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getaddrinfo, I am not getting any canonname

I am trying to read all the information about specific host and print out every information. I can read and print out all the addresses but I am not reading any ai_canonname!

First I thought my examples(www.google.com|www.irs.gov|...) don't have canon name, but after a while I figured I am not getting any name at all. Do you think I am doing something wrong or do you have an example that would work?

Here is my code,

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>
#include <sys/time.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
    struct addrinfo *result, *rp, hints;
    int error;
    char canonname[32][256];
int canonnum = 0;
char ip[32][64];
int ipnum = 0;
struct timeval tv;
uint64_t starttime, endtime;

if(argc<2)
{
    printf("Usage: %s <address>\n", argv[0]);
    return 0;
}

/* Record Start time */
gettimeofday(&tv, NULL);
starttime = tv.tv_usec;

memset(&hints, 0, sizeof(hints));
memset(canonname, 0, 32*256*sizeof(char));
memset(ip, 0, 32*64*sizeof(char));
hints.ai_socktype = SOCK_STREAM;
hints.ai_family = AF_INET;

error = getaddrinfo(argv[1], NULL, &hints, &result);
if (error != 0)
{   
    if (error == EAI_SYSTEM)
    {
        perror("getaddrinfo");
    }
    else
    {
        fprintf(stderr, "error in getaddrinfo: %s\n", gai_strerror(error));
    }
    return -1;
}
strcpy(canonname[0], "");
if(result->ai_canonname != NULL)
    strcpy(canonname[0], result->ai_canonname);
canonnum++;
for(rp = result; rp != NULL; rp = rp->ai_next) {
    if(rp !=result && rp->ai_canonname != NULL)
    {
        if(strcmp(rp->ai_canonname, "")!=0)
        {
            strcpy(canonname[canonnum],rp->ai_canonname);
            canonnum++;
        }
    }
    struct sockaddr_in *inaddr_ptr;
    if (rp->ai_addr->sa_family == AF_INET)
        inaddr_ptr = (struct sockaddr_in *)rp->ai_addr;
    sprintf(ip[ipnum],"%s\n", inet_ntoa(inaddr_ptr->sin_addr));
    ipnum++;
}

/* Gets the end time and prints out the execution time */
gettimeofday(&tv, NULL);
endtime = tv.tv_usec;
printf("Execution time: %llu milliseconds\n",(endtime - starttime)/100);
printf("Official name: %s\n", canonname[0]);
printf("Aliases:\n");
for(int i=1;i<canonnum;i++)
    printf("%s\n",canonname[i]);
printf("Addresses:\n");
for(int i=0;i<ipnum;i++)
    printf("%s",ip[i]);
freeaddrinfo(result);
return 0;
}
like image 569
Younes Nj Avatar asked Sep 18 '13 23:09

Younes Nj


1 Answers

The specification for getaddrinfo() says you should add:

hints.ai_flags = AI_CANONNAME;

and you will get what you ask for.

$ ./gai www.ibm.com
Execution time: 4499 milliseconds
Official name: www.ibm.com
Aliases:
Addresses:
129.42.60.216
$ ./gai www.google.com
Execution time: 248 milliseconds
Official name: www.google.com
Aliases:
Addresses:
74.125.239.50
74.125.239.49
74.125.239.48
74.125.239.52
74.125.239.51
$ ./gai www.irs.gov
Execution time: 2872 milliseconds
Official name: 63-146-70-67.dia.static.qwest.net
Aliases:
Addresses:
63.146.70.67
63.146.70.96
$  ./gai www.irs.gov
Execution time: 2299 milliseconds
Official name: 63-146-70-96.dia.static.qwest.net
Aliases:
Addresses:
63.146.70.96
63.146.70.67
$

I'm not sure what to make of the changing identity of the IRS. Canonical doesn't mean as canonical as all that, it seems.

like image 61
Jonathan Leffler Avatar answered Oct 05 '22 15:10

Jonathan Leffler