cmd/k8s-operator: fix base truncating for extra long Service names (#10825)

cmd/k8s-operator: fix base truncating for extra long Service names

StatefulSet names for ingress/egress proxies are calculated
using Kubernetes name generator and the parent resource name
as a base.
The name generator also cuts the base, but has a higher max cap.
This commit fixes a bug where, if we get a shortened base back
from the generator, we cut off too little as the base that we
have cut will be passed into the generator again, which will
then itself cut less because the base is shorter- so we end up
with a too long name again.

Updates tailscale/tailscale#10807

Co-authored-by: Maisem Ali <maisem@tailscale.com>
Signed-off-by: Irbe Krumina <irbekrm@gmail.com>

cmd/k8s-operator/sts.go

@@ -214,18 +214,19 @@ func (a *tailscaleSTSReconciler) Cleanup(ctx context.Context, logger *zap.Sugare
 // generation will NOT result in a StatefulSet name longer than 52 chars.
 // This is done because of https://github.com/kubernetes/kubernetes/issues/64023.
 func statefulSetNameBase(parent string) string {
-
 	base := fmt.Sprintf("ts-%s-", parent)
-
-	// Calculate what length name GenerateName returns for this base.
 	generator := names.SimpleNameGenerator
+	for {
 		generatedName := generator.GenerateName(base)
-
-	if excess := len(generatedName) - maxStatefulSetNameLength; excess > 0 {
-		base = base[:len(base)-excess-1] // take extra char off to make space for hyphen
-		base = base + "-"                // re-instate hyphen
-	}
+		excess := len(generatedName) - maxStatefulSetNameLength
+		if excess <= 0 {
 			return base
+		}
+		base = base[:len(base)-1-excess]   // cut off the excess chars
+		if !strings.HasSuffix(base, "-") { // dash may have been cut by the generator
+			base = base + "-"
+		}
+	}
 }
 
 func (a *tailscaleSTSReconciler) reconcileHeadlessService(ctx context.Context, logger *zap.SugaredLogger, sts *tailscaleSTSConfig) (*corev1.Service, error) {

cmd/k8s-operator/sts_test.go

@@ -6,6 +6,9 @@
 package main
 
 import (
+	"fmt"
+	"regexp"
+	"strings"
 	"testing"
 )
 
@@ -19,32 +22,20 @@
 // https://github.com/kubernetes/kubernetes/blob/v1.28.4/staging/src/k8s.io/apiserver/pkg/storage/names/generate.go#L45.
 // https://github.com/kubernetes/kubernetes/pull/116430
 func Test_statefulSetNameBase(t *testing.T) {
-	tests := []struct {
-		name string
-		in   string
-		out  string
-	}{
-		{
-			name: "43 chars",
-			in:   "oidhexl9o832hcbhyg4uz6o0s7u9uae54h5k8ofs9xb",
-			out:  "ts-oidhexl9o832hcbhyg4uz6o0s7u9uae54h5k8ofs9xb-",
-		},
-		{
-			name: "44 chars",
-			in:   "oidhexl9o832hcbhyg4uz6o0s7u9uae54h5k8ofs9xbo",
-			out:  "ts-oidhexl9o832hcbhyg4uz6o0s7u9uae54h5k8ofs9xb-",
-		},
-		{
-			name: "42 chars",
-			in:   "oidhexl9o832hcbhyg4uz6o0s7u9uae54h5k8ofs9x",
-			out:  "ts-oidhexl9o832hcbhyg4uz6o0s7u9uae54h5k8ofs9x-",
-		},
+	// Service name lengths can be 1 - 63 chars, be paranoid and test them all.
+	var b strings.Builder
+	for b.Len() < 63 {
+		if _, err := b.WriteString("a"); err != nil {
+			t.Fatalf("error writing to string builder: %v", err)
 		}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := statefulSetNameBase(tt.in); got != tt.out {
-				t.Errorf("stsNamePrefix(%s) = %q, want %s", tt.in, got, tt.out)
+		baseLength := len(b.String())
+		if baseLength > 43 {
+			baseLength = 43 // currently 43 is the max base length
+		}
+		wantsNameR := regexp.MustCompile(`^ts-a{` + fmt.Sprint(baseLength) + `}-$`) // to match a string like ts-aaaa-
+		gotName := statefulSetNameBase(b.String())
+		if !wantsNameR.MatchString(gotName) {
+			t.Fatalf("expected string %s to match regex %s ", gotName, wantsNameR.String()) // fatal rather than error as this test is called 63 times
 		}
-		})
 	}
 }