MimeMagic is a library to detect the mime type of a file by extension or by content. It uses the mime database provided by freedesktop.org (see http://freedesktop.org/wiki/Software/shared-mime-info/).

require 'mimemagic'
MimeMagic.by_extension('html').text?
MimeMagic.by_extension('.html').child_of? 'text/plain'
MimeMagic.by_path('filename.txt')
MimeMagic.by_magic(File.open('test.html'))
# etc...

Microsoft Office 2007+ formats (xlsx, docx, and pptx) are not supported by the mime database at freedesktop.org. These files are all zipped collections of xml files and will be detected as "application/zip". Mimemagic comes with extra magic you can overlay on top of the defaults to correctly detect these file types. Enable it like this:

require 'mimemagic'
require 'mimemagic/overlay'
MimeMagic.by_magic(File.open('test.xlsx'))

You can add your own magic with MimeMagic.add. See lib/mimemagic/overlay.rb.

http://www.rubydoc.info/github/minad/mimemagic

bundle install

rake test

Daniel Mendler