asyn-ares: Don't blank ares servers if none configured.

Best to just let c-ares use it's defaults if none are configured
in (lib)curl.

Signed-off-by: Ben Greear <greearb@candelatech.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/lib/asyn-ares.c b/lib/asyn-ares.c
index 392e50a08..081667dc3 100644
--- a/lib/asyn-ares.c
+++ b/lib/asyn-ares.c
@@ -590,8 +590,19 @@ CURLcode Curl_set_dns_servers(struct SessionHandle *data,
                               char *servers)
 {
   CURLcode result = CURLE_NOT_BUILT_IN;
+  int ares_result;
+
+  /* If server is NULL or empty, this would purge all DNS servers
+   * from ares library, which will cause any and all queries to fail.
+   * So, just return OK if none are configured and don't actually make
+   * any changes to c-ares.  This lets c-ares use it's defaults, which
+   * it gets from the OS (for instance from /etc/resolv.conf on Linux).
+   */
+  if(!(servers && servers[0]))
+    return CURLE_OK;
+
 #if (ARES_VERSION >= 0x010704)
-  int ares_result = ares_set_servers_csv(data->state.resolver, servers);
+  ares_result = ares_set_servers_csv(data->state.resolver, servers);
   switch(ares_result) {
   case ARES_SUCCESS:
     result = CURLE_OK;
@@ -608,7 +619,7 @@ CURLcode Curl_set_dns_servers(struct SessionHandle *data,
   }
 #else /* too old c-ares version! */
   (void)data;
-  (void)servers;
+  (void)(ares_result);
 #endif
   return result;
 }