Encode Content-Disposition filenames

Users downloading non-ASCII attachments would see garbled characters. When used with object storage, AWS S3 would return an InvalidArgument error: Header value cannot be represented using ISO-8859-1.

Per RFC 5987 and RFC 6266, Content-Disposition should be encoded properly. This commit takes the Rails 6 implementation of ActiveSuppport::Http::ContentDisposition (https://github.com/rails/rails/pull/33829) and ports it here.

However, due to gitlab-workhorse#207 (closed), the UTF-8 encoded Content-Disposition doesn't actually get sent to the user. This MR at least fixes AWS S3 access.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/47673

app/controllers/concerns/send_file_upload.rb

@@ -14,7 +14,8 @@ def send_upload(file_upload, send_params: {}, redirect_params: {}, attachment: n
       # content-type of text/javascript, which will trigger Rails'
       # cross-origin JavaScript protection.
       send_params[:content_type] = 'text/plain' if File.extname(attachment) == '.js'
-      send_params.merge!(filename: attachment, disposition: response_disposition)
+
+      send_params.merge!(filename: attachment, disposition: utf8_encoded_disposition(disposition, attachment))
     end
 
     if file_upload.file_storage?
@@ -27,6 +28,18 @@ def send_upload(file_upload, send_params: {}, redirect_params: {}, attachment: n
     end
   end
 
+  # Since Rails 5 doesn't properly support support non-ASCII filenames,
+  # we have to add our own to ensure RFC 5987 compliance. However, Rails
+  # 5 automatically appends `filename#{filename}` here:
+  # https://github.com/rails/rails/blob/v5.0.7/actionpack/lib/action_controller/metal/data_streaming.rb#L137
+  # Rails 6 will have https://github.com/rails/rails/pull/33829, so we
+  # can get rid of this special case handling when we upgrade.
+  def utf8_encoded_disposition(disposition, filename)
+    content = ::Gitlab::ContentDisposition.new(disposition: disposition, filename: filename)
+
+    "#{disposition}; #{content.utf8_filename}"
+  end
+
   def guess_content_type(filename)
     types = MIME::Types.type_for(filename)