resolve: add CURLOPT_DNS_SHUFFLE_ADDRESSES

This patch adds CURLOPT_DNS_SHUFFLE_ADDRESSES to explicitly request
shuffling of IP addresses returned for a hostname when there is more
than one. This is useful when the application knows that a round robin
approach is appropriate and is willing to accept the consequences of
potentially discarding some preference order returned by the system's
implementation.

Closes #1694

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/urldata.h b/lib/urldata.h
index dad31cd4e..35bbb8590 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1674,6 +1674,8 @@ struct UserDefined {
   bool suppress_connect_headers;  /* suppress proxy CONNECT response headers
                                      from user callbacks */
 
+  bool dns_shuffle_addresses; /* whether to shuffle addresses before use */
+
   struct Curl_easy *stream_depends_on;
   bool stream_depends_e; /* set or don't set the Exclusive bit */
   int stream_weight;