s-o-1036 June 1994
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6.12. Xref
The Xref header content indicates where an article was filed
by the last relayer to process it:
Xref-content = relayer 1*( space location )
relayer = relayer-name
location = newsgroup-name ":" article-locator
article-locator = 1*<ASCII printable character>
The relayer's name is included so that software can deter-
mine 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 arti-
cle 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.
INTERNET DRAFT to be NEWS sec. 6.12
NOTE: The traditional form of an article locator
is a decimal number, with articles in each news-
group numbered consecutively starting from 1.
NNTP [rrr] 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: RFC 1036 specified that the Xref header was
not transmitted when an article was passed to
another relayer, but the major news implementa-
tions have never obeyed this rule, and applica-
tions 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.
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#Diff to first older
--- ../rfc1036/Xref.out December 1987
+++ ../s-o-1036/Xref.out June 1994
@@ -1,27 +1,57 @@
-2.2.13. Xref
+6.12. Xref
- This line contains the name of the host (with domains omitted) and a
- white space separated list of colon-separated pairs of newsgroup
- names and message numbers. These are the newsgroups listed in the
- "Newsgroups" line and the corresponding message numbers from the
- spool directory.
-
- This is only of value to the local system, so it should not be
- transmitted. For example, in:
-
- Path: seismo!lll-crg!lll-lcc!pyramid!decwrl!reid
- From: reid@decwrl.DEC.COM (Brian Reid)
- Newsgroups: news.lists,news.groups
- Subject: USENET READERSHIP SUMMARY REPORT FOR SEP 86
- Message-ID: <5658@decwrl.DEC.COM>
- Date: 1 Oct 86 11:26:15 GMT
- Organization: DEC Western Research Laboratory
- Lines: 441
- Approved: reid@decwrl.UUCP
- Xref: seismo news.lists:461 news.groups:6378
-
- the "Xref" line shows that the message is message number 461 in the
- newsgroup news.lists, and message number 6378 in the newsgroup
- news.groups, on host seismo. This information may be used by
- certain user interfaces.
+The Xref header content indicates where an article was filed
+by the last relayer to process it:
+
+ Xref-content = relayer 1*( space location )
+ relayer = relayer-name
+ location = newsgroup-name ":" article-locator
+ article-locator = 1*<ASCII printable character>
+
+The relayer's name is included so that software can deter-
+mine 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 arti-
+cle 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.
+
+INTERNET DRAFT to be NEWS sec. 6.12
+
+
+ NOTE: The traditional form of an article locator
+ is a decimal number, with articles in each news-
+ group numbered consecutively starting from 1.
+ NNTP [rrr] 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: RFC 1036 specified that the Xref header was
+ not transmitted when an article was passed to
+ another relayer, but the major news implementa-
+ tions have never obeyed this rule, and applica-
+ tions 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.