boost boost::asio::read
尝试读一定数量的字节，直到读到为止，或者出错 . Attempt to read a certain amount of data from a stream before returning. 即收到指定的数据才返回。
socket.read_some
读一下socket，读到多少算多少
socket.receive:
Receive some data on the socket. 即收到一些数据就返回。也即会导致所谓的short reads and writes.
带async的类似
