C语言实现PING程序

#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <arpa/inet.h>
#include <sys/time.h>
#include <setjmp.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <netinet/in.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#define MAX_WAIT_TIME   5 /* 最大等待时间 */
#define MAX_NO_PACKETS  4 /* 一次ping发送的ICMP数目 */
#define PACKET_SIZE     4096 /* ICMP包大小 */
int cxsend = 0, cxreceived = 0;
struct sockaddr_in dest_addr; /* 目标地址 */
pid_t pid; /* 记录进程ID */
struct sockaddr_in from;
struct timeval recvtime;  /* 记录时间 */
char sendpacket[PACKET_SIZE];  /* 发送包 */
char recvpacket[PACKET_SIZE];  /* 接收包 */
int sockfd, datalen = 56;

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) {
printf("\n--------------------PING statistics-------------------\n");
printf("%d packets transmitted, %d received , %%%d lost\n", cxsend,
cxreceived, (cxsend - cxreceived) / cxsend * 100);
close(sockfd);
exit(1);
}

/*去除ICMP报头*/
int unpack(char *buf, int len) {
int iphdrlen;
struct ip *ip;
struct icmp *icmp;
struct timeval *tvsend;
double rtt;
ip = (struct ip *) buf;
iphdrlen = ip->ip_hl << 2; /*ip报头的长度标志乘4求得ip报头长度*/
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\n");
return -1;
}
/*确保所接收的是目标主机所发的的ICMP的回应*/
if ((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == pid)) {
tvsend = (struct timeval *) icmp->icmp_data;
tv_sub(&recvtime, tvsend); /*接收和发送的时间差*/
rtt = recvtime.tv_sec * 1000 + recvtime.tv_usec / 1000; /*以毫秒为单位计算rtt*/
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;
}
return 0;
}
/*接收所有的ICMP报文*/
void recv_packet() {
int n, fromlen;
extern int errno;
signal(SIGALRM, statistics);
fromlen = sizeof(from);
while (cxreceived < cxsend) {
alarm(MAX_WAIT_TIME);
if ((n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0,
(struct sockaddr *) &from, (socklen_t*) &fromlen)) < 0) {
if (errno == EINTR)
continue;
perror("recvfrom error");
continue;
}
gettimeofday(&recvtime, NULL); /*记录接收时间*/
if (unpack(recvpacket, n) == -1) {
continue;
}
cxreceived++;
}
}
/*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 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((unsigned short *) icmp, packsize); /*校验算法*/
return packsize;
}
/*发送MAX_NO_PACKETS个ICMP报文*/
void send_packet() {
int packetsize;
while (cxsend < MAX_NO_PACKETS) {
cxsend++;
packetsize = pack(cxsend); /*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*/
}
}
/*两个时间记录结构相减*/
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[]) {
struct hostent *host;
struct protoent *protocol;
unsigned long inaddr = 0l;
int size = 50 * 1024;
if (argc < 2) {
printf("usage:%s hostname/IP address\n", argv[0]);
exit(1);
}

if ((protocol = getprotobyname("icmp")) == NULL)
{
perror("getprotobyname error");
exit(1);
}
/*生成使用ICMP的原始套接字*/
if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0) /*函数socket()在<sys/socket.h>中定义，int socket(int domain, int type, int protocol);*/
{
perror("socket error");
exit(1);
}
setuid(getuid());
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) {
perror("gethostbyname error");
exit(1);
}
/*是主机名*/
memcpy((char *) &dest_addr.sin_addr, host->h_addr, host->h_length);
} else {
/*是IP地址*/
memcpy((char *) &dest_addr.sin_addr, (char*)&inaddr,sizeof(inaddr));
}
/*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);
send_packet(); /*发送所有ICMP报文*/
recv_packet(); /*接收所有ICMP报文*/
statistics(SIGALRM); /*统计*/
return 0;
}