shellcheck 0.10+ reports SC2329 ("This function is never invoked") for
the per-testcase cleanup() functions in TEST-75-RESOLVED.sh, which are
only invoked indirectly via trap. The existing SC2317 markers don't
cover it, and inserting a new testcase shuffles which definitions the
heuristic fires on, making pre-existing findings show up as new in
differential CI runs. Extend the markers to SC2317,SC2329, matching
what testcase_dot_strict_per_link_verify() in this file and other test
units already do.
Verify that a DNS-SD service registered via the D-Bus RegisterService()
call is bound to the lifetime of the client's bus connection: since
busctl disconnects right after the call returns, the service must be
unregistered again shortly after. Wait for resolved's vanish handler
log message as proof that the client tracking triggered the
unregistration, check that a subsequent UnregisterService() fails
specifically because the service is not known anymore, and verify that
the identifier can be registered again — previously it stayed taken by
the vanished client's service forever, failing with
DNSSD_SERVICE_EXISTS.
A dummy link with mDNS enabled makes sure the per-scope goodbye/zone
teardown path actually runs, and since resolved would be restarted
automatically if it crashed in it, letting the D-Bus level checks pass
vacuously, verify the InvocationID stayed the same throughout.
Since the D-Bus DNS-SD API was introduced in c3036641f0 ("resolved:
implement D-Bus API for DNS-SD", v236), RegisterService() has set up an
sd_bus_track object so that a registered service is destroyed when the
client that registered it disconnects from the bus — there's even a
handler logging "Client of active request vanished, destroying DNS-SD
service."
However, the track object was never stored anywhere: it is declared as
a _cleanup_(sd_bus_track_unrefp) local in bus_method_register_service()
and hence destroyed again when the method handler returns, taking the
tracking down with it. The vanish handler was thus dead code, and
services registered via D-Bus silently persisted after their client
disconnected — unowned, impossible to re-register (the identifier
stays taken, failing with DNSSD_SERVICE_EXISTS), and advertised until
systemd-resolved itself exited.
Store the track object in DnssdRegisteredService, pinning it for the
lifetime of the service, so that client tracking works as originally
intended. Route the vanish path through the full unregistration logic
(goodbye packets + removal from the per-link mDNS zones), since freeing
the service alone would leave its RRs published in the zones.
Note for fire-and-forget clients (e.g. one-shot busctl/gdbus calls):
these were never reliable — the registration silently vanished on any
resolved restart — and now behave as documented for the corresponding
Avahi API as well: the bus connection must be kept open for as long as
the service is to remain registered. Document that in the man page and
NEWS, and point to *.dnssd files for registrations independent of a
client's lifetime.
dns_scope_announce(scope, /* goodbye= */ true) is not scoped to a
specific service: it walks the whole per-link mDNS zone and flags every
established RR as goodbye (TTL 0). Unregistering a single DNS-SD
service via the UnregisterService() D-Bus call hence withdrew the
host's own A/AAAA records and every other published service on the
link from remote caches, with nothing re-announcing them afterwards.
Introduce dns_scope_send_goodbye(), which sends an unsolicited response
for a caller-provided RR set, and let the DNS-SD unregistration path
send goodbye only for the RRs of the service actually being removed,
mirroring the flag logic of dns_scope_announce().
The goodbye answer is built per scope, and only includes records
actually established in the respective zone (or under re-verification,
in which case they are still served from it): a per-service goodbye
must take care not to withdraw records that are still being probed for
uniqueness, were withdrawn again after a conflict (in which case the
name belongs to the neighbor), or were never published in the scope in
the first place (e.g. on MulticastDNS=resolve links, which have an mDNS
scope but do not publish DNS-SD services).
This becomes more important with the next commit, which promotes
unregistration from an explicit method call to an automatic consequence
of the registering client disconnecting from the bus.
Move the logic that sends goodbye messages, removes a registered DNS-SD
service's RRs from all mDNS zones and frees the service out of
bus_dnssd_method_unregister() into a new helper. While at it, add the
nowadays customary parameter comments and ", ignoring" log message
suffix to the moved code. No functional change.
This is preparation for unregistering services when the D-Bus client
that registered them disconnects: that path needs the full teardown as
well, not just dnssd_registered_service_free(), which would leave the
service's RRs published in the per-link mDNS zones.
Stefan Agner