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 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);