一个简单的ping代码(转载的)

#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  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 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 tv_sub(struct timeval *out,struct timeval *in);

/**//*
 *ping 是向目的地址发送一个icmp回显请求报文，然后等待回显应答报文
 *并在超时打印超时信息,本代码没有实现超时检测
 *icmp回显请求报文或回显应答报文格式
 *|   类型(0/8) |  代码(0)   |               校验和             |
 *|          标志符                 |               序号                 |
 *|                                选项数据                                |
 *其中标志符是本进程号，用于区别收到的其他报文，这样可以允许多个ping程序同时运行
 *序号是从0开始，每次都加1
 *有时第一个往返时间可能比后面的长，因为第一次可能要查找ARP
 */


void statistics(int signo)
...{       printf(" --------------------PING statistics------------------- ");
        printf("%d packets transmitted, %d received , %%%d lost ",nsend,nreceived,
                        (nsend-nreceived)/nsend*100);
        close(sockfd);
        exit(1);
}
/**//*校验和算法*/
unsigned short cal_chksum(unsigned short *addr,int len)
...{       int nleft=len;
        int sum=0;
        unsigned short *w=addr;
        unsigned short answer=0;

        /**//*把ICMP报头二进制数据以2字节为单位累加起来*/
        while(nleft>1)
        ...{       sum+=*w++;
                nleft-=2;
        }
         /**//*若ICMP报头为奇数个字节，会剩下最后一字节。
          *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*/
        if( nleft==1)
        ...{       *(unsigned char *)(&answer)=*(unsigned char *)w;
                sum+=answer;
        }
        sum=(sum>>16)+(sum&0xffff);
        sum+=(sum>>16);
        answer=~sum;
        return answer;
}
/**//*设置ICMP报头*/
int pack(int pack_no)
...{       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( cicmp,packsize); /**//*校验算法*/
        return packsize;
}

/**//*发送三个ICMP报文*/
void send_packet()
...{       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*/
        }
}

/**//*接收所有ICMP报文*/
void recv_packet()
...{       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;
                        perror("recvfrom error");
                        continue;
                }
                gettimeofday(&tvrecv,NULL);  /**//*记录接收时间*/
                if(unpack(recvpacket,n)==-1)continue;
                nreceived++;
        }
}

//打印ip报文的信息
void printIP(char *packet, int len)
...{
    struct sockaddr_in addr_src,addr_dst;
    struct ip *pip = (struct ip*)packet;
    printf("ip head len:%d ",pip->ip_hl<<2);
    printf("ip len:%d ",ntohs(pip->ip_len));
    printf("ip pro id:%d ",pip->ip_p);
    printf("ip ttl:%d ",pip->ip_ttl);
    printf("ip offset:%d ",ntohs(pip->ip_off)&IP_OFFMASK);

    memset(&addr_src,0,sizeof(struct sockaddr_in));
    memset(&addr_dst,0,sizeof(struct sockaddr_in));
    memcpy(&addr_src,&pip->ip_src,sizeof(struct sockaddr_in));
    memcpy(&addr_dst,&pip->ip_dst,sizeof(struct sockaddr_in));
    printf("src ip:%x ",addr_src.sin_addr);
    printf("dst ip:%x ",addr_dst.sin_addr);
}

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

        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*/
        ...{       printf("ICMP packets's length is less than 8 ");
                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) )
        ...{       tvsend=(struct timeval *)icmp->icmp_data;
                tv_sub(&tvrecv,tvsend);  /**//*接收和发送的时间差*/
                rtt=tvrecv.tv_sec*1000+tvrecv.tv_usec/1000;  /**//*以毫秒为单位计算rtt*/
                /**//*显示相关信息*/
                printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3f ms ",
                        len,
                        inet_ntoa(from.sin_addr),
                        icmp->icmp_seq,
                        ip->ip_ttl,
                        rtt);
        }
        else    return -1;
}

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 ",argv[0]);
                exit(1);
        }
        
    printf("step1 ");
    
        if( (protocol=getprotobyname("icmp") )==NULL)
        ...{       perror("getprotobyname");
                exit(1);
        }
      
        printf("step2 "); 
        
    /**//*生成使用ICMP的原始套接字,这种套接字只有root才能生成*/
        if( (sockfd=socket(AF_INET,SOCK_RAW,protocol->p_proto) )<0)
        ...{       perror("socket error");
                exit(1);
        }
        
    /**//* 回收root权限,设置当前用户权限*/
        setuid(getuid());
        
    /**//*扩大套接字接收缓冲区到50K这样做主要为了减小接收缓冲区溢出的
          的可能性,若无意中ping一个广播地址或多播地址,将会引来大量应答*/
        setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size) );
        bzero(&dest_addr,sizeof(dest_addr));
        dest_addr.sin_family=AF_INET;

        /**//*判断是主机名还是ip地址*/
        if( inaddr=inet_addr(argv[1])==INADDR_NONE)
        ...{
        if((host=gethostbyname(argv[1]) )==NULL) /**//*是主机名*/
                ...{       perror("gethostbyname error");
                        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;
                //memcpy( (char *)&dest_addr,(char *)&inaddr,host->h_length);
        }
        /**//*获取main的进程id,用于设置ICMP的标志符*/
        pid=getpid();
        printf("PING %s(%s): %d bytes data in ICMP packets. ",argv[1],
                        inet_ntoa(dest_addr.sin_addr),datalen);
        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;

}
/**//*两个timeval结构相减*/
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;
}
/**//*------------- The End -----------*/