rbuf.go
func (b *FixedSizeRingBuf) WriteTo(w io.Writer) (n int64, err error) {

	if b.Readable == 0 {
		return 0, io.EOF
	}

	extent := b.Beg + b.Readable
	firstWriteLen := intMin(extent, b.N) - b.Beg
	secondWriteLen := b.Readable - firstWriteLen
	if firstWriteLen > 0 {
		m, e := w.Write(b.A[b.Use][b.Beg:(b.Beg + firstWriteLen)])
		n += int64(m)
		b.Advance(m)

		if e != nil {
			return n, e
		}
		// all bytes should have been written, by definition of
		// Write method in io.Writer
		if m != firstWriteLen {
			return n, io.ErrShortWrite
		}
	}
	if secondWriteLen > 0 {
		m, e := w.Write(b.A[b.Use][0:secondWriteLen])
		n += int64(m)
		b.Advance(m)

		if e != nil {
			return n, e
		}
		// all bytes should have been written, by definition of
		// Write method in io.Writer
		if m != secondWriteLen {
			return n, io.ErrShortWrite
		}
	}

	return n, nil
}
func (b *FixedSizeRingBuf) WriteTo(w io.Writer) (n int64, err error) {

	if b.Readable == 0 {
		return 0, io.EOF
	}

	extent := b.Beg + b.Readable
	firstWriteLen := intMin(extent, b.N) - b.Beg
	secondWriteLen := b.Readable - firstWriteLen
	if firstWriteLen > 0 {
		m, e := w.Write(b.A[b.Use][b.Beg:(b.Beg + firstWriteLen)])
		n += int64(m)
		b.Advance(m)

		if e != nil {
			return n, e
		}
		// all bytes should have been written, by definition of
		// Write method in io.Writer
		if m != firstWriteLen {
			return n, io.ErrShortWrite
		}
	}
	if secondWriteLen > 0 {
		m, e := w.Write(b.A[b.Use][0:secondWriteLen])
		n += int64(m)
		b.Advance(m)

		if e != nil {
			return n, e
		}
		// all bytes should have been written, by definition of
		// Write method in io.Writer
		if m != secondWriteLen {
			return n, io.ErrShortWrite
		}
	}

	return n, nil
}
// WriteTo and ReadFrom avoid intermediate allocation and copies.
// WriteTo avoids intermediate allocation and copies.
// WriteTo writes data to w until there's no more data to write
// or when an error occurs. The return value n is the number of
// bytes written. Any error encountered during the write is also returned.