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Spring Framework on Google Cloud Pub/Sub Module

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/*
 * Copyright 2017-2018 the original author or authors.
 *
 * 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
 *
 *      https://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.spring.pubsub.support;

import java.util.Optional;
import org.springframework.messaging.Message;

/** Google Cloud internal headers for Spring Messaging messages. */
public abstract class GcpPubSubHeaders {

  private GcpPubSubHeaders() {}

  private static final String PREFIX = "gcp_pubsub_";

  /** The client header text. */
  public static final String CLIENT = "googclient_*";

  /** The topic header text. */
  public static final String TOPIC = PREFIX + "topic";

  /** The original message header text. */
  public static final String ORIGINAL_MESSAGE = PREFIX + "original_message";

  /** The Pub/Sub message ordering key. */
  public static final String ORDERING_KEY = PREFIX + "ordering_key";

  /**
   * A simple utility method for pulling the {@link #ORIGINAL_MESSAGE} header out of a {@link
   * Message}.
   *
   * @param message The Spring Message that was converted by a {@link
   *     com.google.cloud.spring.pubsub.integration.inbound.PubSubInboundChannelAdapter}.
   * @return An Optional possibly containing a BasicAcknowledgeablePubsubMessage for acking and
   *     nacking.
   */
  public static Optional getOriginalMessage(Message message) {
    Object originalMessage = message.getHeaders().get(ORIGINAL_MESSAGE);
    if (originalMessage instanceof BasicAcknowledgeablePubsubMessage) {
      return Optional.of((BasicAcknowledgeablePubsubMessage) originalMessage);
    }
    return Optional.empty();
  }
}