operator: bug fix for switch ip addresses

switch ipv6 addresses where buggy, and where having assigned a non compliant ipv6. now implemented some unit tests plus fixed this error

internal/controller/pod_utils.go

@@ -159,7 +159,7 @@ func GenerateAnnotations(overlayName string, ammount int) string {
 	annotationsString := []string{}
 	var newAnnotation string
 	for i := 1; i <= ammount; i++ {
-		newAnnotation = fmt.Sprintf(`{"name": "%s-veth%d", "ips": ["fe80::58d0:b8ff:fe%s:%s/64"]}`, overlayName, i, fmt.Sprintf("%02d", i), Generate4byteChunk)
+		newAnnotation = fmt.Sprintf(`{"name": "%s-veth%d", "ips": ["fe80::58d0:b8ff:fe%s:%s/64"]}`, overlayName, i, fmt.Sprintf("%02d", i), Generate4byteChunk())
 		annotationsString = append(annotationsString, newAnnotation)
 	}
 
@@ -169,9 +169,9 @@ func GenerateAnnotations(overlayName string, ammount int) string {
 func Generate4byteChunk() string {
 
 	// Generating the interface ID (64 bits)
-	interfaceID := rand.Uint64()
+	interfaceID := rand.Uint64() & 0xffff
 
-	// Formatting to a 16 character hexadecimal string
+	// Formatting to a 4 character hexadecimal string
 	interfaceIDHex := fmt.Sprintf("%04x", interfaceID)
 
 	return interfaceIDHex

internal/controller/pod_utils_test.go

+// Copyright 2024 Universidad Carlos III de Madrid
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// generate_test.go
+package controller
+
+import (
+	"regexp"
+	"testing"
+)
+
+// TestGenerate4byteChunk verifies that Generate4byteChunk produces a 4-character hexadecimal string.
+func TestGenerate4byteChunk(t *testing.T) {
+	// Regular expression to match exactly 4 hexadecimal characters
+	re := regexp.MustCompile(`^[0-9a-fA-F]{4}$`)
+
+	// Call Generate4byteChunk multiple times to check if output is always 4 characters
+	for i := 0; i < 100; i++ {
+		output := Generate4byteChunk()
+
+		// Check if the output matches the 4-character hex pattern
+		if !re.MatchString(output) {
+			t.Errorf("Expected a 4-character hexadecimal string, but got: %s", output)
+		}
+	}
+}