bug#25061: consider adding %COMPAT to default gnutls priority string

[Ludovic Courtès]

Ted Zlatanov <tzz@lifelogs.com> skribis:

> On Tue, 29 Nov 2016 11:24:53 +0100 Andy Wingo <wingo@igalia.com> wrote: 
>
> AW> There have been reports of errors from people using melpa and so on
> AW> which manifest themselves as:
>
> AW>     gnutls.c: [0] (Emacs) fatal error: The TLS connection was 
> non-properly terminated.
> ...
> AW> So, as Ludovic suggests in his message, a workaround might be:
>
> AW>     (setq gnutls-algorithm-priority "NORMAL:%COMPAT")
>
> AW> See Ludovic's message for some justification.  Just an idea.  I have
> AW> been trying to reproduce the problem that people report locally as some
> AW> TLS errors but I have not been able to.
>
> We could break down %COMPAT to all its components and find which ones
> are causing the issue.

%DUMBFW may be that option (info "(gnutls) Priority Strings"):

--8<---------------cut here---------------start------------->8---
%DUMBFW                          will add a private extension
                                 with bogus data that make the
                                 client hello exceed 512 bytes.
                                 This avoids a black hole
                                 behavior in some firewalls.
                                 This is the [_rfc7685_] client
                                 hello padding extension, also
                                 enabled with %COMPAT.
--8<---------------cut here---------------end--------------->8---

(Somehow I don’t recall seeing it back in the day.)

Ludo’.