De-duplicate the targets list while refreshing state.

We anyway keep the target information in a map by name, i.e. we lose the information for duplicate targets anyway.

Also, log a warning if we get a duplicate target as it should ideally never happen.

Duplicate targets can lead to spurious behavior from probes:
#436

PiperOrigin-RevId: 325081938

rds/client/client.go

@@ -93,10 +93,23 @@ func (client *Client) updateState(response *pb.ListResourcesResponse) {
 	defer client.mu.Unlock()
 
 	client.names = make([]string, len(response.GetResources()))
-	for i, res := range response.GetResources() {
+	oldcache := client.cache
+	client.cache = make(map[string]*cacheRecord, len(response.GetResources()))
+
+	i := 0
+	for _, res := range response.GetResources() {
+		if oldRes, ok := client.cache[res.GetName()]; ok {
+			client.l.Warningf("Got resource (%s) again, ignoring this instance: {%v}. Previous record: %+v.", res.GetName(), res, *oldRes)
+			continue
+		}
+		if oldcache[res.GetName()] != nil && res.GetIp() != oldcache[res.GetName()].ip {
+			client.l.Infof("Resource (%s) ip has changed: %s -> %s.", res.GetName(), oldcache[res.GetName()].ip, res.GetIp())
+		}
 		client.cache[res.GetName()] = &cacheRecord{res.GetIp(), int(res.GetPort()), res.Labels}
 		client.names[i] = res.GetName()
+		i++
 	}
+	client.names = client.names[:i]
 }
 
 // ListEndpoints returns the list of resources.

rds/client/client_test.go

@@ -61,6 +61,13 @@ var testResourcesMap = map[string][]*pb.Resource{
 			Port:   proto.Int32(80),
 			Labels: map[string]string{"zone": "us-central1-c"},
 		},
+		// Duplicate resource, it should be removed from the result.
+		{
+			Name:   proto.String("testR3"),
+			Ip:     proto.String("testR3.test.com"),
+			Port:   proto.Int32(80),
+			Labels: map[string]string{"zone": "us-central1-c"},
+		},
 	},
 }
 
@@ -136,9 +143,11 @@ func TestListAndResolve(t *testing.T) {
 
 		client.refreshState(time.Second)
 
-		// Test ListEndpoint()
+		// Test ListEndpoint(), note that we remove the duplicate resource from the
+		// exepected output.
 		epList := client.ListEndpoints()
-		for i, res := range testResources {
+		expectedList := testResources[:len(testResources)-1]
+		for i, res := range expectedList {
 			if epList[i].Name != res.GetName() {
 				t.Errorf("Resource name: got=%s, want=%s", epList[i].Name, res.GetName())
 			}
@@ -153,7 +162,7 @@ func TestListAndResolve(t *testing.T) {
 		}
 
 		// Test Resolve()
-		for _, res := range testResources {
+		for _, res := range expectedList {
 			for _, ipVer := range []int{0, 4, 6} {
 				t.Run(fmt.Sprintf("resolve_%s_for_IPv%d", res.GetName(), ipVer), func(t *testing.T) {
 					expectedIP := expectedIPByVersion[res.GetName()][ipVer]