GNU bug report logs - #69442
Discovered substitute servers not removed when they go offline

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From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@HIDDEN>
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Subject: Discovered substitute servers not removed when they go offline
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Hello,

Substitute servers discovered over Avahi don=E2=80=99t disappear when they =
go
off-line: they remain in /var/guix/discover/publish =E2=80=9Cforever=E2=80=
=9D (?) and
=E2=80=98guix substitute=E2=80=99 keeps trying to connect to them, in vain.

The problem AIUI is that the mDNS records are still valid according to
their TTL and thus cached by avahi-daemon; we can only notice that
things go wrong when trying to resolve:

--8<---------------cut here---------------start------------->8---
$ avahi-browse _guix_publish._tcp -r
+ enp0s31f6 IPv6 guix-publish-xyz                            _guix_publish.=
_tcp   local
+ enp0s31f6 IPv4 guix-publish-xyz                            _guix_publish.=
_tcp   local
Failed to resolve service 'guix-publish-xyz' of type '_guix_publish._tcp' i=
n domain 'local': Timeout reached
Failed to resolve service 'guix-publish-xyz' of type '_guix_publish._tcp' i=
n domain 'local': Timeout reached
--8<---------------cut here---------------end--------------->8---

(One way to reproduce that is to =E2=80=98pkill -9 avahi-daemon=E2=80=99 on=
 the machine
that advertises the service.)

Problem is that =E2=80=98avahi-browse-service-thread=E2=80=99 attempts to r=
esolve
services once for all; thus it never notices that services went away, at
least not until some long TTL has expired.

Ludo=E2=80=99.