如何使用ZeroMq实现异步即时消息聊天

Question

Approach

I'm building an asynchronous IM/chat application with ZeroMq, just as a learning exercise, using the following approach.

The server uses two ROUTER sockets, similar to lbbroker.java , reading from incoming and writing to outgoing , while manipulating the envelope for delivery to the intended receiver.

Clients set a unique identity with socket.setIdentity() , and use PULL and PUSH sockets, instead of REQ/REP, for sending and receiving chat messages asynchronously. I've built and tested the code, everything appears to work fine.

Questions

• Is the use of PUSH/PULL with ROUTER a valid approach?

• Why do chat clients become unreachable when dropping off then reconnecting?

Sally becomes unreachable if she disconnects then reconnects, she can no longer receives chat messages. After debugging the server, I confirmed it's definitely sending messages with the correct envelope to sally. I also used outgoing.setRouterMandatory(true) to ensure unaddressable messages weren't being dropped by the server, but no errors got raised.

Answer 1

After further research, while PUSH and PULL sockets work with ROUTER, they are not valid socket combinations as per the ZeroMq spec.

A DEALER socket on the client side is a better approach. DEALER supports bidirectional message transfer, basically doing the job of PUSH and PULL but with a single socket.

I started a thread on Github discussing the issue, it includes some sample code for agent-based pattern using DEALER.

https://github.com/zeromq/jeromq/issues/81