glibdbusgdbusconnman

g_signal_connect on proxy handler results in callback GVariant * data uninitialized

I'm pretty much following the example on https://www.freedesktop.org/software/gstreamer-sdk/data/docs/latest/gio/GDBusProxy.html in order to set up Connman signal callbacks on dbus, however in my callback function: 

g_signal_connect(
        this->manager_proxy,
        "property-changed",
        G_CALLBACK(on_manager_properties_changed),
        this); //Pass in pointer to self so static function can operate on object.
g_signal_connect(
        this->manager_proxy,
        "technology-added",
        G_CALLBACK(on_manager_tech_added),
        this); //Pass in pointer to self so static function can operate on object.
g_signal_connect(
        this->manager_proxy,
        "technology-removed",
        G_CALLBACK(on_manager_tech_removed),
        this); //Pass in pointer to self so static function can operate on object

void
CM_InterfaceController::on_manager_properties_changed (
                       GDBusProxy          *proxy,
                       GVariant            *changed_properties,
                       const gchar* const  *invalidated_properties,
                       gpointer             user_data)
{
    if(!user_data){CM_ERR("NO THIS * on_manager_properties_changed");return;}
    CM_InterfaceController * ths = static_cast<CM_InterfaceController *>(user_data);
    std::cout<<"on_manager_properties_changed"<<std::endl;
    if(changed_properties){
        std::cout<<"children: "<<g_variant_n_children(changed_properties)<<std::endl;
    }    
}

The number of children I am told the GVariant * object contains is completely wrong. For instance, my feedback: 

Calling Extraction
Service List Size: 1
Identified Ethernet Link: 
Path: /net/connman/service/ethernet_0800277d326e_cable
        Type: ethernet
        Sate: ready
        Favorite: 0
        Auto Connect: 0
        Name: Wired
        Net Mode: manual
        Iface: eth0
        Mac: 08:00:27:7D:32:6E
        IP Address: 10.0.2.15
        Net Mask: 255.255.255.0
on_manager_properties_changed
children: 139764141513856
on_manager_properties_changed
children: 145

on_manager_properties_changed children: 139764141513856 on_manager_properties_changed children: 145

Both of those values are way out of the ballpark, one more significantly than the other. Even more, if I try to parsed the values out of the GVariant object, I end up seg faulting even just by trying to call g_variant_get_type_string. Why on earth is my callback returning with a garbage data pointer? Seems like if it has nothing it should at least return a null pointer.

edit: Source Code https://drive.google.com/file/d/1E0Kg9JKW54gghUHbVyBJ0ysBIdqBlpVA/view?usp=sharing

And some of the dbus-monitor --system output:

signal time=1549641357.679460 sender=:1.3 -> destination=(null destination) serial=488 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "State"
   variant       string "ready"
signal time=1549641357.680844 sender=:1.3 -> destination=(null destination) serial=489 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "Nameservers"
   variant       array [
         string "10.0.2.3"
      ]
signal time=1549641357.681186 sender=:1.3 -> destination=(null destination) serial=490 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "Domains"
   variant       array [
      ]
signal time=1549641357.681601 sender=:1.3 -> destination=(null destination) serial=491 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "Proxy"
   variant       array [
         dict entry(
            string "Method"
            variant                string "direct"
         )
      ]
signal time=1549641357.681780 sender=:1.3 -> destination=(null destination) serial=492 path=/net/connman/technology/ethernet; interface=net.connman.Technology; member=PropertyChanged
   string "Connected"
   variant       boolean true
signal time=1549641357.682210 sender=:1.3 -> destination=(null destination) serial=493 path=/; interface=net.connman.Manager; member=PropertyChanged
   string "State"
   variant       string "ready"
signal time=1549641357.696004 sender=:1.3 -> destination=(null destination) serial=494 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "IPv4"
   variant       array [
         dict entry(
            string "Method"
            variant                string "dhcp"
         )
      ]
signal time=1549641357.696227 sender=:1.3 -> destination=(null destination) serial=495 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "IPv4"
   variant       array [
         dict entry(
            string "Method"
            variant                string "dhcp"
         )
         dict entry(
            string "Address"
            variant                string "10.0.2.15"
         )
         dict entry(
            string "Netmask"
            variant                string "255.255.255.0"
         )
      ]
signal time=1549641357.696454 sender=:1.3 -> destination=(null destination) serial=496 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "IPv4"
   variant       array [
         dict entry(
            string "Method"
            variant                string "dhcp"
         )
         dict entry(
            string "Address"
            variant                string "10.0.2.15"
         )
         dict entry(
            string "Netmask"
            variant                string "255.255.255.0"
         )
         dict entry(
            string "Gateway"
            variant                string "10.0.2.2"
         )
      ]

Capture of object in memory

Solution

  • FIGURED IT OUT!

    In my XML file the signal I am watching for is: 

      <signal name="PropertyChanged">
     <arg name="name" type="s" />
     <arg name="value" type="v" />
  </signal>

    And as much as I am trying to figure out why the example callback function on freedesktop.org is in reverse I had to modify the following: 

    static void on_manager_properties_changed (
                       GDBusProxy          *proxy,
                       GVariant            *changed_properties,
                       const gchar* const  *invalidated_properties,
                       gpointer             user_data);

    to:

    static void on_manager_properties_changed (
                       GDBusProxy          *proxy,
                       const gchar* const  *invalidated_properties, //(name)
                       GVariant            *changed_properties, //(value)
                       gpointer             user_data);

    So that the type='s' came before the type='v' in the callback function. After that, everything was good. I think maybe whatever signal freedesktop's example was watching, might have been a different element of information than what I was going for.