• 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

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

• Net::DNS - Perl interface to the DNS resolver

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>