Independent Submission H. Spencer
Request for Comments: 1849 SP Systems
Obsoleted by: 5536, 5537 March 2010
Category: Historic
ISSN: 2070-1721
"Son of 1036": News Article Format and Transmission
Abstract
By the early 1990s, it had become clear that RFC 1036, then the
specification for the Interchange of USENET Messages, was badly in
need of repair. This "Internet-Draft-to-be", though never formally
published at that time, was widely circulated and became the de facto
standard for implementors of News Servers and User Agents, rapidly
acquiring the nickname "Son of 1036". Indeed, under that name, it
could fairly be described as the best-known Internet Draft (n)ever
published, and it formed the starting point for the recently adopted
Proposed Standards for Netnews.
It is being published now in order to provide the historical
background out of which those standards have grown. Present-day
implementors should be aware that it is NOT NOW APPROPRIATE for use
in current implementations.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for the historical record.
This document defines a Historic Document for the Internet community.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc1849.
Spencer Historic [Page 1]RFC 1849 Son of 1036 March 2010
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
This document may not be modified, and derivative works of it may not
be created, except to format it for publication as an RFC or to
translate it into languages other than English.
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Table of Contents
Preface ............................................................5
Original Abstract ..................................................6
1. Introduction ....................................................6
2. Definitions, Notations, and Conventions .........................8
2.1. Textual Notations ..........................................8
2.2. Syntax Notation ............................................9
2.3. Definitions ...............................................10
2.4. End-of-Line ...............................................13
2.5. Case-Sensitivity ..........................................13
2.6. Language ..................................................13
3. Relation to MAIL (RFC822, etc.) ................................14
4. Basic Format ...................................................15
4.1. Overall Syntax ............................................15
4.2. Headers ...................................................16
4.2.1. Names and Contents .................................16
4.2.2. Undesirable Headers ................................18
4.2.3. White Space and Continuations ......................18
4.3. Body ......................................................19
4.3.1. Body Format Issues .................................19
4.3.2. Body Conventions ...................................20
4.4. Characters and Character Sets .............................23
4.5. Non-ASCII Characters in Headers ...........................26
4.6. Size Limits ...............................................28
4.7. Example ...................................................30
5. Mandatory Headers ..............................................30
5.1. Date ......................................................31
5.2. From ......................................................33
5.3. Message-ID ................................................35
5.4. Subject ...................................................36
5.5. Newsgroups ................................................38
5.6. Path ......................................................42
6. Optional Headers ...............................................45
6.1. Followup-To ...............................................45
6.2. Expires ...................................................46
6.3. Reply-To ..................................................47
6.4. Sender ....................................................47
6.5. References ................................................48
6.6. Control ...................................................50
6.7. Distribution ..............................................51
6.8. Keywords ..................................................52
6.9. Summary ...................................................53
6.10. Approved .................................................53
6.11. Lines ....................................................54
6.12. Xref .....................................................55
6.13. Organization .............................................56
6.14. Supersedes ...............................................57
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6.15. Also-Control .............................................57
6.16. See-Also .................................................58
6.17. Article-Names ............................................58
6.18. Article-Updates ..........................................60
7. Control Messages ...............................................60
7.1. cancel ....................................................61
7.2. ihave, sendme .............................................64
7.3. newgroup ..................................................66
7.4. rmgroup ...................................................68
7.5. sendsys, version, whogets .................................68
7.6. checkgroups ...............................................73
8. Transmission Formats ...........................................74
8.1. Batches ...................................................74
8.2. Encoded Batches ...........................................75
8.3. News within Mail ..........................................76
8.4. Partial Batches ...........................................77
9. Propagation and Processing .....................................77
9.1. Relayer General Issues ....................................78
9.2. Article Acceptance and Propagation ........................80
9.3. Administrator Contact .....................................82
10. Gatewaying ....................................................83
10.1. General Gatewaying Issues ................................83
10.2. Header Synthesis .........................................85
10.3. Message ID Mapping .......................................86
10.4. Mail to and from News ....................................88
10.5. Gateway Administration ...................................89
11. Security and Related Issues ...................................90
11.1. Leakage ..................................................90
11.2. Attacks ..................................................91
11.3. Anarchy ..................................................92
11.4. Liability ................................................92
12. References ....................................................93
Appendix A. Archaeological Notes ..................................96
A.1. "A News" Article Format ...................................96
A.2. Early "B News" Article Format .............................96
A.3. Obsolete Headers ..........................................97
A.4. Obsolete Control Messages .................................97
Appendix B. A Quick Tour of MIME ..................................98
Appendix C. Summary of Changes Since RFC 1036 ....................103
Appendix D. Summary of Completely New Features ...................104
Appendix E. Summary of Differences from RFCs 822 and 1123.........105
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Preface
Although [RFC1036] was published in 1987, for many years it remained
the only formally published specification for Netnews format and
processing. It was widely considered obsolete within a few years,
and it has now been superseded by the work of the USEFOR Working
Group, leading to the publication of [RFC5536] and [RFC5537].
However, there was an intermediate step that is of some historical
interest.
In 1993-4, Henry Spencer wrote and informally circulated a document
that became known as "Son of 1036", meant as a first draft of a
replacement for [RFC1036]. It went no further at the time (although,
more recently, the USEFOR Working Group started from it), but has
nevertheless seen considerable use as a technical reference and even
a de facto standard, despite its informal status.
The USEFOR work has eliminated any further relevance of Son of 1036
as a technical reference, but it remains of historical interest. The
USEFOR Working Group has asked that it be published as an Historic
RFC, to ensure its preservation in an accessible form and facilitate
referencing it.
This document is identical to the last distributed version of Son of
1036, dated 2 June 1994, except for reformatting, correction of a few
minor factual or formatting errors, completion of the then-empty
Appendix D and of the References section, minor editing to match
preferred RFC style, and changes to leading and trailing material.
Remarks enclosed within "{...}" indicate explanatory material not
present in the original version. References to the current MIME
standards (and a few others) have been added (that was an unresolved
issue in 1994).
The technical content remains unchanged, including the references to
the document itself as a Draft rather than an RFC and the presence of
unresolved issues. The original section numbering has been
preserved, although the original pagination has not (among other
reasons, it did not fully follow IETF formatting standards).
READERS ARE CAUTIONED THAT THIS DOCUMENT IS OBSOLETE AND SHOULD NOT
BE USED AS A TECHNICAL REFERENCE. Although Son of 1036 largely
documented existing practice, it also proposed some changes, some of
which did not catch on or are no longer considered good ideas. (Of
particular note, the MIME type "message/news" should not be used.)
Consult [RFC5536] and [RFC5537] for modern technical information.
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Although a number of people contributed useful comments or criticism
during the preparation of this document, its contents are entirely
the opinions of the author circa 1994. Not even the author himself
agrees with them all now.
The author thanks Charles Lindsey for his assistance in getting this
document cleaned up and formally published at last (not least, for
supplying some prodding to actually get it done!).
The author thanks Luc Rooijakkers for supplying the MIME summary that
Appendix B is based on.
Original Abstract
This Draft defines the format and procedures for interchange of
network news articles. It is hoped that a later version of this
Draft will obsolete RFC 1036, reflecting more recent experience and
accommodating future directions.
Network news articles resemble mail messages but are broadcast to
potentially large audiences, using a flooding algorithm that
propagates one copy to each interested host (or group thereof),
typically stores only one copy per host, and does not require any
central administration or systematic registration of interested
users. Network news originated as the medium of communication for
Usenet, circa 1980. Since then, Usenet has grown explosively, and
many Internet sites participate in it. In addition, the news
technology is now in widespread use for other purposes, on the
Internet and elsewhere.
This Draft primarily codifies and organizes existing practice. A few
small extensions have been added in an attempt to solve problems that
are considered serious. Major extensions (e.g., cryptographic
authentication) that need significant development effort are left to
be undertaken as independent efforts.
1. Introduction
Network news articles resemble mail messages but are broadcast to
potentially large audiences, using a flooding algorithm that
propagates one copy to each interested host (or groups thereof),
typically stores only one copy per host, and does not require any
central administration or systematic registration of interested
users. Network news originated as the medium of communication for
Usenet, circa 1980. Since then, Usenet has grown explosively, and
many Internet sites participate in it. In addition, the news
technology is now in widespread use for other purposes, on the
Internet and elsewhere.
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The earliest news interchange used the so-called "A News" article
format. Shortly thereafter, an article format vaguely resembling
Internet mail was devised and used briefly. Both of those formats
are completely obsolete; they are documented in Appendix A for
historical reasons only. With the publication of [RFC850] in 1983,
news articles came to closely resemble Internet mail messages, with
some restrictions and some additional headers. In 1987, [RFC1036]
updated [RFC850] without making major changes.
In the intervening five years, the [RFC1036] article format has
proven quite satisfactory, although minor extensions appear desirable
to match recent developments in areas such as multi-media mail.
[RFC1036] itself has not proven quite so satisfactory. It is often
rather vague and does not address some issues at all; this has caused
significant interoperability problems at times, and implementations
have diverged somewhat. Worse, although it was intended primarily to
document existing practice, it did not precisely match existing
practice even at the time it was published, and the deviations have
grown since.
This Draft attempts to specify the format of articles, and the
procedures used to exchange them and process them, in sufficient
detail to allow full interoperability. In addition, some tentative
suggestions are made about directions for future development, in an
attempt to avert unnecessary divergence and consequent loss of
interoperability. Major extensions (e.g., cryptographic
authentication) that need significant development effort are left to
be undertaken as independent efforts.
NOTE: One question all of this may raise is: why is there no News-
Version header, analogous to MIME-Version, specifying a version
number corresponding to this specification? The answer is: it
doesn't appear to be useful, given news's backward-compatibility
constraints. The major use of a version number is indicating
which of several INCOMPATIBLE interpretations is relevant. The
impossibility of orchestrating any sort of simultaneous change
over news's installed base makes it necessary to avoid such
incompatible changes (as opposed to extensions) entirely. MIME
has a version number mostly because it introduced incompatible
changes to the interpretation of several "Content-" headers. This
Draft attempts no changes in interpretation, and it appears
doubtful that future Drafts will find it feasible to introduce
any.
UNRESOLVED ISSUE: Should this be reconsidered? Only if the header
has SPECIFIC IDENTIFIABLE uses today. Otherwise, it's just
useless added bulk.
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As in this Draft's predecessors, the exact means used to transmit
articles from one host to another is not specified. Network News
Transfer Protocol (NNTP) [RFC977] {since replaced by [RFC3977]} is
probably the most common transmission method on the Internet, but a
number of others are known to be in use, including the Unix-To-Unix
Copy Protocol [UUCP], which was extensively used in the early days of
Usenet and is still much used on its fringes today.
Several of the mechanisms described in this Draft may seem somewhat
strange or even bizarre at first reading. As with Internet mail,
there is no reasonable possibility of updating the entire installed
base of news software promptly, so interoperability with old software
is crucial and will remain so. Compatibility with existing practice
and robustness in an imperfect world necessarily take priority over
elegance.
2. Definitions, Notations, and Conventions
2.1. Textual Notations
Throughout this Draft, "MAIL" is short for "[RFC822] as amended by
[RFC1123]". ([RFC1123]'s amendments are mostly relatively small, but
they are not insignificant.) See also the discussion in Section 3
about this Draft's relationship to MAIL. "MIME" is short for
"[RFC1341] and [RFC1342]" (or their {since} updated replacements
{[RFC2045], [RFC2046], and [RFC2047]}).
UNRESOLVED ISSUE: Update these numbers {now resolved!}.
{NOTE: Since the original publication of this Draft [RFC822] has
been updated, firstly to [RFC2822] and more recently to [RFC5322];
however, this Draft is firmly rooted in the original [RFC822].
Similarly, [RFC821] has also received two upgrades in the
meantime.}
"ASCII" is short for "the ANSI X3.4 character set" [X3.4]. While
"ASCII" is often misused to refer to various character sets somewhat
similar to X3.4, in this Draft, "ASCII" means [X3.4] and only [X3.4].
NOTE: The name is traditional (to the point where the ANSI
standard sanctions it), even though it is no longer an acronym for
the name of the standard.
NOTE: ASCII, X3.4, contains 128 characters, not all of them
printable. Character sets with more characters are not ASCII,
although they may include it as a subset.
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Certain words used to define the significance of individual
requirements are capitalized. "MUST" means that the item is an
absolute requirement of the specification. "SHOULD" means that the
item is a strong recommendation: there may be valid reasons to ignore
it in unusual circumstances, but this should be done only after
careful study of the full implications and a firm conclusion that it
is necessary, because there are serious disadvantages to doing so.
"MAY" means that the item is truly optional, and implementors and
users are warned that conformance is possible but not to be relied
on.
The term "compliant", applied to implementations, etc., indicates
satisfaction of all relevant "MUST" and "SHOULD" requirements. The
term "conditionally compliant" indicates satisfaction of all relevant
"MUST" requirements but violation of at least one relevant "SHOULD"
requirement.
This Draft contains explanatory notes using the following format.
These may be skipped by persons interested solely in the content of
the specification. The purpose of the notes is to explain why
choices were made, to place them in context, or to suggest possible
implementation techniques.
NOTE: While such explanatory notes may seem superfluous in
principle, they often help the less-than-omniscient reader grasp
the purpose of the specification and the constraints involved.
Given the limitations of natural language for descriptive
purposes, this improves the probability that implementors and
users will understand the true intent of the specification in
cases where the wording is not entirely clear.
All numeric values are given in decimal unless otherwise indicated.
Octets are assumed to be unsigned values for this purpose. Large
numbers are written using the North American convention, in which ","
separates groups of three digits but otherwise has no significance.
2.2. Syntax Notation
Although the mechanisms specified in this Draft are all described in
prose, most are also described formally in the modified BNF notation
of [RFC822]. Implementors will need to be familiar with this
notation to fully understand this specification and are referred to
[RFC822] for a complete explanation of the modified BNF notation.
Here is a brief illustrative example:
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sentence = clause *( punct clause ) "."
punct = ":" / ";"
clause = 1*word [ "(" clause ")" / "," 1*word ]
word = <any English word>
This defines a sentence as some clauses separated by puncts and ended
by a period, a punct as a colon or semicolon, a clause as at least
one <word> optionally followed by either a parenthesized clause or a
comma and at least one more <word>, and a <word> as (informally) any
English word. The characters "<>" are used to enclose names when
(and only when) distinguishing them from surrounding text is useful.
The full form of the repetition notation is "<m>*<n><thing>",
denoting <m> through <n> repetitions of <thing>; <m> defaults to
zero, <n> to infinity, and the "*" and <n> can be omitted if <m> and
<n> are equal, so 1*word is one or more words, 1*5word is one through
five words, and 2word is exactly two words.
The character "\" is not special in any way in this notation.
This Draft is intended to be self-contained; all syntax rules used in
it are defined within it, and a rule with the same name as one found
in MAIL does not necessarily have the same definition. The lexical
layer of MAIL is NOT, repeat NOT, used in this Draft, and its
presence must not be assumed; notably, this Draft spells out all
places where white space is permitted/required and all places where
constructs resembling MAIL comments can occur.
NOTE: News parsers historically have been much less permissive
than MAIL parsers.
2.3. Definitions
The term "character set", wherever it is used in this Draft, refers
to a coded character set, in the sense of ISO character set
standardization work, and must not be misinterpreted as meaning
merely "a set of characters".
In this Draft, ASCII character 32 is referred to as "blank"; the word
"space" has a more generic meaning.
An "article" is the unit of news, analogous to a MAIL "message".
A "poster" is a human being (or software equivalent) submitting a
possibly compliant article to be "posted", i.e., made available for
reading on all relevant hosts. A "posting agent" is software that
assists posters to prepare articles, including determining whether
the final article is compliant, passing it on to a relayer for
posting if so, and returning it to the poster with an explanation if
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not. A "relayer" is software that receives allegedly compliant
articles from posting agents and/or other relayers, files copies in a
"news database", and possibly passes copies on to other relayers.
NOTE: While the same software may well function both as a relayer
and as part of a posting agent, the two functions are distinct and
should not be confused. The posting agent's purpose is (in part)
to validate an article, supply header information that can or
should be supplied automatically, and generally take reasonable
actions in an attempt to transform the poster's submission into a
compliant article. The relayer's purpose is to move already-
compliant articles around efficiently without damaging them.
A "reader" is a human being reading news articles. A "reading agent"
is software that presents articles to a reader.
NOTE: Informal usage often uses "reader" for both these meanings,
but this introduces considerable potential for confusion and
misunderstanding, so this Draft takes care to make the
distinction.
A "newsgroup" is a single news forum, a logical bulletin board,
having a name and nominally intended for articles on a specific
topic. An article is "posted to" a single newsgroup or several
newsgroups. When an article is posted to more than one newsgroup, it
is said to be "cross-posted"; note that this differs from posting the
same text as part of each of several articles, one per newsgroup. A
"hierarchy" is the set of all newsgroups whose names share a first
component (see the name syntax in Section 5.5).
A newsgroup may be "moderated", in which case submissions are not
posted directly, but mailed to a "moderator" for consideration and
possible posting. Moderators are typically human but may be
implemented partially or entirely in software.
A "followup" is an article containing a response to the contents of
an earlier article (the followup's "precursor"). A "followup agent"
is a combination of reading agent and posting agent that aids in the
preparation and posting of a followup.
Text comparisons are "case-sensitive" if they consider uppercase
letters (e.g., "A") different from lowercase letters (e.g., "a"), and
"case-insensitive" if letters differing only in case (e.g., "A" and
"a") are considered identical. Categories of text are said to be
case-(in)sensitive if comparisons of such texts to others are case-
(in)sensitive.
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A "cooperating subnet" is a set of news-exchanging hosts that is
sufficiently well-coordinated (typically via a central administration
of some sort) that stronger assumptions can be made about hosts in
the set than about news hosts in general. This is typically used to
relax restrictions that are otherwise required for worst-case
interoperability; members of a cooperating subnet MAY interchange
articles that do not conform to this Draft's specifications, provided
all members have agreed to this and provided the articles are not
permitted to leak out of the subnet. The word "subnet" is used to
emphasize that a cooperating subnet is typically not an isolated
universe; care must be taken that traffic leaving the subnet complies
with the restrictions of the larger net, not just those of the
cooperating subnet.
A "message ID" is a unique identifier for an article, usually
supplied by the posting agent that posted it. It distinguishes the
article from every other article ever posted anywhere (in theory).
Articles with the same message ID are treated as identical copies of
the same article even if they are not in fact identical.
A "gateway" is software that receives news articles and converts them
to messages of some other kind (e.g., mail to a mailing list), or
vice versa; in essence, it is a translating relayer that straddles
boundaries between different methods of message exchange. The most
common type of gateway connects newsgroup(s) to mailing list(s),
either unidirectionally or bidirectionally, but there are also
gateways between news networks using this Draft's news format and
those using other formats.
A "control message" is an article that is marked as containing
control information; a relayer receiving such an article will
(subject to permissions, etc.) take actions beyond just filing and
passing on the article.
NOTE: "Control article" would be more consistent terminology, but
"control message" is already well established.
An article's "reply address" is the address to which mailed replies
should be sent. This is the address specified in the article's From
header (see Section 5.2), unless it also has a Reply-To header (see
Section 6.3).
The notation (for example) "(ASCII 17)" following a name means "this
name refers to the ASCII character having value 17". An "ASCII
printable character" is an ASCII character in the range 33-126. An
"ASCII control character" is an ASCII character in the range 0-31, or
the character DEL (ASCII 127). A "non-ASCII character" is a
character having a value exceeding 127.
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NOTE: Blank is neither an "ASCII printable character" nor an
"ASCII control character".
2.4. End-of-Line
How the end of a text line is represented depends on the context and
the implementation. For Internet transmission via protocols such as
SMTP [RFC821], an end-of-line is a CR (ASCII 13) followed by an LF
(ASCII 10). ISO C [ISO/IEC9899] and many modern operating systems
indicate end-of-line with a single character, typically ASCII LF (aka
"newline"), and this is the normal convention when news is
transmitted via UUCP. A variety of other methods are in use,
including out-of-band methods in which there is no specific character
that means end-of-line.
This Draft does not constrain how end-of-line is represented in news,
except that characters other than CR and LF MUST NOT be usurped for
use in end-of-line representations. Also, obviously, all software
dealing with a particular copy of an article must agree on the
convention to be used. "EOL" is used to mean "whatever end-of-line
representation is appropriate"; it is not necessarily a character or
sequence of characters.
NOTE: If faced with picking an EOL representation in the absence
of other constraints, use of a single character simplifies
processing, and the ASCII standard [X3.4] specifies that if one
character is to be used for this purpose, it should be LF (ASCII
10).
NOTE: Inside MIME encodings, use of the Internet canonical EOL
representation (CR followed by LF) is mandatory. See [RFC2049].
2.5. Case-Sensitivity
Text in newsgroup names, header parameters, etc. is case-sensitive
unless stated otherwise.
NOTE: This is at variance with MAIL, which is case-insensitive
unless stated otherwise, but is consistent with news historical
practice and existing news software. See the comments on backward
compatibility in Section 1.
2.6. Language
Various constant strings in this Draft, such as header names and
month names, are derived from English words. Despite their
derivation, these words do NOT change when the poster or reader
employing them is interacting in a language other than English.
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Posting and reading agents SHOULD translate as appropriate in their
interaction with the poster or reader, but the forms that actually
appear in articles are always the English-derived ones defined in
this Draft.
3. Relation to MAIL (RFC822, etc.)
The primary intent of this Draft is to completely describe the news
article format as a subset of MAIL's message format (augmented by
some new headers). Unless explicitly noted otherwise, the intent
throughout is that an article MUST also be a valid MAIL message.
NOTE: Despite obvious similarities between news and mail, opinions
vary on whether it is possible or desirable to unify them into a
single service. However, it is unquestionably both possible and
useful to employ some of the same tools for manipulating both mail
messages and news articles, so there is specific advantage to be
had in defining them compatibly. Furthermore, there is no
apparent need to re-invent the wheel when slight extensions to an
existing definition will suffice.
Given that this Draft attempts to be self-contained, it inevitably
contains considerable repetition of information found in MAIL. This
raises the possibility of unintentional conflicts. Unless
specifically noted otherwise, any wording in this Draft that permits
behavior that is not MAIL-compliant is erroneous and should be
followed only to the extent that the result remains compliant with
MAIL.
NOTE: [RFC1036] said "where this standard conflicts with the
Internet Standard, RFC 822 should be considered correct and this
standard in error". Taken literally, this was obviously
incorrect, since [RFC1036] imposed a number of restrictions not
found in [RFC822]. The intent, however, was reasonable: to
indicate that UNINTENTIONAL differences were errors in [RFC1036].
Implementors and users should note that MAIL is deliberately an
extensible standard, and most extensions devised for mail are also
relevant to (and compatible with) news. Note particularly MIME,
summarized briefly in Appendix B, which extends MAIL in a number of
useful ways that are definitely relevant to news. Also of note is
the work in progress on reconciling Privacy Enhanced Mail (PEM),
which defines extensions for authentication and security) with MIME,
after which this may also be relevant to news.
UNRESOLVED ISSUE: Update the MIME/PEM information.
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Similarly, descriptions here of MIME facilities should be considered
correct only to the extent that they do not require or legitimize
practices that would violate those RFCs. (Note that this Draft does
extend the application of some MIME facilities, but this is an
extension rather than an alteration.)
4. Basic Format
4.1. Overall Syntax
The overall syntax of a news article is:
article = 1*header separator body
header = start-line *continuation
start-line = header-name ":" space [ nonblank-text ] eol
continuation = space nonblank-text eol
header-name = 1*name-character *( "-" 1*name-character )
name-character = letter / digit
letter = <ASCII letter A-Z or a-z>
digit = <ASCII digit 0-9>
separator = eol
body = *( [ nonblank-text / space ] eol )
eol = <EOL>
nonblank-text = [ space ] text-character *( space-or-text )
text-character = <any ASCII character except NUL (ASCII 0),
HT (ASCII 9), LF (ASCII 10), CR (ASCII 13),
or blank (ASCII 32)>
space = 1*( <HT (ASCII 9)> / <blank (ASCII 32)> )
space-or-text = space / text-character
An article consists of some headers followed by a body. An empty
line separates the two. The headers contain structured information
about the article and its transmission. A header begins with a
header name identifying it, and can be continued onto subsequent
lines by beginning the continuation line(s) with white space. (Note
that Section 4.2.3 adds some restrictions to the header syntax
indicated here.) The body is largely unstructured text significant
only to the poster and the readers.
NOTE: Terminology here follows the current custom in the news
community, rather than the MAIL convention of (sometimes)
referring to what is here called a "header" as a "header field" or
"field".
Note that the separator line must be truly empty, and not just a line
containing white space. Further empty lines following it are part of
the body, as are empty lines at the end of the article.
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NOTE: Some systems make no distinction between empty lines and
lines consisting entirely of white space; indeed, some systems
cannot represent entirely empty lines. The grammar's requirement
that header continuation lines contain some printable text is
meant to ensure that the empty/space distinction cannot confuse
identification of the separator line.
NOTE: It is tempting to authorize posting agents to strip empty
lines at the beginning and end of the body, but such empty lines
could possibly be part of a preformatted document.
Implementors are warned that trailing white space, whether alone on
the line or not, MAY be significant in the body, notably in early
versions of the "uuencode" encoding for binary data. Trailing white
space MUST be preserved unless the article is known to have
originated within a cooperating subnet that avoids using significant
trailing white space, and SHOULD be preserved regardless. Posters
SHOULD avoid using conventions or encodings that make trailing white
space significant; for encoding of binary data, MIME's "base64"
encoding is recommended. Implementors are warned that ISO C
implementations are not required to preserve trailing white space,
and special precautions may be necessary in implementations that do
not.
NOTE: Unfortunately, the signature-delimiter convention (described
in Section 4.3.2) does use significant trailing white space. It's
too late to fix this; there is work underway on defining an
organized signature convention as part of MIME, which is a
preferable solution in the long run.
Posters are warned that some very old relayer software misbehaves
when the first non-empty line of an article body begins with white
space.
4.2. Headers
4.2.1. Names and Contents
Despite the restrictions on header-name syntax imposed by the
grammar, relayers and reading agents SHOULD tolerate header names
containing any ASCII printable character other than colon (":",
ASCII 58).
NOTE: MAIL header names can contain any ASCII printable character
(other than colon) in theory, but in practice, arbitrary header
names are known to cause trouble for some news software. Section
4.1's restriction to alphanumeric sequences separated by hyphens
is believed to permit all widely used header names without causing
Spencer Historic [Page 16]RFC 1849 Son of 1036 March 2010
problems for any widely used software. Software is nevertheless
encouraged to cope correctly with the full range of possibilities,
since aberrations are known to occur.
Relayers MUST disregard headers not described in this Draft (that is,
with header names not mentioned in this Draft) and pass them on
unaltered.
Posters wishing to convey non-standard information in headers SHOULD
use header names beginning with "X-". No standard header name will
ever be of this form. Reading agents SHOULD ignore "X-" headers, or
at least treat them with great care.
The order of headers in an article is not significant. However,
posting agents are encouraged to put mandatory headers (see
Section 5) first, followed by optional headers (see Section 6),
followed by headers not defined in this Draft.
NOTE: While relayers and reading agents must be prepared to handle
any order, having the significant headers (the precise definition
of "significant" depends on context) first can noticeably improve
efficiency, especially in memory-limited environments where it is
difficult to buffer up an arbitrary quantity of headers while
searching for the few that matter.
Header names are case-insensitive. There is a preferred case
convention, which posters and posting agents SHOULD use: each hyphen-
separated "word" has its initial letter (if any) in uppercase and the
rest in lowercase, except that some abbreviations have all letters
uppercase (e.g., "Message-ID" and "MIME-Version"). The forms used in
this Draft are the preferred forms for the headers described herein.
Relayers and reading agents are warned that articles might not obey
this convention.
NOTE: Although software must be prepared for the possibility of
random use of case in header names (and other case-independent
text), establishing a preferred convention reduces pointless
diversity and may permit optimized software that looks for the
preferred forms before resorting to less-efficient case-
insensitive searches.
In general, a header can consist of several lines, with each
continuation line beginning with white space. The EOLs preceding
continuation lines are ignored when processing such a header,
effectively combining the start-line and the continuations into a
single logical line. The logical line, less the header name, colon,
and any white space following the colon, is the "header content".
Spencer Historic [Page 17]RFC 1849 Son of 1036 March 2010
4.2.2. Undesirable Headers
A header whose content is empty is said to be an empty header.
Relayers and reading agents SHOULD NOT consider presence or absence
of an empty header to alter the semantics of an article (although
syntactic rules, such as requirements that certain header names
appear at most once in an article, MUST still be satisfied). Posting
agents SHOULD delete empty headers from articles before posting them.
Headers that merely state defaults explicitly (e.g., a Followup-To
header with the same content as the Newsgroups header, or a MIME
Content-Type header with contents "text/plain; charset=us-ascii") or
state information that reading agents can typically determine easily
themselves (e.g., the length of the body in octets) are redundant,
conveying no information whatsoever. Headers that state information
that cannot possibly be of use to a significant number of relayers,
reading agents, or readers (e.g., the name of the software package
used as the posting agent) are useless and pointless. Posters and
posting agents SHOULD avoid including redundant or useless headers in
articles.
NOTE: Information that someone, somewhere, might someday find
useful is best omitted from headers. (There's quite enough of it
in article bodies.) Headers should contain information of known
utility only. This is not meant to preclude inclusion of
information primarily meant for news-software debugging, but such
information should be included only if there is real reason,
preferably based on experience, to suspect that it may be
genuinely useful. Articles passing through gateways are the only
obvious case where inclusion of debugging information appears
clearly legitimate. (See Section 10.1.)
NOTE: A useful rule of thumb for software implementors is: "if I
had to pay a dollar a day for the transmission of this header,
would I still think it worthwhile?".
4.2.3. White Space and Continuations
The colon following the header name on the start-line MUST be
followed by white space, even if the header is empty. If the header
is not empty, at least some of the content MUST appear on the start-
line. Posting agents MUST enforce these restrictions, but relayers
(etc.) SHOULD accept even articles that violate them.
NOTE: MAIL does not require white space after the colon, but it is
usual. [RFC1036] required the white space, even in empty headers,
and some existing software demands it. In MAIL, and arguably in
[RFC1036] (although the wording is vague), it is technically
Spencer Historic [Page 18]RFC 1849 Son of 1036 March 2010
legitimate for the white space to be part of a continuation line
rather than the start-line, but not all existing software will
accept this. Deleting empty headers and placing some content on
the start-line avoids this issue; this is desirable because
trailing blanks, easily deleted by accident, are best not made
significant in headers.
In general, posters and posting agents SHOULD use blank (ASCII 32),
not tab (ASCII 9), where white space is desired in headers. Existing
software does not consistently accept tab as synonymous with blank in
all contexts. In particular, [RFC1036] appeared to specify that the
character immediately following the colon after a header name was
required to be a blank, and some news software insists on that, so
this character MUST be a blank. Again, posting agents MUST enforce
these restrictions but relayers SHOULD be more tolerant.
Since the white space beginning a continuation line remains a part of
the logical line, headers can be "broken" into multiple lines only at
white space. Posting agents SHOULD NOT break headers unnecessarily.
Relayers SHOULD preserve existing header breaks, and SHOULD NOT
introduce new breaks. Breaking headers SHOULD be a last resort;
relayers and reading agents SHOULD handle long header lines
gracefully. (See the discussion of size limits in Section 4.6.)
4.3. Body
Although the article body is unstructured for most of the purposes of
this Draft, structure MAY be imposed on it by other means, notably
MIME headers (see Appendix B).
4.3.1. Body Format Issues
The body of an article MAY be empty, although posting agents SHOULD
consider this an error condition (meriting returning the article to
the poster for revision). A posting agent that does not reject such
an article SHOULD issue a warning message to the poster and supply a
non-empty body. Note that the separator line MUST be present even if
the body is empty.
NOTE: An empty body is probably a poster error except, arguably,
for some control messages, and even they really ought to have a
body explaining the reason for the control message. Some old
reading agents are known to generate empty bodies for "cancel"
control messages, so posting agents might opt not to reject
bodyless articles in such cases (although it would be better to
fix the reading agents to request a body). However, some existing
news software is known to react badly to bodyless articles, hence
the request for posting agents to insert a body in such cases.
Spencer Historic [Page 19]RFC 1849 Son of 1036 March 2010
NOTE: A possible posting-agent-supplied body text (already used by
one widespread posting agent) is "This article was probably
generated by a buggy news reader". (The use of "reader" to refer
to the reading agent is traditional, although this Draft uses more
precise terminology.)
NOTE: The requirement for the separator line even in a bodyless
article is inherited from MAIL and also distinguishes legitimately
bodyless articles from articles accidentally truncated in the
middle of the headers.
Note that an article body is a sequence of lines terminated by EOLs,
not arbitrary binary data, and in particular it MUST end with an EOL.
However, relayers SHOULD treat the body of an article as an
uninterpreted sequence of octets (except as mandated by changes of
EOL representation and by control-message processing) and SHOULD
avoid imposing constraints on it. See also Section 4.6.
4.3.2. Body Conventions
Although body lines can in principle be very long (see Section 4.6
for some discussion of length limits), posters SHOULD restrict body
line lengths to circa 70-75 characters. On systems where text is
conventionally stored with EOLs only at paragraph breaks and other
"hard return" points, with software breaking lines as appropriate for
display or manipulation, posting agents SHOULD insert EOLs as
necessary so that posted articles comply with this restriction.
NOTE: News originated in environments where line breaks in plain
text files were supplied by the user, not the software. Be this
good or bad, much reading-agent and posting-agent software assumes
that news articles follow this convention, so it is often
inconvenient to read or respond to articles that violate it. The
"70-75" number comes from the widespread use of display devices
that are 80 columns wide (with the number reduced to provide a bit
of margin for quoting, see below).
Reading agents confronted with body lines much longer than the
available output-device width SHOULD break lines as appropriate.
Posters are warned that such breaks may not occur exactly where the
poster intends.
NOTE: "As appropriate" would typically include breaking lines when
supplying the text of an article to be quoted in a reply or
followup, something that line-breaking reading agents often
neglect to do now.
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Although styles vary widely, for plain text it is usual to use no
left margin, leave the right edge ragged, use a single empty line to
separate paragraphs, and employ normal natural-language usage on
matters such as upper/lowercase. (In particular, articles SHOULD NOT
be written entirely in uppercase. In environments where posters have
access only to uppercase, posting agents SHOULD translate it to
lowercase.)
NOTE: Most people find substantial bodies of text entirely in
uppercase relatively hard to read, while all-lowercase text merely
looks slightly odd. The common association of uppercase with
strong emphasis adds to this.
Tone of voice does not carry well in written text, and
misunderstandings are common when sarcasm, parody, or exaggeration
for humorous effect is attempted without explicit warning. It has
become conventional to use the sequence ":-)", which (on most output
devices) resembles a rotated "smiley face" symbol, as a marker for
text not meant to be taken literally, especially when humor is
intended. This practice aids communication and averts unintended
ill-will; posters are urged to use it. A variety of analogous
sequences are used with less-standardized meanings [Sanderson].
The order of arrival of news articles at a particular host depends
somewhat on transmission paths, and occasionally articles are lost
for various reasons. When responding to a previous article, posters
SHOULD NOT assume that all readers understand the exact context. It
is common to quote some of the previous article to establish context.
This SHOULD be done by prefacing each quoted line (even if it is
empty) with the character ">". This will result in multiple levels
of ">" when quoted context itself contains quoted context.
NOTE: It may seem superfluous to put a prefix on empty lines, but
it simplifies implementation of functions such as "skip all quoted
text" in reading agents.
Readability is enhanced if quoted text and new text are separated by
an empty line.
Posters SHOULD edit quoted context to trim it down to the minimum
necessary. However, posting agents SHOULD NOT attempt to enforce
this by imposing overly simplistic rules like "no more than 50% of
the lines should be quotes".
NOTE: While encouraging trimming is desirable, the 50% rule
imposed by some old posting agents is both inadequate and
counterproductive. Posters do not respond to it by being more
selective about quoting; they respond by padding short responses,
Spencer Historic [Page 21]RFC 1849 Son of 1036 March 2010
or by using different quoting styles to defeat automatic analysis.
The former adds unnecessary noise and volume, while the latter
also defeats more useful forms of automatic analysis that reading
agents might wish to do.
NOTE: At the very least, if a minimum-unquoted quota is being set,
article bodies shorter than (say) 20 lines, or perhaps articles
that exceed the quota by only a few lines, should be exempt. This
avoids the ridiculous situation of complaining about a 5-line
response to a 6-line quote.
NOTE: A more subtle posting-agent rule, suggested for experimental
use, is to reject articles that appear to contain quoted
signatures (see below). This is almost certainly the result of a
careless poster not bothering to trim down quoted context. Also,
if a posting agent or followup agent presents an article template
to the poster for editing, it really should take note of whether
the poster actually made any changes, and refrain from posting an
unmodified template.
Some followup agents supply "attribution" lines for quoted context,
indicating where it first appeared and under whose name. When
multiple levels of quoting are present and quoted context is edited
for brevity, "inner" attribution lines are not always retained. The
editing process is also somewhat error-prone. Reading agents (and
readers) are warned not to assume that attributions are accurate.
UNRESOLVED ISSUE: Should a standard format for attribution lines
be defined? There is already considerable diversity, but
automatic news analysis would be substantially aided by a standard
convention.
Early difficulties in inferring return addresses from article headers
led to "signatures": short closing texts, automatically added to the
end of articles by posting agents, identifying the poster and giving
his network addresses, etc. If a poster or posting agent does append
a signature to an article, the signature SHOULD be preceded with a
delimiter line containing (only) two hyphens (ASCII 45) followed by
one blank (ASCII 32). Posting agents SHOULD limit the length of
signatures, since verbose excess bordering on abuse is common if no
restraint is imposed; 4 lines is a common limit.
NOTE: While signatures are arguably a blemish, they are a well-
understood convention, and conveying the same information in
headers exposes it to mangling and makes it rather less
conspicuous. A standard delimiter line makes it possible for
reading agents to handle signatures specially if desired.
Spencer Historic [Page 22]RFC 1849 Son of 1036 March 2010
(This is unfortunately hampered by extensive misunderstanding of,
and misuse of, the delimiter.)
NOTE: The choice of delimiter is somewhat unfortunate, since it
relies on preservation of trailing white space, but it is too
well-established to change. There is work underway to define a
more sophisticated signature scheme as part of MIME, and this will
presumably supersede the current convention in due time.
NOTE: Four 75-column lines of signature text is 300 characters,
which is ample to convey name and mail-address information in all
but the most bizarre situations.
4.4. Characters and Character Sets
Header and body lines MAY contain any ASCII characters other than CR
(ASCII 13), LF (ASCII 10), and NUL (ASCII 0).
NOTE: CR and LF are excluded because they clash with common EOL
conventions. NUL is excluded because it clashes with the C
end-of-string convention, which is significant to most existing
news software. These three characters are unlikely to be
transmitted successfully.
However, posters SHOULD avoid using ASCII control characters except
for tab (ASCII 9), formfeed (ASCII 12), and backspace (ASCII 8). Tab
signifies sufficient horizontal white space to reach the next of a
set of fixed positions; posters are warned that there is no standard
set of positions, so tabs should be avoided if precise spacing is
essential. Formfeed signifies a point at which a reading agent
SHOULD pause and await reader interaction before displaying further
text. Backspace SHOULD be used only for underlining, done by a
sequence of underscores (ASCII 95) followed by an equal number of
backspaces, signifying that the same number of text characters
following are to be underlined. Posters are warned that underlining
is not available on all output devices and is best not relied on for
essential meaning. Reading agents SHOULD recognize underlining and
translate it to the appropriate commands for devices that support it.
NOTE: Interpretation of almost all control characters is device-
specific to some degree, and devices differ. Tabs and underlining
are supported, to some extent, by most modern devices and reading
agents, hence the cautious exemptions for them. The underlining
method is specified because the inverse method, text and then
underscores, is tempting to the naive; however, if sent unaltered
to a device that shows only the most recent of several overstruck
characters rather than a composite, the result can be utterly
unreadable.
Spencer Historic [Page 23]RFC 1849 Son of 1036 March 2010
NOTE: A common interpretation of tab is that it is a request to
space forward to the next position whose number is one more than a
multiple of 8, with positions numbered sequentially starting at 1.
(So tab positions are 9, 17, 25, ...) Reading agents not
constrained by existing system conventions might wish to use this
interpretation.
NOTE: It will typically be necessary for a reading agent to catch
and interpret formfeed, not just send it to the output device.
The actions performed by typical output devices on receiving a
formfeed are neither adequate for, nor appropriate to, the pause-
for-interaction meaning.
Cooperating subnets that wish to employ non-ASCII character sets by
using escape sequences (employing, e.g., ESC (ASCII 27), SO
(ASCII 14), and SI (ASCII 15)) to alter the meaning of superficially
ASCII characters MAY do so, but MUST use MIME headers to alert
reading agents to the particular character set(s) and escape
sequences in use. A reading agent SHOULD NOT pass such an escape
sequence through, unaltered, to the output device unless the agent
confirms that the sequence is one used to affect character sets and
has reason to believe that the device is capable of interpreting that
particular sequence properly.
NOTE: Cooperating-subnet organizers are warned that some very old
relayers strip certain control characters out of articles they
pass along. ESC is known to be among the affected characters.
NOTE: There are now standard Internet encodings for Japanese
[RFC1345] and Vietnamese [RFC1456] in particular.
Articles MUST NOT contain any octet with value exceeding 127, i.e.,
any octet that is not an ASCII character.
NOTE: This rule, like others, may be relaxed by unanimous consent
of the members of a cooperating subnet, provided suitable
precautions are taken to ensure that rule-violating articles do
not leak out of the subnet. (This has already been done in many
areas where ASCII is not adequate for the local language(s).)
Beware that articles containing non-ASCII octets in headers are a
violation of the MAIL specifications and are not valid MAIL
messages. MIME offers a way to encode non-ASCII characters in
ASCII for use in headers; see Section 4.5.
Spencer Historic [Page 24]RFC 1849 Son of 1036 March 2010
NOTE: While there is great interest in using 8-bit character sets,
not all software can yet handle them correctly, hence the
restriction to cooperating subnets. MIME encodings can be used to
transmit such characters while remaining within the octet
restriction.
In anticipation of the day when it is possible to use non-ASCII
characters safely anywhere, and to provide for the (substantial)
cooperating subnets that are already using them, transmission paths
SHOULD treat news articles as uninterpreted sequences of octets
(except perhaps for transformations between EOL representations) and
relayers SHOULD treat non-ASCII characters in articles as ordinary
characters.
NOTE: 8-bit enthusiasts are warned that not all software conforms
to these recommendations yet. In particular, standard NNTP
[RFC977] is a 7-bit protocol {but in [RFC3977] it has been upped
to 8-bit}, and there may be implementations that enforce this
rule. Be warned, also, that it will never be safe to send raw
binary data in the body of news articles, because changes of EOL
representation may (will!) corrupt it.
Except where cooperating subnets permit more direct approaches, MIME
headers and encodings SHOULD be used to transmit non-ASCII content
using ASCII characters; see Section 4.5, Appendix B, and the MIME
RFCs for details. If article content can be expressed in ASCII, it
SHOULD be. Failing that, the order of preference for character sets
is that described in MIME.
NOTE: Using the MIME facilities, it is possible to transmit ANY
character set, and ANY form of binary data, using only ASCII
characters. Equally important, such articles are self-describing
and the reading agent can tell which octet-to-symbol mapping is
intended! Designation of some preferred character sets is
intended to minimize the number of character sets that a reading
agent must understand in order to display most articles properly.
Articles containing non-ASCII characters, articles using ASCII
characters (values 0 through 127) to refer to non-ASCII symbols, and
articles using escape sequences to shift character sets SHOULD
include MIME headers indicating which character set(s) and
conventions are being used. They MUST do so unless such articles are
strictly confined to a cooperating subnet that has its own pre-agreed
conventions. MIME encodings are preferred over all of these
techniques. If it comes to a relayer's attention that it is being
asked to pass an article using such techniques outward across what it
knows to be the boundary of such a cooperating subnet, it MUST report
Spencer Historic [Page 25]RFC 1849 Son of 1036 March 2010
this error to its administrator and MAY refuse to pass the article
beyond the subnet boundary. If it does pass the article, it MUST
re-encode it with MIME encodings to make it conform to this Draft.
NOTE: Such re-encoding is a non-trivial task, due to MIME rules
such as the prohibition of nested encodings. It's not just a
matter of pouring the body through a simple filter.
Reading agents SHOULD note MIME headers and attempt to show the
reader the closest possible approximation to the intended content.
They SHOULD NOT just send the octets of the article to the output
device unaltered, unless there is reason to believe that the output
device will indeed interpret them correctly. Reading agents MUST NOT
pass ASCII control characters or escape sequences, other than as
discussed above, unaltered to the output device; only by chance would
the result be the desired one, and there is serious potential for
harmful side effects, either accidental or malicious.
NOTE: Exactly what to do with unwanted control
characters/sequences depends on the philosophy of the reading
agent, but passing them straight to the output device is almost
always wrong. If the reading agent wants to mark the presence of
such a character/sequence in circumstances where only ASCII
printable characters are available, translating it to "#" might be
a suitable method; "#" is a conspicuous character seldom used in
normal text.
NOTE: Reading agents should be aware that many old output devices
(or the transmission paths to them) zero out the top bit of octets
sent to them. This can transform non-ASCII characters into ASCII
control characters.
Followup agents MUST be careful to apply appropriate transformations
of representation to the outbound followup as well as the inbound
precursor. A followup to an article containing non-ASCII material is
very likely to contain non-ASCII material itself.
4.5. Non-ASCII Characters in Headers
All octets found in headers MUST be ASCII characters. However, it is
desirable to have a way of encoding non-ASCII characters, especially
in "human-readable" headers such as Subject. MIME provides a way to
do this. Full details may be found in the MIME specifications;
herewith a quick summary to alert software authors to the issues.
Spencer Historic [Page 26]RFC 1849 Son of 1036 March 2010
encoded-word = "=?" charset "?" encoding "?" codes "?="
charset = 1*tag-char
encoding = 1*tag-char
tag-char = < ASCII printable character except
!()<>@,;:\"[]/?= >
codes = 1*code-char
code-char = <ASCII printable character except ?>
An encoded word is a sequence of ASCII printable characters that
specifies the character set, encoding method, and bits of
(potentially) non-ASCII characters. Encoded words are allowed only
in certain positions in certain headers. Specific headers impose
restrictions on the content of encoded words beyond that specified in
this section. Posting agents MUST ensure that any material
resembling an encoded word (complete with all delimiters), in a
context where encoded words may appear, really is an encoded word.
NOTE: The syntax is a bit ugly, but it was designed to minimize
chances of confusion with legitimate header contents, and to
satisfy difficult constraints on use within existing headers.
An encoded word MUST NOT be more than 75 octets long. Each line of a
header containing encoded word(s) MUST be at most 76 octets long, not
counting the EOL.
NOTE: These limits are meant to bound the lookahead needed to
determine whether text that begins with "=?" is really an encoded
word.
The details of charsets and encodings are defined by MIME; the
sequence of preferred character sets is the same as MIME's. Encoded
words SHOULD NOT be used for content expressible in ASCII.
When an encoded word is used, other than in a newsgroup name (see
Section 5.5), it MUST be separated from any adjacent non-space
characters (including other encoded words) by white space. Reading
agents displaying the contents of encoded words (as opposed to their
encoded form) should ignore white space adjacent to encoded words.
UNRESOLVED ISSUE: Should this section be deleted entirely, or made
much more terse? The material is relevant, but too complex to
discuss fully.
NOTE: The deletion of intervening white space permits using
multiple encoded words, implicitly concatenated by the deletion,
to encode text that will not fit within a single 75-character
encoded word.
Spencer Historic [Page 27]RFC 1849 Son of 1036 March 2010
Reading-agent implementors are warned that although this Draft
completely specifies where encoded words may appear in the headers it
defines, there are other headers (e.g., the MIME Content-Description
header) that MAY contain them.
4.6. Size Limits
Implementations SHOULD avoid fixed constraints on the sizes of lines
within an article and on the size of the entire article.
Relayers SHOULD treat the body of an article as an uninterpreted
sequence of octets (except as mandated by changes of EOL
representation and processing of control messages), not to be altered
or constrained in any way.
If it is absolutely necessary for an implementation to impose a limit
on the length of header lines, body lines, or header logical lines,
that limit shall be at least 1000 octets, including EOL
representations. Relayers and transmission paths confronted with
lines beyond their internal limits (if any) MUST NOT simply inject
EOLs at random places; they MAY break headers (as described in
Section 4.2.3) as a last resort, and otherwise they MUST either pass
the long lines through unaltered, or refuse to pass the article at
all (see Section 9.1 for further discussion).
NOTE: The limit here is essentially the same minimum as that
specified for SMTP mail [RFC821]. Implementors are warned that
Path (see Section 5.6) and References (see Section 6.5) headers,
in particular, often become several hundred characters long, so
1000 is not an overly generous limit.
All implementations MUST be able to handle an article totalling at
least 65,000 octets, including headers and EOL representations,
gracefully and efficiently. All implementations SHOULD be able to
handle an article totalling at least 1,000,000 (one million) octets,
including headers and EOL representations, gracefully and
efficiently. "Gracefully and efficiently" is intended to preclude
not only failures, but also major loss of performance, serious
problems in error recovery, or resource consumption beyond what is
reasonably necessary.
NOTE: The intent here is to prohibit lowering the existing de
facto limit any further, while strongly encouraging movement
towards a higher one. Actually, although improvements are
desirable in some cases, much news software copes reasonably well
with very large articles. The same cannot be said of the
communications software and protocols used to transmit news from
one host to another, especially when slow communications links are
Spencer Historic [Page 28]RFC 1849 Son of 1036 March 2010
involved. Occasional huge articles that appear now (by accident
or through ignorance) typically leave trails of failing software,
system problems, and irate administrators in their wake.
NOTE: It is intended that the successor to this Draft will raise
the "MUST" limit to 1,000,000 and the "SHOULD" limit still
further.
Posters SHOULD limit posted articles to at most 60,000 octets,
including headers and EOL representations, unless the articles are
being posted only within a cooperating subnet that is known to be
capable of handling larger articles gracefully. Posting agents
presented with a large article SHOULD warn the poster and request
confirmation.
NOTE: The difference between this and the earlier "MUST" limit is
due to margin for header growth, differing EOL representations,
and transmission overheads.
NOTE: Disagreeable though these limits are, it is a fact that in
current networks, an article larger than 64K (after header growth,
etc.) simply is not transmitted reliably. Note also the comments
above on the trauma caused by single extremely large articles now;
the problems are real and current. These problems arguably should
be fixed, but this will not happen network-wide in the immediate
future, hence the restriction of larger articles to cooperating
subnets, for now.
Posters using non-ASCII characters in their text MUST take into
account the overhead involved in MIME encoding, unless the article's
propagation will be entirely limited to a cooperating subnet that
does not use MIME encodings for non-ASCII characters. For example,
MIME base64 encoding involves growth by a factor of approximately
4/3, so an article that would likely have to use this encoding should
be at most about 45,000 octets before encoding.
Posters SHOULD use MIME "message/partial" conventions to facilitate
automatic reassembly of a large document split into smaller pieces
for posting. It is recommended that the content identifier used
should be a message ID, generated by the same means as article
message IDs (see Section 5.3), and that all parts should have a
See-Also header (see Section 6.16) giving the message IDs of at least
the previous parts and preferably all of the parts.
NOTE: See-Also is more correct for this purpose than References,
although References is in common use today (with less-formal
reassembly arrangements). MIME reassemblers should probably
Spencer Historic [Page 29]RFC 1849 Son of 1036 March 2010
examine articles suggested by References headers if See-Also
headers are not present to indicate the whereabouts of the other
parts of "message/partial" articles.
To repeat: implementations SHOULD avoid fixed constraints on the
sizes of lines within an article and on the size of the entire
article.
4.7. Example
Here is a sample article:
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: Mon, 17 Jan 1994 11:14:55 -0500 (EST)
Followup-To: news.misc
Expires: Wed, 19 Jan 1994 00:00:00 -0500
Organization: AT&T Bell Laboratories, Murray Hill
body
body
body
5. Mandatory Headers
An article MUST have one, and only one, of each of the following
headers: Date, From, Message-ID, Subject, Newsgroups, Path.
NOTE: MAIL specifies (if read most carefully) that there must be
exactly one Date header and exactly one From header, but otherwise
does not restrict multiple appearances of headers. (Notably, it
permits multiple Message-ID headers!) This appears singularly
useless, or even harmful, in the context of news, and much current
news software will not tolerate multiple appearances of mandatory
headers.
Note also that there are situations, discussed in the relevant parts
of Section 6, where References, Sender, or Approved headers are
mandatory.
In the discussions of the individual headers, the content of each is
specified using the syntax notation. The convention used is that the
content of, for example, the Subject header is defined as
<Subject-content>.
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5.1. Date
The Date header contains the date and time when the article was
submitted for transmission:
Date-content = [ weekday "," space ] date space time
weekday = "Mon" / "Tue" / "Wed" / "Thu"
/ "Fri" / "Sat" / "Sun"
date = day space month space year
day = 1*2digit
month = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun"
/ "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec"
year = 4digit / 2digit
time = hh ":" mm [ ":" ss ] space timezone
timezone = "UT" / "GMT"
/ ( "+" / "-" ) hh mm [ space "(" zone-name ")" ]
hh = 2digit
mm = 2digit
ss = 2digit
zone-name = 1*( <ASCII printable character except ()\>
/ space )
This is a restricted subset of the MAIL date format.
If a weekday is given, it MUST be consistent with the date. The
modern Gregorian calendar is used, and dates MUST be consistent with
its usual conventions; for example, if the month is May, the day must
be between 1 and 31 inclusive. The year SHOULD be given as four
digits, and posting agents SHOULD enforce this; however, relayers
MUST accept the two-digit form, and MUST interpret it as having the
implicit prefix "19".
NOTE: Two-digit year numbers can, should, and must be phased out
by 1999.
The time is given on the 24-hour clock, e.g., two hours before
midnight is "22:00" or "22:00:00". The hh must be between 00 and 23
inclusive, the mm between 0 and 59 inclusive, and the ss between 0
and 60 inclusive.
NOTE: Leap seconds very occasionally result in minutes that are 61
seconds long.
The date and time SHOULD be given in the poster's local time zone,
including a specification of that time zone as a numeric offset
(which SHOULD include the time zone name, e.g., "EST", supplied in
parentheses like a MAIL comment). If not, they MUST be given in
Universal Time (abbreviated "UT"; "GMT" is a historical synonym for
Spencer Historic [Page 31]RFC 1849 Son of 1036 March 2010
"UT"). The time zone name in parentheses, if present, is a comment;
software MUST ignore it, except that reading agents might wish to
display it to the reader. Time zone names other than "UT" and "GMT"
MUST appear only in the comment.
NOTE: Attempts to deal with a full set of time zone names have all
foundered on the vast number of such names in use and the
duplications (for example, there are at least FIVE different time
zones called "EST" by somebody). Even the limited set of North
American zone names authorized by MAIL is subject to confusion and
misinterpretation, hence the flat ban on non-UT time zone names,
except as comments.
NOTE: [RFC1036] specified that use of GMT (aka UT, UTC) was
preferred. However, the local time (in the poster's time zone) is
arguably information of possible interest to the reader, and this
requires some indication of the poster's time zone. Numeric
offsets are an unambiguous way of doing this, and their use was
indeed sanctioned by [RFC1036] (that is, this is a change of
preference only).
NOTE: There is frequent confusion, including errors in some news
software, regarding the sign of numeric time zones. Zones west of
Greenwich have negative offsets. For example, North American
Eastern Standard Time is zone -0500 and North American Eastern
Daylight Time is zone -0400.
NOTE: Implementors are warned that the hh in a time zone can go up
to about 14; it is not limited to 12. This is because the
International Date Line does not run exactly along the boundary
between zone -1200 and zone +1200.
NOTE: The comments in Section 2.6 regarding translation to other
languages are relevant here. The Date-content format, and the
spellings of its components, as found in articles themselves, are
always as defined in this Draft, regardless of the language used
to interact with readers and posters. Reading and posting agents
should translate as appropriate. Actually, even English-language
reading and posting agents will probably want to do some degree of
translation on dates, if only to abbreviate the lengthy format and
(perhaps) translate to and from the reader's time zone.
Spencer Historic [Page 32]RFC 1849 Son of 1036 March 2010
5.2. From
The From header contains the electronic address, and possibly the
full name, of the article's author:
From-content = address [ space "(" paren-phrase ")" ]
/ [ plain-phrase space ] "<" address ">"
paren-phrase = 1*( paren-char / space / encoded-word )
paren-char = <ASCII printable character except ()<>\>
plain-phrase = plain-word *( space plain-word )
plain-word = unquoted-word / quoted-word / encoded-word
unquoted-word = 1*unquoted-char
unquoted-char = <ASCII printable character except !()<>@,;:\".[]>
quoted-word = quote 1*( quoted-char / space ) quote
quote = <" (ASCII 34)>
quoted-char = <ASCII printable character except "()<>\>
address = local-part "@" domain
local-part = unquoted-word *( "." unquoted-word )
domain = unquoted-word *( "." unquoted-word )
(Encoded words are described in Section 4.5.) The full name is
distinguished from the electronic address either by enclosing the
former in parentheses (making it resemble a MAIL comment, after the
address) or by enclosing the latter in angle brackets. The second
form is preferred. In the first form, encoded words inside the full
name MUST be composed entirely of <paren-char>s. In the second form,
encoded words inside the full name may not contain characters other
than letters (of either case), digits, and the characters "!", "*",
"+", "-", "/", "=", and "_". The local part is case-sensitive
(except that all case counterparts of "postmaster" are deemed
equivalent), the domain is case-insensitive, and all other parts of
the From content are comments that MUST be ignored by news software
(except insofar as reading agents may wish to display them to the
reader). Posters and posting agents MUST restrict themselves to this
subset of the MAIL From syntax; relayers MAY accept a broader subset,
but see the discussion in Section 9.1.
NOTE: The syntax here is a restricted subset of the MAIL From
syntax, with quoting particularly restricted, for simple parsing.
In particular, the presence of "<" in the From content indicates
that the second form is being used; otherwise, the first form is
being used. The major restrictions here are those already de
facto imposed by existing software.
NOTE: Overly lenient posting agents sometimes permit the second
form with a full name containing "(" or ")", but it is extremely
rare for a full name to contain "<" or ">", even in mail.
Spencer Historic [Page 33]RFC 1849 Son of 1036 March 2010
Accordingly, reading agents wishing to robustly determine which
form is in use in a particular article should key on the presence
or absence of "<", not the presence or absence of "(".
The address SHOULD be a valid and complete Internet domain address,
capable of being successfully mailed to by an Internet host (possibly
via an MX (Mail Exchange) record and a forwarder). The pseudo-domain
".uucp" MAY be used for hosts registered in the UUCP maps (e.g., name
"xyz.uucp" for registered site "xyz"), but such hosts SHOULD
discontinue this usage (either by arranging a proper Internet address
and forwarder, or by using the "% hack" (see below)), as soon as
possible. Bitnet hosts SHOULD use Internet addresses, avoiding the
obsolescent ".bitnet" pseudo-domain. Other forms of address MUST NOT
be used.
NOTE: "Other forms" specifically include UK-style "backward"
domains ("uk.oxbridge.cs" is in the Czech Republic, not the UK),
pure-UUCP addressing ("knee!shin!foot" instead of
"foot%shin@knee.uucp"), and abbreviated domains ("zebra.zoo"
instead of "zebra.zoo.toronto.edu").
If it is necessary to use the local part to specify a routing
relative to the nearest Internet host, this MUST be done using the "%
hack", using "%" as a secondary "@". For example, to specify that
mail to the address should go to Internet host "foo.bar.edu", then to
non-Internet host "ein", then to non-Internet host "deux", for
delivery there to mailbox "fred", a suitable address would be:
fred%deux%ein@foo.bar.edu
Analogous forms using "!" in the local part MUST NOT be used, as they
are ambiguous; they should be expressed in the "%" form.
NOTE: "a!b@c" can be interpreted as either "b%c@a" or "b%a@c", and
there is no consistency in which choice is made. Such addresses
consequently are unreliable. The "%" form does not suffer from
this problem, and although its use is officially discouraged, it
is a de facto standard, to the point that MAIL recognizes it.
Relayers MUST NOT, repeat MUST NOT, repeat MUST NOT, rewrite From
lines, in any way, however minor or seemingly innocent. Trying to
"fix" a non-conforming address has a very high probability of making
things worse. Either pass it along unchanged or reject the article.
NOTE: An additional reason for banning the use of "!" addressing
is that it has a much higher probability of being rewritten into
mangled unrecognizability by old relayers.
Spencer Historic [Page 34]RFC 1849 Son of 1036 March 2010
Posters and posting agents SHOULD avoid use of the characters "!" and
"@" in full names, as they may trigger unwanted header rewriting by
old, simple-minded news software.
NOTE: Also, the characters "." and ",", not infrequently found in
names (e.g., "John W. Campbell, Jr."), are NOT, repeat NOT,
allowed in an unquoted word. A From header like the following
MUST NOT be written without the quotation marks:
From: "John W. Campbell, Jr." <editor@analog.com>
5.3. Message-ID
The Message-ID header contains the article's message ID, a unique
identifier distinguishing the article from every other article:
Message-ID-content = message-id
message-id = "<" local-part "@" domain ">"
As with From addresses, a message ID's local part is case-sensitive,
and its domain is case-insensitive. The "<" and ">" are parts of the
message ID, not peculiarities of the Message-ID header.
NOTE: News message IDs are a restricted subset of MAIL message
IDs. In particular, no existing news software copes properly with
MAIL quoting conventions within the local part, so they are
forbidden. This is unfortunate, particularly for X.400 gateways
that often wish to include characters that are not legal in
unquoted message IDs, but it is impossible to fix net-wide. See
the notes on gatewaying in Section 10.
The domain in the message ID SHOULD be the full Internet domain name
of the posting agent's host. Use of the ".uucp" pseudo-domain (for
hosts registered in the UUCP maps) or the ".bitnet" pseudo-domain
(for Bitnet hosts) is permissible but SHOULD be avoided.
Posters and posting agents MUST generate the local part of a message
ID using an algorithm that obeys the specified syntax (words
separated by ".", with certain characters not permitted) (see Section
5.2 for details) and will not repeat itself (ever). The algorithm
SHOULD NOT generate message IDs that differ only in case of letters.
Note the specification in Section 6.5 of a recommended convention for
indicating subject changes. Otherwise, the algorithm is up to the
implementor.
NOTE: The crucial use of message IDs is to distinguish circulating
articles from each other and from articles circulated recently.
They are also potentially useful as permanent indexing keys, hence
Spencer Historic [Page 35]RFC 1849 Son of 1036 March 2010
the requirement for permanent uniqueness, but indexers cannot
absolutely rely on this because the earlier RFCs urged it but did
not demand it. All major implementations have always generated
permanently unique message IDs by design, but in some cases this
is sensitive to proper administration, and duplicates may have
occurred by accident.
NOTE: The most popular method of generating local parts is to use
the date and time, plus some way of distinguishing between
simultaneous postings on the same host (e.g., a process number),
and encode them in a suitably restricted alphabet. An older but
now less-popular alternative is to use a sequence number,
incremented each time the host generates a new message ID; this is
workable but requires careful design to cope properly with
simultaneous posting attempts, and it is not as robust in the
presence of crashes and other malfunctions.
NOTE: Some buggy news software considers message IDs completely
case-insensitive, hence the advice to avoid relying on case
distinctions. The restrictions placed on the "alphabet" of local
parts and domains in Section 5.2 have the useful side effect of
making it unnecessary to parse message IDs in complex ways to
break them into case-sensitive and case-insensitive portions.
The local part of a message ID MUST NOT be "postmaster" or any other
string that would compare equal to "postmaster" in a case-insensitive
comparison. Message IDs MUST be no longer than 250 octets, including
the "<" and ">".
NOTE: "Postmaster" is an irksome exception to case-sensitivity in
local parts, inherited from MAIL, and simply avoiding it is the
best way to deal with it (not that it's likely, but the issue
needs to be dealt with). The length limit is undesirable but is
present in widely used existing software. The limit is actually
255, but a small safety margin is wise.
5.4. Subject
The Subject header's content (the "subject" of the article) is a
short phrase describing the topic of the article:
Subject-content = [ "Re: " ] nonblank-text
Encoded words MAY appear in this header.
Spencer Historic [Page 36]RFC 1849 Son of 1036 March 2010
If the article is a followup, the subject SHOULD begin with "Re: " (a
"back reference"). If the article is not a followup, the subject
MUST NOT begin with a back reference. Back references are case-
insensitive, although "Re: " is the preferred form. A followup agent
assisting a poster in preparing a followup SHOULD prepend a back
reference, UNLESS the subject already begins with one. If the poster
determines that the topic of the followup differs significantly from
what is described in the subject, a new, more descriptive subject
SHOULD be substituted (with no back reference). An article whose
subject begins with a back reference MUST have a References header
referencing the precursor.
NOTE: A back reference is FOUR characters, the fourth being a
blank. [RFC1036] was confused about this. Observe also that only
ONE back reference should be present.
NOTE: There is a semi-standard convention, often used, in which a
subject change is flagged by making the new Subject-content of the
form:
new topic (was: old topic)
possibly with "old topic" somewhat truncated. Posters wishing to
do something like this are urged to use this exact form, to
simplify automated analysis.
For historical reasons, the subject MUST NOT begin with "cmsg " (note
that this sequence ends with a blank).
NOTE: Some old news software takes a subject beginning with
"cmsg " as an indication that the article is a control message
(see Sections 6.6 and 7). This mechanism is obsolete and
undesirable, but accidental triggering of it is still possible.
The subject SHOULD be terse. Posters SHOULD avoid trying to cram
their entire article into the headers; even the simplest query
usually benefits from a sentence or two of elaboration and context,
and the details of header display vary widely among reading agents.
NOTE: All-in-the-subject articles are sometimes the result of
misunderstandings over the interaction protocol of a posting
agent. Posting agents might wish to give special attention to the
possibility that a poster specifying a very long subject might
have thought he was typing the body of the article.
Spencer Historic [Page 37]RFC 1849 Son of 1036 March 2010
5.5. Newsgroups
The Newsgroups header's content specifies to which newsgroup(s) the
article is posted:
Newsgroups-content = newsgroup-name *( ng-delim newsgroup-name )
newsgroup-name = plain-component *( "." component )
component = plain-component / encoded-word
plain-component = component-start *13component-rest
component-start = lowercase / digit
lowercase = <letter a-z>
component-rest = component-start / "+" / "-" / "_"
ng-delim = ","
Encoded words used in newsgroup names MUST NOT contain characters
other than letters, digits, "+", "-", "/", "_", "=", and "?"
(although they may encode them).
A newsgroup name consists of one or more components, which may be
plain components or (except for the first) encoded words. A plain
component MUST contain at least one letter, MUST begin with a letter
or digit, and MUST NOT be longer than 14 characters. The first
component MUST begin with a letter; subsequent components SHOULD
begin with a letter. Newsgroup names MUST NOT contain uppercase
letters, except where required by encodings in encoded words. The
sequences "all" and "ctl" MUST NOT be used as components.
NOTE: The alphabet and syntax specified encompasses all existing
names of widespread newsgroups, while avoiding various forms that
are known to cause problems. Important existing software uses
various non-alphanumeric characters as punctuation adjacent to
newsgroup names. (It would, in fact, be preferable to ban "+"
from newsgroup names, were it not that several widespread
newsgroups related to the C++ programming language already use
it.)
NOTE: Much existing software converts the newsgroup name into a
directory path and stores the articles themselves using numeric
filenames, so all-digit name components can be troublesome; the
"Great Renaming" early in the history of Usenet included revisions
of several newsgroup names to eliminate such components.
NOTE: The same storage technique is the reason for the
14-character limit. The limit is now largely historical, since
most modern systems have much larger limits on the length of a
directory entry's name, but many old systems are still in use.
Systems with shorter limits also exist, but news software on such
systems has had to deal with the problem already, since there are
Spencer Historic [Page 38]RFC 1849 Son of 1036 March 2010
several widespread newsgroups with 14-character components in
their names. Implementors are warned that it is intended that the
successor to this Draft will increase the 14-character limit, and
they are urged to fix their software to handle longer names
gracefully (if such fixes are necessary, given the intended domain
of application of the particular software).
NOTE: The requirement that the first character of a name be a
letter accommodates existing software that assumes it can tell the
difference between a newsgroup name and other possible syntactic
entities by inspecting the first character. Similar
considerations motivate excluding "+", "-", and "_" from coming
first in a component, and the preference for components that do
not begin with digits. The "all" sequence is used as a wildcard
symbol in much existing software, and the "ctl" sequence was
involved in an obsolete historical mechanism for marking control
messages, so they are best avoided.
NOTE: Possibly newsgroup names should have been case-insensitive,
but all existing software treats them as case-sensitive.
([RFC977] claims that they are case-insensitive in NNTP, but
existing implementations are believed to ignore this.) The
simplest solution is just to ban use of uppercase letters, since
no widespread newsgroup name uses them anyway; this avoids any
possibility of confusion.
NOTE: The syntax has the disadvantage of containing no white
space, making it impossible to continue a Newsgroups header across
several lines. Implementors of relayers and reading agents are
warned that it is intended that the successor to this Draft will
change the definition of ng-delim to:
ng-delim = "," [ space ]
and are urged to fix their software to handle (i.e., ignore) white
space following the commas. Meanwhile, posters must avoid
inserting such space (despite the natural-language convention that
permits it), and posting agents should strip it out.
NOTE: Encoded words as components are somewhat problematic but are
clearly desirable for use in non-English-speaking nations. They
are not subject to the 14-character limit, and this (plus the
possibility of "/" within them) may require special handling in
news software.
Spencer Historic [Page 39]RFC 1849 Son of 1036 March 2010
Encoded words are allowed in newsgroup names ONLY where non-ASCII
characters are necessary to the name, and they must use the "b"
encoding [RFC2045] and the first suitable character set in the MIME
order of preferred character sets [RFC2047] {ASCII before ISO-8859-*
before anything else}.
NOTE: Since the newsgroup name is the encoded form, NOT the
underlying non-ASCII form, there is room for terrible confusion
here if the choice of encoding for a particular name is not fully
standardized.
Posters SHOULD use only the names of existing newsgroups in the
Newsgroups header, because newsgroups are NOT created simply by being
posted to. However, it is legitimate to cross-post to newsgroup(s)
that do not exist on the posting agent's host, provided that at least
one of the newsgroups DOES exist there, and followup agents MUST
accept this (posting agents MAY accept it, but SHOULD at least alert
the poster to the situation and request confirmation). Relayers MUST
NOT rewrite Newsgroups headers in any way, even if some or all of the
newsgroups do not exist on the relayer's host.
NOTE: Early experience with news software that created newsgroups
when they were mentioned in a Newsgroups header was thoroughly
negative: posters frequently mistype newsgroup names.
NOTE: While it is legitimate for some of an article's newsgroups
not to exist on the host where it is posted, this IS a rather
unusual situation except in followups (which should go to all
newsgroups the precursor was posted to, even if not all of them
reach the site where the followup is being posted).
NOTE: Rewriting Newsgroups headers to strip locally unknown
newsgroups is superficially attractive. However, early experience
with exactly that policy was thoroughly negative: news propagation
is more redundant and much less orderly than many people imagine,
and in particular it is not unheard of for the (sometimes) fastest
path between two (say) University of Toronto sites to pass outside
the University of Toronto, in which case newsgroup stripping can
cause incomplete propagation. Having an article's set of
newsgroups change as it propagates can also result in followups
not achieving the same propagation as the original. It's been
tried; it's more trouble than it's worth; don't do it.
NOTE: In particular, newsgroup stripping superficially looks like
a solution to the problem of duplicate regional newsgroup names.
For example, both the University of Toronto and the University of
Texas have "ut.general" newsgroups, and material cross-posted to
that name and a global newsgroup appears in both universities'
Spencer Historic [Page 40]RFC 1849 Son of 1036 March 2010
local newsgroups. However, the side effects of stripping are
sufficiently unacceptable to disqualify it for this purpose.
Don't do it.
Cross-posting an article to several relevant newsgroups is far
superior to posting separate articles with duplicated content to each
newsgroup, because reading agents can detect the situation and show
the article to a reader only once. Posters SHOULD cross-post rather
than duplicate-post.
NOTE: On the other hand, cross-posting to a large number of
newsgroups usually indicates that the poster has not thought about
his audience; articles are rarely pertinent to more than (say)
half a dozen newsgroups. Posting agents might wish to request
confirmation when the number of newsgroups exceeds (say) five in
the presence of a Followup-To header, or (say) two in the absence
of such a header.
NOTE: One problem with cross-postings is what to do with an
article cross-posted to a set of newsgroups including both
moderated and unmoderated ones. Posters tend to expect such an
article to show up immediately in the unmoderated newsgroups,
especially if they do not realize that one or more of the
newsgroups is moderated. However, since it is not possible for a
moderator to retroactively add an already-posted article to a
moderated newsgroup, the only correct action is to mail such an
article to one (and only one) of the moderators for action. It is
probably best for the posting agent to detect this situation and
ask the poster what action is preferred. The acceptable choices
are to alter the newsgroup list or to mail to a moderator of the
poster's choice; the posting agent should NOT offer duplicate-
posting as an easy-to-request option (if only because many
moderators will reject a submission that has already been posted
to unmoderated newsgroups).
NOTE: An article cross-posted to multiple moderated newsgroups
really should have approval from all of the moderators involved.
In practice, the only straightforward way to do this is to send
the article to one of them and have him consult the others.
A newsgroup SHOULD NOT appear more than once in the Newsgroups
header.
Newsgroup names having only one component are reserved for newsgroups
whose propagation is restricted to a single host (or the
administrative equivalent). It is inadvisable to name a newsgroup
Spencer Historic [Page 41]RFC 1849 Son of 1036 March 2010
"poster" because that word has special meaning in the Followup-To
header (see Section 6.1). The names "control" and "junk" are
frequently used for pseudo-newsgroups internal to relayer
implementations, and hence are also best avoided.
NOTE: Beware of the duplicate-regional-newsgroup-names problem
mentioned above. In particular, there are many, many hosts with a
newsgroup named "general", and some surprising things show up in
such newsgroups when people cross-post. It is probably better to
use multi-component names, which are less likely to be duplicated.
Fred's Widget House should use "fwh.general" rather than just
"general" as its in-house general-topics newsgroup.
It is conventional to reserve newsgroup names beginning with "to."
for test messages sent on an essentially point-to-point basis (see
also the ihave/sendme protocol described in Section 7.2); newsgroup
names beginning with "to." SHOULD NOT be used for any other purpose.
The second (and possibly later) components of such a name should,
together, comprise the relayer name (see Section 5.6) of a relayer.
The newsgroup exists only at the named relayer and its neighbors.
The neighbors all pass that newsgroup to the named relayer, while the
named relayer does not pass it to anyone.
The order of newsgroup names in the Newsgroups header is not
significant.
5.6. Path
The Path header's content indicates which relayers the article has
already visited, so that unnecessary redundant transmission can be
avoided:
Path-content = [ path-list path-delimiter ] local-part
path-list = relayer-name *( path-delimiter relayer-name )
relayer-name = 1*rn-char
rn-char = letter / digit / "." / "-" / "_"
path-delimiter = "!"
The Path content is a list of relayer names, separated by path
delimiters, followed (after a final delimiter) by the local part of a
mailing address. Each relayer MUST prepend its name, and a
delimiter, to the Path content in all articles it processes. A
relayer MUST NOT pass an article to a neighboring relayer whose name
is already mentioned in an article's path list, unless this is
explicitly requested by the neighbor in some way. The Path content
is case-sensitive.
Spencer Historic [Page 42]RFC 1849 Son of 1036 March 2010
NOTE: The Path header supplied by a posting agent should normally
contain only the local part. The relayer that the posting agent
passes the article to for posting will prepend its relayer name to
get the path list started.
NOTE: Observe that the trailing local part is NOT part of the path
list. This Path header:
Path: fee!fie!foe!fum
contains three relayer names: "fee", "fie", and "foe". A relayer
named "fum" is still eligible to be sent this article.
NOTE: This syntax has the disadvantage of containing no white
space, making it impossible to continue a Path header across
several lines. Implementors of relayers and reading agents are
warned that it is intended that the successor to this Draft will
change the definition of path delimiter to:
path-delimiter = "!" [ space ]
and are urged to fix their software to handle (i.e., ignore) white
space following the exclamation points. They are urged to hurry;
some ill-behaved systems reportedly already feel free to add such
white space.
NOTE: [RFC1036] allows considerably more flexibility in choice of
delimiter, in theory, but this flexibility has never been used,
and most news software does not implement it properly. The
grammar reflects the current reality. Note, in particular, that
[RFC1036] treats "_" as a delimiter, but in fact it is known to
appear in relayer names occasionally.
Because an article will not propagate to a relayer already mentioned
in its path list, the path list MUST NOT contain any names other than
those of relayers the article has passed through AS NEWS. This is
trivially obvious for normal news articles but requires attention
from the moderators of moderated newsgroups and the implementors and
maintainers of gateways.
NOTE: For the same reason, a relayer and its neighbors need to
agree on the choice of relayer name, and names should not be
changed without notifying neighbors.
Relayer names need to be unique among all relayers that will ever see
the articles using them. A relayer name is normally either an
"official" name for the host the relayer runs on, or some other
"official" name controlled by the same organization. Except in
Spencer Historic [Page 43]RFC 1849 Son of 1036 March 2010
cooperating subnets that agree to some other convention and don't let
articles using it escape beyond the subnet, a relayer name MUST be
either a UUCP name registered in the UUCP maps (without any domain
suffix such as ".UUCP") or a complete Internet domain name. Use of a
(registered) UUCP name is recommended, where practical, to keep the
length of the path list down.
The use of Internet domain names in the path list presents one
problem: domain names are case-insensitive, but the path list is
case-sensitive. Relayers using domain names as their relayer names
MUST pick a standard form for the name and use that form consistently
to the exclusion of all others. The preferred form for this purpose,
which relayers SHOULD use, is the all-lowercase form.
NOTE: It is arguably unfortunate that the path list is case-
sensitive, but it is much too late to change this. Most Internet
sites do, in any event, use one standardized form of their name
almost everywhere.
In the ordinary case, where the poster is the author of the article,
the local part following the path list SHOULD be the local part of
the poster's full Internet domain mailing address.
NOTE: It should be just the local part, not the full address. The
character "@" does not appear in a Path header.
The Path content somewhat resembles a mailing address, particularly
in the UUCP world with its manual routing and "!" address syntax.
Historically, this resemblance was important, and the Path content
was often used as a reply address. This practice has always been
somewhat unreliable, since news paths are not always mail paths and
news relayer names are not always recognized by mail handlers, and
its reliability has generally worsened in recent times. The
widespread use of and recognition of Internet domain addresses, even
outside the actual Internet, has largely eliminated the problem.
Readers SHOULD NOT use the Path content as a reply address. On the
other hand, relayer administrators are urged not to break this usage
without good reason; where practical, paths followed by news SHOULD
be traversable by mail, and mail handlers SHOULD recognize relayer
names as host names.
It will typically be difficult or impractical for gateways and
moderators to supply a Path content that is useful as a reply address
for the author, bearing in mind that the path list they supply will
normally be empty. (To reiterate: the path list MUST NOT contain any
names other than those of relayers the article has passed through AS
NEWS.) They SHOULD supply a local part that will result in replies
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to a Path-derived address being returned to the sender with a brief
explanation. Software permitting, the local part "not-for-mail" is
recommended.
NOTE: A moderator or gateway administrator who supplies a local
part that delivers such mail to an administrative mailbox will
quickly discover why it should be bounced automatically! It is
best, however, for the returned message to include an explanation
of what has probably happened, rather than just a mysterious
"undeliverable mail" complaint, since the sender may not be aware
that his/her software is unwisely using the Path content as a
reply address. Reply software might wish to question attempts to
reply to a Path-derived address ending in "not-for-mail" (which is
why a specific name is being recommended here).
6. Optional Headers
Many MAIL headers, and many of those specified in present and future
MAIL extensions, are potentially applicable to news. Headers
specific to MAIL's point-to-point transmission paradigm, e.g., To and
Cc, SHOULD NOT appear in news articles. (Gateways wishing to
preserve such information for debugging probably SHOULD hide it under
different names; prefixing "X-" to the original headers, resulting in
forms like "X-To", is suggested.)
The following optional headers are either specific to news or of
particular note in news articles; an article MAY contain some or all
of them. (Note that there are some circumstances in which some of
them are mandatory; these are explained under the individual
headers.) An article MUST NOT contain two or more headers with any
one of these header names.
NOTE: The ban on duplicate header names does not apply to headers
not specified in this Draft, such as "X-" headers. Software
should not assume that all header names in a given article are
unique.
6.1. Followup-To
The Followup-To header contents specify to which newsgroup(s)
followups should be posted:
Followup-To-content = Newsgroups-content / "poster"
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The syntax is the same as that of the Newsgroups content, with the
exception that the magic word "poster" means that followups should be
mailed to the article's reply address rather than posted. In the
absence of Followup-To, the default newsgroup(s) for a followup are
those in the Newsgroups header.
NOTE: The way to request that followups be mailed to a specific
address other than that in the From line is to supply
"Followup-To: poster" and a Reply-To header. Putting a mailing
address in the Followup-To line is incorrect; posting agents
should reject or rewrite such headers.
NOTE: There is no syntax for "no followups allowed" because
"Followup-To: poster" accomplishes this effect without extra
machinery.
Although it is generally desirable to limit followups to the smallest
reasonable set of newsgroups, especially when the precursor was
cross-posted widely, posting agents SHOULD NOT supply a Followup-To
header except at the poster's explicit request.
NOTE: In particular, it is incorrect for the posting agent to
assume that followups to a cross-posted article should be directed
to the first newsgroup only. Trimming the list of newsgroups
should be the poster's decision, not the posting agent's.
However, when an article is to be cross-posted to a considerable
number of newsgroups, a posting agent might wish to SUGGEST to the
poster that followups go to a shorter list.
6.2. Expires
The Expires header content specifies a date and time when the article
is deemed to be no longer useful and should be removed ("expired"):
Expires-content = Date-content
The content syntax is the same as that of the Date content. In the
absence of Expires, the default is decided by the administrators of
each host the article reaches, who MAY also restrict the extent to
which the Expires header is honored.
The Expires header has two main applications: removing articles whose
utility ends on a specific date (e.g., event announcements that can
be removed once the day of the event has passed) and preserving
articles expected to be of prolonged usefulness (e.g., information
aimed at new readers of a newsgroup). The latter application is
sometimes abused. Since individual hosts have local policies for
expiration of news (depending on available disk space, for instance),
Spencer Historic [Page 46]RFC 1849 Son of 1036 March 2010
posters SHOULD NOT provide Expires headers for articles unless there
is a natural expiration date associated with the topic. Posting
agents MUST NOT provide a default Expires header. Leave it out and
allow local policies to be used unless there is a good reason not to.
Expiry dates are properly the decision of individual host
administrators; posters and moderators SHOULD set only expiry dates
with which most administrators would agree.
NOTE: A poster preparing an Expires header for an article whose
utility ends on a specific day should typically specify the NEXT
day as the expiry date. A meeting on July 7th remains of interest
on the 7th.
6.3. Reply-To
The Reply-To header content specifies a reply address different from
the author's address given in the From header:
Reply-To-content = From-content
In the absence of Reply-To, the reply address is the address in the
From header.
Use of a Reply-To header is preferable to including a similar request
in the article body, because reply-preparation software can take
account of Reply-To automatically.
6.4. Sender
The Sender header identifies the poster, in the event that this
differs from the author identified in the From header:
Sender-content = From-content
In the absence of Sender, the default poster is the author (named in
the From header).
NOTE: The intent is that the Sender header have a fairly high
probability of identifying the person who really posted the
article. The ability to specify a From header naming someone
other than the poster is useful but can be abused.
If the poster supplies a From header, the posting agent MUST ensure
that a Sender header is present, unless it can verify that the
mailing address in the From header is a valid mailing address for the
poster. A poster-supplied Sender header MAY be used, if its mailing
address is verifiably a valid mailing address for the poster;
Spencer Historic [Page 47]RFC 1849 Son of 1036 March 2010
otherwise, the posting agent MUST supply a Sender header and delete
(or rename, for example, to X-Unverifiable-Sender) any poster-
supplied Sender header.
NOTE: It might be useful to preserve a poster-supplied Sender
header so that the poster can supply the full-name part of the
content. The mailing address, however, must be right, hence, the
posting agent must generate the Sender header if it is unable to
verify the mailing address of a poster-supplied one.
NOTE: NNTP implementors, in particular, are urged to note this
requirement (which would eliminate the need for ad hoc headers
like NNTP-Posting-Host), although there are admittedly some
implementation difficulties. A user name from an [RFC1413] server
and a host name from an inverse mapping of the address, perhaps
with a "full name" comment noting the origin of the information,
would be at least a first approximation:
Sender: fred@zoo.toronto.edu (RFC-1413@reverse-lookup;
not verified)
While this does not completely meet the specs, it comes a lot closer
than not having a Sender header at all. Even just supplying a
placeholder for the user name:
Sender: somebody@zoo.toronto.edu (user name unknown)
would be better than nothing.
6.5. References
The References header content lists message IDs of precursors:
References-content = message-id *( space message-id )
A followup MUST have a References header, and an article that is not
a followup MUST NOT have a References header. The References-content
of a followup MUST be the precursor's References-content (if any)
followed by the precursor's message ID.
NOTE: Use the See-Also header (Section 6.16) for interconnection
of articles that are not in a followup relationship to each other.
NOTE: In retrospect, RFCs 850 and 1036, and the implementations
whose practice they represented, erred here. The proper MAIL
header to use for references to precursors is In-Reply-To, and the
References header is meant to be used for the purposes here
ascribed to See-Also. This incompatibility is far too solidly
Spencer Historic [Page 48]RFC 1849 Son of 1036 March 2010
established to be fixed, unfortunately. The best that can be done
is to provide a clear mapping between the two and urge gateways to
do the transformation. The news usage is (now) a deliberate
violation of the MAIL specifications; articles containing news
References headers are technically not valid MAIL messages,
although it is unlikely that much MAIL software will notice
because the incompatibility is at a subtle semantic level that
does not affect the syntax.
UNRESOLVED ISSUE: Would it be better to just give up and admit
that news uses References for both purposes?
UNRESOLVED ISSUE: Should the syntax be generalized to include URLs
as alternatives to message IDs? Perhaps not; too many things know
about References already. And non-articles can't be precursors of
articles, not really.
Followup agents SHOULD NOT shorten References headers. If it is
absolutely necessary to shorten the header, as a desperate last
resort, a followup agent MAY do this by deleting some of the message
IDs. However, it MUST NOT delete the first message ID, the last
three message IDs (including that of the immediate precursor), or any
message ID mentioned in the body of the followup. If it is possible
for the followup agent to determine the Subject content of the
articles identified in the References header, it MUST NOT delete the
message ID of any article where the Subject content changed (other
than by prepending of a back reference). The followup agent MUST NOT
delete any message ID whose local part ends with "_-_" (underscore
(ASCII 95), hyphen (ASCII 45), underscore); followup agents are urged
to use this form to mark subject changes and to avoid using it
otherwise.
NOTE: As software capable of exploiting References chains has
grown more common, the random shortening permitted by [RFC1036]
has become increasingly troublesome. ANY shortening is
undesirable, and software should do it only in cases of dire
necessity. In such cases, these rules attempt to limit the
damage.
NOTE: The first message ID is very important as the starting point
of the "thread" of discussion and absolutely should not be
deleted. Keeping the last three message IDs gives thread-
following software a fighting chance to reconstruct a full thread
even if an article or two is missing. Keeping message IDs
mentioned in the body is obviously desirable.
Spencer Historic [Page 49]RFC 1849 Son of 1036 March 2010
NOTE: Subject changes are difficult to determine, but they are
significant as possible beginnings of new threads. The "_-_"
convention is provided so that posting agents (which have more
information about subjects) can flag articles containing a subject
change in a way that followup agents can detect without access to
the articles themselves. The sequence is chosen as one that is
fairly unlikely to occur by accident.
UNRESOLVED ISSUE: Is "_-_" really worth having?
When a References header is shortened, at least three blanks SHOULD
be left between adjacent message IDs at each point where deletions
were made. Software preparing new References headers SHOULD preserve
multiple blanks in older References content.
NOTE: It's desirable to have some marker of where deletions
occurred, but the restricted syntax of the header makes this
difficult. Extra white space is not a very good marker, since it
may be deleted by software that ill-advisedly rewrites headers,
but at least it doesn't break existing software.
To repeat: followup agents SHOULD NOT shorten References headers.
NOTE: Unfortunately, reading agents and other software analyzing
References patterns have to be prepared for the worst anyway. The
worst includes random deletions and the possibility of circular
References chains (when References is misused in place of See-Also
(Section 6.16)).
6.6. Control
The Control header content marks the article as a control message and
specifies the desired actions (other than the usual ones of filing
and passing on the article):
Control-content = verb *( space argument )
verb = 1*( letter / digit )
argument = 1*<ASCII printable character>
The verb indicates what action should be taken, and the argument(s)
(if any) supply details. In some cases, the body of the article may
also contain details. Section 7 describes the standard verbs. See
also the Also-Control header (Section 6.15).
NOTE: Control messages are often processed and filed rather
differently than normal articles.
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NOTE: The restriction of verbs to letters and digits is new but is
consistent with existing practice and potentially simplifies
implementation by avoiding characters significant to command
interpreters. Beware that the arguments are under no such
restriction in general.
NOTE: Two other conventions for distinguishing control messages
from normal articles were formerly in use: a three-component
newsgroup name ending in ".ctl" or a subject beginning with
"cmsg " was considered to imply that the article was a control
message. These conventions are obsolete. Do not use them.
An article with a Control header MUST NOT have an Also-Control or
Supersedes header.
6.7. Distribution
The Distribution header content specifies geographic or
organizational limits on an article's propagation:
Distribution-content = distribution *( dist-delim distribution )
dist-delim = ","
distribution = plain-component
A distribution is syntactically identical to a one-component
newsgroup name and must satisfy the same rules and restrictions. In
the absence of Distribution, the default distribution is "world".
NOTE: This syntax has the disadvantage of containing no white
space, making it impossible to continue a Distribution header
across several lines. Implementors of relayers and reading agents
are warned that it is intended that the successor to this Draft
will change the definition of dist delimiter to:
dist-delim = "," [ space ]
and are urged to fix their software to handle (i.e., ignore) white
space following the commas.
A relayer MUST NOT pass an article to another relayer unless
configuration information specifies transmission to that other
relayer of BOTH (a) at least one of the article's newsgroup(s), and
(b) at least one of the article's distribution(s). In effect, the
only role of distributions is to limit propagation, by preventing
transmission of articles that would have been transmitted had the
decision been based solely on newsgroups.
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A posting agent might wish to present a menu of possible
distributions, or suggest a default, but normally SHOULD NOT supply a
default without giving the poster a chance to override it. A
followup agent SHOULD initially supply the same Distribution header
as found in the precursor, although the poster MAY alter this if
appropriate.
Despite the syntactic similarity and some historical confusion,
distributions are NOT newsgroup names. The whole point of putting a
distribution on an article is that it is DIFFERENT from the
newsgroup(s). In general, a meaningful distribution corresponds to
some sort of region of propagation: a geographical area, an
organization, or a cooperating subnet.
NOTE: Distributions have historically suffered from the completely
uncontrolled nature of their name space, the lack of feedback to
posters on incomplete propagation resulting from use of random
trash in Distribution headers, and confusion with newsgroups
(arising partly because many regions and organizations DO have
internal newsgroups with names resembling their internal
distributions). This has resulted in much garbage in Distribution
headers, notably the pointless practice of automatically supplying
the first component of the newsgroup name as a distribution (which
is MOST unlikely to restrict propagation!). Many sites have opted
to maximize propagation of such ill-formed articles by essentially
ignoring distributions. This unfortunately interferes with
legitimate uses. The situation is bad enough that distributions
must be considered largely useless except within cooperating
subnets that make an organized effort to restrain propagation of
their internal distributions.
NOTE: The distributions "world" and "local" have no standard magic
meaning (except that the former is the default distribution if
none is given). Some pieces of software do assign such meanings
to them.
6.8. Keywords
The Keywords header content is one or more phrases intended to
describe some aspect of the content of the article:
Keywords-content = plain-phrase *( "," [ space ] plain-phrase )
Keywords, separated by commas, each follow the <plain-phrase> syntax
defined in Section 5.2. Encoded words in keywords MUST NOT contain
characters other than letters (of either case), digits, and the
characters "!", "*", "+", "-", "/", "=", and "_".
Spencer Historic [Page 52]RFC 1849 Son of 1036 March 2010
NOTE: Posters and posting agents are asked to take note that
keywords are separated by commas, not by white space. The
following Keywords header contains only one keyword (a rather
unlikely and improbable one):
Keywords: Thompson Ritchie Multics Linux
and should probably have been written:
Keywords: Thompson, Ritchie, Multics, Linux
This particular error is unfortunately rather widespread.
NOTE: Reading agents and archivers preparing indexes of articles
should bear in mind that user-chosen keywords are notoriously poor
for indexing purposes unless the keywords are picked from a
predefined set (which they are not in this case). Also, some
followup agents unwisely propagate the Keywords header from the
precursor into the followup by default. At least one news-based
experiment has found the contents of Keywords headers to be
completely valueless for indexing.
6.9. Summary
The Summary header content is a short phrase summarizing the
article's content:
Summary-content = nonblank-text
As with the subject, no restriction is placed on the content since it
is intended solely for display to humans.
NOTE: Reading agents should be aware that the Summary header is
often used as a sort of secondary Subject header, and (if present)
its contents should perhaps be displayed when the subject is
displayed.
The summary SHOULD be terse. Posters SHOULD avoid trying to cram
their entire article into the headers; even the simplest query
usually benefits from a sentence or two of elaboration and context,
and not all reading agents display all headers.
6.10. Approved
The Approved header content indicates the mailing addresses (and
possibly the full names) of the persons or entities approving the
article for posting:
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Approved-content = From-content *( "," [ space ] From-content )
An Approved header is required in all postings to moderated
newsgroups; the presence or absence of this header allows a posting
agent to distinguish between articles posted by the moderator (which
are normal articles to be posted normally) and attempted
contributions by others (which should be mailed to the moderator for
approval). An Approved header is also required in certain control
messages, to reduce the probability of accidental posting of same;
see the relevant parts of Section 7.
NOTE: There is, at present, no way to authenticate Approved
headers to ensure that the claimed approval really was bestowed.
Nor is there an established mechanism for even maintaining a list
of legitimate approvers (such a list would quickly become out of
date if it had to be maintained by hand). Such mechanisms,
presumably relying on cryptographic authentication, would be a
worthwhile extension to this Draft, and experimental work in this
area is encouraged. (The problem is harder than it sounds because
news is used on many systems that do not have real-time access to
key servers.)
NOTE: Relayer implementors, please note well: it is the POSTING
AGENT that is authorized to distinguish between moderator postings
and attempted contributions, and to mail the latter to the
moderator. As discussed in Section 9.1, relayers MUST NOT, repeat
MUST NOT, send such mail; on receipt of an unApproved article in a
moderated newsgroup, they should discard the article, NOT
transform it into a mail message (except perhaps to a local
administrator).
NOTE: [RFC1036] restricted Approved to a single From-content.
However, multiple moderation is no longer rare, and multi-
moderator Approved headers are already in use.
6.11. Lines
The Lines header content indicates the number of lines in the body of
the article:
Lines-content = 1*digit
The line count includes all body lines, including the signature (if
any) and including empty lines (if any) at the beginning or end of
the body. (The single empty separator line between the headers and
the body is not part of the body.) The "body" here is the body as
found in the posted article, AFTER all transformations such as MIME
encodings.
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Reading agents SHOULD NOT rely on the presence of this header, since
it is optional (and some posting agents do not supply it). They MUST
NOT rely on it being precise, since it frequently is not.
NOTE: The average line length in article bodies is surprisingly
consistent at about 40 characters, and since the line count
typically is used only for approximate judgements ("is this too
long to read quickly?"), dividing the byte count of the body by 40
gives an estimate of the body line count that is adequate for
normal use. This estimate is NOT adequate if the body has been
MIME encoded, but neither is the Lines header: at least one major
relayer will add a Lines header to an article that lacks one,
without considering the possibility of MIME encodings when
computing the line count.
NOTE: It would be better to have a Content-Size header as part of
MIME, so that body parts could have their own sizes, and so that
the units used could be appropriate to the data type (line count
is not a useful measure of the size of an encoded image, for
example). Doing this is preferable to trying to fix Lines.
UNRESOLVED ISSUE: Update on Content-Size?
Relayers SHOULD discard this header if they find it necessary to
re-encode the article in such a way that the original Lines header
would be rendered incorrect.
6.12. Xref
The Xref header content indicates where an article was filed by the
last relayer to process it:
Xref-content = relayer 1*( space location )
relayer = relayer-name
location = newsgroup-name ":" article-locator
article-locator = 1*<ASCII printable character>
The relayer's name is included so that software can determine which
relayer generated the header (and specifically, whether it really was
the one that filed the copy being examined). The locations specify
what newsgroups the article was filed under (which may differ from
those in the Newsgroups header) and where it was filed under them.
The exact form of an article locator is implementation-specific.
NOTE: Reading agents can exploit this information to avoid
presenting the same article to a reader several times. The
information is sometimes available in system databases, but having
it in the article is convenient. Relayers traditionally generate
Spencer Historic [Page 55]RFC 1849 Son of 1036 March 2010
an Xref header only if the article is cross-posted, but this is
not mandatory, and there is at least one new application
("mirroring": keeping news databases on two hosts identical) where
the header is useful in all articles.
NOTE: The traditional form of an article locator is a decimal
number, with articles in each newsgroup numbered consecutively
starting from 1. NNTP [RFC977] demands that such a model be
provided, and there may be other software that expects it, but it
seems desirable to permit flexibility for unorthodox
implementations.
A relayer inserting an Xref header into an article MUST delete any
previous Xref header. A relayer that is not inserting its own Xref
header SHOULD delete any previous Xref header. A relayer MAY delete
the Xref header when passing an article on to another relayer.
NOTE: [RFC1036] specified that the Xref header was not transmitted
when an article was passed to another relayer, but the major news
implementations have never obeyed this rule, and applications like
mirroring depend on this disobedience.
A relayer MUST use the same name in Xref headers as it uses in Path
headers. Reading agents MUST ignore an Xref header containing a
relayer name that differs from the one that begins the path list.
6.13. Organization
The Organization header content is a short phrase identifying the
poster's organization:
Organization-content = nonblank-text
This header is typically supplied by the posting agent. The
Organization content SHOULD mention geographical location (e.g., city
and country) when it is not obvious from the organization's name.
NOTE: The motive here is that the organization is often difficult
to guess from the mailing address, is not always supplied in a
signature, and can help identify the poster to the reader.
NOTE: There is no "s" in "Organization".
The Organization content is provided for identification only and does
not imply that the poster speaks for the organization or that the
article represents organization policy. Posting agents SHOULD permit
the poster to override a local default Organization header.
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6.14. Supersedes
The Supersedes header content specifies articles to be cancelled on
arrival of this one:
Supersedes-content = message-id *( space message-id )
Supersedes is equivalent to Also-Control (Section 6.15) with an
implicit verb of "cancel" (Section 7.1).
NOTE: Supersedes is normally used where the article is an updated
version of the one(s) being cancelled.
NOTE: Although the ability to use multiple message IDs in
Supersedes is highly desirable (see Section 7.1), posters are
warned that existing implementations often do not correctly handle
more than one.
NOTE: There is no "c" in "Supersedes".
An article with a Supersedes header MUST NOT have an Also-Control or
Control header.
6.15. Also-Control
The Also-Control header content marks the article as being a control
message IN ADDITION to being a normal news article and specifies the
desired actions:
Also-Control-content = Control-content
An article with an Also-Control header is filed and passed on
normally, but the content of the Also-Control header is processed as
if it were found in a Control header.
NOTE: It is sometimes desirable to piggyback control actions on a
normal article, so that the article will be filed normally but
will also be acted on as a control message. This header is
essentially a generalization of Supersedes.
NOTE: Be warned that some old relayers do not implement
Also-Control.
An article with an Also-Control header MUST NOT have a Control or
Supersedes header.
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6.16. See-Also
The See-Also header content lists message IDs of articles that are
related to this one but are not its precursors:
See-Also-content = message-id *( space message-id )
See-Also resembles References, but without the restrictions imposed
on References by the followup rules.
NOTE: See-Also provides a way to group related articles, such as
the parts of a single document that had to be split across
multiple articles due to its size, or to cross-reference between
parallel threads.
NOTE: See the discussion (in Section 6.5) on MAIL compatibility
issues of References and See-Also.
NOTE: In the specific case where it is desired to essentially make
another article PART of the current one, e.g., for annotation of
the other article, MIME's "message/external-body" convention can
be used to do so without actual inclusion. "news-message-ID" was
registered as a standard external-body access method, with a
mandatory NAME parameter giving the message ID and an optional
SITE parameter suggesting an NNTP site that might have the article
available (if it is not available locally), by IANA 22 June 1993.
UNRESOLVED ISSUE: Could the syntax be generalized to include URLs
as alternatives to message IDs? Here it makes much more sense
than in References.
6.17. Article-Names
The Article-Names header content indicates any special significance
the article may have in particular newsgroups:
Article-Names-content = 1*( name-clause space )
name-clause = newsgroup-name ":" article-name
article-name = letter 1*( letter / digit / "-" )
Each name clause specifies a newsgroup (which SHOULD be among those
in the Newsgroups header) and an article name local to that
newsgroup. Article names MAY be used by relayers to file the article
in special ways, or they MAY just be noted for possible special
attention by reading agents. Article names are case-sensitive.
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NOTE: This header provides a way to mark special postings, such as
introductions, frequently-asked-question lists, etc., so that
reading agents have a way of finding them automatically. The
newsgroup name is specified for each article name because the
names may be newsgroup-specific; for example, many frequently-
asked-question lists are posted to "news.answers" in addition to
their "home" newsgroup, and they would not be known by the same
name(s) in both newsgroups.
The Article-Names header SHOULD be ignored unless the article also
contains an Approved header.
NOTE: This stipulation is made in anticipation of the possibility
that Approved headers will be involved in cryptographic
authentication.
The presence of an Article-Names header does not necessarily imply
that the article will be retained unusually long before expiration,
or that previous article(s) with similar Article-Names headers will
be cancelled by its arrival. Posters preparing special postings
SHOULD include appropriate other headers, such as Expires and
Supersedes, to request such actions.
Different networks MAY establish different sets of article names for
the special postings they deem significant; it is preferable for
usage to be standardized within networks, although it might be
desirable for individual newsgroups to have different naming
conventions in some situations. Article names MUST be 14 characters
or less. The following names are suggested but are not mandatory:
intro Introduction to the newsgroup for newcomers.
charter Charter, rules, organization, moderation policies, etc.
background Biographies of special participants, history of the
newsgroup, notes on related newsgroups, etc.
subgroups Descriptions of sub-newsgroups under this newsgroup,
e.g., "sci.space.news" under "sci.space".
facts Information relating to the purpose of the newsgroup,
e.g., an acronym glossary in "sci.space".
references Where to get more information: books, journals, FTP
repositories, etc.
faq Answers to frequently asked questions.
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menu If present, a list of all of the other article names
local to this newsgroup, with brief descriptions of their
contents.
Such articles may be divided into subsections using the MIME
"multipart/mixed" conventions. If size considerations make it
necessary to split such articles, names ending in a hyphen and a part
number are suggested; for example, a three-part frequently-asked-
questions list could have article names "faq-1", "faq-2", and
"faq-3".
NOTE: It is somewhat premature to attempt to standardize article
names, since this is essentially a new feature with no experience
behind it. However, if reading agents are to attach special
significance to these names, some attempt at standard conventions
is imperative. This is a first attempt at providing some.
6.18. Article-Updates
The Article-Updates header content indicates what previous articles
this one is deemed (by the poster) to update (i.e., replace):
Article-Updates-content = message-id *( space message-id )
Each message ID identifies a previous article that this one is deemed
to update. This MUST NOT cause the previous article(s) to be
cancelled or otherwise altered, unless this is implied by other
headers (e.g., Supersedes); Article-Updates is merely an advisory
that MAY be noted for special attention by reading agents.
NOTE: This header provides a way to mark articles that are only
minor updates of previous ones, containing no significant new
information and not worth reading if the previous ones have been
read.
NOTE: If suitable conventions using MIME multipart bodies and the
"message/external-body" body-part type can be developed, a
replacing article might contain only differences between the old
text and the new text, rather than a complete new copy. This is
the motivation for not making Article-Updates also function as
Supersedes does: the replacing article might depend on the
continued presence of the replaced article.
7. Control Messages
The following sections document the currently defined control
messages. "Message" is used herein as a synonym for "article" unless
context indicates otherwise.
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Posting agents are warned that since certain control messages require
article bodies in quite specific formats, signatures SHOULD NOT be
appended to such articles, and it may be wise to take greater care
than usual to avoid unintended (although perhaps well-meaning)
alterations to text supplied by the poster. Relayers MUST assume
that control messages mean what they say; they MAY be obeyed as is or
rejected, but MUST NOT be reinterpreted.
The execution of the actions requested by control messages is subject
to local administrative restrictions, which MAY deny requests or
refer them to an administrator for approval. The descriptions below
are generally phrased in terms suggesting mandatory actions, but any
or all of these MAY be subject to local administrative approval
(either as a class or case-by-case). Analogously, where the
description below specifies that a message or portion thereof is to
be ignored, this action MAY include reporting it to an administrator.
NOTE: The exact choice of local action might depend on what action
the control message requests, who it claims to come from, etc.
Relayers MUST propagate even control messages they do not understand.
In the following sections, each type of control message is defined
syntactically by defining its arguments and its body. For example,
"cancel" is defined by defining cancel-arguments and cancel-body.
7.1. cancel
The cancel message requests that one or more previous articles be
"cancelled":
cancel-arguments = message-id *( space message-id )
cancel-body = body
The argument(s) identify the articles to be cancelled, by message ID.
The body is a comment, which software MUST ignore, and SHOULD contain
an indication of why the cancellation was requested. The cancel
message SHOULD be posted to the same newsgroup(s), with the same
distribution(s), as the article(s) it is attempting to cancel.
NOTE: Using the same newsgroups and distributions maximizes the
chances of the cancel message propagating everywhere the target
articles went.
NOTE: [RFC1036] permitted only a single message-id in a cancel
message. Support for cancelling multiple articles is highly
desirable, especially for use with Supersedes (see Section 6.14).
If several revisions of an article appear in fast succession, each
Spencer Historic [Page 61]RFC 1849 Son of 1036 March 2010
using Supersedes to cancel the previous one, it is possible for a
middle revision to be destroyed by cancellation before it is
propagated onward to cancel its predecessor. Allowing each
article to cancel several predecessors greatly alleviates this
problem. (Posting agents preparing a cancel of an article that
itself cancels other articles might wish to add those articles to
the cancel-arguments.) However, posters should be aware that much
old software does not implement multiple cancellation properly and
should avoid using it when reliable cancellation is vitally
important.
When an article (the "target article") is to be cancelled, there are
four cases of interest: the article hasn't arrived yet, it has
arrived and been filed and is available for reading, it has expired
and been archived on some less-accessible storage medium, or it has
expired and been deleted. The next few paragraphs discuss each case
in turn (in reverse order, which is convenient for the explanation).
EXPIRED AND DELETED. Take no action.
EXPIRED AND ARCHIVED. If the article is readily accessible and can
be deleted or made unreadable easily, treat as under AVAILABLE below.
Otherwise, treat as under EXPIRED AND DELETED.
NOTE: While it is desirable for archived articles to be
cancellable, this can easily involve rewriting an entire archive
volume just to get rid of one article, perhaps with manual actions
required to arrange it. It is difficult to envision a situation
so dire as to require such measures from hundreds or thousands of
administrators, or for that matter one in which widespread
compliance with such a request is likely.
AVAILABLE. Compare the mailing addresses from the From lines of the
cancel message and the target article, bearing in mind that local
parts (except for "postmaster") are case-sensitive and domains are
case-insensitive. If they do not match, either refer the issue to an
administrator for a case-by-case decision, or treat as if they
matched.
NOTE: It is generally trivial to forge articles, so nothing short
of cryptographic authentication is really adequate to ensure that
a cancel came from the original article's author. Moreover, it is
highly desirable to permit authorities other than the author to
cancel articles, to allow for cases in which the author is
unavailable, uncooperative, or malicious, and in which damage
and/or legal problems may be minimized by prompt cancellation.
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Reliable authentication that would permit such administrative
cancels would be a worthwhile extension to this Draft, and
experimental work in this area is encouraged.
NOTE: Meanwhile, a simple check of addresses is useful accident
prevention and catches at least the most simple-minded forgers.
Since the intent is accident prevention rather than ironclad
security, use of the From address is appropriate, all the more so
because in the presence of gateways (especially redundant multiple
gateways), the author may not have full control over Sender
headers.
NOTE: The "refer... or treat as if they matched" rule is intended
to specifically forbid quietly ignoring cancels with mismatched
addresses.
If the addresses match, then if technically possible, the relayer
MUST delete the target article completely and immediately. Failing
that, it MUST make the target article unreadable (preferably to
everyone, minimally to everyone but the administrator) and either
arrange for it to be deleted as soon as possible or notify an
administrator at once.
NOTE: To allow for events such as criminal actions, malicious
forgeries, and copyright infringements, where damage and/or legal
problems may be minimized by prompt cancellation, complete removal
is strongly preferred over merely making the target article
unreadable. The potential for malice is outweighed by the
importance of really getting rid of the target article in some
legitimate cases. (In cases of inadvertent copyright violation in
particular, the ability to quickly remedy the violation is of
considerable legal importance.) Failing that, making it
unreadable is better than nothing.
NOTE: Merely annotating the article so that readers see an
indication that the author wanted it cancelled is not acceptable.
Making the article unreadable is the minimum action.
NOTE: There have been experiments with making cancelled articles
unreadable, so that local news administrators could reverse
cancellations. In practice, administrators almost never find
cause to do so. Removal appears to be clearly preferable where
technically feasible.
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NOT ARRIVED YET. If practical, retain the cancel message until the
target article does arrive, or until there is no further possibility
of it arriving and being accepted (see Section 9.2), and then treat
as under AVAILABLE. Failing that, arrange for the target article to
be rejected and discarded if it does arrive.
NOTE: It may well be impractical to retain the control message,
given uncertainty about whether the target article will ever
arrive. Existing practice in such cases is to assume that
addresses would match and arrange the equivalent of deletion.
This is often done by making a spurious entry in a database of
already-seen message IDs (see Section 9.3), so that if the article
does arrive, it will be rejected as a duplicate.
The cancel message MUST be propagated onward in the usual fashion,
regardless of which of the four cases applied, so that the target
article will be cancelled everywhere even if cancellation and target
article follow different routes.
NOTE: [RFC1036] appeared to require stopping cancel propagation in
the NOT ARRIVED YET case, although the wording was somewhat
unclear. This appears to have been an unwise decision; there are
known cases of important cancellations (in situations of
inadvertent copyright violation, for example) achieving rather
poorer propagation than the target article. News propagation is
often a much less orderly process than the authors of [RFC1036]
apparently envisioned. Modern implementations generally propagate
the cancellation regardless.
Posting agents meant for use by ordinary posters SHOULD reject an
attempt to post a cancel message if the target article is available
and the mailing address in its From header does not match the one in
the cancel message's From header.
NOTE: This, again, is primarily accident prevention.
7.2. ihave, sendme
The ihave and sendme control messages implement a crude batched
predecessor of the NNTP [RFC977] protocol. They are largely obsolete
in the Internet but still see use in the UUCP environment, especially
for backup feeds that normally are active only when a primary feed
path has failed.
NOTE: The ihave and sendme messages defined here have ABSOLUTELY
NOTHING TO DO WITH NNTP, despite similarities of terminology.
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The two messages share the same syntax:
ihave-arguments = *( message-id space ) relayer-name
sendme-arguments = ihave-arguments
ihave-body = *( message-id eol )
sendme-body = ihave-body
Message IDs MUST appear in either the arguments or the body, but not
both. Relayers SHOULD generate the form putting message IDs in the
body, but the other form MUST be supported for backward
compatibility.
NOTE: [RFC1036] made the relayer name optional, but difficulties
could easily ensue in determining the origin of the message, and
this option is believed to be unused nowadays. Putting the
message IDs in the body is strongly preferred over putting them in
the arguments because it lends itself much better to large numbers
of message IDs and avoids the empty-body problem mentioned in
Section 4.3.1.
The ihave message states that the named relayer has filed articles
with the specified message IDs, which may be of interest to the
relayer(s) receiving the ihave message. The sendme message requests
that the relayer receiving it send the articles having the specified
message IDs to the named relayer.
These control messages are normally sent essentially as point-to-
point messages, by using "to." newsgroups (see Section 5.5) that are
sent only to the relayer for which the messages are intended. The
two relayers MUST be neighbors, exchanging news directly with each
other. Each relayer advertises its new arrivals to the other using
ihave messages, and each uses sendme messages to request the articles
it lacks.
NOTE: Arguably these point-to-point control messages should flow
by some other protocol, e.g., mail, but administrative and
interfacing issues are simplified if the news system doesn't need
to talk to the mail system.
To reduce overhead, ihave and sendme messages SHOULD be sent
relatively infrequently and SHOULD contain substantial numbers of
message IDs. If ihave and sendme are being used to implement a
backup feed, it may be desirable to insert a delay between reception
of an ihave and generation of a sendme, so that a slightly slow
primary feed will not cause large numbers of articles to be requested
unnecessarily via sendme.
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7.3. newgroup
The newgroup control message requests that a new newsgroup be
created:
newgroup-arguments = newsgroup-name [ space moderation ]
moderation = "moderated" / "unmoderated"
newgroup-body = body
/ [ body ] descriptor [ body ]
descriptor = descriptor-tag eol description-line eol
descriptor-tag = "For your newsgroups file:"
description-line = newsgroup-name space description
description = nonblank-text [ " (Moderated)" ]
The first argument names the newsgroup to be created, and the second
one (if present) indicates whether it is moderated. If there is no
second argument, the default is "unmoderated".
NOTE: Implementors are warned that there is occasional use of
other forms in the second argument. It is suggested that such
violations of this Draft, which are also violations of [RFC1036],
cause the newgroup message to be ignored. [RFC1036] was slightly
vague about how second arguments other than "moderated" were to be
treated (specifically, whether they were illegal or just ignored),
but it is thought that all existing major implementations will
handle "unmoderated" correctly, and it appears desirable to
tighten up the specs to make it possible for other forms to be
used in future.
The body is a comment, which software MUST ignore, except that if it
contains a descriptor, the description line is intended to be
suitable for addition to a list of newsgroup descriptions. The
description cannot be continued onto later lines but is not
constrained to any particular length. Moderated newsgroups have
descriptions that end with the string " (Moderated)" (note that this
string begins with a blank).
NOTE: It is unfortunate that the description line is part of the
body, rather than being supplied in a header, but this is
established practice. Newsgroup creators are cautioned that the
descriptor tag must be reproduced exactly as given above, must be
alone on a line, and that it is case-sensitive. (To reduce errors
in this regard, posting agents might wish to question or reject
newgroup messages that do not contain a descriptor.) Given the
desire for short lines, description writers should avoid content-
free phrases like "discussion of" and "news about", and stick to
defining what the newsgroup is about.
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The remainder of the body SHOULD contain an explanation of the
purpose of the newsgroup and the decision to create it.
NOTE: Criteria for newsgroup creation vary widely and are outside
the scope of this Draft, but if formal procedures of one kind or
another were followed in the decision, the body should mention
this. Administrators often look for such information when
deciding whether to comply with creation/deletion requests.
A newgroup message that lacks an Approved header MUST be ignored.
NOTE: It would also be desirable to ignore a newgroup message
unless its Approved header names a person who is authorized (in
some sense) to create such a newsgroup. A cooperating subnet with
sufficiently strong coordination to maintain a correct and current
list of authorized creators might wish to do so for its internal
newsgroups. It also (or alternatively) might wish to ignore a
newgroup message for an internal newsgroup that was posted (or
cross-posted) to a non-internal newsgroup.
NOTE: As mentioned in Section 6.10, some form of (cryptographic?)
authentication of Approved headers would be highly desirable,
especially for control messages.
It would be desirable to provide some way of supplying a moderator's
address in a newgroup message for a moderated newsgroup, but this
will cause problems unless effective authentication is available, so
it is left for future work.
NOTE: This leaves news administrators stuck with the annoying
chore of arranging proper mailing of moderated-newsgroup
submissions. On Usenet, this can be simplified by exploiting a
forwarding facility that some major sites provide: they maintain
forwarding addresses, each the name of a moderated newsgroup with
all periods (".", ASCII 46) replaced by hyphens ("-", ASCII 45),
which forward mail to the current newsgroup moderators. More
advice on the subject of forwarding to moderators can be found in
the document titled "How to Construct the Mailpaths File", posted
regularly to the Usenet newsgroups news.lists, news.admin.misc,
and news.answers.
A newgroup message naming a newsgroup that already exists is
requesting a change in the moderation status or description of the
newsgroup. The same rules apply.
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7.4. rmgroup
The rmgroup message requests that a newsgroup be deleted:
rmgroup-arguments = newsgroup-name
rmgroup-body = body
The sole argument is the newsgroup name. The body is a comment,
which software MUST ignore; it SHOULD contain an explanation of the
decision to delete the newsgroup.
NOTE: Criteria for newsgroup deletion vary widely and are outside
the scope of this Draft, but if formal procedures of one kind or
another were followed in the decision, the body should mention
this. Administrators often look for such information when
deciding whether to comply with creation/deletion requests.
A rmgroup message that lacks an Approved header MUST be ignored.
NOTE: It would also be desirable to ignore a rmgroup message
unless its Approved header names a person who is authorized (in
some sense) to delete such a newsgroup. A cooperating subnet with
sufficiently strong coordination to maintain a correct and current
list of authorized deleters might wish to do so for its internal
newsgroups. It also (or alternatively) might wish to ignore a
rmgroup message for an internal newsgroup that was posted (or
cross-posted) to a non-internal newsgroup.
Unexpected deletion of a newsgroup being a disruptive action,
implementations are strongly advised to refer rmgroup messages to an
administrator by default, unless perhaps the message can be
determined to have originated within a cooperating subnet whose
members are considered trustworthy. Abuses have occurred.
7.5. sendsys, version, whogets
The sendsys message requests that a description of the relayer's news
feeds to other relayers be mailed to the article's reply address:
sendsys-arguments = [ relayer-name ]
sendsys-body = body
If there is an argument, relayers other than the one named by the
argument MUST NOT respond. The body is a comment, which software
MUST ignore; it SHOULD contain an explanation of the reason for the
request.
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The version message requests that the name and version of the relayer
software be mailed to the reply address:
version-arguments =
version-body = body
There are no arguments. The body is a comment, which software MUST
ignore; it SHOULD contain an explanation of the reason for the
request.
The whogets message requests that a description of the relayer and
its news feeds to other relayers be mailed to the article's reply
address:
whogets-arguments = newsgroup-name [ space relayer-name ]
whogets-body = body
The first argument is the name of the "target newsgroup", specifying
the newsgroup for which propagation information is desired. This
MUST be a complete newsgroup name, not the name of a hierarchy or a
portion of a newsgroup name that is not itself the name of a
newsgroup. If there is a second argument, only the relayer named by
that argument should respond. The body is a comment, which software
MUST ignore; it SHOULD contain an explanation of the reason for the
request.
NOTE: Whogets is intended as a replacement for sendsys (and
version) with a precisely specified reply format. Since the
syntax for specifying what newsgroups get sent to what other
relayers varies widely between different forms of relayer
software, the only practical way to standardize the reply format
is to indicate a specific newsgroup and ask where THAT newsgroup
propagates. The requirement that it be a complete newsgroup name
is intended to (largely) avoid the problem of having to answer
"yes and no" in cases where not all newsgroups in a hierarchy are
sent.
Any of these messages lacking an Approved header MUST be ignored.
Response to any of these messages SHOULD be delayed for at least
24 hours, and no response should be attempted if the message has been
cancelled in that time. Also, no response SHOULD be attempted unless
the local part of the destination address is "newsmap". News
administrators SHOULD arrange for mail to "newsmap" on their systems
to be discarded (without reply) unless legitimate use is in progress.
NOTE: Because these messages can cause many, many relayers to send
mail to one person, such messages, specifying mailing to an
innocent person's mailbox, have been forged as a half-witted
Spencer Historic [Page 69]RFC 1849 Son of 1036 March 2010
practical joke. A delay gives administrators time to notice a
fraudulent message and act (by cancelling the message, preparing
to divert the flood of mail into the bit bucket, or both).
Restriction of the destination address to "newsmap" reduces the
appeal of fraud by making it impossible to use it to harass a
normal user. (A site that does NOT discard mail to "newsmap", but
rather bounces it back, may incur higher communications costs than
if the mail had been accepted into a user's mailbox, but a
malicious forger could accomplish this anyway, by using an address
whose local part is very unlikely to be a legitimate mailbox
name.)
NOTE: [RFC1036] did not require the Approved header for these
control messages. This has been added because of the possibility
that cryptographic authentication of Approved headers will become
available.
The body of the reply to a sendsys message SHOULD be of the form:
sendsys-reply = responder 1*sys-line
responder = "Responding-System:" space domain eol
sys-line = relayer-name ":" newsgroup-patterns
[ ":" text ] eol
newsgroup-patterns = newsgroup-name *( "," newsgroup-name )
The first line identifies the responding system, using a syntax
resembling a header (but note that it is part of the BODY).
Remaining lines indicate what newsgroups are sent to what other
systems. The syntax of newsgroup patterns is not well standardized;
the form described is common (often with newsgroup names only
partially given, denoting all names starting with a particular set of
components) but not universal. The whogets message provides a
better-defined alternative.
The reply to a version message is of somewhat ill-defined form, with
a body normally consisting of a single line of text that somehow
describes the version of the relayer software. The whogets message
provides a better-defined alternative.
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The body of the reply to a whogets message MUST be of the form:
whogets-reply = responder-domain responder-relayer
response-date responding-to arrived-via
responder-version whogets-delimiter
*pass-line
responder-domain = "Responding-System:" space domain eol
responder-relayer = "Responding-Relayer:" space relayer-name eol
response-date = "Response-Date:" space date eol
responding-to = "Responding-To:" space message-id eol
arrived-via = "Arrived-Via:" path-list eol
responder-version = "Responding-Version:" space nonblank-text eol
whogets-delimiter = eol
pass-line = relayer-name [ space domain ] eol
The first six lines identify the responding relayer by its Internet
domain name (use of the ".uucp" and ".bitnet" pseudo-domains is
permissible, for registered hosts in them, but discouraged) and its
relayer name; specify the date when the reply was generated and the
message ID of the whogets message being replied to; give the path
list (from the Path header) of the whogets message (which MAY, if
absolutely necessary, be truncated to a convenient length, but MUST
contain at least the leading three relayer names); and indicate the
version of relayer software responding. Note that these lines are
part of the BODY even though their format resembles that of headers.
Despite the apparently fixed order specified by the syntax above,
they can appear in any order, but there must be exactly one of each.
After those preliminaries, and an empty line to unambiguously define
their end, the remaining lines are the relayer names (which MAY be
accompanied by the corresponding domain names, if known) of systems
to which the responding system passes the target newsgroup. Only the
names of news relayers are to be included.
NOTE: It is desirable for a reply to identify its source by both
domain name and relayer name because news propagation is governed
by the latter but location in a broader context is best determined
by the former. The date and whogets message ID should, in
principle, be present in the MAIL headers but are included in the
body for robustness in the presence of uncooperative mail systems.
The reason for the path list is discussed below. Adding version
information eliminates the need for a separate message to gather
it.
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NOTE: The limitation of pass lines to contain only names of news
relayers is meant to exclude names used within a single host (as
identifiers for mail gateways, portions of ihave/sendme
implementations, etc.), which do not actually refer to other
hosts.
A relayer that is unaware of the existence of the target newsgroup
MUST NOT reply to a whogets message at all, although this MUST NOT
influence decisions on whether to pass the article on to other
relayers.
NOTE: While this may result in discontinuous maps in cases where
some hosts have not honored requests for creation of a newsgroup,
it will also prevent a flood of useless responses in the event
that a whogets message intended to map a small region "leaks" out
to a larger one. The possibility of discontinuous recognition of
a newsgroup does make it important that the whogets message itself
continue to propagate (if other criteria permit). This is also
the reason for the inclusion of the whogets message's path list,
or at least the leading portion of it, in the reply: to permit
reconstruction of at least small gaps in maps.
Different networks set different rules for the legitimacy of these
messages, given that they may reveal details of organization-internal
topology that are sometimes considered proprietary.
NOTE: On Usenet, in particular, willingness to respond to these
messages is held to be a condition of network membership: the
topology of Usenet is public information. Organizations wishing
to belong to such networks while keeping their internal topology
confidential might wish to organize their internal news software
so that all articles reaching outsiders appear to be from a single
"gatekeeper" system, with the details of internal topology hidden
behind that system.
UNRESOLVED ISSUE: It might be useful to have a way to set some
sort of hop limit for these.
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7.6. checkgroups
The checkgroups control message contains a supposedly authoritative
list of the valid newsgroups within some subset of the newsgroup name
space:
checkgroups-arguments =
checkgroups-body = [ invalidation ] valid-groups
/ invalidation
invalidation = "!" plain-component
*( "," plain-component ) eol
valid-groups = 1*( description-line eol )
There are no arguments. The body lines (except possibly for an
initial invalidation) each contain a description line for a
newsgroup, as defined under the newgroup message (Section 7.3).
NOTE: Some other, ill-defined, forms of the checkgroups body were
formerly used. See Appendix A.
The checkgroups message applies to all hierarchies containing any of
the newsgroups listed in the body. The checkgroups message asserts
that the newsgroups it lists are the only newsgroups in those
hierarchies. If there is an invalidation, it asserts that the
hierarchies it names no longer contain any newsgroups.
Processing a checkgroups message MAY cause a local list of newsgroup
descriptions to be updated. It SHOULD also cause the local lists of
newsgroups (and their moderation statuses) in the mentioned
hierarchies to be checked against the message. The results of the
check MAY be used for automatic corrective action or MAY be reported
to the news administrator in some way.
NOTE: Automatically updating descriptions of existing newsgroups
is relatively safe. In the case of newsgroup additions or
deletions, simply notifying the administrator is generally the
wisest action, unless perhaps the message can be determined to
have originated within a cooperating subnet whose members are
considered trustworthy.
NOTE: There is a problem with the checkgroups concept: not all
newsgroups in a hierarchy necessarily propagate to the same set of
machines. (Notably, there is a set of newsgroups known as the
"inet" newsgroups, which have relatively limited distribution but
coexist in several hierarchies with more widely distributed
newsgroups.) The advice of checkgroups should always be taken
with a grain of salt and should never be followed blindly.
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8. Transmission Formats
While this Draft does not specify transmission methods, except to
place a few constraints on them, there are some data formats used
only for transmission that are unique to news.
8.1. Batches
For efficient bulk transmission and processing of news articles, it
is often desirable to transmit a number of them as a single block of
data, i.e., a "batch". The format of a batch is:
batch = 1*( batch-header article )
batch-header = "#! rnews " article-size eol
article-size = 1*digit
A batch is a sequence of articles, each prefixed by a header line
that includes its size. The article size is a decimal count of the
octets in the article, counting each EOL as one octet regardless of
how it is actually represented.
NOTE: A relayer might wish to accept either a single article or a
batch as input. Since "#" cannot appear in a header name,
examination of the first octet of the input will reveal its
nature.
NOTE: In the header line, there is exactly one blank before
"rnews", there is exactly one blank after "rnews", and the EOL
immediately follows the article size. Beware that some software
inserts non-standard trash after the size.
NOTE: Despite the similarity of this format to the executable-
script format used by some operating systems, it is EXTREMELY
unwise to just feed incoming batches to a command interpreter in
the anticipation that it will run a command named "rnews" to
process the batch. Unless arrangements are made to very tightly
restrict the range of commands that can be executed by this means,
the security implications are disastrous.
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8.2. Encoded Batches
When transmitting news, especially over communications links that are
slow or are billed by the bit, it is often desirable to batch news
and apply data compression to the batches. Transmission links
sending compressed batches SHOULD use out-of-band means of
communication to specify the compression algorithm being used. If
there is no way to send out-of-band information along with a batch,
the following encapsulation for a compressed batch MAY be used:
ec-batch = "#! " compression-keyword eol
compressed-batch
compression-keyword = "cunbatch"
A line containing a keyword indicating the type of compression is
followed by the compressed batch. The only truly widespread
compression keyword at present is "cunbatch", indicating compression
using the widely distributed "compress" program. Other compression
keywords MAY be used by mutual agreement between the hosts involved.
NOTE: An encapsulated compressed batch is NOT, in general, a text
file, despite having an initial text line. This combination of
text and non-text data is often awkward to handle; for example,
standard decompression programs cannot be used without first
stripping off the initial line, and that in turn is painful to do
because many text-handling tools that are superficially suited to
the job do not cope well with non-text data, hence the
recommendation that out-of-band communication be used instead when
possible.
NOTE: For UUCP transmission, where a batch is typically
transmitted by invoking the remote command "rnews" with the batch
as its input stream, a plausible out-of-band method for indicating
a compression type would be to give a compression keyword in an
option to "rnews", perhaps in the form:
rnews -d decompressor
where "decompressor" is the name of a decompression program (e.g.,
"uncompress" for a batch compressed with "compress" or "gunzip"
for a batch compressed with "gzip"). How this decompression
program is located and invoked by the receiving relayer is
implementation-specific.
NOTE: See the notes in Section 8.1 on the inadvisability of
feeding batches directly to command interpreters.
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NOTE: There is exactly one blank between "#!" and the compression
keyword, and the EOL immediately follows the keyword.
8.3. News within Mail
It is often desirable to transmit news as mail, either for the
convenience of a human recipient or because that is the only type of
transmission available on a restrictive communication path.
Given the similarity between the news format and the MAIL format, it
is superficially attractive to just send the news article as a mail
message. This is typically a mistake: mail-handling software often
feels free to manipulate various headers in undesirable ways (in some
cases, such as Sender, such manipulation is actually mandatory), and
mail transmission problems, etc. MUST be reported to the
administrators responsible for the mail transmission rather than to
the article's author. In general, news sent as mail should be
encapsulated to separate the MAIL headers and the news headers.
When the intended recipient is a human, any convenient form of
encapsulation may be used. Recommended practice is to use MIME
encapsulation with a content type of "message/news", given that news
articles have additional semantics beyond what "message/rfc822"
implies.
NOTE: "message/news" was registered as a standard subtype by IANA
22 June 1993.
When mail is being used as a transmission path between two relayers,
however, a standard method is desirable. Currently the standard
method is to send the mail to an address whose local part is "rnews",
with whatever MAIL headers are necessary for successful transmission.
The news article (including its headers) is sent as the body of the
mail message, with an "N" prepended to each line.
NOTE: The "N" reduces the probability of an innocent line in a
news article being taken as a magic command to mail software and
makes it easy for receiving software to strip off any lines added
by mail software (e.g., the trailing empty line added by some UUCP
mail software).
This method has its weaknesses. In particular, it assumes that the
mail transmission channel can transmit nearly arbitrary body text
undamaged. When mail is being used as a transmission path of last
resort, however, the mail system often has inconvenient preconceived
notions about the format of message bodies. Various ad hoc encoding
schemes have been used to avoid such problems. The recommended
method is to send a news article or batch as the body of a MIME mail
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message, using content type "application/news-transmission" and
MIME's "base64" encoding (which is specifically designed to survive
all known major mail systems).
NOTE: In the process, MIME conventions could be used to fragment
and reassemble an article that is too large to be sent as a single
mail message over a transmission path that restricts message
length. In addition, the "conversions" parameter to the content
type could be used to indicate what (if any) compression method
has been used. Also, the Content-MD5 header [RFC1544] can be used
as a "checksum" to provide high confidence of detecting accidental
damage to the contents.
UNRESOLVED ISSUE: The "conversions" parameter no longer exists.
What should be done about this, if anything?
NOTE: It might look tempting to use a content type such as
"message/X-netnews", but MIME bans non-trivial encodings of the
entire body of messages with content type "message". The intent
is to avoid obscuring nested structure underneath encodings. For
inter-relayer news transmission, there is no nested structure of
interest, and it is important that the entire article (including
its headers, not just its body) be protected against the vagaries
of intervening mail software. This situation appears to fit the
MIME description of circumstances in which "application" is the
proper content type.
NOTE: "application/news-transmission", with a "conversions"
parameter, was registered as a standard subtype by IANA
22 June 1993.
UNRESOLVED ISSUE: The "conversions" parameter no longer exists in
MIME. What should we do about this?
8.4. Partial Batches
UNRESOLVED ISSUE: The existing batch conventions assemble
(potentially) many articles into one batch. Handling very large
articles would be substantially less troublesome if there was also
a fragmentation convention for splitting a large article into
several batches. Is this worth defining at this time?
9. Propagation and Processing
Most aspects of news propagation and processing are implementation-
specific. The basic propagation algorithms, and certain details of
how they are implemented, nevertheless need to be standard.
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There are two important principles that news implementors (and
administrators) need to keep in mind. The first is the well-known
Internet Robustness Principle:
Be liberal in what you accept, and conservative in what you send.
However, in the case of news there is an even more important
principle, derived from a much older code of practice, the
Hippocratic Oath (we will thus call this the Hippocratic Principle):
First, do no harm.
It is VITAL to realize that decisions that might be merely suboptimal
in a smaller context can become devastating mistakes when amplified
by the actions of thousands of hosts within a few hours.
9.1. Relayer General Issues
Relayers MUST NOT alter the content of articles unnecessarily. Well-
intentioned attempts to "improve" headers, in particular, typically
do more harm than good. It is necessary for a relayer to prepend its
own name to the Path content (see Section 5.6) and permissible for it
to rewrite or delete the Xref header (see Section 6.12). Relayers
MAY delete the thoroughly obsolete headers described in Appendix A.3,
although this behavior no longer seems useful enough to encourage.
Other alterations SHOULD be avoided at all costs, as per the
Hippocratic Principle.
NOTE: As discussed in Section 2.3, tidying up the headers of a
user-prepared article is the job of the posting agent, not the
relayer. The relayer's purpose is to move already-compliant
articles around efficiently without damaging them. Note that in
existing implementations, specific programs may contain both
posting-agent functions and relayer functions. The distinction is
that posting-agent functions are invoked only on articles posted
by local posters, never on articles received from other relayers.
NOTE: A particular corollary of this rule is that relayers should
not add headers unless truly necessary. In particular, this is
not SMTP; do not add Received headers.
Relayers MUST NOT pass non-conforming articles on to other relayers,
except perhaps in a cooperating subnet that has agreed to permit
certain kinds of non-conforming behavior. This is a direct
consequence of the Internet Robustness Principle.
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The two preceding paragraphs may appear to be in conflict. What is
to be done when a non-conforming article is received? The Robustness
Principle argues that it should be accepted but must not be passed on
to other relayers while still non-conforming, and the Hippocratic
Principle strongly discourages attempts at repair. The conclusion
that this appears to lead to is correct: a non-conforming article MAY
be accepted for local filing and processing, or it MAY be discarded
entirely, but it MUST NOT be passed on to other relayers.
A relayer MUST NOT respond to the arrival of an article by sending
mail to any destination, other than a local administrator, except by
explicit prearrangement with the recipient. Neither posting an
article (other than certain types of control messages; see
Section 7.5) nor being the moderator of a moderated newsgroup
constitutes such prearrangement. UNDER NO CIRCUMSTANCES WHATSOEVER
may a relayer attempt to send mail to either an article's originator
or a moderator.
NOTE: Reporting apparent errors in message composition is the job
of a posting agent, not a relayer. The same is true of mailing
moderated-newsgroup postings to moderators. In networks of
thousands of cooperating relayers, it is simply unacceptable for
there to be any circumstance whatsoever that causes any
significant fraction of them to simultaneously send mail to the
same destination. (Some control messages are exceptions, although
perhaps ill-advised ones.) What might, in a smaller network, be a
useful notification or forwarding becomes a deluge of nearly
identical messages that can bring mail software to its knees and
severely inconvenience recipients. Moderators, in particular,
historically have suffered grievously from this.
Notification of problems in incoming articles MAY go to local
administrators, or at most (by prearrangement!) to the
administrators of the neighboring relayer(s) that passed on the
problematic articles.
NOTE: It would be desirable to notify the author that his posting
is not propagating as he expects. However, there is no known
method for doing this that will scale up gracefully. (In
particular, "notify only if within N relayers of the originator"
falls down in the presence of commercial news services like UUNET:
there may be hundreds or thousands of relayers within a couple of
hops of the originator.) The best that can be done right now is
to notify neighbors, in hopes that the word will eventually
propagate up the line, or organize regional monitoring at major
hubs.
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If it is necessary to alter an article, e.g., translate it to another
character set or alter its EOL representation, strenuous efforts
should be made to ensure that such transformations are reversible,
and that relayers or other software that might wish to reverse them
know exactly how to do so.
NOTE: For example, a cooperating subnet that exchanges articles
using a non-ASCII character set like EBCDIC should define a
standard, reversible ASCII-EBCDIC mapping and take pains to see
that it is used at all points where the subnet meets the outside.
If the only reason for using EBCDIC is that the readers typically
employ EBCDIC devices, it would be more robust to employ ASCII as
the interchange format and do the transformation in the reading
and posting agents.
9.2. Article Acceptance and Propagation
When a relayer first receives an article, it must decide whether to
accept it. (This applies regardless of whether the article arrived
by itself or as part of a batch, and in principle regardless of
whether it originated as a local posting or as traffic from another
relayer.) In a cooperating subnet with well-controlled propagation
paths, some of the tests specified here MAY be delegated to centrally
located relayers; that is, relayers that can receive news ONLY via
one of the central relayers might simplify acceptance testing based
on the assumption that incoming traffic has already passed the full
set of tests at a central relayer.
The wording that follows is based on a model in which articles arrive
on a relayer's host before acceptance tests are done. However,
depending on the degree of integration of the transport mechanisms
and the relayer, some or all of these tests MAY be done before the
article is actually transmitted, so that articles that definitely
will not be accepted need not be transmitted at all.
The wording that follows also specifies a particular order for the
acceptance tests. While this order is the obvious one, the tests MAY
be done in any order.
First, the relayer MUST verify that the article is a legal news
article, with all mandatory headers present with legal contents.
NOTE: This check in principle is done by the first relayer to see
an article, so an article received from another relayer should
always be legal, but there is enough old software still
operational that this cannot be taken for granted; see the
discussion of the Internet Robustness Principle in Section 9.1.
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Second, the relayer MUST determine whether it has already seen this
article (identified by its message ID). This is normally done by
retaining a history of all article message IDs seen in the last
N days, where the value of N is decided by the relayer's
administrator but SHOULD be at least 7. Since N cannot practically
be infinite, articles whose Date content indicates that they are
older than N days are declared "stale" and are deemed to have been
seen already.
NOTE: This check is important because news propagation topology is
typically redundant, often highly so, and it is not at all
uncommon for a relayer to receive the same article from several
neighbors. The history of already-seen message IDs can get quite
large, hence, the desire to limit its length, but it is important
that it be long enough that slowly propagating articles are not
classed as stale. News propagation within the Internet is
normally very rapid, but when UUCP links are involved, end-to-end
delays of several days are not rare, so a week is not a
particularly generous minimum.
NOTE: Despite generally more rapid propagation in recent times, it
is still not unheard of for some propagation paths to be very
slow. This can introduce the possibility of old articles arriving
again after they are gone from the history, hence the "stale"
rule.
Third, the relayer MUST determine whether any of the article's
newsgroups are "subscribed to" by the host, i.e., fit a description
of what hierarchies or newsgroups the site wants to receive.
NOTE: This check is significant because information on what
newsgroups a relayer wishes to receive is often stored at its
neighbors, who may not have up-to-date information or may simplify
the rules for implementation reasons. As a hedge against the
possibility of missed or delayed newgroup control messages,
relayers may wish to observe a notion of a newsgroup subscription
that is independent of the list of newsgroups actually known to
the relayer. This would permit reception and relaying of articles
in newsgroups that the relayer is not (yet) aware of, subject to
more general criteria indicating that they are likely to be of
interest.
Once an article has been accepted, it may be passed on to other
relayers. The fundamental news propagation rule is a flooding
algorithm: on receiving and accepting an article, send it to all
neighboring relayers not already in its path list that are sent its
newsgroup(s) and distribution(s).
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NOTE: The path list's role in loop prevention may appear
relatively unimportant, given that looping articles would
typically be rejected as duplicates anyway. However, the path
list's role in preventing superfluous transmissions is not
trivial. In particular, the path list is the only thing that
prevents relayer X, on receiving an article from relayer Y, from
sending it back to Y again. (Indeed, the usual symptom of
confusion about relayer names is that incoming news loops back in
this manner.) The looping articles would be rejected as
duplicates, but doubling the communications load on every news
transmission path is not to be taken lightly!
In general, relayers SHOULD NOT make propagation decisions by
"anticipation": relayer X, noting that the article's path list
already contains relayer Y, decides not to send it to relayer Z
because X anticipates that Z will get the article by a better path.
If that is generally true, then why is there a news feed from X to Z
at all? In fact, the "better path" may be running slowly or may be
down. News propagation is very robust precisely because some
redundant transmission is done "just in case". If it is imperative
to limit unnecessary traffic on a path, use of NNTP [RFC977] or
ihave/sendme (see Section 7.2) to pass articles only when necessary
is better than arbitrary decisions not to pass articles at all.
Anticipation is occasionally justified in special cases. Such cases
should involve both (1) a cooperating subnet whose propagation paths
are well-understood and well-monitored, with failures and slowdowns
noticed and dealt with promptly, and (2) a persistent pattern of
heavy unnecessary traffic on a path that is either slow or costly.
In addition, there should be some reason why neither NNTP nor
ihave/sendme is suitable as a solution to the problem.
9.3. Administrator Contact
It is desirable to have a standardized contact address for a
relayer's administrators, in the spirit of the "postmaster" address
for mail administrators. Mail addressed to "newsmaster" on a
relayer's host MUST go to the administrator(s) of that relayer. Mail
addressed to "usenet" on the relayer's host SHOULD be handled
likewise. Mail addressed to either address on other hosts using the
same news database SHOULD be handled likewise.
NOTE: These addresses are case-sensitive, although it would be
desirable for sequences equivalent to them using case-insensitive
comparison to be handled likewise. While "newsmaster" seems the
preferred network-independent address, by analogy to "postmaster",
there is an existing practice of using "usenet" for this purpose,
Spencer Historic [Page 82]RFC 1849 Son of 1036 March 2010
and so "usenet" should be supported if at all possible (especially
on hosts belonging to Usenet!). The address "news" is also
sometimes used for purposes like this, but less consistently.
10. Gatewaying
Gatewaying of traffic between news networks using this Draft and
those using other exchange mechanisms can be useful but must be done
cautiously. Gateway administrators are taking on significant
responsibilities and must recognize that the consequences of error
can be quite serious.
10.1. General Gatewaying Issues
This section will primarily address the problems of gatewaying
traffic INTO news networks. Little can be said about the other
direction without some specific knowledge of the network(s) involved.
However, the two issues are not entirely independent: if a non-news
network is gatewayed into a news network at more than one point,
traffic injected into the non-news network by one gateway may appear
at another as a candidate for injection back into the news network.
This raises a more general principle, the single most important issue
for gatewaying:
Above all, prevent loops.
The normal loop prevention of news transmission is vitally dependent
on the Message-ID header. Any gateway that finds it necessary to
remove this header, alter it, or supersede it (by moving it into the
body) MUST take equally effective precautions against looping.
NOTE: There are few things more effective at turning news readers
into a lynch mob than a malfunctioning gateway, or pair of
gateways, that takes in news articles, mangles them just enough to
prevent news relayers from recognizing them as duplicates, and
regurgitates them back into the news stream. This happens rather
too often.
Gateway implementors should realize that gateways have all of the
responsibilities of relayers, plus the added complications introduced
by transformations between different information formats. Much of
the discussion in Section 9 about relayer issues is relevant to
gateways as well. In particular, gateways SHOULD keep a history of
recently seen articles, as described in Section 9.2, and not assume
that articles will never reappear. This is particularly important
for networks that have their own concept analogous to message IDs: a
gateway should keep a history of traffic seen from BOTH directions.
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If at all possible, articles entering the non-news network SHOULD be
marked in some way so that they will NOT be re-gatewayed back into
news. Multiple gateways obviously must agree on the marking method
used; if it is done by having them know each others' names, name
changes MUST be coordinated with great care. If marking cannot be
done, all transformations MUST be reversible so that a re-gatewayed
article is identical to the original (except perhaps for a longer
Path header).
Gateways MUST NOT pass control messages (articles containing Control,
Also-Control, or Supersedes headers) without removing the headers
that make them control messages, unless there are compelling reasons
to believe that they are relevant to both sides and that conventions
are compatible. If it is truly desirable to pass them unaltered,
suitable precautions MUST be taken to ensure that there is NO
POSSIBILITY of a looping control message.
NOTE: The damage done by looping articles is multiplied a
thousandfold if one of the affected articles is something like a
sendsys message (see Section 7.5) that requests multiple automatic
replies. Most gateways simply should not pass control messages at
all. If some unusual reason dictates doing so, gateway
implementors and administrators are urged to consider bulletproof
rate-limiting measures for the more destructive ones like sendsys,
e.g., passing only one per hour no matter how many are offered.
Gateways, like relayers, SHOULD make determined efforts to avoid
mangling articles unnecessarily. In the case of gateways, some
transformations may be inevitable, but keeping them to a minimum and
ensuring that they are reversible is still highly desirable.
Gateways MUST avoid destroying information. In particular, the
restrictions of Section 4.2.2 are best taken with a grain of salt in
the context of gateways. Information that does not translate
directly into news headers SHOULD be retained, perhaps in "X-"
headers, both because it may be of interest to sophisticated readers
and because it may be crucial to tracing propagation problems.
Gateway implementors should take particular note of the discussion of
mailed replies, or more precisely the ban on same, in Section 9.1.
Gateway problems MUST be reported to the local administration, not to
the innocent originator of traffic. "Gateway problems" here includes
all forms of propagation anomaly on the non-news side of the gateway,
e.g., unreachable addresses on a mailing list. Note that this
requires consideration of possible misbehavior of "downstream" hosts,
not just the gateway host.
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10.2. Header Synthesis
News articles prepared by gateways MUST be legal news articles. In
particular, they MUST include all of the mandatory headers (see
Section 5) and MUST fully conform to the restrictions on said
headers. This often requires that a gateway function not only as a
relayer but also partly as a posting agent, aiding in the synthesis
of a conforming article from non-conforming input.
NOTE: The full-conformance requirement needs particularly careful
attention when gatewaying mailing lists to news, because a number
of constructs that are legal in MAIL headers are NOT permissible
in news headers. (Note also that not all mail traffic fully
conforms to even the MAIL specification.) The rest of this
section will be phrased in terms of mail-to-news gatewaying, but
most of it is more generally applicable.
The mandatory headers generally present few problems.
If no date information is available, the gateway should supply a Date
header with the gateway's current date. If only partial information
is available (e.g., date but not time), this should be fleshed out to
a full Date header by adding default values, not by mixing in parts
of the gateway's current date. (Defaults should be chosen so that
fleshed-out dates will not be in the future!) It may be necessary to
map time zone information to the restricted forms permitted in the
news Date header. See Section 5.1.
NOTE: The prohibition of mixing dates is on the theory that it is
better to admit ignorance than to lie.
If the author's address as supplied in the original message is not
suitable for inclusion in a From header, the gateway MUST transform
it so it is (for example, by use of the "% hack" and the domain
address of the gateway). The desire to preserve information is NOT
an excuse for violating the rules. If the transformation is drastic
enough that there is reason to suspect loss of information, it may be
desirable to include the original form in an "X-" header, but the
From header's contents MUST be as specified in Section 5.2.
If the message contains a Message-ID header, the contents should be
dealt with as discussed in Section 10.3. If there is no message ID
present, it will be necessary to synthesize one, following the news
rules (see Section 5.3).
Every effort should be made to produce a meaningful Subject header;
see Section 5.4. Many news readers select articles to read based on
Subject headers, and inserting a placeholder like "<no subject
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available>" is considered highly objectionable. Even synthesizing a
Subject header by picking out the first half-dozen nouns and
adjectives in the article body is better than using a placeholder,
since it offers SOME indication of what the article might contain.
The contents of the Newsgroups header (Section 5.5) are usually
predetermined by gateway configuration, but a gateway to a network
that has its own concept of newsgroups or discussions might have to
make transformations. Such transformations should be reversible;
otherwise, confusion is likely on both sides.
It will rarely be possible for gateways to provide a Path header that
is both an accurate history of the relayers the article has passed
through AS NEWS and a usable reply address. The history function
MUST be given priority; see the discussion in Section 5.6. It will
usually be necessary for a gateway to supply an empty path list,
abandoning the reply function.
It is desirable for gatewayed articles to convey as much useful
information as possible, e.g., by use of optional news headers (see
Section 6) when the relevant information is available. Synthesis of
optional headers can generally follow similar rules.
Software synthesizing References headers should note the discussion
in Section 6.5 concerning the incompatibility between MAIL and news.
Also of interest is the possibility of incorporating information from
In-Reply-To headers and from attribution lines in the body; an
incomplete or somewhat conjectural References header is much better
than none at all, and reading agents already have to cope with
incomplete or slightly erroneous References lists.
10.3. Message ID Mapping
This section, like the previous one, is phrased in terms of mail
being gatewayed into news, but most of the discussion should be more
generally applicable.
A particularly sticky problem of gatewaying mail into news is
supplying legal news message IDs. Note, in particular, that not all
MAIL message IDs are legal in news; the news syntax (specified in
Section 5.3, with related material in Section 5.2) is more
restrictive. Generating a fully conforming news article from a mail
message may require transforming the message ID somewhat.
Generation and transformation of message IDs assumes particular
importance if a given mailing list (or whatever) is being handled by
more than one gateway. It is highly desirable that the same article
contents not appear twice in the same newsgroup, which requires that
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RFC 1849 Son of 1036 March 2010
they receive the same message ID from all gateways. Gateways SHOULD
use the following algorithm (possibly modified by the later
discussion of gatewaying into more than one newsgroup) unless local
considerations dictate another:
1. Separate message ID from surroundings, if necessary. A
plausible method for this is to start at the first "<", end at
the next ">", and reject the message if no ">" is found or a
second "<" is seen before the ">". Also reject the message if
the message ID contains no "@" or more than one "@", or if it
contains no ".". Also reject the message if the message ID
contains non-ASCII characters, ASCII control characters, or
white space.
NOTE: Any legitimate domain will include at least one ".".
[RFC822], Section 6.2.2, forbids white space in this context
when passing mail on to non-MAIL software.
2. Delete the leading "<" and trailing ">". Separate message ID
into local part and domain at the "@".
3. In both components, transliterate leading dots (".", ASCII 46),
trailing dots, and dots after the first in sequences of two or
more consecutive dots, into underscores (ASCII 95).
4. In both components, transliterate disallowed characters other
than dots (see the definition of <unquoted-char> in
Section 5.2) to underscores (ASCII 95).
5. Form the message ID as
"<" local-part "@" domain ">"
NOTE: This algorithm is approximately that of Rich Salz's
successful gatewaying package.
Despite the desire to keep message IDs consistent across multiple
gateways, there is also a more subtle issue that can require a
different approach. If the same articles are being gatewayed into
more than one newsgroup, and it is not possible to arrange that all
gateways gateway them to the same cross-posted set of newsgroups,
then the message IDs in the different newsgroups MUST be DIFFERENT.
NOTE: Otherwise, arrival of an article in one newsgroup will
prevent it from appearing in another, and which newsgroup a
particular article appears in will be an accident of which
direction it arrives from first. It is very difficult to maintain
a coherent discussion when each participant sees a randomly
Spencer Historic [Page 87]RFC 1849 Son of 1036 March 2010
selected 50% of the traffic. The fundamental problem here is that
the basic assumption behind message IDs is being violated: the
gateways are assigning the same message ID to articles that differ
in an important respect (Newsgroups header).
In such cases, it is suggested that the newsgroup name, or an agreed-
on abbreviation thereof, be prepended to the local part of the
message ID (with a separating ".") by the gateway. This will ensure
that multiple gateways generate the same message ID, while also
ensuring that different newsgroups can be read independently.
NOTE: It is preferable to have the gateway(s) cross-post the
article, avoiding the issue altogether, but this may not be
feasible, especially if one newsgroup is widespread and the other
is purely local.
10.4. Mail to and from News
Gatewaying mail to news, and vice versa, is the most obvious form of
news gatewaying. It is common to set up gateways between news and
mail rather too casually.
It is hard to go very wrong in gatewaying news into a mailing list,
except for the non-trivial matter of making sure that error reports
go to the local administration rather than to the authors of news
articles. (This requires attention to the "envelope address" as well
as to the message headers.) Doing the reverse connection correctly
is much harder than it looks.
NOTE: In particular, just feeding the mail message to "inews -h"
or the equivalent is NOT, repeat NOT, adequate to gateway mail to
news. Significant gatewaying software is necessary to do it
right. Not all headers of mail messages conform to even the MAIL
specifications, never mind the stricter rules for news.
It is useful to distinguish between two different forms of
mail-to-news gatewaying: gatewaying a mailing list into a newsgroup,
and operating a "post-by-mail" service in which individual articles
can be posted to a newsgroup by mailing them to a specific address.
In the first case, the message is already being "broadcast", and the
situation can be viewed as gatewaying one form of news into another.
The second case is closer to that of a moderator posting submissions
to a moderated newsgroup.
In either case, the discussions in the preceding two sections are
relevant, as is the Hippocratic Principle of Section 9. However,
some additional considerations are specific to mail-to-news
gatewaying.
Spencer Historic [Page 88]RFC 1849 Son of 1036 March 2010
As mentioned in Section 6, point-to-point headers like To and Cc
SHOULD NOT appear as such in news, although it is suggested that they
be transformed to "X-" headers, e.g., X-To and X-Cc, to preserve
their information content for possible use by readers or
troubleshooters. The Received header is entirely specific to MAIL
and SHOULD be deleted completely during gatewaying, except perhaps
for the Received header supplied by the gateway host itself.
The Sender header is a tricky case, one where mailing-list and post-
by-mail practice should differ. For gatewaying mailing lists, the
mailing-list host should be considered a relayer, and the From and
Sender headers supplied in its transmissions left strictly untouched.
For post-by-mail, as for a moderator posting a mailed submission, the
Sender header should reflect the poster rather than the author. If a
post-by-mail gateway receives a message with its own Sender header,
it might wish to preserve the content in an X-Sender header.
It will generally be necessary to transform between mail's
In-Reply-To/References convention and news's References/See-Also
convention, to preserve correct semantics of cross references. This
also requires attention when going the other way, from news to mail.
See the discussion of the difference in Section 6.5.
10.5. Gateway Administration
Any news system will benefit from an attentive administrator,
preferably assisted by automated monitoring for anomalies. This is
particularly true of gateways. Gateway software SHOULD be
instrumented so that unusual occurrences, such as sudden massive
surges in traffic, are reported promptly. It is desirable, in fact,
to go further: gateway software SHOULD endeavor to limit damage in
the event that the administrator does not respond promptly.
NOTE: For example, software might limit the gatewaying rate by
queueing incoming traffic and emptying the queue at a finite
maximum rate (well below the maximum that the host is capable of!)
that is set by the administrator and is not raised automatically.
Traffic gatewayed into a news network SHOULD include a suitable
header, perhaps X-Gateway-Administrator, giving an electronic address
that can be used to report problems. This SHOULD be an address that
goes directly to a human, and not to a "routine administrative
issues" mailbox that is examined only occasionally, since the point
is to be able to reach the administrator quickly in an emergency.
Gateway administrators SHOULD arrange substitutes to cover gateway
operation (with suitable redirection of mail) when they are on
vacation, etc.
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11. Security and Related Issues
Although the interchange format itself raises no significant security
issues, the wider context does.
11.1. Leakage
The most obvious form of security problem with news is "leakage" of
articles that are intended to have only restricted circulation. The
flooding algorithm is EXTREMELY good at finding any path by which
articles can leave a subnet with supposedly restrictive boundaries.
Substantial administrative effort is required to ensure that local
newsgroups remain local, unless connections to the outside world are
tightly restricted.
A related problem is that the sendme control message can be used to
ask for any article by its message ID. The usefulness of this has
declined as message-ID generation algorithms have become less
predictable, but it remains a potential problem for "secure"
newsgroups. Hosts with such newsgroups may wish to disable the
sendme control message entirely.
The sendsys, version, and whogets control messages also allow
"outsiders" to request information from "inside", which may reveal
details of internal topology (etc.) that are considered
confidential. (Note that at least limited openness about such
matters may be a condition of membership in such networks, e.g.,
Usenet.)
Organizations wishing to control these forms of leakage are strongly
advised to designate a small number of "official gateway" hosts to
handle all news exchange with the outside world, so that a bounded
amount of administrative effort is needed to control propagation and
eliminate problems. Attempts to keep news out entirely, by refusing
to support an official gateway, typically result in large numbers of
unofficial partial gateways appearing over time. Such a
configuration is much more difficult to troubleshoot.
A somewhat related problem is the possibility of proprietary material
being disclosed unintentionally by a poster who does not realize how
far his words will propagate, either from sheer misunderstanding or
because of errors made (by human or software) in followup
preparation. There is little that can be done about this except
education.
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11.2. Attacks
Although the limitations of the medium restrict what can be done to
attack a host via news, some possibilities exist, most of them
problems news shares with mail.
If reading agents are careless about transmitting non-printable
characters to output devices, malicious posters may post articles
containing control sequences ("letterbombs") meant to have various
destructive effects on output devices. Possible effects depend on
the device, but they can include hardware damage (e.g., by repeated
writing of values into configuration memories that can tolerate only
a limited number of write cycles) and security violation (e.g., by
reprogramming function keys potentially used by privileged readers).
A more sophisticated variation on the letterbomb is inclusion of
"Trojan horses" in programs. Obviously, readers must be cautious
about using software found in news, but more subtly, reading agents
must also exercise care. MIME messages can include material that is
executable in some sense, such as PostScript documents (which are
programs!), and letterbombs may be introduced into such material.
Given the presence of finite resources and other software
limitations, some degree of system disruption can be achieved by
posting otherwise-innocent material in great volume, either in single
huge articles (see Section 4.6) or in a stream of modest-sized
articles. (Some would say that the steady growth of Usenet volume
constitutes a subtle and unintentional attack of the latter type;
certainly it can have disruptive effects if administrators are
inattentive.) Systems need some ability to cope with surges, because
single huge articles occur occasionally as the result of software
error, innocent misunderstanding, or deliberate malice; and downtime
at upstream hosts can cause droughts, followed by floods, of
legitimate articles. (There is also a certain amount of normal
variation; for example, Usenet traffic is noticeably lighter on
weekends and during Christmas holidays, and rises noticeably at the
start of the school term of North American universities.) However, a
site that normally receives little traffic may be quite vulnerable to
"swamping" attack if its software is insufficiently careful.
In general, careless implementation may open doors that are not
intrinsic to news. In particular, implementation of control messages
(see Sections 6.6 and 7) and unbatchers (see Sections 8.1 and 8.2)
via a command interpreter requires substantial precautions to ensure
that only the intended capabilities are available. Care must also be
taken that article-supplied text is not fed to programs that have
escapes to command interpreters.
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Finally, there is considerable potential for malice in the sendsys,
version, and whogets control messages. They are not harmful to the
hosts receiving them as news, but they can be used to enlist those
hosts (by the thousands) as unwitting allies in a mail-swamping
attack on a victim who may not even receive news. The precautions
discussed in Section 7.5 can reduce the potential for such attacks
considerably, but the hazard cannot be eliminated as long as these
control messages exist.
11.3. Anarchy
The highly distributed nature of news propagation, and the lack of
adequate authentication protocols (especially for use over the less-
interactive transport mechanisms such as UUCP), make article forgery
relatively straightforward. It may be possible to at least track a
forgery to its source, once it is recognized as such, but clever
forgers can make even that relatively difficult. The assumption that
forgeries will be recognized as such is also not to be taken for
granted; readers are notoriously prone to blindly assuming
authenticity. If a forged article's initial path list includes the
relayer name of the supposed poster's host, the article will never be
sent to that host, and the alleged author may learn about the forgery
secondhand or not at all.
A particularly noxious form of forgery is the forged "cancel" control
message. Notably, it is relatively straightforward to write software
that will automatically send out a (forged) cancel message for any
article meeting some criterion, e.g., written by a specific author.
The authentication problems discussed in Section 7.1 make it
difficult to solve this without crippling cancel's important
functionality.
A related problem is the possibility of disagreements over newsgroup
creation, on networks where such things are not decided by central
authorities. There have been cases of "rmgroup wars", where one
poster persistently sends out newgroup messages to create a newsgroup
and another, equally persistently, sends out rmgroup messages asking
that it be removed. This is not particularly damaging, if relayers
are configured to be cautious, but it can cause serious confusion
among innocent third parties who just want to know whether or not
they can use the newsgroup for communication.
11.4. Liability
News shares the legal uncertainty surrounding other forms of
electronic communication: what rules apply to this new medium of
information exchange? News is a particularly problematic case
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because it is a broadcast medium rather than a point-to-point one
like mail, and analogies to older forms of communication are
particularly weak.
Are news-carrying hosts common carriers, like the phone companies,
providing communications paths without having either authority over
or responsibility for content? Or are they publishers, responsible
for the content regardless of whether they are aware of it or not?
Or something in between? Such questions are particularly significant
when the content is technically criminal, e.g., some types of
sexually oriented material in some jurisdictions, in which case
ignorance of its presence may not be an adequate defense.
Even in milder situations such as libel or copyright violation, the
responsibilities of the poster, his host, and other hosts carrying
the traffic are unclear. Note, in particular, the problems arising
when the article is a forgery, or when the alleged author claims it
is a forgery but cannot prove this.
12. References
[ISO/IEC9899] "Information technology - Programming Language C",
ISO/IEC 9899:1990 {more recently 9899:1999}, 1990.
[Metamail] Borenstein, N.,
<http://ftp.funet.fi/pub/unix/mail/metamail/ANNOUNCE>,
February 1994.
[RFC821] Postel, J., "Simple Mail Transfer Protocol", STD 10,
RFC 821, August 1982.
[RFC822] Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET
TEXT MESSAGES", STD 11, RFC 822, August 1982.
[RFC850] Horton, M., "Standard for interchange of Usenet
messages", RFC 850, June 1983.
[RFC977] Kantor, B. and P. Lapsley, "Network News Transfer
Protocol - A Proposed Standard for the Stream-Based
Transmission of News", RFC 977, February 1986.
[RFC1036] Horton, M. and R. Adams, "Standard for interchange of
USENET Messages", RFC 1036, December 1987.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
October 1989.
Spencer Historic [Page 93]RFC 1849 Son of 1036 March 2010
[RFC1341] Borenstein, N. and N. Freed, "MIME (Multipurpose
Internet Mail Extensions): Mechanisms for Specifying
and Describing the Format of Internet Message Bodies",
RFC 1341, June 1992.
[RFC1342] Moore, K., "Representation of Non-ASCII Text in
Internet Message Headers", RFC 1342, June 1992.
[RFC1345] Simonsen, K., "Character Mnemonics and Character
Sets", RFC 1345, June 1992.
[RFC1413] St. Johns, M., "Identification Protocol", RFC 1413,
February 1993.
[RFC1456] Vietnamese Standardization Working Group, "Conventions
for Encoding the Vietnamese Language", RFC 1456,
May 1993.
[RFC1544] Rose, M., "The Content-MD5 Header Field", RFC 1544,
November 1993.
[RFC1896] Resnick, P. and A. Walker, "The text/enriched MIME
Content-type", RFC 1896, February 1996.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part One: Format of Internet
Message Bodies", RFC 2045, November 1996.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types",
RFC 2046, November 1996.
[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
Extensions) Part Three: Message Header Extensions for
Non-ASCII Text", RFC 2047, November 1996.
[RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet
Mail Extensions (MIME) Part Five: Conformance Criteria
and Examples", RFC 2049, November 1996.
[RFC2822] Resnick, P., Ed., "Internet Message Format", RFC 2822,
April 2001.
[RFC3977] Feather, C., "Network News Transfer Protocol (NNTP)",
RFC 3977, October 2006.
Spencer Historic [Page 94]RFC 1849 Son of 1036 March 2010
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
[RFC5536] Murchison, K., Ed., Lindsey, C., and D. Kohn, "Netnews
Article Format", RFC 5536, November 2009.
[RFC5537] Allbery, R., Ed., and C. Lindsey, "Netnews
Architecture and Protocols", RFC 5537, November 2009.
[Sanderson] David Sanderson, Smileys, O'Reilly & Associates Ltd.,
1993.
[UUCP] Tim O'Reilly and Grace Todino, Managing UUCP and
Usenet, O'Reilly & Associates Ltd., January 1992.
[X3.4] "American National Standard for Information Systems -
Coded Character Sets - 7-Bit American National
Standard Code for Information Interchange (7-Bit
ASCII)", ANSI X3.4, March 1986.
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Appendix A. Archaeological Notes
A.1. "A News" Article Format
The obsolete "A News" article format consisted of exactly five lines
of header information, followed by the body. For example:
Aeagle.642
news.misc
cbosgd!mhuxj!mhuxt!eagle!jerry
Fri Nov 19 16:14:55 1982
Usenet Etiquette - Please Read
body
body
body
The first line consisted of an "A" followed by an article ID
(analogous to a message ID and used for similar purposes). The
second line was the list of newsgroups. The third line was the path.
The fourth was the date, in the format above (all fields fixed
width), resembling an Internet date but not quite the same. The
fifth was the subject.
This format is documented for archaeological purposes only. Do not
generate articles in this format.
A.2. Early "B News" Article Format
This obsolete pseudo-Internet article format, used briefly during the
transition between the A News format and the modern format, followed
the general outline of a MAIL message but with some non-standard
headers. For example:
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
body
body
body
The From header contained the information now found in the Path
header, plus possibly the full name now typically found in the From
header. The Title header contained what is now the Subject content.
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The Posted header contained what is now the Date content. The
Article-I.D. header contained an article ID, analogous to a message
ID and used for similar purposes. The Newsgroups and Expires headers
were approximately as they are now. The Received header contained
the date when the latest relayer to process the article first saw it.
All dates were in the above format, with all fields fixed width,
resembling an Internet date but not quite the same.
This format is documented for archaeological purposes only. Do not
generate articles in this format.
A.3. Obsolete Headers
Early versions of news software following the modern format sometimes
generated headers like the following:
Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP
Posting-Version: version B 2.10 2/13/83; site eagle.UUCP
Date-Received: Friday, 19-Nov-82 16:59:30 EST
Relay-Version contained version information about the relayer that
last processed the article. Posting-Version contained version
information about the posting agent that posted the article. Date-
Received contained the date when the last relayer to process the
article first saw it (in a slightly nonstandard format).
These headers are documented for archaeological purposes only. Do
not generate articles using them.
A.4. Obsolete Control Messages
There once was a senduuname control message, resembling sendsys but
requesting transmission of the list of hosts to which the receiving
host had UUCP connections. This rapidly ceased to be of much use,
and many organizations consider information about their internal
connectivity to be confidential.
Historically, a checkgroups body consisting of one or two lines, the
first of the form "-n newsgroup", caused checkgroups to apply to only
that single newsgroup. This form is documented for archaeological
purposes only; do not use it.
Historically, an article posted to a newsgroup whose name had exactly
three components of which the third was "ctl" signified that article
was to be taken as a control message. The Subject header specified
the actions in the same way the Control header does now. This form
is documented for archaeological purposes only; do not use it; do not
implement it.
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Appendix B. A Quick Tour of MIME
(The editor wishes to thank Luc Rooijakkers; most of this appendix is
a lightly edited version of a summary he kindly supplied.)
MIME (Multipurpose Internet Mail Extensions) is an upward-compatible
set of extensions to [RFC822], currently documented in [RFC2045],
[RFC2046], and [RFC2047]. This appendix summarizes these documents.
See the MIME RFCs for more information; they are very readable.
UNRESOLVED ISSUE: These RFC numbers (here and elsewhere in this
Draft) need updating when the new MIME RFCs come out {now
resolved!}.
MIME defines the following new headers:
MIME-Version
Content-Type
Content-Transfer-Encoding
Content-ID
Content-Description
The MIME-Version header is mandatory for all messages conforming to
the MIME specification and carries the version number of the MIME
specification. Example:
MIME-Version: 1.0
The Content-Type header indicates the content type of the message.
Content types are split into a top-level type and a subtype,
separated by a slash. Auxiliary information can also be supplied,
using an attribute-value notation. Example:
Content-Type: text/plain; charset=us-ascii
(In the absence of a Content-Type header this is in fact the default
content type.)
Important type/subtype combinations are:
text/plain Plain text, possibly in a non-ASCII character
set.
text/enriched A very simple wordprocessor-like language
supporting character attributes (e.g.,
underlining), justification control, and
multiple character sets. (This proposal has
Spencer Historic [Page 98]RFC 1849 Son of 1036 March 2010
gone through several iterations and has
recently split off from the main MIME RFCs
into a separate document [RFC1896].)
message/rfc822 A mail message conforming to a slightly
relaxed version of [RFC822].
message/partial Part of a message (supporting the transparent
splitting and joining of messages when they
are too large to be handled by some transport
agent).
message/external-body A message whose body is external. Possible
access methods include via mail, FTP, local
file, etc.
multipart/mixed A message whose body consists of multiple
parts, possibly of different types, intended
to be viewed in serial order. Each part
looks like an [RFC822] message, consisting of
headers and a body. Most of the [RFC822]
headers have no defined semantics for body
parts.
multipart/parallel Likewise, except that the parts are intended
to be viewed in parallel (on user agents that
support it).
multipart/alternative Likewise, except that the parts are intended
to be semantically equivalent such that the
part that best matches the capabilities of
the environment should be displayed. For
example, a message may include plain-text,
enriched-text, and postscript versions of
some document.
multipart/digest A variant of multipart/mixed especially
intended for message digests (the default
type of the parts is message/rfc822 instead
of text/plain, saving on the number of
headers for the parts).
application/postscript A PostScript document. (PostScript is a
trademark of Adobe.)
Other top-level types exist for still images, audio, and video
samples.
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Some of the above types require the ability to transport binary data.
Since the existing message systems usually do not support this, MIME
provides a Content-Transfer-Encoding header to indicate the kind of
encoding used. The possible encodings are:
7bit No encoding; the data consists of short (less than
1000 characters) lines of 7-bit ASCII data,
delimited by EOL sequences. This is the default
encoding.
8bit Like 7bit, except that bytes with the high-order
bit set may be present. Many transmission paths
are incapable of carrying messages that use this
encoding.
binary No encoding; any sequence of bytes may be present.
Many transmission paths are incapable of carrying
messages that use this encoding.
base64 The data is encoded by representing every group of
3 bytes as 4 characters from the alphabet
"A-Za-z0-9+/", which was chosen for its high
robustness through mail gateways (the alphabet used
by uuencode does not survive ASCII-EBCDIC-ASCII
translations). In the final group of 4 characters,
"=" is used for those characters not representing
data bytes. Line length is limited, and EOLs in
the encoded form are ignored.
quoted-printable Any byte can be represented by a three-character
"=XX" sequence where the X's are uppercase
hexadecimal digits. Bytes representing printable
7-bit US-ASCII characters except "=" may be
represented literally. Tabs and blanks may be
represented literally if not at the end of a line.
Line length is limited, and an EOL preceded by "="
was inserted for this purpose and is not present in
the original.
The base64 and quoted-printable encodings are applied to data in
Internet canonical form, which means that any EOL encoded as anything
but EOL must be an Internet canonical EOL: CR followed by LF.
The Content-Description header allows further description of a body
part, analogous to the use of Subject for messages.
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Finally, the Content-ID header can be used to assign an
identification to body parts, analogous to the assignment of
identifications to messages by Message-ID.
Note that most of these headers are structured header fields, as
defined in [RFC822]. Consequently, comments are allowed in their
values. The following is a legal MIME header:
Content-Type: (a comment) text (yeah) /
plain (and now some params:) ; charset= (guess what)
iso-8859-1 (we don't have iso-10646 yet, pity)
NOTE: Although the MIME specification was developed for mail,
there is nothing precluding its use for news as well. While it
might simplify implementation to restrict the MIME headers
somewhat, in the same way that other news headers (e.g., From) are
restricted subsets of the [RFC822] originals, this would add yet
another divergence between two formats that ought to be as
compatible as possible. In the case of the MIME headers, there is
no body of existing code posing compatibility concerns. A full-
featured MIME reading agent needs a full [RFC822] parser anyway,
to properly handle body parts of types like message/rfc822, so
there is little gain from restricting MIME headers. Adopting the
MIME specification unchanged seems best. However, article-level
MIME headers must still comply with the overall news header syntax
given in Section 4, so that news software that is NOT interested
in MIME need not contain a full [RFC822] parser.
"MIME (Multipurpose Internet Mail Extensions) Part Three: Message
Header Extensions for Non-ASCII Text" [RFC2047] addresses the problem
of non-ASCII characters in headers. An example of a header using the
[RFC2047] mechanism is
From: =?ISO-8859-1?Q?Andr=E9_?= Pirard <PIRARD@vm1.ulg.ac.be>
Such encodings are allowed in selected headers, subject to the
restrictions listed in [RFC2047].
The MIME effort has also produced an RFC defining a Content-MD5
header [RFC1544] containing an MD5-based "checksum" of the contents
of an article or body part, giving high confidence of detecting
accidental modifications to the contents.
The "metamail" software package [Metamail] helps provide MIME support
with minimal changes to mailers and may also be relevant to news
reading agents.
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The PEM (Privacy Enhanced Mail) effort is pursuing analogous
facilities to offer stronger guarantees against malicious
modifications, unauthorized eavesdropping, and forgery. This work
too may be applicable to news, once it is reconciled with MIME (by
efforts now underway).
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Appendix C. Summary of Changes Since RFC 1036
This Draft is much longer than [RFC1036], so there is obviously much
change in content. Much of this is just increased precision and
rigor. Noteworthy changes and additions include:
+ restrictions on article bodies (Section 4.3)
+ all references to MIME facilities
+ size limits on articles
+ precise specification of Date-content syntax
+ message IDs must never be re-used, ever
+ "!" is the only Path delimiter
+ multiple moderators in the Approved header
+ rules on References trimming, and the _-_ mechanism
+ generalization of the Xref rules
+ multiple message IDs in Cancel and Supersedes
+ Also-Control
+ See-Also
+ Article-Names
+ Article-Updates
+ more precise rules for cancellation
+ cancellation authorization based on From, not Sender
+ "unmoderated" and descriptors in newgroup messages
+ restrictive rules on handling of sendsys and version messages
+ the whogets control message
+ precise specification of checkgroups messages
+ compression type preferably specified out-of-band
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+ rules for encapsulating news in MIME mail
+ tighter specification of relayer functioning (Section 9.1)
+ the "newsmaster" contact address
+ rules for gatewaying (Section 10)
+ discussion of security issues (Section 11)
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Appendix D. Summary of Completely New Features
Most of this Draft merely documents existing practice, preferred
versions thereof, or straightforward generalizations of it, but there
are a few outright inventions. These are:
+ the _-_ mechanism for References trimming
+ Also-Control
+ See-Also
+ Article-Names
+ Article-Updates
+ the whogets control message
Spencer Historic [Page 105]RFC 1849 Son of 1036 March 2010
Appendix E. Summary of Differences from RFCs 822 and 1123
The following are noteworthy differences between this Draft's
articles and MAIL messages:
+ generally less-permissive header syntax
+ notably, limited From syntax
+ MAIL header comments allowed in only a few contexts
+ slightly more restricted message-ID syntax
+ several more mandatory headers
+ duplicate headers forbidden
+ References/See-Also versus In-Reply-To/References (Section 6.5)
+ case sensitivity in some contexts
+ point-to-point headers, e.g., To and Cc, forbidden (Section 6)
+ several new headers
Author's Address
Henry Spencer
SP Systems
Box 280 Stn. A
Toronto, Ontario M5W1B2
Canada
EMail: henry@zoo.utoronto.ca
Spencer Historic [Page 106]
