Stefan Agner
a3a8e82f25
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from it): a per-service goodbye must take care not to withdraw records that are still being probed for uniqueness, were withdrawn again after a conflict (in which case the name belongs to the neighbor), or were never published in the scope in the first place (e.g. on MulticastDNS=resolve links, which have an mDNS scope but do not publish DNS-SD services).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.
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