Sends whole ArrayBuffer instead of fragment

[Kamil93]

Describe the bug

Engine.io-client(websocket transport) in opposite to raw WebSocket client, when sending binary data represented by Uint8Array which uses larger ArrayBuffer than that Uint8Array states, (eio-client) sends whole ArrayBuffer instead of Uint8Array fragment.

Engine.IO server version: 5.1.1

Server - unimportant part in this bug

import http from "http";
import eio from "engine.io"

const server = http.createServer();

const eios = eio.listen(5678);

eios.on('connection', socket => {});

Engine.IO client version: 5.1.2

Client

function CreateFragBuffer() {
  const buffer = new ArrayBuffer(8000);
  const fragBuffer = new Uint8Array(buffer, 5000, 100);
  fragBuffer.forEach((currVal, index, arr) => arr[index] = index);
  console.log("CreateFragBuffer()", fragBuffer.byteLength, fragBuffer.buffer.byteLength)
  return fragBuffer;
}

const socket = eio('ws://localhost:5678', {transports: ["websocket"]});

socket.on('open', () => {
  socket.on('error', (...args) => console.error("EIO", ...args));
  
  socket.send(CreateFragBuffer());
});

Expected behavior
engine.io-client should (like raw WebSocket in browsers) sends only that part of ArrayBuffer that is used by Uint8Array that is being sent

Platform:

• Device: PC
• OS: Windows 10

[Viatorus]

Ran in the same issue a few moments ago.

One workaround is:

socket.send(Buffer.from(CreateFragBuffer()));

But this copies the data twice (bad performance).

[darrachequesne]

I could indeed reproduce, thanks. I'm working on this.

[darrachequesne]

This should be fixed by socketio/engine.io-parser@6d7dd76.

Thanks a lot for the detailed report 👍