feat(rsc): support export default { fetch } as server handler entry (#839)

Author: hi-ogawa

packages/plugin-rsc/examples/basic/src/server.tsx

@@ -1,7 +1,7 @@
 import { handleRequest } from './framework/entry.rsc.tsx'
 import './styles.css'
 
-export default async function handler(request: Request): Promise<Response> {
+async function handler(request: Request): Promise<Response> {
   const url = new URL(request.url)
   const { Root } = await import('./routes/root.tsx')
   const nonce = !process.env.NO_CSP ? crypto.randomUUID() : undefined
@@ -38,6 +38,10 @@ export default async function handler(request: Request): Promise<Response> {
   return response
 }
 
+export default {
+  fetch: handler,
+}
+
 if (import.meta.hot) {
   import.meta.hot.accept()
 }

packages/plugin-rsc/src/plugin.ts

@@ -45,6 +45,7 @@ import {
   getEntrySource,
   hashString,
   normalizeRelativePath,
+  getFetchHandlerExport,
   sortObject,
   withRollupError,
 } from './plugins/utils'
@@ -514,13 +515,14 @@ export default function vitePluginRsc(
                 `[vite-rsc] failed to resolve server handler '${source}'`,
               )
               const mod = await environment.runner.import(resolved.id)
+              const fetchHandler = getFetchHandlerExport(mod)
               // expose original request url to server handler.
               // for example, this restores `base` which is automatically stripped by Vite.
               // https://github.com/vitejs/vite/blob/84079a84ad94de4c1ef4f1bdb2ab448ff2c01196/packages/vite/src/node/server/middlewares/base.ts#L18-L20
               req.url = req.originalUrl ?? req.url
               // ensure catching rejected promise
               // https://github.com/mjackson/remix-the-web/blob/b5aa2ae24558f5d926af576482caf6e9b35461dc/packages/node-fetch-server/src/lib/request-listener.ts#L87
-              await createRequestListener(mod.default)(req, res)
+              await createRequestListener(fetchHandler)(req, res)
             } catch (e) {
               next(e)
             }
@@ -541,7 +543,8 @@ export default function vitePluginRsc(
         )
         const entry = pathToFileURL(entryFile).href
         const mod = await import(/* @vite-ignore */ entry)
-        const handler = createRequestListener(mod.default)
+        const fetchHandler = getFetchHandlerExport(mod)
+        const handler = createRequestListener(fetchHandler)
 
         // disable compressions since it breaks html streaming
         // https://github.com/vitejs/vite/blob/9f5c59f07aefb1756a37bcb1c0aff24d54288950/packages/vite/src/node/preview.ts#L178

packages/plugin-rsc/src/plugins/utils.ts

@@ -78,3 +78,26 @@ export function getEntrySource(
 export function hashString(v: string): string {
   return createHash('sha256').update(v).digest().toString('hex').slice(0, 12)
 }
+
+// normalize server entry exports to align with server runtimes
+// https://developers.cloudflare.com/workers/runtime-apis/handlers/fetch/
+// https://srvx.h3.dev/guide
+// https://vercel.com/docs/functions/functions-api-reference?framework=other#fetch-web-standard
+// https://github.com/jacob-ebey/rsbuild-rsc-playground/blob/eb1a54afa49cbc5ff93c315744d7754d5ed63498/plugin/fetch-server.ts#L59-L79
+export function getFetchHandlerExport(exports: object): any {
+  if ('default' in exports) {
+    const default_ = exports.default
+    if (
+      default_ &&
+      typeof default_ === 'object' &&
+      'fetch' in default_ &&
+      typeof default_.fetch === 'function'
+    ) {
+      return default_.fetch
+    }
+    if (typeof default_ === 'function') {
+      return default_
+    }
+  }
+  throw new Error('Invalid server handler entry')
+}