Add node interrupt flag checking to *nix external() execution of stdio progs

and abort the execution of the program when the node is interrupted. This
should allow more cases were the node interrupt flag can be used to gracefully
disconnect a user running a DOS or native (stdio) program on *nix.

We have this functionality already in the Windows version of external()

src/sbbs3/xtrn.cpp

@@ -332,7 +332,7 @@ static void add_env_var(str_list_t* list, const char* var, const char* val)
 		SetLastError(last_error)
 
 /****************************************************************************/
-/* Runs an external program 												*/
+/* Runs an external program (on Windows) 									*/
 /****************************************************************************/
 int sbbs_t::external(const char* cmdline, int mode, const char* startup_dir)
 {
@@ -1107,6 +1107,9 @@ static int forkpty(int *amaster, char *name, termios *termp, winsize *winp)
 }
 #endif /* NEED_FORKPTY */
 
+/****************************************************************************/
+/* Runs an external program (on *nix) 										*/
+/****************************************************************************/
 int sbbs_t::external(const char* cmdline, int mode, const char* startup_dir)
 {
 	char          str[MAX_PATH + 1];
@@ -1855,6 +1858,7 @@ int sbbs_t::external(const char* cmdline, int mode, const char* startup_dir)
 			fds[1].fd = err_pipe[0];
 			fds[1].events = POLLIN;
 		}
+		time_t lastnodechk = 0;
 		while (!terminated) {
 			if (waitpid(pid, &i, WNOHANG) != 0)    /* child exited */
 				break;
@@ -1909,8 +1913,17 @@ int sbbs_t::external(const char* cmdline, int mode, const char* startup_dir)
 			}
 
 			data_waiting = fds[0].revents;
-			if (i == 0 && data_waiting == 0)
+			if (i == 0 && data_waiting == 0) {
+				// only check node for interrupt flag every 3 seconds of no I/O
+				if (difftime(time(NULL), lastnodechk) >= 3) {
+					if (getnodedat(cfg.node_num, &thisnode)) {
+						if (thisnode.misc & NODE_INTR)
+							break;
+						lastnodechk = time(NULL);
+					}
+				}
 				continue;
+			}
 
 			avail = (RingBufFree(&outbuf) - i) / 2;   // Leave room for wwiv/telnet expansion
 			if (avail == 0) {