This module handles connection to the another D-Bus peer.

At the moment it handles only connections to the buses.

It basically allows to establish a connection and then send and receive messages. Its interface is intentionally quite low-level. You probably won’t be able to use it properly without understanding how D-Bus protocol works.

An example DBux.PeerConnection process:

defmodule MyApp.Bus do
  require Logger
  use DBux.PeerConnection

  @request_name_message_id :request_name
  @add_match_message_id    :add_match

  @introspection """
  <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
   "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
  <node name="/com/example/sample_object">
    <interface name="com.example.SampleInterface">
      <method name="Frobate">
        <arg name="foo" type="i" direction="in"/>
        <arg name="bar" type="s" direction="out"/>
        <arg name="baz" type="a{us}" direction="out"/>
        <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
      </method>
      <method name="Bazify">
        <arg name="bar" type="(iiu)" direction="in"/>
        <arg name="bar" type="v" direction="out"/>
      </method>
      <method name="Mogrify">
        <arg name="bar" type="(iiav)" direction="in"/>
      </method>
      <signal name="Changed">
        <arg name="new_value" type="b"/>
      </signal>
      <property name="Bar" type="y" access="readwrite"/>
    </interface>
    <node name="child_of_sample_object"/>
    <node name="another_child_of_sample_object"/>
  </node>
  """

  def start_link(hostname, options \ []) do
    DBux.PeerConnection.start_link(__MODULE__, hostname, options)
  end

  def init(hostname) do
    initial_state = %{hostname: hostname}

    {:ok, "tcp:host=" <> hostname <> ",port=8888", [:anonymous], initial_state}
  end

  def handle_up(state) do
    Logger.info("Up")

    {:send, [
      DBux.Message.build_signal("/", "org.example.dbux.MyApp", "Connected", []),
      {@add_match_message_id,    DBux.MessageTemplate.add_match(:signal, nil, "org.example.dbux.OtherIface")},
      {@request_name_message_id, DBux.MessageTemplate.request_name("org.example.dbux.MyApp", 0x4)}
    ], state}
  end

  def handle_down(state) do
    Logger.warn("Down")
    {:backoff, 1000, state}
  end

  def handle_method_call(serial, sender, "/", "Introspect", "org.freedesktop.DBus.Introspectable", _body, _flags, state) do
    Logger.debug("Got Introspect call")

    {:send, [
      DBux.Message.build_method_return(serial, sender, [%DBux.Value{type: :string, value: @introspection}])
    ], state}
  end

  def handle_method_return(_serial, _sender, _reply_serial, _body, @request_name_message_id, state) do
    Logger.info("Name acquired")
    {:noreply, state}
  end

  def handle_method_return(_serial, _sender, _reply_serial, _body, @add_match_message_id, state) do
    Logger.info("Match added")
    {:noreply, state}
  end

  def handle_error(_serial, _sender, _reply_serial, error_name, _body, @request_name_message_id, state) do
    Logger.warn("Failed to acquire name: " <> error_name)
    {:noreply, state}
  end

  def handle_error(_serial, _sender, _reply_serial, error_name, _body, @add_match_message_id, state) do
    Logger.warn("Failed to add match: " <> error_name)
    {:noreply, state}
  end

  def handle_signal(_serial, _sender, _path, _member, "org.example.dbux.OtherIface", _body, state) do
    Logger.info("Got signal from OtherIface")
    {:noreply, state}
  end

  def handle_signal(_serial, _sender, _path, _member, _member, _body, state) do
    Logger.info("Got other signal")
    {:noreply, state}
  end
end