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    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
  
                          Network News Transport Protocol
                           draft-ietf-nntpext-base-14.txt
  
     1. 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 Ned
        Freed and Stan Barber.
  
     2. Abstract
  
        The Network News Transport Protocol has been in use in the Internet
        for a decade and remains one of the most popular protocols (by volume)
        in use today. This document is a replacement for RFC 977 and
        officially updates the protocol specification. It clarifies some
        vagueness in RFC 977, includes some new base functionality and
        provides a specific mechanism to add standardized extensions to NNTP.
  
     3. Introduction
  
        This document specifies the Network News Transport Protocol (NNTP),
        which is used for the distribution, inquiry, retrieval, and posting of
        net news articles using a reliable stream-based mechanism. For news
        reading clients, NNTP enables retrieval of news articles that are
        stored in a central database, giving subscribers the ability to select
        only those articles they wish to read.
  
        The netnews model provides for indexing, cross-referencing, and
        expiration of aged messages. For server-to-server interaction, NNTP is
        designed for efficient transmission of net news articles over a
        reliable full duplex communication method.
  
        Every attempt is made to insure that the protocol specification in
        this document is compatible with the version specified in RFC
        977[[1]. However, this version does not support the ill-defined SLAVE
        command and permits four digit years to be specified in the NEWNEWS
        and NEWGROUPS commands. It changes the default character set to
        UTF-8[2] instead of US-ASCII[3]. It also extends the newsgroup
        name matching capabilities already documented in RFC 977.
  
        Generally, new functionality is available using new keywords. Part of
        that new functionality involves a mechanism to discover what new
        functionality is available to clients from a server.
        This mechanism can also be used to add more functionality as needs
        merit such additions.
  
        The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
        "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
        document are to be interpreted as described in RFC 2119[4].
        An implementation is not compliant if it fails to satisfy one or more
        of the MUST requirements for this protocol.  An implementation that
  
    Barber                                                          Page  [1]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        satisfies all the MUST and all the SHOULD requirements for its
        protocols is said to be "unconditionally compliant"; one that
        satisfies all the MUST requirements but not all the SHOULD
        requirements for NNTP is said to be "conditionally compliant".
  
        For the remainder of this memo, the term "client host" refers to a
        host making use of the NNTP service, while the term "server host"
        refers to a host that offers the NNTP service. In addition, where
        examples of interactions between a client host and a server host are
        provided a "[C]" will be used to represent the client host and a "[S]"
        will be used to represent the server host.
  
        For the remainder of this memo, responses will be described in tables
        listing the required format of a response followed by the meaning that
        should be ascribed to that response.
  
     4. Basic Operation.
  
        Every NNTP session MUST involve the following in this order:
        CONNECTION
        GREETING
        DISCONNECTION
  
        Other steps may occur between the GREETING and DISCONNECTION step.
  
        They are:
  
        CAPABILITIES DISCOVERY
        NEWS EXCHANGE
        CONCLUSION
  
        NNTP operates over any reliable data stream 8-bit-wide channel. When
        running over TCP/IP, the official port for the NNTP service is 119.
        Initially, the server host starts the NNTP service by listening on a
        TCP port.  When a client host wishes to make use of the service, it
        MUST establish a TCP connection with the server host by connecting to
        that host on the same port on which the server is listening. This is
        the CONNECTION step.  When the connection is established, the NNTP
        server host MUST send a greeting. This is the GREETING step. The
        client host and server host SHOULD then exchange commands and
        responses (respectively) until the connection is closed or aborted.
  
        This final step is called the DISCONNECTION step.
        If there is a CONCLUSION step, it MUST immediately precede the
        DISCONNECTION step. There MUST be only one CONNECTION, CONCLUSION and
        DISCONNECTION step for each NNTP session. All other steps MAY be
        repeated as needed. For example, the GREETING step may be repeated if
        the client makes use of the MODE READER command (See Section 7.2 for
        more on the MODE READER command).
  
        The character set for all NNTP commands is UTF-8. Commands in the NNTP
        MUST consist of an US-ASCII case-insensitive keyword, which MAY be
        followed by one or more arguments.  An US-ASCII CRLF pair MUST
        terminate all commands. Multiple commands MUST NOT be on the same
        line. Keywords MUST consist of printable US-ASCII characters.  Unless
        otherwise noted elsewhere in this document, arguments SHOULD consist
        of printable US-ASCII characters. Keywords and arguments MUST be each
        separated by one or more US-ASCII SPACE or US-ASCII TAB characters.
        Keywords MUST be at least three US-ASCII characters and MUST NOT
        exceed 12 US-ASCII characters.  Command lines MUST NOT exceed 512
        octets, which includes the terminating US-ASCII CRLF pair. Arguments
        MUST NOT exceed 497 octets.
  
        Each response MUST start with a three-digit response code that is
        sufficient to distinguish all responses. Certain valid responses are
        defined to be multi-line; for all others, the response is contained in
        a single line. All multi-line responses MUST adhere to the following
        format:
  
        1.  The repsonse consists of a sequence of one or more "lines", each
          being a stream of octets ending with 0x0D 0x0A (US-ASCII CRLF).
          Apart from those line endings, the stream MUST NOT include the
          octets 0x00, 0x0A, or 0x0D (US-ASCII NUL, LF, and CR).
  
   Barber                                                            Page [2]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        2.  The first such line contains the response code as with a single
          line response.
        3.  If any subsequent line begins with the "termination octet" (0x2E
          or US_ASCII "."), that line MUST be "byte-stuffed" by pre-pending an
          additional termination octet (0x2E) to that line of the response.
        4.  The lines of the response MUST be followed by a terminating line
          consisting of a single termination octet (0x2E or US_ASCII
          ".")followed by CRLF in the normal way. Thus a multi-line response
          is always terminated with the five octets "CRLF.CRLF" (in US-ASCII).
        5.  There is NO limit on the length of a line.
        6.  When interpreting a multi-line response, the "byte stuffing" MUST
          be undone; i.e. the client MUST ensure that, in any line beginning
          with the termination octet followed by octets other than US-ASCII
          CRLF, that initial termination octet is disregarded.
        7.  Likewise, the terminating line ".CRLF" (in US-ASCII) MUST NOT be
          considered part of the multi-line response; i.e. the client MUST
          ensure that any line beginning with the termination octet followed
          immediately by US-ASCII CRLF is disregarded; (the first CRLF of the
          terminating "CRLF.CRLF" is, of course, part of the last line of the
          response).
  
        NOTE: Texts using encodings (such as UTF-16 or UTF-32) that may
        contain the NUL octet or the CR or LF octets in contexts other than
        the CRLF line ending cannot be reliably conveyed in the above format.
        Note also that, although this standard does not limit the length of a
        line in any way, the standards that define the format of articles may
        do so.
  
        An NNTP server MAY have an inactivity autologout timer.  Such a timer
        SHOULD be of at least three minutes duration, with the exception that
        there MAY be a shorter limit on how long the server is willing to wait
        for the first command from the client.  The receipt of any command
        from the client during the timer interval SHOULD suffice to reset the
        autologout timer.  Similarly, the receipt of any significant amount of
        data from the client while in the midst of sending a multilane message
        to the server (such as during a POST or IHAVE command) SHOULD suffice
        to reset the autologout timer.  When the timer expires, the server
        SHOULD close the TCP connection without sending any response to the
        client, including when the client is in the middle of sending a
        multi-line message to the server.
  
     4.1  Response Codes
  
        Each response MUST begin with a three-digit status indicator. These
        are status reports from the server and indicate the response to the
        last command received from the client.
  
        The first digit of the response broadly indicates the success,
        failure, or progress of the previous command.
  
        1xx - Informative message
        2xx - Command ok
        3xx - Command ok so far, send the rest of it.
        4xx - Command was correct, but couldn't be performed for some reason.
        5xx - Command unimplemented, or incorrect, or a serious program error
          occurred.
  
        The next digit in the code indicates the function response category.
        x0x - Connection, setup, and miscellaneous messages
        x1x - Newsgroup selection
        x2x - Article selection
        x3x - Distribution functions
        x4x - Posting
        x8x - Reserved for authentication and authorization extensions
        x9x - Reserved for private use (non-standard extensions)
  
        Certain responses contain parameters such as numbers and names in
        addition to the status indicator. In those cases, the number and type
        of such parameters is fixed for each response code to simplify
        interpretation by the client (any extension MUST follow this principle
        as well). In all other cases, the client MUST only use the status
        indicator itself to determine the nature of the response. The exact
  
    Barber                                                           Page [3]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
  
        response codes that can be returned in response to a given command are
        detailed in the description of the keyword that is the first part of
        the command.
  
        Parameters MUST be separated from the numeric status indicator and
        from each other by a single US-ASCII space. All numeric parameters
        MUST be in base 10 (decimal) format, and MAY have leading zeros.
  
        String parameters MUST contain at least one character and MUST NOT
        contain US-ASCII spaces, CR, LF, or tab). The server MAY add any text
        after the response code or last parameter as appropriate, and the
        client MUST NOT make decisions based on this text. Such text MUST be
        separated from the numeric status indicator or the last parameter by
        at least one US-ASCII space.
  
        The server MUST respond to any command with the appropriate generic
        response (given in section 4.1.1) if it represents the situation.
        Otherwise, each recognized command MUST return one of the response
        codes specifically listed in its description or in an extension. A
        server MAY provide extensions to this specification, including new
        commands, new features of existing commands, and other ways of
        changing the internal state of the server. However, the server MUST
        NOT produce any other responses to a client that does not invoke any
        of the additional features. (Therefore a client that restricts itself
        to this specification will only receive the responses that are
        listed).
  
        If a client receives an unexpected response, it SHOULD use the first
        digit of the response to determine the result. For example, an
        unexpected 2xx should be taken as success and an unexpected 4xx or 5xx
        as failure.
  
        Response codes not specified in this standard MAY be used for any
        installation-specific additional commands also not specified. These
        SHOULD be chosen to fit the pattern of x9x specified above.
        Neither this document nor any extension registered with IANA (see
        section 12) will specify any response codes of the x9x pattern.
        (Implementers of extensions are accordingly cautioned not to use such
        responses for extensions that may subsequently be submitted for
        registration.)
  
     4.1.1 Generic Response Codes
  
        The server MUST respond to any command with the appropriate one of the
        following generic responses if it represents the situation.
        If the command is not recognized, or it is an optional command or
        extension that is not implemented by the server, the response code 500
        MUST be returned.
  
        If there is a syntax error in the arguments of a recognized command,
        the response code 501 MUST be returned. Note that where a command has
        variants depending on a keyword (e.g. LIST ACTIVE and LIST
        NEWSGROUPS), then 501 MUST be used when the requested variant is not
        implemented but the base command is.
  
        If the client is not authorized to use the specified facility when the
        server is in its current state, the response code 502 MUST be
        returned. A different command might change the server state and permit
        the command if it is retried.
  
        If the server does not provide an optional feature, then the response
        code 403 MUST be returned if the omission is temporary (e.g. because a
        necessary facility is unavailable) and the code 503 if it is
        permanent  (e.g. because the server does not store the required
        information).
  
        If the server has to terminate the connection for some reason, it MUST
        give a 400 response code to the next command and then immediately
        close the TCP connection. It MAY give a 401 response code to any
        command to indicate that termination is imminent (following a 401
        response, it MUST NOT close the TCP connection immediately).
  
     5. The WILDMAT format
  
        The WILDMAT format[5] described here is based on the version first
  
    Barber                                                           Page [4]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        developed by Rich Salz which was derived from the format used in the
        UNIX "find" command to articulate file names. It was developed to
        provide a uniform mechanism for matching patterns in the same manner
        that the UNIX shell matches filenames. 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 UTF-8 characters. The second is a question mark (?) to match any
        single UTF-8 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 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.
  
        Implementers must be careful to apply the pattern-matching operators
        to whole characters encoded in UTF-8, and not to individual octets.
  
     5.1 Negating the wildmat pattern
  
        The exclamation point can be used at the beginning of a wildmat to
        negate it. That is, if the remainder of the pattern would match the
        string then the negated pattern does not, and vice versa. If it
        appears as any other character other than the first one, it has no
        special meaning.
  
     5.2 Examples
  
                [^]-]         matches any single character other than
                               a close square bracket or a minus
                               sign/dash
                *bdc          matches any string that ends with the
                               string "bdc" including the string "bdc"
                               (without quotes)
                [0-9a-zA-Z]   matches any single printable
                               alphanumeric ASCII character
                a??d          matches any four character string which
                               begins with a and ends with d
                !bc*d         matches any string that does not start
                               with "bc" and end with "d" (without
                               quotes)
                !\\x          matches any string that does not start
                               with "\x" (without quotes)
  
  
     6. Format for Keyword Descriptions
  
        On the following pages are descriptions of each keyword recognized by
        the NNTP server and the responses that will be returned by those
        commands. These keywords are grouped by the functional step in which
        they are used.
        Each keyword is shown in upper case for clarity, although the NNTP
        server ignores case in the interpretation of commands.
        Parameters are shown as follows:
          o  UPPERCASE    indicates literal text to be included in the
             command;
          o  lowercase    indicates a token described elsewhere;
  
    Barber                                                           Page [5]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
          o  [brackets]   indicate that the parameter is optional;
          o  ellipsis...  indicates that the parameter may be repeated
             any number of times (it must occur at least once);
          o  vertical|bar indicates a choice of two mutually exclusive
             parameters (exactly one must be provided).
  
        Parameters are case or language specific only when specified (either
        in this document or in RFC 1036[6]).
  
        The name "wildmat" for a parameter indicates that it is a wildmat
        format pattern as defined in section 5.
  
     7. The GREETING Step
  
     7.1 Initial Connection
  
        There is no keyword presented by the client upon initial connection to
        the server. The server MUST present an appropriate response code as a
        greeting to the client.  This response informs the client about what
        steps the client should take to reach the news exchange step.
        If the server will accept further commands from the client including
        POST, the server MUST present a 200 greeting code.
  
        If the server will accept further commands from the client, but it is
        not authorized to post articles using the POST command, the server
        MUST present a 201 greeting code.
  
        Otherwise the server MUST present a 400 or 502 greeting code and then
        immediately close the connection. 502 MUST be used if the client is
        not permitted under any circumstances to interact with the server and
        400 otherwise.
  
     7.1.1 Responses
  
              200   Service available, posting allowed
              201   Service available, posting prohibited
              400   Service temporarily unavailable
              502   Service unavailable
  
        Following a 400 or 502 response the server MUST immediately close the
        connection.
  
     7.1.2 Initial Connection Example
  
        Example of a normal connection from an authorized client
                [Initial TCP connection setup completed.]
                [C] Initial TCP connection completed
                [S] 200 NNTP Service Ready, posting permitted
        Client can send commands at this point. In this example, the client
        jumps directly to the conclusion step (See section 10).
                [C] QUIT
                [S] 205 NNTP Service exits normally
                [Server closes connection.]
        Example of a normal connection from an unauthorized client
                [C] Initial TCP connection completed
                [S] 502 NNTP Service Unavailable
                [Server closes connection.]
        Example of a normal connection from an authorized client that is not
        permitted to post
                [Initial TCP connection setup completed.]
                [S] 201 NNTP Service Ready, posting prohibited
  
  
    Barber                                                            Page[6]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
  
        Client can send commands at this point. In this example, the client
        jumps directly to the conclusion step (See section 10).
                [C] QUIT
                [S] 205 NNTP Service exits normally
                [Server closes connection.]
        Example of a connection from any client where the server is unable to
        provide service
                [Initial TCP connection setup completed.]
                [S] 400 NNTP Service temporarily unavailable
                [Server closes connection.]
  
     7.2 MODE READER
  
        MODE READER
  
        MODE READER SHOULD be sent by any client that intends to use any
        command other than IHAVE, HEAD, STAT, LIST, LIST EXTENSIONS, or
        commands advertised by the server as available via LIST EXTENSIONS.
        Servers MAY require that this command be issued before any other
        commands are sent and MAY reject any other commands until after a MODE
        READER command has been sent.
  
        The server MUST present a response using the same codes as the
        initial greeting (as described in section 7.1) to indicate its
        ability to provide reading service to the client.
  
        Clients SHOULD wait for a response to MODE READER after sending this
        command and SHOULD NOT send any additional commands until that
        response has been received from the server.
  
        Once MODE READER is sent, IHAVE (and any extensions intended for
        peer-to-peer article transfer) MAY no longer be permitted, even if it
        were permitted before the MODE READER command. The results of LIST
        EXTENSIONS MAY be different following a MODE READER command than prior
        to the issuing of that command.
  
        Servers are encouraged to not require this command even though clients
        SHOULD send it when appropriate. It is present to support some news
        architectures that switch between modes based on whether a given
        connection is a peer-to-peer connection with another server or a news
        reading client.
  
     7.2.1 Responses
              200   Posting permitted
              201   Posting prohibited
              400   Service temporarily unavailable
              502   Service unavailable
  
        Following a 400 or 502 response the server MUST immediately close the
        connection.
        Note that the response need not be the same as the one presented
        during the initial greeting.
  
     7.2.2 MODE READER Examples
  
        Example of use of the MODE READER command by an authorized client
                [C] MODE READER
                [S] 200 NNTP Service Ready, posting permitted
        Client can send commands at this point. In this example, the client
        jumps directly to the conclusion step (See section 10).
                [C] QUIT
                [S] 205 NNTP Service exits normally
                [Server closes connection.]
  
    Barber                                                            Page[7]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        Example of use of MODE READER by a client not authorized to receive
        service from the server as a news reader
                [C] MODE READER
                [S] 502 Service Unavailable
                [Server closes connection.]
  
        Example of a normal connection from an authorized client that is not
        permitted to post
                [C] MODE READER
                [S] 201 NNTP Service Ready, posting prohibited
        Client can send commands at this point. In this example, the client
        jumps directly to the conclusion step (See section 10).
                [C] QUIT
                [S] 205 NNTP Service exits normally
                [Server closes connection.]
  
        Example of a connection from any client where the server is unable to
        provide news reader service
                [C] MODE READER
                [S] 400 NNTP Service temporarily unavailable
                [Server closes connection.]
  
  
     8. The CAPABILITIES DISCOVERY Step
  
        To discover what extensions are available, an NNTP client can query
        the server with the LIST EXTENSIONS command.
        If a particular extension is unavailable, the client can attempt to
        work around it or it may wish to terminate the session.
        See section 12 for further discussion of extensions.
  
     8.1 LIST EXTENSIONS
  
        The LIST EXTENSIONS command allows a client to determine which
        extensions are supported by the server.
  
        To discover what extensions are available, an NNTP client SHOULD query
        the server early in the session for extensions information by issuing
        the LIST EXTENSIONS command. This command MAY be issued at anytime
        during a session.  It is not required that the client issues this
        command before attempting to make use of any extension. The response
        generated by this command MAY change during a session because of other
        state information. However, an NNTP client MUST NOT cache (for use in
        another session) any information returned if the LIST EXTENSIONS
        command succeeds. That is, an NNTP client is only able to get the
        current and correct information concerning available extensions during
        a session by issuing a LIST EXTENSIONS command during that session and
        processing that response.
  
        A successful response starts with a 202 code and is followed by a list
        of extensions, one per line. Each line MUST begin with an
        extension-label and optionally one or more parameters (separated by
        single spaces). The extension-label and the meaning of the parameters
        are specified as part of the definition of the extension. The
        extension-label MUST be in uppercase.
  
        The server MUST NOT list the same extension twice in the response, and
        MUST list all supported extensions. The order in which the extensions
        are listed is not significant. The server need not even consistently
        return the same order.
  
    Barber                                                            Page[8]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
  
        If the server does not support any extensions, it SHOULD return a 402
        failure response but MAY return an empty list instead.
  
     8.1.1 Responses
  
              202   Extension list follows (multi-line response)
              400   Service temporarily unavailable
              402   Server has no extensions
              500   Unknown Command
              501   Syntax Error
              502   Program error, function not performed
  
        Following a 503 response an extension might still be available, and
        the client MAY attempt to use it
        The LIST EXTENSIONS command is optional, and a server MAY issue a 500
        (unknown command) or 501 (syntax error) response to it.
  
     8.1.1.1 LIST EXTENSIONS Examples
  
        Example of a successful response:
  
                [C] LIST EXTENSIONS
                [S] 202 Extensions supported:
                [S] OVER
                [S] PAT
                [S] LISTGROUP
                [S] .
  
        The particular extensions shown here are simply examples of what might
        be defined in other places, and no particular meaning should be
        attributed to them.
        Example where no extensions are available, using preferred
        format:
               [C] LIST EXTENSIONS
               [S] 402 Server has no extensions
  
        Example where no extensions are available, using an empty list:
                [C] LIST EXTENSIONS
                [S] 202 Extensions supported:
                [S] .
  
     9. The NEWS EXCHANGE Step
  
        During this step, two basic types of transactions occur:
  
          o  article retrieval from the server
          o  article posting to the server
  
     9.1 Article Retrieval
  
        News reading clients have available a variety of mechanisms to
        retrieve articles via NNTP. The news articles are stored and indexed
        using three types of keys. One key is the message id of an article.
        According to RFC 1036, this identifier should be globally unique.
  
        Another key is composed of the newsgroup name and the article number
        within that newsgroup. That key MUST be unique to a particular server
        (there will be only one article with that number within a particular
        newsgroup), but is not required to be globally unique.  Additionally,
        because the same article can be cross-posted to multiple newsgroups,
        there may be multiple keys that point to the same article on the same
  
    Barber                                                           Page [9]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        server. The final key is the arrival timestamp, giving the time that
        the article arrived at the server.
  
        The server MUST ensure that article numbers are issued in order of
        arrival timestamp; that is, articles arriving later MUST have higher
        numbers than those that arrive earlier. The server SHOULD allocate the
        next sequential unused number to each new article.
  
        Article numbers MUST lie between 1 and 4,294,967,295 inclusive. The
        client and server SHOULD NOT use leading zeroes in specifying article
        numbers, and MUST NOT use more than 16 digits. In some situations, the
        value zero replaces an article number to show some special situation.
  
     9.1.1 Article Retrieval by Newsgroup Name and Article Number
  
        The following commands are used to set the current newsgroup name and
        the "current article pointer" which is used by other commands for
        article retrieval. At the start of an NNTP session, both of these
        values are undefined.
  
     9.1.1.1 GROUP
  
        GROUP ggg
        The required parameter ggg is the name of the newsgroup to be selected
        (e.g. "news.software.b"). A list of valid newsgroups may be obtained
        by using the LIST keyword.  See section 9.4 for more information on
        the LIST keyword.
  
        The successful selection response will return the article numbers of
        the first and last articles in the group at the moment of selection
        (these numbers are referred to as the "reported low water mark" and
        the "reported high water mark"), and an estimate of the number of
        articles on file in the group.
  
        If the group is not empty, the estimate MUST be at least the actual
        number of articles available, and MUST be no greater than one more
        than the difference between the reported low and high water marks.
        (Some implementations will actually count the number of articles on
        file. Others will just subtract the low water mark from the high water
        mark and add one to get an estimate.)
  
        If the group is empty, one of the following three situations will
        occur. Clients MUST accept all three cases; servers MUST NOT represent
        an empty group in any other way.
          o  The high water mark will be one less than the low water
             mark, and the estimated article count will be zero. Servers
             SHOULD use this method to show an empty group. This is the only
             time that the high water mark can be less than the low water
             mark.
          o  All three numbers will be zero.
          o  The high water mark is greater than or equal to the low
             water mark; the estimated article count might be zero or
             non-zero; if non-zero, the same requirements apply as for a
             non-empty group.
  
        The set of articles in a group may change after the GROUP command is
        carried out. That is:
          o  articles may be removed from the group
          o  articles may be reinstated in the group with the same
             article number, but those articles MUST have numbers no less than
             the reported low water mark (note that this is a reinstatement of
             the previous article, not a new article reusing the number)
          o  new articles may be added with article numbers greater than
             the reported high water mark (if an article that was the one with
             the highest number has been removed, the next new article will
             not have the number one greater than the reported high water
             mark)
  
        Except when the group is empty and all three numbers are zero,
        whenever a subsequent GROUP command for the same newsgroup is issued,
  
    Barber                                                          Page [10]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        either by the same client or a different client, the reported low
        water mark in the response MUST be no less than that in any previous
        response for that newsgroup sent to any client. The client may make
        use of the low water mark to remove all remembered information about
        articles with lower numbers, as these will never recur. This includes
        the situation when the high water mark is one less than the low water
        mark.
  
        No similar assumption can be made about the high water mark, as this
        can decrease if an article is removed, and then increase again if it
        is reinstated or if new articles arrive.
  
        When a valid group is selected by means of this command, the
        internally maintained "current article pointer" MUST be set to the
        first article in the group and the name of the current newsgroup MUST
        be set to the selected newsgroup name. If an invalid group is
        specified, the previously selected group, if any, and article MUST
        remain selected. If an empty newsgroup is selected, the "current
        article pointer" is in an indeterminate state and MUST NOT be used.
  
        The GROUP keyword (or the LISTGROUP keyword, if implemented) MUST be
        used by a client and a successful response received before the any
        other command is used that depends on having the "current article
        pointer" be valid.
  
        If the group specified is not available on the server MUST return a
        411 error code.
  
  
     9.1.1.1.1 Responses
  
                211 n l h ggg   Group successfully selected (n =
                                 estimated number of articles in the
                                 group, l = low water mark, h = high
                                 water mark, ggg = name of the group
                411             No such newsgroup
  
  
     9.1.1.1.2 GROUP Examples
  
        Example for a group known to the server
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
  
        Example for a group unknown to the server
                [C] GROUP example.is.sob.bradner.or.barber
                [S] 411 example.is.sob.bradner.or.barber is unknown
  
     9.1.1.2   LAST
  
        LAST
  
        If the current newsgroup is valid, the internally maintained "current
        article pointer" MUST be set to the previous article in the current
        newsgroup.  If already positioned at the first article of the
        newsgroup, an error message MUST be returned and the current article
        MUST remain selected.
  
        There MAY be no previous article in the group, although the current
        article number is not the reported low water mark. There MUST NOT be a
        previous article when the current article number is the reported low
        water mark.
  
        Because articles can be removed and added, the results of multiple
        LAST and NEXT commands MAY not be consistent over the life of a
        particular NNTP session.
  
        If successful, a response indicating the current article number and a
        message-id string MUST be returned. No article text is sent in
  
    Barber                                                         Page [11]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        response to this command.
  
     9.1.1.2.1 Responses
  
                223 n a     Article found (n = number, a = message-id)
                412         No newsgroup selected
                420         Current article pointer is invalid
                422         No previous article in this group
  
  
     9.1.1.2.2 LAST Examples
  
       Example of a successful article retrieval using LAST
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] NEXT
                [S] 223 3000237 <668929@domain.com> retrieved
                [C] LAST
                [S] 223 3000234 <45223423@to.to> retrieved
  
        Example of an attempt to retrieve an article without having selected a
        group (via the GROUP command) first
                [S] 200 NNTP Service ready
                [C] LAST
                [S] 412 no newsgroup selected
  
        Example of an attempt to retrieve an article using the LAST command
        when the current article pointer is pointing at the first article in
        the group
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] LAST
                [S] 422 No previous article to retrieve
  
        Example of an attempt to retrieve an article using the LAST command
        when the current group selected is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
                [S] 211 0 0 0 example.empty.newsgroup
                [C] LAST
                [S] 420 No current article selected
  
     9.1.1.3 NEXT
  
        NEXT
  
        If the current newsgroup is valid, the internally maintained "current
        article pointer" MUST be advanced to the next article in the current
        newsgroup.  If no more articles remain in the current group, an error
        message MUST be returned and the current article MUST remain selected.
        If successful, a response indicating the current article number and
        the message-id string MUST be returned.  No article text is sent in
        response to this command.
  
    Barber                                                          Page [12]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
     9.1.1.3.1 Responses
  
                223 n a     Article found (n = number, a = message-id)
                412         No newsgroup selected
                420         Current article pointer is invalid
                421         No next article in this group
  
  
     9.1.1.3.2 NEXT Examples
  
       Example of a successful article retrieval using NEXT
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] NEXT
                [S] 223 3000237 <668929@domain.com> retrieved
  
        Example of an attempt to retrieve an article without having selected a
        group (via the GROUP command) first
                [S] 200 NNTP Service ready
                [C] NEXT
                [S] 412 no newsgroup selected
  
        Example of an attempt to retrieve an article using the NEXT command
        when the current article pointer is pointing at the last article in
        the group
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] ARTICLE 3002322
                [S] 220 3002322 <411@whitehouse.gov> retrieved
                [S] Path: pathost!demo!whitehouse!not-for-mail
                [S] From: nobody@whitehouse.gov(Demo User)
                [S] Newsgroups: misc.test
                [S] Subject: I am just a test article
                [S] Date: 6 Oct 1998 04:38:40 -0500
                [S] Organization: The White House, Washington, DC
                [S] Message-ID: <411@whitehouse.gov>
                [S]
                [S] This is just a test article.
                [S] .
                [C] NEXT
                [S] 421 No next article to retrieve
  
        Example of an attempt to retrieve an article using the NEXT command
        when the current group selected is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
                [S] 211 0 0 0 example.empty.newsgroup
  
    Barber                                                          Page [13]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
                [C] NEXT
                [S] 420 No current article selected
  
  
     9.2 Retrieval of Articles and Article Sections
  
        The ARTICLE, BODY, HEAD, and STAT commands are very similar. They
        differ only in the parts of the article that are presented to the
        client and in the successful response code. The ARTICLE command is
        described here in full, while the other commands are described in
        terms of the differences.
  
        An article, as defined by RFC 1036, consists of two parts: the article
        headers and the article body. When responding to one of these
        commands, the server presents the entire article or appropriate part
        and does not attempt to alter or translate it in any way.
  
     9.2.1 ARTICLE
  
        ARTICLE <message-id>
        ARTICLE [number]
  
        The ARTICLE command selects an article based on the arguments and
        presents the header, a blank line, and the body of that article. The
        command has two forms.
  
        In the first form, a message-id is specified (including the angle
        brackets), and the server presents the article with that message-id in
        its headers. In this case, the server MUST NOT alter the "current
        article pointer". This is both to facilitate the presentation of
        articles that may be referenced within another article being read, and
        because of the semantic difficulties of determining the proper
        sequence and membership of an article which may have been posted to
        more than one newsgroup.
  
        In the second form, an article number may be specified. If so, and if
        there is an article with that number in the currently selected group,
        the server MUST set the current article pointer to that number.
        Then, whether or not a number was specified, the article indicated by
        the current article pointer is presented to the client.
        Note that a previously valid article number MAY become invalid if the
        article has been removed. A previously invalid article number MAY
        become valid if the article has been reinstated, but such an article
        number MUST be no less than the reported low water mark for that
        group.
  
        The server MUST NOT change the currently selected group as a result of
        this command. The server MUST NOT change the current selected article
        except when an article number argument was provided and the article
        exists; in particular, it MUST NOT change it following an unsuccessful
        response.
  
     9.2.1.1 Responses
             First form (message-id specified):
  
                220 0 a    Article follows (multi-line response, a =
                            message-id)
                430        No article found with that message-id
                502        Program error, function not performed
  
             Second form (optional article number specified):
  
                220 n a    Article follows (multi-line response, n =
                            article number, a = message-id)
                412        No newsgroup selected
                420        No current article selected
                423        No such article in this newsgroup
                502        Program error, function no performed
  
  
    Barber                                                         Page [14]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
  
        The 420 response only occurs if no article number has been specified.
        In the 220 response, the first parameter is 0 for the first form and
        the article number (within the current group) for the second form. The
        second parameter is the message-id of the article (within angle
        brackets). This is taken from the message-id header line of the
        article (required by RFC 1036). If there is no such line, the
        message-id "<0>" MUST be used instead (without the double quotes).
        Since the message-id field is unique for each article, it may be used
        by a client to skip duplicate displays of articles that have been
        posted more than once, or to more than one newsgroup.
        The article headers and body are returned as a multilane response
        following the initial response line.
  
     9.2.1.2 Examples
        Example of a successful retrieval of an article (using no article
        number)
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] ARTICLE
                [S] 220 3000234 <45223423@to.to>
                [S] Path: pathost!demo!somewhere!not-for-mail
                [S] From: nobody@nowhere.to (Demo User)
                [S] Newsgroups: misc.test
                [S] Subject: I am just a test article
                [S] Date: 6 Oct 1998 04:38:40 -0500
                [S] Organization: Nowhere, To
                [S] Message-ID: <45223423@to.to>
                [S]
                [S] This is just a test article.
                [S] .
  
        Example of a successful retrieval of an article by message-id
                [S] 200 NNTP Service Ready
                [C] ARTICLE <45223423@to.to>
                [S] 220 0 <45223423@to.to>
                [S] Path: pathost!demo!somewhere!not-for-mail
                [S] From: nobody@nowhere.to (Demo User)
                [S] Newsgroups: misc.test
                [S] Subject: I am just a test article
                [S] Date: 6 Oct 1998 04:38:40 -0500
                [S] Organization: Nowhere, To
                [S] Message-ID: <45223423@to.to>
                [S]
                [S] This is just a test article.
                [S] .
  
        Example of an unsuccessful retrieval of an article by message-id
                [S] 200 NNTP Service Ready
                [C] ARTICLE <i.am.not.there@nowhere.to>
                [S] 430 No Such Article Found
  
    Barber                                                         Page [15]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        Example of an unsuccessful retrieval of an article by number
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 news.groups
                [C] ARTICLE 300256
                [S] 423 No such article number in this group
  
        Example of an unsuccessful retrieval of an article by number because
        no newsgroup was selected first
                [S] 200 NNTP Service Ready
                [C] ARTICLE 300256
                [S] 412 No newsgroup selected
  
        Example of an attempt to retrieve an article when the current group
        selected is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
                [S] 211 0 0 0 example.empty.newsgroup
                [C] ARTICLE
                [S] 420 No current article selected
  
        Example of a failure due to the service being unavailable
                [S] 200 NNTP Service Ready
                [C] ARTICLE <i.am.a.test.article@nowhere.to>
                [S] 502 Service unavailable
  
     9.2.2 HEAD
        HEAD <message-id>
        HEAD [number]
  
        The HEAD command behaves identically to the ARTICLE command except
        that, if the article exists, only the headers are presented (the blank
        line separating the headers and body MUST NOT be included).
  
     9.2.2.1 Responses
             First form (message-id specified):
  
                221 0 a    Article follows (multi-line response, a =
                            message-id)
                430        No article found with that message-id
                502        Program error, function not performed
  
             Second form (optional article number specified):
  
                221 n a    Article follows (multi-line response, n =
                            article number, a = message-id)
                412        No newsgroup selected
                420        No current article selected
                423        No such article in this newsgroup
                502        Program error, function no performed
  
  
        Except that only the headers are included in the response, the 221
        response behaves identically to the 220 response of the ARTICLE
        command.
  
     9.2.2.2 Examples
  
        Example of a successful retrieval of the headers in an article (using
        no article number)
  
    Barber                                                         Page [16]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
  
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] HEAD
                [S] 221 3000234 <45223423@to.to>
                [S] Path: pathost!demo!somewhere!not-for-mail
                [S] From: nobody@nowhere.to (Demo User)
                [S] Newsgroups: misc.test
                [S] Subject: I am just a test article
                [S] Date: 6 Oct 1998 04:38:40 -0500
                [S] Organization: Nowhere, To
                [S] Message-ID: <45223423@to.to>
                [S] .
  
        Example of a successful retrieval of the headers in an article by
        message-id
                [S] 200 NNTP Service Ready
                [C] HEAD <45223423@to.to>
                [S] 221 0 <45223423@to.to>
                [S] Path: pathost!demo!somewhere!not-for-mail
                [S] From: nobody@nowhere.to (Demo User)
                [S] Newsgroups: misc.test
                [S] Subject: I am just a test article
                [S] Date: 6 Oct 1998 04:38:40 -0500
                [S] Organization: Nowhere, To
                [S] Message-ID: <45223423@to.to>
                [S] .
  
        Example of an unsuccessful retrieval of the header of an article by
        message-id
                [S] 200 NNTP Service Ready
                [C] HEAD <i.am.not.there@nowhere.to>
                [S] 430 No Such Article Found
  
  
        Example of an unsuccessful retrieval of the header of an article by
        number
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] HEAD 300256
                [S] 423 No such article number in this group
  
        Example of an unsuccessful retrieval the header of an article by
        number because no newsgroup was selected first
                [S] 200 NNTP Service Ready
                [C] HEAD 300256
                [S] 412 No newsgroup selected
  
        Example of an attempt to retrieve the header of an article when the
        current group selected is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
  
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    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
                [S] 211 0 0 0 example.empty.newsgroup
                [C] HEAD
                [S] 420 No current article selected
  
        Example of a failure due to the service being unavailable
                [S] 200 NNTP Service Ready
                [C] HEAD <i.am.a.test.article@nowhere.to>
                [S] 502 Service unavailable
  
     9.2.3 BODY
  
        BODY <message-id>
        BODY [number]
  
        The BODY command behaves identically to the ARTICLE command except
        that, if the article exists, only the body is presented (the blank
        line separating the headers and body MUST NOT be included).
  
     9.2.3.1 Responses
  
             First form (message-id specified):
  
                222 0 a    Article follows (multi-line response, a =
                            message-id)
                430        No article found with that message-id
                502        Program error, function not performed
  
             Second form (optional article number specified):
  
                222 n a    Article follows (multi-line response, n =
                            article number, a = message-id)
                412        No newsgroup selected
                420        No current article selected
                423        No such article in this newsgroup
                502        Program error, function no performed
  
  
        Except that only the body is included in the response, the 222
        response behaves identically to the 220 response of the ARTICLE
        command.
  
     9.2.3.2 Examples
  
        Example of a successful retrieval of the body of an article (using no
        article number)
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] BODY
                [S] 222 3000234 <45223423@to.to>
                [S] This is just a test article.
                [S] .
  
        Example of a successful retrieval of the body of an article by
        message-id
                [S] 200 NNTP Service Ready
                [C] BODY <45223423@to.to>
                [S] 222 0 <45223423@to.to>
                [S] This is just a test article.
                [S] .
  
        Example of an unsuccessful retrieval of the body of an article by
  
    Barber                                                         Page [18]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        message-id
  
                [S] 200 NNTP Service Ready
                [C] BODY <i.am.not.there@nowhere.to>
                [S] 430 No Such Article Found
  
        Example of an unsuccessful retrieval of the body of an article by
        number
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] BODY 300256
                [S] 423 No such article number in this group
  
        Example of an unsuccessful retrieval of the body of an article by
        number because no newsgroup was selected first
                [S] 200 NNTP Service Ready
                [C] BODY 300256
                [S] 412 No newsgroup selected
  
        Example of an attempt to retrieve the body of an article when the
        current group selected is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
                [S] 211 0 0 0 example.empty.newsgroup
                [C] BODY
                [S] 420 No current article selected
  
        Example of a failure due to the service being unavailable
                [S] 200 NNTP Service Ready
                [C] BODY <i.am.a.test.article@nowhere.to>
                [S] 502 Service unavailable
  
     9.2.4 STAT
        STAT <message-id>
        STAT [number]
  
        The STAT command behaves identically to the ARTICLE command except
        that, if the article exists, it is NOT presented to the client.
        This command allows the client to determine whether an article exists,
        and in the second form what its message-id is, without having to
        process an arbitrary amount of text.
  
     9.2.4.1 Responses
  
             First form (message-id specified):
  
                223 0 a    Article follows (a = message-id)
                430        No article found with that message-id
                502        Program error, function not performed
  
             Second form (optional article number specified):
  
                223 n a    Article follows (n = article number, a =
                            message-id)
                412        No newsgroup selected
                420        No current article selected
                423        No such article in this newsgroup
                502        Program error, function no performed
  
        The parameters of the 223 response are identical to those that would
  
    Barber                                                         Page  [19]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
        have been given in a 220 response to the equivalent ARTICLE command.
        However, the response is NOT multi-line.
  
     9.2.4.2 Examples
  
        Example of STAT on an existing article (using no article number)
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] STAT
                [S] 223 3000234 <45223423@to.to>
  
        Example of a STAT of an existing article by message-id
                [S] 200 NNTP Service Ready
                [C] STAT <45223423@to.to>
                [S] 223 0 <45223423@to.to>
  
        Example of an STAT of an article not on the server by message-id
                [S] 200 NNTP Service Ready
                [C] STAT <i.am.not.there@nowhere.to>
                [S] 430 No Such Article Found
  
        Example of STAT of an article not in the server by number
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] STAT 300256
                [S] 423 No such article number in this group
  
       Example of STAT of an article by number when no newsgroup was selected
       first
                [S] 200 NNTP Service Ready
                [C] STAT 300256
                [S] 412 No newsgroup selected
  
       Example of STAT of an article when the current group selected is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
                [S] 211 0 0 0 example.empty.newsgroup
                [C] STAT
                [S] 420 No current article selected
  
       Example of a failure due to the service being unavailable
                [S] 200 NNTP Service Ready
                [C] STAT <i.am.a.test.article@nowhere.to>
                [S] 502 Service unavailable
  
  
     9.3 Article Posting
  
        Article posting is done in one of two modes: individual article
        posting from news reading clients and article transfer from other news
        servers.
  
     9.3.1 POST
  
  
    Barber                                                         Page  [20]
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
                                                                November 2001
  
        POST
  
        If posting is allowed, response code 340 MUST be returned to indicate
        that the article to be posted should be sent.  Response code 440 MUST
        be sent if that posting is prohibited for some installation-dependent
        reason.
  
        If posting is permitted, the article MUST be presented to the server
        by the client in the format specified by RFC 1036 (or by any of its
        successors or extensions). The text forming the header and body of the
        message to be posted MUST be sent by the client in the format defined
        above (section 4) for multi-line responses (except that there is no
        initial line containing a response code).  Thus a single period (".")
        on a line indicates the end of the text, and lines starting with a
        period in the original text have that period doubled during
        transmission.
  
        Following the presentation of the termination sequence by the client,
        the server MUST return a response code indicating success or failure
        of the article transfer. Note that response codes 340 and 440 are used
        in direct response to the POST command. Others are returned following
        the sending of the article.
  
        No attempt shall be made by the server to filter characters, fold or
        limit lines, or otherwise process incoming text. The intent is that
        the server just passes the incoming message to be posted to the server
        installation's news posting software, which is not part of this
        specification.
  
        The client SHOULD NOT assume that the article has been successfully
        transferred unless it receives an affirmative response from the
        server.  Since, however, the affirmative response may have been sent
        and lost, the client SHOULD use the same message-id in the article
        when resending it or check whether the article was successfully posted
        before resending it to ensure that the resend will not result in a
        duplicate article.
  
     9.3.1.1 Responses
  
                240   Article received ok
                340   Send article to be posted
                440   Posting not permitted
                441   Posting failed
  
     9.3.1.2 Examples
  
     Example of a successful posting
                [S] 200 NNTP Service Ready
                [C] POST
                [S] 340 Input article. End with <CR-LF>.<CR-LF>
                [C] From: demo@testdomain.com(Demo User)
                [C] Newsgroups: misc.test
                [C] Subject: I am just a test article
                [C] Organization: Testdomain, USA
                [C]
                [C] This is just a test article.
                [C] .
                [S] 240 Article received ok
  
     Example of an unsuccessful posting
                [S] 200 NNTP Service Ready
                [C] POST
                [S] 340 Input article. End with <CR-LF>.<CR-LF>
                [C] From: demo@testdomain.com(Demo User)
  
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                                                                November 2001
  
                [C] Newsgroups: misc.test
                [C] Subject: I am just a test article
                [C] Organization: Testdomain, USA
                [C]
                [C] This is just a test article.
                [C] .
                [S] 441 Posting failed
  
     Example of an attempt to posting when posting is not allowed
                [S] 201 NNTP Service Ready, read-only
                [C] POST
                [S] 440 Posting not permitted
  
  
     9.3.2 IHAVE
  
        IHAVE <message-id>
  
        The IHAVE command informs the server that the client has an article
        whose id is <message-id>.  If the server desires a copy of that
        article, it MUST return response code 335 instructing the client to
        send the entire article.  If the server does not want the article (if,
        for example, the server already has a copy of it), response code 435
        indicating that the article is not wanted MUST be returned.  Finally,
        if the article isn't wanted immediately but the client should retry
        later if possible (if, for example, another client is in the process
        of sending the same article to the server), response code 436 MUST be
        returned.
  
        If transmission of the article is requested, the client MUST send the
        entire article, including header and body, in the format defined above
        (section 4) for multi-line responses (except that there is no initial
        line containing a response code). Thus a single period (".") on a line
        indicates the end of the text, and lines starting with a period in the
        original text have that period doubled during transmission. The server
        MUST then return a response code indicating success or failure of the
        transferal of the article.
  
        This function differs from the POST command in that it is intended for
        use in transferring already-posted articles between hosts. It SHOULD
        NOT be used when the client is a personal news reading program, since
        this command indicates that the forthcoming article has already been
        posted at another site and is being forwarded from another host.
        However, the server MAY elect not to post or forward the article if
        after further examination of the article it deems it inappropriate to
        do so. Reasons for such subsequent rejection of an article may include
        such problems as inappropriate newsgroups or distributions, disk space
        limitations, article lengths, garbled headers, and the like. These are
        typically restrictions enforced by the server host's news software and
        not necessarily the NNTP server itself.
  
        The client SHOULD NOT assume that the article has been successfully
        transferred unless it receives an affirmative response from the
        server.  A lack of response (such as a dropped network connection or a
        network timeout) SHOULD be treated the same as a 436 error response.
        Because some news server software may not be able to immediately
        determine whether or not an article is suitable for posting or
        forwarding, an NNTP server MAY acknowledge the successful transfer of
        the article (with a 235 response) but later silently discard it.
  
     9.3.2.1 Responses
  
                235   Article transferred ok
                335   Send article to be transferred
                435   Article not wanted, please don't send it.
  
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                436   Transfer failed, try again later.
                437   Article rejected, please don't sent it again.
  
  
     9.3.2.2 Examples
  
     Example of successfully sending an article to another site
                [S] 200 NNTP Service Ready
                [C] IHAVE <i.am.an.article.you.will.want@nowhere.to>
                [S] 335 Send it. End with <CR-LF>.<CR-LF>
                [C] Path: pathost!demo!somewhere!not-for-mail
                [C] From: nobody@nowhere.to (Demo User)
                [C] Newsgroups: misc.test
                [C] Subject: I am just a test article
                [C] Date: 6 Oct 1998 04:38:40 -0500
                [C] Organization: Nowhere, To
                [C] Message-ID: <i.am.a.test.article@nowhere.to>
                [C]
                [C] This is just a test article.
                [C] .
                [S] 235 Article transferred ok
  
     Example of sending an article to another site that rejects it
                [S] 200 NNTP Service Ready
                [C] IHAVE <i.am.an.article.you.will.want@nowhere.to>
                [S] 335 Send it. End with <CR-LF>.<CR-LF>
                [C] Path: pathost!demo!somewhere!not-for-mail
                [C] From: nobody@nowhere.to (Demo User)
                [C] Newsgroups: misc.test
                [C] Subject: I am just a test article
                [C] Date: 6 Oct 1998 04:38:40 -0500
                [C] Organization: Nowhere, To
                [C] Message-ID: <i.am.a.test.article@nowhere.to>
                [C]
                [C] This is just a test article.
                [C] .
                [S] 437 Article rejected. Don't send again
  
     Example of sending an article to another site where the transfer fails
                [S] 200 NNTP Service Ready
                [C] IHAVE <i.am.an.article.you.will.want@nowhere.to>
                [S] 335 Send it. End with <CR-LF>.<CR-LF>
                [C] Path: pathost!demo!somewhere!not-for-mail
                [C] From: nobody@nowhere.to (Demo User)
                [C] Newsgroups: misc.test
                [C] Subject: I am just a test article
                [C] Date: 6 Oct 1998 04:38:40 -0500
  
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                                                                November 2001
                [C] Organization: Nowhere, To
                [C] Message-ID: <i.am.a.test.article@nowhere.to>
                [C]
                [C] This is just a test article.
                [C] .
                [S] 436 Transfer failed
  
     Example of sending an article to a site that already has it
                [S] 200 NNTP Service Ready
                [C] IHAVE <i.am.an.article.you.have@nowhere.to>
                [S] 435 Duplicate
  
     Example of sending an article to a site that requests the article be
     tried again later
                [S] 200 NNTP Service Ready
                [C] IHAVE <i.am.an.article.you.defer@nowhere.to>
                [S] 436 Retry later
  
     9.4 The LIST Keyword
  
     9.4.1 LIST
  
        LIST [ACTIVE [wildmat]]
  
        The response to the LIST keyword with no parameters returns a list of
        valid newsgroups and associated information.  Each newsgroup is sent
        as a line of text in the following format:
  
          group first last status
  
        where <group> is the name of the newsgroup, <last> is the number of
        the last known article currently in that newsgroup, <first> is the
        number of the first article currently in the newsgroup, and <status>
        indicates the current status of the group on this server. Typically,
        the <status> will be consist of the US-ASCII character 'y' where
        posting is permitted, 'n' where posting is not permitted and 'm' where
        postings will be forwarded to the newsgroup moderator by the news
        server. Other status strings may exist. The definition of these other
        values and the circumstances under which they are returned is covered
        in other specifications. Each field in the line is separated from its
        neighboring fields by one or more US-ASCII spaces.
  
        The <first> and <last> fields will always be numeric.  They may have
        leading zeros. The <first> field corresponds to the "reported low
        water mark" and the <last> field corresponds to the "reported high
        water mark" described in the GROUP command (see Section 9.1.1.1).
  
        The status of a newsgroup only indicates how posts to that newsgroup
        are processed. It does not indicate if the current client is permitted
        to post. That is indicated by the status code returned as part of the
        greeting.
  
        Please note that an empty list (i.e., the text body returned by this
        command consists only of the terminating period) is a possible valid
        response, and indicates that there are currently no valid newsgroups.
  
        If the optional wildmat parameter is specified, the list is limited to
        only the groups that match the pattern.
  
        Specifying a single group is usually very efficient for the server.
        Multiple groups may be specified by using wildmat patterns (described
        in section 5).
  
     9.4.1.1 Responses
                215   Information Follows (multi-line response)
  
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     9.4.1.2 Examples
  
     Example of LIST returning a list of newsgroups
                [S] 200 NNTP Service Ready
                [C] LIST
                [S] 215 list of newsgroups follows
                [S] misc.test 3000234 3002322 y
                [S] alt.fc-writers.recovery 1 4 y
                [S] tx.natives.recovery 56 89 y
                [S] .
  
     Example of LIST returning no newsgroups
                [S] 200 NNTP Service Ready
                [C] LIST
                [S] 215 list of newsgroups follows
                [S] .
  
     9.4.2 LIST ACTIVE.TIMES
  
        LIST ACTIVE.TIMES [wildmat]
        The active.times file is maintained by some news transport systems to
        contain information about who created a particular newsgroup and when.
  
        The format of this file includes three fields separated from each
        other by one or more US-ASCII space characters. The first field is the
        name of the newsgroup. The second is the time when this group was
        created on this news server measured in seconds since the start of
        January 1, 1970.  The third is the email address of the entity that
        created the newsgroup and must be a mailbox as defined in RFC 2822.
  
        When executed, the information is displayed following the 215
        response. When display is completed, the server will send a period on
        a line by itself. If the information is not available, the server will
        return the 503 error response. If the server does not recognize the
        command, it SHOULD return the 501 error response.
  
        If the optional wildmat parameter is specified, the list is limited to
        only the groups that match the pattern.
        Multiple groups may be specified by using wildmat patterns(described
        in section 5).
  
     9.4.2.1 Responses
  
                215   Information Follows (multi-line response)
                501   Syntax error
                503   Program error, function not performed
  
     9.4.2.2 Examples
  
     Example of LIST ACTIVE.TIMES returning a list of newsgroups
                [S] 200 NNTP Service Ready
                [C] LIST ACTIVE.TIMES
                [S] 215 information follows
                [S] misc.test 930445408 <creatme@isc.org>
                [S] alt.rfc-writers.recovery 930562309 <m@nowhere.to>
                [S] tx.natives.recovery 930678923 <sob@academ.com>
                [S]  .
  
  
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     Example of LIST ACTIVE.TIMES returning an error (The server software is
     not configured to maintain this information, but does recognize the
     command as valid.)
                [S] 200 NNTP Service Ready
                [C] LIST ACTIVE.TIMES
                [S] 503 program error, function not performed
  
     Example of LIST ACTIVE.TIMES sent to a server that does not recognize
     this argument (e.g. The software does not maintain this information.)
                [S] 200 NNTP Service Ready
                [C] LIST ACTIVE.TIMES
                [S] 501 Syntax Error
  
     9.4.3 LIST DISTRIBUTIONS
  
        LIST DISTRIBUTIONS
        The distributions file is maintained by some news transport systems to
        contain information about valid values for the Distribution: line in a
        news article header and about what the values mean. Each line contains
        two fields, the value and a short explanation on the meaning of the
        value. The first field is separated from the second field by one or
        more US-ASCII spaces. When executed, the information is displayed
        following the 215 response. When display is completed, the server will
        send a period on a line by itself. If the information is not
        available, the server will return the 503 error response. If the
        server does not recognize this command, it SHOULD return the 501 error
        response.
  
     9.4.3.1 Responses
  
                215   Information Follows (multi-line response)
                501   Syntax error
                503   Program error, function not performed
  
  
     9.4.3.2 Examples
  
     Example of LIST DISTRIBUTIONS returning a list of newsgroups
                [S] 200 NNTP Service Ready
                [C] LIST DISTRIBUTIONS
                [S] 215 information follows
                [S] usa United States of America
                [S] na North America
                [S] world All over the World
                [S] .
  
     Example of LIST DISTRIBUTIONS returning an error (e.g. The server
     software is not configured to maintain this information, but does
     recognize the command as valid.)
                [S] 200 NNTP Service Ready
                [C] LIST DISTRIBUTIONS
                [S] 503 program error, function not performed
  
     Example of LIST DISTRIBUTIONS sent to a server that does not recognize
     the command (e.g. The server does not maintain this information
     regardless of configuration.)
                [S] 200 NNTP Service Ready
                [C] LIST DISTRIBUTIONS
  
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                                                                November 2001
                [S] 501 Syntax Error
  
     9.4.4 LIST DISTRIB.PATS
  
        LIST DISTRIB.PATS
        The distrib.pats file is maintained by some news transport systems to
        allow clients to choose a value for the Distribution: line in the
        header of a news article being posted. The information returned
        consists of lines, in no particular order, each of which contains
        three fields separated by colons. These fields are a weight, a group
        name or wildmat pattern, and a Distribution: value, in that order.
        The client MAY use this information to select a Distribution: value
        based on the name of a newsgroup. To do so, it should determine the
        lines whose second field matches the newsgroup name, select that line
        with the highest weight (with 0 being the lowest), and use the
        Distribution: field from that line.
  
        When executed, the information is displayed following the 215
        response.  When display is completed, the server will send a period on
        a line by itself. If the information is not available, the server will
        return the 503 error response. If this command is not recognized, the
        server SHOULD return the 501 error response.
  
     9.4.4.1 Responses
  
                215   Information Follows (multi-line response)
                501   Syntax error
                503   Program error, function not performed
  
     9.4.4.2 Examples
  
     Example of LIST DISTRIB.PATS returning a list of newsgroups
                [S] 200 NNTP Service Ready
                [C] LIST DISTRIB.PATS
                [S] 215 information follows
                [S] 10:local.*:local
                [S] .
  
     Example of LIST DISTRIB.PATS returning an error (e.g. The server software
     is not configured to maintain this information, but does recognize the
     command as valid.)
                [S] 200 NNTP Service Ready
                [C] LIST DISTRIB.PATS
                [S] 503 program error, function not performed
  
     Example of LIST DISTRIB.PATS sent to a server that does not recognize the
     command (e.g. The software does not maintain this information regardless
     of configuration.)
                [S] 200 NNTP Service Ready
                [C] LIST DISTRIB.PATS
                [S] 501 Syntax Error
  
     9.4.5 LIST NEWSGROUPS
  
          LIST NEWSGROUPS [wildmat]
          The newsgroups file is maintained by some news transport systems to
          contain the name of each newsgroup that is active on the server and
          a short description about the purpose of each newsgroup. Each line
          in the file contains two fields, the newsgroup name and a short
          explanation of the purpose of that newsgroup. The first field is
          separated from the second field by one or more US-ASCII spaces. When
  
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                                                                November 2001
          executed, the information is displayed following the 215 response.
          When display is completed, the server will send a period on a line
          by itself. If the information is not available, the server will
          return the 503 response. If the server does not recognize the
          command it should return a 501 response. If the optional matching
          parameter is specified, the list is limited to only the groups that
          match the pattern (no matching is done on the group descriptions).
          Multiple groups may be specified by using a wildmat(see section 5),
          not regular expressions. If nothing is matched an empty list is
          returned, not an error.
  
     9.4.5.1 Responses
  
                215   Information Follows (multi-line response)
                501   Syntax error
                503   Program error, function not performed
  
     9.4.5.2 Examples
  
     Example of LIST NEWSGROUPS returning a list of newsgroups
                [S] 200 NNTP Service Ready
                [C] LIST NEWSGROUPS
                [S] 215 information follows
                [S] misc.test General Usenet testing
                [S] alt.rfc-writers.recovery RFC Writers Recovery
                [S] tx.natives.recovery Texas Natives Recovery
                [S] .
  
     Example of LIST NEWSGROUPS returning an error (e.g. The server
     software recognizes the command as valid, but the information is not
     available.)
                [S] 200 NNTP Service Ready
                [C] LIST NEWSGROUPS
                [S] 503 program error, function not performed
  
  
     9.5 Standard extensions
  
        Each of the following sections describes an extension that a server
        MAY provide. If the server provides the extension, it MUST include the
        appropriate extension label in the response to LIST EXTENSIONS. If it
        does not provide it, it MUST NOT include the appropriate extension
        label. The descriptions of facilities in each section are written as
        if the extension is provided. If it is not provided, the entire
        section should be ignored.
  
     9.5.1 LISTGROUP extension
  
        This extension provides one command and has the extension label
        LISTGROUP.
  
  
     9.5.1.1 The LISTGROUP Command
  
          LISTGROUP [ggg]
          The LISTGROUP command is used to get a listing of all the article
          numbers in a particular newsgroup.
          The optional parameter ggg is the name of the newsgroup to be
          selected (e.g. "news.software.b").  A list of valid newsgroups may
          be obtained from the LIST command. If no group is specified, the
          current group is used as the default argument.
  
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          The successful selection response will be a list of the article
          numbers in the group followed by a period on a line by itself. The
          list starts on the next line following the 211 response code.
  
          When a valid group is selected by means of this command, the
          internally maintained "current article pointer" MUST be set to the
          first article in the group and the name of the current newsgroup
          MUST be set to the selected newsgroup name. If an invalid group is
          specified, the previously selected group and article remain
          selected.  If an empty newsgroup is selected, the "current article
          pointer" may be in an indeterminate state and should not be used.
  
          The LISTGROUP keyword MAY be used by a client as a replacement for
          the GROUP command in establishing a valid "current article pointer."
          After a successful response is received, any other command may be
          used that depends on having the "current article pointer" be valid.
  
          If a group name is specified and that group is not available on that
          server, the server MUST respond with the 411 error code.
  
          A server that does not implement this command SHOULD return a 500
          error response.
  
     9.5.1.1.1 Responses
  
                211   List of article numbers follow (multi-line
                       response)
                411   No such group
                412   No newsgroup currently selected
                500   Command not recognized
  
  
     9.5.1.1.2 Examples
  
     Example of LISTGROUP on an empty group:
                [S] 200 NNTP Service Ready
                [C] LISTGROUP example.empty.newsgroup
                [S] 211 list of article numbers follows
                [S] .
  
     Example of LISTGROUP on a valid current group:
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 2000 3000234 3002322 misc.test selected
                [C] LISTGROUP
                [S] 211 list follows
                [S] 3000234
                [S] 3000237
                [S] 3000238
                [S] 3000239
                [S] 3002322
                [S] .
  
     Example of LISTGROUP failing because no group has been selected:
                [S] 200 NNTP Service Ready
                [C] LISTGROUP
                [S] 412 no current group
                [C] GROUP example.is.sob.bradner.or.barber
  
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                [S] 411 no such group
                [C] LISTGROUP
                [S] 412 no current group
  
     9.5.2 The OVER Extension
  
        This extension provides two commands, OVER and LIST OVERVIEW.FMT. The
        label for this extension is OVER.
  
     9.5.2.1 LIST OVERVIEW.FMT
  
        LIST OVERVIEW.FMT
  
        The overview.fmt file is maintained by some news transport systems to
        contain the order in which header information is stored in the
        overview databases for each newsgroup.  When executed, news article
        header fields are displayed one line at a time in the order in which
        they are stored in the overview database[6] following the 215
        response.  When display is completed, the server will send a period on
        a line by itself. If the information is not available, the server will
        return the 503 response.
  
        If the header has the word "full" (without quotes) after the colon,
        the header's name is prepended to its field in the output returned by
        the server.
  
        This is command is part of the optional OVER extension which includes
        the OVER command defined in section . If the OVER extension is not
        implemented, then this command MUST NOT be implemented. If that case,
        the server MUST return a 501 error response when this command is
        presented by the client.
  
  
     9.5.2.1.1 Responses
  
                215   Information follows (multi-line response)
                501   Syntax Error
                503   Program error, function not performed
  
  
     9.5.2.1.2 Examples
  
     Example of LIST OVERVIEW.FMT returning a list of newsgroups
                [S] 200 NNTP Service Ready
                [C] LIST OVERVIEW.FMT
                [S] 215 Order of fields in overview database.
                [S] Subject:
                [S] From:
                [S] Date:
                [S] Message-ID:
                [S] .
  
     Example of LIST OVERVIEW.FMT returning an error
                [S] 200 NNTP Service Ready
                [C] LIST OVERVIEW.FMT
                [S] 503 program error, function not performed
  
  
     9.5.2.2 OVER
  
        OVER [range]
        The OVER command returns specific header information for the
        article(s) specified from the current selected group. The information
  
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        returned in the response to this command can be used by clients to
        follow discussion threads.
  
        The optional range argument may be any of the following:
  
          o   an article number
          o   an article number followed by a dash to indicate all
              following
          o   an article number followed by a dash followed by another
              article number
  
        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
        newsgroup must have been selected earlier, else a 412 error response
        is returned. If no articles are in the range specified, the server
        returns a 420 error response. A 502 response will be returned if the
        client only has permission to transfer articles. A 500 response SHOULD
        be returned by servers do not implement this command.
  
        The output consists of one line per article, sorted in numerical order
        of article number. Each line consists of a number of fields separated
        by an US-ASCII TAB character. The first 8 fields MUST be the
        following, in order:
  
        article number, subject, author, date, message-ID, references,
        byte count, line count.
  
        The content of each field is formed by taking the original content
        (such as the raw subject line from the article), removing all US-ASCII
        CRLF pairs, and then replacing each remaining US-ASCII NUL, TAB, CR,
        or LF character with a single US-ASCII space.
  
        The content of any subsequent field is given by the response to the
        LIST OVERVIEW.FMT command.  A field may be empty (in which case there
        will be two adjacent US-ASCII tabs, and a sequence of trailing
        US-ASCII tabs may be omitted).
  
        The server SHOULD not produce output for articles that no longer
        exist.
  
     9.5.2.2.1 Responses
  
                224   Overview information follows (multi-line
                       response)
                412   No newsgroup currently selected
                420   No article(s) selected
                500   Command not recognized
                502   Program error, functions no performed
  
  
     9.5.2.2.2 Examples
  
     Example of a successful retrieval of overview information for an article
     (using no article number)
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] OVER
                [S] 224 Overview information follows
                    300234|I am just a test article|nobody@nowhere.to
                    (Demo User)|6 Oct 1998 04:38:40 -0500|
                    <45223423@to.to>
                [S] .
     [Please note that the line that begins with 300234 is all one line that
     has been wrapped for readability. A vertical bar has been inserted to
  
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     show where the US-ASCII TAB should actually be.]
  
     Example of an unsuccessful retrieval of overview information on an
     article by number
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] OVER 300256
                [S] 420 No such article in this group
  
     Example of an unsuccessful retrieval of overview information by number
     because no newsgroup was selected first
                [S] 200 NNTP Service Ready
                [C] OVER
                [S] 412 No newsgroup selected
  
     Example of an attempt to retrieve an article when the current group
     selected is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
                [S] 211 0 0 0 example.empty.newsgroup
                [C] OVER
                [S] 420 No current article selected
  
     9.5.3 The HDR Extension
  
        This extension provides one new command, HDR. The label for this
        extension is PAT.
  
     9.5.3.1 HDR
  
        HDR range|<message-id>
  
        The HDR command is used to retrieve specific headers from specific
        articles in the currently selected group.
        The required header parameter is the name of a header line (e.g.
        "subject") in a newsgroup article. See RFC-1036 for a list of valid
        header lines. The required range argument may be any of the following:
          o  an article number
          o  an article number followed by a dash to indicate all
             following
          o  an article number followed by a dash followed by another
             article number.
  
        The required message-id argument indicates a specific article. The
        range and message-id arguments are mutually exclusive.
  
        A successful response consists of a 221 code followed by the output
        from the command. The output consists of one line for each article
        where the relevant header line exists. The line consists of the
        article number, a US-ASCII space, and then the contents of the header
        (without the header name). A valid response includes an empty list
        (indicating that there were no matches). Once the output is complete,
        a period is sent on a line by itself. If the optional argument is a
        message-id and no such article exists, a 430 error response shall be
        returned. A 502 response shall be returned if the client only has
        permission to transfer articles. A 500 response SHOULD be issued by
        all servers that do not recognize this command.
  
     9.5.3.1.1 Responses
  
                221    Header follows (multi-line response)
                412    No newsgroup selected
  
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                430    No such article
                500    Command not recognized
                502    Program error, function not performed
  
  
     9.5.3.1.2 Examples
  
     Example of a successful retrieval of subject lines from a range of
     articles
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] HDR Subject 3000234-300238
                [S] 221 Header Follows
                [S] 3000234 I am just a test article
                [S] 3000237 Re: I am just a test article
                [S] 3000238 Ditto
                [S] .
  
     Example of a successful retrieval of header from an article by message-id
                [S] 200 NNTP Service Ready
                [C] GROUP misc.test
                [S] 211 1234 3000234 3002322 misc.test
                [C] HDR subject <i.am.a.test.article@nowhere.to>
                [S] 221 Header information follows
                [S] 3000345 I am just a test article
                [S] .
  
     Example of an unsuccessful retrieval of a header from an article by
     message-id
                [S] 200 NNTP Service Ready
                [C] HDR subject <i.am.not.there@nowhere.to>
                [S] 430 No Such Article Found
  
     Example of an unsuccessful retrieval of headers from articles by number
     because no newsgroup was selected first
                [S] 200 NNTP Service Ready
                [C] HDR subject 300256-
                [S] 412 No newsgroup selected
  
     Example of an unsuccessful retrieval of headers from articles by
     message-id because no newsgroup was selected first
                [S] 200 NNTP Service Ready
                [C] HDR subject <i.am.a.test.article@nowhere.to>
                [S] 412 No newsgroup selected
  
     Example of retrieving header information when the current group selected
     is empty
                [S] 200 NNTP Service Ready
                [C] GROUP example.empty.newsgroup
                [S] 211 0 0 0 example.empty.newsgroup
                [C] HDR subject 0-
                [S] 221 Headers follow
                    .
  
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     Example of a failure due to restrictions configured into the server
                [S] 200 NNTP Service Ready
                [C] GROUP news.group
                [S] 211 1234 3000234 3002322 misc.test
                [C] HDR Subject 3000234-300238
                [S] 502 Service Unavailable
  
     10. The CONCLUSION Step
  
     10.1 QUIT
  
        QUIT
  
        The server process MUST acknowledge the QUIT command and then close
        the connection to the client.  This is the preferred method for a
        client to indicate that it has finished all its transactions with the
        NNTP server.
  
        If a client simply disconnects (or the connection times out or some
        other fault occurs), the server MUST gracefully cease its attempts to
        service the client, disconnecting from its end if necessary.
  
     10.1.1 Responses
  
                250   Connection closing
  
  
     10.1.2 Example
                [S] 200 NNTP Service Ready
                [C] QUIT
                [S] 205 closing connection
                [Server closes connection.]
  
     11. Other Keywords
  
        There are other keywords that may be used at any time between the
        beginning of a session and its termination.  Using these keywords does
        not alter any state information, but the response generated from the
        use of these keywords may provide useful information to clients that
        use them.
  
     11.1 DATE
  
        DATE
        This command exists to help clients find out the current Coordinated
        Universal Time[7] from the server's perspective.  This command
        SHOULD NOT be used as a substitute for NTP[8], but to provide
        information that might be useful when using the NEWNEWS command (see
        section 11.4). A system providing NNTP service SHOULD implement NTP
        for the purposes of keeping the system clock as accurate as possible.
        This command returns a one-line response code of 111 followed by the
        date and time on the server in the form YYYYMMDDhhmmss.
  
     11.1.1 Response
  
                111 YYYYMMDDhhmmss   Local date on server
  
     11.1.2 Example
                [S] 200 NNTP Service Ready
                [C] DATE
  
  
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    INTERNET DRAFT                                                  S. Barber
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                [S] 111 19990623135624
  
     11.2 The HELP Command
  
        HELP
        This command provides a short summary of commands that are understood
        by this implementation of the server. The help text will be presented
        as a textual response terminated by a single period on a line by
        itself.
  
        This text is not guaranteed to be in any particular format and SHALL
        NOT be used by clients as a replacement for the LIST EXTENSIONS
        command described in section 8.1.
  
  
     11.2.1 Responses
  
                100   Help text follows (multi-line response)
  
     11.2.2 Example
                [S] 200 NNTP Service Ready
                [C] HELP
                [S] 100 Help text follows
                [S] This is some help text. There is no specific
                [S] formatting requirement for this test, though
                [S] it is customary for it to list the valid commands
                [S] and give a brief definition of what they do
                [S] .
  
     11.3 NEWGROUPS
  
        NEWGROUPS date time [GMT]
  
        A list of newsgroups created since <date and time> MUST be listed in
        the same format as the LIST command.
        The date is sent as 6 or 8 digits in the format [XX]YYMMDD, where XX
        is the first two digits of the year, YY is the last two digits of the
        year, MM is the two digits of the month (with leading zero, if
        appropriate), and DD is the day of the month (with leading zero, if
        appropriate). If the first two digits of the year are not specified,
        the year is to be taken from the current century if YY is smaller than
        or equal to the current year, otherwise the year is from the previous
        century.
  
        Time must also be specified.  It must be as 6 digits HHMMSS with HH
        being hours in the 24-hour clock 00-23, MM minutes 00-59, and SS
        seconds 00-60, which allows for leap seconds. The token "GMT"
        specifies that the date and time are given in Coordinated Universal
        Time. If the token "GMT" is omitted then the date and time are
        specified in the server's local timezone. Note that there is no way
        within this specification of NNTP to establish the server's local
        timezone.
  
        Note that an empty list (i.e., the text body returned by this command
        consists only of the terminating period) is a possible valid response,
        and indicates that there are currently no new newsgroups.
  
        Clients SHOULD make all queries using Coordinated Universal Time when
        possible.
  
     11.3.1 Responses
  
                231   List of new newsgroups follows (multi-line
                       response)
  
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     11.3.2 Examples
  
     Example where there are new groups
                [S] 200 NNTP Service Ready
                [C] NEWGROUPS 19990624 000000 GMT
                [S] 231 list of new newsgroups follows
                [S] alt.rfc-writers.recovery
                [S] tx.natives.recovery
                [S] .
  
     Example where there are no new groups
                [S] 200 NNTP Service Ready
                [C] NEWGROUPS 19990624 000000 GMT
                [S] 231 list of new newsgroups follows
                [S] .
  
     11.4 NEWNEWS
  
        NEWNEWS newsgroups date time [GMT]
  
        A list of message-ids of articles posted or received to the specified
        newsgroup or groups since "date" will be listed. The format of the
        listing will be one message-id per line, as though text were being
        sent. Each message-id SHALL appear only once in a response. The order
        of the response has no specific significance and may vary from
        response to response in the same session. A single line consisting
        solely of one period followed by CR-LF will terminate the list.
  
        Date and time are in the same format as the NEWGROUPS command. The
        newsgroups parameter MUST be in wildmat format and MAY consist of
        multiple wildmat constructs separated by an US-ASCII comma character.
  
        Note that an empty list (i.e., the text body returned by this command
        consists only of the terminating period) is a possible valid response,
        and indicates that there is currently no new news.
  
        Clients SHOULD make all queries in Coordinated Universal Time when
        possible.
  
     11.4.1 Responses
  
           230   List of new articles by message-id follows (may be a
                  multi-line response)
  
  
     11.4.2 Examples
  
     Example where there are new articles
                [S] 200 NNTP Service Ready
                [C] NEWNEWS news.*,sci.* 19990624 000000
                [S] 230 list of new articles by message-id follows
                [S] <i.am.a.new.article@nowhere.to>
                [S] <i.am.another.new.article@nowhere.to>
  
     Example where there are no new articles
                [S] 200 NNTP Service Ready
                [C] NEWNEWS alt.* 19990624 000000
                [S] 230 list of new articles by message-id follows
  
  
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                [S] .
  
     12. Framework for NNTP Extensions
  
        Although NNTP is widely and robustly deployed, some parts of the
        Internet community might wish to extend the NNTP service.  This memo
        defines a means whereby an extended NNTP client may query the server
        to determine the service extensions that it supports.
  
        It must be emphasized that any extension to the NNTP service should
        not be considered lightly. NNTP's strength comes primarily from its
        simplicity.  Experience with many protocols has shown that:
  
        Protocols with few options tend towards ubiquity, whilst protocols
        with many options tend towards obscurity.
  
        This means that each and every extension, regardless of its benefits,
        must be carefully scrutinized with respect to its implementation,
        deployment, and interoperability costs. In many cases, the cost of
        extending the NNTP service will likely outweigh the benefit.
  
        Given this environment, the framework for the extensions described in
        this memo consists of:
  
        a)a mechanism for clients to determine a server's available extensions
        b)a registry of NNTP service extensions
  
        The LIST EXTENSIONS command is described in section 8.1 of this memo
        and is the mechanism for clients to use to determine what extensions
        are available for client use.
  
        The IANA shall maintain a registry of NNTP service extensions.
  
        An extension is identified by a unique extension-label, which is a
        string of 1 to 12 uppercase letters. The extension-label will often be
        the name of a new command that the extension adds. However this is not
        a requirement: an extension might not add any new commands or
        keywords.
  
        An extension is either a private extension or else it is included in
        the IANA registry and is defined in an RFC. Such RFCs either must be
        on the standards-track or must define an IESG-approved experimental
        protocol.
  
        The definition of an extension must include:
  
          o  a descriptive name for the extension
          o  the extension-label (which is returned by LIST EXTENSIONS
             to indicate to the client that the server supports this
             particular extension)
          o  the syntax, values, and meanings of any parameters
             following the extension-label in the output of LIST EXTENSIONS
          o  any new NNTP keywords associated with the extension
          o  the syntax and possible values of parameters associated
             with the new NNTP keywords
          o  any new parameters the extension associates with any other
             pre-existing NNTP keywords
          o  how support for the extension affects the behavior of a
             server and NNTP client
          o  any increase in the maximum length of commands over the
             value specified in this memo
  
        The extension-label of private extensions MUST begin with "X". The
        extension-label of registered extensions MUST NOT begin with "X".
  
        Any keyword values presented in the NNTP response that do not begin
        with "X" MUST correspond to a standard, standards-track, or
        IESG-approved experimental NNTP service extension registered with
        IANA.  A conforming server MUST NOT offer non "X" prefixed keyword
        values that are not described in a registered extension.
  
        Except where stated otherwise, the commands in this document are
        understood (even if not supported) by all servers and are not
        described in the list of features returned by the LIST EXTENSIONS
        command.
  
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        A server MAY provide additional keywords - either new commands or new
        parameters to existing commands - as part of a private extension.
  
        These new keywords MUST begin with "X".
  
        A server MUST NOT send different response codes to basic NNTP commands
        documented here or commands documented in registered extensions in
        response to the availability or use of a private extension.
  
     12.1 Initial IANA Registry
  
        The IANA's initial registry of NNTP service extensions consists of
        these entries:
  
     Service Extension        NNTP Extension Label   Added Behavior
  
     Overview                 OVER                   Defined
     Support                                         in this
                                                     document
  
     Specific Article Numbers LISTGROUP              Defined
                                                     in this
                                                     document
  
     Header Pattern Matching  HDR                    Defined
                                                     in this
                                                     document
  
     13. Augmented BNF[9] Syntax for NNTP Commands
  
     This syntax defines the non-terminal "command". The non-terminal
     "parameter" is used for command parameters whose syntax is specified
     elsewhere. The syntax is in alphabetical order. Note that ABNF strings
     are case insensitive.
        article-command = "ARTICLE" [1*WSP (msg-id / article-number)] *WSP
          CRLF
        article-number = 1*16DIGIT
        argument = parameter ; excluding sequence ".."
        body-command = "BODY" [1*WSP (msg-id / article-number)] *WSP CRLF
        command = article-command /
          body-command /
          date-command /
          group-command /
          head-command /
          help-command /
          ihave-command /
          last-command /
          list-active-times-command /
          list-distrib-pats-command /
          list-distributions-command /
          list-extensions-command /
          list-newsgroups-command /
          list-overview-fmt-command /
          list-command /
          listgroup-command /
          mode-reader-command /
          newgroups-command /
          newnews-command /
          next-command /
          over-command /
          hdr-command /
          post-command /
          quit-command /
          stat-command
        CR = %x0D
        CRLF = CR LF
        date-command = "DATE" *WSP CRLF
        date = 6*8DIGIT
        DIGIT = %x30-39
        group-command = "GROUP" 1*WSP newsgroup *WSP CRLF
        hdr-command = "PAT" 1*WSP header 1*WSP (range / msg-id) *WSP CRLF
        head-command = "HEAD" [1*WSP (msg-id / article-number)] *WSP CRLF
  
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        header = parameter
        help-command = "HELP" *WSP CRLF
        HT = %x09
        ihave-command = "IHAVE" 1*WSP msg-id *WSP CRLF
        last-command = "LAST" *WSP CRLF
        LF = %x0A
        list-active-times-command = "LIST" 1*WSP "ACTIVE.TIMES"
          [1*WSP wildmat] *WSP CRLF
        list-command = "LIST" [1*WSP "ACTIVE" [1*WSP wildmat] *WSP CRLF
        list-distrib-pats-command = "LIST" 1*WSP "DISTRIB.PATS" *WSP CRLF
        list-distributions-command = "LIST" 1*WSP "DISTRIBUTIONS" *WSP CRLF
        list-extensions-command = "LIST" 1*WSP "EXTENSIONS" *WSP CRLF
        list-newsgroups-command = "LIST" 1*WSP "NEWSGROUPS" [1*WSP wildmat]
          *WSP CRLF
        list-overview-fmt-command = "LIST" 1*WSP "OVERVIEW.FMT" *WSP CRLF
        listgroup-command = "LISTGROUP" [1*WSP newsgroup] *WSP CRLF
        mode-reader-command = "MODE" 1*WSP "READER" *WSP CRLF
        msg-id = <defined in RFC2822>
        newgroups-command = "NEWGROUPS" 1*WSP date 1*WSP time [1*WSP
          "GMT"/"UTC"] *WSP CRLF
        newnews-command = "NEWNEWS" 1*WSP newsgroup *("," newsgroup)
          1*WSP date 1*WSP time [1*WSP "GMT"/"UTC"]
          *WSP CRLF
        newsgroup = parameter
        next-command = "NEXT" *WSP CRLF
        over-command = "OVER" [1*WSP range] *WSP CRLF
        parameter = 1*(%x21-FF) ; generic command parameter
        post-command = "POST" *WSP CRLF
        quit-command = "QUIT" *WSP CRLF
        range = article-number ["-" [article-number]]
        SP = %x20
        stat-command = "STAT" [1*WSP (msg-id / article-number)] *WSP CRLF
        time = 6DIGIT
        UTF-8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4 / UTF8-5 / UTF8-6
        UTF8-1 = %x80-BF
        UTF8-2 = %xC0-DF UTF8-1
        UTF8-3 = %xE0-EF 2UTF8-1
        UTF8-4 = %xF0-F7 3UTF8-1
        UTF8-5 = %xF8-FB 4UTF8-1
        UTF8-6 = %xFC-FD 5UTF8-1
        wildmat = ["!"]1*("*" / "?" / wildmat-exact / wildmat-set /
        "\" (%x22-7F / UTF-8-non-ascii))
        wildmat-exact = %x22-29 / %x2B-3E / %x40-5A / %x5D-7F /
          UTF-8-non-ascii ; exclude space ! * ? [ \
        wildmat-non-hyphen = %x21-2C / %x2E-7F / UTF-8-non-ascii ; exclude
          space -
        wildmat-set = "[" ["^"] ["]" / "-"] *(wildmat-non-hyphen"["-"
          wildmat-non-hyphen]) ["-"]
        WSP = SP / HT
  
     14. Security Considerations
  
        This section is meant to inform application developers, information
        providers, and users of the security limitations in NNTP as described
        by this document. The discussion does not include definitive solutions
        to the problems revealed, though it does make some suggestions for
        reducing security risks.
  
     14.1 Personal and Proprietary Information
  
        NNTP, because it was created to distribute network news articles, will
        forward whatever information is stored in those articles.
        Specification of that information is outside this scope of this
        document, but it is likely that some personal and/or proprietary
        information is available in some of those articles. It is very
        important that designers and implementers provide informative warnings
        to users so personal and/or proprietary information is not disclosed
        inadvertently. Additionally, effective and easily understood
        mechanisms to manage the distribution of news articles must be
        provided to NNTP Server administrators, so that they are able to
        report with confidence what information is and is not being forwarded
        in news articles passing though their servers.
  
  
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     14.2 Abuse of Server Log Information
  
        A server is in the position to save session data about a user's
        requests that might identify their reading patterns or subjects of
        interest. This information is clearly confidential in nature and its
        handling can be constrained by law in certain countries. People using
        the NNTP protocol to provide data are responsible for ensuring that
        such material is not distributed without the permission of any
        individuals that are identifiable by the published results.
  
     14.3 Weak Authentication and Access Control
  
        There is no user-based or token-based authentication in the basic NNTP
        specification. Access is normally controlled by server configuration
        files. Those files specify access by using domain names or IP
        addresses. However, this specification does permit the creation of
        extensions to the NNTP protocol itself for such purposes. While
        including such mechanisms is optional, doing so is strongly
        encouraged.
  
        Other mechanisms are also available. For example, a proxy server could
        be put in place that requires authentication before connecting via the
        proxy to the NNTP server.
  
     14.4 DNS Spoofing
  
        Many existing NNTP implementations authorize incoming connections by
        checking the IP address of that connection against the IP addresses
        obtained via DNS lookups of lists of domain names given in local
        configuration files.  Servers that use this type of authentication,
        and clients that find a server by doing a DNS lookup of the server
        name, rely very heavily on the Domain Name Service, and are thus
        generally prone to security attacks based on the deliberate
        misassociation of IP addresses and DNS names.  Clients and servers
        need to be cautious in assuming the continuing validity of an IP
        number/DNS name association.
  
        In particular, NNTP clients and servers SHOULD rely on their name
        resolver for confirmation of an IP number/DNS name association, rather
        than caching the result of previous host name lookups. Many platforms
        already can cache host name lookups locally when appropriate, and they
        SHOULD be configured to do so. It is proper for these lookups to be
        cached, however, only when the TTL (Time To Live) information reported
        by the name server makes it likely that the cached information will
        remain useful.
  
        If NNTP clients or servers cache the results of host name lookups in
        order to achieve a performance improvement, they MUST observe the TTL
        information reported by DNS.
  
        If NNTP clients or servers do not observe this rule, they could be
        spoofed when a previously accessed server's IP address changes. As
        network renumbering is expected to become increasingly common, the
        possibility of this form of attack will grow. Observing this
        requirement thus reduces this potential security vulnerability.
  
        This requirement also improves the load-balancing behavior of clients
        for replicated servers using the same DNS name and reduces the
        likelihood of a user's experiencing failure in accessing sites that
        use that strategy.
  
     15. References
  
        [1] Kantor, B and P. Lapsley, "Network News Transfer Protocol",
        RFC-977, U.C. San Diego and U.C. Berkeley.
        [2] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
        2279, Alis Technologies.
        [3] Coded Character Set-7-bit American Standard Code for Information
        Interchange, ANSI x3.4-1986.
        [4] Bradner, Scott, "Keywords for use in RFCs to Indicate Requirement
  
  40]
    INTERNET DRAFT                                                  S. Barber
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        Levels", RFC-2119, Harvard University.
        [5] Salz, Rich, Manual Page for wildmat(3) from the INN 1.4
        distribution, UUNET Technologies, Revision 1.10, April, 1992.
        [6] Robertson, Rob, "FAQ: Overview database / NOV General
        Information", ftp://ftp.uu.net/networking/news/nntp/inn/faq-nov.Z,
        January, 1995.
        [7] International Telecommunications Union-Radio, "Glossary", ITU-R
        Recommendation TF.686-1, October, 1997.
        [8] Mills, David L., "Network Time Protocol (Version 3),
        Specification, Implementation and Analysis", RFC-1305, University of
        Delaware, March 1992.
        [9] Crocker, D. and Overell, P., "Augmented BNF for Syntax
        Specifications: ABNF", RFC-2234, Internet Mail Consortium and Demon
        Internet, Ltd.
  
     16. Notes
  
        UNIX is a registered trademark of the X/Open Consortium.
  
     17. Acknowledgments
  
        The author acknowledges the original authors of NNTP as documented in
        RFC 977: Brian Kantor and Phil Lapsey.
  
        The author gratefully acknowledges the work of the NNTP committee
        chaired by Eliot Lear. The organization of this document was
        influenced by the last available draft from this working group. A
        special thanks to Eliot for generously providing the original
        machine-readable sources for that document.
  
        The author gratefully acknowledges the work of the Marshall Rose &
        John G. Meyers in RFC 1939 and the work of the DRUMS working group,
        specifically RFC 1869, which is the basis of the NNTP extensions
        mechanism detailed in this document.
  
        The author gratefully acknowledges the authors of RFC 2616 for
        providing specific and relevant examples of security issues that
        should be considered for HTTP. Since many of the same considerations
        exist for NNTP, those examples that are relevant have been included
        here with some minor rewrites.
  
        The author gratefully acknowledges the comments and additional
        information provided by the following individuals in preparing one of
        the progenitors of this document:
          o  Russ Allbery <rra@stanford.edu>
          o  Wayne Davison <davison@armory.com>
          o  Clive D.W. Feather <clive@demon.net>
          o  Chris Lewis <clewis@bnr.ca>
          o  Tom Limoncelli <tal@mars.superlink.net>
          o  Eric Schnoebelen <eric@egsner.cirr.com>
          o  Rich Salz <rsalz@osf.org>
  
        This work was motivated by the work of various news reader authors and
        news server authors, which includes those listed below:
          o  Rick Adams-Original author of the NNTP extensions to the RN
             news reader and last maintainer of Bnews
          o  Stan Barber-Original author of the NNTP extensions to the
             news readers that are part of Bnews.
          o  Geoff Collyer-Original author of the OVERVIEW database
             proposal and one of the original authors of CNEWS
          o  Dan Curry-Original author of the xvnews news reader
          o  Wayne Davison-Author of the first threading extensions to
             the RN news reader (commonly called TRN).
          o  Geoff Huston-Original author of ANU NEWS
          o  Phil Lapsey-Original author of the UNIX reference
             implementation for NNTP
          o  Iain Lea-Original maintainer of the TIN news reader
          o  Chris Lewis-First known implementer of the AUTHINFO GENERIC
  
    Barber                                                          Page [41]
  
  
    INTERNET DRAFT                                                  S. Barber
    Expires: May 15, 2002                          Academ Consulting Services
  
          extension
          o        Rich Salz-Original author of INN
          o        Henry Spencer-One of the original authors of CNEWS
          o        Kim Storm-Original author of the NN news reader
  
     18. Author's Address
  
        Stan Barber
        P.O. Box 300481
        Houston, Texas 77230
        Email: sob@academ.com
  
        This document expires May 15, 2002.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
    Barber                                                          Page [42]
  

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