fixup! build: add woodpecker

Use a single channel per consumer, instead of one channel per
consumer/event tuple. This ensures that overall ordering of events
remains consistent, and avoids introducing subtle race conditions.

.github/workflows/build.yml

@@ -1,4 +1,4 @@
-name: ci-build
+name: build
 run-name: Building ${{ github.ref_name }}
 on:
   push:

.github/workflows/codeql.yml

@@ -1,4 +1,4 @@
-name: ci-scan
+name: codeql
 
 on:
   push:

.woodpecker.yml

@@ -0,0 +1,9 @@
+---
+when:
+- event: push
+
+steps:
+- name: lint
+  image: koalaman/shellcheck:stable
+  commands:
+  - shellcheck $(find . -type f -name "*.sh")

CONTRIBUTING.md

@@ -33,11 +33,12 @@ broadcast to localhost:1935 or localhost:1936.
 
 ## Opening a pull request
 
-Pull requests are welcome, but please propose significant changes in a
+Pull requests are welcome, please propose significant changes in a
 [discussion](https://github.com/rfwatson/octoplex/discussions) first.
 
 1. Fork the repo
-2. Make your changes, including test coverage
+1. Make your changes, including test coverage
-3. Push the changes to a branch
+1. Run the formatter (`mise run format`)
-4. Ensure the branch is passing
+1. Push the changes to a branch
-5. Open a pull request
+1. Ensure the branch is passing
+1. Open a pull request

README.md

@@ -1,11 +1,12 @@
 # Octoplex :octopus:
 
-![build status](https://github.com/rfwatson/octoplex/actions/workflows/build.yml/badge.svg)
+[![build status](https://github.com/rfwatson/octoplex/actions/workflows/build.yml/badge.svg)](https://github.com/rfwatson/octoplex/actions/workflows/build.yml)
-![scan status](https://github.com/rfwatson/octoplex/actions/workflows/codeql.yml/badge.svg)
+[![scan status](https://github.com/rfwatson/octoplex/actions/workflows/codeql.yml/badge.svg)](https://github.com/rfwatson/octoplex/actions/workflows/codeql.yml)
 ![GitHub Release](https://img.shields.io/github/v/release/rfwatson/octoplex)
+[![Go Report Card](https://goreportcard.com/badge/git.netflux.io/rob/octoplex)](https://goreportcard.com/report/git.netflux.io/rob/octoplex)
 [![License: AGPL v3](https://img.shields.io/badge/License-AGPL_v3-blue.svg)](https://www.gnu.org/licenses/agpl-3.0)
 
-Octoplex is a live video restreamer for the terminal.
+Octoplex is a Docker-native live video restreamer.
 
 * Restream RTMP/RTMPS to unlimited destinations
 * Broadcast using OBS or any standard tool
@@ -38,8 +39,7 @@ Octoplex is a live video restreamer for the terminal.
 
 ### Docker Engine
 
-First, make sure Docker Engine is installed. Octoplex uses Docker to manage
+First, ensure that Docker Engine is installed.
-FFmpeg and other streaming tools.
 
 Linux: See https://docs.docker.com/engine/install/.
 
@@ -160,14 +160,12 @@ localhost (`127.0.0.1`) or use `0.0.0.0` to bind to all network interfaces.
 
 ## Contributing
 
+See [CONTRIBUTING.md](/CONTRIBUTING.md).
+
 ### Bug reports
 
 Open bug reports [on GitHub](https://github.com/rfwatson/octoplex/issues/new).
 
-### Pull requests
-
-Pull requests are welcome.
-
 ## Acknowledgements
 
 Octoplex is built on and/or makes use of other free and open source software,

internal/app/app.go

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"cmp"
 	"context"
 	"errors"
 	"fmt"
@@ -18,10 +19,25 @@ import (
 	"github.com/docker/docker/client"
 )
 
-// RunParams holds the parameters for running the application.
+// App is an instance of the app.
-type RunParams struct {
+type App struct {
+	cfg                config.Config
+	configService      *config.Service
+	eventBus           *event.Bus
+	dispatchC          chan event.Command
+	dockerClient       container.DockerClient
+	screen             *terminal.Screen // Screen may be nil.
+	clipboardAvailable bool
+	configFilePath     string
+	buildInfo          domain.BuildInfo
+	logger             *slog.Logger
+}
+
+// Params holds the parameters for running the application.
+type Params struct {
 	ConfigService      *config.Service
 	DockerClient       container.DockerClient
+	ChanSize           int
 	Screen             *terminal.Screen // Screen may be nil.
 	ClipboardAvailable bool
 	ConfigFilePath     string
@@ -29,31 +45,44 @@ type RunParams struct {
 	Logger             *slog.Logger
 }
 
+// defaultChanSize is the default size of the dispatch channel.
+const defaultChanSize = 64
+
+// New creates a new application instance.
+func New(params Params) *App {
+	return &App{
+		cfg:                params.ConfigService.Current(),
+		configService:      params.ConfigService,
+		eventBus:           event.NewBus(params.Logger.With("component", "event_bus")),
+		dispatchC:          make(chan event.Command, cmp.Or(params.ChanSize, defaultChanSize)),
+		dockerClient:       params.DockerClient,
+		screen:             params.Screen,
+		clipboardAvailable: params.ClipboardAvailable,
+		configFilePath:     params.ConfigFilePath,
+		buildInfo:          params.BuildInfo,
+		logger:             params.Logger,
+	}
+}
+
 // Run starts the application, and blocks until it exits.
-func Run(ctx context.Context, params RunParams) error {
+func (a *App) Run(ctx context.Context) error {
-	logger := params.Logger
-	eventBus := event.NewBus(logger.With("component", "event_bus"))
-
-	// cfg is the current configuration of the application, as reflected in the
-	// config file.
-	cfg := params.ConfigService.Current()
-
 	// state is the current state of the application, as reflected in the UI.
 	state := new(domain.AppState)
-	applyConfig(cfg, state)
+	applyConfig(a.cfg, state)
 
 	// Ensure there is at least one active source.
-	if !cfg.Sources.MediaServer.RTMP.Enabled && !cfg.Sources.MediaServer.RTMPS.Enabled {
+	if !a.cfg.Sources.MediaServer.RTMP.Enabled && !a.cfg.Sources.MediaServer.RTMPS.Enabled {
 		return errors.New("config: either sources.mediaServer.rtmp.enabled or sources.mediaServer.rtmps.enabled must be set")
 	}
 
 	ui, err := terminal.StartUI(ctx, terminal.StartParams{
-		EventBus:           eventBus,
+		EventBus:           a.eventBus,
-		Screen:             params.Screen,
+		Dispatcher:         func(cmd event.Command) { a.dispatchC <- cmd },
-		ClipboardAvailable: params.ClipboardAvailable,
+		Screen:             a.screen,
-		ConfigFilePath:     params.ConfigFilePath,
+		ClipboardAvailable: a.clipboardAvailable,
-		BuildInfo:          params.BuildInfo,
+		ConfigFilePath:     a.configFilePath,
-		Logger:             logger.With("component", "ui"),
+		BuildInfo:          a.buildInfo,
+		Logger:             a.logger.With("component", "ui"),
 	})
 	if err != nil {
 		return fmt.Errorf("start terminal user interface: %w", err)
@@ -69,50 +98,56 @@ func Run(ctx context.Context, params RunParams) error {
 	// It is only needed for integration tests when rendering modals before the
 	// main loop starts. It would be nice to remove this but the risk/impact on
 	// non-test code is pretty low.
-	emptyUI := func() { ui.SetState(domain.AppState{}) }
+	emptyUI := func() {
+		a.eventBus.Send(event.AppStateChangedEvent{State: domain.AppState{}})
+	}
 
-	containerClient, err := container.NewClient(ctx, params.DockerClient, logger.With("component", "container_client"))
+	containerClient, err := container.NewClient(ctx, a.dockerClient, a.logger.With("component", "container_client"))
 	if err != nil {
 		err = fmt.Errorf("create container client: %w", err)
 
-		var errString string
+		var msg string
 		if client.IsErrConnectionFailed(err) {
-			errString = "Could not connect to Docker. Is Docker installed and running?"
+			msg = "Could not connect to Docker. Is Docker installed and running?"
 		} else {
-			errString = err.Error()
+			msg = err.Error()
 		}
-		ui.ShowFatalErrorModal(errString)
+		a.eventBus.Send(event.FatalErrorOccurredEvent{Message: msg})
 
 		emptyUI()
-		<-ui.C()
+		<-a.dispatchC
 		return err
 	}
 	defer containerClient.Close()
 
-	updateUI := func() { ui.SetState(*state) }
+	updateUI := func() {
+		// The state is mutable so can't be passed into another goroutine
+		// without cloning it first.
+		a.eventBus.Send(event.AppStateChangedEvent{State: state.Clone()})
+	}
 	updateUI()
 
 	var tlsCertPath, tlsKeyPath string
-	if cfg.Sources.MediaServer.TLS != nil {
+	if a.cfg.Sources.MediaServer.TLS != nil {
-		tlsCertPath = cfg.Sources.MediaServer.TLS.CertPath
+		tlsCertPath = a.cfg.Sources.MediaServer.TLS.CertPath
-		tlsKeyPath = cfg.Sources.MediaServer.TLS.KeyPath
+		tlsKeyPath = a.cfg.Sources.MediaServer.TLS.KeyPath
 	}
 
 	srv, err := mediaserver.NewActor(ctx, mediaserver.NewActorParams{
-		RTMPAddr:        buildNetAddr(cfg.Sources.MediaServer.RTMP),
+		RTMPAddr:        buildNetAddr(a.cfg.Sources.MediaServer.RTMP),
-		RTMPSAddr:       buildNetAddr(cfg.Sources.MediaServer.RTMPS),
+		RTMPSAddr:       buildNetAddr(a.cfg.Sources.MediaServer.RTMPS),
-		Host:            cfg.Sources.MediaServer.Host,
+		Host:            a.cfg.Sources.MediaServer.Host,
 		TLSCertPath:     tlsCertPath,
 		TLSKeyPath:      tlsKeyPath,
-		StreamKey:       mediaserver.StreamKey(cfg.Sources.MediaServer.StreamKey),
+		StreamKey:       mediaserver.StreamKey(a.cfg.Sources.MediaServer.StreamKey),
 		ContainerClient: containerClient,
-		Logger:          logger.With("component", "mediaserver"),
+		Logger:          a.logger.With("component", "mediaserver"),
 	})
 	if err != nil {
 		err = fmt.Errorf("create mediaserver: %w", err)
-		ui.ShowFatalErrorModal(err.Error())
+		a.eventBus.Send(event.FatalErrorOccurredEvent{Message: err.Error()})
 		emptyUI()
-		<-ui.C()
+		<-a.dispatchC
 		return err
 	}
 	defer srv.Close()
@@ -120,7 +155,7 @@ func Run(ctx context.Context, params RunParams) error {
 	repl := replicator.StartActor(ctx, replicator.StartActorParams{
 		SourceURL:       srv.RTMPInternalURL(),
 		ContainerClient: containerClient,
-		Logger:          logger.With("component", "replicator"),
+		Logger:          a.logger.With("component", "replicator"),
 	})
 	defer repl.Close()
 
@@ -128,87 +163,45 @@ func Run(ctx context.Context, params RunParams) error {
 	uiUpdateT := time.NewTicker(uiUpdateInterval)
 	defer uiUpdateT.Stop()
 
-	startupCheckC := doStartupCheck(ctx, containerClient, ui.ShowStartupCheckModal)
+	startMediaServerC := make(chan struct{}, 1)
+	if ok, startupErr := doStartupCheck(ctx, containerClient, a.eventBus); startupErr != nil {
+		startupErr = fmt.Errorf("startup check: %w", startupErr)
+		a.eventBus.Send(event.FatalErrorOccurredEvent{Message: startupErr.Error()})
+		<-a.dispatchC
+		return startupErr
+	} else if ok {
+		startMediaServerC <- struct{}{}
+	}
 
 	for {
 		select {
-		case err := <-startupCheckC:
+		case <-startMediaServerC:
-			if errors.Is(err, errStartupCheckUserQuit) {
-				return nil
-			} else if err != nil {
-				return fmt.Errorf("startup check: %w", err)
-			} else {
-				startupCheckC = nil
-
 			if err = srv.Start(ctx); err != nil {
 				return fmt.Errorf("start mediaserver: %w", err)
 			}
 
-				eventBus.Send(event.MediaServerStartedEvent{RTMPURL: srv.RTMPURL(), RTMPSURL: srv.RTMPSURL()})
+			a.eventBus.Send(event.MediaServerStartedEvent{RTMPURL: srv.RTMPURL(), RTMPSURL: srv.RTMPSURL()})
-			}
+		case <-a.configService.C():
-		case <-params.ConfigService.C():
 			// No-op, config updates are handled synchronously for now.
-		case cmd, ok := <-ui.C():
+		case cmd := <-a.dispatchC:
-			if !ok {
+			if _, err := a.handleCommand(ctx, cmd, state, repl, containerClient, startMediaServerC); errors.Is(err, errExit) {
-				// TODO: keep UI open until all containers have closed
-				logger.Info("UI closed")
-				return nil
-			}
-
-			logger.Debug("Command received", "cmd", cmd.Name())
-			switch c := cmd.(type) {
-			case domain.CommandAddDestination:
-				newCfg := cfg
-				newCfg.Destinations = append(newCfg.Destinations, config.Destination{
-					Name: c.DestinationName,
-					URL:  c.URL,
-				})
-				if err := params.ConfigService.SetConfig(newCfg); err != nil {
-					logger.Error("Config update failed", "err", err)
-					ui.ConfigUpdateFailed(err)
-					continue
-				}
-				cfg = newCfg
-				handleConfigUpdate(cfg, state, ui)
-				ui.DestinationAdded()
-			case domain.CommandRemoveDestination:
-				repl.StopDestination(c.URL) // no-op if not live
-				newCfg := cfg
-				newCfg.Destinations = slices.DeleteFunc(newCfg.Destinations, func(dest config.Destination) bool {
-					return dest.URL == c.URL
-				})
-				if err := params.ConfigService.SetConfig(newCfg); err != nil {
-					logger.Error("Config update failed", "err", err)
-					ui.ConfigUpdateFailed(err)
-					continue
-				}
-				cfg = newCfg
-				handleConfigUpdate(cfg, state, ui)
-				ui.DestinationRemoved()
-			case domain.CommandStartDestination:
-				if !state.Source.Live {
-					ui.ShowSourceNotLiveModal()
-					continue
-				}
-
-				repl.StartDestination(c.URL)
-			case domain.CommandStopDestination:
-				repl.StopDestination(c.URL)
-			case domain.CommandQuit:
 				return nil
+			} else if err != nil {
+				return fmt.Errorf("handle command: %w", err)
 			}
 		case <-uiUpdateT.C:
 			updateUI()
 		case serverState := <-srv.C():
-			logger.Debug("Server state received", "state", serverState)
+			a.logger.Debug("Server state received", "state", serverState)
 			applyServerState(serverState, state)
 			updateUI()
 		case replState := <-repl.C():
-			logger.Debug("Replicator state received", "state", replState)
+			a.logger.Debug("Replicator state received", "state", replState)
 			destErrors := applyReplicatorState(replState, state)
 
 			for _, destError := range destErrors {
-				handleDestError(destError, repl, ui)
+				a.eventBus.Send(event.DestinationStreamExitedEvent{Name: destError.name, Err: destError.err})
+				repl.StopDestination(destError.url)
 			}
 
 			updateUI()
@@ -216,10 +209,100 @@ func Run(ctx context.Context, params RunParams) error {
 	}
 }
 
-// handleConfigUpdate applies the config to the app state, and updates the UI.
+type syncCommand struct {
-func handleConfigUpdate(cfg config.Config, appState *domain.AppState, ui *terminal.UI) {
+	event.Command
-	applyConfig(cfg, appState)
+
-	ui.SetState(*appState)
+	done chan<- event.Event
+}
+
+// Dispatch dispatches a command to be executed synchronously.
+func (a *App) Dispatch(cmd event.Command) event.Event {
+	ch := make(chan event.Event, 1)
+	a.dispatchC <- syncCommand{Command: cmd, done: ch}
+	return <-ch
+}
+
+// errExit is an error that indicates the app should exit.
+var errExit = errors.New("exit")
+
+// handleCommand handles an incoming command. It may return an Event which will
+// already have been published to the event bus, but which is returned for the
+// benefit of synchronous callers. The event may be nil. It may also publish
+// other events to the event bus which are not returned. Currently the only
+// error that may be returned is [errExit], which indicates to the main event
+// loop that the app should exit.
+func (a *App) handleCommand(
+	ctx context.Context,
+	cmd event.Command,
+	state *domain.AppState,
+	repl *replicator.Actor,
+	containerClient *container.Client,
+	startMediaServerC chan struct{},
+) (evt event.Event, _ error) {
+	a.logger.Debug("Command received", "cmd", cmd.Name())
+	defer func() {
+		if evt != nil {
+			a.eventBus.Send(evt)
+		}
+		if c, ok := cmd.(syncCommand); ok {
+			c.done <- evt
+		}
+	}()
+
+	switch c := cmd.(type) {
+	case event.CommandAddDestination:
+		newCfg := a.cfg
+		newCfg.Destinations = append(newCfg.Destinations, config.Destination{
+			Name: c.DestinationName,
+			URL:  c.URL,
+		})
+		if err := a.configService.SetConfig(newCfg); err != nil {
+			a.logger.Error("Add destination failed", "err", err)
+			return event.AddDestinationFailedEvent{Err: err}, nil
+		}
+		a.cfg = newCfg
+		a.handleConfigUpdate(state)
+		a.eventBus.Send(event.DestinationAddedEvent{URL: c.URL})
+	case event.CommandRemoveDestination:
+		repl.StopDestination(c.URL) // no-op if not live
+		newCfg := a.cfg
+		newCfg.Destinations = slices.DeleteFunc(newCfg.Destinations, func(dest config.Destination) bool {
+			return dest.URL == c.URL
+		})
+		if err := a.configService.SetConfig(newCfg); err != nil {
+			a.logger.Error("Remove destination failed", "err", err)
+			a.eventBus.Send(event.RemoveDestinationFailedEvent{Err: err})
+			break
+		}
+		a.cfg = newCfg
+		a.handleConfigUpdate(state)
+		a.eventBus.Send(event.DestinationRemovedEvent{URL: c.URL}) //nolint:gosimple
+	case event.CommandStartDestination:
+		if !state.Source.Live {
+			a.eventBus.Send(event.StartDestinationFailedEvent{})
+			break
+		}
+
+		repl.StartDestination(c.URL)
+	case event.CommandStopDestination:
+		repl.StopDestination(c.URL)
+	case event.CommandCloseOtherInstance:
+		if err := closeOtherInstances(ctx, containerClient); err != nil {
+			return nil, fmt.Errorf("close other instances: %w", err)
+		}
+
+		startMediaServerC <- struct{}{}
+	case event.CommandQuit:
+		return nil, errExit
+	}
+
+	return nil, nil
+}
+
+// handleConfigUpdate applies the config to the app state, and sends an AppStateChangedEvent.
+func (a *App) handleConfigUpdate(appState *domain.AppState) {
+	applyConfig(a.cfg, appState)
+	a.eventBus.Send(event.AppStateChangedEvent{State: appState.Clone()})
 }
 
 // applyServerState applies the current server state to the app state.
@@ -265,13 +348,6 @@ func applyReplicatorState(replState replicator.State, appState *domain.AppState)
 	return errorsToDisplay
 }
 
-// handleDestError displays a modal to the user, and stops the destination.
-func handleDestError(destError destinationError, repl *replicator.Actor, ui *terminal.UI) {
-	ui.ShowDestinationErrorModal(destError.name, destError.err)
-
-	repl.StopDestination(destError.url)
-}
-
 // applyConfig applies the config to the app state. For now we only set the
 // destinations.
 func applyConfig(cfg config.Config, appState *domain.AppState) {
@@ -301,40 +377,34 @@ func resolveDestinations(destinations []domain.Destination, inDestinations []con
 	return destinations[:len(inDestinations)]
 }
 
-var errStartupCheckUserQuit = errors.New("user quit startup check modal")
-
 // doStartupCheck performs a startup check to see if there are any existing app
 // containers.
 //
-// It returns a channel that will be closed, possibly after receiving an error.
+// It returns a bool if the check is clear. If the bool is false, then
-// If the error is non-nil the app must not be started. If the error is
+// startup should be paused until the choice selected by the user is received
-// [errStartupCheckUserQuit], the user voluntarily quit the startup check
+// via a command.
-// modal.
+func doStartupCheck(ctx context.Context, containerClient *container.Client, eventBus *event.Bus) (bool, error) {
-func doStartupCheck(ctx context.Context, containerClient *container.Client, showModal func() bool) <-chan error {
-	ch := make(chan error, 1)
-
-	go func() {
-		defer close(ch)
-
 	if exists, err := containerClient.ContainerRunning(ctx, container.AllContainers()); err != nil {
-			ch <- fmt.Errorf("check existing containers: %w", err)
+		return false, fmt.Errorf("check existing containers: %w", err)
 	} else if exists {
-			if showModal() {
+		eventBus.Send(event.OtherInstanceDetectedEvent{})
-				if err = containerClient.RemoveContainers(ctx, container.AllContainers()); err != nil {
-					ch <- fmt.Errorf("remove existing containers: %w", err)
-					return
-				}
-				if err = containerClient.RemoveUnusedNetworks(ctx); err != nil {
-					ch <- fmt.Errorf("remove unused networks: %w", err)
-					return
-				}
-			} else {
-				ch <- errStartupCheckUserQuit
-			}
-		}
-	}()
 
-	return ch
+		return false, nil
+	}
+
+	return true, nil
+}
+
+func closeOtherInstances(ctx context.Context, containerClient *container.Client) error {
+	if err := containerClient.RemoveContainers(ctx, container.AllContainers()); err != nil {
+		return fmt.Errorf("remove existing containers: %w", err)
+	}
+
+	if err := containerClient.RemoveUnusedNetworks(ctx); err != nil {
+		return fmt.Errorf("remove unused networks: %w", err)
+	}
+
+	return nil
 }
 
 // buildNetAddr builds a [mediaserver.OptionalNetAddr] from the config.

internal/app/integration_helpers_test.go

@@ -31,10 +31,10 @@ func buildAppParams(
 	screen tcell.SimulationScreen,
 	screenCaptureC chan<- terminal.ScreenCapture,
 	logger *slog.Logger,
-) app.RunParams {
+) app.Params {
 	t.Helper()
 
-	return app.RunParams{
+	return app.Params{
 		ConfigService: configService,
 		DockerClient:  dockerClient,
 		Screen: &terminal.Screen{
@@ -150,25 +150,36 @@ func printScreen(t *testing.T, getContents func() []string, label string) {
 func sendKey(t *testing.T, screen tcell.SimulationScreen, key tcell.Key, ch rune) {
 	t.Helper()
 
-	screen.InjectKey(key, ch, tcell.ModNone)
+	const (
-	time.Sleep(50 * time.Millisecond)
+		waitTime = 50 * time.Millisecond
+		maxTries = 50
+	)
+
+	for i := 0; i < maxTries; i++ {
+		if err := screen.PostEvent(tcell.NewEventKey(key, ch, tcell.ModNone)); err != nil {
+			time.Sleep(waitTime)
+		} else {
+			return
+		}
+	}
+
+	t.Fatalf("Failed to send key event after %d tries", maxTries)
 }
 
 func sendKeys(t *testing.T, screen tcell.SimulationScreen, keys string) {
 	t.Helper()
 
-	screen.InjectKeyBytes([]byte(keys))
+	for _, ch := range keys {
-	time.Sleep(500 * time.Millisecond)
+		sendKey(t, screen, tcell.KeyRune, ch)
+	}
 }
 
 func sendBackspaces(t *testing.T, screen tcell.SimulationScreen, n int) {
 	t.Helper()
 
 	for range n {
-		screen.InjectKey(tcell.KeyBackspace, ' ', tcell.ModNone)
+		sendKey(t, screen, tcell.KeyBackspace, 0)
-		time.Sleep(50 * time.Millisecond)
 	}
-	time.Sleep(500 * time.Millisecond)
 }
 
 // kickFirstRTMPConn kicks the first RTMP connection from the mediaMTX server.

internal/app/integration_test.go

@@ -132,7 +132,7 @@ func testIntegration(t *testing.T, mediaServerConfig config.MediaServerSource) {
 			done <- struct{}{}
 		}()
 
-		err := app.Run(ctx, app.RunParams{
+		require.NoError(t, app.New(app.Params{
 			ConfigService: configService,
 			DockerClient:  dockerClient,
 			Screen: &terminal.Screen{
@@ -144,8 +144,7 @@ func testIntegration(t *testing.T, mediaServerConfig config.MediaServerSource) {
 			ClipboardAvailable: false,
 			BuildInfo:          domain.BuildInfo{Version: "0.0.1", GoVersion: "go1.16.3"},
 			Logger:             logger,
-		})
+		}).Run(ctx))
-		require.NoError(t, err)
 	}()
 
 	require.EventuallyWithT(
@@ -182,11 +181,11 @@ func testIntegration(t *testing.T, mediaServerConfig config.MediaServerSource) {
 	// Add a second destination in-app:
 	sendKey(t, screen, tcell.KeyRune, 'a')
 
-	sendBackspaces(t, screen, 30)
+	sendBackspaces(t, screen, 10)
 	sendKeys(t, screen, "Local server 2")
 	sendKey(t, screen, tcell.KeyTab, ' ')
 
-	sendBackspaces(t, screen, 30)
+	sendBackspaces(t, screen, 10)
 	sendKeys(t, screen, destURL2)
 	sendKey(t, screen, tcell.KeyTab, ' ')
 	sendKey(t, screen, tcell.KeyEnter, ' ')
@@ -320,7 +319,7 @@ func TestIntegrationCustomHost(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+		require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 	}()
 
 	time.Sleep(time.Second)
@@ -391,7 +390,7 @@ func TestIntegrationCustomTLSCerts(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+		require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 	}()
 
 	require.EventuallyWithT(
@@ -472,7 +471,7 @@ func TestIntegrationRestartDestination(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+		require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 	}()
 
 	require.EventuallyWithT(
@@ -609,7 +608,7 @@ func TestIntegrationStartDestinationFailed(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+		require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 	}()
 
 	require.EventuallyWithT(
@@ -682,7 +681,7 @@ func TestIntegrationDestinationValidations(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+		require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 	}()
 
 	require.EventuallyWithT(
@@ -824,7 +823,7 @@ func TestIntegrationStartupCheck(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+		require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 	}()
 
 	require.EventuallyWithT(
@@ -893,7 +892,7 @@ func TestIntegrationMediaServerError(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+		require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 	}()
 
 	require.EventuallyWithT(
@@ -934,7 +933,7 @@ func TestIntegrationDockerClientError(t *testing.T) {
 
 		require.EqualError(
 			t,
-			app.Run(ctx, buildAppParams(t, configService, &dockerClient, screen, screenCaptureC, logger)),
+			app.New(buildAppParams(t, configService, &dockerClient, screen, screenCaptureC, logger)).Run(ctx),
 			"create container client: network create: boom",
 		)
 	}()
@@ -974,7 +973,7 @@ func TestIntegrationDockerConnectionError(t *testing.T) {
 			done <- struct{}{}
 		}()
 
-		err := app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger))
+		err := app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx)
 		require.ErrorContains(t, err, "dial tcp: lookup docker.example.com")
 		require.ErrorContains(t, err, "no such host")
 	}()
@@ -1070,7 +1069,7 @@ func TestIntegrationCopyURLs(t *testing.T) {
 					done <- struct{}{}
 				}()
 
-				require.NoError(t, app.Run(ctx, buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)))
+				require.NoError(t, app.New(buildAppParams(t, configService, dockerClient, screen, screenCaptureC, logger)).Run(ctx))
 			}()
 
 			time.Sleep(3 * time.Second)

internal/domain/events.go

@@ -1 +0,0 @@
-package domain

internal/event/bus.go

@@ -7,29 +7,9 @@ import (
 
 const defaultChannelSize = 64
 
-type Name string
-
-const (
-	EventNameMediaServerStarted Name = "media_server_started"
-)
-
-type Event interface {
-	name() Name
-}
-
-// MediaServerStartedEvent is emitted when the mediaserver component starts successfully.
-type MediaServerStartedEvent struct {
-	RTMPURL  string
-	RTMPSURL string
-}
-
-func (e MediaServerStartedEvent) name() Name {
-	return "media_server_started"
-}
-
 // Bus is an event bus.
 type Bus struct {
-	consumers map[Name][]chan Event
+	consumers []chan Event
 	mu        sync.Mutex
 	logger    *slog.Logger
 }
@@ -37,18 +17,17 @@ type Bus struct {
 // NewBus returns a new event bus.
 func NewBus(logger *slog.Logger) *Bus {
 	return &Bus{
-		consumers: make(map[Name][]chan Event),
 		logger: logger,
 	}
 }
 
-// Register registers a consumer for a given event.
+// Register registers a consumer for all events.
-func (b *Bus) Register(name Name) <-chan Event {
+func (b *Bus) Register() <-chan Event {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
 	ch := make(chan Event, defaultChannelSize)
-	b.consumers[name] = append(b.consumers[name], ch)
+	b.consumers = append(b.consumers, ch)
 	return ch
 }
 
@@ -60,7 +39,7 @@ func (b *Bus) Send(evt Event) {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
-	for _, ch := range b.consumers[evt.name()] {
+	for _, ch := range b.consumers {
 		select {
 		case ch <- evt:
 		default:

internal/event/bus_test.go

@@ -11,8 +11,8 @@ import (
 func TestBus(t *testing.T) {
 	bus := event.NewBus(testhelpers.NewTestLogger(t))
 
-	ch1 := bus.Register(event.EventNameMediaServerStarted)
+	ch1 := bus.Register()
-	ch2 := bus.Register(event.EventNameMediaServerStarted)
+	ch2 := bus.Register()
 
 	evt := event.MediaServerStartedEvent{
 		RTMPURL:  "rtmp://rtmp.example.com/live",

internal/event/command.go

@@ -1,4 +1,4 @@
-package domain
+package event
 
 // CommandAddDestination adds a destination.
 type CommandAddDestination struct {
@@ -41,6 +41,14 @@ func (c CommandStopDestination) Name() string {
 	return "stop_destination"
 }
 
+// CommandCloseOtherInstance closes the other instance of the application.
+type CommandCloseOtherInstance struct{}
+
+// Name implements the Command interface.
+func (c CommandCloseOtherInstance) Name() string {
+	return "close_other_instance"
+}
+
 // CommandQuit quits the app.
 type CommandQuit struct{}
 

internal/event/events.go

@@ -0,0 +1,114 @@
+package event
+
+import "git.netflux.io/rob/octoplex/internal/domain"
+
+type Name string
+
+const (
+	EventNameAppStateChanged         Name = "app_state_changed"
+	EventNameDestinationAdded        Name = "destination_added"
+	EventNameAddDestinationFailed    Name = "add_destination_failed"
+	EventNameDestinationStreamExited Name = "destination_stream_exited"
+	EventNameStartDestinationFailed  Name = "start_destination_failed"
+	EventNameDestinationRemoved      Name = "destination_removed"
+	EventNameRemoveDestinationFailed Name = "remove_destination_failed"
+	EventNameFatalErrorOccurred      Name = "fatal_error_occurred"
+	EventNameOtherInstanceDetected   Name = "other_instance_detected"
+	EventNameMediaServerStarted      Name = "media_server_started"
+)
+
+// Event represents something which happened in the appllication.
+type Event interface {
+	name() Name
+}
+
+// AppStateChangedEvent is emitted when the application state changes.
+type AppStateChangedEvent struct {
+	State domain.AppState
+}
+
+func (e AppStateChangedEvent) name() Name {
+	return EventNameAppStateChanged
+}
+
+// DestinationAddedEvent is emitted when a destination is successfully added.
+type DestinationAddedEvent struct {
+	URL string
+}
+
+func (e DestinationAddedEvent) name() Name {
+	return EventNameDestinationAdded
+}
+
+// AddDestinationFailedEvent is emitted when a destination fails to be added.
+type AddDestinationFailedEvent struct {
+	Err error
+}
+
+func (e AddDestinationFailedEvent) name() Name {
+	return EventNameAddDestinationFailed
+}
+
+// DestinationStreamExitedEvent is emitted when a destination goes off-air unexpectedly.
+type DestinationStreamExitedEvent struct {
+	Name string
+	Err  error
+}
+
+func (e DestinationStreamExitedEvent) name() Name {
+	return EventNameDestinationStreamExited
+}
+
+// StartDestinationFailedEvent is emitted when a destination fails to start.
+type StartDestinationFailedEvent struct{}
+
+func (e StartDestinationFailedEvent) name() Name {
+	return EventNameStartDestinationFailed
+}
+
+// DestinationRemovedEvent is emitted when a destination is successfully
+// removed.
+type DestinationRemovedEvent struct {
+	URL string
+}
+
+func (e DestinationRemovedEvent) name() Name {
+	return EventNameDestinationRemoved
+}
+
+// RemoveDestinationFailedEvent is emitted when a destination fails to be
+// removed.
+type RemoveDestinationFailedEvent struct {
+	Err error
+}
+
+func (e RemoveDestinationFailedEvent) name() Name {
+	return EventNameRemoveDestinationFailed
+}
+
+// FatalErrorOccurredEvent is emitted when a fatal application
+// error occurs.
+type FatalErrorOccurredEvent struct {
+	Message string
+}
+
+// OtherInstanceDetectedEvent is emitted when the app launches and detects another instance.
+type OtherInstanceDetectedEvent struct{}
+
+func (e OtherInstanceDetectedEvent) name() Name {
+	return EventNameOtherInstanceDetected
+}
+
+func (e FatalErrorOccurredEvent) name() Name {
+	return "fatal_error_occurred"
+}
+
+// MediaServerStartedEvent is emitted when the mediaserver component starts successfully.
+type MediaServerStartedEvent struct {
+	RTMPURL  string
+	RTMPSURL string
+}
+
+func (e MediaServerStartedEvent) name() Name {
+	return "media_server_started"
+}

internal/terminal/terminal.go

@@ -42,7 +42,7 @@ const (
 // UI is responsible for managing the terminal user interface.
 type UI struct {
 	eventBus           *event.Bus
-	commandC           chan domain.Command
+	dispatch           func(event.Command)
 	clipboardAvailable bool
 	configFilePath     string
 	rtmpURL, rtmpsURL  string
@@ -96,7 +96,7 @@ type ScreenCapture struct {
 // interface.
 type StartParams struct {
 	EventBus           *event.Bus
-	ChanSize           int
+	Dispatcher         func(event.Command)
 	Logger             *slog.Logger
 	ClipboardAvailable bool
 	ConfigFilePath     string
@@ -104,13 +104,8 @@ type StartParams struct {
 	Screen             *Screen // Screen may be nil.
 }
 
-const defaultChanSize = 64
-
 // StartUI starts the terminal user interface.
 func StartUI(ctx context.Context, params StartParams) (*UI, error) {
-	chanSize := cmp.Or(params.ChanSize, defaultChanSize)
-	commandCh := make(chan domain.Command, chanSize)
-
 	app := tview.NewApplication()
 
 	var screen tcell.Screen
@@ -213,8 +208,8 @@ func StartUI(ctx context.Context, params StartParams) (*UI, error) {
 	app.EnableMouse(false)
 
 	ui := &UI{
-		commandC:           commandCh,
 		eventBus:           params.EventBus,
+		dispatch:           params.Dispatcher,
 		clipboardAvailable: params.ClipboardAvailable,
 		configFilePath:     params.ConfigFilePath,
 		buildInfo:          params.BuildInfo,
@@ -271,15 +266,13 @@ func (ui *UI) renderAboutView() {
 	ui.aboutView.AddItem(tview.NewTextView().SetDynamicColors(true).SetText("[grey]?[-]        About"), 1, 0, false)
 }
 
-// C returns a channel that receives commands from the user interface.
-func (ui *UI) C() <-chan domain.Command {
-	return ui.commandC
-}
-
 func (ui *UI) run(ctx context.Context) {
-	defer close(ui.commandC)
+	defer func() {
+		// Ensure the application is stopped when the UI is closed.
+		ui.dispatch(event.CommandQuit{})
+	}()
 
-	mediaServerStartedC := ui.eventBus.Register(event.EventNameMediaServerStarted)
+	eventC := ui.eventBus.Register()
 
 	uiDone := make(chan struct{})
 	go func() {
@@ -294,8 +287,34 @@ func (ui *UI) run(ctx context.Context) {
 
 	for {
 		select {
-		case evt := <-mediaServerStartedC:
+		case evt := <-eventC:
-			ui.handleMediaServerStarted(evt.(event.MediaServerStartedEvent))
+			ui.app.QueueUpdateDraw(func() {
+				switch evt := evt.(type) {
+				case event.AppStateChangedEvent:
+					ui.handleAppStateChanged(evt)
+				case event.DestinationAddedEvent:
+					ui.handleDestinationAdded(evt)
+				case event.StartDestinationFailedEvent:
+					ui.handleStartDestinationFailed(evt)
+				case event.AddDestinationFailedEvent:
+					ui.handleDestinationEventError(evt.Err)
+				case event.DestinationStreamExitedEvent:
+					ui.handleDestinationStreamExited(evt)
+				case event.DestinationRemovedEvent:
+					ui.handleDestinationRemoved(evt)
+				case event.RemoveDestinationFailedEvent:
+					ui.handleDestinationEventError(evt.Err)
+				case event.OtherInstanceDetectedEvent:
+					ui.handleOtherInstanceDetected(evt)
+				case event.MediaServerStartedEvent:
+					ui.handleMediaServerStarted(evt)
+				case event.FatalErrorOccurredEvent:
+					ui.handleFatalErrorOccurred(evt)
+				default:
+					ui.logger.Warn("unhandled event", "event", evt)
+				}
+
+			})
 		case <-ctx.Done():
 			return
 		case <-uiDone:
@@ -310,7 +329,7 @@ func (ui *UI) handleMediaServerStarted(evt event.MediaServerStartedEvent) {
 	ui.rtmpsURL = evt.RTMPSURL
 	ui.mu.Unlock()
 
-	ui.app.QueueUpdateDraw(ui.renderAboutView)
+	ui.renderAboutView()
 }
 
 func (ui *UI) inputCaptureHandler(event *tcell.EventKey) *tcell.EventKey {
@@ -381,28 +400,17 @@ func (ui *UI) fkeyHandler(key tcell.Key) {
 	}
 }
 
-func (ui *UI) ShowSourceNotLiveModal() {
+func (ui *UI) handleStartDestinationFailed(event.StartDestinationFailedEvent) {
-	ui.app.QueueUpdateDraw(func() {
 	ui.showModal(
-			pageNameModalNotLive,
+		pageNameModalStartDestinationFailed,
 		"Waiting for stream.\n\nStart streaming to a source URL then try again.",
 		[]string{"Ok"},
 		false,
 		nil,
 	)
-	})
 }
 
-// ShowStartupCheckModal shows a modal dialog to the user, asking if they want
+func (ui *UI) handleOtherInstanceDetected(event.OtherInstanceDetectedEvent) {
-// to kill a running instance of Octoplex.
-//
-// The method will block until the user has made a choice, after which the
-// channel will receive true if the user wants to quit the other instance, or
-// false to quit this instance.
-func (ui *UI) ShowStartupCheckModal() bool {
-	done := make(chan bool)
-
-	ui.app.QueueUpdateDraw(func() {
 	ui.showModal(
 		pageNameModalStartupCheck,
 		"Another instance of Octoplex may already be running.\n\nPressing continue will close that instance. Continue?",
@@ -410,50 +418,41 @@ func (ui *UI) ShowStartupCheckModal() bool {
 		false,
 		func(buttonIndex int, _ string) {
 			if buttonIndex == 0 {
-					done <- true
+				ui.dispatch(event.CommandCloseOtherInstance{})
 			} else {
-					done <- false
+				ui.dispatch(event.CommandQuit{})
 			}
 		},
 	)
-	})
-
-	return <-done
 }
 
-func (ui *UI) ShowDestinationErrorModal(name string, err error) {
+func (ui *UI) handleDestinationStreamExited(evt event.DestinationStreamExitedEvent) {
-	ui.app.QueueUpdateDraw(func() {
 	ui.showModal(
 		pageNameModalDestinationError,
 		fmt.Sprintf(
 			"Streaming to %s failed:\n\n%s",
-				cmp.Or(name, "this destination"),
+			cmp.Or(evt.Name, "this destination"),
-				err,
+			evt.Err,
 		),
 		[]string{"Ok"},
 		true,
 		nil,
 	)
-	})
 }
 
-// ShowFatalErrorModal displays the provided error. It sends a CommandQuit to the
+func (ui *UI) handleFatalErrorOccurred(evt event.FatalErrorOccurredEvent) {
-// command channel when the user selects the Quit button.
-func (ui *UI) ShowFatalErrorModal(errString string) {
-	ui.app.QueueUpdateDraw(func() {
 	ui.showModal(
 		pageNameModalFatalError,
 		fmt.Sprintf(
 			"An error occurred:\n\n%s",
-				errString,
+			evt.Message,
 		),
 		[]string{"Quit"},
 		false,
 		func(int, string) {
-				ui.commandC <- domain.CommandQuit{}
+			ui.dispatch(event.CommandQuit{})
 		},
 	)
-	})
 }
 
 func (ui *UI) afterDrawHandler(screen tcell.Screen) {
@@ -484,8 +483,9 @@ func (ui *UI) captureScreen(screen tcell.Screen) {
 	}
 }
 
-// SetState sets the state of the terminal user interface.
+func (ui *UI) handleAppStateChanged(evt event.AppStateChangedEvent) {
-func (ui *UI) SetState(state domain.AppState) {
+	state := evt.State
+
 	if state.Source.ExitReason != "" {
 		ui.handleMediaServerClosed(state.Source.ExitReason)
 	}
@@ -500,10 +500,7 @@ func (ui *UI) SetState(state domain.AppState) {
 	ui.hasDestinations = len(state.Destinations) > 0
 	ui.mu.Unlock()
 
-	// The state is mutable so can't be passed into QueueUpdateDraw, which
+	ui.redrawFromState(state)
-	// passes it to another goroutine, without cloning it first.
-	stateClone := state.Clone()
-	ui.app.QueueUpdateDraw(func() { ui.redrawFromState(stateClone) })
 }
 
 func (ui *UI) updatePullProgress(state domain.AppState) {
@@ -524,9 +521,7 @@ func (ui *UI) updatePullProgress(state domain.AppState) {
 	}
 
 	if len(pullingContainers) == 0 {
-		ui.app.QueueUpdateDraw(func() {
 		ui.hideModal(pageNameModalPullProgress)
-		})
 		return
 	}
 
@@ -540,7 +535,6 @@ func (ui *UI) updatePullProgress(state domain.AppState) {
 }
 
 func (ui *UI) updateProgressModal(container domain.Container) {
-	ui.app.QueueUpdateDraw(func() {
 	modalName := string(pageNameModalPullProgress)
 
 	var status string
@@ -562,7 +556,6 @@ func (ui *UI) updateProgressModal(container domain.Container) {
 	} else {
 		ui.pages.AddPage(modalName, ui.pullProgressModal, true, true)
 	}
-	})
 }
 
 // page names represent a specific page in the terminal user interface.
@@ -583,8 +576,8 @@ const (
 	pageNameModalQuit                   = "modal-quit"
 	pageNameModalRemoveDestination      = "modal-remove-destination"
 	pageNameModalSourceError            = "modal-source-error"
+	pageNameModalStartDestinationFailed = "modal-start-destination-failed"
 	pageNameModalStartupCheck           = "modal-startup-check"
-	pageNameModalNotLive           = "modal-not-live"
 )
 
 // modalVisible returns true if any modal, including the add destination form,
@@ -692,7 +685,6 @@ func (ui *UI) hideModal(pageName string) {
 }
 
 func (ui *UI) handleMediaServerClosed(exitReason string) {
-	ui.app.QueueUpdateDraw(func() {
 	if ui.pages.HasPage(pageNameModalSourceError) {
 		return
 	}
@@ -703,12 +695,11 @@ func (ui *UI) handleMediaServerClosed(exitReason string) {
 		SetBackgroundColor(tcell.ColorBlack).
 		SetTextColor(tcell.ColorWhite).
 		SetDoneFunc(func(int, string) {
-				ui.commandC <- domain.CommandQuit{}
+			ui.dispatch(event.CommandQuit{})
 		})
 	modal.SetBorderStyle(tcell.StyleDefault.Background(tcell.ColorBlack).Foreground(tcell.ColorWhite))
 
 	ui.pages.AddPage(pageNameModalSourceError, modal, true, true)
-	})
 }
 
 const dash = "—"
@@ -856,24 +847,6 @@ func (ui *UI) Close() {
 	ui.app.Stop()
 }
 
-func (ui *UI) ConfigUpdateFailed(err error) {
-	ui.app.QueueUpdateDraw(func() {
-		ui.showModal(
-			pageNameConfigUpdateFailed,
-			"Configuration update failed:\n\n"+err.Error(),
-			[]string{"Ok"},
-			false,
-			func(int, string) {
-				pageName, frontPage := ui.pages.GetFrontPage()
-				if pageName != pageNameAddDestination {
-					ui.logger.Warn("Unexpected page when configuration form closed", "page", pageName)
-				}
-				ui.app.SetFocus(frontPage)
-			},
-		)
-	})
-}
-
 func (ui *UI) addDestination() {
 	const (
 		inputLen        = 60
@@ -893,10 +866,10 @@ func (ui *UI) addDestination() {
 		AddInputField(inputLabelName, "My stream", inputLen, nil, nil).
 		AddInputField(inputLabelURL, "rtmp://", inputLen, nil, nil).
 		AddButton("Add", func() {
-			ui.commandC <- domain.CommandAddDestination{
+			ui.dispatch(event.CommandAddDestination{
 				DestinationName: form.GetFormItemByLabel(inputLabelName).(*tview.InputField).GetText(),
 				URL:             form.GetFormItemByLabel(inputLabelURL).(*tview.InputField).GetText(),
-			}
+			})
 		}).
 		AddButton("Cancel", func() {
 			ui.closeAddDestinationForm()
@@ -951,30 +924,42 @@ func (ui *UI) removeDestination() {
 		false,
 		func(buttonIndex int, _ string) {
 			if buttonIndex == 0 {
-				ui.commandC <- domain.CommandRemoveDestination{URL: url}
+				ui.dispatch(event.CommandRemoveDestination{URL: url})
 			}
 		},
 	)
 }
 
-// DestinationAdded should be called when a new destination is added.
+func (ui *UI) handleDestinationAdded(event.DestinationAddedEvent) {
-func (ui *UI) DestinationAdded() {
 	ui.mu.Lock()
 	ui.hasDestinations = true
 	ui.mu.Unlock()
 
-	ui.app.QueueUpdateDraw(func() {
 	ui.pages.HidePage(pageNameNoDestinations)
 	ui.closeAddDestinationForm()
 	ui.selectLastDestination()
-	})
 }
 
-// DestinationRemoved should be called when a destination is removed.
+func (ui *UI) handleDestinationRemoved(event.DestinationRemovedEvent) {
-func (ui *UI) DestinationRemoved() {
 	ui.selectPreviousDestination()
 }
 
+func (ui *UI) handleDestinationEventError(err error) {
+	ui.showModal(
+		pageNameConfigUpdateFailed,
+		"Configuration update failed:\n\n"+err.Error(),
+		[]string{"Ok"},
+		false,
+		func(int, string) {
+			pageName, frontPage := ui.pages.GetFrontPage()
+			if pageName != pageNameAddDestination {
+				ui.logger.Warn("Unexpected page when configuration form closed", "page", pageName)
+			}
+			ui.app.SetFocus(frontPage)
+		},
+	)
+}
+
 func (ui *UI) closeAddDestinationForm() {
 	var hasDestinations bool
 	ui.mu.Lock()
@@ -1015,12 +1000,12 @@ func (ui *UI) toggleDestination() {
 	switch ss {
 	case startStateNotStarted:
 		ui.urlsToStartState[url] = startStateStarting
-		ui.commandC <- domain.CommandStartDestination{URL: url}
+		ui.dispatch(event.CommandStartDestination{URL: url})
 	case startStateStarting:
 		// do nothing
 		return
 	case startStateStarted:
-		ui.commandC <- domain.CommandStopDestination{URL: url}
+		ui.dispatch(event.CommandStopDestination{URL: url})
 	}
 }
 
@@ -1073,7 +1058,7 @@ func (ui *UI) confirmQuit() {
 		false,
 		func(buttonIndex int, _ string) {
 			if buttonIndex == 0 {
-				ui.commandC <- domain.CommandQuit{}
+				ui.dispatch(event.CommandQuit{})
 			}
 		},
 	)

main.go

@@ -97,9 +97,7 @@ func run(ctx context.Context) error {
 		return fmt.Errorf("read build info: %w", err)
 	}
 
-	return app.Run(
+	app := app.New(app.Params{
-		ctx,
-		app.RunParams{
 		ConfigService:      configService,
 		DockerClient:       dockerClient,
 		ClipboardAvailable: clipboardAvailable,
@@ -111,8 +109,9 @@ func run(ctx context.Context) error {
 			Date:      date,
 		},
 		Logger: logger,
-		},
+	})
-	)
+
+	return app.Run(ctx)
 }
 
 // editConfigFile opens the config file in the user's editor.