Add service-worker-allowed header by default

README.md

@@ -37,6 +37,13 @@ If you have a lot of assets in your project, you can improve performance by addi
 config.file_watcher = ActiveSupport::EventedFileUpdateChecker
 ```
 
+## Custom Headers
+
+Customs headers can be added through the `Rails.configuration.assets.headers` variable in your environment configuration file. Your headers will be merged with default headers, overriding existing headers.
+
+```ruby
+Rails.configuration.assets.headers = {"service-worker-allowed" => "/", "cache-control" => "public, max-age=604800, immutable"}
+```
 
 ## Migrating from Sprockets
 

lib/propshaft/server.rb

@@ -11,18 +11,17 @@ def call(env)
 
     if (asset = @assembly.load_path.find(path)) && asset.fresh?(digest)
       compiled_content = @assembly.compilers.compile(asset)
+      headers = {
+        Rack::CONTENT_LENGTH  => compiled_content.length.to_s,
+        Rack::CONTENT_TYPE    => asset.content_type.to_s,
+        VARY                  => "Accept-Encoding",
+        Rack::ETAG            => asset.digest,
+        Rack::CACHE_CONTROL   => "public, max-age=31536000, immutable"
+      }
 
-      [
-        200,
-        {
-          Rack::CONTENT_LENGTH  => compiled_content.length.to_s,
-          Rack::CONTENT_TYPE    => asset.content_type.to_s,
-          VARY                  => "Accept-Encoding",
-          Rack::ETAG            => asset.digest,
-          Rack::CACHE_CONTROL   => "public, max-age=31536000, immutable"
-        },
-        [ compiled_content ]
-      ]
+      headers.merge!(Rails.configuration.assets.headers) if Rails.configuration.assets.headers
+
+      [ 200, headers, [ compiled_content ] ]
     else
       [ 404, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "9" }, [ "Not found" ] ]
     end

test/propshaft/server_test.rb

@@ -29,6 +29,23 @@ class Propshaft::ServerTest < ActiveSupport::TestCase
                  last_response.body
   end
 
+  test "serve a compiled file with custom headers" do
+    Rails.configuration.assets.stub :headers, {"service-worker-allowed" => "/", "cache-control" => "public, max-age=604800, immutable"} do
+      asset = @assembly.load_path.find("foobar/source/test.css")
+      get "/#{asset.digested_path}"
+
+      assert_equal 200, last_response.status
+      assert_equal "62", last_response.headers['content-length']
+      assert_equal "text/css", last_response.headers['content-type']
+      assert_equal "Accept-Encoding", last_response.headers['vary']
+      assert_equal asset.digest, last_response.headers['etag']
+      assert_equal "/", last_response.headers['service-worker-allowed']
+      assert_equal "public, max-age=604800, immutable", last_response.headers['cache-control']
+      assert_equal ".hero { background: url(\"/foobar/source/file-3e6a1297.jpg\") }\n",
+                   last_response.body
+    end
+  end
+
   test "serve a predigested file" do
     asset = @assembly.load_path.find("file-already-abcdefVWXYZ0123456789_-.digested.css")
     get "/#{asset.digested_path}"