Merge pull request #48956 from skipkayhil/hm-rack-lint-show-exceptions-failsafe

Add test coverage for ShowExceptions failsafe

actionpack/lib/action_dispatch/middleware/show_exceptions.rb

@@ -54,7 +54,7 @@ module ActionDispatch
       rescue Exception => failsafe_error
         $stderr.puts "Error during failsafe response: #{failsafe_error}\n  #{failsafe_error.backtrace * "\n  "}"
 
-        [500, { "Content-Type" => "text/plain; charset=utf-8" },
+        [500, { Rack::CONTENT_TYPE => "text/plain; charset=utf-8" },
           ["500 Internal Server Error\n" \
           "If you are the administrator of this website, then please read this web " \
           "application's log file and/or the web server's log file to find out what " \

actionpack/test/dispatch/show_exceptions_test.rb

@@ -135,6 +135,18 @@ class ShowExceptionsTest < ActionDispatch::IntegrationTest
     assert_equal("{\"status\":400,\"error\":\"Bad Request\"}", body)
   end
 
+  test "failsafe prevents raising if exceptions_app raises" do
+    old_stderr, $stderr = $stderr, StringIO.new
+    @app = build_app(->(_) { raise })
+
+    get "/"
+
+    assert_response 500
+    assert_match(/500 Internal Server Error/, body)
+  ensure
+    $stderr = old_stderr
+  end
+
   private
     def build_app(exceptions_app = nil)
       exceptions_app ||= ActionDispatch::PublicExceptions.new("#{FIXTURE_LOAD_PATH}/public")