WIP binder producer error propagation

spring-cloud-gcp-pubsub-stream-binder/src/main/java/org/springframework/cloud/gcp/stream/binder/pubsub/PubSubMessageChannelBinder.java

@@ -34,6 +34,8 @@
 import org.springframework.integration.core.MessageProducer;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.messaging.MessageHandler;
+import org.springframework.messaging.support.ErrorMessage;
+import org.springframework.util.concurrent.ListenableFutureCallback;
 
 /**
  * Message channel binder for Pub/Sub.
@@ -74,6 +76,21 @@ protected MessageHandler createProducerMessageHandler(ProducerDestination destin
 		PubSubMessageHandler messageHandler = new PubSubMessageHandler(this.pubSubTemplate, destination.getName());
 		messageHandler.setBeanFactory(getBeanFactory());
 		messageHandler.setSync(producerProperties.getExtension().isSync());
+		if (errorChannel != null) {
+			messageHandler.setPublishCallback(new ListenableFutureCallback<String>() {
+				@Override
+				public void onFailure(Throwable throwable) {
+					System.out.println("Sending throwable to error channel: " + throwable);
+					errorChannel.send(new ErrorMessage(throwable));
+				}
+
+				@Override
+				public void onSuccess(String messageId) {
+					// no-op
+					System.out.println("Successfully published message " + messageId);
+				}
+			});
+		}
 		return messageHandler;
 	}
 

spring-cloud-gcp-pubsub-stream-binder/src/test/java/org/springframework/cloud/gcp/stream/binder/pubsub/TempClientLibraryTest.java

@@ -0,0 +1,81 @@
+package org.springframework.cloud.gcp.stream.binder.pubsub;
+
+import com.google.api.core.ApiFutureCallback;
+import com.google.api.core.ApiFutures;
+import com.google.cloud.pubsub.v1.Publisher;
+import com.google.protobuf.ByteString;
+import com.google.pubsub.v1.PubsubMessage;
+import org.awaitility.Awaitility;
+import org.awaitility.Duration;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+public class TempClientLibraryTest {
+
+	@Test
+	public void failedPublishCallsListener() throws IOException, InterruptedException {
+		Publisher publisher = Publisher.newBuilder("projects/elfel-spring/topics/exampleTopic")
+				.setEndpoint("cecicestnespasunendpoint:443")
+				.build();
+
+		PubsubMessage message = PubsubMessage.newBuilder()
+				.setData(ByteString.copyFromUtf8("test message"))
+				.build();
+
+		AtomicBoolean errorSet = new AtomicBoolean(false);
+
+		ApiFutures.addCallback(publisher.publish(message),
+				new ApiFutureCallback<String>() {
+					@Override
+					public void onFailure(Throwable throwable) {
+						System.out.println("Sending throwable to error channel: " + throwable);
+						errorSet.set(true);
+					}
+
+					@Override
+					public void onSuccess(String messageId) {
+						System.out.println("Successfully published message " + messageId);
+					}
+				});
+
+		Awaitility.await()
+				.atMost(Duration.TWO_MINUTES)
+				.until(() -> errorSet.get());
+
+	}
+
+
+	@Test
+	public void successfulPublishCallsListener() throws IOException, InterruptedException {
+		Publisher publisher = Publisher.newBuilder("projects/elfel-spring/topics/exampleTopic")
+				.build();
+
+		PubsubMessage message = PubsubMessage.newBuilder()
+				.setData(ByteString.copyFromUtf8("test successful message"))
+				.build();
+
+		AtomicBoolean successSet = new AtomicBoolean(false);
+
+		ApiFutures.addCallback(publisher.publish(message),
+				new ApiFutureCallback<String>() {
+					@Override
+					public void onFailure(Throwable throwable) {
+						System.out.println("publish errored out: " + throwable);
+					}
+
+					@Override
+					public void onSuccess(String messageId) {
+						System.out.println("Successfully published message " + messageId);
+						successSet.set(true);
+					}
+				});
+
+		Awaitility.await()
+				.atMost(Duration.FIVE_SECONDS)
+				.until(() -> successSet.get());
+
+	}
+}

spring-cloud-gcp-samples/spring-cloud-gcp-pubsub-binder-sample/src/main/resources/application.properties

@@ -1,6 +1,8 @@
 spring.cloud.stream.bindings.input.destination=my-topic
 spring.cloud.stream.bindings.output.destination=my-topic
 
+spring.cloud.stream.bindings.output.producer.errorChannelEnabled=true
+
 # If group is specified, the Pub/Sub subscription name will be [PUBSUB_TOPIC_NAME].[PUBSUB_GROUP_NAME]
 spring.cloud.stream.bindings.input.group=my-group