[Qgis-developer] Server plugins call order

[Alessandro Pasotti]

Hi,

I'm mostly done with a first highly experimental server plugin implementation.

I would like to hear your opinion about the order of plugin filters call.

The current implementation is the "Observer" pattern described in the
RFC, together with Martin Dobias we decided to start with two filter
hooks:

* requestReady
* responseReady

having the opportunity to alter the parameters (coming from the query
string or soap or whatever) before entering the core services switch,
we can effectively skip it over completely in case of need. For this
reason (and because a raised exception is stored in the request), the
exceptionRaised hook is not necessary anymore.

Plugin filters can be optionally ordered by a "priority" (defaults to
0) and filters with lower priority will run first.

Beside the fact that a filter is not forced to implement both hooks
(and hence it can decide to have requestReady and responseReady
filters with arbitrary priority), my question is if is it better to
invert the priority order on responseReady hook.

This is a common pattern in web applications, where filters are
creating kind of "onion" wrappers or "middleware" (for example in
Django framework).

So, for instance

registerFilter( filter1, 200) # priority 200
registerFilter( filter2, 100) # priority 100

will result in the following calls:

filter2.requestReady
  filter1.requestReady
   core services (if matches)
  filter1.responseReady
filter2.responseReady

I prefer the solution above to the same priority ordering on both hooks:

filter2.requestReady
filter1.requestReady
   core services (if matches)
filter2.responseReady
filter1.responseReady



-- 
Alessandro Pasotti
w3:   www.itopen.it