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|
# Streaming Data
## Overview
This guide builds a live data viewer that receives streaming data from a Go channel, using channel watchers, scrollable containers, and auto-scroll. It builds on the [Watchers](watchers) and [Scrolling](scrolling) guides.
## The Producer Pattern
The streaming pattern starts outside the component: a goroutine produces data and sends it through a channel. The component receives the channel in its constructor and watches it for new data.
Create a buffered channel and pass it to the component:
```go
func main() {
dataCh := make(chan string, 100)
app, err := tui.NewApp(
tui.WithRootComponent(Streaming(dataCh)),
)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to create app: %v\n", err)
os.Exit(1)
}
defer app.Close()
go produce(dataCh, app.StopCh())
if err := app.Run(); err != nil {
fmt.Fprintf(os.Stderr, "App error: %v\n", err)
os.Exit(1)
}
}
```
The producer goroutine uses `app.StopCh()` for clean shutdown. When the app stops, `StopCh()` closes, and the goroutine exits:
```go
func produce(ch chan<- string, stopCh <-chan struct{}) {
defer close(ch)
for {
select {
case <-stopCh:
return
default:
}
line := generateLine()
select {
case <-stopCh:
return
case ch <- line:
}
time.Sleep(time.Duration(100+rand.Intn(400)) * time.Millisecond)
}
}
```
The double `select` pattern (one before work, one before send) ensures the goroutine responds promptly to shutdown signals.
## Channel Watcher for Streaming
The component watches the channel using `tui.Watch` in its `Watchers()` method. Each time a value arrives, the callback fires and the UI re-renders:
```go
func (s *streamingApp) Watchers() []tui.Watcher {
return []tui.Watcher{
tui.Watch(s.dataCh, s.addLine),
}
}
func (s *streamingApp) addLine(line string) {
current := s.lines.Get()
s.lines.Set(append(current, line))
}
```
The `lines` state holds a `[]string` that grows over time. Each new line triggers a re-render, which updates the scrollable content area.
## Auto-Scroll (Sticky Bottom)
A live data viewer should stay scrolled to the bottom as new data arrives, but let the user scroll up to read history. The `stickToBottom` state boolean controls this:
```go
type streamingApp struct {
lines *tui.State[[]string]
scrollY *tui.State[int]
stickToBottom *tui.State[bool]
content *tui.Ref
// ...
}
```
When `stickToBottom` is `true`, new lines set `scrollY` to `math.MaxInt` (the framework clamps this to the actual maximum):
```go
func (s *streamingApp) addLine(line string) {
current := s.lines.Get()
s.lines.Set(append(current, line))
if s.stickToBottom.Get() {
s.scrollY.Set(math.MaxInt)
}
}
```
Manual scrolling disables auto-scroll. The `scrollBy` helper checks whether the user has scrolled to the bottom and updates `stickToBottom` accordingly:
```go
func (s *streamingApp) scrollBy(delta int) {
el := s.content.El()
if el == nil {
return
}
_, maxY := el.MaxScroll()
newY := s.scrollY.Get() + delta
if newY < 0 {
newY = 0
} else if newY > maxY {
newY = maxY
}
s.scrollY.Set(newY)
s.stickToBottom.Set(newY >= maxY)
}
```
The Space key toggles auto-scroll, and End re-enables it:
```go
tui.On(tui.Rune(' '), func(ke tui.KeyEvent) {
if s.stickToBottom.Get() {
s.stickToBottom.Set(false)
} else {
s.scrollY.Set(math.MaxInt)
s.stickToBottom.Set(true)
}
}),
tui.On(tui.KeyEnd, func(ke tui.KeyEvent) {
s.scrollY.Set(math.MaxInt)
s.stickToBottom.Set(true)
}),
```
## Dynamic Content Coloring
To visually distinguish different types of streaming data, write a helper function that inspects the line content and returns a Tailwind class string:
```go
func lineColor(line string) string {
if len(line) < 20 {
return ""
}
for i := 0; i < len(line)-3; i++ {
sub := line[i : i+3]
if sub == "cpu" {
return "text-cyan"
}
if sub == "mem" {
return "text-magenta"
}
if sub == "net" {
return "text-green"
}
if sub == "dis" {
return "text-yellow"
}
if sub == "io:" {
return "text-blue"
}
}
return ""
}
```
Use it in the template with a dynamic `class` attribute:
```gsx
for _, line := range s.lines.Get() {
<span class={lineColor(line)}>{line}</span>
}
```
The `class` attribute accepts any expression that returns a string, so you can compute it per-element.
## Timer and Channel Together
A component can combine multiple watcher types. The streaming example uses both `OnTimer` (for an elapsed time counter) and `Watch` (for incoming data) in the same `Watchers()` slice:
```go
func (s *streamingApp) Watchers() []tui.Watcher {
return []tui.Watcher{
tui.OnTimer(time.Second, s.tick),
tui.Watch(s.dataCh, s.addLine),
}
}
func (s *streamingApp) tick() {
s.elapsed.Set(s.elapsed.Get() + 1)
}
```
The timer fires every second regardless of channel activity. Both watchers trigger re-renders independently.
## Complete Example
This live stream viewer receives timestamped metrics from a background goroutine, with auto-scroll, manual scrolling, and color-coded output:
```gsx
package main
import (
"fmt"
"math"
"time"
tui "github.com/grindlemire/go-tui"
)
type streamingApp struct {
dataCh <-chan string
lines *tui.State[[]string]
scrollY *tui.State[int]
stickToBottom *tui.State[bool]
elapsed *tui.State[int]
content *tui.Ref
}
func Streaming(dataCh <-chan string) *streamingApp {
return &streamingApp{
dataCh: dataCh,
lines: tui.NewState([]string{}),
scrollY: tui.NewState(0),
stickToBottom: tui.NewState(true),
elapsed: tui.NewState(0),
content: tui.NewRef(),
}
}
func (s *streamingApp) scrollBy(delta int) {
el := s.content.El()
if el == nil {
return
}
_, maxY := el.MaxScroll()
newY := s.scrollY.Get() + delta
if newY < 0 {
newY = 0
} else if newY > maxY {
newY = maxY
}
s.scrollY.Set(newY)
s.stickToBottom.Set(newY >= maxY)
}
func (s *streamingApp) KeyMap() tui.KeyMap {
return tui.KeyMap{
tui.On(tui.Rune('q'), func(ke tui.KeyEvent) { ke.App().Stop() }),
tui.On(tui.KeyEscape, func(ke tui.KeyEvent) { ke.App().Stop() }),
tui.On(tui.Rune('j'), func(ke tui.KeyEvent) { s.scrollBy(1) }),
tui.On(tui.Rune('k'), func(ke tui.KeyEvent) { s.scrollBy(-1) }),
tui.On(tui.KeyUp, func(ke tui.KeyEvent) { s.scrollBy(-1) }),
tui.On(tui.KeyDown, func(ke tui.KeyEvent) { s.scrollBy(1) }),
tui.On(tui.KeyPageUp, func(ke tui.KeyEvent) { s.scrollBy(-10) }),
tui.On(tui.KeyPageDown, func(ke tui.KeyEvent) { s.scrollBy(10) }),
tui.On(tui.KeyHome, func(ke tui.KeyEvent) {
s.scrollY.Set(0)
s.stickToBottom.Set(false)
}),
tui.On(tui.KeyEnd, func(ke tui.KeyEvent) {
s.scrollY.Set(math.MaxInt)
s.stickToBottom.Set(true)
}),
tui.On(tui.Rune(' '), func(ke tui.KeyEvent) {
if s.stickToBottom.Get() {
s.stickToBottom.Set(false)
} else {
s.scrollY.Set(math.MaxInt)
s.stickToBottom.Set(true)
}
}),
}
}
func (s *streamingApp) HandleMouse(me tui.MouseEvent) bool {
switch me.Button {
case tui.MouseWheelUp:
s.scrollBy(-1)
return true
case tui.MouseWheelDown:
s.scrollBy(1)
return true
}
return false
}
func (s *streamingApp) Watchers() []tui.Watcher {
return []tui.Watcher{
tui.OnTimer(time.Second, s.tick),
tui.Watch(s.dataCh, s.addLine),
}
}
func (s *streamingApp) tick() {
s.elapsed.Set(s.elapsed.Get() + 1)
}
func (s *streamingApp) addLine(line string) {
current := s.lines.Get()
s.lines.Set(append(current, line))
if s.stickToBottom.Get() {
s.scrollY.Set(math.MaxInt)
}
}
func lineColor(line string) string {
if len(line) < 20 {
return ""
}
for i := 0; i < len(line)-3; i++ {
sub := line[i : i+3]
if sub == "cpu" {
return "text-cyan"
}
if sub == "mem" {
return "text-magenta"
}
if sub == "net" {
return "text-green"
}
if sub == "dis" {
return "text-yellow"
}
if sub == "io:" {
return "text-blue"
}
}
return ""
}
templ (s *streamingApp) Render() {
<div class="flex-col gap-1 p-1 h-full border-rounded border-cyan">
<div class="flex justify-between shrink-0">
<span class="text-gradient-cyan-magenta font-bold shrink-0">Live Stream</span>
<span class="text-cyan font-bold" minWidth={0}>{fmt.Sprintf("%d lines", len(s.lines.Get()))}</span>
</div>
<div
ref={s.content}
class="flex-col flex-grow border-single p-1"
scrollable={tui.ScrollVertical}
scrollOffset={0, s.scrollY.Get()}
>
for _, line := range s.lines.Get() {
<span class={lineColor(line)}>{line}</span>
}
</div>
<div class="flex gap-2 shrink-0 justify-center">
<span class="font-dim">Elapsed:</span>
<span class="text-cyan font-bold">{fmt.Sprintf("%ds", s.elapsed.Get())}</span>
<span class="font-dim">Auto-scroll:</span>
if s.stickToBottom.Get() {
<span class="text-green font-bold">ON</span>
} else {
<span class="text-yellow">OFF</span>
}
</div>
<span class="font-dim shrink-0">j/k scroll | Space toggle auto-scroll | q quit</span>
</div>
}
```
With `main.go`:
```go
package main
import (
"fmt"
"math/rand"
"os"
"time"
tui "github.com/grindlemire/go-tui"
)
func main() {
dataCh := make(chan string, 100)
app, err := tui.NewApp(
tui.WithRootComponent(Streaming(dataCh)),
)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to create app: %v\n", err)
os.Exit(1)
}
defer app.Close()
go produce(dataCh, app.StopCh())
if err := app.Run(); err != nil {
fmt.Fprintf(os.Stderr, "App error: %v\n", err)
os.Exit(1)
}
}
func produce(ch chan<- string, stopCh <-chan struct{}) {
defer close(ch)
metrics := []string{"cpu", "mem", "net", "disk", "io"}
for {
select {
case <-stopCh:
return
default:
}
metric := metrics[rand.Intn(len(metrics))]
value := rand.Intn(100)
ts := time.Now().Format("15:04:05.000")
var line string
switch metric {
case "cpu":
line = fmt.Sprintf("[%s] cpu: %d%%", ts, value)
case "mem":
line = fmt.Sprintf("[%s] mem: %.1fG", ts, float64(value)/10.0)
case "net":
line = fmt.Sprintf("[%s] net: %d req/s", ts, value*5)
case "disk":
line = fmt.Sprintf("[%s] disk: %d%% used", ts, 40+value/2)
case "io":
line = fmt.Sprintf("[%s] io: %d MB/s", ts, value*2)
}
select {
case <-stopCh:
return
case ch <- line:
}
time.Sleep(time.Duration(100+rand.Intn(400)) * time.Millisecond)
}
}
```
Generate and run:
```bash
tui generate ./...
go run .
```
Watch the live metrics stream in, scroll up to pause auto-scroll:
## Next Steps
- [Watchers Guide](watchers) - Timers, channels, and the WatcherProvider interface
- [Inline Streaming Guide](inline-streaming) - Stream character-by-character output above an inline widget
- [Building a Dashboard](dashboard) - Combine streaming, layout, and state into a full application
|