Christian Glombek
8352974158
When a BrowseServices subscription uses ifindex=0 ("all interfaces"),
mdns_browser_revisit_cache() looked up each mDNS scope's cache separately
and called mdns_manage_services_answer() once per scope. That function
derives "removed" events by diffing the browser's *global* service list
(all interfaces, filtered only by owner family) against the single answer
it is handed. So with two or more mDNS-relevant interfaces of the same
family, a service present on interface A is not contained in interface B's
answer and is therefore spuriously removed (emitting "removed") while B is
reconciled, then re-added (emitting "added") on the next revisit tick.
The result is a continuous added/removed/added/removed flap, within a
second, for a service that is still present and without any goodbye packet
involved -- as reported for the mDNS/DNS-SD browsing API.
Fix it by accumulating the pruned cache answers from every matching mDNS
scope into a single combined answer and reconciling exactly once, so the
removed pass diffs the global service list against the union across all
interfaces. Each scope's cache is still pruned before lookup, so genuinely
expired records still drop out of the union and real removals still fire.
The items are merged with dns_answer_add_full() rather than
dns_answer_extend(), so each item's ifindex, flags, rrsig and cache-expiry
"until" are preserved. dns_answer_extend()/dns_answer_merge() are not
expiry-aware and do not carry the source items' "until" through: it
defaults to USEC_INFINITY (the "no expiry" sentinel), which would skew the
RFC 6762 section 5.2 TTL maintenance schedule that
mdns_manage_services_answer() derives from item->until.
The single-interface (ifindex>0) path is unchanged.
System and Service Manager
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