Since the D-Bus DNS-SD API was introduced in c3036641f0ed (v236),
`RegisterService()` has created an `sd_bus_track` object to destroy the
registered service when the registering client disconnects from the bus.
However, the track object is a `_cleanup_(sd_bus_track_unrefp)` local in
`bus_method_register_service()` that is never stored anywhere, so it is
destroyed again as soon as the method handler returns. The vanish
handler (`dnssd_registered_service_on_bus_track()`) has thus been dead
code for the past ~8 years.
The observable effect: services registered via D-Bus silently persist
after the client disconnects — unowned, advertised until resolved exits,
and impossible to re-register since the identifier stays taken
(`DNSSD_SERVICE_EXISTS`). At the same time, the registration doesn't
survive a resolved restart, so the current behavior is neither reliably
ephemeral nor reliably persistent. Noticed while reviewing a project
that (unknowingly relying on this bug) registers a service with a
one-shot `gdbus call` and expects it to persist.
This PR:
1. splits the goodbye/zone-removal logic out of
`bus_dnssd_method_unregister()` into a helper — the vanish path needs
the full teardown, not just `dnssd_registered_service_free()`, which
would leave the service's RRs published in the per-link mDNS zones;
2. stores the track object in `DnssdRegisteredService`, making client
tracking work as originally intended;
3. documents the lifetime semantics in `org.freedesktop.resolve1(5)`
(matching the equivalent Avahi D-Bus API, whose entry groups are
likewise bound to the client connection) and points to `*.dnssd` files
for registrations independent of a client's lifetime;
4. adds a TEST-75 case covering the connection-bound lifetime.
Note this is a behavioral change for fire-and-forget clients (one-shot
`busctl`/`gdbus` invocations). Arguably those were never working
reliably (registrations silently vanished on any resolved restart, and
stale entries blocked re-registration), but if this is deemed too risky,
the alternative would be to drop the dead tracking code and codify the
persist-until-exit behavior instead — I'd argue tracking as originally
intended is the better contract.
Verification: code compiles; the new integration test is included.
Yu Watanabe
736cb91535