New Sink: GCP Pub/Sub (#616)

* Add google-cloud-pubsub to requirements * Add Google Cloud Pub/Sub Sink - bare minimal implementation * Pass key, timestamp and header to PubSub message as metadata attributes * PR fixes and other improvements * Reorder API Docs / Sinks API table of contents * docs * Pass service_acount_json * Correct docs * Add __all__ remove logging * Correct docs * Fix indentation in docs * More docs work * Update quixstreams/sinks/community/pubsub.py Co-authored-by: Daniil Gusev <[email protected]> * Edit local testing section --------- Co-authored-by: Daniil Gusev <[email protected]>
quixio · Nov 14, 2024 · 9fbe690 · 9fbe690
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diff --git a/LICENSES/LICENSE.google-cloud-pubsub b/LICENSES/LICENSE.google-cloud-pubsub
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diff --git a/conda/meta.yaml b/conda/meta.yaml
@@ -24,6 +24,7 @@ requirements:
     - jsonschema >=4.3.0
     - fastavro >=1.8,<2.0
     - jsonlines >=4,<5
+    - google-cloud-pubsub >=2.23.1,<3
 
 test:
   imports:

diff --git a/docs/build/build.py b/docs/build/build.py
@@ -111,21 +111,24 @@
             "quixstreams.context",
         ]
     },
+    # Order: base, core, community
     "sinks.md": {
         k: None
         for k in [
+            "quixstreams.sinks.base.sink",
+            "quixstreams.sinks.base.batch",
+            "quixstreams.sinks.base.exceptions",
+            "quixstreams.sinks.core.influxdb3",
+            "quixstreams.sinks.core.csv",
             "quixstreams.sinks.community.iceberg",
             "quixstreams.sinks.community.file.sink",
             "quixstreams.sinks.community.file.formats.base",
             "quixstreams.sinks.community.file.formats.json",
             "quixstreams.sinks.community.file.formats.parquet",
-            "quixstreams.sinks.core.influxdb3",
-            "quixstreams.sinks.core.csv",
-            "quixstreams.sinks.base.sink",
-            "quixstreams.sinks.base.exceptions",
-            "quixstreams.sinks.base.batch",
+            "quixstreams.sinks.community.pubsub",
         ]
     },
+    # Order: base, core, community
     "sources.md": {
         k: None
         for k in [

diff --git a/docs/connectors/sinks/google-cloud-pubsub-sink.md b/docs/connectors/sinks/google-cloud-pubsub-sink.md
@@ -0,0 +1,104 @@
+# Google Cloud Pub/Sub Sink
+
+!!! info
+
+    This is a **Community** connector. Test it before using in production.
+
+    To learn more about differences between Core and Community connectors, see the [Community and Core Connectors](../community-and-core.md) page.
+
+This sink writes data to a Google Cloud Pub/Sub topic. The sink preserves the original Kafka message metadata including key, timestamp, offset, and headers.
+
+## Prerequisites
+
+To use the Pub/Sub sink, you need to install the required dependencies:
+
+```bash
+pip install quixstreams[pubsub]
+```
+
+## How the Pub/Sub Sink Works
+
+`PubSubSink` is a streaming sink that publishes messages to Pub/Sub topics. For each message:
+
+- The value is serialized (defaults to JSON)
+- The key is converted to string
+- Additional metadata (timestamp, offset, headers) is included as attributes
+- Messages are published asynchronously
+
+## How To Use Pub/Sub Sink
+
+Create an instance of `PubSubSink` and pass it to the `StreamingDataFrame.sink()` method:
+
+```python
+from google.api_core import retry
+from google.cloud.pubsub_v1.types import PublisherOptions
+from quixstreams import Application
+from quixstreams.sinks.community.pubsub import PubSubSink
+
+app = Application(broker_address="localhost:9092")
+topic = app.topic("topic-name")
+
+# Read the service account credentials in JSON format from some environment variable.
+service_account_json = os.environ["PUBSUB_SERVICE_ACCOUNT_JSON"]
+
+# Configure the sink
+pubsub_sink = PubSubSink(
+    project_id="<project ID>",
+    topic_id="<topic ID>",
+    # Optional: service account credentials as a JSON string
+    service_account_json=service_account_json,
+    # Optional: customize serialization and flush timeout
+    value_serializer=json.dumps,
+    key_serializer=str,
+    flush_timeout=10,
+    # Optional: Additional keyword arguments are passed to the PublisherClient
+    publisher_options=PublisherOptions(
+        # Configure publisher options to retry on any exception
+        retry=retry.Retry(predicate=retry.if_exception_type(Exception)),
+    )
+)
+
+sdf = app.dataframe(topic=topic)
+sdf.sink(pubsub_sink)
+
+if __name__ == "__main__":
+    app.run()
+```
+
+### Configuration Options
+
+- `project_id`: Your Google Cloud project ID
+- `topic_id`: The ID of the Pub/Sub topic
+- `service_account_json`: A JSON string containing service account credentials for authentication
+- `value_serializer`: Function to serialize message values (default: `json.dumps`)
+- `key_serializer`: Function to serialize message keys (default: `bytes.decode`)
+- `flush_timeout`: Maximum time in seconds to wait for pending publishes during flush (default: 5)
+- Additional keyword arguments are passed to the Pub/Sub `PublisherClient`
+
+## Error Handling and Delivery Guarantees
+
+The sink provides **at-least-once** delivery guarantees, which means:
+
+- Messages are published asynchronously for better performance
+- During checkpointing, the sink waits for all pending publishes to complete
+- The wait time is controlled by `flush_timeout` parameter (defaults to 5 seconds)
+- If any messages fail to publish within the flush timeout, a `SinkBackpressureError` is raised
+- When `SinkBackpressureError` occurs:
+  - The application will retry the entire batch from the last successful offset
+  - Some messages that were successfully published in the failed batch may be published again
+  - This ensures no messages are lost, but some might be delivered more than once
+
+This behavior makes the sink reliable but means downstream systems should be prepared to handle duplicate messages. If your application requires exactly-once semantics, you'll need to implement deduplication logic in your consumer.
+
+## Testing locally
+
+Rather than connect to Google Cloud, you can alternatively test your application using 
+a local "emulated" Pub/Sub host via docker:
+
+1. DO NOT pass a `service_account_json` to `PubSubSource`, instead set environment variable:
+
+    `PUBSUB_EMULATOR_HOST=localhost:8085`
+
+2. execute in terminal:
+
+    `docker run -d --name pubsub-emulator -p 8085:8085 gcr.io/google.com/cloudsdktool/google-cloud-cli:emulators gcloud beta emulators pubsub start --host-port=0.0.0.0:8085`
diff --git a/mkdocs.yml b/mkdocs.yml
@@ -51,8 +51,9 @@ nav:
         - 'connectors/sinks/README.md'
         - Apache Iceberg Sink: connectors/sinks/apache-iceberg-sink.md
         - CSV Sink: connectors/sinks/csv-sink.md
-        - InfluxDB v3 Sink: connectors/sinks/influxdb3-sink.md
         - File Sink: connectors/sinks/file-sink.md
+        - Google Cloud Pub/Sub Sink: connectors/sinks/google-cloud-pubsub-sink.md
+        - InfluxDB v3 Sink: connectors/sinks/influxdb3-sink.md
         - Creating a Custom Sink: connectors/sinks/custom-sinks.md
     - Sources:
         - 'connectors/sources/README.md'

diff --git a/pyproject.toml b/pyproject.toml
@@ -32,13 +32,15 @@ all = [
     "protobuf>=5.27.2,<6.0",
     "influxdb3-python>=0.7,<1.0",
     "pyiceberg[pyarrow,glue]>=0.7,<0.8",
+    "google-cloud-pubsub>=2.23.1,<3",
 ]
 
 avro = ["fastavro>=1.8,<2.0"]
 protobuf = ["protobuf>=5.27.2,<6.0"]
 influxdb3 = ["influxdb3-python>=0.7,<1.0"]
 iceberg = ["pyiceberg[pyarrow]>=0.7,<0.8"]
 iceberg_aws = ["pyiceberg[pyarrow,glue]>=0.7,<0.8"]
+pubsub = ["google-cloud-pubsub>=2.23.1,<3"]
 
 [tool.setuptools.packages.find]
 include = ["quixstreams*"]