- Phil Blundell: If you ask ares_gethostbyname() to do an AF_INET6 lookup and

the target host has only A records, it automatically falls back to an
  AF_INET lookup and gives you the A results.  However, if the target host has
  a CNAME record, this behaviour is defeated since the original query does
  return some data even though ares_parse_aaa_reply() doesn't consider it
  relevant. Here's a small patch to make it behave the same with and without
  the CNAME.

ares/CHANGES

@@ -1,5 +1,14 @@
   Changelog for the c-ares project
 
+* Jul 3 2008 (Daniel Stenberg)
+- Phil Blundell: If you ask ares_gethostbyname() to do an AF_INET6 lookup and
+  the target host has only A records, it automatically falls back to an
+  AF_INET lookup and gives you the A results.  However, if the target host has
+  a CNAME record, this behaviour is defeated since the original query does
+  return some data even though ares_parse_aaa_reply() doesn't consider it
+  relevant. Here's a small patch to make it behave the same with and without
+  the CNAME.
+
 * Jul 2 2008 (Yang Tse)
 - Fallback to gettimeofday when monotonic clock is unavailable at run-time.
 

ares/ares_gethostbyname.c

@@ -176,6 +176,15 @@ static void host_callback(void *arg, int status, int timeouts,
       else if (hquery->family == AF_INET6)
         {
           status = ares_parse_aaaa_reply(abuf, alen, &host, NULL, NULL);
+          if (status == ARES_ENODATA)
+            {
+              /* The query returned something (e.g. CNAME) but there were no
+                 AAAA records.  Try looking up A instead.  */
+              hquery->family = AF_INET;
+              ares_search(hquery->channel, hquery->name, C_IN, T_A, host_callback,
+                          hquery);
+              return;
+            }
           if (host && channel->nsort)
             sort6_addresses(host, channel->sortlist, channel->nsort);
         }