/*
 * 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.sdk.util;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import org.apache.beam.sdk.annotations.Internal;

/** Utility functions for stream operations. */
@Internal
@SuppressWarnings({
  "nullness" // TODO(https://issues.apache.org/jira/browse/BEAM-10402)
})
public class StreamUtils {

  private StreamUtils() {}

  private static final int BUF_SIZE = 8192;

  private static ThreadLocal<SoftReference<byte[]>> threadLocalBuffer = new ThreadLocal<>();

  /** Efficient converting stream to bytes. */
  public static byte[] getBytesWithoutClosing(InputStream stream) throws IOException {
    if (stream instanceof ExposedByteArrayInputStream) {
      // Fast path for the exposed version.
      return ((ExposedByteArrayInputStream) stream).readAll();
    } else if (stream instanceof ByteArrayInputStream) {
      // Fast path for ByteArrayInputStream.
      byte[] ret = new byte[stream.available()];
      stream.read(ret);
      return ret;
    }
    // Falls back to normal stream copying.
    SoftReference<byte[]> refBuffer = threadLocalBuffer.get();
    byte[] buffer = refBuffer == null ? null : refBuffer.get();
    if (buffer == null) {
      buffer = new byte[BUF_SIZE];
      threadLocalBuffer.set(new SoftReference<>(buffer));
    }
    ByteArrayOutputStream outStream = new ByteArrayOutputStream();
    while (true) {
      int r = stream.read(buffer);
      if (r == -1) {
        break;
      }
      outStream.write(buffer, 0, r);
    }
    return outStream.toByteArray();
  }
}
