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 I can hide the indicator.
I’m making the request in 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, in the hope 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, then shows the “Save” dialog for the downloadable file. But it fails on IE and Safari; IE fires the “load” event but 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 make a call to start the file creation, then poll the server until it’s ready, then download the already-created file. But I’d rather avoid creating temporary files on the server.
Does anyone have a better idea?