fix(darwin): add DidUpdateNotificationState when enabling notifications (#433)

* fix(darwin): add DidUpdateNotificationState when enabling notifications

Currently, enabling notifications does not check for errors.

* apply code review

Author: acouvreur

gap_darwin.go

@@ -256,3 +256,20 @@ func (pd *peripheralDelegate) DidWriteValueForCharacteristic(_ cbgo.Peripheral,
 		}
 	}
 }
+
+// DidUpdateNotificationState is called when the notification state for a characteristic
+// has been updated. It reports whether enabling/disabling notifications succeeded.
+func (pd *peripheralDelegate) DidUpdateNotificationState(prph cbgo.Peripheral, chr cbgo.Characteristic, err error) {
+	uuid, _ := ParseUUID(chr.UUID().String())
+	svcuuid, _ := ParseUUID(chr.Service().UUID().String())
+
+	if svc, ok := pd.d.services[svcuuid]; ok {
+		for _, char := range svc.characteristics {
+			if char.characteristic == chr && uuid == char.UUID() {
+				if char.notifyChan != nil {
+					char.notifyChan <- err
+				}
+			}
+		}
+	}
+}

gattc_darwin.go

@@ -8,7 +8,10 @@ import (
 	"github.com/tinygo-org/cbgo"
 )
 
-var errCannotSendWriteWithoutResponse = errors.New("bluetooth: cannot send write without response (buffer full)")
+var (
+	errCannotSendWriteWithoutResponse = errors.New("bluetooth: cannot send write without response (buffer full)")
+	errTimeoutEnableNotifications     = errors.New("timeout on EnableNotifications")
+)
 
 var (
 	_ GATTCService        = (*DeviceService)(nil)
@@ -208,6 +211,7 @@ type deviceCharacteristic struct {
 	callback       func(buf []byte)
 	readChan       chan error
 	writeChan      chan error
+	notifyChan     chan error
 }
 
 // UUID returns the UUID for this DeviceCharacteristic.
@@ -256,15 +260,35 @@ func (c DeviceCharacteristic) WriteWithoutResponse(p []byte) (int, error) {
 // changes.
 // Users may call EnableNotifications with a nil callback to disable notifications.
 func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) error {
-	// If callback is nil, disable notifications
+	c.notifyChan = make(chan error)
+
 	if callback == nil {
 		c.service.device.prph.SetNotify(false, c.characteristic)
-		c.callback = nil // Clear notification callback
 	} else {
-		// Enable notifications and set notification callback
 		c.callback = callback
 		c.service.device.prph.SetNotify(true, c.characteristic)
 	}
+
+	// Wait for CoreBluetooth to confirm the notification state change.
+	var err error
+	select {
+	case err = <-c.notifyChan:
+	case <-time.After(10 * time.Second):
+		err = errTimeoutEnableNotifications
+	}
+
+	c.notifyChan = nil
+
+	if err != nil {
+		c.callback = nil
+		return err
+	}
+
+	// Clear callback after confirmed disable.
+	if callback == nil {
+		c.callback = nil
+	}
+
 	return nil
 }