fix: Webcontainer AsyncLocalStorage workaround (#14521)

* don't reset `sync_store` and handle one request at a time

* dry Promise.withResolvers

* hardening webcontainer detection based on @webcontainer/env

* Revert "hardening webcontainer detection based on @webcontainer/env"

This reverts commit 0f5e744.

* changeset

* Update packages/kit/src/runtime/server/constants.js

Co-authored-by: Tee Ming <[email protected]>

* try this

---------

Co-authored-by: Rich Harris <[email protected]>
Co-authored-by: Tee Ming <[email protected]>
Co-authored-by: Rich Harris <[email protected]>

Author: 3 people

.changeset/deep-insects-do.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: Webcontainer AsyncLocalStorage workaround

packages/kit/src/core/postbuild/queue.js

@@ -1,3 +1,6 @@
+/** @import { PromiseWithResolvers } from '../../utils/promise.js' */
+import { with_resolvers } from '../../utils/promise.js';
+
 /**
  * @typedef {{
  *   fn: () => Promise<any>,
@@ -10,24 +13,12 @@
 export function queue(concurrency) {
 	/** @type {Task[]} */
 	const tasks = [];
+	const { promise, resolve, reject } = /** @type {PromiseWithResolvers<void>} */ (with_resolvers());
 
 	let current = 0;
-
-	// TODO: Whenever Node >21 is minimum supported version, we can use `Promise.withResolvers` to avoid this ceremony
-	/** @type {(value?: any) => void} */
-	let fulfil;
-
-	/** @type {(error: Error) => void} */
-	let reject;
-
 	let closed = false;
 
-	const done = new Promise((f, r) => {
-		fulfil = f;
-		reject = r;
-	});
-
-	done.catch(() => {
+	promise.catch(() => {
 		// this is necessary in case a catch handler is never added
 		// to the done promise by the user
 	});
@@ -51,7 +42,7 @@ export function queue(concurrency) {
 					});
 			} else if (current === 0) {
 				closed = true;
-				fulfil();
+				resolve();
 			}
 		}
 	}
@@ -72,10 +63,10 @@ export function queue(concurrency) {
 		done: () => {
 			if (current === 0) {
 				closed = true;
-				fulfil();
+				resolve();
 			}
 
-			return done;
+			return promise;
 		}
 	};
 }

packages/kit/src/exports/internal/event.js

@@ -2,6 +2,8 @@
 /** @import { RequestStore } from 'types' */
 /** @import { AsyncLocalStorage } from 'node:async_hooks' */
 
+import { IN_WEBCONTAINER } from '../../runtime/server/constants.js';
+
 /** @type {RequestStore | null} */
 let sync_store = null;
 
@@ -74,6 +76,10 @@ export function with_request_store(store, fn) {
 		sync_store = store;
 		return als ? als.run(store, fn) : fn();
 	} finally {
-		sync_store = null;
+		// Since AsyncLocalStorage is not working in webcontainers, we don't reset `sync_store`
+		// and handle only one request at a time in `src/runtime/server/index.js`.
+		if (!IN_WEBCONTAINER) {
+			sync_store = null;
+		}
 	}
 }

packages/kit/src/runtime/server/constants.js

@@ -1 +1,4 @@
 export const NULL_BODY_STATUS = [101, 103, 204, 205, 304];
+
+// eslint-disable-next-line n/prefer-global/process
+export const IN_WEBCONTAINER = !!globalThis.process?.versions?.webcontainer;

packages/kit/src/runtime/server/index.js

@@ -1,3 +1,6 @@
+/** @import { PromiseWithResolvers } from '../../utils/promise.js' */
+import { with_resolvers } from '../../utils/promise.js';
+import { IN_WEBCONTAINER } from './constants.js';
 import { respond } from './respond.js';
 import { set_private_env, set_public_env } from '../shared-server.js';
 import { options, get_hooks } from '__SERVER__/internal.js';
@@ -23,6 +26,26 @@ export class Server {
 		this.#options = options;
 		this.#manifest = manifest;
 
+		// Since AsyncLocalStorage is not working in webcontainers, we don't reset `sync_store`
+		// in `src/exports/internal/event.js` and handle only one request at a time.
+		if (IN_WEBCONTAINER) {
+			const respond = this.respond.bind(this);
+
+			/** @type {Promise<void> | null} */
+			let current = null;
+
+			/** @type {typeof respond} */
+			this.respond = async (...args) => {
+				const { promise, resolve } = /** @type {PromiseWithResolvers<void>} */ (with_resolvers());
+
+				const previous = current;
+				current = promise;
+
+				await previous;
+				return respond(...args).finally(resolve);
+			};
+		}
+
 		set_manifest(manifest);
 	}
 

packages/kit/src/utils/promise.js

@@ -0,0 +1,29 @@
+/** @see https://github.com/microsoft/TypeScript/blob/904e7dd97dc8da1352c8e05d70829dff17c73214/src/lib/es2024.promise.d.ts */
+
+/**
+ * @template T
+ * @typedef {{
+ *   promise: Promise<T>;
+ *   resolve: (value: T | PromiseLike<T>) => void;
+ *   reject: (reason?: any) => void;
+ * }} PromiseWithResolvers<T>
+ */
+
+/**
+ * TODO: Whenever Node >21 is minimum supported version, we can use `Promise.withResolvers` to avoid this ceremony
+ *
+ * @template T
+ * @returns {PromiseWithResolvers<T>}
+ */
+export function with_resolvers() {
+	let resolve;
+	let reject;
+
+	const promise = new Promise((res, rej) => {
+		resolve = res;
+		reject = rej;
+	});
+
+	// @ts-expect-error `resolve` and `reject` are assigned!
+	return { promise, resolve, reject };
+}