Leverage the netip package when dealing with IP addresses

When configuring Kubernetes with multiple nodes, EIB requires an IP address to be used
as a target for load balancing purposes. However, it assumes this address to be in an IPv4
format, resulting in a broken mangling when IPv6 is used instead.

Correct this problem by letting netip package do the handling of IP addresses, hiding
version specific issues. This also allows for easier and additional input validation with
minimal effort.

Signed-off-by: Marco Chiappero <[email protected]>

pkg/kubernetes/cluster.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"io/fs"
+	"net/netip"
 	"os"
 	"path/filepath"
 	"strings"
@@ -196,13 +197,26 @@ func setClusterCNI(config map[string]any) {
 	config[cniKey] = cniDefaultValue
 }
 
-func setClusterAPIAddress(config map[string]any, apiAddress string, port int) {
-	if apiAddress == "" {
-		zap.S().Warn("Attempted to set an empty cluster API address")
+func setClusterAPIAddress(config map[string]any, apiAddress string, port uint16) {
+	ip, err := netip.ParseAddr(apiAddress)
+	if err != nil {
+		zap.S().Errorf("Invalid cluster API address ('%s')", err)
+		return
+	}
+
+	if ip.IsUnspecified() || ip.IsMulticast() {
+		zap.S().Errorf("Invalid cluster API address (%s)", ip.String())
 		return
 	}
 
-	config[serverKey] = fmt.Sprintf("https://%s:%d", apiAddress, port)
+	if port == 0 {
+		zap.S().Error("Invalid port number")
+		return
+	}
+
+	endpoint := netip.AddrPortFrom(ip, port)
+
+	config[serverKey] = fmt.Sprintf("https://%s", endpoint.String())
 }
 
 func setSELinux(config map[string]any) {