kubelet/cni/kubenet: use common container IP address functions

pkg/kubelet/network/plugins.go

@@ -199,3 +199,41 @@ func (plugin *NoopNetworkPlugin) GetPodNetworkStatus(namespace string, name stri
 func (plugin *NoopNetworkPlugin) Status() error {
 	return nil
 }
+
+func getOnePodIP(execer utilexec.Interface, nsenterPath, netnsPath, interfaceName, addrType string) (net.IP, error) {
+	// Try to retrieve ip inside container network namespace
+	output, err := execer.Command(nsenterPath, fmt.Sprintf("--net=%s", netnsPath), "-F", "--",
+		"ip", "-o", addrType, "addr", "show", "dev", interfaceName, "scope", "global").CombinedOutput()
+	if err != nil {
+		return nil, fmt.Errorf("Unexpected command output %s with error: %v", output, err)
+	}
+
+	lines := strings.Split(string(output), "\n")
+	if len(lines) < 1 {
+		return nil, fmt.Errorf("Unexpected command output %s", output)
+	}
+	fields := strings.Fields(lines[0])
+	if len(fields) < 4 {
+		return nil, fmt.Errorf("Unexpected address output %s ", lines[0])
+	}
+	ip, _, err := net.ParseCIDR(fields[3])
+	if err != nil {
+		return nil, fmt.Errorf("CNI failed to parse ip from output %s due to %v", output, err)
+	}
+
+	return ip, nil
+}
+
+// GetPodIP gets the IP of the pod by inspecting the network info inside the pod's network namespace.
+func GetPodIP(execer utilexec.Interface, nsenterPath, netnsPath, interfaceName string) (net.IP, error) {
+	ip, err := getOnePodIP(execer, nsenterPath, netnsPath, interfaceName, "-4")
+	if err != nil {
+		// Fall back to IPv6 address if no IPv4 address is present
+		ip, err = getOnePodIP(execer, nsenterPath, netnsPath, interfaceName, "-6")
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	return ip, nil
+}