perl and getaddrinfo API

swissknife has asked for the wisdom of the Perl Monks concerning the following question:

Dear Experts

i am trying to get the IP address returned by the API getaddrinfo(). i have no experience with Socket module but i found some code online and giving a try. i use the following code.

#!/usr/bin/perl
use Socket;

my $server = shift @ARGV;
my $pip = gethostbyname($server);
my $IP_add = inet_ntoa($pip);

print $IP_add;
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this returns the IP address of the server passed as argument.

but when i try to print the value of $pip, it returns nothing and if i try to pass the $server directly instead of $pip it gives me error. i am not able to understand when $pip has nothing in it, it works but if i pass $server which has name of server in it it gives error.

could someone explain?

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Re: perl and getaddrinfo API
by Athanasius (Archbishop) on Apr 20, 2016 at 11:23 UTC

Hello swissknife,

If you display the contents of $pip using Data::Dump, say, you’ll see that it actually contains four bytes:

#! perl
use strict;
use warnings;
use Socket;
use Data::Dump;

my $server = shift @ARGV;
my $pip = gethostbyname($server);
dd $pip;
my $IP_add = inet_ntoa($pip);
print $IP_add;
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Output:

21:17 >perl 1602_SoPW.pl perlmonks.pair.com
"\xD1\xC5{\x99"
209.197.123.153
21:17 >
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If these bytes don’t appear when you print $pip, that’s likely because they happen to be unprintable.

BTW, the documentation for Socket mentions that gethostbyname is a legacy subroutine.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^2: perl and getaddrinfo API

by swissknife (Sexton) on Apr 20, 2016 at 12:28 UTC

 use Socket qw(:addrinfo SOCK_RAW);

 my ($err, @res) = getaddrinfo($hostname, "", {socktype => SOCK_RAW});
 die "Cannot getaddrinfo - $err" if $err;

 while( my $ai = shift @res ) {
     my ($err, $ipaddr) = getnameinfo($ai->{addr}, NI_NUMERICHOST, NIx
+_NOSERV);
    die "Cannot getnameinfo - $err" if $err;

     print "$ipaddr\n";
 }
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copied from http://perldoc.perl.org/Socket.html#(%24err%2c-%40result)-%3d-getaddrinfo-%24host%2c-%24service%2c-%5b%24hints%5d

it gives me error "addrinfo not defined in %Socket::EXPORT_TAGS

perl i am using is 5.8.4. is this because of perl version i am using? or it is something else?

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Re^3: perl and getaddrinfo API

by Athanasius (Archbishop) on Apr 20, 2016 at 12:47 UTC

Perl 5.8 is very old. Whether that’s the problem I don’t know; but when I add a line defining $hostname to the code you posted:

#! perl
use strict;
use warnings;
use Socket qw(:addrinfo SOCK_RAW);

my $hostname = 'perlmonks.pair.com';

my ($err, @res) = getaddrinfo($hostname, "", { socktype => SOCK_RAW })
+;
die "Cannot getaddrinfo - $err" if $err;

while (my $ai = shift @res)
{
    my ($err, $ipaddr) = getnameinfo($ai->{addr}, NI_NUMERICHOST, NIx_
+NOSERV);
    die "Cannot getnameinfo - $err" if $err;

    print "$ipaddr\n";
}
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it works correctly on my system:

22:41 >perl 1602_SoPW.pl
209.197.123.153

22:42 >
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(Windows 8.1 64-bit, Strawberry Perl 5.22.1, Socket v2.021.)

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^3: perl and getaddrinfo API

by VinsWorldcom (Prior) on Apr 20, 2016 at 17:29 UTC

Yes, the old Perl version is the problem. The core Socket module didn't start supporting IPv6 (and the address family independent routines get*info()) until at least 5.14 or so.

Socket is now dual-lived so you can get the latest copy from CPAN, but not sure how a new version of Socket will work on such an old Perl.

You could try Socket6 and / or Socket::GetAddrInfo. I've used in the past and the API was a bit different than the "standard" supplied directly in the new Socket module versions.

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Re: perl and getaddrinfo API
by trippledubs (Deacon) on Apr 20, 2016 at 12:53 UTC

my @ip = map { hex($_) } map { /(..)/g } unpack("H*",$pip);

print join '.',@ip;
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gethostbyname

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