libwebsockets增加自定义头内容

解答：

LWS_CALLBACK_CLIENT_APPEND_HANDSHAKE_HEADER        = 24,
    /**< this callback happens
     * when a client handshake is being compiled.  user is NULL,
     * in is a char **, it's pointing to a char * which holds the
     * next location in the header buffer where you can add
     * headers, and len is the remaining space in the header buffer,
     * which is typically some hundreds of bytes.  So, to add a canned
     * cookie, your handler code might look similar to:
     *
     *    char **p = (char **)in, *end = (*p) + len;
     *
     *    if (lws_add_http_header_by_token(wsi, WSI_TOKEN_HTTP_COOKIE,
     *            (unsigned char)"a=b", 3, p, end))
     *        return -1;
     *
     * See LWS_CALLBACK_ADD_HEADERS for adding headers to server
     * transactions.
     */

How can I add an customer header to wssclient