Rails: image_tag helper / umlaut in file name throws error in production

I am uploading an image with a file name containing an umlaut via dragonfly in a Rails 3 app on Heroku. Then I'm trying to display the image using

image_tag @model.image.url, …

In development everything works just fine, but in production I'm getting:

incompatible character encodings: UTF-8 and ASCII-8BIT
.bundle/gems/ruby/1.9.1/gems/actionpack-3.0.7/lib/action_view/helpers/tag_helper.rb:129:in `*'

After reading a bit I've added

E开发者_开发技巧ncoding.default_external = Encoding::UTF_8
Encoding.default_internal = Encoding::UTF_8

in environment.rb but the problem remains.

What is the proper way to go about this? Do I have to fix the file name when uploading? I was under the impression this should work just fine in Rails 3?

---

Well, you could try something like url.force_encoding('utf8')

You could also simply sanitize the url in the model before saving it to the database - that's what I did. And, yes, I sometimes stumble over this in the weirdest places, too.

This is what my model looked like:

# encoding: UTF-8
class Page < ActiveRecord::Base
  before_save :sanitize_title

  private
  def sanitize_title
    self.title = self.title.force_encoding('UTF-8').downcase.gsub(/[ \-äöüß]/, ' ' => '_', '-' => '_', 'ä' => 'ae', 'ö' => 'oe', 'ü' => 'ue', 'ß' => 'ss').gsub(/[^a-z_]/,'')
  end
end

This will replace the German umlaute with their ASCII counterparts, convert spaces to underscores and drop everything else. The first line # encoding: UTF-8 is important or ruby will complain of non-ASCII characters in the model.rb file...

---

In addition to @Rhywden's answer, here my solution specific for Dragonfly:

image_accessor :image do :after_assign
  after_assign{|i| i.name = sanitize_filename(image.name) }
end

def sanitize_filename(filename)
  filename.strip.tap do |name|
    name.sub! /\A.*(\\|\/)/, ''
    name.gsub! /[^\w\.\-]/, '_'
  end
end

Details here http://markevans.github.com/dragonfly/file.Models.html and here http://guides.rubyonrails.org/security.html#file-uploads .