Should GetManagedObjects include the current path?

[John Mercouris]

Hi Rony,

that's a bug with Firefox, and not related to DBus, nor this mailing
list. Simply use a different browser to print your document.

-- 
-John

> Trying to print the "https://dbus.freedesktop.org/doc/dbus-api-design.html" document you supplied
> using the latest Firefox 69.0.3 (64-bit) on Windows, but get the first page only!
>
> Please advise what to do in order to become able to print the entire document (did not find a
> "print" menu on the page that would render the text in a printable form either).
>
> ---rony
>
>
> On 21.10.2019 15:09, Simon McVittie wrote:
>> On Sat, 19 Oct 2019 at 22:18:26 +0200, David Henningsson wrote:
>>> Suppose we have two paths, /hello and /hello/world, where /hello implements
>>> org.freedesktop.DBus.ObjectManager. When GetManagedObjects is called on
>>> /hello, should it return data for both /hello and /hello/world, or just
>>> /hello/world?
>> I would expect just /hello/world, because ObjectManager is designed
>> for situations where a service manages a collection of similar objects
>> (windows, documents, pictures, communication channels, whatever). If
>> /hello is conceptually a "document manager" that manages a collection of
>> documents, then /hello is probably not itself a document, so it should
>> not usually list itself as a child.
>>
>> This might help:
>> https://dbus.freedesktop.org/doc/dbus-api-design.html#interface-object-manager
>>
>>>  - When calling AddMatch, the "path_namespace" in the example a few lines
>>> below is written so that it does include the path itself
>> If you are interested in the objects managed by the object manager, you
>> also need to pay attention to signals emitted by the object manager itself,
>> because newly created objects are signalled by InterfacesAdded from the
>> object manager, and deleted objects are signalled by InterfacesRemoved
>> from the object manager.
>>
>> Also, in general signal subscription is designed so that it is harmless
>> to receive and ignore signals that you weren't expecting (minimizing
>> the signals you receive is a good performance and power consumption
>> optimization, but is not strictly required). If your process contains more
>> than one D-Bus client sharing a connection, you will in fact be receiving
>> the union of all the signals requested by any of those D-Bus clients.
>>
>> Some past D-Bus implementations have even used bloom filters (a
>> probabilistic data structure) instead of an exact data structure for
>> signal matching, which means you are guaranteed to receive all the signals
>> you subscribed to, but you also receive a small number of signals that
>> you didn't subscribe to.
>>
>>>  - The last part is not true for the root path "/", because if ObjectManager
>>> is implemented on "/", then "/" + "/" = "//" so this needs special handling
>> Yes, that's true. But D-Bus API designers probably shouldn't do this
>> anyway, because if one API (let's say "document manager") says "/" is
>> an ObjectManager for a collection of document objects, and another API
>> (let's say "communication channel manager") says "/" is an ObjectManager
>> for a collection of communication channels, and you are writing a
>> document-sharing service that uses both documents and communication
>> channels, then you're stuck. The closest you can get to implementing
>> both APIs correctly is that clients that try to list either documents
>> or communication channels get a list containing both, which is not what
>> they will be expecting.
>>
>> Normally you would implement "document manager" at an entry-point object
>> path like /com/example/DocumentManager1, "communication channel manager"
>> at /net/example/ChannelManager1, and so on (where the reversed domain
>> name like example.com belongs to the designer of each API). Each path
>> describes its own collection of objects and they do not collide.
>>
>> If you use GNOME, you can see this by inspecting GNOME Shell in d-feet:
>> it implements many D-Bus interfaces, which can easily coexist because
>> none of them are on "/".
>>
>> See https://dbus.freedesktop.org/doc/dbus-api-design.html#naming-conventions
>> and https://dbus.freedesktop.org/doc/dbus-api-design.html#api-versioning
>> for more on this topic.
>>
>>     smcv
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