libcurl: New options to bind DNS to local interfaces or IP addresses

lib/hostip.h

@@ -200,6 +200,27 @@ extern sigjmp_buf curl_jmpenv;
  */
 CURLcode Curl_set_dns_servers(struct SessionHandle *data, char *servers);
 
+/*
+ * Function provided by the resolver backend to set
+ * outgoing interface to use for DNS requests
+ */
+CURLcode Curl_set_dns_interface(struct SessionHandle *data,
+                                const char *interface);
+
+/*
+ * Function provided by the resolver backend to set
+ * local IPv4 address to use as source address for DNS requests
+ */
+CURLcode Curl_set_dns_local_ip4(struct SessionHandle *data,
+                                const char *local_ip4);
+
+/*
+ * Function provided by the resolver backend to set
+ * local IPv6 address to use as source address for DNS requests
+ */
+CURLcode Curl_set_dns_local_ip6(struct SessionHandle *data,
+                                const char *local_ip6);
+
 /*
  * Clean off entries from the cache
  */