Ring buffer

ring.go

type ring struct {
	data []byte
	size int
	pos  int
	len  int
}

func newRing(size int) *ring {
	return &ring{
		size: size,
		data: make([]byte, size),
	}
}

func (r *ring) append(b ...byte) {
	var start int
	if len(b) > r.size {
		// get bytes that could be stored
		// from the end of b
		start = len(b) - r.size
	}

	var end int
	if len(b) < r.size-r.pos {
		end = len(b)
	} else {
		end = r.size - r.pos
	}

	rc := copy(r.data[r.pos:], b[start:end])
	lc := copy(r.data[:r.pos], b[start+end:])

	r.pos = (r.pos + rc + lc) % r.size
	if r.len+rc+lc > r.size {
		r.len = r.size
	} else {
		r.len += rc + lc
	}
}