cls-tracer-test-app.js

'use strict'

const rTracer = require('cls-rtracer')

// first - configure winston logger

const { createLogger, format, transports } = require('winston')
const { combine, timestamp, printf } = format

// a custom format that outputs request id
const rTracerFormat = printf((info) => {
  // HINT: change to the following to disable request ids/CLS usage
  const rid = false
  // const rid = rTracer.id()
  
  return rid
    ? `${info.timestamp} [request-id:${rid}]: ${info.message}`
    : `${info.timestamp}: ${info.message}`
})

const logger = createLogger({
  format: combine(
    timestamp(),
    rTracerFormat
  ),
  transports: [new transports.Console()]
})

// next - configure and start Express app

const express = require('express')

const app = express()
// HINT: comment the following line to disable request ids/CLS usage
// app.use(rTracer.expressMiddleware())

app.get('/', function (req, res) {
  logger.info('Starting request handling')
  fakeDbAccess()
    .then((result) => res.json(result))
})

async function fakeDbAccess () {
  return new Promise((resolve) => {
    setTimeout(() => {
      logger.info('Logs from fakeDbAccess')
      resolve({ message: 'Hello from express-rtracer example' })
    }, 0)
  })
}

app.listen(3000, (err) => {
  if (err) {
    logger.err('The app could not start')
  }
  logger.info('The app is listening on 3000')
})