feat: add support for Pub/Sub emulator configuration

Introduced a new configuration option cps.useEmulator to allow users to switch between the production service and the Pub/Sub emulator. Updated the README to document this feature and modified the relevant classes to handle the emulator endpoint based on the configuration. Added a test to verify the emulator configuration is correctly defined and parsed.

Author: jusemon

README.md

@@ -196,6 +196,7 @@ configurations:
 | cps.topic                  | String                        | REQUIRED (No default)       | The Pub/Sub topic ID, e.g. "foo" for topic "/projects/bar/topics/foo".                                                                                                                                                                                                                                                              |
 | cps.project                | String                        | REQUIRED (No default)       | The project containing the Pub/Sub topic, e.g. "bar" from above.                                                                                                                                                                                                                                                                    |
 | cps.endpoint               | String                        | "pubsub.googleapis.com:443" | The [Pub/Sub endpoint](https://cloud.google.com/pubsub/docs/reference/service_apis_overview#service_endpoints) to use.                                                                                                                                                                                                              |
+| cps.useEmulator            | Boolean                       | false                       | When true, use the Pub/Sub emulator instead of the production service. The emulator endpoint will be determined by the PUBSUB_EMULATOR_HOST environment variable, or fallback to the cps.endpoint configuration. |
 | maxBufferSize              | Integer                       | 100                         | The maximum number of messages that can be received for the messages on a topic partition before publishing them to Pub/Sub.                                                                                                                                                                                                        |
 | maxBufferBytes             | Long                          | 10,000,000                  | The maximum number of bytes that can be received for the messages on a topic partition before publishing them to Pub/Sub.                                                                                                                                                                                                           |
 | maxOutstandingRequestBytes | Long                          | Long.MAX_VALUE              | The maximum number of total bytes that can be outstanding (including incomplete and pending batches) before the publisher will block further publishing.                                                                                                                                                                            |

src/main/java/com/google/pubsub/kafka/common/ConnectorUtils.java

@@ -29,6 +29,8 @@ public class ConnectorUtils {
   public static final String CPS_TOPIC_CONFIG = "cps.topic";
   public static final String CPS_ENDPOINT = "cps.endpoint";
   public static final String CPS_DEFAULT_ENDPOINT = "pubsub.googleapis.com:443";
+  public static final String CPS_USE_EMULATOR = "cps.useEmulator";
+  public static final String PUBSUB_EMULATOR_HOST = "PUBSUB_EMULATOR_HOST";
   public static final String CPS_MESSAGE_KEY_ATTRIBUTE = "key";
   public static final String CPS_ORDERING_KEY_ATTRIBUTE = "orderingKey";
   public static final String GCP_CREDENTIALS_FILE_PATH_CONFIG = "gcp.credentials.file.path";

src/main/java/com/google/pubsub/kafka/sink/CloudPubSubSinkConnector.java

@@ -273,7 +273,13 @@ public ConfigDef config() {
             Type.STRING,
             ConnectorUtils.CPS_DEFAULT_ENDPOINT,
             Importance.LOW,
-            "The Pub/Sub endpoint to use.");
+            "The Pub/Sub endpoint to use.")
+        .define(
+            ConnectorUtils.CPS_USE_EMULATOR,
+            Type.BOOLEAN,
+            false,
+            Importance.LOW,
+            "When true, use the Pub/Sub emulator instead of the production service.");
   }
 
   @Override

src/main/java/com/google/pubsub/kafka/sink/CloudPubSubSinkTask.java

@@ -69,6 +69,7 @@ public class CloudPubSubSinkTask extends SinkTask {
   private String cpsProject;
   private String cpsTopic;
   private String cpsEndpoint;
+  private boolean useEmulator;
   private String messageBodyName;
   private long maxBufferSize;
   private long maxBufferBytes;
@@ -118,6 +119,7 @@ public void start(Map<String, String> props) {
     cpsProject = validatedProps.get(ConnectorUtils.CPS_PROJECT_CONFIG).toString();
     cpsTopic = validatedProps.get(ConnectorUtils.CPS_TOPIC_CONFIG).toString();
     cpsEndpoint = validatedProps.get(ConnectorUtils.CPS_ENDPOINT).toString();
+    useEmulator = (Boolean) validatedProps.get(ConnectorUtils.CPS_USE_EMULATOR);
     maxBufferSize = (Integer) validatedProps.get(CloudPubSubSinkConnector.MAX_BUFFER_SIZE_CONFIG);
     maxBufferBytes = (Long) validatedProps.get(CloudPubSubSinkConnector.MAX_BUFFER_BYTES_CONFIG);
     maxOutstandingRequestBytes =
@@ -399,7 +401,6 @@ private void createPublisher() {
 
     com.google.cloud.pubsub.v1.Publisher.Builder builder =
         com.google.cloud.pubsub.v1.Publisher.newBuilder(fullTopic)
-            .setCredentialsProvider(gcpCredentialsProvider)
             .setBatchingSettings(batchingSettings.build())
             .setRetrySettings(
                 RetrySettings.newBuilder()
@@ -413,8 +414,24 @@ private void createPublisher() {
                     .setInitialRpcTimeout(Duration.ofSeconds(10))
                     .setRpcTimeoutMultiplier(2)
                     .build())
-            .setExecutorProvider(FixedExecutorProvider.create(getSystemExecutor()))
-            .setEndpoint(cpsEndpoint);
+            .setExecutorProvider(FixedExecutorProvider.create(getSystemExecutor()));
+
+    // Configure endpoint, credentials and channel based on whether we're using emulator or production
+    if (useEmulator) {
+      // For emulator: use PUBSUB_EMULATOR_HOST env var, fallback to configured cps.endpoint, then default
+      String emulatorHost = System.getenv(ConnectorUtils.PUBSUB_EMULATOR_HOST);
+      String endpoint = emulatorHost != null ? emulatorHost : cpsEndpoint;
+      builder.setCredentialsProvider(com.google.api.gax.core.NoCredentialsProvider.create())
+          .setChannelProvider(
+              com.google.api.gax.grpc.InstantiatingGrpcChannelProvider.newBuilder()
+                  .setEndpoint(endpoint)
+                  .setChannelConfigurator(channel -> channel.usePlaintext())
+                  .build());
+    } else {
+      // For production: use configured credentials and endpoint
+      builder.setCredentialsProvider(gcpCredentialsProvider)
+          .setEndpoint(cpsEndpoint);
+    }
     if (orderingKeySource != OrderingKeySource.NONE) {
       builder.setEnableMessageOrdering(true);
     }

src/test/java/com/google/pubsub/kafka/sink/CloudPubSubSinkTaskTest.java

@@ -16,6 +16,7 @@
 package com.google.pubsub.kafka.sink;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.RETURNS_DEEP_STUBS;
 import static org.mockito.Mockito.mock;
@@ -38,6 +39,7 @@
 import java.util.concurrent.TimeUnit;
 import org.apache.kafka.clients.consumer.OffsetAndMetadata;
 import org.apache.kafka.common.TopicPartition;
+import org.apache.kafka.common.config.ConfigDef;
 import org.apache.kafka.common.record.TimestampType;
 import org.apache.kafka.connect.data.Schema;
 import org.apache.kafka.connect.data.SchemaBuilder;
@@ -612,6 +614,42 @@ public void testPublisherShutdownOnStop() throws Exception {
     verify(publisher, times(1)).awaitTermination(maxShutdownTimeoutMs, TimeUnit.MILLISECONDS);
   }
 
+  /** Tests that the emulator configuration is properly defined and parsed. */
+  @Test
+  public void testEmulatorConfiguration() {
+    CloudPubSubSinkConnector connector = new CloudPubSubSinkConnector();
+    ConfigDef configDef = connector.config();
+    
+    assertTrue("Emulator configuration should be defined", 
+        configDef.names().contains(ConnectorUtils.CPS_USE_EMULATOR));
+    
+    Map<String, String> emulatorProps = new HashMap<>();
+    emulatorProps.put(ConnectorUtils.CPS_TOPIC_CONFIG, CPS_TOPIC);
+    emulatorProps.put(ConnectorUtils.CPS_PROJECT_CONFIG, CPS_PROJECT);
+    emulatorProps.put(ConnectorUtils.CPS_USE_EMULATOR, "true");
+    
+    Map<String, Object> parsedProps = configDef.parse(emulatorProps);
+    assertTrue("Emulator should be enabled", (Boolean) parsedProps.get(ConnectorUtils.CPS_USE_EMULATOR));
+  }
+
+  @Test
+  public void testCreatePublisherWithEmulatorEnabled() {
+    props.put(ConnectorUtils.CPS_USE_EMULATOR, "true");
+    props.put(ConnectorUtils.CPS_ENDPOINT, "localhost:8085");
+    CloudPubSubSinkTask task = new CloudPubSubSinkTask(publisher);
+    task.start(props);
+    assertEquals(CloudPubSubSinkTask.class, task.getClass());
+  }
+
+  @Test
+  public void testCreatePublisherWithEmulatorDisabled() {
+    props.put(ConnectorUtils.CPS_USE_EMULATOR, "false");
+    props.put(ConnectorUtils.CPS_ENDPOINT, "pubsub.googleapis.com:443");
+    CloudPubSubSinkTask task = new CloudPubSubSinkTask(publisher);
+    task.start(props);
+    assertEquals(CloudPubSubSinkTask.class, task.getClass());
+  }
+
   /** Get some sample SinkRecords's to use in the tests. */
   private List<SinkRecord> getSampleRecords() {
     List<SinkRecord> records = new ArrayList<>();