Merge pull request #863 from zxzxwu/eatt-mtu

Correct ATT_MTU in enhanced bearers

bumble/gatt_client.py

@@ -288,8 +288,6 @@ class Client:
             self._bearer_id = (
                 f'[0x{bearer.connection.handle:04X}|CID=0x{bearer.source_cid:04X}]'
             )
-            # Fill the mtu.
-            bearer.on_att_mtu_update(att.ATT_DEFAULT_MTU)
             self.connection = bearer.connection
         else:
             bearer.on(bearer.EVENT_DISCONNECTION, self.on_disconnection)

bumble/gatt_server.py

@@ -115,7 +115,6 @@ class Server(utils.EventEmitter):
                 channel.connection.handle,
                 channel.source_cid,
             )
-            channel.att_mtu = att.ATT_DEFAULT_MTU
             channel.sink = lambda pdu: self.on_gatt_pdu(
                 channel, att.ATT_PDU.from_bytes(pdu)
             )

bumble/l2cap.py

@@ -1647,7 +1647,9 @@ class LeCreditBasedChannel(utils.EventEmitter):
         self.connection_result = None
         self.disconnection_result = None
         self.drained = asyncio.Event()
-        self.att_mtu = 0  # Filled by GATT client or server later.
+        # Core Specification Vol 3, Part G, 5.3.1 ATT_MTU
+        # ATT_MTU shall be set to the minimum of the MTU field values of the two devices.
+        self.att_mtu = min(mtu, peer_mtu)
 
         self.drained.set()