转到-检查IP地址是否在专用网络空间中

Question

I have a program in go which accepts URLs from clients and gets them using the net/http package. Before doing further processing, I would like to check if the URL maps to private (non-routable / RFC1918 networks) address space.

The straight-forward way would be to perform an explicit DNS request and check the address for the known private ranges. After that, perform the HTTP GET request for the URL.

Is there a better way to accomplish this? Preferably integrating with http.Client so it can be performed as a part of the GET request.

Answer 1

You might also want to include checks for loopback (IPv4 or IPv6) and/or IPv6 link-local or unique-local addresses. Here is an example with a list of RFC1918 address plus these others and a simple check against them as isPrivateIP(ip net.IP):

var privateIPBlocks []*net.IPNet

func init() {
    for _, cidr := range []string{
        "127.0.0.0/8",    // IPv4 loopback
        "10.0.0.0/8",     // RFC1918
        "172.16.0.0/12",  // RFC1918
        "192.168.0.0/16", // RFC1918
        "::1/128",        // IPv6 loopback
        "fe80::/10",      // IPv6 link-local
        "fc00::/7",       // IPv6 unique local addr
    } {
        _, block, err := net.ParseCIDR(cidr)
        if err != nil {
            panic(fmt.Errorf("parse error on %q: %v", cidr, err))
        }
        privateIPBlocks = append(privateIPBlocks, block)
    }
}

func isPrivateIP(ip net.IP) bool {
    for _, block := range privateIPBlocks {
        if block.Contains(ip) {
            return true
        }
    }
    return false
}