gatt/darwin: macOS implementation and ensure pointer usage

Signed-off-by: deadprogram <ron@hybridgroup.com>

gap_darwin.go

@@ -162,5 +162,9 @@ func (pd *peripheralDelegate) DidUpdateValueForCharacteristic(prph cbgo.Peripher
 		if char != nil && char.callback != nil {
 			go char.callback(chr.Value())
 		}
+
+		if char.readChan != nil {
+			char.readChan <- nil
+		}
 	}
 }

gattc_darwin.go

@@ -114,6 +114,7 @@ type DeviceCharacteristic struct {
 
 	characteristic cbgo.Characteristic
 	callback       func(buf []byte)
+	readChan       chan error
 }
 
 // UUID returns the UUID for this DeviceCharacteristic.
@@ -147,6 +148,18 @@ func (c *DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) er
 }
 
 // Read reads the current characteristic value.
-func (c DeviceCharacteristic) Read() (data []byte, err error) {
-	return nil, nil
+func (c *DeviceCharacteristic) Read() (data []byte, err error) {
+	c.readChan = make(chan error)
+	c.service.device.prph.ReadCharacteristic(c.characteristic)
+
+	// wait for result
+	select {
+	case <-c.readChan:
+		c.readChan = nil
+	case <-time.NewTimer(10 * time.Second).C:
+		c.readChan = nil
+		return nil, errors.New("timeout on Read()")
+	}
+
+	return c.characteristic.Value(), nil
 }

gattc_linux.go

@@ -234,7 +234,7 @@ func (c *DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) er
 }
 
 // Read reads the current characteristic value.
-func (c DeviceCharacteristic) Read() ([]byte, error) {
+func (c *DeviceCharacteristic) Read() ([]byte, error) {
 	options := make(map[string]interface{})
 	return c.characteristic.ReadValue(options)
 }

gattc_sd.go

@@ -348,7 +348,7 @@ var readingCharacteristic struct {
 // Read reads the current characteristic value up to MTU length.
 // A future enhancement would be to be able to retrieve a longer
 // value by making multiple calls.
-func (c DeviceCharacteristic) Read() ([]byte, error) {
+func (c *DeviceCharacteristic) Read() ([]byte, error) {
 	errCode := C.sd_ble_gattc_read(c.connectionHandle, c.valueHandle, 0)
 	if errCode != 0 {
 		return nil, Error(errCode)