What will happen if I use recv(sockfd, buffer, len, 0); on a non-blocking socket?
If the socket sockfd is closed or nothing to be read, does the recv() block? (note: the flag in recv () is 0).
If the socket is marked non blocking, recv will never block. period.
If the socket is fine but there is no data to be read you will get -1 as return value and errno will be set to EAGAIN.
If there is an error (closed socket etc.), you still get a -1 return value but errno will be set to the appropriate value.