#coding=utf-8

from socket import *

from threading import Thread

import struct

def recvData(fileName,udpSocket,lastBlockNum):

    lastBlockNum = lastBlockNum

    cycleIndex = 0 #当文件较大，块编号大于65535时，循环索引加1，重置块编号为1

    while True:

        dataInfo, dstInfo = udpSocket.recvfrom(1024)

        opCode,blockNum = struct.unpack("!HH",dataInfo[:4])

        if opCode == 3:

            if blockNum == 1 and cycleIndex==0:

                f = open(fileName,'wb')

            data_fmt = '!%ds'%(len(dataInfo)-4)

            data_content = struct.unpack(data_fmt,dataInfo[4:])

            if lastBlockNum+1 == blockNum:

                f.write(data_content[0])

            ack_data = struct.pack("!HH",4,blockNum)

            udpSocket.sendto(ack_data,dstInfo)

            if blockNum==65535:

                cycleIndex += 1

                lastBlockNum = blockNumelif blockNum>65535:

                lastBlockNum=0

            else:

                lastBlockNum = blockNum

            if len(dataInfo)<516:

                print("下载完毕！")

                f.close()

                break

        elif opCode == 5:

            errorNum = blockNum

            err_fmt = "!%ds"%(len(dataInfo)-5)

            errorMsg = struct.unpack(err_fmt,dataInfo[4:-1])

            print("出错信息%s %s"%(errorMsg,errorNum))

            break

def sendData(fileName,udpSocket):

    ipInfo = ("10.0.0.4", 69)

    dataInfo = struct.pack("!H%dsB5sB"%len(fileName), 1, fileName.encode("gb2312"), 0, 'octet'.encode("gb2312"), 0)

    udpSocket.sendto(dataInfo, ipInfo)

def main():

    fileName = "CentOS-7-x86_64-Minimal-1611.iso"

    udpSocket = socket(AF_INET, SOCK_DGRAM)

    bind = ("", 38438)

    udpSocket.bind(bind)

    lastBlockNum = 0

    t1 = Thread(target=sendData,args=(fileName,udpSocket,))

    t1.start()

    t2 = Thread(target=recvData,args=(fileName,udpSocket,lastBlockNum))

    t2.start()

if __name__ == "__main__":

    main()