null probe for user_mapping extension from RFC4681

prober.py

@@ -164,7 +164,10 @@
     OCSPUnderflow12PFS(),
     DoubleExtension(),
     DoubleExtension12(),
-    DoubleExtension12PFS()
+    DoubleExtension12PFS(),
+    UserMappingNull(),
+    UserMappingNull12(),
+    UserMappingNull12PFS()
 ]
 
 def probe(ipaddress, port, starttls, specified_probe):

probes.py

@@ -1583,3 +1583,29 @@ class DoubleExtension12(DoubleExtension, NormalHandshake12):
 class DoubleExtension12PFS(DoubleExtension, NormalHandshake12PFS):
     '''Duplicate secure renegotiation extension in PFS TLSv1.2 hello'''
     pass
+
+
+class UserMappingNull(NormalHandshake):
+    '''Send empty user mapping extension in hello'''
+
+    def make_user_mapping_ext(self, value):
+        user_mapping_ext = Extension.create(
+            extension_type=6,
+            data=value)
+        return self.make_hello([user_mapping_ext])
+
+    def test(self, sock):
+        logging.debug('Sending Client Hello...')
+        # extension consists of an array and the array needs at least one
+        # element, don't send any
+        sock.write(self.make_user_mapping_ext(b''))
+
+
+class UserMappingNull12(UserMappingNull, NormalHandshake12):
+    '''Send empty user mapping extension in TLSv1.2 hello'''
+    pass
+
+
+class UserMappingNull12PFS(UserMappingNull, NormalHandshake12PFS):
+    '''Send empty user mapping extension in PFS TLSv1.2 hello'''
+    pass

tests/test_probes.py

@@ -3013,3 +3013,64 @@ def test_test(self):
                           b'\x00'
                           b'\xff\x01\x00\x01'
                           b'\x00'])
+
+
+class TestUserMappingNull(unittest.TestCase):
+    def test_test(self):
+        probe = UserMappingNull()
+        sock = MockSock()
+
+        probe.test(sock)
+
+        self.assertEqual(sock.sent_data,
+                         [b'\x16\x03\x01\x00?'
+                          b'\x01\x00\x00;'
+                          b'\x03\x01' +
+                          RANDOM_STR +
+                          b'\x00'
+                          b'\x00\x0e' +
+                          DEFAULT_CIPHERS_STR +
+                          b'\x01\x00'
+                          b'\x00\x04'
+                          b'\x00\x06\x00\x00'])
+
+
+class TestUserMappingNull12(unittest.TestCase):
+    def test_test(self):
+        probe = UserMappingNull12()
+        sock = MockSock()
+
+        probe.test(sock)
+
+        self.assertEqual(sock.sent_data,
+                         [b'\x16\x03\x01\x00W'
+                          b'\x01\x00\x00S'
+                          b'\x03\x03' +
+                          RANDOM_STR +
+                          b'\x00'
+                          b'\x00&' +
+                          DEFAULT_12_CIPHERS_STR +
+                          b'\x01\x00'
+                          b'\x00\x04'
+                          b'\x00\x06\x00\x00'])
+
+
+class TestUserMappingNull12PFS(unittest.TestCase):
+    def test_test(self):
+        probe = UserMappingNull12PFS()
+        sock = MockSock()
+
+        probe.test(sock)
+
+        self.maxDiff = None
+        self.assertEqual(sock.sent_data,
+                         [b"\x16\x03\x01\x00\x8f"
+                          b"\x01\x00\x00\x8b"
+                          b"\x03\x03" +
+                          RANDOM_STR +
+                          b"\x00"
+                          b"\x00^" +
+                          DEFAULT_PFS_CIPHERS_STR +
+                          b"\x01\x00"
+                          b'\x00\x04'
+                          b'\x00\x06\x00\x00'])