gdbus-codegen - Online in the Cloud

PROGRAM:

NAME

gdbus-codegen - D-Bus code and documentation generator

SYNOPSIS

gdbus-codegen [-h, --help] [--interface-prefix org.project.Prefix]
[--generate-c-code OUTFILES] [--c-namespace YourProject]
[--c-generate-object-manager] [--generate-docbook OUTFILES]
[--xml-files FILE] [--annotate ELEMENT KEY VALUE]... FILE [FILE...]

DESCRIPTION

gdbus-codegen is used to generate code and/or documentation for one or more D-Bus
interfaces. The tool reads D-Bus Introspection XML[1] files and generates output files.
The tool currently supports generating C code (via --generate-c-code) and Docbook XML (via
--generate-docbook).

GENERATING C CODE

When generating C code, a #GInterface -derived type is generated for each D-Bus interface.
Additionally, for every generated type, FooBar, two concrete instantiable types,
FooBarProxy and FooBarSkeleton, implementing said interface are also generated. The former
is derived from #GDBusProxy and intended for use on the client side while the latter is
derived from the #GDBusInterfaceSkeleton type making it easy to export on a
#GDBusConnection either directly or via a #GDBusObjectManagerServer instance.

The name of each generated C type is derived from the D-Bus interface name stripped with
the prefix given with --interface-prefix and with the dots removed and initial characters
capitalized. For example, for the D-Bus interface com.acme.Coyote the name used is
ComAcmeCoyote. For the D-Bus interface org.project.Bar.Frobnicator with --interface-prefix
org.project., the name used is BarFrobnicator.

For methods, signals and properties, if not specified, the name defaults to the name of
the method, signal or property.

Two forms of the name are used - the CamelCase form and the lower-case form. The CamelCase
form is used for the #GType and struct name, while lower-case form is used in function
names. The lower-case form is calculated by converting from CamelCase to lower-case and
inserting underscores at word boundaries (using certain heuristics).

If the value given by the org.gtk.GDBus.C.Name annotation or the --c-namespace option
contains an underscore (sometimes called Ugly_Case), then the camel-case name is derived
by removing all underscores, and the lower-case name is derived by lower-casing the
string. This is useful in some situations where abbreviations are used. For example, if
the annotation is used on the interface net.MyCorp.MyApp.iSCSITarget with the value
iSCSI_Target the CamelCase form is iSCSITarget while the lower-case form is iscsi_target.
If the annotation is used on the method EjectTheiPod with the value Eject_The_iPod, the
lower-case form is eject_the_ipod.

GENERATING DOCBOOK DOCUMENTATION

Each generated Docbook XML file (see the --generate-docbook option for details) is a
RefEntry[2] article describing the D-Bus interface.

OPTIONS

The following options are supported:

-h, --help
Show help and exit.

--xml-files FILE
The D-Bus introspection XML file.

--interface-prefix org.project.Prefix.
A prefix to strip from all D-Bus interface names when calculating the typename for the
C binding and the Docbook sortas attribute[3].

--generate-docbook OUTFILES
Generate Docbook Documentation for each D-Bus interface and put it in
OUTFILES-NAME.xml where NAME is a place-holder for the interface name, e.g.
net.Corp.FooBar and so on.

--generate-c-code OUTFILES
Generate C code for all D-Bus interfaces and put it in OUTFILES.c and OUTFILES.h.

--c-namespace YourProject
The namespace to use for generated C code. This is expected to be in CamelCase[4] or
Ugly_Case (see above).

--c-generate-object-manager
If this option is passed, suitable #GDBusObject, #GDBusObjectProxy,
#GDBusObjectSkeleton and #GDBusObjectManagerClient subclasses are generated.

--annotate ELEMENT KEY VALUE
Used to inject D-Bus annotations into the given XML files. It can be used with
interfaces, methods, signals, properties and arguments in the following way:

gdbus-codegen --c-namespace MyApp \
--generate-c-code myapp-generated \
--annotate "org.project.InterfaceName" \
org.gtk.GDBus.C.Name MyFrobnicator \
--annotate "org.project.InterfaceName:Property" \
bar bat \
--annotate "org.project.InterfaceName.Method()" \
org.freedesktop.DBus.Deprecated true \
--annotate "org.project.InterfaceName.Method()[arg_name]" \
snake hiss \
--annotate "org.project.InterfaceName::Signal" \
cat meow \
--annotate "org.project.InterfaceName::Signal[arg_name]" \
dog wuff \
myapp-dbus-interfaces.xml
Any UTF-8 string can be used for KEY and VALUE.

SUPPORTED D-BUS ANNOTATIONS

The following D-Bus annotations are supported by gdbus-codegen:

org.freedesktop.DBus.Deprecated
Can be used on any <interface>, <method>, <signal> and <property> element to specify
that the element is deprecated if its value is true. Note that this annotation is
defined in the D-Bus specification[1] and can only assume the values true and false.
In particular, you cannot specify the version that the element was deprecated in nor
any helpful deprecation message. Such information should be added to the element
documentation instead.

When generating C code, this annotation is used to add #G_GNUC_DEPRECATED to generated
functions for the element.

When generating Docbook XML, a deprecation warning will appear along the documentation
for the element.

org.gtk.GDBus.Since
Can be used on any <interface>, <method>, <signal> and <property> element to specify
the version (any free-form string but compared using a version-aware sort function)
the element appeared in.

When generating C code, this field is used to ensure function pointer order for
preserving ABI/API, see the section called “STABILITY GUARANTEES”.

When generating Docbook XML, the value of this tag appears in the documentation.

org.gtk.GDBus.DocString
A string with Docbook content for documentation. This annotation can be used on
<interface>, <method>, <signal>, <property> and <arg> elements.

org.gtk.GDBus.DocString.Short
A string with Docbook content for short/brief documentation. This annotation can only
be used on <interface> elements.

org.gtk.GDBus.C.Name
Can be used on any <interface>, <method>, <signal> and <property> element to specify
the name to use when generating C code. The value is expected to be in CamelCase[4] or
Ugly_Case (see above).

org.gtk.GDBus.C.ForceGVariant
If set to a non-empty string, a #GVariant instance will be used instead of the natural
C type. This annotation can be used on any <arg> and <property> element.

org.gtk.GDBus.C.UnixFD
If set to a non-empty string, the generated code will include parameters to exchange
file descriptors using the #GUnixFDList type. This annotation can be used on <method>
elements.

As an easier alternative to using the org.gtk.GDBus.DocString annotation, note that parser
used by gdbus-codegen parses XML comments in a way similar to gtk-doc[5]:

Note that @since can be used in any inline documentation bit (e.g. for interfaces,
methods, signals and properties) to set the org.gtk.GDBus.Since annotation. For the
org.gtk.GDBus.DocString annotation (and inline comments), note that substrings of the form
#net.Corp.Bar, net.Corp.Bar.FooMethod(), #net.Corp.Bar::BarSignal and
#net.Corp.InlineDocs:BazProperty are all expanded to links to the respective interface,
method, signal and property. Additionally, substrings starting with @ and % characters are
rendered as parameter[6] and constant[7] respectively.

If both XML comments and org.gtk.GDBus.DocString or org.gtk.GDBus.DocString.Short
annotations are present, the latter wins.

EXAMPLE

Consider the following D-Bus Introspection XML.

<node>
<interface name="net.Corp.MyApp.Frobber">
<method name="HelloWorld">
<arg name="greeting" direction="in" type="s"/>
<arg name="response" direction="out" type="s"/>
</method>

<signal name="Notification">
<arg name="icon_blob" type="ay"/>
<arg name="height" type="i"/>
<arg name="messages" type="as"/>
</signal>

<property name="Verbose" type="b" access="readwrite"/>
</interface>
</node>

If gdbus-codegen is used on this file like this:

gdbus-codegen --generate-c-code myapp-generated \
--c-namespace MyApp \
--interface-prefix net.corp.MyApp. \
net.Corp.MyApp.Frobber.xml

two files called myapp-generated.[ch] are generated. The files provide an abstract
#GTypeInterface -derived type called MyAppFrobber as well as two instantiable types with
the same name but suffixed with Proxy and Skeleton. The generated file, roughly, contains
the following facilities:

/* GType macros for the three generated types */
#define MY_APP_TYPE_FROBBER (my_app_frobber_get_type ())
#define MY_APP_TYPE_FROBBER_SKELETON (my_app_frobber_skeleton_get_type ())
#define MY_APP_TYPE_FROBBER_PROXY (my_app_frobber_proxy_get_type ())

typedef struct _MyAppFrobber MyAppFrobber; /* Dummy typedef */

typedef struct
{
GTypeInterface parent_iface;

/* Signal handler for the ::notification signal */
void (*notification) (MyAppFrobber *proxy,
GVariant *icon_blob,
gint height,
const gchar* const *messages);

/* Signal handler for the ::handle-hello-world signal */
gboolean (*handle_hello_world) (MyAppFrobber *proxy,
GDBusMethodInvocation *invocation,
const gchar *greeting);
} MyAppFrobberIface;

/* Asynchronously calls HelloWorld() */
void
my_app_frobber_call_hello_world (MyAppFrobber *proxy,
const gchar *greeting,
GCancellable *cancellable,
GAsyncReadyCallback callback,
gpointer user_data);
gboolean
my_app_frobber_call_hello_world_finish (MyAppFrobber *proxy,
gchar **out_response,
GAsyncResult *res,
GError **error);

/* Synchronously calls HelloWorld(). Blocks calling thread. */
gboolean
my_app_frobber_call_hello_world_sync (MyAppFrobber *proxy,
const gchar *greeting,
gchar **out_response,
GCancellable *cancellable,
GError **error);

/* Completes handling the HelloWorld() method call */
void
my_app_frobber_complete_hello_world (MyAppFrobber *object,
GDBusMethodInvocation *invocation,
const gchar *response);

/* Emits the ::notification signal / Notification() D-Bus signal */
void
my_app_frobber_emit_notification (MyAppFrobber *object,
GVariant *icon_blob,
gint height,
const gchar* const *messages);

/* Gets the :verbose GObject property / Verbose D-Bus property.
* Does no blocking I/O.
*/
gboolean my_app_frobber_get_verbose (MyAppFrobber *object);

/* Sets the :verbose GObject property / Verbose D-Bus property.
* Does no blocking I/O.
*/
void my_app_frobber_set_verbose (MyAppFrobber *object,
gboolean value);

/* Gets the interface info */
GDBusInterfaceInfo *my_app_frobber_interface_info (void);

/* Creates a new skeleton object, ready to be exported */
MyAppFrobber *my_app_frobber_skeleton_new (void);

/* Client-side proxy constructors.
*
* Additionally, _new_for_bus(), _new_for_bus_finish() and
* _new_for_bus_sync() proxy constructors are also generated.
*/
void
my_app_frobber_proxy_new (GDBusConnection *connection,
GDBusProxyFlags flags,
const gchar *name,
const gchar *object_path,
GCancellable *cancellable,
GAsyncReadyCallback callback,
gpointer user_data);
MyAppFrobber *
my_app_frobber_proxy_new_finish (GAsyncResult *res,
GError **error);
MyAppFrobber *
my_app_frobber_proxy_new_sync (GDBusConnection *connection,
GDBusProxyFlags flags,
const gchar *name,
const gchar *object_path,
GCancellable *cancellable,
GError **error);

Thus, for every D-Bus method, there will be three C functions for calling the method, one
#GObject signal for handling an incoming call and one C function for completing an
incoming call. For every D-Bus signal, there's one #GObject signal and one C function for
emitting it. For every D-Bus property, two C functions are generated (one setter, one
getter) and one #GObject property. The following table summarizes the generated facilities
and where they are applicable:

┌─────────────────────┬─────────────────────────┬──────────────────────────────┐
│ │ Client │ Server │
├─────────────────────┼─────────────────────────┼──────────────────────────────┤
│Types │ Use MyAppFrobberProxy │ Any type implementing │
│ │ │ the MyAppFrobber │
│ │ │ interface │
├─────────────────────┼─────────────────────────┼──────────────────────────────┤
│Methods │ Use m_a_f_hello_world() │ Receive via the │
│ │ to call. │ handle_hello_world() │
│ │ │ signal handler. Complete │
│ │ │ the call with │
│ │ │ m_a_f_complete_hello_world() │
├─────────────────────┼─────────────────────────┼──────────────────────────────┤
│Signals │ Connect to the │ Use │
│ │ ::notification GObject │ m_a_f_emit_notification() to │
│ │ signal. │ emit signal. │
├─────────────────────┼─────────────────────────┼──────────────────────────────┤
│Properties (Reading) │ Use m_a_f_get_verbose() │ Implement #GObject's │
│ │ or :verbose. │ get_property() vfunc. │
├─────────────────────┼─────────────────────────┼──────────────────────────────┤
│Properties (writing) │ Use m_a_f_set_verbose() │ Implement #GObject's │
│ │ or :verbose. │ set_property() vfunc. │
└─────────────────────┴─────────────────────────┴──────────────────────────────┘

Client-side usage
You can use the generated proxy type with the generated constructors:

MyAppFrobber *proxy;
GError *error;

error = NULL;
proxy = my_app_frobber_proxy_new_for_bus_sync (
G_BUS_TYPE_SESSION,
G_DBUS_PROXY_FLAGS_NONE,
"net.Corp.MyApp", /* bus name */
"/net/Corp/MyApp/SomeFrobber", /* object */
NULL, /* GCancellable* */
&error);
/* do stuff with proxy */
g_object_unref (proxy);

Instead of using the generic #GDBusProxy facilities, one can use the generated methods
such as my_app_frobber_call_hello_world() to invoke the
net.Corp.MyApp.Frobber.HelloWorld() D-Bus method, connect to the the ::notification
GObject signal to receive the net.Corp.MyApp.Frobber::Notication D-Bus signal and get/set
the net.Corp.MyApp.Frobber:Verbose D-Bus Property using either the GObject property
:verbose or the my_app_get_verbose() and my_app_set_verbose() methods. Use the standard
#GObject::notify signal to listen to property changes.

Note that all property access is via #GDBusProxy 's property cache so no I/O is ever done
when reading properties. Also note that setting a property will cause the
org.freedesktop.DBus.Properties.Set[8] method to be called on the remote object. This
call, however, is asynchronous so setting a property won't block. Further, the change is
delayed and no error checking is possible.

Server-side usage
The generated MyAppFrobber interface is designed so it is easy to implement it in a
#GObject subclass. For example, to handle HelloWorld() method invocations, set the vfunc
for handle_hello_hello_world() in the MyAppFrobberIface structure. Similary, to handle the
net.Corp.MyApp.Frobber:Verbose property override the :verbose #GObject property from the
subclass. To emit a signal, use e.g. my_app_emit_signal() or g_signal_emit_by_name().

Instead of subclassing, it is often easier to use the generated MyAppFrobberSkeleton
subclass. To handle incoming method calls, use g_signal_connect() with the ::handle-*
signals and instead of overriding #GObject 's get_property() and set_property() vfuncs,
use g_object_get() and g_object_set() or the generated property getters and setters (the
generated class has an internal property bag implementation).

static gboolean
on_handle_hello_world (MyAppFrobber *interface,
GDBusMethodInvocation *invocation,
const gchar *greeting,
gpointer user_data)
{
if (g_strcmp0 (greeting, "Boo") != 0)
{
gchar *response;
response = g_strdup_printf ("Word! You said `%s'.", greeting);
my_app_complete_hello_world (interface, invocation, response);
g_free (response);
}
else
{
g_dbus_method_invocation_return_error (invocation,
MY_APP_ERROR,
MY_APP_ERROR_NO_WHINING,
"Hey, %s, there will be no whining!",
g_dbus_method_invocation_get_sender (invocation));
}
return TRUE;
}

[...]

interface = my_app_frobber_skeleton_new ();
my_app_frobber_set_verbose (interface, TRUE);

g_signal_connect (interface,
"handle-hello-world",
G_CALLBACK (on_handle_hello_world),
some_user_data);

[...]

error = NULL;
if (!g_dbus_interface_skeleton_export (G_DBUS_INTERFACE_SKELETON (interface),
connection,
"/path/of/dbus_object",
&error))
{
/* handle error */
}

To facilitate atomic changesets (multiple properties changing at the same time),
#GObject::notify signals are queued up when received. The queue is drained in an idle
handler (which is called from the thread-default main loop of the thread where the
skeleton object was contructed) and will cause emissions of the
org.freedesktop.DBus.Properties::PropertiesChanged[8] signal with all the properties that
have changed. Use g_dbus_interface_skeleton_flush() or g_dbus_object_skeleton_flush() to
empty the queue immediately. Use g_object_freeze_notify() and g_object_thaw_notify() for
atomic changesets if on a different thread.

C TYPE MAPPING

Scalar types (type-strings 'b', 'y', 'n', 'q', 'i', 'u', 'x', 't' and 'd') ), strings
(type-strings 's', 'ay', 'o' and 'g') and arrays of string (type-strings 'as', 'ao' and
'aay') are mapped to the natural types, e.g. #gboolean, #gdouble, #gint, gchar*, gchar**
and so on. Everything else is mapped to the #GVariant type.

This automatic mapping can be turned off by using the annotation
org.gtk.GDBus.C.ForceGVariant - if used then a #GVariant is always exchanged instead of
the corresponding native C type. This annotation may be convenient to use when using
bytestrings (type-string 'ay') for data that could have embedded NUL bytes.

STABILITY GUARANTEES

The generated C functions are guaranteed to not change their ABI that is, if a method,
signal or property does not change its signature in the introspection XML, the generated C
functions will not change its C ABI either. The ABI of the generated instance and class
structures will be preserved as well.

The ABI of the generated #GType s will be preserved only if the org.gtk.GDBus.Since
annotation is used judiciously — this is because the VTable for the #GInterface relies on
functions pointers for signal handlers. Specifically, if a D-Bus method, property or
signal or is added to a D-Bus interface, then ABI of the generated #GInterface type is
preserved if, and only if, each added method, property signal is annotated with they
org.gtk.GDBus.Since annotation using a greater version number than previous versions.

The generated C code currently happens to be annotated with gtk-doc[5] / GObject
Introspection[9] comments / annotations. The layout and contents might change in the
future so no guarantees about e.g. SECTION usage etc. is given.

While the generated Docbook for D-Bus interfaces isn't expected to change, no guarantees
are given at this point.

It is important to note that the generated code should not be checked into revision
control systems, nor it should be included in distributed source archives.

Use gdbus-codegen online using onworks.net services