ØMQ/2.2 - The Guide

//
// Freelance client - Model 1
// Uses REQ socket to query one or more services
//
#include "czmq.h"

#define REQUEST_TIMEOUT 1000
#define MAX_RETRIES 3 // Before we abandon

static zmsg_t *
s_try_request (zctx_t *ctx, char *endpoint, zmsg_t *request)
{
printf ("I: trying echo service at %s…\n", endpoint);
void *client = zsocket_new (ctx, ZMQ_REQ);
zsocket_connect (client, endpoint);

// Send request, wait safely for reply
zmsg_t *msg = zmsg_dup (request);
zmsg_send (&msg, client);
zmq_pollitem_t items [] = { { client, 0, ZMQ_POLLIN, 0 } };
zmq_poll (items, 1, REQUEST_TIMEOUT * ZMQ_POLL_MSEC);
zmsg_t *reply = NULL;
if (items [0].revents & ZMQ_POLLIN)
reply = zmsg_recv (client);

// Close socket in any case, we're done with it now
zsocket_destroy (ctx, client);
return reply;
}

// The client uses a Lazy Pirate strategy if it only has one server to talk
// to. If it has 2 or more servers to talk to, it will try each server just
// once:

int main (int argc, char *argv [])
{
zctx_t *ctx = zctx_new ();
zmsg_t *request = zmsg_new ();
zmsg_addstr (request, "Hello world");
zmsg_t *reply = NULL;

int endpoints = argc - 1;
if (endpoints == 0)
printf ("I: syntax: %s <endpoint> …\n", argv [0]);
else
if (endpoints == 1) {
// For one endpoint, we retry N times
int retries;
for (retries = 0; retries < MAX_RETRIES; retries++) {
char *endpoint = argv [1];
reply = s_try_request (ctx, endpoint, request);
if (reply)
break; // Successful
printf ("W: no response from %s, retrying…\n", endpoint);
}
}
else {
// For multiple endpoints, try each at most once
int endpoint_nbr;
for (endpoint_nbr = 0; endpoint_nbr < endpoints; endpoint_nbr++) {
char *endpoint = argv [endpoint_nbr + 1];
reply = s_try_request (ctx, endpoint, request);
if (reply)
break; // Successful
printf ("W: no response from %s\n", endpoint);
}
}
if (reply)
printf ("Service is running OK\n");

zmsg_destroy (&request);
zmsg_destroy (&reply);
zctx_destroy (&ctx);
return 0;
}