[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 RFC 2980

INTERNET-DRAFT                                               S. Barber
Expires: February 13, 2001                  Academ Consulting Services
                                                           August 2000
                         Common NNTP Extensions
                     draft-ietf-nntpext-imp-04.txt

Status of this Document

    This document is an Internet-Draft and is in full conformance
    with Section 10 of RFC 2026. Internet-Drafts are working
    documents of the Internet Engineering Task Force (IETF), its
    areas, and its working groups.  Note that other groups may
    also distribute working documents as Internet-Drafts.

    Internet-Drafts are draft documents valid for a maximum of six
    months and may be updated, replaced, or made obsolete by other
    documents at any time.  It is inappropriate to use Internet-
    Drafts as reference material or to cite them other than as
    "work in progress."

    The list of current Internet-Drafts can be accesses at
    http://www.ietf.org/ietf/1id-abstracts.txt.

    The list of Internet-Draft shadow directories can be accessed
    at http://www.ietf.org/shadow.html.

    This section will be updated with the appropriate verbiage
    from RFC 2223 should this document has been found ready for
    publication as an RFC.

    This document is a product of the NNTP Working Group, chaired
    by Stan Barber and Ned Freed.

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 extensions.

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



                                                                [Page 1]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 implementations of NNTP.
    Additionally, many other extensions, often created by
    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 authoritative 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
    prospective 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 document.

    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 categories. Examples of other
    extensions include authentication and time-of-day extensions.





                                                                [Page 2]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 inter-
    server communications. 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 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.

1.1.1  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
    implementations 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.

1.1.2.  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



                                                                [Page 3]


INTERNET DRAFT           Common NNTP Extensions              August 2000


1.2.1  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.

1.2.2.  Responses

        203 Streaming is OK
        500 Command not understood

1.3.1  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 immediately 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.

1.3.2.  Responses

        239 article transferred ok
        400 not accepting articles
        439 article transfer failed
        480 Transfer permission denied
        500 Command not understood

1.4.1  The XREPLIC command

    XREPLIC ggg:nnn[,ggg:nnn...]

    The XREPLIC command makes is possible to exactly duplicate
    the news spool structure of one server in another server. It
    first appeared in INN.




                                                                [Page 4]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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.

    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, sim-
ply
    by having the article's Xref header transferred. (In previous ver-
sions,
    this header was generated locally and stripped off on outgoing
feeds.)
    It is likely that future versions of INN will no longer support
    XREPLIC.

1.4.2.  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 brackets] is optional.  For
    example, [GMT] indicates that the triglyph GMT may present
    or omitted. A parameter that may be repeated is followed



                                                                [Page 5]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 discussed
    in detail in section 3.3 of this document.

2.1.1 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 transport software in
    addition to the active file, extensions to the LIST command
    were created to make that information available to NNTP
    newsreaders. There may be other extensions to the LIST command
    that simply return the contents of a file. This approach is
    suggested over the addition of over verbs. For example, LIST
    MOTD could be used instead of adding XMOTD.

2.1.2 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 without 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.

2.1.3 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



                                                                [Page 6]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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.

2.1.3.1 Responses

        215 information follows
        503 program error, function not performed

2.1.4 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
    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.


2.1.4.1 Responses

        215 information follows
        503 program error, function not performed

2.1.5 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



                                                                [Page 7]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 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 INN.

2.1.5.1 Responses

        215 information follows
        503 program error, function not performed

2.1.6 LIST NEWSGROUPS

    LIST NEWSGROUPS [wildmat]

    The newsgroups file is maintained by some news transport
    systems to contain 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 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 (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.

2.1.6.1 Responses

        215 information follows



                                                                [Page 8]


INTERNET DRAFT           Common NNTP Extensions              August 2000


        503 program error, function not performed

2.1.7 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 output 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.

2.1.7.1 Responses

        215 information follows
        503 program error, function not performed

2.1.8 LIST SUBSCRIPTIONS

    LIST SUBSCRIPTIONS

    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.

2.1.8.1 Responses

        215 information follows
        503 program error, function not performed




                                                                [Page 9]


INTERNET DRAFT           Common NNTP Extensions              August 2000


2.2 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" 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

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



                                                               [Page 10]


INTERNET DRAFT           Common NNTP Extensions              August 2000


        201 Hello, you can't post

2.4 XGTITLE

    XGTITLE [wildmat]

    The XGTITLE command is used to retrieve news group descriptions
    for specific 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 argument 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.

2.5.1 Responses

        481 Groups and descriptions unavailable
        282 list of groups and descriptions follows

2.6 XHDR

    XHDR header [range|<message-id>]

    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



                                                               [Page 11]


INTERNET DRAFT           Common NNTP Extensions              August 2000


                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 specified, then information
    from the current article is displayed. Successful responses
    start with a 221 response followed by a the matched headers
    from all matched messages. Each line containing matched
    headers returned by the server has an article number (or
    message ID, if a message 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 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. 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.

2.6.1 Responses

        221 Header follows
        412 No news group current selected
        420 No current article selected
        430 no such article
        502 no permission

2.7 XINDEX

    XINDEX ggg

    The XINDEX command is used to retrieve an index file in
    the format of originally created for use by the TIN[6] news
    reader.





                                                               [Page 12]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 implementations.

2.7.1 Responses

        218 tin-style index follows
        418 no tin-style index is available for this news group

2.8 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



                                                               [Page 13]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 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 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. 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 implemented. A client can use LIST OVERVIEW.FMT to determine
    what optional fields  and in which order all fields will be
    supplied by the XOVER command. 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.

2.8.1 Responses

      224 Overview information follows
      412 No news group current selected
      420 No article(s) selected
      502 no permission

2.9 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



                                                               [Page 14]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    the header. This command was first available in INN.

    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. 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 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
    is returned. A 502 response will be returned if the client only
    has permission to transfer articles.

2.9.1 Responses

        221 Header follows
        430 no such article
        502 no permission

2.10 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 article is stored separated by spaces or a response
    indicating that no article with the specified message-id
    exists. The returned data is only useful if the news client



                                                               [Page 15]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    knows the implementation details of the server. Because of
    this, it is recommended that client avoid using this command.


2.10.1  Responses

        223 path1[ path2 ...]
        430 no such article on server

2.11 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 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.

    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.

2.11.1 Responses

        224 Overview information follows
        412 No news group current selected
        420 No article(s) selected
        502 no permission



                                                               [Page 16]


INTERNET DRAFT           Common NNTP Extensions              August 2000


2.12 XTHREAD

    XTHREAD [DBINIT|THREAD]

    The XTHREAD command is used to retrieve threading information
    in format of originally created for use by the TRN[6] 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.

    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 documentation 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.

2.12.1 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 authentication information that is
    volunteered by the client. Clients must accommodate 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



                                                               [Page 17]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 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
    information 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 dotted-quad format, will
    be used. Once authenticated, the server shall generate 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



                                                               [Page 18]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    This will provide 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

    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
    requesting authorization from the client. The client must enter
    AUTHINFO SIMPLE. 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



                                                               [Page 19]


INTERNET DRAFT           Common NNTP Extensions              August 2000


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,
    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[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.





                                                               [Page 20]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 newsgroup references 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 followed 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.

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 perspective.
    At the time this command was discussed (1991-1992), the
    Network 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



                                                               [Page 21]


INTERNET DRAFT           Common NNTP Extensions              August 2000


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 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 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.

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.



                                                               [Page 22]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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.

4.0 Common Implementation Issues

    Many NNTP implementations do not follow the specifications in
    RFC 977. In this section, some common implementation issues are
    summarized.

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





                                                               [Page 23]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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 generate 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. However, the current practice is simple: article numbers
    are monotonically increasing, articles may disappear, and therefore
    the high and low water marks returned in a GROUP command should be
    treated as maximum minima, and minimum maxima, respectively.

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 complexity 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.

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



                                                               [Page 24]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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.

5.0 Further Work

    With the continued use of NNTP on the Internet, there
    remains an interest in creating an optimized transport
    protocol for server-to-server transfers and an optimized
    client protocol for client-to-server interactions. 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.

6.0 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.

7.0 References

[1]  Kantor, B and P. Lapsley, "Network News Transfer Protocol",
     RFC-977, U.C. San Diego and U.C. Berkeley, February, 1986.

[2]  Limoncelli, Tom, "Read This Before You Write a Newsreader",
     http://mars.superlink.net/tal/news-software-authors.html, June,
     1996.

[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",
     ftp://ftp.uu.net/networking/news/nntp/inn/faq-nov.Z, January, 1995.





                                                               [Page 25]


INTERNET DRAFT           Common NNTP Extensions              August 2000


[6]  Lea, Ian, "FAQ about the TIN newsreader",
     http://www.scn.de/~iain/tin/faq.html, April, 1995.

[7]  Kappesser, Peter, "[news.software.readers] trn newsreader FAQ", 2
     parts, ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/news/ soft-
     ware/readers/%5Bnews.software.readers%5D_trn_newsreader_FAQ
     %2C_part_1%3A_Basics and ftp://rtfm.mit.edu/pub/usenet-by-hierar-
     chy/news/software/ readers/%5Bnews.software.readers%5D_trn_news-
     reader_FAQ %2C_part_2%3A_Advanced, 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.

8.0 Notes

         DEC is a registered trademark of Digital Equipment Corporation.
         UNIX is a registered trademark of the X/Open Consortium.
         VMS is a registered trademark of Digital Equipment Corporation.

9.0 Acknowledgments

    The author gratefully acknowledges the comments and additional
    information provided by the following individuals:
    Wayne Davison <davison@armory.com>
    Chris Lewis <clewis@bnr.ca>
    Tom Limoncelli <tal@lucent.com>
    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



                                                               [Page 26]


INTERNET DRAFT           Common NNTP Extensions              August 2000


    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

10.0 Author's Address

    Stan Barber
    P.O. Box 300481
    Houston, Texas, 77230
    Email: <sob@academ.com>

This document expires August 13, 1998.





































                                                               [Page 27]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/