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From Rajith Attapattu <rajit...@gmail.com>
Subject Address validation Queues vs Topics
Date Tue, 28 Feb 2012 04:30:12 GMT
As per the discussion on QPID-792, I'm moving the discussion onto the
dev list under.
I have attempted to summarise the current behaviour and some of the
comments expressed by Rob and Robbie.

Currently the clients (C++, python and JMS) resolves an address (with
the 0-10 protocol) as follows.

1. If the name resolves to a queue, we treat it as a Queue
2. If the name resolves to an exchange, we treat is a Topic
3. If it doesn't resolve to either, we treat it as a Queue.

Rob made the following comments
"I don't think that we should be trying to do this because I'm pretty
sure that it is impossible to determine what is a Queue and what is a
Topic.

I think the closest we can come is to say that an address that says
you have to create a new temporary auto-delete exclusive queue for
every consumer should be treated as a topic... but the converse is not
true. As far as I am concerned the distinction between Queue and Topic
is something that only the "administrator" can determine, and the code
cannot determine dynamically."

Robbie also expressed the following,
"I also think that the (Java) client shouldnt be making gueses as to
whether something is a Queue or a Topic, as I'm sure was fairly
evident from previous mailings on the subject last year. If that
questionable behaviour is causing pain, then we should at least
consider simply not doing it. Destination is itself only the parent
interface of Queue and Topic, it doesnt actually offer any methods
(even the toString, though for backwards compatibility reasons
admitedly) and really only serves to allow creating Topic and Queue
consumers etc without having to have a specific Session type. I
realise forcing users to specify queue or topic in the address string
wouldnt be consistent with the other clients, but I do think its worth
noting that the Java client isn't entirely consistent with the other
clients for obvious reasons and trying to make it more so isnt
necessarily always going to be a helpful or useful thing."

Rob, further states that we could utilize the queue and topic
qualifiers that is currently present in our JNDI mechanism.
"I don't think the queue/topic distinction even needs to go into the
address - it should only needs to be defined some way in the JNDI
source

e.g. in a properties file then things that begin

queue.<NAME>=<address string>

would be queues, and

topic.<NAME>=<address string>

would be topics"

Regards,

Rajith

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