I'm writing piece of code detecting file extensions and I was getting quite a lot of garbage like . Jones - Some Document Title just because file name was starting with Dr. Jones. So I decided to put some additional filters like isalnum(c) to filter out only strings that contain alphanum characters but I'm still getting names like .65aab294d987659953343e8da131b2091c0c81c8 because some filenames happen to end with sha1 checksum.
So what are the longest extension names used in actual applications? I know DOS used to have 3 characters extension names but it's long gone since a lot of modern applications actually use 4 letters extensions namely jpeg, .mpeg, .webm, docx and so on so I'm rather asking about real world experience. Has anyone ever seen real extension longer than lets say 16 characters?