fix: improve the worker integrity warning

src/browser/setupWorker/glossary.ts

@@ -54,7 +54,10 @@ export type ServiceWorkerIncomingResponse = Pick<
  */
 export interface ServiceWorkerIncomingEventsMap {
   MOCKING_ENABLED: boolean
-  INTEGRITY_CHECK_RESPONSE: string
+  INTEGRITY_CHECK_RESPONSE: {
+    packageVersion: string
+    checksum: string
+  }
   KEEPALIVE_RESPONSE: never
   REQUEST: ServiceWorkerIncomingRequest
   RESPONSE: ServiceWorkerIncomingResponse

src/browser/setupWorker/start/createStartHandler.ts

@@ -1,10 +1,9 @@
-import { until } from '@open-draft/until'
 import { devUtils } from '~/core/utils/internal/devUtils'
 import { getWorkerInstance } from './utils/getWorkerInstance'
 import { enableMocking } from './utils/enableMocking'
 import { SetupWorkerInternalContext, StartHandler } from '../glossary'
 import { createRequestListener } from './createRequestListener'
-import { requestIntegrityCheck } from '../../utils/requestIntegrityCheck'
+import { checkWorkerIntegrity } from '../../utils/checkWorkerIntegrity'
 import { createResponseListener } from './createResponseListener'
 import { validateWorkerScope } from './utils/validateWorkerScope'
 
@@ -74,23 +73,14 @@ Please consider using a custom "serviceWorker.url" option to point to the actual
         window.clearInterval(context.keepAliveInterval)
       })
 
-      // Check if the active Service Worker is the latest published one
-      const integrityCheckResult = await until(() =>
-        requestIntegrityCheck(context, worker),
-      )
-
-      if (integrityCheckResult.error) {
-        devUtils.warn(`\
-Detected outdated Service Worker: ${integrityCheckResult.error.message}
-
-The mocking is still enabled, but it's highly recommended that you update your Service Worker by running:
-
-$ npx msw init <PUBLIC_DIR>
-
-This is necessary to ensure that the Service Worker is in sync with the library to guarantee its stability.
-If this message still persists after updating, please report an issue: https://github.com/open-draft/msw/issues\
-      `)
-      }
+      // Check if the active Service Worker has been generated
+      // by the currently installed version of MSW.
+      await checkWorkerIntegrity(context).catch((error) => {
+        devUtils.error(
+          'Error while checking the worker script integrity. Please report this on GitHub (https://github.com/mswjs/msw/issues), including the original error below.',
+        )
+        console.error(error)
+      })
 
       context.keepAliveInterval = window.setInterval(
         () => context.workerChannel.send('KEEPALIVE_REQUEST'),

src/browser/utils/checkWorkerIntegrity.ts

@@ -0,0 +1,34 @@
+import { devUtils } from '~/core/utils/internal/devUtils'
+import type { SetupWorkerInternalContext } from '../setupWorker/glossary'
+
+/**
+ * Check whether the registered Service Worker has been
+ * generated by the installed version of the library.
+ * Prints a warning message if the worker scripts mismatch.
+ */
+export async function checkWorkerIntegrity(
+  context: SetupWorkerInternalContext,
+): Promise<void> {
+  // Request the integrity checksum from the registered worker.
+  context.workerChannel.send('INTEGRITY_CHECK_REQUEST')
+
+  const { payload } = await context.events.once('INTEGRITY_CHECK_RESPONSE')
+
+  // Compare the response from the Service Worker and the
+  // global variable set during the build.
+
+  // The integrity is validated based on the worker script's checksum
+  // that's derived from its minified content during the build.
+  // The "SERVICE_WORKER_CHECKSUM" global variable is injected by the build.
+  if (payload.checksum !== SERVICE_WORKER_CHECKSUM) {
+    devUtils.warn(
+      `The currently registered Service Worker has been generated by a different version of MSW (${payload.packageVersion}) and may not be fully compatible with the installed version.
+
+It's recommended you update your worker script by running this command:
+
+  \u2022 npx msw init <PUBLIC_DIR>
+
+You can also automate this process and make the worker script update automatically upon the library installations. Read more: https://mswjs.io/docs/cli/init.`,
+    )
+  }
+}

src/mockServiceWorker.js

@@ -2,12 +2,13 @@
 /* tslint:disable */
 
 /**
- * Mock Service Worker (<PACKAGE_VERSION>).
+ * Mock Service Worker.
  * @see https://github.com/mswjs/msw
  * - Please do NOT modify this file.
  * - Please do NOT serve this file on production.
  */
 
+const PACKAGE_VERSION = '<PACKAGE_VERSION>'
 const INTEGRITY_CHECKSUM = '<INTEGRITY_CHECKSUM>'
 const IS_MOCKED_RESPONSE = Symbol('isMockedResponse')
 const activeClientIds = new Set()
@@ -48,7 +49,10 @@ self.addEventListener('message', async function (event) {
     case 'INTEGRITY_CHECK_REQUEST': {
       sendToClient(client, {
         type: 'INTEGRITY_CHECK_RESPONSE',
-        payload: INTEGRITY_CHECKSUM,
+        payload: {
+          packageVersion: PACKAGE_VERSION,
+          checksum: INTEGRITY_CHECKSUM,
+        },
       })
       break
     }

test/browser/msw-api/integrity-check.test.ts

@@ -2,6 +2,7 @@ import * as fs from 'fs'
 import * as path from 'path'
 import { test, expect } from '../playwright.extend'
 import copyServiceWorker from '../../../config/copyServiceWorker'
+import { version } from '../../../package.json'
 
 const { SERVICE_WORKER_SOURCE_PATH } = require('../../../config/constants')
 
@@ -67,7 +68,13 @@ test('errors when activating the worker with an outdated integrity', async ({
     // Produces a meaningful error in the browser's console.
     expect(consoleSpy.get('warning')).toEqual(
       expect.arrayContaining([
-        expect.stringContaining('[MSW] Detected outdated Service Worker'),
+        `[MSW] The currently registered Service Worker has been generated by a different version of MSW (${version}) and may not be fully compatible with the installed version.
+
+It's recommended you update your worker script by running this command:
+
+  \u2022 npx msw init <PUBLIC_DIR>
+
+You can also automate this process and make the worker script update automatically upon the library installations. Read more: https://mswjs.io/docs/cli/init.`,
       ]),
     )
   })