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Subject: JMS Destination handling


Hi everyone,

I would like to have a discussion around JMS destination handling in the JMS Mapping for AMQP 1.0, in particular around how to handle JMS Destination names via the AMQP "address" field of a link (producer/consumer) source/target and the "to", and "reply-to" field of messages.

Apologies for the length of the mail, there is a fair bit to outline. I moved some information for full context to the end to help a tiny bit. I didn't use JIRA for this as mentioned on the call yesterday, as I noticed a problem with my account.

JMS defines multiple Destination types that each have their own inherent name space, so it is possible for example to have a Queue and a Topic with the same name (e.g "foo"). AMQP defines an "address" field on the source/target of links (producers/consumers), and a "to" and "reply-to" field are available on messages, to indicate the destination node (e.g queue/topic) address. These are typically string values, and they form a single space since as there is no additional node type information only the address name itself.

This is is mostly an issue for non-temporary Queues and Topics since TemporaryQueue and TemporaryTopic destinations will be given generated addresses by the 'broker' peer through use of dynamic nodes, and so can naturally be prevented from having the same addresses as each other, and be made unlikely or unable to clash with non-temporary nodes.

To handle this mapping between JMS and AMQP it would seem we must either:
1. Not support JMS Queues and Topics with the same name existing at all, OR
2. Allow multiple nodes to have the same address string but use type metadata (via capabilities + annotations, see additional context) to discriminate between them, OR
3. Utilise address string naming conventions (e.g prefixes) for them to separate the types into subspaces.

The first option is an issue for implementations that already do, and wish to continue to, allow Queues and Topics with the same name via other protocols while also supporting AMQP, and would be a limitation in terms of full JMS support. The second option would break reply-to usage for any clients or intermediaries that don't understand the message annotations and/or source+target capabilities carrying type metadata (see additional context). The third option either requires clients to always utilise the full address strings in session.createQueue("<queue-prefix>foo") etc calls, or providing a means to configure the prefixes within the client so that they are added/removed behind the scenes and the application just uses session.createQueue("foo"), but the resulting AMQP address string would be "<queue-prefix>foo". The main issue with requiring clients always use the full address as the session.createQueue(..) value would be for bridging between different systems using different conventions, though the values for those methods are noted as being provider-specific.

Both the old Qpid AMQP 1.0 JMS client, and the new JMS client we are creating that implements the JMS Mapping for AMQP being worked on, currently do some form of the third option, providing a way to configure a 'queue prefix' and 'topic prefix' that are used to prefix the application provided strings in session.createQueue(..) etc for outgoing addresses used for links and messages and be stripped from incoming addresses on messages to give the names used for the JMSDestination and JMSReplyTo objects. Temporary destinations are named by the 'broker' peer and their addresses are used as provided.

The main issue with this approach is that such configuration makes it more difficult to use the client against a number of different brokers, which is a goal, since this configuration is likely to differ between them meaning even the simplest HelloWorld type example may be unable to work against them without additional configuration.

An idea to handle this was to have the brokers use connection properties to inform the client of the prefixes (if any) they require it to use, allowing different brokers to supply their own specific value (if any) to meet their requirements, and allowing clients/simple applications to work against many of them without further configuration change.

An alternative suggestion was to have the JMS Mapping define a set of standard name prefixes the client would use by default, such that the issue of Topics and Queues with the same name is addressed by the mapping, while also allowing brokers to specify their own values via connection properties so that their specific needs can still be met if different (e.g they have existing naming conventions they wish/need to retain).

There was also a suggestion that something beyond a simple prefix may be needed, I will let the person behind those thoughts expand further to stop this getting any longer for now.

Thoughts?

Robbie



Additional Context:

We also need to transmit the destination type information during link (e.g producer/consumer) attachment and on sent messages to ensure we can support the required JMS behaviours (e.g. to indicate we are attaching to a particular type of node, say a queue, and for carrying JMSDestination and JMSReplyTo type on messages to indicate/discover where a message was sent).

For handling these points we are defining the following behaviour:

# During link attachment for producers/consumers:
- Node name carried in source/target "address" field string.
- JMS Destination type represented by capabilities on the source/target (e.g "queue", "topic", "temporary-queue", "temporary-topic").
- Clients can optionally assert on the attach response that the required capabilities exist in the source/target to ensure they have attached to a node that meets their requirements.
- 'Broker' peers can use the capabilities to determine the type of node to create if it is a dynamic node being requested (or if they support auto-creation of non-temporary nodes).

# When sending messages:
- Node names carried in "to" and "reply-to" fields as appropriate.
- JMS Destination type carried in "x-opt-jms-dest" and "x-opt-jms-reply-to" message annotations as a byte.


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