A ping function implemented on c++

Ping.cpp

#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/file.h>
#include <sys/time.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#include <unistd.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <iostream>
#define	DEFDATALEN	(64-ICMP_MINLEN)
#define	MAXIPLEN	60
#define	MAXICMPLEN	76
#define	MAXPACKET	(65536 - 60 - ICMP_MINLEN)

using namespace std;

uint16_t in_cksum(uint16_t *addr, unsigned len);


int ping(string target)
{

    int s, i, cc, packlen, datalen = DEFDATALEN;
	struct hostent *hp;
	struct sockaddr_in to, from;
	struct ip *ip;
	u_char *packet, outpack[MAXPACKET];
	char hnamebuf[MAXHOSTNAMELEN];
	string hostname;
	struct icmp *icp;
	int ret, fromlen, hlen;
	fd_set rfds;
	struct timeval tv;
	int retval;
	struct timeval start, end;
	int end_t;
	bool cont = true;

	to.sin_family = AF_INET;

	to.sin_addr.s_addr = inet_addr(target.c_str());
	if (to.sin_addr.s_addr != (u_int)-1)
		hostname = target;
	else 
	{
		hp = gethostbyname(target.c_str());
		if (!hp)
		{
			cerr << "unknown host "<< target << endl;
			return -1;
		}
		to.sin_family = hp->h_addrtype;
		bcopy(hp->h_addr, (caddr_t)&to.sin_addr, hp->h_length);
		strncpy(hnamebuf, hp->h_name, sizeof(hnamebuf) - 1);
		hostname = hnamebuf;
	}
	packlen = datalen + MAXIPLEN + MAXICMPLEN;
	if ( (packet = (u_char *)malloc((u_int)packlen)) == NULL)
	{
		cerr << "malloc error\n";
		return -1;
	}


	if ( (s = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) < 0)
	{
		return -1; /* Needs to run as superuser!! */
	}

	icp = (struct icmp *)outpack;
	icp->icmp_type = ICMP_ECHO;
	icp->icmp_code = 0;
	icp->icmp_cksum = 0;
	icp->icmp_seq = 12345;
	icp->icmp_id = getpid();


	cc = datalen + ICMP_MINLEN;
	icp->icmp_cksum = in_cksum((unsigned short *)icp,cc);

	gettimeofday(&start, NULL);

	i = sendto(s, (char *)outpack, cc, 0, (struct sockaddr*)&to, (socklen_t)sizeof(struct sockaddr_in));
	if (i < 0 || i != cc)
	{
		if (i < 0)
			perror("sendto error");
		cout << "wrote " << hostname << " " <<  cc << " chars, ret= " << i << endl;
	}
	
	FD_ZERO(&rfds);
	FD_SET(s, &rfds);
	tv.tv_sec = 1;
	tv.tv_usec = 0;

	while(cont)
	{
		retval = select(s+1, &rfds, NULL, NULL, &tv);
		if (retval == -1)
		{
			perror("select()");
			return -1;
		}
		else if (retval)
		{
			fromlen = sizeof(sockaddr_in);
			if ( (ret = recvfrom(s, (char *)packet, packlen, 0,(struct sockaddr *)&from, (socklen_t*)&fromlen)) < 0)
			{
				perror("recvfrom error");
				return -1;
			}

			// Check the IP header
			ip = (struct ip *)((char*)packet); 
			hlen = sizeof( struct ip ); 
			if (ret < (hlen + ICMP_MINLEN)) 
			{ 
				cerr << "packet too short (" << ret  << " bytes) from " << hostname << endl;;
				return -1; 
			} 

			// Now the ICMP part 
			icp = (struct icmp *)(packet + hlen); 
			if (icp->icmp_type == ICMP_ECHOREPLY)
			{
				if (icp->icmp_seq != 12345)
				{
					cout << "received sequence # " << icp->icmp_seq << endl;
					continue;
				}
				if (icp->icmp_id != getpid())
				{
					cout << "received id " << icp->icmp_id << endl;
					continue;
				}
				cont = false;
			}
			else
			{
				cout << "Recv: not an echo reply" << endl;
				continue;
			}
	
			gettimeofday(&end, NULL);
			end_t = 1000000*(end.tv_sec - start.tv_sec) + (end.tv_usec - start.tv_usec);

			if(end_t < 1)
				end_t = 1;

			cout << "Elapsed time = " << end_t << " usec" << endl;
			return end_t;
		}
		else
		{
			cout << "No data within one seconds.\n";
			return 0;
		}
	}
	return 0;
}

uint16_t in_cksum(uint16_t *addr, unsigned len)
{
  uint16_t answer = 0;
  /*
   * Algorithm is simple, using a 32 bit accumulator (sum), add
   * sequential 16 bit words to it, and at the end, fold back all the
   * carry bits from the t   16 bits into the lower 16 bits.
   */
  uint32_t sum = 0;
  while (len > 1)  {
    sum += *addr++;
    len -= 2;
  }

  if (len == 1) {
    *(unsigned char *)&answer = *(unsigned char *)addr ;
    sum += answer;
  }

  sum = (sum >> 16) + (sum & 0xffff);
  sum += (sum >> 16);
  answer = ~sum;
  return answer;
}

你好~ 我觉得 socket 应该要关闭，不然在运行很长一段时间之后，会出现 error:24 ，此时 lsof -p | wc -l 已经显示一千多了，而且大部分是 “00000000:0001->00000000:0000 st=07”, 我尝试在 ping 函数中除第一个 return 之外的每一个 return 前面加上 close(s)，就不会出现这个问题。

Debian Bullseye, 64-bit

strange behavior, when system is 64-bit and

cat /proc/sys/kernel/pid_max
4194304

line 140. produces error

because icp->icmp_id
is
unsigned short

which is definitely less than PID