text: # Copyright 2019, Google LLC All rights reserved.
  #
  # 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.
  
  from __future__ import absolute_import
  
  import os
  import pkg_resources
  
  from google.auth.credentials import AnonymousCredentials
  from google.oauth2 import service_account
  
  from google.cloud.pubsub_v1 import _gapic
  from google.cloud.pubsub_v1 import types
  from google.cloud.pubsub_v1.subscriber import futures
  from google.cloud.pubsub_v1.subscriber._protocol import streaming_pull_manager
  from google.pubsub_v1.services.subscriber import client as subscriber_client
  
  
  try:
      __version__ = pkg_resources.get_distribution("google-cloud-pubsub").version
  except pkg_resources.DistributionNotFound:
      # Distribution might not be available if we are not running from within
      # a PIP package.
      __version__ = "0.0"
  
  _BLACKLISTED_METHODS = (
      "publish",
      "from_service_account_file",
      "from_service_account_json",
  )
  
  
  @_gapic.add_methods(subscriber_client.SubscriberClient, blacklist=_BLACKLISTED_METHODS)
  class Client(object):
      """A subscriber client for Google Cloud Pub/Sub.
  
      This creates an object that is capable of subscribing to messages.
      Generally, you can instantiate this client with no arguments, and you
      get sensible defaults.
  
      Args:
          kwargs (dict): Any additional arguments provided are sent as keyword
              keyword arguments to the underlying
              :class:`~google.cloud.pubsub_v1.gapic.subscriber_client.SubscriberClient`.
              Generally you should not need to set additional keyword
              arguments. Optionally, regional endpoints can be set via
              ``client_options`` that takes a single key-value pair that
              defines the endpoint.
  
      Example:
  
      .. code-block:: python
  
          from google.cloud import pubsub_v1
  
          subscriber_client = pubsub_v1.SubscriberClient(
              # Optional
              client_options = {
                  "api_endpoint": REGIONAL_ENDPOINT
              }
          )
      """
  
      def __init__(self, **kwargs):
          # Sanity check: Is our goal to use the emulator?
          # If so, create a grpc insecure channel with the emulator host
          # as the target.
          if os.environ.get("PUBSUB_EMULATOR_HOST"):
              kwargs["client_options"] = {
                  "api_endpoint": os.environ.get("PUBSUB_EMULATOR_HOST")
              }
              kwargs["credentials"] = AnonymousCredentials()
  
          # Instantiate the underlying GAPIC client.
          self._api = subscriber_client.SubscriberClient(**kwargs)
          self._target = self._api._transport._host
  
      @classmethod
      def from_service_account_file(cls, filename, **kwargs):
          """Creates an instance of this client using the provided credentials
          file.
  
          Args:
              filename (str): The path to the service account private key json
                  file.
              kwargs: Additional arguments to pass to the constructor.
  
          Returns:
              A Subscriber :class:`~google.cloud.pubsub_v1.subscriber.client.Client`
              instance that is the constructed client.
          """
          credentials = service_account.Credentials.from_service_account_file(filename)
          kwargs["credentials"] = credentials
          return cls(**kwargs)
  
      from_service_account_json = from_service_account_file
  
      @property
      def target(self):
          """Return the target (where the API is).
  
          Returns:
              str: The location of the API.
          """
          return self._target
  
      @property
      def api(self):
          """The underlying gapic API client."""
          return self._api
  
      def subscribe(
          self,
          subscription,
          callback,
          flow_control=(),
          scheduler=None,
          use_legacy_flow_control=False,
          await_callbacks_on_shutdown=False,
      ):
          """Asynchronously start receiving messages on a given subscription.
  
          This method starts a background thread to begin pulling messages from
          a Pub/Sub subscription and scheduling them to be processed using the
          provided ``callback``.
  
          The ``callback`` will be called with an individual
          :class:`google.cloud.pubsub_v1.subscriber.message.Message`. It is the
          responsibility of the callback to either call ``ack()`` or ``nack()``
          on the message when it finished processing. If an exception occurs in
          the callback during processing, the exception is logged and the message
          is ``nack()`` ed.
  
          The ``flow_control`` argument can be used to control the rate of at
          which messages are pulled. The settings are relatively conservative by
          default to prevent "message hoarding" - a situation where the client
          pulls a large number of messages but can not process them fast enough
          leading it to "starve" other clients of messages. Increasing these
          settings may lead to faster throughput for messages that do not take
          a long time to process.
  
          The ``use_legacy_flow_control`` argument disables enforcing flow control
          settings at the Cloud Pub/Sub server, and only the client side flow control
          will be enforced.
  
          This method starts the receiver in the background and returns a
          *Future* representing its execution. Waiting on the future (calling
          ``result()``) will block forever or until a non-recoverable error
          is encountered (such as loss of network connectivity). Cancelling the
          future will signal the process to shutdown gracefully and exit.
  
          .. note:: This uses Pub/Sub's *streaming pull* feature. This feature
              properties that may be surprising. Please take a look at
              https://cloud.google.com/pubsub/docs/pull#streamingpull for
              more details on how streaming pull behaves compared to the
              synchronous pull method.
  
          Example:
  
          .. code-block:: python
  
              from google.cloud import pubsub_v1
  
              subscriber_client = pubsub_v1.SubscriberClient()
  
              # existing subscription
              subscription = subscriber_client.subscription_path(
                  'my-project-id', 'my-subscription')
  
              def callback(message):
                  print(message)
                  message.ack()
  
              future = subscriber_client.subscribe(
                  subscription, callback)
  
              try:
                  future.result()
              except KeyboardInterrupt:
                  future.cancel()  # Trigger the shutdown.
                  future.result()  # Block until the shutdown is complete.
  
          Args:
              subscription (str): The name of the subscription. The
                  subscription should have already been created (for example,
                  by using :meth:`create_subscription`).
              callback (Callable[~google.cloud.pubsub_v1.subscriber.message.Message]):
                  The callback function. This function receives the message as
                  its only argument and will be called from a different thread/
                  process depending on the scheduling strategy.
              flow_control (~google.cloud.pubsub_v1.types.FlowControl): The flow control
                  settings. Use this to prevent situations where you are
                  inundated with too many messages at once.
              scheduler (~google.cloud.pubsub_v1.subscriber.scheduler.Scheduler): An optional
                  *scheduler* to use when executing the callback. This controls
                  how callbacks are executed concurrently. This object must not be shared
                  across multiple SubscriberClients.
              use_legacy_flow_control (bool):
                  If set to ``True``, flow control at the Cloud Pub/Sub server is disabled,
                  though client-side flow control is still enabled. If set to ``False``
                  (default), both server-side and client-side flow control are enabled.
              await_callbacks_on_shutdown (bool):
                  If ``True``, after canceling the returned future, the latter's
                  ``result()`` method will block until the background stream and its
                  helper threads have been terminated, and all currently executing message
                  callbacks are done processing.
  
                  If ``False`` (default), the returned future's ``result()`` method will
                  not block after canceling the future. The method will instead return
                  immediately after the background stream and its helper threads have been
                  terminated, but some of the message callback threads might still be
                  running at that point.
  
          Returns:
              A :class:`~google.cloud.pubsub_v1.subscriber.futures.StreamingPullFuture`
              instance that can be used to manage the background stream.
          """
          flow_control = types.FlowControl(*flow_control)
  
          manager = streaming_pull_manager.StreamingPullManager(
              self,
              subscription,
              flow_control=flow_control,
              scheduler=scheduler,
              use_legacy_flow_control=use_legacy_flow_control,
              await_callbacks_on_shutdown=await_callbacks_on_shutdown,
          )
  
          future = futures.StreamingPullFuture(manager)
  
          manager.open(callback=callback, on_callback_error=future.set_exception)
  
          return future
  
      def close(self):
          """Close the underlying channel to release socket resources.
  
          After a channel has been closed, the client instance cannot be used
          anymore.
  
          This method is idempotent.
          """
          self.api._transport.grpc_channel.close()
  
      def __enter__(self):
          return self
  
      def __exit__(self, exc_type, exc_val, exc_tb):
          self.close()
  