CODEWITHSUNDEEP
c++glibdbusgdbus
anorm
anorm

Reputation: 2263

How to validate a D-Bus property when using gdbus-codegen skeleton

I'm creating a service on D-Bus using gdbus and gdbus-codegen.

Introspection is this:

<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
                      "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<node>
  <interface name="com.example.foo">

    <property name="Bar" type="s" access="readwrite" />

  </interface>
</node>

I'm executing gdbus-codegen like this:

gdbus-codegen --interface-prefix com.example --generate-c-code=foo foo.xml

And my main.cpp looks like this:

#include <iostream>

#include "foo.h"

void OnBarChanged(GObject * gobject, GParamSpec * pspec, gpointer user_data)
{
  std::cout << "Bar: " << foo_get_bar((Foo *)gobject) << std::endl;
}

void OnBusNameAquired(GDBusConnection * connection,
                      const gchar *     name,
                      gpointer          user_data)
{
  Foo * foo = foo_skeleton_new();

  g_signal_connect(foo, "notify::bar", G_CALLBACK(&OnBarChanged), NULL);

  g_dbus_interface_skeleton_export(G_DBUS_INTERFACE_SKELETON(foo),
                                   connection,
                                   "/com/example/foo",
                                   NULL);
}

int main()
{
  std::cout << "Testing DBus properties" << std::endl;

  GMainLoop * loop;
  loop = g_main_loop_new(NULL, FALSE);
  g_bus_own_name(G_BUS_TYPE_SESSION,
                 "com.example.foo",
                 G_BUS_NAME_OWNER_FLAGS_NONE,
                 NULL,
                 OnBusNameAquired,
                 NULL,
                 NULL,
                 NULL);
  g_main_loop_run(loop);
  return 0;
}

This works as expected and I'm able to set and get properties using:

gdbus call --session --dest com.example.foo --object-path /com/example/foo --method org.freedesktop.DBus.Properties.Set "com.example.foo" "Bar" "<'baz'>"

and

gdbus call --session --dest com.example.foo --object-path /com/example/foo --method org.freedesktop.DBus.Properties.Get "com.example.foo" "Bar"
(<'baz'>,)

The problem:

I want to validate the setting of the property synchronously and be able to return an error if it fails. How can this be accomplished using the gdbus-codegen-generated code?

PS:

The code leaks and is generally not production ready. I'm fine with that for now :-)

Edit

After continues research, it seems like the D-Bus properties are using the underlying GObject property feature. Is it possible to install a custom validator when all of this is set up by the gdbus-codegen-code?

Upvotes: 4

Views: 1611

Answers (1)

Philip Withnall
Philip Withnall

Reputation: 5713

Connect to the GDBusInterfaceSkeleton::g-authorize-method signal from your foo skeleton. Your callback will be invoked for every D-Bus method invocation handled by your exported object — you can match on org.freedesktop.DBus.Properties.Set calls and do the validation then.

There’s an example of this (for arbitrary method calls, not D-Bus property setting; but the principle is the same) in flatpak: https://github.com/flatpak/flatpak/blob/c915f73b41688a7dc2ec7f0ab2fbcf1a7c738841/system-helper/flatpak-system-helper.c#L1192

Upvotes: 1

Related Questions