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Beam IO for Google Cloud Pub/Sub Lite

There is a newer version: 0.23.0

/*
 * 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 static com.google.cloud.pubsublite.cloudpubsub.MessageTransforms.toCpsPublishTransformer;

import com.google.cloud.pubsublite.Message;
import com.google.cloud.pubsublite.proto.PubSubMessage;
import org.apache.beam.sdk.transforms.MapElements;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.TypeDescriptor;

/**
 * A class providing a conversion validity check between Cloud Pub/Sub and Pub/Sub Lite message
 * types.
 */
public final class CloudPubsubChecks {
  private CloudPubsubChecks() {}

  /**
   * Ensure that all messages that pass through can be converted to Cloud Pub/Sub messages using the
   * standard transformation methods in the client library.
   *
   * Will fail the pipeline if a message has multiple attributes per key.
   */
  public static PTransform, PCollection>
      ensureUsableAsCloudPubsub() {
    return MapElements.into(TypeDescriptor.of(PubSubMessage.class))
        .via(
            message -> {
              Object unused = toCpsPublishTransformer().transform(Message.fromProto(message));
              return message;
            });
  }
}