Return a 400 Bad Request when path encoding is invalid

CHANGELOG.md

@@ -4,6 +4,8 @@ Get upgrade notes from Sprockets 3.x to 4.x at https://github.com/rails/sprocket
 
 ## Master
 
+- Return a `400 Bad Request` when the path encoding is invalid. [#514]
+
 ## 4.0.0.beta5
 
 - Reduce string allocations

lib/sprockets/server.rb

@@ -37,6 +37,10 @@ def call(env)
       # Extract the path from everything after the leading slash
       path = Rack::Utils.unescape(env['PATH_INFO'].to_s.sub(/^\//, ''))
 
+      unless path.valid_encoding?
+        return bad_request_response(env)
+      end
+
       # Strip fingerprint
       if fingerprint = path_fingerprint(path)
         path = path.sub("-#{fingerprint}", '')
@@ -131,6 +135,15 @@ def not_modified_response(env, etag)
         [ 304, cache_headers(env, etag), [] ]
       end
 
+      # Returns a 400 Forbidden response tuple
+      def bad_request_response(env)
+        if head_request?(env)
+          [ 400, { "Content-Type" => "text/plain", "Content-Length" => "0" }, [] ]
+        else
+          [ 400, { "Content-Type" => "text/plain", "Content-Length" => "11" }, [ "Bad Request" ] ]
+        end
+      end
+
       # Returns a 403 Forbidden response tuple
       def forbidden_response(env)
         if head_request?(env)

test/test_server.rb

@@ -333,4 +333,9 @@ def app
     delete "/assets/foo.js"
     assert_equal 405, last_response.status
   end
+
+  test "invalid URLs" do
+    get "/assets/%E2%EF%BF%BD%A6.js"
+    assert_equal 400, last_response.status
+  end
 end