code: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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 org.apache.skywalking.oap.server.library.client.elasticsearch;
  
  import lombok.Builder;
  import lombok.RequiredArgsConstructor;
  import org.apache.skywalking.library.elasticsearch.requests.search.Search;
  import org.apache.skywalking.library.elasticsearch.requests.search.SearchParams;
  import org.apache.skywalking.library.elasticsearch.response.search.SearchHit;
  
  import java.time.Duration;
  import java.util.ArrayList;
  import java.util.HashSet;
  import java.util.List;
  import java.util.function.Function;
  
  @Builder
  @RequiredArgsConstructor
  public class ElasticSearchScroller<T> {
      public static final Duration SCROLL_CONTEXT_RETENTION = Duration.ofSeconds(30);
  
      final ElasticSearchClient client;
      final Search search;
      final String index;
      @Builder.Default
      final int queryMaxSize = 0;
      @Builder.Default
      final SearchParams params = new SearchParams();
      final Function<SearchHit, T> resultConverter;
  
      public List<T> scroll() {
          final var results = new ArrayList<T>();
          final var scrollIds = new HashSet<String>();
  
          params.scroll(SCROLL_CONTEXT_RETENTION);
  
          var response = client.search(index, search, params);
  
          try {
              while (true) {
                  final var scrollId = response.getScrollId();
                  scrollIds.add(scrollId);
                  if (response.getHits().getTotal() == 0) {
                      break;
                  }
                  for (final var searchHit : response.getHits()) {
                      results.add(resultConverter.apply(searchHit));
                  }
                  if (search.getSize() != null && response.getHits().getHits().size() < search.getSize()) {
                      break;
                  }
                  if (queryMaxSize > 0 && results.size() >= queryMaxSize) {
                      break;
                  }
                  response = client.scroll(SCROLL_CONTEXT_RETENTION, scrollId);
              }
          } finally {
              scrollIds.forEach(client::deleteScrollContextQuietly);
          }
  
          return results;
      }
  }
  