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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
                           Network News Transport Protocol
                           draft-ietf-nntpext-base-15.txt
          
          1  Status of this memo
          
             This memo is an Internet-Draft and is in full conformance
             with Section 10 of RFC 2026. Internet-Drafts are working
             documents of the Internet Engineering Task Force (IETF), its
             areas, and its working groups.  Note that other groups may
             also distribute working documents as Internet-Drafts.
          
             Internet-Drafts are draft documents valid for a maximum of
             six months and may be updated, replaced, or made obsolete by
             other documents at any time.  It is inappropriate to use
             Internet-Drafts as reference material or to cite them other
             than as "work in progress."
          
             The list of current Internet-Drafts can be accesses at
             http://www.ietf.org/ietf/1id-abstracts.txt.
          
             The list of Internet-Draft shadow directories can be accessed
             at http://www.ietf.org/shadow.html.
          
             This section will be updated with the appropriate verbiage
             from RFC 2223 should this memo have been found ready for
             publication as an RFC. This update will include its standards
             track status.
          
             This memo is a product of the NNTP Working Group, chaired by
             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 memo is a
             replacement for RFC 977 and officially updates the protocol
             specification. It clarifies some vagueness in RFC 977,
             includes some new base functionality and provides a specific
             mechanism to add standardized extensions to NNTP.
          
          Barber                                                 [Page 1]
          

          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
          3   Introduction
          
             This memo specifies the Network News Transport Protocol
             (NNTP), which is used for the distribution, inquiry,
             retrieval, and posting of net news articles using a reliable
             stream-based mechanism. For news reading clients, NNTP
             enables retrieval of news articles that are stored in a
             central database, giving subscribers the ability to select
             only those articles they wish to read.
          
             The netnews model provides for indexing, cross-referencing,
             and expiration of aged messages. For server-to-server
             interaction, NNTP is designed for efficient transmission of
             net news articles over a reliable full duplex communication
             channel.
          
             Every attempt is made to ensure that the protocol
             specification in this memo is compatible with the version
             specified in RFC 977[1]. However, this version does not
             support the ill-defined SLAVE command and permits four digit
             years to be specified in the NEWNEWS and NEWGROUPS commands.
             It changes the default character set to UTF-8[2] instead of
             US-ASCII[3]. It also extends the newsgroup name matching
             capabilities already documented in RFC 977.
          
             Generally, new functionality is available using new keywords.
             Part of that new functionality involves a mechanism to
             discover what new functionality is available to clients from
             a server.
          
             This mechanism can also be used to add more functionality as
             needs merit such additions.
          
             The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
             NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
             "OPTIONAL" in this memo are to be interpreted as described in
             RFC 2119[4].
          
             An implementation is not compliant if it fails to satisfy one
             or more of the MUST requirements for this protocol.  An
             implementation that satisfies all the MUST and all the SHOULD
             requirements for its protocols is said to be "unconditionally
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             compliant"; one that satisfies all the MUST requirements but
             not all the SHOULD requirements for NNTP is said to be
             "conditionally compliant".
          
             For the remainder of this memo, the term "client host" refers
             to a host making use of the NNTP service, while the term
             "server host" refers to a host that offers the NNTP service.
             In addition, where examples of interactions between a client
             host and a server host are provided a "[C]" will be used to
             represent the client host and a "[S]" will be used to
             represent the server host.
          
             For the remainder of this memo, responses will be described
             in tables listing the required format of a response followed
             by the meaning that should be ascribed to that response.
          
          4  Basic Operation.
          
             Every NNTP session MUST involve the following in this order:
                CONNECTION
                GREETING
                DISCONNECTION
          
             Other steps may occur between the GREETING and DISCONNECTION
             step. They are:
                CAPABILITIES DISCOVERY
                NEWS EXCHANGE
                CONCLUSION
          
             NNTP operates over any reliable data stream 8-bit-wide
             channel. When running over TCP/IP, the official port for the
             NNTP service is 119. Initially, the server host starts the
             NNTP service by listening on a TCP port.  When a client host
             wishes to make use of the service, it MUST establish a TCP
             connection with the server host by connecting to that host on
             the same port on which the server is listening. This is the
             CONNECTION step.  When the connection is established, the
             NNTP server host MUST send a greeting. This is the GREETING
             step. The client host and server host SHOULD then exchange
             commands and responses (respectively) until the connection is
             closed or aborted. This final step is called the
             DISCONNECTION step.
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
          
             If there is a CONCLUSION step, it MUST immediately precede
             the DISCONNECTION step. There MUST be only one CONNECTION,
             CONCLUSION and DISCONNECTION step for each NNTP session. All
             other steps MAY be repeated as needed. For example, the
             GREETING step may be repeated if the client makes use of the
             MODE READER command (See Section 7.2 for more on the MODE
             READER command).
          
             The character set for all NNTP commands is UTF-8. Commands in
             the NNTP MUST consist of an US-ASCII case-insensitive
             keyword, which MAY be followed by one or more arguments.  An
             US-ASCII CRLF pair MUST terminate all commands. Multiple
             commands MUST NOT be on the same line. Keywords MUST consist
             of printable US-ASCII characters.  Unless otherwise noted
             elsewhere in this memo, arguments SHOULD consist of printable
             US-ASCII characters. Keywords and arguments MUST be each
             separated by one or more US-ASCII SPACE or US-ASCII TAB
             characters. Keywords MUST be at least three US-ASCII
             characters and MUST NOT exceed 12 US-ASCII characters.
             Command lines MUST NOT exceed 512 octets, which includes the
             terminating US-ASCII CRLF pair. Arguments MUST NOT exceed 497
             octets.
          
             Each response MUST start with a three-digit response code
             that is sufficient to distinguish all responses. Certain
             valid responses are defined to be multi-line; for all others,
             the response is contained in a single line. All multi-line
             responses MUST adhere to the following format:
          
             The response consists of a sequence of one or more "lines",
             each being a stream of octets ending with 0x0D 0x0A (US-ASCII
             CRLF). Apart from those line endings, the stream MUST NOT
             include the octets 0x00, 0x0A, or 0x0D (US-ASCII NUL, LF, and
             CR).
          
             The first such line contains the response code as with a
             single line response.
          
             If any subsequent line begins with the "termination octet"
             (0x2E or US_ASCII "."), that line MUST be "byte-stuffed" by
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             pre-pending an additional termination octet (0x2E) to that
             line of the response.
          
             The lines of the response MUST be followed by a terminating
             line consisting of a single termination octet (0x2E or
             US_ASCII ".")followed by CRLF in the normal way. Thus a
             multi-line response is always terminated with the five octets
             "CRLF.CRLF" (in US-ASCII).
          
             There is NO limit on the length of a line.
          
             When interpreting a multi-line response, the "byte stuffing"
             MUST be undone; i.e. the client MUST ensure that, in any line
             beginning with the termination octet followed by octets other
             than US-ASCII CRLF, that initial termination octet is
             disregarded.
          
             Likewise, the terminating line ".CRLF" (in US-ASCII) MUST NOT
             be considered part of the multi-line response; i.e. the
             client MUST ensure that any line beginning with the
             termination octet followed immediately by US-ASCII CRLF is
             disregarded; (the first CRLF of the terminating "CRLF.CRLF"
             is, of course, part of the last line of the response).
          
             NOTE: Texts using an encoding (such as UTF-16 or UTF-32) that
             may contain the NUL octet or the CR or LF octets in contexts
             other than the CRLF line ending cannot be reliably conveyed
             in the above format.
          
             Note also that, although this memo does not limit the length
             of a line in any way, the standards that define the format of
             articles may do so.
          
             An NNTP server MAY have an inactivity autologout timer.  Such
             a timer SHOULD be of at least three minutes duration, with
             the exception that there MAY be a shorter limit on how long
             the server is willing to wait for the first command from the
             client.  The receipt of any command from the client during
             the timer interval SHOULD suffice to reset the autologout
             timer.  Similarly, the receipt of any significant amount of
             data from the client while in the midst of sending a multi-
             line message to the server (such as during a POST or IHAVE
          Barber                                                 [Page 5]
          

          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             command) SHOULD suffice to reset the autologout timer.  When
             the timer expires, the server SHOULD close the TCP connection
             without sending any response to the client, including when
             the client is in the middle of sending a multi-line message
             to the server.
          
          4.1  Response Codes
          
             Each response MUST begin with a three-digit status indicator.
             These are status reports from the server and indicate the
             response to the last command received from the client.
          
             The first digit of the response broadly indicates the
             success, failure, or progress of the previous command.
          
                1xx - Informative message
                2xx - Command ok
                3xx - Command ok so far, send the rest of it.
                4xx - Command was correct, but couldn't be performed for
                      some reason.
                5xx - Command unimplemented, or incorrect, or a serious
                      program error occurred.
          
             The next digit in the code indicates the function response
             category.
          
                x0x - Connection, setup, and miscellaneous messages
                x1x - Newsgroup selection
                x2x - Article selection
                x3x - Distribution functions
                x4x - Posting
                x8x - Reserved for authentication and authorization
                      extensions
                x9x - Reserved for private use (non-standard extensions)
          
             Certain responses contain parameters such as numbers and
             names in addition to the status indicator. In those cases,
             the number and type of such parameters is fixed for each
             response code to simplify interpretation by the client (any
             extension MUST follow this principle as well). In all other
             cases, the client MUST only use the status indicator itself
             to determine the nature of the response. The exact response
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             codes that can be returned in response to a given command are
             detailed in the description of the keyword that is the first
             part of the command.
          
             Parameters MUST be separated from the numeric status
             indicator and from each other by a single US-ASCII space. All
             numeric parameters MUST be in base 10 (decimal) format, and
             MAY have leading zeros. String parameters MUST contain at
             least one character and MUST NOT contain US-ASCII spaces, CR,
             LF, or tab). The server MAY add any text after the response
             code or last parameter as appropriate, and the client MUST
             NOT make decisions based on this text. Such text MUST be
             separated from the numeric status indicator or the last
             parameter by at least one US-ASCII space.
          
             The server MUST respond to any command with the appropriate
             generic response (given in section 4.1.1) if it represents
             the situation. Otherwise, each recognized command MUST return
             one of the response codes specifically listed in its
             description or in an extension. A server MAY provide
             extensions to this memo, including new commands, new features
             of existing commands, and other ways of changing the internal
             state of the server. However, the server MUST NOT produce any
             other responses to a client that does not invoke any of the
             additional features. (Therefore a client that restricts
             itself to this memo will only receive the responses that are
             listed).
          
             If a client receives an unexpected response, it SHOULD use
             the first digit of the response to determine the result. For
             example, an unexpected 2xx should be taken as success and an
             unexpected 4xx or 5xx as failure.
          
             Response codes not specified in this memo MAY be used for any
             installation-specific additional commands also not specified.
             These SHOULD be chosen to fit the pattern of x9x specified
             above.
          
             Neither this memo nor any extension registered with IANA (see
             section 12) will specify any response codes of the x9x
             pattern. (Implementers of extensions are accordingly
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             cautioned not to use such responses for extensions that may
             subsequently be submitted for registration.)
          
          4.1.1  Generic Response Codes
          
             The server MUST respond to any command with the appropriate
             one of the following generic responses if it represents the
             situation.
          
             If the command is not recognized, or it is an optional
             command or extension that is not implemented by the server,
             the response code 500 MUST be returned.
          
             If there is a syntax error in the arguments of a recognized
             command, the response code 501 MUST be returned. Note that
             where a command has variants depending on a keyword (e.g.
             LIST ACTIVE and LIST NEWSGROUPS), then 501 MUST be used when
             the requested variant is not implemented but the base command
             is.
          
             If the client is not authorized to use the specified facility
             when the server is in its current state, the response code
             502 MUST be returned. A different command might change the
             server state and permit the command if it is retried.
          
             If the server does not provide an optional feature, then the
             response code 403 MUST be returned if the omission is
             temporary (e.g. because a necessary facility is unavailable)
             and the code 503 if it is permanent  (e.g. because the server
             does not store the required information).
          
             If the server has to terminate the connection for some
             reason, it MUST give a 400 response code to the next command
             and then immediately close the TCP connection. It MAY give a
             401 response code to any command to indicate that termination
             is imminent (following a 401 response, it MUST NOT close the
             TCP connection immediately).
          
          4.2  Streaming
          
             NNTP is designed to operate over a reliable bi-directional
             connection such as TCP. Therefore, if a command does not
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             depend on the response to the previous one, it should not
             matter if it is sent before that response is received. Doing
             this is called "streaming". However, certain server
             implementations throw away all text received from the client
             following certain commands before sending their response. If
             this happens, streaming will be affected because one or more
             commands will have been ignored or misinterpreted, and the
             client will be matching the wrong responses to each command.
             Since there are significant benefits to streaming, but also
             circumstances where it is reasonable or common for servers to
             behave in the above manner, this memo puts certain
             requirements on both clients and servers.
          
             Except where stated otherwise, a client MAY use streaming.
             That is, it may send a command before receiving the response
             for the previous command. The server MUST allow streaming and
             MUST NOT throw away any text received after a command.
             Finally, the server MUST process commands in the order they
             are sent.
          
             If the specific description of a command describes it as "not
             streamable", that command MUST end any stream of commands.
             That is, the client MUST NOT send any following command until
             receiving the CRLF at the end of the response from the
             command. The server MAY ignore any data received after the
             command and before the CRLF at the end of the response is
             sent to the client.
          
             The initial connection must not be part of a stream; that is,
             the client MUST NOT send any command until receiving the CRLF
             at the end of the greeting.
          
             If the client uses blocking system calls to send commands, it
             MUST ensure that the amount of text sent in streaming does
             not cause a deadlock between transmission and reception. The
             amount of text involved will depend on window sizes in the
             transmission layer, and is typically 4k bytes for TCP.
          
          5   The WILDMAT format
          
             The WILDMAT format described here is based on the version
             first developed by Rich Salz [5], which in turn was derived
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             from the format used in the UNIX "find" command to articulate
             file names. It was developed to provide a uniform mechanism
             for matching newsgroup names in the same manner that the UNIX
             shell matches filenames.
          
          5.1  Wildmat syntax
          
             A wildmat is described by the following augmented BNF[6]
             syntax (note that this syntax contains ambiguities and
             special cases described at the end):
                wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
          
                wildmat-pattern = 1*wildmat-item
          
                wildmat-item = wildmat-exact / wildmat-wild
          
                wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-
                      7F /UTF-8-non-ascii  ; exclude * , ? [ \ ]
          
                wildmat-wild = "*" / "?"
          
             UTF-8-non-ascii is defined in section 13.
          
             This syntax must be interpreted subject to the following
             rule:
             Where a wildmat-pattern is not immediately preceded by "!",
             it shall not begin with a "!".
          
             NOTE: the characters \ , [ and ] are not allowed in wildmats,
             while * and ? are always wildcards. This should not be a
             problem since these characters cannot occur in newsgroup
             names, which is the only current use of wildmats. Backslash
             is commonly used to supress the special meaning of characters
             and brackets to introduce sets, but there is no existing
             standard practice for these in wildmats and so they were
             omitted from this memo. A future extension to this memo may
             provide semantics for these characters.
          
          5.2  Wildmat semantics
          
             A wildmat is tested against a string, and either matches or
             does not match. To do this, each constituent wildmat-pattern
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             is matched against the string and the rightmost pattern that
             matches is identified. If that wildmat-pattern is not
             preceded with "!", the whole wildmat matches. If it is
             preceded by "!", or if no wildmat-pattern matches, the whole
             wildmat does not match.
          
             For example, consider the wildmat "a*,!*b,*c*":
          
                the string "aaa" matches because the rightmost match is
                      with "a*"
                the string "abb" does not match because the rightmost
                      match is with "*b"
                the string "ccb" matches because the rightmost match is
                      with "*c*"
                the string "xxx" does not match because no wildmat-pattern
                      matches
          
             A wildmat-pattern matches a string if the string can be
             broken into components, each of which matches the
             corresponding wildmat-item in the pattern; the matches must
             be in the same order, and the whole string must be used in
             the match. The pattern is "anchored"; that is, the first and
             last characters in the string must match the first and last
             item respectively (unless that item is an asterisk matching
             zero characters).
          
             A wildmat-exact matches the same character (which may be more
             than one octet in UTF-8).
          
             "?" matches exactly one character (which may be more than one
             octet).
          
             "*" matches zero or more characters. It can match an empty
             string, but it cannot match a subsequence of a UTF-8 sequence
             that is not aligned to the character boundaries.
          
          5.3  Extensions
          
             An NNTP server or extension MAY extend the syntax or
             semantics of wildmats provided that all wildmats that meet
             the requirements of section 5.1 have the meaning ascribed to
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             them by section 5.2. Future editions of this memo may also
             extend wildmats.
          
          5.4  Examples
          
             In these examples, $ and @ are used to represent the two
             octets 0xC2 and 0xA3 respectively; $@ is thus the UTF-8
             encoding for the pound sterling symbol, shown as # in the
             descriptions.
          
             Wildmat    Description of strings that match
               abc      the one string "abc"
               abc,def  the two strings "abc" and "def"
               $@       the one character string "#"
               a*       any string that begins with "a"
               a*b      any string that begins with "a" and ends with "b"
               a*,*b    any string that begins with "a" or ends with "b"
               a*,!*b   any string that begins with "a" and does not end with
                        "b"
                        any string that begins with "a" and does not end with
             a*,!*b,c*  "b", and any string that begins with "c" no matter
                        what it ends with
                        any string that begins with "a" or "c" and does not
             a*,c*,!*b  end with "b"
               ?a*      any string with "a" as its second character
               ??a*     any string with "a" as its third character
               *a?      any string with "a" as its penultimate character
               *a??     any string with "a" as its antepenultimate character
          
          6  Format for Keyword Descriptions
          
             On the following pages are descriptions of each keyword
             recognized by the NNTP server and the responses that will be
             returned by those commands. These keywords are grouped by the
             functional step in which they are used.
          
             Each keyword is shown in upper case for clarity, although the
             NNTP server ignores case in the interpretation of commands.
             Parameters are shown as follows:
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
                UPPERCASE    indicates literal text to be included in the
                             command;
                lowercase    indicates a token described elsewhere;
                [brackets]   indicate that the parameter is optional;
                ellipsis...  indicates that the parameter may be repeated
                             any number of times (it must occur at least
                             once);
                vertical|bar indicates a choice of two mutually exclusive
                             parameters (exactly one must be provided).
          
             Parameters are case or language specific only when specified
             (either in this memo or in RFC 1036[7]).
          
             The name "wildmat" for a parameter indicates that it is a
             wildmat format pattern as defined in section 5. If the
             parameter does not meet the requirements of that section (for
             example, if it does not fit the grammar of 5.1) the NNTP
             server MAY place some interpretation on it (not specified by
             this memo) or otherwise MUST generate a 501 response.
          
          7   The GREETING Step
          
          7.1  Initial Connection
          
             There is no keyword presented by the client upon initial
             connection to the server. The server MUST present an
             appropriate response code as a greeting to the client.  This
             response informs the client about what steps the client
             should take to reach the news exchange step.
          
             If the server will accept further commands from the client
             including POST, the server MUST present a 200 greeting code.
             If the server will accept further commands from the client,
             but it is not authorized to post articles using the POST
             command, the server MUST present a 201 greeting code.
          
             Otherwise the server MUST present a 400 or 502 greeting code
             and then immediately close the connection. 502 MUST be used
             if the client is not permitted under any circumstances to
             interact with the server and 400 otherwise.
          
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
          7.1.1  Responses
          
                 200 Service available, posting allowed
                 201 Service available, posting prohibited
                 400 Service temporarily unavailable
                 502 Service unavailable
          
             Following a 400 or 502 response the server MUST immediately
             close the connection.
          
          7.1.2  Initial Connection Example
          
             Example of a normal connection from an authorized client
                  [Initial TCP connection setup completed.]
                  [C] Initial TCP connection completed
                  [S] 200 NNTP Service Ready, posting permitted
             Client can send commands at this point. In this example, the
             client jumps directly to the conclusion step (See section
             10).
                  [C] QUIT
                  [S] 205 NNTP Service exits normally
                  [Server closes connection.]
             Example of a normal connection from an unauthorized client
                  [C] Initial TCP connection completed
                  [S] 502 NNTP Service Unavailable
                  [Server closes connection.]
             Example of a normal connection from an authorized client that
             is not permitted to post
                  [Initial TCP connection setup completed.]
                  [S] 201 NNTP Service Ready, posting prohibited
             Client can send commands at this point. In this example, the
             client jumps directly to the conclusion step (See section
             10).
                  [C] QUIT
                  [S] 205 NNTP Service exits normally
                  [Server closes connection.]
             Example of a connection from any client where the server is
             unable to provide service
                  [Initial TCP connection setup completed.]
                  [S] 400 NNTP Service temporarily unavailable
                  [Server closes connection.]
          
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
          7.2  MODE READER
          
             MODE READER
             MODE READER SHOULD be sent by any client that intends to use
             any command other than IHAVE, HEAD, STAT, LIST, LIST
             EXTENSIONS, or commands advertised by the server as available
             via LIST EXTENSIONS. This command is not streamable.
          
             Servers MAY require that this command be issued before any
             other commands are sent and MAY reject any other commands
             until after a MODE READER command has been sent.
          
             The server MUST present a response using the same codes as
             the initial greeting (as described in section 7.1) to
             indicate its ability to provide reading service to the
             client.
          
             Clients SHOULD wait for a response to MODE READER after
             sending this command and SHOULD NOT send any additional
             commands until that response has been received from the
             server.
          
             Once MODE READER is sent, IHAVE (and any extensions intended
             for peer-to-peer article transfer) MAY no longer be
             permitted, even if it were permitted before the MODE READER
             command. The results of LIST EXTENSIONS MAY be different
             following a MODE READER command than prior to the issuing of
             that command.
          
             Servers are encouraged to not require this command even
             though clients SHOULD send it when appropriate. It is present
             to support some news architectures that switch between modes
             based on whether a given connection is a peer-to-peer
             connection with another server or a news reading client.
          
          7.2.1  Responses
                  200 Posting permitted
                  201 Posting prohibited
                  400 Service temporarily unavailable
                  502 Service unavailable
          
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          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             Following a 400 or 502 response the server MUST immediately
             close the connection.
          
             Note that the response need not be the same as the one
             presented during the initial greeting.
          
          7.2.2  MODE READER Examples
          
             Example of use of the MODE READER command by an authorized
             client
                  [C] MODE READER
                  [S] 200 NNTP Service Ready, posting permitted
             Client can send commands at this point. In this example, the
             client jumps directly to the conclusion step (See section
             10).
                  [C] QUIT
                  [S] 205 NNTP Service exits normally
                  [Server closes connection.]
             Example of use of MODE READER by a client not authorized to
             receive service from the server as a news reader
                  [C] MODE READER
                  [S] 502 Service Unavailable
                  [Server closes connection.]
             Example of a normal connection from an authorized client that
             is not permitted to post
                  [C] MODE READER
                  [S] 201 NNTP Service Ready, posting prohibited
             Client can send commands at this point. In this example, the
             client jumps directly to the conclusion step (See section
             10).
                  [C] QUIT
                  [S] 205 NNTP Service exits normally
                  [Server closes connection.]
             Example of a connection from any client where the server is
             unable to provide news reader service
                  [C] MODE READER
                  [S] 400 NNTP Service temporarily unavailable
                  [Server closes connection.]
          
          8   The CAPABILITIES DISCOVERY Step
          
          Barber                                                 [Page 16]
          

          INTERNET DRAFT                                          S. Barber
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                                                               January 2002
             To discover what extensions are available, an NNTP client can
             query the server with the LIST EXTENSIONS command.
             If a particular extension is unavailable, the client can
             attempt to work around it or it may wish to terminate the
             session.
          
             See section 12 for further discussion of extensions.
          
          8.1  LIST EXTENSIONS
          
             The LIST EXTENSIONS command allows a client to determine
             which extensions are supported by the server. This command
             MUST be implemented by any server that implements any
             extensions defined in this memo. This command is not
             streamable.
          
             To discover what extensions are available, an NNTP client
             SHOULD query the server early in the session for extensions
             information by issuing the LIST EXTENSIONS command. This
             command MAY be issued at anytime during a session.  It is not
             required that the client issues this command before
             attempting to make use of any extension. The response
             generated by this command MAY change during a session because
             of other state information. However, an NNTP client MUST NOT
             cache (for use in another session) any information returned
             if the LIST EXTENSIONS command succeeds. That is, an NNTP
             client is only able to get the current and correct
             information concerning available extensions during a session
             by issuing a LIST EXTENSIONS command during that session and
             processing that response.
          
             A successful response starts with a 202 code and is followed
             by a list of extensions, one per line. Each line MUST begin
             with an extension-label and optionally one or more parameters
             (separated by single spaces). The extension-label and the
             meaning of the parameters are specified as part of the
             definition of the extension. The extension-label MUST be in
             uppercase.
          
             The server MUST NOT list the same extension twice in the
             response, and MUST list all supported extensions. The order
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          INTERNET DRAFT                                          S. Barber
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                                                               January 2002
             in which the extensions are listed is not significant. The
             server need not even consistently return the same order.
             If the server does not support any extensions, it SHOULD
             return a 402 failure response but MAY return an empty list
             instead.
          
          8.1.1  Responses
          
                  202  Extension list follows (multi-line response)
                  400  Service temporarily unavailable
                  402  Server has no extensions
                  500  Unknown Command
                  501  Syntax Error
                  502  Program error, function not performed
          
             Following a 502 response an extension might still be
             available, and the client MAY attempt to use it
             The LIST EXTENSIONS command is optional, and a server MAY
             issue a 500 (unknown command) or 501 (syntax error) response
             to it.
          8.1.1.1  LIST EXTENSIONS Examples
          
             Example of a successful response:
                  [C] LIST EXTENSIONS
                  [S] 202 Extensions supported:
                  [S] OVER
                  [S] HDR
                  [S] LISTGROUP
                  [S] .
             The particular extensions shown here are simply examples of
             what might be defined in other places, and no particular
             meaning should be attributed to them.
             Example where no extensions are available, using preferred
             format:
                 [C] LIST EXTENSIONS
                 [S] 402 Server has no extensions
             Example where no extensions are available, using an empty
             list:
                  [C] LIST EXTENSIONS
                  [S] 202 Extensions supported:
                  [S] .
          Barber                                                 [Page 18]
          

          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
          
          9   The NEWS EXCHANGE Step
          
             During this step, two basic types of transactions occur:
             *  article retrieval from the server
             *  article posting to the server
          
          9.1  Article Retrieval
          
             News reading clients have available a variety of mechanisms
             to retrieve articles via NNTP. The news articles are stored
             and indexed using three types of keys. One key is the message
             id of an article. According to RFC 1036, this identifier
             should be globally unique. Another key is composed of the
             newsgroup name and the article number within that newsgroup.
             That key MUST be unique to a particular server (there will be
             only one article with that number within a particular
             newsgroup), but is not required to be globally unique.
             Additionally, because the same article can be cross-posted to
             multiple newsgroups, there may be multiple keys that point to
             the same article on the same server. The final key is the
             arrival timestamp, giving the time that the article arrived
             at the server.
          
             The server MUST ensure that article numbers are issued in
             order of arrival timestamp; that is, articles arriving later
             MUST have higher numbers than those that arrive earlier. The
             server SHOULD allocate the next sequential unused number to
             each new article.
          
             Article numbers MUST lie between 1 and 4,294,967,295
             inclusive. The client and server SHOULD NOT use leading
             zeroes in specifying article numbers, and MUST NOT use more
             than 16 digits. In some situations, the value zero replaces
             an article number to show some special situation.
          
             Message ids are defined in RFC 2822 with the following
             modifications:
             *  A message id MUST NOT contain a US-ASCII space within any
                quoted-pair.
             *  A message id MUST NOT be longer than 250 octets.
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             *  RFC 2822 obsolete syntax for message ids are not supported
                by the protocol specified in this memo.
          
          9.1.1 Article Retrieval by Newsgroup Name and Article Number
          
             The following commands are used to set the current newsgroup
             name and the "current article pointer" which is used by other
             commands for article retrieval. At the start of an NNTP
             session, both of these values are undefined.
          9.1.1.1 GROUP
          
             GROUP ggg
             The required parameter ggg is the name of the newsgroup to be
             selected (e.g. "news.software.b"). A list of valid newsgroups
             may be obtained by using the LIST keyword.  See section 9.4
             for more information on the LIST keyword.
          
             The successful selection response will return the article
             numbers of the first and last articles in the group at the
             moment of selection (these numbers are referred to as the
             "reported low water mark" and the "reported high water
             mark"), and an estimate of the number of articles on file in
             the group.
          
             If the group is not empty, the estimate MUST be at least the
             actual number of articles available, and MUST be no greater
             than one more than the difference between the reported low
             and high water marks. (Some implementations will actually
             count the number of articles on file. Others will just
             subtract the low water mark from the high water mark and add
             one to get an estimate.)
          
             If the group is empty, one of the following three situations
             will occur. Clients MUST accept all three cases; servers MUST
             NOT represent an empty group in any other way.
          
             The high water mark will be one less than the low water mark,
             and the estimated article count will be zero. Servers SHOULD
             use this method to show an empty group. This is the only time
             that the high water mark can be less than the low water mark.
             All three numbers will be zero.
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          INTERNET DRAFT                                          S. Barber
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             The high water mark is greater than or equal to the low water
             mark; the estimated article count might be zero or non-zero;
             if non-zero, the same requirements apply as for a non-empty
             group.
          
             The set of articles in a group may change after the GROUP
             command is carried out. That is:
             *  articles may be removed from the group
             *  articles may be reinstated in the group with the same
                article number, but those articles MUST have numbers no
                less than the reported low water mark (note that this is a
                reinstatement of the previous article, not a new article
                reusing the number)
             *  new articles may be added with article numbers greater
                than the reported high water mark (if an article that was
                the one with the highest number has been removed, the next
                new article will not have the number one greater than the
                reported high water mark)
          
             Except when the group is empty and all three numbers are
             zero, whenever a subsequent GROUP command for the same
             newsgroup is issued, either by the same client or a different
             client, the reported low water mark in the response MUST be
             no less than that in any previous response for that newsgroup
             sent to any client. The client may make use of the low water
             mark to remove all remembered information about articles with
             lower numbers, as these will never recur. This includes the
             situation when the high water mark is one less than the low
             water mark.
          
             No similar assumption can be made about the high water mark,
             as this can decrease if an article is removed, and then
             increase again if it is reinstated or if new articles arrive.
             When a valid group is selected by means of this command, the
             internally maintained "current article pointer" MUST be set
             to the first article in the group and the name of the current
             newsgroup MUST be set to the selected newsgroup name. If an
             invalid group is specified, the previously selected group, if
             any, and article MUST remain selected. If an empty newsgroup
             is selected, the "current article pointer" is in an
             indeterminate state and MUST NOT be used.
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          INTERNET DRAFT                                          S. Barber
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             The GROUP keyword (or the LISTGROUP keyword, if implemented)
             MUST be used by a client and a successful response received
             before the any other command is used that depends on having
             the "current article pointer" be valid.
          
             If the group specified is not available on the server, it
             MUST return a 411 error code.
          
          9.1.1.1.1  Responses
          
                    211 n l h ggg Group successfully selected (n =
                                  estimated number of articles in the
                                  group, l = low water mark, h = high
                                  water mark, ggg = name of the group
                    411           No such newsgroup
          
          9.1.1.1.2  GROUP Examples
          
             Example for a group known to the server
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
          
             Example for a group unknown to the server
                  [C] GROUP example.is.sob.bradner.or.barber
                  [S] 411 example.is.sob.bradner.or.barber is unknown
          9.1.1.2   LAST
          
             LAST
             If the current newsgroup is valid, the internally maintained
             "current article pointer" MUST be set to the previous article
             in the current newsgroup.  If already positioned at the first
             article of the newsgroup, an error message MUST be returned
             and the current article MUST remain selected.
          
             There MAY be no previous article in the group, although the
             current article number is not the reported low water mark.
             There MUST NOT be a previous article when the current article
             number is the reported low water mark.
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          INTERNET DRAFT                                          S. Barber
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             Because articles can be removed and added, the results of
             multiple LAST and NEXT commands MAY not be consistent over
             the life of a particular NNTP session.
          
             If successful, a response indicating the current article
             number and a message-id string MUST be returned. No article
             text is sent in response to this command.
          9.1.1.2.1  Responses
          
                    223 n a   Article found (n = number, a = message-id)
                    412       No newsgroup selected
                    420       Current article pointer is invalid
                    422       No previous article in this group
          
          9.1.1.2.2  LAST Examples
          
              Example of a successful article retrieval using LAST
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] NEXT
                  [S] 223 3000237 <668929@example.org> retrieved
                  [C] LAST
                  [S] 223 3000234 <45223423@example.com> retrieved
             Example of an attempt to retrieve an article without having
             selected a group (via the GROUP command) first
                  [S] 200 NNTP Service ready
                  [C] LAST
                  [S] 412 no newsgroup selected
             Example of an attempt to retrieve an article using the LAST
             command when the current article pointer is pointing at the
             first article in the group
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] LAST
                  [S] 422 No previous article to retrieve
             Example of an attempt to retrieve an article using the LAST
             command when the current group selected is empty
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          INTERNET DRAFT                                          S. Barber
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                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] LAST
                  [S] 420 No current article selected
          9.1.1.3  NEXT
          
             NEXT
             If the current newsgroup is valid, the internally maintained
             "current article pointer" MUST be advanced to the next
             article in the current newsgroup.  If no more articles remain
             in the current group, an error message MUST be returned and
             the current article MUST remain selected.
          
             If successful, a response indicating the current article
             number and the message-id string MUST be returned.  No
             article text is sent in response to this command.
          
          9.1.1.3.1  Responses
          
                    223 n a   Article found (n = number, a = message-id)
                    412       No newsgroup selected
                    420       Current article pointer is invalid
                    421       No next article in this group
          
          9.1.1.3.2  NEXT Examples
          
             Example of a successful article retrieval using NEXT
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] NEXT
                  [S] 223 3000237 <668929@example.org> retrieved
             Example of an attempt to retrieve an article without having
             selected a group (via the GROUP command) first
                  [S] 200 NNTP Service ready
                  [C] NEXT
                  [S] 412 no newsgroup selected
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          INTERNET DRAFT                                          S. Barber
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                                                               January 2002
             Example of an attempt to retrieve an article using the NEXT
             command when the current article pointer is pointing at the
             last article in the group
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] ARTICLE 3002322
                  [S] 220 3002322 <411@example.net> retrieved
                  [S] Path: pathost!demo!whitehouse!not-for-mail
                  [S] From: ôDemo Userö <nobody@example.net>
                  [S] Newsgroups: misc.test
                  [S] Subject: I am just a test article
                  [S] Date: 6 Oct 1998 04:38:40 -0500
                  [S] Organization: An Example Net, Uncertain, Texas
                  [S] Message-ID: <411@example.net>
                  [S]
                  [S] This is just a test article.
                  [S] .
                  [C] NEXT
                  [S] 421 No next article to retrieve
             Example of an attempt to retrieve an article using the NEXT
             command when the current group selected is empty
                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] NEXT
                  [S] 420 No current article selected
          
          9.2  Retrieval of Articles and Article Sections
          
             The ARTICLE, BODY, HEAD, and STAT commands are very similar.
             They differ only in the parts of the article that are
             presented to the client and in the successful response code.
             The ARTICLE command is described here in full, while the
             other commands are described in terms of the differences.
             An article, as defined by RFC 1036, consists of two parts:
             the article headers and the article body. When responding to
             one of these commands, the server presents the entire article
             or appropriate part and does not attempt to alter or
             translate it in any way.
          
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          INTERNET DRAFT                                          S. Barber
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          9.2.1  ARTICLE
          
             ARTICLE <message-id>
             ARTICLE [number]
             The ARTICLE command selects an article based on the arguments
             and presents the header, a blank line, and the body of that
             article. The command has two forms.
          
             In the first form, a message-id is specified (including the
             angle brackets), and the server presents the article with
             that message-id in its headers. In this case, the server MUST
             NOT alter the "current article pointer". This is both to
             facilitate the presentation of articles that may be
             referenced within another article being read, and because of
             the semantic difficulties of determining the proper sequence
             and membership of an article that may have been crossposted
             to more than one newsgroup.
          
             In the second form, an article number may be specified. If
             so, and if there is an article with that number in the
             currently selected group, the server MUST set the current
             article pointer to that number.
          
             Then, whether or not a number was specified, the article
             indicated by the current article pointer is presented to the
             client.
          
             Note that a previously valid article number MAY become
             invalid if the article has been removed. A previously invalid
             article number MAY become valid if the article has been
             reinstated, but such an article number MUST be no less than
             the reported low water mark for that group.
          
             The server MUST NOT change the currently selected group as a
             result of this command. The server MUST NOT change the
             current selected article except when an article number
             argument was provided and the article exists; in particular,
             it MUST NOT change it following an unsuccessful response.
          9.2.1.1  Responses
             First form (message-id specified):
          
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          INTERNET DRAFT                                          S. Barber
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                    220 0 a  Article follows (multi-line response, a =
                             message-id)
                    430      No article found with that message-id
                    502      Program error, function not performed
          
             Second form (optional article number specified):
          
                    220 n a  Article follows (multi-line response, n =
                             article number, a = message-id)
                    412      No newsgroup selected
                    420      No current article selected
                    423      No such article in this newsgroup
                    502      Program error, function not performed
          
          
             The 420 response only occurs if no article number has been
             specified.
          
             In the 220 response, the first parameter is 0 for the first
             form and the article number (within the current group) for
             the second form. The second parameter is the message-id of
             the article (within angle brackets). This is taken from the
             message-id header line of the article (required by RFC 1036).
             If there is no such line, the message-id "<0>" MUST be used
             instead (without the double quotes).
          
             Since the message-id field is unique for each article, it may
             be used by a client to skip duplicate displays of articles
             that have been posted more than once, or to more than one
             newsgroup.
          
             The article headers and body are returned as a multi-line
             response following the initial response line.
          9.2.1.2  Examples
             Example of a successful retrieval of an article (using no
             article number)
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] ARTICLE
                  [S] 220 3000234 <45223423@example.com>
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          INTERNET DRAFT                                          S. Barber
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                  [S] Path: pathost!demo!somewhere!not-for-mail
                  [S] From: ôDemo Userö <nobody@example.com>
                  [S] Newsgroups: misc.test
                  [S] Subject: I am just a test article
                  [S] Date: 6 Oct 1998 04:38:40 -0500
                  [S] Organization: An Example Com, San Jose, CA
                  [S] Message-ID: <45223423@example.com>
                  [S]
                  [S] This is just a test article.
                  [S] .
             Example of a successful retrieval of an article by message-id
                  [S] 200 NNTP Service Ready
                  [C] ARTICLE <45223423@example.com>
                  [S] 220 0 <45223423@example.com>
                  [S] Path: pathost!demo!somewhere!not-for-mail
                  [S] From: ôDemo Userö <nobody@example.com>
                  [S] Newsgroups: misc.test
                  [S] Subject: I am just a test article
                  [S] Date: 6 Oct 1998 04:38:40 -0500
                  [S] Organization: An Example Com, San Jose, CA
                  [S] Message-ID: <45223423@example.com>
                  [S]
                  [S] This is just a test article.
                  [S] .
             Example of an unsuccessful retrieval of an article by
             message-id
                  [S] 200 NNTP Service Ready
                  [C] ARTICLE <i.am.not.there@example.com>
                  [S] 430 No Such Article Found
             Example of an unsuccessful retrieval of an article by number
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 news.groups
                  [C] ARTICLE 300256
                  [S] 423 No such article number in this group
             Example of an unsuccessful retrieval of an article by number
             because no newsgroup was selected first
                  [S] 200 NNTP Service Ready
                  [C] ARTICLE 300256
                  [S] 412 No newsgroup selected
             Example of an attempt to retrieve an article when the current
             group selected is empty
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                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] ARTICLE
                  [S] 420 No current article selected
             Example of a failure due to the service being unavailable
                  [S] 200 NNTP Service Ready
                  [C] ARTICLE <i.am.a.test.article@example.com>
                  [S] 502 Service unavailable
          
          9.2.2  HEAD
          
             HEAD <message-id>
             HEAD [number]
             The HEAD command behaves identically to the ARTICLE command
             except that, if the article exists, only the headers are
             presented (the blank line separating the headers and body
             MUST NOT be included).
          9.2.2.1  Responses
          
             First form (message-id specified):
          
                    221 0 a  Article follows (multi-line response, a =
                             message-id)
                    430      No article found with that message-id
                    502      Program error, function not performed
          
             Second form (optional article number specified):
          
                    221 n a  Article follows (multi-line response, n =
                             article number, a = message-id)
                    412      No newsgroup selected
                    420      No current article selected
                    423      No such article in this newsgroup
                    502      Program error, function not performed
          
          
             Except that only the headers are included in the response,
             the 221 response behaves identically to the 220 response of
             the ARTICLE command.
          
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          INTERNET DRAFT                                          S. Barber
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          9.2.2.2  Examples
          
             Example of a successful retrieval of the headers in an
             article (using no article number)
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] HEAD
                  [S] 221 3000234 <45223423@example.com>
                  [S] Path: pathost!demo!somewhere!not-for-mail
                  [S] From: ôDemo Userö <nobody@example.com>
                  [S] Newsgroups: misc.test
                  [S] Subject: I am just a test article
                  [S] Date: 6 Oct 1998 04:38:40 -0500
                  [S] Organization: An Example Com, San Jose, CA
                  [S] Message-ID: <45223423@example.com>
                  [S] .
             Example of a successful retrieval of the headers in an
             article by message-id
                  [S] 200 NNTP Service Ready
                  [C] HEAD <45223423@example.com>
                  [S] 221 0 <45223423@example.com>
                  [S] Path: pathost!demo!somewhere!not-for-mail
                  [S] From: ôDemo Userö <nobody@example.com>
                  [S] Newsgroups: misc.test
                  [S] Subject: I am just a test article
                  [S] Date: 6 Oct 1998 04:38:40 -0500
                  [S] Organization: An Example Com, San Jose, CA
                  [S] Message-ID: <45223423@example.com>
                  [S] .
             Example of an unsuccessful retrieval of the header of an
             article by message-id
                  [S] 200 NNTP Service Ready
                  [C] HEAD <i.am.not.there@example.com>
                  [S] 430 No Such Article Found
             Example of an unsuccessful retrieval of the header of an
             article by number
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] HEAD 300256
                  [S] 423 No such article number in this group
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             Example of an unsuccessful retrieval the header of an article
             by number because no newsgroup was selected first
                  [S] 200 NNTP Service Ready
                  [C] HEAD 300256
                  [S] 412 No newsgroup selected
             Example of an attempt to retrieve the header of an article
             when the current group selected is empty
                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] HEAD
                  [S] 420 No current article selected
             Example of a failure due to the service being unavailable
                  [S] 200 NNTP Service Ready
                  [C] HEAD <i.am.a.test.article@example.com>
                  [S] 502 Service unavailable
          
          9.2.3  BODY
          
             BODY <message-id>
             BODY [number]
             The BODY command behaves identically to the ARTICLE command
             except that, if the article exists, only the body is
             presented (the blank line separating the headers and body
             MUST NOT be included).
          9.2.3.1  Responses
          
             First form (message-id specified):
          
                    222 0 a  Article follows (multi-line response, a =
                             message-id)
                    430      No article found with that message-id
                    502      Program error, function not performed
          
             Second form (optional article number specified):
          
                    222 n a  Article follows (multi-line response, n =
                             article number, a = message-id)
                    412      No newsgroup selected
                    420      No current article selected
                    423      No such article in this newsgroup
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                    502      Program error, function not performed
          
          
             Except that only the body is included in the response, the
             222 response behaves identically to the 220 response of the
             ARTICLE command.
          9.2.3.2  Examples
          
             Example of a successful retrieval of the body of an article
             (using no article number)
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] BODY
                  [S] 222 3000234 <45223423@example.com>
                  [S] This is just a test article.
                  [S] .
             Example of a successful retrieval of the body of an article
             by message-id
                  [S] 200 NNTP Service Ready
                  [C] BODY <45223423@example.com>
                  [S] 222 0 <45223423@example.com>
                  [S] This is just a test article.
                  [S] .
             Example of an unsuccessful retrieval of the body of an
             article by message-id
                  [S] 200 NNTP Service Ready
                  [C] BODY <i.am.not.there@example.com>
                  [S] 430 No Such Article Found
             Example of an unsuccessful retrieval of the body of an
             article by number
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] BODY 300256
                  [S] 423 No such article number in this group
             Example of an unsuccessful retrieval of the body of an
             article by number because no newsgroup was selected first
                  [S] 200 NNTP Service Ready
                  [C] BODY 300256
                  [S] 412 No newsgroup selected
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             Example of an attempt to retrieve the body of an article when
             the current group selected is empty
                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] BODY
                  [S] 420 No current article selected
             Example of a failure due to the service being unavailable
                  [S] 200 NNTP Service Ready
                  [C] BODY <i.am.a.test.article@example.com>
                  [S] 502 Service unavailable
          
          9.2.4  STAT
          
             STAT <message-id>
             STAT [number]
             The STAT command behaves identically to the ARTICLE command
             except that, if the article exists, it is NOT presented to
             the client.
          
             This command allows the client to determine whether an
             article exists, and in the second form what its message-id
             is, without having to process an arbitrary amount of text.
          9.2.4.1  Responses
          
             First form (message-id specified):
          
                    223 0 a  Article exists (a = message-id)
                    430      No article found with that message-id
                    502      Program error, function not performed
          
             Second form (optional article number specified):
          
                    223 n a  Article exists (n = article number, a =
                             message-id)
                    412      No newsgroup selected
                    420      No current article selected
                    423      No such article in this newsgroup
                    502      Program error, function not performed
          
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             The parameters of the 223 response are identical to those
             that would have been given in a 220 response to the
             equivalent ARTICLE command. However, the response is NOT
             multi-line.
          9.2.4.2  Examples
          
             Example of STAT on an existing article (using no article
             number)
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] STAT
                  [S] 223 3000234 <45223423@example.com>
             Example of a STAT of an existing article by message-id
                  [S] 200 NNTP Service Ready
                  [C] STAT <45223423@example.com>
                  [S] 223 0 <45223423@example.com>
             Example of an STAT of an article not on the server by
             message-id
                  [S] 200 NNTP Service Ready
                  [C] STAT <i.am.not.there@example.com>
                  [S] 430 No Such Article Found
             Example of STAT of an article not in the server by number
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] STAT 300256
                  [S] 423 No such article number in this group
             Example of STAT of an article by number when no newsgroup was
             selected first
                  [S] 200 NNTP Service Ready
                  [C] STAT 300256
                  [S] 412 No newsgroup selected
             Example of STAT of an article when the current group selected
             is empty
                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] STAT
                  [S] 420 No current article selected
             Example of a failure due to the service being unavailable
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                  [S] 200 NNTP Service Ready
                  [C] STAT <i.am.a.test.article@example.com>
                  [S] 502 Service unavailable
          
          9.3  Article Posting
          
             Article posting is done in one of two modes: individual
             article posting from news reading clients and article
             transfer from other news servers.
          
          9.3.1  POST
          
             POST
             If posting is allowed, response code 340 MUST be returned to
             indicate that the article to be posted should be sent.
             Response code 440 MUST be sent if that posting is prohibited
             for some installation-dependent reason.
          
             If posting is permitted, the article MUST be presented to the
             server by the client in the format specified by RFC 1036 (or
             by any of its successors or extensions). The text forming the
             header and body of the message to be posted MUST be sent by
             the client in the format defined above (section 0) for multi-
             line responses (except that there is no initial line
             containing a response code).  Thus a single period (".") on a
             line indicates the end of the text, and lines starting with a
             period in the original text have that period doubled during
             transmission.
          
             Following the presentation of the termination sequence by the
             client, the server MUST return a response code indicating
             success or failure of the article transfer. Note that
             response codes 340 and 440 are used in direct response to the
             POST command. Others are returned following the sending of
             the article.
          
             No attempt shall be made by the server to filter characters,
             fold or limit lines, or otherwise process incoming text. The
             intent is that the server just passes the incoming message to
             be posted to the server installation's news posting software,
             which is not defined by this memo.
          
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             The client SHOULD NOT assume that the article has been
             successfully transferred unless it receives an affirmative
             response from the server.  Since, however, the affirmative
             response may have been sent and lost, the client SHOULD use
             the same message-id in the article when resending it or check
             whether the article was successfully posted before resending
             it to ensure that the resend will not result in a duplicate
             article.
          
             This command is not streamable.
          9.3.1.1  Responses
          
                    240 Article received ok
                    340 Send article to be posted
                    440 Posting not permitted
                    441 Posting failed
          
          9.3.1.2  Examples
          
             Example of a successful posting
                  [S] 200 NNTP Service Ready
                  [C] POST
                  [S] 340 Input article. End with <CR-LF>.<CR-LF>
                  [C] From: ôDemo Userö <nobody@example.net>
                  [C] Newsgroups: misc.test
                  [C] Subject: I am just a test article
                  [C] Organization: An Example Net
                  [C]
                  [C] This is just a test article.
                  [C] .
                  [S] 240 Article received ok
             Example of an unsuccessful posting
                  [S] 200 NNTP Service Ready
                  [C] POST
                  [S] 340 Input article. End with <CR-LF>.<CR-LF>
                  [C] From: ôDemo Userö <nobody@example.net>
                  [C] Newsgroups: misc.test
                  [C] Subject: I am just a test article
                  [C] Organization: An Example Net
                  [C]
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                  [C] This is just a test article.
                  [C] .
                  [S] 441 Posting failed
             Example of an attempt to post when posting is not allowed
                  [S] 201 NNTP Service Ready, read-only
                  [C] POST
                  [S] 440 Posting not permitted
          
          9.3.2  IHAVE
          
             IHAVE <message-id>
             The IHAVE command informs the server that the client has an
             article whose id is <message-id>.  If the server desires a
             copy of that article, it MUST return response code 335
             instructing the client to send the entire article.  If the
             server does not want the article (if, for example, the server
             already has a copy of it), response code 435 indicating that
             the article is not wanted MUST be returned.  Finally, if the
             article isn't wanted immediately but the client should retry
             later if possible (if, for example, another client is in the
             process of sending the same article to the server), response
             code 436 MUST be returned.
          
             If transmission of the article is requested, the client MUST
             send the entire article, including header and body, in the
             format defined above (section 4) for multi-line responses
             (except that there is no initial line containing a response
             code). Thus a single period (".") on a line indicates the end
             of the text, and lines starting with a period in the original
             text have that period doubled during transmission. The server
             MUST return either response code 235, indicating that the
             article was successfully transferred, response code 436,
             indicating that the transfer failed but should be tried again
             later, or response code 437, indicating that the article was
             rejected.
          
             This function differs from the POST command in that it is
             intended for use in transferring already-posted articles
             between hosts. It SHOULD NOT be used when the client is a
             personal news reading program, since this command indicates
             that the forthcoming article has already been posted at
             another site and is being forwarded from another host.
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             However, the server MAY elect not to post or forward the
             article if after further examination of the article it deems
             it inappropriate to do so. Reasons for such subsequent
             rejection of an article may include such problems as
             inappropriate newsgroups or distributions, disk space
             limitations, article lengths, garbled headers, and the like.
             These are typically restrictions enforced by the server
             host's news software and not necessarily the NNTP server
             itself.
          
             The client SHOULD NOT assume that the article has been
             successfully transferred unless it receives an affirmative
             response from the server.  A lack of response (such as a
             dropped network connection or a network timeout) SHOULD be
             treated the same as a 436 error response.
          
             Because some news server software may not be able immediately
             to determine whether or not an article is suitable for
             posting or forwarding, an NNTP server MAY acknowledge the
             successful transfer of the article (with a 235 response) but
             later silently discard it.
          9.3.2.1  Responses
          
                    235 Article transferred ok
                    335 Send article to be transferred
                    435 Article not wanted, please donÆt send it.
                    436 Transfer failed, try again later.
                    437 Article rejected, please donÆt sent it again.
          
          9.3.2.2  Examples
          
             Example of successfully sending an article to another site
                  [S] 200 NNTP Service Ready
                  [C] IHAVE <i.am.an.article.you.will.want@example.com>
                  [S] 335 Send it. End with <CR-LF>.<CR-LF>
                  [C] Path: pathost!demo!somewhere!not-for-mail
                  [C] From: ôDemo Userö <nobody@example.com>
                  [C] Newsgroups: misc.test
                  [C] Subject: I am just a test article
                  [C] Date: 6 Oct 1998 04:38:40 -0500
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                  [C] Organization: An Example Com, San Jose, CA
                  [C] Message-ID: <i.am.a.test.article@example.com>
                  [C]
                  [C] This is just a test article.
                  [C] .
                  [S] 235 Article transferred ok
             Example of sending an article to another site that rejects it
                  [S] 200 NNTP Service Ready
                  [C] IHAVE <i.am.an.article.you.will.want@example.com>
                  [S] 335 Send it. End with <CR-LF>.<CR-LF>
                  [C] Path: pathost!demo!somewhere!not-for-mail
                  [C] From: ôDemo Userö <nobody@example.com>
                  [C] Newsgroups: misc.test
                  [C] Subject: I am just a test article
                  [C] Date: 6 Oct 1998 04:38:40 -0500
                  [C] Organization: An Example Com, San Jose, CA
                  [C] Message-ID: <i.am.a.test.article@example.com>
                  [C]
                  [C] This is just a test article.
                  [C] .
                  [S] 437 Article rejected. Don't send again
             Example of sending an article to another site where the
             transfer fails
                  [S] 200 NNTP Service Ready
                  [C] IHAVE <i.am.an.article.you.will.want@example.com>
                  [S] 335 Send it. End with <CR-LF>.<CR-LF>
                  [C] Path: pathost!demo!somewhere!not-for-mail
                  [C] From: ôDemo Userö <nobody@example.com>
                  [C] Newsgroups: misc.test
                  [C] Subject: I am just a test article
                  [C] Date: 6 Oct 1998 04:38:40 -0500
                  [C] Organization: An Example Com, San Jose, CA
                  [C] Message-ID: <i.am.a.test.article@example.com>
                  [C]
                  [C] This is just a test article.
                  [C] .
                  [S] 436 Transfer failed
             Example of sending an article to a site that already has it
                  [S] 200 NNTP Service Ready
                  [C] IHAVE <i.am.an.article.you.have@example.com>
                  [S] 435 Duplicate
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             Example of sending an article to a site that requests the
             article be tried again later
                  [S] 200 NNTP Service Ready
                  [C] IHAVE <i.am.an.article.you.defer@example.com>
                  [S] 436 Retry later
          
          9.4  The LIST Keyword
          
          9.4.1  LIST
          
             LIST [ACTIVE [wildmat]]
             The response to the LIST keyword with no parameters returns a
             list of valid newsgroups and associated information.  Each
             newsgroup is sent as a line of text in the following format:
                group first last status
             where <group> is the name of the newsgroup, <last> is the
             number of the last known article currently in that newsgroup,
             <first> is the number of the first article currently in the
             newsgroup, and <status> indicates the current status of the
             group on this server. Typically, the <status> will consist of
             the US-ASCII character 'y' where posting is permitted, 'n'
             where posting is not permitted and 'm' where postings will be
             forwarded to the newsgroup moderator by the news server.
             Other status strings may exist. The definition of these other
             values and the circumstances under which they are returned is
             covered in other specifications. Each field in the line is
             separated from its neighboring fields by one or more US-ASCII
             spaces.
          
             The <first> and <last> fields will always be numeric.  They
             may have leading zeros. The <first> field corresponds to the
             "reported low water mark" and the <last> field corresponds to
             the "reported high water mark" described in the GROUP command
             (see Section 9.1.1.1).
          
             The status of a newsgroup only indicates how posts to that
             newsgroup are processed. It does not indicate if the current
             client is permitted to post. That is indicated by the status
             code returned as part of the greeting.
             Please note that an empty list (i.e., the text body returned
             by this command consists only of the terminating period) is a
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             possible valid response, and indicates that there are
             currently no valid newsgroups.
          
             If the optional wildmat parameter is specified, the list is
             limited to only the groups that match the pattern.
          9.4.1.1  Responses
                    215 Information Follows (multi-line response)
          
          9.4.1.2  Examples
          
             Example of LIST returning a list of newsgroups
                  [S] 200 NNTP Service Ready
                  [C] LIST
                  [S] 215 list of newsgroups follows
                  [S] misc.test 3000234 3002322 y
                  [S] alt.fc-writers.recovery 1 4 y
                  [S] tx.natives.recovery 56 89 y
                  [S] .
             Example of LIST returning no newsgroups
                  [S] 200 NNTP Service Ready
                  [C] LIST
                  [S] 215 list of newsgroups follows
                  [S] .
          
          9.4.2  LIST ACTIVE.TIMES
          
             LIST ACTIVE.TIMES [wildmat]
             The active.times file is maintained by some news transport
             systems to contain information about who created a particular
             newsgroup and when. The format of this file includes three
             fields separated from each other by one or more US-ASCII
             space characters. The first field is the name of the
             newsgroup. The second is the time when this group was created
             on this news server measured in seconds since the start of
             January 1, 1970.  The third is the email address of the
             entity that created the newsgroup and must be a mailbox as
             defined in RFC 28228. When executed, the information is
             displayed following the 215 response. When display is
             completed, the server will send a period on a line by itself.
             If the information is not available, the server will return
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             the 503 error response. If the server does not recognize the
             command, it SHOULD return the 501 error response.
          
             If the optional wildmat parameter is specified, the list is
             limited to only the groups that match the pattern.
          9.4.2.1  Responses
          
                    215 Information Follows (multi-line response)
                    501 Syntax error
                    503 Program error, function not performed
          9.4.2.2  Examples
          
             Example of LIST ACTIVE.TIMES returning a list of newsgroups
                  [S] 200 NNTP Service Ready
                  [C] LIST ACTIVE.TIMES
                  [S] 215 information follows
                  [S] misc.test 930445408 <creatme@isc.org>
                  [S] alt.rfc-writers.recovery 930562309 <m@example.com>
                  [S] tx.natives.recovery 930678923 <sob@academ.com>
                  [S]  .
             Example of LIST ACTIVE.TIMES returning an error (The server
             software is not configured to maintain this information, but
             does recognize the command as valid.)
                  [S] 200 NNTP Service Ready
                  [C] LIST ACTIVE.TIMES
                  [S] 503 program error, function not performed
             Example of LIST ACTIVE.TIMES sent to a server that does not
             recognize this argument (e.g. The software does not maintain
             this information.)
                  [S] 200 NNTP Service Ready
                  [C] LIST ACTIVE.TIMES
                  [S] 501 Syntax Error
          
          9.4.3  LIST DISTRIBUTIONS
          
             LIST DISTRIBUTIONS
             The distributions file is maintained by some news transport
             systems to contain information about valid values for the
             Distribution: line in a news article header and about what
             the values mean. Each line contains two fields, the value and
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             a short explanation on the meaning of the value. The first
             field is separated from the second field by one or more US-
             ASCII spaces. When executed, the information is displayed
             following the 215 response. When display is completed, the
             server will send a period on a line by itself. If the
             information is not available, the server will return the 503
             error response. If the server does not recognize this
             command, it SHOULD return the 501 error response.
          9.4.3.1  Responses
          
                    215 Information Follows (multi-line response)
                    501 Syntax error
                    503 Program error, function not performed
          
          9.4.3.2  Examples
          
             Example of LIST DISTRIBUTIONS returning a list of newsgroups
                  [S] 200 NNTP Service Ready
                  [C] LIST DISTRIBUTIONS
                  [S] 215 information follows
                  [S] usa United States of America
                  [S] na North America
                  [S] world All over the World
                  [S] .
             Example of LIST DISTRIBUTIONS returning an error (e.g. The
             server software is not configured to maintain this
             information, but does recognize the command as valid.)
                  [S] 200 NNTP Service Ready
                  [C] LIST DISTRIBUTIONS
                  [S] 503 program error, function not performed
             Example of LIST DISTRIBUTIONS sent to a server that does not
             recognize the command (e.g. The server does not maintain this
             information regardless of configuration.)
                  [S] 200 NNTP Service Ready
                  [C] LIST DISTRIBUTIONS
                  [S] 501 Syntax Error
          
          9.4.4  LIST DISTRIB.PATS
          
             LIST DISTRIB.PATS
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             The distrib.pats file is maintained by some news transport
             systems to allow clients to choose a value for the
             Distribution: line in the header of a news article being
             posted. The information returned consists of lines, in no
             particular order, each of which contains three fields
             separated by colons. These fields are a weight, a wildmat
             (which may be a simple group name), and a Distribution:
             value, in that order.
          
             The client MAY use this information to select a Distribution:
             value based on the name of a newsgroup. To do so, it should
             determine the lines whose second field matches the newsgroup
             name, select that line with the highest weight (with 0 being
             the lowest), and use the Distribution: field from that line.
             When executed, the information is displayed following the 215
             response.  When display is completed, the server will send a
             period on a line by itself. If the information is not
             available, the server will return the 503 error response. If
             this command is not recognized, the server SHOULD return the
             501 error response.
          9.4.4.1  Responses
          
                    215 Information Follows (multi-line response)
                    501 Syntax error
                    503 Program error, function not performed
          
          9.4.4.2  Examples
          
             Example of LIST DISTRIB.PATS returning a list of newsgroups
                  [S] 200 NNTP Service Ready
                  [C] LIST DISTRIB.PATS
                  [S] 215 information follows
                  [S] 10:local.*:local
                  [S] .
             Example of LIST DISTRIB.PATS returning an error (e.g. The
             server software is not configured to maintain this
             information, but does recognize the command as valid.)
                  [S] 200 NNTP Service Ready
                  [C] LIST DISTRIB.PATS
                  [S] 503 program error, function not performed
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             Example of LIST DISTRIB.PATS sent to a server that does not
             recognize the command (e.g. The software does not maintain
             this information regardless of configuration.)
                  [S] 200 NNTP Service Ready
                  [C] LIST DISTRIB.PATS
                  [S] 501 Syntax Error
          
          9.4.5  LIST NEWSGROUPS
          
             LIST NEWSGROUPS [wildmat]
             The newsgroups file is maintained by some news transport
             systems to contain the name of each newsgroup that is active
             on the server and a short description about the purpose of
             each newsgroup. Each line in the file contains two fields,
             the newsgroup name and a short explanation of the purpose of
             that newsgroup. The first field is separated from the second
             field by one or more US-ASCII spaces. When executed, the
             information is displayed following the 215 response. When
             display is completed, the server will send a period on a line
             by itself. If the information is not available, the server
             will return the 503 response. If the server does not
             recognize the command it should return a 501 response. If the
             optional wildmat parameter is specified, the list is limited
             to only those groups that match the wildmat (no matching is
             done on the group descriptions). If nothing is matched an
             empty list is returned, not an error.
          9.4.5.1  Responses
          
                    215 Information Follows (multi-line response)
                    501 Syntax error
                    503 Program error, function not performed
          
          9.4.5.2  Examples
          
             Example of LIST NEWSGROUPS returning a list of newsgroups
                  [S] 200 NNTP Service Ready
                  [C] LIST NEWSGROUPS
                  [S] 215 information follows
                  [S] misc.test General Usenet testing
                  [S] alt.rfc-writers.recovery RFC Writers Recovery
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                  [S] tx.natives.recovery Texas Natives Recovery
                  [S] .
             Example of LIST NEWSGROUPS returning an error (e.g. The
             server software recognizes the command as valid, but the
             information is not available.)
                  [S] 200 NNTP Service Ready
                  [C] LIST NEWSGROUPS
                  [S] 503 program error, function not performed
          
          9.5  Standard extensions
          
             Each of the following sections describes an extension that a
             server MAY provide. If the server provides the extension, it
             MUST include the appropriate extension label in the response
             to LIST EXTENSIONS. If it does not provide it, it MUST NOT
             include the appropriate extension label. The descriptions of
             facilities in each section are written as if the extension is
             provided. If it is not provided, the entire section should be
             ignored.
          
          9.5.1  LISTGROUP extension
          
             This extension provides one command and has the extension
             label LISTGROUP.
          9.5.1.1  The LISTGROUP Command
          
             LISTGROUP [ggg]
             The LISTGROUP command is used to get a listing of all the
             article numbers in a particular newsgroup.
          
             The optional parameter ggg is the name of the newsgroup to be
             selected (e.g. "news.software.misc").  A list of valid
             newsgroups may be obtained from the LIST command. If no group
             is specified, the current group is used as the default
             argument.
          
             The successful selection response will be a list of the
             article numbers in the group followed by a period on a line
             by itself. The list starts on the next line following the 211
             response code.
          
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             When a valid group is selected by means of this command, the
             internally maintained "current article pointer" MUST be set
             to the first article in the group and the name of the current
             newsgroup MUST be set to the selected newsgroup name. If an
             invalid group is specified, the previously selected group and
             article remain selected.  If an empty newsgroup is selected,
             the "current article pointer" may be in an indeterminate
             state and should not be used.
          
             The LISTGROUP keyword MAY be used by a client as a
             replacement for the GROUP command in establishing a valid
             "current article pointer." After a successful response is
             received, any other command may be used that depends on
             having the "current article pointer" be valid.
          
             If a group name is specified and that group is not available
             on that server, the server MUST respond with the 411 error
             code.
          
             A server that does not implement this command SHOULD return a
             500 error response.
          9.5.1.1.1  Responses
          
                    211 List of article numbers follow (multi-line
                        response)
                    411 No such group
                    412 No newsgroup currently selected
                    500 Command not recognized
          
          9.5.1.1.2  Examples
          
             Example of LISTGROUP on an empty group:
                  [S] 200 NNTP Service Ready
                  [C] LISTGROUP example.empty.newsgroup
                  [S] 211 list of article numbers follows
                  [S] .
             Example of LISTGROUP on a valid current group:
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 2000 3000234 3002322 misc.test selected
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                  [C] LISTGROUP
                  [S] 211 list follows
                  [S] 3000234
                  [S] 3000237
                  [S] 3000238
                  [S] 3000239
                  [S] 3002322
                  [S] .
             Example of LISTGROUP failing because no group has been
             selected:
                  [S] 200 NNTP Service Ready
                  [C] LISTGROUP
                  [S] 412 no current group
                  [C] GROUP example.is.sob.bradner.or.barber
                  [S] 411 no such group
                  [C] LISTGROUP
                  [S] 412 no current group
          
          9.5.2  The OVER Extension
          
          This extension provides two commands, OVER and LIST
          OVERVIEW.FMT. The label for this extension is OVER.
          9.5.2.1  LIST OVERVIEW.FMT
          
             LIST OVERVIEW.FMT
             The overview.fmt file is maintained by some news transport
             systems to contain the order in which header information is
             stored in the overview databases for each newsgroup.  When
             executed, news article header fields are displayed one line
             at a time in the order in which they are stored in the
             overview database[9] following the 215 response.  When
             display is completed, the server will send a period on a line
             by itself. If the information is not available, the server
             will return the 503 response.
          
             If the header has the word "full" (without quotes) after the
             colon, the header's name is prepended to its field in the
             output returned by the server.
          
             This is command is part of the optional OVER extension which
             includes the OVER command defined in section . If the OVER
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             extension is not implemented, then this command MUST NOT be
             implemented. If that case, the server MUST return a 501 error
             response when this command is presented by the client.
          
          9.5.2.1.1  Responses
          
                    215 Information follows (multi-line response)
                    501 Syntax Error
                    503 Program error, function not performed
          
          9.5.2.1.2  Examples
          
             Example of LIST OVERVIEW.FMT returning a list of newsgroups
                  [S] 200 NNTP Service Ready
                  [C] LIST OVERVIEW.FMT
                  [S] 215 Order of fields in overview database.
                  [S] Subject:
                  [S] From:
                  [S] Date:
                  [S] Message-ID:
                  [S] .
             Example of LIST OVERVIEW.FMT returning an error
                  [S] 200 NNTP Service Ready
                  [C] LIST OVERVIEW.FMT
                  [S] 503 program error, function not performed
          9.5.2.2  OVER
          
          OVER [range]
             The OVER command returns specific header information for the
             article(s) specified from the current selected group. The
             information returned in the response to this command can be
             used by clients to follow discussion threads.
             The optional range argument may be any of the following:
             *  an article number
             *  an article number followed by a dash to indicate all
                following
             *  an article number followed by a dash followed by another
                article number
          
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             If no argument is specified, then information from the
             current article is displayed. Successful responses start with
             a 224 response followed by the overview information for all
             matched messages. Once the output is complete, a period is
             sent on a line by itself. A newsgroup must have been selected
             earlier, else a 412 error response is returned. If no
             articles are in the range specified, the server returns a 420
             error response. A 502 response will be returned if the client
             only has permission to transfer articles. A 500 response
             SHOULD be returned by servers that do not implement this
             command.
          
             The output consists of one line per article, sorted in
             numerical order of article number. Each line consists of a
             number of fields separated by an US-ASCII TAB character. The
             first 8 fields MUST be the following, in order: article
             number, subject, author, date, message-ID, references, byte
             count, line count.
          
             The article number field should contain the article number
             (within the group). The line count and byte count are
             calculated by the server based on the actual size and number
             of lines in the article. The content of the rest of the
             fields is formed by taking the original header content (such
             as the raw subject line from the article), removing all US-
             ASCII CRLF pairs, and then replacing each remaining US-ASCII
             NUL, TAB, CR, or LF character with a single US-ASCII space.
             The content of any subsequent field is given by the response
             to the LIST OVERVIEW.FMT command.  A field may be empty (in
             which case there will be two adjacent US-ASCII tabs, and a
             sequence of trailing US-ASCII tabs may be omitted).
             The server SHOULD not produce output for articles that no
             longer exist.
          9.5.2.2.1  Responses
          
                    224 Overview information follows (multi-line
                        response)
                    412 No newsgroup currently selected
                    420 No article(s) selected
                    500 Command not recognized
                    502 Program error, functions no performed
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          9.5.2.2.2  Examples
          
             Example of a successful retrieval of overview information for
             an article (using no article number)
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] OVER
                  [S] 224 Overview information follows
                      300234|I am just a test article|öDemo Userö
                       <nobody@example.com>|6 Oct 1998 04:38:40 -0500|
                       <45223423@example.com>|<45454@example.net>|1234|
                       17|Xref: news.example.com misc.test:3000363
                  [S] .
             [Please note that the line that begins with 300234 is all one
             line that has been wrapped for readability. A vertical bar
             has been inserted to show where the US-ASCII TAB should
             actually be.]
             Example of an unsuccessful retrieval of overview information
             on an article by number
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] OVER 300256
                  [S] 420 No such article in this group
             Example of an unsuccessful retrieval of overview information
             by number because no newsgroup was selected first
                  [S] 200 NNTP Service Ready
                  [C] OVER
                  [S] 412 No newsgroup selected
             Example of an attempt to retrieve an article when the current
             group selected is empty
                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] OVER
                  [S] 420 No current article selected
          
          9.5.3  The HDR Extension
          
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             This extension provides one new command, HDR. The label for
             this extension is HDR
          9.5.3.1  HDR
          
             HDR header range|<message-id>
             The HDR command is used to retrieve specific headers from
             specific articles in the currently selected group.
          
             The required header parameter is the name of a header line
             (e.g.  "subject") in a newsgroup article. See RFC-1036 for a
             list of valid header lines. The required range argument may
             be any of the following:
             *  an article number
             *  an article number followed by a dash to indicate all
                following
             *  an article number followed by a dash followed by another
                article number.
          
             The required message-id argument indicates a specific
             article. The range and message-id arguments are mutually
             exclusive.
          
             A successful response consists of a 221 code followed by the
             output from the command. The output consists of one line for
             each article where the relevant header line exists. The line
             consists of the article number, a US-ASCII space, and then
             the contents of the header (without the header name). A valid
             response includes an empty list (indicating that there were
             no matches). Once the output is complete, a period is sent on
             a line by itself. If the optional argument is a message-id
             and no such article exists, a 430 error response shall be
             returned. A 502 response shall be returned if the client only
             has permission to transfer articles. A 500 response SHOULD be
             issued by all servers that do not recognize this command.
          9.5.3.1.1  Responses
          
                    221  Header follows (multi-line response)
                    412  No newsgroup selected
                    430  No such article
                    500  Command not recognized
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                    502  Program error, function not performed
          
          9.5.3.1.2  Examples
          
             Example of a successful retrieval of subject lines from a
             range of articles
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] HDR Subject 3000234-300238
                  [S] 221 Header Follows
                  [S] 3000234 I am just a test article
                  [S] 3000237 Re: I am just a test article
                  [S] 3000238 Ditto
                  [S] .
             Example of a successful retrieval of header from an article
             by message-id
                  [S] 200 NNTP Service Ready
                  [C] GROUP misc.test
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] HDR subject <i.am.a.test.article@example.com>
                  [S] 221 Header information follows
                  [S] 3000345 I am just a test article
                  [S] .
             Example of an unsuccessful retrieval of a header from an
             article by message-id
                  [S] 200 NNTP Service Ready
                  [C] HDR subject <i.am.not.there@example.com>
                  [S] 430 No Such Article Found
             Example of an unsuccessful retrieval of headers from articles
             by number because no newsgroup was selected first
                  [S] 200 NNTP Service Ready
                  [C] HDR subject 300256-
                  [S] 412 No newsgroup selected
             Example of an unsuccessful retrieval of headers from articles
             by message-id because no newsgroup was selected first
                  [S] 200 NNTP Service Ready
                  [C] HDR subject <i.am.a.test.article@example.com>
                  [S] 412 No newsgroup selected
             Example of retrieving header information when the current
             group selected is empty
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                  [S] 200 NNTP Service Ready
                  [C] GROUP example.empty.newsgroup
                  [S] 211 0 0 0 example.empty.newsgroup
                  [C] HDR subject 0-
                  [S] 221 Headers follow
                      .
             Example of a failure due to restrictions configured into the
             server
                  [S] 200 NNTP Service Ready
                  [C] GROUP news.group
                  [S] 211 1234 3000234 3002322 misc.test
                  [C] HDR Subject 3000234-300238
                  [S] 502 Service Unavailable
          
          10  The CONCLUSION Step
          
          10.1  QUIT
          
             QUIT
             The server process MUST acknowledge the QUIT command and then
             close the connection to the client.  This is the preferred
             method for a client to indicate that it has finished all its
             transactions with the NNTP server.
          
             If a client simply disconnects (or the connection times out
             or some other fault occurs), the server MUST gracefully cease
             its attempts to service the client, disconnecting from its
             end if necessary.
          
          10.1.1  Responses
          
                    250 Connection closing
          
          10.1.2  Example
          
                  [S] 200 NNTP Service Ready
                  [C] QUIT
                  [S] 205 closing connection
                     [Server closes connection.]
          
          11  Other Keywords
          
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             There are other keywords that may be used at any time between
             the beginning of a session and its termination.  Using these
             keywords does not alter any state information, but the
             response generated from the use of these keywords may provide
             useful information to clients that use them.
          
          11.1  DATE
          
             DATE
             This command exists to help clients find out the current
             Coordinated Universal Time[10] from the server's perspective.
             This command MUST NOT be used as a substitute for NTP[11],
             but to provide information that might be useful when using
             the NEWNEWS command (see section 11.4). A system providing
             NNTP service SHOULD implement NTP for the purposes of keeping
             the system clock as accurate as possible.
          
             This command returns a one-line response code of 111 followed
             by the date and time on the server in the form
             YYYYMMDDhhmmss. This date and time is presented in
             Coordinated Universal Time.
          
          11.1.1  Response
          
                    111 YYYYMMDDhhmmss Current date and time on server
                                       presented in Coordinated
                                       Universal Time
          
          11.1.2  Example
          
                  [S] 200 NNTP Service Ready
                  [C] DATE
                  [S] 111 19990623135624
          
          11.2  The HELP Command
          
             HELP
             This command provides a short summary of commands that are
             understood by this implementation of the server. The help
             text will be presented as a textual response terminated by a
             single period on a line by itself.
          
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             This text is not guaranteed to be in any particular format
             and SHALL NOT be used by clients as a replacement for the
             LIST EXTENSIONS command described in section 8.1.
          
          11.2.1  Responses
          
                    100 Help text follows (multi-line response)
          
          11.2.2  Example
          
                  [S] 200 NNTP Service Ready
                  [C] HELP
                  [S] 100 Help text follows
                  [S] This is some help text. There is no specific
                  [S] formatting requirement for this test, though
                  [S] it is customary for it to list the valid commands
                  [S] and give a brief definition of what they do
                  [S] .
          
          11.3  NEWGROUPS
          
             NEWGROUPS date time [GMT]
             A list of newsgroups created since <date and time> MUST be
             listed in the same format as the LIST command.
          
             The date is sent as 6 or 8 digits in the format [XX]YYMMDD,
             where XX is the first two digits of the year, YY is the last
             two digits of the year, MM is the two digits of the month
             (with leading zero, if appropriate), and DD is the day of the
             month (with leading zero, if appropriate). If the first two
             digits of the year are not specified, the year is to be taken
             from the current century if YY is smaller than or equal to
             the current year, otherwise the year is from the previous
             century.
          
             Time must also be specified.  It must be as 6 digits HHMMSS
             with HH being hours in the 24-hour clock 00-23, MM minutes
             00-59, and SS seconds 00-60, which allows for leap seconds.
             The token "GMT" specifies that the date and time are given in
             Coordinated Universal Time. If the token "GMT" is omitted
             then the date and time are specified in the server's local
             timezone. Note that there is no way using the protocol
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             specified in this memo to establish the server's local
             timezone.
          
             Note that an empty list (i.e., the text body returned by this
             command consists only of the terminating period) is a
             possible valid response, and indicates that there are
             currently no new newsgroups.
          
             Clients SHOULD make all queries using Coordinated Universal
             Time (i.e. by including the ôGMTö parameter) when possible.
          
          11.3.1  Responses
          
                    231 List of new newsgroups follows (multi-line
                        response)
          
          11.3.2  Examples
          
             Example where there are new groups
                  [S] 200 NNTP Service Ready
                  [C] NEWGROUPS 19990624 000000 GMT
                  [S] 231 list of new newsgroups follows
                  [S] alt.rfc-writers.recovery
                  [S] tx.natives.recovery
                  [S] .
             Example where there are no new groups
                  [S] 200 NNTP Service Ready
                  [C] NEWGROUPS 19990624 000000 GMT
                  [S] 231 list of new newsgroups follows
                  [S] .
          
          11.4  NEWNEWS
          
             NEWNEWS wildmat date time [GMT]
             A list of message-ids of articles posted or received on the
             server to the list of newsgroups that match the wildmat since
             "date" will be listed. The format of the listing will be one
             message-id per line, as though text were being sent. The
             order of the response has no specific significance and may
             vary from response to response in the same session. If a
             message-id appears more than once it has the same meaning as
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             if it appears only once. A single line consisting solely of
             one period followed by CR-LF will terminate the list.
          
             Date and time are in the same format as the NEWGROUPS
             command.
          
             Note that an empty list (i.e., the text body returned by this
             command consists only of the terminating period) is a
             possible valid response, and indicates that there is
             currently no new news.
          
             Clients SHOULD make all queries in Coordinated Universal Time
             (i.e. by using the ôGMTö parameter) when possible.
          
          11.4.1  Responses
          
               230 List of new articles by message-id follows (may be a
                    multi-line response)
          
          11.4.2  Examples
          
             Example where there are new articles
                  [S] 200 NNTP Service Ready
                  [C] NEWNEWS news.*,sci.* 19990624 000000 GMT
                  [S] 230 list of new articles by message-id follows
                  [S] <i.am.a.new.article@example.com>
                  [S] <i.am.another.new.article@example.com>
          
             Example where there are no new articles
                  [S] 200 NNTP Service Ready
                  [C] NEWNEWS alt.* 19990624 000000 GMT
                  [S] 230 list of new articles by message-id follows
                  [S] .
          
          12  Framework for NNTP Extensions
          
             Although NNTP is widely and robustly deployed, some parts of
             the Internet community might wish to extend the NNTP service.
             This memo defines a means whereby an extended NNTP client may
             query the server to determine the service extensions that it
             supports.
          
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             It must be emphasized that any extension to the NNTP service
             should not be considered lightly. NNTP's strength comes
             primarily from its simplicity.  Experience with many
             protocols has shown that:
          
             Protocols with few options tend towards ubiquity, whilst
             protocols with many options tend towards obscurity.
          
             This means that each and every extension, regardless of its
             benefits, must be carefully scrutinized with respect to its
             implementation, deployment, and interoperability costs. In
             many cases, the cost of extending the NNTP service will
             likely outweigh the benefit.
          
             Given this environment, the framework for the extensions
             described in this memo consists of:
             *  a mechanism for clients to determine a server's available
                extensions
             *  a registry of NNTP service extensions
          
             The LIST EXTENSIONS command is described in section 8.1 of
             this memo and is the mechanism for clients to use to
             determine what extensions are available for client use.
          
             The IANA shall maintain a registry of NNTP service
             extensions.
          
             An extension is identified by a unique extension-label, which
             is a string of 1 to 12 uppercase letters. The extension-label
             will often be the name of a new command that the extension
             adds. However this is not a requirement: an extension might
             not add any new commands or keywords.
          
             An extension is either a private extension or else it is
             included in the IANA registry and is defined in an RFC. Such
             RFCs either must be on the standards-track or must define an
             IESG-approved experimental protocol.
          
             The definition of an extension must include:
             *  a descriptive name for the extension
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             *  the extension-label (which is returned by LIST EXTENSIONS
                to indicate to the client that the server supports this
                particular extension)
             *  the syntax, values, and meanings of any parameters
                following the extension-label in the output of LIST
                EXTENSIONS
             *  any new NNTP keywords associated with the extension
             *  the syntax and possible values of parameters associated
                with the new NNTP keywords
             *  any new parameters the extension associates with any other
                pre-existing NNTP keywords
             *  how support for the extension affects the behavior of a
                server and NNTP client
             *  any increase in the maximum length of commands over the
                value specified in this memo
             *  a specific statement about the effect on streaming this
                extension may have (if any)
          
             The extension-label of private extensions MUST begin with
             "X". The extension-label of registered extensions MUST NOT
             begin with "X".
          
             Any keyword values presented in the NNTP response that do not
             begin with "X" MUST correspond to a standard, standards-
             track, or IESG-approved experimental NNTP service extension
             registered with IANA.  A conforming server MUST NOT offer non
             "X" prefixed keyword values that are not described in a
             registered extension.
          
             Except where stated otherwise, the commands in this memo are
             understood (even if not supported) by all servers and are not
             described in the list of features returned by the LIST
             EXTENSIONS command.
          
             A server MAY provide additional keywords - either new
             commands or new parameters to existing commands - as part of
             a private extension. These new keywords MUST begin with "X".
          
             A server MUST NOT send different response codes to basic NNTP
             commands documented here or commands documented in registered
             extensions in response to the availability or use of a
             private extension.
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          12.1  Initial IANA Registry
          
             The IANA's initial registry of NNTP service extensions
             consists of these entries:
            Service Extension   NNTP Extension Label    Added Behavior
            Overview Support           OVER         Defined in this memo
            Specific Article
                                      LISTGROUP       Defined in this memo
                 Numbers
             Header Pattern
                                         HDR          Defined in this memo
                Matching
          
          13  Augmented BNF Syntax for NNTP Commands
          
             This syntax defines the non-terminal "command". The non-
             terminal "parameter" is used for command parameters whose
             syntax is specified elsewhere. The syntax is in alphabetical
             order. Note that ABNF strings are case insensitive.
          
                article-command = "ARTICLE" [1*WSP (msg-id / article-
                      number)] *WSP CRLF
                article-number = 1*16DIGIT
                argument = parameter ; excluding sequence ".."
                body-command = "BODY" [1*WSP (msg-id / article-number)]
                      *WSP CRLF
                command = article-command /
                      body-command /
                      date-command /
                      group-command /
                      head-command /
                      help-command /
                      ihave-command /
                      last-command /
                      list-active-times-command /
                      list-distrib-pats-command /
                      list-distributions-command /
                      list-extensions-command /
                      list-newsgroups-command /
                      list-overview-fmt-command /
                      list-command /
                      listgroup-command /
                      mode-reader-command /
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                      newgroups-command /
                      newnews-command /
                      next-command /
                      over-command /
                      hdr-command /
                      post-command /
                      quit-command /
                      stat-command
                CR = %x0D
                CRLF = CR LF
                date-command = "DATE" *WSP CRLF
                date = 6*8DIGIT
                DIGIT = %x30-39
                group-command = "GROUP" 1*WSP wildmat *WSP CRLF
                hdr-command = "HDR" 1*WSP header 1*WSP (range / msg-id)
                      *WSP CRLF
                head-command = "HEAD" [1*WSP (msg-id / article-number)]
                      *WSP CRLF
                header = parameter
                help-command = "HELP" *WSP CRLF
                HT = %x09
                ihave-command = "IHAVE" 1*WSP msg-id *WSP CRLF
                last-command = "LAST" *WSP CRLF
                LF = %x0A
                list-active-times-command = "LIST" 1*WSP "ACTIVE.TIMES"
                      [1*WSP wildmat] *WSP CRLF
                list-command = "LIST" [1*WSP "ACTIVE" [1*WSP wildmat]]
                      *WSP CRLF
                list-distrib-pats-command = "LIST" 1*WSP "DISTRIB.PATS"
                      *WSP CRLF
                list-distributions-command = "LIST" 1*WSP "DISTRIBUTIONS"
                      *WSP CRLF
                list-extensions-command = "LIST" 1*WSP "EXTENSIONS" *WSP
                      CRLF
                list-newsgroups-command = "LIST" 1*WSP "NEWSGROUPS" [1*WSP
                      wildmat] *WSP CRLF
                list-overview-fmt-command = "LIST" 1*WSP "OVERVIEW.FMT"
                      *WSP CRLF
                listgroup-command = "LISTGROUP" [1*WSP wildmat] *WSP CRLF
                mode-reader-command = "MODE" 1*WSP "READER" *WSP CRLF
                msg-id = <defined in section 9.1 of this memo>
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                newgroups-command = "NEWGROUPS" 1*WSP date 1*WSP time
                      1*WSP "GMT"] *WSP CRLF
                newnews-command = "NEWNEWS" 1*WSP wildmat 1*WSP date
                   1*WSP time [1*WSP "GMTö]*WSP CRLF
                next-command = "NEXT" *WSP CRLF
                over-command = "OVER" [1*WSP range] *WSP CRLF
                parameter = 1*(%x21-FF) ; generic command parameter
                post-command = "POST" *WSP CRLF
                quit-command = "QUIT" *WSP CRLF
                range = article-number ["-" [article-number]]
                SP = %x20
                stat-command = "STAT" [1*WSP (msg-id / article-number)]
                      *WSP CRLF
                time = 6DIGIT
                UTF-8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4 / UTF8-5 /
                      UTF8-6
                UTF8-1 = %x80-BF
                UTF8-2 = %xC0-DF UTF8-1
                UTF8-3 = %xE0-EF 2UTF8-1
                UTF8-4 = %xF0-F7 3UTF8-1
                UTF8-5 = %xF8-FB 4UTF8-1
                UTF8-6 = %xFC-FD 5UTF8-1
                wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
                wildmat-pattern = 1*wildmat-item
                wildmat-item = wildmat-exact / wildmat-wild
                wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-
                      7F /UTF-8-non-ascii  ; exclude * , ? [ \ ]
                wildmat-wild = "*" / "?"
                WSP = SP / HT
          
          14  Security Considerations
          
             This section is meant to inform application developers,
             information providers, and users of the security limitations
             in NNTP as described by this memo. The discussion does not
             include definitive solutions to the problems revealed, though
             it does make some suggestions for reducing security risks.
          
          14.1  Personal and Proprietary Information
          
             NNTP, because it was created to distribute network news
             articles, will forward whatever information is stored in
          Barber                                                 [Page 63]
          

          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             those articles. Specification of that information is outside
             this scope of this memo, but it is likely that some personal
             and/or proprietary information is available in some of those
             articles. It is very important that designers and
             implementers provide informative warnings to users so
             personal and/or proprietary information is not disclosed
             inadvertently. Additionally, effective and easily understood
             mechanisms to manage the distribution of news articles must
             be provided to NNTP Server administrators, so that they are
             able to report with confidence what information is and is not
             being forwarded in news articles passing though their
             servers.
          
          14.2  Abuse of Server Log Information
          
             A server is in the position to save session data about a
             user's requests that might identify their reading patterns or
             subjects of interest. This information is clearly
             confidential in nature and its handling can be constrained by
             law in certain countries. People using the NNTP protocol to
             provide data are responsible for ensuring that such material
             is not distributed without the permission of any individuals
             that are identifiable by the published results.
          
          14.3  Weak Authentication and Access Control
          
             There is no user-based or token-based authentication in the
             basic NNTP specification. Access is normally controlled by
             server configuration files. Those files specify access by
             using domain names or IP addresses. However, this memo does
             permit the creation of extensions to the NNTP protocol itself
             for such purposes. While including such mechanisms is
             optional, doing so is strongly encouraged.
          
             Other mechanisms are also available. For example, a proxy
             server could be put in place that requires authentication
             before connecting via the proxy to the NNTP server.
          
          14.4  DNS Spoofing
          
             Many existing NNTP implementations authorize incoming
             connections by checking the IP address of that connection
          Barber                                                 [Page 64]
          

          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             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.
          
          Barber                                                 [Page 65]
          

          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
          15  References
          
             1 Kantor, B and P. Lapsley, "Network News Transfer Protocol",
                RFC-977, U.C. San Diego and U.C. Berkeley, February, 1986.
             2 Yergeau, F., "UTF-8, a transformation format of ISO 10646",
                RFC 2279, Alis Technologies, January, 1998.
             3 Coded Character Set-7-bit American Standard Code for
                Information Interchange, ANSI x3.4-1986.
             4 Bradner, Scott, "Keywords for use in RFCs to Indicate
                Requirement Levels", RFC-2119, Harvard University, March,
                1997.
             5 Salz, Rich, Manual Page for wildmat(3) from the INN 1.4
                distribution, UUNET Technologies, Revision 1.10, April,
                1992.
             6 Crocker, D. and Overell, P., "Augmented BNF for Syntax
                Specifications: ABNF", RFC-2234, Internet Mail Consortium
                and Demon Internet, Ltd., November, 1997.
             7 Horton, M. and Adams, R., "Standard for the Interchange of
                USENET messages", RFC 1036, AT&T Bell Laboratories and The
                Center for Seismic Studies, December, 1987.
             8 Resnick, P., Editor, "Internet Message Format", RFC 2822,
                QUALCOMM Incorporated, April 2001.
             9 Robertson, Rob, "FAQ: Overview database / NOV General
                Information",
                ftp://ftp.uu.net/networking/news/nntp/inn/faq-nov.Z,
                January, 1995.
             10 International Telecommunications Union-Radio, "Glossary",
                ITU-R Recommendation TF.686-1, October, 1997.
             11 Mills, David L., "Network Time Protocol (Version 3),
                Specification, Implementation and Analysis", RFC-1305,
                University of Delaware, March 1992.
          
          16  Notes
          
             UNIX is a registered trademark of the X/Open Company Ltd.
          
          17  Acknowledgments
          
             The author acknowledges the original authors of NNTP as
             documented in RFC 977: Brian Kantor and Phil Lapsey.
          
          Barber                                                 [Page 66]
          

          INTERNET DRAFT                                          S. Barber
          Expires: July 15, 2002                 Academ Consulting Services
                                                               January 2002
             The author gratefully acknowledges the work of the NNTP
             committee chaired by Eliot Lear. The organization of this
             memo was influenced by the last available draft from this
             working group. A special thanks to Eliot for generously
             providing the original machine-readable sources for that
             document.
          
             The author gratefully acknowledges the work of the Marshall
             Rose & John G. Meyers in RFC 1939 and the work of the DRUMS
             working group, specifically RFC 1869, which is the basis of
             the NNTP extensions mechanism detailed in this memo.
          
             The author gratefully acknowledges the authors of RFC 2616
             for providing specific and relevant examples of security
             issues that should be considered for HTTP. Since many of the
             same considerations exist for NNTP, those examples that are
             relevant have been included here with some minor rewrites.
          
             The author gratefully acknowledges the comments and
             additional information provided by the following individuals
             in preparing one or more of the progenitors of this memo:
                Russ Allbery <rra@stanford.edu>
                Wayne Davison <davison@armory.com>
                Clive D.W. Feather <clive@demon.net>
                Chris Lewis <clewis@bnr.ca>
                Tom Limoncelli <tal@mars.superlink.net>
                Eric Schnoebelen <eric@egsner.cirr.com>
                Rich Salz <rsalz@osf.org>
          
             This work was motivated by the work of various news reader
             authors and news server authors, which includes those listed
             below:
                Rick Adams-Original author of the NNTP extensions to the
                      RN news reader and last maintainer of Bnews
                Stan Barber-Original author of the NNTP extensions to the
                      news readers that are part of Bnews.
                Geoff Collyer-Original author of the OVERVIEW database
                      proposal and one of the original authors of CNEWS
                Dan Curry-Original author of the xvnews news reader
                Wayne Davison-Author of the first threading extensions to
                      the RN news reader (commonly called TRN).
                Geoff Huston-Original author of ANU NEWS
                Phil Lapsey-Original author of the UNIX reference
                      implementation for NNTP
                Iain Lea-Original maintainer of the TIN news reader
                Chris Lewis-First known implementer of the AUTHINFO
                      GENERIC extension
                Rich Salz-Original author of INN
                Henry Spencer-One of the original authors of CNEWS
                Kim Storm-Original author of the NN news reader
          
          18  Author's Address
          
          Stan Barber
          P.O. Box 300481
          Houston, Texas 77230
          Email: sob@academ.com
          
          This memo expires July 15, 2002.
          
          Barber                                                 [Page 67]
          

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