Rails 3.2 asset_host setting ignored - ruby-on-rails

Question

My production environment -
# Code is not reloaded between requests
config.cache_classes = true
config.assets.enabled = true
# Full error reports are disabled and caching is turned on
config.consider_all_requests_local = false
config.action_controller.perform_caching = true
# Disable Rails's static asset server (Apache or nginx will already do this)
config.serve_static_assets = true
config.static_cache_control = "public, max-age=31536000"
# Compress JavaScripts and CSS
config.assets.compress = true
config.assets.js_compressor = :uglifier
#config.assets.css_compressor = :yui
# Don't fallback to assets pipeline if a precompiled asset is missed
config.assets.compile = true
# Generate digests for assets URLs
config.assets.digest = true
# See everything in the log (default is :info)
config.log_level = :warn
config.log_tags = [:remote_ip, lambda { |req| Time.now }]
# Enable serving of images, stylesheets, and JavaScripts from an asset server
ActionController::Base.asset_host = Proc.new { |source|
unless source.starts_with?('/stylesheets' || '/javascripts')
"//dddd.cloudfront.net/"
end
}
However, when I using image_tag it still returns me '/assets..' relative url and not absolute url to the asset host.
irb(main):034:0> helper.image_tag('noimage.gif')
=> "<img alt=\"Noimage\" src=\"/assets/noimage.gif\" />"
irb(main):035:0> helper.image_path('noimage.gif')
I can not seem to figure what might be missing. I even tried doing simple config.asset_host setting, and still it does not recognize the setting.

Answer 1

Have you tried setting the designated config?
config.action_controller.asset_host = 'https://abcd.cloudfront.net'
Not sure it works with protocol relative urls. I simply use https in my apps.
It might also be worth noting that action mailer has a similar setting:
config.action_mailer.asset_host = 'https://abcd.cloudfront.net'

Answer 2

There's something odd in Rails configuration. According to the documentation asset_host is supposed to hold just the host part ('yoursite.com'). I resolved with an helper:
module EmailsHelper
def email_image_tag(src)
protocol = ActionMailer::Base.default_url_options[:protocol] || 'http'
image_tag asset_path(src, protocol: protocol)
end
end
Configure it in your mailer:
class EmailNotificationsMailer < ActionMailer::Base
add_template_helper(EmailsHelper)
...
end
There's no way to force image_tag to use a URL other than to pass a URL to it.