content: /*
   * 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.beam.runners.dataflow.worker;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.List;
  import org.apache.beam.runners.dataflow.worker.util.common.worker.NativeReader;
  
  /** Utilities for working with {@link NativeReader} objects. */
  public class ReaderUtils {
    /**
     * Creates a {@link NativeReader.NativeReaderIterator} from the given {@link NativeReader} and
     * reads it to the end.
     *
     * @param reader {@link NativeReader} to read from
     */
    public static <T> List<T> readAllFromReader(NativeReader<T> reader) throws IOException {
      try (NativeReader.NativeReaderIterator<T> iterator = reader.iterator()) {
        return readRemainingFromIterator(iterator, false);
      }
    }
  
    /**
     * Read elements from a {@link NativeReader.NativeReaderIterator} until either the reader is
     * exhausted, or {@code n} elements are read. Specifying {@code n == Integer.MAX_VALUE} means read
     * all remaining elements.
     */
    public static <T> List<T> readNItemsFromIterator(
        NativeReader.NativeReaderIterator<T> reader, int n, boolean started) throws IOException {
      List<T> res = new ArrayList<>();
      for (long i = 0; n == Integer.MAX_VALUE || i < n; i++) {
        if (!((i == 0 && !started) ? reader.start() : reader.advance())) {
          break;
        }
        res.add(reader.getCurrent());
      }
      return res;
    }
  
    /**
     * Read elements from a {@link NativeReader.NativeReaderIterator} until either the reader is
     * exhausted, or n elements are read. Specifying {@code n == Integer.MAX_VALUE} means read all
     * remaining elements.
     */
    public static <T> List<T> readNItemsFromUnstartedIterator(
        NativeReader.NativeReaderIterator<T> reader, int n) throws IOException {
      return readNItemsFromIterator(reader, n, false);
    }
  
    /**
     * Read elements from a {@link NativeReader.NativeReaderIterator} until the reader is exhausted.
     */
    public static <T> List<T> readRemainingFromIterator(
        NativeReader.NativeReaderIterator<T> reader, boolean started) throws IOException {
      return readNItemsFromIterator(reader, Integer.MAX_VALUE, started);
    }
  }
  