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From Karl Goldstein <>
Subject Adding a status callback to FileUpload
Date Mon, 29 Mar 2004 19:45:53 GMT

I plan to try to add a status callback to the FileUpload package.  Here 
is the scenario I would like to support (I'm making this up as I go, but 
something like this):

1) User uploads a large file (form target is an invisible IFRAME so that 
the browser does not leave the form page on submit).
2) The onsubmit handler for the file upload form uses setTimeout to call 
a "checkStatus" function (in Javascript) in a few seconds.
3) The checkStatus function makes a request in an invisible IFRAME to 
the server.
4) The server responds with with a message on the status of the file upload.
5) Upon receiving a reply from the server, an onload handler in the 
IFRAME updates a visible status message on the form.
6) When the upload is complete, the onload handler displays a success 
message and moves the user to the next page (or displays an error).

To support this scenario, I plan to try and add the following to FileUpload:

1) As FileUpload processes an incoming request, it updates a session 
attribute associated with the request.  I'm assuming in most cases it 
should be possible to provide a percentage complete status, since the 
total size is available in the header even before the upload is complete.
2) A status page returned to the invisible IFRAME can check this session 
attribute and inform the client what FileUpload is doing at the moment.

Anybody thought of doing something similar?  Any thoughts on why this 
wouldn't work?  Thanks for any feedback, and unless I hear otherwise 
I'll take a shot and let you know if/when I come up with something.


Karl Goldstein

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