return newErrorMessage([]byte(errorCode), []byte(errorMessage))
}

type messageWriter struct {
	writer          http.ResponseWriter
	getProgressFunc func() (int64, int64)
	bytesReturned   int64

	payloadBuffer      []byte
	payloadBufferIndex int
	payloadCh          chan *bytes.Buffer

	finBytesScanned, finBytesProcessed int64

	errCh  chan []byte
	doneCh chan struct{}
}