loadbalancer: Use ServiceName.Bytes() in BackedInstanceKey.Key

This is more compact than the String() representation and it does need to
match the longer form with non-zero source.

Add a test case to verify.

Signed-off-by: Jussi Maki <jussi@isovalent.com>

Author: joamaki

pkg/loadbalancer/backend.go

@@ -4,7 +4,6 @@
 package loadbalancer
 
 import (
-	"bytes"
 	"fmt"
 	"iter"
 	"strings"
@@ -87,11 +86,10 @@ func (k BackendInstanceKey) Key() []byte {
 	if k.SourcePriority == 0 {
 		return k.ServiceName.Key()
 	}
-	var buf bytes.Buffer
-	buf.WriteString(k.ServiceName.String())
-	buf.WriteByte(' ')
-	buf.WriteByte(k.SourcePriority)
-	return buf.Bytes()
+	sk := k.ServiceName.Key()
+	buf := make([]byte, 0, 2+len(sk))
+	buf = append(buf, sk...)
+	return append(buf, ' ', k.SourcePriority)
 }
 
 func (be *Backend) GetInstance(name ServiceName) *BackendParams {

pkg/loadbalancer/backend_test.go

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Cilium
+
+package loadbalancer
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBackendInstanceKey(t *testing.T) {
+	name := NewServiceNameInCluster("foo", "bar", "baz")
+	key := BackendInstanceKey{
+		ServiceName:    name,
+		SourcePriority: 0,
+	}
+	assert.True(t, bytes.Equal(key.Key(), name.Key()), "BackendInstanceKey with prio 0 is the ServiceName key")
+	key.SourcePriority = 1
+	assert.True(t, bytes.HasPrefix(key.Key(), name.Key()), "BackendInstanceKey with prio 1 has ServiceName key as prefix")
+
+	keyBytes := key.Key()
+	suffix := keyBytes[len(name.Key()):]
+	assert.Equal(t, []byte{' ', 1}, suffix, "suffix should be space + priority")
+}