- Fix 0x20 capsforid fallback to omit gratuitous NS and additional

section changes.


git-svn-id: file:///svn/unbound/trunk@3323 be551aaa-1e26-0410-a405-d3ace91eadb9

doc/Changelog

@@ -1,3 +1,7 @@
+30 January 2015: Wouter
+	- Fix 0x20 capsforid fallback to omit gratuitous NS and additional
+	  section changes.
+
 29 January 2015: Wouter
 	- Fix pyunbound byte string representation for python3.
 

iterator/iter_utils.c

@@ -714,6 +714,42 @@ reply_equal(struct reply_info* p, struct reply_info* q, struct regional* region)
 	return 1;
 }
 
+void 
+caps_strip_reply(struct reply_info* rep)
+{
+	size_t i;
+	if(!rep) return;
+	/* see if message is a referral, in which case the additional and
+	 * NS record cannot be removed */
+	/* referrals have the AA flag unset (strict check, not elsewhere in
+	 * unbound, but for 0x20 this is very convenient). */
+	if(!(rep->flags&BIT_AA))
+		return;
+	/* remove the additional section from the reply */
+	if(rep->ar_numrrsets != 0) {
+		verbose(VERB_ALGO, "caps fallback: removing additional section");
+		rep->rrset_count -= rep->ar_numrrsets;
+		rep->ar_numrrsets = 0;
+	}
+	/* is there an NS set in the authority section to remove? */
+	/* the failure case (Cisco firewalls) only has one rrset in authsec */
+	for(i=rep->an_numrrsets; i<rep->an_numrrsets+rep->ns_numrrsets; i++) {
+		struct ub_packed_rrset_key* s = rep->rrsets[i];
+		if(ntohs(s->rk.type) == LDNS_RR_TYPE_NS) {
+			/* remove NS rrset and break from loop (loop limits
+			 * have changed) */
+			/* move last rrset into this position (there is no
+			 * additional section any more) */
+			verbose(VERB_ALGO, "caps fallback: removing NS rrset");
+			if(i < rep->rrset_count-1)
+				rep->rrsets[i]=rep->rrsets[rep->rrset_count-1];
+			rep->rrset_count --;
+			rep->ns_numrrsets --;
+			break;
+		}
+	}
+}
+
 void 
 iter_store_parentside_rrset(struct module_env* env, 
 	struct ub_packed_rrset_key* rrset)

iterator/iter_utils.h

@@ -222,6 +222,15 @@ int iter_msg_from_zone(struct dns_msg* msg, struct delegpt* dp,
  */
 int reply_equal(struct reply_info* p, struct reply_info* q, struct regional* region);
 
+/**
+ * Remove unused bits from the reply if possible.
+ * So that caps-for-id (0x20) fallback is more likely to be successful.
+ * This removes like, the additional section, and NS record in the authority
+ * section if those records are gratuitous (not for a referral).
+ * @param rep: the reply to strip stuff out of.
+ */
+void caps_strip_reply(struct reply_info* rep);
+
 /**
  * Store parent-side rrset in seperate rrset cache entries for later 
  * last-resort * lookups in case the child-side versions of this information 

iterator/iterator.c

@@ -2882,6 +2882,9 @@ process_response(struct module_qstate* qstate, struct iter_qstate* iq,
 			iq->response->rep);
 	
 	if(event == module_event_capsfail || iq->caps_fallback) {
+		/* for fallback we care about main answer, not additionals */
+		/* removing that makes comparison more likely to succeed */
+		caps_strip_reply(iq->response->rep);
 		if(!iq->caps_fallback) {
 			/* start fallback */
 			iq->caps_fallback = 1;