+int recvfrom(int s, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen);
+int sendto(int s, const void *msg, size_t len, int flags, const struct sockaddr *to, socklen_t tolen);
+int select(int n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);