wgengine/monitor: skip some macOS route updates, fix debounce regression

Debound was broken way back in 5c1e443d34 and we never noticed.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/monitor/monitor.go

@@ -143,17 +143,24 @@ func (m *Mon) Close() error {
 	return err
 }
 
+func (m *Mon) stopped() bool {
+	select {
+	case <-m.stop:
+		return true
+	default:
+		return false
+	}
+}
+
 // pump continuously retrieves messages from the connection, notifying
 // the change channel of changes, and stopping when a stop is issued.
 func (m *Mon) pump() {
 	defer m.goroutines.Done()
-	for {
+	for !m.stopped() {
 		msg, err := m.om.Receive()
 		if err != nil {
-			select {
-			case <-m.stop:
+			if m.stopped() {
 				return
-			default:
 			}
 			// Keep retrying while we're not closed.
 			m.logf("error from link monitor: %v", err)
@@ -165,8 +172,10 @@ func (m *Mon) pump() {
 		}
 		select {
 		case m.change <- struct{}{}:
-		case <-m.stop:
-			return
+		default:
+			// Another change signal is already
+			// buffered. Debounce will wake up soon
+			// enough.
 		}
 	}
 }
@@ -199,7 +208,7 @@ func (m *Mon) debounce() {
 		select {
 		case <-m.stop:
 			return
-		case <-time.After(100 * time.Millisecond):
+		case <-time.After(250 * time.Millisecond):
 		}
 	}
 }

wgengine/monitor/monitor_darwin.go

@@ -51,21 +51,48 @@ func (m *darwinRouteMon) Close() error {
 }
 
 func (m *darwinRouteMon) Receive() (message, error) {
+	for {
 		n, err := unix.Read(m.fd, m.buf[:])
 		if err != nil {
 			return nil, err
 		}
 		msgs, err := route.ParseRIB(route.RIBTypeRoute, m.buf[:n])
 		if err != nil {
+			if debugRouteMessages {
 				m.logf("read %d bytes (% 02x), failed to parse RIB: %v", n, m.buf[:n], err)
+			}
 			return unspecifiedMessage{}, nil
 		}
+		if len(msgs) == 0 {
+			if debugRouteMessages {
+				m.logf("read %d bytes with no messages (% 02x)", n, m.buf[:n])
+			}
+			continue
+		}
+		nSkip := 0
+		for _, msg := range msgs {
+			if m.skipMessage(msg) {
+				nSkip++
+			}
+		}
 		if debugRouteMessages {
-		m.logf("read: %d bytes, %d msgs", n, len(msgs))
+			m.logf("read %d bytes, %d messages (%d skipped)", n, len(msgs), nSkip)
 			m.logMessages(msgs)
 		}
+		if nSkip == len(msgs) {
+			continue
+		}
 		return unspecifiedMessage{}, nil
 	}
+}
+
+func (m *darwinRouteMon) skipMessage(msg route.Message) bool {
+	switch msg.(type) {
+	case *route.InterfaceMulticastAddrMessage:
+		return true
+	}
+	return false
+}
 
 func (m *darwinRouteMon) logMessages(msgs []route.Message) {
 	for i, msg := range msgs {

wgengine/monitor/monitor_test.go

@@ -5,7 +5,10 @@
 package monitor
 
 import (
+	"flag"
 	"testing"
+
+	"tailscale.com/net/interfaces"
 )
 
 func TestMonitorStartClose(t *testing.T) {
@@ -28,3 +31,35 @@ func TestMonitorJustClose(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+var monitor = flag.String("monitor", "", `go into monitor mode like 'route monitor'; test never terminates. Value can be either "raw" or "callback"`)
+
+func TestMonitorMode(t *testing.T) {
+	switch *monitor {
+	case "":
+		t.Skip("skipping non-test without --monitor")
+	case "raw", "callback":
+	default:
+		t.Skipf(`invalid --monitor value: must be "raw" or "callback"`)
+	}
+	mon, err := New(t.Logf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	switch *monitor {
+	case "raw":
+		for {
+			msg, err := mon.om.Receive()
+			if err != nil {
+				t.Fatal(err)
+			}
+			t.Logf("msg: %#v", msg)
+		}
+	case "callback":
+		mon.RegisterChangeCallback(func(changed bool, st *interfaces.State) {
+			t.Logf("cb: changed=%v, ifSt=%v", changed, st)
+		})
+		mon.Start()
+		select {}
+	}
+}