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in depth revision of AssetTagHelper rdoc

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This commit is contained in:
Xavier Noria
2009-01-18 14:30:03 +01:00
parent dad45fa21b
commit 01337e06dd
1 changed files with 62 additions and 44 deletions
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106
actionpack/lib/action_view/helpers/asset_tag_helper.rb
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@@ -6,13 +6,19 @@ module ActionView
module Helpers #:nodoc:
# This module provides methods for generating HTML that links views to assets such
# as images, javascripts, stylesheets, and feeds. These methods do not verify
# the assets exist before linking to them.
# the assets exist before linking to them:
#
# image_tag("rails.png")
# # => <img alt="Rails src="/images/rails.png?1230601161" />
# stylesheet_link_tag("application")
# # => <link href="/stylesheets/application.css?1232285206" media="screen" rel="stylesheet" type="text/css" />
#
# === Using asset hosts
#
# By default, Rails links to these assets on the current host in the public
# folder, but you can direct Rails to link to assets from a dedicated asset server by
# setting ActionController::Base.asset_host in your <tt>config/environment.rb</tt>.
# folder, but you can direct Rails to link to assets from a dedicated asset
# server by setting ActionController::Base.asset_host in the application
# configuration, typically in <tt>config/environments/production.rb</tt>.
# For example, you'd define <tt>assets.example.com</tt> to be your asset
# host this way:
#
@@ -21,45 +27,49 @@ module ActionView
# Helpers take that into account:
#
# image_tag("rails.png")
# => <img src="http://assets.example.com/images/rails.png" alt="Rails" />
# # => <img alt="Rails" src="http://assets.example.com/images/rails.png?1230601161" />
# stylesheet_link_tag("application")
# => <link href="http://assets.example.com/stylesheets/application.css" media="screen" rel="stylesheet" type="text/css" />
# # => <link href="http://assets.example.com/stylesheets/application.css?1232285206" media="screen" rel="stylesheet" type="text/css" />
#
# Browsers typically open at most two simultaneous connections to a single host,
# which means your assets often have to wait for other assets to finish downloading.
# You can alleviate this by using a <tt>%d</tt> wildcard in <tt>asset_host</tt>
# (for example, "assets%d.example.com") to automatically distribute asset requests
# among four hosts (e.g., "assets0.example.com" through "assets3.example.com") so
# browsers will open eight simultaneous connections rather than two.
# Browsers typically open at most two simultaneous connections to a single
# host, which means your assets often have to wait for other assets to finish
# downloading. You can alleviate this by using a <tt>%d</tt> wildcard in the
# +asset_host+. For example, "assets%d.example.com". If that wildcard is
# present Rails distributes asset requests among the corresponding four hosts
# "assets0.example.com", ..., "assets3.example.com". With this trick browsers
# will open eight simultaneous connections rather than two.
#
# image_tag("rails.png")
# => <img src="http://assets0.example.com/images/rails.png" alt="Rails" />
# # => <img alt="Rails" src="http://assets0.example.com/images/rails.png?1230601161" />
# stylesheet_link_tag("application")
# => <link href="http://assets3.example.com/stylesheets/application.css" media="screen" rel="stylesheet" type="text/css" />
# # => <link href="http://assets2.example.com/stylesheets/application.css?1232285206" media="screen" rel="stylesheet" type="text/css" />
#
# To do this, you can either setup 4 actual hosts, or you can use wildcard DNS to CNAME
# the wildcard to a single asset host. You can read more about setting up your DNS CNAME records from
# your ISP.
# To do this, you can either setup four actual hosts, or you can use wildcard
# DNS to CNAME the wildcard to a single asset host. You can read more about
# setting up your DNS CNAME records from your ISP.
#
# Note: This is purely a browser performance optimization and is not meant
# for server load balancing. See http://www.die.net/musings/page_load_time/
# for background.
#
# Alternatively, you can exert more control over the asset host by setting <tt>asset_host</tt> to a proc
# that takes a single source argument. This is useful if you are unable to setup 4 actual hosts or have
# fewer/more than 4 hosts. The example proc below generates http://assets1.example.com and
# http://assets2.example.com randomly.
# Alternatively, you can exert more control over the asset host by setting
# +asset_host+ to a proc like this:
#
# ActionController::Base.asset_host = Proc.new { |source| "http://assets#{rand(2) + 1}.example.com" }
# ActionController::Base.asset_host = Proc.new { |source|
# "http://assets#{rand(2) + 1}.example.com"
# }
# image_tag("rails.png")
# => <img src="http://assets2.example.com/images/rails.png" alt="Rails" />
# # => <img alt="Rails" src="http://assets0.example.com/images/rails.png?1230601161" />
# stylesheet_link_tag("application")
# => <link href="http://assets1.example.com/stylesheets/application.css" media="screen" rel="stylesheet" type="text/css" />
# # => <link href="http://assets1.example.com/stylesheets/application.css?1232285206" media="screen" rel="stylesheet" type="text/css" />
#
# The proc takes a <tt>source</tt> parameter (which is the path of the source asset) and an optional
# <tt>request</tt> parameter (which is an entire instance of an <tt>ActionController::AbstractRequest</tt>
# subclass). This can be used to generate a particular asset host depending on the asset path and the particular
# request.
# The example above generates http://assets1.example.com and
# http://assets2.example.com randomly. This option is useful for example if
# you need fewer/more than four hosts, custom host names, etc.
#
# As you see the proc takes a +source+ parameter. That's a string with the
# absolute path of the asset with any extensions and timestamps in place,
# for example "/images/rails.png?1230601161".
#
# ActionController::Base.asset_host = Proc.new { |source|
# if source.starts_with?('/images')
@@ -69,14 +79,16 @@ module ActionView
# end
# }
# image_tag("rails.png")
# => <img src="http://images.example.com/images/rails.png" alt="Rails" />
# # => <img alt="Rails" src="http://images.example.com/images/rails.png?1230601161" />
# stylesheet_link_tag("application")
# => <link href="http://assets.example.com/stylesheets/application.css" media="screen" rel="stylesheet" type="text/css" />
# # => <link href="http://assets.example.com/stylesheets/application.css?1232285206" media="screen" rel="stylesheet" type="text/css" />
#
# The optional <tt>request</tt> parameter to the proc is useful in particular for serving assets from an
# SSL-protected page. The example proc below disables asset hosting for HTTPS connections, while still sending
# assets for plain HTTP requests from asset hosts. This is useful for avoiding mixed media warnings when serving
# non-HTTP assets from HTTPS web pages when you don't have an SSL certificate for each of the asset hosts.
# Alternatively you may ask for a second parameter +request+. That one is
# particularly useful for serving assets from an SSL-protected page. The
# example proc below disables asset hosting for HTTPS connections, while
# still sending assets for plain HTTP requests from asset hosts. If you don't
# have SSL certificates for each of the asset hosts this technique allows you
# to avoid warnings in the client about mixed media.
#
# ActionController::Base.asset_host = Proc.new { |source, request|
# if request.ssl?
@@ -86,7 +98,8 @@ module ActionView
# end
# }
#
# You can also implement a custom asset host object that responds to the call method and tasks one or two parameters just like the proc.
# You can also implement a custom asset host object that responds to +call+
# and takes either one or two parameters just like the proc.
#
# config.action_controller.asset_host = AssetHostingWithMinimumSsl.new(
# "http://asset%d.example.com", "https://asset1.example.com"
@@ -94,12 +107,15 @@ module ActionView
#
# === Using asset timestamps
#
# By default, Rails will append all asset paths with that asset's timestamp. 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).
# By default, Rails appends asset's timestamps to all 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:
# 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
@@ -107,11 +123,13 @@ module ActionView
# 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 drift out of sync, you'll see different timestamps at random and the cache won't
# work. Which means that 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 (and that the assets are not being
# requested over and over).
# 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.
module AssetTagHelper
ASSETS_DIR = defined?(Rails.public_path) ? Rails.public_path : "public"
JAVASCRIPTS_DIR = "#{ASSETS_DIR}/javascripts"