make-promises-safe

A node.js module to make the use of promises safe. It implements the deprecation DEP0018 of Node.js in versions 6+. Using Promises without this module might cause file descriptor and memory leaks.

The Problem

Node.js crashes if there is an uncaught exception, while it does not crash if there is an 'unhandledRejection', i.e. a Promise without a .catch() handler.

If you are using promises, you should attach a .catch() handler synchronously.

As an example, the following server will leak a file descriptor because of a missing .catch() handler:

const http = require('http')
const server = http.createServer(handle)

server.listen(3000)

function handle (req, res) {
  doStuff()
    .then((body) => {
      res.end(body)
    })
}

function doStuff () {
  if (Math.random() < 0.5) {
    return Promise.reject(new Error('kaboom'))
  }

  return Promise.resolve('hello world')
}

The Solution

make-promises-safe installs an process.on('unhandledRejection') handler that prints the stacktrace and exits the process with an exit code of 1, just like any uncaught exception.

Install

npm install make-promises-safe --save

Usage

'use strict'

require('make-promises-safe') // installs an 'unhandledRejection' handler
const http = require('http')
const server = http.createServer(handle)

server.listen(3000)

function handle (req, res) {
  doStuff()
    .then((body) => {
      res.end(body)
    })
}

function doStuff () {
  if (Math.random() < 0.5) {
    return Promise.reject(new Error('kaboom'))
  }

  return Promise.resolve('hello world')
}

as a preloader

You can add this behavior to any Node.js application by using it as a preloader:

node -r make-promises-safe server.js

with core dumps

You can also create a core dump when an unhandled rejection occurs:

require('make-promises-safe').abort = true

License

MIT

BridgeAR/make-promises-safe