ping命令的實現

ping命令的實現

#include

#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);

void statistics(int signo)

/*校驗和演算法*/

unsigned short cal_chksum(unsigned short *addr,int len)

/*若icmp報頭為奇數個位元組，會剩下最後乙個位元組。把最後乙個位元組視為2位元組資料的高位元組，這個2位元組資料的低位元組為0，繼續累加*/

if(nleft==1)

sum=(sum>>16)+(sum&0xffff);

sum+=(sum>>16);

answer=~sum;

return answer;

}/*設定icmp報頭*/

int pack(int pack_no)

/*傳送3個icmp報文*/

void send_packet()

sleep(1);/*每隔一秒傳送乙個icmp報文*/}}

/*接收所有icmp報文*/

void recv_packet()

perror("recvfrom error\n");

continue;

}gettimeofday(&tvrecv,null); /*記錄接收時間*/

if(unpack(recvpacket,n)==-1)

continue;

nreceived++;}}

/*剝去icmp報頭*/

int unpack(char *buf,int len)

/*確保所接收的是使用者所發的icmp的回應*/

if((icmpp->icmp_type==icmp_echoreply)&&(icmpp->icmp_id==pid))

else

return -1;

}void tv_sub(struct timeval *out,struct timeval *in)

out->tv_sec-=in->tv_sec;

}int main(int argc,char **ar**)

if((protocol=getprotobyname("icmp"))==null)

/*生成使用icmp的原始套接字，這種套接字只是root才能生成*/

if((sockfd=socket(af_inet,sock_raw,protocol->p_proto))<0)

/***root許可權，設定當前使用者許可權*/

setuid(getuid());

/*擴大套接字接收緩衝區到50k，這樣做主要為了減少接收緩衝區溢位的可能性，若無意中ping乙個廣播位址或多播位址，將會引來大量應答*/

setsockopt(sockfd,sol_socket,so_rcvbuf,&size,sizeof(size));

bzero(&dest_addr,sizeof(dest_addr));

dest_addr.sin_family=af_inet;

if((host=gethostbyname(ar**[1]))==null)

dest_addr.sin_addr=*((struct in_addr *)host->h_addr);

pid=getpid();

printf("ping %s(%s): %d bytes data in icmp packets.\n",ar**[1],inet_ntoa(dest_addr.sin_addr),datalen);

send_packet();/*傳送所有icmp報文*/

recv_packet();/*接收所有icmp報文*/

statistics(sigalrm);/*進行統計*/

return 0;}

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