code: def buffered_write(self, buf):
          
          if self.closed:
              raise ConnectionClosed()
  
          if len(buf) + len(self.write_buffer) > self.max_size:
              raise BufferOverflowError()
          else:
              self.write_buffer.extend(buf)
docs: Appends a bytes like object to the transport write buffer.
  
          Raises BufferOverflowError if buf would cause the buffer to grow beyond
          the specified maximum.
  
          buf -- bytes to send