I have a page that allows the user to download a dynamically-generated file. It takes a long time to generate, so I'd like to show a "waiting" indicator. The problem is, I can't figure out how to detect when the browser has received the file so that I can hide the indicator.
I'm requesting a hidden form, which POSTs to the server, and targets a hidden iframe for its results. This is, so I don't replace the entire browser window with the result. I listen for a "load" event on the iframe, hoping that it will fire when the download is complete.
I return a "Content-Disposition: attachment" header with the file, which causes the browser to show the "Save" dialog. But the browser doesn't fire a "load" event in the iframe.
One approach I tried is using a multi-part response. So it would send an empty HTML file, as well as the attached downloadable file.
For example:
Content-type: multipart/x-mixed-replace;boundary="abcde"
--abcde
Content-type: text/html
--abcde
Content-type: application/vnd.fdf
Content-Disposition: attachment; filename=foo.fdf
file-content
--abcde
This works in Firefox; it receives the empty HTML file, fires the "load" event, and then shows the "Save" dialog for the downloadable file. But it fails on Internet Explorer and Safari; Internet Explorer fires the "load" event, but it doesn't download the file, and Safari downloads the file (with the wrong name and content-type) and doesn't fire the "load" event.
A different approach might be to call to start the file creation, poll the server u