[pox-dev] Listeners in class

[Murphy McCauley]

On Nov 6, 2013, at 11:47 AM, AMER <amer7777 at hotmail.com> wrote:

> Hello,
>  
> Thank you, it is OK
> what I did:
>     from pox.openflow.of_json import *
>     core.openflow.addListeners(self)
>     core.openflow.addListenerByName("FlowStatsReceived", self._handle_flowstats_received)
>     def _handle_flowstats_received (self, event)

So if you renamed the method to _handle_FlowStatsReceived, you wouldn't need the specific addListenerByName (the addListeners() call would take care of it).

>  Best regards,
> 
> 
> Eng Amer Alghadhban
> COE
> SANS-GCFW
> CEH, SCNP, CCNA
> 
>  
> Subject: Re: [pox-dev] Listeners in class
> From: murphy.mccauley at gmail.com
> Date: Wed, 6 Nov 2013 10:48:22 -0800
> CC: amer7777 at hotmail.com; pox-dev at lists.noxrepo.org
> To: sul4bh at gmail.com
> 
> On Nov 6, 2013, at 9:39 AM, Sulabh Bista <sul4bh at gmail.com> wrote:
> 
> I don't think there are flow and port status events. I guess these are not 'events' at all and you should fetch them when you require them.
> 
> There are, in fact (mentioned in the Statistics Events section of the manual).  Though you may need to send requests to get them to fire. :)
> 
> On Wed, Nov 6, 2013 at 12:30 PM, Sulabh Bista <sul4bh at gmail.com> wrote:
> Use the event name with proper case as:
> self.addListenersByname("FlowStatsReceived", self._handle_flowstate_received)
> 
> This is good advice.  Also use the correct name, as done here (the original had "flow*state*received" which I think would have raised an exception...).  Adding by name is sometimes convenient, but it's fairly "unstructured".  A safer bet is to actually use the event class itself (addListener(of.FlowStatsReceived, ...)).
> 
> But there's a bigger problem here.  Events are raised by specific objects.  Does "self" raise the FlowStatsReceived event?  Considering it wants to *handle* that event, probably not.  (Continued below.)
> 
> On Wed, Nov 6, 2013 at 9:01 AM, Amer <amer7777 at hotmail.com>wrote:
> Hello,
> 
> I would like to add listeners to flow and port status inl3.learning.py.
> There is a command
> Self.listento(core)
> 
> Sidenote: .listenTo() isn't used much anymore (the version of l3_learning in dart doesn't, for example).  Use .addListenersByName().
> 
> But it is not calling flow or port status function
> 
> It wouldn't.  You're telling it to listen to events on the core object.  Take a look at the events raised by the core object:
> https://github.com/noxrepo/pox/blob/carp/pox/core.py#L177
> 
> None of them have anything to do with OpenFlow.
> 
> I tried with self.addListenersByname("flowstatereceived", self._handle_flowstate_received)
> and without self
> 
> But it is not work
> 
> Coming back to this, your event source here is "self", but this object probably doesn't raise the flow stats event (neither does the core object as mentioned just above).  POX raises OpenFlow events on the OpenFlow nexus (core.openflow) and on individual Connection objects, so you need to listen to those objects.  See:
> https://github.com/noxrepo/pox/blob/carp/pox/openflow/__init__.py#L306
> https://github.com/noxrepo/pox/blob/carp/pox/openflow/of_01.py#L571
> 
> You might want to skim through the "The Event System" and "OpenFlow Events" section of the manual.
> 
> 
> TLDR:
> Examples...
> 
> If you want to listen to all OpenFlow events, name your methods correctly and then use:
> core.openflow.addListeners(self)
> 
> If you want to listen to a specific event on a specific connection with a specific method, try:
> some_connection.addListenerByName("FlowStatsReceived", self._handle_flowstate_received)
> 
> Examples in code (there are many, but here are three at random):
> https://github.com/noxrepo/pox/blob/carp/pox/forwarding/l2_learning.py#L182
> https://github.com/noxrepo/pox/blob/carp/pox/forwarding/l2_learning.py#L86
> https://github.com/noxrepo/pox/blob/carp/pox/forwarding/l2_pairs.py#L85
> 
> 
> Hope  that's helpful.
> 
> -- Murphy

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