void xbind (int, const struct sockaddr *, socklen_t);
void xlisten (int, int);
int xaccept (int, struct sockaddr *, socklen_t *);
+int xaccept4 (int, struct sockaddr *, socklen_t *, int);
void xsendto (int, const void *, size_t, int,
const struct sockaddr *, socklen_t);
size_t xrecvfrom (int, void *, size_t, int, struct sockaddr *, socklen_t *);