Can Homa do unreliable messages? #114

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1. johnousterhout commented on Oct 7, 2026

   

   johnousterhout

   on Oct 7, 2026

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   Homa doesn't support unreliable messages; if that's what you want, can't you just use UDP?

   Homa doesn't currently allow applications to specify the priority of messages (Homa computes priorities automatically based on message length) but this is something that could potentially be added in the future.
2. ValorZard commented on Oct 8, 2026

   

   ValorZard

   on Oct 8, 2026

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   @johnousterhout

   1. I mean, yes I guess? I've been using QUIC which is built on top of UDP.
   2. Okay so let me give an example of what I"m talking about:
      Here's how QUIC can use streams to do unreliable messaging for video calls and other use cases
      (taken from the webtransport explainer)
      https://github.com/w3c/webtransport/blob/main/explainer.md

   6. Sending Video one Stream per Frame or Segment with Send Order

   As video frames tend to exceed the size of a datagram, a common way to send video is to use a stream per frame or segment. This ensures frames arrive whole without blocking on previous frames, allowing for frame loss. The streams can be assigned a send order to avoid them competing with one another. In this particular example, earlier frames are given a higher priority to assist decode order.

   let sendOrder = 0;
   for await (const encodedVideoChunk of realtimeEncodedVideoChunks.readable) {
     const bytes = new Uint8Array(encodedVideoChunk.byteLength);
     encodedVideoChunk.copyTo(bytes);
     const writable = await wt.createUnidirectionalStream({ sendOrder: sendOrder-- });
     const writer = writable.getWriter();
     writer.write(bytes).catch(() => {});
     writer.close();
   }

   Note that sending a video in real-time might require additional effort, such as different priorities for I-frames versus P-frames, sendOrder++ and an age-based aborting scheme.

   7. Sending Real-time Game Data per Stream with Send Order

   Similar to sending real-time video but without the I-frame/P-frame complexity, is sending real-time game data from a server. Here we use sendOrder++ which sends the latest data with the highest priority, and we age out old data.

   let sendOrder = 0;
   for await (const gameDataChunk of realtimeGameDataChunks.readable) {
     const writable = await wt.createUnidirectionalStream({ sendOrder: sendOrder++});
     const writer = writable.getWriter();
     writer.write(gameDataChunk).catch(() => {});
     writer.close();
     setTimeout(() => writer.abort(), 500); // age-based abort
   }

   Would something like this be in scope for Homa, or is this out of scope?