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_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);