This method shouldn't set response_body, I saw it is "reverting" to nil in an ensure block but same could be accomplished as https://gist.github.com/spastorino/19079770e255adc97027.
Even more, shouldn't super already return a string instead of something that returns an object which responds to each?. In that case all the method is useless.

/cc @josevalim @strzalek