plugin/etcd: Stop target stripping at the end of a name (#8584)

Stops stripping when the next-label operation reaches the end sentinel in DNS

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/etcd/msg/service.go

@@ -165,6 +165,9 @@ func targetStrip(name string, targetStrip int) string {
 	offset, end := 0, false
 	for range targetStrip {
 		offset, end = dns.NextLabel(name, offset)
+		if end {
+			break
+		}
 	}
 	if end {
 		// We overshot the name, use the original one.

plugin/etcd/msg/service_test.go

@@ -1,6 +1,9 @@
 package msg
 
-import "testing"
+import (
+	"testing"
+	"time"
+)
 
 func TestSplit255(t *testing.T) {
 	xs := split255("abc")
@@ -29,6 +32,23 @@ func TestSplit255(t *testing.T) {
 	}
 }
 
+func TestTargetStripLargeValueReturns(t *testing.T) {
+	const name = "b.z1.test."
+	done := make(chan string, 1)
+	go func() {
+		done <- targetStrip(name, int(^uint(0)>>1))
+	}()
+
+	select {
+	case got := <-done:
+		if got != name {
+			t.Fatalf("targetStrip returned %q, want %q", got, name)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("targetStrip did not return after reaching the end of the name")
+	}
+}
+
 func TestGroup(t *testing.T) {
 	// Key are in the wrong order, but for this test it does not matter.
 	sx := Group(