code: def write_header(self, chunk):
          
  
          if self.serializer:
              header = self.serializer.serialize_header(chunk)
          else:
              header = chunk
  
          if self.flushed:
              raise TChannelError("write operation invalid after flush call")
  
          if (self.argstreams[0].state != StreamState.completed and
                  self.argstreams[0].auto_close):
              self.argstreams[0].close()
  
          return self.argstreams[1].write(header)
docs: Write to header.
  
          Note: the header stream is only available to write before write body.
  
          :param chunk: content to write to header
  
          :except TChannelError:
              Raise TChannelError if the response's flush() has been called