fix: revert SPA mode while keeping SSR mode as-is

packages/vite/src/node/preview.ts

@@ -100,12 +100,6 @@ export async function preview(
 
   const { spa } = config
 
-  if (spa) {
-    // We need to apply the plugins' server post hooks before `sirv()`. (Because
-    // `sirv(_, { single: true })` catches all routes.)
-    postHooks.forEach((fn) => fn && fn())
-  }
-
   // static assets
   const distDir = path.resolve(config.root, config.build.outDir)
   app.use(
@@ -117,11 +111,10 @@ export async function preview(
     })
   )
 
-  if (!spa) {
-    // We apply the plugins' server post hooks after `sirv()` so that `sirv()`
-    // can serve pre-rendered pages before any SSR middleware.
-    postHooks.forEach((fn) => fn && fn())
+  // apply post server hooks from plugins
+  postHooks.forEach((fn) => fn && fn())
 
+  if (!spa) {
     // 404 handling (this simulates what most static hosts do)
     app.use(config.base, (_, res, next) => {
       const file = path.join(distDir, './404.html')

packages/vite/src/node/server/index.ts

@@ -503,23 +503,24 @@ export async function createServer(
   middlewares.use(serveRawFsMiddleware(server))
   middlewares.use(serveStaticMiddleware(root, server))
 
-  // We need to apply post server hooks before `spaFallbackMiddleware()`.
-  // (Because `spaFallbackMiddleware()` catches all routes.)
-  postHooks.forEach((fn) => fn && fn())
-
   const isMiddlewareModeSSR = middlewareMode && middlewareMode !== 'html'
 
   if (config.spa && !isMiddlewareModeSSR) {
-    // SPA catch-all fallback routing
+    // spa fallback
     middlewares.use(spaFallbackMiddleware(root))
+  }
+
+  // run post config hooks
+  // This is applied before the html middleware so that user middleware can
+  // serve custom content instead of index.html.
+  postHooks.forEach((fn) => fn && fn())
+
+  if (config.spa && !isMiddlewareModeSSR) {
     // transform index.html
     middlewares.use(indexHtmlMiddleware(server))
   }
 
-  // Handle 404s.
-  // We keep 404 handling when `config.spa === false` because some SSR tools,
-  // such as vite-plugin-ssr, cannot always render 404 pages. (E.g. if the
-  // vite-plugin-ssr user didn't define a `_error.page.js`.)
+  // handle 404s
   if (!isMiddlewareModeSSR) {
     // Keep the named function. The name is visible in debug logs via
     // `DEBUG=connect:dispatcher ...`.