Add format string attributes

http_response.h

@@ -20,7 +20,7 @@ void send_header_textplain(int clientsock);
 
 void send_http_error(int clientsock, const char *code, const char *message);
 void send_http_ok(int clientsock, const char *message);
-void send_http_ok_msg(int clientsock, const char *fmt, ...);
+void send_http_ok_msg(int clientsock, const char *fmt, ...) __attribute__ ((format(printf, 2, 3)));
 
 void send_200_ok(int clientsock);
 void send_302_redirect(int clientsock, const char * url);

io.h

@@ -29,7 +29,7 @@ ssize_t fdread_nowaitfull(int fd, char *buf, size_t buf_size);
 ssize_t fdwrite(int fd, char *buf, size_t buf_size);
 
 int fdputs(int fd, char *msg);
-int fdputsf(int fd, char *fmt, ...);
+int fdputsf(int fd, char *fmt, ...) __attribute__ ((format(printf, 2, 3)));
 
 void set_log_io_errors(int report_io_errors);