[bencode] Fix unhandled TypeError with string

Passing a non-bencoded dict to bdecode resulted in an unhandled
TypeError.

- Catch TypeError in decode_func.
- Add bdecode tests.
- Replace KeyError and IndexError with base LookupError.

deluge/bencode.py

@@ -84,7 +84,7 @@ decode_func[b'9'] = decode_string
 def bdecode(x):
     try:
         r, __ = decode_func[x[0:1]](x, 0)
-    except (IndexError, KeyError, ValueError):
+    except (LookupError, TypeError, ValueError):
         raise BTFailure('Not a valid bencoded string')
     else:
         return r

deluge/tests/test_bencode.py

@@ -21,4 +21,14 @@ class BencodeTestCase(unittest.TestCase):
         bencode.bencode({b'info': metainfo})
 
     def test_bencode_unicode_value(self):
+        self.assertEqual(bencode.bencode(b'abc'), b'3:abc')
         self.assertEqual(bencode.bencode('abc'), b'3:abc')
+
+    def test_bdecode(self):
+        self.assertEqual(bencode.bdecode(b'3:dEf'), b'dEf')
+        with self.assertRaises(bencode.BTFailure):
+            bencode.bdecode('dEf')
+        with self.assertRaises(bencode.BTFailure):
+            bencode.bdecode(b'dEf')
+        with self.assertRaises(bencode.BTFailure):
+            bencode.bdecode({'dEf': 123})