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Config

connector_type: google_cloud_pubsub
project_id: test-project-id
topic_id: test-topic-id
subscription_id: test-subscription-id-0
timeout: 5
batch_size: 100
pubsub_emulator_host: null  # "host.docker.internal:8085"
path_to_credentials_json_file: "./google_credentials.json"

The pubsub_emulator_host parameter is optional, which could be used when you need to test the Google Cloud PubSub service locally through an emulator (see more details at the bottom).

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Start Mage

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Create a new pipeline

  1. Open Mage in your browser.

  2. Click + New pipeline, then select Streaming.

  3. Add a data loader block, select Google Cloud PubSub, and change the settings to those of your PubSub project:

    connector_type: google_cloud_pubsub
project_id: test-project-id
topic_id: test-topic-id
subscription_id: test-subscription-id-0
timeout: 5
batch_size: 100
pubsub_emulator_host: null
path_to_credentials_json_file: "./google_credentials.json"

  4. Add a transformer block and paste the following:

    from typing import Dict, List

if 'transformer' not in globals():
    from mage_ai.data_preparation.decorators import transformer


@transformer
def transform(messages: List[Dict], *args, **kwargs):
    """
    Template code for a transformer block.

    Args:
        messages: List of messages in the stream.

    Returns:
        Transformed messages
    """
    # Specify your transformation logic here
    print(f'Transform: {messages}')
    return messages

  5. Add a data exporter block, select Dummy and keep the default settings:

    connector_type: dummy
print_msg: true

​

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Test pipeline

Open the streaming pipeline you just created, and in the right side panel near the bottom, click the button Execute pipeline to test the pipeline.

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Publish some testing messages

Please use the publisher example given in the Testing apps locally with the emulator

python publisher.py test-project-id publish test-topic-id

You should see an output similar to the following:

[silent_mountain] [GoogleCloudPubSubSource] Subscription already exists: projects/my-pubsub-project-385206/subscriptions/my-topic-1-sub
[silent_mountain] [GoogleCloudPubSubSource] Start consuming batch messages.
[silent_mountain] [GoogleCloudPubSubSource] Number of received messages: 4
[late_wood] Transform: [{'data': 'Google Cloud PubSub Message number 1'}, {'data': 'Google Cloud PubSub Message number 8'}, {'data': 'Google Cloud PubSub Message number 2'}, {'data': 'Google Cloud PubSub Message number 3'}]
[silent_mountain] [DummySink] Batch ingest 4 records, time=1682968557.6466439. Sample: {'data': 'Google Cloud PubSub Message number 1'}
[silent_mountain] [GoogleCloudPubSubSource] Received and acknowledged 4 messages from projects/my-pubsub-project-385206/subscriptions/my-topic-1-sub.
[silent_mountain] [GoogleCloudPubSubSource] Number of received messages: 4
[late_wood] Transform: [{'data': 'Google Cloud PubSub Message number 7'}, {'data': 'Google Cloud PubSub Message number 9'}, {'data': 'Google Cloud PubSub Message number 4'}, {'data': 'Google Cloud PubSub Message number 5'}]
[silent_mountain] [DummySink] Batch ingest 4 records, time=1682968559.027885. Sample: {'data': 'Google Cloud PubSub Message number 7'}
[silent_mountain] [GoogleCloudPubSubSource] Received and acknowledged 4 messages from projects/my-pubsub-project-385206/subscriptions/my-topic-1-sub.
[silent_mountain] [GoogleCloudPubSubSource] Number of received messages: 1
[late_wood] Transform: [{'data': 'Google Cloud PubSub Message number 6'}]
[silent_mountain] [DummySink] Batch ingest 1 records, time=1682968560.894928. Sample: {'data': 'Google Cloud PubSub Message number 6'}
[silent_mountain] [GoogleCloudPubSubSource] Received and acknowledged 1 messages from projects/my-pubsub-project-385206/subscriptions/my-topic-1-sub.

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Set up Google Cloud Pubsub emulator

To test out Google Cloud PubSub source locally, follow the instructions in Testing apps locally with the emulator to set up the local Google Cloud PubSub emulator.

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Create a project_id for testing

Use the command listed under the Starting the emulator section to create a project_id, e.g.,

gcloud beta emulators pubsub start --project=test-project-id

$(gcloud beta emulators pubsub env-init)

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Create a topic and a subscription

Use the gcloud pubsub topics create command to create a topic:

gcloud pubsub topics create test-topic-id

After you create a topic, you can subscribe or publish to it. Use the gcloud pubsub subscriptions create command to create a subscription.

gcloud pubsub subscriptions create test-subscription-id-0 --topic test-topic-id

Only messages published to the topic after the subscription is created are available to subscriber applications.

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