File size and mime-type before upload

I've scavenged on every single topic on th开发者_运维技巧is forum to try and find an answer before I posted this. Most people say you should simply use SWFUpload, some others mention Activex, and it keeps going.

I know this is do-able, as Google does it with gMail when you try to upload a file that's bigger than 25mb, or executable.

My question is, how can I determine the file size and mime-type before the file actually hits my server.

I primarily thought it was an impossible task, but Google proves me wrong.

Could anyone give me a definitive answer on how to accomplish such task?

Thanks

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Gmail do use a flash uploader, inspect the attach link in Firebug and you will see it uses uploader/uploaderapi2.swf. Disable the Flash add-in and it will behave differently.