How to use the buffer.concat function in buffer

authClientSocket.on('data', function (data) {
        console.log('data received from auth');
        var buf = new buffer.Buffer(data);
        if (!expectingMoreData) {
            obj = exports.parseIoTSP(buf);
            if (obj.payload.length < obj.payloadLen) {
                expectingMoreData = true;
                console.log('more data will come. current: ' + obj.payload.length +
                    ' expected: ' + obj.payloadLen);
            }
        } else {
            obj.payload = buffer.concat([obj.payload, new buffer.Buffer(data)]);
            if (obj.payload.length == obj.payloadLen) {
                expectingMoreData = false;
            } else {
                console.log('more data will come. current: ' + obj.payload.length +
                    ' expected: ' + obj.payloadLen);
            }
        }

        if (expectingMoreData) {
            // do not process the packet yet
            return;
        } else if (obj.msgType == msgType.AUTH_HELLO) {
            var authHello = parseAuthHello(obj.payload);
            myNonce = new buffer.Buffer(crypto.randomBytes(AUTH_NONCE_SIZE));

            var sessionKeyReq = {

entityClientSocket.on('data', function (data) {
        console.log('data received from server');
        var buf = new buffer.Buffer(data);
        var ret;
        if (!expectingMoreData) {
            obj = exports.parseIoTSP(buf);
            if (obj.payload.length < obj.payloadLen) {
                expectingMoreData = true;
                console.log('more data will come. current: ' + obj.payload.length +
                    ' expected: ' + obj.payloadLen);
            }
        } else {
            obj.payload = buffer.concat([obj.payload, new buffer.Buffer(data)]);
            if (obj.payload.length == obj.payloadLen) {
                expectingMoreData = false;
            } else {
                console.log('more data will come. current: ' + obj.payload.length +
                    ' expected: ' + obj.payloadLen);
            }
        }

        if (expectingMoreData) {
            // do not process the packet yet
            return;
        } else if (obj.msgType == msgType.SKEY_HANDSHAKE_2) {
            console.log('received session key handshake2!');
            if (entityClientState != entityClientCommState.HANDSHAKE_1_SENT) {
                eventHandlers.onError('Comm init failed: Wrong sequence of handshake, disconnecting...');
                entityClientSocket.close();

export const registerTransaction = ($assetName, $assetAmount, $publicKeyEncoded) => {
	var ecparams = ecurve.getCurveByName('secp256r1');
	var curvePt = ecurve.Point.decodeFrom(ecparams,new Buffer($publicKeyEncoded,"hex"));
	var curvePtX = curvePt.affineX.toBuffer(32);
	var curvePtY = curvePt.affineY.toBuffer(32);
	var publicKey = buffer.concat([new Buffer([0x04]), curvePtX, curvePtY]);

	var signatureScript = createSignatureScript($publicKeyEncoded);

	var myProgramHash = getHash(signatureScript);

	// data
	var data = "40";

	// version
	data = data + "00";

	// asset name
	var assetName = ab2hexstring(stringToBytes($assetName));
	var assetNameLen = (assetName.length / 2).toString()
	if (assetNameLen.length == 1) assetNameLen = "0" + assetNameLen;
	data = data + assetNameLen + assetName;

var serializeSessionKeyReq = function (obj) {
    if (typeof obj.nonce === 'undefined' || typeof obj.replyNonce === 'undefined' ||
        typeof obj.sender === 'undefined' || typeof obj.purpose === 'undefined' ||
        typeof obj.numKeysPerRequest === 'undefined') {
        console.log('Error: SessionKeyReq nonce or replyNonce ' +
            'or purpose or numKeysPerRequest is missing.');
        return;
    }
    var buf = new buffer.Buffer(AUTH_NONCE_SIZE * 2 + 4);
    obj.nonce.copy(buf, 0);
    obj.replyNonce.copy(buf, AUTH_NONCE_SIZE);
    buf.writeUInt32BE(obj.numKeysPerRequest, AUTH_NONCE_SIZE * 2);

    var senderBuf = serializeStringParam(obj.sender);
    var purposeBuf = serializeStringParam(JSON.stringify(obj.purpose));
    return buffer.concat([buf, senderBuf, purposeBuf]);
};

var serializeSessionMessage = function (obj) {
    if (typeof obj.seqNum === 'undefined' || typeof obj.data === 'undefined') {
        console.log('Error: Secure session message seqNum or data is missing.');
        return;
    }
    var seqNumBuf = new buffer.Buffer(SEQ_NUM_SIZE);
    seqNumBuf.writeUIntBE(obj.seqNum, 0, SEQ_NUM_SIZE);
    return buffer.concat([seqNumBuf, obj.data]);
};
var parseSessionMessage = function (buf) {

function numToVarLenInt(num) {
    var extraBuf;
    var buf = new buffer.Buffer(0);
    while (num > 127) {
        extraBuf = new buffer.Buffer(1);
        extraBuf.writeUInt8(128 | num & 127);
        buf = buffer.concat([buf, extraBuf]);
        num >>= 7;
    }
    extraBuf = new buffer.Buffer(1);
    extraBuf.writeUInt8(num);
    buf = buffer.concat([buf, extraBuf]);
    return buf;
}

var serializeSessionKeyReqWithDistributionKey = function (senderName,
    encryptedSessionKeyReqBuf) {
    var senderBuf = new buffer.Buffer(senderName);
    var lengthBuf = new buffer.Buffer(1);
    lengthBuf.writeUInt8(senderBuf.length);
    return buffer.concat([lengthBuf, senderBuf, encryptedSessionKeyReqBuf]);
};

function serializeStringParam(stringParam) {
    var result;
    if (stringParam === null) {
        result = numToVarLenInt(0);
    } else {
        var strLenBuf = numToVarLenInt(stringParam.length);
        var strBuf = new buffer.Buffer(stringParam);
        result = buffer.concat([strLenBuf, strBuf]);
    }
    return result;
}