Michal Marek introduced CURLOPT_PROXY_TRANSFER_MODE which is used to control

the appending of the "type=" thing on FTP URLs when they are passed to a
HTTP proxy. Some proxies just don't like that appending (which is done
unconditionally in 7.17.1), and some proxies treat binary/ascii transfers
better with the appending done!

lib/url.c

@@ -2036,6 +2036,23 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
      */
     data->set.new_directory_perms = va_arg(param, long);
     break;
+  case CURLOPT_PROXY_TRANSFER_MODE:
+    /*
+     * set transfer mode (;type=<a|i>) when doing FTP via an HTTP proxy
+     */
+    switch (va_arg(param, long)) {
+      case 0:
+        data->set.proxy_transfer_mode = FALSE;
+        break;
+      case 1:
+        data->set.proxy_transfer_mode = TRUE;
+        break;
+      default:
+        /* reserve other values for future use */
+        result = CURLE_FAILED_INIT;
+        break;
+    }
+    break;
 
   default:
     /* unknown tag and its companion, just ignore: */