Newsgroups header: part of the message header?
Esther & Fester Bestertester
included? Or is this part of the body of the message that is downloaded when
requested?
I am trying to filter news groups based on newsgroups and cross-posting
information. My news reader app doesn't have this information when it
downloads headers.
Is this just because the application author chooses not to download these
headers? Or is this information only available after the entire message has
been downloaded?
Thanks
Whiskers
There is a basic sub-set of the article headers which is known as the
'overview', and that is what a news-reader gets when it 'downloads the
headers'. The essential headers in the 'overview' are
Subject:
From:
Date:
Message-ID:
References:
Bytes:
Lines:
so you can only be sure of being able to filter messages based on those
headers, until you have downloaded the full set of headers which normally
comes when you download the complete article. Filtering on those other
headers is known as 'expensive' because it uses a lot more 'bandwidth'.
Not all newsreader programs are able to filter using headers that are
not part of the overview, and some are even more limited than that.
Some news-servers include an Xref header in the overview; this contains
the name and article number of each of the newsgroups [carried by that
server] to which the article has been 'cross-posted'. If your program can
filter on the Xref header, that can be an efficient way of detecting
cross-posts without downloading the complete set of headers (including the
Newsgroups header) when you fetch the articles.
Some newsreader programs are able to ask the news-server to send a
particular header for a particular article, if it is required for
filtering. But not all news-servers permit that.
--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~
Bill Cole
Esther & Fester Bestertester <n...@me.really> wrote:
> When headers are downloaded from a news server, is the newsgroups header
> included? Or is this part of the body of the message that is downloaded when
> requested?
That's dependent on the details of both your news reader and news
server. In practice, many readers only know how to retrieve the set of
headers that a server caches in its "overview" database, and most
servers only serve the de facto standard set of overview fields:
Subject, From, Date, Message-ID, References, Bytes, Lines, and Xref. In
principle a server can have a more expansive overview database and some
clients know how take advantage of that, and in principle a reader can
ask for other individual headers and servers can answer such queries,
but with modern news servers the most common practice is to only put
those 8 fields into the overview and to only provide answers to the XHDR
command (asking for a single specific header field from a range of
messages) when the header is in the overview. This is largely because
readers generally never really developed robust support for more
complete overviews or sane use of non-overview header filtering. The
cost of the server offering more than the default set of overview
headers is more than it is worth for most sites where the bulk of users
can't filter on anything other than the standard set.
However, you should note that the Xref header is a close relative of the
Newsgroups header. Xref is a cross-reference for a specific server of a
cross-posted article of the article numbers it has in the various groups
where it is present on that one server. It is a normal member of the
overview set and is provided by the news system you seem to be using.
> I am trying to filter news groups based on newsgroups and cross-posting
> information. My news reader app doesn't have this information when it
> downloads headers.
>
> Is this just because the application author chooses not to download these
> headers? Or is this information only available after the entire message has
> been downloaded?
It has to do with both the server and the newsreader program. It looks
like you are using the AT&T news system descended from the Prodigy and
SBC news system. Those servers only provide the default overview
headers. You apper to be using Asar's Hogwasher news reader, and from
what I can tell from a very fast re-examination of that program, it
seems to not support filtering on Xref, but only on Newsgroups.
You may find it useful to look at MT-NewsWatcher as an alternative to
Hogwasher. It's a less competent tool for binaries, but if you want a
good Mac newsreader with highly flexible filtering for text newsgroups,
it is one of the best in that role.
--
Now where did I hide that website...
Esther & Fester Bestertester
included? Or is this part of the body of the message that is downloaded when
requested?
I am trying to filter news groups based on newsgroups and cross-posting
information. My news reader app doesn't have this information when it
downloads headers.
Is this just because the application author not to download these headers? Or
is this information only available after the entire message has been
downloaded?
Thanks
Russ Allbery
> When headers are downloaded from a news server, is the newsgroups header
> included? Or is this part of the body of the message that is downloaded
> when requested?
It is part of the header of the message, but my guess is that you're
actually asking slightly the wrong question (a confusion made very easy by
the mislabelling of things in many news readers).
When a news reader says that it's downloading headers, what it's generally
doing is downloading overview information, which isn't the same thing.
The overview is a database of selected headers, not all of the headers of
the message, reformatted to make it easy to provide summary data about
large numbers of messages at once.
Retrieving overview information is highly optimised by news servers and is
much faster than actually downloading all of the article headers.
> I am trying to filter news groups based on newsgroups and cross-posting
> information. My news reader app doesn't have this information when it
> downloads headers.
Most news servers include the Xref header in overview information, but
it's not mandatory and some don't. The Xref header is very similar to the
Newsgroups header, but has two major differences: the format is different
(site name, followed by space-separated entries of newsgroup name, colon,
and article number in that newsgroup), and the Xref header generally
contains only newsgroups carried by that server so you can't filter based
on Xref on newsgroups that your local news server doesn't carry.
Most news servers do not include the Newsgroups header in overview
information, although some do.
--
Russ Allbery (r...@stanford.edu) <http://www.eyrie.org/~eagle/>
Please post questions rather than mailing me directly.
<http://www.eyrie.org/~eagle/faqs/questions.html> explains why.