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I'm trying to implement a mini ping. just test if another host is still up. The code I have so far only works if I ping my localhost but nothing else. I don't know what I'm doing wrong.
When I send an echo request to localhost, first I receive an echo request (strange!!) and the second time I receive the echo reply correctly. But when I echo any other host, I don't receive anything. Here is my code, Please HELP
Code:
#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 <netinet/ip_var.h>
#include <netdb.h>
#include <unistd.h>
#include <stdio.h>
#include <ctype.h>
//#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#define DEFDATALEN (64-8) /* default data length */
#define MAXIPLEN 60
#define MAXICMPLEN 76
#define MAXPACKET (65536 - 60 - 8)/* max packet size */
int ping(string target)
{
int s, i, cc, packlen, datalen = DEFDATALEN;
struct hostent *hp;
struct sockaddr_in *to, *from;
struct protoent *proto;
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 start_t, end_t;
bool cont = true;
to->sin_family = AF_INET;
// try to convert as dotted decimal address, else if that fails assume it's a hostname
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 ( (proto = getprotobyname("icmp")) == NULL)
{
cerr << "unknown protocol icmp" << endl;
return -1;
}
if ( (s = socket(AF_INET, SOCK_RAW, proto->p_proto)) < 0)
{
perror("socket"); /* probably not running as superuser */
return -1;
}
icp = (struct icmp *)outpack;
icp->icmp_type = ICMP_ECHO;
icp->icmp_code = 0;
icp->icmp_seq = 12345; /* seq and id must be reflected */
icp->icmp_id = getpid();
cc = datalen + 8;
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;
}
// Watch stdin (fd 0) to see when it has input.
FD_ZERO(&rfds);
FD_SET(s, &rfds);
// Wait up to one seconds.
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)
{
cout << "Recv: echo reply"<< endl;
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;
}
}
}
int main(int argc, char** argv)
{
if (argc != 2)
{
cout << "Usage: ping hostname" << endl;
exit(1);
}
cout << "ping returned " << ping(argv[1]) << endl;
return 0;
}
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