Net::LibResolv - a Perl wrapper around libresolv

NAME  SYNOPSIS  DESCRIPTION  FUNCTIONS  $answer = res_query( $dname, $class, $type )  $answer = res_search( $dname, $class, $type )  VARIABLES  $h_errno  CONSTANTS  Class IDs  $id = class_name2value( $name )  $name = class_value2name( $id )  Type IDs  $id = type_name2value( $name )  $name = type_value2name( $id )  Errors  SEE ALSO  AUTHOR 

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NAME

"Net::LibResolv" − a Perl wrapper around libresolv

SYNOPSIS

use Net::LibResolv qw( res_query NS_C_IN NS_T_A $h_errno );
use Net::DNS::Packet;
my $answer = res_query( "www.cpan.org", NS_C_IN, NS_T_A );
defined $answer or die "DNS failure − $h_errno\n";
foreach my $rr ( Net::DNS::Packet−>new( \$answer )−>answer ) {
print $rr−>string, "\n";
}

DESCRIPTION

The libresolv library provides functions to use the platform's standard DNS resolver to perform DNS queries. This Perl module provides a wrapping for the two primary functions, res_query(3) and res_search(3), allowing them to be used from Perl.

The return value from each function is a byte buffer containing the actual DNS response packet. This will need to be parsed somehow to obtain the useful information out of it; most likely by using Net::DNS.

FUNCTIONS

$answer = res_query( $dname, $class, $type )

Calls the res_query(3) function on the given domain name, class and type number. Returns the answer byte buffer on success, or "undef" on failure. On failure sets the value of the $h_errno package variable.

$dname should be a plain string. $class and $type should be numerical codes. See the "CONSTANTS" section for convenient definitions.

$answer = res_search( $dname, $class, $type )

Calls the res_search(3) function on the given domain name, class and type number. Returns the answer byte buffer on success, or "undef" on failure. On failure sets the value of the $h_errno package variable.

$dname should be a plain string. $class and $type should be numerical codes. See the "CONSTANTS" section for convenient definitions.

VARIABLES

$h_errno

After an error from "res_query" or "res_search", this variable will be set to the error value, as a dual−valued scalar. Its numerical value will be one of the error constants (see below); it string value will be an error message version of the same (similar to the $! perl core variable).

if( !defined( my $answer = res_query( ... ) ) ) {
print "Try again later...\n" if $h_errno == TRY_AGAIN;
}

defined( my $answer = res_query( ... ) ) or
die "Cannot res_query() − $h_errno\n";

CONSTANTS

Class IDs

The following set of constants define values for the $class parameter. Typically only "NS_C_IN" is actually used, for Internet.

NS_C_IN NS_C_CHAOS NS_C_HS
NS_C_INVALD NS_C_NONE NS_C_ANY

$id = class_name2value( $name )

$name = class_value2name( $id )

Functions to convert between class names and ID values.

Type IDs

The following are examples of constants define values for the $type parameter. (They all follow the same naming pattern, named after the record type, so only a few are listed here.)

NS_T_A NS_T_NS NS_T_CNAME NS_T_PTR NS_T_MX NS_T_TXT NS_T_SRV NS_T_AAAA
NS_T_INVALID NS_T_ANY

$id = type_name2value( $name )

$name = type_value2name( $id )

Functions to convert between type names and ID values.

Errors

The following constants define error values for $h_errno.

HOST_NOT_FOUND NO_ADDRESS NO_DATA NO_RECOVERY TRY_AGAIN

The values of "NO_ADDRESS" and "NO_DATA" may be the same.

SEE ALSO

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Net::DNS − Perl interface to the DNS resolver

AUTHOR

Paul Evans <[email protected]>

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