fix(ipv6_ext): give the version gate's message the house form

pcapkit/protocols/internet/ipv6_ext.py

@@ -584,8 +584,8 @@ def __post_init__(self, file: 'Optional[IO[bytes] | bytes]' = None, length: 'Opt
             :class:`~pcapkit.protocols.internet.ah.AH` and
             :class:`~pcapkit.protocols.internet.esp.ESP` both default to
             ``version=4`` and are valid under IPv4, so an unconditional gate
-            would reject them (``ProtocolError: ESP: only valid for IPv6, got
-            version=4``).
+            would reject them (``ProtocolError: ESP: invalid version: must be
+            6, not 4``).
 
             The gate exists because this class is registered into
             :attr:`Internet.__proto__
@@ -608,7 +608,7 @@ def __post_init__(self, file: 'Optional[IO[bytes] | bytes]' = None, length: 'Opt
         """
         if self.__data__ is Data_IPv6_Ext and version != 6:
             raise ProtocolError(
-                f'{self.__class__.__name__}: only valid for IPv6, got version={version}')
+                f'{self.__class__.__name__}: invalid version: must be 6, not {version!r}')
 
         #: bool: If the protocol is used as an IPv6 extension header.
         self._extf = extension

tests/protocols/internet/test_ipv6_ext_unit.py

@@ -312,6 +312,31 @@ def test_version_gate_rejects_non_ipv6_construction(self) -> None:
             IPv6_Ext(io.BytesIO(raw), len(raw), version=4, extension=True,
                      alias=int(ExtensionHeader.HOPOPT))
 
+    def test_version_gate_message_is_in_the_house_form(self) -> None:
+        """GitHub issue #2302: the gate said ``only valid for IPv6, got
+        version=4``, which carries the prefix but not the
+        ``<prefix>: <lowercase description>: ... <value>`` tail #2232 and
+        #2257 gave the rest of the library, and never named the version it
+        wanted. Both the issue's own bare-bytes call and the stream form are
+        pinned whole, since the two reach the gate by different routes.
+        """
+        from pcapkit.const.ipv6.extension_header import ExtensionHeader
+        from pcapkit.const.reg.transtype import TransType
+        from pcapkit.protocols.internet.ipv6_ext import IPv6_Ext
+        from pcapkit.utilities.exceptions import ProtocolError
+
+        expected = 'IPv6_Ext: invalid version: must be 6, not 4'
+
+        with self.assertRaises(ProtocolError) as context:
+            IPv6_Ext(b'\x06\x00\x00\x00\x00\x00\x00\x00', version=4)
+        self.assertEqual(str(context.exception), expected)
+
+        raw = bytes([int(TransType.UDP), 1]) + b'\x00' * 14
+        with self.assertRaises(ProtocolError) as context:
+            IPv6_Ext(io.BytesIO(raw), len(raw), version=4, extension=True,
+                     alias=int(ExtensionHeader.HOPOPT))
+        self.assertEqual(str(context.exception), expected)
+
     def test_shim6_registration_does_not_leak_into_ipv4_parsing(self) -> None:
         """GitHub issue #891: registering ``IPv6_Ext``
         into the shared ``Internet.__proto__`` for Shim6 must not make an