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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.integration;

import com.google.cloud.spring.pubsub.support.GcpPubSubHeaders;
import java.util.Arrays;
import java.util.Map;
import java.util.stream.Collectors;
import org.springframework.integration.history.MessageHistory;
import org.springframework.integration.mapping.HeaderMapper;
import org.springframework.integration.support.utils.PatternMatchUtils;
import org.springframework.messaging.MessageHeaders;
import org.springframework.messaging.support.NativeMessageHeaderAccessor;
import org.springframework.util.Assert;

/**
 * Maps headers from {@link com.google.pubsub.v1.PubsubMessage}s to {@link
 * org.springframework.messaging.Message}s and vice-versa.
 *
 * By default, filters out headers called "id", "timestamp", "gcp_pubsub_acknowledgement" or
 * "nativeHeaders" on the {@link org.springframework.messaging.Message} to {@link
 * com.google.pubsub.v1.PubsubMessage} header conversion.
 */
public class PubSubHeaderMapper implements HeaderMapper> {

  /**
   * Patterns of headers to map in {@link #fromHeaders(MessageHeaders, Map)}. First patterns take
   * precedence.
   */
  @SuppressWarnings("deprecation")
  private String[] outboundHeaderPatterns = {
    "!" + MessageHeaders.ID,
    "!" + MessageHeaders.TIMESTAMP,
    "!" + GcpPubSubHeaders.ORIGINAL_MESSAGE,
    "!" + GcpPubSubHeaders.CLIENT,
    "!" + NativeMessageHeaderAccessor.NATIVE_HEADERS,
    "!" + MessageHistory.HEADER_NAME,
    "*"
  };

  /** Patterns of headers to map in {@link #toHeaders(Map)}. First patterns take precedence. */
  private String[] inboundHeaderPatterns = {"*"};

  /**
   * Set the patterns of the headers to be mapped in {@link #fromHeaders(MessageHeaders, Map)}.
   * First patterns take precedence.
   *
   * @param outboundHeaderPatterns header patterns to be mapped
   */
  public void setOutboundHeaderPatterns(String... outboundHeaderPatterns) {
    Assert.notNull(outboundHeaderPatterns, "Header patterns can't be null.");
    Assert.noNullElements(outboundHeaderPatterns, "No header pattern can be null.");
    this.outboundHeaderPatterns =
        Arrays.copyOf(outboundHeaderPatterns, outboundHeaderPatterns.length);
  }

  /**
   * Set the patterns of the headers to be mapped in {@link #toHeaders(Map)}. First patterns take
   * precedence.
   *
   * @param inboundHeaderPatterns header patterns to be mapped
   */
  public void setInboundHeaderPatterns(String... inboundHeaderPatterns) {
    Assert.notNull(inboundHeaderPatterns, "Header patterns can't be null.");
    Assert.noNullElements(inboundHeaderPatterns, "No header pattern can be null.");
    this.inboundHeaderPatterns = Arrays.copyOf(inboundHeaderPatterns, inboundHeaderPatterns.length);
  }

  /**
   * Generate headers in {@link com.google.pubsub.v1.PubsubMessage} format from {@link
   * MessageHeaders}. All headers are converted into strings.
   *
   * 
Will map only the headers that match the patterns in {@code outboundHeaderPatternsMap}.
   *
   * @param messageHeaders headers to map from
   * @param pubsubMessageHeaders headers in their final format
   */
  @Override
  public void fromHeaders(
      MessageHeaders messageHeaders, final Map pubsubMessageHeaders) {
    messageHeaders.entrySet().stream()
        .filter(
            entry ->
                Boolean.TRUE.equals(
                    PatternMatchUtils.smartMatch(entry.getKey(), this.outboundHeaderPatterns)))
        .forEach(entry -> pubsubMessageHeaders.put(entry.getKey(), entry.getValue().toString()));
  }

  /**
   * Generate headers in {@link org.springframework.messaging.Message} format from {@code
   * Map}.
   *
   * Will map only the headers that match the patterns in {@code inboundHeaderPatternsMap}.
   *
   * @param pubsubMessageHeaders headers in {@link com.google.pubsub.v1.PubsubMessage} format
   * @return a map with headers in the {@link org.springframework.messaging.Message} format
   */
  @Override
  public Map toHeaders(Map pubsubMessageHeaders) {
    return pubsubMessageHeaders.entrySet().stream()
        .filter(
            entry ->
                Boolean.TRUE.equals(
                    PatternMatchUtils.smartMatch(entry.getKey(), this.inboundHeaderPatterns)))
        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
  }
}