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POTATOGIM

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Author image Felipe Gasper
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NAME

Protocol::DBus - D-Bus in pure Perl

SYNOPSIS

(NB: Examples below assume use of subroutine signatures.)

For blocking I/O:

    my $dbus = Protcol::DBus::Client::system();

    # Authentication and “Hello” call/response:
    $dbus->initialize();

    $dbus->send_call(
        path => '/org/freedesktop/DBus',
        interface => 'org.freedesktop.DBus.Properties',
        member => 'GetAll',
        destination => 'org.freedesktop.DBus',
        signature => 's',
        body => [ 'org.freedesktop.DBus' ],
    )->then( sub ($resp_msg) { .. } );

    my $msg = $dbus->get_message();

For non-blocking I/O, it is recommended to use an event loop. This distribution includes some connectors to simplify that work:

Example:

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

    my $dbus = Protcol::DBus::Client::IOAsync::login_session($loop);

    $dbus->initialize()->then(
        sub ($dbus) {
            return $dbus->send_call( … );  # same arguments as above
        },
    )->finally( sub { $loop->stop() } );

    $loop->run();

You can also interface with a manually-written event loop. See the example below.

DESCRIPTION

This is an original, pure-Perl implementation of client messaging logic for the D-Bus protocol.

It’s not much more than an implementation of the wire protocol; it doesn’t know about objects, services, or anything else besides the actual messages. This is fine, of course, if all you want to do is, e.g., replace an invocation of gdbus or dbus-send with pure Perl.

If you want an interface that mimics D-Bus’s actual object system, you’ll need to implement it yourself or use something like Net::DBus. (See "DIFFERENCES FROM Net::DBus" below.)

STATUS

This project is in BETA status. While the API should be pretty stable now, breaking changes can still happen. If you use this module in your project, you MUST check the changelog before deploying a new version. Please file bug reports as appropriate.

EXAMPLES

See Protocol::DBus::Client and the above samples for a starting point.

Also see the distribution’s examples/ directory.

DIFFERENCES FROM Net::DBus

Net::DBus is an XS binding to libdbus, the reference D-Bus implementation. It is CPAN’s most mature D-Bus implementation.

There are several reasons why you might prefer this module instead, though, such as:

  • Net::DBus discerns how to send a method call via D-Bus introspection. While handy, this costs extra network overhead and requires an XML parser. With Protocol::DBus you give a signature directly to send a method call,

  • Protocol::DBus can work smoothly with any event system you like, including custom-written ones. (The distribution ships with connectors for three popular ones.) Net::DBus, on the other hand, expects you to use its own event loop, Net::DBus::Reactor.

  • Protocol::DBus has a considerably lighter memory footprint.

  • Protocol::DBus is pure Perl, so on most OSes you can fat-pack it for easy distribution.

  • Protocol::DBus exposes a simpler API.

Of course, there are tradeoffs: most notably, Protocol::DBus’s API is simpler because it doesn’t attempt to implement D-Bus’s object system. (You never need the object system, but it can be a useful abstraction.) An XS-powered D-Bus library is also likely to outperform a pure-Perl one, introspection overhead notwithstanding. YMMV. BYOB.

NOTES

  • UNIX FD support requires that Socket::MsgHdr be loaded at authentication time.

  • Certain OSes may require Socket::MsgHdr in order to authenticate via a UNIX socket. (Linux, notably, does not.) It depends if your OS can send local socket credentials without using sendmsg(2).

  • EXTERNAL and DBUS_COOKIE_SHA1 authentications are supported.

TODO

  • Improve parsing of bus paths in environment variables.

  • Add more tests.

EXAMPLE USING MANUALLY-WRITTEN EVENT LOOP

    my $dbus = Protcol::DBus::Client::system();

    $dbus->blocking(0);

    my $fileno = $dbus->fileno();

    # You can use whatever polling method you prefer;
    # the following is just for demonstration:
    vec( my $mask, $fileno, 1 ) = 1;

    while (!$dbus->initialize()) {
        if ($dbus->init_pending_send()) {
            select( undef, my $wout = $mask, undef, undef );
        }
        else {
            select( my $rout = $mask, undef, undef, undef );
        }
    }

    $dbus->send_call( .. );     # same parameters as above

    while (1) {
        my $wout = $dbus->pending_send() || q<>;
        $wout &&= $mask;

        select( my $rout = $mask, $wout, undef, undef );

        if ($wout =~ tr<\0><>c) {
            $dbus->flush_write_queue();
        }

        if ($rout =~ tr<\0><>c) {

            # It’s critical to get_message() until undef is returned.
            1 while $dbus->get_message();
        }
    }

Life is easier if you use someone else’s event loop. :)