Document: FSC-0059 Version: 001 Date: 08-Mar-1992 Newsgroup Interchange within FidoNet Jack Decker 1:154/8@fidonet A proposed standard for the interchange of USENET News messages among FidoNet nodes. Status of this document: This FSC suggests a proposed protocol for the FidoNet(r) community, and requests discussion and suggestions for improvements. Distribution of this document is unlimited. Fido and FidoNet are registered marks of Tom Jennings and Fido Software. Introduction: This document defines the standard format for the interchange of USENET news messages among FidoNet nodes. It incorporates by reference the document RFC-1036, "Standard for Interchange of USENET Messages" by M. Horton of AT&T Bell Laboratories and R. Adams of the Center for Seismic Studies. A copy of RFC-1036 should be included in the distribution archive of this standard. However, RFC-1036 is NOT applicable in its entirety to FidoNet. Therefore, unless specifically referenced elsewhere in this document, only section 2 of RFC-1036 should be considered part of this standard. Section 3, which deals with "control messages", may be implemented in FidoNet on an optional basis, and if processing of control messages is included in a FidoNet implementation, it should be done in accordance with section 3 of RFC-1036 to the extent possible. Section 4 of RFC-1036 is *NOT* applicable to FidoNet (except for section 4.3, which will be discussed later) and therefore is NOT included as part of this standard. Section 5 of RFC-1036 is a treatise on the News Propagation Algorithm used within UseNet, and should be studied even though it is not directly applicable to FidoNet, in particular because it contains a discussion on the prevention of loops (what we in FidoNet commonly refer to as "dupe loops"). Please note that FidoNet implementations do not recognize nor support what is referred to as the "old format" or the "A format" in section 2 of RFC-1036. The goal of this document is to define a standard for the interchange of news messages between FidoNet nodes in a format that will also be acceptable to UseNet hosts. In order to simplify the creation of software that conforms to this standard, we do not intend to support every news format that has ever existed in UseNet. The standard described in RFC-1036 is used by the majority of UseNet hosts, and therefore it is the standard that will be adopted in this document. This standard will contain three sections: General theory of newsgroup transmission, Format and protocols of batched newsgroups, and the translation of newsgroup messages to and from FidoNet message format. 1. General theory of newsgroup transmission: Prior to the introduction of the DoveMail program, the usual method of gating a UseNet newsgroup into FidoNet was to convert it to FidoNet echomail, and then send it to "downstream" nodes in echomail format. This method is still used at the majority of gateway systems at this writing. Unfortunately, no conversion process is perfect, and some useful control information is usually lost in the conversion. In addition, most FidoNet echomail processors don't handle long messages (which are fairly common in newsgroups) well at all, and many gateway systems either try to split these messages into multiple parts (a somewhat awkward process) or discard them entirely. Because the duplicate message detection algorithms used in many FidoNet echomail processors incorrectly identify some of the parts of a split message as duplicates, parts of long messages often get "lost" when transmitted as echomail. Also, UseNet allows a message to be posted to multiple newsgroups, and when such messages are converted to echomail, it may be necessary to create multiple copies of the message (one for each echomail area that it would be placed in), thus increasing the transmission time for such messages. Even normal-length newsgroup messages may be falsely discarded as duplicates by some "downstream" echomail processors. The reason this is a particular problem in newsgroups converted to echomail is because some echomail processors use a checksum of parts of FidoNet message headers to determine if messages are duplicates. Since all newsgroup messages are assumed to be addressed to "All", and since some gateway software uses the date and time that the message was converted to echomail rather than the original date and time from the message, it's quite possible that the remainder of the message header contains information that is similar enough to information in another message's header to cause it to be discarded as a duplicate message. This happens far more frequently with converted newsgroup messages than with messages originally entered as echomail. Finally, when a BBS user enters a reply to a news message that has been converted to echomail, in many cases the information is simply not available in the original message to generate a proper "References:" line in the reply, as required by RFC-1036. If the original message contained a "Followup-To:" line, which requires that replies be posted to a different newsgroup than the one in which the original message was entered, this line may not transmitted in the message as converted to echomail. And even if this information is available, no echomail processor currently available will modify the reply message as required (to add the "References:" line where necessary, or to move the message to a different area if it is a reply to a message that contained a "Followup-To:" line). Under this proposed standard, none of the UseNet message header information is lost in transmission between nodes, and reply messages can be generated that conform to UseNet specifications. If a message is posted to multiple newsgroups, it is only transmitted once (instead of multiple times as it might be if converted to echomail). Also, long messages are not truncated or changed in transmission between nodes, and finally, there is no chance that a message will be improperly discarded as a duplicate. The main thing to remember is that under this standard, news messages are never converted to echomail. Echomail is an irrelevant concept in this context, since we are not passing echomail between nodes. Instead, newsgroups are transmitted in the native format specified by RFC-1036, and tossed directly from batched newsgroup packets to the FidoNet message format (e.g. the *.msg format) if necessary. Keep in mind that most FidoNet BBS software uses the same general format not only for echomail messages, but also for netmail and local message areas, so it is not necessary to transmit messages between nodes in echomail format if another format is more suitable for the type of message being transmitted. 2. Format and protocols of batched newsgroups: When newsgroup messages are transmitted between systems, the individual messages must conform to the specifications of section 2 of RFC-1036, and section 3 of this document. Where section 3 of this document defines a more restrictive standard than RFC-1036, this document shall take precedence. When transmitting news messages between FidoNet nodes, they must be sent in a batched newsgroup file (as described in section 4.3 of RFC-1036) unless some other format is agreed upon in advance. The transmission of unbatched news messages, or the use of any batching method other than that described in section 4.3 of RFC-1036 shall be considered non-standard. Please note that RFC-1036 section 4.3 refers to this batching process as combining several messages into "one large message", but we will refer to this "one large message" as a "batched newsgroup file", or a "UseNet format mail packet" rather than as a "large message", since FidoNet systems do not normally handle large "messages". When messages pass through a FidoNet system on their way to other nodes, the header lines in the message may be modified to conform with the standards given here. However, the text (body) of a message should NEVER be altered (one exception: Carriage Returns MAY be converted to Line Feeds in order to conform to this standard, but this is neither required nor expected of software). The standard format for sending a batched newsgroup file to other FidoNet nodes is as follows: First, as will be noted in section 3 of this document, individual lines of the batched newsgroup file must be terminated with Line Feeds only, and the file must NOT contain Carriage Return characters (ASCII 13). Batched newsgroup files shall be transmitted between FidoNet nodes as files named using the filename ????????.PKU, where the eight character root name can be any of the hexadecimal digits 0 - 9 or A - F. The .PKU extension (which stands for "PacKet - Usenet format") is the news equivalent of the .PKT file used to transmit FidoNet format netmail and echomail between nodes. Batched newsgroup files with the filespec ????????.PKU may be archived into a standard mail archive file (bearing the extension *.MO?, *.TU?, *.WE? ... *.SU?). It is assumed that the receiver of batched newsgroup files will take any necessary steps to make sure that both *.PKU and *.PKT files are extracted from incoming mail archive files before the mail archive files are deleted. In certain cases, this may mean that an external unarchive shell may have to be used, instead of allowing the echomail processor to call the unarchiver (typical external unarchive shell programs at this writing are GUS, POLYXARC, and SPAZ). A batched newsgroup file awaiting transmission may be stored in a FidoNet system's "outbound" area in uncompressed form, prior to being archived for transmission or sent in uncompressed form. It is suggested that when a system uses the .OUT extension to indicate an uncompressed netmail or echomail packet, the .UUT extension be used to indicate an uncompressed batched newsgroup packet. It is expected that a .UUT file in a system's "outbound" area will be treated in much the same way as an .OUT file, except it will be renamed to a file with an extension of .PKU (rather than .PKT) before being archived into the mail archive. This implies that the root name of the .UUT file will contain the net number and node number of the destination system, expressed as four hexadecimal digits each for net and node numbers, in the same manner as the root name for a FidoNet .OUT file is constructed. The root filename of the *.PKU file should be an eight digit hexadecimal number, with leading zeroes used if necessary, in order to make an eight character root filename. It is suggested that this hexadecimal number be based on time of year, with 00000000.PKU generated at exactly midnight on January 1 and FFFFFFFF.PKU generated at just a moment before midnight on December 31. However, it is permissible to use the same algorithm that is used to generate the root filename for *.PKT files. The normal sequence for transmission of messages between FidoNet nodes might then be described as follows: a. Messages created on the originating system are placed into a batched newsgroup file conforming to the specifications of RFC-1036 section 4.3. When this batched newsgroup file is destined for another FidoNet node, it will have a filename of the format: [4 hex digit net number][4 hex digit node number].UUT This file will then be placed in the outbound mail area for packing. b. A mail packing program will examine the outbound mail area and, upon finding the .UUT file, will rename it to a file with an extension of .PKU, and then shell to a compression program in order to place the *.PKU file into a new or existing mail archive file for the destination node. Mail archive files bear extension names consisting of the first two letters of a day of the week (in the English language) plus a numeric character in the range 0 - 9 (for example, .MO5 or .TH7). The method of compression for the mail archive is as agreed upon between the originating and destination nodes. No "standard" method of compression for the mail archive is specified in this document. NOTE: If the compression program fails for any reason (such as running out of disk space), the mail packing program MUST rename the .PKU file back to the original *.UUT filename before exiting. Since batched newsgroup files do not contain a header that indicates the destination node, there would be no way to determine the proper destination node if the file were not renamed back to the original filename. c. The mail archive is transmitted in the usual manner by a FidoNet compatible mailer, or such other means as may be agreed upon in advance by the sysops of the originating and destination nodes. d. At the destination system, the individual files are extracted from the mail archive. *.PKT files are processed in the usual manner to extract any netmail or echomail messages, while *.PKU files are processed by software designed to handle batched newsgroup files. In this context, such files could be "handled" by re-processing the messages and batching them to be sent on to one or more additional node(s), or by tossing the messages to the local message base, or both. Please note that this standard does not anticipate that batched newsgroup files will be converted to FidoNet echomail at any point along the way. It is realized that this may indeed happen, but such conversions should be considered as something to be avoided if at all possible due to the problems discussed in section 1 of this document. 3. Translation of newsgroup messages to and from FidoNet message format: NOTE: Where applicable, the standards defined in this section for messages shall apply not only to locally created messages, but also to all messages sent to "downstream" FidoNet nodes. In this context, "FidoNet message format" means that format in which messages commonly reside on a FidoNet BBS. At this writing, there are three formats commonly used for message storage on FidoNet systems, but other formats may be in use as well. The three most common formats are the "*.msg" format as used by the original Fido program (and a host of programs since), also commonly referred to as the "single message per file format"; the "Hudson" format, used by QuickBBS, Remote Access, and some other products; and the "Squish" format used by the Maximus BBS and the "Squish" echomail processor. Because there are so many message formats, some other programs have taken the approach of trying to convert UseNet news into echomail, creating *.PKT files which can theoretically be processed by any FidoNet system. However, since the *.PKT files are processed by the echomail processor, all the limitations and pitfalls associated with converting newsgroup messages to echomail come into play. The preferred way of handling incoming messages would be to have the BBS (or message reader/editor) software directly read batched newsgroup files. In this way, the files would not have to be "processed" per se. As new batched newsgroup files arrived on a system, they could simply be concatenated to the existing message base, and then a utility could be run that would build an index to the message base, in a manner somewhat similar to the way "flat file" message bases are currently implemented on some BBS's. Of course, you'd need to occasionally run a utility to delete old messages in order to keep the message base from growing too large, and new messages entered on the system would have to be exported from the system in a separate batched newsgroup file. However, at this writing no FidoNet-compatible BBS or message editor is capable of directly reading a batched newsgroup file. The second most preferable method is to convert news messages directly to the message format used by that system. At this writing the DoveMail software includes utilities (NewsToss and NewsScan) that can convert batched newsgroup files to and from messages in the *.msg (single message per file) format. It should be possible to convert batched newsgroup files to and from other FidoNet message formats as well. The method in which messages are stored on a BBS, and the method in which it is determined which new (locally-entered) messages need to be exported from the system will necessarily be implementation-specific. One method that can be used with *.msg type message bases is to maintain a "high water mark" in 1.msg, similar to the "high water mark" used for echomail messages, and additionally to mark messages received from other nodes as "sent" when they arrive, and locally-entered messages as "sent" when they have been exported, and to never re-send a message marked as "sent". When tossing incoming messages, duplicate messages can be detected by comparing the contents of the "Message-ID:" line with those of previously received messages. This may be slow processing considerably, however, and would require storage of a history file of "previously seen" messages. Another method is to look in the "Path" line and see if we are already listed in the path; if so, the message is a duplicate and should be deleted. This method is faster and does not require maintenance of a history file, but will not guard against duplicate messages arriving from one's feed that have not passed through the system twice (for example, a message that arrived from two different paths). Fortunately, UseNet folks seem to understand the need for proper topology, so those types of dupes are relatively rare. FidoNet sysops taking UseNet feeds must understand that it is IMPERATIVE that a feed of any one newsgroup be obtained from only ONE source, especially if they are then passing that newsgroup to any "downstream" nodes. This absolutely does NOT imply that geographic restrictions on newsgroup distribution are necessary or desirable! Additional comments on preventing "loops" can be found in section 5 of RFC-1036, in the discussion of the News Propagation Algorithm. Please note that only two methods of loop prevention are included in this standard: 1) The history mechanism. Each host keeps track of all messages it has seen (by their Message-ID) and whenever a message comes in that it has already seen, the incoming message is discarded immediately. 2) Not sending a message to a system listed in the "Path" line of the header, or to the system that originated the message (which, in practice, should be listed in the Path line). No other methods of dupe loop prevention are acceptable. In particular, checksums of portions of the message header or message itself are NOT permitted to be used for loop prevention, except perhaps as a method to quickly identify POTENTIAL duplicate messages before doing a full string comparison with the Message-ID data in the history file. In no case should a checksum be used as the SOLE method of determining whether a message is a duplicate. When newsgroup messages are created for transmission to other systems, or when received messages are transmitted other systems, the individual messages must conform to the specifications of section 2 of RFC-1036. However, in order to simply programming of software designed to handle such messages, the following modifications to the standard are proposed for use within FidoNet. Please note that these are slightly more restrictive than the standard permitted by RFC-1036: a. The "old format" or "A format" described in section 2 of RFC-1036 is NOT supported in FidoNet. Only the format detailed in RFC-1036 (sometimes referred to as the "B" News format) is supported. The vast majority of UseNet sites currently use the "B" News format. b. The UseNet standard permits the use of "white space" to separate certain items in the message header, with "white space" defined as blanks or tabs. It also states that "the Internet convention of continuation header lines (beginning with a blank or tab) is allowed." However, it should NOT be ASSUMED that "continuation header lines" will be used in any message. It is suggested that when creating newsgroup messages for transmission to other systems, the use of tab characters be avoided in header lines, and that "continuation header lines" NOT be used, even if this means that a header line will be considerably longer than the length of a screen line. Software that creates FidoNet-format messages (for display to BBS callers) from batched newsgroup files (that is, newsgroup message tossers) should break up such extra-long header lines, using a single space character ONLY (NOT a tab!) at the start of "continuation header lines." Since batched newsgroup files received from a UseNet site may contain "continuation header lines" and/or tabs as "white space" in header lines, it is necessary to be able to decode such header lines properly, but it is strongly suggested that FidoNet software not CREATE messages with tabs or "continuation header lines" for transmission through the network. c. All lines in news messages, including header lines, shall be terminated with a LINE FEED (ASCII 10 decimal) ONLY. Under NO circumstances shall a CARRIAGE RETURN (ASCII 13 decimal) appear in news messages transmitted through FidoNet (if a Carriage Return is found in an in-transit message it MAY be changed to a Line Feed, this being the sole exception to the rule about not changing the body of a message, but the expectation is that no Carriage Returns will appear in a news message). Also, spaces appearing at the end of lines (just prior to the Line Feed character) are strongly discouraged since they convey no useful information. Finally, there should be only a single line feed at the end of each message (blank lines following the last line of a message are not allowed, again because they convey no useful information). Please note that the use of the Line Feed as a line terminator is fairly standard throughout UseNet, and when a news message is converted to a FidoNet format message it is a simple matter to replace Line Feeds with Carriage Returns so that the message will display properly. d. When constructing or adding to "Path" lines, RFC-1036 (section 2.1.6) states that "The names may be separated by any punctuation character or characters (except '.' which is considered part of the hostname)." However, in actual practice, only the "!" (exclamation point or "bang" character) is commonly used to separate names. Therefore, the "!" character will be considered the "standard" separator for system names in Path lines in messages generated in FidoNet. Also, RFC-1036 states that "Normally, the rightmost name will be the name of the originating system. However, it is also permissible to include an extra entry on the right, which is the name of the sender. This is for upward compatibility with older systems." In actual practice, it appears that most Path lines originating in UseNet have a user name as the rightmost entry. Therefore, when a Path line is created for a message originating in FidoNet, it is suggested that the following format be used (assuming a message entered by user John Smith at node 1:123/456): Path: f456.n123.z1.fidonet.org!john.smith When a user name is placed in the path, all spaces in the user name must be replaced with periods, and all uppercase characters in the name should be converted to lowercase. It is permissible to use an alias in place of a user's real name if the originating system runs software that will recognize that alias in incoming netmail messages, and remap such messages to the proper user if necessary. Also, note the restrictions on prohibited characters in the user name as specified in RFC-1036 section 2.1.1. Although section 2.1.1. deals with the "From" line, common sense would indicate that these same restrictions on prohibited characters should apply if the user name is placed in the Path line (with the obvious exception of the use of the period to replace spaces in the user name, which is required). e. Header lines defined as "optional" may be more or less optional depending on the keyword. For example, the "Reply-To" and "Followup-To" lines should be automatically honored, if at all possible, when reply messages are created, and the "References" line, even though listed as an "optional" line, is "required for all follow-up messages" (replies). On the other hand, lines such as "Control" and "Distribution" may have little meaning to FidoNet nodes (in particular, "Distribution" is meant to control distribution of a message along hierarchial lines, but since FidoNet topology has little relation to UseNet hierarchies, it is probably best to just ignore "Distribution" lines on in-transit messages). Additional specifications for messages, including required and optional header lines, are detailed in section 2 of RFC-1036. When a newsgroup is moderated, it is the responsibility of the sysop of each participating BBS to prevent users from entering messages in that area (unless the message exporting software is capable of sending any locally-entered messages to the conference moderator via MAIL). However, if a software newsgroup processor is written that both imports (tosses) messages to a FidoNet-format message base, and exports locally entered messages, and if the software does not have a way to send replies to the moderator via mail, then some mechanism must be provided to prevent the export of messages from a moderated area, so that in the unlikely event that there is no easy way to prevent users from posting messages in the moderated area, such messages will still not be sent out. Since this standard does not deal with the transport of UseNet MAIL within FidoNet, the method for transmission of replies in moderated newsgroups is undefined by this document. However, software authors are encouraged to provide some mechanism for private mail replies to newsgroup messages, in both moderated and unmoderated areas. Note that if a moderated newsgroup is carried on a system, it is the responsibility of the sysop to provide mail access to users so that replies can be (manually) sent to the conference moderator, especially if replies in the newsgroup area cannot be automatically routed to the conference moderator. One point that needs to be emphasized is there is NO message length limit on UseNet messages. If a FidoNet node passes newsgroup messages to, or on behalf of other FidoNet nodes, it is NOT permissible to discard or truncate messages that exceed a preset length limit. Note that in a batched newsgroup file, each message is preceded by a header of the form "#! rnews ". Since the message text length is never changed in processing, it is possible to determine the length of a message after processing by reading in all the header lines, calculating the combined length of the header lines prior to making changes in the header (e.g. the Path line), then calculating the combined length of the header lines after making changes. The difference between the original and the new length of the header lines can then be applied to the value given in the "#! rnews" line to determine the new message length, when is then used in the "#! rnews" header of the modified message. Also, the number of bytes given in the "#! rnews" line, MINUS the length of the message header lines, is the length of the body of the message. Once this length is known, the body of the message can be copied from the input file to the output file(s) in "chunks" small enough to fit in memory, until the end of the message is reached. The following comments are implementation suggestions applicable to current FidoNet-compatible BBS systems, though not necessarily to software that may be written in the future: It should be noted that when a BBS user enters a reply message, most FidoNet BBS software will "link" the reply message to the original by placing the message number of the original message in the message header (this is almost always the case if messages are stored in the "*.msg" format, in which case the number of the message being replied to is found at bytes 185-186 in the message header). If the appropriate header lines have been stored in the text of the original message, it is possible to construct a reply message that meets all RFC-1036 specifications. For example, a "References" line can be constructed from the "Message-ID" line (and the "References" line, if any) of the original message. Similarly, if the original message contains a "Followup-To:" line, the reply can be posted to the newsgroup(s) specified in that line. This may not work as expected if a message renumbering program or similar program messes with the message base before reply message is exported, so it is highly recommended that locally-entered newsgroup messages be exported as soon as practicable after they are entered. Since the user of a BBS may reply to a message entered by another user of the same BBS, it is recommended that when a message is exported, any UseNet format header lines created for the exported message also be written back to the original message if possible. This will permit reply linking to remain intact even if two or more users of the same BBS participate in the same message thread. If a message is received that specifies more than one newsgroup in the "Newsgroups" header line, and corresponding message areas are available on the local system, one copy of the message should be placed in each such area. For example, if the message is posted to four different newsgroups, and two of those groups are carried on the local BBS, then a copy of the message should be placed in the message base for each of those groups. If users of a BBS are allowed to post a message to multiple newsgroups, then any message thus posted should be copied to the message bases of any of the other areas that are also carried on that system (and that the message was posted to) at the time the message is exported. Corrections and Additions to this document: Proposed corrections and additions to this document should be submitted to Jack Decker at 1:154/8, or jack.decker@f8.n154.z1.fidonet.org