INTERNET-DRAFT S. Barber
Expires: January 7, 1999 Academ Consulting Services
August 1998
Common NNTP Extensions
draft-ietf-nntpext-imp-03.txt
Status of this Document
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Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
In this document, a number of popular extensions to the NNTP protocol
defined in RFC977 are documented and discussed. While this document is
not intended to serve as a standard of any kind, it will hopefully serve
as a reference document for future implementers of the NNTP protocol. In
the role, this document would hopefully create the possibility for some
level of interoperability among implementations that make use of exten-
sions.
Introduction
RFC977[1] defines the NNTP protocol and was released over a decade ago.
Since then, NNTP has become one of the most popular protocols in use on
the Internet. Many implementations of the protocol have been created on
many different platforms and operating systems. With the growth in use
of the protocol, work began on a revision to NNTP in 1991, but that work
did not result in a new standard protocol specification. However, many
ideas from that working group did find their way into many implementa-
tions of NNTP. Additionally, many other extensions, often created by
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newsreader authors, are also in use. This document will capture and
define all known extensions to NNTP available in official NNTP server
releases of some type as of this writing. Where possible, the server
software first implementing a particular extension will be noted. It is
the hope of the author that using this document in tandem with RFC977
will limit the addition of new extensions that essentially do the same
thing. Software developers may wish to use this document and others[2]
as a resource for the development of new software.
This document does not specify an Internet Standard of any kind. It
only attempts to document current practices. While this document may
clarify some ambiguity in RFC977, RFC977 should be regarded as authori-
tative in all cases. There are some implementations that are not
strictly RFC977 compliant and where necessary, these deviations from the
standard will be noted. This document does reflect the work of the IETF
NNTP-EXT working group chaired by Ned Freed and Stan Barber.
This document is provided to help implementers have a uniform source of
information about extensions, however, it is important for any prospec-
tive implementer to understand that the extensions listed here are NOT
part of any current standard for NNTP. In fact, some of the ones listed
in this document should not be included in new NNTP implementations as
they should no longer be used modern NNTP environments. Such commands
should be considered historic and are documented as such in this docu-
ment.
Extensions fall into three categories: transport, newsreader and other.
Transport extensions are additions to the NNTP specification that were
made specifically to move news articles from one server to another
server. Newsreader extensions are additions to the NNTP specification
that were made to assist NNTP clients in selecting and retrieving news
articles from servers. Other extensions to the NNTP specification are
those which did not specifically fall into either of the other two cate-
gories. Examples of other extensions include authentication and time-of-
day extensions.
For each command, the format of section 3 of RFC977 will be used.
1. Transport Extensions
A transport extension is one which is primarily used in interserver com-
munications. Following are the descriptions of each transport extension
commands and the responses which will be returned by those commands.
Each command 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 shown in [square brack-
ets] is optional. For example, [GMT] indicates that the triglyph GMT
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may present or omitted. A parameter that may be repeated is followed by
an ellipsis.
1.1. The CHECK command
CHECK <message-id>
CHECK is used by a peer to discover if the article with the specified
message-id should be sent to the server using the TAKETHIS command. The
peer does not have to wait for a response from the server before sending
the next command.
>From using the responses to the sequence of CHECK commands, a list of
articles to be sent can be constructed for subsequent use by the
TAKETHIS command.
The use of the CHECK command for streaming is optional. Some implementa-
tions will directly use the TAKETHIS command and send all articles in
the send queue on that peer for the server.
On some implementations, the use of the CHECK command is not permitted
when the server is in slave mode (via the SLAVE command).
Responses that are of the form X3X must specify the message-id in the
response.
1.1.1. Responses
238 no such article found, please send it to me
400 not accepting articles
431 try sending it again later
438 already have it, please don't send it to me
480 Transfer permission denied
500 Command not understood
1.2. The MODE STREAM command
MODE STREAM
MODE STREAM is used by a peer to indicate to the server that it would
like to suspend the lock step conversational nature of NNTP and send
commands in streams. This command should be used before TAKETHIS and
CHECK. See the section on the commands TAKETHIS and CHECK for more
details.
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1.2.1. Responses
203 Streaming is OK
500 Command not understood
1.3. The TAKETHIS command
TAKETHIS <message-id>
TAKETHIS is used to send articles to a server when in streaming mode.
The entire article (header and body, in that sequence) is sent immedi-
ately after the peer sends the TAKETHIS command. The peer does not have
to wait for a response from the server before sending the next command
and the associated article.
During transmission of the article, the peer should send the entire
article, including header and body, in the manner specified for text
transmission from the server. See RFC977, Section 2.4.1 for details.
Responses that are of the form X3X must specify the message-id in the
response.
1.3.1. Responses
239 article transferred ok
400 not accepting articles
439 article transfer failed
480 Transfer permission denied
500 Command not understood
1.4. The XREPLIC command
XREPLIC ggg:nnn[,ggg:nnn...]
The XREPLIC command makes it possible to exactly duplicate the news
spool structure of one server in another server. It first appeared in
INN.
This command works similarly to the IHAVE command as specified in
RFC977. The same response codes are used. The command line arguments
consist of entries separated by a single comma. Each entry consists of a
news group name, a colon, and an article number. If the server responds
with a 335 response, the article should be filed in the news group(s)
and article number(s) specified in the XREPLIC command line. If the
server cannot do successfully install the article once it has accepted
it, a 436 or 437 response code can be used to indicate the failure.
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This command should only be used when the receiving server is being fed
by only one other server. It is likely that when used with servers that
have multiple feeds that this command will frequently fail.
XREPLIC slaving has been deprecated in INN version 1.7.2 and later. INN
now has the ability to slave servers via transparent means, simply by
having the article's Xref header transferred. (In previous versions,
this header was generated locally and stripped off on outgoing feeds.)
It is likely that future versions of INN will no longer support XREPLIC.
1.4.1. 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
2. Newsreader Extensions
Newsreader extensions are those which are primarily used by newsreading
clients. Following are the descriptions of each newsreader extension
commands and the responses which will be returned by those commands.
Each command 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 shown in [square brack-
ets] 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,
notably <message-id>, is case specific. See RFC 1036 for these details.
Also, certain commands make use of a pattern for selection of multiple
news groups. The pattern in all cases is based on the wildmat[4] format
introduced by Rich Salz in 1986. Arguments expected to be in wildmat
format will be represented by the string wildmat. This format is dis-
cussed in detail in section 3.3 of this document.
2.1. Extensions to the LIST command
The original LIST command took no arguments in RFC977 and returned the
contents of the active file in a specific format. Since the original
newsreaders made use of other information available in the news trans-
port software in addition to the active file, extensions to the LIST
command were created to make that information available to NNTP news-
readers. There may be other extensions to the LIST command that simply
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return the contents of a file. This approach is suggested over the addi-
tion of over verbs. For example, LIST MOTD could be used instead of
adding XMOTD.
2.1.1. LIST ACTIVE
LIST ACTIVE [wildmat]
LIST ACTIVE is exactly the same as the LIST command specified in RFC977.
The responses and the format should exactly match the LIST command with-
out arguments. 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 later in
this document), not regular expressions. If nothing is matched an empty
list is returned, not an error. This command first appeared in the UNIX
reference version.
2.1.2. LIST ACTIVE.TIMES
LIST ACTIVE.TIMES
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 include 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. This command first appeared in the
UNIX reference version.
2.1.2.1. Responses
215 information follows
503 program error, function not performed
2.1.3. 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 a short explanation on the meaning of the
value. When executed, the information is displayed following the 215
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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. This command first appeared in the UNIX
reference version.
2.1.3.1. Responses
215 information follows
503 program error, function not performed
2.1.4. 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 involves three fields
separated by colons. The first column is a weight. The second is a
group name or a pattern that can be used to match a group name in the
wildmat format. 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 just provides this information to the
client for it to use or ignore as it chooses. When executed, the infor-
mation is displayed following the 215 response. When display is com-
pleted, the server will send a period on a line by itself. If the infor-
mation is not available, the server will return the 503 error response.
This command first appeared in INN.
2.1.4.1. Responses
215 information follows
503 program error, function not performed
2.1.5. LIST NEWSGROUPS
LIST NEWSGROUPS [wildmat]
The newsgroups file is maintained by some news transport systems to con-
tain the name of each news group which 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 dis-
played following the 215 response. When display is completed, the server
will send a period on a line by itself. If the information is not avail-
able, the server will return the 503 response. If the optional matching
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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 (similar to
file globbing), not regular expressions. If nothing is matched an empty
list is returned, not an error.
When the optional parameter is specified, this command is equivalent to
the XGTITLE command, though the response code are different.
2.1.5.1. Responses
215 information follows
503 program error, function not performed
2.1.6. 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[5] 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 out-
put returned by the server.
Many newsreaders work better if Xref: is one of the optional fields.
It is STRONGLY recommended that this command be implemented in any
server that implements the XOVER command. See section 2.8 for more
details about the XOVER command.
2.1.6.1. Responses
215 information follows
503 program error, function not performed
2.1.7. 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 fol-
lowed by a period on a line by itself. When this list is not available,
the server returns a 503 response code.
2.1.7.1. Responses
215 information follows
503 program error, function not performed
2.2. LISTGROUP
LISTGROUP [ggg]
The LISTGROUP command is used to get a listing of all the article num-
bers 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" is 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" is 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.
2.2.1. Responses
211 list of article numbers follow
412 Not currently in newsgroup
502 no permission
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2.3. MODE READER
MODE READER is used by the client to indicate to the server that it is a
news reading client. Some implementations make use of this information
to reconfigure themselves for better performance in responding to news
reader commands. This command can be contrasted with the SLAVE command
in RFC 977, which was not widely implemented. MODE READER was first
available in INN.
2.3.1. Responses
200 Hello, you can post
201 Hello, you can't post
2.4. XGTITLE
XGTITLE [wildmat]
The XGTITLE command is used to retrieve news group descriptions for spe-
cific news groups.
This extension first appeared in ANU-NEWS, an NNTP implementation for
DEC's VMS. The optional parameter is a pattern in wildmat format. When
executed, a 282 response is given followed by lines that have two
fields, the news group name (which matches the pattern in the argument)
and a short explanation of the purpose of the news group. When no argu-
ment is specified, the default argument is the current group name. When
display is completed, the server sends a period on a line by itself.
Please note that this command and the LIST NEWSGROUP command provide the
same functionality with different response codes.
Since this command provides the same functionality as LIST NEWSGROUP it
is suggested that this extension be deprecated and no longer be used in
newsreading clients.
Note that there is a conflict in one of the response codes from XGTITLE
and some of the authentication extensions.
2.4.1. Responses
481 Groups and descriptions unavailable
282 list of groups and descriptions follows
2.5. XHDR
XHDR header [range|<message-id>]
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The XHDR command is used to retrieve specific headers from specific
articles.
The required 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
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
The optional message-id argument indicates a specific article. The range
and message-id arguments are mutually exclusive. If no argument is spec-
ified, then information from the current article is displayed. Success-
ful responses start with a 221 response followed by a the matched head-
ers from all matched messages. Each line containing matched headers
returned by the server has an article number (or message ID, if a mes-
sage ID was specified in the command), then one or more spaces, then the
value of the requested header in that article. Once the output is com-
plete, 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 is
returned. If a range is specified, 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.
Some implementations will return "(none)" followed by a period on a line
by itself if no headers match in any of the articles searched. Others
return the 221 response code followed by a period on a line by itself.
The XHDR command has been available in the UNIX reference implementation
from its first release. However, until now, it has been documented only
in the source for the server.
2.5.1. Responses
221 Header follows
412 No news group current selected
420 No current article selected
430 no such article
502 no permission
2.6. XINDEX
XINDEX ggg
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The XINDEX command is used to retrieve an index file in the format of
originally created for use by the TIN[6] news reader.
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
from the LIST command.
The successful selection response will return index file in the format
used by the TIN news reader 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" is 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" is 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.
The format of the tin-style index file is discussed in the documentation
for the TIN newsreader. Since more recent versions of TIN support the
news overview (NOV) format, it is recommended that this extension become
historic and no longer be used in current servers or future implementa-
tions.
2.6.1. Responses
218 tin-style index follows
418 no tin-style index is available for this news group
2.7. XOVER
XOVER [range]
The XOVER command returns information from the overview database for the
article(s) specified. This command was originally suggested as part of
the OVERVIEW work described in "The Design of a Common Newsgroup
Overview Database for Newsreaders" by Geoff Collyer. This document is
distributed in the Cnews distribution.
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. If no argument is speci-
fied, 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 will 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 arti-
cle 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. Other
optional fields may follow line count. These fields are specified by
examining the response to the LIST OVERVIEW.FMT command. 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 XOVER database was created.
The LIST OVERVIEW.FMT command should be implemented if XOVER is imple-
mented. A client can use LIST OVERVIEW.FMT to determine what optional
fields and in which order all fields will be supplied by the XOVER com-
mand. See Section 2.1.7 for more details about the LIST OVERVIEW.FMT
command.
Note that any tab and end-of-line characters in any header data that is
returned will be converted to a space character.
2.7.1. Responses
224 Overview information follows
412 No news group current selected
420 No article(s) selected
502 no permission
2.8. XPAT
XPAT header range|<message-id> pat [pat...]
The XPAT command is used to retrieve specific headers from specific
articles, based on pattern matching on the contents of the header. This
command was first available in INN.
The required header parameter is the name of a header line (e.g. "sub-
ject") in a news group article. See RFC-1036 for a list of valid header
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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. At least one pattern in
wildmat must be specified as well. If there are additional arguments the
are joined together separated by a single space to form one complete
pattern. Successful responses start with a 221 response followed by a
the headers from all messages in which the pattern matched the contents
of the specified header line. This includes an empty list. Once the out-
put 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 is returned. A 502 response will be returned if the client only
has permission to transfer articles.
2.8.1. Responses
221 Header follows
430 no such article
502 no permission
2.9. The XPATH command
XPATH <message-id>
The XPATH command is used to determine the filenames in which an article
is filed. It first appeared in INN.
The required parameter message-id is the message id of an article as
shown in that article's message-id header. According to RFC 1036[3], all
message ids for all articles within the netnews environment are unique,
but articles may be crossposted to multiple groups. The response to an
XPATH command will include a listing of all filenames in which an arti-
cle is stored separated by spaces or a response indicating that no arti-
cle with the specified message-id exists. The returned data is only use-
ful if the news client knows the implementation details of the server.
Because of this, it is recommended that client avoid using this command.
2.9.1. Responses
223 path1[ path2 ...]
430 no such article on server
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2.10. The XROVER command
XROVER [range]
The XROVER command returns reference information from the overview
database for the article(s) specified. This command first appeared in
the Unix reference implementation.
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
Successful responses start with a 224 response followed by the contents
of reference information for all matched messages. Once the output is
complete, a period is sent on a line by itself. If no argument is speci-
fied, 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.
The output will be formatted with the article number, followed by the
contents of the References: line for that article, but does not contain
the field name itself.
This command provides the same basic functionality as using the XHDR
command and "references" as the header argument.
2.10.1. Responses
224 Overview information follows
412 No news group current selected
420 No article(s) selected
502 no permission
2.11. XTHREAD
XTHREAD [DBINIT|THREAD]
The XTHREAD command is used to retrieve threading information in format
of originally created for use by the TRN[7] news reader.
The command XTHREAD DBINIT may be issued prior to entering any groups to
see if a thread database exists. If it does, the database's byte order
and version number are returned as binary data.
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If no parameter is given, XTHREAD THREAD is assumed.
To use XTHREAD THREAD, a news group must have been selected earlier,
else a 412 error response is returned.
A 502 response will be returned if the client only has permission to
transfer articles. A 503 response is returned if the threading files are
not available.
The format of the trn-style thread format is discussed in the documenta-
tion for the TRN newsreader. Since more recent versions of TRN support
the news overview (NOV) format, it is recommended that this extension
become historic and no longer be used in current servers or future
implementations.
2.11.1. Responses
288 Binary data to follow
412 No newsgroup current selected
502 No permission
503 program error, function not performed
3. Other Extensions
3.1. 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 authentica-
tion information that is volunteered by the client. Clients must accom-
modate servers that reject any authentication information volunteered by
the client.
There are three forms of AUTHINFO in use. The original version, an NNTP
v2 revision called AUTHINFO SIMPLE and a more recent version which is
called AUTHINFO GENERIC.
3.1.1. Original AUTHINFO
AUTHINFO USER username
AUTHINFO PASS password
The original AUTHINFO is used to identify a specific entity to the
server using a simple username/password combination. It first appeared
in the UNIX reference implementation.
When authorization is required, the server will send a 480 response
requesting authorization from the client. The client must enter AUTHINFO
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USER followed by the username. Once sent, the server will cache the
username and may send a 381 response requesting the password associated
with that username. Should the server request a password using the 381
respose, the client must enter AUTHINFO PASS followed by a password and
the server will then check the authentication database to see if the
username/password combination is valid. If the combination is valid or
if no password is required, the server will return a 281 response. The
client should then retry the original command to which the server
responded with the 480 response. The command should then be processed by
the server normally. If the combination is not valid, the server will
return a 502 response.
Clients must provide authentication when requested by the server. It is
possible that some implementations will accept authentication informa-
tion at the beginning of a session, but this was not the original intent
of the specification. If a client attempts to reauthenticate, the server
may return 482 response indicating that the new authentication data is
rejected by the server. The 482 code will also be returned when the
AUTHINFO commands are not entered in the correct sequence (like two
AUTHINFO USERs in a row, or AUTHINFO PASS preceding AUTHINFO USER).
All information is passed in cleartext.
When authentication succeeds, the server will create an email address
for the client from the user name supplied in the AUTHINFO USER command
and the hostname generated by a reverse lookup on the IP address of the
client. If the reverse lookup fails, the IP address, represented in dot-
ted-quad format, will be used. Once authenticated, the server shall gen-
erate a Sender: line using the email address provided by authentication
if it does not match the client-supplied From: line. Additionally, the
server should log the event, including the email address This will pro-
vide a means by which subsequent statistics generation can associate
newsgroup references with unique entities - not necessarily by name.
3.1.1.1. Responses
281 Authentication accepted
381 More authentication information required
480 Authentication required
482 Authentication rejected
502 No permission
3.1.2. AUTHINFO SIMPLE
AUTHINFO SIMPLE
user password
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This version of AUTHINFO was part of a proposed NNTP V2 specification,
which was started in 1991 but never completed, and is implemented in
some servers and clients. It is a refinement of the original AUTHINFO
and provides the same basic functionality, but the sequence of commands
is much simpler.
When authorization is required, the server sends a 450 response request-
ing authorization from the client. The client must enter AUTHINFO SIM-
PLE. If the server will accept this form of authentication, the server
responds with a 350 response. The client must then send the username
followed by one or more space characters followed by the password. If
accepted, the server returns a 250 response and the client should then
retry the original command to which the server responded with the 450
response. The command should then be processed by the server normally.
If the combination is not valid, the server will return a 452 response.
Note that the response codes used here were part of the proposed NNTP V2
specification and are violations of RFC 977. It is recommended that
this command not be implemented, but use either or both of the other
forms of AUTHINFO if such functionality if required.
3.1.2.1. Responses
250 Authorization accepted
350 Continue with authorization sequence
450 Authorization required for this command
452 Authorization rejected
3.1.3. 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 480 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, simi-
larly, 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
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protocols are not included in this document, but are similar in struc-
ture to those referenced in RFC 1731[8] 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 AUTHINFO USER command.
If the requested authenticator capability is not found, the server
returns the 503 response code.
If there is some other unspecified server program error, the server
returns the 500 response code.
The authenticators converse using their protocol until complete. If the
authentication succeeds, the server authenticator will terminate with a
281, and the client can continue by reissuing the command that prompted
the 380. If the authentication fails, the server will respond with a
502.
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 poten-
tially 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 newsgroup refer-
ences with unique entities - not necessarily by name.
Some implementations make it possible to obtain a list of authentication
procedures available by sending the server AUTHINFO GENERIC with no
arguments. The server then returns a list of supported mechanisms fol-
lowed by a period on a line by itself.
3.1.3.1. Responses
281 Authentication succeeded
480 Authentication required
500 Command not understood
501 Command not supported
502 No permission
503 Program error, function not performed
nnn authenticator-specific protocol.
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3.2. DATE
DATE
The first NNTP working group discussed and proposed a syntax for this
command to help clients find out the current time from the server's per-
spective. At the time this command was discussed (1991-1992), the Net-
work Time Protocol [9] (NTP) was not yet in wide use and there was also
some concern that small systems may not be able to make effective use of
NTP.
This command returns a one-line response code of 111 followed by the
GMT date and time on the server in the form YYYYMMDDhhmmss.
3.2.1. Responses
111 YYYYMMDDhhmmss
3.3. The WILDMAT Format
The WILDMAT format was first developed by Rich Salz based on the format
used in the UNIX "find" command to articulate file names. It was devel-
oped 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) char-
acter, or as any combination of lists and ranges. The dash can also be
included in the set as a character it if 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 a 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.
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3.3.1. 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.
3.4. Additional Headers
Many NNTP implementations add headers to Usenet articles when then are
POSTed via NNTP. These headers are discussed in this section. None of
these headers conflict with those specified in RFC 1036 and should be
passed unchanged by Usenet transports conforming to RFC 1036.
3.4.1. NNTP-Posting-Host
This line is added to the header of a posted article by the server. The
contents of the header is either the IP address or the fully qualified
domain name of the client host posting the article. The fully qualified
domain name should be determined by doing a reverse lookup in the DNS on
the IP address of the client. If the client article contains this line,
it is removed by the server before acceptance of the article by the
Usenet transport system.
This header provides some idea of the actual host posting the article as
opposed to information in the Sender or From lines that may be present
in the article. This is not a fool-proof methodology since reverse
lookups in the DNS are vulnerable to certain types of spoofing, but such
discussions are outside the scope of this document.
3.4.2. X-Newsreader and others
There are other lines that are added by clients as well. Most of these
indicate the type of newsreader software that is posting the article.
4. Common Implementation Issues
Many NNTP implementations do not follow the specifications in RFC 977.
In this section, some common implementation issues are summarized.
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4.1. The Response to the LIST command
RFC 977 says that the fourth field of the "list of valid newsgroups
associated information" returned must be "either 'y' or 'n' indicating
whether posting to this newsgroup is allowed ('y') or prohibited ('n').
Most implementations simply output the exact contents of the transport
system's active newsgroup list. For more implementations, the fourth
field usually has more values that 'y' or 'n'.
4.2. The Required Headers in an Article and the POST command
RFC 977 notes in section 3.10.1 that articles presented "should include
all required header lines." In fact, modern implementations only require
From, Subject, and Newsgroups header lines and will supply the rest;
further, many implementers believe that it is best for clients to gener-
ate as few headers as possible, since clients often do not format other
headers correctly.
This implementation behavior is consistent with both Bnews and Cnews
which would supply missing headers for articles directly submitted to
them.
4.3. Article Numbering
RFC977 does not directly address the rules concerning articles number,
but the current practice is simple. New articles have monotonically
increasing numbers within a group, and articles may disappear or be
reinstated at any time (and thus between any two commands). The low
water mark returned in a GROUP command is an absolute minimum (though
that article might not exist), but there could be articles above the
high water mark (that have appeared since the GROUP command was issued),
and so it should be treated as advisory only. Similarly, the results of
sequences of NEXT and LAST commands might not be consistent.
4.4. Availability of commands defined in RFC977
Some implementations permit administrators to disable commands defined
RFC977. Some implementations have some set of commands disabled by
default. This means that client implementations cannot depend on the
availability of the disabled set of commands. This increases the com-
plexity of the client and does not encourage implementors to optimize
the implementation of commands that don't perform well.
NEWNEWS is one of the commands frequently disabled by news server man-
agers.
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4.5. The Distribution header and NEWNEWS
In section 12.4 of RFC977, the optional distributions argument is
described. This argument, according to RFC977, would limit the responses
to articles that were in newsgroups with prefixes that matched the
optional distributions argument.
Some implementations implement this by matching the Distributions header
in articles to the distribution argument. Others do the match against
segments of the newsgroup's name.
This variation is probably best explained by the evolution of the USENET
article format. At the time RFC977 was specified, the newsgroup name
defined how the group was distributed thoughout USENET. RFC1036 changed
this convention. So, those that are strictly implementing RFC977 would
match the newsgroup name prefix against the distribution arguement and
only display matches. Those that implement against the intent of the
command (as modified by the redefinition of the article format)would
match the Distributions header against the distribution argument and
only display those matches.
5. Further Work
With the continued use of NNTP on the Internet, there remains an inter-
est in creating an optimized transport protocol for server-to-server
transfers and an optimized client protocol for client-to-server interac-
tions. There is also considerable interest is building better mechanisms
to provide audit information on which news groups are being read by
which users.
An IETF working group has been formed and it is the hope of this author
that these issues will be addressed in that forum.
6. 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 plaintext 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 cleartext passwords. RFC 1731[8] discusses these issues in
greater detail.
7. References
[1] Kantor, B and P. Lapsley, "Network News Transfer Protocol",
RFC-977, U.C. San Diego and U.C. Berkeley, February, 1986.
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[2] Limoncelli, Tom, "Read This Before You Write a Newsreader",
http://mars.superlink.net/tal/writings/news-software-authors.html,
May, 1995.
[3] Horton, M.R. and R. Adams, "Standard for interchange of USENET mes-
sages", RFC-1036, AT&T Bell Laboratories and Center for Seismic
Studies, December, 1987.
[4] Salz, Rich, Manual Page for wildmat(3) from the INN 1.4 distribu-
tion, UUNET Technologies, Revision 1.10, April, 1992.
[5] Robertson, Rob, "FAQ: Overview database / NOV General Information",
http://web.infoave.net/~anonymous/unix/FAQ-NOV, January, 1995.
[6] Lea, Iain, "FAQ about the TIN newsreader", http://nimbus.tem-
ple.edu/pds/tinfaq.html, May 1995. [More recent info about TIN is
at http://www.tin.org.]
[7] Kappesser, Peter, "[news.software.readers] trn newsreader FAQ", 2
parts, http://www.faqs.org/faqs/usenet/software/trn-
faq/part1/index.html and http://www.faqs.org/faqs/usenet/soft-
ware/trn-faq/part2/index.html February, 1995.
[8] Meyers, J, "IMAP4 Authentication Mechanisms", RFC-1731, Carnegie
Mellon, December, 1994.
[9] Mills, David L., "Network Time Protocol (Version 3), Specification,
Implementation and Analysis", RFC-1305, University of Delaware,
March 1992.
8. Notes
DEC is a registered trademark of Compaq Computer Corporation.
UNIX is a registered trademark of the Open Group.
VMS is a registered trademark of Compaq Computer Corporation.
9. Acknowledgments
The author gratefully acknowledges the comments and additional informa-
tion provided by the following individuals:
Wayne Davison <davison@clari.net>
Clive D.W. Feather <clive@demon.net>
Chris Lewis <clewis@bnr.ca>
Tom Limoncelli <tal@lucent.com>
Eric Schnoebelen <eric@egsner.cirr.com>
Rich Salz <rsalz@osf.org>
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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 Davison -- 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 implementa-
tion of NNTP
Iain Lea -- Original author 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
10. Author's Address
Stan Barber
P.O. Box 300481
Houston, Texas, 77230
Email: <sob@academ.com>
This document expires January 7, 1999
11. Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document and translations of it may be copied and furnished to oth-
ers, and derivative works that comment on or otherwise explain it or
assist in its implmentation may be prepared, copied, published and dis-
tributed, in whole or in part, without restriction of any kind, provided
that the above copyright notice and this paragraph are included on all
such copies and derivative works. However, this document itself may not
be modified in any way, such as by removing the copyright notice or ref-
erences to the Internet Society or other Internet organizations, except
as needed for the purpose of developing Internet standards in which case
the procedures for copyrights defined in the Internet Standards process
must be followed, or as required to translate it into languages other
than English.
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The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FIT-
NESS FOR A PARTICULAR PURPOSE.
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