[GitHub] [flink] Xeli commented on a change in pull request #6594: [FLINK-9311] [pubsub] Added PubSub source connector with support for checkpointing (ATLEAST_ONCE)

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Xeli commented on a change in pull request #6594: [FLINK-9311] [pubsub] Added PubSub source connector with support for checkpointing (ATLEAST_ONCE)
URL: https://github.com/apache/flink/pull/6594#discussion_r270996549
 
 

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 File path: flink-connectors/flink-connector-gcp-pubsub/src/main/java/org/apache/flink/streaming/connectors/gcp/pubsub/PubSubSink.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.streaming.connectors.gcp.pubsub;
+
+import org.apache.flink.api.common.serialization.SerializationSchema;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.runtime.state.FunctionInitializationContext;
+import org.apache.flink.runtime.state.FunctionSnapshotContext;
+import org.apache.flink.streaming.api.checkpoint.CheckpointedFunction;
+import org.apache.flink.streaming.api.functions.sink.RichSinkFunction;
+import org.apache.flink.streaming.api.functions.sink.SinkFunction;
+
+import com.google.api.core.ApiFutureCallback;
+import com.google.api.core.ApiFutures;
+import com.google.api.gax.core.FixedCredentialsProvider;
+import com.google.api.gax.core.NoCredentialsProvider;
+import com.google.api.gax.grpc.GrpcTransportChannel;
+import com.google.api.gax.rpc.FixedTransportChannelProvider;
+import com.google.api.gax.rpc.TransportChannel;
+import com.google.auth.Credentials;
+import com.google.cloud.pubsub.v1.Publisher;
+import com.google.protobuf.ByteString;
+import com.google.pubsub.v1.ProjectTopicName;
+import com.google.pubsub.v1.PubsubMessage;
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+import static com.google.cloud.pubsub.v1.SubscriptionAdminSettings.defaultCredentialsProviderBuilder;
+import static org.apache.flink.runtime.concurrent.Executors.directExecutor;
+
+/**
+ * A sink function that outputs to PubSub.
+ *
+ * @param <IN> type of PubSubSink messages to write
+ */
+public class PubSubSink<IN> extends RichSinkFunction<IN> implements CheckpointedFunction {
+	private static final Logger LOG = LoggerFactory.getLogger(PubSubSink.class);
+
+	private final ApiFutureCallback<String> failureHandler;
+	private final Credentials credentials;
+	private final SerializationSchema<IN> serializationSchema;
+	private final String projectName;
+	private final String topicName;
+	private final String hostAndPortForEmulator;
+
+	private transient Publisher publisher;
+
+	private PubSubSink(
+		Credentials credentials,
+		SerializationSchema<IN> serializationSchema,
+		String projectName,
+		String topicName,
+		String hostAndPortForEmulator) {
+		this.failureHandler = new FailureHandler();
+		this.credentials = credentials;
+		this.serializationSchema = serializationSchema;
+		this.projectName = projectName;
+		this.topicName = topicName;
+		this.hostAndPortForEmulator = hostAndPortForEmulator;
+	}
+
+	private transient ManagedChannel managedChannel = null;
+	private transient TransportChannel channel = null;
+
+	@Override
+	public void open(Configuration configuration) throws Exception {
+		Publisher.Builder builder = Publisher
+			.newBuilder(ProjectTopicName.of(projectName, topicName))
+			.setCredentialsProvider(FixedCredentialsProvider.create(credentials));
+
+		if (hostAndPortForEmulator != null) {
+			managedChannel = ManagedChannelBuilder
+				.forTarget(hostAndPortForEmulator)
+				.usePlaintext(true) // This is 'Ok' because this is ONLY used for testing.
+				.build();
+			channel = GrpcTransportChannel.newBuilder().setManagedChannel(managedChannel).build();
+			builder.setChannelProvider(FixedTransportChannelProvider.create(channel))
+					.setCredentialsProvider(NoCredentialsProvider.create());
+		}
+
+		publisher = builder.build();
+	}
+
+	@Override
+	public void close() throws Exception {
+		super.close();
+		shutdownPublisher();
+		shutdownTransportChannel();
+		shutdownManagedChannel();
+	}
+
+	private void shutdownPublisher() {
+		try {
+			if (publisher != null) {
+				publisher.shutdown();
+			}
+		} catch (Exception e) {
+			LOG.info("Shutting down Publisher failed.", e);
+		}
+	}
+
+	private void shutdownTransportChannel() {
+		if (channel == null) {
+			return;
+		}
+		try {
+			channel.close();
+		} catch (Exception e) {
+			LOG.info("Shutting down TransportChannel failed.", e);
+		}
+	}
+
+	private void shutdownManagedChannel() {
+		if (managedChannel == null) {
+			return;
+		}
+		try {
+			managedChannel.shutdownNow();
+			managedChannel.awaitTermination(1000L, TimeUnit.MILLISECONDS);
+		} catch (Exception e) {
+			LOG.info("Shutting down ManagedChannel failed.", e);
+		}
+	}
+
+	@Override
+	public void invoke(IN message, SinkFunction.Context context) {
+		PubsubMessage pubsubMessage = PubsubMessage
+			.newBuilder()
+			.setData(ByteString.copyFrom(serializationSchema.serialize(message)))
+			.build();
+		ApiFutures.addCallback(publisher.publish(pubsubMessage), failureHandler, directExecutor());
+	}
+
+	/**
+	 * Create a builder for a new PubSubSink.
+	 *
+	 * @param <IN> The generic of the type that is to be written into the sink.
+	 * @return a new PubSubSinkBuilder instance
+	 */
+	public static <IN> PubSubSinkBuilder<IN> newBuilder(SerializationSchema<IN> serializationSchema, String projectName, String topicName) {
+		return new PubSubSinkBuilder<>(serializationSchema, projectName, topicName);
+	}
+
+	@Override
+	public void snapshotState(FunctionSnapshotContext context) throws Exception {
+		//before checkpoints make sure all the batched / buffered pubsub messages have actually been sent
+		publisher.publishAllOutstanding();
+	}
+
+	@Override
+	public void initializeState(FunctionInitializationContext context) throws Exception {
+	}
+
+	/**
+	 * PubSubSinkBuilder to create a PubSubSink.
+	 *
+	 * @param <IN> Type of PubSubSink to create.
+	 */
+	@SuppressWarnings("unchecked")
+	public static class PubSubSinkBuilder<IN> {
+		private SerializationSchema<IN> serializationSchema;
+		private String projectName;
+		private String topicName;
+
+		private Credentials credentials;
+		private String hostAndPort;
+
+		private PubSubSinkBuilder(SerializationSchema<IN> serializationSchema, String projectName, String topicName) {
+			this.serializationSchema = serializationSchema;
+			this.projectName = projectName;
+			this.topicName = topicName;
+		}
+
+		/**
+		 * Set the credentials.
+		 * If this is not used then the credentials are picked up from the environment variables.
+		 *
+		 * @param credentials the Credentials needed to connect.
+		 * @return The current PubSubSinkBuilder instance
+		 */
+		public PubSubSinkBuilder<IN> withCredentials(Credentials credentials) {
+			this.credentials = credentials;
+			return this;
+		}
+
+		/**
+		 * @param serializationSchema Instance of a SerializationSchema that converts the IN into a byte[]
+		 * @return The current PubSubSinkBuilder instance
+		 */
+		public PubSubSinkBuilder<IN> withSerializationSchema(SerializationSchema<IN> serializationSchema) {
+			this.serializationSchema = serializationSchema;
+			return this;
+		}
+
+		/**
+		 * @param projectName The name of the project in PubSub
+		 * @return The current PubSubSinkBuilder instance
+		 */
+		public PubSubSinkBuilder<IN> withProjectName(String projectName) {
+			this.projectName = projectName;
+			return this;
+		}
+
+		/**
+		 * @param topicName The name of the topic in PubSub
+		 * @return The current PubSubSinkBuilder instance
+		 */
+		public PubSubSinkBuilder<IN> withTopicName(String topicName) {
+			this.topicName = topicName;
+			return this;
+		}
+
+		/**
+		 * Set the custom hostname/port combination of PubSub.
+		 * The ONLY reason to use this is during tests with the emulator provided by Google.
+		 *
+		 * @param hostAndPort The combination of hostname and port to connect to ("hostname:1234")
+		 * @return The current PubSubSinkBuilder instance
+		 */
+		public PubSubSinkBuilder<IN> withHostAndPortForEmulator(String hostAndPort) {
 
 Review comment:
   Personally I find a method like this very useful when running integration tests. If we would make this package prive it would not be possible for end users to use the connector in integration tests.
   
   I'd like to keep it as-is if you agree

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