Asset URLs without cache timestamps in Rails

Question

I'm using a transparent PNG with the Google IE fix library. This fix only works on images urls that end in "-trans.png".

Rails' timestamp-based caching is causing problems with this. When I use image_path() to generate the URL for the image, it appends the file's last-modified timestamp to the image's query string. Since the URL no longer ends in "-trans.png" (instead ending in "?" plus a long integer), Google's javascript fails to activate.

I don't want to disable asset caching entirely; just on certain images. I also don't want to hardcode a relative URL to the root of the server. I want to use Rails to generate the URL correctly if the site is deployed to the server root or an (unknown) subdirectory.

What options do I have?

Answer 1

# apologies I'm doing this off the cuff and haven't run-tested this code
alias_method_chain :image_path, :google_sense

def image_path_with_google_sense(source)
  raw_image_path = image_path_without_google_sense(source)
  if source.end_with?('-trans.png')
    # strip off the time stamp
    raw_image_path.split('?').first
  else
    raw_image_path
  end
end

Answer 2

I came up with a completely different way of solving this problem, using jQuery to replace the appropriate URLs:

jQuery(document).ready(function($) {
  $("img.logo").attr("src", "/images/logo-trans.png");
});

The benefit of this is that I can make the cache-stripping IE-only using IE's conditional HTML comments.

Answer 3

The easiest solution is probably just add a special case when the asset tag is appended to the file name to make it work correctly, for example:

   def rewrite_asset_path(source)
      asset_id = rails_asset_id(source)
      if asset_id.blank?
        source
      elsif source.end_with?("-trans.png")
        "#{source[0..-11]}.#{asset_id}-trans.png"
      else
        source + "?#{asset_id}"
      end
    end

This way any of the images will have their paths rewritten to have the cache-buster inline. This still works as you would expect it to.