[jdev] Cancelling an iq query

[Ralph Meijer]

On Mon, Aug 29, 2005 at 08:12:09PM +1000, Trejkaz wrote:
> On Mon, 29 Aug 2005 19:31, Ralph Meijer wrote:
> > On Sun, Aug 28, 2005 at 11:42:25AM -0700, Ralph Giles wrote:
> > > I'd like to collect suggestions for "cancelling" an in-process iq
> > > transaction.
> >
> > I would also go with a similar approach as yours. An <iq/> for the
> > transaction request and a <message/> with the results when the
> > transaction is completed. The two then matched up by a application
> > specific handle. There is no generic solution to the pattern you
> > describe, yet.
> 
> The difficulty with that approach, of course, is that it can't possibly with 
> with existing, standard IQ queries.  I don't suppose we need some kind of <iq 
> type='cancel'/> where you pass the same ID of the query you want to cancel...

Ehm, yes, that's what Ralph en Ralph said. There is no generic solution,
so far, but you could do this like:

Client sends request:

<iq from='client at example.com/client'
    to='service.example.com'
    type='set' id='H_2'>
  <transaction xmlns='http://example.com/transaction'>
    <query id='query_5'>
      ...
    </query>
  </transaction>
</iq>

Service responds with "Ok, I'm doing this":

<iq from='service.example.com'
    to='client at example.com/client'
    type='result' id='H_2'/>

And, then when the result is done:

<message from='service.example.com'
         to='client at example.com/client'>
  <results xmlns='http://example.com/transaction#results' id='query_5'>
    ...
  </results>
</message>

If you want to cancel in the middle of processing you can just send:

<iq from='client at example.com/client'
    to='service.example.com'
    type='set' id='H_3'>
  <transaction xmlns='http://example.com/transaction'>
    <cancel id='query_5'/>
  </transaction>
</iq>

Yielding:

<iq from='service.example.com'
    to='client at example.com/client'
    type='result' id='H_3'/>

or in case of an error (nicely annotated with a machine readable
construct and a diagnostic text for humans):

<iq from='service.example.com'
    to='client at example.com/client'
    type='error' id='H_3'>
  <transaction xmlns='http://example.com/transaction'>
    <cancel id='query_5'/>
  </transaction>
  <error type='cancel'>
    <item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    <completed xmlns='http://example.com/transaction#error'/>
    <text xmlns='urn:ietf:params:xml:ns:xmpp-stanzas' xml:lang='en'>
      The referenced query has already been completed and cannot be
      cancelled.
    </text>
  </error>
</iq>

-- 
Groetjes,

ralphm