@gopalroy/landu-package/lib/package.js

landu package

/**
 * Created by Jesse on 2/25/14.
 */
'use strict';
var dataManager = require('./dataManager');
//ͨ�����ݰ�����ҵ������
exports.packetResolve=function(datagram){
    var dataBuffer=dataManager.init(datagram,0);
    if (dataBuffer.length < 0x0C){
        console.log("���ݰ����ȹ���...");
        return null;
    }
    var packetLeading =dataManager.nextWord();
    if (packetLeading !== 0xAA55){
        console.log('���ݰ�ͷ'+packetLeading+'δ֪...');
        return null;
    }
    var packetLength = dataManager.nextWord();
    var packetLenNot = dataManager.nextWord();
    if ((packetLength | packetLenNot) !== 0xFFFF){
        console.log("���ݰ�������֤ʧ��...");
        return null;
    }
    var packetId =dataManager.nextByte();
    var version = dataManager.nextByte();
    var command=dataManager.nextWord();
    var obdCode=dataManager.nextString();
    dataManager.setOffset(packetLength);
    var checksumInPacket = dataManager.nextWord();
    var checksum=dataManager.getCheckSum(2,packetLength);
    if (checksum !== checksumInPacket){
        console.log("���ݰ�У�����֤ʧ��,����ֵ��"+checksum+",����ֵ��"+checksumInPacket);
        return null;
    }
    var content= dataBuffer.slice(8, packetLength);
    return {
        data:dataBuffer,
        leading:packetLeading,
        length:packetLength,
        lengthNot:packetLenNot,
        packetId:packetId,
        version:version,
        content:content,
        checksum:checksumInPacket,
        command:command,
        obdCode:obdCode
    };
};
exports.packetBuild=function(packageJson,datagram){
    var dataGramBuffer = null;
    var offset = 0;
    if (Buffer.isBuffer(datagram))
        dataGramBuffer = datagram;
    else
        dataGramBuffer = new Buffer(datagram);

    var dataBuffer = new Buffer(dataGramBuffer.length + 0x000A);

    dataBuffer.writeUInt16BE(packageJson.leading, offset);
    offset += 2;
    dataBuffer.writeUInt16BE(dataGramBuffer.length + 0x0008, offset);
    offset += 2;
    dataBuffer.writeUInt16BE((0xFFFF - (dataGramBuffer.length + 0x0008)), offset);
    offset += 2;
    dataBuffer.writeUInt8(packageJson.packetId, offset);
    offset += 1;
    dataBuffer.writeUInt8(packageJson.version, offset);
    offset += 1;

    dataGramBuffer.copy(dataBuffer, offset);
    offset += dataGramBuffer.length;

    var checksum = 0;
    var byteValue = 0;
    for (var i = 2; i < offset; i++) {
        byteValue = dataBuffer.readUInt8(i);
        checksum += byteValue;
    }
    dataBuffer.writeUInt16BE(checksum, offset);

    return dataBuffer;
};