Rails (3.2.7): override image_tag for asset_host

Question

development.rb:

config.action_controller.asset_host = "assets.myserver.com"

view script:

<%= image_tag('header.jpg') %>

yields:

<img alt="Header" src="/header.jpg" />

should be:

<img alt="Header" src="http://assets.myserver.com/header.jpg" />

I am using the rails-api gem which I am guessing disables some asset and view rendering stuff.

It seems like it should not be too hard to re-implement (override image_tag) to add this very small feature. It may seem a little odd to want to do this. However, I am new-ish to rails would like to know how to do this as a learning experience.

Questions:

1. As a best practice where should I place this new code in the file structure?
2. What should I name the file with the new code?
3. How does rails know to look at the new code instead of looking at the old image_tag function?

Answer 1

I've tried your configuration, but when I use config.action_controller.asset_host = "assets.myserver.com" in my development.rb image_tag works as expected:

<img alt="Header" src="http://assets.myserver.com/assets/header.jpg" />

I've tested it both under Rails 3.2.7 and 3.2.8, but it works in both versions.

UPDATE

In my original answer I didn't use the rails-api gem. When using the rails-api gem image_tag works as described in the question.

Well to answer the actual question, you could add an initializer in config/initializers. Just create a file, lets say image_tag_helper.rb, with the following code:

# config/initializers/image_tag_helper.rb
module ActionView
  module Helpers
    module AssetTagHelper
      def image_tag(source, options = {})
        options[:src] = "http://#{source}"
        tag("img", options)
      end
    end
  end
end

What this basically does is reopening the module and replace the image_tag method with your own method. All other methods within the module AssetTagHelper remain the same. Take a look at the Rails repository at github for a complete 'example' of the image_tag method.

The name of the file doesn't really matter. All files within config/initializers are loaded when the application is booted.

Basically this is a language feature of Ruby, Ruby allows you to reopen classes everywhere in your code and add or replace methods (you find more on this subject at rubylearning.com).