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INTERNET DRAFT S. Barber Expires: February 5, 1998 Academ Consulting Services September 1997 Network News Transport Protocol draft-ietf-nntpext-base-02.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 Barber [Page 3] INTERNET DRAFT September 1997 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 if it 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 Barber [Page 6] INTERNET DRAFT September 1997 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 through 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. Barber [Page 11] INTERNET DRAFT September 1997 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: Barber [Page 12] INTERNET DRAFT September 1997 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 Barber [Page 13] 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. Barber [Page 14] INTERNET DRAFT September 1997 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. Barber [Page 15] INTERNET DRAFT September 1997 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. Barber [Page 16] INTERNET DRAFT September 1997 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 Barber [Page 17] INTERNET DRAFT September 1997 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. Barber [Page 18] INTERNET DRAFT September 1997 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. Barber [Page 19] INTERNET DRAFT September 1997 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, Barber [Page 20] INTERNET DRAFT September 1997 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 Barber [Page 21] INTERNET DRAFT September 1997 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] Barber [Page 22] INTERNET DRAFT September 1997 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 Barber [Page 23] INTERNET DRAFT September 1997 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] INTERNET DRAFT September 1997 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. Barber [Page 25] INTERNET DRAFT September 1997 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 Barber [Page 26] INTERNET DRAFT September 1997 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 Barber [Page 27] INTERNET DRAFT September 1997 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. Barber [Page 28] INTERNET DRAFT September 1997 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 Barber [Page 29] 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, Barber [Page 30] INTERNET DRAFT September 1997 . 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 Barber [Page 31] INTERNET DRAFT September 1997 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. Barber [Page 32] INTERNET DRAFT September 1997 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 5, 1998. Barber [Page 33]