Yes, with AMQP 0-10, the only time a producer indicates the destination of the
message is when it actually sends the message. The message.transfer command
includes the destination of the message, which is an exchange. A producer may
send to various exchanges, simply by changing the destination in the
message.transfer command with each message. As a result, from the broker's
perspective, there's not really any way to look at a producer client and
determine which exchange(s) it's sending to.
Thanks Andy that kind of makes sense.
I think that part of the confusion might stem from some of the higher
level APIs, I've only really used JMS and qpid::messaging (I've steered
well clear of qpid::client as recommended by Gordon and several others
and I know plenty of people who've been bitten by qpid::client which
makes me glad I did :-)).
So for qpid::messaging and JMS the model tends to be that one creates a
connection, then one creates a session and in general in qpid::messaging
one would create Senders specifying an address and in JMS similarly one
would create a MessageProducer. So I guess that it's fairly easy to
*assume* that the address (which in the case of a producer could just be
the exchange name for something like amq.match) is associated with the
Connection/Session.
if you normally do:
connection.open();
Session session = connection.createSession();
Sender sender = session.createSender("amq.match");
........
sender.send(message);
.........
it's easy to fall into that trap.
I guess that the alternate send which actually takes an address (e.g.
the JMS MessageProducer |*send
<http://docs.oracle.com/javaee/5/api/javax/jms/MessageProducer.html#send%28javax.jms.Destination,%20javax.jms.Message%29>*(Destination
<http://docs.oracle.com/javaee/5/api/javax/jms/Destination.html> destination,
Message
<http://docs.oracle.com/javaee/5/api/javax/jms/Message.html> message)| )
is a closer analogue to the underlying AMQP message.transfer I guess
that the higher level abstraction just acts as a cache for the real AMQP
destinations.
Thanks again Andy I think that your explanation has helped clarify in my
mind the transient association between Connection and Exchange even
though I suspect in practice the vast majority of producer code is
likely to be written in a way that retains what looks like a more
sustained association, but that's only in the client runtime not in the
broker.
Frase.
