我几天来一直无法为TCP做校验和.我在互联网上查看了很多来源,但我见过的所有示例都没有向您展示如何进行TCP校验和.我还查看了
RFC文档,但我仍遇到问题：
unsigned short checksum(unsigned short * buffer,int bytes)
{
unsigned long sum = 0;
unsigned short answer = 0;
int i = bytes;
while(i>0)
{
sum+=*buffer;
buffer+=1;
i-=2;
}
sum = (sum >> 16) + (sum & htonl(0x0000ffff));
sum += (sum >> 16);
return ~sum;
}
此功能适用于IP校验和.
下面是我为TCP标头制作的结构：
struct tcp_header
{
unsigned short tcp_sprt;
unsigned short tcp_dprt;
unsigned int tcp_seq;
unsigned int tcp_ack;
unsigned char tcp_res:4;
unsigned char tcp_off:4;
unsigned char tcp_flags;
unsigned short tcp_win;
unsigned short tcp_csum;
unsigned short tcp_urp;
};
我一直在使用Wireshark来测试这些数据包,唯一不对的就是校验和.
最后,这里是伪标头结构,我加载了TCP标头和来自IP标头的信息：
struct pseudoTcpHeader
{
unsigned int ip_src;
unsigned int ip_dst;
unsigned char zero;//always zero
unsigned char protocol;// = 6;//for tcp
unsigned short tcp_len;
struct tcp_header tcph;
};
一旦我用正确的信息加载这个结构,我就在整个伪头结构上使用校验和函数,并将TCP校验和分配给该值.你看到我提供的东西有什么问题吗？如果问题不在这里,可能是我看不到的粗心错误.
解决方法
我在
winpcap-users mailing list上找到了一个相当不错的例子,它应该解决Greg关于奇数长度数据的评论,并给你一些比较代码的东西.
USHORT CheckSum(USHORT *buffer,int size)
{
unsigned long cksum=0;
while(size >1)
{
cksum+=*buffer++;
size -=sizeof(USHORT);
}
if(size)
cksum += *(UCHAR*)buffer;
cksum = (cksum >> 16) + (cksum & 0xffff);
cksum += (cksum >>16);
return (USHORT)(~cksum);
}
