代码 C++ ping

Ping 是一种基于 ICMP 协议的网络诊断工具，使用 C++ 编写的 ping 程序需要使用原始套接字（raw socket），并且需要使用 root 权限才能运行。下面是一个简单的 ping 程序实现，可以发送 ICMP echo 请求并接收 ICMP echo 响应：

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <cmath>
#include <unistd.h>
#include <netinet/ip_icmp.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <arpa/inet.h>

using namespace std;

const int PACKET_SIZE = 4096;
const int MAX_HOPS = 64;

// 计算校验和
unsigned short checksum(unsigned short *buf, int len) {
    unsigned long sum = 0;
    while (len > 1) {
        sum += *buf++;
        len -= 2;
    }
    if (len == 1) {
        sum += *(unsigned char *) buf;
    }
    sum = (sum >> 16) + (sum & 0xFFFF);
    sum += (sum >> 16);
    return (unsigned short) ~sum;
}

// 发送 ICMP echo 请求
bool send_icmp_request(int sockfd, const sockaddr_in &addr, int seq) {
    timeval tv{};
    gettimeofday(&tv, nullptr);

    icmp icmp_request{};
    icmp_request.icmp_type = ICMP_ECHO;
    icmp_request.icmp_code = 0;
    icmp_request.icmp_id = getpid() & 0xFFFF;
    icmp_request.icmp_seq = seq;
    icmp_request.icmp_cksum = 0;
    icmp_request.icmp_timestamp = tv.tv_sec * 1000 + tv.tv_usec / 1000;

    icmp_request.icmp_cksum = checksum((unsigned short *) &icmp_request, sizeof(icmp_request));

    int n = sendto(sockfd, &icmp_request, sizeof(icmp_request), 0, (sockaddr *) &addr, sizeof(addr));
    if (n == -1) {
        cerr << "Failed to send ICMP request: " << strerror(errno) << endl;
        return false;
    }

    return true;
}

// 接收 ICMP echo 响应
bool recv_icmp_reply(int sockfd, int seq, sockaddr_in &addr, double &rtt) {
    char buf[PACKET_SIZE]{};
    sockaddr_in from{};
    socklen_t from_len = sizeof(from);

    timeval tv{};
    fd_set readfds{};
    FD_ZERO(&readfds);
    FD_SET(sockfd, &readfds);
    tv.tv_sec = 1;
    tv.tv_usec = 0;

    int n = select(sockfd + 1, &readfds, nullptr, nullptr, &tv);
    if (n == -1) {
        cerr << "Failed to select: " << strerror(errno) << endl;
        return false;
    } else if (n == 0) {  // 超时
        return false;
    }

    n = recvfrom(sockfd, buf, PACKET_SIZE, 0, (sockaddr *) &from, &from_len);
    if (n == -1) {
        cerr << "Failed to receive ICMP reply: " << strerror(errno) << endl;
        return false;
    }

    timeval now{};
    gettimeofday(&now, nullptr);

    iphdr *ip_hdr = reinterpret_cast<iphdr *>(buf);
    unsigned int ip_hdr_len = ip_hdr->ihl * 4;
    icmp *icmp_reply = reinterpret_cast<icmp *>(buf + ip_hdr_len);

    if (icmp_reply->icmp_type != ICMP_ECHOREPLY || icmp_reply->icmp_id != (getpid() & 0xFFFF) ||
        icmp_reply->icmp_seq != seq) {
        return false;
    }

    rtt = (now.tv_sec - icmp_reply->icmp_timestamp / 1000) * 1000 +
          (now.tv_usec - icmp_reply->icmp_timestamp % 1000 * 1000) / 1000.0;

    addr = from;

    return true;
}

// 打印 IP 地址
void print_ip_address(const sockaddr_in &addr) {
    char ip_str[INET_ADDRSTRLEN];
    inet_ntop(AF_INET, &addr.sin_addr, ip_str, INET_ADDRSTRLEN);
    cout << ip_str;
}

// ping 操作
void ping(const char *host) {
    int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd == -1) {
        cerr << "Failed to create raw socket: " << strerror(errno) << endl;
        return;
    }

    sockaddr_in dest_addr{};
    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    dest_addr.sin_addr.s_addr = inet_addr(host);

    cout << "PING " << host << " (" << host << ") 56(84) bytes of data." << endl;

    for (int ttl = 1; ttl <= MAX_HOPS; ++ttl) {
        cout << ttl << " ";

        // 设置 TTL
        if (setsockopt(sockfd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl)) == -1) {
            cerr << "Failed to set TTL: " << strerror(errno) << endl;
            break;
        }

        // 发送 3 个 ICMP echo 请求
        double rtt_sum = 0;
        int n_received = 0;
        for (int i = 0; i < 3; ++i) {
            if (send_icmp_request(sockfd, dest_addr, i + 1)) {
                sockaddr_in from{};
                double rtt = 0;
                if (recv_icmp_reply(sockfd, i + 1, from, rtt)) {
                    print_ip_address(from);
                    cout << "  time=" << rtt << " ms" << endl;
                    rtt_sum += rtt;
                    n_received++;
                } else {
                    cout << "  *" << endl;
                }
            } else {
                cout << "  *" << endl;
            }
            usleep(100000);  // 等待 100 毫秒
        }

        if (n_received > 0) {
            double avg_rtt = rtt_sum / n_received;
            cout << "  avg=" << avg_rtt << " ms" << endl;
        }

        if (dest_addr.sin_addr.s_addr == inet_addr("127.0.0.1")) {
            break;
        }

        // 到达目标主机
        if (n_received > 0) {
            break;
        }
    }

    close(sockfd);
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        cerr << "Usage: " << argv[0] << " <host>" << endl;
        return -1;
    }

    ping(argv[1]);

    return 0;
}

该程序使用 raw socket 发送 ICMP echo 请求，并接收 ICMP echo 响应。程序首先创建一个 raw socket，然后使用 setsockopt 函数设置 TTL（Time To Live，生存时间），从 1 开始循环发送 ICMP echo 请求，并接收 ICMP echo 响应。每发送一个 ICMP echo 请求，就等待 100 毫秒，然后尝试接收 3 次 ICMP echo 响应。如果接收到响应，就输出主机 IP 地址和往返时间（RTT，Round Trip Time）；如果没有接收到响应，则输出星号。当 TTL 达到 64 或者到达目标主机时，程序退出。

使用该程序时，需要传入一个参数：目标主机的 IP 地址或域名。例如，如果要 ping 百度网站，可以运行以下命令：

sudo ./ping www.baidu.com

程序会输出每个 TTL 的主机 IP 地址和 RTT。如果程序没有输出任何信息，则说明目标主机不可达。