[Standards] XEP-107 and XEP-108: Empty Value?

Florian Zeitz florian.zeitz at gmx.de
Mon May 5 00:30:39 UTC 2008

Hash: SHA1

Stephan Maka wrote:
> No, I think the missing part is that only some PEP extensions include
> an empty variant of their XML representation to reset the indicated
> event node. There is a fine »Delete And Notify« request in section
> of XEP-0060 (Publish-Subscribe), but no PEP XEP is using it,
> although it is the generic PubSub way of retracting an item.
Actually no PEP extension includes an empty variant of their XML
representation. The only PEP extension that has an empty variant defines
it to mean "I have stopped music playback" and not "I'm not sending you
information any more".
PEP XEPs don't have to "use" anything specifically they can just rely on
what is defined in XEP-0163. Item retracting isn't really needed see below.

>> But I don't know why you think it is optional. XEP-0163 says a PEP
>> service MUST implement it. I think client implementations should
> From http://www.xmpp.org/extensions/xep-0163.html#defaults
> | 5. Recommended Defaults
> | 
> | A PEP service MUST:
> | 
> |     * Support the node discovery, node creation, node deletion,
> |       publish item, subscribe, unsubscribe, and item retrieval use
> |       cases specified in XEP-0060.
> node deletion:
>     http://www.xmpp.org/extensions/xep-0060.html#owner-delete
Yes I confused node deletion and item retraction somehow. I'm sorry

> Yip, and this should be specified. Gajim trunk is sensible to the
> currently-specified empty element event.
Yes it is, and that actually is wrong.
Only XEP-0118 (User Tune) actually defines an empty element event. All
others don't, but Gajim reacts to empty elements and actually sends them
to for all the XEPs it supports (Tune, Activity and Mood).

As far as I can tell there are currently 3 behaviors as far as
retracting information:
1. Send an item retraction as defined in of XEP-0060 (PubSub)
This is what Miranda and Psi do.
It's bad because not all implementations support it and supporting it is
not required in XEP-0163 (PEP).

2. Send empty elements
Gajim does this if you turn off sending events.

3. Don't allow it
Gajim and Pidgin don't offer the possibility to retract information in
the UI. Gajim as mentioned above sends empty elements if you turn
sending PEP events off completely, but otherwise it does nothing.

My proposed solution:
What XEP-0163 (PEP) does require is node deletion. For some reason no
implementation I know off does support this, but IMHO it is actually the
way to go.
PEP has the concept of one node per namespace, so to retract information
from a certain PEP extension you just have to delete the node with it's
namespace as name.

This has two benefits.
1. Theoretically every implementation supports it as it is required by
2. You don't have to specify notify="1" to make it work, as is the case
for <retract/> (Well maybe not really a benefit but something I stumbled
over ;) )

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