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 = @env['RAW_POST_DATA']
    raw_post.force_encoding(Encoding::BINARY)
    StringIO.new(raw_post)
  else
    @env['rack.input']
  end
end