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<TITLE>Newsgroup Interchange within FidoNet.</TITLE>
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<PRE>
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 jack.decker@f8.n154.z1.fidonet.org
</PRE>
<HR>
<PRE>
Network Working Group M. Horton
Request for Comments: 1036 AT&T Bell Laboratories
Obsoletes: RFC-850 R. Adams
Center for Seismic Studies
December 1987
Standard for Interchange of USENET Messages
STATUS OF THIS MEMO
This document defines the standard format for the interchange of
network News messages among USENET hosts. It updates and replaces
RFC-850, reflecting version B2.11 of the News program. This memo is
disributed as an RFC to make this information easily accessible to
the Internet community. It does not specify an Internet standard.
Distribution of this memo is unlimited.
1. Introduction
This document defines the standard format for the interchange of
network News messages among USENET hosts. It describes the format
for messages themselves and gives partial standards for transmission
of news. The news transmission is not entirely in order to give a
good deal of flexibility to the hosts to choose transmission
hardware and software, to batch news, and so on.
There are five sections to this document. Section two defines the
format. Section three defines the valid control messages. Section
four specifies some valid transmission methods. Section five
describes the overall news propagation algorithm.
2. Message Format
The primary consideration in choosing a message format is that it
fit in with existing tools as well as possible. Existing tools
include implementations of both mail and news. (The notesfiles
system from the University of Illinois is considered a news
implementation.) A standard format for mail messages has existed
for many years on the Internet, and this format meets most of the
needs of USENET. Since the Internet format is extensible,
extensions to meet the additional needs of USENET are easily made
within the Internet standard. Therefore, the rule is adopted that
all USENET news messages must be formatted as valid Internet mail
messages, according to the Internet standard RFC-822. The USENET
News standard is more restrictive than the Internet standard,
Horton & Adams [Page 1]
RFC 1036 Standard for USENET Messages December 1987
placing additional requirements on each message and forbidding use
of certain Internet features. However, it should always be possible
to use a tool expecting an Internet message to process a news
message. In any situation where this standard conflicts with the
Internet standard, RFC-822 should be considered correct and this
standard in error.
Here is an example USENET message to illustrate the fields.
From: jerry@eagle.ATT.COM (Jerry Schwarz)
Path: cbosgd!mhuxj!mhuxt!eagle!jerry
Newsgroups: news.announce
Subject: Usenet Etiquette -- Please Read
Message-ID: <642@eagle.ATT.COM>
Date: Fri, 19 Nov 82 16:14:55 GMT
Followup-To: news.misc
Expires: Sat, 1 Jan 83 00:00:00 -0500
Organization: AT&T Bell Laboratories, Murray Hill
The body of the message comes here, after a blank line.
Here is an example of a message in the old format (before the
existence of this standard). It is recommended that
implementations also accept messages in this format to ease upward
conversion.
From: cbosgd!mhuxj!mhuxt!eagle!jerry (Jerry Schwarz)
Newsgroups: news.misc
Title: Usenet Etiquette -- Please Read
Article-I.D.: eagle.642
Posted: Fri Nov 19 16:14:55 1982
Received: Fri Nov 19 16:59:30 1982
Expires: Mon Jan 1 00:00:00 1990
The body of the message comes here, after a blank line.
Some news systems transmit news in the A format, which looks like
this:
Aeagle.642
news.misc
cbosgd!mhuxj!mhuxt!eagle!jerry
Fri Nov 19 16:14:55 1982
Usenet Etiquette - Please Read
The body of the message comes here, with no blank line.
A standard USENET message consists of several header lines, followed
by a blank line, followed by the body of the message. Each header
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line consist of a keyword, a colon, a blank, and some additional
information. This is a subset of the Internet standard, simplified
to allow simpler software to handle it. The "From" line may
optionally include a full name, in the format above, or use the
Internet angle bracket syntax. To keep the implementations simple,
other formats (for example, with part of the machine address after
the close parenthesis) are not allowed. The Internet convention of
continuation header lines (beginning with a blank or tab) is
allowed.
Certain headers are required, and certain other headers are
optional. Any unrecognized headers are allowed, and will be passed
through unchanged. The required header lines are "From", "Date",
"Newsgroups", "Subject", "Message-ID", and "Path". The optional
header lines are "Followup-To", "Expires", "Reply-To", "Sender",
"References", "Control", "Distribution", "Keywords", "Summary",
"Approved", "Lines", "Xref", and "Organization". Each of these
header lines will be described below.
2.1. Required Header lines
2.1.1. From
The "From" line contains the electronic mailing address of the
person who sent the message, in the Internet syntax. It may
optionally also contain the full name of the person, in parentheses,
after the electronic address. The electronic address is the same as
the entity responsible for originating the message, unless the
"Sender" header is present, in which case the "From" header might
not be verified. Note that in all host and domain names, upper and
lower case are considered the same, thus "mark@cbosgd.ATT.COM",
"mark@cbosgd.att.com", and "mark@CBosgD.ATt.COm" are all equivalent.
User names may or may not be case sensitive, for example,
"Billy@cbosgd.ATT.COM" might be different from
"BillY@cbosgd.ATT.COM". Programs should avoid changing the case of
electronic addresses when forwarding news or mail.
RFC-822 specifies that all text in parentheses is to be interpreted
as a comment. It is common in Internet mail to place the full name
of the user in a comment at the end of the "From" line. This
standard specifies a more rigid syntax. The full name is not
considered a comment, but an optional part of the header line.
Either the full name is omitted, or it appears in parentheses after
the electronic address of the person posting the message, or it
appears before an electronic address which is enclosed in angle
brackets. Thus, the three permissible forms are:
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From: mark@cbosgd.ATT.COM
From: mark@cbosgd.ATT.COM (Mark Horton)
From: Mark Horton <mark@cbosgd.ATT.COM>
Full names may contain any printing ASCII characters from space
through tilde, except that they may not contain "(" (left
parenthesis), ")" (right parenthesis), "<" (left angle bracket), or
">" (right angle bracket). Additional restrictions may be placed on
full names by the mail standard, in particular, the characters ","
(comma), ":" (colon), "@" (at), "!" (bang), "/" (slash), "="
(equal), and ";" (semicolon) are inadvisable in full names.
2.1.2. Date
The "Date" line (formerly "Posted") is the date that the message was
originally posted to the network. Its format must be acceptable
both in RFC-822 and to the getdate(3) routine that is provided with
the Usenet software. This date remains unchanged as the message is
propagated throughout the network. One format that is acceptable to
both is:
Wdy, DD Mon YY HH:MM:SS TIMEZONE
Several examples of valid dates appear in the sample message above.
Note in particular that ctime(3) format:
Wdy Mon DD HH:MM:SS YYYY
is not acceptable because it is not a valid RFC-822 date. However,
since older software still generates this format, news
implementations are encouraged to accept this format and translate
it into an acceptable format.
There is no hope of having a complete list of timezones. Universal
Time (GMT), the North American timezones (PST, PDT, MST, MDT, CST,
CDT, EST, EDT) and the +/-hhmm offset specifed in RFC-822 should be
supported. It is recommended that times in message headers be
transmitted in GMT and displayed in the local time zone.
2.1.3. Newsgroups
The "Newsgroups" line specifies the newsgroup or newsgroups in which
the message belongs. Multiple newsgroups may be specified,
separated by a comma. Newsgroups specified must all be the names of
existing newsgroups, as no new newsgroups will be created by simply
posting to them.
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Wildcards (e.g., the word "all") are never allowed in a "News-
groups" line. For example, a newsgroup comp.all is illegal,
although a newsgroup rec.sport.football is permitted.
If a message is received with a "Newsgroups" line listing some valid
newsgroups and some invalid newsgroups, a host should not remove
invalid newsgroups from the list. Instead, the invalid newsgroups
should be ignored. For example, suppose host A subscribes to the
classes btl.all and comp.all, and exchanges news messages with host
B, which subscribes to comp.all but not btl.all. Suppose A receives
a message with Newsgroups: comp.unix,btl.general.
This message is passed on to B because B receives comp.unix, but B
does not receive btl.general. A must leave the "Newsgroups" line
unchanged. If it were to remove btl.general, the edited header
could eventually re-enter the btl.all class, resulting in a message
that is not shown to users subscribing to btl.general. Also,
follow-ups from outside btl.all would not be shown to such users.
2.1.4. Subject
The "Subject" line (formerly "Title") tells what the message is
about. It should be suggestive enough of the contents of the
message to enable a reader to make a decision whether to read the
message based on the subject alone. If the message is submitted in
response to another message (e.g., is a follow-up) the default
subject should begin with the four characters "Re:", and the
"References" line is required. For follow-ups, the use of the
"Summary" line is encouraged.
2.1.5. Message-ID
The "Message-ID" line gives the message a unique identifier. The
Message-ID may not be reused during the lifetime of any previous
message with the same Message-ID. (It is recommended that no
Message-ID be reused for at least two years.) Message-ID's have the
syntax:
<string not containing blank or ">">
In order to conform to RFC-822, the Message-ID must have the format:
<unique@full_domain_name>
where full_domain_name is the full name of the host at which the
message entered the network, including a domain that host is in, and
unique is any string of printing ASCII characters, not including "<"
(left angle bracket), ">" (right angle bracket), or "@" (at sign).
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For example, the unique part could be an integer representing a
sequence number for messages submitted to the network, or a short
string derived from the date and time the message was created. For
example, a valid Message-ID for a message submitted from host ucbvax
in domain "Berkeley.EDU" would be "<4123@ucbvax.Berkeley.EDU>".
Programmers are urged not to make assumptions about the content of
Message-ID fields from other hosts, but to treat them as unknown
character strings. It is not safe, for example, to assume that a
Message-ID will be under 14 characters, that it is unique in the
first 14 characters, nor that is does not contain a "/".
The angle brackets are considered part of the Message-ID. Thus, in
references to the Message-ID, such as the ihave/sendme and cancel
control messages, the angle brackets are included. White space
characters (e.g., blank and tab) are not allowed in a Message-ID.
Slashes ("/") are strongly discouraged. All characters between the
angle brackets must be printing ASCII characters.
2.1.6. Path
This line shows the path the message took to reach the current
system. When a system forwards the message, it should add its own
name to the list of systems in the "Path" line. The names may be
separated by any punctuation character or characters (except "."
which is considered part of the hostname). Thus, the following are
valid entries:
cbosgd!mhuxj!mhuxt
cbosgd, mhuxj, mhuxt
@cbosgd.ATT.COM,@mhuxj.ATT.COM,@mhuxt.ATT.COM
teklabs, zehntel, sri-unix@cca!decvax
(The latter path indicates a message that passed through decvax,
cca, sri-unix, zehntel, and teklabs, in that order.) Additional
names should be added from the left. For example, the most recently
added name in the fourth example was teklabs. Letters, digits,
periods and hyphens are considered part of host names; other
punctuation, including blanks, are considered separators.
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.
The "Path" line is not used for replies, and should not be taken as
a mailing address. It is intended to show the route the message
traveled to reach the local host. There are several uses for this
information. One is to monitor USENET routing for performance
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reasons. Another is to establish a path to reach new hosts.
Perhaps the most important use is to cut down on redundant USENET
traffic by failing to forward a message to a host that is known to
have already received it. In particular, when host A sends a
message to host B, the "Path" line includes A, so that host B will
not immediately send the message back to host A. The name each host
uses to identify itself should be the same as the name by which its
neighbors know it, in order to make this optimization possible.
A host adds its own name to the front of a path when it receives a
message from another host. Thus, if a message with path "A!X!Y!Z"
is passed from host A to host B, B will add its own name to the path
when it receives the message from A, e.g., "B!A!X!Y!Z". If B then
passes the message on to C, the message sent to C will contain the
path "B!A!X!Y!Z", and when C receives it, C will change it to
"C!B!A!X!Y!Z".
Special upward compatibility note: Since the "From", "Sender", and
"Reply-To" lines are in Internet format, and since many USENET hosts
do not yet have mailers capable of understanding Internet format, it
would break the reply capability to completely sever the connection
between the "Path" header and the reply function. It is recognized
that the path is not always a valid reply string in older
implementations, and no requirement to fix this problem is placed on
implementations. However, the existing convention of placing the
host name and an "!" at the front of the path, and of starting the
path with the host name, an "!", and the user name, should be
maintained when possible.
2.2. Optional Headers
2.2.1. Reply-To
This line has the same format as "From". If present, mailed replies
to the author should be sent to the name given here. Otherwise,
replies are mailed to the name on the "From" line. (This does not
prevent additional copies from being sent to recipients named by the
replier, or on "To" or "Cc" lines.) The full name may be optionally
given, in parentheses, as in the "From" line.
2.2.2. Sender
This field is present only if the submitter manually enters a "From"
line. It is intended to record the entity responsible for
submitting the message to the network. It should be verified by the
software at the submitting host.
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For example, if John Smith is visiting CCA and wishes to post a
message to the network, using friend Sarah Jones' account, the
message might read:
From: smith@ucbvax.Berkeley.EDU (John Smith)
Sender: jones@cca.COM (Sarah Jones)
If a gateway program enters a mail message into the network at host
unix.SRI.COM, the lines might read:
From: John.Doe@A.CS.CMU.EDU
Sender: network@unix.SRI.COM
The primary purpose of this field is to be able to track down
messages to determine how they were entered into the network. The
full name may be optionally given, in parentheses, as in the "From"
line.
2.2.3. Followup-To
This line has the same format as "Newsgroups". If present, follow-
up messages are to be posted to the newsgroup or newsgroups listed
here. If this line is not present, follow-ups are posted to the
newsgroup or newsgroups listed in the "Newsgroups" line.
If the keyword poster is present, follow-up messages are not
permitted. The message should be mailed to the submitter of the
message via mail.
2.2.4. Expires
This line, if present, is in a legal USENET date format. It
specifies a suggested expiration date for the message. If not
present, the local default expiration date is used. This field is
intended to be used to clean up messages with a limited usefulness,
or to keep important messages around for longer than usual. For
example, a message announcing an upcoming seminar could have an
expiration date the day after the seminar, since the message is not
useful after the seminar is over. Since local hosts have local
policies for expiration of news (depending on available disk space,
for instance), users are discouraged from providing expiration dates
for messages unless there is a natural expiration date associated
with the topic. System software should almost never provide a
default "Expires" line. Leave it out and allow local policies to be
used unless there is a good reason not to.
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2.2.5. References
This field lists the Message-ID's of any messages prompting the
submission of this message. It is required for all follow-up
messages, and forbidden when a new subject is raised.
Implementations should provide a follow-up command, which allows a
user to post a follow-up message. This command should generate a
"Subject" line which is the same as the original message, except
that if the original subject does not begin with "Re:" or "re:", the
four characters "Re:" are inserted before the subject. If there is
no "References" line on the original header, the "References" line
should contain the Message-ID of the original message (including the
angle brackets). If the original message does have a "References"
line, the follow-up message should have a "References" line
containing the text of the original "References" line, a blank, and
the Message-ID of the original message.
The purpose of the "References" header is to allow messages to be
grouped into conversations by the user interface program. This
allows conversations within a newsgroup to be kept together, and
potentially users might shut off entire conversations without
unsubscribing to a newsgroup. User interfaces need not make use of
this header, but all automatically generated follow-ups should
generate the "References" line for the benefit of systems that do
use it, and manually generated follow-ups (e.g., typed in well after
the original message has been printed by the machine) should be
encouraged to include them as well.
It is permissible to not include the entire previous "References"
line if it is too long. An attempt should be made to include a
reasonable number of backwards references.
2.2.6. Control
If a message contains a "Control" line, the message is a control
message. Control messages are used for communication among USENET
host machines, not to be read by users. Control messages are
distributed by the same newsgroup mechanism as ordinary messages.
The body of the "Control" header line is the message to the host.
For upward compatibility, messages that match the newsgroup pattern
"all.all.ctl" should also be interpreted as control messages. If no
"Control" header is present on such messages, the subject is used as
the control message. However, messages on newsgroups matching this
pattern do not conform to this standard.
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Also for upward compatibility, if the first 4 characters of the
"Subject:" line are "cmsg", the rest of the "Subject:" line should
be interpreted as a control message.
2.2.7. Distribution
This line is used to alter the distribution scope of the message.
It is a comma separated list similar to the "Newsgroups" line. User
subscriptions are still controlled by "Newsgroups", but the message
is sent to all systems subscribing to the newsgroups on the
"Distribution" line in addition to the "Newsgroups" line. For the
message to be transmitted, the receiving site must normally receive
one of the specified newsgroups AND must receive one of the
specified distributions. Thus, a message concerning a car for sale
in New Jersey might have headers including:
Newsgroups: rec.auto,misc.forsale
Distribution: nj,ny
so that it would only go to persons subscribing to rec.auto or misc.
for sale within New Jersey or New York. The intent of this header
is to restrict the distribution of a newsgroup further, not to
increase it. A local newsgroup, such as nj.crazy-eddie, will
probably not be propagated by hosts outside New Jersey that do not
show such a newsgroup as valid. A follow-up message should default
to the same "Distribution" line as the original message, but the
user can change it to a more limited one, or escalate the
distribution if it was originally restricted and a more widely
distributed reply is appropriate.
2.2.8. Organization
The text of this line is a short phrase describing the organization
to which the sender belongs, or to which the machine belongs. The
intent of this line is to help identify the person posting the
message, since host names are often cryptic enough to make it hard
to recognize the organization by the electronic address.
2.2.9. Keywords
A few well-selected keywords identifying the message should be on
this line. This is used as an aid in determining if this message is
interesting to the reader.
2.2.10. Summary
This line should contain a brief summary of the message. It is
usually used as part of a follow-up to another message. Again, it
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is very useful to the reader in determining whether to read the
message.
2.2.11. Approved
This line is required for any message posted to a moderated
newsgroup. It should be added by the moderator and consist of his
mail address. It is also required with certain control messages.
2.2.12. Lines
This contains a count of the number of lines in the body of the
message.
2.2.13. Xref
This line contains the name of the host (with domains omitted) and a
white space separated list of colon-separated pairs of newsgroup
names and message numbers. These are the newsgroups listed in the
"Newsgroups" line and the corresponding message numbers from the
spool directory.
This is only of value to the local system, so it should not be
transmitted. For example, in:
Path: seismo!lll-crg!lll-lcc!pyramid!decwrl!reid
From: reid@decwrl.DEC.COM (Brian Reid)
Newsgroups: news.lists,news.groups
Subject: USENET READERSHIP SUMMARY REPORT FOR SEP 86
Message-ID: <5658@decwrl.DEC.COM>
Date: 1 Oct 86 11:26:15 GMT
Organization: DEC Western Research Laboratory
Lines: 441
Approved: reid@decwrl.UUCP
Xref: seismo news.lists:461 news.groups:6378
the "Xref" line shows that the message is message number 461 in the
newsgroup news.lists, and message number 6378 in the newsgroup
news.groups, on host seismo. This information may be used by
certain user interfaces.
3. Control Messages
This section lists the control messages currently defined. The body
of the "Control" header line is the control message. Messages are a
sequence of zero or more words, separated by white space (blanks or
tabs). The first word is the name of the control message, remaining
words are parameters to the message. The remainder of the header
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and the body of the message are also potential parameters; for
example, the "From" line might suggest an address to which a
response is to be mailed.
Implementors and administrators may choose to allow control messages
to be carried out automatically, or to queue them for annual
processing. However, manually processed messages should be dealt
with promptly.
Failed control messages should NOT be mailed to the originator of
the message, but to the local "usenet" account.
3.1. Cancel
cancel <Message-ID>
If a message with the given Message-ID is present on the local
system, the message is cancelled. This mechanism allows a user to
cancel a message after the message has been distributed over the
network.
If the system is unable to cancel the message as requested, it
should not forward the cancellation request to its neighbor systems.
Only the author of the message or the local news administrator is
allowed to send this message. The verified sender of a message is
the "Sender" line, or if no "Sender" line is present, the "From"
line. The verified sender of the cancel message must be the same as
either the "Sender" or "From" field of the original message. A
verified sender in the cancel message is allowed to match an
unverified "From" in the original message.
3.2. Ihave/Sendme
ihave <Message-ID list> [<remotesys>]
sendme <Message-ID list> [<remotesys>]
This message is part of the ihave/sendme protocol, which allows one
host (say A) to tell another host (B) that a particular message has
been received on A. Suppose that host A receives message
"<1234@ucbvax.Berkeley.edu>", and wishes to transmit the message to
host B.
A sends the control message "ihave <1234@ucbvax.Berkeley.edu> A" to
host B (by posting it to newsgroup to.B). B responds with the
control message "sendme <1234@ucbvax.Berkeley.edu> B" (on newsgroup
to.A), if it has not already received the message. Upon receiving
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the sendme message, A sends the message to B.
This protocol can be used to cut down on redundant traffic between
hosts. It is optional and should be used only if the particular
situation makes it worthwhile. Frequently, the outcome is that,
since most original messages are short, and since there is a high
overhead to start sending a new message with UUCP, it costs as much
to send the ihave as it would cost to send the message itself.
One possible solution to this overhead problem is to batch requests.
Several Message-ID's may be announced or requested in one message.
If no Message-ID's are listed in the control message, the body of
the message should be scanned for Message-ID's, one per line.
3.3. Newgroup
newgroup <groupname> [moderated]
This control message creates a new newsgroup with the given name.
Since no messages may be posted or forwarded until a newsgroup is
created, this message is required before a newsgroup can be used.
The body of the message is expected to be a short paragraph
describing the intended use of the newsgroup.
If the second argument is present and it is the keyword moderated,
the group should be created moderated instead of the default of
unmoderated. The newgroup message should be ignored unless there is
an "Approved" line in the same message header.
3.4. Rmgroup
rmgroup <groupname>
This message removes a newsgroup with the given name. Since the
newsgroup is removed from every host on the network, this command
should be used carefully by a responsible administrator. The
rmgroup message should be ignored unless there is an "Approved:"
line in the same message header.
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3.5. Sendsys
sendsys (no arguments)
The sys file, listing all neighbors and the newsgroups to be sent to
each neighbor, will be mailed to the author of the control message
("Reply-To", if present, otherwise "From"). This information is
considered public information, and it is a requirement of membership
in USENET that this information be provided on request, either
automatically in response to this control message, or manually, by
mailing the requested information to the author of the message.
This information is used to keep the map of USENET up to date, and
to determine where netnews is sent.
The format of the file mailed back to the author should be the same
as that of the sys file. This format has one line per neighboring
host (plus one line for the local host), containing four colon
separated fields. The first field has the host name of the
neighbor, the second field has a newsgroup pattern describing the
newsgroups sent to the neighbor. The third and fourth fields are
not defined by this standard. The sys file is not the same as the
UUCP L.sys file. A sample response is:
From: cbosgd!mark (Mark Horton)
Date: Sun, 27 Mar 83 20:39:37 -0500
Subject: response to your sendsys request
To: mark@cbosgd.ATT.COM
Responding-System: cbosgd.ATT.COM
cbosgd:osg,cb,btl,bell,world,comp,sci,rec,talk,misc,news,soc,to,
test
ucbvax:world,comp,to.ucbvax:L:
cbosg:world,comp,bell,btl,cb,osg,to.cbosg:F:/usr/spool/outnews
/cbosg
cbosgb:osg,to.cbosgb:F:/usr/spool/outnews/cbosgb
sescent:world,comp,bell,btl,cb,to.sescent:F:/usr/spool/outnews
/sescent
npois:world,comp,bell,btl,ug,to.npois:F:/usr/spool/outnews/npois
mhuxi:world,comp,bell,btl,ug,to.mhuxi:F:/usr/spool/outnews/mhuxi
3.6. Version
version (no arguments)
The name and version of the software running on the local system is
to be mailed back to the author of the message ("Reply-to" if
present, otherwise "From").
3.7. Checkgroups
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The message body is a list of "official" newsgroups and their
description, one group per line. They are compared against the list
of active newsgroups on the current host. The names of any obsolete
or new newsgroups are mailed to the user "usenet" and descriptions
of the new newsgroups are added to the help file used when posting
news.
4. Transmission Methods
USENET is not a physical network, but rather a logical network
resting on top of several existing physical networks. These
networks include, but are not limited to, UUCP, the Internet, an
Ethernet, the BLICN network, an NSC Hyperchannel, and a BERKNET.
What is important is that two neighboring systems on USENET have
some method to get a new message, in the format listed here, from
one system to the other, and once on the receiving system, processed
by the netnews software on that system. (On UNIX systems, this
usually means the rnews program being run with the message on the
standard input. <1>)
It is not a requirement that USENET hosts have mail systems capable
of understanding the Internet mail syntax, but it is strongly
recommended. Since "From", "Reply-To", and "Sender" lines use the
Internet syntax, replies will be difficult or impossible without an
Internet mailer. A host without an Internet mailer can attempt to
use the "Path" header line for replies, but this field is not
guaranteed to be a working path for replies. In any event, any host
generating or forwarding news messages must have an Internet address
that allows them to receive mail from hosts with Internet mailers,
and they must include their Internet address on their From line.
4.1. Remote Execution
Some networks permit direct remote command execution. On these
networks, news may be forwarded by spooling the rnews command with
the message on the standard input. For example, if the remote
system is called remote, news would be sent over a UUCP link
with the command:
uux - remote!rnews
and on a Berknet:
net -mremote rnews
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RFC 1036 Standard for USENET Messages December 1987
It is important that the message be sent via a reliable mechanism,
normally involving the possibility of spooling, rather than direct
real-time remote execution. This is because, if the remote system
is down, a direct execution command will fail, and the message will
never be delivered. If the message is spooled, it will eventually
be delivered when both systems are up.
4.2. Transfer by Mail
On some systems, direct remote spooled execution is not possible.
However, most systems support electronic mail, and a news message
can be sent as mail. One approach is to send a mail message which
is identical to the news message: the mail headers are the news
headers, and the mail body is the news body. By convention, this
mail is sent to the user newsmail on the remote machine.
One problem with this method is that it may not be possible to
convince the mail system that the "From" line of the message is
valid, since the mail message was generated by a program on a
system different from the source of the news message. Another
problem is that error messages caused by the mail transmission
would be sent to the originator of the news message, who has no
control over news transmission between two cooperating hosts
and does not know whom to contact. Transmission error messages
should be directed to a responsible contact person on the
sending machine.
A solution to this problem is to encapsulate the news message into a
mail message, such that the entire message (headers and body) are
part of the body of the mail message. The convention here is that
such mail is sent to user rnews on the remote system. A mail
message body is generated by prepending the letter N to each line of
the news message, and then attaching whatever mail headers are
convenient to generate. The N's are attached to prevent any special
lines in the news message from interfering with mail transmission,
and to prevent any extra lines inserted by the mailer (headers,
blank lines, etc.) from becoming part of the news message. A
program on the receiving machine receives mail to rnews, extracting
the message itself and invoking the rnews program. An example in
this format might look like this:
Horton & Adams [Page 16]
RFC 1036 Standard for USENET Messages December 1987
Date: Mon, 3 Jan 83 08:33:47 MST
From: news@cbosgd.ATT.COM
Subject: network news message
To: rnews@npois.ATT.COM
NPath: cbosgd!mhuxj!harpo!utah-cs!sask!derek
NFrom: derek@sask.UUCP (Derek Andrew)
NNewsgroups: misc.test
NSubject: necessary test
NMessage-ID: <176@sask.UUCP>
NDate: Mon, 3 Jan 83 00:59:15 MST
N
NThis really is a test. If anyone out there more than 6
Nhops away would kindly confirm this note I would
Nappreciate it. We suspect that our news postings
Nare not getting out into the world.
N
Using mail solves the spooling problem, since mail must always be
spooled if the destination host is down. However, it adds more
overhead to the transmission process (to encapsulate and extract the
message) and makes it harder for software to give different
priorities to news and mail.
4.3. Batching
Since news messages are usually short, and since a large number of
messages are often sent between two hosts in a day, it may make
sense to batch news messages. Several messages can be combined into
one large message, using conventions agreed upon in advance by the
two hosts. One such batching scheme is described here; its use is
highly recommended.
News messages are combined into a script, separated by a header of
the form:
#! rnews 1234
where 1234 is the length of the message in bytes. Each such line is
followed by a message containing the given number of bytes. (The
newline at the end of each line of the message is counted as one
byte, for purposes of this count, even if it is stored as <CARRIAGE
RETURN><LINE FEED>.) For example, a batch of message might look
like this:
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RFC 1036 Standard for USENET Messages December 1987
#! rnews 239
From: jerry@eagle.ATT.COM (Jerry Schwarz)
Path: cbosgd!mhuxj!mhuxt!eagle!jerry
Newsgroups: news.announce
Subject: Usenet Etiquette -- Please Read
Message-ID: <642@eagle.ATT.COM>
Date: Fri, 19 Nov 82 16:14:55 EST
Approved: mark@cbosgd.ATT.COM
Here is an important message about USENET Etiquette.
#! rnews 234
From: jerry@eagle.ATT.COM (Jerry Schwarz)
Path: cbosgd!mhuxj!mhuxt!eagle!jerry
Newsgroups: news.announce
Subject: Notes on Etiquette message
Message-ID: <643@eagle.ATT.COM>
Date: Fri, 19 Nov 82 17:24:12 EST
Approved: mark@cbosgd.ATT.COM
There was something I forgot to mention in the last
message.
Batched news is recognized because the first character in the
message is #. The message is then passed to the unbatcher for
interpretation.
The second argument (in this example rnews) determines which
batching scheme is being used. Cooperating hosts may use whatever
scheme is appropriate for them.
5. The News Propagation Algorithm
This section describes the overall scheme of USENET and the
algorithm followed by hosts in propagating news to the entire
logical network. Since all hosts are affected by incorrectly
formatted messages and by propagation errors, it is important
for the method to be standardized.
USENET is a directed graph. Each node in the graph is a host
computer, and each arc in the graph is a transmission path from
one host to another host. Each arc is labeled with a newsgroup
pattern, specifying which newsgroup classes are forwarded along
that link. Most arcs are bidirectional, that is, if host A
sends a class of newsgroups to host B, then host B usually sends
the same class of newsgroups to host A. This bidirectionality
is not, however, required.
USENET is made up of many subnetworks. Each subnet has a name, such
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RFC 1036 Standard for USENET Messages December 1987
as comp or btl. Each subnet is a connected graph, that is, a path
exists from every node to every other node in the subnet. In
addition, the entire graph is (theoretically) connected. (In
practice, some political considerations have caused some hosts to be
unable to post messages reaching the rest of the network.)
A message is posted on one machine to a list of newsgroups. That
machine accepts it locally, then forwards it to all its neighbors
that are interested in at least one of the newsgroups of the
message. (Site A deems host B to be "interested" in a newsgroup if
the newsgroup matches the pattern on the arc from A to B. This
pattern is stored in a file on the A machine.) The hosts receiving
the incoming message examine it to make sure they really want the
message, accept it locally, and then in turn forward the message to
all their interested neighbors. This process continues until the
entire network has seen the message.
An important part of the algorithm is the prevention of loops. The
above process would cause a message to loop along a cycle forever.
In particular, when host A sends a message to host B, host B will
send it back to host A, which will send it to host B, and so on.
One solution to this is 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. This solution is sufficient to
prevent loops, but additional optimizations can be made to avoid
sending messages to hosts that will simply throw them away.
One optimization is that a message should never be sent to a machine
listed in the "Path" line of the header. When a machine name is
in the "Path" line, the message is known to have passed through the
machine. Another optimization is that, if the message originated
on host A, then host A has already seen the message. Thus, if a
message is posted to newsgroup misc.misc, it will match the pattern
misc.all (where all is a metasymbol that matches any string), and
will be forwarded to all hosts that subscribe to misc.all (as
determined by what their neighbors send them). These hosts make up
the misc subnetwork. A message posted to btl.general will reach all
hosts receiving btl.all, but will not reach hosts that do not get
btl.all. In effect, the messages reaches the btl subnetwork. A
messages posted to newsgroups misc.misc,btl.general will reach all
hosts subscribing to either of the two classes.
Notes
<1> UNIX is a registered trademark of AT&T.
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