Stop browsers from caching songs

/music/rand and the other song endpoints return a different song from the
same URL, but the responses had a Last-Modified header and no Cache-Control,
so browsers cached them. The same song played again and the server never
picked a new one, so /music/addQue added nothing. Send Cache-Control:
no-store again, as the server did before the rewrite.

Also allow the Cache-Control request header in CORS, which the frontend
sends to bypass responses that browsers have already cached.

internal/server/files.go

@@ -52,9 +52,21 @@ func streamOpenFile(f *os.File, contentType string, audio bool) (*huma.StreamRes
 }
 
 // streamSong streams the song at path, or returns err mapped to an API error.
+// The same URL returns a different song each time (random songs, next, previous),
+// so browsers must not cache it. Without this they cache the response because of
+// its Last-Modified header, and play the same song again.
 func streamSong(path string, err error) (*huma.StreamResponse, error) {
 	if err != nil {
 		return nil, apiError(err)
 	}
-	return streamFile(path, "audio/mpeg", true)
+	resp, err := streamFile(path, "audio/mpeg", true)
+	if err != nil {
+		return nil, err
+	}
+	body := resp.Body
+	resp.Body = func(ctx huma.Context) {
+		ctx.SetHeader("Cache-Control", "no-store")
+		body(ctx)
+	}
+	return resp, nil
 }

internal/server/handlers_test.go

@@ -92,6 +92,19 @@ func TestMusicQueueEndsAfterSync(t *testing.T) {
 	assert.JSONEq(t, "[]", rec.Body.String())
 }
 
+func TestMusicSongsAreNotCached(t *testing.T) {
+	e := newTestEnv(t)
+	e.addSong("Game A", "Song", "x")
+	e.do(http.MethodGet, "/api/v1/music/rand")
+	e.do(http.MethodGet, "/api/v1/music/addQue")
+	for _, path := range []string{"/api/v1/music/rand", "/api/v1/music/rand/low", "/api/v1/music/rand/classic",
+		"/api/v1/music/next", "/api/v1/music/previous", "/api/v1/music?song=0", "/api/v1/music/soundTest"} {
+		rec := e.do(http.MethodGet, path)
+		require.Equal(t, http.StatusOK, rec.Code, path)
+		assert.Equal(t, "no-store", rec.Header().Get("Cache-Control"), path)
+	}
+}
+
 func TestMusicRangeRequest(t *testing.T) {
 	e := newTestEnv(t)
 	e.addSong("Game A", "Song", "0123456789")

internal/server/routes.go

@@ -46,7 +46,7 @@ func (s *Server) routes() (*echo.Echo, huma.API) {
 		e.Use(echoMiddleware.CORSWithConfig(echoMiddleware.CORSConfig{
 			AllowOrigins:  s.cfg.CORSAllowedOrigins,
 			AllowMethods:  []string{"GET", "POST", "PUT", "DELETE", "OPTIONS", "PATCH"},
-			AllowHeaders:  []string{"Accept", "Authorization", "Content-Type", "Range", middleware.QueueHeader},
+			AllowHeaders:  []string{"Accept", "Authorization", "Cache-Control", "Content-Type", "Range", middleware.QueueHeader},
 			ExposeHeaders: []string{middleware.QueueHeader, "Content-Range", "Accept-Ranges"},
 			MaxAge:        300,
 		}))