Add features to prevent sleeping, fixes #2

functions/refresh-vp.js

@@ -0,0 +1,8 @@
+const SaveVehiclePositions = require('./protobufs/exec-vp')
+
+// Recursively refresh VehiclePositions
+const RefreshVP = () => SaveVehiclePositions().then(() => {
+  setTimeout(RefreshVP, 10000)
+})
+
+module.exports = RefreshVP

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@wayline/express",
   "private": true,
-  "version": "1.4.7",
+  "version": "1.4.8",
   "description": "Generates GTFS-RT files for Miami-Dade Transit",
   "main": "server.js",
   "scripts": {

router/keepAlive.js

@@ -0,0 +1,25 @@
+const fs = require('fs')
+const path = require('path')
+const RefreshVP = require('../functions/refresh-vp')
+
+const filesrc = dir => path.join(process.cwd(), dir)
+
+const getLastUpdateTime = () => new Promise((resolve, reject) => {
+  fs.stat(filesrc('./tmp/realtime/VehiclePositions.pb'), (err, stats) => {
+    if (err) reject(err)
+    const timestamp = new Date(stats.mtime).valueOf()
+    resolve(timestamp)
+  })
+})
+
+module.exports = async (req, res, next) => {
+  const lut = await getLastUpdateTime()
+
+  // 20 seconds without an update
+  // so trigger recursion loop again
+  if (Date.now() - 20000 > lut) {
+    RefreshVP()
+  }
+
+  next()
+}

server.js

@@ -3,7 +3,8 @@ require('./functions/tmp-precheck')()
 const express = require('express')
 const fs = require('fs')
 const mainRouter = require('./router/index.js')
-const SaveVehiclePositions = require('./functions/protobufs/exec-vp')
+const keepAlive = require('./router/keepAlive.js')
+const RefreshVP = require('./functions/refresh-vp')
 const app = express()
 
 const {
@@ -25,19 +26,15 @@ const loadGTFSintoFs = async () => {
 const CronJob = require('cron').CronJob
 const feedUpdater = new CronJob('0 0 */1 * * *', loadGTFSintoFs) // every hour at the 00:00 mark
 
-// Recursively refresh VehiclePositions
-const RefreshVP = async () => {
-  await SaveVehiclePositions()
-  setTimeout(RefreshVP, 10000)
-}
-
 async function start () {
   const host = process.env.$HOST || process.env.HOST || '127.0.0.1'
   const port = process.env.$PORT || process.env.PORT || 3000
 
   // start cron jobs
   feedUpdater.start()
 
+  app.use('/realtime', keepAlive)
+
   app.use(express.static('./static', {
     dotfiles: 'ignore'
   }))