Simple async-hook server use.

server.js

'use strict'

var asyncHooks = require('async_hooks')
var ids = new Map()
var toReturn
var noopHook = asyncHooks.createHook({
     init: function initHook(id, type) {
      if (type !== 'PROMISE') {
        return
      }

      ids.set(id, {})
    },

    before: function beforeHook(id) {
      var hookSegment = ids.get(id)

      if (!hookSegment) {
        return
      }
      toReturn = hookSegment
      ids.set(id, null)
    },
    after: function afterHook(id) {
      var hookSegment = ids.get(id)

      // hookSegment is the segment that was active before the promise
      // executed. If the promise is executing before a segment has been
      // restored, hookSegment will be null and should be restored. Thus
      // undefined is the only invalid value here.
      if (hookSegment === undefined) {
        return
      }
      ids.set(id, toReturn)
      toReturn = hookSegment 
    },
    destroy: function destHook(id) {
      ids.delete(id)
    }

})

var http = require('http')
var lastCPUSample = process.cpuUsage()

var server = http.createServer(function(req, res) {
  req.resume()

  if (req.url === '/health') {
    res.writeHead(200, 'Content-Type', 'application/json')
    res.write(JSON.stringify(healthCheck()))
    res.end()
  } else if (req.url === '/guid') {
    res.writeHead(200, 'Content-Type', 'application/json')
    res.write(JSON.stringify({ guid: GUID }))
    res.end()
  } else if (req.url === '/stats') {
    var cpuDiff = process.cpuUsage(lastCPUSample)
    lastCPUSample = process.cpuUsage()

    var memorySample = process.memoryUsage()
    res.writeHead(200, 'Content-Type', 'application/json')
    res.write(JSON.stringify({
      cpu: {
        user: cpuDiff.user,
        system: cpuDiff.system
      },
      memory: {
        heapUsed: memorySample.heapUsed,
        heapFree: memorySample.heapTotal - memorySample.heapUsed,
        nonHeap: memorySample.rss - memorySample.heapTotal
      }
    }))
    res.end()
  } else if (req.url === '/') {
    var p = Promise.resolve(1)
    for (var i = 0; i < 1000; ++i) {
      p = p.then(result => {
        return 1
      })
    }
    p.then(result => {
      res.write('ok')
      res.end()
    }, error => {
      res.write(error)
      res.end()
    })
  }
})

var server = server.listen(process.env.PORT, function serverReady () {
  var port = server.address().port
  console.log('listening on ' + port)
})