002.ICMP--拼接ICMP包,实现简单Ping程序(原始套接字)

/*
============================================================================
Name        : myping.c
Author      : huh
Version     : 0.01
Copyright   : Your copyright notice
Description : Hello World in C, Ansi-style
============================================================================
*/

#include <sys/types.h>
#include <sys/select.h>
#include <stdio.h>
#include <time.h>
#include <string.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/ip_icmp.h>

#define PACKET_SIZE 1024*4

int pid;
int sockfd;
int datalen = 56;
int nsent = 1, nrecv = 1;
char sendbuf[PACKET_SIZE];
char recvbuf[PACKET_SIZE];
struct sockaddr_in dest_addr; //socket目的地址
struct sockaddr_in src_addr;
struct timeval tvrecv;

void send_packet();
void un_packet(int);
void tv_sub(struct timeval *out, struct timeval *in);
unsigned short in_chksum(unsigned short *addr, int len);

int main()
{
pid = getpid();
char str[20];
unsigned int inaddr;
struct hostent *host;
int size = 1024 * 25;
strcpy(str,"www.baidu.com");
//IP地址(域名)到无符号整数的转换
inaddr = inet_addr(str);
if (inaddr == INADDR_NONE)
{
host = gethostbyname(str);
if (host == NULL)
{
printf("参数格式不正确，请重新输入！\n");
return 0;
}
memcpy((char*) &inaddr, host->h_addr, sizeof(dest_addr.sin_addr));
}
//设置套接字地址
dest_addr.sin_family = AF_INET;
memcpy((char *)&dest_addr.sin_addr, (char *)&inaddr,sizeof(inaddr));
//创建套接字
sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
//改变socket缓冲区大小
setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));

printf("PING %s (%s) %d(84) bytes of data.\n",str, inet_ntoa(dest_addr.sin_addr), datalen);
//不停的发送和接受ICMP数据包
while (1)
{
send_packet();
int src_addr_len = sizeof(struct sockaddr_in);
//接收数据包，一直阻塞到有数据包到达为止
int len = recvfrom(sockfd, recvbuf, sizeof(recvbuf), 0, (struct sockaddr *) &src_addr, (socklen_t *) &src_addr_len);
if(len < 0)
printf("recvfrom error!\n");
un_packet(len);
sleep(1); //间隔一秒，后面会用信号实现每秒发送一个ICMP包。
}
return 0;
}

//解包
void un_packet(int len)
{
int hlen1;
double rtt;
struct ip *ip;
struct icmp *icmp;
struct timeval *tvsend;

ip = (struct ip *) recvbuf;
hlen1 = ip->ip_hl << 2;
if (ip->ip_p != IPPROTO_ICMP)
return ;

icmp = (struct icmp *) (recvbuf + hlen1);
len -= hlen1;

if ((icmp->icmp_type == ICMP_ECHOREPLY))
{
if (icmp->icmp_id != pid)
return;
tvsend = (struct timeval *) icmp->icmp_data;  //发送时间
gettimeofday(&tvrecv, NULL);  //得到当前时间

tv_sub(&tvrecv, tvsend); //计算接收和发送的时间差
rtt = tvrecv.tv_sec * 1000.0 + tvrecv.tv_usec / 1000.0; //以毫秒单位计算rtt
printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3fms\n", len, inet_ntoa(src_addr.sin_addr), icmp->icmp_seq, ip->ip_ttl, rtt);
nrecv++;
}
}

//手动构建数据包，并通过原始套接字发送
void send_packet()
{
int len;
struct icmp *icmp;
icmp = (struct icmp *) (sendbuf);
icmp->icmp_type = ICMP_ECHO;  //拼接icmp
icmp->icmp_code = 0;
icmp->icmp_id = pid;   //2字节
icmp->icmp_seq = nsent++; //2字节
memset(icmp->icmp_data, 0xa5, datalen);
gettimeofday((struct timeval *) icmp->icmp_data, NULL);    //将发送时间作为数据传递过去

len = datalen + 8;
icmp->icmp_cksum = 0;  //校验和需要先置0
icmp->icmp_cksum = in_chksum((unsigned short *) icmp, len);  //计算效验和

sendto(sockfd, sendbuf, len, 0, (struct sockaddr *) &dest_addr,
sizeof(dest_addr));  //将包发出去
//printf("package have sent!\n");
}

//计算效验和
unsigned short in_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;
}
if (nleft == 1)
{
*(unsigned char *) (&answer) = *(unsigned char *) w;
sum += answer;
}
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
answer = ~sum;
return answer;
}

//计算时间差
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;
}