[Boost-users] [Asio] null_buffer behaviors

Hi, guys. In the doc of asio, it says 'A null_buffers operation doesn't return until the I/O object is "ready" to perform the operation'. But when I use it on a server side socket, i.e. a socket created by "accept" call when a new connection has arrived. It seems to return immediately even the other end has not started to send the data yet. Is this normal?