Fix ArrayBuffer detached error with uWebSockets.js by ruochenjia · Pull Request #5331 · socketio/socket.io · GitHub
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Fix ArrayBuffer detached error with uWebSockets.js#5331

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Fix ArrayBuffer detached error with uWebSockets.js#5331
ruochenjia wants to merge 1 commit intosocketio:mainfrom
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@ruochenjia
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@ruochenjia ruochenjia commented Apr 20, 2025

The kind of change this PR does introduce

  • a bug fix
  • a new feature
  • an update to the documentation
  • a code change that improves performance
  • other

Current behavior

When using engine.io server with uWebSockets.js, the message buffer becomes detached after executing some async tasks, and throws TypeError when trying to access the buffer later on.

import uWebSocket from "uWebSockets.js";
import { uServer as Engine } from "engine.io";

const httpServer = uWebSocket.App().any("/*", (res, req) => {
	// handle regular HTTP request
}).listen("0.0.0.0", 808080, () => {
	console.log("HTTP server started!");
});

const eio = new Engine({
	transports: ["polling", "websocket"]
});

eio.on("connection", (socket) => {
	socket.on("close", () => {
		console.log("Socket closed");
	});
	socket.on("message", (buffer) => {
		console.log(buffer.toString()); // ok here

		someAsyncTask().then(() => {
			console.log(buffer.subarray(0, 3).toString()); // TypeError: Cannot perform Construct on a detached ArrayBuffer
		});
	});
});

eio.attach(httpServer);

New behavior

The original ArrayBuffer passed by the uWebSockets.js is always copied to prevent it being detached. This matches the behavior for a regular engine.io server using the built-in http module.

The documentation of uWebSockets.js states that for the message handler, the given ArrayBuffer is valid during the lifetime of this callback (until first await or return) and will be neutered.

Other information (e.g. related issues)

@darrachequesne
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darrachequesne commented Apr 24, 2025

@ruochenjia
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ruochenjia commented Apr 24, 2025

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@ruochenjia @darrachequesne