Add support for asset host

lib/propshaft/compilers/css_asset_urls.rb

@@ -1,12 +1,13 @@
 # frozen_string_literal: true
 
 class Propshaft::Compilers::CssAssetUrls
-  attr_reader :assembly
+  attr_reader :assembly, :url_prefix
 
   ASSET_URL_PATTERN = /url\(\s*["']?(?!(?:\#|%23|data|http|\/\/))([^"'\s?#)]+)([#?][^"')]+)?\s*["']?\)/
 
   def initialize(assembly)
-    @assembly = assembly
+    @assembly   = assembly
+    @url_prefix = File.join(assembly.config.host.to_s, assembly.config.prefix.to_s).chomp("/")
   end
 
   def compile(logical_path, input)
@@ -26,7 +27,7 @@ def resolve_path(directory, filename)
 
     def asset_url(resolved_path, logical_path, fingerprint, pattern)
       if asset = assembly.load_path.find(resolved_path)
-        %[url("#{assembly.config.prefix}/#{asset.digested_path}#{fingerprint}")]
+        %[url("#{url_prefix}/#{asset.digested_path}#{fingerprint}")]
       else
         Propshaft.logger.warn "Unable to resolve '#{pattern}' for missing asset '#{resolved_path}' in #{logical_path}"
         %[url("#{pattern}")]

lib/propshaft/railtie.rb

@@ -17,6 +17,7 @@ class Railtie < ::Rails::Railtie
     ]
     config.assets.sweep_cache = Rails.env.development?
     config.assets.server = Rails.env.development? || Rails.env.test?
+    config.assets.host = nil
 
     # Register propshaft initializer to copy the assets path in all the Rails Engines.
     # This makes possible for us to keep all `assets` config in this Railtie, but still
@@ -30,6 +31,7 @@ class Railtie < ::Rails::Railtie
     end
 
     config.after_initialize do |app|
+      config.assets.host = app.config.asset_host
       config.assets.output_path ||=
         Pathname.new(File.join(app.config.paths["public"].first, app.config.assets.prefix))
 

test/propshaft/compilers/css_asset_urls_test.rb

@@ -6,13 +6,11 @@
 
 class Propshaft::Compilers::CssAssetUrlsTest < ActiveSupport::TestCase
   setup do
-    @assembly = Propshaft::Assembly.new(ActiveSupport::OrderedOptions.new.tap { |config|
+    @options = ActiveSupport::OrderedOptions.new.tap { |config|
       config.paths = [ Pathname.new("#{__dir__}/../../fixtures/assets/vendor") ]
       config.output_path = Pathname.new("#{__dir__}/../../fixtures/output")
       config.prefix = "/assets"
-    })
-
-    @assembly.compilers.register "text/css", Propshaft::Compilers::CssAssetUrls
+    }
   end
 
   test "basic" do
@@ -120,14 +118,23 @@ class Propshaft::Compilers::CssAssetUrlsTest < ActiveSupport::TestCase
     assert_match(/{ background: url\("file-not-found.jpg"\); }/, compiled)
   end
 
+  test "host" do
+    @options.host = "https://example.com"
+
+    compiled = compile_asset_with_content(%({ background: url(file.jpg); }))
+    assert_match(/{ background: url\("https:\/\/example.com\/assets\/foobar\/source\/file-[a-z0-9]{40}.jpg"\); }/, compiled)
+  end
+
   private
     def compile_asset_with_content(content)
       root_path    = Pathname.new("#{__dir__}/../../fixtures/assets/vendor")
       logical_path = "foobar/source/test.css"
 
       asset     = Propshaft::Asset.new(root_path.join(logical_path), logical_path: logical_path)
       asset.stub :content, content do
-        @assembly.compilers.compile(asset)
+        assembly = Propshaft::Assembly.new(@options)
+        assembly.compilers.register "text/css", Propshaft::Compilers::CssAssetUrls
+        assembly.compilers.compile(asset)
       end
     end
 end