Force RST on client sockets during shutdown

On OpenBSD, SO_REUSEADDR and SO_REUSEPORT are not sufficient
to rebind when orphaned FIN_WAIT_2 connections hold the listen
address.  Set SO_LINGER with l_linger=0 on accepted client
sockets before closing during shutdown so the kernel sends RST
instead of FIN and releases the PCB immediately.

Author: renaudallard

thinproxy.c

@@ -1844,8 +1844,20 @@ main(int argc, char *argv[])
 
 	logmsg(LOG_INFO, "shutting down");
 	for (i = 0; i < MAX_FDS; i++) {
-		if (fdmap[i] != NULL && fdtype_arr[i] == FD_CLIENT)
-			conn_close(fdmap[i]);
+		if (fdmap[i] != NULL && fdtype_arr[i] == FD_CLIENT) {
+			struct linger lg = { 1, 0 };
+			struct conn *c = fdmap[i];
+			/*
+			 * Force RST on client sockets so the kernel
+			 * releases the PCB immediately.  Without this,
+			 * connections in FIN_WAIT_2 hold the listen
+			 * address and block bind() on restart.
+			 */
+			if (c->cfd >= 0)
+				(void)setsockopt(c->cfd, SOL_SOCKET,
+				    SO_LINGER, &lg, sizeof(lg));
+			conn_close(c);
+		}
 	}
 	close(lfd);