feat: add the pubsublite sink

pom.xml

@@ -101,6 +101,16 @@
             <artifactId>flink-metrics-core</artifactId>
             <version>1.13.0</version>
         </dependency>
+        <dependency>
+            <groupId>org.apache.flink</groupId>
+            <artifactId>flink-streaming-java_2.11</artifactId>
+            <version>1.13.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.flink</groupId>
+            <artifactId>flink-runtime_2.11</artifactId>
+            <version>1.13.0</version>
+        </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>

src/main/java/com/google/cloud/pubsublite/flink/PubsubLiteSerializationSchema.java

@@ -22,6 +22,7 @@
 import java.sql.Date;
 import java.time.Instant;
 import org.apache.flink.api.common.serialization.SerializationSchema;
+import org.apache.flink.api.common.serialization.SerializationSchema.InitializationContext;
 
 public interface PubsubLiteSerializationSchema<T> extends Serializable {
   static <T> PubsubLiteSerializationSchema<T> dataOnly(SerializationSchema<T> schema) {
@@ -42,6 +43,18 @@ public Message serialize(T value, Instant timestamp) {
     };
   }
 
+  static PubsubLiteSerializationSchema<Message> messageSchema() {
+    return new PubsubLiteSerializationSchema<Message>() {
+      @Override
+      public void open(InitializationContext context) {}
+
+      @Override
+      public Message serialize(Message value, Instant timestamp) {
+        return value;
+      }
+    };
+  }
+
   void open(SerializationSchema.InitializationContext context) throws Exception;
 
   Message serialize(T value, Instant timestamp);

src/main/java/com/google/cloud/pubsublite/flink/PubsubLiteSink.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright 2021 Google LLC
+ *
+ * Licensed 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 com.google.cloud.pubsublite.flink;
+
+import com.google.cloud.Tuple;
+import com.google.cloud.pubsublite.flink.sink.BulkWaitPublisher;
+import com.google.cloud.pubsublite.flink.sink.MessagePublisher;
+import com.google.cloud.pubsublite.flink.sink.PerServerPublisherCache;
+import com.google.cloud.pubsublite.flink.sink.SerializingPublisher;
+import com.google.errorprone.annotations.concurrent.GuardedBy;
+import java.time.Instant;
+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;
+
+public class PubsubLiteSink<T> extends RichSinkFunction<T> implements CheckpointedFunction {
+  private final PubsubLiteSinkSettings<T> settings;
+
+  @GuardedBy("this")
+  private transient BulkWaitPublisher<Tuple<T, Instant>> publisher;
+
+  public PubsubLiteSink(PubsubLiteSinkSettings<T> settings) {
+    this.settings = settings;
+  }
+
+  @Override
+  public void initializeState(FunctionInitializationContext functionInitializationContext)
+      throws Exception {}
+
+  @Override
+  public synchronized void snapshotState(FunctionSnapshotContext functionSnapshotContext)
+      throws Exception {
+    publisher.waitUntilNoOutstandingPublishes();
+  }
+
+  @Override
+  public synchronized void invoke(T value, Context context) throws Exception {
+    Long timestamp = context.timestamp();
+    if (timestamp == null) {
+      timestamp = context.currentProcessingTime();
+    }
+    publisher.publish(Tuple.of(value, Instant.ofEpochMilli(timestamp)));
+  }
+
+  @Override
+  public synchronized void open(Configuration parameters) throws Exception {
+    super.open(parameters);
+    publisher =
+        new SerializingPublisher<>(
+            new MessagePublisher(
+                PerServerPublisherCache.getOrCreate(settings.getPublisherConfig())),
+            settings.serializationSchema());
+  }
+
+  @Override
+  public synchronized void close() throws Exception {
+    publisher.waitUntilNoOutstandingPublishes();
+  }
+}

src/main/java/com/google/cloud/pubsublite/flink/PubsubLiteSinkSettings.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2021 Google LLC
+ *
+ * Licensed 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 com.google.cloud.pubsublite.flink;
+
+import com.google.auto.value.AutoValue;
+import com.google.cloud.pubsublite.Message;
+import com.google.cloud.pubsublite.TopicPath;
+import com.google.cloud.pubsublite.flink.sink.PublisherOptions;
+import java.io.Serializable;
+
+@AutoValue
+public abstract class PubsubLiteSinkSettings<InputT> implements Serializable {
+  // Create a builder which will accept messages of type InputT and serialize them using the
+  // provided serialization schema.
+  public static <InputT> Builder<InputT> builder(PubsubLiteSerializationSchema<InputT> schema) {
+    return new AutoValue_PubsubLiteSinkSettings.Builder<InputT>().setSerializationSchema(schema);
+  }
+
+  // Create a sink which will accept already serialized pubsub messages/
+  public static Builder<Message> messagesBuilder() {
+    return builder(PubsubLiteSerializationSchema.messageSchema());
+  }
+
+  // Required. The path of the topic to publish messages to.
+  public abstract TopicPath topicPath();
+
+  // Internal.
+  abstract PubsubLiteSerializationSchema<InputT> serializationSchema();
+
+  PublisherOptions getPublisherConfig() {
+    return PublisherOptions.create(topicPath());
+  }
+
+  @AutoValue.Builder
+  abstract static class Builder<InputT> {
+    // Required.
+    public abstract Builder<InputT> setTopicPath(TopicPath value);
+
+    // Internal.
+    abstract Builder<InputT> setSerializationSchema(PubsubLiteSerializationSchema<InputT> value);
+
+    public abstract PubsubLiteSinkSettings<InputT> build();
+  }
+}

src/main/java/com/google/cloud/pubsublite/flink/sink/MessagePublisher.java

@@ -32,8 +32,6 @@ public class MessagePublisher implements BulkWaitPublisher<Message> {
   public MessagePublisher(Publisher<MessageMetadata> publisher) {
     this.publisher = publisher;
     this.publishes = new ArrayList<>();
-    this.publisher.startAsync();
-    this.publisher.awaitRunning();
   }
 
   @Override