growbuf.go

package none

import "io"

func min(a int, b int) int {
	if a < b {
		return a
	}
	return b
}

func max(a int, b int) int {
	if a > b {
		return a
	}
	return b
}

type growbuf struct {
	Min int
	Max int

	// keep a ref to the buffer instead of its len to support replacing the
	// buffer with a new one in a single statement, which gives the compiler
	// an opportunity to optimize the call if it can.
	buf []byte
}

func boundedScale(baseline, lower, upper, coefficient int) int {
	x := max(lower, baseline*coefficient)
	return min(upper, x)
}

// Buffer returns a new zero-initialized buffer with a length between g.Min and
// g.Max. Each successive call returns a new buffer that is twice the length
// of the last one returned, up to g.Max. Once g.Max is reached, the next call
// will return an io.ErrShortBuffer error.
func (g *growbuf) Buffer() ([]byte, error) {
	if len(g.buf) >= g.Max {
		return nil, io.ErrShortBuffer
	}

	ln := boundedScale(len(g.buf), g.Min, g.Max, 2)
	g.buf = make([]byte, ln)
	return g.buf, nil
}