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Author image Felipe Gasper
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NAME

DNS::Unbound - Query DNS recursively via libunbound

Coverage Status

SYNOPSIS

    my $dns = DNS::Unbound->new()->set_option( verbosity => 2 );

    # This appears to be safe:
    $dns->enable_threads();

    my $verbosity = $dns->get_option( 'verbosity' );

    $dns->set_option( verbosity => 1 + $verbosity );

Synchronous queries:

    my $res_hr = $dns->resolve( 'cpan.org', 'NS' );

    # See below about encodings in “data”.
    my @ns = map { $dns->decode_name($_) } @{ $res_hr->data() };

Asynchronous queries use the “Promise” pattern. Assuming you’re using an off-the-shelf event loop, you can do something like:

    my $dns = DNS::Unbound::AnyEvent->new();

    my $query1 = $dns->resolve_async( 'usa.gov', 'A' )->then(
        sub { my $data = shift()->data(); ... },  # success handler
        sub { ... },                              # failure handler
    );

    my $query2 = $dns->resolve_async( 'in-addr.arpa', 'NS' )->then(
        sub { ... },
        sub { ... },
    );

You can also integrate with a custom event loop; see "EVENT LOOPS" below.

DESCRIPTION

Typical DNS lookups involve a request to a local server that caches information from DNS. The caching makes it fast, but it also means updates to DNS aren’t always available via that local server right away. Most applications don’t need to care and so can enjoy the speed of cached results.

Applications that need up-to-date DNS query results, though, need fully-recursive DNS queries. NLnet Labs’s libunbound is a popular solution for such queries; the present Perl module is an interface to that library.

CHARACTER ENCODING

DNS doesn’t know about character encodings, so neither does Unbound. Thus, all strings given to this module must be byte strings. All returned strings will be byte strings as well.

EVENT LOOPS

This distribution includes the classes DNS::Unbound::AnyEvent, DNS::Unbound::IOAsync, and DNS::Unbound::Mojo, which provide out-of-the-box compatibility with those popular event loop interfaces. You should probably use one of these.

You can also integrate with a custom event loop via the fd() method of this class: wait for that file descriptor to be readable, then call this class’s perform() method.

MEMORY LEAK DETECTION

Objects in this namespace will, if left alive at global destruction, throw a warning about memory leaks. To silence these warnings, either allow all queries to complete, or cancel queries you no longer care about.

ERRORS

This library throws 3 kinds of errors:

  • Plain strings. Generally thrown in “simple” failure cases, e.g., invalid inputs.

  • DNS::Unbound::X::Unbound instances. Thrown whenever Unbound gives an error.

  • DNS::Unbound::X::ResolveError instances. A subclass of the last kind, for (Unbound-reported) resolution failures. (This is NOT for DNS-reported failures.)

CONSTANTS

The following from libunbound/context.h are defined here: UB_NOERROR, UB_SOCKET, UB_NOMEM, UB_SYNTAX, UB_SERVFAIL, UB_FORKFAIL, UB_AFTERFINAL, UB_INITFAIL, UB_PIPE, UB_READFILE, UB_NOID

METHODS

CLASS->new()

Instantiates this class.

$result_obj = OBJ->resolve( $NAME, $TYPE [, $CLASS ] )

Runs a synchronous query for a given $NAME and $TYPE. $TYPE may be expressed numerically or, for convenience, as a string. $CLASS is optional and defaults to 1 (IN), which is probably what you want.

Returns a DNS::Unbound::Result instance.

NOTE: libunbound doesn’t seem to offer effective controls for timing out a synchronous query. If timeouts are relevant for you, you probably need to use resolve_async() instead.

$query_obj = OBJ->resolve_async( $NAME, $TYPE [, $CLASS ] );

Like resolve() but starts an asynchronous query rather than a synchronous one.

This returns an instance of DNS::Unbound::AsyncQuery (a subclass thereof, to be precise).

If you’re using one of the special event interface subclasses (e.g., DNS::Unbound::IOAsync) then the returned promise will resolve as part of the event loop’s normal operation. Otherwise, see below for the methods you’ll need to use in tandem with this one to get your query result.

OBJ->enable_threads()

Sets OBJ’s asynchronous queries to use threads rather than forking. Off by default. Throws an exception if called after an asynchronous query has already been sent.

Returns OBJ.

OBJ->set_option( $NAME => $VALUE )

Sets a configuration option. Returns OBJ.

Note that this is basically just a passthrough to the underlying ub_ctx_set_option() function and is thus subject to the same limitations as that function; for example, you can’t set verbosity after the configuration has been “finalized”. (So use debuglevel() for that instead.)

$value = OBJ->get_option( $NAME )

Gets a configuration option’s value.

OBJ->debuglevel( $LEVEL )

Sets the debug level (an integer). Returns OBJ.

As of libunbound v1.9.2, this is just a way to set the verbosity option regardless of whether the configuration is finalized.

OBJ->debugout( $FD_OR_FH )

Accepts a file descriptor or Perl filehandle and designates that as the destination for libunbound diagnostic information.

Returns OBJ.

$str = CLASS->unbound_version()

Gives the libunbound version string.

METHODS FOR ALTERING RESOLVER LOGIC

The following parallel their equivalents in libunbound. They return OBJ and throw errors on failure.

OBJ->hosts( $FILENAME )

OBJ->resolveconf( $FILENAME )

CUSTOM EVENT LOOP INTEGRATION

Unless otherwise noted, the following methods correspond to their equivalents in libunbound. They return the same values as the libunbound equivalents.

You don’t need these if you use one of the event loop subclasses (which is recommended).

OBJ->poll()

OBJ->fd()

OBJ->wait()

OBJ->process()

OBJ->count_pending_queries()

Returns the number of outstanding asynchronous queries.

METHODS FOR DEALING WITH DNSSEC

The following correspond to their equivalents in libunbound and will only work if the underlying libunbound version supports them.

They return OBJ and throw errors on failure.

OBJ->add_ta( $TA )

OBJ->add_ta_autr( $PATH )

(Available only if libunbound supports it.)

OBJ->add_ta_file( $PATH )

OBJ->trustedkeys( $PATH )

CONVENIENCE FUNCTIONS

The following may be called either as object methods or as static functions (but not as class methods). In addition to these, Socket provides the inet_ntoa() and inet_ntop() functions for decoding the values of A and AAAA records.

NOTE: Consider parsing DNS::Unbound::Result’s answer_packet() as a more robust, albeit heavier, way to parse query result data. Net::DNS::Packet and AnyEvent::DNS’s dns_unpack() are two good ways to parse DNS packets.

$decoded = decode_name($encoded)

Decodes a DNS name. Useful for, e.g., NS, CNAME, and PTR query results.

Note that this function’s return will normally include a trailing . because of the trailing NUL byte in an encoded DNS name. This is normal and expected.

$strings_ar = decode_character_strings($encoded)

Decodes a list of character-strings into component strings, returned as an array reference. Useful for TXT query results.

SEE ALSO

Net::DNS::Resolver::Recurse provides comparable logic to this module in pure Perl. Like Unbound, it is maintained by NLnet Labs.

Net::DNS::Resolver::Unbound is another XS binding to Unbound, implemented as a subclass of Net::DNS::Resolver.

LICENSE & COPYRIGHT

Copyright 2019-2022 Gasper Software Consulting.

This library is licensed under the same terms as Perl itself.

REPOSITORY

https://github.com/FGasper/p5-DNS-Unbound

THANK YOU

Special thanks to ATOOMIC for making some helpful review notes.