CODEWITHSUNDEEP
c#.netasp.net-mvc-3file
freethinker
freethinker

Reputation: 2425

Detect incorrect file type

My application is allowed users to upload jpeg/png files.I must to detect files with changed extensions.For example: if somebody take example.txt file and change his name to example.jpg so it not enough to check this file by javascript, need server solution. How i can do this? Can somebody show code example? Thanks

Upvotes: 1

Views: 325

Answers (2)

Hakan Serce
Hakan Serce

Reputation: 11256

You can do this most of the time using magic bytes in the beginning of files. See this link for a list of these numbers for different file types: http://www.astro.keele.ac.uk/oldusers/rno/Computing/File_magic.html

For instance, JPEG files start with ff d8 ff e0, and png files start with 89 50 4e 47.

Upvotes: 5

Tigran
Tigran

Reputation: 62256

The file with not correct format, for your application (considering post) is an exceptional situation. So I would think about simple try/catch block where you try to load image of declared format. If exception ocures (say) => notify to a user, that the file seems to be in non correct format.

Upvotes: 3

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