Get a file type from the contents and NOT from extension

Question

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How can you read a files MIME-type in objective-c

In Cocoa, I am trying to get file type, I.E. JPG, JPEG, or PNG, using

LSCopyKindStringForURL((CFURLRef)URL, (CFStringRef *)&kind);

This helps only when the file extension is valid. However, if I rename a PNG file extension to JPEG, it returns JPEG, because LSCopyKindStringForURL returns file type from extension.

Is there any other method that will return me the exact type from the underlying contents of the file?

score 1 · Answer 1 · answered Jan 12 '11 at 19:25

There is MagicKit.framework, which is a wrapper around libmagic. (This is what the file command uses). In my tests, its determining of UTIs could maybe use a bit of work, but it's probably a good start.

The majority of Launch Services APIs and the like don't look internally at the file's data, AFAIK. That said, the frameworks that would actually deal with such data (in this case of image data, ImageIO.framework, NSImage, etc.), can usually cope with such discrepancies. (For example, change a PNG file extension to .gif, and Preview.app will still gladly open it.)

I found the solution. You need to get metadata of the file using Core Graphics framework. — user598789, Jan 12 '11 at 19:38

score 1 · Answer 2 · edited Jan 15 '11 at 06:37

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CGImageSourceRef source = CGImageSourceCreateWithURL( (CFURLRef) URL, NULL);
NSDictionary* metadata = (NSDictionary *)CGImageSourceCopyPropertiesAtIndex(source,0,NULL);

edited Jan 15 '11 at 06:37

Peter Hosey

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answered Jan 12 '11 at 19:39

user598789

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Don't forget to release these objects. – Peter Hosey Jan 14 '11 at 09:11

Get a file type from the contents and NOT from extension

2 Answers2