Robert Godfrey wrote:
To shed some light on the use of the custom property...
It is used to support the notion of getJMSDestination() on a JMSMessage
That is JMS requires us to know the original destination (in JMS terms)
that
the message was sent to, We originally did this by sending the BindingURL
as a long string, however this proved to be very inefficient.
The current solution of sending a byte-encoded representation of the
Destination is still not correct. In general we need to think through the
whole notion of what a destination is in QPID / AMQP.
We probably need a change at the protocol level to ensure that the original
intended destination is included in the header, but for this we need to be
clear on what a destination is. It cannot simply be exchange and routing
key, as we need to consider the case of topologies of brokers wired
together. Thus we need a globally unique destination name to provide
correct equality semantics.
The new message.transfer method (0-9, WIP) has both the exchange and
routing key in it which should at least allow the custom property to be
removed.
I appreciate that the original host should be recorded as well once it
is possible to construct topologies of brokers wired together. Perhaps
we can use a custom (long string) property for that if we need it before
the spec is updated.
In AMQP I think a destination is simply an exchange (on a particular
broker, perhaps in a particular virtual host). However an AMQP
destination and a JMS destination are different things. For JMS purposes
the destination is an AMQDestination (or subclass) instance populated
with the 'correct' settings, which need to be obtainable in some way
from the message.
How we define 'correct' is, as Rajith's mail points out, still a little
open: it could either be the details with which the message was
published or details that would uniquely address the queue from which
the message has been consumed. From a JMS compliance perspective, I'm
not sure that this difference would even be visible. I would lean
towards what Rajith described as the 'publisher's view'.
