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Investigate embedding Partytown via a cross-origin iframe

See original GitHub issue

I believe that Partytown’s isolation could be improved by embedding it via a cross-origin iframe rather than directly as a worker.


Because the worker inherits the embedding page’s origin, it can access data from that origin via APIs like self.indexedDB that are available in the WorkerGlobalScope.

Proposed solution

Instead of integrating Partytown directly into the embedding document as described in the documentation, users could instead host the service worker, the web worker, and a minimal HTML document on a separate origin:

    • /index.html - the embedding document
    • /sandbox.html - the sandbox iframe
    • /web-worker.js - the web worker script
    • /service-worker.js - the service worker script

The sandbox iframe would be responsible for

  1. registering the service worker
  2. starting the web worker
  3. exposing Partytown’s API to the embedding document via postMessage

This will impose a small latency cost for the extra postMessage hop between the iframe and the embedding document, but would ensure that the web worker cannot access any resources from the embedding document that are subject to the same origin policy.

Issue Analytics

  • State:open
  • Created 2 years ago
  • Comments:7 (7 by maintainers)

github_iconTop GitHub Comments

emilisbcommented, Dec 7, 2022

Hi @adamdbradley @steve8708 , I started working on this feature. I made a quick and hacky POC to get it work (both SW and Atomics). I moved the service worker and the web worker to a cross-origin iframe which communicates with the main thread via postMessage and then passes all messages to web worker/service worker. Now I am trying to use a MessageChannel instead, that way we would avoid an additional message hop and performance should stay more or less the same as it is now. Atomics also work with this approach as long as both the main document and the new iframe satisfy crossOriginIsolated requirements.

I can finish it and open a PR, but I have a few questions:

  1. Would you take a PR for this? Do you have any specific requirements for this feature, such as make this new communication mechanism opt-in?
  2. Why does SW sandbox currently run inside an iframe? I cannot understand how it improves the isolation.

We can discuss this on Discord if that is more convenient for you, I left a message in partytown-general channel.

lawnseacommented, Sep 27, 2021

@steve8708, I agree that Atomics plus a sandbox iframe without the allow-same-origin permission would be simpler and faster. Unfortunately, it doesn’t look like it’s possible to use a service worker with such an iframe: w3c/ServiceWorker#1390.

One consequence of this situation to note is that the service worker implementation provides an opportunity for stronger isolation, as the SW controls network requests from the web worker. For that reason, I hope we can support the Atomics implementation with the cross-origin iframe setup as well.

Read more comments on GitHub >

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