网络通信TFTP

TFTP下载

TFTP下载器流程图.png

#构造下载请求数据
cmd_buf = struct.pack("!H8sb5sb",1,"test.jpg",0,"octet",0)
#解析返回数据格式
cmdTuple = struct.unpack("!HH", recvData[:4])
#构造ACK(应答包)
ackBuf = struct.pack("!HH",4,p_num)

TFTP数据包格式.png

from socket import *
import struct
import sys

if len(sys.argv) != 2:
    print('-'*30)
    print("tips:")
    print("python xxxx.py 192.168.1.1")
    print('-'*30)
    exit()
else:
    ip = sys.argv[1]

# 创建udp套接字
udpSocket = socket(AF_INET, SOCK_DGRAM)

#构造下载请求数据
cmd_buf = struct.pack("!H8sb5sb",1,"test.jpg",0,"octet",0)

#发送下载文件请求数据到指定服务器
sendAddr = (ip, 69)
udpSocket.sendto(cmd_buf, sendAddr)

p_num = 0

recvFile = ''

while True:
    recvData,recvAddr = udpSocket.recvfrom(1024)

    recvDataLen = len(recvData)

    # print recvAddr # for test

    # print len(recvData) # for test

    cmdTuple = struct.unpack("!HH", recvData[:4])

    # print cmdTuple # for test

    cmd = cmdTuple[0]
    currentPackNum = cmdTuple[1]        

    if cmd == 3: #是否为数据包

        # 如果是第一次接收到数据，那么就创建文件
        if currentPackNum == 1:
            recvFile = open("test.jpg", "a")

        # 包编号是否和上次相等
        if p_num+1 == currentPackNum:
            recvFile.write(recvData[4:]);
            p_num +=1
            print '(%d)次接收到的数据'%(p_num)

            ackBuf = struct.pack("!HH",4,p_num)

            udpSocket.sendto(ackBuf, recvAddr)
        # 如果收到的数据小于516则认为出错
        if recvDataLen<516:
            recvFile.close()
            print '已经成功下载！！！'
            break

    elif cmd == 5: #是否为错误应答
        print "error num:%d"%currentPackNum
        break

udpSocket.close()