Need help in correcting issues in CRC-ITU check method written in Javascript (node.js)

Question

We are trying to code GPS device listener on Javascript.

While doing this, we are unable to develop the right script for the CRC-ITU error check. The explanation for

Answer 1

This is my code

var net = require('net');

var HOST = '192.168.1.151';
var PORT = 5023;


function protocall_decorder(data,sbit,plength,protono,ebit){

// Login data   
if(plength.toString('hex') == '0d') {
    var ret = crc16Ccitt(data.slice(2,14));
    var err_code = ret;
    console.log(err_code.toString(16));
    plength = new Buffer('05','hex');
    var res = sbit + plength + protono + data.slice(12,14) + err_code.toString(16) + ebit;

    data = "device_imei: " + parseInt(data.slice(4,12).toString('hex'));
    console.log(data);


    res = new Buffer(res)
    var dataArr = {response:res, type:"login", data:data};
}
/*
// Location data
else if(plength == '1F') {
    var res = '787805' + ***** +  data.slice(60,64) + data.slice(24,28) +'D9DC' + '0D0A';
    dataArr = data.substring(2);
}

// Alarm data
else if(plength == '25') {
    dataArr = data.substring(2);
}
// Heart Beat
else if(plength == '08') {
    dataArr = data.substring(2);
}
// Undefined data length
*/
else {
    var dataArr = {response:"error", data:plength};
}


return dataArr;

}

// The sock object the callback function receives UNIQUE for each connection
net.createServer(function(sock) {

// We have a connection - a socket object is assigned to the connection automatically
console.log('CONNECTED: ' + sock.remoteAddress +':'+ sock.remotePort);

// Add a 'data' event handler to this instance of socket
sock.on('data', function(data) {

    console.log('DATA ' + sock.remoteAddress + ': ' + data);
    // Write the data back to the socket, the client will receive it as data from the server


//////////////// MySQL | Begin ////////////////////
var mysql      = require('mysql');
var con = mysql.createConnection({
    host     : 'localhost',
    user     : 'root',
    password : 'lahirutm',
    database : 'gt06n'
});
con.connect();


var sbit = data.slice(0,2);
var plength = data.slice(2,3);
var protono = data.slice(3,4);
var ebit = data.slice(-2)

if(sbit.toString('hex') == '7878') {
    var res = protocall_decorder(data,sbit,plength,protono,ebit);
    if(res['response'] != 'error') {
        sock.write(res['response']);
        var response = res['response'];
    }
}
else {
    console.log('Undefined protocol data');
}

console.log(response); // Write data to socket

var message  = {start_bit: sbit, packet_length: plength, proto_no: protono, serial:'*', end_bit: ebit};
var query = con.query('INSERT INTO incoming_data SET ?', message,
//var message = {data: data} 
//var query = con.query('INSERT INTO row_data SET ?', message,
function(err, result) {
        // Neat!
});
console.log(query.sql);

var message = {data: data} 
var query = con.query('INSERT INTO row_data SET ?', message,
function(err, result) {
        // Neat!
});
console.log(query.sql);
con.end();
///////////////  MySQL | Begin ////////////////

});

// Add a 'close' event handler to this instance of socket
sock.on('close', function(data) {
    console.log('CLOSED: ' + sock.remoteAddress +' '+ sock.remotePort);
});

}).listen(PORT, HOST);

console.log('Server listening on ' + HOST +':'+ PORT);



/**
* CRC functions
*/

var crc16CcittTableReverse = [
    0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
    0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
    0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
    0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876,
    0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD,
    0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
    0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C,
    0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974,
    0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
    0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3,
    0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A,
    0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
    0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9,
    0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1,
    0x7387, 0x620E, 0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738,
    0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70,
    0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7,
    0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF,
    0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036,
    0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E,
    0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5,
    0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD,
    0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134,
    0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C,
    0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3,
    0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB,
    0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232,
    0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A,
    0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1,
    0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9,
    0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330,
    0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78
];


var crc16CcittStart = 0xFFFF;
var crc16CcittXorout = 0xFFFF;

function crc16Reflected(buf, crc_in, table) {
    var crc16 = crc_in;

    for (i = 0; i < buf.length; i++) {
        crc16 = table[(crc16 ^ buf[i]) & 0xff] ^ (crc16 >> 8);
    }

    return crc16 & 0xFFFF;
}

function crc16Ccitt(buf) {
    return crc16Reflected(buf, crc16CcittStart, crc16CcittTableReverse) ^ crc16CcittXorout;
}