When a user uploads a file, I generate a unique string for that file using hash_file(). I would like to be able to figure out what this string is without making my server do all the work. In other words, have the hash calculated client-side with JS (impossible, I think) or some other language (java?). I _could_ write a program in C++ to do it, but I don't particularly want to force my users to download a program just so they can upload files.
Any ideas where to start with this? Or, even better... an open source upload utility that has his ability built in?
Thanks.