TCP-Web-Server.js

var net = require('net');

var server = net.createServer(function(socket) {
  console.log('CONNECTED: ' + socket.remoteAddress +':'+ socket.remotePort);
  startPyScript()
  //console.log(socket);

  // incoming messages from clients.
  socket.on('data', function (data) {
    //console.log(data.toString('utf8'));
  });

  // Detect if the TCP client leaves
  socket.on('end', function () {
    console.log('DISCONNECTED');
  });

  //socket.destroy();
  //socket.end();
  // If for some reasons the socket closing not happened, the connection can still be manually closed 
  setTimeout(function(){ socket.end(); }, 15000);
});

// Port 443 would require sudo
//server.listen(443, '0.0.0.0');
server.listen(9000, '0.0.0.0');

var python=null;

// A python script as child process will be started, if it still not exists.
function startPyScript(){
  if(python) return console.log('py already running....');
  console.log('starting py....');
  python = require('child_process').spawn('python',["/home/pi/modbus/ws7-server_with_file_server.py"]); // second argument is array of parameters
  //python.stdout.on('data', function(data){ console.log('python data:',data); });
  python.on('close', function(code){
    console.log('Python closing');
    python=null;
  });
}