README.md

@@ -2721,7 +2721,7 @@ abuse limit later; they are tracked as future work.
 | ------ | --------------------------- | ----------- |
 | `GET`  | `/`                         | Root redirect, 303 (authenticated → `/sources`, unauthenticated → `/pages/login`) |
 | `GET`  | `/.well-known/healthcheck`  | Health check (JSON: `status`, `now`, `uptimeSeconds`, `uptimeHuman`, `version`, `appname`, `maintenanceMode`) |
-| any    | `/s/*`                      | Static file serving (embedded CSS, JS). Mounted for every method, not just `GET`/`HEAD`: chi's `Mount` registers all methods and `http.FileServer` special-cases only `HEAD` (by omitting the body), so a `POST` or `DELETE` to an asset is answered `200` with the file. Pinned by `TestStaticServesEveryMethod` |
+| `GET`, `HEAD` | `/s/*`              | Static file serving (embedded CSS, JS). `GET` and `HEAD` only — every other method is answered `405 Method Not Allowed` with `Allow: GET, HEAD`. Pinned by `TestStaticServesOnlyGetAndHead` |
 | `POST` | `/webhook/{uuid}`           | Webhook receiver endpoint. `POST` only — every other method is answered `405 Method Not Allowed` with `Allow: POST`. Rate limited (see [Rate Limiting](#rate-limiting)) |
 
 #### Authentication Endpoints

internal/server/routes.go

@@ -92,11 +92,25 @@ func (s *Server) setupGlobalMiddleware() {
 func (s *Server) setupRoutes() {
 	s.router.Get("/", s.h.HandleIndex())
 
-	s.router.Mount(
-		"/s",
-		http.StripPrefix("/s", http.FileServer(http.FS(static.Static))),
+	// Static assets answer GET and HEAD only. chi's default 405
+	// carries no Allow header, so this group supplies its own.
+	staticFiles := http.StripPrefix(
+		"/s", http.FileServer(http.FS(static.Static)),
 	)
 
+	s.router.Route("/s", func(r chi.Router) {
+		r.MethodNotAllowed(func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Allow", "GET, HEAD")
+			http.Error(
+				w,
+				"Method Not Allowed",
+				http.StatusMethodNotAllowed,
+			)
+		})
+		r.Method(http.MethodGet, "/*", staticFiles)
+		r.Method(http.MethodHead, "/*", staticFiles)
+	})
+
 	s.router.Route("/api/v1", func(_ chi.Router) {
 		// API routes will be added here.
 	})

internal/server/routes_test.go

@@ -396,13 +396,12 @@ func (e *testEnv) storedHash(t *testing.T, username string) string {
 
 // --- /s static group ---
 
-// TestStaticServesEveryMethod pins what the static mount actually
-// answers. chi's Mount registers the handler for all methods and
-// http.FileServer only special-cases HEAD (by suppressing the body),
-// so a POST or a DELETE to an asset is served the file rather than
-// refused. The README documents this; the test is what keeps the two
-// from drifting.
-func TestStaticServesEveryMethod(t *testing.T) {
+// TestStaticServesOnlyGetAndHead pins the methods the static group
+// answers: GET and HEAD are served the asset, and any other method
+// is refused with 405 and an Allow header naming those two. The
+// README documents this; the test is what keeps the two from
+// drifting.
+func TestStaticServesOnlyGetAndHead(t *testing.T) {
 	t.Parallel()
 
 	env := newTestEnv(t)
@@ -428,18 +427,27 @@ func TestStaticServesEveryMethod(t *testing.T) {
 			w := httptest.NewRecorder()
 			env.router.ServeHTTP(w, req)
 
-			assert.Equal(t, http.StatusOK, w.Code,
-				"static mount answers every method")
-
-			if method == http.MethodHead {
+			switch method {
+			case http.MethodGet:
+				assert.Equal(t, http.StatusOK, w.Code)
+				assert.Equal(t, body, w.Body.Bytes(),
+					"the asset itself is returned")
+			case http.MethodHead:
+				assert.Equal(t, http.StatusOK, w.Code)
 				assert.Empty(t, w.Body.Bytes(),
 					"HEAD must not carry a body")
-
-				return
+			default:
+				assert.Equal(
+					t, http.StatusMethodNotAllowed, w.Code,
+				)
+				assert.Equal(
+					t, "GET, HEAD", w.Header().Get("Allow"),
+				)
+				assert.NotContains(
+					t, w.Body.String(), string(body),
+					"a refused method must not get the asset",
+				)
 			}
-
-			assert.Equal(t, body, w.Body.Bytes(),
-				"the asset itself is returned")
 		})
 	}
 }