code: def body(self):
          
          for chunk in self.gen_chunks(self.envelope.file_open(self.name)):
              yield chunk
          for chunk in self.gen_chunks(self.data):
              yield chunk
          for chunk in self.gen_chunks(self.envelope.file_close()):
              yield chunk
          for chunk in self.close():
              yield chunk
docs: Yields the encoded body.