support: Provide a way to clear the RA bit in DNS server responses

support/resolv_test.c

@@ -181,7 +181,9 @@ resolv_response_init (struct resolv_response_builder *b,
   b->buffer[2] |= b->query_buffer[2] & 0x01; /* Copy the RD bit.  */
   if (flags.tc)
     b->buffer[2] |= 0x02;
-  b->buffer[3] = 0x80 | flags.rcode; /* Always set RA.  */
+  b->buffer[3] = flags.rcode;
+  if (!flags.clear_ra)
+    b->buffer[3] |= 0x80;
   if (flags.ad)
     b->buffer[3] |= 0x20;
 

support/resolv_test.h

@@ -148,6 +148,10 @@ struct resolv_response_flags
   /* If true, the AD (authenticated data) flag will be set.  */
   bool ad;
 
+  /* If true, do not set the RA (recursion available) flag in the
+     response.  */
+  bool clear_ra;
+
   /* Initial section count values.  Can be used to artificially
      increase the counts, for malformed packet testing.*/
   unsigned short qdcount;