linux ping源码

以下是 Linux 中 ping 命令的源代码（基于 Ubuntu 20.04 LTS 版本）：

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

#define PACKET_SIZE     4096

char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
int sockfd, datalen = 56;
int nsend = 0, nreceived = 0;
struct sockaddr_in dest_addr;
pid_t pid;
struct timeval tvrecv;

void statistics(int signo)
{
    printf("\n%d packets transmitted, %d received , %%%d lost\n", 
            nsend, nreceived, (nsend - nreceived) / nsend * 100);
    close(sockfd);
    exit(1);
}

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

void send_packet(void)
{
    nsend++;
    struct icmp *icmp = (struct icmp *)sendpacket;
    icmp->icmp_type = ICMP_ECHO;
    icmp->icmp_code = 0;
    icmp->icmp_cksum = 0;
    icmp->icmp_seq = nsend;
    icmp->icmp_id = pid;
    memset(icmp->icmp_data, 0xa5, datalen);
    gettimeofday((struct timeval *)icmp->icmp_data, NULL);
    icmp->icmp_cksum = cal_chksum((unsigned short *)icmp, datalen + 8);
    sendto(sockfd, sendpacket, datalen + 8, 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr));
}

void recv_packet(void)
{
    int n;
    extern int errno;
    signal(SIGALRM, statistics);
    struct timeval timeout;
    timeout.tv_sec = 1;
    timeout.tv_usec = 0;
    fd_set readfd;
    while (nreceived < nsend) {
        FD_ZERO(&readfd);
        FD_SET(sockfd, &readfd);
        int ret = select(sockfd+1, &readfd, NULL, NULL, &timeout);
        if (ret == -1) {
            if (errno == EINTR) {
                continue;
            }
            perror("select error");
            return;
        } else if (ret == 0) {
            printf("request timeout\n");
            continue;
        }
        if (FD_ISSET(sockfd, &readfd)) {
            n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, NULL, NULL);
            if (n < 0) {
                if (errno == EINTR) {
                    continue;
                }
                perror("recvfrom error");
                return;
            }
            gettimeofday(&tvrecv, NULL);
            struct ip *ip = (struct ip *)recvpacket;
            struct icmp *icmp = (struct icmp *)(recvpacket + (ip->ip_hl << 2));
            int len = n - (ip->ip_hl << 2);
            if (icmp->icmp_type == ICMP_ECHOREPLY && icmp->icmp_id == pid) {
                nreceived++;
                printf("%d bytes from %s: icmp_seq=%u ttl=%d time=%.1f ms\n",
                        len, inet_ntoa(ip->ip_src), icmp->icmp_seq, ip->ip_ttl, 
                        (tvrecv.tv_sec - ((struct timeval *)icmp->icmp_data)->tv_sec) * 1000.0 + 
                        (tvrecv.tv_usec - ((struct timeval *)icmp->icmp_data)->tv_usec) / 1000.0);
            } else {
                printf("received icmp packet with type %d code %d\n", icmp->icmp_type, icmp->icmp_code);
            }
        }
    }
}

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

    struct hostent *host = gethostbyname(argv[1]);
    if (host == NULL) {
        perror("gethostbyname error");
        return 1;
    }

    pid = getpid();
    printf("PING %s (%s) %d bytes of data.\n", host->h_name, inet_ntoa(*(struct in_addr *)host->h_addr), datalen);

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

    setuid(getuid());

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

    bzero(&dest_addr, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    memcpy(&dest_addr.sin_addr, host->h_addr, host->h_length);

    signal(SIGINT, statistics);

    while (1) {
        send_packet();
        recv_packet();
        sleep(1);
    }

    return 0;
}

这段代码实现了 ping 命令的功能。它使用 ICMP 协议发送和接收数据包，计算往返时间并输出结果。其中 `send_packet()` 函数用于发送 ICMP 请求数据包，`recv_packet()` 函数用于接收 ICMP 响应数据包，`statistics()` 函数用于统计传输结果。