IO::Async::Resolver::DNS - resolve DNS queries using IO::Async
IO::Async::Resolver::DNS
IO::Async
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;
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.
MX
SRV
getaddrinfo
getnameinfo
IO::Async::Resolver
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.
Net::LibResolv
Net::DNS::Resolver
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
my ( $pkt, @data ) = $f->get; $on_resolved->( $pkt, @data )
The type of the elements in @data will depend on the DNS record query type:
@data
A and AAAA
The A or AAAA records will be unpacked and returned in a list of strings.
A
AAAA
@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" );
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.
preference
exchange
additional
address
@data = ( { exchange => "mail.example.com", preference => 10, address => [ "10.0.0.1", "fd00:0:0:0:0:0:0:1" ] } );
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.
priority
weight
target
port
@data = ( { priority => 10, weight => 10, target => "server1.service.example.com", port => 1234, address => [ "10.0.1.1" ] } );
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.
->get
( $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:
Domain name to look up
Name of the record type to look up (e.g. MX)
Name of the record class to look up. Defaults to IN so normally this argument is not required.
IN
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.
ERR_*
->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.
$errnum
When not returning a Future, the following extra arguments are used as callbacks instead:
Future
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
$pkt
$on_resolved->( $pkt, @data )
See the Record Extraction section above for more detail.
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.
res_query
Paul Evans <leonerd@leonerd.org.uk>
To install IO::Async::Resolver::DNS, copy and paste the appropriate command in to your terminal.
cpanm
cpanm IO::Async::Resolver::DNS
CPAN shell
perl -MCPAN -e shell install IO::Async::Resolver::DNS
For more information on module installation, please visit the detailed CPAN module installation guide.