web-sensor-proxy.js

/**
 * Creates an HTTP server to allow to read the sensor data via
 * HTTP. Improvements could include caching the data, to avoid
 * the sensor being hit too frequently.
 * 
 * Not tested in-situ.
 */
const express = require('express');
const app = express();
const net = require('net');

app.get('/sensor', function (req, res) {
   const port = 1700;
   const host = '172.20.8.198';

   var client = new net.Socket();
   client.connect(port, host, function() {
       console.log('connected to: ' + host + ':' + port);
       client.write(new Buffer('1234567', 'hex')[0]);
   });

   client.on('data', function(data) {
       var json = JSON.parse(data);
       res.json(json);
       client.destroy();
   });

   client.on('error', function(error) {
       res.json( { message: 'error: ' + error} );
   });

   client.on('timeout', function(error) {
       res.json( { message: 'timeout connecting to device' } );
   });

   client.on('close', function() {
       console.log('Connection closed');
   });
});

app.get('/', function (req, res) {
  res.send('Hello World!')
});

app.listen(3000, function () {
  console.log('Example app listening on port 3000!')
});

// ref: https://www.hacksparrow.com/tcp-socket-programming-in-node-js.html