Add charset=utf-8 to Content-Type for CSS and HTML assets

flavorjones · flavorjones · commit c5cbc653396a · 2026-04-10T09:25:49.000-04:00
CSS and HTML assets served by Propshaft::Server now include
"; charset=utf-8" in their Content-Type response header. This fixes
browser encoding issues where non-ASCII characters in CSS files (e.g.,
en-dash in content properties) render as mojibake when Chrome falls back
to Windows-1252 encoding.
diff --git a/lib/propshaft/server.rb b/lib/propshaft/server.rb
@@ -19,11 +19,16 @@ def call(env)
       if (asset = @assembly.load_path.find(path)) && asset.fresh?(digest)
         compiled_content = asset.compiled_content
 
+        content_type = asset.content_type.to_s
+        if DEFAULT_UTF8_CONTENT_TYPES.include?(content_type)
+          content_type = "#{content_type}; charset=utf-8"
+        end
+
         [
           200,
           {
             Rack::CONTENT_LENGTH  => compiled_content.length.to_s,
-            Rack::CONTENT_TYPE    => asset.content_type.to_s,
+            Rack::CONTENT_TYPE    => content_type,
             VARY                  => "Accept-Encoding",
             Rack::ETAG            => "\"#{asset.digest}\"",
             Rack::CACHE_CONTROL   => "public, max-age=31536000, immutable"
@@ -43,6 +48,12 @@ def inspect
   end
 
   private
+    DEFAULT_UTF8_CONTENT_TYPES = [
+      Rack::Mime::MIME_TYPES[".css"],
+      Rack::Mime::MIME_TYPES[".html"],
+    ]
+    private_constant :DEFAULT_UTF8_CONTENT_TYPES
+
     def extract_path_and_digest(path)
       path = path.delete_prefix(@assembly.prefix)
       path = Rack::Utils.unescape(path)
diff --git a/test/fixtures/assets/first_path/test.html b/test/fixtures/assets/first_path/test.html
@@ -0,0 +1 @@
+<html><body>hello</body></html>
diff --git a/test/propshaft/server_test.rb b/test/propshaft/server_test.rb
@@ -47,7 +47,7 @@ def call(env)
 
     assert_equal 200, last_response.status
     assert_equal last_response.body.bytesize.to_s, last_response.headers['content-length']
-    assert_equal "text/css", last_response.headers['content-type']
+    assert_equal "text/css; charset=utf-8", 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']
@@ -67,6 +67,22 @@ def call(env)
     assert_equal 200, last_response.status
   end
 
+  test "serve an HTML file with charset" do
+    asset = @assembly.load_path.find("test.html")
+    get "/assets/#{asset.digested_path}"
+
+    assert_equal 200, last_response.status
+    assert_equal "text/html; charset=utf-8", last_response.headers['content-type']
+  end
+
+  test "serve a JS file without charset" do
+    asset = @assembly.load_path.find("again.js")
+    get "/assets/#{asset.digested_path}"
+
+    assert_equal 200, last_response.status
+    assert_equal "text/javascript", last_response.headers['content-type']
+  end
+
   test "not found" do
     get "/assets/not-found.js"
 
