Working with IPs and CIDR blocks in golang is quite easy. Because binary is just a number, first we can create helper functions to convert from integer to IP (and vice versa) plus get CIDR mask as integer.
package main
import (
"encoding/binary"
"net"
)
func getMask(ip *net.IPNet) uint32 {
return 0xFFFFFFFF ^ binary.BigEndian.Uint32(ip.Mask)
}
func intToIP(i uint32) net.IP {
b := make([]byte, 4)
binary.BigEndian.PutUint32(b, i)
return b
}
func ipToInt(ip net.IP) uint32 {
return binary.BigEndian.Uint32(ip.To4())
}
getMask function just toggles bits of the mask, so it can be used to set bits to 0. We could use right shift as well:
maskOnes, _ := ip.Mask.Size()
return uint32(0xFFFFFFFF >> maskOnes)
The helper functions make it easy to calculate IPs from supplied CIDR block:
package main
import (
"encoding/binary"
"net"
)
func BroadcastIPv4(ip *net.IPNet) net.IP {
// set non-set bits from the mask
out := ipToInt(ip.IP) | getMask(ip)
return intToIP(out)
}
func HostMinIPv4(ip *net.IPNet) net.IP {
// network address - clear (AND NOT) non-set bits from the mask
out := ipToInt(ip.IP) &^ getMask(ip)
// increment by one
out++
return intToIP(out)
}
func HostMaxIPv4(ip *net.IPNet) net.IP {
bcastInt := ipToInt(BroadcastIPv4(ip))
bcastInt--
return intToIP(bcastInt)
}
// CIDRIPs returns list of IPs not including network and broadcast IP
func CIDRIPs(ip *net.IPNet) []net.IP {
return IPs(HostMinIPv4(ip), HostMaxIPv4(ip))
}
// IPs returns list of IPs including from and to arguments
func IPs(from net.IP, to net.IP) []net.IP {
var out []net.IP
for i := ipToInt(from); i <= ipToInt(to); i++ {
out = append(out, intToIP(i))
}
return out
}
func getMask(ip *net.IPNet) uint32 {
return 0xFFFFFFFF ^ binary.BigEndian.Uint32(ip.Mask)
}
func intToIP(i uint32) net.IP {
b := make([]byte, 4)
binary.BigEndian.PutUint32(b, i)
return b
}
func ipToInt(ip net.IP) uint32 {
return binary.BigEndian.Uint32(ip.To4())
}