add nodejs_compat runtime check (#236)

cloudflare · May 15, 2023 · e053756 · e053756
1 parent 3277f72
commit e053756
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Showing 4 changed files with 57 additions and 26 deletions.
diff --git a/.changeset/new-waves-refuse.md b/.changeset/new-waves-refuse.md
@@ -0,0 +1,9 @@
+---
+'@cloudflare/next-on-pages': minor
+---
+
+add nodejs_compat runtime check
+
+add a runtime check for the presence of the nodejs_compat flag at runtime so that if developers
+forget to use such flag instead of receiving an internal server error they receive an error specifically
+telling them that they have not specified the flag
diff --git a/src/buildApplication/generateGlobalJs.ts b/src/buildApplication/generateGlobalJs.ts
@@ -6,26 +6,29 @@
  */
 export function generateGlobalJs(): string {
 	return `
-		import { AsyncLocalStorage } from 'node:async_hooks';
-		globalThis.AsyncLocalStorage = AsyncLocalStorage;
+		const __ENV_ALS_PROMISE__ = import('node:async_hooks').then(({ AsyncLocalStorage }) => {
+			globalThis.AsyncLocalStorage = AsyncLocalStorage;
 
-		const __ENV_ALS__ = new AsyncLocalStorage();
+			const envAsyncLocalStorage = new AsyncLocalStorage();
 
-		globalThis.process = {
-			env: new Proxy(
-				{},
-				{
-					get: (_, property) => {
-						${/* TODO: remove try-catch ASAP (after runtime fix) @dario */ ''}
-						try {
-							const result = Reflect.get(__ENV_ALS__.getStore(), property);
-							return result;
-						} catch (e) {
-							return undefined;
-						}
-					},
-					set: (_, property, value) => Reflect.set(__ENV_ALS__.getStore(), property, value),
-			}),
-		};
+			globalThis.process = {
+				env: new Proxy(
+					{},
+					{
+						get: (_, property) => {
+							${/* TODO: remove try-catch ASAP (after runtime fix) @dario */ ''}
+							try {
+								const result = Reflect.get(envAsyncLocalStorage.getStore(), property);
+								return result;
+							} catch (e) {
+								return undefined;
+							}
+						},
+						set: (_, property, value) => Reflect.set(envAsyncLocalStorage.getStore(), property, value),
+				}),
+			};
+			return envAsyncLocalStorage;
+		})
+		.catch(() => null);
 	`;
 }
diff --git a/templates/_worker.js/index.ts b/templates/_worker.js/index.ts
@@ -8,13 +8,19 @@ declare const __CONFIG__: ProcessedVercelConfig;
 
 declare const __BUILD_OUTPUT__: VercelBuildOutput;
 
-declare const __ENV_ALS__: AsyncLocalStorage<unknown> & {
-	NODE_ENV: string;
-};
+declare const __ENV_ALS_PROMISE__: Promise<null | AsyncLocalStorage<unknown>>;
 
 export default {
 	async fetch(request, env, ctx) {
-		return __ENV_ALS__.run({ ...env, NODE_ENV: __NODE_ENV__ }, () => {
+		const envAsyncLocalStorage = await __ENV_ALS_PROMISE__;
+		if (!envAsyncLocalStorage) {
+			return new Response(
+				'Error: Could not access built-in node modules, please make sure that your Cloudflare Pages' +
+					" project has the 'nodejs_compat' compatibility flag set.",
+				{ status: 503 }
+			);
+		}
+		return envAsyncLocalStorage.run({ ...env, NODE_ENV: __NODE_ENV__ }, () => {
 			const adjustedRequest = adjustRequestForVercel(request);
 
 			return handleRequest(

diff --git a/tests/src/buildApplication/generateGlobalJs.test.ts b/tests/src/buildApplication/generateGlobalJs.test.ts
@@ -3,6 +3,13 @@ import { generateGlobalJs } from '../../../src/buildApplication/generateGlobalJs
 
 describe('generateGlobalJs', async () => {
 	describe('AsyncLocalStorage', () => {
+		test('should generate a promise for the AsyncLocalStorage import', async () => {
+			const globalJs = generateGlobalJs();
+			expect(globalJs).toContain(
+				"const __ENV_ALS_PROMISE__ = import('node:async_hooks')"
+			);
+		});
+
 		test('should make the AsyncLocalStorage globally available', async () => {
 			const globalJs = generateGlobalJs();
 			expect(globalJs).toContain(
@@ -12,7 +19,9 @@ describe('generateGlobalJs', async () => {
 
 		test('create an AsyncLocalStorage and set it as a proxy to process.env', async () => {
 			const globalJs = generateGlobalJs();
-			expect(globalJs).toContain('const __ENV_ALS__ = new AsyncLocalStorage()');
+			expect(globalJs).toContain(
+				'const envAsyncLocalStorage = new AsyncLocalStorage()'
+			);
 
 			const proxyRegexMatch = globalJs.match(
 				/globalThis.process = {[\S\s]*Proxy\(([\s\S]+)\)[\s\S]+}/
@@ -21,8 +30,12 @@ describe('generateGlobalJs', async () => {
 			expect(proxyRegexMatch?.length).toBe(2);
 
 			const proxyBody = proxyRegexMatch?.[1];
-			expect(proxyBody).toContain('Reflect.get(__ENV_ALS__.getStore()');
-			expect(proxyBody).toContain('Reflect.set(__ENV_ALS__.getStore()');
+			expect(proxyBody).toContain(
+				'Reflect.get(envAsyncLocalStorage.getStore()'
+			);
+			expect(proxyBody).toContain(
+				'Reflect.set(envAsyncLocalStorage.getStore()'
+			);
 		});
 	});
 });