growByteSlice will return a byte slice with a capacity at least equal to the specified size.

growByteSlice.go

// growByteSlice will return a byte slice with a capacity at least equal to the
// specified size.
func growByteSlice(buf []byte, need int) []byte {
	// Optimization for when buffer might be required to grow by more than
	// double its size.
	if need > cap(buf)<<1 {
		t := make([]byte, need)
		copy(t, buf)
		return t
	}
	for cap(buf) < need {
		buf = append(buf[:cap(buf)], 0)
	}
	return buf[:cap(buf)]
}