Cory O'Daniel – These are just words Software development, thoughts, and randomness

Attaching local or remote files to Paperclip and Milton Models in Rails (Mocking content_type and original_filename in a Tempfile)

I was working on a project today where I needed to import some data from MySpace accounts (yeah, MySpace), which included importing the users profile image. In the controller that did the importing I was using OpenURI to retrieve the image and then turn it into a Tempfile to be attached the the model, like so:

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def import
#...snip
  tempfile = Tempfile.new( my_filename)
  tempfile.write open( image_url ).read
  @imported_user.images.create(:file => tempfile)
#...snip
end

This doesn't work. It blows up missing one of two methods:

1. #original_filename
2. #content_type

If you inspect a normal file upload in Rails which has these methods, you'll find that is just a regular old Tempfile. But it has the methods! If you create a Tempfile manually, it won't have the methods. That's because Rails magics them on. I am not sure why they don't create a subclass like Rails::Tempfile that contains these methods and just use that. I guess its because OOP is retarded (sarcasm).

So, I wrote a little subclass that will take a file path, and quack like the magic'd rails Tempfiles you get from an upload so you can attach local files to models or even remote files.

This works pretty straightforward and I'm currently using it in production. It won't work on windows systems because the dependency on the 'file' binary. Also, some linux systems are missing this library by default, so make sure you yum|dpkg|apt|port or whatever to get it installed.

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require 'open-uri'
require 'digest/sha1'
 
class RemoteFile < ::Tempfile
 
  def initialize(path, tmpdir = Dir::tmpdir)
    @original_filename  = File.basename(path)
    @remote_path        = path
 
    super Digest::SHA1.hexdigest(path), tmpdir
    fetch
  end
 
  def fetch
    string_io = OpenURI.send(:open, @remote_path)
    self.write string_io.read
    self.rewind
    self
  end
 
  def original_filename
    @original_filename
  end
 
  def content_type
    mime = `file --mime -br #{self.path}`.strip
    mime = mime.gsub(/^.*: */,"")
    mime = mime.gsub(/;.*$/,"")
    mime = mime.gsub(/,.*$/,"")
    mime
  end
end

Usage is pretty simple:

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remote_file = RemoteFile.new("http://www.google.com/intl/en_ALL/images/logo.gif")
remote_file.original_filename #=> logo.gif
remote_file.content_type #= image/gif

Using it in your controller:

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def import
  #...snip
  @imported_user.images.create(:file => RemoteFile.new( url_to_image ))
  #...snip
end