Dont redirect private IPs and localhost

pkg/netutil/netutil.go

@@ -0,0 +1,40 @@
+package netutil
+
+import "net"
+
+var privateNets []*net.IPNet
+
+func init() {
+	for _, cidr := range []string{
+		"127.0.0.0/8",
+		"10.0.0.0/8",
+		"172.16.0.0/12",
+		"192.168.0.0/16",
+		"::1/128",
+		"fe80::/10",
+		"fc00::/7",
+	} {
+		_, network, _ := net.ParseCIDR(cidr)
+		privateNets = append(privateNets, network)
+	}
+}
+
+func IsPrivate(host string) bool {
+	if host == "localhost" {
+		return true
+	}
+	return IsPrivateIP(net.ParseIP(host))
+}
+
+func IsPrivateIP(ip net.IP) bool {
+	if ip == nil {
+		return false
+	}
+
+	for _, privateNet := range privateNets {
+		if privateNet.Contains(ip) {
+			return true
+		}
+	}
+	return false
+}