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_test.go

@@ -6,6 +6,9 @@
 package main
 
 import (
+	"fmt"
+	"regexp"
+	"strings"
 	"testing"
 )
 
@@ -19,32 +22,20 @@ import (
 // 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-",
-		},
-	}
-	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)
-			}
-		})
+	// 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)
+		}
+		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
+		}
 	}
 }