introduce a function to distinguish between IPv4 and IPv6 addresses

internal/utils/ip.go

@@ -0,0 +1,10 @@
+package utils
+
+import "net"
+
+func IsIPv4(ip net.IP) bool {
+	// If ip is not an IPv4 address, To4 returns nil.
+	// Note that there might be some corner cases, where this is not correct.
+	// See https://stackoverflow.com/questions/22751035/golang-distinguish-ipv4-ipv6.
+	return ip.To4() != nil
+}

internal/utils/ip_test.go

@@ -0,0 +1,17 @@
+package utils
+
+import (
+	"net"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("IP", func() {
+	It("tells IPv4 and IPv6 addresses apart", func() {
+		Expect(IsIPv4(net.IPv4(127, 0, 0, 1))).To(BeTrue())
+		Expect(IsIPv4(net.IPv4zero)).To(BeTrue())
+		Expect(IsIPv4(net.IPv6zero)).To(BeFalse())
+		Expect(IsIPv4(net.IPv6loopback)).To(BeFalse())
+	})
+})