linux ping源码

以下是 Linux 系统中 ping 命令的源代码：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/select.h>
#include <sys/uio.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>

#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   5
#define MAX_NO_PACKETS  3
#define IP_HEADER_LEN   20
#define ICMP_HEADER_LEN 8

struct packet {
    struct timeval tv;
    char msg[PACKET_SIZE];
};

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

void statistics(int signo) {
    printf("\n--- %s ping statistics ---\n", inet_ntoa(dest_addr.sin_addr));
    printf("%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) {
    struct icmp *icmp;
    int len;
    icmp = (struct icmp *)sendpacket;
    icmp->icmp_type = ICMP_ECHO;
    icmp->icmp_code = 0;
    icmp->icmp_id = pid;
    icmp->icmp_seq = nsend++;
    memset(icmp->icmp_data, 0xa5, datalen);
    gettimeofday((struct timeval *)icmp->icmp_data, NULL);
    len = datalen + ICMP_HEADER_LEN;
    icmp->icmp_cksum = 0;
    icmp->icmp_cksum = cal_chksum((unsigned short *)icmp, len);
    sendto(sockfd, sendpacket, len, 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr));
}

int recv_packet(void) {
    int n, fromlen;
    extern int errno;
    fromlen = sizeof(dest_addr);
    while (1) {
        if ((n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, (struct sockaddr *)&dest_addr, &fromlen)) < 0) {
            if (errno == EINTR)
                continue;
            return -1;
        }
        gettimeofday(&tvrecv, NULL);
        struct ip *ip = (struct ip *)recvpacket;
        int ip_header_len = ip->ip_hl << 2;
        struct icmp *icmp = (struct icmp *)(recvpacket + ip_header_len);
        int icmp_header_len = ICMP_HEADER_LEN;
        if (n - ip_header_len < ICMP_HEADER_LEN) {
            printf("ICMP packet length is less than %d\n", ICMP_HEADER_LEN);
            return -1;
        }
        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",
                n - ip_header_len - icmp_header_len,
                inet_ntoa(dest_addr.sin_addr),
                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);
        }
        return 0;
    }
}

void set_sockaddr(const char *host) {
    struct hostent *hp;
    struct sockaddr_in tmp;

    memset(&tmp, 0, sizeof(tmp));
    tmp.sin_family = AF_INET;

    if ((tmp.sin_addr.s_addr = inet_addr(host)) == INADDR_NONE) {
        if ((hp = gethostbyname(host)) == NULL) {
            fprintf(stderr, "ping: unknown host %s\n", host);
            exit(1);
        }
        tmp.sin_family = hp->h_addrtype;
        memcpy((caddr_t)&tmp.sin_addr, hp->h_addr, hp->h_length);
    }
    dest_addr = tmp;
}

int main(int argc, char **argv) {
    struct sockaddr_in from;
    struct timeval timeout;
    fd_set readfds;
    int size = 50 * 1024;
    pid = getpid();

    if (argc < 2) {
        printf("usage: %s hostname\n", argv[0]);
        exit(1);
    }

    if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0) {
        printf("create socket error\n");
        exit(1);
    }

    if (setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size))) {
        printf("setsockopt error\n");
        exit(1);
    }

    set_sockaddr(argv[1]);

    signal(SIGINT, statistics);

    while (nsend < MAX_NO_PACKETS) {
        send_packet();
        n = recv_packet();

        if (n < 0) {
            printf("recv error\n");
            continue;
        }

        timeout.tv_sec = MAX_WAIT_TIME;
        timeout.tv_usec = 0;

        FD_ZERO(&readfds);
        FD_SET(sockfd, &readfds);

        if (select(sockfd + 1, &readfds, NULL, NULL, &timeout) <= 0) {
            printf("select timeout\n");
            continue;
        }

        if (FD_ISSET(sockfd, &readfds)) {
            if (recv_packet() == -1) {
                printf("recv_packet error\n");
                continue;
            }
        }
    }

    statistics(SIGINT);
    return 0;
}

以上代码实现了 ping 命令的基本功能，包括发送 ICMP 报文、接收 ICMP 报文并计算 RTT、输出统计信息等。其中，cal_chksum() 函数用于计算 ICMP 报文的校验和，set_sockaddr() 函数用于设置目标主机的地址信息，recv_packet() 函数用于接收 ICMP 报文并解析其中的信息。