https://github.com/likeastore/maintenance

express_maintenance.js

const express = require('express')

export default function maintenance (app, options) {
  let mode = false
  let endpoint = false
  let url = '/maintenance'
  let accessKey
  let view = 'maintenance.html'
  let api = false
  let status = 503
  let message = 'sorry, we are on maintenance'

  if (typeof options === 'boolean') {
    mode = options
  } else if (typeof options === 'object') {
    mode = options.current || mode
    endpoint = options.httpEndpoint || endpoint
    url = options.url || url
    accessKey = options.accessKey
    view = options.view || view
    api = options.api || api
    status = options.status || status
    message = options.message || message
  } else {
    throw new Error('unsupported options')
  }

  const checkAccess = (req, res, next) => {
    if (!accessKey) {
      return next()
    }

    if (req.query['access_key'] === accessKey) {
      return next()
    }

    res.sendStatus(401)
  }

  const server = function (app) {
    if (endpoint) {
      const router = express.Router()
      router.post(url, checkAccess, (req, res) => {
        mode = true
        res.sendStatus(200)
      })

      router.delete(url, checkAccess, (req, res) => {
        mode = false
        res.sendStatus(200)
      })

      app.use('/', router)
    }
  }

  const handle = (req, res) => {
    const isApi = api && req.url.indexOf(api) === 0

    res.status(status)

    if (isApi) {
      return res.json({ message: message })
    }

    return res.render(view)
  }

  const middleware = (req, res, next) => {
    if (mode) {
      const requestUrl = req.url.split('?')[0]
      if (requestUrl === url && (req.method === 'DELETE' || req.method === 'POST')) {
        next()
      } else {
        return handle(req, res)
      }
    }

    next()
  }

  const inject = (app) => {
    app.use(middleware)
    return app
  }

  return server(inject(app))
}