Node.JS app quits after 4th use

Question

I'm having quite a weird problem with a node.js app I made.

The app is designed to accept a request from a web application. A page has a button which says "get RFID". Using this button, a signal gets sent to my node.js server (a Raspberry Pi). The raspberry pi opens a serial connection with the RFID reader in it, and reads the tag. After tag reading, the Raspberry Pi sents back an RFID tag.

This works perfectly well 3 times. (Press button, get tag, refresh site, press button, get tag, etcetera). However, after the 4th try, the node.js server instantly shuts down, passing the last two letters of the tag.

The output during the crash; shows a third scan of a tag that is succesfull, then the 4th read of a tag, that causes the app to crash.

user connected
open
   debug - websocket writing 5:::{"name":"pong","args":["0F00DB3BF4\r"]}
   info  - booting client
   info  - transport end by forced client disconnection
   debug - websocket writing 0::
   info  - transport end (booted)
   debug - set close timeout for client 4G-HA1VgwTR54eNWaj3w
   debug - cleared close timeout for client 4G-HA1VgwTR54eNWaj3w
   debug - cleared heartbeat interval for client 4G-HA1VgwTR54eNWaj3w
   debug - discarding transport
   debug - client authorized
   info  - handshake authorized KSrkMxYYBNkXJO3Vaj3x
   debug - setting request GET /socket.io/1/websocket/KSrkMxYYBNkXJO3Vaj3x
   debug - set heartbeat interval for client KSrkMxYYBNkXJO3Vaj3x
   debug - client authorized for
   debug - websocket writing 1::
user connected
open
   debug - websocket writing 5:::{"name":"pong","args":["F4\r"]}
   info  - booting client
   info  - transport end by forced client disconnection
   debug - websocket writing 0::
   info  - transport end (booted)
   debug - set close timeout for client KSrkMxYYBNkXJO3Vaj3x
   debug - cleared close timeout for client KSrkMxYYBNkXJO3Vaj3x
   debug - cleared heartbeat interval for client KSrkMxYYBNkXJO3Vaj3x
   debug - discarding transport
Aborted

The code is the following;

  GNU nano 2.2.6                                                       File: nocoin.js

// Socket.io server details
var io = require('socket.io').listen(3000);
// Serialport plugin declared and made a serialport variable
var serialport = require("serialport");
var SerialPort = serialport.SerialPort;
// Variable containing technical USB port details
var serialPort = new SerialPort("/dev/ttyUSB0", {baudrate: 2400, parser: serialport.parsers.readline("\n")}, false); // this is the openImmediately flag [default is true]

io.sockets.on('connection', function (socket) {

        console.log('user connected');

        socket.on('ping', function (data) {

                serialPort.open(function () {

                        // Open notification
                        console.log('open');

                        //Start listening
                        serialPort.on('data', function(data) {

                                // If content is empty, filter out
                                if (data.trim() !== '') {

                                        socket.emit('pong', data);
                                        socket.disconnect();

                                        //Execute function again, get tag, handle tag and end process
                                        serialPort.flush(function(err) {
                                                setTimeout(function() {
                                                    serialPort.close(function(err) { });
                                                }, 10);
                                        });
                                }
                        });
                });
        });
});

What could I be possibly be doing wrong here? Does node.JS require flushing of buffers? Why does it always instantly crash after the 4th try?

josh3736 · Accepted Answer · 2014-06-03 20:50:54Z

0

Firstly, you're ignoring errors. (serialPort.close(function(err) { });) Always handle errors – how else can you diagnose what is wrong?

Secondly, why not just keep the serial connection open persistently and emit data out to all connected clients?

var serialPort = new SerialPort("/dev/ttyUSB0", {baudrate: 2400, parser: serialport.parsers.readline("\n")});
serialPort.on('data', function(data) {
    io.sockets.emit('tag', data);
});

Much simpler.

answered Jun 3, 2014 at 20:50

josh3736

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2 Comments

MichaelP Over a year ago

Hi Josh, thanks for the input. When I use your code, it starts listening and clients can connect. However, it just emits debug - websocket writing 1::

josh3736 Over a year ago

Did you catch that I removed the false parameter in the SerialPort constructor? (To enable auto-open)

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