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docs: Move migrating-gdbus.xml to Markdown

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This copies the test code inline into the Markdown, which means it could
diverge from the test code which is compiled and run as part of the
tests. That needs improving, but that can happen in a subsequent commit.

Helps: #3037
This commit is contained in:
Matthias Clasen 2023-10-09 23:22:20 +01:00 committed by Philip Withnall
parent e1d6168e5b
commit 682e9c9f56
5 changed files with 635 additions and 313 deletions
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1
docs/reference/gio/gio-docs.xml
View File

@ -268,7 +268,6 @@
<part id="migrating">
<title>Migrating to GIO</title>
<xi:include href="xml/migrating-posix.xml"/>
<xi:include href="xml/migrating-gdbus.xml"/>
</part>
<chapter id="gio-hierarchy">

1
docs/reference/gio/gio.toml.in
View File

@ -42,6 +42,7 @@ urlmap_file = "urlmap.js"
content_files = [
"overview.md",
"migrating-gdbus.md",
"migrating-gconf.md",
"migrating-gnome-vfs.md",
]

3
docs/reference/gio/meson.build
View File

@ -162,7 +162,6 @@ if get_option('gtk_doc')
content_files = [
'migrating-posix.xml',
'migrating-gdbus.xml',
'gio-querymodules.xml',
'glib-compile-schemas.xml',
'glib-compile-resources.xml',
@ -196,7 +195,6 @@ if get_option('gtk_doc')
content_files : content_files,
expand_content_files : [
'migrating-posix.xml',
'migrating-gdbus.xml',
'gdbus-codegen.xml',
],
html_assets : [
@ -232,6 +230,7 @@ endif
# gi-docgen version
expand_content_files = [
'migrating-gconf.md',
'migrating-gdbus.md',
'migrating-gnome-vfs.md',
'overview.md',
]

633
docs/reference/gio/migrating-gdbus.md Normal file
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@ -0,0 +1,633 @@
Title: Migrating to GDBus
SPDX-License-Identifier: LGPL-2.1-or-later
SPDX-FileCopyrightText: 2010 Matthias Clasen
SPDX-FileCopyrightText: 2010, 2011 David Zeuthen
# Migrating to GDBus
## Conceptual differences
The central concepts of D-Bus are modelled in a very similar way in
dbus-glib and GDBus. Both have objects representing connections, proxies and
method invocations. But there are some important differences:
- dbus-glib uses the libdbus reference implementation, GDBus doesn't.
Instead, it relies on GIO streams as transport layer, and has its own
implementation for the D-Bus connection setup and authentication. Apart
from using streams as transport, avoiding libdbus also lets GDBus avoid
some thorny multithreading issues.
- dbus-glib uses the GObject type system for method arguments and return
values, including a homegrown container specialization mechanism. GDBus
relies on the GVariant type system which is explicitly designed to match
D-Bus types.
- dbus-glib models only D-Bus interfaces and does not provide any types for
objects. GDBus models both D-Bus interfaces (via the GDBusInterface,
GDBusProxy and GDBusInterfaceSkeleton types) and objects (via the
GDBusObject, GDBusObjectSkeleton and GDBusObjectProxy types).
- GDBus includes native support for the org.freedesktop.DBus.Properties (via
the GDBusProxy type) and org.freedesktop.DBus.ObjectManager D-Bus
interfaces, dbus-glib doesn't.
- The typical way to export an object in dbus-glib involves generating glue
code from XML introspection data using dbus-binding-tool. GDBus provides a
similar tool called gdbus-codegen that can also generate Docbook D-Bus
interface documentation.
- dbus-glib doesn't provide any convenience API for owning and watching bus
names, GDBus provides the `g_bus_own_name()` and `g_bus_watch_name()`
family of convenience functions.
- GDBus provides API to parse, generate and work with Introspection XML,
dbus-glib doesn't.
- GTestDBus provides API to create isolated unit tests
## API comparison
| dbus-glib | GDBus |
|-----------|-------|
| `DBusGConnection` | `GDBusConnection` |
| `DBusGProxy` | `GDBusProxy`, `GDBusInterface` - also see `GDBusObjectProxy` |
| `DBusGObject` | `GDBusInterfaceSkeleton`, `GDBusInterface` - also see `GDBusObjectSkeleton` |
| `DBusGMethodInvocation` | `GDBusMethodInvocation` |
| `dbus_g_bus_get()` | `g_bus_get_sync()`, also see `g_bus_get()` |
| `dbus_g_proxy_new_for_name()` | `g_dbus_proxy_new_sync()` and `g_dbus_proxy_new_for_bus_sync()`, also see `g_dbus_proxy_new()` |
| `dbus_g_proxy_add_signal()` | not needed, use the generic “g-signal” |
| `dbus_g_proxy_connect_signal()` | use `g_signal_connect()` with “g-signal” |
| `dbus_g_connection_register_g_object()` | `g_dbus_connection_register_object()` - also see `g_dbus_object_manager_server_export()` |
| `dbus_g_connection_unregister_g_object()` | `g_dbus_connection_unregister_object()` - also see `g_dbus_object_manager_server_unexport()` |
| `dbus_g_object_type_install_info()` | introspection data is installed while registering an object, see `g_dbus_connection_register_object()` |
| `dbus_g_proxy_begin_call()` | `g_dbus_proxy_call()` |
| `dbus_g_proxy_end_call()` | `g_dbus_proxy_call_finish()` |
| `dbus_g_proxy_call()` | `g_dbus_proxy_call_sync()` |
| `dbus_g_error_domain_register()` | `g_dbus_error_register_error_domain()` |
| `dbus_g_error_has_name()` | no direct equivalent, see `g_dbus_error_get_remote_error()` |
| `dbus_g_method_return()` | `g_dbus_method_invocation_return_value()` |
| `dbus_g_method_return_error()` | `g_dbus_method_invocation_return_error()` and variants |
| `dbus_g_method_get_sender()` | `g_dbus_method_invocation_get_sender()` |
## Owning bus names
Using dbus-glib, you typically call RequestName manually to own a name, like in the following excerpt:
```c
error = NULL;
res = dbus_g_proxy_call (system_bus_proxy,
"RequestName",
&error,
G_TYPE_STRING, NAME_TO_CLAIM,
G_TYPE_UINT, DBUS_NAME_FLAG_ALLOW_REPLACEMENT,
G_TYPE_INVALID,
G_TYPE_UINT, &result,
G_TYPE_INVALID);
if (!res)
{
if (error != NULL)
{
g_warning ("Failed to acquire %s: %s",
NAME_TO_CLAIM, error->message);
g_error_free (error);
}
else
{
g_warning ("Failed to acquire %s", NAME_TO_CLAIM);
}
goto out;
}
if (result != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
{
if (error != NULL)
{
g_warning ("Failed to acquire %s: %s",
NAME_TO_CLAIM, error->message);
g_error_free (error);
}
else
{
g_warning ("Failed to acquire %s", NAME_TO_CLAIM);
}
exit (1);
}
dbus_g_proxy_add_signal (system_bus_proxy, "NameLost",
G_TYPE_STRING, G_TYPE_INVALID);
dbus_g_proxy_connect_signal (system_bus_proxy, "NameLost",
G_CALLBACK (on_name_lost), NULL, NULL);
/* further setup ... */
```
While you can do things this way with GDBus too, using
`g_dbus_proxy_call_sync()`, it is much nicer to use the high-level API for
this:
```c
static void
on_name_acquired (GDBusConnection *connection,
const gchar *name,
gpointer user_data)
{
/* further setup ... */
}
/* ... */
owner_id = g_bus_own_name (G_BUS_TYPE_SYSTEM,
NAME_TO_CLAIM,
G_BUS_NAME_OWNER_FLAGS_ALLOW_REPLACEMENT,
on_bus_acquired,
on_name_acquired,
on_name_lost,
NULL,
NULL);
g_main_loop_run (loop);
g_bus_unown_name (owner_id);
```
Note that `g_bus_own_name()` works asynchronously and requires you to enter
your mainloop to await the `on_name_aquired()` callback. Also note that in
order to avoid race conditions (e.g. when your service is activated by a
method call), you have to export your manager object before acquiring the
name. The `on_bus_acquired()` callback is the right place to do such
preparations.
## Creating proxies for well-known names
dbus-glib lets you create proxy objects for well-known names, like the following example:
```c
proxy = dbus_g_proxy_new_for_name (system_bus_connection,
"org.freedesktop.Accounts",
"/org/freedesktop/Accounts",
"org.freedesktop.Accounts");
```
For a DBusGProxy constructed like this, method calls will be sent to the current owner of the name, and that owner can change over time.
The same can be achieved with GDBusProxy:
```c
error = NULL;
proxy = g_dbus_proxy_new_for_bus_sync (G_BUS_TYPE_SYSTEM,
G_DBUS_PROXY_FLAGS_NONE,
NULL, /* GDBusInterfaceInfo */
"org.freedesktop.Accounts",
"/org/freedesktop/Accounts",
"org.freedesktop.Accounts",
NULL, /* GCancellable */
&error);
```
For an added layer of safety, you can specify what D-Bus interface the proxy
is expected to conform to by using the GDBusInterfaceInfo type.
Additionally, GDBusProxy loads, caches and tracks changes to the D-Bus
properties on the remote object. It also sets up match rules so D-Bus
signals from the remote object are delivered locally.
The GDBusProxy type normally isn't used directly - instead proxies
subclassing GDBusProxy generated by `gdbus-codegen` is used, see the section
called “Using gdbus-codegen”.
## Generating code and docs
### Using gdbus-codegen
dbus-glib comes with dbus-binding-tool, which can produce somewhat nice
client- and server-side wrappers for a D-Bus interface. With GDBus,
gdbus-codegen is used and like its counterpart, it also takes D-Bus
Introspection XML as input:
#### Example D-Bus Introspection XML
```xml
<node>
<!-- org.gtk.GDBus.Example.ObjectManager.Animal:
@short_description: Example docs generated by gdbus-codegen
@since: 2.30
This D-Bus interface is used to describe a simple animal.
-->
<interface name="org.gtk.GDBus.Example.ObjectManager.Animal">
<!-- Mood: The mood of the animal.
@since: 2.30
Known values for this property include
<literal>Happy</literal> and <literal>Sad</literal>. Use the
org.gtk.GDBus.Example.ObjectManager.Animal.Poke() method to
change this property.
This property influences how often the animal jumps up and
down, see the
#org.gtk.GDBus.Example.ObjectManager.Animal::Jumped signal
for more details.
-->
<property name="Mood" type="s" access="read"/>
<!--
Poke:
@make_sad: Whether to make the animal sad.
@make_happy: Whether to make the animal happy.
@since: 2.30
Method used to changing the mood of the animal. See also the
#org.gtk.GDBus.Example.ObjectManager.Animal:Mood property.
-->
<method name="Poke">
<arg direction="in" type="b" name="make_sad"/>
<arg direction="in" type="b" name="make_happy"/>
</method>
<!--
Jumped:
@height: Height, in meters, that the animal jumped.
@since: 2.30
Emitted when the animal decides to jump.
-->
<signal name="Jumped">
<arg type="d" name="height"/>
</signal>
<!--
Foo:
Property with no <quote>since</quote> annotation (should inherit the 2.30 from its containing interface).
-->
<property name="Foo" type="s" access="read"/>
<!--
Bar:
@since: 2.36
Property with a later <quote>since</quote> annotation.
-->
<property name="Bar" type="s" access="read"/>
</interface>
<!-- org.gtk.GDBus.Example.ObjectManager.Cat:
@short_description: More example docs generated by gdbus-codegen
This D-Bus interface is used to describe a cat. Right now there
are no properties, methods or signals associated with this
interface so it is essentially a <ulink
url="http://en.wikipedia.org/wiki/Marker_interface_pattern">Marker
Interface</ulink>.
Note that D-Bus objects implementing this interface also
implement the #org.gtk.GDBus.Example.ObjectManager.Animal
interface.
-->
<interface name="org.gtk.GDBus.Example.ObjectManager.Cat">
</interface>
</node>
```
If this XML is processed like this
```
gdbus-codegen --interface-prefix org.gtk.GDBus.Example.ObjectManager. \
--generate-c-code generated-code \
--c-namespace Example \
--c-generate-object-manager \
--generate-docbook generated-docs \
gdbus-example-objectmanager.xml
```
then two files generated-code.h and generated-code.c are generated.
Additionally, two XML files
generated-docs-org.gtk.GDBus.Example.ObjectManager.Animal and
generated-docs-org.gtk.GDBus.Example.ObjectManager.Cat with Docbook XML are
generated.
While the contents of `generated-code.h` and `generated-code.c` are best described by the `gdbus-codegen` manual page, here's a brief example of how this generated code can be used:
```c
#include "gdbus-object-manager-example/objectmanager-gen.h"
/* ---------------------------------------------------------------------------------------------------- */
static GDBusObjectManagerServer *manager = NULL;
static gboolean
on_animal_poke (ExampleAnimal *animal,
GDBusMethodInvocation *invocation,
gboolean make_sad,
gboolean make_happy,
gpointer user_data)
{
if ((make_sad && make_happy) || (!make_sad && !make_happy))
{
g_dbus_method_invocation_return_dbus_error (invocation,
"org.gtk.GDBus.Examples.ObjectManager.Error.Failed",
"Exactly one of make_sad or make_happy must be TRUE");
goto out;
}
if (make_sad)
{
if (g_strcmp0 (example_animal_get_mood (animal), "Sad") == 0)
{
g_dbus_method_invocation_return_dbus_error (invocation,
"org.gtk.GDBus.Examples.ObjectManager.Error.SadAnimalIsSad",
"Sad animal is already sad");
goto out;
}
example_animal_set_mood (animal, "Sad");
example_animal_complete_poke (animal, invocation);
goto out;
}
if (make_happy)
{
if (g_strcmp0 (example_animal_get_mood (animal), "Happy") == 0)
{
g_dbus_method_invocation_return_dbus_error (invocation,
"org.gtk.GDBus.Examples.ObjectManager.Error.HappyAnimalIsHappy",
"Happy animal is already happy");
goto out;
}
example_animal_set_mood (animal, "Happy");
example_animal_complete_poke (animal, invocation);
goto out;
}
g_assert_not_reached ();
out:
return G_DBUS_METHOD_INVOCATION_HANDLED;
}
static void
on_bus_acquired (GDBusConnection *connection,
const gchar *name,
gpointer user_data)
{
ExampleObjectSkeleton *object;
guint n;
g_print ("Acquired a message bus connection\n");
/* Create a new org.freedesktop.DBus.ObjectManager rooted at /example/Animals */
manager = g_dbus_object_manager_server_new ("/example/Animals");
for (n = 0; n < 10; n++)
{
gchar *s;
ExampleAnimal *animal;
/* Create a new D-Bus object at the path /example/Animals/N where N is 000..009 */
s = g_strdup_printf ("/example/Animals/%03d", n);
object = example_object_skeleton_new (s);
g_free (s);
/* Make the newly created object export the interface
* org.gtk.GDBus.Example.ObjectManager.Animal (note
* that @object takes its own reference to @animal).
*/
animal = example_animal_skeleton_new ();
example_animal_set_mood (animal, "Happy");
example_object_skeleton_set_animal (object, animal);
g_object_unref (animal);
/* Cats are odd animals - so some of our objects implement the
* org.gtk.GDBus.Example.ObjectManager.Cat interface in addition
* to the .Animal interface
*/
if (n % 2 == 1)
{
ExampleCat *cat;
cat = example_cat_skeleton_new ();
example_object_skeleton_set_cat (object, cat);
g_object_unref (cat);
}
/* Handle Poke() D-Bus method invocations on the .Animal interface */
g_signal_connect (animal,
"handle-poke",
G_CALLBACK (on_animal_poke),
NULL); /* user_data */
/* Export the object (@manager takes its own reference to @object) */
g_dbus_object_manager_server_export (manager, G_DBUS_OBJECT_SKELETON (object));
g_object_unref (object);
}
/* Export all objects */
g_dbus_object_manager_server_set_connection (manager, connection);
}
static void
on_name_acquired (GDBusConnection *connection,
const gchar *name,
gpointer user_data)
{
g_print ("Acquired the name %s\n", name);
}
static void
on_name_lost (GDBusConnection *connection,
const gchar *name,
gpointer user_data)
{
g_print ("Lost the name %s\n", name);
}
gint
main (gint argc, gchar *argv[])
{
GMainLoop *loop;
guint id;
loop = g_main_loop_new (NULL, FALSE);
id = g_bus_own_name (G_BUS_TYPE_SESSION,
"org.gtk.GDBus.Examples.ObjectManager",
G_BUS_NAME_OWNER_FLAGS_ALLOW_REPLACEMENT |
G_BUS_NAME_OWNER_FLAGS_REPLACE,
on_bus_acquired,
on_name_acquired,
on_name_lost,
loop,
NULL);
g_main_loop_run (loop);
g_bus_unown_name (id);
g_main_loop_unref (loop);
return 0;
}
```
This, on the other hand, is a client-side application using generated code:
```c
#include "gdbus-object-manager-example/objectmanager-gen.h"
/* ---------------------------------------------------------------------------------------------------- */
static void
print_objects (GDBusObjectManager *manager)
{
GList *objects;
GList *l;
g_print ("Object manager at %s\n", g_dbus_object_manager_get_object_path (manager));
objects = g_dbus_object_manager_get_objects (manager);
for (l = objects; l != NULL; l = l->next)
{
ExampleObject *object = EXAMPLE_OBJECT (l->data);
GList *interfaces;
GList *ll;
g_print (" - Object at %s\n", g_dbus_object_get_object_path (G_DBUS_OBJECT (object)));
interfaces = g_dbus_object_get_interfaces (G_DBUS_OBJECT (object));
for (ll = interfaces; ll != NULL; ll = ll->next)
{
GDBusInterface *interface = G_DBUS_INTERFACE (ll->data);
g_print (" - Interface %s\n", g_dbus_interface_get_info (interface)->name);
/* Note that @interface is really a GDBusProxy instance - and additionally also
* an ExampleAnimal or ExampleCat instance - either of these can be used to
* invoke methods on the remote object. For example, the generated function
*
* void example_animal_call_poke_sync (ExampleAnimal *proxy,
* gboolean make_sad,
* gboolean make_happy,
* GCancellable *cancellable,
* GError **error);
*
* can be used to call the Poke() D-Bus method on the .Animal interface.
* Additionally, the generated function
*
* const gchar *example_animal_get_mood (ExampleAnimal *object);
*
* can be used to get the value of the :Mood property.
*/
}
g_list_free_full (interfaces, g_object_unref);
}
g_list_free_full (objects, g_object_unref);
}
static void
on_object_added (GDBusObjectManager *manager,
GDBusObject *object,
gpointer user_data)
{
gchar *owner;
owner = g_dbus_object_manager_client_get_name_owner (G_DBUS_OBJECT_MANAGER_CLIENT (manager));
g_print ("Added object at %s (owner %s)\n", g_dbus_object_get_object_path (object), owner);
g_free (owner);
}
static void
on_object_removed (GDBusObjectManager *manager,
GDBusObject *object,
gpointer user_data)
{
gchar *owner;
owner = g_dbus_object_manager_client_get_name_owner (G_DBUS_OBJECT_MANAGER_CLIENT (manager));
g_print ("Removed object at %s (owner %s)\n", g_dbus_object_get_object_path (object), owner);
g_free (owner);
}
static void
on_notify_name_owner (GObject *object,
GParamSpec *pspec,
gpointer user_data)
{
GDBusObjectManagerClient *manager = G_DBUS_OBJECT_MANAGER_CLIENT (object);
gchar *name_owner;
name_owner = g_dbus_object_manager_client_get_name_owner (manager);
g_print ("name-owner: %s\n", name_owner);
g_free (name_owner);
}
static void
on_interface_proxy_properties_changed (GDBusObjectManagerClient *manager,
GDBusObjectProxy *object_proxy,
GDBusProxy *interface_proxy,
GVariant *changed_properties,
const gchar *const *invalidated_properties,
gpointer user_data)
{
GVariantIter iter;
const gchar *key;
GVariant *value;
gchar *s;
g_print ("Properties Changed on %s:\n", g_dbus_object_get_object_path (G_DBUS_OBJECT (object_proxy)));
g_variant_iter_init (&iter, changed_properties);
while (g_variant_iter_next (&iter, "{&sv}", &key, &value))
{
s = g_variant_print (value, TRUE);
g_print (" %s -> %s\n", key, s);
g_variant_unref (value);
g_free (s);
}
}
gint
main (gint argc, gchar *argv[])
{
GDBusObjectManager *manager;
GMainLoop *loop;
GError *error;
gchar *name_owner;
manager = NULL;
loop = NULL;
loop = g_main_loop_new (NULL, FALSE);
error = NULL;
manager = example_object_manager_client_new_for_bus_sync (G_BUS_TYPE_SESSION,
G_DBUS_OBJECT_MANAGER_CLIENT_FLAGS_NONE,
"org.gtk.GDBus.Examples.ObjectManager",
"/example/Animals",
NULL, /* GCancellable */
&error);
if (manager == NULL)
{
g_printerr ("Error getting object manager client: %s", error->message);
g_error_free (error);
goto out;
}
name_owner = g_dbus_object_manager_client_get_name_owner (G_DBUS_OBJECT_MANAGER_CLIENT (manager));
g_print ("name-owner: %s\n", name_owner);
g_free (name_owner);
print_objects (manager);
g_signal_connect (manager,
"notify::name-owner",
G_CALLBACK (on_notify_name_owner),
NULL);
g_signal_connect (manager,
"object-added",
G_CALLBACK (on_object_added),
NULL);
g_signal_connect (manager,
"object-removed",
G_CALLBACK (on_object_removed),
NULL);
g_signal_connect (manager,
"interface-proxy-properties-changed",
G_CALLBACK (on_interface_proxy_properties_changed),
NULL);
g_main_loop_run (loop);
out:
if (manager != NULL)
g_object_unref (manager);
if (loop != NULL)
g_main_loop_unref (loop);
return 0;
}
```

310
docs/reference/gio/migrating-gdbus.xml
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@ -1,310 +0,0 @@
<?xml version="1.0"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % local.common.attrib "xmlns:xi CDATA #FIXED 'http://www.w3.org/2003/XInclude'">
<!ENTITY version SYSTEM "version.xml">
]>
<chapter>
<title>Migrating to GDBus</title>
<section>
<title>Conceptual differences</title>
<para>
The central concepts of D-Bus are modelled in a very similar way
in dbus-glib and GDBus. Both have objects representing connections,
proxies and method invocations. But there are some important
differences:
<itemizedlist>
<listitem><para>
dbus-glib uses the <ulink
url="http://www.freedesktop.org/wiki/Software/dbus#ReferenceImplementation.28dbus-daemonandlibdbus.29">libdbus
reference implementation</ulink>, GDBus doesn't. Instead, it
relies on GIO streams as transport layer, and has its own
implementation for the D-Bus connection setup and
authentication. Apart from using streams as transport,
avoiding libdbus also lets GDBus avoid some thorny
multithreading issues.
</para></listitem>
<listitem><para>
dbus-glib uses the GObject type system for method arguments and
return values, including a homegrown container specialization
mechanism. GDBus relies on the #GVariant type system which is
explicitly designed to match D-Bus types.
</para></listitem>
<listitem><para>
dbus-glib models only D-Bus interfaces and does not provide
any types for objects. GDBus models both D-Bus interfaces
(via the #GDBusInterface, #GDBusProxy and
#GDBusInterfaceSkeleton types) and objects (via the
#GDBusObject, #GDBusObjectSkeleton and #GDBusObjectProxy types).
</para></listitem>
<listitem><para>
GDBus includes native support for the <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-properties">org.freedesktop.DBus.Properties</ulink> (via the #GDBusProxy type) and <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces-objectmanager">org.freedesktop.DBus.ObjectManager</ulink> D-Bus interfaces, dbus-glib doesn't.
</para></listitem>
<listitem><para>
The typical way to export an object in dbus-glib involves
generating glue code from XML introspection data using
<command>dbus-binding-tool</command>. GDBus provides a
similar tool called <command><link
linkend="gdbus-codegen">gdbus-codegen</link></command> that
can also generate Docbook D-Bus interface documentation.
</para></listitem>
<listitem><para>
dbus-glib doesn't provide any convenience API for owning and
watching bus names, GDBus provides the g_bus_own_name() and
g_bus_watch_name() family of convenience functions.
</para></listitem>
<listitem><para>
GDBus provides API to parse, generate and work with <link
linkend="gio-D-Bus-Introspection-Data">Introspection
XML</link>, dbus-glib doesn't.
</para></listitem>
<listitem><para>
GTestDBus provides API to create isolated unit tests <link
linkend="gio-D-Bus-Test-Scaffolding">GDBus Test Scaffolding</link>.
</para></listitem>
</itemizedlist>
</para>
</section>
<section>
<title>API comparison</title>
<table id="dbus-glib-vs-gdbus">
<title>dbus-glib APIs and their GDBus counterparts</title>
<tgroup cols="2">
<thead>
<row><entry>dbus-glib</entry><entry>GDBus</entry></row>
</thead>
<tbody>
<row><entry>#DBusGConnection</entry><entry>#GDBusConnection</entry></row>
<row><entry>#DBusGProxy</entry><entry>#GDBusProxy, #GDBusInterface - also see #GDBusObjectProxy</entry></row>
<row><entry>#DBusGObject</entry><entry>#GDBusInterfaceSkeleton, #GDBusInterface - also see #GDBusObjectSkeleton</entry></row>
<row><entry>#DBusGMethodInvocation</entry><entry>#GDBusMethodInvocation</entry></row>
<row><entry>dbus_g_bus_get()</entry><entry>g_bus_get_sync(), also see
g_bus_get()</entry></row>
<row><entry>dbus_g_proxy_new_for_name()</entry><entry>g_dbus_proxy_new_sync() and
g_dbus_proxy_new_for_bus_sync(), also see g_dbus_proxy_new()</entry></row>
<row><entry>dbus_g_proxy_add_signal()</entry><entry>not needed, use the generic #GDBusProxy::g-signal</entry></row>
<row><entry>dbus_g_proxy_connect_signal()</entry><entry>use g_signal_connect() with #GDBusProxy::g-signal</entry></row>
<row><entry>dbus_g_connection_register_g_object()</entry><entry>g_dbus_connection_register_object() - also see g_dbus_object_manager_server_export()</entry></row>
<row><entry>dbus_g_connection_unregister_g_object()</entry><entry>g_dbus_connection_unregister_object() - also see g_dbus_object_manager_server_unexport()</entry></row>
<row><entry>dbus_g_object_type_install_info()</entry><entry>introspection data is installed while registering
an object, see g_dbus_connection_register_object()</entry></row>
<row><entry>dbus_g_proxy_begin_call()</entry><entry>g_dbus_proxy_call()</entry></row>
<row><entry>dbus_g_proxy_end_call()</entry><entry>g_dbus_proxy_call_finish()</entry></row>
<row><entry>dbus_g_proxy_call()</entry><entry>g_dbus_proxy_call_sync()</entry></row>
<row><entry>dbus_g_error_domain_register()</entry><entry>g_dbus_error_register_error_domain()</entry></row>
<row><entry>dbus_g_error_has_name()</entry><entry>no direct equivalent, see g_dbus_error_get_remote_error()</entry></row>
<row><entry>dbus_g_method_return()</entry><entry>g_dbus_method_invocation_return_value()</entry></row>
<row><entry>dbus_g_method_return_error()</entry><entry>g_dbus_method_invocation_return_error() and variants</entry></row>
<row><entry>dbus_g_method_get_sender()</entry><entry>g_dbus_method_invocation_get_sender()</entry></row>
</tbody>
</tgroup>
</table>
</section>
<section>
<title>Owning bus names</title>
<para>
Using dbus-glib, you typically call RequestName manually
to own a name, like in the following excerpt:
<informalexample><programlisting><![CDATA[
error = NULL;
res = dbus_g_proxy_call (system_bus_proxy,
"RequestName",
&error,
G_TYPE_STRING, NAME_TO_CLAIM,
G_TYPE_UINT, DBUS_NAME_FLAG_ALLOW_REPLACEMENT,
G_TYPE_INVALID,
G_TYPE_UINT, &result,
G_TYPE_INVALID);
if (!res)
{
if (error != NULL)
{
g_warning ("Failed to acquire %s: %s",
NAME_TO_CLAIM, error->message);
g_error_free (error);
}
else
{
g_warning ("Failed to acquire %s", NAME_TO_CLAIM);
}
goto out;
}
if (result != DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER)
{
if (error != NULL)
{
g_warning ("Failed to acquire %s: %s",
NAME_TO_CLAIM, error->message);
g_error_free (error);
}
else
{
g_warning ("Failed to acquire %s", NAME_TO_CLAIM);
}
exit (1);
}
dbus_g_proxy_add_signal (system_bus_proxy, "NameLost",
G_TYPE_STRING, G_TYPE_INVALID);
dbus_g_proxy_connect_signal (system_bus_proxy, "NameLost",
G_CALLBACK (on_name_lost), NULL, NULL);
/* further setup ... */
]]>
</programlisting></informalexample>
</para>
<para>
While you can do things this way with GDBus too, using
g_dbus_proxy_call_sync(), it is much nicer to use the high-level API
for this:
<informalexample><programlisting><![CDATA[
static void
on_name_acquired (GDBusConnection *connection,
const gchar *name,
gpointer user_data)
{
/* further setup ... */
}
/* ... */
owner_id = g_bus_own_name (G_BUS_TYPE_SYSTEM,
NAME_TO_CLAIM,
G_BUS_NAME_OWNER_FLAGS_ALLOW_REPLACEMENT,
on_bus_acquired,
on_name_acquired,
on_name_lost,
NULL,
NULL);
g_main_loop_run (loop);
g_bus_unown_name (owner_id);
]]>
</programlisting></informalexample>
Note that g_bus_own_name() works asynchronously and requires
you to enter your mainloop to await the on_name_aquired()
callback. Also note that in order to avoid race conditions (e.g.
when your service is activated by a method call), you have to export
your manager object <emphasis>before</emphasis> acquiring the
name. The on_bus_acquired() callback is the right place to do
such preparations.
</para>
</section>
<section>
<title>Creating proxies for well-known names</title>
<para>
dbus-glib lets you create proxy objects for well-known names, like the
following example:
<informalexample><programlisting><![CDATA[
proxy = dbus_g_proxy_new_for_name (system_bus_connection,
"org.freedesktop.Accounts",
"/org/freedesktop/Accounts",
"org.freedesktop.Accounts");
]]>
</programlisting></informalexample>
For a #DBusGProxy constructed like this, method calls will be sent to
the current owner of the name, and that owner can change over time.
</para>
<para>
The same can be achieved with #GDBusProxy:
<informalexample><programlisting><![CDATA[
error = NULL;
proxy = g_dbus_proxy_new_for_bus_sync (G_BUS_TYPE_SYSTEM,
G_DBUS_PROXY_FLAGS_NONE,
NULL, /* GDBusInterfaceInfo */
"org.freedesktop.Accounts",
"/org/freedesktop/Accounts",
"org.freedesktop.Accounts",
NULL, /* GCancellable */
&error);
]]>
</programlisting></informalexample>
For an added layer of safety, you can specify what D-Bus
interface the proxy is expected to conform to by using the
#GDBusInterfaceInfo type. Additionally, #GDBusProxy loads,
caches and tracks changes to the D-Bus properties on the remote
object. It also sets up match rules so D-Bus signals from the
remote object are delivered locally.
</para>
<para>
The #GDBusProxy type normally isn't used directly - instead
proxies subclassing #GDBusProxy generated by <command><link
linkend="gdbus-codegen">gdbus-codegen</link></command> is used, see <xref linkend="gdbus-example-gdbus-codegen"/>
</para>
</section>
<section>
<title>Generating code and docs</title>
<section id="gdbus-example-gdbus-codegen">
<title>Using gdbus-codegen</title>
<para>
dbus-glib comes with <command>dbus-binding-tool</command>, which
can produce somewhat nice client- and server-side wrappers for a D-Bus interface.
With GDBus, <command><link
linkend="gdbus-codegen">gdbus-codegen</link></command> is used and like
its counterpart, it also takes D-Bus Introspection XML as input:
</para>
<example id="gdbus-example-codegen-input"><title>Example D-Bus Introspection XML</title><programlisting><xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="text" href="../../../../../gio/tests/gdbus-object-manager-example/gdbus-example-objectmanager.xml"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: gdbus-example-objectmanager.xml</xi:fallback></xi:include></programlisting></example>
<para>
If this XML is processed like this
<informalexample><programlisting><![CDATA[
gdbus-codegen --interface-prefix org.gtk.GDBus.Example.ObjectManager. \
--generate-c-code generated-code \
--c-namespace Example \
--c-generate-object-manager \
--generate-docbook generated-docs \
gdbus-example-objectmanager.xml
]]></programlisting></informalexample>
then two files <filename>generated-code.h</filename> and
<filename>generated-code.c</filename> are
generated. Additionally, two XML files
<filename>generated-docs-org.gtk.GDBus.Example.ObjectManager.Animal</filename> and
<filename>generated-docs-org.gtk.GDBus.Example.ObjectManager.Cat</filename>
with Docbook XML are generated. For an example of what the docs look
like see <link
linkend="gdbus-interface-org-gtk-GDBus-Example-ObjectManager-Animal">the Animal D-Bus interface documentation</link>.
and
<link
linkend="gdbus-interface-org-gtk-GDBus-Example-ObjectManager-Cat">the Cat D-Bus interface documentation</link>.
</para>
<para>
While the contents of <filename>generated-code.h</filename> and
<filename>generated-code.c</filename> are best described by the
<command><link
linkend="gdbus-codegen">gdbus-codegen</link></command> manual
page, brief examples of how this generated code can be used can be found in
<xref linkend="gdbus-example-codegen-server"/>
and <xref
linkend="gdbus-example-codegen-client"/>. Additionally, since
the generated code has 100% gtk-doc coverage, see
#ExampleAnimal, #ExampleCat, #ExampleObject and
#ExampleObjectManagerClient pages for documentation.
</para>
<example id="gdbus-example-codegen-server"><title>Server-side application using generated code</title><programlisting><xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="text" href="../../../../../gio/tests/gdbus-example-objectmanager-server.c"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: gdbus-example-objectmanager-server.c</xi:fallback></xi:include></programlisting></example>
<example id="gdbus-example-codegen-client"><title>Client-side application using generated code</title><programlisting><xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="text" href="../../../../../gio/tests/gdbus-example-objectmanager-client.c"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: gdbus-example-objectmanager-client.c</xi:fallback></xi:include></programlisting></example>
</section>
<!-- All XInclude paths are relative to the html/ directory under the build root directory -->
<xi:include href="../../../../gio/tests/gdbus-object-manager-example/objectmanager-gen-org.gtk.GDBus.Example.ObjectManager.Animal.xml"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: objectmanager-gen-org.gtk.GDBus.Example.ObjectManager.Animal.xml</xi:fallback></xi:include>
<xi:include href="../../../../gio/tests/gdbus-object-manager-example/objectmanager-gen-org.gtk.GDBus.Example.ObjectManager.Cat.xml"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: objectmanager-gen-org.gtk.GDBus.Example.ObjectManager.Cat.xml</xi:fallback></xi:include>
<xi:include href="../gdbus-object-manager-example/xml/ExampleAnimal.xml"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: ExampleAnimal.xml</xi:fallback></xi:include>
<xi:include href="../gdbus-object-manager-example/xml/ExampleCat.xml"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: ExampleCat.xml</xi:fallback></xi:include>
<xi:include href="../gdbus-object-manager-example/xml/ExampleObject.xml"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: ExampleObject.xml</xi:fallback></xi:include>
<xi:include href="../gdbus-object-manager-example/xml/ExampleObjectManagerClient.xml"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT: ExampleObjectManagerClient.xml</xi:fallback></xi:include>
</section>
</chapter>