c - 收到的IP地址错误

Question

我正在用 C 实现原始套接字。我有两个程序(例如服务器和客户端)。客户端向服务器发送信息，然后服务器发送 ACK。客户端已发送信息，服务器已成功接收。现在服务器正在发送回 ACK。现在，客户端已成功解析以太网 header 。我在接收 IP 地址时遇到问题。

1. What should be the type of arguments of the function CreateIPHeader()?
2. How to print IP addresses in ParseIPHeader()?
3. What should be the data type of value returned by ParseIPHeader, if I want just the IP addresses?

struct iphdr *CreateIPHeader(char *src_ip,char *dst_ip)
{
struct iphdr *ip_header;
ip_header=malloc(sizeof(struct iphdr));
//OTHER FIELDS OF IP HEADER
ip_header->saddr = inet_ntoa(*((struct in_addr *)(src_ip)));
ip_header->daddr = inet_ntoa(*((struct in_addr *)(dst_ip)));
ip_header->check=ComputeChecksum((unsigned char *)ip_header,ip_header->ihl*4);
printf("\nip to be sent = %s",ip_header->saddr); //printing correct IP
printf("\nip to be rcvd = %s",ip_header->daddr);

return(ip_header);
}

char* ParseIPHeader(unsigned char *packet,int len)
{
struct iphdr *ip_header,*ret_ip;
unsigned char *out;
struct ethhdr *ethernet_header;
out=malloc(2048);
memset(out, 0, 2048);
ethernet_header=(struct ethhdr *) out;
ret_ip=(struct iphdr *) (out + sizeof(struct ethhdr));
if(ntohs(ethernet_header->h_proto)==ETH_P_IP)
{
    if(len>=(sizeof(struct ethhdr)+sizeof(struct iphdr)))
    {
        ip_header=(struct iphdr*)(packet+sizeof(struct ethhdr));
        ret_ip->saddr = ip_header->daddr;
            ret_ip->daddr = ip_header->saddr;
    printf("daddr SENT = %s",ret_ip->daddr);  //how to print them?
        printf("saddr SENT = %s",ret_ip->saddr);
    }
    else
    printf("IP packet does not have full header\n");
}
else
{ 
//not an IP packet
}
return out;
}


int main()
{
unsigned char in[2048];
int len;
char *rcv_ip;
Struct iphdr *ip_header;

    memset(in,0,2048);
len=recvfrom(raw,in,2048,0,(struct sockaddr *)&packet_info,&packet_info_size);
rcv_ip=ParseIPHeader(in,len); /*I want this function to return me the ip addresses which I would use in the next line.*/
ip_header =CreateIPHeader(rcv_ip+5,rcv_ip);

memset(in,0,2048);
memcpy(in+sizeof(struct ethhdr),ip_header,ip_header->ihl*4);

sendrawpacket(raw,in,pkt_len);
    free(ip_header);
return 0;
}

如有任何帮助，我们将不胜感激。谢谢:)

Answer 1

而不是:

printf("\nDest Addr %s \n",inet_ntoa(*((struct in_addr *)&((ip_header->daddr)))));

printf("\nSource Addr %s \n",inet_ntoa(*((struct in_addr *)&(ip_header->saddr))));

也许:

printf("\nDest Addr %s \n",inet_ntoa(ip_header->daddr));

printf("\nSource Addr %s \n",inet_ntoa(ip_header->saddr));