char *(*fmtaddr)(in_addr_t addr, int n);
sessionidt (*get_session_by_username)(char *username);
sessiont *(*get_session_by_id)(sessionidt s);
char *(*fmtaddr)(in_addr_t addr, int n);
sessionidt (*get_session_by_username)(char *username);
sessiont *(*get_session_by_id)(sessionidt s);