deno: Sending a string longer than exactly 44,350 characters over `wss://` hangs indefinitely in Deno v1.33.0 and greater

Very simple to replicate:

// main.js
const ws = new WebSocket('wss://bleeding-imagine-scsi-ruled.trycloudflare.com'); // hosting this for ease of replication while this issue is debugged - see instructions below to host your own if needed

ws.addEventListener('open', () => {
  ws.send('a'.repeat(44351));
  console.log('Sent message.');

  ws.addEventListener('message', (event) => {
    if(event.data === 'success') {
      console.log('Got response.');
    }
  });
});

deno upgrade --version 1.33.0 # bug replicates in all later versions too, including latest (1.36.4) and canary
deno run --allow-net main.js

I’ve only tested on Ubuntu 22.04 - for me it hangs at “Sent message.” forever, about 80% of the time. If I drop the string length from 44351 to 44350, it works fine 100% of the time, and it also works fine on versions prior to Deno v1.32.5 and earlier. It also works fine if you paste the above code in the browser console (regardless of string length), of course.

If for some reason it works fine for you (e.g. it could be OS-version dependent), increase the string length to a high number like 1,000,000.

I’m hosting the referenced remote websocket server for ease of replication, but here’s the code in case you want to do it yourself. Note that the bug isn’t related to the server at all - I’ve replicated it with Node.js/Python/Deno WebSocket server across various runtime versions.

@bartlomieju @littledivy The above code is a much more minimal replication of the same problem I mentioned here:

• https://github.com/denoland/deno/issues/18735#issuecomment-1701946239

Opening a separate issue because the bug seems distinct (different version cut-off), though it is perhaps related.