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require 'thread'
require 'active_support/core_ext/file'
require 'active_support/core_ext/module/attribute_accessors'
module ActionView
# = Action View Asset Cache ID Helpers
#
# Rails appends asset's timestamps to public asset paths. This allows
# you to set a cache-expiration date for the asset far into the future, but
# still be able to instantly invalidate it by simply updating the file (and
# hence updating the timestamp, which then updates the URL as the timestamp
# is part of that, which in turn busts the cache).
#
# It's the responsibility of the web server you use to set the far-future
# expiration date on cache assets that you need to take advantage of this
# feature. Here's an example for Apache:
#
# # Asset Expiration
# ExpiresActive On
# <FilesMatch "\.(ico|gif|jpe?g|png|js|css)$">
# ExpiresDefault "access plus 1 year"
# </FilesMatch>
#
# Also note that in order for this to work, all your application servers must
# return the same timestamps. This means that they must have their clocks
# synchronized. If one of them drifts out of sync, you'll see different
# timestamps at random and the cache won't work. In that case the browser
# will request the same assets over and over again even thought they didn't
# change. You can use something like Live HTTP Headers for Firefox to verify
# that the cache is indeed working.
#
# This strategy works well enough for most server setups and requires the
# least configuration, but if you deploy several application servers at
# different times - say to handle a temporary spike in load - then the
# asset time stamps will be out of sync. In a setup like this you may want
# to set the way that asset paths are generated yourself.
#
# Altering the asset paths that Rails generates can be done in two ways.
# The easiest is to define the RAILS_ASSET_ID environment variable. The
# contents of this variable will always be used in preference to
# calculated timestamps. A more complex but flexible way is to set
# <tt>ActionController::Base.config.asset_path</tt> to a proc
# that takes the unmodified asset path and returns the path needed for
# your asset caching to work. Typically you'd do something like this in
# <tt>config/environments/production.rb</tt>:
#
# # Normally you'd calculate RELEASE_NUMBER at startup.
# RELEASE_NUMBER = 12345
# config.action_controller.asset_path = proc { |asset_path|
# "/release-#{RELEASE_NUMBER}#{asset_path}"
# }
#
# This example would cause the following behavior on all servers no
# matter when they were deployed:
#
# image_tag("rails.png")
# # => <img alt="Rails" src="/release-12345/images/rails.png" />
# stylesheet_link_tag("application")
# # => <link href="/release-12345/stylesheets/application.css?1232285206" media="screen" rel="stylesheet" />
#
# Changing the asset_path does require that your web servers have
# knowledge of the asset template paths that you rewrite to so it's not
# suitable for out-of-the-box use. To use the example given above you
# could use something like this in your Apache VirtualHost configuration:
#
# <LocationMatch "^/release-\d+/(images|javascripts|stylesheets)/.*$">
# # Some browsers still send conditional-GET requests if there's a
# # Last-Modified header or an ETag header even if they haven't
# # reached the expiry date sent in the Expires header.
# Header unset Last-Modified
# Header unset ETag
# FileETag None
#
# # Assets requested using a cache-busting filename should be served
# # only once and then cached for a really long time. The HTTP/1.1
# # spec frowns on hugely-long expiration times though and suggests
# # that assets which never expire be served with an expiration date
# # 1 year from access.
# ExpiresActive On
# ExpiresDefault "access plus 1 year"
# </LocationMatch>
#
# # We use cached-busting location names with the far-future expires
# # headers to ensure that if a file does change it can force a new
# # request. The actual asset filenames are still the same though so we
# # need to rewrite the location from the cache-busting location to the
# # real asset location so that we can serve it.
# RewriteEngine On
# RewriteRule ^/release-\d+/(images|javascripts|stylesheets)/(.*)$ /$1/$2 [L]
#
module Helpers #:nodoc:
module AssetIdHelper
# You can enable or disable the asset tag ids cache.
# With the cache enabled, the asset tag helper methods will make fewer
# expensive file system calls (the default implementation checks the file
# system timestamp). However this prevents you from modifying any asset
# files while the server is running.
#
# ActionView::Helpers::AssetIdHelper.cache_asset_ids = false
mattr_accessor :cache_asset_ids
# Add or change an asset id in the asset id cache. This can be used
# for SASS on Heroku.
# :api: public
def add_to_asset_ids_cache(source, asset_id)
self.asset_ids_cache_guard.synchronize do
self.asset_ids_cache[source] = asset_id
end
end
mattr_accessor :asset_ids_cache
self.asset_ids_cache = {}
mattr_accessor :asset_ids_cache_guard
self.asset_ids_cache_guard = Mutex.new
# Use the RAILS_ASSET_ID environment variable or the source's
# modification time as its cache-busting asset id.
def rails_asset_id(source)
if asset_id = ENV["RAILS_ASSET_ID"]
asset_id
else
if self.cache_asset_ids && (asset_id = self.asset_ids_cache[source])
asset_id
else
path = File.join(config.assets_dir, source)
asset_id = File.exist?(path) ? File.mtime(path).to_i.to_s : ''
if self.cache_asset_ids
add_to_asset_ids_cache(source, asset_id)
end
asset_id
end
end
end
# Override +compute_asset_path+ to add asset id query strings to
# generated urls. See +compute_asset_path+ in AssetUrlHelper.
def compute_asset_path(source, options = {})
source = super(source, options)
path = config.asset_path
if path && path.respond_to?(:call)
path.call(source)
elsif path && path.is_a?(String)
path % [source]
elsif asset_id = rails_asset_id(source)
asset_id.empty? ? source : "#{source}?#{asset_id}"
end
end
end
end
end
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