linux c ping 实现
用c语言实现的linux中的ping命令
1 #include <stdio.h> 2 #include <signal.h> 3 #include <arpa/inet.h> 4 #include <pthread.h> 5 #include <sys/types.h> 6 #include <sys/socket.h> 7 #include <unistd.h> 8 #include <netinet/in.h> 9 #include <netinet/ip.h> 10 #include <netinet/ip_icmp.h> 11 #include <netdb.h> 12 #include <setjmp.h> 13 #include <errno.h> 14 #define PACKET_SIZE 4096 15 #define MAX_WAIT_TIME 5 16 #define MAX_NO_PACKETS 3 17 char sendpacket[PACKET_SIZE]; 18 char recvpacket[PACKET_SIZE]; 19 int sockfd,datalen=56; 20 int nsend=0,nreceived=0; 21 struct sockaddr_in dest_addr; 22 pid_t pid; 23 struct sockaddr_in from; 24 struct timeval tvrecv; 25 pthread_t tid; 26 void statistics(); 27 unsigned short cal_chksum(unsigned short *addr,int len); 28 int pack(int pack_no); 29 void send_packet(void); 30 void recv_packet(void ); 31 int unpack(char *buf,int len); 32 void tv_sub(struct timeval *out,struct timeval *in); 33 void statistics() 34 { printf("\n--------------------PING statistics-------------------\n"); 35 printf("%d packets transmitted, %d received , %%%d lost\n",nsend,nreceived, 36 (nsend-nreceived)/nsend*100); 37 close(sockfd); 38 exit(1); 39 } 40 /*校验和算法*/ 41 unsigned short cal_chksum(unsigned short *addr,int len) 42 { int nleft=len; 43 int sum=0; 44 unsigned short *w=addr; 45 unsigned short answer=0; 46 47 /*把ICMP报头二进制数据以2字节为单位累加起来*/ 48 while(nleft>1) 49 { sum+=*w++; 50 nleft-=2; 51 } 52 /*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*/ 53 if( nleft==1) 54 { *(unsigned char *)(&answer)=*(unsigned char *)w; 55 sum+=answer; 56 } 57 sum=(sum>>16)+(sum&0xffff); 58 sum+=(sum>>16); 59 answer=~sum; 60 return answer; 61 } 62 /*设置ICMP报头*/ 63 int pack(int pack_no) 64 { int i,packsize; 65 struct icmp *icmp; 66 struct timeval *tval; 67 icmp=(struct icmp*)sendpacket; 68 icmp->icmp_type=ICMP_ECHO; 69 icmp->icmp_code=0; 70 icmp->icmp_cksum=0; 71 icmp->icmp_seq=pack_no; 72 icmp->icmp_id=pid; 73 packsize=8+datalen; 74 tval= (struct timeval *)icmp->icmp_data; 75 gettimeofday(tval,NULL); /*记录发送时间*/ 76 icmp->icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize); /*校验算法*/ 77 return packsize; 78 } 79 /*发送三个ICMP报文*/ 80 void send_packet() 81 { int packetsize; 82 nsend++; 83 packetsize=pack(nsend); /*设置ICMP报头*/ 84 if( sendto(sockfd,sendpacket,packetsize,0,(struct sockaddr *)&dest_addr,sizeof(dest_addr) )<0 ) 85 { 86 perror("sendto error"); 87 return; 88 } 89 alarm(1); 90 91 } 92 /*接收所有ICMP报文*/ 93 void recv_packet(void ) 94 { 95 //int send = *(int *) arg; 96 int n,fromlen; 97 extern int errno; 98 fromlen=sizeof(from); 99 while(1) 100 { if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0, (struct sockaddr *)&from,&fromlen)) <0) 101 { 102 if(errno==EINTR) 103 { 104 perror("recvfrom error"); 105 } 106 continue; 107 108 } 109 gettimeofday(&tvrecv,NULL); /*记录接收时间*/ 110 unpack(recvpacket,n); 111 nreceived++; 112 } 113 } 114 /*剥去ICMP报头*/ 115 int unpack(char *buf,int len) 116 { int i,iphdrlen; 117 struct ip *ip; 118 struct icmp *icmp; 119 struct timeval *tvsend; 120 double rtt; 121 ip=(struct ip *)buf; 122 iphdrlen=ip->ip_hl<<2; /*求ip报头长度,即ip报头的长度标志乘4*/ 123 icmp=(struct icmp *)(buf+iphdrlen); /*越过ip报头,指向ICMP报头*/ 124 len-=iphdrlen; /*ICMP报头及ICMP数据报的总长度*/ 125 if( len<8) /*小于ICMP报头长度则不合理*/ 126 { printf("ICMP packets\'s length is less than 8\n"); 127 return -1; 128 } 129 /*确保所接收的是我所发的的ICMP的回应*/ 130 if( (icmp->icmp_type==ICMP_ECHOREPLY) && (icmp->icmp_id==pid) ) 131 { tvsend=(struct timeval *)icmp->icmp_data; 132 tv_sub(&tvrecv,tvsend); /*接收和发送的时间差*/ 133 rtt=tvrecv.tv_sec*1000+tvrecv.tv_usec/1000; /*以毫秒为单位计算rtt*/ 134 /*显示相关信息*/ 135 printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3f ms\n", 136 len, 137 inet_ntoa(from.sin_addr), 138 icmp->icmp_seq, 139 ip->ip_ttl, 140 rtt); 141 } 142 else return -1; 143 } 144 main(int argc,char *argv[]) 145 { struct hostent *host; 146 struct protoent *protocol; 147 unsigned long inaddr=0l; 148 int waittime=MAX_WAIT_TIME; 149 int size=50*1024; 150 if(argc<2) 151 { printf("usage:%s hostname/IP address\n",argv[0]); 152 exit(1); 153 } 154 if( (protocol=getprotobyname("icmp") )==NULL) 155 { perror("getprotobyname"); 156 exit(1); 157 } 158 /*生成使用ICMP的原始套接字,这种套接字只有root才能生成*/ 159 if( (sockfd=socket(AF_INET,SOCK_RAW,protocol->p_proto) )<0) 160 { perror("socket error"); 161 exit(1); 162 } 163 /* 回收root权限,设置当前用户权限*/ 164 //setuid(getuid()); 165 /*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 166 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*/ 167 168 setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size) ); 169 bzero(&dest_addr,sizeof(dest_addr)); 170 dest_addr.sin_family=AF_INET; 171 /*判断是主机名还是ip地址*/ 172 if( inaddr=inet_addr(argv[1])==INADDR_NONE) 173 { if((host=gethostbyname(argv[1]) )==NULL) /*是主机名*/ 174 { perror("gethostbyname error"); 175 exit(1); 176 } 177 memcpy( (char *)&dest_addr.sin_addr,host->h_addr,host->h_length); 178 } 179 else /*是ip地址*/ 180 memcpy( (char *)&dest_addr,(char *)&inaddr,host->h_length); 181 /*获取main的进程id,用于设置ICMP的标志符*/ 182 pid=getpid(); 183 printf("PING %s(%s): %d bytes data in ICMP packets.\n",argv[1], 184 inet_ntoa(dest_addr.sin_addr),datalen); 185 186 signal(SIGALRM,send_packet); 187 signal(SIGINT,statistics); 188 send_packet(); /*发送所有ICMP报文*/ 189 //recv_packet(); /*接收所有ICMP报文*/ 190 int ret = pthread_create(&tid, NULL, (void*)recv_packet, NULL); 191 if(ret != 0) 192 { 193 printf("Thread Create Error\n"); 194 exit(0); 195 } 196 //statistics(SIGALRM); /*进行统计*/ 197 pthread_join(tid, NULL); 198 return 0; 199 } 200 /*两个timeval结构相减*/ 201 void tv_sub(struct timeval *out,struct timeval *in) 202 { if( (out->tv_usec-=in->tv_usec)<0) 203 { --out->tv_sec; 204 out->tv_usec+=1000000; 205 } 206 out->tv_sec-=in->tv_sec; 207 }
涉及到的技术线程，信号量。
在使用线程的时候注意pthread_join的使用，该函数类似于waitpid 。由于不知道哪个进程先结束，如果主线程先结束了，那么有些变量多个线程都在使用，有可能由于主线程的结束使一些资源（该例子中的socket），致使其他线程无法使用。
su root
gcc ping.c -o ping -lpthread
./ping www.baidu.com
