fragmenting_writer.go
func newFragmentingWriter(logger Logger, sender fragmentSender, checksum Checksum) *fragmentingWriter {
	return &fragmentingWriter{
		logger:   logger,
		sender:   sender,
		checksum: checksum,
		state:    fragmentingWriteStart,
	}
}
func newFragmentingWriter(logger Logger, sender fragmentSender, checksum Checksum) *fragmentingWriter {
	return &fragmentingWriter{
		logger:   logger,
		sender:   sender,
		checksum: checksum,
		state:    fragmentingWriteStart,
	}
}
// newFragmentingWriter creates a new fragmenting writer