ZeroMq IRC Log

Monday August 2, 2010

[Time] Name	Message
[03:23] indygreg	I have a client-server model where a stateless server receives a request from a client. But instead of a single response message, I'd like the server to send multiple response messages. I'm seeking advice for the best way to do this in 0MQ.
[03:24] indygreg	I tried ZMQ_REP/ZMQ_REP sockets with sending a multipart response message, but it appears the message parts are being buffered
[03:25] indygreg	as far as I can tell, the only other solution is to open a new PUB socket on the server and instruct the client how to connect to it. is there a better way?
[05:43] sustrik	indygreg: use XREQ/XREP sockets
[05:51] sustrik	even better, use multi-part messages
[05:53] indygreg	sustrik: I was using multi-part messages but it appears the entire message is being buffered. I'm looking to send a long-running (over hours) stream of messages
[05:53] sustrik	then use XREQ/XREP
[05:55] indygreg	I'm relatively new to 0MQ - is there documentation on XREQ/XREP vs REQ/REP? I've seen them mentioned here and there but can't find a concise description
[05:56] sustrik	nope, the documentation is missing yet
[05:56] sustrik	xreq/xrep is similar to req/rep but doesn't require strictly alternate sequence of reqs and reps
[05:57] sustrik	otoh, you'll have to do a bit of routing by hand
[05:57] indygreg	ahh - sounds just what I'm looking for
[05:57] sustrik	REQ socket prepends an empty message part (bottom of the backtrace stack) to each message you send. It also removes the empty message part from the beginning of each message you receive.
[05:57] sustrik	REP socket stores all the message parts up to the first empty message part when you receive and passes the rest to the user. When message is sent, it prepends the saved backtrace stack to the message.
[05:57] sustrik	XREQ does basically nothing but load balances the sent messages and fair queues the received messages.
[05:57] sustrik	XREP prepends a message part containing peer's identity to each received message. It also chops of the first message part from every sent message and uses that as a routing info to find out which peer the message should be sent to.
[05:58] indygreg	interesting. I'll definitely take a look. thanks for the pointer
[06:54] indygreg	well, that was easy: just capture the first message part of a XREQ request and send it out as the first message part in the response
[06:59] sustrik	yes
[16:13] Balistic	Can one create a SUB socket, then bind it and have a PUB socket connect to it?
[16:26] sustrik	yes
[16:27] Balistic	hmm, so far I cant get it to work. Having a SUB connecting to a PUB works fine, but not the other way round.
[16:27] sustrik	?
[16:27] sustrik	what's goign wrong?
[16:28] Balistic	recv() on the SUB side never returns, even though I can see the packets of messages via wireshark
[16:29] sustrik	is that on TCP?
[16:29] Balistic	yea
[16:29] Balistic	btw, this is with pyzmq also
[16:29] sustrik	have you subscribed btw?
[16:29] Balistic	yea, to ''
[16:29] Balistic	ie emtpy string
[16:30] sustrik	strange
[16:30] sustrik	report it as a bug then
[16:30] Balistic	ill try with the c lib and see if it does the same
[16:30] sustrik	please, do
[16:30] sustrik	when reporting the bug, attach your test prog
[16:31] Balistic	anycase, what im trying todo is write a basic 'hub' that will relay messages of clients to each other. there isnt anything like that atm?
[16:34] sustrik	check the zmq_forwarder device
[16:34] Balistic	i saw it, but there are little docs for it
[16:34] sustrik	http://github.com/zeromq/zeromq-chat/blob/master/README
[16:35] Balistic	heh, i think ill go read the source also
[16:36] sustrik	have a look :)
[16:36] Balistic	ta
[16:36] sustrik	it's ~5 lines long :)
[17:27] Balistic	sustrik: found my problem. my sender would exit immediatly after doing .send(). adding a slight delay before exiting solved the problem
[23:27] zmqserverQ	HI
[23:27] zmqserverQ	where is zmq_server?i can find it
[23:27] zmqserverQ	thinks