gdbus-codegen-glibmm: A C++ repository from Pelagicore Group

This is a cpp code generator for generating D-Bus stubs and proxies from XML introspection files. The generated stubs and proxies are implemented using glibmm and giomm.

This generator is based on the gdbus-codegen code generator which ships with glib.

Installing

setup.py is used for installing gdbus-codegen-glibmm. This is a Setuptools script, and can be invoked according to the developer's guide. In a nutshell, python3 ./setup.py install with sufficient priveleges should get you going.

Once installed, the gdbus-codegen-glibmm command should be available in the bin directory of your selected prefix, and the required python modules should be installed in the python path.

Running

The code generator is a command line executable, suitable for running either manually from a terminal or via a build-system such as CMake (there's an example of this below).

The following parameters are supported by the gdbus-codegen-glibmm code generator executable:

-h

Show a short help, detailing the command line parameters of the code generator
--interface-prefix=PREFIX1,PREFIX2

Comma-separated list of prefix-strings to strip from the generated C++ functions and classes. The D-Bus names in the D-Bus introspection XML files are used to generate namespaces in the generated C++ code, roughly a dot (.) is translated to a double colon (::). As an example, the function org.foo.Bar.Baz(), in the name org.foo.Bar will be used to generate the org::foo::Bar::Baz(void) function in the Bar class of the org::foo namespace. This might be too verbose for long names, and --interface-prefix can be used to prune the org.foo part from the name, resulting in the shorter Bar::Baz(void) C++ function (and non-namespaced class). Beware that this may cause name collisions if several interfaces with functions of the same names are used in the same D-Bus introspection XML files.
--cpp-namespace=NAMESPACE

A string to prepend to the namespaces of the generated functions.
--errors-namespace=ERROR_NAMESPACE

The namespace where error classes should be generated. Can contain ::.
--generate-cpp-code=OUTFILES

Path and prefix of the file names to generate for the proxy and stub generated by the code generator. The filename prefix is suffixed by _stub.[h|cpp], _proxy.[h|cpp] and _common[.h|cpp]. The file names generated usign this path are also used for inclusion of headers in the generated code, so it is not recommended to rename the files generated using the path supplied here.
Following parameters

List of D-Bus introspection XML files. These files are used to describe the D-Bus interfaces. Several files can be supplied. The interfaces from all files will be gathered and then emitted in the same output headers and cpp-files. See the introspection chapter of the the D-Bus specification by freedesktop for more information on the format of the D-Bus introspection XML files.

Example invocation

dbus-codegen-glibmm --generate-cpp-code=${HOME}/temperature-service-example/build/generated/temperature-service
                    ${HOME}/temperature-service-example/temperature-service.xml

This will create the following files in ${HOME}/temperature-service-example/build/generated/:

temperature-service_common.cpp
temperature-service_common.h
temperature-service_proxy.cpp
temperature-service_proxy.h
temperature-service_stub.cpp
temperature-service_stub.h

Generation of error classes

gdbus-codegen-glibmm can generate classes for error handling: these classes will inherit from Glib::Error, and can be used both in the backend and in the client library.

Errors are declared by inserting annotations as child elements of a D-Bus interface:

<!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.MyService">
    ...
    <!--
      Invalid parameters (this comment will also end up in the generated code)
    -->
    <annotation name="org.gdbus.glibmm.Error" value="com.example.Error.InvalidParams" />

    <!-- The backend ran out of memory -->
    <annotation name="org.gdbus.glibmm.Error" value="com.example.Error.OutOfMemory" />
    ...

Implementing a stub

First, a D-Bus interface must be specified in XML. We will use the following:

<?xml version="1.0" encoding="UTF-8" ?>
<node name="/org/foo/Bar">
	<interface name="org.foo.Bar">
		<method name="Baz">
		</method>
	</interface>
</node>

In this tutorial we will keep the generated code in a subdirectory called generated, so go ahead and mkdir generated before continuing. The following invocation will generate a stub (and also a proxy, but this is unused in this section): gdbus-codegen-glibmm --generate-cpp-code=generated/bar bar.xml

The generated stub is a virtual class, designed to be implemented by a concrete C++ class. In our example, the following will suffice:

#include "bar_stub.h"

class BarImpl : public org::foo::BarStub {
public:
    // Called wben org.foo.bar.Baz() is invoked
    void Baz (MethodInvocation &invocation) override {
        // Return void
        invocation.ret();
    }
};

int main(int argc, char **argv) {
    // Initialize Glib and Gio
    Glib::init();
    Gio::init();

    // Instantiate and run the main loop
    Glib::RefPtr<Glib::MainLoop> ml = Glib::MainLoop::create();

    // Connect to the system bus and acquire our name
    BarImpl bi;
    guint connection_id = Gio::DBus::own_name(
            Gio::DBus::BUS_TYPE_SESSION,
            "org.foo.Bar",
            [&](const Glib::RefPtr<Gio::DBus::Connection> &connection,
                const Glib::ustring & /* name */) {
                g_print("Connected to bus.\n");
                if (bi.register_object(connection, "/org/foo/Bar") == 0)
                    ml->quit();
            },
            [&](const Glib::RefPtr<Gio::DBus::Connection> & /* connection */,
                const Glib::ustring & /* name */) {
                g_print("Name acquired.\n");
            },
            [&](const Glib::RefPtr<Gio::DBus::Connection> & /* connection */,
                const Glib::ustring & /* name */) {
                g_print("Name lost.\n");
                ml->quit();
            });

    ml->run();

    Gio::DBus::unown_name(connection_id);

    return 0;
}

The example above doesn't do much in terms of functionality, but it shows how to implement a very simple stub. Properties are supported in a similar fashion, where the stub implements _set() and/or _get() functions (depending on the accessibility of the property).

Signals are simply connected to, and no implementation code needs to be written.

The above example can be compiled using the following command:

clang++ -I . -I generated `pkg-config --cflags --libs glibmm-2.4 giomm-2.4`
            generated/bar_common.cpp
            generated/bar_stub.cpp
            barimpl.cpp

Just update the filenames accordingly.

Implementing a proxy

In order to implement a proxy, run the same generation commands as in the previous example, and use the _proxy.[h|cpp] files instead of the _stub.[h|cpp]. The output from the previous execution of the generator will also work, so there is no need to re-run if the files are already available.

The following file shows the proxy corresponding to the stub above:

#include "bar_proxy.h"

Glib::RefPtr<org::foo::BarProxy> proxy;

void on_baz_finished(const Glib::RefPtr<Gio::AsyncResult> &result) {
    proxy->Baz_finish(result);
}

void proxy_created(const Glib::RefPtr<Gio::AsyncResult> result) {
    proxy = org::foo::BarProxy::createForBusFinish(result);
    proxy->Baz(sigc::ptr_fun(&on_baz_finished));
}

int main(int argc, char **argv) {
    Glib::init();
    Gio::init();

    org::foo::BarProxy::createForBus(Gio::DBus::BUS_TYPE_SESSION,
                                     Gio::DBus::PROXY_FLAGS_NONE,
                                     "org.foo.Bar",
                                     "/org/foo/Bar",
                                     sigc::ptr_fun(&proxy_created));

    Glib::RefPtr<Glib::MainLoop> ml = Glib::MainLoop::create();
    ml->run();

    return 0;
}

It can be compiled in a similar fashion as the previous example.

There are synchronous versions available for method invocations, setting properties and creating a proxy that have a _sync suffix. These should only be used if it is acceptable to block the application for a very long time. For instance, the default method invocation timeout for a proxy is 25 seconds. Blocking for that amount of time is most likely not a good idea when writing e.g. a system daemon. The asynchronous version, that calls a callback when the D-Bus method returns, should be used instead.

CMake integration

Running the code generator from CMake can be done using the following snippet:

SET (CODEGEN gdbus-codegen-glibmm)
SET (INTROSPECTION_XML ${CMAKE_SOURCE_DIR}/bar.xml)

SET (GENERATED_STUB
    ${CMAKE_BINARY_DIR}/generated/bar_stub.cpp
    ${CMAKE_BINARY_DIR}/generated/bar_stub.h
    ${CMAKE_BINARY_DIR}/generated/bar_common.cpp
    ${CMAKE_BINARY_DIR}/generated/bar_common.h
)

ADD_CUSTOM_COMMAND (OUTPUT ${GENERATED_STUB}
                    COMMAND mkdir -p ${CMAKE_BINARY_DIR}/generated/
                    COMMAND ${CODEGEN} --generate-cpp-code=${CMAKE_BINARY_DIR}/generated/bar
                                        ${INTROSPECTION_XML}
                    DEPENDS ${INTROSPECTION_XML}
                    COMMENT "Generate the stub for the test program")

The usage of the $GENERATED_STUB files will trigger the execution of the code generator.

License and copyright

SPDX-License-Identifier: CC-BY-SA-4.0

The python code is

Source code licensed under the LGPL 2.1 (please see source code headers for more.)