feat: Add the checkpoint and serializer for the split enumerator

src/main/java/com/google/cloud/pubsublite/flink/enumerator/SplitEnumeratorCheckpointSerializer.java

@@ -0,0 +1,38 @@
+/*
+ * 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.enumerator;
+
+import com.google.cloud.pubsublite.flink.proto.SplitEnumeratorCheckpoint;
+import java.io.IOException;
+import org.apache.flink.core.io.SimpleVersionedSerializer;
+
+public class SplitEnumeratorCheckpointSerializer
+    implements SimpleVersionedSerializer<SplitEnumeratorCheckpoint> {
+  @Override
+  public int getVersion() {
+    return 0;
+  }
+
+  @Override
+  public byte[] serialize(SplitEnumeratorCheckpoint message) throws IOException {
+    return message.toByteArray();
+  }
+
+  @Override
+  public SplitEnumeratorCheckpoint deserialize(int i, byte[] bytes) throws IOException {
+    return SplitEnumeratorCheckpoint.parseFrom(bytes);
+  }
+}

src/main/proto/checkpoints.proto

@@ -32,4 +32,27 @@ message SubscriptionPartitionSplitProto {
       int64 partition = 2;
       // The cursor for this split.
       Cursor start = 3;
+}
+
+message SplitEnumeratorCheckpoint {
+      message Subtask {
+            int32 id = 1;
+      }
+      message Discovery {
+            // The subscription for which to discover splits.
+            string subscription = 1;
+            // The topic corresponding to the subscription.
+            string topic = 2;
+      }
+      message Assignment {
+            // The subtask this split is assigned to. Not present if the
+            // split is unassigned.
+            Subtask subtask = 1;
+            // The split.
+            SubscriptionPartitionSplitProto split = 2;
+      }
+      // State for split discovery.
+      Discovery discovery = 1;
+      // Discovered splits, and their assignment state.
+      repeated Assignment assignments = 2;
 }

src/test/java/com/google/cloud/pubsublite/flink/enumerator/SplitEnumeratorCheckpointSerializerTest.java

@@ -0,0 +1,39 @@
+/*
+ * 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.enumerator;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.cloud.pubsublite.flink.proto.SplitEnumeratorCheckpoint;
+import java.io.IOException;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.junit.MockitoJUnitRunner;
+
+@RunWith(MockitoJUnitRunner.class)
+public class SplitEnumeratorCheckpointSerializerTest {
+
+  @Test
+  public void testSerialization() throws IOException {
+    SplitEnumeratorCheckpoint proto =
+        SplitEnumeratorCheckpoint.newBuilder()
+            .setDiscovery(SplitEnumeratorCheckpoint.Discovery.newBuilder().setSubscription("sub"))
+            .build();
+    SplitEnumeratorCheckpointSerializer serializer = new SplitEnumeratorCheckpointSerializer();
+    assertThat(serializer.deserialize(serializer.getVersion(), serializer.serialize(proto)))
+        .isEqualTo(proto);
+  }
+}