Golang parse IPv4 to bytes array without unnecessary allocation

ipv4_parse.go

package main

// parseIPv4 fast path clone of net.ParseIP that don't wrap IPv4 into IPv6 array
func parseIPv4(s string) []byte {
	var p [4]byte
	for i := 0; i < 4; i++ {
		octet, pos := dtoi(s)
		p[i] = octet
		if i < 3 {
			s = s[pos+1:]
		}
	}
	return p[:]
}

func dtoi(octetStr string) (n byte, pos int) {
	n = 0
	for pos = 0; pos < len(octetStr); pos++ {
		u := octetStr[pos]
		if u == '.' {
			break
		}
		n = n*10 + (u - '0')
	}
	return n, pos
}