How to check the content of an uploaded file without relying on its extension?

Question

How do you go about verifying the type of an uploaded file reliably without using the extension? I\'m guessing that you have to examine the header / read some of the bytes,

Answer 1

Reading the contents of the file is the fool proof way. Since you are building it in .Net, you could probably check the MIME Type of the uploaded file.

You can DllImport urlmon.dll to help. Please refer a post at: http://coding-passion.blogspot.com/2008/11/validating-file-type.html

And to clarify regarding Content-type, it invariably is driven by the extension of the file. So even a .zip file got its extension renamed to .txt, the content type will still say Text only.