feat: close buttons as a red cross in a square; static files revalidated by content, so a release reaches the browser at once

internal/server/server.go

@@ -1,7 +1,9 @@
 package server
 
 import (
+	"crypto/sha256"
 	"embed"
+	"encoding/hex"
 	"html/template"
 	"io/fs"
 	"log"
@@ -184,7 +186,7 @@ func (s *Server) Handler() http.Handler {
 
 	// Static assets (xterm.js etc.) from the embedded FS.
 	staticFS, _ := fs.Sub(webFS, "web/static")
-	mux.Handle("GET /static/", http.StripPrefix("/static/", http.FileServer(http.FS(staticFS))))
+	mux.Handle("GET /static/", http.StripPrefix("/static/", staticHandler(staticFS)))
 
 	// Public: install script + agent binary downloads.
 	mux.HandleFunc("GET /install.sh", s.handleInstallScript)
@@ -333,3 +335,33 @@ func clientIP(r *http.Request) string {
 	}
 	return host
 }
+
+// staticHandler serves the embedded assets with a content hash as ETag. The
+// browser asks each time whether a file changed (no-cache) and gets a 304
+// when it did not, so a new release reaches it at once without reloading
+// what stayed the same.
+func staticHandler(fsys fs.FS) http.Handler {
+	files := http.FileServer(http.FS(fsys))
+	var mu sync.Mutex
+	etags := map[string]string{}
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		name := strings.TrimPrefix(r.URL.Path, "/")
+		mu.Lock()
+		tag, ok := etags[name]
+		mu.Unlock()
+		if !ok {
+			if data, err := fs.ReadFile(fsys, name); err == nil {
+				sum := sha256.Sum256(data)
+				tag = `"` + hex.EncodeToString(sum[:8]) + `"`
+			}
+			mu.Lock()
+			etags[name] = tag
+			mu.Unlock()
+		}
+		if tag != "" {
+			w.Header().Set("ETag", tag)
+		}
+		w.Header().Set("Cache-Control", "no-cache")
+		files.ServeHTTP(w, r)
+	})
+}