
check the "1id-abstracts.txt" listing contained in the
Internet-Drafts Shadow Directories on ftp.is.co.za (Africa),
nic.nordu.net (Europe), munnari.oz.au (Pacific Rim),
ds.internic.net (US East Coast), or ftp.isi.edu (US West
Coast).
This document is a product of the NNTP Working Group, chaired
by Ned Freed and Stan Barber.
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 document is a
replacement for RFC 977 and officially updates the protocol
specification. It clarifies some vagueness in RFC 977,
includes some new base functionality and provides a specific
mechanism to add standardized extensions to NNTP.
3. Introduction
This document specifies the Network News Transport Protocol
(NNTP), which is used for the distribution, inquiry,
retrieval, and posting of Usenet 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
Barber [Page 1]
INTERNET DRAFT September 1997
interaction, NNTP is designed for efficient transmission of
Usenet articles over a reliable full duplex communication
method.
Every attempt is made to insure that the protocol
specification in this document is compatible with the version
specified in RFC 977[1].
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.
In this document, the words that are used to define the
significance of each particular requirement are capitalized.
These words are:
. "MUST"
This word or the adjective "REQUIRED" means that the item is
an absolute requirement of the specification.
. "SHOULD"
This word or the adjective "RECOMMENDED" means that there may
exist valid reasons in particular circumstances to ignore this
item, but the full implications should be understood and the
case carefully weighed before choosing a different course.
. "MAY"
This word or the adjective "OPTIONAL" means that this item is
truly optional. One vendor may choose to include the item
because a particular marketplace requires it or because it
enhances the product, for example; another vendor may omit the
same item.
An implementation is not compliant if it fails to satisfy one
or more of the MUST requirements for this protocol. An
implementation that satisfies all the MUST and all the SHOULD
requirements for its protocols is said to be "unconditionally
compliant"; one that satisfies all the MUST requirements but
not all the SHOULD requirements for NNTP is said to be
"conditionally compliant".
For the remainder of this 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.
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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
AUTHENTICATION
NEWS TRANSFER
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 then SHOULD then exchange
commands and responses (respectively) until the connection is
closed or aborted. This final step is called the DISCONNECTION
step.
If there is a CONCLUSION step, it MUST immediately precede the
DISCONNECTION step. There MUST be only one CONNECTION,
CONCLUSION and DISCONNECTION step for each NNTP session. All
other steps MAY be repeated as needed.
The default character set for all NNTP commands is US-
ASCII[2]. Commands in the NNTP MUST consist of a case-
insensitive keyword, which MAY be followed by one or more
arguments. All commands MUST be terminated by a CRLF pair.
Multiple commands MUST not be permitted on the same line.
Keywords MUST consist of printable US-ASCII characters.
Unless otherwise noted elsewhere in this document, Arguments
SHOULD consist of printable US-ASCII characters. Keywords and
arguments MUST be each separated by one or more SPACE or TAB
characters. Keywords MUST be at least three characters and
MUST NOT exceed 12 characters. Command lines MUST not exceed
512 characters, which includes the terminating CRLF pair.
Each response MUST start with a three-digit status indicator
that is sufficient to distinguish all responses. Responses to
certain commands MAY be multi-line. In these cases, which are
clearly indicated below, after sending the first line of the
response and a CRLF, any additional lines are sent, each
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terminated by a CRLF pair. When all lines of the response have
been sent, a final line MUST be sent, consisting of a
termination octet (ASCII decimal code 046, ".") and a CRLF
pair. If any line of the multi-line response begins with the
termination octet, the line MUST be "byte-stuffed" by pre-
pending the termination octet to that line of the response.
Hence, a multi-line response is terminated with the five
octets "CRLF.CRLF". When examining a multi-line response, the
client MUST check to see if the line begins with the
termination octet. If so and if octets other than CRLF follow,
the first octet of the line (the termination octet) MUST be
stripped away. If so and if CRLF immediately follows the
termination character, then the response from the NNTP server
is ended and the line containing ".CRLF" MUST not considered
part of the multi-line response.
A NNTP server MAY have an inactivity autologout timer. Such a
timer MUST be of at least 10 minutes duration. The receipt of
any command from the client during that interval 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.
4.1 Responses Codes
Each response MUST begin with a three-digit response code.
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
x5x - Authentication and Authorization
x8x - Nonstandard (private implementation) extensions
x9x - Debugging output
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The exact response codes that MUST be expected from each
command are detailed in the description of the keyword that is
the first part of the command. In addition, below is listed a
general set of response codes that MAY be received at any
time.
Certain status responses contain parameters such as numbers
and names. The number and type of such parameters SHOULD be
fixed for each response code to simplify interpretation of the
response.
Parameters MUST be separated from the numeric response code
and from each other by a single space. All numeric parameters
MUST be in base 10 (decimal) format, and may have leading
zeros. All string parameters MUST begin after the separating
space, and MUST end before the following separating space or
the CR-LF pair at the end of the line. (Therefore, string
parameters MUST not contain spaces.) All text, if any, in the
response which is not a parameter of the response must follow
and be separated from the last parameter by a space. Also,
note that the text following a response number may vary in
different implementations of the server. The 3-digit numeric
code should be used to determine what response was sent.
Response codes not specified in this standard MAY be used for
any installation-specific additional commands also not
specified. These SHOULD be chosen to fit the pattern of x8x
specified above. (Note that debugging is provided for
explicitly in the x9x response codes.)
The use of unspecified response codes for a standard command
is prohibited.
The response pattern x9x is provided for debugging. Since
much debugging output may be classed as "informative
messages", it MUST be the case that responses 190 through 199
WILL be used for various debugging outputs. There is no
requirement in this specification for debugging output.
However, if such is provided over the connected stream, it
MUST use these response codes. If appropriate to a specific
implementation, other x9x codes MAY be used for debugging.
(For example, response code 290 could be used to acknowledge a
remote debugging request.)
A server MUST respond to an unrecognized, unimplemented, or
syntactically invalid command with a negative status indicator
(response codes of the form 5XX). A server MUST respond to a
command issued when the session is in an incorrect state by
responding with a negative status indicator. This may be from
either the 4XX or 5XX group as appropriate.
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5. The WILDMAT format
The WILDMAT format[3] was first developed by Rich Salz based
on the format used in the UNIX "find" command to articulate
file names. It was developed to provide a uniform mechanism
for matching patterns in the same manner that the UNIX shell
matches filenames. Patterns are implicitly anchored at the
beginning and end of each string when testing for a match.
There are five pattern-matching operations other than a strict
one-to-one match between the pattern and the source to be
checked for a match. The first is an asterisk (*) to match any
sequence of zero or more characters. The second is a question
mark (?) to match any single character. The third specifies a
specific set of characters. The set is specified as a list of
characters, or as a range of characters where the beginning
and end of the range are separated by a minus (or dash)
character, or as any combination of lists and ranges. The dash
can also be included in the set as a character if it is the
beginning or end of the set. This set is enclosed in square
brackets. The close square bracket (]) may be used in a set if
it is the first character in the set. The fourth operation is
the same as the logical not of the third operation and is
specified the same way as the third with the addition of a
caret character (^) at the beginning of the test string just
inside the open square bracket. The final operation uses the
backslash character to invalidate the special meaning of the
open square bracket ([), the asterisk, backslash or the
question mark. Two backslashes in sequence will result in the
evaluation of the backslash as a character with no special
meaning.
5.1 Examples
a) [^]-] -- matches any single character other than a
close square bracket or a minus sign/dash.
b) *bdc -- matches any string that ends with the string
"bdc" including the string "bdc" (without quotes).
c) [0-9a-zA-Z] -- matches any single printable alphanumeric
ASCII character.
d) a??d -- matches any four character string which
begins with a and ends with d.
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 case
is ignored in the interpretation of commands by the NNTP
server. Any parameters are shown in lower case. A parameter
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INTERNET DRAFT September 1997
shown in [square brackets] is optional. For example, [GMT]
indicates that the triglyph GMT may present or omitted. A
parameter that may be repeated is followed by an ellipsis.
Mutually exclusive parameters are separated by a vertical bar
(|) character. For example, ggg|<message-id> indicates that a
group name or a <message-id> may be specified, but not both.
Some parameters may be case or language specific. See RFC
1036[4] for these details.
In addition, certain commands make use of a pattern for
selection of multiple news groups. The pattern in all cases is
based on the WILDMAT format introduced by Rich Salz in 1986.
Arguments expected to be in wildmat format will be represented
by the string wildmat. This format is discussed in detail in
section 5 of this memo.
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.
The server must present a 200 greeting code if the client is
authorized to post articles through the use of the POST keyword
on this server.
The server must present a 201 greeting code if the client is
not authorized to post articles using the POST keyword, but no
other authentication is required.
The server must present a 205 greeting code if the client is
required to present authentication before it is permitted to
use any keywords available in the news exchange step.
The server must present a 502 greeting code if the client is
not permitted under any circumstances from interacting with
the server. The server should immediately close the connection
with the client after presenting this code.
In all other cases, the server must present a 400 greeting
code.
7.1.1 MODE READER
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MODE READER
MODE READER MAY be used by the client to indicate to the
server that it is a news reading client. This command may be
entered at any time. The server must present a greeting code
(as described in section 7.1) appropriate to the server's
ability to provide service to this client in this mode.
7.1.1.1 Responses
200 Hello, you can post
201 Hello, you can't post
205 Authentication required
400 Service temporarily unavailable
502 Service unavailable
8. The CAPABILITIES DISCOVERY Step
A client NNTP supporting NNTP service extensions should query
a server early in the session for extensions session by
issuing the LIST EXTENSIONS command. If the NNTP server
supports the NNTP service extensions it MUST give a successful
response (see section 8.1.1), a failure response (see section
8.1.2), or an error response (see section 8.1.3). If the NNTP
server does not support any NNTP service extensions, it MUST
generate an error response (see section 8.1.4).
8.1 LIST EXTENSIONS
If successful, the server NNTP MUST respond with code 202. On
failure, the server NNTP MUST respond with code 503. On error,
the server NNTP MUST respond with one of codes 400, 402, 500
and 501.
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 (e.g. authentication or server
administration). However, a client NNTP MUST not cache (for
use in another session) any information returned if the LIST
EXTENSIONS command succeeds. That is, a client NNTP MUST issue
the LIST EXTENSIONS command at least once during each session
to get the current and correct information concerning
available extensions during that session.
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8.1.1 Successful response
If the server NNTP implements and is able to perform the LIST
EXTENSIONS command, it MUST return code 202.
This response MUST be a multi-line reply. Each line of the
response MUST contain a supported keyword and, optionally, one
or more parameters. The list MUST end with a period on a line
by itself.
Although LIST EXTENSIONS keywords may be specified in upper,
lower, or mixed case, they must always be recognized and
processed in a case-insensitive manner.
8.1.2 Failure response
If for some reason the server NNTP is unable to list the
service extensions it supports, it MUST return code 503.
In the case of a failure response, the client NNTP may try the
extensions either as the need arises or configure itself for
the basic NNTP functionality defined in this document.
8.1.3 Error responses from extended servers
If the server NNTP recognizes the LIST EXTENSIONS command, but
due to various conditions cannot make any extensions available
to the client at the time the client issued the LIST
EXTENSIONS command, it MUST return code 402. No list (even an
empty one) will be returned.
The client NNTP should configure itself for the basic NNTP
functionality defined in this document, or issue commands that
might change the state of the server (authentication, for
example), or issue the QUIT command (see section 11.1) if a
particular extension is required for the client to properly
operate.
If the server NNTP determines that the NNTP service is no
longer available (e.g., due to imminent system shutdown), it
must return code 400.
In the case of an error response, the client NNTP should issue
the QUIT command (see section 11.1).
8.1.4 Responses from servers without extensions
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A server NNTP that conforms to this memo but does not support
the extensions specified here will not recognize the LIST
EXTENSIONS command and MUST consequently return code 500 or
code 501. The server NNTP SHALL stay in the same state after
returning this code. The client NNTP may try the extensions
either as the need arises or configure itself for the basic
NNTP functionality defined in this document.
8.1.5 Responses from improperly implemented servers
A server NNTP that improperly implements the LIST EXTENSIONS
command may return an empty list. Clients SHALL accommodate
this protocol violation and interpret it as a response code
402.
9. The AUTHENTICATION Step
9.1 AUTHINFO
AUTHINFO is used to inform a server about the identity of a
user of the server. In all cases, clients MUST provide this
information when requested by the server. Servers are not
required to accept authentication information that is
volunteered by the client. Clients MUST accommodate servers
that reject any authentication information volunteered by the
client.
9.1.1 AUTHINFO
AUTHINFO USER username
AUTHINFO PASS password
When authorization is required, the server MUST send a 450
response requesting authorization from the client. The client
MUST enter AUTHINFO USER username in order to make use of the
AUTHINFO authentication step. If the server will accept this
form of authentication and a password is required to complete
the authentication step, the server MUST respond with a 350
response. The client MUST then send AUTHINFO PASS followed by
one or more space characters followed by the password. If the
username/password combination is valid or no password is
required, the server MUST return a 250 response and the client
should then retry the original command to which the server
responded with the 450 response. The command SHALL then be
processed by the server normally. If the combination is not
valid, the server MUST return a 452 response.
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If the server returns 501, this means that the authenticator
invocation was syntactically incorrect, or that this form of
AUTHINFO is not supported.
If the requested authenticator capability is not found or
there is some other unspecified server program error, the
server MUST return the 503 response code.
9.1.1.1 Responses
250 Authorization accepted
350 Continue with authorization sequence
450 Authorization required for this command
452 Authorization rejected
501 Command not supported or Command Syntax Error
502 Program error, function not performed
9.1.2 AUTHINFO GENERIC
AUTHINFO GENERIC authenticator arguments...
AUTHINFO GENERIC is used to identify a specific entity to the
server using arbitrary authentication or identification
protocols. The desired protocol is indicated by the
authenticator parameter, and any number of parameters can be
passed to the authenticator.
When authorization is required, the server will send a 350
response requesting authorization from the client.
The client should enter AUTHINFO GENERIC followed by the
authenticator name and the arguments if any. The
authenticator and arguments must not contain the sequence
"..".
The server will attempt to engage the server end
authenticator; similarly, the client should engage the client
end authenticator. The server end authenticator will then
initiate authentication using the NNTP sockets (if appropriate
for that authentication protocol), using the protocol
specified by the authenticator name. These authentication
protocols are not included in this document, but are similar
in structure to those referenced in RFC 1731[5] for the IMAP-4
protocol.
If the server returns 501, this means that the authenticator
invocation was syntactically incorrect, or that AUTHINFO
GENERIC is not supported. The client should retry using the
regular AUTHINFO command.
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If the requested authenticator capability is not found or
there is some other unspecified server program error, the
server returns the 503 response code.
The authenticators converse using their protocol until
complete. If the authentication succeeds, the server
authenticator will terminate with a 250, and the client can
continue by reissuing the command that prompted the 350. If
the authentication fails, the server will respond with a 452.
The client must provide authentication when requested by the
server. The server may request authentication at any time.
Servers may request authentication more than once during a
single session.
When the server authenticator completes, it provides to the
server (by a mechanism herein undefined) the email address of
the user, and potentially what the user is allowed to access.
Once authenticated, the server shall generate a Sender: line
using the email address provided by the authenticator if it
does not match the user-supplied From: line. Additionally, the
server should log the event, including the user's
authenticated email address (if available). This will provide
a means by which subsequent statistics generation can
associate news group references with unique entities - not
necessarily by name.
9.1.2.1 Responses
250 Authorization accepted
350 Continue with authorization sequence
450 Authorization required for this command
452 Authorization rejected
501 Command not supported or Command Syntax Error
502 Program error, function not performed
nnn authenticator-specific protocol.
9.1.3 Transition Issues
The implementations of AUTHINFO commonly in use prior to the
release of this memo have a difference response code set. The
code 281 was used in place of 250, 381 was used in place of
350, 480 was used in place of 450 and 482 was used in place of
452. Client coded to be compliant with this spec may also want
to be able to accommodate the older codes to lessen the impact
of the transition to this specification.
10. The NEWS EXCHANGE Step
During this step, two basic types of transactions occur:
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article retrieval from the server and article posting to the
server.
10.1 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 news group
name and the article number within that news group. That key
MUST be unique to a particular server (there will be only one
article with that number within a particular news group), but
is not required to be globally unique. Additionally, because
the same article can be cross-posted to multiple news groups,
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 first 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
10.1.1 Article Retrieval by News Group Name and Article Number
The following commands are used to set the current news group
name and the "current article pointer" which is used by other
commands for article retrieval.
10.1.1.1 GROUP
GROUP ggg
The required parameter ggg is the name of the news group to be
selected (e.g. "news.software.b"). A list of valid news groups
may be obtained by using the LIST keyword. See section 10.4 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
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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.
. 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 news group 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 news group 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.
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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
news group MUST be set to the selected news group name. If an
invalid group is specified, the previously selected group and
article MUST remain selected. If an empty news group is
selected, the "current article pointer" is in an indeterminate
state and MUST not be used.
The GROUP keyword 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.
10.1.1.1.1 Responses
211 n f l s group selected
(n = estimated number of articles in group, f = first
article number in the group, l = last article number in
the group, s = name of the group.)
411 no such news group
10.1.1.2 LAST
LAST
The internally maintained "current article pointer" MUST be
set to the previous article in the current news group. If
already positioned at the first article of the news group, 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.
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.
The internally-maintained "current article pointer" MUST be
set by this command.
A response indicating the current article number and a
message-id string MUST be returned. No text is sent in
response to this command.
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10.1.1.2.1 Responses
223 n a article retrieved - request text separately (n =
article number, a = unique article id)
412 no news group selected
420 no current article has been selected
422 no previous article in this group
10.1.1.3 NEXT
NEXT
The internally maintained "current article pointer" MUST be
advanced to the next article in the current news group. If no
more articles remain in the current group, an error message
MUST be returned and the current article MUST remain selected.
The internally-maintained "current article pointer" MUST be
set by this command.
A response indicating the current article number and the
message-id string MUST be returned. No text is sent in
response to this command.
10.1.1.3.1 Responses
223 n a article retrieved - request text separately (n =
article number, a = unique article id)
412 no news group selected
420 no current article has been selected
421 no next article in this group
10.2 Retrieval of Articles and Article Sections
There are two forms to the ARTICLE command (and the related
BODY, HEAD, and STAT commands), each using a different method
of specifying which article is to be retrieved. When the
ARTICLE keyword is followed by a message-id in angle brackets
("<" and ">"), the first form of the command MUST be used;
when a numeric parameter or no parameter is supplied, the
second form MUST be invoked.
An article, as defined by RFC 1036, consists of two parts: the
article headers and the article body. When responding to an
article command, the server returns the entire article
contents and does not attempt to alter or translate them in
any way.
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The HEAD and BODY commands are identical to the ARTICLE
command except that they respectively return only the article
headers or the article body of the article.
The STAT command is similar to the ARTICLE command except that
no text is returned. When selecting by message number within
a group, the STAT command MUST set the current article pointer
without sending text. The returned acknowledgment response
MUST contain the message-id, which may be of some value.
Using the STAT command to select by message-id is valid but of
questionable value, since a selection by message-id MUST NOT
alter the "current article pointer".
10.2.1 ARTICLE
ARTICLE [<message-id>|nnn]
This response displays the header, a blank line, then the body
(text) of the specified article. The optional parameter nnn is
the numeric id of an article in the current news group and
MUST be chosen from the range of articles provided when the
news group was selected. If it is omitted, the current
article is assumed. Message-id is the message id of an article
as shown in that article's header.
Please note that the internally-maintained "current article
pointer" MUST NOT be altered when the message-id argument is
used. This is both to facilitate the presentation of articles
that may be referenced within an article being read, and
because of the semantic difficulties of determining the proper
sequence and membership of an article which may have been
posted to more than one news group.
The internally-maintained "current article pointer" MUST be
set when a valid article number is specified as the argument.
This includes the case when an article number is implied by
the use of no argument.
A previously valid article number MAY not remain valid 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.
A response indicating the current article number, a message-id
string, and that text is to follow MUST be returned.
The message-id string returned is an identification string
contained within angle brackets ("<" and ">"), which is
derived from the header of the article itself. The Message-ID
header line (required by RFC 1036) from the article must be
used to supply this information. If the message-id header line
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is missing from the article, a single digit "0" (zero) should
be supplied within the angle brackets.
Since the message-id field is unique for each article, it may
be used by a news reading program to skip duplicate displays
of articles that have been posted more than once, or to more
than one news group.
10.2.1.1 Responses
220 n <a> article retrieved - head and body follow (n =
article number, <a> = message-id)
221 n <a> article retrieved - head follows
222 n <a> article retrieved - body follows
223 n <a> article retrieved - request text separately
412 no news group has been selected
420 no current article has been selected
423 no such article number in this group
430 no such article found
10.3 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.
10.3.1 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 in the
format specified by RFC 1036, and MUST include all required
header lines. After the article's header and body have been
completely sent by the client to the server, a further
response code MUST be returned to indicate success or failure
of the posting attempt.
The text forming the header and body of the message to be
posted MUST be sent by the client using the conventions for
text received from the news server: A single period (".") on a
line indicates the end of the text, with lines starting with a
period in the original text having that period doubled during
transmission.
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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 part of this specification.
10.3.1.1 Responses
240 article posted ok
340 send article to be posted. End with <CR-LF>.<CR-LF>
440 posting not allowed
441 posting failed
10.3.2 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 a response instructing the
client to send the entire article. If the server does not want
the article (if, for example, the server already has a copy of
it), a response indicating that the article is not wanted MUST
be returned.
If transmission of the article is requested, the client MUST
send the entire article, including header and body, in the
manner specified for text transmission from the server. A
response code indicating success or failure of the transferal
of the article MUST be returned by the server.
This function differs from the POST command in that it is
intended for use in transferring already-posted articles
between hosts. Normally it will not be used when the client is
a personal news reading program. In particular, this function
will invoke the server's news posting program with the
appropriate settings (flags, options, etc.) to indicate that
the forthcoming article is being forwarded from another host.
However, the server may elect not to post or forward the
article if after further examination of the article it deems
it inappropriate to do so. The 436 or 437 error codes MUST be
returned as appropriate to the situation.
Reasons for such subsequent rejection of an article may
include such problems as inappropriate news groups 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.
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10.3.2.1 Responses
235 article transferred ok
335 send article to be transferred. End with <CR-
LF>.<CR-LF>
435 article not wanted - do not send it
436 transfer failed - try again later
437 article rejected - do not try again
Because some host news posting software may not be able to
immediately render status on the whether an article is
inappropriate for posting or forwarding, an NNTP server MAY
acknowledge the successful transfer of the article and later
silently discard it. Thus an NNTP server may return the 235
acknowledgment code and later discard the received article.
10.4 The LIST Keyword
10.4.1 LIST
LIST [ACTIVE [wildmat]]
The response to the LIST keyword with no parameters returns a
list of valid news groups and associated information. Each
news group is sent as a line of text in the following format:
group last first status
where <group> is the name of the news group, <last> is the
number of the last known article currently in that news group,
<first> is the number of the first article currently in the
news group, and <status> indicates the current status of the
group on this server. Typically, the <status> will be consist
of the ASCII character `y' where posting is permitted, `n'
where posting is not permitted and `m' where postings will be
forwarded to the news group moderator by the news server.
Other status strings exist and their definition is outside the
scope of this specification.
The <first> and <last> fields will always be numeric. They
may have leading zeros. If the <last> field evaluates to less
than the <first> field, there are no articles currently on
file in the news group.
Note that posting may still be prohibited to a client although
the LIST command indicates that posting is permitted to a
particular news group. See the POST command for an explanation
of client prohibitions. The posting flag exists for each news
group because some news groups are moderated or are digests,
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and therefore cannot be posted to; that is, articles posted to
them must be mailed to a moderator who will post them for the
original poster. This is independent of the posting
permission granted to a client by the NNTP server.
Please 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 valid news groups.
If the optional matching parameter is specified, the list is
limited to only the groups that match the pattern.
Specifying a single group is usually very efficient for the
server, and multiple groups may be specified by using wildmat
patterns (described in section 5), not regular expressions.
10.4.1.1 Responses
215 list of news groups follows
10.4.2 LIST ACTIVE.TIMES
LIST ACTIVE.TIMES [wildmat]
The active.times file is maintained by some news transports
systems to contain information about the when and who created
a particular news group. The format of this file generally
includes three fields. The first field is the name of the news
group. The second is the time when this group was created on
this news server measured in seconds since January 1, 1970.
The third is the email address of the entity that created the
news group. 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 optional matching parameter is specified, the list is
limited to only the groups that match the pattern.
Specifying a single group is usually very efficient for the
server, and multiple groups may be specified by using wildmat
patterns (described in section 5), not regular expression
10.4.2.1 Responses
215 information follows
503 program error, function not performed
10.4.3 LIST DISTRIBUTIONS
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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 a
short explanation on the meaning of the value. 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.
10.4.3.1 Responses
215 information follows
503 program error, function not performed
10.4.4 LIST DISTRIB.PATS
LIST DISTRIB.PATS
The distrib.pats file is maintained by some news transport
systems to contain default values for the Distribution: line
in a news article header when posting to particular news
groups. This information could be used to provide a default
value for the Distribution: line in the header when posting an
article. The information returned contains three fields
separated by colons. The first column is a weight. The second
is a group name or a wildmat pattern that can be used to match
a group name. The third is the value of the Distribution:
line that should be used when the group name matches and the
weight value is the highest. All this processing is done by
the news posting client and not by the server itself. The
server provides this information to the client for it to use
or ignore as it chooses. 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.
10.4.4.1 Responses
215 information follows
503 program error, function not performed
10.4.5 LIST NEWSGROUPS
LIST NEWSGROUPS [wildmat]
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The newsgroups file is maintained by some news transport
systems to contain the name of each news group that is
active on the server and a short description about the
purpose of each news group. Each line in the file contains
two fields, the news group name and a short explanation of
the purpose of that news group. 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 optional
matching parameter is specified, the list is limited to only
the groups that match the pattern (no matching is done on
the group descriptions). Specifying a single group is
usually very efficient for the server, and multiple groups
may be specified by using wildmat patterns (see section 5),
not regular expressions. If nothing is matched an empty list
is returned, not an error.
10.4.5.1 Responses
215 information follows
503 program error, function not performed
10.4.6 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 news group. 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[6] 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.
Please note that 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.
10.4.6.1 Responses
215 information follows
503 program error, function not performed
10.4.7 LIST SUBSCRIPTIONS
LIST SUBSCRIPTIONS
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This command is used to get a default subscription list for
new users of this server. The order of groups is significant.
When this list is available, it is preceded by the 215
response and followed by a period on a line by itself. When
this list is not available, the server returns a 503 response
code.
10.4.7.1 Responses
215 information follows
503 program error, function not performed
10.4.8 LISTGROUP
LISTGROUP [ggg]
The LISTGROUP command is used to get a listing of all the
article numbers in a particular news group.
The optional parameter ggg is the name of the news group to
be selected (e.g. "news.software.b"). A list of valid news
groups 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.
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. If an invalid group is
specified, the previously selected group and article remain
selected. If an empty news group is selected, the "current
article pointer" may be in an indeterminate state and should
not be used.
Note that the name of the news group is not case-dependent.
It must otherwise match a news group obtained from the LIST
command or an error will result.
10.4.8.1 Responses
211 list of article numbers follow
412 Not currently in news group
10.4.9 OVER
OVER [range]
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The OVER command returns information from the overview
database for the article(s) specified. 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
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. If no argument is specified, the information
for the current article is returned. A news group must have
been selected earlier, else a 412 error response is returned.
If no articles are in the range specified, a 420 error
response is returned by the server. A 502 response will be
returned if the client only has permission to transfer
articles.
Each line of output MUST be formatted with the article number,
followed by each of the headers in the overview database or
the article itself (when the data is not available in the
overview database) for that article separated by a tab
character. The sequence of fields must be in this order:
subject, author, date, message-id, references, byte count, and
line count. Other optional fields may follow line count. Where
no data exists, a null field must be provided (i.e. the output
will have two tab characters adjacent to each other). Servers
should not output fields for articles that have been removed
since the overview database was created.
10.4.9.1 Responses
224 Overview information follows
412 No news group current selected
420 No article(s) selected
502 no permission
10.4.10 PAT
PAT header range|<message-id> [pat [pat...]]
The PAT command is used to retrieve specific headers from
specific articles, based on pattern matching on the contents
of the header.
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The required header parameter is the name of a header line
(e.g. "subject") in a news group 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. If
there are additional arguments, they are joined together
separated by a single space to form one complete pattern. If
there are no additional arguments, a wildmat "*" is the
default. Successful responses start with a 221 response
followed by the headers from all messages in which the pattern
matched the contents of the specified header line. This
includes an empty list. 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, the 430 error response
shall be returned. A 502 response shall be returned if the
client only has permission to transfer articles.
10.4.10.1 Responses
221 Header follows
430 no such article
502 no permission
11. The CONCLUSION Step
11.1 QUIT
QUIT
The server process MUST acknowledge the QUIT command and then
closes 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 SHALL gracefully cease
its attempts to service the client.
11.1.1 Responses
205 closing connection - goodbye!
12. 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 do not alter any state information, but the response
generated from the use of these keywords may provide useful
information to clients that use them.
12.1 CHARSET
CHARSET [charset]
The CHARSET command is used to change the default character
set for certain types of arguments: group names and the
contents of article headers. The argument must be the name of
a character set registered with the IANA. The server MUST
return 204 if the specified character set is supported.
Otherwise, the server MUST return 404.
When used as arguments to commands, group names and the
contents of article headers MUST be decoded before comparing
text in a character set other than US-ASCII. US-ASCII must be
supported; other character sets may be supported.
The use of CHARSET with no argument will reset the default
character set to US-ASCII.
Note that only argument processing is affected by the
character set. The server MUST not translate any part of any
multi-line response returned to the client based on the
current character set.
12.1.1 Responses
204 Character set is now charset
404 Character set charset is not supported by this
server
500 Command not supported
12.2 DATE
DATE
This command exists to help clients find out the current time
from the server's perspective. This command should not be
used as a substitute for NTP[7], but to provide information
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that might be useful when using the NEWNEWS command (see
section 12.5).
This command returns a one-line response code of 111 followed
by the GMT date and time on the server in the form
YYYYMMDDhhmmss.
12.2.1 Responses
111 YYYYMMDDhhmmss
12.3 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.
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.
12.3.1 Responses
100 help text follows
12.4 NEWGROUPS
NEWGROUPS date time [GMT] [<wildmat>]
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 closest century is assumed
as part of the year (i.e., 86 specifies 1986, 30 specifies
2030, 99 is 1999, 00 is 2000).
Time must also be specified. It must be as 6 digits HHMMSS
with HH being hours on the 24-hour clock, MM minutes 00-59,
and SS seconds 00-59. The time is assumed to be in the
server's timezone unless the token "GMT" appears in which case
both time and date are evaluated at the 0 meridian.
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An optional parameter may be specified at the end of the
command line consisting of a wildmat pattern against which new
newsgroup names can be matched enclosed in angle brackets.
Only those news groups that have names that match the pattern
(and any other criteria specified in the command) will be
returned.
Please 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.
12.4.1 Responses
231 list of new newsgroups follows
12.5 NEWNEWS
NEWNEWS newsgroups date time [GMT] [<distributions>]
A list of message-ids of articles posted or received to the
specified news group since "date" will be listed. The format
of the listing will be one message-id per line, as though text
were being sent. 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.
The newsgroups parameter must be in wildmat format.
The optional parameter "distributions" is a list of
distribution groups, enclosed in angle brackets. If
specified, the distribution portion of an article's header
will be examined for a match with the distribution categories
listed, and only those articles which have a distribution in
the list will be listed. If more than one distribution is to
be supplied, they must be separated by commas within the angle
brackets.
The use of the IHAVE, NEWNEWS, and NEWGROUPS commands to
distribute news is discussed in an earlier part of this
document.
Please 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.
12.5.1 Responses
230 list of new articles by message-id follows
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13. 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.
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) a mechanism for clients to determine a server's available
extensions
b) a registry of NNTP service extensions
The LIST EXTENSIONS command is described in section 8 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.
Associated with each such extension is a corresponding NNTP
keyword value. Each service extension registered with the IANA
MUST be defined in an RFC. Such RFCs either must be on the
standards-track or must define an IESG-approved experimental
protocol. The definition must include:
. the textual name of the NNTP service extension;
. the NNTP keyword value associated with the extension;
. the syntax and possible values of parameters associated with
the NNTP keyword value;
. any additional NNTP verbs associated with the extension
. (additional verbs will usually be, but are not required to be,
the same as the NNTP keyword value);
. any new parameters the extension associated with any other
NNTP verbs;
. how support for the extension affects the behavior of a server
and client NNTP; and,
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. the increment by which the extension is increasing the maximum
length of the any commands over that specified in this
document.
In addition, any NNTP keyword value that starts with an upper
or lower case "X" refers to a local NNTP service extension,
which is used through bilateral, rather than standardized,
agreement. Keywords beginning with "X" may not be used in a
registered service extension.
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.
Additional verbs are bound by the same rules as NNTP keywords;
specifically, verbs beginning with "X" are local extensions
that may not be registered or standardized and verbs not
beginning with "X" must always be registered.
13.1 Initial IANA Registry
The IANA's initial registry of NNTP service extensions
consists of these entries:
Service Extension NNTP Keyword(s) Added Behavior
Overview Support OVER Defined in this
LIST OVERVIEW.FMT document
Specific Article LISTGROUP Defined in this
Numbers document
Identification and AUTHINFO Defined in this
Authentication AUTHINFO GENERIC document
Character Set CHARSET Defined in this
Selection document
Header Pattern PAT Defined in this
Matching document
14. Security Considerations
The use of the AUTHINFO is optional. This command as
documented has a number of security implications. In the
original and simple forms, all passwords are passed in plain
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text and could be discovered by various forms of network or
system surveillance. The AUTHINFO GENERIC command has the
potential for the same problems if a mechanism is used that
also passes clear text passwords. RFC 1731 discusses these
issues in greater detail.
15. References
[1] Kantor, B and P. Lapsley, "Network News Transfer
Protocol", RFC-977, U.C. San Diego and U.C. Berkeley.
[2] Coded Character Set"7-bit American Standard Code for
Information Interchange, ANSI x3.4-1986.
[3] Salz, Rich, Manual Page for wildmat(3) from the INN 1.4
distribution, UUNET Technologies, Revision 1.10, April, 1992.
[4] Horton, M.R. and R. Adams, "Standard for interchange of
USENET messages", RFC-1036, AT&T Bell Laboratories and Center
for Seismic Studies, December, 1987.
[5] Meyers, J, "IMAP4 Authentication Mechanisms", RFC-1731,
Carnegie Mellon, December, 1994.
[6] Robertson, Rob, "FAQ: Overview database / NOV General
Information", ftp://ftp.uu.net/networking/news/nntp/inn/faq-
nov.Z, January, 1995.
[7] Mills, David L., "Network Time Protocol (Version 3),
Specification,Implementation and Analysis", RFC-1305,
University of Delaware, March 1992.
15.1 Notes
DEC is a registered trademark of Digital Equipment
Corporation.
UNIX is a registered trademark of the Open Group.
VMS is a registered trademark of Digital Equipment
Corporation.
15.2 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
document was influenced by the last available draft from this
working group. A special thanks to Eliot for generously
providing the original machine readable sources for that
document.
The author gratefully acknowledges the work of the Marshall
Rose & John G. Meyers in RFC 1939 and the work of the DRUMS
working group, specifically RFC 1869, which is the basis of
the NNTP extensions mechanism detailed in this document.
The author gratefully acknowledges the comments and additional
information provided by the following individuals in preparing
one of the progenitors of this document:
. Wayne Davison <davison@armory.com>
. Clive D.W. Feather <clive@demon.net>
. 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 precipitated by the work of various newsreader
authors and newsserver authors, which includes those listed
below:
. Rick Adams -- Original author of the NNTP extensions to the RN
newsreader and last maintainer of Bnews
. Stan Barber -- Original author of the NNTP extensions to the
newsreaders 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 newsreader
. Wayne Davision -- Author of the first threading extensions to the
RN newsreader (commonly called TRN).
. Geoff Huston -- Original author of ANU NEWS
. Phil Lapsey -- Original author of the UNIX reference
implementation
. Ian Lea -- Maintainer of the TIN newsreader
. Chris Lewis -- First known implementor 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 newsreader
15.3 Author's Address
Stan Barber
P.O. Box 300481
Houston, Texas, 77230
Email: <sob@academ.com>
This document expires February 5, 1998.
Barber [Page 33]