Paul Evans > IO-Async-Resolver-DNS-0.06 > IO::Async::Resolver::DNS



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IO::Async::Resolver::DNS - resolve DNS queries using IO::Async


 use IO::Async::Loop;
 use IO::Async::Resolver::DNS;

 my $loop = IO::Async::Loop->new;
 my $resolver = $loop->resolver;

    dname => "",
    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;


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:

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


The following methods documented with a trailing call to ->get return Future instances.


   ( $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.


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.


Paul Evans <>

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