rawsocket发送数据包代码

以下是一个使用 raw socket 发送数据包的示例代码，其中包括了构造 IP 和 TCP 报文、计算校验和等操作：

#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>
#include <unistd.h>

#define SRC_IP "192.168.1.100"
#define DST_IP "192.168.1.1"
#define SRC_PORT 1234
#define DST_PORT 80
#define DATA "Hello, world!"

struct pseudo_header {
    uint32_t src_addr;
    uint32_t dst_addr;
    uint8_t zero;
    uint8_t protocol;
    uint16_t len;
};

uint16_t checksum(uint16_t *buf, int len) {
    uint32_t sum = 0;
    while (len > 1) {
        sum += *buf++;
        len -= 2;
    }
    if (len == 1) {
        sum += *(uint8_t *)buf;
    }
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    return ~sum;
}

int main() {
    int sockfd;
    struct sockaddr_in dst_addr;
    char packet[4096];
    struct iphdr *ip_hdr;
    struct tcphdr *tcp_hdr;
    struct pseudo_header phdr;
    int packet_len;

    // 创建 raw socket
    sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    // 构造目的地址结构体
    memset(&dst_addr, 0, sizeof(dst_addr));
    dst_addr.sin_family = AF_INET;
    dst_addr.sin_port = htons(DST_PORT);
    dst_addr.sin_addr.s_addr = inet_addr(DST_IP);

    // 构造 TCP 报文
    tcp_hdr = (struct tcphdr *)(packet + sizeof(struct iphdr));
    memset(tcp_hdr, 0, sizeof(struct tcphdr));
    tcp_hdr->source = htons(SRC_PORT);
    tcp_hdr->dest = htons(DST_PORT);
    tcp_hdr->seq = htonl(1);
    tcp_hdr->ack_seq = 0;
    tcp_hdr->doff = 5;
    tcp_hdr->syn = 1;
    tcp_hdr->window = htons(65535);
    tcp_hdr->check = 0;

    // 构造 IP 报文
    ip_hdr = (struct iphdr *)packet;
    memset(ip_hdr, 0, sizeof(struct iphdr));
    ip_hdr->version = 4;
    ip_hdr->ihl = 5;
    ip_hdr->tot_len = sizeof(struct iphdr) + sizeof(struct tcphdr);
    ip_hdr->id = htons(0x1234);
    ip_hdr->ttl = 255;
    ip_hdr->protocol = IPPROTO_TCP;
    ip_hdr->saddr = inet_addr(SRC_IP);
    ip_hdr->daddr = inet_addr(DST_IP);
    ip_hdr->check = 0;

    // 计算 TCP 校验和
    phdr.src_addr = ip_hdr->saddr;
    phdr.dst_addr = ip_hdr->daddr;
    phdr.zero = 0;
    phdr.protocol = IPPROTO_TCP;
    phdr.len = htons(sizeof(struct tcphdr));
    memcpy(&packet[sizeof(struct iphdr) + sizeof(struct tcphdr)], &phdr, sizeof(struct pseudo_header));
    memcpy(&packet[sizeof(struct iphdr) + sizeof(struct tcphdr) + sizeof(struct pseudo_header)], tcp_hdr, sizeof(struct tcphdr));
    tcp_hdr->check = checksum((uint16_t *)&packet[sizeof(struct iphdr) + sizeof(struct tcphdr)], sizeof(struct tcphdr) + sizeof(struct pseudo_header));

    // 计算 IP 校验和
    ip_hdr->check = checksum((uint16_t *)ip_hdr, sizeof(struct iphdr));

    // 发送数据包
    packet_len = sizeof(struct iphdr) + sizeof(struct tcphdr);
    if (sendto(sockfd, packet, packet_len, 0, (struct sockaddr *)&dst_addr, sizeof(dst_addr)) < 0) {
        perror("sendto");
        exit(1);
    }

    close(sockfd);

    return 0;
}

需要注意的是，在实际使用中需要根据具体的情况修改源地址、目的地址、端口号、数据等字段，同时需要根据具体的操作系统和网络环境进行调整。