Overleaf/services/real-time/socket.io.patch.js

// EventEmitter has been removed from process in node >= 7
// https://github.com/nodejs/node/commit/62b544290a075fe38e233887a06c408ba25a1c71
/*
  A socket.io dependency expects the EventEmitter to be available at
    `process.EventEmitter`.
  See this trace:
  ---

  /app/node_modules/policyfile/lib/server.js:254
  Object.keys(process.EventEmitter.prototype).forEach(function proxy (key){
                                   ^

  TypeError: Cannot read property 'prototype' of undefined
    at Object.<anonymous> (/app/node_modules/policyfile/lib/server.js:254:34)
 */
if (process.versions.node.split('.')[0] >= 7) {
  // eslint-disable-next-line node/no-deprecated-api
  process.EventEmitter = require('events')
}

var io = require('socket.io')

if (io.version === '0.9.16' || io.version === '0.9.19') {
  console.log('patching socket.io hybi-16 transport frame prototype')
  var transports = require('socket.io/lib/transports/websocket/hybi-16.js')
  transports.prototype.frame = patchedFrameHandler
  // file hybi-07-12 has the same problem but no browsers are using that protocol now
}

function patchedFrameHandler(opcode, str) {
  var dataBuffer = Buffer.from(str)
  var dataLength = dataBuffer.length
  var startOffset = 2
  var secondByte = dataLength
  if (dataLength === 65536) {
    console.log('fixing invalid frame length in socket.io')
  }
  if (dataLength > 65535) {
    // original code had > 65536
    startOffset = 10
    secondByte = 127
  } else if (dataLength > 125) {
    startOffset = 4
    secondByte = 126
  }
  var outputBuffer = Buffer.alloc(dataLength + startOffset)
  outputBuffer[0] = opcode
  outputBuffer[1] = secondByte
  dataBuffer.copy(outputBuffer, startOffset)
  switch (secondByte) {
    case 126:
      outputBuffer[2] = dataLength >>> 8
      outputBuffer[3] = dataLength % 256
      break
    case 127:
      var l = dataLength
      for (var i = 1; i <= 8; ++i) {
        outputBuffer[startOffset - i] = l & 0xff
        l >>>= 8
      }
  }
  return outputBuffer
}

const parser = require('socket.io/lib/parser')
const decodePacket = parser.decodePacket
parser.decodePacket = function (data) {
  if (typeof data !== 'string') return {}
  const firstColon = data.indexOf(':')
  if (firstColon === -1) return {}
  if (data.indexOf(':', firstColon + 1) === -1) return {}
  return decodePacket(data)
}