Author

James M Snell <jsnell@cloudflare.com> 2024-11-22 14:33:14 -0800

Parents

a23e95c

Tree

507ab7a

Fixup TransformStream backpressure

```
export default {
  async fetch(req, env, ctx) {

    async function sleep(ns) {
      await new Promise((res) => setTimeout(res, ns));
    }

    const strategy = new ByteLengthQueuingStrategy({ highWaterMark: 2024 });

    const { writable, readable } = new TransformStream(undefined, strategy);

    let writes = 0, reads = 0;

    // Start writing chunks to the stream
    async function write(writable) {
      const writer = writable.getWriter();
      for (let n = 0; n < 10000; n++) {
        console.log('waiting on backpressure', writer.ready, writer.desiredSize);
        await writer.ready;
        console.log('backpressure cleared. writing a chunk');
        writer.write(crypto.getRandomValues(new Uint8Array(1024)));
        console.log('chunk written', ++writes, writer.desiredSize);
      }
      await writer.close();
      console.log('done writing');
    }

    async function read(readable) {
      console.log('reading pending...');
      await sleep(5_000);

      // const reader = readable.getReader();
      // console.log(await reader.read());

      console.log('reading....');
      for await (const chunk of readable) {
        console.log(`read ${chunk.length}`, ++reads);
        await sleep(100);
      }
      console.log('done reading');
    }

    await Promise.all([
      write(writable),
      read(readable)
    ]);

    return new Response("Hello World\n");
  }
};
```