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Versions: 00 01 RFC 1849
INTERNET-DRAFT Henry Spencer
Intended status: Historic SP Systems
Superseded by RFC5536 and RFC5537 27 July 2009
"Son of 1036": News Article Format and Transmission
<draft-spencer-usefor-son-of-1036-01.txt>
Henry Spencer
Status of this Memo
This is an Internet Draft.
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Abstract
By the early 1990s it had become clear that RFC 1036, the then
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
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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.
Table of Contents
Preface ........................................................... 4
Original Abstract ................................................. 5
1. Introduction .................................................. 5
2. Definitions, Notations, and Conventions ....................... 6
2.1. Textual Notations ......................................... 7
2.2. Syntax Notation ........................................... 8
2.3. Definitions ............................................... 9
2.4. End Of Line ............................................... 11
2.5. Case-Sensitivity .......................................... 11
2.6. Language .................................................. 12
3. Relation To MAIL (RFC 822 etc.) .............................. 12
4. Basic Format .................................................. 13
4.1. Overall Syntax ............................................ 13
4.2. Headers ................................................... 14
4.2.1. Names and Contents .................................... 14
4.2.2. Undesirable Headers ................................... 15
4.2.3. White Space and Continuations ......................... 16
4.3. Body ...................................................... 17
4.3.1. Body Format Issues .................................... 17
4.3.2. Body Conventions ...................................... 17
4.4. Characters And Character Sets ............................. 20
4.5. Non-ASCII Characters In Headers ........................... 23
4.6. Size Limits ............................................... 24
4.7. Example ................................................... 26
5. Mandatory Headers ............................................. 26
5.1. Date ...................................................... 27
5.2. From ...................................................... 29
5.3. Message-ID ................................................ 31
5.4. Subject ................................................... 32
5.5. Newsgroups ................................................ 33
5.6. Path ...................................................... 37
6. Optional Headers .............................................. 39
6.1. Followup-To ............................................... 40
6.2. Expires ................................................... 40
6.3. Reply-To .................................................. 41
6.4. Sender .................................................... 41
6.5. References ................................................ 42
6.6. Control ................................................... 44
6.7. Distribution .............................................. 45
6.8. Keywords .................................................. 46
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6.9. Summary ................................................... 47
6.10. Approved ................................................. 47
6.11. Lines .................................................... 48
6.12. Xref ..................................................... 48
6.13. Organization ............................................. 49
6.14. Supersedes ............................................... 50
6.15. Also-Control ............................................. 50
6.16. See-Also ................................................. 51
6.17. Article-Names ............................................ 51
6.18. Article-Updates .......................................... 53
7. Control Messages .............................................. 53
7.1. cancel .................................................... 54
7.2. ihave, sendme ............................................. 57
7.3. newgroup .................................................. 58
7.4. rmgroup ................................................... 59
7.5. sendsys, version, whogets ................................. 60
7.6. checkgroups ............................................... 64
8. Transmission Formats .......................................... 64
8.1. Batches ................................................... 65
8.2. Encoded Batches ........................................... 65
8.3. News Within Mail .......................................... 66
8.4. Partial Batches ........................................... 68
9. Propagation and Processing .................................... 68
9.1. Relayer General Issues .................................... 68
9.2. Article Acceptance And Propagation ........................ 70
9.3. Administrator Contact ..................................... 72
10. Gatewaying ................................................... 72
10.1. General Gatewaying Issues ................................ 73
10.2. Header Synthesis ......................................... 74
10.3. Message ID Mapping ....................................... 76
10.4. Mail to and from News .................................... 77
10.5. Gateway Administration ................................... 78
11. Security And Related Issues .................................. 79
11.1. Leakage .................................................. 79
11.2. Attacks .................................................. 80
11.3. Anarchy .................................................. 81
11.4. Liability ................................................ 81
12. References ................................................... 82
A. Archaeological Notes ........................................... 84
A.1. A-News Article Format ...................................... 84
A.2. Early B-News Article Format ................................ 84
A.3. Obsolete Headers ........................................... 85
A.4. Obsolete Control Messages .................................. 85
B. A Quick Tour Of MIME ........................................... 85
C. Summary of Changes Since RFC 1036 .............................. 89
D. Summary of Completely New Features ............................. 90
E. Summary of Differences From RFC 822+1123 ....................... 91
Author's Address .................................................. 91
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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 which is of some historical
interest.
In 1993-4, Henry Spencer wrote and informally circulated a document
which 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 WG 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, 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, 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 it 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.
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
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supplying some prodding to actually get it done!).
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.
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 publication of [RFC 850] in 1983, news
articles came to closely resemble Internet mail messages, with some
restrictions and some additional headers. [RFC1036] in 1987 updated
[RFC 850] 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
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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 this all 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.
As in this Draft's predecessors, the exact means used to transmit
articles from one host to another is not specified. NNTP [RFC 977]
{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 UUCP protocol [UUCP] extensively used in
the early days of Usenet and 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
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2.1. Textual Notations
Throughout this Draft, "MAIL" is short for "[RFC 822] 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 [RFC 822]
has been updated, firstly to [RFC2822] and more recently to
[RFC5322]; however, this Draft is firmly rooted in the original
[RFC 822]. Similarly, [RFC 821] 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.
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
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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 [RFC 822]. Implementors will need to be familiar with this
notation to fully understand this specification, and are referred to
[RFC 822] for a complete explanation of the modified BNF notation.
Here is a brief illustrative example:
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. <> 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.
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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": 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
not. A "relayer" is software which 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 which 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.
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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.
A "cooperating subnet" is a set of news-exchanging hosts which 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 which 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 which 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 which 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 which 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).
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The notation (e.g.) "(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.
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 [RFC 821], an end-of-line is a CR (ASCII 13) followed by an LF
(ASCII 10). ISO C [ISO/IEC 9899] 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.
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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.
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 (RFC 822 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 which 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 [RFC 822]. 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 PEM (Privacy Enhanced Mail, 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, 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.
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
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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 which 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 which 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 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.
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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".
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,
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conveying no information whatsoever. Headers that state information
which 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 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...
which 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
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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 which 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 body-less 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
body-less articles, hence the request for posting agents to
insert a body in such cases.
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
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"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 which
violate it. The "70-75" number comes from the widespread use
of display devices which are 80 columns wide, and the desire to
leave a bit of margin for quoting etc. (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.
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.
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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, 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 which 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
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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.
(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
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method, text and then underscores, is tempting to the naive...
but 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.
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 which 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.
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
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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 [RFC 977] is a 7-bit protocol {but in [RFC3977] it has
been upped to 8-bit}, and there may be implementations which
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, and MUST do so unless such articles are
strictly confined to a cooperating subnet which has its own pre-
agreed conventions. MIME encodings are preferred over all 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
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.
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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...
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.
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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 "=?" 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.
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 4.2.3)
as a last resort, and otherwise they MUST either pass the long lines
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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 [RFC 821]. 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 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 which 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 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.
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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 which
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 which 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 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 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.
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(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>.
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.
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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 timezone,
including a specification of that timezone as a numeric offset (which
SHOULD include the timezone 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 "UT"). The
timezone name in parentheses, if present, is a comment; software MUST
ignore it, except that reading agents might wish to display it to the
reader. Timezone names other than "UT" and "GMT" MUST appear only in
the comment.
NOTE: Attempts to deal with a full set of timezone names have
all foundered on the vast number of such names in use and the
duplications (for example, there are at least FIVE different
timezones 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
timezone names except as comments.
NOTE: [RFC1036] specified that use of GMT (aka UT, UTC) was
preferred. However, the local time (in the poster's timezone)
is arguably information of possible interest to the reader, and
this requires some indication of the poster's timezone.
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 timezones. 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 timezone 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 timezone.
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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 which 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. 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 "(".
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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 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 innocent-seeming. 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.
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>
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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 which 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 which 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 which 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 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 is not as robust in the
presence of crashes and other malfunctions.
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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.
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.
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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.
5.5. Newsgroups
The Newsgroups header's content specifies which newsgroup(s) the
article is posted to:
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.)
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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 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 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 which 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.([RFC 977] 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 which permits it) and posting agents should strip it
out.
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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.
Encoded words are allowed in newsgroup names ONLY where non-ASCII
characters are necessary to the name, and 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)
which 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) U of Toronto
sites to pass outside U 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 University of Toronto and University
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of Texas have "ut.general" newsgroups, and material cross-
posted to that name and a global newsgroup appears in both
universities' 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 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
"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
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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.
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.
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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 which 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
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.
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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 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
e.g. "X-To", is suggested.)
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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 at all, 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 which newsgroup(s) followups
should be posted to:
Followup-To-content = Newsgroups-content / "poster"
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
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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
which can be removed once the day of the event is past) 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), 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 that most administrators would agree with.
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.
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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;
otherwise the posting agent MUST supply a Sender header and delete
(or rename, e.g. 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 which 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 which are not in a followup
relationship to each other.
NOTE: In retrospect, , 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 established
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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.
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.
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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.
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.
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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.
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
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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 "_".
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.
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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:
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
which 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
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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, including empty lines (if any) at 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.
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, since at least one major relayer will supply a Lines
header for an article that lacks one, and will not consider 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:
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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 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 [RFC 977] demands that such a model be
provided, and there may be other software which 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 which 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.
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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.
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.
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An article with an Also-Control header MUST NOT have a Control or
Supersedes header.
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.
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
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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.
menu If present, a list of all 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".
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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
which MAY be noted for special attention by reading agents.
NOTE: This header provides a way to mark articles which 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.
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
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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 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 which 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).
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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. 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,
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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.
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, e.g., inadvertent copyright violation) 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.
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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 [RFC 977] 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.
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 the messages are intended for. 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.
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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.
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,
alone on a line, and is case-sensitive. (To reduce errors in
this regard, posting agents might wish to question or reject
newgroup messages which 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
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stick to defining what the newsgroup is about.
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 which 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.
7.4. rmgroup
The rmgroup message requests that a newsgroup be deleted:
rmgroup-arguments = newsgroup-name
rmgroup-body = body
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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 which 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.
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:
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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
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 which 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.
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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.
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
which the responding system passes the target newsgroup to. Only the
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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.
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 which 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.
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.
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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, 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.
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.
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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.
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
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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
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 which 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. And 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.
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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.
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 which 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
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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.
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 message, 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 near-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
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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.
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 which 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).
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
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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 [RFC 977] 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, 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.
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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 which 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 the
responsibilities of relayers, plus the added complications introduced
by transformations between different information formats. Much of
section 9's discussion of 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.
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.
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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 7.3) 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.
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
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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 timezone 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, e.g. 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
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
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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 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
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
".". [RFC 822] 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
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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-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
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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.
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 endeavour 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!) which 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 direct to a human, not to a "routine administrative issues"
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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.
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 which 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 section 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.
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
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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 can cause serious confusion among
innocent third parties who just want to know whether they can use the
newsgroup for communication or not.
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
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 defence.
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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/IEC 9899]
"Information technology - Programming Language C", ISO/IEC
9899:1990 {more recently 9899:1999}, 1990.
[Metamail] N. Borenstein,
<http://ftp.funet.fi/pub/unix/mail/metamail/ANNOUNCE>,
February 1994.
[RFC 821] Jonathan B. Postel, "Simple Mail Transfer Protocol", RFC
821, August 1982.
[RFC 822] D. Crocker, "Standard for the Format of ARPA Internet Text
Messages.", STD 11, RFC 822, August 1982.
[RFC 850] Mark R. Horton, "Standard for interchange of Usenet
messages", RFC 850, June 1983.
[RFC 977] Brian Kantor and Phil Lapsley, "Network news transfer
protocol - a proposed standard for the stream-based
transmission of news", RFC 977, February 1986.
[RFC1036] M. Horton and R. Adams, "Standard for Interchange of
USENET Messages", RFC 1036, December 1987.
[RFC1123] R. Braden, "Requirements for Internet Hosts -- Application
and Support", RFC 1123, October 1989.
[RFC1341] N. Borenstein and N. Freed, "MIME (Multipurpose Internet
Mail Extensions): Mechanisms for Specifying and Describing
the Format of Internet Message Bodies", RFC 1341, June
1992.
[RFC1342] K Moore, "Representation of Non-Ascii Text in Internet
Message Headers", RFC 1342, June 1992.
[RFC1345] K. Simonsen, "Character Mnemonics & Character Sets", RFC
1345, June 1992.
[RFC1413] M. St. Johns, "Identification Protocol", RFC 1413,
February 1993.
[RFC1456] Vietnamese Standardization Working Group, "Conventions for
Encoding the Vietnamese Language", RFC 1456, May 1993.
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[RFC1544] M. Rose, "The Content-MD5 Header Field", RFC 1544,
November 1993.
[RFC1896] P. Resnick and A. Walker, "The text/enriched MIME
Content-type", RFC 1896, February 1996.
[RFC2045] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2046] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[RFC2047] K. Moore, "MIME (Multipurpose Internet Mail Extensions)
Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996.
[RFC2049] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Five: Conformance Criteria and
Examples", RFC 2049, November 1996.
[RFC2822] P. Resnick, "Internet Message Format", RFC 2822, April
2001.
[RFC3977] C. Feather, "Network News Transport Protocol (NNTP)", RFC
3977.
[RFC5322] P. Resnick, "Internet Message Format", RFC 5322, October
2008.
[RFC5536] K. Murchison, C. H. Lindsey, and D. Kohn, "News Article
Format", RFC 5536, May 2009.
[RFC5537] R. Allbery and C. H. Lindsey, "News Article Architecture
and Protocols", RFC 5537, May 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, 1986.
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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
The 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.
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 now. The Received header contained the date
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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 that the receiving host
had UUCP connections to. 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.
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.)
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MIME (Multipurpose Internet Mail Extensions) is an upward-compatible
set of extensions to [RFC 822], 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
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 [RFC 822].
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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 [RFC 822] message, consisting of
headers and a body. Most of the [RFC 822]
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.
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 which use this
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encoding.
binary No encoding; any sequence of bytes may be present.
Many transmission paths are incapable of carrying
messages which 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 upper case
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.
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 [RFC 822]. 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 [RFC 822] 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
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concerns. A full-featured MIME reading agent needs a full [RFC
822] 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 which is NOT interested in MIME need not contain a
full [RFC 822] parser.
The second part of MIME, [RFC2047] (Message Header Extensions for
Non-ASCII Text), 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.
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).
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:
+ section 4.3's restrictions on article bodies
+ 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
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+ 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
+ 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)
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
Henry Spencer Expires January 2010 [Page 90]
Internet-Draft Son of 1036 22 July 2009
+ Article-Names
+ Article-Updates
+ the whogets control message
E. Summary of Differences From RFC 822+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
henry@zoo.utoronto.ca
SP Systems
Box 280 Stn. A
Toronto, Ont. M5W1B2 Canada
Henry Spencer Expires January 2010 [Page 91]
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