content: // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
  // for details. All rights reserved. Use of this source code is governed by a
  // BSD-style license that can be found in the LICENSE file.
  
  part of dart.io;
  
  /**
   * Builds a list of bytes, allowing bytes and lists of bytes to be added at the
   * end.
   *
   * Used to efficiently collect bytes and lists of bytes, using an internal
   * buffer. Note that it's optimized for IO, using an initial buffer of 1K bytes.
   */
  class BytesBuilder {
    // Start with 1024 bytes.
    static const int _INIT_SIZE = 1024;
  
    int _length = 0;
    Uint8List _buffer;
  
    /**
     * Construct a new empty [BytesBuilder].
     */
    BytesBuilder();
  
    /**
     * Appends [bytes] to the current contents of the builder.
     *
     * Each value of [bytes] will be bit-representation truncated to the range
     * 0 .. 255.
     */
    void add(List<int> bytes) {
      int bytesLength = bytes.length;
      if (bytesLength == 0) return;
      int required = _length + bytesLength;
      if (_buffer == null) {
        int size = _pow2roundup(required);
        size = max(size, _INIT_SIZE);
        _buffer = new Uint8List(size);
      } else if (_buffer.length < required) {
        // We will create a list in the range of 2-4 times larger than
        // required.
        int size = _pow2roundup(required) * 2;
        var newBuffer = new Uint8List(size);
        newBuffer.setRange(0, _buffer.length, _buffer);
        _buffer = newBuffer;
      }
      assert(_buffer.length >= required);
      if (bytes is Uint8List) {
        _buffer.setRange(_length, required, bytes);
      } else {
        for (int i = 0; i < bytesLength; i++) {
          _buffer[_length + i] = bytes[i];
        }
      }
      _length = required;
    }
  
    /**
     * Append [byte] to the current contents of the builder.
     *
     * The [byte] will be bit-representation truncated to the range 0 .. 255.
     */
    void addByte(int byte) => add([byte]);
  
    /**
     * Returns the contents of `this` and clears `this`.
     *
     * The list returned is a view of the the internal buffer, limited to the
     * [length].
     */
    List<int> takeBytes() {
      if (_buffer == null) return new Uint8List(0);
      var buffer = new Uint8List.view(_buffer.buffer, 0, _length);
      clear();
      return buffer;
    }
  
    /**
     * Returns a copy of the current contents of the builder.
     *
     * Leaves the contents of the builder intact.
     */
    List<int> toBytes() {
      if (_buffer == null) return new Uint8List(0);
      return new Uint8List.fromList(
          new Uint8List.view(_buffer.buffer, 0, _length));
    }
  
    /**
     * The number of bytes in the builder.
     */
    int get length => _length;
  
    /**
     * Returns `true` if the buffer is empty.
     */
    bool get isEmpty => _length == 0;
  
    /**
     * Returns `true` if the buffer is empty.
     */
    bool get isNotEmpty => _length != 0;
  
    /**
     * Clear the contents of the builder.
     */
    void clear() {
      _length = 0;
      _buffer = null;
    }
  
    int _pow2roundup(int x) {
      --x;
      x |= x >> 1;
      x |= x >> 2;
      x |= x >> 4;
      x |= x >> 8;
      x |= x >> 16;
      return x + 1;
    }
  }
  