[trac914] simplified the existing TSIG related tests a bit.

IMO we don't have detailed inspection of TSIG at this level.  These are
done in pydnspp tests.

src/bin/xfrin/tests/xfrin_test.py

@@ -54,13 +54,6 @@ default_answers = [soa_rrset]
 class XfrinTestException(Exception):
     pass
 
-def strip_mutable_tsig_data(data):
-    # Unfortunately we cannot easily compare TSIG RR because we can't tweak
-    # current time.  As a work around this helper function strips off the time
-    # dependent part of TSIG RDATA, i.e., the MAC (assuming HMAC-MD5) and
-    # Time Signed.
-    return data[0:-32] + data[-26:-22] + data[-6:]
-
 class MockXfrin(Xfrin):
     # This is a class attribute of a callable object that specifies a non
     # default behavior triggered in _cc_check_command().  Specific test methods
@@ -217,6 +210,15 @@ class TestXfrinConnection(unittest.TestCase):
             query_question = Question(Name("example.com."), RRClass.IN(), query_type)
             msg.add_question(query_question)
             return msg
+
+        def message_has_tsig(data):
+            # a simple check if the actual data contains a TSIG RR.
+            # At our level this simple check should suffice; other detailed
+            # tests regarding the TSIG protocol are done in pydnspp.
+            msg = Message(Message.PARSE)
+            msg.from_wire(data)
+            return msg.get_tsig_record() is not None
+
         self.conn._create_query = create_msg
         # soa request
         self.conn._send_query(RRType.SOA())
@@ -228,13 +230,11 @@ class TestXfrinConnection(unittest.TestCase):
         # soa request with tsig
         self.conn._tsig_ctx = MockTSIGContext(TSIG_KEY)
         self.conn._send_query(RRType.SOA())
-        tsig_soa_data = strip_mutable_tsig_data(self.conn.query_data)
+        self.assertTrue(message_has_tsig(self.conn.query_data[2:]))
-        self.assertEqual(tsig_soa_data, b'\x00n\x105\x00\x00\x00\x01\x00\x00\x00\x00\x00\x01\x07example\x03com\x00\x00\x06\x00\x01\x07example\x03com\x00\x00\xfa\x00\xff\x00\x00\x00\x00\x00:\x08hmac-md5\x07sig-alg\x03reg\x03int\x00\x01,\x00\x10\x105\x00\x00\x00\x00')
 
         # axfr request with tsig
         self.conn._send_query(RRType.AXFR())
-        tsig_axfr_data = strip_mutable_tsig_data(self.conn.query_data)
+        self.assertTrue(message_has_tsig(self.conn.query_data[2:]))
-        self.assertEqual(tsig_axfr_data, b'\x00n\x105\x00\x00\x00\x01\x00\x00\x00\x00\x00\x01\x07example\x03com\x00\x00\xfc\x00\x01\x07example\x03com\x00\x00\xfa\x00\xff\x00\x00\x00\x00\x00:\x08hmac-md5\x07sig-alg\x03reg\x03int\x00\x01,\x00\x10\x105\x00\x00\x00\x00')
 
     def test_response_with_invalid_msg(self):
         self.conn.reply_data = b'aaaxxxx'