darwin: add Write command to the gattc implementation

gap_darwin.go

@@ -211,3 +211,20 @@ func (pd *peripheralDelegate) DidUpdateValueForCharacteristic(prph cbgo.Peripher
 
 	}
 }
+
+// DidWriteValueForCharacteristic is called after the characteristic for a Service
+// for a Peripheral trigger a write with response. It contains the returned error or nil.
+func (pd *peripheralDelegate) DidWriteValueForCharacteristic(_ 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() { // compare pointers
+				if char.writeChan != nil {
+					char.writeChan <- err
+				}
+			}
+		}
+	}
+}

gattc_darwin.go

@@ -168,6 +168,7 @@ type deviceCharacteristic struct {
 	characteristic cbgo.Characteristic
 	callback       func(buf []byte)
 	readChan       chan error
+	writeChan      chan error
 }
 
 // UUID returns the UUID for this DeviceCharacteristic.
@@ -175,6 +176,27 @@ func (c DeviceCharacteristic) UUID() UUID {
 	return c.uuidWrapper
 }
 
+// Write replaces the characteristic value with a new value. The
+// call will return after all data has been written.
+func (c DeviceCharacteristic) Write(p []byte) (n int, err error) {
+	c.writeChan = make(chan error)
+	c.service.device.prph.WriteCharacteristic(p, c.characteristic, true)
+
+	// wait for result
+	select {
+	case <-time.NewTimer(10 * time.Second).C:
+		err = errors.New("timeout on Write()")
+	case err = <-c.writeChan:
+	}
+
+	c.writeChan = nil
+	if err != nil {
+		return 0, err
+	}
+
+	return len(p), nil
+}
+
 // WriteWithoutResponse replaces the characteristic value with a new value. The
 // call will return before all data has been written. A limited number of such
 // writes can be in flight at any given time. This call is also known as a