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 Barber [Page 2] 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. Barber [Page 3] 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 Barber [Page 4] 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 Barber [Page 6] 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 Barber [Page 7] 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 Barber [Page 8] 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 Barber [Page 9] 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 Barber [Page 10] 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 Barber [Page 11] 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: Barber [Page 12] 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. Barber [Page 13] 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.] Barber [Page 14] 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 Barber [Page 15] 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 Expires: July 15, 2002 Academ Consulting Services 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 Barber [Page 17] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services 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. Barber [Page 19] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 * 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. Barber [Page 20] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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. Barber [Page 21] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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. Barber [Page 22] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 23] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [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 Barber [Page 24] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services 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 [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. Barber [Page 25] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 9.2.1 ARTICLE ARTICLE 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): Barber [Page 26] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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> Barber [Page 27] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [S] Path: pathost!demo!somewhere!not-for-mail [S] From: ôDemo Userö [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 [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 [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 Barber [Page 28] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [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 [S] 502 Service unavailable 9.2.2 HEAD HEAD 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. Barber [Page 29] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [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 [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 [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 Barber [Page 30] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [S] 502 Service unavailable 9.2.3 BODY BODY 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 Barber [Page 31] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [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 Barber [Page 32] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [S] 502 Service unavailable 9.2.4 STAT STAT 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 Barber [Page 33] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [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 Barber [Page 34] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [S] 200 NNTP Service Ready [C] STAT [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. Barber [Page 35] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 . [C] From: ôDemo Userö [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 . [C] From: ôDemo Userö [C] Newsgroups: misc.test [C] Subject: I am just a test article [C] Organization: An Example Net [C] Barber [Page 36] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [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 The IHAVE command informs the server that the client has an article whose id is . 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. Barber [Page 37] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [S] 335 Send it. End with . [C] Path: pathost!demo!somewhere!not-for-mail [C] From: ôDemo Userö [C] Newsgroups: misc.test [C] Subject: I am just a test article [C] Date: 6 Oct 1998 04:38:40 -0500 Barber [Page 38] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [C] Organization: An Example Com, San Jose, CA [C] Message-ID: [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 [S] 335 Send it. End with . [C] Path: pathost!demo!somewhere!not-for-mail [C] From: ôDemo Userö [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: [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 [S] 335 Send it. End with . [C] Path: pathost!demo!somewhere!not-for-mail [C] From: ôDemo Userö [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: [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 [S] 435 Duplicate Barber [Page 39] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 Example of sending an article to a site that requests the article be tried again later [S] 200 NNTP Service Ready [C] IHAVE [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 is the name of the newsgroup, is the number of the last known article currently in that newsgroup, is the number of the first article currently in the newsgroup, and indicates the current status of the group on this server. Typically, the 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 and fields will always be numeric. They may have leading zeros. The field corresponds to the "reported low water mark" and the 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 Barber [Page 40] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 41] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [S] alt.rfc-writers.recovery 930562309 [S] tx.natives.recovery 930678923 [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 Barber [Page 42] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 43] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 44] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 45] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [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. Barber [Page 46] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 47] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [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 Barber [Page 48] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 49] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 Barber [Page 50] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 |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 Barber [Page 51] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 This extension provides one new command, HDR. The label for this extension is HDR 9.5.3.1 HDR HDR header range| 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 Barber [Page 52] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 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 [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 [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 [S] 412 No newsgroup selected Example of retrieving header information when the current group selected is empty Barber [Page 53] INTERNET DRAFT S. Barber Expires: July 15, 2002 Academ Consulting Services January 2002 [S] 200 NNTP Service Ready [C] GROUP ex