nodejs-serialport => RE-Establish connection to port after closed

Question

Accordding to my last question SerialPort 'close' event never fire. I was unabled to detected if the COM is disconnected so I have created my own way to detect it.

I have created timestamp, and checked it with interval() every 1 sec to see if it is connected. when it's detect the COM is unplugged I have try to re-establish the connection or re-instance port with SerialPort like you'll see inside the code below.

When it's try to reconnect I've get Error: Access denied.

There is a way to refresh or clean the cache? , because I think the server still hold the connection when isn't closed propely.

I've also tried port.close() and it's throw me out: Error: Port is not open.

var comPort = '\\\\.\\COM7',
    lastDataTime,
    lastresult,
    count = 0,
    lastDataTime,
    comStatus,
    error;
var port = new SerialPort(comPort, function (err) {
    if (err) {
        comStatus = false;
        return console.log('Error: ', err.message);
    }
});
const parser = port.pipe(new Readline());
port.on('open', function () {
    console.log('~Port is open.');

    parser.on('data', function (data) {
        comStatus = true;
        lastDataTime = Date.now();
        if (++count == 10) {
            count = 0;
            lastresult = data;
        }
    });
});

setInterval(function () {
    if (Date.now() - lastDataTime > 1000 || !comStatus) {
        comStatus = false;
        port.close();
        port = new SerialPort(comPort, function (err) {
            if (err) {
                error = 'Error: ' + err.message;
                return console.log(error);
            }
        });
    }
}, 1000);


app.get('/', function (req, res) {
    res.send((comStatus) ? lastresult : 'Disconnected - ' + error);
    console.log(lastresult);
})

Thanks!

Answer 1

As you can see in /node_modules/serialport/lib/serialport.js: close-event may not be emitted (unlike disconnect).

You can add console.log locally like below to simple debug.

P.S. I tested it on Win7x32. Close-event is emitted.

SerialPort.prototype._disconnected = function(err) {
  this.paused = true;
  this.emit('disconnect', err);

  // add: console.log('1', this.closing);

  if (this.closing) {
    return;
  }

  // add: console.log('2', this.fd);

  if (this.fd === null) {
    return;
  }

  this.closing = true;
  if (process.platform !== 'win32') {
    this.readable = false;
    this.serialPoller.close();
  }

  // add: console.log('3');

  SerialPortBinding.close(this.fd, function(err) {
    // add: console.log('4', this._events.close.toString());

    this.closing = false;
    if (err) {
      debug('Disconnect close completed with error: ', err);
    }
    this.fd = null;
    this.emit('close'); // it's your target
  }.bind(this));
};

---

Reconnect example

var SerialPort = require('serialport');
var port = new SerialPort('COM1', {autoOpen: false, baudRate: 9600});

function open () {
    port.open(functon (err) {
        if (!err)
           return;

        console.log('Port is not open: ' + err.message);
        setTimeout(open, 10000); // next attempt to open after 10s
    });
}

port.on('open', function() {
    function send() {
        if (!port.isOpen()) // v5.x require
            return console.log('Port closed. Data is not sent.');

        port.write(123, function (err) {
            if (err)
                console.log('Error on write: ' +  err.message)

            port.drain(() => console.log('DONE'));
        });
    }

    setInterval(send, 1000);
});

port.on('close', function () {
    console.log('CLOSE');
    open(); // reopen 
});

port.on('data', (data) => console.log('Data: ' + data));
port.on('error', (err) => console.error('Error: ', err.message));

open(); // open manually