用C语言写一个原始套接字使用示例

以下是一个简单的原始套接字使用示例，使用C语言编写：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>

#define BUF_SIZE 1024

int main(int argc, char *argv[]) {
    int sockfd, ret;
    char buf[BUF_SIZE];
    struct sockaddr_in addr;
    struct iphdr *ip_header;
    struct tcphdr *tcp_header;

    // 创建原始套接字
    sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
    if (sockfd < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    // 构造目标地址结构
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr(argv[1]);

    // 构造TCP数据包
    memset(buf, 0, BUF_SIZE);
    ip_header = (struct iphdr *)buf;
    tcp_header = (struct tcphdr *)(buf + sizeof(struct iphdr));
    ip_header->version = 4;
    ip_header->ihl = sizeof(struct iphdr) / 4;
    ip_header->tos = 0;
    ip_header->tot_len = htons(sizeof(struct iphdr) + sizeof(struct tcphdr));
    ip_header->id = htons(54321);
    ip_header->frag_off = 0;
    ip_header->ttl = 255;
    ip_header->protocol = IPPROTO_TCP;
    ip_header->check = 0;
    ip_header->saddr = inet_addr("192.168.1.100");
    ip_header->daddr = inet_addr(argv[1]);
    tcp_header->source = htons(12345);
    tcp_header->dest = htons(80);
    tcp_header->seq = htonl(1);
    tcp_header->ack_seq = 0;
    tcp_header->doff = sizeof(struct tcphdr) / 4;
    tcp_header->fin = 0;
    tcp_header->syn = 1;
    tcp_header->rst = 0;
    tcp_header->psh = 0;
    tcp_header->ack = 0;
    tcp_header->urg = 0;
    tcp_header->window = htons(14600);
    tcp_header->check = 0;
    tcp_header->urg_ptr = 0;

    // 发送TCP数据包
    ret = sendto(sockfd, buf, sizeof(struct iphdr) + sizeof(struct tcphdr), 0, (struct sockaddr *)&addr, sizeof(addr));
    if (ret < 0) {
        perror("sendto");
        exit(EXIT_FAILURE);
    }

    printf("TCP SYN packet sent.\n");

    return 0;
}

该示例中创建了一个原始套接字，并构造了一个TCP SYN数据包，然后通过`sendto`函数发送该数据包到指定的目标地址。请注意，使用原始套接字需要特权用户权限。