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"""This module contains a Google PubSub sensor."""
from typing import TYPE_CHECKING, Any, Callable, List, Optional, Sequence, Union
from google.cloud.pubsub_v1.types import ReceivedMessage
from airflow.providers.google.cloud.hooks.pubsub import PubSubHook
from airflow.sensors.base import BaseSensorOperator
if TYPE_CHECKING:
from airflow.utils.context import Context
[docs]class PubSubPullSensor(BaseSensorOperator):
"""Pulls messages from a PubSub subscription and passes them through XCom.
Always waits for at least one message to be returned from the subscription.
.. seealso::
For more information on how to use this operator, take a look at the guide:
:ref:`howto/operator:PubSubPullSensor`
.. seealso::
If you don't want to wait for at least one message to come, use Operator instead:
:class:`~airflow.providers.google.cloud.operators.pubsub.PubSubPullOperator`
This sensor operator will pull up to ``max_messages`` messages from the
specified PubSub subscription. When the subscription returns messages,
the poke method's criteria will be fulfilled and the messages will be
returned from the operator and passed through XCom for downstream tasks.
If ``ack_messages`` is set to True, messages will be immediately
acknowledged before being returned, otherwise, downstream tasks will be
responsible for acknowledging them.
If you want a non-blocking task that does not to wait for messages, please use
:class:`~airflow.providers.google.cloud.operators.pubsub.PubSubPullOperator`
instead.
``project_id`` and ``subscription`` are templated so you can use
variables in them.
:param project_id: the Google Cloud project ID for the subscription (templated)
:param subscription: the Pub/Sub subscription name. Do not include the
full subscription path.
:param max_messages: The maximum number of messages to retrieve per
PubSub pull request
:param ack_messages: If True, each message will be acknowledged
immediately rather than by any downstream tasks
:param gcp_conn_id: The connection ID to use connecting to
Google Cloud.
:param delegate_to: The account to impersonate using domain-wide delegation of authority,
if any. For this to work, the service account making the request must have
domain-wide delegation enabled.
:param messages_callback: (Optional) Callback to process received messages.
It's return value will be saved to XCom.
If you are pulling large messages, you probably want to provide a custom callback.
If not provided, the default implementation will convert `ReceivedMessage` objects
into JSON-serializable dicts using `google.protobuf.json_format.MessageToDict` function.
:param impersonation_chain: Optional service account to impersonate using short-term
credentials, or chained list of accounts required to get the access_token
of the last account in the list, which will be impersonated in the request.
If set as a string, the account must grant the originating account
the Service Account Token Creator IAM role.
If set as a sequence, the identities from the list must grant
Service Account Token Creator IAM role to the directly preceding identity, with first
account from the list granting this role to the originating account (templated).
"""
[docs] template_fields: Sequence[str] = (
'project_id',
'subscription',
'impersonation_chain',
)
def __init__(
self,
*,
project_id: str,
subscription: str,
max_messages: int = 5,
ack_messages: bool = False,
gcp_conn_id: str = 'google_cloud_default',
messages_callback: Optional[Callable[[List[ReceivedMessage], "Context"], Any]] = None,
delegate_to: Optional[str] = None,
impersonation_chain: Optional[Union[str, Sequence[str]]] = None,
**kwargs,
) -> None:
super().__init__(**kwargs)
self.gcp_conn_id = gcp_conn_id
self.delegate_to = delegate_to
self.project_id = project_id
self.subscription = subscription
self.max_messages = max_messages
self.ack_messages = ack_messages
self.messages_callback = messages_callback
self.impersonation_chain = impersonation_chain
self._return_value = None
[docs] def execute(self, context: "Context") -> Any:
"""Overridden to allow messages to be passed"""
super().execute(context)
return self._return_value
[docs] def poke(self, context: "Context") -> bool:
hook = PubSubHook(
gcp_conn_id=self.gcp_conn_id,
delegate_to=self.delegate_to,
impersonation_chain=self.impersonation_chain,
)
pulled_messages = hook.pull(
project_id=self.project_id,
subscription=self.subscription,
max_messages=self.max_messages,
return_immediately=True,
)
handle_messages = self.messages_callback or self._default_message_callback
self._return_value = handle_messages(pulled_messages, context)
if pulled_messages and self.ack_messages:
hook.acknowledge(
project_id=self.project_id,
subscription=self.subscription,
messages=pulled_messages,
)
return bool(pulled_messages)
def _default_message_callback(
self,
pulled_messages: List[ReceivedMessage],
context: "Context",
):
"""
This method can be overridden by subclasses or by `messages_callback` constructor argument.
This default implementation converts `ReceivedMessage` objects into JSON-serializable dicts.
:param pulled_messages: messages received from the topic.
:param context: same as in `execute`
:return: value to be saved to XCom.
"""
messages_json = [ReceivedMessage.to_dict(m) for m in pulled_messages]
return messages_json
