+extern int recvfrom(int sockfd, void *buffer, size_t length, int flags, struct sockaddr *clientaddr, socklen_t *addrlen);
+extern int recv(int sockfd, void *buffer, size_t length, int flags);
+extern int sendto(int sockfd, const void *buffer, size_t length, int flags, const struct sockaddr *clientaddr, socklen_t addrlen);
+extern int send(int sockfd, void *buffer, size_t length, int flags);
+