send_buffer = b'' * 18 + payload + b'' * 4
ptr = ctypes.cast (send_buffer, ctypes.c_void_p)
ptr.value += 18
lws.libwebsocket_write (wsi, ptr, len (payload), 0)

send_buf = ctypes.create_string_buffer(b'' * 18 + payload + b'' * 4)
lws.libwebsocket_write(wsi, ctypes.byref(send_buf, 18), len(payload), 0)

send_buf.value # null terminated
send_buf.raw   # complete array