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Error when implementing DBus ObjectManager #50

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mdw87 opened this issue May 8, 2019 · 7 comments
Closed

Error when implementing DBus ObjectManager #50

mdw87 opened this issue May 8, 2019 · 7 comments

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@mdw87
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mdw87 commented May 8, 2019 •
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I am attempting to implement the org.freedesktop.DBus.ObjectManager interface, as defined here.

Through introspection of other DBus services, I was able to produce an XML interface definition for the ObjectManager interface. The ObjectManager requires a method GetManagedObjects with the argument signature a{oa{sa{sv}}}, and emits two signals for InterfacesAdded and InterfacesRemoved.

The XML I generated looks like this:

<node>
	<interface name="org.freedesktop.DBus.ObjectManager">
		<method name="GetManagedObjects">
			<arg type="a{oa{sa{sv}}}" name="object_paths_interfaces_and_properties" direction="out"/>
		</method>
		<signal name="InterfacesAdded">
			<arg type="o" name="object_path"/>
			<arg type="a{sa{sv}}" name="interfaces_and_properties"/>
		</signal>
		<signal name="InterfacesRemoved">
			<arg type="o" name="object_path"/>
			<arg type="as" name="interfaces"/>
		</signal>
	</interface>
</node>

The problem I am having is that when I go to create this service and register with DBus, I am getting the following error:

terminate called after throwing an instance of 'sdbus::Error'
  what():  [org.freedesktop.DBus.Error.InvalidArgs] Failed to register object vtable (Invalid argument)

So, it seems that for some reason my implementation is not valid according to the DBus ObjectManager interface. I have not been able to figure out why. If I change my code to use an interface name other than "org.freedesktop.DBus.ObjectManager", it works fine, so it seems that there is some kind of validation going on when I try to register something as an ObjectManager. I have not been able to figure out where my DBus service differs from the spec.

I have copied below the code from 3 files: the source code of the simple application I am trying to run, the class I created for the ObjectManager adapter, and the auto-generated adapter glue code that was generated using the sdbus-c++-xml2cpp` tool.

I have also tried manually registering the interface, using gattService->registerMethod(interfaceName, "GetManagedObjects", "", "a{oa{sa{sv}}}", &GetManagedObjects) rather than the stubs generated from XML, but I still got the same error.

Any help is greatly appreciated!

Source code of simple-gatt-service.cpp

#include "interfaces/objectmanager_adapter.h"
#include <vector>
#include <string>
#include <iostream>
#include <unistd.h>


int main(int argc, char *argv[])
{
    // Create D-Bus connection to the system bus and requests name on it.
    const char* serviceName = "org.gattservice";
    auto connection = sdbus::createSystemBusConnection(serviceName);

    // Create D-Bus object.
    const char* objectPath = "/org/gattservice";
    
    auto gattService = sdbus::createObject(*connection, objectPath);
    ObjectManagerAdapter objectManager(*connection, objectPath);

    connection->enterProcessingLoop();
}

Source code of objectmanager_adapter.h

#include "objectmanager_adapter_glue.h"

using ObjectManagerAdapterInterface = sdbus::AdaptorInterfaces<org::freedesktop::DBus::ObjectManager_adaptor>;

class ObjectManagerAdapter : public ObjectManagerAdapterInterface
{
public:
    ObjectManagerAdapter(sdbus::IConnection& connection, std::string objectPath)
        : ObjectManagerAdapterInterface(connection, objectPath)
    {
        registerAdaptor();
    }

    ~ObjectManagerAdapter()
    {
        unregisterAdaptor();
    }
private:
    std::map<sdbus::ObjectPath, std::map<std::string, std::map<std::string, sdbus::Variant>>> GetManagedObjects() override
    {
        std::map<sdbus::ObjectPath, std::map<std::string, std::map<std::string, sdbus::Variant>>> mapOfObjects;

        return {mapOfObjects};
    }
};

Source code of objectmanager_adapter_glue.h (auto-generated from xml)

/*
 * This file was automatically generated by sdbus-c++-xml2cpp; DO NOT EDIT!
 */

#ifndef __sdbuscpp__objectmanager_adapter_glue_h__adaptor__H__
#define __sdbuscpp__objectmanager_adapter_glue_h__adaptor__H__

#include <sdbus-c++/sdbus-c++.h>
#include <string>
#include <tuple>

namespace org {
namespace freedesktop {
namespace DBus {

class ObjectManager_adaptor
{
public:
    static constexpr const char* interfaceName = "org.freedesktop.DBus.ObjectManager";

protected:
    ObjectManager_adaptor(sdbus::IObject& object)
        : object_(object)
    {
        object_.registerMethod("GetManagedObjects").onInterface(interfaceName).implementedAs([this](){ return this->GetManagedObjects(); });
        object_.registerSignal("InterfacesAdded").onInterface(interfaceName).withParameters<sdbus::ObjectPath, std::map<std::string, std::map<std::string, sdbus::Variant>>>();
        object_.registerSignal("InterfacesRemoved").onInterface(interfaceName).withParameters<sdbus::ObjectPath, std::vector<std::string>>();
    }

public:
    void InterfacesAdded(const sdbus::ObjectPath& object_path, const std::map<std::string, std::map<std::string, sdbus::Variant>>& interfaces_and_properties)
    {
        object_.emitSignal("InterfacesAdded").onInterface(interfaceName).withArguments(object_path, interfaces_and_properties);
    }

    void InterfacesRemoved(const sdbus::ObjectPath& object_path, const std::vector<std::string>& interfaces)
    {
        object_.emitSignal("InterfacesRemoved").onInterface(interfaceName).withArguments(object_path, interfaces);
    }

private:
    virtual std::map<sdbus::ObjectPath, std::map<std::string, std::map<std::string, sdbus::Variant>>> GetManagedObjects() = 0;

private:
    sdbus::IObject& object_;
};

}}} // namespaces

#endif
@sangelovic
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sangelovic commented May 8, 2019 via email

@mdw87
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mdw87 commented May 8, 2019

Oh wow, that makes my job easier :) Thanks!

@sangelovic
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sangelovic commented May 8, 2019 •
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I've just added a subsection on this behavior to the docs: https://github.com/Kistler-Group/sdbus-cpp/blob/master/docs/using-sdbus-c++.md#standard-d-bus-interfaces

I think I should also add *_proxy classes for these standard interfaces. introspectable_proxy is there already, but others are missing. That would perhaps also help you writing clients to these interfaces...

@mdw87
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mdw87 commented May 9, 2019 •
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For some reason I am still having trouble getting the ObjectManager to show up. I put together a simple c++ application that creates a D-Bus object with a single interface and property. When I look at that object in D-Feet, it doesn't list the ObjectManager interface.

However, I was able to get it to show up by explicitly calling sd_bus_add_object_manager on the connection. I made a branch here showing the work to do that:
https://github.com/Kistler-Group/sdbus-cpp/compare/master...mdw87:feature/add-objectmanager-to-connection?expand=1

When I add this function call, I am able to see the ObjectManager in D-Feet, and calling the GetManagedObjects function works as expected. Do you know why I am not be seeing the ObjectManager added by default?

Here's the simple c++ program:

#include <sdbus-c++/sdbus-c++.h>

int main(int argc, char *argv[])
{
    // Create D-Bus connection to the system bus and requests name on it.
    const char* serviceName = "org.example.service";
    auto connection = sdbus::createSystemBusConnection(serviceName);


    // Create D-Bus object.
    const char* objectPath = "/org/example/service";
    auto serviceObject = sdbus::createObject(*connection, objectPath);

    // Register D-Bus methods and signals on the object, and export the object.
    const char* interfaceName = "org.example.service";
    serviceObject->registerProperty("Name").onInterface(interfaceName).withGetter([](){ return "hello"; }).withSetter([](const uint32_t& value){  });

    serviceObject->finishRegistration();

    // Start the service
    connection->enterProcessingLoop();
}

Here's the same program with the call to sd_bus_add_object_manager added. This will require the changes on my branch to compile.

#include <sdbus-c++/sdbus-c++.h>

int main(int argc, char *argv[])
{
    // Create D-Bus connection to the system bus and requests name on it.
    const char* serviceName = "org.example.service";
    auto connection = sdbus::createSystemBusConnection(serviceName);


    // Create D-Bus object.
    const char* objectPath = "/org/example/service";
    auto serviceObject = sdbus::createObject(*connection, objectPath);

    // Register D-Bus property on the object, and export the object.
    const char* interfaceName = "org.example.service";
    serviceObject->registerProperty("Name").onInterface(interfaceName).withGetter([](){ return "hello"; }).withSetter([](const uint32_t& value){  });

    serviceObject->finishRegistration();

    // Add an objectManager interface at the root of the service
    connection->addObjectManager("/");

    // Start the service
    connection->enterProcessingLoop();
}

The attached screenshots show how the service shows up in D-Feet before and after adding the function call.
without-objectmanager
with-object-manager

@sangelovic
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Having ObjectManager not as a default interface for every D-Bus object is a design decision of sd-bus, the underlying D-Bus implementation. It is available, just that it has to be added explicitly for a given object path. I've accepted your changes (thank you) and extended the IObject API as well. I've added a *_proxy classes for convenience. So sdbus-c++ now natively supports ObjectManager API as well as other D-Bus interfaces. However there's still lacking support for emitting Properties- and ObjectManager-related signals. This will follow in near future...

@wpd
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wpd commented Apr 26, 2021

Returning to this after a month away...

Hello @mdw87 - were you able to get sdbus-cpp, Bluez, and ObjectManager to play well with each other? Is your code public? Could I look at it for inspirational purposes?

Hello @sangelovic - did you add support for emitting Properties- and ObjectManager-related signals? How critical (do you think) support for those is?

--wpd

@sangelovic
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@wpd Yes, that was added just a few days later. See 01e2a7a and 38b51bd

@DanWillans DanWillans mentioned this issue Dec 5, 2023
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@wpd @sangelovic @mdw87