Fix two crashes in the default DNS forward/cache path

lib/rex/proto/dns/server.rb

@@ -185,10 +185,10 @@ def default_dispatch_request(cli,data)
     # Finalize answers in response
     # Check for empty response prior to sending
     if req.answer.size < 1
-      req.header.rCode = Dnsruby::RCode::NOERROR
+      req.header.rcode = Dnsruby::RCode::NOERROR
     end
     req.header.qr = true # Set response bit
-    send_response(cli, req.data)
+    send_response(cli, req.encode)
   end
 
   #

spec/lib/rex/proto/dns/server_spec.rb

@@ -0,0 +1,40 @@
+require 'rex/proto/dns'
+
+RSpec.describe Rex::Proto::DNS::Server do
+  subject(:server) { described_class.new }
+
+  let(:cli) { double('client', write: nil) }
+
+  # a real, encodable query for a name that is in neither the cache nor
+  # anything the stubbed resolver knows about
+  def query_for(name)
+    query = Dnsruby::Message.new
+    query.add_question(Dnsruby::Name.create("#{name}."), Dnsruby::Types::A)
+    query.encode
+  end
+
+  describe '#default_dispatch_request' do
+    context 'when the forwarded response carries no answers' do
+      before do
+        # the resolver forwards the query and comes back empty, which is the
+        # path that finalizes an empty response - the one that crashed
+        empty_response = Dnsruby::Message.new
+        server.fwd_res = double('resolver', send: empty_response)
+      end
+
+      it 'does not raise' do
+        expect { server.default_dispatch_request(cli, query_for('empty.example.com')) }.not_to raise_error
+      end
+
+      it 'sends a well formed, encoded response back to the client' do
+        expect(cli).to receive(:write) do |data|
+          expect(data).to be_a(String)
+          reply = Dnsruby::Message.decode(data)
+          expect(reply.header.get_header_rcode).to eq(Dnsruby::RCode::NOERROR)
+          expect(reply.header.qr).to eq(true)
+        end
+        server.default_dispatch_request(cli, query_for('empty.example.com'))
+      end
+    end
+  end
+end