ZeroMQ pub-sub send last message to new subscribers

Question

Can ZeroMQ Publisher Subscriber sockets be configured so that a newly-connected client always receive last published message (if any)?

What am I trying to do: My message is a kind of system state so that new one deprecates previous one. All clients has to have current states. It works for already connected clients (subscribers) but when the new subscriber appears it has to wait for a new state update that triggers a new message. Can I configure PubSub model to send the state to the client immediately after connection or do I have to use a different model?

Answer 1

There is an example in the ZMQ guide called Last Value Caching. The idea is to put a proxy in between that caches the last messages for each topic and forwards it to new subscribes. It uses an XPUB instead of a PUB socket to react on new connections.