ByteBufferUtils.java

/*
 * Copyright (c) 2010-2020 Nathan Rajlich
 *
 *  Permission is hereby granted, free of charge, to any person
 *  obtaining a copy of this software and associated documentation
 *  files (the "Software"), to deal in the Software without
 *  restriction, including without limitation the rights to use,
 *  copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the
 *  Software is furnished to do so, subject to the following
 *  conditions:
 *
 *  The above copyright notice and this permission notice shall be
 *  included in all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 *  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 *  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 *  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 *  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 *  OTHER DEALINGS IN THE SOFTWARE.
 */

package org.java_websocket.util;

import java.nio.ByteBuffer;

/**
 * Utility class for ByteBuffers
 */
public class ByteBufferUtils {

  /**
   * Shared empty ByteBuffer to avoid repeated allocations.
   * Safe to share because it has zero capacity and duplicate() provides independent position/limit state.
   */
  private static final ByteBuffer EMPTY_BYTE_BUFFER = ByteBuffer.allocate(0);

  /**
   * Private constructor for static class
   */
  private ByteBufferUtils() {
  }

  /**
   * Transfer from one ByteBuffer to another ByteBuffer
   *
   * @param source the ByteBuffer to copy from
   * @param dest   the ByteBuffer to copy to
   * @return the number of transferred bytes
   */
  public static int transferByteBuffer(ByteBuffer source, ByteBuffer dest) {
    if (source == null || dest == null) {
      throw new IllegalArgumentException();
    }
    int fremain = source.remaining();
    int toremain = dest.remaining();
    if (fremain > toremain) {
      // We know fremain > toremain, so no need for Math.min
      int originalLimit = source.limit();
      source.limit(source.position() + toremain);
      dest.put(source);
      source.limit(originalLimit);
      return toremain;
    } else {
      dest.put(source);
      return fremain;
    }
  }

  /**
   * Get a ByteBuffer with zero capacity. Returns a duplicate of a shared empty buffer
   * for efficiency - each duplicate has independent position/limit/mark state.
   *
   * @return empty ByteBuffer with zero capacity
   */
  public static ByteBuffer getEmptyByteBuffer() {
    return EMPTY_BYTE_BUFFER.duplicate();
  }
}