def set_alpn_select_callback(self, callback):
        """
        Specify a callback function that will be called on the server when a
        client offers protocols using ALPN.

        :param callback: The callback function.  It will be invoked with two
            arguments: the Connection, and a list of offered protocols as
            bytestrings, e.g ``[b'http/1.1', b'spdy/2']``.  It should return
            one of those bytestrings, the chosen protocol.
        """
        self._alpn_select_helper = _ALPNSelectHelper(callback)
        self._alpn_select_callback = self._alpn_select_helper.callback
        _lib.SSL_CTX_set_alpn_select_cb(
            self._context, self._alpn_select_callback, _ffi.NULL)
Specify a callback function that will be called on the server when a
        client offers protocols using ALPN.

        :param callback: The callback function.  It will be invoked with two
            arguments: the Connection, and a list of offered protocols as
            bytestrings, e.g ``[b'http/1.1', b'spdy/2']``.  It should return
            one of those bytestrings, the chosen protocol.