When we were implementing the MQ Light broker, we wanted to be able to support sharing of subscriptions across a group of clients - in particular for the worker offload scenario. At the time we were unable to find guidance in the specification or extensions thereof, so we went ahead with encoding this into the terminus addresses of an attach. Using a `private:` prefix to denote an exclusive subscription, and `share:sharename` to indicate a shared one.
i.e., -> @attach(18) [name="share:sharename:topicname", handle=0, role=true, snd-settle-mode=0, rcv-settle-mode=0, source=@source(40) [address="share:sharename:topicname", durable=0, timeout=0, dynamic=false], target=@target(41) [address="share:sharename:topicname", durable=0, timeout=0, dynamic=false], initial-delivery-count=0] vs -> @attach(18) [name="private:topicname", handle=0, role=true, snd-settle-mode=0, rcv-settle-mode=0, source=@source(40) [address="private:topicname", durable=0, timeout=0, dynamic=false], target=@target(41) [address="private:topicname", durable=0, timeout=0, dynamic=false], initial-delivery-count=0] The other day I happened to notice that the qpid-cpp broker also supports a similar functionality since https://issues.apache.org/jira/browse/QPID-4917 / https://github.com/apache/qpid/commit/d4dafd3 - and it does this by supporting a capability of 'shared' on the exchange, and expecting a client @attach to request this capability, whereupon the link-name is used as-is for the name of the share. I wasn't able to find this behaviour documented any further than that, and it wasn't clear to me what the behaviour should be for the various scenarios. Ideally we'd like to conform to a common standard. Does anyone know if there were any plans to register this (or another) shared subscription behaviour with the working group as an extension? -- Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
