在Golang中获取公共IP

Question

How do we get public IP in golang? Method req.Header.Get("X-Forwarded-For") returns array of IPs. How do we identify which one is public and which on internal? Is there any other method to fetch public(external) IP?

Answer 1

The following IP blocks are reserved for private IP addresses.

Class        Starting IPAddress    Ending IP Address    # of Hosts
A            10.0.0.0              10.255.255.255       16,777,216
B            172.16.0.0            172.31.255.255       1,048,576
C            192.168.0.0           192.168.255.255      65,536
Link-local-u 169.254.0.0           169.254.255.255      65,536
Link-local-m 224.0.0.0             224.0.0.255          256
Local        127.0.0.0             127.255.255.255      16777216

You may write a function that checks for if the ip comes under these

Here is an attempt to do the same,the code below is not handling ipv6 please add if needed

func IsPublicIP(IP net.IP) bool {
    if IP.IsLoopback() || IP.IsLinkLocalMulticast() || IP.IsLinkLocalUnicast() {
        return false
    }
    if ip4 := IP.To4(); ip4 != nil {
        switch {
        case ip4[0] == 10:
            return false
        case ip4[0] == 172 && ip4[1] >= 16 && ip4[1] <= 31:
            return false
        case ip4[0] == 192 && ip4[1] == 168:
            return false
        default:
            return true
        }
    }
    return false
}

Here is play link