fix: use sig_atomic_t for signal handler flag and remove async-signal-unsafe calls

The 'exiting' variable is accessed from signal handler context and
should use sig_atomic_t type with volatile qualifier as required by
the C standard.

Remove calls to deinit_all() and exit() from sigint_handler since
neither WinDivertShutdown/WinDivertClose nor exit() are
async-signal-safe functions. Move cleanup to after the main loop.

Also register SIGTERM in addition to SIGINT so that the handler is
invoked when the process is terminated via GUI close button, and
change the main loop condition from while(1) to while(!exiting) so
that the flag is checked on every iteration.

Closes #770

src/goodbyedpi.c

@@ -149,7 +149,7 @@ enum ERROR_CODE{
 };
 
 static int running_from_service = 0;
-static int exiting = 0;
+static volatile sig_atomic_t exiting = 0;
 static HANDLE filters[MAX_FILTERS];
 static int filter_num = 0;
 static const char http10_redirect_302[] = "HTTP/1.0 302 ";
@@ -367,8 +367,6 @@ void deinit_all() {
 
 static void sigint_handler(int sig __attribute__((unused))) {
     exiting = 1;
-    deinit_all();
-    exit(EXIT_SUCCESS);
 }
 
 static void mix_case(char *pktdata, unsigned int pktlen) {
@@ -1171,8 +1169,9 @@ int main(int argc, char *argv[]) {
     }
     printf("Filter activated, GoodbyeDPI is now running!\n");
     signal(SIGINT, sigint_handler);
+    signal(SIGTERM, sigint_handler);
 
-    while (1) {
+    while (!exiting) {
         if (WinDivertRecv(w_filter, packet, sizeof(packet), &packetLen, &addr)) {
             debug("Got %s packet, len=%d!\n", addr.Outbound ? "outbound" : "inbound",
                    packetLen);
@@ -1294,7 +1293,7 @@ int main(int argc, char *argv[]) {
                     }
                 }
                 /* Handle OUTBOUND packet on port 80, search for Host header */
-                else if (addr.Outbound && 
+                else if (addr.Outbound &&
                         packet_dataLen > 16 &&
                         (do_http_allports ? 1 : (ppTcpHdr->DstPort == htons(80))) &&
                         find_http_method_end(packet_data,
@@ -1560,4 +1559,6 @@ int main(int argc, char *argv[]) {
             break;
         }
     }
+    deinit_all();
+    exit(EXIT_SUCCESS);
 }