Fix fileno error on Windows (Serial bus) (#1333)

* Add conda-forge badge to readme

* Update fileno method in serial_can.py

Change implemented similar to that made in #1313. This means notifiers will now work with the Serial interface.

* Format serial_test.py with black

* Revert "Add conda-forge badge to readme"

This reverts commit 59d0b3c.

can/interfaces/serial/serial_can.py

@@ -7,6 +7,7 @@
 See the interface documentation for the format being used.
 """
 
+import io
 import logging
 import struct
 from typing import Any, List, Tuple, Optional
@@ -212,10 +213,14 @@ def _recv_internal(
             raise CanOperationError("could not read from serial") from error
 
     def fileno(self) -> int:
-        if hasattr(self._ser, "fileno"):
+        try:
             return self._ser.fileno()
-        # Return an invalid file descriptor on Windows
-        return -1
+        except io.UnsupportedOperation:
+            raise NotImplementedError(
+                "fileno is not implemented using current CAN bus on this platform"
+            )
+        except Exception as exception:
+            raise CanOperationError("Cannot fetch fileno") from exception
 
     @staticmethod
     def _detect_available_configs() -> List[AutoDetectedConfig]:

test/serial_test.py

@@ -136,6 +136,24 @@ def test_rx_tx_min_timestamp_error(self):
         msg = can.Message(timestamp=-1)
         self.assertRaises(ValueError, self.bus.send, msg)
 
+    def test_when_no_fileno(self):
+        """
+        Tests for the fileno method catching the missing pyserial implementeation on the Windows platform
+        """
+        try:
+            fileno = self.bus.fileno()
+        except NotImplementedError:
+            pass  # allow it to be left non-implemented for Windows platform
+        else:
+            fileno.__gt__ = (
+                lambda self, compare: True
+            )  # Current platform implements fileno, so get the mock to respond to a greater than comparison
+            self.assertIsNotNone(fileno)
+            self.assertFalse(
+                fileno == -1
+            )  # forcing the value to -1 is the old way of managing fileno on Windows but it is not compatible with notifiers
+            self.assertTrue(fileno > 0)
+
 
 class SimpleSerialTest(unittest.TestCase, SimpleSerialTestBase):
     def __init__(self, *args, **kwargs):