feat(storage): Enable full object checksum PR 1/3 : parse finalize_time and server crc32c in async object stream (#17261)

chandra-siri · web-flow · commit 72c7a2728bf6 · 2026-06-04T15:12:05.000+05:30
### 1. Overview of the Solution
This solution implements end-to-end full-object checksum validation in
`AsyncMultiRangeDownloader` for the asynchronous Google Cloud Storage
Python client library. As asynchronous multiplexed downloads of
non-contiguous ranges are performed concurrently over a single
bidirectional gRPC connection, this feature automatically and
incrementally calculates a rolling checksum as bytes arrive and
validates it against the server's authoritative object checksum once the
download completes.

The technical approach consists of three coordinated layers:
* **`_AsyncReadObjectStream` (Stream Ingestion)**: Safely extracts the
authoritative server checksum (`full_obj_server_crc32c`) and
finalization status (`is_finalized`) from the object metadata received
in the first data payload response of the stream.
* **`_ReadResumptionStrategy` &amp; `_DownloadState` (Verification Logic)**:
Computes an isolated, persistent rolling checksum in the individual
`_DownloadState` object to ensure calculations do not bleed across
concurrent multiplexed ranges. Crucially, the rolling hash updates only
*after* buffer writes succeed to prevent state corruption during retry
re-connects, raising a `DataCorruption` exception on completion if a
mismatch occurs.
* **`AsyncMultiRangeDownloader` (Orchestration &amp; Cleanup)**: Detects
candidate full-object ranges (e.g., `(0, 0)` or `(0, persisted_size)`),
propagates checksum settings to the resumption strategy, and guarantees
robust cleanup (closing the stream immediately and unregistering IDs) if
data corruption or write errors occur.

### 2. What This PR Specifically Does
This PR implements **Step 1: Stream Metadata Ingestion** of the
solution:
* Modifies `_AsyncReadObjectStream` to safely parse GCS object metadata
from the first data payload of the response.
* Populates `is_finalized`, `full_obj_server_crc32c`, and
`object_metadata` attributes in `_AsyncReadObjectStream.open()`.
* Adds an autouse pytest event loop fixture in `tests/unit/conftest.py`
to resolve compatibility issues with `pytest-asyncio` under Python
3.11+.
* Adds unit tests in `test_async_read_object_stream.py` to verify that
finalization status and server-authoritative checksums are correctly
extracted or skipped for unfinalized objects.
diff --git a/packages/google-cloud-storage/google/cloud/storage/asyncio/async_read_object_stream.py b/packages/google-cloud-storage/google/cloud/storage/asyncio/async_read_object_stream.py
@@ -79,6 +79,9 @@ def __init__(
         self.socket_like_rpc: Optional[AsyncBidiRpc] = None
         self._is_stream_open: bool = False
         self.persisted_size: Optional[int] = None
+        self.is_finalized: bool = False
+        self.full_obj_server_crc32c: Optional[int] = None
+        self.object_metadata: Optional[_storage_v2.Object] = None
 
     async def open(self, metadata: Optional[List[Tuple[str, str]]] = None) -> None:
         """Opens the bidi-gRPC connection to read from the object.
@@ -132,6 +135,18 @@ async def open(self, metadata: Optional[List[Tuple[str, str]]] = None) -> None:
                 self.generation_number = response.metadata.generation
             # update persisted size
             self.persisted_size = response.metadata.size
+            self.object_metadata = response.metadata
+            if (
+                hasattr(response.metadata, "finalize_time")
+                and response.metadata.finalize_time
+                and response.metadata.finalize_time.second > 0
+            ):
+                self.is_finalized = True
+                if (
+                    hasattr(response.metadata, "checksums")
+                    and response.metadata.checksums
+                ):
+                    self.full_obj_server_crc32c = response.metadata.checksums.crc32c
 
         if response and response.read_handle:
             self.read_handle = response.read_handle
diff --git a/packages/google-cloud-storage/tests/unit/asyncio/test_async_read_object_stream.py b/packages/google-cloud-storage/tests/unit/asyncio/test_async_read_object_stream.py
@@ -38,9 +38,11 @@ async def instantiate_read_obj_stream(mock_client, mock_cls_async_bidi_rpc, open
     socket_like_rpc.open = AsyncMock()
 
     recv_response = mock.MagicMock(spec=_storage_v2.BidiReadObjectResponse)
-    recv_response.metadata = mock.MagicMock(spec=_storage_v2.Object)
+    recv_response.metadata = mock.MagicMock()
     recv_response.metadata.generation = _TEST_GENERATION_NUMBER
     recv_response.metadata.size = _TEST_OBJECT_SIZE
+    recv_response.metadata.finalize_time.second = 30
+    recv_response.metadata.checksums.crc32c = 98765
     recv_response.read_handle = _TEST_READ_HANDLE
     socket_like_rpc.recv = AsyncMock(return_value=recv_response)
 
@@ -130,6 +132,8 @@ async def test_open(mock_client, mock_cls_async_bidi_rpc):
     assert read_obj_stream.generation_number == _TEST_GENERATION_NUMBER
     assert read_obj_stream.read_handle == _TEST_READ_HANDLE
     assert read_obj_stream.persisted_size == _TEST_OBJECT_SIZE
+    assert read_obj_stream.is_finalized is True
+    assert read_obj_stream.full_obj_server_crc32c == 98765
     assert read_obj_stream.is_stream_open
 
 
@@ -381,3 +385,36 @@ async def test_recv_updates_read_handle_on_refresh(
 
     await stream.recv()
     assert stream.read_handle == refreshed_handle
+
+
+@mock.patch("google.cloud.storage.asyncio.async_read_object_stream.AsyncBidiRpc")
+@mock.patch(
+    "google.cloud.storage.asyncio.async_grpc_client.AsyncGrpcClient.grpc_client"
+)
+@pytest.mark.asyncio
+async def test_open_unfinalized_object_skips_checksum(
+    mock_client, mock_cls_async_bidi_rpc
+):
+    socket_like_rpc = AsyncMock()
+    mock_cls_async_bidi_rpc.return_value = socket_like_rpc
+    socket_like_rpc.open = AsyncMock()
+
+    recv_response = mock.MagicMock(spec=_storage_v2.BidiReadObjectResponse)
+    recv_response.metadata = mock.MagicMock()
+    recv_response.metadata.generation = _TEST_GENERATION_NUMBER
+    recv_response.metadata.size = _TEST_OBJECT_SIZE
+    recv_response.metadata.finalize_time.second = 0  # NOT finalized!
+    recv_response.metadata.checksums.crc32c = 98765
+    recv_response.read_handle = _TEST_READ_HANDLE
+    socket_like_rpc.recv = AsyncMock(return_value=recv_response)
+
+    read_obj_stream = _AsyncReadObjectStream(
+        client=mock_client,
+        bucket_name=_TEST_BUCKET_NAME,
+        object_name=_TEST_OBJECT_NAME,
+    )
+
+    await read_obj_stream.open()
+
+    assert read_obj_stream.is_finalized is False
+    assert read_obj_stream.full_obj_server_crc32c is None
diff --git a/packages/google-cloud-storage/tests/unit/conftest.py b/packages/google-cloud-storage/tests/unit/conftest.py
@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*-
+# Copyright 2026 Google LLC
+#
+# 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.
+
+import asyncio
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def set_event_loop():
+    try:
+        asyncio.get_running_loop()
+        yield
+    except RuntimeError:
+        loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(loop)
+        try:
+            yield
+        finally:
+            loop.close()
+            asyncio.set_event_loop(None)
