izackp/webterm
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Add optional PNG screenshot mode

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PNG screenshots are now gated by WEBTERM_SCREENSHOT_MODE.
The dashboard selects SVG by default and switches to PNG when enabled,
with ETag caching and eviction for both formats.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
GitHub Copilot
2026-02-18 15:45:22 +00:00
parent 8d54de6407
commit a6ada31aa6
6 changed files with 393 additions and 4 deletions
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webterm/server.go
+147 -4
View File
@@ -52,6 +52,12 @@ type screenshotCacheEntry struct {
etag string
}
type screenshotPNGCacheEntry struct {
when time.Time
png []byte
etag string
}
type wsClient struct {
routeKey string
conn *websocket.Conn
@@ -164,6 +170,7 @@ type LocalServer struct {
theme string
fontFamily string
fontSize int
screenshotMode string
sessionManager *SessionManager
landingApps []App
@@ -177,6 +184,7 @@ type LocalServer struct {
mu sync.RWMutex
wsClients map[string]*wsClient
screenshotCache map[string]screenshotCacheEntry
screenshotPNGCache map[string]screenshotPNGCacheEntry
routeLastActivity map[string]time.Time
routeLastSSE map[string]time.Time
sseSubscribers map[chan string]struct{}
@@ -231,6 +239,10 @@ func NewLocalServer(config Config, options ServerOptions) *LocalServer {
if fontSize <= 0 {
fontSize = DefaultFontSize
}
screenshotMode := strings.ToLower(strings.TrimSpace(os.Getenv(ScreenshotModeEnv)))
if screenshotMode != "png" {
screenshotMode = "svg"
}
apps := append([]App{}, config.Apps...)
for _, app := range options.LandingApps {
apps = append(apps, app)
@@ -241,6 +253,7 @@ func NewLocalServer(config Config, options ServerOptions) *LocalServer {
theme: theme,
fontFamily: options.FontFamily,
fontSize: fontSize,
screenshotMode: screenshotMode,
sessionManager: NewSessionManager(apps),
landingApps: append([]App{}, options.LandingApps...),
@@ -253,6 +266,7 @@ func NewLocalServer(config Config, options ServerOptions) *LocalServer {
},
wsClients: map[string]*wsClient{},
screenshotCache: map[string]screenshotCacheEntry{},
screenshotPNGCache: map[string]screenshotPNGCacheEntry{},
routeLastActivity: map[string]time.Time{},
routeLastSSE: map[string]time.Time{},
sseSubscribers: map[chan string]struct{}{},
@@ -812,6 +826,118 @@ func (s *LocalServer) handleScreenshot(w http.ResponseWriter, r *http.Request) {
writeSVG(responseSVG, responseETag)
}
func (s *LocalServer) handleScreenshotPNG(w http.ResponseWriter, r *http.Request) {
if s.screenshotMode != "png" {
http.Error(w, "PNG screenshots disabled", http.StatusNotFound)
return
}
download := r.URL.Query().Get("download") == "1"
routeKey := r.URL.Query().Get("route_key")
routeKey, session, ok := s.chooseRouteForScreenshot(routeKey)
if !ok && routeKey != "" {
if _, exists := s.sessionManager.AppBySlug(routeKey); exists {
_ = s.createTerminalSession(routeKey, DefaultTerminalWidth, DefaultTerminalHeight)
deadline := time.Now().Add(500 * time.Millisecond)
for {
session = s.sessionManager.GetSessionByRouteKey(routeKey)
if session != nil {
ok = true
break
}
if time.Now().After(deadline) {
break
}
time.Sleep(20 * time.Millisecond)
}
}
}
if !ok || session == nil {
http.Error(w, "Session not found", http.StatusNotFound)
return
}
writeNotModified := func(etag string) {
w.Header().Set("Cache-Control", "no-cache")
w.Header().Set("ETag", etag)
w.WriteHeader(http.StatusNotModified)
}
writePNG := func(pngBytes []byte, etag string) {
w.Header().Set("Cache-Control", "no-cache")
w.Header().Set("ETag", etag)
w.Header().Set("Content-Type", "image/png")
if download {
filename := sanitizeFilenameToken(routeKey) + "-screenshot.png"
w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="%s"`, filename))
}
_, _ = w.Write(pngBytes)
}
useConditional := !download
s.mu.RLock()
cached, hasCached := s.screenshotPNGCache[routeKey]
lastActivity := s.routeLastActivity[routeKey]
s.mu.RUnlock()
if hasCached && time.Since(cached.when) < s.screenshotTTL(routeKey) && len(cached.png) > 0 {
if useConditional && etagMatches(r.Header.Get("If-None-Match"), cached.etag) {
if !lastActivity.After(cached.when) {
writeNotModified(cached.etag)
return
}
} else {
writePNG(cached.png, cached.etag)
return
}
}
if s.screenshotForceRedraw {
_ = session.ForceRedraw()
}
snapshot := session.GetScreenSnapshot()
if hasCached && !snapshot.HasChanges && len(cached.png) > 0 {
if useConditional && etagMatches(r.Header.Get("If-None-Match"), cached.etag) {
writeNotModified(cached.etag)
return
}
writePNG(cached.png, cached.etag)
return
}
app, _ := s.sessionManager.AppBySlug(routeKey)
theme := strings.ToLower(strings.TrimSpace(app.Theme))
if theme == "" {
theme = strings.ToLower(s.theme)
}
palette := ThemePalettes[theme]
if palette == nil {
palette = ThemePalettes["xterm"]
}
background := palette["background"]
if background == "" {
background = ThemeBackgrounds["xterm"]
}
foreground := palette["foreground"]
if foreground == "" {
foreground = "#e5e5e5"
}
pngBytes, err := RenderTerminalPNG(snapshot.Buffer, snapshot.Width, snapshot.Height, background, foreground, palette)
if err != nil || len(pngBytes) == 0 {
http.Error(w, "Screenshot render failed", http.StatusInternalServerError)
return
}
hash := sha1.Sum(pngBytes)
etag := fmt.Sprintf(`"%x"`, hash[:])
s.mu.Lock()
s.screenshotPNGCache[routeKey] = screenshotPNGCacheEntry{when: time.Now(), png: pngBytes, etag: etag}
s.mu.Unlock()
if useConditional && etagMatches(r.Header.Get("If-None-Match"), etag) {
writeNotModified(etag)
return
}
writePNG(pngBytes, etag)
}
func (s *LocalServer) handleCPUSparkline(w http.ResponseWriter, r *http.Request) {
container := r.URL.Query().Get("container")
if strings.TrimSpace(container) == "" {
@@ -960,6 +1086,14 @@ func (s *LocalServer) handleRoot(w http.ResponseWriter, r *http.Request) {
if s.dockerWatch {
dockerWatchJS = "true"
}
screenshotEndpoint := "/screenshot.svg"
screenshotDownloadQuery := "sanitize_font_urls=1&download=1"
screenshotDownloadExt := "svg"
if s.screenshotMode == "png" {
screenshotEndpoint = "/screenshot.png"
screenshotDownloadQuery = "download=1"
screenshotDownloadExt = "png"
}
html := fmt.Sprintf(`<!DOCTYPE html>
<html>
<head>
@@ -1016,6 +1150,9 @@ func (s *LocalServer) handleRoot(w http.ResponseWriter, r *http.Request) {
let tiles = %s;
const composeMode = %s;
const dockerWatchMode = %s;
const screenshotEndpoint = %q;
const screenshotDownloadQuery = %q;
const screenshotDownloadExt = %q;
let cardsBySlug = {};
let searchQuery = '';
@@ -1035,8 +1172,8 @@ func (s *LocalServer) handleRoot(w http.ResponseWriter, r *http.Request) {
function downloadSanitizedScreenshot(slug) {
if (!slug) return;
const link = document.createElement('a');
link.href = '/screenshot.svg?route_key=' + encodeURIComponent(slug) + '&sanitize_font_urls=1&download=1&_t=' + Date.now();
link.download = slug + '-screenshot.svg';
link.href = screenshotEndpoint + '?route_key=' + encodeURIComponent(slug) + '&' + screenshotDownloadQuery + '&_t=' + Date.now();
link.download = slug + '-screenshot.' + screenshotDownloadExt;
document.body.appendChild(link);
link.click();
link.remove();
@@ -1282,7 +1419,7 @@ func (s *LocalServer) handleRoot(w http.ResponseWriter, r *http.Request) {
return;
}
screenshotRequestInFlight = true;
const url = '/screenshot.svg?route_key=' + encodeURIComponent(slug);
const url = screenshotEndpoint + '?route_key=' + encodeURIComponent(slug);
const controller = new AbortController();
const timeout = setTimeout(() => controller.abort(), 5000);
const headers = {};
@@ -1468,7 +1605,7 @@ func (s *LocalServer) handleRoot(w http.ResponseWriter, r *http.Request) {
}
</script>
</body>
</html>`, string(tilesJSON), composeModeJS, dockerWatchJS)
</html>`, string(tilesJSON), composeModeJS, dockerWatchJS, screenshotEndpoint, screenshotDownloadQuery, screenshotDownloadExt)
w.Header().Set("Content-Type", "text/html; charset=utf-8")
_, _ = io.WriteString(w, html)
return
@@ -1604,6 +1741,7 @@ func (s *LocalServer) Handler() http.Handler {
mux := http.NewServeMux()
mux.HandleFunc("/ws/", s.handleWebSocket)
mux.HandleFunc("/screenshot.svg", s.handleScreenshot)
mux.HandleFunc("/screenshot.png", s.handleScreenshotPNG)
mux.HandleFunc("/cpu-sparkline.svg", s.handleCPUSparkline)
mux.HandleFunc("/events", s.handleEvents)
mux.HandleFunc("/health", s.handleHealth)
@@ -1633,6 +1771,11 @@ func (s *LocalServer) evictStaleScreenshots(ctx context.Context) {
delete(s.screenshotCache, key)
}
}
for key, entry := range s.screenshotPNGCache {
if time.Since(entry.when) > maxScreenshotCacheTTL {
delete(s.screenshotPNGCache, key)
}
}
s.mu.Unlock()
}
}