Always register for TCP events even if there are no outstanding queries, as...

Always register for TCP events even if there are no outstanding queries, as the other side could always close the connection, which is a valid event which should be responded to.

ares/ares_fds.c

@@ -30,20 +30,23 @@ int ares_fds(ares_channel channel, fd_set *read_fds, fd_set *write_fds)
   ares_socket_t nfds;
   int i;
 
-  /* No queries, no file descriptors. */
-  if (!channel->queries)
-    return 0;
-
   nfds = 0;
   for (i = 0; i < channel->nservers; i++)
     {
       server = &channel->servers[i];
-      if (server->udp_socket != ARES_SOCKET_BAD)
+      /* We only need to register interest in UDP sockets if we have
+       * outstanding queries.
+       */
+      if (channel->queries && server->udp_socket != ARES_SOCKET_BAD)
         {
           FD_SET(server->udp_socket, read_fds);
           if (server->udp_socket >= nfds)
             nfds = server->udp_socket + 1;
         }
+      /* We always register for TCP events, because we want to know
+       * when the other side closes the connection, so we don't waste
+       * time trying to use a broken connection.
+       */
       if (server->tcp_socket != ARES_SOCKET_BAD)
        {
          FD_SET(server->tcp_socket, read_fds);