fix(httpv2): SETTINGS ListField reads past the last pair and warns 'packet length < 0'

pcapkit/protocols/schema/application/httpv2.py

@@ -330,7 +330,7 @@ class Flags(FrameType.Flags):
     #: Settings.
     settings: 'list[SettingPair]' = ListField(
         length=lambda pkt: pkt['__length__'],
-        item_type=SchemaField(schema=SettingPair),
+        item_type=SchemaField(length=6, schema=SettingPair),
     )
 
     if TYPE_CHECKING:

tests/protocols/application/test_httpv2_settings_list_1140_unit.py

@@ -0,0 +1,72 @@
+# -*- coding: utf-8 -*-
+"""HTTP/2 ``SETTINGS`` frames parse their setting pairs without warnings.
+
+GitHub issue #1140. ``SettingsFrame.settings`` built each item as a
+``SchemaField`` with no length, so every ``SettingPair`` was unpacked with a
+``__length__`` of ``-1`` and warned ``packet length < 0`` twice, at ``-3`` and
+``-7``, once per pair. The frames below are packed by scapy's independent
+:mod:`scapy.contrib.http2`, which serves as the oracle for the round trip.
+
+"""
+
+from __future__ import annotations
+
+import importlib.util
+import io
+import unittest
+import warnings
+
+RUNTIME_DEPS = ('tbtrim', 'aenum', 'chardet', 'dictdumper', 'scapy')
+HAS_RUNTIME = all(importlib.util.find_spec(name) is not None for name in RUNTIME_DEPS)
+
+#: ``name -> (setting pairs, ACK flag)``.
+CASES = {
+    '0 pairs': ([], False),
+    '1 pair': ([(1, 4096)], False),
+    '2 pairs': ([(1, 4096), (3, 100)], False),
+    '6 pairs': ([(1, 4096), (2, 0), (3, 100), (4, 65535), (5, 16384), (6, 8192)], False),
+    'ACK': ([], True),
+}
+
+
+def scapy_frame(pairs: 'list[tuple[int, int]]', ack: 'bool') -> 'bytes':
+    """Pack a ``SETTINGS`` frame with scapy."""
+    from scapy.contrib import http2
+
+    frame = http2.H2Frame(type=4, flags={'A'} if ack else set(), stream_id=0)
+    return bytes(frame / http2.H2SettingsFrame(
+        settings=[http2.H2Setting(id=id, value=value) for id, value in pairs],
+    ))
+
+
+@unittest.skipUnless(HAS_RUNTIME, 'runtime dependencies not installed')
+class HTTPv2SettingsListUnitTests(unittest.TestCase):
+    """``SETTINGS`` parses quietly and round-trips byte for byte."""
+
+    def test_settings_parse_without_warnings(self) -> None:
+        """No warning of any kind is emitted, and every pair is read."""
+        from pcapkit.protocols.application.httpv2 import HTTP as HTTPv2
+
+        for name, (pairs, ack) in CASES.items():
+            raw = scapy_frame(pairs, ack)
+            with self.subTest(frame=name):
+                with warnings.catch_warnings(record=True) as caught:
+                    warnings.simplefilter('always')
+                    info = HTTPv2(io.BytesIO(raw), len(raw)).info
+                self.assertEqual([str(w.message) for w in caught], [])
+                self.assertEqual(info.flags.ACK, ack)
+                self.assertEqual([(int(k), v) for k, v in info.settings.items(multi=True)], pairs)
+
+    def test_settings_round_trip_to_the_scapy_octets(self) -> None:
+        """parse -> ``make`` reproduces scapy's octets exactly."""
+        from pcapkit.protocols.application.httpv2 import HTTP as HTTPv2
+
+        for name, (pairs, ack) in CASES.items():
+            raw = scapy_frame(pairs, ack)
+            with self.subTest(frame=name):
+                info = HTTPv2(io.BytesIO(raw), len(raw)).info
+                self.assertEqual(bytes(HTTPv2(type=info.type, sid=info.sid, frame=info)), raw)
+
+
+if __name__ == '__main__':
+    unittest.main()