Service worker stream transferring

1-service-worker.js

"use strict";

const worker = new Worker("worker.js");

self.onfetch = e => {
  const transform = new TransformStream(); // creates an identity transform
  e.respondWith(new Response(transform.readable));
  
  // Give the worker the writable end. An identity transform stream will just shuffle
  // bytes written there into transform.readable.
  worker.postMessage(transform.writable, [transform.writable]);
  
  // transform.writable has now been transferred/neutered/detached.
  // This means that transform.writable.getWriter() will never work anymore in this thread.
  // However, the *creator* of transform.writable (i.e., the logic inside
  // new TransformStream()) can still see data that is written to it. That logic
  // will then shuffle it over to transform.readable.
};

2-worker.js

"use strict";

self.onmessage = ({ data: writableStream }) => {
  const writer = writableStream.getWriter();
  writer.write(new Uint8Array([1, 2, 3, 4]));
  writer.close();
  
  // You can, of course, do the writing/closing asynchronously.
};

Are you performing any other fetches client side? fetch event can be called multiple times for the document itself, icons, etc. You can include a query string in the URL requested , or use other means to identify the request where a Response() with ReadableStream passed is expected

  if (event.request.url.includes('stream')) {
    event.respondWith(
      new Response(readable, {
        cache: 'no-store',
        headers: { 'Content-Type': 'application/octet-stream' },
      })
    );
    console.log(readable);
  }
`

@guest271314, no, I'm not. It's a test page and I'm doing only that request. For some reason, the way I'm handling it in the example above is incorrect. So it's not a request-matching issue. I do have a slightly more complex setup than above, so maybe some other things affect this.

@kettanaito Try passing a Uint8Array to enqueue().

@guest271314, yes, that was the root cause! 🎉 I've come to discover it as well. You should transfer encoded data over ReadableStream.