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"
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 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"
)
- A
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Constants
ASSET_EXTENSIONS | = | { javascript: ".js", stylesheet: ".css" } |
ASSET_PUBLIC_DIRECTORIES | = | { audio: "/audios", font: "/fonts", image: "/images", javascript: "/javascripts", stylesheet: "/stylesheets", video: "/videos" } |
Maps asset types to public directory. |
||
URI_REGEXP | = | %r{^[-a-z]+://|^(?:cid|data):|^//}i |
Instance Public methods
asset_path(source, options = {}) Link
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.
With the asset pipeline
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"
Without the asset pipeline (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"
Options applying to all assets
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 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
asset_url(source, options = {}) Link
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
audio_path(source, options = {}) Link
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
audio_url(source, options = {}) Link
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
compute_asset_extname(source, options = {}) Link
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 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_asset_host(source = "", options = {}) Link
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 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
compute_asset_path(source, options = {}) Link
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.
font_path(source, options = {}) Link
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
font_url(source, options = {}) Link
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
image_path(source, options = {}) Link
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.
image_url(source, options = {}) Link
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
javascript_path(source, options = {}) Link
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
javascript_url(source, options = {}) Link
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
stylesheet_path(source, options = {}) Link
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
stylesheet_url(source, options = {}) Link
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
video_path(source, options = {}) Link
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
video_url(source, options = {}) Link
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