net/netmon: publish events to event bus

Updates #15160

Signed-off-by: David Anderson <dave@tailscale.com>

net/netmon/netmon.go

@@ -16,6 +16,7 @@ import (
 
 	"tailscale.com/types/logger"
 	"tailscale.com/util/clientmetric"
+	"tailscale.com/util/eventbus"
 	"tailscale.com/util/set"
 )
 
@@ -50,7 +51,10 @@ type osMon interface {
 
 // Monitor represents a monitoring instance.
 type Monitor struct {
-	logf   logger.Logf
+	logf    logger.Logf
+	b       *eventbus.Client
+	changed *eventbus.Publisher[*ChangeDelta]
+
 	om     osMon         // nil means not supported on this platform
 	change chan bool     // send false to wake poller, true to also force ChangeDeltas be sent
 	stop   chan struct{} // closed on Stop
@@ -114,21 +118,23 @@ type ChangeDelta struct {
 // New instantiates and starts a monitoring instance.
 // The returned monitor is inactive until it's started by the Start method.
 // Use RegisterChangeCallback to get notified of network changes.
-func New(logf logger.Logf) (*Monitor, error) {
+func New(bus *eventbus.Bus, logf logger.Logf) (*Monitor, error) {
 	logf = logger.WithPrefix(logf, "monitor: ")
 	m := &Monitor{
 		logf:     logf,
+		b:        bus.Client("netmon"),
 		change:   make(chan bool, 1),
 		stop:     make(chan struct{}),
 		lastWall: wallTime(),
 	}
+	m.changed = eventbus.Publish[*ChangeDelta](m.b)
 	st, err := m.interfaceStateUncached()
 	if err != nil {
 		return nil, err
 	}
 	m.ifState = st
 
-	m.om, err = newOSMon(logf, m)
+	m.om, err = newOSMon(bus, logf, m)
 	if err != nil {
 		return nil, err
 	}
@@ -465,6 +471,7 @@ func (m *Monitor) handlePotentialChange(newState *State, forceCallbacks bool) {
 	if delta.TimeJumped {
 		metricChangeTimeJump.Add(1)
 	}
+	m.changed.Publish(delta)
 	for _, cb := range m.cbs {
 		go cb(delta)
 	}