用C语言完成 ping代码

以下是C语言实现Ping的代码：

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

#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   5
#define MAX_NO_PACKETS  4

struct packet
{
    struct icmphdr hdr;
    char msg[PACKET_SIZE-sizeof(struct icmphdr)];
};

static char recv_packet[PACKET_SIZE];
static char send_packet[PACKET_SIZE];
static int sockfd;
static int packets_sent = 0;
static int packets_received = 0;
static struct sockaddr_in dest_addr;
static struct sockaddr_in from_addr;
static struct timeval start_time;

static unsigned short get_checksum(unsigned short *ptr, int nbytes)
{
    unsigned long sum;
    for (sum=0; nbytes>1; nbytes-=2)
        sum += *ptr++;
    if (nbytes==1)
        sum += *(unsigned char *)ptr;
    sum = (sum >> 16) + (sum & 0xFFFF);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}

static void send_packet_signal(int signo)
{
    struct packet *pkt = (struct packet *)send_packet;
    gettimeofday(&pkt->hdr.timestamp, NULL);
    pkt->hdr.type = ICMP_ECHO;
    pkt->hdr.code = 0;
    pkt->hdr.un.echo.id = getpid();

    ++packets_sent;
    pkt->hdr.un.echo.sequence = packets_sent;

    memset(pkt->msg, 0xa5, sizeof(pkt->msg));

    pkt->hdr.checksum = get_checksum((unsigned short *)pkt, sizeof(struct packet));
    sendto(sockfd, pkt, sizeof(*pkt), 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr));
}

int ping(const char *ip_addr)
{
    struct hostent *host;
    struct icmp *icmp;
    struct timeval tv;
    struct sigaction sa;
    int n;

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

    dest_addr.sin_family = AF_INET;
    dest_addr.sin_addr.s_addr = inet_addr(ip_addr);

    icmp = (struct icmp *)send_packet;
    icmp->icmp_type = ICMP_ECHO;
    icmp->icmp_code = 0;
    icmp->icmp_id = getpid();
    icmp->icmp_seq = 1;
    memset(&icmp->icmp_data, 0xa5, sizeof(icmp->icmp_data));
    gettimeofday(&icmp->icmp_rtime, NULL);

    icmp->icmp_cksum = get_checksum((unsigned short *)icmp, sizeof(*icmp));

    if ((host = gethostbyname(ip_addr)) == NULL)
        return -2;

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sa.sa_handler = send_packet_signal;
    if (sigaction(SIGALRM, &sa, NULL) < 0)
    {
        perror("sigaction");
        return -3;
    }

    packets_sent = packets_received = 0;

    while (packets_sent < MAX_NO_PACKETS)
    {
        tv.tv_sec = MAX_WAIT_TIME;
        tv.tv_usec = 0;
        alarm(MAX_WAIT_TIME);

        n = recvfrom(sockfd, recv_packet, sizeof(recv_packet), 0, (struct sockaddr *)&from_addr, (socklen_t *)sizeof(from_addr));
        if (n < 0 && errno == EINTR)
            continue;
        else if (n < 0)
        {
            perror("recvfrom");
            return -4;
        }

        gettimeofday(&tv, NULL);
        memcpy(&icmp->icmp_rtime, &tv, sizeof(tv));

        if (icmp->icmp_type == ICMP_ECHOREPLY)
            ++packets_received;
    }

    close(sockfd);
    return 0;
}

int main(int argc, char *argv[])
{
    if (argc < 2)
    {
        printf("Usage: %s IP\n", argv[0]);
        return -1;
    }
    if (ping(argv[1]) != 0)
        printf("Ping failed.\n");
    else
        printf("Ping succeeded.\n");

    return 0;
}

该代码通过ICMP协议实现了Ping功能，使用该函数需要传入一个字符串类型的IP地址作为参数。函数返回值为0表示Ping成功，否则表示Ping失败。