NAME
IO::Async::Resolver::DNS
- resolve DNS queries using IO::Async
SYNOPSIS
use IO::Async::Loop;
use IO::Async::Resolver::DNS;
my $loop = IO::Async::Loop->new;
my $resolver = $loop->resolver;
$resolver->res_query(
dname => "cpan.org",
type => "MX",
)->then( sub {
my ( $pkt ) = @_;
foreach my $mx ( $pkt->answer ) {
next unless $mx->type eq "MX";
printf "preference=%d exchange=%s\n",
$mx->preference, $mx->exchange;
}
})->get;
DESCRIPTION
This module extends the IO::Async::Resolver class with extra methods and resolver functions to perform DNS-specific resolver lookups. It does not directly provide any methods or functions of its own.
These functions are provided for performing DNS-specific lookups, to obtain MX
or SRV
records, for example. For regular name resolution, the usual getaddrinfo
and getnameinfo
methods on the standard IO::Async::Resolver
should be used.
If Net::LibResolv is installed then it will be used for actually sending and receiving DNS packets, in preference to a internally-constructed Net::DNS::Resolver object. Net::LibResolv
will be more efficient and shares its implementation with the standard resolver used by the rest of the system. Net::DNS::Resolver
reimplements the logic itself, so it may have differences in behaviour from that provided by libresolv. The ability to use the latter is provided to allow for an XS-free dependency chain, or for other situations where Net::LibResolv
is not available.
Record Extraction
If certain record type queries are made, extra information is returned to the on_resolved
continuation, containing the results from the DNS packet in a more useful form. This information will be in a list of extra values following the packet value.
my ( $pkt, @data ) = $f->get;
$on_resolved->( $pkt, @data )
The type of the elements in @data
will depend on the DNS record query type:
A and AAAA
The
A
orAAAA
records will be unpacked and returned in a list of strings.@data = ( "10.0.0.1", "10.0.0.2" ); @data = ( "fd00:0:0:0:0:0:0:1" );
PTR
The
PTR
records will be unpacked and returned in a list of domain names.@data = ( "foo.example.com" );
MX
The
MX
records will be unpacked, in order ofpreference
, and returned in a list of HASH references. Each HASH reference will contain keys calledexchange
andpreference
. If the exchange domain name is included in the DNSadditional
data, then the HASH reference will also include a key calledaddress
, its value containing a list ofA
andAAAA
recordaddress
fields.@data = ( { exchange => "mail.example.com", preference => 10, address => [ "10.0.0.1", "fd00:0:0:0:0:0:0:1" ] } );
SRV
The
SRV
records will be unpacked and sorted first by order of priority, then by a weighted shuffle by weight, and returned in a list of HASH references. Each HASH reference will contain keys calledpriority
,weight
,target
andport
. If the target domain name is included in the DNSadditional
data, then the HASH reference will also contain a key calledaddress
, its value containing a list ofA
andAAAA
recordaddress
fields.@data = ( { priority => 10, weight => 10, target => "server1.service.example.com", port => 1234, address => [ "10.0.1.1" ] } );
Error Reporting
The two possible back-end modules that implement the resolver query functions provided here differ in their semantics for error reporting. To account for this difference and to lead to more portable user code, errors reported by the back-end modules are translated to one of the following (exported) constants.
ERR_NO_HOST # The specified host name does not exist
ERR_NO_ADDRESS # The specified host name does not provide answers for the
given query type
ERR_TEMPORARY # A temporary failure that may disappear on retry
ERR_UNRECOVERABLE # Any other error
RESOLVER METHODS
The following methods documented with a trailing call to ->get
return Future instances.
res_query
( $pkt, @data ) = $resolver->res_query( %params )->get
Performs a resolver query on the name, class and type, and invokes a continuation when a result is obtained.
Takes the following named parameters:
- dname => STRING
-
Domain name to look up
- type => STRING
-
Name of the record type to look up (e.g.
MX
) - class => STRING
-
Name of the record class to look up. Defaults to
IN
so normally this argument is not required.
On failure on IO::Async
versions that support extended failure results (0.68 and later), the extra detail will be an error value matching one of the ERR_*
constants listed above.
->fail( $message, resolve => res_query => $errnum )
Note that due to the two possible back-end implementations it is not guaranteed that messages have any particular format; they are intended for human consumption only, and the $errnum
value should be used for making decisions in other code.
When not returning a Future
, the following extra arguments are used as callbacks instead:
- on_resolved => CODE
-
Continuation which is invoked after a successful lookup. Will be passed a Net::DNS::Packet object containing the result.
$on_resolved->( $pkt )
For certain query types, this continuation may also be passed extra data in a list after the
$pkt
$on_resolved->( $pkt, @data )
See the Record Extraction section above for more detail.
- on_error => CODE
-
Continuation which is invoked after a failed lookup.
res_search
Performs a resolver query on the name, class and type, and invokes a continuation when a result is obtained. Identical to res_query
except that it additionally implements the default domain name search behaviour.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>