Re: fetch only a portion of an article? (nnimap mainly)

[Simon Josefsson <jas@extundo.com>]

"Ted Zlatanov" <tzz@lifelogs.com> writes:

> In Gnus, you call gnus-request-article to get an article.  What if you
> know you only need the first N lines (or bytes)?  Can nnimap.el
> support that?  I can change the gnus-request-article function to
> accomodate such an option, and it will be passed to
> nnimap-request-article.  I just don't know enough about the IMAP
> protocol to implement it.
>
> I need this specifically for nnimap interactions, but I'm sure it can
> be implemented for other backends as well.  It's useful, for instance,
> when summarizing something about the contents of the article, but you
> don't want to fetch more than N lines of it.  I would use it to
> summarize qmail bounce reports - right now, I have to fetch the whole
> article just because I need to see what's in the first 10 lines.

IMAP support partial retrieval (byte counts), and even retrieval based
on the selected MIME structures (i.e., retrieve entire message except
one big attachment).  I think the problem may be in designing the back
end interface properly, so it is flexible enough.  Ideally there
should be some way to retrieve the MIME structure of an article, and
then make Gnus chose which MIME parts to retrieve.  But having a line
count may be sufficient as a start.  However, there is a big problem
with caching.  If an incomplete article ends up in the asynchronous
pre-fetcher, agent cache, user cache, etc, it will require some
tinkering to invalidate that copy and force a re-query on the entire
article.