def METHOD_NAME(self, final=False):
    """Internal function to add a chunk of data to a started upload"""
    self.buffer.seek(0)
    data = self.buffer.getvalue()
    data_chunks = [
        data[start:end] for start, end in self._to_sized_blocks(end=len(data))
    ]
    for data_chunk in data_chunks:
        self.fs._add_data(handle=self.handle, data=data_chunk)
    if final:
        self.fs._close_handle(handle=self.handle)
        return True