always invoke (Add|Remove)MatchSignal on bus object, add additional filter options

Author: mechmind

object.go

@@ -13,6 +13,8 @@ type BusObject interface {
 	CallWithContext(ctx context.Context, method string, flags Flags, args ...interface{}) *Call
 	Go(method string, flags Flags, ch chan *Call, args ...interface{}) *Call
 	GoWithContext(ctx context.Context, method string, flags Flags, ch chan *Call, args ...interface{}) *Call
+	AddMatchSignal(iface, member string, options ...MatchOption) *Call
+	RemoveMatchSignal(iface, member string, options ...MatchOption) *Call
 	GetProperty(p string) (Variant, error)
 	Destination() string
 	Path() ObjectPath
@@ -35,23 +37,65 @@ func (o *Object) CallWithContext(ctx context.Context, method string, flags Flags
 	return <-o.createCall(ctx, method, flags, make(chan *Call, 1), args...).Done
 }
 
-// AddMatchSignal subscribes BusObject to signals from specified interface and
-// method (member).
-func (o *Object) AddMatchSignal(iface, member string) *Call {
-	return o.Call(
+// MatchOption specifies option for dbus routing match rule. Options can be constructed with WithMatch* helpers.
+// For full list of available options consult
+// https://dbus.freedesktop.org/doc/dbus-specification.html#message-bus-routing-match-rules
+type MatchOption struct {
+	key   string
+	value string
+}
+
+// WithMatchOption creates match option with given key and value
+func WithMatchOption(key, value string) MatchOption {
+	return MatchOption{key, value}
+}
+
+// WithMatchObjectPath creates match option that filters events based on given path
+func WithMatchObjectPath(path ObjectPath) MatchOption {
+	return MatchOption{"path", string(path)}
+}
+
+func formatMatchOptions(options []MatchOption) string {
+	items := make([]string, 0, len(options))
+	for _, option := range options {
+		items = append(items, option.key+"='"+option.value+"'")
+	}
+
+	return strings.Join(items, ",")
+}
+
+// AddMatchSignal subscribes BusObject to signals from specified interface,
+// method (member). Additional filter rules can be added via WithMatch* option constructors.
+// Note: To filter events by object path you have to specify this path via an option.
+func (o *Object) AddMatchSignal(iface, member string, options ...MatchOption) *Call {
+	base := []MatchOption{
+		{"type", "signal"},
+		{"interface", iface},
+		{"member", member},
+	}
+
+	options = append(base, options...)
+	return o.conn.BusObject().Call(
 		"org.freedesktop.DBus.AddMatch",
 		0,
-		"type='signal',interface='"+iface+"',member='"+member+"'",
+		formatMatchOptions(options),
 	)
 }
 
-// RemoveMatchSignal unsubscribes BusObject to signals from specified interface and
-// method (member).
-func (o *Object) RemoveMatchSignal(iface, member string) *Call {
-	return o.Call(
+// RemoveMatchSignal unsubscribes BusObject from signals from specified interface,
+// method (member). Additional filter rules can be added via WithMatch* option constructors
+func (o *Object) RemoveMatchSignal(iface, member string, options ...MatchOption) *Call {
+	base := []MatchOption{
+		{"type", "signal"},
+		{"interface", iface},
+		{"member", member},
+	}
+
+	options = append(base, options...)
+	return o.conn.BusObject().Call(
 		"org.freedesktop.DBus.RemoveMatch",
 		0,
-		"type='signal',interface='"+iface+"',member='"+member+"'",
+		formatMatchOptions(options),
 	)
 }
 

object_test.go

@@ -57,3 +57,94 @@ func TestObjectGoWithContext(t *testing.T) {
 		t.Fatal("Expected call to respond in 1 Millisecond")
 	}
 }
+
+type nopServer struct{}
+
+func (_ nopServer) Nop() *Error {
+	return nil
+}
+
+func fetchSignal(t *testing.T, ch chan *Signal, timeout time.Duration) *Signal {
+	select {
+	case sig := <-ch:
+		return sig
+	case <-time.After(timeout):
+		t.Fatalf("Failed to fetch signal in specified timeout %s", timeout)
+	}
+	return nil
+}
+
+func TestObjectSignalHandling(t *testing.T) {
+	bus, err := SessionBus()
+	if err != nil {
+		t.Fatalf("Unexpected error connecting to session bus: %s", err)
+	}
+
+	name := bus.Names()[0]
+	path := ObjectPath("/org/godbus/DBus/TestSignals")
+	otherPath := ObjectPath("/org/other-godbus/DBus/TestSignals")
+	iface := "org.godbus.DBus.TestSignals"
+	otherIface := "org.godbus.DBus.OtherTestSignals"
+	err = bus.Export(nopServer{}, path, iface)
+	if err != nil {
+		t.Fatalf("Unexpected error registering nop server: %v", err)
+	}
+
+	obj := bus.Object(name, path)
+	obj.AddMatchSignal(iface, "Heartbeat", WithMatchObjectPath(obj.Path()))
+
+	ch := make(chan *Signal, 5)
+	bus.Signal(ch)
+
+	go func() {
+		defer func() {
+			if err := recover(); err != nil {
+				t.Errorf("Catched panic in emitter goroutine: %v", err)
+			}
+		}()
+
+		// desired signals
+		bus.Emit(path, iface+".Heartbeat", uint32(1))
+		bus.Emit(path, iface+".Heartbeat", uint32(2))
+		// undesired signals
+		bus.Emit(otherPath, iface+".Heartbeat", uint32(3))
+		bus.Emit(otherPath, otherIface+".Heartbeat", uint32(4))
+		bus.Emit(path, iface+".Updated", false)
+		// sentinel
+		bus.Emit(path, iface+".Heartbeat", uint32(5))
+
+		time.Sleep(100 * time.Millisecond)
+		bus.Emit(path, iface+".Heartbeat", uint32(6))
+	}()
+
+	checkSignal := func(sig *Signal, value uint32) {
+		if sig.Path != path {
+			t.Errorf("signal.Path mismatch: %s != %s", path, sig.Path)
+		}
+
+		name := iface + ".Heartbeat"
+		if sig.Name != name {
+			t.Errorf("signal.Name mismatch: %s != %s", name, sig.Name)
+		}
+
+		if len(sig.Body) != 1 {
+			t.Errorf("Invalid signal body length: %d", len(sig.Body))
+			return
+		}
+
+		if sig.Body[0] != interface{}(value) {
+			t.Errorf("signal value mismatch: %d != %d", value, sig.Body[0])
+		}
+	}
+
+	checkSignal(fetchSignal(t, ch, 50*time.Millisecond), 1)
+	checkSignal(fetchSignal(t, ch, 50*time.Millisecond), 2)
+	checkSignal(fetchSignal(t, ch, 50*time.Millisecond), 5)
+
+	obj.RemoveMatchSignal(iface, "Heartbeat", WithMatchObjectPath(obj.Path()))
+	select {
+	case sig := <-ch:
+		t.Errorf("Got signal after removing subscription: %v", sig)
+	case <-time.After(200 * time.Millisecond):
+	}
+}