tree cb9b08b5f712dc5e9f52d3888c12ceeb20128536
parent b96b753b815feea5800f3f5711e542539400cf12
author Asim Shankar <ashankar@google.com> 1464726372 -0700
committer Asim Shankar <ashankar@google.com> 1464744593 +0000

lib/discovery: Prevent plugins from stomping on each other.

Prior to this commit, when multiple plugins are used for discovery then
events from one could stomp those from the other. For example, consider
two devices that have both mDNS and BLE connectivity to each other.
Services advertised will be picked up on both channels. If they move
out of BLE range (but are still on the same IP network), then the
"Lost" event from the BLE plugin would be delivered to the client which
might then mistakenly determine that the advertisement is no longer
valid (even though the mDNS plugin still sees it).

This commit fixes that by introducing reference counts per-plugin.
"Lost" events are delivered to the client only if *all* plugins that
previously saw an advertisement no longer see it.

The test added in discovery_test.go tests this behavior and fails
without the corresponding changes in scan.go

Change-Id: I455ba4c0b7c3211e2b8db84c53086a147e1d7587