tstest/integration/vms: end-to-end UDP test (#2361)

This tests incoming and outgoing UDP traffic. It would test incoming UDP
traffic however our socks server doesn't seem to allow for connecting to
destinations over UDP. When the socks server gets that support the
incoming test should pass without issue.

Signed-off-by: Christine Dodrill <xe@tailscale.com>

tstest/integration/vms/vms_test.go

@@ -859,6 +859,122 @@ func (h Harness) testDistro(t *testing.T, d Distro, ipm ipMapping) {
 			t.Fatalf("wanted reported ip to be %q, got: %q", string(ipBytes), string(testIPBytes))
 		}
 	})
+
+	t.Run("outgoing-udp-ipv4", func(t *testing.T) {
+		cwd, err := os.Getwd()
+		if err != nil {
+			t.Fatalf("can't get working directory: %v", err)
+		}
+		dir := t.TempDir()
+		run(t, cwd, "go", "build", "-o", filepath.Join(dir, "udp_tester"), "./udp_tester.go")
+
+		sftpCli, err := sftp.NewClient(cli)
+		if err != nil {
+			t.Fatalf("can't connect over sftp to copy binaries: %v", err)
+		}
+		defer sftpCli.Close()
+
+		copyFile(t, sftpCli, filepath.Join(dir, "udp_tester"), "/udp_tester")
+
+		uaddr, err := net.ResolveUDPAddr("udp", net.JoinHostPort("::", "0"))
+		if err != nil {
+			t.Fatalf("can't resolve udp listener addr: %v", err)
+		}
+
+		buf := make([]byte, 1024)
+
+		ln, err := net.ListenUDP("udp", uaddr)
+		if err != nil {
+			t.Fatalf("can't listen for UDP traffic: %v", err)
+		}
+		defer ln.Close()
+
+		sess, err := cli.NewSession()
+		if err != nil {
+			t.Fatalf("can't open session: %v", err)
+		}
+		defer sess.Close()
+
+		sess.Stdin = strings.NewReader("hi")
+		sess.Stdout = logger.FuncWriter(t.Logf)
+		sess.Stderr = logger.FuncWriter(t.Logf)
+
+		_, port, _ := net.SplitHostPort(ln.LocalAddr().String())
+
+		go func() {
+			cmd := fmt.Sprintf("/udp_tester -client %s\n", net.JoinHostPort("100.64.0.1", port))
+			time.Sleep(10 * time.Millisecond)
+			t.Logf("sending packet: %s", cmd)
+			err := sess.Run(cmd)
+			if err != nil {
+				t.Errorf("can't send UDP packet: %v", err)
+			}
+		}()
+
+		t.Log("listening for packet")
+		n, _, err := ln.ReadFromUDP(buf)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if n == 0 {
+			t.Fatal("got nothing")
+		}
+
+		if !bytes.Contains(buf, []byte("hi")) {
+			t.Fatal("did not get UDP message")
+		}
+	})
+
+	t.Run("incoming-udp-ipv4", func(t *testing.T) {
+		// vms_test.go:947: can't dial: socks connect udp 127.0.0.1:36497->100.64.0.2:33409: network not implemented
+		t.Skip("can't make outgoing sockets over UDP with our socks server")
+
+		sess, err := cli.NewSession()
+		if err != nil {
+			t.Fatalf("can't open session: %v", err)
+		}
+		defer sess.Close()
+
+		ip, err := sess.Output("tailscale ip -4")
+		if err != nil {
+			t.Fatalf("can't nab ipv4 address: %v", err)
+		}
+
+		port, err := getProbablyFreePortNumber()
+		if err != nil {
+			t.Fatalf("unable to fetch port number: %v", err)
+		}
+
+		go func() {
+			time.Sleep(10 * time.Millisecond)
+
+			conn, err := h.testerDialer.Dial("udp", net.JoinHostPort(string(bytes.TrimSpace(ip)), strconv.Itoa(port)))
+			if err != nil {
+				t.Errorf("can't dial: %v", err)
+			}
+
+			fmt.Fprint(conn, securePassword)
+		}()
+
+		sess, err = cli.NewSession()
+		if err != nil {
+			t.Fatalf("can't open session: %v", err)
+		}
+		defer sess.Close()
+		sess.Stderr = logger.FuncWriter(t.Logf)
+
+		msg, err := sess.Output(
+			fmt.Sprintf(
+				"/udp_tester -server %s",
+				net.JoinHostPort(string(bytes.TrimSpace(ip)), strconv.Itoa(port)),
+			),
+		)
+
+		if msg := string(bytes.TrimSpace(msg)); msg != securePassword {
+			t.Fatalf("wanted %q from vm, got: %q", securePassword, msg)
+		}
+	})
 }
 
 func runTestCommands(t *testing.T, timeout time.Duration, cli *ssh.Client, batch []expect.Batcher) {