Linux 下模拟Ping命令的 C 实现

/********************************************************
*	IP报头格式数据结构定义在<netinet/ip.h>中	*
*	ICMP数据结构定义在<netinet/ip_icmp.h>中		*
*	套接字地址数据结构定义在<netinet/in.h>中	*
********************************************************/

#include <stdio.h>
#include <stdlib.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	10000

char *addr[];
char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
int sockfd,datalen = 56;
int nsend = 0, nreceived = 0;
double temp_rtt[MAX_NO_PACKETS];
double all_time = 0;
double min = 0;
double max = 0;
double avg = 0;
double mdev = 0;

struct sockaddr_in dest_addr;
struct sockaddr_in from;
struct timeval tvrecv;
pid_t pid;

void statistics(int sig);
void send_packet(void);
void recv_packet(void);
void computer_rtt(void);
void tv_sub(struct timeval *out,struct timeval *in);
int pack(int pack_no);
int unpack(char *buf,int len);
unsigned short cal_checksum(unsigned short *addr, int len);

/*计算rtt最小、大值，平均值，算术平均数差*/
void computer_rtt()
{
double sum_avg = 0;
int i;
min = max = temp_rtt[0];
avg = all_time/nreceived;

for(i=0; i<nreceived; i++)
{
if(temp_rtt[i] < min)
min = temp_rtt[i];
else if(temp_rtt[i] > max)
max = temp_rtt[i];

if((temp_rtt[i]-avg) < 0)
sum_avg += avg - temp_rtt[i];
else
sum_avg += temp_rtt[i] - avg;
}
mdev = sum_avg/nreceived;
}

/****统计数据函数****/
void statistics(int sig)
{
computer_rtt();		//计算rtt
printf("\n------ %s ping statistics ------\n",addr[0]);
printf("%d packets transmitted,%d received,%d%% packet loss,time %.f ms\n",
nsend,nreceived,(nsend-nreceived)/nsend*100,all_time);
printf("rtt min/avg/max/mdev = %.3f/%.3f/%.3f/%.3f ms\n",
min,avg,max,mdev);
close(sockfd);
exit(1);
}

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

while(nleft > 1)		//ICMP包头以字（2字节）为单位累加
{
sum += *w++;
nleft -= 2;
}

if(nleft == 1)		//ICMP为奇数字节时，转换最后一个字节，继续累加
{
*(unsigned char *)(&check_sum) = *(unsigned char *)w;
sum += check_sum;
}
sum = (sum >> 16) + (sum & 0xFFFF);
sum += (sum >> 16);
check_sum = ~sum;	//取反得到校验和
return check_sum;
}

/*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_ECHO类型的类型号为0
icmp->icmp_code = 0;
icmp->icmp_cksum = 0;
icmp->icmp_seq = pack_no;	//发送的数据报编号
icmp->icmp_id = pid;

packsize = 8 + datalen;		//数据报大小为64字节
tval = (struct timeval *)icmp->icmp_data;
gettimeofday(tval,NULL);		//记录发送时间
//校验算法
icmp->icmp_cksum =  cal_chksum((unsigned short *)icmp,packsize);
return packsize;
}

/****发送三个ICMP报文****/
void send_packet()
{
int packetsize;
if(nsend < MAX_NO_PACKETS)
{
nsend++;
packetsize = pack(nsend);	//设置ICMP报头
//发送数据报
if(sendto(sockfd,sendpacket,packetsize,0,
(struct sockaddr *)&dest_addr,sizeof(dest_addr)) < 0)
{
perror("sendto error");
}
}
}

/****接受所有ICMP报文****/
void recv_packet()
{
int n, fromlen;
extern int error;
fromlen = sizeof(from);
if(nreceived < nsend)
{
//接收数据报
if((n = recvfrom(sockfd,recvpacket, sizeof(recvpacket), 0,
(struct sockaddr *)&from,&fromlen)) < 0)
{
perror("recvfrom error");
}
gettimeofday(&tvrecv,NULL);		//记录接收时间
unpack(recvpacket,n);		//剥去ICMP报头
nreceived++;
}

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

ip = (struct ip *)buf;
iphdrlen = ip->ip_hl << 2;	//求IP报文头长度，即IP报头长度乘4
icmp = (struct icmp *)(buf + iphdrlen);	//越过IP头，指向ICMP报头
len -= iphdrlen;	//ICMP报头及数据报的总长度
if(len < 8)		//小于ICMP报头的长度则不合理
{
printf("ICMP packet\'s length is less than 8\n");
return -1;
}
//确保所接收的是所发的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
//以毫秒为单位计算rtt
rtt = tvrecv.tv_sec*1000 + tvrecv.tv_usec/1000;
temp_rtt[nreceived] = rtt;
all_time += rtt;	//总时间
//显示相关的信息
printf("%d bytes from %s: icmp_seq=%u ttl=%d time=%.1f ms\n",
len,inet_ntoa(from.sin_addr),
icmp->icmp_seq,ip->ip_ttl,rtt);
}
else return -1;
}

//两个timeval相减
void tv_sub(struct timeval *recvtime,struct timeval *sendtime)
{
long sec = recvtime->tv_sec - sendtime->tv_sec;
long usec = recvtime->tv_usec - sendtime->tv_usec;
if(usec >= 0)
{
recvtime->tv_sec = sec;
recvtime->tv_usec = usec;
}
else
{
recvtime->tv_sec = sec - 1;
recvtime->tv_usec = -usec;
}
}

/*主函数*/
int main(int argc,char *argv[])
{
struct hostent *host;
struct protoent *protocol;
unsigned long inaddr = 0;
//	int waittime = MAX_WAIT_TIME;
int size = 50 * 1024;
addr[0] = argv[1];
//参数小于两个
if(argc < 2)
{
printf("usage:%s hostname/IP address\n",argv[0]);
exit(1);
}
//不是ICMP协议
if((protocol = getprotobyname("icmp")) == NULL)
{
perror("getprotobyname");
exit(1);
}

//生成使用ICMP的原始套接字，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，设置当前权限
setuid(getuid());

/*扩大套接字的接收缓存区导50K，这样做是为了减小接收缓存区溢出的
可能性，若无意中ping一个广播地址或多播地址，将会引来大量的应答*/
setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size));
bzero(&dest_addr,sizeof(dest_addr));	//初始化
dest_addr.sin_family = AF_INET;		//套接字域是AF_INET(网络套接字)

//判断主机名是否是IP地址
if(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 = inet_addr(argv[1]);
}
pid = getpid();
printf("PING %s(%s):%d bytes of data.\n",argv[1],
inet_ntoa(dest_addr.sin_addr),datalen);

//当按下ctrl+c时发出中断信号，并开始执行统计函数
signal(SIGINT,statistics);
while(nsend < MAX_NO_PACKETS)
{
sleep(1);		//每隔一秒发送一个ICMP报文
send_packet();		//发送ICMP报文
recv_packet();		//接收ICMP报文
}
return 0;
}