Fix driver stuck on RecursionError on COMMIT SUCCESS

robsdedude · robsdedude · commit 1ba8b8048ea7 · 2025-05-30T10:59:53.000+02:00
The driver could get stuck when the result summary was so deeply nested that it
caused an `RecursionError`. It would also get stuck on certain protocol
violations in the same place (e.g., unknown PackStream tag). However, the
latter is much more unlikely to occur.

This patch will make the driver ditch the connection when it's not able to
properly read a message for unexpected reasons and let the error bubble up.
diff --git a/neo4j/io/__init__.py b/neo4j/io/__init__.py
@@ -586,6 +586,15 @@ def _set_defunct_write(self, error=None, silent=False):
 
     def _set_defunct(self, message, error=None, silent=False):
         direct_driver = isinstance(self.pool, BoltPool)
+        connection_failed = isinstance(
+            error,
+            (
+                ServiceUnavailable,
+                SessionExpired,
+                OSError,
+                SocketDeadlineExceeded,
+            ),
+        )
 
         if error:
             log.debug("[#%04X]  %r", self.local_port, error)
@@ -595,6 +604,12 @@ def _set_defunct(self, message, error=None, silent=False):
         # connection from the client side, and remove the address
         # from the connection pool.
         self._defunct = True
+        if not connection_failed:
+            # Something else but the connection failed
+            # => we're not sure which state we're in
+            # => ditch the connection and raise the error for user-awareness
+            self.close()
+            raise error
         if not self._closing:
             # If we fail while closing the connection, there is no need to
             # remove the connection from the pool, nor to try to close the
diff --git a/neo4j/io/_common.py b/neo4j/io/_common.py
@@ -46,12 +46,11 @@ def __init__(self, s, on_error):
         self._messages = self._yield_messages(s)
 
     def _yield_messages(self, sock):
-        try:
-            buffer = UnpackableBuffer()
-            unpacker = Unpacker(buffer)
-            chunk_size = 0
-            while True:
-
+        buffer = UnpackableBuffer()
+        unpacker = Unpacker(buffer)
+        chunk_size = 0
+        while True:
+            try:
                 while chunk_size == 0:
                     # Determine the chunk size and skip noop
                     buffer.receive(sock, 2)
@@ -61,18 +60,27 @@ def _yield_messages(self, sock):
 
                 buffer.receive(sock, chunk_size + 2)
                 chunk_size = buffer.pop_u16()
+            except (OSError, socket.timeout, SocketDeadlineExceeded) as error:
+                self.on_error(error)
 
-                if chunk_size == 0:
-                    # chunk_size was the end marker for the message
+            if chunk_size == 0:
+                # chunk_size was the end marker for the message
+                try:
                     size, tag = unpacker.unpack_structure_header()
                     fields = [unpacker.unpack() for _ in range(size)]
                     yield tag, fields
+                except Exception as error:
+                    log.debug(
+                        "[#%04X]  _: Failed to unpack response: %r",
+                        self._local_port,
+                        error,
+                    )
+                    self.on_error(error)
+                    raise
+                finally:
                     # Reset for new message
                     unpacker.reset()
 
-        except (OSError, socket.timeout, SocketDeadlineExceeded) as error:
-            self.on_error(error)
-
     def pop(self):
         return next(self._messages)
 
diff --git a/tests/unit/io/_common/__init__.py b/tests/unit/io/_common/__init__.py
@@ -0,0 +1,16 @@
+# Copyright (c) "Neo4j"
+# Neo4j Sweden AB [http://neo4j.com]
+#
+# This file is part of Neo4j.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
diff --git a/tests/unit/io/_common/test_inbox.py b/tests/unit/io/_common/test_inbox.py
@@ -0,0 +1,118 @@
+# Copyright (c) "Neo4j"
+# Neo4j Sweden AB [https://neo4j.com]
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.import asyncio
+
+
+import pytest
+
+from neo4j._exceptions import SocketDeadlineExceeded
+from neo4j.io._common import Inbox
+from neo4j.packstream import Unpacker
+
+
+def _on_error_side_effect(e):
+    raise e
+
+
+class InboxMockHolder:
+    def __init__(self, mocker):
+        self.socket_mock = mocker.Mock()
+        self.socket_mock.getsockname.return_value = ("host", 1234)
+        self.on_error = mocker.MagicMock()
+        self.on_error.side_effect = _on_error_side_effect
+        self.inbox = Inbox(self.socket_mock, self.on_error)
+        self.unpacker = None
+        self._unpacker_failure = None
+        mocker.patch(
+            "neo4j.io._common.Unpacker",
+            new=self._make_unpacker,
+        )
+        self.inbox._unpacker = self.unpacker
+        # plenty of nonsense messages to read
+        self.mock_set_data(b"\x00\x01\xff\x00\x00" * 1000)
+        self._mocker = mocker
+
+    def _make_unpacker(self, buffer):
+        if self.unpacker is not None:
+            pytest.fail("Unexpected 2nd instantiation of Unpacker")
+        self.unpacker = self._mocker.Mock(wraps=Unpacker(buffer))
+        if self._unpacker_failure is not None:
+            self.mock_unpack_failure(self._unpacker_failure)
+        return self.unpacker
+
+    def mock_set_data(self, data):
+        def side_effect(buffer, n):
+            nonlocal data
+
+            if not data:
+                pytest.fail("Read more data than mocked")
+
+            n = min(len(data), len(buffer), n)
+            buffer[:n] = data[:n]
+            data = data[n:]
+            return n
+
+        self.socket_mock.recv_into.side_effect = side_effect
+
+    def assert_no_error(self):
+        self.on_error.assert_not_called()
+        assert next(self.inbox, None) is not None
+
+    def mock_receive_failure(self, exception):
+        self.socket_mock.recv_into.side_effect = exception
+
+    def mock_unpack_failure(self, exception):
+        self._unpacker_failure = exception
+        if self.unpacker is not None:
+            self.unpacker.unpack_structure_header.side_effect = exception
+
+
+@pytest.mark.parametrize(
+    "error",
+    (
+        SocketDeadlineExceeded("test"),
+        OSError("test"),
+    ),
+)
+def test_inbox_receive_failure_error_handler(mocker, error):
+    mocks = InboxMockHolder(mocker)
+    mocks.mock_receive_failure(error)
+    inbox = mocks.inbox
+
+    with pytest.raises(type(error)) as exc:
+        next(inbox)
+
+    assert exc.value is error
+    mocks.on_error.assert_called_once_with(error)
+
+
+@pytest.mark.parametrize(
+    "error",
+    (
+        SocketDeadlineExceeded("test"),
+        OSError("test"),
+        RecursionError("2deep4u"),
+        RuntimeError("something funny happened"),
+    ),
+)
+def test_inbox_unpack_failure(mocker, error):
+    mocks = InboxMockHolder(mocker)
+    mocks.mock_unpack_failure(error)
+    inbox = mocks.inbox
+
+    with pytest.raises(type(error)) as exc:
+        next(inbox)
+
+    assert exc.value is error
+    mocks.on_error.assert_called_once_with(error)
diff --git a/tests/unit/io/_common/test_oubox.py b/tests/unit/io/_common/test_oubox.py
@@ -0,0 +1,48 @@
+# Copyright (c) "Neo4j"
+# Neo4j Sweden AB [https://neo4j.com]
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import pytest
+
+from neo4j.io._common import Outbox
+
+
+@pytest.mark.parametrize(("chunk_size", "data", "result"), (
+    (
+        2,
+        (bytes(range(10, 15)),),
+        bytes((0, 2, 10, 11, 0, 2, 12, 13, 0, 1, 14))
+    ),
+    (
+        2,
+        (bytes(range(10, 14)),),
+        bytes((0, 2, 10, 11, 0, 2, 12, 13))
+    ),
+    (
+        2,
+        (bytes((5, 6, 7)), bytes((8, 9))),
+        bytes((0, 2, 5, 6, 0, 2, 7, 8, 0, 1, 9))
+    ),
+))
+def test_outbox_chunking(chunk_size, data, result):
+    outbox = Outbox(max_chunk_size=chunk_size)
+    assert bytes(outbox.view()) == b""
+    for d in data:
+        outbox.write(d)
+    assert bytes(outbox.view()) == result
+    # make sure this works multiple times
+    assert bytes(outbox.view()) == result
+    outbox.clear()
+    assert bytes(outbox.view()) == b""
diff --git a/tests/unit/io/_common/test_response_handler.py b/tests/unit/io/_common/test_response_handler.py
@@ -1,13 +1,11 @@
 # Copyright (c) "Neo4j"
-# Neo4j Sweden AB [http://neo4j.com]
-#
-# This file is part of Neo4j.
+# Neo4j Sweden AB [https://neo4j.com]
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
-#     http://www.apache.org/licenses/LICENSE-2.0
+#     https://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
@@ -20,40 +18,7 @@
 
 import pytest
 
-from neo4j.io._common import (
-    Outbox,
-    ResetResponse,
-)
-
-
-@pytest.mark.parametrize(("chunk_size", "data", "result"), (
-    (
-        2,
-        (bytes(range(10, 15)),),
-        bytes((0, 2, 10, 11, 0, 2, 12, 13, 0, 1, 14))
-    ),
-    (
-        2,
-        (bytes(range(10, 14)),),
-        bytes((0, 2, 10, 11, 0, 2, 12, 13))
-    ),
-    (
-        2,
-        (bytes((5, 6, 7)), bytes((8, 9))),
-        bytes((0, 2, 5, 6, 0, 2, 7, 8, 0, 1, 9))
-    ),
-))
-def test_outbox_chunking(chunk_size, data, result):
-    outbox = Outbox(max_chunk_size=chunk_size)
-    assert bytes(outbox.view()) == b""
-    for d in data:
-        outbox.write(d)
-    assert bytes(outbox.view()) == result
-    # make sure this works multiple times
-    assert bytes(outbox.view()) == result
-    outbox.clear()
-    assert bytes(outbox.view()) == b""
-
+from neo4j.io._common import ResetResponse
 
 def get_handler_arg(response):
     if response == "RECORD":
diff --git a/tests/unit/io/test_class_bolt.py b/tests/unit/io/test_class_bolt.py
