文件是否正在下载到网站，即使它不应该被下载？

Question

I am sure this is the one of the most epic titles ever. So, I have upload form like here. I made that people could upload their files only up to 1 MB. But, if I try to upload for example 1 GB file, it takes ages before it gives me an error. So, here comes a question. Before checking file's size, does that file is being downloaded in my hosting or does it takes resources from my hosting? Why it takes ages and ages before it gives me an error although if I try to upload 2 MB file it gives me an error in 1 second? Thank you for your explanations.

Answer 1

If you're checking the file size on the server then, yes, it will have to upload to the server in order to just run the if statement that checks the size.

Anything you do on the client side to check will, of course, be at the mercy of the client. So there is no 100% reliable way to do it. Artefacto pointed out one good way to catch most users. There's also a JavaScript ActiveX object that might help (http://www.kavoir.com/2009/01/check-for-file-size-with-javascript-before-uploading.html) but, again, users can easily disable it (even quite unintentionally) or have browsers that don't support it at all.