How do i verify a file format?

Question

Basically this question except i am using ASP.NET. How do i take a given file and check if it is

• image (all formats except bitmap including photoshop)
• archive (7z, rar, zip, etc). NOTE: I know a file can be both an image and zip. I can check if its both in code.
• sound (most such as m4a, flac, ogg, but not wav)
• model (3ds, X, B3D, etc)

The solution does not need to check all of these but if i can get a few to check all of these then great.

Answer 1

Given the variety of your file types, checking the extension may be the best option. Anyone has other thoughts?

Answer 2

You can try to either:

• Find documentation for the file format and check for known bytes in the file header, etc
• Attempt to load the file using an API - if the file loads successfully then you know it is of the proper type.

For example, here is an example of how to verify an image file: validate-image-from-file-in-c#

Of course, the mime type and/or file extension can give you a good guess of what file format you are dealing with, but (depending on the source) you should not rely on it exclusively.