Get file size of an URL without download

Question

To get the file size of an URL without download, I wrote:

public static long getFileSizeWithoutDownload(String url) {
        ConnectionRequest cr = new GZConnectionRequest();
        cr.setUrl(url);
        cr.setPost(false);
        NetworkManager.getInstance().addProgressListener((NetworkEvent evt) -> {
            if (cr == evt.getConnectionRequest() && evt.getLength() > 0) {
                cr.kill();
            }
        });
        NetworkManager.getInstance().addToQueueAndWait(cr);
        return cr.getContentLength();
    }

It seems to work on Simulator, Android and iOS with a testing URL of my Spring Boot server.

Anyway, I consider this code as a workaround, as I couldn't find an API that directly gives me the file size without starting the download first. Starting the download and then killing it works, but maybe there may be a better way to get the same result. By the way, the condition && evt.getLength() > 0 may never be satisfied in some cases (depending on the headers received), so it would be better to read only the headers, in which "Content-Length" may be present or absent.

So, my question is if, with Codename One, there is a way to download only the response headers, without starting the download. Thank you.

Answer 1

Using the HTTP head request should give you the content length header that you can then use to get the size of the file without triggering a download. Your code might not follow through on the download but it does physically happen so a head request would be superior.

Unfortunately while there's a nice wrapper to head in Rest. This wrapper isn't very useful since there's no API to query response headers. That would make sense as an enhancement. You would need to derive ConnectionRequest and read the server response headers to get the content length.