Data race warning

[krostar]

Hello,

I'm using you awesome library to help testing something that creates a ssh client without relying on something installed on the host that execute the tests.

When testing, I got the following data race:

 ==================
 WARNING: DATA RACE
 Write at 0x00c0001680d8 by goroutine 38:
   sync.(*WaitGroup).Wait()
       /usr/local/go/src/internal/race/race.go:41 +0xef
   github.com/gliderlabs/ssh.(*Server).Shutdown.func1()
       /go/pkg/mod/github.com/gliderlabs/ssh@v0.2.2/server.go:178 +0x55

 Previous read at 0x00c0001680d8 by goroutine 25:
   sync.(*WaitGroup).Add()
       /usr/local/go/src/internal/race/race.go:37 +0x169
   github.com/gliderlabs/ssh.(*Server).trackConn()
       /go/pkg/mod/github.com/gliderlabs/ssh@v0.2.2/server.go:389 +0x107
   github.com/gliderlabs/ssh.(*Server).handleConn()
       /go/pkg/mod/github.com/gliderlabs/ssh@v0.2.2/server.go:259 +0x2c7

 Goroutine 38 (running) created at:
   github.com/gliderlabs/ssh.(*Server).Shutdown()
       /go/pkg/mod/github.com/gliderlabs/ssh@v0.2.2/server.go:176 +0xef
   app/pkg/sshx.newSSHServer.func3()
       /app/pkg/sshx/client_test.go:89 +0xd0
   app/pkg/sshx.TestNewClient.func3()
       /app/pkg/sshx/client_test.go:118 +0x39b
   testing.tRunner()
       /usr/local/go/src/testing/testing.go:865 +0x163

 Goroutine 25 (running) created at:
   github.com/gliderlabs/ssh.(*Server).Serve()
       /go/pkg/mod/github.com/gliderlabs/ssh@v0.2.2/server.go:230 +0x184
   app/pkg/sshx.newSSHServer.func2()
       /app/pkg/sshx/client_test.go:77 +0x59
 ==================

It happened only one time, and I didn't succeeds to reproduce as restarting the same test without touching anything make it PASS, and so far I didn't get this data race again.

Here is how I call your library:

func TestNewClient(t *testing.T) {
	addr, stop, exited, err := newSSHServer()
	require.NoError(t, err)

	client, err := NewClient(addr) // GITHUB: this returns a *ssh.Client configured to hit the configured ssh server
	require.NoError(t, err)
	assert.Equal(t, "SSH-2.0-go-test_"+addr, string(client.ServerVersion())) // GITHUB: dumb test, just making sure we're connected on the server we wanted
	assert.NoError(t, client.Close())

	stop()
	assert.NoError(t, <-exited)
}

func newSSHServer() (string, func(), <-chan error, error) {
	listener, err := findFreeListener() // GITHUB: this helps to find a listener available
	if err != nil {
		return "", nil, nil, errors.Wrap(err, "unable to get free listener")
	}
	addr := listener.Addr().String()

	srv := gssh.Server{
		Addr:                        addr,
		Version:                     "go-test_" + addr,

		LocalPortForwardingCallback: func(gssh.Context, string, uint32) bool { return true },
		ChannelHandlers: map[string]gssh.ChannelHandler{
			"direct-tcpip": gssh.DirectTCPIPHandler,
		},
	}
	cerr := make(chan error)
	go func() {
		if err := srv.Serve(listener); err != nil {
			if errors.Cause(err) != gssh.ErrServerClosed {
				cerr <- errors.Wrap(err, "unable to serve ssh")
			}
		}
		cerr <- nil
	}()

	return addr, func() {
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		defer cancel()

		if err := srv.Shutdown(ctx); err != nil {
			select {
			case cerr <- err:
			default:
			}
		}
	}, cerr, nil
}

I'm not sure how critical this can be, nor why I got it only one time, but I wanted to notify you about this.

Thanks for your work on this library,
krostar