ping源码

  
    http://www.rfc-editor.org/rfc/rfc791.txt
  
    0                   1                   2                   3   
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version|  IHL  |Type of Service|          Total Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Identification        |Flags|      Fragment Offset    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Time to Live |    Protocol   |         Header Checksum       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Source Address                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Destination Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Options                    |    Padding    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

struct ip
{
#if __BYTE_ORDER == __LITTLE_ENDIAN
    unsigned int ip_hl:4;       /* header length */
    unsigned int ip_v:4;        /* version */
#endif
#if __BYTE_ORDER == __BIG_ENDIAN
    unsigned int ip_v:4;        /* version */
    unsigned int ip_hl:4;       /* header length */
#endif
    u_int8_t ip_tos;            /* type of service */
    u_short ip_len;         /* total length */
    u_short ip_id;          /* identification */
    u_short ip_off;         /* fragment offset field */
#define IP_RF 0x8000            /* reserved fragment flag */
#define IP_DF 0x4000            /* dont fragment flag */
#define IP_MF 0x2000            /* more fragments flag */
#define IP_OFFMASK 0x1fff       /* mask for fragmenting bits */
    u_int8_t ip_ttl;            /* time to live */
    u_int8_t ip_p;          /* protocol */
    u_short ip_sum;         /* checksum */
    struct in_addr ip_src, ip_dst;  /* source and dest address */
};

TCP/IP教程：http://www.rfc-editor.org/rfc/rfc1180.txt

TCP/IP协议校验和算法：http://www.rfc-editor.org/rfc/rfc1071.txt

#include <string.h>
#include <stdlib.h>
#include <stdio.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>
#inlcude <netinet/ip_icmp.h>
#include <netdb.h>
#include <setjmp.h>
#inlcude <errno.h>

#define PACKET_SIZE     4096
#define MAX_WAIT_TIME   5
#define MAX_NO_PACKETS  3

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

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

int sockfd;
struct sockaddr_in  dest_addr, from;
struct timeval tvrecv;
pid_t pid;

void statistics(int signo);
unsigned short cal_checksum(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 packet transmitted , %d received, %%%d lost\n",nsend, nreceived, \
	         (nsend-nreceived)/nsend*100);
	close(sockfd);
	exit(1);
}

/*-------校验和算法--------*/
unsigned short cal_checksum(unsigned short *addr, int len)
{
	int nleft = len;
	int sum = 0;
	unsigned short *w = addr;
	unsigned short answer = 0;
	
	/*--将ICMP报头二进制数据以2字节为单位累加--*/
	while(nleft > 1)
	{
		sum += *w++;
		nleft -= 2;
	}
	
	/*--若ICMP报头为奇数个字节，把最后一个字节最为一个2字节数据的高字节，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;
	
	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;
}

/*---发送三个报文---*/
void send_packet()
{
	int packetsize;
	while( nsend < MAX_NO_PACKETS )
	{
		nsend++;
		packetsize = pack(nsend);/*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*/
	}
}
		
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;
		}
		gettimeofday(&tvrecv,NULL); /*记录接收时间*/
		if(unpack(recvpacket,n) == -1)
			continue;
		nreceived++;
	}	
}

int unpack(char *buf, int len)
{
	int i, iphdrlen;
	struct ip *ip;
	struct icmp *icmp;
	struct timeval *tvsend;
	double rtt;
	
	ip = (struct ip *)buf;
	iphdrlen = ip->ip_hl<<2; /*求ip报头长度，即ip报头的长度标志乘4*/
	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 )
	{
		printf("ICMP packet\'s length is less than 8\n");
		return -1;
	}
	
	/*确保所收到的是我所发的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*/
		rtt = tvrecv.tv_sec * 1000 + tvrecv.tv_usec / 1000; /*以毫秒为单位计算rtt*/
		
		/*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->ttl,
				rtt);
	}
	else 
		return -1;
}

int main(int argc, char *argv[])
{
	struct hostent *host;
	struct protoent *protocol;
	unsigned long inaddr = 0L;
	int waittime = MAX_WAIT_TIME;
	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");
		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, protocol->p_proto)) < 0)
	{
		perror("socket error");
		exit(1);
	}
	
	/*收回root权限，设置当前用户权限*/
	setuid(getuid());
	
	/*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
	  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*/
	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) /*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*/
		memcpy((char *)&dest_addr, (char *)&inaddr, host->h_length);
		
	/*获取main的进程id，用于设置ICMP的标志符*/
	pid = getid();
	printf("PING %s(%s):%d bytes data in ICMP packets.\n", argv[1], inet_ntoa(dest_addr.sin_addr),datalen);
	send_packet();
	recv_packet();
	statistics(SIGALRM);
	
	return 0;
}

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;
}

sudo gcc -o ping ping.c
sudo chmod u+s ping #目的是把ping程序设置成SUID的属性
		

使用SCTP优化网络：http://www.ibm.com/developerworks/cn/linux/l-sctp/