Adding a pubsub publisher message transformer

google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java

@@ -16,6 +16,7 @@
 
 package com.google.cloud.pubsub.v1;
 
+import com.google.api.core.ApiFunction;
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutureCallback;
 import com.google.api.core.ApiFutures;
@@ -95,6 +96,7 @@ public class Publisher {
   private final List<AutoCloseable> closeables;
   private final MessageWaiter messagesWaiter;
   private ScheduledFuture<?> currentAlarmFuture;
+  private final ApiFunction<PubsubMessage, PubsubMessage> messageTransform;
 
   /** The maximum number of messages in one request. Defined by the API. */
   public static long getApiMaxRequestElementCount() {
@@ -110,6 +112,7 @@ private Publisher(Builder builder) throws IOException {
     topicName = builder.topicName;
 
     this.batchingSettings = builder.batchingSettings;
+    this.messageTransform = builder.messageTransform;
 
     messagesBatch = new LinkedList<>();
     messagesBatchLock = new ReentrantLock();
@@ -192,6 +195,7 @@ public ApiFuture<String> publish(PubsubMessage message) {
       throw new IllegalStateException("Cannot publish on a shut-down publisher.");
     }
 
+    message = messageTransform.apply(message);
     final int messageSize = message.getSerializedSize();
     OutstandingBatch batchToSend = null;
     SettableApiFuture<String> publishResult = SettableApiFuture.<String>create();
@@ -528,6 +532,14 @@ public static final class Builder {
     CredentialsProvider credentialsProvider =
         TopicAdminSettings.defaultCredentialsProviderBuilder().build();
 
+    ApiFunction<PubsubMessage, PubsubMessage> messageTransform =
+        new ApiFunction<PubsubMessage, PubsubMessage>() {
+          @Override
+          public PubsubMessage apply(PubsubMessage input) {
+            return input;
+          }
+        };
+
     private Builder(String topic) {
       this.topicName = Preconditions.checkNotNull(topic);
     }
@@ -610,6 +622,16 @@ public Builder setExecutorProvider(ExecutorProvider executorProvider) {
       return this;
     }
 
+    /**
+     * Gives the ability to set an {@link ApiFunction} that will transform the {@link PubsubMessage}
+     * before it is sent
+     */
+    public Builder setTransform(ApiFunction<PubsubMessage, PubsubMessage> messageTransform) {
+      this.messageTransform =
+          Preconditions.checkNotNull(messageTransform, "The messageTransform cannnot be null.");
+      return this;
+    }
+
     public Publisher build() throws IOException {
       return new Publisher(this);
     }

google-cloud-clients/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/PublisherImplTest.java

@@ -23,6 +23,7 @@
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
+import com.google.api.core.ApiFunction;
 import com.google.api.core.ApiFuture;
 import com.google.api.gax.batching.BatchingSettings;
 import com.google.api.gax.core.ExecutorProvider;
@@ -43,6 +44,7 @@
 import io.grpc.inprocess.InProcessServerBuilder;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -433,6 +435,33 @@ public void testBuilderParametersAndDefaults() {
     assertEquals(Publisher.Builder.DEFAULT_RETRY_SETTINGS, builder.retrySettings);
   }
 
+  @Test
+  public void testTransformer() throws Exception {
+    final AtomicBoolean transformed = new AtomicBoolean();
+    ApiFunction<PubsubMessage, PubsubMessage> transform =
+        new ApiFunction<PubsubMessage, PubsubMessage>() {
+          @Override
+          public PubsubMessage apply(PubsubMessage input) {
+            transformed.set(true);
+            return input;
+          }
+        };
+    Publisher publisher =
+        getTestPublisherBuilder()
+            .setBatchingSettings(
+                Publisher.Builder.DEFAULT_BATCHING_SETTINGS
+                    .toBuilder()
+                    .setElementCountThreshold(1L)
+                    .setDelayThreshold(Duration.ofSeconds(100))
+                    .build())
+            .setTransform(transform)
+            .build();
+    publisher.publish(PubsubMessage.getDefaultInstance());
+    testPublisherServiceImpl.addPublishResponse(PublishResponse.getDefaultInstance());
+    publisher.shutdown();
+    assertTrue(transformed.get());
+  }
+
   @Test
   public void testBuilderInvalidArguments() {
     Publisher.Builder builder = Publisher.newBuilder(TEST_TOPIC);