Append ftp transfer mode to url for proxy
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY_TRANSFER_MODE, long enabled);
Pass a long. If the value is set to 1 (one), it tells libcurl to set the transfer mode (binary or ASCII) for FTP transfers done via a HTTP proxy, by appending ;type=a or ;type=i to the URL. Without this setting, or it being set to 0 (zero, the default), CURLOPT_TRANSFERTEXT(3) has no effect when doing FTP via a proxy. Beware that not all proxies support this feature.
FTP over proxy
Added in 7.18.0
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if the enabled value is not supported.