Readline parser doesn't read correctly from serial port - NodeJS

Question

I have a connection with POS (point of sale) device. I send it information in hex code and the device prints a receipt.

My problem is that the parser (Readline) doesn't work. When I try to use parser.on("data", console.log), it doesn't return anything. Here is my code:

const SerialPort = require('serialport');// include the library
const WebSocketServer = require('ws').Server;
const SERVER_PORT = 7000;               // port number for the webSocket server
const wss = new WebSocketServer({port: SERVER_PORT}); // the webSocket server
var connections = new Array;          // list of connections to the server
const Readline = SerialPort.parsers.Readline;

wss.on('connection', handleConnection);
const myPort = new SerialPort("COM3", {
    baudRate: 115200,
});
myPort.on('open', showPortOpen);
myPort.on('close', showPortClose);
myPort.on('error', showError);

const parser = myPort.pipe(new Readline('\r\n'))
console.log('parser setup');
parser.on('data', function(data) {
    console.log('data received: ', data);
});

function handleConnection(client) {
    console.log("New Connection"); // you have a new client
    connections.push(client); // add this client to the connections array

    client.on('message', sendToSerial); // when a client sends a message,

    client.on('close', function() { // when a client closes its connection
        console.log("connection closed"); // print it out
        var position = connections.indexOf(client); // get the client's position in the array
        connections.splice(position, 1); // and delete it from the array
    });
}

function sendToSerial(data) {
    console.log("sending to serial: " + data);
    myPort.write(data, 'hex');
}

// This function broadcasts messages to all webSocket clients
function broadcast(data) {
    console.log(data);
    for (myConnection in connections) {  // iterate over the array of connections
        connections[myConnection].send(JSON.stringify(data)); // send the data to each connection
    }
}

function showPortOpen() {
   console.log('port open. Data rate: ' + myPort.baudRate);
}

function readSerialData(data) {
   // if there are webSocket connections, send the serial data
   // to all of them:
   if (connections.length > 0) {
     broadcast(data);
   }
}

function showPortClose() {
   console.log('port closed.');
}

function showError(error) {
   console.log('Serial port error: ' + error);
}

I receive messages, but they are split and I want to send to client whole message. I tried to define the parser and after that to pipe it. I tried to set parser in SerialPort constructor, changed the delimiter, but no result. I think that my error is something with the parser.

Here you can see that doesn't return console.log

And here is the result if I use

myPort.on('data', function(data) {
    console.log('data received: ', data);
});

The idea is to get whole message after every command and send it to the client.

Answer 1

The message is split again. So I want it whole message to decode it by hex code. Did the problem come from parser?

Answer 2

Use the built-in readline api from SerialPort:

const SerialPort = require('serialport');// include the library
const WebSocketServer = require('ws').Server;
const SERVER_PORT = 7000;               // port number for the webSocket server
const wss = new WebSocketServer({port: SERVER_PORT}); // the webSocket server
var connections = new Array;          // list of connections to the server
const Readline = SerialPort.parsers.Readline;

wss.on('connection', handleConnection);

const myPort = new SerialPort('COM3', {
  baudRate: 115200,
  parser: SerialPort.parsers.readline('\r\n')
});

myPort.on('open', showPortOpen);
myPort.on('close', showPortClose);
myPort.on('error', showError);

myPort.on('data', data => readSerialData(data.toString());


// ...

function broadcast(data) {
    console.log(data);
    for (myConnection in connections) {
        connections[myConnection].send(JSON.stringify(data));
    }
}

// ...

function readSerialData(data) {
   // if there are webSocket connections, send the serial data
   // to all of them:
   if (connections.length > 0) {
     broadcast(data);
   }
}

// ...