Add support for TP-Link smartbulbs (#30)

* Add support for new-style protocol

Newer devices (including my LB130) seem to include the request length in
the previously empty message header, and ignore requests that lack it. They
also don't send an empty packet as the final part of a response, which can
lead to hangs. Add support for this, with luck not breaking existing devices
in the process.

* Fix tests

We now include the request length in the encrypted packet header, so strip
the header rather than assuming that it's just zeroes.

* Create a SmartDevice parent class

Add a generic SmartDevice class that SmartPlug can inherit from, in
preparation for adding support for other device types.

* Add support for TP-Link smartbulbs

These bulbs use the same protocol as the smart plugs, but have additional
commands for controlling bulb-specific features. In addition, the bulbs
have their emeter under a different target and return responses that
include the energy unit in the key names.

* Add tests for bulbs

Not entirely comprehensive, but has pretty much the same level of testing
as plugs

pyHS100/protocol.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 
 import json
 import socket
+import struct
 import logging
 
 _LOGGER = logging.getLogger(__name__)
@@ -49,10 +50,16 @@ class TPLinkSmartHomeProtocol:
             sock.send(TPLinkSmartHomeProtocol.encrypt(request))
 
             buffer = bytes()
+            # Some devices send responses with a length header of 0 and
+            # terminate with a zero size chunk. Others send the length and
+            # will hang if we attempt to read more data.
+            length = -1
             while True:
                 chunk = sock.recv(4096)
+                if length == -1:
+                    length = struct.unpack(">I", chunk[0:4])[0]
                 buffer += chunk
-                if not chunk:
+                if (length > 0 and len(buffer) >= length + 4) or not chunk:
                     break
 
         finally:
@@ -115,7 +122,7 @@ class TPLinkSmartHomeProtocol:
         :return: ciphertext request
         """
         key = TPLinkSmartHomeProtocol.INITIALIZATION_VECTOR
-        buffer = bytearray(4)  # 4 nullbytes
+        buffer = bytearray(struct.pack(">I", len(request)))
 
         for char in request:
             cipher = key ^ ord(char)