Add opt-out for AsyncLocalStorage

.changeset/fast-stingrays-leave.md

@@ -0,0 +1,23 @@
+---
+"@inlang/paraglide-sveltekit": minor
+---
+
+Adds a `disableAsyncLocalStorage` option to `i18n.handle`. This allows you to opt out of using the experimental `AsyncLocalStorage` API.
+
+**Warning**
+Disabling `AsyncLocalStorage` removes the protection against concurrent requests overriding each other's language state. 
+
+Only opt out if `AsyncLocalStorage` if you are certain your environment does not handle concurrent requests in the same process. For example in Vercel Edge functions or Cloudflare Workers. 
+
+In environments where only one request is processed in a given process disabling `AsyncLocalStorage` can yield performance gains. 
+
+**Example**
+```ts
+// src/hooks.server.js
+import { i18n } from "$lib/i18n"
+
+export const handle = i18n.handle({
+    disableAsyncLocalStorage: true // @default = false
+})
+
+```

inlang/source-code/paraglide/paraglide-sveltekit/package.json

@@ -30,8 +30,7 @@
 		"dedent": "1.5.1",
 		"devalue": "^4.3.2",
 		"magic-string": "^0.30.5",
-		"svelte": "^5.0.0 || ^5.0.0-next.1 || ^5.0.0-rc.1",
-		"unctx": "^2.3.1"
+		"svelte": "^5.0.0 || ^5.0.0-next.1 || ^5.0.0-rc.1"
 	},
 	"peerDependencies": {
 		"@sveltejs/kit": "^2.4.3"

inlang/source-code/paraglide/paraglide-sveltekit/src/runtime/hooks/handle.server.ts

@@ -7,7 +7,7 @@ import type { Handle } from "@sveltejs/kit"
 import type { I18nConfig } from "../adapter.server.js"
 import type { RoutingStrategy } from "../strategy.js"
 import type { ParaglideLocals } from "../locals.js"
-import { createContext } from "unctx"
+import { ALSContext, GlobalContext, type Context } from "./utils.js"
 
 /**
  * The default lang attribute string that's in SvelteKit's `src/app.html` file.
@@ -58,39 +58,43 @@ export type HandleOptions = {
 	 * ONLY DISABLE THIS IF YOU ARE CERTAIN YOUR ENVIRONMENT DOES
 	 * NOT ALLOW CONCURRENT REQUESTS.
 	 *
-	 * For example: Edge functions
+	 * For example in Vercel Edge functions
 	 *
-	 * @default true
+	 * @default false
 	 */
-	asyncLocalStorage?: boolean
+	disableAsyncLocalStorage?: boolean
 }
 
 export const createHandle = <T extends string>(
 	strategy: RoutingStrategy<T>,
 	i18n: I18nConfig<T>,
 	options: HandleOptions
 ): Handle => {
-	const shouldUseAsyncLocalStorage = options.asyncLocalStorage ?? true
-
-	let ALS = undefined
-	const languageContext = createContext<T>({
-		asyncContext: true,
-		AsyncLocalStorage: ALS,
-	})
-
-	i18n.runtime.setLanguageTag(() => {
-		const val = languageContext.tryUse()
-		return i18n.runtime.isAvailableLanguageTag(val) ? val : i18n.defaultLanguageTag
-	})
+	let languageContext: Context<T> | undefined = undefined
+	function initializeLanguageContext(
+		AsyncLocalStorage: typeof import("node:async_hooks").AsyncLocalStorage | undefined
+	) {
+		languageContext = AsyncLocalStorage ? new ALSContext(AsyncLocalStorage) : new GlobalContext()
+		i18n.runtime.setLanguageTag(() => {
+			if (!languageContext)
+				throw new Error(
+					"languageContext not initialized - This should never happen, please file an issue"
+				)
+			const val = languageContext.get()
+			return i18n.runtime.isAvailableLanguageTag(val) ? val : i18n.defaultLanguageTag
+		})
+	}
 
 	const langPlaceholder = options.langPlaceholder ?? "%paraglide.lang%"
 	const dirPlaceholder = options.textDirectionPlaceholder ?? "%paraglide.textDirection%"
 
 	return async ({ resolve, event }) => {
-		// make sure `node:async_hooks` has been loaded
-		if (shouldUseAsyncLocalStorage) {
-			const { AsyncLocalStorage } = await import("node:async_hooks")
-			ALS = AsyncLocalStorage
+		// if the langauge context is not yet initialized
+		if (!languageContext) {
+			const als = options.disableAsyncLocalStorage
+				? undefined
+				: (await import("node:async_hooks")).AsyncLocalStorage
+			initializeLanguageContext(als)
 		}
 
 		const [localisedPath, suffix] = parseRoute(event.url.pathname as `/${string}`, base)
@@ -140,6 +144,10 @@ export const createHandle = <T extends string>(
 		// @ts-expect-error
 		event.locals.paraglide = paraglideLocals
 
+		if (!languageContext)
+			throw new Error(
+				"languageContext not initialized - This should never happen, please file an issue"
+			)
 		return languageContext.callAsync(paraglideLocals.lang, async () => {
 			return await resolve(event, {
 				transformPageChunk({ html, done }) {

inlang/source-code/paraglide/paraglide-sveltekit/src/runtime/hooks/reroute.test.ts

@@ -7,7 +7,7 @@ import * as runtime from "$paraglide/runtime.js"
 import { PrefixStrategy } from "../strategy"
 
 const reroute = createReroute<"en" | "de">(
-	PrefixStrategy(runtime.availableLanguageTags, runtime.sourceLanguageTag, {}, {})
+	PrefixStrategy(runtime.availableLanguageTags, runtime.sourceLanguageTag, {}, {}, "always")
 )
 
 describe("reroute", () => {

inlang/source-code/paraglide/paraglide-sveltekit/src/runtime/hooks/utils.ts

@@ -0,0 +1,34 @@
+export type ALS<T> = import("node:async_hooks").AsyncLocalStorage<T>
+export type ALSPrototype = typeof import("node:async_hooks").AsyncLocalStorage
+
+export interface Context<T> {
+	get(): T | undefined
+	callAsync: <CB extends () => any>(val: T, cb: CB) => Promise<Awaited<ReturnType<CB>>>
+}
+
+export class ALSContext<T> implements Context<T> {
+	ctx: ALS<T>
+	constructor(ALS: ALSPrototype) {
+		this.ctx = new ALS<T>()
+	}
+
+	get(): T | undefined {
+		return this.ctx.getStore()
+	}
+
+	async callAsync(val: T, cb: () => any) {
+		return await this.ctx.run(val, cb)
+	}
+}
+export class GlobalContext<T> implements Context<T> {
+	value: T | undefined = undefined
+
+	get(): T | undefined {
+		return this.value
+	}
+
+	async callAsync(val: T, cb: () => any) {
+		this.value = val
+		return await cb()
+	}
+}