#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <string.h>

//伪头部
struct psd
{
    struct in_addr src;
    struct in_addr dst;
    char zero;
    char p;
    unsigned short len;
};
//校验函数
unsigned short chksum(unsigned char *data,  int len)
{
   int sum=0;
    int odd = len & 0x01;
    unsigned short *value = (unsigned short*)data;    
    while( len & 0xfffe)
    {
        sum += *(unsigned short*)data;
        data += 2;
        len -=2;
    }    
    if(odd)
    {
        unsigned short tmp = ((*data)<<8)&0xff00;
        sum += tmp;
    }
    sum = (sum >>16) + (sum & 0xffff);
    sum += (sum >>16) ;       
    return ~sum;    
}
//发送包
void sendtcp()
{
    int ret =0;
    char buffer[1024];
    
    struct psd * psd = (struct psd *)buffer; //伪头部 = 12字节
    struct tcphdr *tcp = (struct tcphdr *)(buffer+12); 
    
    struct sockaddr_in addr;
    int s = socket(AF_INET, SOCK_RAW, 6);
    
    memset(buffer, '\0', 1024);
    
    addr.sin_family = AF_INET;
    addr.sin_port = htons(80);
    addr.sin_addr.s_addr = inet_addr("192.168.205.64"); //目标地址
    
    //伪头部 
    psd->src.s_addr = inet_addr("192.168.205.113"); //源地址
    psd->dst.s_addr = inet_addr("192.168.205.64");
    psd->p = 6;
    psd->zero = 0;
    psd->len = htons(8);  //TCP数据包 = 64字节
    
    tcp->source = htons(9090);
    tcp->dest = htons(80);
    tcp->seq = htons(1234);
    tcp->doff = 5;  //TCP头部 = 5*4 = 20字节
    tcp->syn = 1;
    tcp->window = htons(1024);
    tcp->check = htons(chksum(buffer, 76)); //伪头部 + TCP数据包 = 76字节
    
    //TCP数据包 = 64字节
    ret = sendto(s, (char*)tcp, 64, 0, (struct sockaddr*)&addr, sizeof(addr));
    if(ret < 0)
    {
        perror("sendto");
    }         
    printf("send over, send %d bytes\n", ret);
}

int main()
{
    sendtcp();
    return 0;
}