Snider · Snider · Feb 2, 2026 · Feb 2, 2026 · Feb 2, 2026
diff --git a/cmd/dapp-fm-app/main.go b/cmd/dapp-fm-app/main.go
@@ -9,6 +9,7 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io/fs"
+	"mime"
 	"net/http"
 	"strconv"
 	"strings"
@@ -57,16 +58,34 @@ func (s *MediaStore) Clear() {
 	s.media = make(map[string]*MediaItem)
 }
 
+func init() {
+	mime.AddExtensionType(".wasm", "application/wasm")
+	mime.AddExtensionType(".js", "application/javascript")
+	mime.AddExtensionType(".css", "text/css")
+	mime.AddExtensionType(".html", "text/html; charset=utf-8")
+}
+
 // AssetHandler serves both static assets and decrypted media
 type AssetHandler struct {
-	assets fs.FS
+	assets     fs.FS
+	fileServer http.Handler
+}
+
+// NewAssetHandler creates a new AssetHandler
+func NewAssetHandler(assets fs.FS) *AssetHandler {
+	sub, err := fs.Sub(assets, "frontend")
+	if err != nil {
+		// Fallback to assets if sub fails (e.g. test mock)
+		sub = assets
+	}
+	return &AssetHandler{
+		assets:     assets,
+		fileServer: http.FileServer(http.FS(sub)),
+	}
 }
 
 func (h *AssetHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	path := r.URL.Path
-	if path == "/" {
-		path = "/index.html"
-	}
 	path = strings.TrimPrefix(path, "/")
 
 	// Check if this is a media request
@@ -112,25 +131,12 @@ func (h *AssetHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Serve static assets
-	data, err := fs.ReadFile(h.assets, "frontend/"+path)
-	if err != nil {
+	if h.fileServer == nil {
+		// Fallback if not initialized via NewAssetHandler (should not happen in prod)
 		http.NotFound(w, r)
 		return
 	}
-
-	// Set content type
-	switch {
-	case strings.HasSuffix(path, ".html"):
-		w.Header().Set("Content-Type", "text/html; charset=utf-8")
-	case strings.HasSuffix(path, ".js"):
-		w.Header().Set("Content-Type", "application/javascript")
-	case strings.HasSuffix(path, ".css"):
-		w.Header().Set("Content-Type", "text/css")
-	case strings.HasSuffix(path, ".wasm"):
-		w.Header().Set("Content-Type", "application/wasm")
-	}
-
-	w.Write(data)
+	h.fileServer.ServeHTTP(w, r)
 }
 
 // App wraps player functionality
@@ -307,7 +313,7 @@ func main() {
 		MinWidth:  800,
 		MinHeight: 600,
 		AssetServer: &assetserver.Options{
-			Handler: &AssetHandler{assets: frontendAssets},
+			Handler: NewAssetHandler(frontendAssets),
 		},
 		BackgroundColour: &options.RGBA{R: 18, G: 18, B: 18, A: 1},
 		OnStartup:        app.Startup,

diff --git a/cmd/dapp-fm-app/main_test.go b/cmd/dapp-fm-app/main_test.go
@@ -0,0 +1,125 @@
+package main
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"testing/fstest"
+)
+
+func TestAssetHandler_ServeHTTP_Static(t *testing.T) {
+	mockFS := fstest.MapFS{
+		"frontend/index.html": {Data: []byte("<html><body>Hello</body></html>")},
+		"frontend/style.css":  {Data: []byte("body { color: red; }")},
+		"frontend/app.js":     {Data: []byte("console.log('hi')")},
+		"frontend/test.wasm":  {Data: []byte{0x00, 0x61, 0x73, 0x6d}},
+	}
+
+	handler := NewAssetHandler(mockFS)
+
+	tests := []struct {
+		name        string
+		path        string
+		wantCode    int
+		wantType    string
+		wantContent string
+	}{
+		{
+			name:        "Root",
+			path:        "/",
+			wantCode:    http.StatusOK,
+			wantType:    "text/html; charset=utf-8",
+			wantContent: "<html><body>Hello</body></html>",
+		},
+		{
+			name:     "Index",
+			path:     "/index.html",
+			wantCode: http.StatusMovedPermanently, // http.FileServer redirects index.html to /
+		},
+		{
+			name:        "CSS",
+			path:        "/style.css",
+			wantCode:    http.StatusOK,
+			wantType:    "text/css",
+			wantContent: "body { color: red; }",
+		},
+		{
+			name:        "JS",
+			path:        "/app.js",
+			wantCode:    http.StatusOK,
+			wantType:    "application/javascript",
+			wantContent: "console.log('hi')",
+		},
+		{
+			name:        "WASM",
+			path:        "/test.wasm",
+			wantCode:    http.StatusOK,
+			wantType:    "application/wasm",
+			wantContent: "\x00\x61\x73\x6d",
+		},
+		{
+			name:     "NotFound",
+			path:     "/missing.html",
+			wantCode: http.StatusNotFound,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := httptest.NewRequest("GET", tt.path, nil)
+			w := httptest.NewRecorder()
+
+			handler.ServeHTTP(w, req)
+
+			resp := w.Result()
+			if resp.StatusCode != tt.wantCode {
+				t.Errorf("path %s: status code = %d, want %d", tt.path, resp.StatusCode, tt.wantCode)
+			}
+
+			if tt.wantCode == http.StatusOK {
+				ct := resp.Header.Get("Content-Type")
+				if !strings.Contains(ct, tt.wantType) {
+					t.Errorf("path %s: content type = %q, want %q", tt.path, ct, tt.wantType)
+				}
+
+				// Read body
+				if tt.wantContent != "" {
+					body := w.Body.String()
+					if body != tt.wantContent {
+						t.Errorf("path %s: body = %q, want %q", tt.path, body, tt.wantContent)
+					}
+				}
+			}
+		})
+	}
+}
+
+func TestAssetHandler_ServeHTTP_Media(t *testing.T) {
+	// Setup test data
+	globalStore.Set("123", &MediaItem{
+		Data:     []byte("mediadata"),
+		MimeType: "audio/mp3",
+		Name:     "song.mp3",
+	})
+	defer globalStore.Clear()
+
+	mockFS := fstest.MapFS{}
+	handler := NewAssetHandler(mockFS)
+
+	req := httptest.NewRequest("GET", "/media/123", nil)
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	resp := w.Result()
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("status code = %d, want %d", resp.StatusCode, http.StatusOK)
+	}
+	if ct := resp.Header.Get("Content-Type"); ct != "audio/mp3" {
+		t.Errorf("content type = %s, want audio/mp3", ct)
+	}
+	if body := w.Body.String(); body != "mediadata" {
+		t.Errorf("body = %s, want mediadata", body)
+	}
+}
diff --git a/dapp-fm-app b/dapp-fm-app
diff --git a/pkg/player/assets.go b/pkg/player/assets.go
@@ -11,7 +11,6 @@ import (
 //go:embed frontend/index.html
 //go:embed frontend/wasm_exec.js
 //go:embed frontend/stmf.wasm
-//go:embed frontend/demo-track.smsg
 var assets embed.FS
 
 // Assets returns the embedded filesystem with frontend/ prefix stripped