c语言实现ping命令

实现 `ping` 命令需要使用原始套接字，具体步骤如下：

1. 创建原始套接字：

int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);

2. 设置套接字选项：

struct timeval timeout;
timeout.tv_sec = 1; // 设定超时时间为1秒
timeout.tv_usec = 0;
setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));

3. 构造 ICMP 包：

struct icmp* icmp = (struct icmp*)sendbuf;
icmp->icmp_type = ICMP_ECHO;
icmp->icmp_code = 0;
icmp->icmp_id = getpid();
icmp->icmp_seq = 0;
memset(icmp->icmp_data, 0xa5, datalen);
icmp->icmp_cksum = 0;
icmp->icmp_cksum = in_cksum((unsigned short*)icmp, datalen + 8);

4. 发送 ICMP 包并接收回复：

struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(ip);

sendto(sockfd, sendbuf, datalen + 8, 0, (struct sockaddr*)&addr, sizeof(addr));

struct sockaddr_in from;
socklen_t fromlen = sizeof(from);
if (recvfrom(sockfd, recvbuf, sizeof(recvbuf), 0, (struct sockaddr*)&from, &fromlen) < 0) {
    printf("timeout\n");
} else {
    printf("received from %s\n", inet_ntoa(from.sin_addr));
}

5. 计算校验和：

unsigned short in_cksum(unsigned short *addr, int len) {
    int nleft = len;
    unsigned short *w = addr;
    unsigned short answer;
    int sum = 0;

    while (nleft > 1) {
        sum += *w++;
        nleft -= 2;
    }

    if (nleft == 1) {
        *(unsigned char*)(&answer) = *(unsigned char*)w;
        sum += answer;
    }

    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    answer = ~sum;
    return answer;
}

完整代码如下：

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

unsigned short in_cksum(unsigned short *addr, int len) {
    int nleft = len;
    unsigned short *w = addr;
    unsigned short answer;
    int sum = 0;

    while (nleft > 1) {
        sum += *w++;
        nleft -= 2;
    }

    if (nleft == 1) {
        *(unsigned char*)(&answer) = *(unsigned char*)w;
        sum += answer;
    }

    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    answer = ~sum;
    return answer;
}

int main(int argc, char* argv[]) {
    if (argc != 2) {
        printf("Usage: %s <ip>\n", argv[0]);
        exit(1);
    }

    const char* ip = argv[1];
    int datalen = 56;

    char sendbuf[1024] = {0};
    char recvbuf[1024] = {0};

    int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd < 0) {
        perror("socket error");
        exit(1);
    }

    struct timeval timeout;
    timeout.tv_sec = 1;
    timeout.tv_usec = 0;
    setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));

    struct icmp* icmp = (struct icmp*)sendbuf;
    icmp->icmp_type = ICMP_ECHO;
    icmp->icmp_code = 0;
    icmp->icmp_id = getpid();
    icmp->icmp_seq = 0;
    memset(icmp->icmp_data, 0xa5, datalen);
    icmp->icmp_cksum = 0;
    icmp->icmp_cksum = in_cksum((unsigned short*)icmp, datalen + 8);

    struct sockaddr_in addr;
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr(ip);

    while (1) {
        sendto(sockfd, sendbuf, datalen + 8, 0, (struct sockaddr*)&addr, sizeof(addr));

        struct sockaddr_in from;
        socklen_t fromlen = sizeof(from);
        if (recvfrom(sockfd, recvbuf, sizeof(recvbuf), 0, (struct sockaddr*)&from, &fromlen) < 0) {
            printf("timeout\n");
        } else {
            printf("received from %s\n", inet_ntoa(from.sin_addr));
        }

        sleep(1);
    }

    return 0;
}