ping.c

此文件为linux环境下的PING程序

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

#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   5
#define MAX_NO_PACKETS  2		//发包的个数
#define ICMP_ECHO 8
#define ICMP_ECHOREPLY 0

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 sockaddr_in from;
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);
void recv_packet(void);
int unpack(char *buf,int len);

void statistics(int signo)
{
    if (MAX_NO_PACKETS != nreceived)
        printf ("not found\n");
    else
        printf ("found\n");
    close(sockfd);
    exit(1);
}

unsigned short cal_chksum(unsigned short *addr,int len)			//校验和算法
{
    int nleft = len;
    int sum = 0;
    unsigned short *w = addr;
    unsigned short answer = 0;

    while(nleft>1)							//把ICMP报头二进制数据以2字节为单位累加起来
    {
        sum += *w++;
        nleft-=2;
    }										//若ICMP报头为奇数个字节，会剩下最后一字节。
    if( nleft == 1)							//把最后一个字节视为一个2字节数据的高字节，这个2字节数据的低字节为0，继续累加
    {
        *(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)						//设置ICMP报头
{
    int i,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);				//记录发送时间
    icmp->icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize);		//校验算法
    return packsize;
}


void send_packet()							//发送三个ICMP报文
{
    int packetsize;
    while( nsend < MAX_NO_PACKETS)
    {
        nsend++;
        packetsize = pack(nsend);				//设置ICMP报头
        if( sendto(sockfd,sendpacket,packetsize,0,
                   (struct sockaddr *)&dest_addr,sizeof(dest_addr) )<0  ) {
            perror("sendto error");
            continue;
        }
        sleep(1);							 //每隔一秒发送一个ICMP报文
    }
}

void recv_packet()							//接收所有ICMP报文
{
    int n,fromlen;
    extern int errno;

    signal(SIGALRM,statistics);
    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;
        }
        gettimeofday(&tvrecv,NULL);			//记录接收时间
        if(unpack(recvpacket,n) == -1) {
            continue;
        }
        nreceived++;
    }
}

int unpack(char *buf,int len)				//剥去ICMP报头
{
    int i,iphdrlen;
    struct ip *ip;
    struct icmp *icmp;
    struct timeval *tvsend;

    ip = (struct ip *)buf;
    iphdrlen = ip->ip_hl<<2;					//求ip报头长度,即ip报头的长度标志乘4
    icmp = (struct icmp *)(buf + iphdrlen);		//越过ip报头,指向ICMP报头
    len -= iphdrlen;						    //ICMP报头及ICMP数据报的总长度
    if(len < 8)							    	//小于ICMP报头长度则不合理
        return -1;								//确保所接收的是我所发的的ICMP的回应
    if( (icmp->icmp_type != ICMP_ECHOREPLY) || (icmp->icmp_id != pid) )
        return -1;
}

int main(int argc,char *argv[])
{
    struct hostent *host;
    struct protoent *protocol;
    unsigned long inaddr = 0l;
    int waittime = MAX_WAIT_TIME;
    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 )	//生成使用ICMP的原始套接字,这种套接字只有root才能生成
    {
        perror("socket error");
        exit(1);
    }
    setuid(getuid());							//回收root权限,设置当前用户权限
    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)		//判断是主机名还是ip地址
    {
        if((host = gethostbyname(argv[1]) ) == NULL)		//是主机名
        {
            printf("gethostbyname error\n");
            exit(1);
        }
        memcpy( (char *)&dest_addr.sin_addr,host->h_addr,host->h_length);
    } else						//是ip地址
        dest_addr.sin_addr.s_addr = inaddr;
    pid = getpid();				//获取main的进程id,用于设置ICMP的标志符
    send_packet();				//发送所有ICMP报文
    recv_packet();				//接收所有ICMP报文
    statistics(SIGALRM);		//进行统计
    return 0;
}