feat: Implement committer (#13)

* feat: Implement committer

Also small fix to retrying connection so it doesn't leak reads/writes from previous connections.

* fix: Patch retrying connection and add comments.

* Update committer.py

* Update committer_impl.py

google/cloud/pubsublite/internal/wire/committer.py

@@ -0,0 +1,13 @@
+from abc import abstractmethod
+from typing import AsyncContextManager
+
+from google.cloud.pubsublite_v1 import Cursor
+
+
+class Committer(AsyncContextManager):
+  """
+  A Committer is able to commit subscribers' completed offsets.
+  """
+  @abstractmethod
+  async def commit(self, cursor: Cursor) -> None:
+    pass

google/cloud/pubsublite/internal/wire/committer_impl.py

@@ -0,0 +1,138 @@
+import asyncio
+from typing import Optional, List, Iterable
+
+from absl import logging
+
+from google.cloud.pubsublite.internal.wire.committer import Committer
+from google.cloud.pubsublite.internal.wire.retrying_connection import RetryingConnection, ConnectionFactory
+from google.api_core.exceptions import FailedPrecondition, GoogleAPICallError
+from google.cloud.pubsublite.internal.wire.connection_reinitializer import ConnectionReinitializer
+from google.cloud.pubsublite.internal.wire.connection import Connection
+from google.cloud.pubsublite.internal.wire.serial_batcher import SerialBatcher, BatchTester
+from google.cloud.pubsublite_v1 import Cursor
+from google.cloud.pubsublite_v1.types import StreamingCommitCursorRequest, StreamingCommitCursorResponse, InitialCommitCursorRequest
+from google.cloud.pubsublite.internal.wire.work_item import WorkItem
+
+
+class CommitterImpl(Committer, ConnectionReinitializer[StreamingCommitCursorRequest, StreamingCommitCursorResponse], BatchTester[Cursor]):
+  _initial: InitialCommitCursorRequest
+  _flush_seconds: float
+  _connection: RetryingConnection[StreamingCommitCursorRequest, StreamingCommitCursorResponse]
+
+  _batcher: SerialBatcher[Cursor, None]
+
+  _outstanding_commits: List[List[WorkItem[Cursor, None]]]
+
+  _receiver: Optional[asyncio.Future]
+  _flusher: Optional[asyncio.Future]
+
+  def __init__(self, initial: InitialCommitCursorRequest, flush_seconds: float,
+               factory: ConnectionFactory[StreamingCommitCursorRequest, StreamingCommitCursorResponse]):
+    self._initial = initial
+    self._flush_seconds = flush_seconds
+    self._connection = RetryingConnection(factory, self)
+    self._batcher = SerialBatcher(self)
+    self._outstanding_commits = []
+    self._receiver = None
+    self._flusher = None
+
+  async def __aenter__(self):
+    await self._connection.__aenter__()
+
+  def _start_loopers(self):
+    assert self._receiver is None
+    assert self._flusher is None
+    self._receiver = asyncio.ensure_future(self._receive_loop())
+    self._flusher = asyncio.ensure_future(self._flush_loop())
+
+  async def _stop_loopers(self):
+    if self._receiver:
+      self._receiver.cancel()
+      await self._receiver
+      self._receiver = None
+    if self._flusher:
+      self._flusher.cancel()
+      await self._flusher
+      self._flusher = None
+
+  def _handle_response(self, response: StreamingCommitCursorResponse):
+    if "commit" not in response:
+      self._connection.fail(FailedPrecondition("Received an invalid subsequent response on the commit stream."))
+    if response.commit.acknowledged_commits > len(self._outstanding_commits):
+      self._connection.fail(
+        FailedPrecondition("Received a commit response on the stream with no outstanding commits."))
+    for _ in range(response.commit.acknowledged_commits):
+      batch = self._outstanding_commits.pop(0)
+      for item in batch:
+        item.response_future.set_result(None)
+
+  async def _receive_loop(self):
+    try:
+      while True:
+        response = await self._connection.read()
+        self._handle_response(response)
+    except asyncio.CancelledError:
+      return
+
+  async def _flush_loop(self):
+    try:
+      while True:
+        await asyncio.sleep(self._flush_seconds)
+        await self._flush()
+    except asyncio.CancelledError:
+      return
+
+  async def __aexit__(self, exc_type, exc_val, exc_tb):
+    if self._connection.error():
+      self._fail_if_retrying_failed()
+    else:
+      await self._flush()
+    await self._connection.__aexit__(exc_type, exc_val, exc_tb)
+
+  def _fail_if_retrying_failed(self):
+    if self._connection.error():
+      for batch in self._outstanding_commits:
+        for item in batch:
+          item.response_future.set_exception(self._connection.error())
+
+  async def _flush(self):
+    batch = self._batcher.flush()
+    if not batch:
+      return
+    self._outstanding_commits.append(batch)
+    req = StreamingCommitCursorRequest()
+    req.commit.cursor = batch[-1].request
+    try:
+      await self._connection.write(req)
+    except GoogleAPICallError as e:
+      logging.debug(f"Failed commit on stream: {e}")
+      self._fail_if_retrying_failed()
+
+  async def commit(self, cursor: Cursor) -> None:
+    future = self._batcher.add(cursor)
+    if self._batcher.should_flush():
+      # always returns false currently, here in case this changes in the future.
+      await self._flush()
+    await future
+
+  async def reinitialize(self, connection: Connection[StreamingCommitCursorRequest, StreamingCommitCursorResponse]):
+    await self._stop_loopers()
+    await connection.write(StreamingCommitCursorRequest(initial=self._initial))
+    response = await connection.read()
+    if "initial" not in response:
+      self._connection.fail(FailedPrecondition("Received an invalid initial response on the publish stream."))
+    if self._outstanding_commits:
+      # Roll up outstanding commits
+      rollup: List[WorkItem[Cursor, None]] = []
+      for batch in self._outstanding_commits:
+        for item in batch:
+          rollup.append(item)
+      self._outstanding_commits = [rollup]
+      req = StreamingCommitCursorRequest()
+      req.commit.cursor = rollup[-1].request
+      await connection.write(req)
+    self._start_loopers()
+
+  def test(self, requests: Iterable[Cursor]) -> bool:
+    # There is no bound on the number of outstanding cursors.
+    return False

google/cloud/pubsublite/internal/wire/connection_reinitializer.py

@@ -7,7 +7,8 @@ class ConnectionReinitializer(Generic[Request, Response], metaclass=ABCMeta):
     """A class capable of reinitializing a connection after a new one has been created."""
     @abstractmethod
     def reinitialize(self, connection: Connection[Request, Response]):
-        """Reinitialize a connection.
+        """Reinitialize a connection. Must ensure no calls to the associated RetryingConnection
+        occur until this completes.
 
         Args:
             connection: The connection to reinitialize

google/cloud/pubsublite/internal/wire/publisher.py

@@ -1,20 +1,13 @@
-from abc import ABC, abstractmethod
+from abc import abstractmethod
+from typing import AsyncContextManager
 from google.cloud.pubsublite_v1.types import PubSubMessage
 from google.cloud.pubsublite.publish_metadata import PublishMetadata
 
 
-class Publisher(ABC):
+class Publisher(AsyncContextManager):
   """
   A Pub/Sub Lite asynchronous wire protocol publisher.
   """
-  @abstractmethod
-  async def __aenter__(self):
-    raise NotImplementedError()
-
-  @abstractmethod
-  async def __aexit__(self, exc_type, exc_val, exc_tb):
-    raise NotImplementedError()
-
   @abstractmethod
   async def publish(self, message: PubSubMessage) -> PublishMetadata:
     """

google/cloud/pubsublite/internal/wire/retrying_connection.py

@@ -48,15 +48,22 @@ async def _run_loop(self):
     """
     Processes actions on this connection and handles retries until cancelled.
     """
+    last_failure: GoogleAPICallError
     try:
       bad_retries = 0
       while True:
         try:
           async with self._connection_factory.new() as connection:
+            # Needs to happen prior to reinitialization to clear outstanding waiters.
+            while not self._write_queue.empty():
+              self._write_queue.get_nowait().response_future.set_exception(last_failure)
+            self._read_queue = asyncio.Queue(maxsize=1)
+            self._write_queue = asyncio.Queue(maxsize=1)
             await self._reinitializer.reinitialize(connection)
             bad_retries = 0
             await self._loop_connection(connection)
         except GoogleAPICallError as e:
+          last_failure = e
           if not is_retryable(e):
             self.fail(e)
             return

setup.py

@@ -25,40 +25,46 @@
 
 readme_filename = os.path.join(package_root, "README.rst")
 with io.open(readme_filename, encoding="utf-8") as readme_file:
-    readme = readme_file.read()
+  readme = readme_file.read()
 
 dependencies = [
     "google-api-core >= 1.22.0",
     "absl-py >= 0.9.0",
     "proto-plus >= 0.4.0",
+    "grpcio",
     "setuptools"
 ]
 
+test_dependencies = [
+    "asynctest",
+    "pytest",
+    "pytest-asyncio"
+]
+
 setuptools.setup(
-    name="google-cloud-pubsublite",
-    version=version,
-    long_description=readme,
-    author="Google LLC",
-    author_email="googleapis-packages@google.com",
-    license="Apache 2.0",
-    url="https://github.com/googleapis/python-pubsublite",
-    packages=setuptools.PEP420PackageFinder.find(),
-    namespace_packages=("google", "google.cloud"),
-    platforms="Posix; MacOS X; Windows",
-    include_package_data=True,
-    install_requires=dependencies,
-    setup_requires=('pytest-runner',),
-    tests_require=['asynctest', 'pytest', 'pytest-asyncio'],
-    python_requires=">=3.6",
-    classifiers=[
-        "Development Status :: 4 - Beta",
-        "Intended Audience :: Developers",
-        "Operating System :: OS Independent",
-        "Programming Language :: Python :: 3.6",
-        "Programming Language :: Python :: 3.7",
-        "Programming Language :: Python :: 3.8",
-        "Topic :: Internet",
-        "Topic :: Software Development :: Libraries :: Python Modules",
-    ],
-    zip_safe=False,
+  name="google-cloud-pubsublite",
+  version=version,
+  long_description=readme,
+  author="Google LLC",
+  author_email="googleapis-packages@google.com",
+  license="Apache 2.0",
+  url="https://github.com/googleapis/python-pubsublite",
+  packages=setuptools.PEP420PackageFinder.find(),
+  namespace_packages=("google", "google.cloud"),
+  platforms="Posix; MacOS X; Windows",
+  include_package_data=True,
+  install_requires=dependencies,
+  extras_require={"tests": test_dependencies},
+  python_requires=">=3.6",
+  classifiers=[
+    "Development Status :: 4 - Beta",
+    "Intended Audience :: Developers",
+    "Operating System :: OS Independent",
+    "Programming Language :: Python :: 3.6",
+    "Programming Language :: Python :: 3.7",
+    "Programming Language :: Python :: 3.8",
+    "Topic :: Internet",
+    "Topic :: Software Development :: Libraries :: Python Modules",
+  ],
+  zip_safe=False,
 )