src: add a two-second timeout to the escape character

Now if the escape character is pressed by accident, in the worst case
after two seconds it will be dropped so that pressing another key will
have no effect. This can be important for users switching between
multiple windows as it's easy to send a break or DTR change by accident
for example.

src/bt.c

@@ -1769,6 +1769,8 @@ void forward(int fd)
 	struct buffer port_obuf = { };
 	struct buffer user_ibuf = { };
 	struct buffer user_obuf = { };
+	struct timeval escape_timeout = tv_unset();
+	struct timeval now;
 	int in_utf8 = 0;
 	int in_esc = 0;
 
@@ -1809,6 +1811,7 @@ void forward(int fd)
 	 */
 	while (((user_obuf.len + port_ibuf.len || port_ibuf.room >= 0) && (user_obuf.data >= 0)) ||
 	       ((port_obuf.len + user_ibuf.len || user_ibuf.room >= 0) && (port_obuf.data >= 0 && port_ibuf.room >= 0))) {
+		struct timeval interval;
 		int cnt;
 
 		if (user_ibuf.room >= 0 && user_ibuf.len < BUFSIZE)
@@ -1831,8 +1834,22 @@ void forward(int fd)
 		else
 			FD_CLR(fd, &wfds);
 
-		cnt = select(FD_SETSIZE, &rfds, &wfds, NULL, NULL);
-		if (cnt <= 0) // signal
+		gettimeofday(&now, NULL);
+		interval = tv_unset();
+
+		if (in_esc)
+			interval = tv_min(interval, tv_diff(now, escape_timeout));
+
+		cnt = select(FD_SETSIZE, &rfds, &wfds, NULL, tv_isset(interval) ? &interval : NULL);
+
+		gettimeofday(&now, NULL);
+
+		if (in_esc && !tv_isbefore(now, escape_timeout)) {
+			/* abort escape mode */
+			in_esc = 0;
+		}
+
+		if (cnt <= 0) // signal or timeout
 			continue;
 
 		set_capture_name();
@@ -1945,8 +1962,11 @@ void forward(int fd)
 
 		/* transfer between IN and opposite OUT buffers */
 		if (!in_esc && xfer_user_to_port(&user_ibuf, &port_obuf, escape) < 0) {
-			/* we stopped in front of the escape character */
+			/* we stopped in front of the escape character, let's
+			 * wait up to two seconds for the sequence to be entered.
+			 */
 			b_skip(&user_ibuf, 1);
+			escape_timeout = tv_add(now, tv_set(2, 0));
 			in_esc = 1;
 		}