read_str
*client_username = read_str (s, USERNAME_SZ, "local username");
*server_username = read_str (s, USERNAME_SZ, "remote username");
*cmd = read_str (s, ARG_MAX + 1, "command");
*server_username = read_str (s, USERNAME_SZ, "remote username");
*cmd = read_str (s, ARG_MAX + 1, "command");
*client_username = read_str (s, ARG_MAX + 1, "local username");