Replace server context with AsyncLocalStorage and client context

Because [server context has been
deprecated](facebook/react#27424), we needed to
find a replacement for sharing the current location.

Using conditional exports, we can create a universal `useRouterLocation`
hook that utilizes `AsyncLocalStorage` on the server, and normal client
context in the browser. Even though the client context would also be
accessible in the SSR client (we could render the context provider in
`ServerRoot`), we are instead using `AsyncLocalStorage` here as well,
primarily for its convenience. Although this does require placing the
module containing the `AsyncLocalStorage` instance into a shared webpack
layer.

Author: unstubbable

apps/cloudflare-app/src/worker/create-rsc-app-options.tsx

@@ -0,0 +1,11 @@
+// This is in a separate file so that we can configure webpack to use the
+// `react-server` layer for this module, and therefore the imported modules
+// (React and the server components) will be imported with the required
+// `react-server` condition.
+
+import {App} from '@mfng/shared-app/app.js';
+import * as React from 'react';
+
+export function createRscApp(): React.ReactNode {
+  return <App getTitle={(pathname) => `Cloudflare RSC/SSR demo ${pathname}`} />;
+}

apps/cloudflare-app/src/worker/create-rsc-app.tsx

@@ -1,8 +1,9 @@
+import {routerLocationAsyncLocalStorage} from '@mfng/core/router-location-async-local-storage';
 import type {ServerManifest} from '@mfng/core/server/rsc';
 import {createRscActionStream, createRscAppStream} from '@mfng/core/server/rsc';
 import {createHtmlStream} from '@mfng/core/server/ssr';
 import type {ClientManifest, SSRManifest} from 'react-server-dom-webpack';
-import {createRscAppOptions} from './create-rsc-app-options.js';
+import {createRscApp} from './create-rsc-app.js';
 import type {EnvWithStaticContent, HandlerParams} from './get-json-from-kv.js';
 import {getJsonFromKv} from './get-json-from-kv.js';
 
@@ -24,25 +25,29 @@ const handleGet: ExportedHandlerFetchHandler<EnvWithStaticContent> = async (
       getJsonFromKv<Record<string, string>>(`client/css-manifest.json`, params),
     ]);
 
-  const rscAppStream = createRscAppStream({
-    ...createRscAppOptions({requestUrl: request.url}),
-    reactClientManifest,
-    mainCssHref: cssManifest[`main.css`]!,
-  });
+  const {pathname, search} = new URL(request.url);
 
-  if (request.headers.get(`accept`) === `text/x-component`) {
-    return new Response(rscAppStream, {
-      headers: {'Content-Type': `text/x-component; charset=utf-8`},
+  return routerLocationAsyncLocalStorage.run({pathname, search}, async () => {
+    const rscAppStream = createRscAppStream({
+      app: createRscApp(),
+      reactClientManifest,
+      mainCssHref: cssManifest[`main.css`]!,
     });
-  }
 
-  const htmlStream = await createHtmlStream(rscAppStream, {
-    reactSsrManifest,
-    bootstrapScripts: [jsManifest[`main.js`]!],
-  });
+    if (request.headers.get(`accept`) === `text/x-component`) {
+      return new Response(rscAppStream, {
+        headers: {'Content-Type': `text/x-component; charset=utf-8`},
+      });
+    }
+
+    const htmlStream = await createHtmlStream(rscAppStream, {
+      reactSsrManifest,
+      bootstrapScripts: [jsManifest[`main.js`]!],
+    });
 
-  return new Response(htmlStream, {
-    headers: {'Content-Type': `text/html; charset=utf-8`},
+    return new Response(htmlStream, {
+      headers: {'Content-Type': `text/html; charset=utf-8`},
+    });
   });
 };
 

apps/cloudflare-app/src/worker/index.ts

@@ -95,19 +95,24 @@ export default function createConfigs(_env, argv) {
     },
     resolve: {
       plugins: [new ResolveTypeScriptPlugin()],
-      conditionNames: [`workerd`, `...`],
+      conditionNames: [`workerd`, `node`, `...`],
     },
     module: {
       rules: [
         {
           resource: (value) =>
             /core\/lib\/server\/rsc\.js$/.test(value) ||
-            /create-rsc-app-options\.tsx$/.test(value),
+            /create-rsc-app\.tsx$/.test(value),
           layer: webpackRscLayerName,
         },
+        {
+          // AsyncLocalStorage module instances must be in a shared layer.
+          layer: `shared`,
+          test: /(router-location-async-local-storage|core\/lib\/server\/use-router-location\.js)/,
+        },
         {
           issuerLayer: webpackRscLayerName,
-          resolve: {conditionNames: [`react-server`, `...`]},
+          resolve: {conditionNames: [`react-server`, `node`, `...`]},
         },
         {
           oneOf: [

apps/cloudflare-app/webpack.config.js

@@ -1,16 +1,16 @@
 'use client';
 
 import {useRouter} from '@mfng/core/client';
+import {useRouterLocation} from '@mfng/core/use-router-location';
 import * as React from 'react';
-import {LocationServerContext} from '../shared/location-server-context.js';
 
 export function CountriesSearch(): JSX.Element {
-  const location = React.useContext(LocationServerContext);
+  const {search} = useRouterLocation();
   const {replace} = useRouter();
   const [, startTransition] = React.useTransition();
 
   const [query, setQuery] = React.useState(
-    () => new URL(location).searchParams.get(`q`) || ``,
+    () => new URLSearchParams(search).get(`q`) || ``,
   );
 
   const handleChange: React.ChangeEventHandler<HTMLInputElement> = (event) => {

apps/shared-app/src/client/countries-search.tsx

@@ -1,6 +1,6 @@
+import {useRouterLocation} from '@mfng/core/use-router-location';
 import * as React from 'react';
 import {NavigationContainer} from '../client/navigation-container.js';
-import {LocationServerContext} from '../shared/location-server-context.js';
 import {Navigation} from '../shared/navigation.js';
 import {Routes} from './routes.js';
 
@@ -9,8 +9,7 @@ export interface AppProps {
 }
 
 export function App({getTitle}: AppProps): JSX.Element {
-  const location = React.useContext(LocationServerContext);
-  const {pathname} = new URL(location);
+  const {pathname} = useRouterLocation();
 
   return (
     <html>
@@ -21,14 +20,12 @@ export function App({getTitle}: AppProps): JSX.Element {
         <link rel="icon" href="/client/favicon.ico" type="image/x-icon" />
       </head>
       <body>
-        <LocationServerContext.Provider value={location}>
-          <React.Suspense>
-            <Navigation />
-            <NavigationContainer>
-              <Routes />
-            </NavigationContainer>
-          </React.Suspense>
-        </LocationServerContext.Provider>
+        <React.Suspense>
+          <Navigation />
+          <NavigationContainer>
+            <Routes />
+          </NavigationContainer>
+        </React.Suspense>
       </body>
     </html>
   );

apps/shared-app/src/server/app.tsx

@@ -1,10 +1,10 @@
+import {useRouterLocation} from '@mfng/core/use-router-location';
 import * as React from 'react';
-import {LocationServerContext} from '../shared/location-server-context.js';
 import {countriesFuse} from './countries-fuse.js';
 
 export function CountriesList(): JSX.Element {
-  const location = React.useContext(LocationServerContext);
-  const query = new URL(location).searchParams.get(`q`);
+  const {search} = useRouterLocation();
+  const query = new URLSearchParams(search).get(`q`);
 
   if (!query) {
     return (

apps/shared-app/src/server/countries-list.tsx

@@ -1,12 +1,11 @@
+import {useRouterLocation} from '@mfng/core/use-router-location';
 import * as React from 'react';
-import {LocationServerContext} from '../shared/location-server-context.js';
 import {FastPage} from './fast-page.js';
 import {HomePage} from './home-page.js';
 import {SlowPage} from './slow-page.js';
 
 export function Routes(): JSX.Element {
-  const location = React.useContext(LocationServerContext);
-  const {pathname} = new URL(location);
+  const {pathname} = useRouterLocation();
 
   switch (pathname) {
     case `/slow-page`:

apps/shared-app/src/server/routes.tsx

@@ -1,6 +1,6 @@
+import {useRouterLocation} from '@mfng/core/use-router-location';
 import * as React from 'react';
 import {Link} from '../client/link.js';
-import {LocationServerContext} from './location-server-context.js';
 
 export type NavigationItemProps = React.PropsWithChildren<{
   readonly pathname: string;
@@ -10,9 +10,9 @@ export function NavigationItem({
   children,
   pathname,
 }: NavigationItemProps): JSX.Element {
-  const location = React.useContext(LocationServerContext);
+  const {pathname: currentPathname} = useRouterLocation();
 
-  if (pathname === new URL(location).pathname) {
+  if (pathname === currentPathname) {
     return (
       <span className="inline-block rounded-md bg-zinc-800 py-1 px-3 text-zinc-50">
         {children}