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", on_resolved => sub { my ( $pkt ) = @_; foreach my $mx ( $pkt->answer ) { next unless $mx->type eq "MX"; printf "preference=%d exchange=%s\n", $mx->preference, $mx->exchange; } $loop->stop; }, on_error => sub { die "Cannot resolve - $_[-1]\n" }, ); $loop->run; 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 $on_resolved->( $pkt, @data ) The type of the elements in `@data' will depend on the DNS record query type: * A and AAAA The `A' or `AAAA' 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 of `preference', and returned in a list of HASH references. Each HASH reference will contain keys called `exchange' and `preference'. If the exchange domain name is included in the DNS `additional' data, then the HASH reference will also include a key called `address', its value containing a list of `A' and `AAAA' record `address' 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 called `priority', `weight', `target' and `port'. If the target domain name is included in the DNS `additional' data, then the HASH reference will also contain a key called `address', its value containing a list of `A' and `AAAA' record `address' fields. @data = ( { priority => 10, weight => 10, target => "server1.service.example.com", port => 1234, address => [ "10.0.1.1" ] } ); RESOLVER METHODS $resolver->res_query( %params ) 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_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. $resolver->res_search( %params ) 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