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

def buffered_write(self, buf):
        """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

        """
        if self.closed:
            raise ConnectionClosed()

        if len(buf) + len(self.write_buffer) > self.max_size:
            raise BufferOverflowError()
        else:
            self.write_buffer.extend(buf)