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          INTERNET DRAFT                                          S. Barber
          Expires: February 3, 1998              Academ Consulting Services
                                                             September 1997
          
                           Network News Transport Protocol
          
                           draft-ietf-nntpext-base-01.txt
          
          1.   Status of this Document
          
            This document is an Internet-Draft. Internet-Drafts are
            working documents of the Internet Engineering Task Force
            (IETF), its areas, and its working groups.  Note that other
            groups may also distribute working documents as Internet-
            Drafts.
          
            Internet-Drafts are draft documents valid for a maximum of six
            months and may be updated, replaced, or made obsolete by other
            documents at any time.  It is inappropriate to use Internet-
            Drafts as reference material or to cite them other than as
            "work in progress."
          
          
            To learn the current status of any Internet-Draft, please
            check the "1id-abstracts.txt" listing contained in the
            Internet-Drafts Shadow Directories on ftp.is.co.za (Africa),
            nic.nordu.net (Europe), munnari.oz.au (Pacific Rim),
            ds.internic.net (US East Coast), or ftp.isi.edu (US West
            Coast).
          
            This document is a product of the NNTP Working Group, chaired
            by Ned Freed and Stan Barber.
          
          
          
          2.    Abstract
            The Network News Transport Protocol has been in use in the
            Internet for a decade and remains one of the most popular
            protocols (by volume) in use today. This document is a
            replacement for RFC 977 and officially updates the protocol
            specification. It clarifies some vagueness in RFC 977,
            includes some new base functionality and provides a specific
            mechanism to add standardized extensions to NNTP.
          
          
          
          3.   Introduction
            This document specifies the Network News Transport Protocol
            (NNTP), which is used for the distribution, inquiry,
            retrieval, and posting of Usenet articles using a reliable
            stream-based mechanism. For news reading clients, NNTP enables
            retrieval of news articles that are stored in a central
            database, giving subscribers the ability to select only those
            articles they wish to read.
          
            The netnews model provides for indexing, cross-referencing,
            and expiration of aged messages. For server-to-server
          
          
          Barber                                              [Page 1]
          

          INTERNET DRAFT                                September 1997
          
          
            interaction, NNTP is designed for efficient transmission of
            Usenet articles over a reliable full duplex communication
            method.
          
            Every attempt is made to insure that the protocol
            specification in this document is compatible with the version
            specified in RFC 977[1].
          
            Generally, new functionality is available using new keywords.
            Part of that new functionality involves a mechanism to
            discover what new functionality is available to clients from a
            server.
          
            This mechanism can also be used to add more functionality as
            needs merit such additions.
          
            In this document, the words that are used to define the
            significance of each particular requirement are capitalized.
          
            These words are:
          
            . "MUST"
          
            This word or the adjective "REQUIRED" means that the item is
            an absolute requirement of the specification.
          
            . "SHOULD"
          
            This word or the adjective "RECOMMENDED" means that there may
            exist valid reasons in particular circumstances to ignore this
            item, but the full implications should be understood and the
            case carefully weighed before choosing a different course.
          
            . "MAY"
          
            This word or the adjective "OPTIONAL" means that this item is
            truly optional.  One vendor may choose to include the item
            because a particular marketplace requires it or because it
            enhances the product, for example; another vendor may omit the
            same item.
          
            An implementation is not compliant if it fails to satisfy one
            or more of the MUST requirements for this protocol.  An
            implementation that satisfies all the MUST and all the SHOULD
            requirements for its protocols is said to be "unconditionally
            compliant"; one that satisfies all the MUST requirements but
            not all the SHOULD requirements for NNTP is said to be
            "conditionally compliant".
          
            For the remainder of this memo, the term "client host" refers
            to a host making use of the NNTP service, while the term
            "server host" refers to a host that offers the NNTP service.
          
          
          
          
          Barber                                              [Page 2]
          

          INTERNET DRAFT                                September 1997
          
          
          4.   Basic Operation.
          
          
            Every NNTP session MUST involve the following in this order:
          
            CONNECTION
            GREETING
            DISCONNECTION
          
            Other steps may occur between the GREETING and DISCONNECTION
            step. They are:
          
            CAPABILITIES DISCOVERY
            AUTHENTICATION
            NEWS TRANSFER
            CONCLUSION
          
            NNTP operates over any reliable data stream 8-bit-wide
            channel. When running over TCP/IP, the official port for the
            NNTP service is 119. Initially, the server host starts the
            NNTP service by listening on a TCP port.  When a client host
            wishes to make use of the service, it MUST establish a TCP
            connection with the server host by connecting to that host on
            the same port on which the server is listening. This is the
            CONNECTION step.  When the connection is established, the NNTP
            server host MUST send a greeting. This is the GREETING step.
            The client host and server host then SHOULD then exchange
            commands and responses (respectively) until the connection is
            closed or aborted. This final step is called the DISCONNECTION
            step.
          
            If there is a CONCLUSION step, it MUST immediately precede the
            DISCONNECTION step. There MUST be only one CONNECTION,
            CONCLUSION and DISCONNECTION step for each NNTP session. All
            other steps MAY be repeated as needed.
          
            The default character set for all NNTP commands is US-
            ASCII[2]. Commands in the NNTP MUST consist of a case-
            insensitive keyword, which MAY be followed by one or more
            arguments.  All commands MUST be terminated by a CRLF pair.
            Multiple commands MUST not be permitted on the same line.
            Keywords MUST consist of printable US-ASCII characters.
            Unless otherwise noted elsewhere in this document, Arguments
            SHOULD consist of printable US-ASCII characters. Keywords and
            arguments MUST be each separated by one or more SPACE or TAB
            characters. Keywords MUST be at least three characters and
            MUST NOT exceed 12 characters.  Command lines MUST not exceed
            512 characters, which includes the terminating CRLF pair.
          
            Each response MUST start with a three-digit status indicator
            that is sufficient to distinguish all responses. Responses to
            certain commands MAY be multi-line. In these cases, which are
            clearly indicated below, after sending the first line of the
            response and a CRLF, any additional lines are sent, each
          
          
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            terminated by a CRLF pair. When all lines of the response have
            been sent, a final line MUST be sent, consisting of a
            termination octet (ASCII decimal code 046, ".") and a CRLF
            pair.  If any line of the multi-line response begins with the
            termination octet, the line MUST be "byte-stuffed" by pre-
            pending the termination octet to that line of the response.
            Hence, a multi-line response is terminated with the five
            octets "CRLF.CRLF".  When examining a multi-line response, the
            client MUST check to see if the line begins with the
            termination octet. If so and if octets other than CRLF follow,
            the first octet of the line (the termination octet) MUST be
            stripped away.  If so and if CRLF immediately follows the
            termination character, then the response from the NNTP server
            is ended and the line containing ".CRLF" MUST not considered
            part of the multi-line response.
          
            A NNTP server MAY have an inactivity autologout timer. Such a
            timer MUST be of at least 10 minutes duration.  The receipt of
            any command from the client during that interval should
            suffice to reset the autologout timer.  When the timer
            expires, the server should close the TCP connection without
            sending any response to the client.
          
          
          
          4.1       Responses Codes
          
            Each response MUST begin with a three-digit response code.
            These are status reports from the server and indicate the
            response to the last command received from the client.
          
            The first digit of the response broadly indicates the success,
            failure, or progress of the previous command.
          
            1xx - Informative message
            2xx - Command ok
            3xx - Command ok so far, send the rest of it.
            4xx - Command was correct, but couldn't be performed for some
               reason.
            5xx - Command unimplemented, or incorrect, or a serious
               program error occurred.
            The next digit in the code indicates the function response
            category.
          
            x0x - Connection, setup, and miscellaneous messages
            x1x - Newsgroup selection
            x2x - Article selection
            x3x - Distribution functions
            x4x - Posting
            x5x - Authentication and Authorization
            x8x - Nonstandard (private implementation) extensions
            x9x - Debugging output
          
          
          
          
          Barber                                              [Page 4]
          

          INTERNET DRAFT                                September 1997
          
          
            The exact response codes that MUST be expected from each
            command are detailed in the description of the keyword that is
            the first part of the command. In addition, below is listed a
            general set of response codes that MAY be received at any
            time.
          
            Certain status responses contain parameters such as numbers
            and names. The number and type of such parameters SHOULD be
            fixed for each response code to simplify interpretation of the
            response.
          
            Parameters MUST be separated from the numeric response code
            and from each other by a single space. All numeric parameters
            MUST be in base 10 (decimal) format, and may have leading
            zeros. All string parameters MUST begin after the separating
            space, and MUST end before the following separating space or
            the CR-LF pair at the end of the line. (Therefore, string
            parameters MUST not contain spaces.) All text, if any, in the
            response which is not a parameter of the response must follow
            and be separated from the last parameter by a space.  Also,
            note that the text following a response number may vary in
            different implementations of the server. The 3-digit numeric
            code should be used to determine what response was sent.
          
            Response codes not specified in this standard MAY be used for
            any installation-specific additional commands also not
            specified. These SHOULD be chosen to fit the pattern of x8x
            specified above. (Note that debugging is provided for
            explicitly in the x9x response codes.)
          
            The use of unspecified response codes for a standard command
            is prohibited.
          
            The response pattern x9x is provided for debugging.  Since
            much debugging output may be classed as "informative
            messages", it MUST be the case that responses 190 through 199
            WILL be used for various debugging outputs.  There is no
            requirement in this specification for debugging output.
            However, if such is provided over the connected stream, it
            MUST use these response codes.  If appropriate to a specific
            implementation, other x9x codes MAY be used for debugging.
            (For example, response code 290 could be used to acknowledge a
            remote debugging request.)
          
            A server MUST respond to an unrecognized, unimplemented, or
            syntactically invalid command with a negative status indicator
            (response codes of the form 5XX).  A server MUST respond to a
            command issued when the session is in an incorrect state by
            responding with a negative status indicator. This may be from
            either the 4XX or 5XX group as appropriate.
          
          
          
          
          
          
          Barber                                              [Page 5]
          

          INTERNET DRAFT                                September 1997
          
          
          5.   The WILDMAT format
          
            The WILDMAT format[3] was first developed by Rich Salz based
            on the format used in the UNIX "find" command to articulate
            file names. It was developed to provide a uniform mechanism
            for matching patterns in the same manner that the UNIX shell
            matches filenames. Patterns are implicitly anchored at the
            beginning and end of each string when testing for a match.
            There are five pattern-matching operations other than a strict
            one-to-one match between the pattern and the source to be
            checked for a match. The first is an asterisk (*) to match any
            sequence of zero or more characters. The second is a question
            mark (?) to match any single character. The third specifies a
            specific set of characters. The set is specified as a list of
            characters, or as a range of characters where the beginning
            and end of the range are separated by a minus (or dash)
            character, or as any combination of lists and ranges. The dash
            can also be included in the set as a character it if is the
            beginning or end of the set. This set is enclosed in square
            brackets. The close square bracket (]) may be used in a set if
            it is the first character in the set. The fourth operation is
            the same as the logical not of the third operation and is
            specified the same way as the third with the addition of a
            caret character (^) at the beginning of the test string just
            inside the open square bracket. The final operation uses the
            backslash character to invalidate the special meaning of the
            open square bracket ([), the asterisk, backslash or the
            question mark. Two backslashes in sequence will result in the
            evaluation of the backslash as a character with no special
            meaning.
          
          
          
          5.1       Examples
          
                 a) [^]-] -- matches any single character other than a
                    close square bracket or a minus sign/dash.
                 b) *bdc  -- matches any string that ends with the string
                    "bdc" including the string "bdc" (without quotes).
                 c) [0-9a-zA-Z] -- matches any single printable alphanumeric
                    ASCII character.
                 d) a??d  --  matches any four character string which
                    begins with a and ends with d.
          
          6.   Format for Keyword Descriptions
          
            On the following pages are descriptions of each keyword
            recognized by the NNTP server and the responses that will be
            returned by those commands. These keywords are grouped by the
            functional step in which they are used.
          
            Each keyword is shown in upper case for clarity, although case
            is ignored in the interpretation of commands by the NNTP
            server. Any parameters are shown in lower case.  A parameter
          
          
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            shown in [square brackets] is optional. For example, [GMT]
            indicates that the triglyph GMT may present or omitted. A
            parameter that may be repeated is followed by an ellipsis.
            Mutually exclusive parameters are separated by a vertical bar
            (|) character. For example, ggg|<message-id> indicates that a
            group name or a <message-id> may be specified, but not both.
            Some parameters may be case or language specific. See RFC
            1036[4] for these details.
          
            In addition, certain commands make use of a pattern for
            selection of multiple news groups. The pattern in all cases is
            based on the WILDMAT format introduced by Rich Salz in 1986.
            Arguments expected to be in wildmat format will be represented
            by the string wildmat. This format is discussed in detail in
            section 5 of this memo.
          
          
          
          7.   The GREETING Step
          
          
          
          7.1       Initial Connection
          
            There is no keyword presented by the client upon initial
            connection to the server. The server MUST present an
            appropriate response code as a greeting to the client.  This
            response informs the client about what steps the client should
            take to reach the news exchange step.
          
            The server must present a 200 greeting code if the client is
            authorized to post articles though the use of the POST keyword
            on this server.
          
            The server must present a 201 greeting code if the client is
            not authorized to post articles using the POST keyword, but no
            other authentication is required.
          
            The server must present a 205 greeting code if the client is
            required to present authentication before it is permitted to
            use any keywords available in the news exchange step.
          
            The server must present a 502 greeting code if the client is
            not permitted under any circumstances from interacting with
            the server. The server should immediately close the connection
            with the client after presenting this code.
          
            In all other cases, the server must present a 400 greeting
            code.
          
          
          
          7.1.1     MODE READER
          
          
          
          Barber                                              [Page 7]
          

          INTERNET DRAFT                                September 1997
          
          
            MODE READER
          
            MODE READER MAY be used by the client to indicate to the
            server that it is a news reading client. This command may be
            entered at any time. The server must present a greeting code
            (as described in section 7.1) appropriate to the server's
            ability to provide service to this client in this mode.
          
          
          
          7.1.1.1   Responses
          
                 200 Hello, you can post
                 201 Hello, you can't post
                 205 Authentication required
                 400 Service temporarily unavailable
                 502 Service unavailable
          
          
          
          8.   The CAPABILITIES DISCOVERY Step
          
          
            A client NNTP supporting NNTP service extensions should query
            a server early in the session for extensions session by
            issuing the LIST EXTENSIONS command. If the NNTP server
            supports the NNTP service extensions it MUST give a successful
            response (see section 8.1.1), a failure response (see section
            8.1.2), or an error response (see section 8.1.3). If the NNTP
            server does not support any NNTP service extensions, it MUST
            generate an error response (see section 8.1.4).
          
          
          
          8.1  LIST EXTENSIONS
          
            If successful, the server NNTP MUST respond with code 202. On
            failure, the server NNTP MUST respond with code 503. On error,
            the server NNTP MUST respond with one of codes 400, 402, 500
            and 501.
          
            This command MAY be issued at anytime during a session.  It is
            not required that the client issues this command before
            attempting to make use of any extension. The response
            generated by this command MAY change during a session because
            of other state information (e.g. authentication or server
            administration). However, a client NNTP MUST not cache (for
            use in another session) any information returned if the LIST
            EXTENSIONS command succeeds. That is, a client NNTP MUST issue
            the LIST EXTENSIONS command at least once during each session
            to get the current and correct information concerning
            available extensions during that session.
          
          
          
          
          Barber                                              [Page 8]
          

          INTERNET DRAFT                                September 1997
          
          
          8.1.1     Successful response
          
            If the server NNTP implements and is able to perform the LIST
            EXTENSIONS command, it MUST return code 202.
          
            This response MUST be a multi-line reply. Each line of the
            response MUST contain a supported keyword and, optionally, one
            or more parameters. The list MUST end with a period on a line
            by itself.
          
            Although LIST EXTENSIONS keywords may be specified in upper,
            lower, or mixed case, they must always be recognized and
            processed in a case-insensitive manner.
          
          
          
          8.1.2     Failure response
          
            If for some reason the server NNTP is unable to list the
            service extensions it supports, it MUST return code 503.
          
            In the case of a failure response, the client NNTP may try the
            extensions either as the need arises or configure itself for
            the basic NNTP functionality defined in this document.
          
          
          
          8.1.3     Error responses from extended servers
          
            If the server NNTP recognizes the LIST EXTENSIONS command, but
            due to various conditions cannot make any extensions available
            to the client at the time the client issued the LIST
            EXTENSIONS command, it MUST return code 402. No list (even an
            empty one) will be returned.
          
            The client NNTP should configure itself for the basic NNTP
            functionality defined in this document, or issue commands that
            might change the state of the server (authentication, for
            example), or issue the QUIT command (see section 11.1) if a
            particular extension is required for the client to properly
            operate.
          
            If the server NNTP determines that the NNTP service is no
            longer available (e.g., due to imminent system shutdown), it
            must return code 400.
          
            In the case of an error response, the client NNTP should issue
            the QUIT command (see section 11.1).
          
          
          
          8.1.4     Responses from servers without extensions
          
          
          
          
          Barber                                              [Page 9]
          

          INTERNET DRAFT                                September 1997
          
          
            A server NNTP that conforms to this memo but does not support
            the extensions specified here will not recognize the LIST
            EXTENSIONS command and MUST consequently return code 500 or
            code 501. The server NNTP SHALL stay in the same state after
            returning this code. The client NNTP may try the extensions
            either as the need arises or configure itself for the basic
            NNTP functionality defined in this document.
          
          
          
          8.1.5     Responses from improperly implemented servers
          
            A server NNTP that improperly implements the LIST EXTENSIONS
            command may return an empty list. Clients SHALL accommodate
            this protocol violation and interpret it as a response code
            402.
          
          
          9.   The AUTHENTICATION Step
          
          9.1  AUTHINFO
          
            AUTHINFO is used to inform a server about the identity of a
            user of the server. In all cases, clients MUST provide this
            information when requested by the server. Servers are not
            required to accept authentication information that is
            volunteered by the client. Clients MUST accommodate servers
            that reject any authentication information volunteered by the
            client.
          
          
          
          9.1.1     AUTHINFO
          
            AUTHINFO USER username
          
            AUTHINFO PASS password
          
            When authorization is required, the server MUST send a 450
            response requesting authorization from the client.  The client
            MUST enter AUTHINFO USER username in order to make use of the
            AUTHINFO authentication step. If the server will accept this
            form of authentication and a password is required to complete
            the authentication step, the server MUST respond with a 350
            response. The client MUST then send AUTHINFO PASS followed by
            one or more space characters followed by the password. If the
            username/password combination is valid or no password is
            required, the server MUST return a 250 response and the client
            should then retry the original command to which the server
            responded with the 450 response. The command SHALL then be
            processed by the server normally. If the combination is not
            valid, the server MUST return a 452 response.
          
          
          
          
          Barber                                             [Page 10]
          

          INTERNET DRAFT                                September 1997
          
          
            If the server returns 501, this means that the authenticator
            invocation was syntactically incorrect, or that this form of
            AUTHINFO is not supported.
          
            If the requested authenticator capability is not found or
            there is some other unspecified server program error, the
            server MUST return the 503 response code.
          
          
          9.1.1.1   Responses
          
                 250 Authorization accepted
                 350 Continue with authorization sequence
                 450 Authorization required for this command
                 452 Authorization rejected
                 501 Command not supported or Command Syntax Error
                 502 Program error, function not performed
          
          9.1.2     AUTHINFO GENERIC
          
          
            AUTHINFO GENERIC authenticator arguments...
          
            AUTHINFO GENERIC is used to identify a specific entity to the
            server using arbitrary authentication or identification
            protocols. The desired protocol is indicated by the
            authenticator parameter, and any number of parameters can be
            passed to the authenticator.
          
            When authorization is required, the server will send a 350
            response requesting authorization from the client.
          
            The client should enter AUTHINFO GENERIC followed by the
            authenticator name and the arguments if any.  The
            authenticator and arguments must not contain the sequence
            "..".
          
            The server will attempt to engage the server end
            authenticator; similarly, the client should engage the client
            end authenticator.  The server end authenticator will then
            initiate authentication using the NNTP sockets (if appropriate
            for that authentication protocol), using the protocol
            specified by the authenticator name.  These authentication
            protocols are not included in this document, but are similar
            in structure to those referenced in RFC 1731[5] for the IMAP-4
            protocol.
          
            If the server returns 501, this means that the authenticator
            invocation was syntactically incorrect, or that AUTHINFO
            GENERIC is not supported.  The client should retry using the
            regular AUTHINFO command.
          
          
          
          
          
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            If the requested authenticator capability is not found or
            there is some other unspecified server program error, the
            server returns the 503 response code.
          
            The authenticators converse using their protocol until
            complete.  If the authentication succeeds, the server
            authenticator will terminate with a 250, and the client can
            continue by reissuing the command that prompted the 350. If
            the authentication fails, the server will respond with a 452.
          
            The client must provide authentication when requested by the
            server. The server may request authentication at any time.
            Servers may request authentication more than once during a
            single session.
          
            When the server authenticator completes, it provides to the
            server (by a mechanism herein undefined) the email address of
            the user, and potentially what the user is allowed to access.
            Once authenticated, the server shall generate a Sender: line
            using the email address provided by the authenticator if it
            does not match the user-supplied From: line. Additionally, the
            server should log the event, including the user's
            authenticated email address (if available). This will provide
            a means by which subsequent statistics generation can
            associate news group references with unique entities - not
            necessarily by name.
          
          
          
          9.1.2.1   Responses
                 250 Authorization accepted
                 350 Continue with authorization sequence
                 450 Authorization required for this command
                 452 Authorization rejected
                 501 Command not supported or Command Syntax Error
                 502 Program error, function not performed
                 nnn authenticator-specific protocol.
          
          9.1.3     Transition Issues
            The implementations of AUTHINFO commonly in use prior to the
            release of this memo have a difference response code set. The
            code 281 was used in place of 250, 381 was used in place of
            350, 480 was used in place of 450 and 482 was used in place of
            452. Client coded to be compliant with this spec may also want
            to be able to accommodate the older codes to lessen the impact
            of the transition to this specification.
          
          
          
          
          10.  The NEWS EXCHANGE Step
          
            During this step, two basic types of transactions occur:
          
          
          
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            article retrieval from the server and article posting to the
            server.
          
          
          
          10.1 Article Retrieval
          
            News reading clients have available a variety of mechanisms to
            retrieve articles via NNTP. The news articles are stored and
            indexed using three types of keys. One key is the message id
            of an article. According to RFC 1036, this identifier should
            be globally unique. Another key is composed of the news group
            name and the article number within that news group. That key
            MUST be unique to a particular server (there will be only one
            article with that number within a particular news group), but
            is not required to be globally unique.  Additionally, because
            the same article can be cross-posted to multiple news groups,
            there may be multiple keys that point to the same article on
            the same server. The final key is the arrival timestamp,
            giving the time that the article arrived at the server.
          
            The server MUST ensure that article numbers are issued in
            order of arrival timestamp; that is, articles arriving later
            MUST have higher numbers than those that arrive earlier. The
            server SHOULD allocate the first unused number to each new
            article.
          
          
            Article numbers MUST lie between 1 and 4,294,967,295
            inclusive. The client and server SHOULD NOT use leading zeroes
            in specifying article numbers, and MUST NOT use more than 16
            digits. In some situations, the value zero replaces an article
            number to show some special situation
          
          
          10.1.1    Article Retrieval by News Group Name and Article Number
          
            The following commands are used to set the current news group
            name and the "current article pointer" which is used by other
            commands for article retrieval.
          
          
          
          10.1.1.1  GROUP
          
            GROUP ggg
          
            The required parameter ggg is the name of the news group to be
            selected (e.g. "news.software.b"). A list of valid news groups
            may be obtained by using the LIST keyword.  See section 10.4 for
            more information on the LIST keyword.
          
            The successful selection response will return the article
            numbers of the first and last articles in the group at the
          
          
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          INTERNET DRAFT                                September 1997
          
          
            moment of selection (these numbers are referred to as the
            "reported low water mark" and the "reported high water mark"),
            and an estimate of the number of articles on file in the
            group.
          
            If the group is not empty, the estimate MUST be at least the
            actual number of articles available, and MUST be no greater
            than one more than the difference between the reported low and
            high water marks. (Some implementations will actually count
            the number of articles on file. Others will just subtract the
            low water mark from the high water mark and add one to get an
            estimate.)
          
          
          
            If the group is empty, one of the following three situations
            will occur. Clients MUST accept all three cases; servers MUST
            NOT represent an empty group in any other way.
          
          . The high water mark will be one less than the low water mark,
            and the estimated article count will be zero. Servers SHOULD
            use this method to show an empty group. This is the only time
            that the high water mark can be less than the low water mark.
          . All three numbers will be zero.
          . The high water mark is greater than or equal to the low water
            mark; the estimated article count might be zero or non-zero;
            if non- zero, the same requirements apply as for a non-empty
            group.
          
            The set of articles in a group may change after the GROUP
            command is carried out. That is:
          
          . articles may be removed from the group;
          . articles may be reinstated in the group with the same article
            number, but those articles MUST have numbers no less than the
            reported low water mark (note that this is a reinstatement of
            the previous article, not a new article reusing the number);
          . new articles may be added with article numbers greater than
            the reported high water mark (if an article that was the one
            with the highest number has been removed, the next new article
            will not have the number one greater than the reported high
            water mark).
            Except when the group is empty and all three numbers are zero,
            whenever a subsequent GROUP command for the same news group is
            issued, either by the same client or a different client, the
            reported low water mark in the response MUST be no less than
            that in any previous response for that news group sent to any
            client. The client may make use of the low water mark to
            remove all remembered information about articles with lower
            numbers, as these will never recur. This includes the
            situation when the high water mark is one less than the low
            water mark.
          
          
          
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            No similar assumption can be made about the high water mark,
            as this can decrease if an article is removed, and then
            increase again if it is reinstated or if new articles arrive.
          
            When a valid group is selected by means of this command, the
            internally maintained "current article pointer" MUST be set to
            the first article in the group and the name of the current
            news group MUST be set to the selected news group name.  If an
            invalid group is specified, the previously selected group and
            article MUST remain selected.  If an empty news group is
            selected, the "current article pointer" is in an indeterminate
            state and MUST not be used.
          
            The GROUP keyword MUST be used by a client and a successful
            response received before the any other command is used that
            depends on having the "current article pointer" be valid.
          
          
          
          10.1.1.1.1     Responses
          
                 211 n f l s group selected
                 (n = estimated number of articles in group, f = first
                    article number in the group, l = last article number in
                    the group, s = name of the group.)
                 411 no such news group
          
          10.1.1.2       LAST
          
            LAST
          
            The internally maintained "current article pointer" MUST be
            set to the previous article in the current news group.  If
            already positioned at the first article of the news group, an
            error message MUST be returned and the current article MUST
            remain selected.
          
            There MAY be no previous article in the group, although the
            current article number is not the reported low water mark.
            There MUST NOT be a previous article when the current article
            number is the reported low water mark.
          
            Because articles can be removed and added, the results of
            multiple LAST and NEXT commands MAY not be consistent over the
            life of a particular NNTP session.
          
            The internally-maintained "current article pointer" MUST be
            set by this command.
          
            A response indicating the current article number and a
            message-id string MUST be returned. No text is sent in
            response to this command.
          
          
          
          
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          10.1.1.2.1     Responses
          
                 223 n a article retrieved - request text separately (n =
                    article number, a = unique article id)
                 412 no news group selected
                 420 no current article has been selected
                 422 no previous article in this group
          
          
          10.1.1.3  NEXT
          
            NEXT
          
            The internally maintained "current article pointer" MUST be
            advanced to the next article in the current news group.  If no
            more articles remain in the current group, an error message
            MUST be returned and the current article MUST remain selected.
          
            The internally-maintained "current article pointer" MUST be
            set by this command.
          
            A response indicating the current article number and the
            message-id string MUST be returned.  No text is sent in
            response to this command.
          
          
          
          10.1.1.3.1     Responses
          
                 223 n a article retrieved - request text separately (n =
                    article number, a = unique article id)
                 412 no news group selected
                 420 no current article has been selected
                 421 no next article in this group
          
          
          10.2 Retrieval of Articles and Article Sections
          
            There are two forms to the ARTICLE command (and the related
            BODY, HEAD, and STAT commands), each using a different method
            of specifying which article is to be retrieved. When the
            ARTICLE keyword is followed by a message-id in angle brackets
            ("<" and ">"), the first form of the command MUST be used;
            when a numeric parameter or no parameter is supplied, the
            second form MUST be invoked.
          
            An article, as defined by RFC 1036, consists of two parts: the
            article headers and the article body. When responding to an
            article command, the server returns the entire article
            contents and does not attempt to alter or translate them in
            any way.
          
          
          
          
          
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            The HEAD and BODY commands are identical to the ARTICLE
            command except that they respectively return only the article
            headers or the article body of the article.
          
            The STAT command is similar to the ARTICLE command except that
            no text is returned.  When selecting by message number within
            a group, the STAT command MUST set the current article pointer
            without sending text. The returned acknowledgment response
            MUST contain the message-id, which may be of some value.
            Using the STAT command to select by message-id is valid but of
            questionable value, since a selection by message-id MUST NOT
            alter the "current article pointer".
          
          
          
          10.2.1    ARTICLE
          
            ARTICLE [<message-id>|nnn]
          
            This response displays the header, a blank line, then the body
            (text) of the specified article. The optional parameter nnn is
            the numeric id of an article in the current news group and
            MUST be chosen from the range of articles provided when the
            news group was selected.  If it is omitted, the current
            article is assumed. Message-id is the message id of an article
            as shown in that article's header.
          
            Please note that the internally-maintained "current article
            pointer" MUST NOT be altered when the message-id argument is
            used. This is both to facilitate the presentation of articles
            that may be referenced within an article being read, and
            because of the semantic difficulties of determining the proper
            sequence and membership of an article which may have been
            posted to more than one news group.
          
            The internally-maintained "current article pointer" MUST be
            set when a valid article number is specified as the argument.
            This includes the case when an article number is implied by
            the use of no argument.
          
            A previously valid article number MAY not remain valid if the
            article has been removed. A previously invalid article number
            MAY become valid if the article has been reinstated, but such
            an article number MUST be no less than the reported low water
            mark for that group.
          
            A response indicating the current article number, a message-id
            string, and that text is to follow MUST be returned.
          
            The message-id string returned is an identification string
            contained within angle brackets ("<" and ">"), which is
            derived from the header of the article itself.  The Message-ID
            header line (required by RFC 1036) from the article must be
            used to supply this information. If the message-id header line
          
          
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            is missing from the article, a single digit "0" (zero) should
            be supplied within the angle brackets.
          
            Since the message-id field is unique for each article, it may
            be used by a news reading program to skip duplicate displays
            of articles that have been posted more than once, or to more
            than one news group.
          
          
          
          10.2.1.1  Responses
          
                 220 n <a> article retrieved - head and body follow (n =
                    article number, <a> = message-id)
                 221 n <a> article retrieved - head follows
                 222 n <a> article retrieved - body follows
                 223 n <a> article retrieved - request text separately
                 412 no news group has been selected
                 420 no current article has been selected
                 423 no such article number in this group
                 430 no such article found
          
          
          10.3 Article Posting
          
            Article posting is done in one of two modes: individual
            article posting from news reading clients and article transfer
            from other news servers.
          
          
          
          10.3.1    POST
          
            POST
          
            If posting is allowed, response code 340 MUST be returned to
            indicate that the article to be posted should be sent.
            Response code 440 MUST be sent if that posting is prohibited
            for some installation-dependent reason.
          
            If posting is permitted, the article MUST be presented in the
            format specified by RFC 1036, and MUST include all required
            header lines. After the article's header and body have been
            completely sent by the client to the server, a further
            response code MUST be returned to indicate success or failure
            of the posting attempt.
          
            The text forming the header and body of the message to be
            posted MUST be sent by the client using the conventions for
            text received from the news server: A single period (".") on a
            line indicates the end of the text, with lines starting with a
            period in the original text having that period doubled during
            transmission.
          
          
          
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            No attempt shall be made by the server to filter characters,
            fold or limit lines, or otherwise process incoming text. The
            intent is that the server just passes the incoming message to
            be posted to the server installation's news posting software,
            which is not part of this specification.
          
          
          
          10.3.1.1  Responses
          
                 240 article posted ok
                 340 send article to be posted. End with <CR-LF>.<CR-LF>
                 440 posting not allowed
                 441 posting failed
          
          
          
          10.3.2    IHAVE
          
            IHAVE <message-id>
          
            The IHAVE command informs the server that the client has an
            article whose id is <message-id>. If the server desires a copy
            of that article, it MUST return a response instructing the
            client to send the entire article. If the server does not want
            the article (if, for example, the server already has a copy of
            it), a response indicating that the article is not wanted MUST
            be returned.
          
            If transmission of the article is requested, the client MUST
            send the entire article, including header and body, in the
            manner specified for text transmission from the server. A
            response code indicating success or failure of the transferal
            of the article MUST be returned by the server.
          
            This function differs from the POST command in that it is
            intended for use in transferring already-posted articles
            between hosts. Normally it will not be used when the client is
            a personal news reading program. In particular, this function
            will invoke the server's news posting program with the
            appropriate settings (flags, options, etc.) to indicate that
            the forthcoming article is being forwarded from another host.
          
            However, the server may elect not to post or forward the
            article if after further examination of the article it deems
            it inappropriate to do so. The 436 or 437 error codes MUST be
            returned as appropriate to the situation.
          
            Reasons for such subsequent rejection of an article may
            include such problems as inappropriate news groups or
            distributions, disk space limitations, article lengths,
            garbled headers, and the like. These are typically
            restrictions enforced by the server host's news software and
            not necessarily the NNTP server itself.
          
          
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          10.3.2.1  Responses
          
                 235 article transferred ok
                 335 send article to be transferred.  End with <CR-
                 LF>.<CR-LF>
                 435 article not wanted - do not send it
                 436 transfer failed - try again later
                 437 article rejected - do not try again
          
            Because some host news posting software may not be able to
            immediately render status on the whether an article is
            inappropriate for posting or forwarding, an NNTP server MAY
            acknowledge the successful transfer of the article and later
            silently discard it. Thus an NNTP server may return the 235
            acknowledgment code and later discard the received article.
          
          
          
          10.4 The LIST Keyword
          
          
          10.4.1    LIST
          
            LIST [ACTIVE [wildmat]]
          
            The response to the LIST keyword with no parameters returns a
            list of valid news groups and associated information.  Each
            news group is sent as a line of text in the following format:
          
               group last first status
          
            where <group> is the name of the news group, <last> is the
            number of the last known article currently in that news group,
            <first> is the number of the first article currently in the
            news group, and <status> indicates the current status of the
            group on this server. Typically, the <status> will be consist
            of the ASCII character `y' where posting is permitted, `n'
            where posting is not permitted and `m' where postings will be
            forwarded to the news group moderator by the news server.
            Other status strings exist and their definition is outside the
            scope of this specification.
          
            The <first> and <last> fields will always be numeric.  They
            may have leading zeros.  If the <last> field evaluates to less
            than the <first> field, there are no articles currently on
            file in the news group.
          
            Note that posting may still be prohibited to a client although
            the LIST command indicates that posting is permitted to a
            particular news group. See the POST command for an explanation
            of client prohibitions. The posting flag exists for each news
            group because some news groups are moderated or are digests,
          
          
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            and therefore cannot be posted to; that is, articles posted to
            them must be mailed to a moderator who will post them for the
            original poster.  This is independent of the posting
            permission granted to a client by the NNTP server.
          
            Please note that an empty list (i.e., the text body returned
            by this command consists only of the terminating period) is a
            possible valid response, and indicates that there are
            currently no valid news groups.
          
            If the optional matching parameter is specified, the list is
            limited to only the groups that match the pattern.
          
            Specifying a single group is usually very efficient for the
            server, and multiple groups may be specified by using wildmat
            patterns (described in section 5), not regular expressions.
          
          
          
          10.4.1.1  Responses
                 215 list of news groups follows
          
          10.4.2    LIST ACTIVE.TIMES
          
            LIST ACTIVE.TIMES [wildmat]
          
            The active.times file is maintained by some news transports
            systems to contain information about the when and who created
            a particular news group. The format of this file generally
            includes three fields. The first field is the name of the news
            group. The second is the time when this group was created on
            this news server measured in seconds since January 1, 1970.
            The third is the email address of the entity that created the
            news group. When executed, the information is displayed
            following the 215 response. When display is completed, the
            server will send a period on a line by itself. If the
            information is not available, the server will return the 503
            error response.
          
            If the optional matching parameter is specified, the list is
            limited to only the groups that match the pattern.
          
            Specifying a single group is usually very efficient for the
            server, and multiple groups may be specified by using wildmat
            patterns (described in section 5), not regular expression
          
          
          10.4.2.1  Responses
          
                 215 information follows
                 503 program error, function not performed
          
          10.4.3    LIST DISTRIBUTIONS
          
          
          
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            LIST DISTRIBUTIONS
          
            The distributions file is maintained by some news transport
            systems to contain information about valid values for the
            Distribution: line in a news article header and about what the
            values mean. Each line contains two fields, the value and a
            short explanation on the meaning of the value. When executed,
            the information is displayed following the 215 response. When
            display is completed, the server will send a period on a line
            by itself. If the information is not available, the server
            will return the 503 error response.
          
          
          
          10.4.3.1  Responses
          
                 215 information follows
                 503 program error, function not performed
          
          10.4.4    LIST DISTRIB.PATS
          
            LIST DISTRIB.PATS
          
            The distrib.pats file is maintained by some news transport
            systems to contain default values for the Distribution: line
            in a news article header when posting to particular news
            groups. This information could be used to provide a default
            value for the Distribution: line in the header when posting an
            article. The information returned contains three fields
            separated by colons. The first column is a weight.  The second
            is a group name or a wildmat pattern that can be used to match
            a group name.  The third is the value of the Distribution:
            line that should be used when the group name matches and the
            weight value is the highest. All this processing is done by
            the news posting client and not by the server itself. The
            server provides this information to the client for it to use
            or ignore as it chooses. When executed, the information is
            displayed following the 215 response.  When display is
            completed, the server will send a period on a line by itself.
            If the information is not available, the server will return
            the 503 error response.
          
          
          
          10.4.4.1  Responses
          
                 215 information follows
                 503 program error, function not performed
          
          10.4.5    LIST NEWSGROUPS
          
               LIST NEWSGROUPS [wildmat]
          
          
          
          
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            The newsgroups file is maintained by some news transport
            systems to contain the name of each news group that is
            active on the server and a short description about the
            purpose of each news group. Each line in the file contains
            two fields, the news group name and a short explanation of
            the purpose of that news group. When executed, the
            information is displayed following the 215 response. When
            display is completed, the server will send a period on a
            line by itself. If the information is not available, the
            server will return the 503 response.  If the optional
            matching parameter is specified, the list is limited to only
            the groups that match the pattern (no matching is done on
            the group descriptions).  Specifying a single group is
            usually very efficient for the server, and multiple groups
            may be specified by using wildmat patterns (see section 5),
            not regular expressions. If nothing is matched an empty list
            is returned, not an error.
          
          10.4.5.1  Responses
          
                 215 information follows
                 503 program error, function not performed
          
          10.4.6    LIST OVERVIEW.FMT
          
            LIST OVERVIEW.FMT
          
            The overview.fmt file is maintained by some news transport
            systems to contain the order in which header information is
            stored in the overview databases for each news group.  When
            executed, news article header fields are displayed one line at
            a time in the order in which they are stored in the overview
            database[6] following the 215 response.  When display is
            completed, the server will send a period on a line by itself.
            If the information is not available, the server will return
            the 503 response.
          
            Please note that if the header has the word "full" (without
            quotes) after the colon, the header's name is prepended to its
            field in the output returned by the server.
          
          
          
          10.4.6.1  Responses
          
                 215 information follows
                 503 program error, function not performed
          
          10.4.7    LIST SUBSCRIPTIONS
          
            LIST SUBSCRIPTIONS
          
          
          
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            This command is used to get a default subscription list for
            new users of this server. The order of groups is significant.
          
            When this list is available, it is preceded by the 215
            response and followed by a period on a line by itself.  When
            this list is not available, the server returns a 503 response
            code.
          
          
          
          10.4.7.1  Responses
          
                 215 information follows
                 503 program error, function not performed
          
          10.4.8    LISTGROUP
          
               LISTGROUP [ggg]
          
               The LISTGROUP command is used to get a listing of all the
               article numbers in a particular news group.
          
               The optional parameter ggg is the name of the news group to
               be selected (e.g. "news.software.b").  A list of valid news
               groups may be obtained from the LIST command. If no group is
               specified, the current group is used as the default
               argument.
          
               The successful selection response will be a list of the
               article numbers in the group followed by a period on a line
               by itself.
          
               When a valid group is selected by means of this command, the
               internally maintained "current article pointer" MUST be set
               to the first article in the group.  If an invalid group is
               specified, the previously selected group and article remain
               selected.  If an empty news group is selected, the "current
               article pointer" may be in an indeterminate state and should
               not be used.
          
               Note that the name of the news group is not case-dependent.
               It must otherwise match a news group obtained from the LIST
               command or an error will result.
          
          
          
          10.4.8.1  Responses
          
                 211 list of article numbers follow
                 412 Not currently in news group
          
          10.4.9    OVER
          
            OVER [range]
          
          
          Barber                                             [Page 24]
          

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            The OVER command returns information from the overview
            database for the article(s) specified. The information
            returned in the response to this command can be used by
            clients to follow discussion threads.
          
            The optional range argument may be any of the following:
          
          . an article number
          . an article number followed by a dash to indicate all following
          . an article number followed by a dash followed by another
            article number
            If no argument is specified, then information from the current
            article is displayed. Successful responses start with a 224
            response followed by the overview information for all matched
            messages. Once the output is complete, a period is sent on a
            line by itself. If no argument is specified, the information
            for the current article is returned.  A news group must have
            been selected earlier, else a 412 error response is returned.
            If no articles are in the range specified, a 420 error
            response is returned by the server. A 502 response will be
            returned if the client only has permission to transfer
            articles.
          
            Each line of output MUST be formatted with the article number,
            followed by each of the headers in the overview database or
            the article itself (when the data is not available in the
            overview database) for that article separated by a tab
            character.  The sequence of fields must be in this order:
            subject, author, date, message-id, references, byte count, and
            line count. Other optional fields may follow line count. Where
            no data exists, a null field must be provided (i.e. the output
            will have two tab characters adjacent to each other). Servers
            should not output fields for articles that have been removed
            since the overview database was created.
          
          
          
          10.4.9.1  Responses
          
                 224 Overview information follows
                 412 No news group current selected
                 420 No article(s) selected
                 502 no permission
          
          
          10.4.10   PAT
          
            PAT header range|<message-id> [pat [pat...]]
          
            The PAT command is used to retrieve specific headers from
            specific articles, based on pattern matching on the contents
            of the header.
          
          
          
          
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            The required header parameter is the name of a header line
            (e.g.  "subject") in a news group article. See RFC-1036 for a
            list of valid header lines. The required range argument may be
            any of the following:
          
          . an article number
          . an article number followed by a dash to indicate all following
          . an article number followed by a dash followed by another
            article number.
            The required message-id argument indicates a specific article.
            The range and message-id arguments are mutually exclusive. If
            there are additional arguments, they are joined together
            separated by a single space to form one complete pattern. If
            there are no additional arguments, a wildmat "*" is the
            default. Successful responses start with a 221 response
            followed by the headers from all messages in which the pattern
            matched the contents of the specified header line. This
            includes an empty list. Once the output is complete, a period
            is sent on a line by itself. If the optional argument is a
            message-id and no such article exists, the 430 error response
            shall be returned. A 502 response shall be returned if the
            client only has permission to transfer articles.
          
          10.4.10.1 Responses
          
                 221 Header follows
                 430 no such article
                 502 no permission
          
          
          11.  The CONCLUSION Step
          
          11.1 QUIT
          
            QUIT
          
            The server process MUST acknowledge the QUIT command and then
            closes the connection to the client.  This is the preferred
            method for a client to indicate that it has finished all its
            transactions with the NNTP server.
          
            If a client simply disconnects (or the connection times out or
            some other fault occurs), the server SHALL gracefully cease
            its attempts to service the client.
          
          
          11.1.1    Responses
          
                 205 closing connection - goodbye!
          
          12.  Other Keywords
          
          
          
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            There are other Keywords that may be used at any time between
            the beginning of a session and its termination.  Using these
            keywords do not alter any state information, but the response
            generated from the use of these keywords may provide useful
            information to clients that use them.
          
          
          12.1 CHARSET
          
            CHARSET [charset]
          
            The CHARSET command is used to change the default character
            set for certain types of arguments: group names and the
            contents of article headers. The argument must be the name of
            a character set registered with the IANA. The server MUST
            return 204 if the specified character set is supported.
            Otherwise, the server MUST return 404.
          
            When used as arguments to commands, group names and the
            contents of article headers MUST be decoded before comparing
            text in a character set other than US-ASCII. US-ASCII must be
            supported; other character sets may be supported.
          
            The use of CHARSET with no argument will reset the default
            character set to US-ASCII.
          
            Note that only argument processing is affected by the
            character set. The server MUST not translate any part of any
            multi-line response returned to the client based on the
            current character set.
          
          12.1.1    Responses
                 204     Character set is now charset
                 404     Character set charset is not supported by this
                         server
                 500     Command not supported
          
          12.2 DATE
          
            DATE
          
            This command exists to help clients find out the current time
            from the server's perspective.  This command should not be
            used as a substitute for NTP[7], but to provide information
          
          
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            that might be useful when using the NEWNEWS command (see
            section 12.5).
          
            This command returns a one-line response code of 111 followed
            by the GMT date and time on the server in the form
            YYYYMMDDhhmmss.
          
          
          12.2.1    Responses
          
                 111 YYYYMMDDhhmmss
          
          12.3 The HELP Command
          
            HELP
          
            This command provides a short summary of commands that are
            understood by this implementation of the server. The help text
            will be presented as a textual response terminated by a single
            period on a line by itself.
          
            This text is not guaranteed to be in any particular format and
            shall not be used by clients as a replacement for the LIST
            EXTENSIONS command described in section 8.
          
          
          
          12.3.1    Responses
          
                 100 help text follows
          
          
          12.4 NEWGROUPS
          
            NEWGROUPS date time [GMT] [<wildmat>]
          
            A list of newsgroups created since <date and time> MUST be
            listed in the same format as the LIST command.
          
            The date is sent as 6 or 8  digits in the format [XX]YYMMDD,
            where XX is the first two digits of the year, YY is the last two
            digits of the year, MM is the two digits of the month (with
            leading zero, if appropriate), and DD is the day of the month
            (with leading zero, if appropriate). If the first two digits
            of the year are not specified, the closest century is assumed
            as part of the year (i.e., 86 specifies 1986, 30 specifies
            2030, 99 is 1999, 00 is 2000).
          
            Time must also be specified.  It must be as 6 digits HHMMSS
            with HH being hours on the 24-hour clock, MM minutes 00-59,
            and SS seconds 00-59.  The time is assumed to be in the
            server's timezone unless the token "GMT" appears in which case
            both time and date are evaluated at the 0 meridian.
          
          
          
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            An optional parameter may be specified at the end of the
            command line consisting of a wildmat pattern against which new
            newsgroup names can be matched enclosed in angle brackets.
            Only those news groups that have names that match the pattern
            (and any other criteria specified in the command) will be
            returned.
          
            Please note that an empty list (i.e., the text body returned
            by this command consists only of the terminating period) is a
            possible valid response, and indicates that there are
            currently no new newsgroups.
          
          
          12.4.1    Responses
          
                 231 list of new newsgroups follows
          
          12.5 NEWNEWS
          
            NEWNEWS newsgroups date time [GMT] [<distributions>]
          
            A list of message-ids of articles posted or received to the
            specified news group since "date" will be listed. The format
            of the listing will be one message-id per line, as though text
            were being sent.  A single line consisting solely of one
            period followed by CR-LF will terminate the list.
          
            Date and time are in the same format as the NEWGROUPS command.
            The newsgroups parameter must be in wildmat format.
          
            The optional parameter "distributions" is a list of
            distribution groups, enclosed in angle brackets.  If
            specified, the distribution portion of an article's header
            will be examined for a match with the distribution categories
            listed, and only those articles which have a distribution in
            the list will be listed.  If more than one distribution is to
            be supplied, they must be separated by commas within the angle
            brackets.
          
            The use of the IHAVE, NEWNEWS, and NEWGROUPS commands to
            distribute news is discussed in an earlier part of this
            document.
          
            Please note that an empty list (i.e., the text body returned
            by this command consists only of the terminating period) is a
            possible valid response, and indicates that there is currently
            no new news.
          
          
          12.5.1    Responses
          
               230 list of new articles by message-id follows
          
          
          
          
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          INTERNET DRAFT                                September 1997
          
          
          13. Framework for NNTP Extensions
          
            Although NNTP is widely and robustly deployed, some parts of
            the Internet community might wish to extend the NNTP service.
            This memo defines a means whereby an extended NNTP client may
            query the server to determine the service extensions that it
            supports.
          
            It must be emphasized that any extension to the NNTP service
            should not be considered lightly. NNTP's strength comes
            primarily from its simplicity.  Experience with many protocols
            has shown that:
          
            Protocols with few options tend towards ubiquity, whilst
            protocols with many options tend towards obscurity.
          
            This means that each and every extension, regardless of its
            benefits, must be carefully scrutinized with respect to its
            implementation, deployment, and interoperability costs. In
            many cases, the cost of extending the NNTP service will likely
            outweigh the benefit.
          
            Given this environment, the framework for the extensions
            described in this memo consists of:
          
            a)   a mechanism for clients to determine a server's available
               extensions
            b)   a registry of NNTP service extensions
          
            The LIST EXTENSIONS command is described in section 8 of this
            memo and is the mechanism for clients to use to determine what
            extensions are available for client use.
          
            The IANA shall maintain a registry of NNTP service extensions.
          
            Associated with each such extension is a corresponding NNTP
            keyword value. Each service extension registered with the IANA
            MUST be defined in an RFC. Such RFCs either must be on the
            standards-track or must define an IESG-approved experimental
            protocol.  The definition must include:
          
          . the textual name of the NNTP service extension;
          . the NNTP keyword value associated with the extension;
          . the syntax and possible values of parameters associated with
            the NNTP keyword value;
          . any additional NNTP verbs associated with the extension
          . (additional verbs will usually be, but are not required to be,
            the same as the NNTP keyword value);
          . any new parameters the extension associated with any other
            NNTP verbs;
          . how support for the extension affects the behavior of a server
            and client NNTP; and,
          
          
          
          
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          . the increment by which the extension is increasing the maximum
            length of the any commands over that specified in this
            document.
            In addition, any NNTP keyword value that starts with an upper
            or lower case "X" refers to a local NNTP service extension,
            which is used through bilateral, rather than standardized,
            agreement. Keywords beginning with "X" may not be used in a
            registered service extension.
          
            Any keyword values presented in the NNTP response that do not
            begin with "X" must correspond to a standard, standards-track,
            or IESG-approved experimental NNTP service extension
            registered with IANA.  A conforming server must not offer non
            "X" prefixed keyword values that are not described in a
            registered extension.
          
            Additional verbs are bound by the same rules as NNTP keywords;
            specifically, verbs beginning with "X" are local extensions
            that may not be registered or standardized and verbs not
            beginning with "X" must always be registered.
          
          
          
          13.1 Initial IANA Registry
          
            The IANA's initial registry of NNTP service extensions
            consists of these entries:
          
          
          Service Extension     NNTP Keyword(s)       Added Behavior
          
          Overview Support      OVER                  Defined in this
                                LIST OVERVIEW.FMT     document
          
          Specific Article      LISTGROUP             Defined in this
          Numbers                                     document
          
          Identification and    AUTHINFO              Defined in this
          Authentication        AUTHINFO GENERIC      document
          
          Character Set         CHARSET               Defined in this
          Selection                                   document
          
          Header Pattern        PAT                   Defined in this
          Matching                                    document
          
          
          
          
          14.  Security Considerations
          
            The use of the AUTHINFO is optional. This command as
            documented has a number of security implications. In the
            original and simple forms, all passwords are passed in plain
          
          
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            text and could be discovered by various forms of network or
            system surveillance.  The AUTHINFO GENERIC command has the
            potential for the same problems if a mechanism is used that
            also passes clear text passwords.  RFC 1731 discusses these
            issues in greater detail.
          
          
          
          15.  References
          
            [1] Kantor, B and P. Lapsley, "Network News Transfer
            Protocol", RFC-977, U.C. San Diego and U.C. Berkeley.
          
            [2] Coded Character Set"7-bit American Standard Code for
            Information Interchange, ANSI x3.4-1986.
          
            [3] Salz, Rich, Manual Page for wildmat(3) from the INN 1.4
            distribution, UUNET Technologies, Revision 1.10, April, 1992.
          
            [4] Horton, M.R. and R. Adams, "Standard for interchange of
            USENET messages",  RFC-1036, AT&T Bell Laboratories and Center
            for Seismic Studies, December, 1987.
          
            [5] Meyers, J, "IMAP4 Authentication Mechanisms", RFC-1731,
            Carnegie Mellon, December, 1994.
          
            [6] Robertson, Rob, "FAQ: Overview database / NOV General
            Information", ftp://ftp.uu.net/networking/news/nntp/inn/faq-
            nov.Z, January, 1995.
          
            [7] Mills, David L., "Network Time Protocol (Version 3),
            Specification,Implementation and Analysis", RFC-1305,
            University of Delaware, March 1992.
          
          15.1 Notes
          
          
            DEC is a registered trademark of Digital Equipment
            Corporation.
          
            UNIX is a registered trademark of the Open Group.
          
            VMS is a registered trademark of Digital Equipment
            Corporation.
          
          15.2 Acknowledgments
          
            The author acknowledges the original authors of NNTP as
            documented in RFC 977: Brian Kantor and Phil Lapsey.
          
          
          
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            The author gratefully acknowledges the work of the NNTP
            committee chaired by Eliot Lear. The organization of this
            document was influenced by the last available draft from this
            working group. A special thanks to Eliot for generously
            providing the original machine readable sources for that
            document.
          
            The author gratefully acknowledges the work of the Marshall
            Rose & John G. Meyers in RFC 1939 and the work of the DRUMS
            working group, specifically RFC 1869, which is the basis of
            the NNTP extensions mechanism detailed in this document.
          
            The author gratefully acknowledges the comments and additional
            information provided by the following individuals in preparing
            one of the progenitors of this document:
          
          . Wayne Davison <davison@armory.com>
          . Clive D.W. Feather <clive@demon.net>
          . Chris Lewis <clewis@bnr.ca>
          . Tom Limoncelli <tal@mars.superlink.net>
          . Eric Schnoebelen <eric@egsner.cirr.com>
          . Rich Salz <rsalz@osf.org>
          
            This work was precipitated by the work of various newsreader
            authors and newsserver authors, which includes those listed
            below:
          
          . Rick Adams -- Original author of the NNTP extensions to the RN
            newsreader and last maintainer of Bnews
          . Stan Barber -- Original author of the NNTP extensions to the
            newsreaders that are part of Bnews.
          . Geoff Collyer -- Original author of the OVERVIEW database
            proposal and one of the original authors of CNEWS
          . Dan Curry -- Original author of the xvnews newsreader
          . Wayne Davision -- Author of the first threading extensions to the
            RN newsreader (commonly called TRN).
          . Geoff Huston -- Original author of ANU NEWS
          . Phil Lapsey -- Original author of the UNIX reference
            implementation
          . Ian Lea -- Maintainer of the TIN newsreader
          . Chris Lewis -- First known implementor of the AUTHINFO GENERIC
            extension
          . Rich Salz -- Original author of INN
          . Henry Spencer -- One of the original authors of CNEWS
          . Kim Storm -- Original author of the NN newsreader
          
          15.3 Author's Address
          
            Stan Barber
            P.O. Box 300481
            Houston, Texas, 77230
            Email: <sob@academ.com>
          
            This document expires February 3, 1998.
          
          Barber                                             [Page 33]
          

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