[GitHub] [beam] boyuanzz commented on a change in pull request #12888: [BEAM-10861]Moves PubSub Runner API encoding to Read/Write transforms

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boyuanzz commented on a change in pull request #12888:
URL: https://github.com/apache/beam/pull/12888#discussion_r492971691



##########
File path: sdks/python/apache_beam/io/iobase.py
##########
@@ -992,6 +1012,43 @@ def expand(self, pcoll):
           'A sink must inherit iobase.Sink, iobase.NativeSink, '
           'or be a PTransform. Received : %r' % self.sink)
 
+  def _pubsub_write_payload(self):
+    return beam_runner_api_pb2.PubSubWritePayload(
+        topic=self.sink.full_topic,
+        id_attribute=self.sink.id_label,
+        timestamp_attribute=self.sink.timestamp_attribute)
+
+  def to_runner_api_parameter(self, context):
+    # type: (PipelineContext) -> Tuple[str, Any]
+    # Importing locally to prevent circular dependencies.
+    from apache_beam.io.gcp.pubsub import _PubSubSink
+    if isinstance(self.sink, _PubSubSink):
+      payload = self._pubsub_write_payload()
+      return (common_urns.composites.PUBSUB_WRITE.urn, payload)
+    else:
+      return super(Write, self).to_runner_api_parameter(context)
+
+  @staticmethod
+  @ptransform.PTransform.register_urn(
+      common_urns.composites.PUBSUB_WRITE.urn,
+      beam_runner_api_pb2.PubSubWritePayload)
+  def from_runner_api_parameter(ptransform, payload, unused_context):
+    # type: (Any, Any, PipelineContext) -> Write
+    if ptransform.spec.urn != common_urns.composites.PUBSUB_WRITE.urn:
+      raise ValueError(
+          'Write transform cannot be constructed for the given proto %r',
+          ptransform)
+
+    # Importing locally to prevent circular dependencies.
+    from apache_beam.io.gcp.pubsub import _PubSubSink
+    sink = _PubSubSink(
+        topic=payload.topic,
+        id_label=payload.id_attribute,
+        with_attributes=True,

Review comment:
       If `with_attributes` is always `True`, should we also remove `with_attributes` from `_PubSubSink` and  `_PubSubSource`? This change requires `_PubSubSource` only outputs `PubSubMessage` and `_PubSubSink` only accepts `PubSubMessage`. 




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