[systemd-devel] sd-bus: ObjectManager difference with gdbus

[David Härdeman]

On Thu, Apr 20, 2017 at 02:19:22PM +0200, David Herrmann wrote:
>On Thu, Apr 20, 2017 at 12:06 PM, David Härdeman <david at hardeman.nu> wrote:
>> Hi,
>>
>> I'm implementing a server which creates an ObjectManager using the
>> sd-bus API and there seems to be some differences between how gdbus and
>> sd-bus implements the API.
>>
>> I implemented a simple ObjectManager at /org/gnome/TestManager which
>> exports objects /org/gnome/TestManager/fooX with interface
>> org.gnome.TestManager.Device.
>>
>> Under sd-bus, if an object is removed, the following signal is
>> generated:
>>
>> signal time=1492642227.714223 sender=:1.104 -> destination=(null destination)
>>         serial=90 path=/org/gnome/TestManager;
>>         interface=org.freedesktop.DBus.ObjectManager;
>>         member=InterfacesRemoved
>>    object path "/org/gnome/TestManager/foo0"
>>    array [
>>       string "org.freedesktop.DBus.Peer"
>>       string "org.freedesktop.DBus.Introspectable"
>>       string "org.freedesktop.DBus.Properties"
>>       string "org.freedesktop.DBus.ObjectManager"
>>       string "org.gnome.TestManager.Device"
>>    ]
>>
>> If I implement the same simple server in gdbus, the signal is instead:
>>
>> signal time=1492642227.714223 sender=:1.104 -> destination=(null destination)
>>         serial=90 path=/org/gnome/TestManager;
>>         interface=org.freedesktop.DBus.ObjectManager;
>>         member=InterfacesRemoved
>>    object path "/org/gnome/TestManager/foo0"
>>    array [
>>       string "org.gnome.TestManager.Device"
>>    ]
>>
>> The corresponding signals are also generated when an object is added.
>>
>> Beside simply being different, this difference seems to confuse gdbus.
>> If I create a test client, it will report that any object which is
>> already existing when I start the client has 1 interface and any object
>> which is added/removed subsequently is reported as having 5 interfaces,
>> 4 of which are nameless (this would appear to be one or more gdbus
>> bug(s)).
>>
>> This bug in gdbus also means that it doesn't correctly catch the removal
>> of an object which existed at the time the client was started (because
>> of the interface count mismatch).
>>
>> Anyway, gdbus bugs aside, it seems that the interfaces reported by
>> sd-bus should match what gdbus does? (assuming, of course, that gdbus
>> can be considered the "reference" implementation).
>
>Does the appended patch fix your issue?
>(line-breaks might be screwed, sorry)

Haven't tried it yet, but just from reading the patch...it seems to do
the opposite of what I'd expect? I.e. add *more* interfaces?

>diff --git a/src/libsystemd/sd-bus/bus-objects.c
>b/src/libsystemd/sd-bus/bus-objects.c
>index 9bd07ffca..b6f5afe1b 100644
>--- a/src/libsystemd/sd-bus/bus-objects.c
>+++ b/src/libsystemd/sd-bus/bus-objects.c
>@@ -1057,6 +1057,22 @@ static int object_manager_serialize_path(
>                         if (r < 0)
>                                 return r;
>
>+                        r = sd_bus_message_append(reply, "{sa{sv}}",
>"org.freedesktop.DBus.Peer", 0);
>+                        if (r < 0)
>+                                return r;
>+
>+                        r = sd_bus_message_append(reply, "{sa{sv}}",
>"org.freedesktop.DBus.Introspectable", 0);
>+                        if (r < 0)
>+                                return r;
>+
>+                        r = sd_bus_message_append(reply, "{sa{sv}}",
>"org.freedesktop.DBus.Properties", 0);
>+                        if (r < 0)
>+                                return r;
>+
>+                        r = sd_bus_message_append(reply, "{sa{sv}}",
>"org.freedesktop.DBus.ObjectManager", 0);
>+                        if (r < 0)
>+                                return r;
>+
>                         found_something = true;
>                 }

-- 
David Härdeman