msw/src/browser/utils/checkWorkerIntegrity.ts

Seamless REST/GraphQL API mocking library for browser and Node.js.

import { devUtils } from '~/core/utils/internal/devUtils'
import type { SetupWorkerInternalContext } from '../setupWorker/glossary'
import { DeferredPromise } from '@open-draft/deferred-promise'

/**
 * 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 function checkWorkerIntegrity(
  context: SetupWorkerInternalContext,
): Promise<void> {
  const integrityCheckPromise = new DeferredPromise<void>()

  // Request the integrity checksum from the registered worker.
  context.workerChannel.postMessage('INTEGRITY_CHECK_REQUEST')
  context.workerChannel.once('INTEGRITY_CHECK_RESPONSE', (event) => {
    const { checksum, packageVersion } = event.data

    // 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 (checksum !== SERVICE_WORKER_CHECKSUM) {
      devUtils.warn(
        `The currently registered Service Worker has been generated by a different version of MSW (${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.`,
      )
    }

    integrityCheckPromise.resolve()
  })

  return integrityCheckPromise
}