fix: compile factories

e2e/react-start/server-functions/src/routeTree.gen.ts

@@ -37,6 +37,7 @@ import { Route as RedirectTestSsrTargetRouteImport } from './routes/redirect-tes
 import { Route as MiddlewareServerImportMiddlewareRouteImport } from './routes/middleware/server-import-middleware'
 import { Route as MiddlewareSendServerFnRouteImport } from './routes/middleware/send-serverFn'
 import { Route as MiddlewareRequestMiddlewareRouteImport } from './routes/middleware/request-middleware'
+import { Route as MiddlewareMiddlewareFactoryRouteImport } from './routes/middleware/middleware-factory'
 import { Route as MiddlewareClientMiddlewareRouterRouteImport } from './routes/middleware/client-middleware-router'
 import { Route as CookiesSetRouteImport } from './routes/cookies/set'
 import { Route as AbortSignalMethodRouteImport } from './routes/abort-signal/$method'
@@ -184,6 +185,12 @@ const MiddlewareRequestMiddlewareRoute =
     path: '/middleware/request-middleware',
     getParentRoute: () => rootRouteImport,
   } as any)
+const MiddlewareMiddlewareFactoryRoute =
+  MiddlewareMiddlewareFactoryRouteImport.update({
+    id: '/middleware/middleware-factory',
+    path: '/middleware/middleware-factory',
+    getParentRoute: () => rootRouteImport,
+  } as any)
 const MiddlewareClientMiddlewareRouterRoute =
   MiddlewareClientMiddlewareRouterRouteImport.update({
     id: '/middleware/client-middleware-router',
@@ -226,6 +233,7 @@ export interface FileRoutesByFullPath {
   '/abort-signal/$method': typeof AbortSignalMethodRoute
   '/cookies/set': typeof CookiesSetRoute
   '/middleware/client-middleware-router': typeof MiddlewareClientMiddlewareRouterRoute
+  '/middleware/middleware-factory': typeof MiddlewareMiddlewareFactoryRoute
   '/middleware/request-middleware': typeof MiddlewareRequestMiddlewareRoute
   '/middleware/send-serverFn': typeof MiddlewareSendServerFnRoute
   '/middleware/server-import-middleware': typeof MiddlewareServerImportMiddlewareRoute
@@ -260,6 +268,7 @@ export interface FileRoutesByTo {
   '/abort-signal/$method': typeof AbortSignalMethodRoute
   '/cookies/set': typeof CookiesSetRoute
   '/middleware/client-middleware-router': typeof MiddlewareClientMiddlewareRouterRoute
+  '/middleware/middleware-factory': typeof MiddlewareMiddlewareFactoryRoute
   '/middleware/request-middleware': typeof MiddlewareRequestMiddlewareRoute
   '/middleware/send-serverFn': typeof MiddlewareSendServerFnRoute
   '/middleware/server-import-middleware': typeof MiddlewareServerImportMiddlewareRoute
@@ -295,6 +304,7 @@ export interface FileRoutesById {
   '/abort-signal/$method': typeof AbortSignalMethodRoute
   '/cookies/set': typeof CookiesSetRoute
   '/middleware/client-middleware-router': typeof MiddlewareClientMiddlewareRouterRoute
+  '/middleware/middleware-factory': typeof MiddlewareMiddlewareFactoryRoute
   '/middleware/request-middleware': typeof MiddlewareRequestMiddlewareRoute
   '/middleware/send-serverFn': typeof MiddlewareSendServerFnRoute
   '/middleware/server-import-middleware': typeof MiddlewareServerImportMiddlewareRoute
@@ -331,6 +341,7 @@ export interface FileRouteTypes {
     | '/abort-signal/$method'
     | '/cookies/set'
     | '/middleware/client-middleware-router'
+    | '/middleware/middleware-factory'
     | '/middleware/request-middleware'
     | '/middleware/send-serverFn'
     | '/middleware/server-import-middleware'
@@ -365,6 +376,7 @@ export interface FileRouteTypes {
     | '/abort-signal/$method'
     | '/cookies/set'
     | '/middleware/client-middleware-router'
+    | '/middleware/middleware-factory'
     | '/middleware/request-middleware'
     | '/middleware/send-serverFn'
     | '/middleware/server-import-middleware'
@@ -399,6 +411,7 @@ export interface FileRouteTypes {
     | '/abort-signal/$method'
     | '/cookies/set'
     | '/middleware/client-middleware-router'
+    | '/middleware/middleware-factory'
     | '/middleware/request-middleware'
     | '/middleware/send-serverFn'
     | '/middleware/server-import-middleware'
@@ -434,6 +447,7 @@ export interface RootRouteChildren {
   AbortSignalMethodRoute: typeof AbortSignalMethodRoute
   CookiesSetRoute: typeof CookiesSetRoute
   MiddlewareClientMiddlewareRouterRoute: typeof MiddlewareClientMiddlewareRouterRoute
+  MiddlewareMiddlewareFactoryRoute: typeof MiddlewareMiddlewareFactoryRoute
   MiddlewareRequestMiddlewareRoute: typeof MiddlewareRequestMiddlewareRoute
   MiddlewareSendServerFnRoute: typeof MiddlewareSendServerFnRoute
   MiddlewareServerImportMiddlewareRoute: typeof MiddlewareServerImportMiddlewareRoute
@@ -648,6 +662,13 @@ declare module '@tanstack/react-router' {
       preLoaderRoute: typeof MiddlewareRequestMiddlewareRouteImport
       parentRoute: typeof rootRouteImport
     }
+    '/middleware/middleware-factory': {
+      id: '/middleware/middleware-factory'
+      path: '/middleware/middleware-factory'
+      fullPath: '/middleware/middleware-factory'
+      preLoaderRoute: typeof MiddlewareMiddlewareFactoryRouteImport
+      parentRoute: typeof rootRouteImport
+    }
     '/middleware/client-middleware-router': {
       id: '/middleware/client-middleware-router'
       path: '/middleware/client-middleware-router'
@@ -698,6 +719,7 @@ const rootRouteChildren: RootRouteChildren = {
   AbortSignalMethodRoute: AbortSignalMethodRoute,
   CookiesSetRoute: CookiesSetRoute,
   MiddlewareClientMiddlewareRouterRoute: MiddlewareClientMiddlewareRouterRoute,
+  MiddlewareMiddlewareFactoryRoute: MiddlewareMiddlewareFactoryRoute,
   MiddlewareRequestMiddlewareRoute: MiddlewareRequestMiddlewareRoute,
   MiddlewareSendServerFnRoute: MiddlewareSendServerFnRoute,
   MiddlewareServerImportMiddlewareRoute: MiddlewareServerImportMiddlewareRoute,

e2e/react-start/server-functions/src/routes/middleware/index.tsx

@@ -41,6 +41,15 @@ function RouteComponent() {
             Server imports in middleware are stripped from client build
           </Route.Link>
         </li>
+        <li>
+          <Route.Link
+            to="./middleware-factory"
+            data-testid="middleware-factory-link"
+          >
+            Middleware factories with server imports are stripped from client
+            build
+          </Route.Link>
+        </li>
       </ul>
     </div>
   )

e2e/react-start/server-functions/src/routes/middleware/middleware-factory.tsx

@@ -0,0 +1,126 @@
+import { createFileRoute } from '@tanstack/react-router'
+import { createMiddleware, createServerFn } from '@tanstack/react-start'
+import { getRequestHeaders } from '@tanstack/react-start/server'
+import React from 'react'
+
+/**
+ * This test verifies that middleware factories (functions that return createMiddleware().server())
+ * have their server-only code properly stripped from the client bundle.
+ *
+ * If the .server() part inside the factory is not stripped from the client build, this will fail with:
+ * "Module node:async_hooks has been externalized for browser compatibility"
+ * because @tanstack/react-start/server uses node:async_hooks internally.
+ */
+
+// Middleware factory function - returns a middleware with .server() call
+function createHeaderMiddleware(headerName: string) {
+  return createMiddleware({ type: 'function' }).server(async ({ next }) => {
+    // Use a server-only import - this should be stripped from client build
+    const headers = getRequestHeaders()
+    const headerValue = headers.get(headerName) ?? 'missing'
+
+    console.log(`[middleware-factory] ${headerName}:`, headerValue)
+
+    return next({
+      context: {
+        headerName,
+        headerValue,
+      },
+    })
+  })
+}
+
+// Arrow function factory variant
+const createPrefixedHeaderMiddleware = (prefix: string) => {
+  return createMiddleware({ type: 'function' }).server(async ({ next }) => {
+    // Use a server-only import - this should be stripped from client build
+    const headers = getRequestHeaders()
+    const allHeaderNames = [...headers.keys()]
+    const prefixedHeaders = allHeaderNames.filter((name) =>
+      name.toLowerCase().startsWith(prefix.toLowerCase()),
+    )
+
+    console.log(
+      `[middleware-factory] Prefixed headers (${prefix}):`,
+      prefixedHeaders,
+    )
+
+    return next({
+      context: {
+        prefix,
+        matchedHeaders: prefixedHeaders,
+      },
+    })
+  })
+}
+
+// Create middleware instances using the factories
+const customHeaderMiddleware = createHeaderMiddleware('x-custom-factory-header')
+const prefixedMiddleware = createPrefixedHeaderMiddleware('x-factory-')
+
+const serverFn = createServerFn()
+  .middleware([customHeaderMiddleware, prefixedMiddleware])
+  .handler(async ({ context }) => {
+    return {
+      headerName: context.headerName,
+      headerValue: context.headerValue,
+      prefix: context.prefix,
+      matchedHeaders: context.matchedHeaders,
+    }
+  })
+
+export const Route = createFileRoute('/middleware/middleware-factory')({
+  component: RouteComponent,
+})
+
+function RouteComponent() {
+  const [result, setResult] = React.useState<{
+    headerName: string
+    headerValue: string
+    prefix: string
+    matchedHeaders: Array<string>
+  } | null>(null)
+  const [error, setError] = React.useState<string | null>(null)
+
+  async function handleClick() {
+    try {
+      const data = await serverFn({
+        headers: {
+          'x-custom-factory-header': 'factory-header-value',
+          'x-factory-one': 'one',
+          'x-factory-two': 'two',
+        },
+      })
+      setResult(data)
+      setError(null)
+    } catch (e) {
+      setResult(null)
+      setError(e instanceof Error ? e.message : String(e))
+    }
+  }
+
+  return (
+    <div>
+      <h2>Middleware Factory Test</h2>
+      <p>
+        This test verifies that middleware factories (functions returning
+        createMiddleware().server()) have their server-only code properly
+        stripped from the client build.
+      </p>
+      <button onClick={handleClick} data-testid="test-middleware-factory-btn">
+        Call server function with factory middlewares
+      </button>
+      {result && (
+        <div data-testid="middleware-factory-result">
+          <div data-testid="header-value">{result.headerValue}</div>
+          <div data-testid="matched-headers">
+            {result.matchedHeaders.join(',')}
+          </div>
+        </div>
+      )}
+      {error && (
+        <div data-testid="middleware-factory-error">Error: {error}</div>
+      )}
+    </div>
+  )
+}

e2e/react-start/server-functions/tests/server-functions.spec.ts

@@ -635,3 +635,32 @@ test('server-only imports in middleware.server() are stripped from client build'
     page.getByTestId('server-import-middleware-result'),
   ).toContainText('test-header-value')
 })
+
+test('middleware factories with server-only imports are stripped from client build', async ({
+  page,
+}) => {
+  // This test verifies that middleware factories (functions returning createMiddleware().server())
+  // with server-only imports are properly stripped from the client build.
+  // If the .server() part inside the factory is not removed, the build would fail with
+  // node:async_hooks externalization errors because getRequestHeaders uses node:async_hooks internally.
+  // The fact that this page loads at all proves the server code was stripped correctly.
+  await page.goto('/middleware/middleware-factory')
+
+  await page.waitForLoadState('networkidle')
+
+  // Click the button to call the server function with factory middlewares
+  await page.getByTestId('test-middleware-factory-btn').click()
+
+  // Wait for the result - should contain our custom header value from the factory middleware
+  await expect(page.getByTestId('header-value')).toContainText(
+    'factory-header-value',
+  )
+
+  // Also verify the prefixed headers were matched correctly
+  await expect(page.getByTestId('matched-headers')).toContainText(
+    'x-factory-one',
+  )
+  await expect(page.getByTestId('matched-headers')).toContainText(
+    'x-factory-two',
+  )
+})