class ActionDispatch::Request

def body

variable is already set, wrap it in a StringIO.
The request body is an IO input stream. If the RAW_POST_DATA environment 
def body
  if raw_post = get_header("RAW_POST_DATA")
    raw_post = (+raw_post).force_encoding(Encoding::BINARY)
    StringIO.new(raw_post)
  else
    body_stream
  end
end