func execWithTimeout(timeout time.Duration, cmd string, args ...string) (output []byte, err error) {
	var buf safe.Buffer
	ch := make(chan []byte, 1)
	errCh := make(chan error, 1)
	command := osexec.Command(cmd, args...)
	command.Stdout = &Writer{&buf}
	command.Stderr = &Writer{&buf}
	if err = command.Start(); err != nil {
		return nil, err
	}
	go func() {
		if err := command.Wait(); err == nil {
			ch <- buf.Bytes()
		} else {
			errCh <- err
			ch <- buf.Bytes()
		}
	}()
	select {
	case output = <-ch:
		select {
		case err = <-errCh:
		case <-time.After(1e9):
		}
	case err = <-errCh:
		output = <-ch
	case <-time.After(timeout):
		argsStr := strings.Join(args, " ")
		err = fmt.Errorf("%q ran for more than %s.", cmd+" "+argsStr, timeout)
		command.Process.Kill()
	}
	return output, err
}

func TestPullImage(t *testing.T) {
	server1 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Pulling from 1!"))
	}))
	defer server1.Close()
	server2 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Pulling from 2!"))
	}))
	defer server2.Close()
	var buf safe.Buffer
	cluster, err := New(nil,
		Node{ID: "handler0", Address: server1.URL},
		Node{ID: "handler1", Address: server2.URL},
	)
	if err != nil {
		t.Fatal(err)
	}
	err = cluster.PullImage(docker.PullImageOptions{Repository: "tsuru/python"}, &buf)
	if err != nil {
		t.Error(err)
	}
	alternatives := []string{
		"Pulling from 1!Pulling from 2!",
		"Pulling from 2!Pulling from 1!",
	}
	if r := buf.String(); r != alternatives[0] && r != alternatives[1] {
		t.Errorf("Wrong output: Want %q. Got %q.", "Pulling from 1!Pulling from 2!", buf.String())
	}
}

func TestImportImage(t *testing.T) {
	server1 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("importing from 1"))
	}))
	defer server1.Close()
	server2 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("importing from 2"))
	}))
	defer server2.Close()
	cluster, err := New(nil,
		Node{ID: "handler0", Address: server1.URL},
		Node{ID: "handler1", Address: server2.URL},
	)
	if err != nil {
		t.Fatal(err)
	}
	var buf safe.Buffer
	err = cluster.ImportImage(docker.ImportImageOptions{Repository: "tsuru/python", Source: "http://url.to/tar"}, nil, &buf)
	if err != nil {
		t.Error(err)
	}
	re := regexp.MustCompile(`^importing from \d`)
	if !re.MatchString(buf.String()) {
		t.Errorf("Wrong output: Want %q. Got %q.", "importing from [12]", buf.String())
	}
}

// replicateImage replicates the given image through all nodes in the cluster.
func replicateImage(name string) error {
	var buf safe.Buffer
	if _, err := config.GetString("docker:registry"); err == nil {
		pushOpts := docker.PushImageOptions{Name: name, OutputStream: &buf}
		for i := 0; i < maxTry; i++ {
			err = dockerCluster().PushImage(pushOpts, docker.AuthConfiguration{})
			if err == nil {
				buf.Reset()
				break
			}
			log.Errorf("[docker] Failed to push image %q (%s): %s", name, err, buf.String())
			buf.Reset()
		}
		if err != nil {
			return err
		}
		pullOpts := docker.PullImageOptions{Repository: name, OutputStream: &buf}
		for i := 0; i < maxTry; i++ {
			err = dockerCluster().PullImage(pullOpts)
			if err == nil {
				break
			}
			buf.Reset()
		}
		if err != nil {
			log.Errorf("[docker] Failed to replicate image %q through nodes (%s): %s", name, err, buf.String())
			return err
		}
	}
	return nil
}

// pushImage sends the given image to the registry server defined in the
// configuration file.
func pushImage(name string) error {
	if _, err := config.GetString("docker:registry"); err == nil {
		var buf safe.Buffer
		pushOpts := docker.PushImageOptions{Name: name, OutputStream: &buf}
		err = dockerCluster().PushImage(pushOpts, docker.AuthConfiguration{})
		if err != nil {
			log.Errorf("[docker] Failed to push image %q (%s): %s", name, err, buf.String())
			return err
		}
	}
	return nil
}

func TestPushImage(t *testing.T) {
	server1 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Pushing to server 1!"))
	}))
	defer server1.Close()
	server2 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Pushing to server 2!"))
	}))
	defer server2.Close()
	var buf safe.Buffer
	cluster, err := New(nil,
		Node{ID: "handler0", Address: server1.URL},
		Node{ID: "handler1", Address: server2.URL},
	)
	if err != nil {
		t.Fatal(err)
	}
	var auth docker.AuthConfiguration
	err = cluster.PushImage(docker.PushImageOptions{Name: "tsuru/ruby"}, auth, &buf)
	re := regexp.MustCompile(`^Pushing to server \d`)
	if !re.MatchString(buf.String()) {
		t.Errorf("Wrong output: Want %q. Got %q.", "Pushing to server [12]", buf.String())
	}
}