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randomip.go
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randomip.go
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package randomip
import (
"math/rand"
"net"
"github.com/pkg/errors"
iputil "github.com/projectdiscovery/utils/ip"
)
const (
maxIterations = 255
)
func GetRandomIPWithCidr(cidrs ...string) (net.IP, error) {
if len(cidrs) == 0 {
return nil, errors.Errorf("must specify at least one cidr")
}
cidr := cidrs[rand.Intn(len(cidrs))]
if !iputil.IsCIDR(cidr) {
return nil, errors.Errorf("%s is not a valid cidr", cidr)
}
baseIp, ipnet, err := net.ParseCIDR(cidr)
if err != nil {
return nil, err
}
switch {
case 255 == ipnet.Mask[len(ipnet.Mask)-1]:
return baseIp, nil
case iputil.IsIPv4(baseIp.String()):
return getRandomIP(ipnet, 4), nil
case iputil.IsIPv6(baseIp.String()):
return getRandomIP(ipnet, 16), nil
default:
return nil, errors.New("invalid base ip")
}
}
func getRandomIP(ipnet *net.IPNet, size int) net.IP {
ip := ipnet.IP
var iteration int
for iteration < maxIterations {
iteration++
ones, _ := ipnet.Mask.Size()
quotient := ones / 8
remainder := ones % 8
var r []byte
switch size {
case 4, 16:
r = make([]byte, size)
default:
return ip
}
rand.Read(r)
for i := 0; i <= quotient; i++ {
if i == quotient {
shifted := byte(r[i]) >> remainder
r[i] = ipnet.IP[i] + (^ipnet.IP[i] & shifted)
} else {
r[i] = ipnet.IP[i]
}
}
ip = r
if !ip.Equal(ipnet.IP) {
break
}
}
return ip
}