Support CANdapter extended length arbitration ID (#1528)

* Support CANdapter extended length arbitration ID

* Update can/interfaces/slcan.py

More efficient check of arbitration ID

Co-authored-by: zariiii9003 <52598363+zariiii9003@users.noreply.github.com>

* Add description of x extended arbitration identifier

* Add test for CANDapter extended arbitration ID

* Update test/test_slcan.py

Type fix in slcan test

Co-authored-by: zariiii9003 <52598363+zariiii9003@users.noreply.github.com>

* format black

---------

Co-authored-by: zariiii9003 <52598363+zariiii9003@users.noreply.github.com>

can/interfaces/slcan.py

@@ -215,7 +215,10 @@ def _recv_internal(
 
         if not string:
             pass
-        elif string[0] == "T":
+        elif string[0] in (
+            "T",
+            "x",  # x is an alternative extended message identifier for CANDapter
+        ):
             # extended frame
             canId = int(string[1:9], 16)
             dlc = int(string[9])

test/test_slcan.py

@@ -43,6 +43,16 @@ def test_recv_extended(self):
         self.assertEqual(msg.dlc, 2)
         self.assertSequenceEqual(msg.data, [0xAA, 0x55])
 
+        # Ewert Energy Systems CANDapter specific
+        self.serial.write(b"x12ABCDEF2AA55\r")
+        msg = self.bus.recv(TIMEOUT)
+        self.assertIsNotNone(msg)
+        self.assertEqual(msg.arbitration_id, 0x12ABCDEF)
+        self.assertEqual(msg.is_extended_id, True)
+        self.assertEqual(msg.is_remote_frame, False)
+        self.assertEqual(msg.dlc, 2)
+        self.assertSequenceEqual(msg.data, [0xAA, 0x55])
+
     def test_send_extended(self):
         msg = can.Message(
             arbitration_id=0x12ABCDEF, is_extended_id=True, data=[0xAA, 0x55]