RFC says (5.1):
>   To avoid confusing network intermediaries (such as
>   intercepting proxies) and for security reasons that are further
>  discussed in Section 10.3, a client MUST mask all frames that it
>   sends to the server (see Section 5.3 for further details).  (...)
>   The server MUST close the connection upon receiving a
>   frame that is not masked.

I can add a comment in the code (and remove the useless `*maskkey = 0;`).