Function shrink

demo_example/asio/asio/buffer.hpp:1775–1778

@b DynamicBuffer_v2: Shrink the underlying memory by the specified number of bytes. * Erases @c n bytes from the end of the string by resizing the basic_string * object. If @c n is greater than the current size of the string, the string * is emptied. */

   * is emptied.
   */
  void shrink(std::size_t n)
  {
    string_.resize(n > size() ? 0 : size() - n);
  }

  /// @b DynamicBuffer_v1: Remove characters from the input sequence.
  /// @b DynamicBuffer_v2: Consume the specified number of bytes from the