linux上Ping程序的实现

/*
* 	Ping程序
* 	2014年5月15日
* 	Version 1.0
* 	Designed by WJY
*
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <netdb.h>
#include <setjmp.h>
#include <errno.h>

#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>

#define PACKET_SIZE		4096
#define MAX_WAIT_TIME	5
#define MAX_NO_PACKETS	4

char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];

int sockfd;
int datalen = 56;
int nsend = 0;
int nreceived = 0;

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

//统计报文发送和接收情况
void statistics(int signo);
//计算校验和
unsigned short cal_chksum(unsigned short *addr, int len);
//设置ICMP报头
int pack(int pack_no);
//发送报文
void send_packet(void);
//接收报文
void recv_packet(void);
//解析ICMP报文
int unpack(char *buf, int len);
//计算时间
void tv_sub(struct timeval *out, struct timeval *in);

/* 统计发送的ICMP报文和丢失的ICMP报文 */
void statistics(int signo)
{
printf("\n--------------------PING statistics-------------------\n");
printf("%d packets transmitted, %d received , %%%d lost\n",
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;

/*记录发送时间*/
tval = (struct timeval *) icmp->icmp_data;
gettimeofday(tval,NULL);

/*校验算法*/
icmp->icmp_cksum = cal_chksum((unsigned short *)icmp, packsize);
return packsize;
}

/*发送四个ICMP报文*/
void send_packet()
{
int packetsize;
while(nsend < MAX_NO_PACKETS)
{
/* 设置ICMP报头 */
nsend++;
packetsize = pack(nsend);
if(sendto(sockfd, sendpacket, packetsize , 0,
(struct sockaddr *) &dest_addr, sizeof(dest_addr)) < 0)
{
printf("发送ICMP报文失败!\n");
continue;
}
/* 每隔1毫秒发送一个ICMP报文 */
usleep(1);
}
}

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

}
/* 解析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;
/* 求IP报头长度，即ip报头的长度标志乘4（IP首部的长度是以32位为单位的）*/
iphdrlen = ip->ip_hl << 2;
/* 越过IP报头,指向ICMP报头 */
icmp= (struct icmp *)(buf + iphdrlen);
/* ICMP报头及ICMP数据报的总长度 */
len -= iphdrlen;
/* 小于ICMP报头长度则不合理 */
if( len < 8)
{
printf("ICMP packets\'s length is less than 8.\n");
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*/
/* 以毫秒为单位计算rtt */
rtt = tvrecv.tv_sec * 1000 + tvrecv.tv_usec / 1000;
/* 显示相关信息 */
printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3f ms\n",
len, inet_ntoa(from.sin_addr), icmp->icmp_seq, ip->ip_ttl, rtt);
}
else
return -1;
}

/* 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;
}

int main(int argc, char *argv[])
{
unsigned long inaddr = 0l;
int waittime = MAX_WAIT_TIME;
int size = 50*1024;

struct hostent *host;
struct protoent *protocol;

if (argc != 2) {
printf("Error. Usage: %s <Hostname or IP address>\n", argv[0]);
exit(1);
}

/* 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, IPPROTO_ICMP)) < 0) {
printf("创建原始套接字失败！\n");
exit(1);
}

/* 扩大接收缓冲区，主要是防止ping到一个广播地址或多播地址，造成缓冲区溢出 */
setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
bzero(&dest_addr, sizeof(dest_addr));
dest_addr.sin_family = AF_INET;

/* 判断输入的是主机名还是ip地址 */
if((inaddr = inet_addr(argv[1])) == INADDR_NONE)
{
if((host = gethostbyname(argv[1])) == NULL)
{
printf("通过主机名获取主机IP失败!\n");
exit(1);
}
memcpy((char *) &dest_addr.sin_addr, host->h_addr, host->h_length);
}
else
{
if (inet_pton(AF_INET, argv[1], &dest_addr.sin_addr) <= 0)
{
printf("inet_pton error for %s\n", argv[1]);
exit(1);
}
}

/* 获取进程的id，用于设置ICMP的标志符 */
pid = getpid();
printf("PING %s (%s): %d bytes data in ICMP packets.\n",
argv[1], inet_ntoa(dest_addr.sin_addr), datalen);

/*发送所有ICMP报文*/
send_packet();
/*接收所有ICMP报文*/
recv_packet();
/*进行统计*/
statistics(SIGALRM);

return 0;
}