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Text File | 1992-03-08 | 31KB | 538 lines

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 <length in bytes>".  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 [e-mail]