TCP_IP第四次作业

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由于自己的偷懒，现在才开始补作业。
2017年1月10日0点

#第四次作业 myping
这个作业主要是用到icmp差错检查的知识，不是很难

设置ICMP报头函数,压包

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/*设置ICMP报头*/  
int pack(int pack_no)  
{  
    int i,packsize;  
    struct icmp *icmp;  
    struct timeval *tval;  
    icmp = (struct icmp*)sendpacket;  
    icmp->icmp_type = ICMP_ECHO; //ICMP_ECHO类型的类型号为0  
    icmp->icmp_code = 0;  
    icmp->icmp_cksum = 0;  
    icmp->icmp_seq = pack_no;    //发送的数据报编号  
    icmp->icmp_id = pid;  
  
    packsize = 8 + datalen;     //数据报大小为64字节  
    tval = (struct timeval *)icmp->icmp_data;  
    gettimeofday(tval,NULL);        //记录发送时间  
    //校验算法  
    icmp->icmp_cksum =  cal_chksum((unsigned shortshort *)icmp,packsize);   
    return packsize;  
}

#发送ICMP报文

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void send_packet()  
{  
    int packetsize;  
    if(nsend < MAX_NO_PACKETS)  
    {  
        nsend++;  
        packetsize = pack(nsend);   //设置ICMP报头  
        //发送数据报  
        if(sendto(sockfd,sendpacket,packetsize,0,  
            (struct sockaddr *)&dest_addr,sizeof(dest_addr)) < 0)  
        {  
            perror("sendto error");  
        }  
    } 
}

#接受ICMP报文

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void recv_packet()  
{  
    int n,fromlen;  
    extern int error;  
    fromlen = sizeof(from);  
    if(nreceived < nsend)  
    {     
        //接收数据报  
        if((n = recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,  
            (struct sockaddr *)&from,&fromlen)) < 0)  
        {  
            perror("recvfrom error");  
        }  
        gettimeofday(&tvrecv,NULL);     //记录接收时间  
        unpack(recvpacket,n);       //剥去ICMP报头  
        nreceived++;  
    }  
}

拆包，做时间计算等

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int unpack(charchar *buf,int len)  
{  
    int i;  
    int iphdrlen;       //ip头长度  
    struct ip *ip;  
    struct icmp *icmp;  
    struct timeval *tvsend;  
    double rtt;  
  
  
    ip = (struct ip *)buf;  
    iphdrlen = ip->ip_hl << 2; //求IP报文头长度，即IP报头长度乘4  
    icmp = (struct icmp *)(buf + iphdrlen); //越过IP头，指向ICMP报头  
    len -= iphdrlen;    //ICMP报头及数据报的总长度  
    if(len < 8)      //小于ICMP报头的长度则不合理  
    {  
        printf("ICMP packet\'s length is less than 8\n");  
        return -1;  
    }  
    //确保所接收的是所发的ICMP的回应  
    if((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == pid))  
    {  
        tvsend = (struct timeval *)icmp->icmp_data;  
        tv_sub(&tvrecv,tvsend); //接收和发送的时间差  
        //以毫秒为单位计算rtt  
        rtt = tvrecv.tv_sec*1000 + tvrecv.tv_usec/1000;  
        temp_rtt[nreceived] = rtt;  
        all_time += rtt;    //总时间  
        //显示相关的信息  
        printf("%d bytes from %s: icmp_seq=%u ttl=%d time=%.1f ms\n",  
                len,inet_ntoa(from.sin_addr),  
                icmp->icmp_seq,ip->ip_ttl,rtt);  
    }  
    else return -1;  
}

#主调用函数
生成ICMP的原始套接字，压入ip，发包，守包，检查包内内容，然后设置ttl

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main(int argc,charchar *argv[])  
{  
    struct hostent *host;  
    struct protoent *protocol;  
    unsigned long inaddr = 0;  
    int size = 550 * 1024;  
    addr[0] = argv[1];  
    //参数小于两个  
    if(argc < 2)       
    {  
        printf("usage:%s hostname/IP address\n",argv[0]);  
        exit(1);  
    }  
    //不是ICMP协议  
    if((protocol = getprotobyname("icmp")) == NULL)  
    {  
        perror("getprotobyname");  
        exit(1);  
    }  
	
    //生成使用ICMP的原始套接字
    if((sockfd = socket(AF_INET,SOCK_RAW,protocol->p_proto)) < 0)  
    {  
        perror("socket error");  
        exit(1);  
    } 
    
    setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size));  
    bzero(&dest_addr,sizeof(dest_addr));    //初始化  
    dest_addr.sin_family = AF_INET;     //套接字域是AF_INET(网络套接字)  
	
	//压入ip
	dest_addr.sin_addr.s_addr = inet_addr(argv[1]);  
	
    pid = getpid();  
    printf("PING %s(%s):%d bytes of data.\n",argv[1],  
		inet_ntoa(dest_addr.sin_addr),datalen);  
	
    //当按下ctrl+c时发出中断信号，并开始执行统计函数  
    signal(SIGINT,statistics);    
    while(nsend < MAX_NO_PACKETS){  
        sleep(1);       //每隔一秒发送一个ICMP报文  
        send_packet();      //发送ICMP报文  
        recv_packet();      //接收ICMP报文  
    }  
    return 0;  
}