Add custom HTTP headers configuration for assets

README.md

@@ -37,6 +37,15 @@ If you have a lot of assets in your project, you can improve performance by addi
 config.file_watcher = ActiveSupport::EventedFileUpdateChecker
 ```
 
+## Customizing the HTTP headers for assets
+
+If you need to custom you response header not only for standard web requests but also for your assets, you can specify them in your environment file:
+
+```ruby
+config.propshaft_headers = { "your-custom-key" =>  "your-value" }
+```
+
+Since `content-length`, `content-type` and `etag` are computed values, you are not allowed to modified them. `vary` and `cache-control` have default values, respectively `"Accept-Encoding"` and `public, max-age=31536000, immutable`, that you can overwrite.
 
 ## Migrating from Sprockets
 

lib/propshaft/server.rb

@@ -10,16 +10,23 @@ def call(env)
 
     if (asset = @assembly.load_path.find(path)) && asset.fresh?(digest)
       compiled_content = @assembly.compilers.compile(asset)
+      computed_headers = {
+        "content-length"  => compiled_content.length.to_s,
+        "content-type"    => asset.content_type.to_s,
+        "etag"            => asset.digest
+      }
 
-      [ 
-        200, 
-        {
-          "content-length"  => compiled_content.length.to_s,
-          "content-type"    => asset.content_type.to_s,
-          "vary"            => "Accept-Encoding",
-          "etag"            => asset.digest,
-          "cache-control"   => "public, max-age=31536000, immutable"
-        },
+      headers = if Rails.configuration.respond_to?(:propshaft_headers)
+        Rails.configuration.propshaft_headers.transform_keys(&:downcase).merge(computed_headers)
+      else
+        computed_headers
+      end
+      headers["vary"] ||= "Accept-Encoding"
+      headers["cache-control"] ||= "public, max-age=31536000, immutable"
+
+      [
+        200,
+        headers,
         [ compiled_content ]
       ]
     else

test/propshaft/server_test.rb

@@ -29,6 +29,30 @@ class Propshaft::ServerTest < ActiveSupport::TestCase
                  last_response.body
   end
 
+  test "serve a compiled file with custom headers" do
+    Rails.configuration.propshaft_headers = { "custom-header" => "CustomHeaderValue"}
+    asset = @assembly.load_path.find("foobar/source/test.css")
+    get "/#{asset.digested_path}"
+
+    assert_equal 200, last_response.status
+    assert_equal "CustomHeaderValue", last_response.headers['custom-header']
+    assert_equal ".hero { background: url(\"/foobar/source/file-3e6a129785ee3caf8eff23db339997e85334bfa9.jpg\") }\n",
+                 last_response.body
+    Rails.configuration.propshaft_headers = {}
+  end
+
+  test "serve a compiled file with custom headers overriding default value" do
+    Rails.configuration.propshaft_headers = { "cache-control" => "public, max-age=2592000, immutable"}
+    asset = @assembly.load_path.find("foobar/source/test.css")
+    get "/#{asset.digested_path}"
+
+    assert_equal 200, last_response.status
+    assert_equal "public, max-age=2592000, immutable", last_response.headers['cache-control']
+    assert_equal ".hero { background: url(\"/foobar/source/file-3e6a129785ee3caf8eff23db339997e85334bfa9.jpg\") }\n",
+                 last_response.body
+    Rails.configuration.propshaft_headers = {}
+  end
+
   test "serve a predigested file" do
     asset = @assembly.load_path.find("file-already-abcdefVWXYZ0123456789.digested.css")
     get "/#{asset.digested_path}"