Tag implementation

controlhost/__init__.py

@@ -20,11 +20,35 @@ __status__ = "Development"
 
 
 class Tag(object):
-    def __init__(self):
-        pass
+    SIZE = 8
+    def __init__(self, data=None):
+        self._data = b''
+        self.data = data
+
+    @property
+    def data(self):
+        return self._data
+
+    @data.setter
+    def data(self, value):
+        if not value:
+            value = b''
+        if len(value) > self.SIZE:
+            raise ValueError("The maximum tag size is {0}".format(self.SIZE))
+        self._data = value
+        while len(self._data) < self.SIZE:
+            self._data += b'\x00'
+
+    def __str__(self):
+        return str(self.data).strip('\x00')
+
+    def __len__(self):
+        return len(self._data)
 
-class Message(object):
-    pass
 
 class Prefix(object):
     pass
+
+
+class Message(object):
+    pass

controlhost/tests/test_controlhost.py

@@ -14,12 +14,36 @@ class TestTag(unittest.TestCase):
     def test_init(self):
         tag = Tag()
 
+    def test_empty_tag_has_correct_length(self):
+        tag = Tag()
+        self.assertEqual(Tag.SIZE, len(tag))
+
+    def test_tag_has_correct_length(self):
+        for tag_name in ('foo', 'bar', 'baz', '1'):
+            tag = Tag(tag_name)
+            self.assertEqual(Tag.SIZE, len(tag))
+
+    def test_tag_with_invalid_length_raises_valueerror(self):
+        with self.assertRaises(ValueError):
+            tag = Tag('123456789')
+
+    def test_tag_has_correct_data(self):
+        tag = Tag('foo')
+        self.assertEqual('foo\x00\x00\x00\x00\x00', tag.data)
+        tag = Tag('abcdefgh')
+        self.assertEqual('abcdefgh', tag.data)
+
+    def test_tag_has_correct_string_representation(self):
+        tag = Tag('foo')
+        self.assertEqual('foo', str(tag))
 
-class TestMessage(unittest.TestCase):
-    def test_init(self):
-        message = Message()
 
 
 class TestPrefix(unittest.TestCase):
     def test_init(self):
         prefix = Prefix()
+
+
+class TestMessage(unittest.TestCase):
+    def test_init(self):
+        message = Message()