fix(ipv6): _read_ip_hextet slices include the version nibble

pcapkit/protocols/internet/ipv6.py

@@ -330,8 +330,8 @@ def _read_ip_hextet(self) -> 'tuple[int, int, int]':
         """
         _htet = self._read_fileng(4).hex()
         _vers = int(_htet[0], base=16)      # version number (6)
-        _tcls = int(_htet[0:2], base=16)    # traffic class
-        _flow = int(_htet[2:], base=16)     # flow label
+        _tcls = int(_htet[1:3], base=16)    # traffic class
+        _flow = int(_htet[3:], base=16)     # flow label
 
         return (_vers, _tcls, _flow)
 

tests/protocols/internet/test_ipv6_read_ip_hextet_unit.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+import importlib.util
+import unittest
+from unittest import mock
+
+from tests._support import reimport_once_per_class
+
+RUNTIME_DEPS = ('tbtrim', 'aenum', 'chardet', 'dictdumper')
+HAS_RUNTIME = all(importlib.util.find_spec(name) is not None for name in RUNTIME_DEPS)
+
+
+@unittest.skipUnless(HAS_RUNTIME, 'runtime dependencies not installed')
+class IPv6ReadIPHextetUnitTests(unittest.TestCase):
+    """GitHub issue #1094: the traffic class and flow label exclude the version nibble."""
+
+    def setUp(self) -> None:
+        reimport_once_per_class(self)
+
+    def test_read_ip_hextet_splits_version_class_and_label(self) -> None:
+        from pcapkit.protocols.internet.ipv6 import IPv6
+
+        proto = object.__new__(IPv6)
+        proto._read_fileng = mock.Mock(return_value=bytes.fromhex('6abcdef0'))
+
+        self.assertEqual(proto._read_ip_hextet(), (6, 0xab, 0xcdef0))
+        proto._read_fileng.assert_called_once_with(4)
+
+    def test_read_ip_hextet_agrees_with_schema_packing(self) -> None:
+        from pcapkit.const.reg.transtype import TransType
+        from pcapkit.protocols.internet.ipv6 import IPv6
+
+        proto = object.__new__(IPv6)
+        header = proto.make(
+            traffic_class=0xff,
+            flow_label=0xfffff,
+            next=TransType.UDP,
+            hop_limit=64,
+            src='2001:db8::1',
+            dst='2001:db8::2',
+            payload=b'',
+        ).pack()
+
+        proto._read_fileng = mock.Mock(return_value=header[:4])
+        self.assertEqual(proto._read_ip_hextet(), (6, 0xff, 0xfffff))
+
+
+if __name__ == '__main__':
+    unittest.main()

tests/protocols/internet/test_ipv6_unit.py

@@ -128,7 +128,7 @@ def test_ipv6_properties_read_and_low_level_field_readers(self) -> None:
             bytes.fromhex('6abcdef0'),
             ip_address('2001:db8::5').packed,
         ])
-        self.assertEqual(proto._read_ip_hextet(), (6, 0x6a, 0xbcdef0))
+        self.assertEqual(proto._read_ip_hextet(), (6, 0xab, 0xcdef0))
         self.assertEqual(proto._read_ip_addr(), ip_address('2001:db8::5'))
 
     def test_ipv6_decode_next_layer_handles_extension_headers_and_fragments(self) -> None: