// Returns a writer that delegates calls to Write(...) while ensuring
// that it is never called with less bytes than the specified amount.
//
// Calls with fewer bytes are buffered while a call with a nil slice
// causes the buffer to be flushed to the underlying writer.
func SizedWriter(writer io.Writer, size int) io.Writer {
	var sw sizedWriter
	sw.writer = writer
	var buffer []byte = make([]byte, 0, size)
	var write WriterFunc

	write = func(input []byte) (int, error) {
	sw.buffer = make([]byte, 0, size)
	sw.size = size
	return &sw
}

type sizedWriter struct {
	writer io.Writer
	buffer []byte
	size   int
}

func (sw *sizedWriter) Write(input []byte) (int, error) {
		var (
			count int
			err   error
		)

		// Flush the buffer when called with no bytes to write
		if input == nil {
			// Call the writer with whatever we have in store..
			count, err = writer.Write(buffer)
		count, err = sw.writer.Write(sw.buffer)

			// Advance the buffer
			buffer = buffer[:copy(buffer, buffer[count:])]
		sw.buffer = sw.buffer[:copy(sw.buffer, sw.buffer[count:])]

			return 0, err
		}

		// Delegate to the writer if the size is right
		if len(buffer) == 0 && len(input) >= size {
			reduced := (len(input) / size) * size
			count, err = writer.Write(input[:reduced])
	if len(sw.buffer) == 0 && len(input) >= sw.size {
		reduced := (len(input) / sw.size) * sw.size
		count, err = sw.writer.Write(input[:reduced])
			if count < reduced || err != nil {
				return count, err
			}

			// Stage any remaining data in the buffer
			buffer = append(buffer, input[count:]...)
		sw.buffer = append(sw.buffer, input[count:]...)
			return len(input), nil
		}

		// Append data to the buffer
		count = copy(buffer[len(buffer):size], input)
		buffer = buffer[:len(buffer)+count]
	count = copy(sw.buffer[len(sw.buffer):sw.size], input)
	sw.buffer = sw.buffer[:len(sw.buffer)+count]

		// Return if we don't have enough bytes to write
		if len(buffer) < size {
	if len(sw.buffer) < sw.size {
			return len(input), nil
		}

		// Flush the buffer as it is filled
		_, err = write(nil)
	_, err = sw.Write(nil)
		if err != nil {
			return count, err
		}

		// Handle the rest of the input
		return write(input[count:])
	return sw.Write(input[count:])
	}

	return write
}

type sizedReader struct {
	reader         io.Reader
	buffer         []byte
	from, to, size int
}

// Returns a reader that delegates calls to Read(...) while ensuring
// that the output buffer is never smaller than the required size
// and is downsized to a multiple of the required size if larger.
func SizedReader(reader io.Reader, size int) io.Reader {
	var sr sizedReader
	sr.reader = reader
	sr.buffer = make([]byte, size)
	sr.size, sr.from, sr.to = size, 0, 0
	return &sr
}

type sizedReader struct {
	reader         io.Reader
	buffer         []byte
	from, to, size int
}

func (sr *sizedReader) Read(output []byte) (int, error) {
	var (
		count int
		err   error
	)