Hello!
I need a simple request/response interaction, though I am not happy with
ZMQ_REQ/ZMQ_REP pattern.
The main reason is it is unclear what I supposed to do if a response from a
server is delayed or lost.
Do we have an example covers e.g. reopening the socket in this case?
Is it reasonable to look into XREQ/XREQ direction to have the reliability
problem addressed?
Converting the simplest REQ/REP example to XREP/XREP, I've found out it crashes
with
"Assertion failed: msg_->flags & ZMQ_MSG_MORE (xrep.cpp:146)".
To keep the ball rolling, I've added extra recv (after getsockopt with
ZMQ_RCVMORE) and
extra send with ZMQ_SNDMORE at ZMQ_XREP side, so my server looks like
==
// Initialise 0MQ context with one I/O thread
zmq::context_t ctx (1);
// Create a ZMQ_REP socket to recieve requests and send replies
zmq::socket_t s (ctx, ZMQ_XREP);
s.bind("tcp://*:23001");
{
zmq::message_t msg_req_head;
int ret = s.recv(&msg_req_head);
int64_t more = 0;
size_t more_size = sizeof more;
s.getsockopt(ZMQ_RCVMORE, &more, &more_size);
std::cout << "received:" <<
std::string((const char*)msg_req_head.data(), msg_req_head.size()) <<
", more=" << more <<
", ret=" << ret << std::endl;
if (more)
{
zmq::message_t msg_req;
int ret = s.recv(&msg_req);
std::cout << "received (more):" <<
std::string((const char*)msg_req.data(), msg_req.size()) <<
", ret=" << ret << std::endl;
}
char* response_area = (char*) malloc(100);
strcpy(response_area, "this is a response");
zmq::message_t msg_rep(response_area, strlen(response_area) + 1, my_free);
s.send(msg_req_head, ZMQ_SNDMORE);
std::cout << "sent first part" << std::endl;
s.send(msg_rep);
}
==
The questions (besides general REQ/REQ reliability advice request) are if it is
expected 0mq user have to add extra recv/send
and if it is correct to return first part of a message to sender.
Thanks.
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