TDE DBus Tutorial

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This is a brief introduction on auto-generated DBus interfaces and proxies and their use in TDE.

I hope it will save many people time and headache. Some more information can be found in the documentation of package dbus-1-tqt.

All the examples are based on the example in dbus-1-tqt for a service providing method ListSorter and for such a client.

Create DBus Interface

To create a DBus interface we need first a definition of the interface. More information on the interface type and signatures can be found in official dbus tutorial

The definition of the interface is a XML file. We take as example a file describing org.example.Service that has one method ListSorter. The generated code will automatically include the Introspection interface and we will see how we can create a service to handle both interfaces.

<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN" "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<node name="/org/example/Service">
    <interface name="org.example.Service">
        <method name="ListSorter">
            <arg name="input" type="as" direction="in" />
            <arg name="output" type="as" direction="out" />
        </method>
    </interface>
</node>

Generate the code

To generate the TQt C++ classes we use dbusxml2qt3

$ dbusxml2qt3 sortexample.xml
ClassGenerator: processing interface 'org.example.Service'
Generating org.freedesktop.DBus.Introspectable on demand

in the second step generate the proxy with unique namespace to fit your application

$ /usr/bin/dbusxml2qt3 sortexample.xml

the result is

$ ls -1
dbusbaseNode.cpp
dbusbaseNode.h
introspectableInterface.cpp
introspectableInterface.h
serviceInterface.cpp
serviceInterface.h
serviceNode.cpp
serviceNode.h
serviceProxy.cpp
serviceProxy.h
sortexample.xml

Implement the Service

Now we can create our own service using the interface use the proxy as shown below.

testservice.h

#include <tqdbusconnection.h>
#include <tqdbusobject.h>
#include <tqmap.h>
#include "serviceInterface.h"
#include "serviceNode.h"

class Interface1 : public org::example::ServiceInterface
{
public:
    Interface1(TQT_DBusConnection&);
    virtual ~Interface1();
protected: // implement methods
    virtual bool ListSorter(const TQStringList& input, TQStringList& output, TQT_DBusError& error);
protected: // implement sending replies
    virtual void handleMethodReply(const TQT_DBusMessage& reply);
private:
    TQT_DBusConnection *m_connection;
};

class MultiInterfaceService : public org::example::ServiceNode
{
public:
    MultiInterfaceService(TQT_DBusConnection&);
    ~MultiInterfaceService();
protected:
    virtual TQT_DBusObjectBase* createInterface(const TQString&);
private:
    TQMap<TQString, TQT_DBusObjectBase*> m_interfaces;
    TQT_DBusConnection m_connection;
};

testservice.cpp

#include <kdebug.h>

// TQt includes
#include <tqdom.h>
#include <tqstring.h>
#include <tqstringlist.h>
#include <tqdbuserror.h>
#include <tqdbusmessage.h>
#include <tqdbusdatalist.h>
#include "testservice.h"

Interface1::Interface1(TQT_DBusConnection &conn)
   : m_connection(&conn)
{
    kdDebug() << k_funcinfo << endl;
}
Interface1::~Interface1(){
    kdDebug() << k_funcinfo << endl;
}

void Interface1::handleMethodReply(const TQT_DBusMessage& reply) {
    kdDebug() << k_funcinfo << endl;
    // do something
    m_connection->send(reply);
}

bool Interface1::ListSorter(const TQStringList& input, TQStringList& output, TQT_DBusError& error) {
    kdDebug() << k_funcinfo << endl;
    output = input;
    output.sort();
    return true;
}

MultiInterfaceService::MultiInterfaceService(TQT_DBusConnection &connection )
    : org::example::ServiceNode(), m_connection(connection)
{
    kdDebug() << k_funcinfo << endl;
    m_interfaces.insert("org.freedesktop.DBus.Introspectable", this);
    m_interfaces.insert("org.example.Service", new Interface1(m_connection));
    registerObject(m_connection,"/");
}

MultiInterfaceService::~MultiInterfaceService(){
    kdDebug() << k_funcinfo << endl;
}

TQT_DBusObjectBase* MultiInterfaceService::createInterface(const TQString& interfaceName)
{
    kdDebug() << k_funcinfo << endl;
    kdDebug() << "Interface Name: " << interfaceName << endl;
    return (TQT_DBusObjectBase*) m_interfaces[interfaceName];
}

tqdbusexample.cpp

#include "testservice.h"
#include <tqapplication.h>
#include <tqdbusconnection.h>

int main(int argc, char** argv)
{
    TQApplication app(argc, argv, false);
    TQT_DBusConnection connection = TQT_DBusConnection::sessionBus();
//  TQT_DBusConnection connection = TQT_DBusConnection::systemBus();
    if (!connection.isConnected())
        tqFatal("Cannot connect to session bus");

    // try to get a specific service name
    if (!connection.requestName("org.example.Service"))
    {
        tqWarning("Requesting name 'org.example.Service' failed. "
               "Will only be addressable through unique name '%s'",
                connection.uniqueName().local8Bit().data());
    }
    else
    {
        tqDebug("Requesting name 'org.example.Service' successfull");
    }
    MultiInterfaceService service(connection);

    return app.exec();
}

buildtqdbusexample.sh

Messagebox info.png
Warning! Unflexible code!
This command contains paths which may differ from system to system. You had better use a build system (e.g. CMake) for serious development!
/usr/bin/g++   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time \
-D_FORTIFY_SOURCE=2  -DQT_NO_ASCII_CAST -DQT_CLEAN_NAMESPACE -DQT_NO_STL -DQT_NO_COMPAT \
-DQT_NO_TRANSLATION -DQT_THREAD_SUPPORT -D_REENTRANT -include tqt.h -I/usr/include/tqt3 \
-I/opt/trinity/include/ -I/usr/include/dbus-1-tqt -I/usr/include/tqt -I -DQT_NO_ASCII_CAST \
-DQT_CLEAN_NAMESPACE -DQT_NO_STL -DQT_NO_COMPAT -DQT_NO_TRANSLATION -DQT_THREAD_SUPPORT \
-D_REENTRANT -include tqt.h -g  -Wl,-z,relro tqdbusexample.cpp  testservice.cpp \
serviceNode.cpp introspectableInterface.cpp serviceInterface.cpp \
-o tqdbusexample -ldbus-1-tqt \
/opt/trinity/lib/libtdeparts.so.2.1.0 /opt/trinity/lib/libtdeio.so.14.0.0 \
/opt/trinity/lib/libtdecore.so.14.0.0 -ltqt -ltqt-mt -lXrender -lX11 -lc \
/usr/lib/x86_64-linux-gnu/libz.so -lidn -lXcomposite -lICE -lSM -lutil -lr -lacl -lattr -ltqui

Using a Proxy

We will use the service from our first example and implement a proxy to utilize the service.

tqdbusproxy.cpp

#include <tqstringlist.h>
#include <tqdbusconnection.h>
#include "serviceProxy.h"

int main(int argc, char** argv)
{
    TQT_DBusConnection connection = TQT_DBusConnection::sessionBus();
//  TQT_DBusConnection connection = TQT_DBusConnection::systemBus();
    if (!connection.isConnected())
        tqFatal("Cannot connect to session bus");

    org::example::ServiceProxy serviceProxy("org.example.Service", "/");

    serviceProxy.setConnection(connection);

    TQStringList list;
    list << "D" << "C" << "B" << "A";

    tqWarning("OUTPUT BEFORE SORT");
    for (TQStringList::iterator it= list.begin(); it != list.end(); ++it) {
        tqWarning("\t%s",(*it).utf8().data());
    }

    TQStringList data;
    TQT_DBusError error;
    if (!serviceProxy.ListSorter(list,data,error)) {
        tqFatal("'org.example.Service.ListSorter' failed. ");
    }
    else {
        tqWarning("OUTPUT AFTER SORT");
        for (TQStringList::iterator it = data.begin(); it != data.end(); ++it) {
            tqWarning("\t%s",(*it).utf8().data());
        }
    }

    return 0;
}

buildtqdbusproxy.sh

Messagebox info.png
Warning! Unflexible code!
This command contains paths which may differ from system to system. You had better use a build system (e.g. CMake) for serious development!
tmoc serviceProxy.h -o serviceProxy.moc
/usr/bin/g++   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time \
-D_FORTIFY_SOURCE=2  -DQT_NO_ASCII_CAST -DQT_CLEAN_NAMESPACE -DQT_NO_STL -DQT_NO_COMPAT \
-DQT_NO_TRANSLATION -DQT_THREAD_SUPPORT -D_REENTRANT -include tqt.h -I/usr/include/tqt3 \
-I/opt/trinity/include/ -I/usr/include/dbus-1-tqt -I/usr/include/tqt -I -DQT_NO_ASCII_CAST \
-DQT_CLEAN_NAMESPACE -DQT_NO_STL -DQT_NO_COMPAT -DQT_NO_TRANSLATION -DQT_THREAD_SUPPORT \
-D_REENTRANT -include tqt.h -g  -Wl,-z,relro tqdbusproxy.cpp serviceProxy.cpp \
-o tqdbusproxy -ldbus-1-tqt \
/opt/trinity/lib/libtdeparts.so.2.1.0 /opt/trinity/lib/libtdeio.so.14.0.0 \
/opt/trinity/lib/libtdecore.so.14.0.0 -ltqt -ltqt-mt -lXrender -lX11 -lc \
/usr/lib/x86_64-linux-gnu/libz.so -lidn -lXcomposite -lICE -lSM -lutil -lr -lacl -lattr -ltqui

Try it

Start the service

$ ./tqdbusexample

Test the service from command line

$ dbus-send --print-reply  --session --dest=org.example.Service / org.example.Service.ListSorter array:string:"B","A","C"
method return time=1571779738.342213 sender=:1.91 -> destination=:1.94 serial=7 reply_serial=2
  array [
     string "A"
     string "B"
     string "C"
  ]

Test the service with proxy client

$ ./tqdbusproxy
[2019/10/22 23:28:11.982] OUTPUT BEFORE SORT
[2019/10/22 23:28:11.983]       D
[2019/10/22 23:28:11.983]       C
[2019/10/22 23:28:11.983]       B
[2019/10/22 23:28:11.983]       A
[2019/10/22 23:28:11.983] OUTPUT AFTER SORT
[2019/10/22 23:28:11.983]       A
[2019/10/22 23:28:11.983]       B
[2019/10/22 23:28:11.983]       C
[2019/10/22 23:28:11.983]       D

External resources