[Flight][Float] Preinitialize module imports during SSR (#27314)

Currently when we SSR a Flight response we do not emit any resources for
module imports. This means that when the client hydrates it won't have
already loaded the necessary scripts to satisfy the Imports defined in
the Flight payload which will lead to a delay in hydration completing.

This change updates `react-server-dom-webpack` and
`react-server-dom-esm` to emit async script tags in the head when we
encounter a modules in the flight response.

To support this we need some additional server configuration. We need to
know the path prefix for chunk loading and whether the chunks will load
with CORS or not (and if so with what configuration).

Author: gnoff

fixtures/flight-esm/.nvmrc

@@ -0,0 +1 @@
+v18

fixtures/flight-esm/server/global.js

@@ -10,6 +10,7 @@ const compress = require('compression');
 const chalk = require('chalk');
 const express = require('express');
 const http = require('http');
+const React = require('react');
 
 const {renderToPipeableStream} = require('react-dom/server');
 const {createFromNodeStream} = require('react-server-dom-esm/client');
@@ -62,23 +63,39 @@ app.all('/', async function (req, res, next) {
   if (req.accepts('text/html')) {
     try {
       const rscResponse = await promiseForData;
-
       const moduleBaseURL = '/src';
 
       // For HTML, we're a "client" emulator that runs the client code,
       // so we start by consuming the RSC payload. This needs the local file path
       // to load the source files from as well as the URL path for preloads.
-      const root = await createFromNodeStream(
-        rscResponse,
-        moduleBasePath,
-        moduleBaseURL
-      );
+
+      let root;
+      let Root = () => {
+        if (root) {
+          return React.use(root);
+        }
+
+        return React.use(
+          (root = createFromNodeStream(
+            rscResponse,
+            moduleBasePath,
+            moduleBaseURL
+          ))
+        );
+      };
       // Render it into HTML by resolving the client components
       res.set('Content-type', 'text/html');
-      const {pipe} = renderToPipeableStream(root, {
-        // TODO: bootstrapModules inserts a preload before the importmap which causes
-        // the import map to be invalid. We need to fix that in Float somehow.
-        // bootstrapModules: ['/src/index.js'],
+      const {pipe} = renderToPipeableStream(React.createElement(Root), {
+        importMap: {
+          imports: {
+            react: 'https://esm.sh/react@experimental?pin=v124&dev',
+            'react-dom': 'https://esm.sh/react-dom@experimental?pin=v124&dev',
+            'react-dom/': 'https://esm.sh/react-dom@experimental&pin=v124&dev/',
+            'react-server-dom-esm/client':
+              '/node_modules/react-server-dom-esm/esm/react-server-dom-esm-client.browser.development.js',
+          },
+        },
+        bootstrapModules: ['/src/index.js'],
       });
       pipe(res);
     } catch (e) {
@@ -89,6 +106,7 @@ app.all('/', async function (req, res, next) {
   } else {
     try {
       const rscResponse = await promiseForData;
+
       // For other request, we pass-through the RSC payload.
       res.set('Content-type', 'text/x-component');
       rscResponse.on('data', data => {

fixtures/flight-esm/src/App.js

@@ -9,16 +9,6 @@ import {getServerState} from './ServerState.js';
 
 const h = React.createElement;
 
-const importMap = {
-  imports: {
-    react: 'https://esm.sh/react@experimental?pin=v124&dev',
-    'react-dom': 'https://esm.sh/react-dom@experimental?pin=v124&dev',
-    'react-dom/': 'https://esm.sh/react-dom@experimental&pin=v124&dev/',
-    'react-server-dom-esm/client':
-      '/node_modules/react-server-dom-esm/esm/react-server-dom-esm-client.browser.development.js',
-  },
-};
-
 export default async function App() {
   const res = await fetch('http://localhost:3001/todos');
   const todos = await res.json();
@@ -42,12 +32,6 @@ export default async function App() {
         rel: 'stylesheet',
         href: '/src/style.css',
         precedence: 'default',
-      }),
-      h('script', {
-        type: 'importmap',
-        dangerouslySetInnerHTML: {
-          __html: JSON.stringify(importMap),
-        },
       })
     ),
     h(
@@ -84,9 +68,7 @@ export default async function App() {
             'Like'
           )
         )
-      ),
-      // TODO: Move this to bootstrapModules.
-      h('script', {type: 'module', src: '/src/index.js'})
+      )
     )
   );
 }

fixtures/flight-esm/yarn.lock

@@ -540,17 +540,17 @@ [email protected]:
     unpipe "1.0.0"
 
 react-dom@experimental:
-  version "0.0.0-experimental-018c58c9c-20230601"
-  resolved "https://registry.yarnpkg.com/react-dom/-/react-dom-0.0.0-experimental-018c58c9c-20230601.tgz#2cc0ac824b83bab2ac1c6187f241dbd5dcd5201b"
-  integrity sha512-hwRsyoG1R3Tub0nUa72YvNcqPvU+pTcr9dadOnUCKKfSiYVbBCy7LxmkqLauCD8OjNJMlwtMgG4UAgtidclYGQ==
+  version "0.0.0-experimental-b9be4537c-20230905"
+  resolved "https://registry.yarnpkg.com/react-dom/-/react-dom-0.0.0-experimental-b9be4537c-20230905.tgz#b078d6d06041e0c98ce5a2f5e9ff26a2e308eb41"
+  integrity sha512-veAFNVj81lUYhYlucYm3kbj2BhakG57XYkWC/QHVEZDk4Hm2qxM9RUk7gn8dWs9Eq7KR6Q+JWiSH3ZbObQTV9g==
   dependencies:
     loose-envify "^1.1.0"
-    scheduler "0.0.0-experimental-018c58c9c-20230601"
+    scheduler "0.0.0-experimental-b9be4537c-20230905"
 
 react@experimental:
-  version "0.0.0-experimental-018c58c9c-20230601"
-  resolved "https://registry.yarnpkg.com/react/-/react-0.0.0-experimental-018c58c9c-20230601.tgz#ab04d1243c8f83b0166ed342056fa6b38ab2cd23"
-  integrity sha512-nSQIBsZ26Ii899pZ9cRt/6uQLbIUEAcDIivvAQyaHp4pWm289aB+7AK7VCWojAJIf4OStCuWs2berZsk4mzLVg==
+  version "0.0.0-experimental-b9be4537c-20230905"
+  resolved "https://registry.yarnpkg.com/react/-/react-0.0.0-experimental-b9be4537c-20230905.tgz#3c2352b42b8024544a12dcd96f2700313cebcb6b"
+  integrity sha512-QNeK74S7AU94j4vCxet2S76HqxpF6CJo1pG3XcgY2NravyXdWYszrRDNHrfu86gGNwAQvSU+YpStYn/i0b9tLA==
   dependencies:
     loose-envify "^1.1.0"
 
@@ -588,10 +588,10 @@ [email protected]:
   resolved "https://registry.yarnpkg.com/safer-buffer/-/safer-buffer-2.1.2.tgz#44fa161b0187b9549dd84bb91802f9bd8385cd6a"
   integrity sha512-YZo3K82SD7Riyi0E1EQPojLz7kpepnSQI9IyPbHHg1XXXevb5dJI7tpyN2ADxGcQbHG7vcyRHk0cbwqcQriUtg==
 
-[email protected]018c58c9c-20230601:
-  version "0.0.0-experimental-018c58c9c-20230601"
-  resolved "https://registry.yarnpkg.com/scheduler/-/scheduler-0.0.0-experimental-018c58c9c-20230601.tgz#4f083614f8e857bab63dd90b4b37b03783dafe6b"
-  integrity sha512-otUM7AAAnCoJ5/0jTQwUQ7NhxjgcPEdrfzW7NfkpocrDoTUbql1kIGIhj9L9POMVFDI/wcZzRNK/oIEWsB4DPw==
+[email protected]b9be4537c-20230905:
+  version "0.0.0-experimental-b9be4537c-20230905"
+  resolved "https://registry.yarnpkg.com/scheduler/-/scheduler-0.0.0-experimental-b9be4537c-20230905.tgz#f0fe5a710ce15a9d637c28e9f019a4100e1f3f34"
+  integrity sha512-V5P9LOS+c5CG7qaCJu+Qgcz9eh/dP4nBszj3w1MCgZnMtAna6+J8ZuuUnRDMeY86F8KH+cY8Q5beIvAL2noMzA==
   dependencies:
     loose-envify "^1.1.0"
 

fixtures/flight/.nvmrc

@@ -0,0 +1 @@
+v18

fixtures/flight/server/global.js

@@ -33,6 +33,7 @@ const compress = require('compression');
 const chalk = require('chalk');
 const express = require('express');
 const http = require('http');
+const React = require('react');
 
 const {renderToPipeableStream} = require('react-dom/server');
 const {createFromNodeStream} = require('react-server-dom-webpack/client');
@@ -62,6 +63,11 @@ if (process.env.NODE_ENV === 'development') {
     webpackMiddleware(compiler, {
       publicPath: paths.publicUrlOrPath.slice(0, -1),
       serverSideRender: true,
+      headers: () => {
+        return {
+          'Cache-Control': 'no-store, must-revalidate',
+        };
+      },
     })
   );
   app.use(webpackHotMiddleware(compiler));
@@ -121,12 +127,13 @@ app.all('/', async function (req, res, next) {
         buildPath = path.join(__dirname, '../build/');
       }
       // Read the module map from the virtual file system.
-      const moduleMap = JSON.parse(
+      const ssrManifest = JSON.parse(
         await virtualFs.readFile(
           path.join(buildPath, 'react-ssr-manifest.json'),
           'utf8'
         )
       );
+
       // Read the entrypoints containing the initial JS to bootstrap everything.
       // For other pages, the chunks in the RSC payload are enough.
       const mainJSChunks = JSON.parse(
@@ -138,15 +145,35 @@ app.all('/', async function (req, res, next) {
       // For HTML, we're a "client" emulator that runs the client code,
       // so we start by consuming the RSC payload. This needs a module
       // map that reverse engineers the client-side path to the SSR path.
-      const {root, formState} = await createFromNodeStream(
-        rscResponse,
-        moduleMap
-      );
+
+      // This is a bad hack to set the form state after SSR has started. It works
+      // because we block the root component until we have the form state and
+      // any form that reads it necessarily will come later. It also only works
+      // because the formstate type is an object which may change in the future
+      const lazyFormState = [];
+
+      let cachedResult = null;
+      async function getRootAndFormState() {
+        const {root, formState} = await createFromNodeStream(
+          rscResponse,
+          ssrManifest
+        );
+        // We shouldn't be assuming formState is an object type but at the moment
+        // we have no way of setting the form state from within the render
+        Object.assign(lazyFormState, formState);
+        return root;
+      }
+      let Root = () => {
+        if (!cachedResult) {
+          cachedResult = getRootAndFormState();
+        }
+        return React.use(cachedResult);
+      };
       // Render it into HTML by resolving the client components
       res.set('Content-type', 'text/html');
-      const {pipe} = renderToPipeableStream(root, {
+      const {pipe} = renderToPipeableStream(React.createElement(Root), {
         bootstrapScripts: mainJSChunks,
-        experimental_formState: formState,
+        experimental_formState: lazyFormState,
       });
       pipe(res);
     } catch (e) {

packages/react-client/src/ReactFlightClient.js

@@ -13,8 +13,9 @@ import type {LazyComponent} from 'react/src/ReactLazy';
 import type {
   ClientReference,
   ClientReferenceMetadata,
-  SSRManifest,
+  SSRModuleMap,
   StringDecoder,
+  ModuleLoading,
 } from './ReactFlightClientConfig';
 
 import type {
@@ -36,6 +37,7 @@ import {
   readPartialStringChunk,
   readFinalStringChunk,
   createStringDecoder,
+  prepareDestinationForModule,
 } from './ReactFlightClientConfig';
 
 import {registerServerReference} from './ReactFlightReplyClient';
@@ -178,8 +180,10 @@ Chunk.prototype.then = function <T>(
 };
 
 export type Response = {
-  _bundlerConfig: SSRManifest,
+  _bundlerConfig: SSRModuleMap,
+  _moduleLoading: ModuleLoading,
   _callServer: CallServerCallback,
+  _nonce: ?string,
   _chunks: Map<number, SomeChunk<any>>,
   _fromJSON: (key: string, value: JSONValue) => any,
   _stringDecoder: StringDecoder,
@@ -706,13 +710,17 @@ function missingCall() {
 }
 
 export function createResponse(
-  bundlerConfig: SSRManifest,
+  bundlerConfig: SSRModuleMap,
+  moduleLoading: ModuleLoading,
   callServer: void | CallServerCallback,
+  nonce: void | string,
 ): Response {
   const chunks: Map<number, SomeChunk<any>> = new Map();
   const response: Response = {
     _bundlerConfig: bundlerConfig,
+    _moduleLoading: moduleLoading,
     _callServer: callServer !== undefined ? callServer : missingCall,
+    _nonce: nonce,
     _chunks: chunks,
     _stringDecoder: createStringDecoder(),
     _fromJSON: (null: any),
@@ -774,6 +782,12 @@ function resolveModule(
     clientReferenceMetadata,
   );
 
+  prepareDestinationForModule(
+    response._moduleLoading,
+    response._nonce,
+    clientReferenceMetadata,
+  );
+
   // TODO: Add an option to encode modules that are lazy loaded.
   // For now we preload all modules as early as possible since it's likely
   // that we'll need them.

packages/react-client/src/forks/ReactFlightClientConfig.custom.js

@@ -25,7 +25,8 @@
 
 declare var $$$config: any;
 
-export opaque type SSRManifest = mixed;
+export opaque type ModuleLoading = mixed;
+export opaque type SSRModuleMap = mixed;
 export opaque type ServerManifest = mixed;
 export opaque type ServerReferenceId = string;
 export opaque type ClientReferenceMetadata = mixed;
@@ -35,6 +36,8 @@ export const resolveServerReference = $$$config.resolveServerReference;
 export const preloadModule = $$$config.preloadModule;
 export const requireModule = $$$config.requireModule;
 export const dispatchHint = $$$config.dispatchHint;
+export const prepareDestinationForModule =
+  $$$config.prepareDestinationForModule;
 export const usedWithSSR = true;
 
 export opaque type Source = mixed;

packages/react-client/src/forks/ReactFlightClientConfig.dom-browser-esm.js

@@ -8,6 +8,7 @@
  */
 
 export * from 'react-client/src/ReactFlightClientConfigBrowser';
-export * from 'react-server-dom-esm/src/ReactFlightClientConfigESMBundler';
+export * from 'react-server-dom-esm/src/ReactFlightClientConfigBundlerESM';
+export * from 'react-server-dom-esm/src/ReactFlightClientConfigTargetESMBrowser';
 export * from 'react-dom-bindings/src/shared/ReactFlightClientConfigDOM';
 export const usedWithSSR = false;

packages/react-client/src/forks/ReactFlightClientConfig.dom-browser.js

@@ -8,6 +8,8 @@
  */
 
 export * from 'react-client/src/ReactFlightClientConfigBrowser';
-export * from 'react-server-dom-webpack/src/ReactFlightClientConfigWebpackBundler';
+export * from 'react-server-dom-webpack/src/ReactFlightClientConfigBundlerWebpack';
+export * from 'react-server-dom-webpack/src/ReactFlightClientConfigBundlerWebpackBrowser';
+export * from 'react-server-dom-webpack/src/ReactFlightClientConfigTargetWebpackBrowser';
 export * from 'react-dom-bindings/src/shared/ReactFlightClientConfigDOM';
 export const usedWithSSR = false;