Merge pull request #36 from jlusiardi/issue_35_read_descriptors

#35  Proposes an extension to access GATT descriptors

Author: kelada

examples/read_descriptor.py

@@ -0,0 +1,45 @@
+import gatt
+
+from argparse import ArgumentParser
+
+
+class AnyDevice(gatt.Device):
+    def connect_succeeded(self):
+        super().connect_succeeded()
+        print("[%s] Connected" % (self.mac_address))
+
+    def connect_failed(self, error):
+        super().connect_failed(error)
+        print("[%s] Connection failed: %s" % (self.mac_address, str(error)))
+
+    def disconnect_succeeded(self):
+        super().disconnect_succeeded()
+        print("[%s] Disconnected" % (self.mac_address))
+
+    def services_resolved(self):
+        super().services_resolved()
+
+        print("[%s] Resolved services" % (self.mac_address))
+        for service in self.services:
+            print("[%s]\tService [%s]" % (self.mac_address, service.uuid))
+            for characteristic in service.characteristics:
+                print("[%s]\t\tCharacteristic [%s]" % (self.mac_address, characteristic.uuid))
+                for descriptor in characteristic.descriptors:
+                    print("[%s]\t\t\tDescriptor [%s] (%s)" % (self.mac_address, descriptor.uuid, descriptor.read_value()))
+
+    def descriptor_read_value_failed(self, descriptor, error):
+        print('descriptor_value_failed')
+
+
+arg_parser = ArgumentParser(description="GATT Connect Demo")
+arg_parser.add_argument('mac_address', help="MAC address of device to connect")
+args = arg_parser.parse_args()
+
+print("Connecting...")
+
+manager = gatt.DeviceManager(adapter_name='hci0')
+
+device = AnyDevice(manager=manager, mac_address=args.mac_address)
+device.connect()
+
+manager.run()

gatt/gatt_linux.py

@@ -456,6 +456,13 @@ def characteristic_enable_notifications_failed(self, characteristic, error):
         # To be implemented by subclass
         pass
 
+    def descriptor_read_value_failed(self, descriptor, error):
+        """
+        Called when a descriptor read command failed.
+        """
+        # To be implemented by subclass
+        pass
+
 
 class Service:
     """
@@ -505,6 +512,35 @@ def characteristics_resolved(self):
         self._connect_characteristic_signals()
 
 
+class Descriptor:
+    """
+    Represents a GATT Descriptor which can contain metadata or configuration of its characteristic.
+    """
+
+    def __init__(self, characteristic, path, uuid):
+        self.characteristic = characteristic
+        self.uuid = uuid
+        self._bus = characteristic._bus
+        self._path = path
+        self._object = self._bus.get_object('org.bluez', self._path)
+
+    def read_value(self, offset=0):
+        """
+        Reads the value of this descriptor.
+
+        When successful, the value will be returned, otherwise `descriptor_read_value_failed()` of the related
+        device is invoked.
+        """
+        try:
+            val = self._object.ReadValue(
+                {'offset': dbus.UInt16(offset, variant_level=1)},
+                dbus_interface='org.bluez.GattDescriptor1')
+            return val
+        except dbus.exceptions.DBusException as e:
+            error = _error_from_dbus_error(e)
+            self.service.device.descriptor_read_value_failed(self, error=error)
+
+
 class Characteristic:
     """
     Represents a GATT characteristic.
@@ -521,6 +557,13 @@ def __init__(self, service, path, uuid):
         self._properties = dbus.Interface(self._object, "org.freedesktop.DBus.Properties")
         self._properties_signal = None
 
+        descriptor_regex = re.compile(self._path + '/desc[0-9abcdef]{4}$')
+        self.descriptors = [
+            Descriptor(self, desc[0], desc[1]['org.bluez.GattDescriptor1']['UUID'])
+            for desc in self._object_manager.GetManagedObjects().items()
+            if descriptor_regex.match(desc[0])
+        ]
+
     def _connect_signals(self):
         if self._properties_signal is None:
             self._properties_signal = self._properties.connect_to_signal('PropertiesChanged', self.properties_changed)