WebTransport

WebTransport is a new transport protocol that allows for low-latency, bidirectional, and multiplexed communication between a client and a server. The protocol is built on top of HTTP/3 and QUIC, which in turn is built on UDP instead of TCP.

Unreliable delivery

WebTransport is the only Colyseus transport with a real unreliable channel: QUIC datagrams, delivered at most once and never retransmitted. Two features depend on it, and both are experimental alongside it:

• .unreliable() schema fields: a value replaced every tick ships on the datagram channel. A dropped packet then costs nothing, instead of stalling the ordered stream behind a retransmit.
• Unreliable input: room.input({ mode: "unreliable" }), where each packet carries the last few inputs as redundancy against drops.

Every WebSocket transport lacks that channel. .unreliable() fields then stop updating after the full state sync, with a warning logged once. Unreliable input falls back to the reliable channel, its redundancy wasted. Client-side WebTransport support is currently limited to the JavaScript/TypeScript SDK.

npm install --save @colyseus/h3-transport

pnpm add @colyseus/h3-transport

yarn add @colyseus/h3-transport

bun add @colyseus/h3-transport

Usage

import express from "express";
import { defineServer } from "colyseus";
import { H3Transport } from "@colyseus/h3-transport"
 
const app = express();
app.get("/hello", (req, res) => {
  res.json({ hello: "world!" });
});
 
const server = defineServer({
  // ...
  transport: new H3Transport({
    app, // required: H3Transport serves HTTP through this Express app
    /* other H3Transport options */
  }),
  // ...
});

Available options

• app: (required) The Express app served over HTTP/3.
• cert: Certificate contents (cert.pem)
• key: Private key contents (key.pem)
• secret: (?)
• server: The http.Server instance to be used.
• localProxy: (optional) Fallback every URL through the this local proxy.