check for uninitialized fields when closing the Transport (#3908)

* close Transport: check for possibly uninitialized fields

* close Transport: close Conn, as conn might not be initialized

* close Transport: add test case

transport.go

@@ -244,14 +244,16 @@ func (t *Transport) runSendQueue() {
 func (t *Transport) Close() error {
 	t.close(errors.New("closing"))
 	if t.createdConn {
-		if err := t.conn.Close(); err != nil {
+		if err := t.Conn.Close(); err != nil {
 			return err
 		}
-	} else {
+	} else if t.conn != nil {
 		t.conn.SetReadDeadline(time.Now())
 		defer func() { t.conn.SetReadDeadline(time.Time{}) }()
 	}
-	<-t.listening // wait until listening returns
+	if t.listening != nil {
+		<-t.listening // wait until listening returns
+	}
 	return nil
 }
 
@@ -280,7 +282,9 @@ func (t *Transport) close(e error) {
 		return
 	}
 
-	t.handlerMap.Close(e)
+	if t.handlerMap != nil {
+		t.handlerMap.Close(e)
+	}
 	if t.server != nil {
 		t.server.setCloseError(e)
 	}

transport_test.go

@@ -291,4 +291,20 @@ var _ = Describe("Transport", func() {
 		close(packetChan)
 		tr.Close()
 	})
+
+	It("closes uninitialized Transport and closes underlying PacketConn", func() {
+		packetChan := make(chan packetToRead)
+		pconn := newMockPacketConn(packetChan)
+
+		tr := &Transport{
+			Conn:        pconn,
+			createdConn: true, // owns pconn
+		}
+		// NO init
+
+		// shutdown
+		close(packetChan)
+		pconn.EXPECT().Close()
+		Expect(tr.Close()).To(Succeed())
+	})
 })