fix: locale polluted by cross request

spec/integration.spec.ts

@@ -140,4 +140,65 @@ describe('custom locale detection', () => {
       expect(res.body).toEqual(translated[locale])
     }
   })
+  test('async parallel', async () => {
+    const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms))
+
+    const loader = (path: string) => import(path).then((m) => m.default || m)
+    const messages: Record<string, () => ReturnType<typeof loader>> = {
+      en: () => loader('./fixtures/en.json'),
+      ja: () => loader('./fixtures/ja.json'),
+    }
+
+    // async locale detector
+    const localeDetector = async (
+      event: H3Event,
+      i18n: CoreContext<string, DefineLocaleMessage>,
+    ) => {
+      const locale = getQueryLocale(event).toString()
+      await sleep(100)
+      const loader = messages[locale]
+      if (loader && !i18n.messages[locale]) {
+        const message = await loader()
+        i18n.messages[locale] = message
+      }
+      return locale
+    }
+
+    const middleware = defineI18nMiddleware({
+      locale: localeDetector,
+      messages: {
+        en: {
+          hello: 'hello, {name}',
+        },
+      },
+    })
+    app = createApp({ ...middleware })
+    request = supertest(toNodeListener(app))
+
+    app.use(
+      '/',
+      eventHandler(async (event) => {
+        await sleep(100)
+        const t = await useTranslation(event)
+        await sleep(100)
+        return { message: t('hello', { name: 'h3' }) }
+      }),
+    )
+
+    const translated: Record<string, { message: string }> = {
+      en: {
+        message: 'hello, h3',
+      },
+      ja: {
+        message: 'こんにちは, h3',
+      },
+    }
+    // request in parallel
+    const resList = await Promise.all(
+      ['en', 'ja'].map((locale) =>
+        request.get(`/?locale=${locale}`).then((res: { body: string }) => res.body)
+      ),
+    )
+    expect(resList).toEqual([translated['en'], translated['ja']])
+  })
 })

src/index.test.ts

@@ -73,6 +73,8 @@ describe('useTranslation', () => {
     const bindLocaleDetector = (locale as LocaleDetector).bind(null, eventMock)
     // @ts-ignore ignore type error because this is test
     context.locale = bindLocaleDetector
+    // @ts-ignore ignore type error because this is test
+    eventMock.context._i18nLocale = bindLocaleDetector
 
     // test `useTranslation`
     const t = await useTranslation(eventMock)

src/index.ts

@@ -1,6 +1,12 @@
 // deno-lint-ignore-file no-explicit-any ban-types
 
-import { createCoreContext, NOT_REOSLVED, translate as _translate } from '@intlify/core'
+import {
+  createCoreContext,
+  NOT_REOSLVED,
+  // @ts-expect-error internal function
+  parseTranslateArgs,
+  translate as _translate,
+} from '@intlify/core'
 import { getHeaderLocale } from '@intlify/utils/h3'
 
 export * from '@intlify/utils/h3'
@@ -27,6 +33,7 @@ import type {
 declare module 'h3' {
   interface H3EventContext {
     i18n?: CoreContext
+    _i18nLocale?: LocaleDetector
   }
 }
 
@@ -129,7 +136,8 @@ export function defineI18nMiddleware<
 
   return {
     onRequest(event: H3Event) {
-      i18n.locale = getLocaleDetector(event, i18n as CoreContext)
+      event.context._i18nLocale = getLocaleDetector(event, i18n as CoreContext)
+      i18n.locale = event.context._i18nLocale
       event.context.i18n = i18n as CoreContext
     },
     onAfterResponse(event: H3Event) {
@@ -349,16 +357,25 @@ export async function useTranslation<
     )
   }
 
-  const localeDetector = event.context.i18n.locale as unknown as LocaleDetector
+  const localeDetector = event.context._i18nLocale as unknown as LocaleDetector
+  let locale: string
   if (localeDetector.constructor.name === 'AsyncFunction') {
-    event.context.i18n.locale = await localeDetector(event)
+    locale = await localeDetector(event)
+    event.context.i18n.locale = locale
   }
 
   function translate(key: string, ...args: unknown[]): string {
+    const [_, options] = parseTranslateArgs(key, ...args)
+    const [arg2] = args
     const result = Reflect.apply(_translate, null, [
       event.context.i18n!,
       key,
-      ...args,
+      arg2,
+      {
+        // bind to request locale
+        locale,
+        ...options,
+      },
     ])
     return NOT_REOSLVED === result ? key : result as string
   }