Fix standalone mode with appDir running in a single process (#49116)

Fixes #49055, fixes #48918. 

App dir will always require the server to run in the workers mode, so it
can keep a separate Node.js process for pages. This PR updates the
standalone server to initialize a "standalone server" (which works
similar to `start-server`), and changes the tracked files to include
Jest worker.

docs/advanced-features/custom-server.md

@@ -51,7 +51,7 @@ app.prepare().then(() => {
     } catch (err) {
       console.error('Error occurred handling', req.url, err)
       res.statusCode = 500
-      res.end('internal server error')
+      res.end('Internal Server Error')
     }
   })
     .once('error', (err) => {

packages/next/src/build/index.ts

@@ -1899,10 +1899,21 @@ export default async function build(
               config.experimental?.turbotrace?.contextDirectory ??
               outputFileTracingRoot
 
+            // Under standalone mode, we need to trace the extra IPC server and
+            // worker files.
+            const isStandalone = config.output === 'standalone'
+
             const nextServerEntry = require.resolve(
               'next/dist/server/next-server'
             )
-            const toTrace = [nextServerEntry]
+            const toTrace = [
+              nextServerEntry,
+              isStandalone
+                ? require.resolve(
+                    'next/dist/server/lib/render-server-standalone'
+                  )
+                : null,
+            ].filter(nonNullable)
 
             // ensure we trace any dependencies needed for custom
             // incremental cache handler
@@ -1927,7 +1938,7 @@ export default async function build(
               '**/*.d.ts',
               '**/*.map',
               '**/next/dist/pages/**/*',
-              '**/next/dist/compiled/jest-worker/**/*',
+              isStandalone ? null : '**/next/dist/compiled/jest-worker/**/*',
               '**/next/dist/compiled/webpack/(bundle4|bundle5).js',
               '**/node_modules/webpack5/**/*',
               '**/next/dist/server/lib/squoosh/**/*.wasm',
@@ -1944,7 +1955,8 @@ export default async function build(
                 ? ['**/next/dist/compiled/@ampproject/toolbox-optimizer/**/*']
                 : []),
               ...additionalIgnores,
-            ]
+            ].filter(nonNullable)
+
             const ignoreFn = (pathname: string) => {
               if (path.isAbsolute(pathname) && !pathname.startsWith(root)) {
                 return true
@@ -1957,6 +1969,26 @@ export default async function build(
             }
             const traceContext = path.join(nextServerEntry, '..', '..')
             const tracedFiles = new Set<string>()
+
+            function addToTracedFiles(base: string, file: string) {
+              tracedFiles.add(
+                path
+                  .relative(distDir, path.join(base, file))
+                  .replace(/\\/g, '/')
+              )
+            }
+
+            if (isStandalone) {
+              addToTracedFiles(
+                '',
+                require.resolve('next/dist/compiled/jest-worker/processChild')
+              )
+              addToTracedFiles(
+                '',
+                require.resolve('next/dist/compiled/jest-worker/threadChild')
+              )
+            }
+
             if (config.experimental.turbotrace) {
               const files: string[] = await nodeFileTrace(
                 {
@@ -1972,11 +2004,7 @@ export default async function build(
               )
               for (const file of files) {
                 if (!ignoreFn(path.join(traceContext, file))) {
-                  tracedFiles.add(
-                    path
-                      .relative(distDir, path.join(traceContext, file))
-                      .replace(/\\/g, '/')
-                  )
+                  addToTracedFiles(traceContext, file)
                 }
               }
             } else {
@@ -1987,11 +2015,7 @@ export default async function build(
               })
 
               serverResult.fileList.forEach((file) => {
-                tracedFiles.add(
-                  path
-                    .relative(distDir, path.join(root, file))
-                    .replace(/\\/g, '/')
-                )
+                addToTracedFiles(root, file)
               })
             }
             await promises.writeFile(

packages/next/src/build/utils.ts

@@ -1913,17 +1913,20 @@ export async function copyTracedFiles(
     serverOutputPath,
     `${
       moduleType
-        ? `import Server from 'next/dist/server/next-server.js'
-import http from 'http'
+        ? `import http from 'http'
 import path from 'path'
 import { fileURLToPath } from 'url'
 const __dirname = fileURLToPath(new URL('.', import.meta.url))
-const NextServer = Server.default`
+import { createServerHandler } from 'next/dist/server/lib/render-server-standalone.js'
+`
         : `
-const NextServer = require('next/dist/server/next-server').default
 const http = require('http')
-const path = require('path')`
+const path = require('path')
+const { createServerHandler } = require('next/dist/server/lib/render-server-standalone')`
     }
+
+const dir = path.join(__dirname)
+
 process.env.NODE_ENV = 'production'
 process.chdir(__dirname)
 
@@ -1944,24 +1947,15 @@ const nextConfig = ${JSON.stringify({
       distDir: `./${path.relative(dir, distDir)}`,
     })}
 
-${
-  // In standalone mode, we don't have separated render workers so if both
-  // app and pages are used, we need to resolve to the prebundled React
-  // to ensure the correctness of the version for app.
-  `\
-if (nextConfig && nextConfig.experimental && nextConfig.experimental.appDir) {
-  process.env.__NEXT_PRIVATE_PREBUNDLED_REACT = nextConfig.experimental.serverActions ? 'experimental' : 'next'
-}
-`
-}
+process.env.__NEXT_PRIVATE_STANDALONE_CONFIG = JSON.stringify(nextConfig)
 
 const server = http.createServer(async (req, res) => {
   try {
     await handler(req, res)
   } catch (err) {
     console.error(err);
     res.statusCode = 500
-    res.end('internal server error')
+    res.end('Internal Server Error')
   }
 })
 
@@ -1972,20 +1966,18 @@ if (
 ) {
   server.keepAliveTimeout = keepAliveTimeout
 }
-server.listen(currentPort, (err) => {
+server.listen(currentPort, async (err) => {
   if (err) {
     console.error("Failed to start server", err)
     process.exit(1)
   }
-  const nextServer = new NextServer({
-    hostname,
+
+  handler = await createServerHandler({
     port: currentPort,
-    dir: path.join(__dirname),
-    dev: false,
-    customServer: false,
+    hostname,
+    dir,
     conf: nextConfig,
   })
-  handler = nextServer.getRequestHandler()
 
   console.log(
     'Listening on port',

packages/next/src/server/config.ts

@@ -689,6 +689,10 @@ export default async function loadConfig(
   rawConfig?: boolean,
   silent?: boolean
 ): Promise<NextConfigComplete> {
+  if (process.env.__NEXT_PRIVATE_STANDALONE_CONFIG) {
+    return JSON.parse(process.env.__NEXT_PRIVATE_STANDALONE_CONFIG)
+  }
+
   const curLog = silent
     ? {
         warn: () => {},

packages/next/src/server/image-optimizer.ts

@@ -460,7 +460,7 @@ export async function optimizeImage({
       console.error(
         `Error: 'sharp' is required to be installed in standalone mode for the image optimization to function correctly. Read more at: https://nextjs.org/docs/messages/sharp-missing-in-production`
       )
-      throw new ImageError(500, 'internal server error')
+      throw new ImageError(500, 'Internal Server Error')
     }
     // Show sharp warning in production once
     if (showSharpMissingWarning) {

packages/next/src/server/lib/render-server-standalone.ts

@@ -0,0 +1,107 @@
+import type { IncomingMessage, ServerResponse } from 'http'
+import type { ChildProcess } from 'child_process'
+
+import httpProxy from 'next/dist/compiled/http-proxy'
+import { Worker } from 'next/dist/compiled/jest-worker'
+import { normalizeRepeatedSlashes } from '../../shared/lib/utils'
+
+const renderServerPath = require.resolve('./render-server')
+
+export const createServerHandler = async ({
+  port,
+  hostname,
+  dir,
+  minimalMode,
+}: {
+  port: number
+  hostname: string
+  dir: string
+  minimalMode: boolean
+}) => {
+  const routerWorker = new Worker(renderServerPath, {
+    numWorkers: 1,
+    maxRetries: 10,
+    forkOptions: {
+      env: {
+        FORCE_COLOR: '1',
+        ...process.env,
+      },
+    },
+    exposedMethods: ['initialize'],
+  }) as any as InstanceType<typeof Worker> & {
+    initialize: typeof import('./render-server').initialize
+  }
+
+  let didInitialize = false
+
+  for (const _worker of ((routerWorker as any)._workerPool?._workers || []) as {
+    _child: ChildProcess
+  }[]) {
+    // eslint-disable-next-line no-loop-func
+    _worker._child.on('exit', (code, signal) => {
+      // catch failed initializing without retry
+      if ((code || signal) && !didInitialize) {
+        routerWorker?.end()
+        process.exit(1)
+      }
+    })
+  }
+
+  const workerStdout = routerWorker.getStdout()
+  const workerStderr = routerWorker.getStderr()
+
+  workerStdout.on('data', (data) => {
+    process.stdout.write(data)
+  })
+  workerStderr.on('data', (data) => {
+    process.stderr.write(data)
+  })
+
+  const { port: routerPort } = await routerWorker.initialize({
+    dir,
+    port,
+    dev: false,
+    hostname,
+    minimalMode,
+    workerType: 'router',
+  })
+  didInitialize = true
+
+  const getProxyServer = (pathname: string) => {
+    const targetUrl = `http://${hostname}:${routerPort}${pathname}`
+    const proxyServer = httpProxy.createProxy({
+      target: targetUrl,
+      changeOrigin: false,
+      ignorePath: true,
+      xfwd: true,
+      ws: true,
+      followRedirects: false,
+    })
+    return proxyServer
+  }
+
+  // proxy to router worker
+  return async (req: IncomingMessage, res: ServerResponse) => {
+    const urlParts = (req.url || '').split('?')
+    const urlNoQuery = urlParts[0]
+
+    // this normalizes repeated slashes in the path e.g. hello//world ->
+    // hello/world or backslashes to forward slashes, this does not
+    // handle trailing slash as that is handled the same as a next.config.js
+    // redirect
+    if (urlNoQuery?.match(/(\\|\/\/)/)) {
+      const cleanUrl = normalizeRepeatedSlashes(req.url!)
+      res.statusCode = 308
+      res.setHeader('Location', cleanUrl)
+      res.end(cleanUrl)
+      return
+    }
+    const proxyServer = getProxyServer(req.url || '/')
+    proxyServer.web(req, res)
+    proxyServer.on('error', (err) => {
+      res.statusCode = 500
+      res.end('Internal Server Error')
+      console.error(err)
+    })
+  }
+}

packages/next/src/server/lib/render-server.ts

@@ -42,6 +42,7 @@ export async function initialize(opts: {
   dir: string
   port: number
   dev: boolean
+  minimalMode?: boolean
   hostname?: string
   workerType: 'router' | 'render'
   keepAliveTimeout?: number
@@ -54,18 +55,24 @@ export async function initialize(opts: {
   let requestHandler: RequestHandler
 
   const server = http.createServer((req, res) => {
-    return requestHandler(req, res).finally(() => {
-      if (
-        process.memoryUsage().heapUsed / 1024 / 1024 >
-        MAXIMUM_HEAP_SIZE_ALLOWED
-      ) {
-        warn(
-          'The server is running out of memory, restarting to free up memory.'
-        )
-        server.close()
-        process.exit(WORKER_SELF_EXIT_CODE)
-      }
-    })
+    return requestHandler(req, res)
+      .catch((err) => {
+        res.statusCode = 500
+        res.end('Internal Server Error')
+        console.error(err)
+      })
+      .finally(() => {
+        if (
+          process.memoryUsage().heapUsed / 1024 / 1024 >
+          MAXIMUM_HEAP_SIZE_ALLOWED
+        ) {
+          warn(
+            'The server is running out of memory, restarting to free up memory.'
+          )
+          server.close()
+          process.exit(WORKER_SELF_EXIT_CODE)
+        }
+      })
   })
 
   if (opts.keepAliveTimeout) {

packages/next/src/server/lib/server-ipc/index.ts

@@ -104,6 +104,8 @@ export const createWorker = (
         __NEXT_PRIVATE_RENDER_WORKER: type,
         __NEXT_PRIVATE_ROUTER_IPC_PORT: ipcPort + '',
         __NEXT_PRIVATE_ROUTER_IPC_KEY: ipcValidationKey,
+        __NEXT_PRIVATE_STANDALONE_CONFIG:
+          process.env.__NEXT_PRIVATE_STANDALONE_CONFIG,
         NODE_ENV: process.env.NODE_ENV,
         ...(type === 'app'
           ? {

packages/next/src/server/next-server.ts

@@ -263,6 +263,7 @@ export default class NextNodeServer extends BaseServer {
         dir: this.dir,
         workerType: 'render',
         hostname: this.hostname,
+        minimalMode: this.minimalMode,
         dev: !!options.dev,
       }
       const { createWorker, createIpcServer } =

packages/next/src/server/next.ts

@@ -169,9 +169,11 @@ export class NextServer {
       this.serverPromise = this.loadConfig().then(async (conf) => {
         if (!this.options.dev) {
           if (conf.output === 'standalone') {
-            log.warn(
-              `"next start" does not work with "output: standalone" configuration. Use "node .next/standalone/server.js" instead.`
-            )
+            if (!process.env.__NEXT_PRIVATE_STANDALONE_CONFIG) {
+              log.warn(
+                `"next start" does not work with "output: standalone" configuration. Use "node .next/standalone/server.js" instead.`
+              )
+            }
           } else if (conf.output === 'export') {
             throw new Error(
               `"next start" does not work with "output: export" configuration. Use "npx serve@latest out" instead.`

test/e2e/streaming-ssr/custom-server/server.js

@@ -14,7 +14,7 @@ const server = http.createServer(async (req, res) => {
   } catch (err) {
     console.error(err)
     res.statusCode = 500
-    res.end('internal server error')
+    res.end('Internal Server Error')
   }
 })
 const currentPort = parseInt(process.env.PORT, 10) || 3000