xds: fix panic involving double close of channel in xDS transport

xds/internal/xdsclient/transport/loadreport.go

@@ -62,6 +62,11 @@ func (t *Transport) lrsStartStream() {
 
 	ctx, cancel := context.WithCancel(context.Background())
 	t.lrsCancelStream = cancel
+
+	// Create a new done channel everytime a new stream is created. This ensures
+	// that we don't close the same channel multiple times (from lrsRunner()
+	// goroutine) when multiple streams are created and closed.
+	t.lrsRunnerDoneCh = make(chan struct{})
 	go t.lrsRunner(ctx)
 }
 
@@ -78,6 +83,9 @@ func (t *Transport) lrsStopStream() {
 
 	t.lrsCancelStream()
 	t.logger.Infof("Stopping LRS stream")
+
+	// Wait for the runner goroutine to exit. The done channel will be
+	// recreated when a new stream is created.
 	<-t.lrsRunnerDoneCh
 }
 

xds/internal/xdsclient/transport/loadreport_test.go

@@ -54,7 +54,7 @@ func (s) TestReportLoad(t *testing.T) {
 		NodeProto:    nodeProto,
 	}
 
-	// Create a transport to the fake server.
+	// Create a transport to the fake management server.
 	tr, err := transport.New(transport.Options{
 		ServerCfg:          serverCfg,
 		UpdateHandler:      func(transport.ResourceUpdate) error { return nil }, // No ADS validation.
@@ -190,4 +190,16 @@ func (s) TestReportLoad(t *testing.T) {
 	if _, err := mgmtServer.LRSStreamCloseChan.Receive(ctx); err != nil {
 		t.Fatal("Timeout waiting for LRS stream to close")
 	}
+
+	// Calling the load reporting API again should result in the creation of a
+	// new LRS stream. This ensures that creating and closing multiple streams
+	// works smoothly.
+	_, cancelLRS3 := tr.ReportLoad()
+	if err != nil {
+		t.Fatalf("Failed to start LRS load reporting: %v", err)
+	}
+	if _, err := mgmtServer.LRSStreamOpenChan.Receive(ctx); err != nil {
+		t.Fatalf("Timeout when waiting for LRS stream to be created: %v", err)
+	}
+	cancelLRS3()
 }

xds/internal/xdsclient/transport/transport.go

@@ -202,7 +202,6 @@ func New(opts Options) (*Transport, error) {
 		versions:        make(map[string]string),
 		nonces:          make(map[string]string),
 		adsRunnerDoneCh: make(chan struct{}),
-		lrsRunnerDoneCh: make(chan struct{}),
 	}
 
 	// This context is used for sending and receiving RPC requests and