ZeroMQ pattern query

Question

I want to implement a server/client interaction in C++ using ZeroMQ (http://zeromq.org/).

My requirement is to implement a function where if a client sends a request to the server, the server should send multiple pieces of data (in a sequence) back to the client. The client should be able to repeatedly send the request with the server replying with multiple pieces of data on each request.

ZeroMQ prescribes models like req-res, pub-sub, push-pull, but this does not support my requirement because:

1) Req-rep pattern always expects a return message i.e. it is designed as a combination of send and receive

2) pub-sub and push-pull are unidirectional

Which ZeroMQ pattern would suit my requirement, and also which protocol would be better TCP, PGM, EPGM etc....!

Thank you

Answer 1

Have a look at ZMQ dealer-router architectures: http://www.zeromq.org/tutorials:dealer-and-router

You should be able to address specific clients and not have to adhere to the strict request reply type message flow.

Answer 2

A fully asynchronous approach is as follows.

Client Side

Make your client use a DEALER socket. Connect to your server ROUTER.

When you send a request, send (k, v) where k is a unique (in the context of this client) request key and v is the actual request data for whatever operation you're performing.

Listen for incoming messages on the same DEALER socket. Expect a sequence of messages that look like:

• (k, START)
• (k, (0, 10), A[0..9])
• (k, (10, 8), A[10..17])
• (k, (18, 2), A[18..19])
• (k, END)

Server Side

Make your server use a ROUTER socket. Bind it.

Listen for incoming messages of the form [sender, (k, v)].

Send back a sequence of messages that look something like:

• [sender, (k, START)]
• [sender, (k, (0, 10), A[0..9])]
• [sender, (k, (10, 8), A[10..17])]
• [sender, (k, (18, 2), A[18..19])]
• [sender, (k, END)]

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I'm using square brackets to denote ZMQ multipart messages and parentheses to denote tuples.