This module provides methods for generating asset paths and URLs.
image_path("rails.png")
# => "/assets/rails.png"
image_url("rails.png")
# => "http://www.example.com/assets/rails.png"
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 the application configuration, typically in config/environments/production.rb. For example, you'd define assets.example.com to be your asset host this way, inside the configure block of your environment-specific configuration files or config/application.rb:
config.action_controller.asset_host = "assets.example.com"
Helpers take that into account:
image_tag("rails.png")
# => <img src="http://assets.example.com/assets/rails.png" />
stylesheet_link_tag("application")
# => <link href="http://assets.example.com/assets/application.css" rel="stylesheet" />
Browsers open a limited number of simultaneous connections to a single host. The exact number varies by browser and version. This limit may cause some asset downloads to wait for previous assets to finish before they can begin. You can use the %d wildcard in the asset_host to distribute the requests over four hosts. For example, assets%d.example.com will spread the asset requests over “assets0.example.com”, …, “assets3.example.com”.
image_tag("rails.png")
# => <img src="http://assets0.example.com/assets/rails.png" />
stylesheet_link_tag("application")
# => <link href="http://assets2.example.com/assets/application.css" rel="stylesheet" />
This may improve the asset loading performance of your application. It is also possible the combination of additional connection overhead (DNS, SSL) and the overall browser connection limits may result in this solution being slower. You should be sure to measure your actual performance across targeted browsers both before and after this change.
To implement the corresponding hosts you can either set up four actual hosts or 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 www.die.net/musings/page_load_time/ for background and www.browserscope.org/?category=network for connection limit data.
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#{OpenSSL::Digest::SHA256.hexdigest(source).to_i(16) % 2 + 1}.example.com"
}
image_tag("rails.png")
# => <img src="http://assets1.example.com/assets/rails.png" />
stylesheet_link_tag("application")
# => <link href="http://assets2.example.com/assets/application.css" rel="stylesheet" />
The example above generates “assets1.example.com” and “assets2.example.com”. 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, for example “/assets/rails.png”.
ActionController::Base.asset_host = Proc.new { |source|
if source.end_with?('.css')
"http://stylesheets.example.com"
else
"http://assets.example.com"
end
}
image_tag("rails.png")
# => <img src="http://assets.example.com/assets/rails.png" />
stylesheet_link_tag("application")
# => <link href="http://stylesheets.example.com/assets/application.css" rel="stylesheet" />
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. Note that the request parameter might not be supplied, e.g. when the assets are precompiled with the command bin/rails assets:precompile. Make sure to use a Proc instead of a lambda, since a Proc allows missing parameters and sets them to nil.
config.action_controller.asset_host = Proc.new { |source, request|
if request && request.ssl?
"#{request.protocol}#{request.host_with_port}"
else
"#{request.protocol}assets.example.com"
end
}
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" )
Maps asset types to public directory.
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 186
def asset_path(source, options = {})
raise ArgumentError, "nil is not a valid asset source" if source.nil?
source = source.to_s
return "" if source.blank?
return source if URI_REGEXP.match?(source)
tail, source = source[/([?#].+)$/], source.sub(/([?#].+)$/, "")
if extname = compute_asset_extname(source, options)
source = "#{source}#{extname}"
end
if source[0] != ?/
if options[:skip_pipeline]
source = public_compute_asset_path(source, options)
else
source = compute_asset_path(source, options)
end
end
relative_url_root = defined?(config.relative_url_root) && config.relative_url_root
if relative_url_root
source = File.join(relative_url_root, source) unless source.start_with?("#{relative_url_root}/")
end
if host = compute_asset_host(source, options)
source = File.join(host, source)
end
"#{source}#{tail}"
end This is the entry point for all assets. When using an asset pipeline gem (e.g. propshaft or sprockets-rails), the behavior is “enhanced”. You can bypass the asset pipeline by passing in skip_pipeline: true to the options.
All other asset *_path helpers delegate through this method.
All options passed to asset_path will be passed to compute_asset_path which is implemented by asset pipeline gems.
asset_path("application.js") # => "/assets/application-60aa4fdc5cea14baf5400fba1abf4f2a46a5166bad4772b1effe341570f07de9.js"
asset_path('application.js', host: 'example.com') # => "//example.com/assets/application.js"
asset_path("application.js", host: 'example.com', protocol: 'https') # => "https://example.com/assets/application.js"
skip_pipeline: true)Accepts a type option that can specify the asset's extension. No error checking is done to verify the source passed into asset_path is valid and that the file exists on disk.
asset_path("application.js", skip_pipeline: true) # => "application.js"
asset_path("filedoesnotexist.png", skip_pipeline: true) # => "filedoesnotexist.png"
asset_path("application", type: :javascript, skip_pipeline: true) # => "/javascripts/application.js"
asset_path("application", type: :stylesheet, skip_pipeline: true) # => "/stylesheets/application.css"
Below lists scenarios that apply to asset_path whether or not you're using the asset pipeline.
All fully qualified URLs are returned immediately. This bypasses the asset pipeline and all other behavior described.
asset_path("http://www.example.com/js/xmlhr.js") # => "http://www.example.com/js/xmlhr.js"
All assets that begin with a forward slash are assumed to be full URLs and will not be expanded. This will bypass the asset pipeline.
asset_path("/foo.png") # => "/foo.png"
All blank strings will be returned immediately. This bypasses the asset pipeline and all other behavior described.
asset_path("") # => ""
If config.relative_url_root is specified, all assets will have that root prepended.
Rails.application.config.relative_url_root = "bar"
asset_path("foo.js", skip_pipeline: true) # => "bar/foo.js"
A different asset host can be specified via config.action_controller.asset_host this is commonly used in conjunction with a CDN.
Rails.application.config.action_controller.asset_host = "assets.example.com"
asset_path("foo.js", skip_pipeline: true) # => "http://assets.example.com/foo.js"
An extension name can be specified manually with extname.
asset_path("foo", skip_pipeline: true, extname: ".js") # => "/foo.js"
asset_path("foo.css", skip_pipeline: true, extname: ".js") # => "/foo.css.js"
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 230
def asset_url(source, options = {})
path_to_asset(source, options.merge(protocol: :request))
end Computes the full URL to an asset in the public directory. This will use asset_path internally, so most of their behaviors will be the same. If :host options is set, it overwrites global config.action_controller.asset_host setting.
All other options provided are forwarded to asset_path call.
asset_url "application.js" # => http://example.com/assets/application.js asset_url "application.js", host: "http://cdn.example.com" # => http://cdn.example.com/assets/application.js
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 429
def audio_path(source, options = {})
path_to_asset(source, { type: :audio }.merge!(options))
end Computes the path to an audio asset in the public audios directory. Full paths from the document root will be passed through. Used internally by audio_tag to build the audio path.
audio_path("horse") # => /audios/horse
audio_path("horse.wav") # => /audios/horse.wav
audio_path("sounds/horse.wav") # => /audios/sounds/horse.wav
audio_path("/sounds/horse.wav") # => /sounds/horse.wav
audio_path("http://www.example.com/sounds/horse.wav") # => http://www.example.com/sounds/horse.wav
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 441
def audio_url(source, options = {})
url_to_asset(source, { type: :audio }.merge!(options))
end Computes the full URL to an audio asset in the public audios directory. This will use audio_path internally, so most of their behaviors will be the same. Since audio_url is based on asset_url method you can set :host options. If :host options is set, it overwrites global config.action_controller.asset_host setting.
audio_url "horse.wav", host: "http://stage.example.com" # => http://stage.example.com/audios/horse.wav
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 242
def compute_asset_extname(source, options = {})
return if options[:extname] == false
extname = options[:extname] || ASSET_EXTENSIONS[options[:type]]
if extname && File.extname(source) != extname
extname
else
nil
end
end Compute extname to append to asset path. Returns nil if nothing should be added.
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 276
def compute_asset_host(source = "", options = {})
request = self.request if respond_to?(:request)
host = options[:host]
host ||= config.asset_host if defined? config.asset_host
if host
if host.respond_to?(:call)
arity = host.respond_to?(:arity) ? host.arity : host.method(:call).arity
args = [source]
args << request if request && (arity > 1 || arity < 0)
host = host.call(*args)
elsif host.include?("%d")
host = host % (Zlib.crc32(source) % 4)
end
end
host ||= request.base_url if request && options[:protocol] == :request
return unless host
if URI_REGEXP.match?(host)
host
else
protocol = options[:protocol] || config.default_asset_host_protocol || (request ? :request : :relative)
case protocol
when :relative
"//#{host}"
when :request
"#{request.protocol}#{host}"
else
"#{protocol}://#{host}"
end
end
end Pick an asset host for this source. Returns nil if no host is set, the host if no wildcard is set, the host interpolated with the numbers 0-3 if it contains %d (the number is the source hash mod 4), or the value returned from invoking call on an object responding to call (proc or otherwise).
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 265
def compute_asset_path(source, options = {})
dir = ASSET_PUBLIC_DIRECTORIES[options[:type]] || ""
File.join(dir, source)
end Computes asset path to public directory. Plugins and extensions can override this method to point to custom assets or generate digested paths or query strings.
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 454
def font_path(source, options = {})
path_to_asset(source, { type: :font }.merge!(options))
end Computes the path to a font asset. Full paths from the document root will be passed through.
font_path("font") # => /fonts/font
font_path("font.ttf") # => /fonts/font.ttf
font_path("dir/font.ttf") # => /fonts/dir/font.ttf
font_path("/dir/font.ttf") # => /dir/font.ttf
font_path("http://www.example.com/dir/font.ttf") # => http://www.example.com/dir/font.ttf
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 466
def font_url(source, options = {})
url_to_asset(source, { type: :font }.merge!(options))
end Computes the full URL to a font asset. This will use font_path internally, so most of their behaviors will be the same. Since font_url is based on asset_url method you can set :host options. If :host options is set, it overwrites global config.action_controller.asset_host setting.
font_url "font.ttf", host: "http://stage.example.com" # => http://stage.example.com/fonts/font.ttf
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 377
def image_path(source, options = {})
path_to_asset(source, { type: :image }.merge!(options))
end Computes the path to an image asset. Full paths from the document root will be passed through. Used internally by image_tag to build the image path:
image_path("edit") # => "/assets/edit"
image_path("edit.png") # => "/assets/edit.png"
image_path("icons/edit.png") # => "/assets/icons/edit.png"
image_path("/icons/edit.png") # => "/icons/edit.png"
image_path("http://www.example.com/img/edit.png") # => "http://www.example.com/img/edit.png"
If you have images as application resources this method may conflict with their named routes. The alias path_to_image is provided to avoid that. Rails uses the alias internally, and plugin authors are encouraged to do so.
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 389
def image_url(source, options = {})
url_to_asset(source, { type: :image }.merge!(options))
end Computes the full URL to an image asset. This will use image_path internally, so most of their behaviors will be the same. Since image_url is based on asset_url method you can set :host options. If :host options is set, it overwrites global config.action_controller.asset_host setting.
image_url "edit.png", host: "http://stage.example.com" # => http://stage.example.com/assets/edit.png
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 320
def javascript_path(source, options = {})
path_to_asset(source, { type: :javascript }.merge!(options))
end Computes the path to a JavaScript asset in the public javascripts directory. If the source filename has no extension, .js will be appended (except for explicit URIs) Full paths from the document root will be passed through. Used internally by javascript_include_tag to build the script path.
javascript_path "xmlhr" # => /assets/xmlhr.js javascript_path "dir/xmlhr.js" # => /assets/dir/xmlhr.js javascript_path "/dir/xmlhr" # => /dir/xmlhr.js javascript_path "http://www.example.com/js/xmlhr" # => http://www.example.com/js/xmlhr javascript_path "http://www.example.com/js/xmlhr.js" # => http://www.example.com/js/xmlhr.js
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 332
def javascript_url(source, options = {})
url_to_asset(source, { type: :javascript }.merge!(options))
end Computes the full URL to a JavaScript asset in the public javascripts directory. This will use javascript_path internally, so most of their behaviors will be the same. Since javascript_url is based on asset_url method you can set :host options. If :host options is set, it overwrites global config.action_controller.asset_host setting.
javascript_url "js/xmlhr.js", host: "http://stage.example.com" # => http://stage.example.com/assets/js/xmlhr.js
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 347
def stylesheet_path(source, options = {})
path_to_asset(source, { type: :stylesheet }.merge!(options))
end Computes the path to a stylesheet asset in the public stylesheets directory. If the source filename has no extension, .css will be appended (except for explicit URIs). Full paths from the document root will be passed through. Used internally by stylesheet_link_tag to build the stylesheet path.
stylesheet_path "style" # => /assets/style.css stylesheet_path "dir/style.css" # => /assets/dir/style.css stylesheet_path "/dir/style.css" # => /dir/style.css stylesheet_path "http://www.example.com/css/style" # => http://www.example.com/css/style stylesheet_path "http://www.example.com/css/style.css" # => http://www.example.com/css/style.css
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 359
def stylesheet_url(source, options = {})
url_to_asset(source, { type: :stylesheet }.merge!(options))
end Computes the full URL to a stylesheet asset in the public stylesheets directory. This will use stylesheet_path internally, so most of their behaviors will be the same. Since stylesheet_url is based on asset_url method you can set :host options. If :host options is set, it overwrites global config.action_controller.asset_host setting.
stylesheet_url "css/style.css", host: "http://stage.example.com" # => http://stage.example.com/assets/css/style.css
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 403
def video_path(source, options = {})
path_to_asset(source, { type: :video }.merge!(options))
end Computes the path to a video asset in the public videos directory. Full paths from the document root will be passed through. Used internally by video_tag to build the video path.
video_path("hd") # => /videos/hd
video_path("hd.avi") # => /videos/hd.avi
video_path("trailers/hd.avi") # => /videos/trailers/hd.avi
video_path("/trailers/hd.avi") # => /trailers/hd.avi
video_path("http://www.example.com/vid/hd.avi") # => http://www.example.com/vid/hd.avi
# File actionview/lib/action_view/helpers/asset_url_helper.rb, line 415
def video_url(source, options = {})
url_to_asset(source, { type: :video }.merge!(options))
end Computes the full URL to a video asset in the public videos directory. This will use video_path internally, so most of their behaviors will be the same. Since video_url is based on asset_url method you can set :host options. If :host options is set, it overwrites global config.action_controller.asset_host setting.
video_url "hd.avi", host: "http://stage.example.com" # => http://stage.example.com/videos/hd.avi
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Licensed under the MIT License.