Allow sending empty messages

This is perfectly valid in the protocol, and may be meningful to some
applications. However send() is still stream oriented so it will ignore
an empty buffer.

websockify/websocket.py

@@ -421,6 +421,9 @@ class WebSocket(object):
         WebSocketWantWriteError can be raised if there is insufficient
         space in the underlying socket.
         """
+        if len(bytes) == 0:
+            return 0
+
         return self.sendmsg(bytes)
 
     def sendmsg(self, msg):
@@ -435,8 +438,7 @@ class WebSocket(object):
         """
         if not self._sent_close:
             # Only called to flush?
-            if msg:
-                self._sendmsg(0x2, msg)
+            self._sendmsg(0x2, msg)
 
         self._flush()
         return len(msg)