Paperclip is a wonderful module by Thoughtbot that lets makes handling attachments in Rails a breeze, except for one minor niggle - file types. It relies on the content type header sent by the browser which is woefully inconsistent. For example, when uploading a zip the possible values sent for content type are:
- '
application/octet-stream' - '
application/x-zip-compressed' - '
application/zip' - '' (yes empty)
In short you can't rely on Content-Type from the browser to ever have a sensible value.
Thus the purpose of this module: it uses the wonderful
libmagic to work out the file type based
on the contents of the uploaded file without shelling out to file to do its
work.
The ruby-filemagic gem (which this gem uses) depends upon libmagic must be
installed to give us file type detection. On Linux this means installing the
relevant package:
sudo apt-get install libmagic-dev # Deb
sudo yum install file-devel # rpm
sudo emerge file # gentoo
OSX ships with the file binary but not the libmagic shared library so I
recommend installing it via homebrew:
brew install libmagic
# Since this will be in a non-standard place we need to build ruby-filemagic specially
gem install ruby-filemagic -- --with-opt-dir=$(brew list libmagic | head -n1 | xargs dirname)
Include the gem in your Gemfile:
gem 'magic-paperclip'
Its all automatic - magic-paperclip does its trick by just being in the Gemfile (via a Railtie).
When a Paperclip attachment is assigned to its content_type will be detected and will overwrite what the browser sends.
libmagic often returns charset info or similar for files (i.e. text/plain; charset=us-asci) that this module attempts to remove to use just the base
type. Supposedly older versions of libmagic might return this in a
different format and thus not get removed. If you find an example of this
happening please let me know.
This gem was developed for use at DigiResults and pulled out into a reusable gem.
Released under the MIT License
Copyright (c) 2011, Ash Berlin and DigiResults Ltd.