channelz: cleanup channel registration if Dial fails (#2733)

Author: lyuxuan

Diff for: clientconn.go

@@ -134,6 +134,18 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 		opt.apply(&cc.dopts)
 	}
 
+	defer func() {
+		select {
+		case <-ctx.Done():
+			conn, err = nil, ctx.Err()
+		default:
+		}
+
+		if err != nil {
+			cc.Close()
+		}
+	}()
+
 	if channelz.IsOn() {
 		if cc.dopts.channelzParentID != 0 {
 			cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, cc.dopts.channelzParentID, target)
@@ -196,18 +208,6 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 		defer cancel()
 	}
 
-	defer func() {
-		select {
-		case <-ctx.Done():
-			conn, err = nil, ctx.Err()
-		default:
-		}
-
-		if err != nil {
-			cc.Close()
-		}
-	}()
-
 	scSet := false
 	if cc.dopts.scChan != nil {
 		// Try to get an initial service config.
@@ -820,7 +820,7 @@ func (cc *ClientConn) Close() error {
 		}
 		channelz.AddTraceEvent(cc.channelzID, ted)
 		// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add trace reference to
-		// the entity beng deleted, and thus prevent it from being deleted right away.
+		// the entity being deleted, and thus prevent it from being deleted right away.
 		channelz.RemoveEntry(cc.channelzID)
 	}
 	return nil

Diff for: test/channelz_test.go

@@ -190,6 +190,18 @@ func (s) TestCZTopChannelRegistrationAndDeletion(t *testing.T) {
 	}
 }
 
+func (s) TestCZTopChannelRegistrationAndDeletionWhenDialFail(t *testing.T) {
+	channelz.NewChannelzStorage()
+	// Make dial fails (due to no transport security specified)
+	_, err := grpc.Dial("fake.addr")
+	if err == nil {
+		t.Fatal("expecting dial to fail")
+	}
+	if tcs, end := channelz.GetTopChannels(0, 0); tcs != nil || !end {
+		t.Fatalf("GetTopChannels(0, 0) = %v, %v, want <nil>, true", tcs, end)
+	}
+}
+
 func (s) TestCZNestedChannelRegistrationAndDeletion(t *testing.T) {
 	channelz.NewChannelzStorage()
 	e := tcpClearRREnv