Add service-worker-allowed header by default

README.md

@@ -29,14 +29,17 @@ If you need to put multiple files that refer to each other through Propshaft, li
 
 ## Improving performance in development
 
-Before every request Propshaft checks if any asset was updated to decide if a cache sweep is needed. This verification is done using the application's configured file watcher which, by default, is `ActiveSupport::FileUpdateChecker`. 
+Before every request Propshaft checks if any asset was updated to decide if a cache sweep is needed. This verification is done using the application's configured file watcher which, by default, is `ActiveSupport::FileUpdateChecker`.
 
 If you have a lot of assets in your project, you can improve performance by adding the `listen` gem to the development group in your Gemfile, and this line to the `development.rb` environment file:
 
 ```ruby
 config.file_watcher = ActiveSupport::EventedFileUpdateChecker
 ```
 
+## Service-Worker-Allowed Header
+
+A **"Service-Worker-Allowed"** header can be added through the `Rails.configuration.assets.service_worker_scope` variable in your environment configuration file.
 
 ## Migrating from Sprockets
 

lib/propshaft/server.rb

@@ -10,18 +10,17 @@ 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!("Service-Worker-Allowed" => Rails.configuration.assets.service_worker_scope) if Rails.configuration.assets.service_worker_scope
+
+      [ 200, headers, [ compiled_content ] ]
     else
       [ 404, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "9" }, [ "Not found" ] ]
     end

test/propshaft/server_test.rb

@@ -16,17 +16,30 @@ class Propshaft::ServerTest < ActiveSupport::TestCase
   end
 
   test "serve a compiled file" do
+    Rails.configuration.assets.stub :service_worker_scope, "/" do
+      asset = @assembly.load_path.find("foobar/source/test.css")
+      get "/#{asset.digested_path}"
+
+      assert_equal 200, last_response.status
+      assert_equal "94", 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=31536000, immutable", last_response.headers['cache-control']
+      assert_equal ".hero { background: url(\"/foobar/source/file-3e6a129785ee3caf8eff23db339997e85334bfa9.jpg\") }\n",
+                  last_response.body
+    end
+  end
+
+  test "serve a compiled file without service-worker-allowed" do
     asset = @assembly.load_path.find("foobar/source/test.css")
     get "/#{asset.digested_path}"
 
     assert_equal 200, last_response.status
-    assert_equal "94", 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 "public, max-age=31536000, immutable", last_response.headers['cache-control']
+    assert_nil last_response.headers['service-worker-allowed']
     assert_equal ".hero { background: url(\"/foobar/source/file-3e6a129785ee3caf8eff23db339997e85334bfa9.jpg\") }\n",
-                 last_response.body
+                last_response.body
   end
 
   test "serve a predigested file" do