app.js

var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');

var indexRouter = require('./routes/index');
var trainsRouter = require('./routes/trains');
var metricsRouter = require('./routes/metrics');
const Prometheus = require('prom-client')

var app = express();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

const httpRequestDurationMicroseconds = new Prometheus.Histogram({
  name: 'http_request_duration_ms',
  help: 'Duration of HTTP requests in ms',
  labelNames: ['method', 'route', 'code'],
  buckets: [0.10, 5, 15, 50, 100, 200, 300, 400, 500]
})

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use((req, res, next) => {
  res.locals.startEpoch = Date.now()
  next()
})

app.use('/', indexRouter);
app.use('/trains', trainsRouter);
app.use('/metrics', metricsRouter);

// catch 404 and forward to error handler
/*app.use(function(req, res, next) {
  next(createError(404));
});*/

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
  next()
});

app.use((req, res, next) => {
  const responseTimeInMs = Date.now() - res.locals.startEpoch
  httpRequestDurationMicroseconds
    .labels(req.method, req.originalUrl, res.statusCode)
    .observe(responseTimeInMs)

  next()
})

module.exports = app;