fix: Move settings for the topic backlog reader to TopicBacklogReaderSettings (#254)

* Add an independent TopicBacklogReaderSettings

* Delete Example.java

Author: palmere-google

pubsublite-beam-io/src/main/java/com/google/cloud/pubsublite/beam/PubsubLiteUnboundedSource.java

@@ -102,7 +102,7 @@ public UnboundedReader<SequencedMessage> createReader(
       return new PubsubLiteUnboundedReader(
           this,
           statesBuilder.build(),
-          subscriberOptions.topicBacklogReader(),
+          TopicBacklogReader.create(subscriberOptions.topicBacklogReaderSettings()),
           Ticker.systemTicker());
     } catch (StatusException e) {
       throw new IOException(e);

pubsublite-beam-io/src/main/java/com/google/cloud/pubsublite/beam/SubscriberOptions.java

@@ -17,16 +17,10 @@
 package com.google.cloud.pubsublite.beam;
 
 import com.google.auto.value.AutoValue;
-import com.google.cloud.pubsublite.AdminClient;
-import com.google.cloud.pubsublite.AdminClientSettings;
 import com.google.cloud.pubsublite.Partition;
 import com.google.cloud.pubsublite.PartitionLookupUtils;
 import com.google.cloud.pubsublite.SubscriptionPath;
-import com.google.cloud.pubsublite.TopicPath;
 import com.google.cloud.pubsublite.cloudpubsub.FlowControlSettings;
-import com.google.cloud.pubsublite.internal.ExtractStatus;
-import com.google.cloud.pubsublite.internal.TopicStatsClient;
-import com.google.cloud.pubsublite.internal.TopicStatsClientSettings;
 import com.google.cloud.pubsublite.internal.wire.Committer;
 import com.google.cloud.pubsublite.internal.wire.CommitterBuilder;
 import com.google.cloud.pubsublite.internal.wire.PubsubContext;
@@ -40,7 +34,6 @@
 import com.google.common.collect.ImmutableSet;
 import io.grpc.StatusException;
 import java.io.Serializable;
-import java.util.concurrent.ExecutionException;
 
 @AutoValue
 public abstract class SubscriberOptions implements Serializable {
@@ -57,8 +50,8 @@ public abstract class SubscriberOptions implements Serializable {
   /** A set of partitions. If empty, retrieve the set of partitions using an admin client. */
   public abstract ImmutableSet<Partition> partitions();
 
-  /** The class used to read backlog for the subscription described by subscriptionPath() */
-  public abstract TopicBacklogReader topicBacklogReader();
+  /** The class used to read backlog for the subscription described by subscriptionPath(). */
+  public abstract TopicBacklogReaderSettings topicBacklogReaderSettings();
 
   /** A supplier for the subscriber stub to be used. */
   public abstract Optional<SerializableSupplier<SubscriberServiceStub>> subscriberStubSupplier();
@@ -143,7 +136,8 @@ public abstract Builder setSubscriberStubSupplier(
     public abstract Builder setCommitterStubSupplier(
         SerializableSupplier<CursorServiceStub> stubSupplier);
 
-    public abstract Builder setTopicBacklogReader(TopicBacklogReader topicBacklogReader);
+    public abstract Builder setTopicBacklogReaderSettings(
+        TopicBacklogReaderSettings topicBacklogReaderSettings);
 
     // Used in unit tests
     abstract Builder setSubscriberFactory(SubscriberFactory subscriberFactory);
@@ -155,41 +149,29 @@ public abstract Builder setCommitterStubSupplier(
 
     abstract ImmutableSet<Partition> partitions();
 
-    abstract Optional<TopicBacklogReader> topicBacklogReader();
+    abstract Optional<TopicBacklogReaderSettings> topicBacklogReaderSettings();
 
     abstract SubscriberOptions autoBuild();
 
     public SubscriberOptions build() throws StatusException {
-      if (!partitions().isEmpty() && topicBacklogReader().isPresent()) {
+      if (!partitions().isEmpty() && topicBacklogReaderSettings().isPresent()) {
         return autoBuild();
       }
-      TopicPath path;
-      try (AdminClient adminClient =
-          AdminClient.create(
-              AdminClientSettings.newBuilder()
-                  .setRegion(subscriptionPath().location().region())
-                  .build())) {
-        path = TopicPath.parse(adminClient.getSubscription(subscriptionPath()).get().getTopic());
-      } catch (ExecutionException e) {
-        throw ExtractStatus.toCanonical(e.getCause());
-      } catch (Throwable t) {
-        throw ExtractStatus.toCanonical(t);
-      }
 
       if (partitions().isEmpty()) {
-        int partition_count = PartitionLookupUtils.numPartitions(path);
+        int partitionCount = PartitionLookupUtils.numPartitions(subscriptionPath());
         ImmutableSet.Builder<Partition> partitions = ImmutableSet.builder();
-        for (int i = 0; i < partition_count; i++) {
+        for (int i = 0; i < partitionCount; i++) {
           partitions.add(Partition.of(i));
         }
         setPartitions(partitions.build());
       }
-      if (!topicBacklogReader().isPresent()) {
-        setTopicBacklogReader(
-            new TopicBacklogReaderImpl(
-                TopicStatsClient.create(TopicStatsClientSettings.newBuilder().build()), path));
+      if (!topicBacklogReaderSettings().isPresent()) {
+        setTopicBacklogReaderSettings(
+            TopicBacklogReaderSettings.newBuilder()
+                .setTopicPathFromSubscriptionPath(subscriptionPath())
+                .build());
       }
-
       return autoBuild();
     }
   }

pubsublite-beam-io/src/main/java/com/google/cloud/pubsublite/beam/TopicBacklogReader.java

@@ -19,6 +19,7 @@
 import com.google.cloud.pubsublite.Offset;
 import com.google.cloud.pubsublite.Partition;
 import com.google.cloud.pubsublite.proto.ComputeMessageStatsResponse;
+import io.grpc.StatusException;
 import java.util.Map;
 
 /**
@@ -27,6 +28,10 @@
  * partitions within a subscription.
  */
 public interface TopicBacklogReader {
+  /** Create a TopicBacklogReader from settings. */
+  static TopicBacklogReader create(TopicBacklogReaderSettings settings) throws StatusException {
+    return settings.instantiate();
+  }
   /**
    * Compute and aggregate message statistics for message between the provided start offset and HEAD
    * for each partition.

pubsublite-beam-io/src/main/java/com/google/cloud/pubsublite/beam/TopicBacklogReaderSettings.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2020 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.beam;
+
+import com.google.auto.value.AutoValue;
+import com.google.cloud.pubsublite.AdminClient;
+import com.google.cloud.pubsublite.AdminClientSettings;
+import com.google.cloud.pubsublite.SubscriptionPath;
+import com.google.cloud.pubsublite.TopicPath;
+import com.google.cloud.pubsublite.internal.ExtractStatus;
+import com.google.cloud.pubsublite.internal.TopicStatsClient;
+import com.google.cloud.pubsublite.internal.TopicStatsClientSettings;
+import com.google.cloud.pubsublite.proto.TopicStatsServiceGrpc.TopicStatsServiceBlockingStub;
+import com.google.common.base.Optional;
+import io.grpc.StatusException;
+import java.io.Serializable;
+import java.util.concurrent.ExecutionException;
+
+@AutoValue
+public abstract class TopicBacklogReaderSettings implements Serializable {
+  /**
+   * The topic path for this backlog reader. Either topicPath or subscriptionPath must be set. If
+   * both are set, subscriptionPath will be ignored.
+   */
+  abstract TopicPath topicPath();
+
+  // Optional parameters
+  abstract Optional<SerializableSupplier<TopicStatsServiceBlockingStub>> stub();
+
+  public static Builder newBuilder() {
+    return new AutoValue_TopicBacklogReaderSettings.Builder();
+  }
+
+  @AutoValue.Builder
+  public abstract static class Builder {
+    // Required parameters.
+    public abstract Builder setTopicPath(TopicPath topicPath);
+
+    public Builder setTopicPathFromSubscriptionPath(SubscriptionPath subscriptionPath)
+        throws StatusException {
+      try (AdminClient adminClient =
+          AdminClient.create(
+              AdminClientSettings.newBuilder()
+                  .setRegion(subscriptionPath.location().region())
+                  .build())) {
+        setTopicPath(
+            TopicPath.parse(adminClient.getSubscription(subscriptionPath).get().getTopic()));
+        return this;
+      } catch (ExecutionException e) {
+        throw ExtractStatus.toCanonical(e.getCause());
+      } catch (Throwable t) {
+        throw ExtractStatus.toCanonical(t);
+      }
+    }
+
+    public abstract Builder setStub(SerializableSupplier<TopicStatsServiceBlockingStub> stub);
+
+    public abstract TopicBacklogReaderSettings build();
+  }
+
+  TopicBacklogReader instantiate() throws StatusException {
+    TopicStatsClientSettings.Builder builder = TopicStatsClientSettings.newBuilder();
+    if (stub().isPresent()) {
+      builder.setStub(stub().get().get());
+    }
+    builder.setRegion(topicPath().location().region());
+    return new TopicBacklogReaderImpl(TopicStatsClient.create(builder.build()), topicPath());
+  }
+}