[zeromq-dev] Need help with Request-Reply Message Broker

[Chernyshev Vyacheslav]

Hello.

I'm currently trying to use zeromq as a message-passing layer in a 
single process to deliver messages from clients to worker threads that 
represent a single service. Each client's request results in either 0 or 
1 reply from server. After reading the guide I still have something 
unclear. As I understood, in case of REQ-REP message broker, we have 
fully synchronous communication between clients and worker threads, that 
means handling of one message at a time and sending empty replies in 
some cases just to keep REQ socket happy. In case of ROUTER-DEALER 
solutions we have fully asynchronous communication, where messages from 
single client are processed in arbitrary order. But what should I do if 
I want to ensure that messages from client are processed in the same 
order they are received without rolling back to single message at a time?

I think that I can "fake" what I want using multipart messages and 
REQ-REP message broker. As clients communicate with server using a 
custom protocol on top of TCP, I still have to parse packets from 
clients without zeromq's help, so I can buffer these packets and send 
them all as a single multipart zeromq message. After worker replies 
back, I'll send everything that was buffered while worker was busy, and 
this cycle is repeated. But may be there is a cleaner way to "tell" 
zeromq to buffer requests from clients and drain everything that was 
buffered when worker can accept its work.

Thanks in advance.