bug#34341: 26.1; url-retrieve-synchronously returns blank buffer

[Robert Pluim]

>>>>> On Mon, 06 May 2019 20:16:52 -0400, Noam Postavsky <npostavs@gmail.com> 
>>>>> said:

    Noam> Eli Zaretskii <eliz@gnu.org> writes:
    >>> From: Robert Pluim <rpluim@gmail.com> Date: Mon, 06 May 2019
    >>> 14:15:27 +0200 Cc: Laurent Charignon <l.charignon@gmail.com>,
    >>> 34341@debbugs.gnu.org
    >>> 
    >>> >>>>> On Mon, 06 May 2019 08:10:32 -0400, Noam Postavsky
    >>> <npostavs@gmail.com> said:
    >>> 
    Noam> Thanks, I wasn't aware of this, I'll check if that helps
    Noam> later today.  I think it makes sense to backport regardless
    Noam> though.

    Noam> I can confirm that

    Noam>     (setq gnutls-algorithm-priority "NORMAL:-VERS-TLS1.3")

    Noam> avoids the problem on my Arch box (has gnutls v3.6.7).

OK, so itʼs the same issue.

    Noam> I found this smaller change fixes it also.  Is it simple
    Noam> enough to for emacs-26?  Otherwise, we should set
    Noam> gnutls-algorithm-priority because (as far as I understand)
    Noam> we have a broken TLS1.3 implementation at the momement.

If we do decide to disable TLS1.3, which Iʼm not really in favour of,
changing the defaults in lisp/net/gnutls.el:gnutls-boot-parameters
might be better than setting gnutls-algorithm-priority. Iʼd prefer
your gnutls.c patch, although I haven't had a chance to test it yet.

Robert