Boost asio udp socket using asio null_buffers

Question

I want to receive data from an UDP socket asynchronously using Boost ASIO library. I don't want to use a fixed length buffer while receiving data using async_receive_from.

The following code is how I used boost asio::null_buffers to determine the incoming packet size and create buffer accordingly.

socket.async_receive_from(boost::asio::null_buffers(),
                           remote_endpoint,
                           [&](boost::system::error_code ec, std::size_t bytes) {
  unsigned int readbytes = socket.available();
  if (readbytes > buffer_size) {
    //reallocate buffer
  }
  std::size_t recvbytes = socket.receive_from(
      boost::asio::buffer(buffer, buffer_size), remote_endpoint, 0, error);

Everything works as expected, however, I want to know if boost null_buffer allocates an internal buffer to keep a copy of the UDP packet received and copies to the given buffer when socket.receive_from() is called.

Also I want to know what is the impact of using null_buffer on performance and memory usage while using a UDP socket.

Answer 1

What RichardHodges said.

In addition, Boost 1.66.0 has the new interface where null_buffers are obsolete and reactor-style integration can be dones using the async_wait operations on your socket:

See eg the docs here https://www.boost.org/doc/libs/1_66_0/doc/html/boost_asio/reference/basic_socket/wait/overload1.html

Answer 2

null_buffers is not a buffer. It's a value of a type used to select a different (and special) overload of the receive/read/write functions.

These overloads simply test the state of the socket in order to tell you whether there is data to read (and how much of it there is).

Your approach is fine and it is efficient.