ping程序剖析

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   在剖析ping之前我们先补充一点知识。。。

    （1）结构体addinfo

     头文件：#include<netdb.h>

    struct addrinfo

    {

           int  ai_flags;

           int  ai_family;      //AF_INET，AF_INET6，UNIX etc

           int  ai_socktype;   //STREAW，DATAGRAM，RAW

           int  ai_protocol;    //IPPROTO_IP，IPPROTO_IPV4，IPPROTO_IPV6 etc

           size_t  ai_addrlen;    //length of  ai_addr

           char*  ai_canonname;   //full hostname

          struct sockaddr* ai_addr;  //addr of host

          struct addrinfo*    ai_next;

    }

   （2）getopt函数（分析命令行参数）：

           头文件：#include<unistd.h>

           函数原型： int  getopt （int argc，char* const argv[ ]，const char*optstring）；

           extern char* optarg;

           extern  int optind，opterr，optopt;

           getopt（）所设置的全局变量包括：

             optarg-----指向当前选项参数（如果有）的指针。optind------再次调用getopt（）时的下一个指针的索引。

             optopt-----最后一个未知选项。

          补充说明：
         

         gethostbyname和gethostbyaddr这两个函数仅仅支持IPv4，getaddrinfo函数能够处理名字到地址以及服务到端口这两种转换，返回的是一个sockaddr结构的链表而不是一个地址清单。

          头文件：#include<netdb.h>------>linux下

                          #include<ws2tcpip.h>------->windows下

         函数原型：
          int   getaddrinfo（const char *hostname，const char* service，const struct addrinfo *hints，

                                           struct addrinfo**result）

       参数说明：
          

    msg.msg_iov = { struct iovec = { iov_base = { icmp头+填充字符‘E‘ }, iov_len = 40 } }

    msg.msg_len = 1

    第三组是msg_control和msg_controllen，它们可被用于发送任何的控制信息，在我们的例子中，没有控制信息要发送。暂时略过。

    第四组是msg_flags。其值即为传入的参数flags。raw协议不支持MSG_OOB向标志，即带外数据

 在其中我们可以看到icmp报文是作为ip数据报的数据，所以icmp的报头起始位置等于ip报头加上其报文的长度。。。。

  下面给出部分的源码（主要是针对IPv4进行注释）：

ping.h:

#include	"unp.h"
#include	<netinet/in_systm.h>
#include	<netinet/ip.h>
#include	<netinet/ip_icmp.h>

#define	BUFSIZE		1500

			/* globals */
char	 sendbuf[BUFSIZE];

int		 datalen;			/* # bytes of data following ICMP header */
char	*host;
int		 nsent;				/* add 1 for each sendto() */
pid_t	 pid;				/* our PID */
int		 sockfd;
int		 verbose;

			/* function prototypes */
void	 init_v6(void);
void	 proc_v4(char *, ssize_t, struct msghdr *, struct timeval *);
void	 proc_v6(char *, ssize_t, struct msghdr *, struct timeval *);
void	 send_v4(void);
void	 send_v6(void);
void	 readloop(void);
void	 sig_alrm(int);
void	 tv_sub(struct timeval *, struct timeval *);

struct proto {
  void	 (*fproc)(char *, ssize_t, struct msghdr *, struct timeval *);
  void	 (*fsend)(void);
  void	 (*finit)(void);
  struct sockaddr  *sasend;	/* sockaddr{} for send, from getaddrinfo */
  struct sockaddr  *sarecv;	/* sockaddr{} for receiving */
  socklen_t	    salen;		/* length of sockaddr{}s */
  int	   	    icmpproto;	/* IPPROTO_xxx value for ICMP */
} *pr;

#ifdef	IPV6

#include	<netinet/ip6.h>
#include	<netinet/icmp6.h>

#endif

main.c

#include	"ping.h"

struct proto	proto_v4 = { proc_v4, send_v4, NULL, NULL, NULL, 0, IPPROTO_ICMP };


int	datalen = 56;		/* data that goes with ICMP echo request */

int main(int argc, char **argv)
{
	int				c;
	struct addrinfo	*ai;
	char *h;

	opterr = 0;		/* don't want getopt() writing to stderr */
        //处理命令行参数
        //例如：./ping 127.0.0.1
	while ( (c = getopt(argc, argv, "v")) != -1) {
		switch (c) {
		case 'v':
			verbose++;
			break;

		case '?':
			err_quit("unrecognized option: %c", c);
		}
	}

	if (optind != argc-1)
		err_quit("usage: ping [ -v ] <hostname>");
        //host保存ip地址
	host = argv[optind];

        //获取当前的进程号
	pid = getpid() & 0xffff;	/* ICMP ID field is 16 bits */
        //发送信号函数
	Signal(SIGALRM, sig_alrm);
        
        //在命令行参数中必须有一个主机名或ip地址，调用Host_serv函数进行处理
        //返回addrinfo结构
	ai = Host_serv(host, NULL, 0, 0);

	h = Sock_ntop_host(ai->ai_addr, ai->ai_addrlen);
	printf("PING %s (%s): %d data bytes\n",
			ai->ai_canonname ? ai->ai_canonname : h,
			h, datalen);

		/* 4initialize according to protocol */
        //初始化协议结构体pr
	if (ai->ai_family == AF_INET) {
		pr = &proto_v4;
	} else
		err_quit("unknown address family %d", ai->ai_family);

	pr->sasend = ai->ai_addr;
	pr->sarecv = Calloc(1, ai->ai_addrlen);
	pr->salen = ai->ai_addrlen;
        //调用函数
	readloop();

	exit(0);
}

/* include host_serv */
#include	"unp.h"

struct addrinfo *
host_serv(const char *host, const char *serv, int family, int socktype)
{
	int				n;
	struct addrinfo	hints, *res;
        //清零
	bzero(&hints, sizeof(struct addrinfo));
        //用于返回主机的规范名称
	hints.ai_flags = AI_CANONNAME;	/* always return canonical name */
        //其值为0代表：协议无关
	hints.ai_family = family;		/* AF_UNSPEC, AF_INET, AF_INET6, etc. */
	hints.ai_socktype = socktype;	/* 0, SOCK_STREAM, SOCK_DGRAM, etc. */

	if ( (n = getaddrinfo(host, serv, &hints, &res)) != 0)
		return(NULL);

	return(res);	/* return pointer to first on linked list */
}
/* end host_serv */

/*
 * There is no easy way to pass back the integer return code from
 * getaddrinfo() in the function above, short of adding another argument
 * that is a pointer, so the easiest way to provide the wrapper function
 * is just to duplicate the simple function as we do here.
 */

struct addrinfo *
Host_serv(const char *host, const char *serv, int family, int socktype)
{
	int				n;
	struct addrinfo	hints, *res;

	bzero(&hints, sizeof(struct addrinfo));
	hints.ai_flags = AI_CANONNAME;	/* always return canonical name */
	hints.ai_family = family;		/* 0, AF_INET, AF_INET6, etc. */
	hints.ai_socktype = socktype;	/* 0, SOCK_STREAM, SOCK_DGRAM, etc. */

	if ( (n = getaddrinfo(host, serv, &hints, &res)) != 0)
		err_quit("host_serv error for %s, %s: %s",
				 (host == NULL) ? "(no hostname)" : host,
				 (serv == NULL) ? "(no service name)" : serv,
				 gai_strerror(n));

	return(res);	/* return pointer to first on linked list */
}

#include	"unp.h"

#ifdef	HAVE_SOCKADDR_DL_STRUCT
#include	<net/if_dl.h>
#endif

/* include sock_ntop */
char *
sock_ntop(const struct sockaddr *sa, socklen_t salen)
{
    char		portstr[8];
    static char str[128];		/* Unix domain is largest */

	switch (sa->sa_family) {
        //当是IPv4协议时
	case AF_INET: {
		struct sockaddr_in	*sin = (struct sockaddr_in *) sa;
                //点分十进制与二进制的转化
		if (inet_ntop(AF_INET, &sin->sin_addr, str, sizeof(str)) == NULL)
			return(NULL);
                //将端口的网络字节序转换为主机字节序
		if (ntohs(sin->sin_port) != 0) {
			snprintf(portstr, sizeof(portstr), ":%d", ntohs(sin->sin_port));
			strcat(str, portstr);
		}
		return(str);
	}
/* end sock_ntop */

#ifdef	IPV6
	case AF_INET6: {
		struct sockaddr_in6	*sin6 = (struct sockaddr_in6 *) sa;

		str[0] = '[';
		if (inet_ntop(AF_INET6, &sin6->sin6_addr, str + 1, sizeof(str) - 1) == NULL)
			return(NULL);
		if (ntohs(sin6->sin6_port) != 0) {
			snprintf(portstr, sizeof(portstr), "]:%d", ntohs(sin6->sin6_port));
			strcat(str, portstr);
			return(str);
		}
		return (str + 1);
	}
#endif

#ifdef	AF_UNIX
	case AF_UNIX: {
		struct sockaddr_un	*unp = (struct sockaddr_un *) sa;

			/* OK to have no pathname bound to the socket: happens on
			   every connect() unless client calls bind() first. */
		if (unp->sun_path[0] == 0)
			strcpy(str, "(no pathname bound)");
		else
			snprintf(str, sizeof(str), "%s", unp->sun_path);
		return(str);
	}
#endif

#ifdef	HAVE_SOCKADDR_DL_STRUCT
	case AF_LINK: {
		struct sockaddr_dl	*sdl = (struct sockaddr_dl *) sa;

		if (sdl->sdl_nlen > 0)
			snprintf(str, sizeof(str), "%*s (index %d)",
					 sdl->sdl_nlen, &sdl->sdl_data[0], sdl->sdl_index);
		else
			snprintf(str, sizeof(str), "AF_LINK, index=%d", sdl->sdl_index);
		return(str);
	}
#endif
	default:
		snprintf(str, sizeof(str), "sock_ntop: unknown AF_xxx: %d, len %d",
				 sa->sa_family, salen);
		return(str);
	}
    return (NULL);
}

char *
Sock_ntop(const struct sockaddr *sa, socklen_t salen)
{
	char	*ptr;

	if ( (ptr = sock_ntop(sa, salen)) == NULL)
		err_sys("sock_ntop error");	/* inet_ntop() sets errno */
	return(ptr);
}

#include	"ping.h"

void
proc_v4(char *ptr, ssize_t len, struct msghdr *msg, struct timeval *tvrecv)
{
	int				hlen1, icmplen;
	double			rtt;
	struct ip		*ip;
	struct icmp		*icmp;
	struct timeval	*tvsend;

	ip = (struct ip *) ptr;		/* start of IP header */
        //获取ip首部长度
	hlen1 = ip->ip_hl << 2;		/* length of IP header */
        //如果不是ICMP协议，直接返回
	if (ip->ip_p != IPPROTO_ICMP)
		return;				/* not ICMP */
        //icmp的头部等于ip+ip长度
	icmp = (struct icmp *) (ptr + hlen1);	/* start of ICMP header */
	if ( (icmplen = len - hlen1) < 8)
		return;				/* malformed packet */
        //设置类型为回显
	if (icmp->icmp_type == ICMP_ECHOREPLY) {
		if (icmp->icmp_id != pid)
			return;			/* not a response to our ECHO_REQUEST */
		if (icmplen < 16)
			return;			/* not enough data to use */
                //计算往返时间
		tvsend = (struct timeval *) icmp->icmp_data;
		tv_sub(tvrecv, tvsend);
		rtt = tvrecv->tv_sec * 1000.0 + tvrecv->tv_usec / 1000.0;

		printf("%d bytes from %s: seq=%u, ttl=%d, rtt=%.3f ms\n",
				icmplen, Sock_ntop_host(pr->sarecv, pr->salen),
				icmp->icmp_seq, ip->ip_ttl, rtt);

	} else if (verbose) {
		printf("  %d bytes from %s: type = %d, code = %d\n",
				icmplen, Sock_ntop_host(pr->sarecv, pr->salen),
				icmp->icmp_type, icmp->icmp_code);
	}
}

#include	"ping.h"

void
sig_alrm(int signo)
{
	(*pr->fsend)();

	alarm(1);
	return;
}

#include	"ping.h"

void
send_v4(void)
{
	int			len;
	struct icmp	*icmp;

	icmp = (struct icmp *) sendbuf;
	icmp->icmp_type = ICMP_ECHO;
	icmp->icmp_code = 0;
	icmp->icmp_id = pid;
	icmp->icmp_seq = nsent++;
	memset(icmp->icmp_data, 0xa5, datalen);	/* fill with pattern */
	Gettimeofday((struct timeval *) icmp->icmp_data, NULL);

	len = 8 + datalen;		/* checksum ICMP header and data */
	icmp->icmp_cksum = 0;
	icmp->icmp_cksum = in_cksum((u_short *) icmp, len);

	Sendto(sockfd, sendbuf, len, 0, pr->sasend, pr->salen);
}

分别使用自己的ping命令和系统的ping命令。。。该ping程序目前没有系统ping的功能那么完整，至少能实现基本的检测。。。。。

    上图就是我们整个程序的大致流程。。。。

ping程序剖析

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原文地址：http://blog.csdn.net/ooooo12345re/article/details/51601202