Describe the bug

• Everytime a certain amunt of data is sent by the client, the socket disconnects instantly.
• I am using [email protected]
• Client in browser (latest Chrome)
• Server on Node@16

Steps to reproduce

• Connect to server
• Let client send a packet that is at least 1e6 in size (code sample below)
• You will see it disconnect instantly.

Code Sample

Socket.IO server version: 4.1.2

Server

import { Server } from "socket.io";

const io = new Server(3000, {});

io.on("connection", (socket) => {
  console.log(`connect ${socket.id}`);

  socket.on("disconnect", () => {
    console.log(`disconnected ${socket.id}`);
  });

  socket.on("noop", (data) => {
    console.log(`noop received: ${data.length}`);
  });
});

Socket.IO client version: 4.1.2

Client

import { io } from "socket.io-client";

const socket = io("ws://localhost:3000/", {});

socket.on("connect", () => {
  console.log(`connect ${socket.id}`);

  // NOTE: if you change N to 999000, it will NOT disconnect!
  const N = 1e6;
  const noopData = new Array(N).fill(1).join('');
  socket.emit('noop', noopData);
  console.warn(`noop sent, N=${N}`);
});

socket.on("disconnect", () => {
  console.log("disconnect");
});

Expected behavior

Don't disconnect arbitrarily.

Platform:

• Device: PC
• OS: Windows10

Further Analysis

• I find the issue to also exist in socket.io@3, but not in socket.io@2, which works just fine.
• I debugged the issue and found that N=1e6 will disconnect, while N=999000 will NOT disconnect.
  • That seems to indicate that whatever bug it is, it is largely tied to some sort of 1MB quota.
• When putting a breakpoint in the onClose handler in ./node_modules/engine.io-client/lib/transports/websocket.js, you can debug the native WebSocket error event (which is in arguments[0]).
  • It's code is 1005.
  • According to MDN, code 1005 - "Indicates that no status code was provided even though one was expected."