From 5f3192e09981dabf321b10271ea798535ef04484 Mon Sep 17 00:00:00 2001
From: David Kerkeslager <kerkeslager@gmail.com>
Date: Sat, 24 Sep 2016 16:23:41 -0400
Subject: [PATCH] Added serialization for tag-only types

---
 serial/binary.py      | 51 +++++++++++++++++++++++++++++++++++++++++
 serial/test_binary.py | 53 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 104 insertions(+)
 create mode 100644 serial/binary.py
 create mode 100644 serial/test_binary.py

diff --git a/serial/binary.py b/serial/binary.py
new file mode 100644
index 0000000..2b18bfb
--- /dev/null
+++ b/serial/binary.py
@@ -0,0 +1,51 @@
+import collections
+
+TAG_NULL = 0x00
+TAG_TRUE = 0x01
+TAG_FALSE = 0x02
+
+TaggedObject = collections.namedtuple(
+    'TaggedObject',
+    [
+        'tag',
+        'instance',
+    ],
+)
+
+def _make_tag_only_serializer(tag, expected_value):
+    tag = bytes([tag])
+
+    def serializer(to):
+        assert to.instance == expected_value
+        return tag
+
+    return serializer
+
+_TAGS_TO_SERIALIZERS = {
+    TAG_NULL: _make_tag_only_serializer(TAG_NULL, None),
+    TAG_TRUE: _make_tag_only_serializer(TAG_TRUE, True),
+    TAG_FALSE: _make_tag_only_serializer(TAG_FALSE, False),
+}
+
+def serialize(to):
+    return _TAGS_TO_SERIALIZERS[to.tag](to)
+
+def _make_tag_only_parser(tag, value):
+    def parser(b):
+        return TaggedObject(tag = tag, instance = value), b
+
+    return parser
+
+_TAGS_TO_PARSERS = {
+    TAG_NULL: _make_tag_only_parser(TAG_NULL, None),
+    TAG_TRUE: _make_tag_only_parser(TAG_TRUE, True),
+    TAG_FALSE: _make_tag_only_parser(TAG_FALSE, False),
+}
+
+def deserialize(b):
+    result, remainder = _TAGS_TO_PARSERS[b[0]](b[1:])
+
+    if len(remainder) == 0:
+        return result
+
+    raise Exception('Unable to parse remainder: {}'.format(remainder))
diff --git a/serial/test_binary.py b/serial/test_binary.py
new file mode 100644
index 0000000..b9acaa5
--- /dev/null
+++ b/serial/test_binary.py
@@ -0,0 +1,53 @@
+import unittest
+
+import binary
+
+class SerializeTests(unittest.TestCase):
+    def test_serializes_tag_only_types(self):
+        self.assertEqual(
+            binary.serialize(binary.TaggedObject(
+                tag = binary.TAG_NULL,
+                instance = None,
+            )),
+            b'\x00',
+        )
+        self.assertEqual(
+            binary.serialize(binary.TaggedObject(
+                tag = binary.TAG_TRUE,
+                instance = True,
+            )),
+            b'\x01',
+        )
+        self.assertEqual(
+            binary.serialize(binary.TaggedObject(
+                tag = binary.TAG_FALSE,
+                instance = False,
+            )),
+            b'\x02',
+        )
+
+class DeserializeTests(unittest.TestCase):
+    def test_deserializes_tag_only_types(self):
+        self.assertEqual(
+            binary.deserialize(b'\x00'),
+            binary.TaggedObject(
+                tag = binary.TAG_NULL,
+                instance = None,
+            ),
+        )
+        self.assertEqual(
+            binary.deserialize(b'\x01'),
+            binary.TaggedObject(
+                tag = binary.TAG_TRUE,
+                instance = True,
+            ),
+        )
+        self.assertEqual(
+            binary.deserialize(b'\x02'),
+            binary.TaggedObject(
+                tag = binary.TAG_FALSE,
+                instance = False,
+            )
+        )
+
+unittest.main()
-- 
2.20.1