aioble/client.py: Use characteristic end handle (when available).

The `bluetooth` module replaced the def_handle field with end_handle
in the characteristic result IRQ. Use this when querying for
descriptors.

In the case where this is not available (older versions of micropython)
continue the existing behavior of searching just past the value handle,
although decrease this to +2 to avoid finding other characteristic's
descriptors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

micropython/bluetooth/aioble/aioble/client.py

@@ -48,9 +48,9 @@ def _client_irq(event, data):
         conn_handle, status = data
         ClientDiscover._discover_done(conn_handle, status)
     elif event == _IRQ_GATTC_CHARACTERISTIC_RESULT:
-        conn_handle, def_handle, value_handle, properties, uuid = data
+        conn_handle, end_handle, value_handle, properties, uuid = data
         ClientDiscover._discover_result(
-            conn_handle, def_handle, value_handle, properties, bluetooth.UUID(uuid)
+            conn_handle, end_handle, value_handle, properties, bluetooth.UUID(uuid)
         )
     elif event == _IRQ_GATTC_CHARACTERISTIC_DONE:
         conn_handle, status = data
@@ -284,12 +284,15 @@ class BaseClientCharacteristic:
 # this class directly, instead use `async for characteristic in
 # service.characteristics([uuid])` or `await service.characteristic(uuid)`.
 class ClientCharacteristic(BaseClientCharacteristic):
-    def __init__(self, service, def_handle, value_handle, properties, uuid):
+    def __init__(self, service, end_handle, value_handle, properties, uuid):
         self.service = service
         self.connection = service.connection
 
+        # Used for descriptor discovery. If available, otherwise assume just
+        # past the value handle (enough for two descriptors without risking
+        # going into the next characteristic).
+        self._end_handle = end_handle if end_handle > value_handle else value_handle + 2
         # Used for read/write/notify ops.
-        self._def_handle = def_handle
         self._value_handle = value_handle
 
         # Which operations are supported.
@@ -323,7 +326,7 @@ class ClientCharacteristic(BaseClientCharacteristic):
 
     def __str__(self):
         return "Characteristic: {} {} {} {}".format(
-            self._def_handle, self._value_handle, self.properties, self.uuid
+            self._end_handle, self._value_handle, self.properties, self.uuid
         )
 
     def _connection(self):
@@ -444,9 +447,7 @@ class ClientDescriptor(BaseClientCharacteristic):
         self.properties = _FLAG_READ | _FLAG_WRITE_NO_RESPONSE
 
     def __str__(self):
-        return "Descriptor: {} {} {} {}".format(
-            self._def_handle, self._value_handle, self.properties, self.uuid
-        )
+        return "Descriptor: {} {} {}".format(self._value_handle, self.properties, self.uuid)
 
     def _connection(self):
         return self.characteristic.service.connection
@@ -456,5 +457,5 @@ class ClientDescriptor(BaseClientCharacteristic):
         ble.gattc_discover_descriptors(
             characteristic._connection()._conn_handle,
             characteristic._value_handle,
-            characteristic._value_handle + 5,
+            characteristic._end_handle,
         )