[InterNetNews/inn] 947213: nnrpd: Speed up searches when gaps in article numbers

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: 947213ff89f19f8d490d1e7fa9c60c1c35650382
      https://github.com/InterNetNews/inn/commit/947213ff89f19f8d490d1e7fa9c60c1c35650382
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2023-01-08 (Sun, 08 Jan 2023)

  Changed paths:
    M doc/pod/news.pod
    M nnrpd/article.c

  Log Message:
  -----------
  nnrpd: Speed up searches when gaps in article numbers

LAST and NEXT, as well as (X)HDR and XPAT when the requested header field is
not in the overview, try to retrieve each article number, one by one, with
ARTopen.

On newsgroups with huge gaps in article numbers, like 1 million, these
commands take a long time to respond.  Several minutes in a newsgroup with 2
articles, numbered 1 and 2147483647 for instance.

We now use OVopensearch to directly retrieve the information of available
article numbers in overview data and then verify that the article exists with
ARTopen (like it is currently done).  The responses of the above NNTP commands
are then immediate!

close #249