dnsforward: imp code

internal/dnsforward/filter.go

@@ -40,12 +40,7 @@ func (s *Server) filterDNSRequest(dctx *dnsContext) (res *filtering.Result, err
 	// TODO(a.garipov): Make CheckHost return a pointer.
 	res = &resVal
 	switch {
-	case res.Reason.In(
-		filtering.Rewritten,
-		filtering.RewrittenRule,
-		filtering.FilteredSafeSearch) &&
-		res.CanonName != "" &&
-		len(res.IPList) == 0:
+	case isRewrittenCNAME(res):
 		// Resolve the new canonical name, not the original host name.  The
 		// original question is readded in processFilteringAfterResponse.
 		dctx.origQuestion = q
@@ -64,6 +59,17 @@ func (s *Server) filterDNSRequest(dctx *dnsContext) (res *filtering.Result, err
 	return res, err
 }
 
+// isRewrittenCNAME returns true if the request considered to be rewritten with
+// CNAME and has no resolved IPs.
+func isRewrittenCNAME(res *filtering.Result) (ok bool) {
+	return res.Reason.In(
+		filtering.Rewritten,
+		filtering.RewrittenRule,
+		filtering.FilteredSafeSearch) &&
+		res.CanonName != "" &&
+		len(res.IPList) == 0
+}
+
 // checkHostRules checks the host against filters.  It is safe for concurrent
 // use.
 func (s *Server) checkHostRules(