fix(loopback): reject an address family that is not an int (#2289)

pcapkit/protocols/link/loopback.py

@@ -233,12 +233,16 @@ def make(self,
 
         Raises:
             ProtocolError: If ``byteorder`` is neither ``'big'`` nor
-                ``'little'``, or ``family`` does not fit in 4 octets.
+                ``'little'``, or ``family`` is not an :obj:`int` (a
+                :obj:`bool` included, :issue:`2289`) or does not fit in 4
+                octets.
 
         """
         if byteorder not in ('big', 'little'):
             raise ProtocolError(f'Loopback: invalid byte order: {byteorder!r}')
-        if not 0 <= family <= 0xFFFF_FFFF:
+        # NOTE: ``bool`` is an ``int`` subclass, so without the explicit check
+        # ``True`` would pack as address family 1 (#2289).
+        if isinstance(family, bool) or not isinstance(family, int) or not 0 <= family <= 0xFFFF_FFFF:
             raise ProtocolError(f'Loopback: invalid address family: {family!r}')
 
         return Schema_Loopback(

tests/protocols/link/test_loopback_unit.py

@@ -127,6 +127,19 @@ def test_make_rejects_what_does_not_fit(self) -> None:
             with self.subTest(**kwargs), self.assertRaises(ProtocolError):
                 Loopback(**kwargs)
 
+    def test_make_rejects_a_family_that_is_not_an_int(self) -> None:
+        # #2289: a bool is an int and packs as family 1; a non-int fails the
+        # range comparison or ``to_bytes`` with a bare ``TypeError`` or
+        # ``AttributeError``. Each must raise ``ProtocolError``.
+        from pcapkit.protocols.link.loopback import Loopback
+        from pcapkit.utilities.exceptions import ProtocolError
+
+        for family in (True, False, '2', 2.0, None):
+            with self.subTest(family=family):
+                with self.assertRaises(ProtocolError) as ctx:
+                    Loopback(family=family)
+                self.assertEqual(str(ctx.exception), f'Loopback: invalid address family: {family!r}')
+
     def test_registered_for_null_and_loop(self) -> None:
         from pcapkit.const.reg.linktype import LinkType
         from pcapkit.corekit.module import ModuleDescriptor