linux ping源码

以下是Linux系统中的ping命令的源代码：

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

#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   5
#define MAX_NO_PACKETS  3

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);
unsigned short cal_chksum(unsigned short *addr, int len);
int pack(int pack_no);
void send_packet();
void recv_packet();
void tv_sub(struct timeval *out, struct timeval *in);
void sig_int(int signo);

int main(int argc, char *argv[])
{
    struct hostent *host;
    struct protoent *protocol;
    unsigned long inaddr = 0l;
    int size = 50 * 1024;
    if (argc < 2)
    {
        printf("usage: %s hostname/IP address\n", argv[0]);
        exit(1);
    }
    if ((protocol = getprotobyname("icmp")) == NULL)
    {
        perror("getprotobyname");
        exit(1);
    }
    if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0)
    {
        perror("socket error");
        exit(1);
    }
    setuid(getuid());
    setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
    bzero(&dest_addr, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    if ((inaddr = inet_addr(argv[1])) == INADDR_NONE)
    {
        if ((host = gethostbyname(argv[1])) == NULL)
        {
            perror("gethostbyname error");
            exit(1);
        }
        memcpy((char *)&dest_addr.sin_addr, host->h_addr, host->h_length);
    }
    else
    {
        dest_addr.sin_addr.s_addr = inaddr;
    }
    pid = getpid();
    signal(SIGALRM, statistics);
    signal(SIGINT, sig_int);
    printf("PING %s (%s): %d data bytes\n", argv[1], inet_ntoa(dest_addr.sin_addr), datalen);
    send_packet();
    recv_packet();
    return 0;
}

void statistics(int signo)
{
    printf("\n%d packets transmitted, %d received, %%%d lost\n", 
        nsend, nreceived, (nsend - nreceived) / nsend * 100);
    close(sockfd);
    exit(0);
}

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;
}

int pack(int pack_no)
{
    int packsize;
    struct icmp *icmp;
    struct timeval *tval;
    icmp = (struct icmp *)sendpacket;
    icmp->icmp_type = ICMP_ECHO;
    icmp->icmp_code = 0;
    icmp->icmp_cksum = 0;
    icmp->icmp_seq = pack_no;
    icmp->icmp_id = pid;
    packsize = 8 + datalen;
    tval = (struct timeval *)icmp->icmp_data;
    gettimeofday(tval, NULL);
    icmp->icmp_cksum = cal_chksum((unsigned short *)icmp, packsize);
    return packsize;
}

void send_packet()
{
    int packetsize;
    while (nsend < MAX_NO_PACKETS) 
    {
        nsend++;
        packetsize = pack(nsend);
        if (sendto(sockfd, sendpacket, packetsize, 0, 
            (struct sockaddr *)&dest_addr, sizeof(dest_addr)) < 0)
        {
            perror("sendto error");
            continue;
        }
        sleep(1);
    }
}

void recv_packet()
{
    int n, fromlen;
    extern int errno;
    struct sockaddr_in from;
    fromlen = sizeof(from);
    while (nreceived < nsend) 
    {
        alarm(MAX_WAIT_TIME);
        if ((n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, 
            (struct sockaddr *)&from, &fromlen)) < 0)
        {
            if (errno == EINTR)
            {
                continue;
            }
            perror("recvfrom error");
            continue;
        }
        gettimeofday(&tvrecv, NULL);
        recv_packet();
    }
}

void tv_sub(struct timeval *out, struct timeval *in)
{
    if ((out->tv_usec -= in->tv_usec) < 0) 
    {
        --out->tv_sec;
        out->tv_usec += 1000000;
    }
    out->tv_sec -= in->tv_sec;
}

void sig_int(int signo)
{
    statistics(signo);
}

这是一个简单的程序，使用了原始套接字来发送和接收 ICMP 报文，实现了 ping 命令的功能。它通过发送 ICMP ECHO 请求报文，然后等待接收 ICMP ECHO 应答报文来判断目标主机的状态。其中，变量 nsend 表示已发送的报文数量，变量 nreceived 表示已接收的报文数量，变量 sockfd 表示套接字描述符，变量 dest_addr 表示目标主机的地址信息，变量 datalen 表示 ICMP 数据负载的长度，变量 pid 表示进程 ID。函数 pack 是用来构造 ICMP 报文，函数 send_packet 是用来发送报文，函数 recv_packet 是用来接收报文，函数 tv_sub 是用来计算时间差的。当用户按下 Ctrl+C 组合键时，程序会调用函数 sig_int 来输出统计信息并退出。