CZMQ Manual - CZMQ/4.0.2


zbeacon - LAN discovery and presence


//  Create new zbeacon actor instance:
//      zactor_t *beacon = zactor_new (zbeacon, NULL);
//  Destroy zbeacon instance:
//      zactor_destroy (&beacon);
//  Enable verbose logging of commands and activity:
//      zstr_send (beacon, "VERBOSE");
//  Configure beacon to run on specified UDP port, and return the name of
//  the host, which can be used as endpoint for incoming connections. To
//  force the beacon to operate on a given interface, set the environment
//  variable ZSYS_INTERFACE, or call zsys_set_interface() before creating
//  the beacon. If the system does not support UDP broadcasts (lacking a
//  workable interface), returns an empty hostname:
//      //  Pictures: 's' = C string, 'i' = int
//      zsock_send (beacon, "si", "CONFIGURE", port_number);
//      char *hostname = zstr_recv (beacon);
//  Start broadcasting a beacon at a specified interval in msec. The beacon
//  data can be at most UDP_FRAME_MAX bytes; this constant is defined in
//  zsys.h to be 255:
//      //  Pictures: 'b' = byte * data + size_t size
//      zsock_send (beacon, "sbi", "PUBLISH", data, size, interval);
//  Stop broadcasting the beacon:
//      zstr_sendx (beacon, "SILENCE", NULL);
//  Start listening to beacons from peers. The filter is used to do a prefix
//  match on received beacons, to remove junk. Note that any received data
//  that is identical to our broadcast beacon_data is discarded in any case.
//  If the filter size is zero, we get all peer beacons:
//      zsock_send (beacon, "sb", "SUBSCRIBE", filter_data, filter_size);
//  Stop listening to other peers
//      zstr_sendx (beacon, "UNSUBSCRIBE", NULL);
//  Receive next beacon from a peer. Received beacons are always a 2-frame
//  message containing the ipaddress of the sender, and then the binary
//  beacon data as published by the sender:
//      zmsg_t *msg = zmsg_recv (beacon);
//  This is the zbeacon constructor as a zactor_fn:
    zbeacon (zsock_t *pipe, void *unused);

//  Self test of this class
    zbeacon_test (bool verbose);
Please add '@interface' section in './../src/zbeacon.c'.


The zbeacon class implements a peer-to-peer discovery service for local networks. A beacon can broadcast and/or capture service announcements using UDP messages on the local area network. This implementation uses IPv4 UDP broadcasts. You can define the format of your outgoing beacons, and set a filter that validates incoming beacons. Beacons are sent and received asynchronously in the background.

This class replaces zbeacon_v2, and is meant for applications that use the CZMQ v3 API (meaning, zsock).


From zbeacon_test method

// Test 1 - two beacons, one speaking, one listening
// Create speaker beacon to broadcast our service
zactor_t *speaker = zactor_new (zbeacon, NULL);
assert (speaker);
if (verbose)
 zstr_sendx (speaker, "VERBOSE", NULL);

zsock_send (speaker, "si", "CONFIGURE", 9999);
char *hostname = zstr_recv (speaker);
if (!*hostname) {
 printf ("OK (skipping test, no UDP broadcasting)\n");
 zactor_destroy (&speaker);
 free (hostname);
free (hostname);

// Create listener beacon on port 9999 to lookup service
zactor_t *listener = zactor_new (zbeacon, NULL);
assert (listener);
if (verbose)
 zstr_sendx (listener, "VERBOSE", NULL);
zsock_send (listener, "si", "CONFIGURE", 9999);
hostname = zstr_recv (listener);
assert (*hostname);
free (hostname);

// We will broadcast the magic value 0xCAFE
byte announcement [2] = { 0xCA, 0xFE };
zsock_send (speaker, "sbi", "PUBLISH", announcement, 2, 100);
// We will listen to anything (empty subscription)
zsock_send (listener, "sb", "SUBSCRIBE", "", 0);

// Wait for at most 1/2 second if there's no broadcasting
zsock_set_rcvtimeo (listener, 500);
char *ipaddress = zstr_recv (listener);
if (ipaddress) {
 zframe_t *content = zframe_recv (listener);
 assert (zframe_size (content) == 2);
 assert (zframe_data (content) [0] == 0xCA);
 assert (zframe_data (content) [1] == 0xFE);
 zframe_destroy (&content);
 zstr_free (&ipaddress);
 zstr_sendx (speaker, "SILENCE", NULL);
zactor_destroy (&listener);
zactor_destroy (&speaker);

// Test subscription filter using a 3-node setup
zactor_t *node1 = zactor_new (zbeacon, NULL);
assert (node1);
zsock_send (node1, "si", "CONFIGURE", 5670);
hostname = zstr_recv (node1);
assert (*hostname);
free (hostname);

zactor_t *node2 = zactor_new (zbeacon, NULL);
assert (node2);
zsock_send (node2, "si", "CONFIGURE", 5670);
hostname = zstr_recv (node2);
assert (*hostname);
free (hostname);

zactor_t *node3 = zactor_new (zbeacon, NULL);
assert (node3);
zsock_send (node3, "si", "CONFIGURE", 5670);
hostname = zstr_recv (node3);
assert (*hostname);
free (hostname);

zsock_send (node1, "sbi", "PUBLISH", "NODE/1", 6, 250);
zsock_send (node2, "sbi", "PUBLISH", "NODE/2", 6, 250);
zsock_send (node3, "sbi", "PUBLISH", "RANDOM", 6, 250);
zsock_send (node1, "sb", "SUBSCRIBE", "NODE", 4);

// Poll on three API sockets at once
zpoller_t *poller = zpoller_new (node1, node2, node3, NULL);
assert (poller);
int64_t stop_at = zclock_mono () + 1000;
while (zclock_mono () < stop_at) {
 long timeout = (long) (stop_at - zclock_mono ());
 if (timeout < 0)
 timeout = 0;
 void *which = zpoller_wait (poller, timeout * ZMQ_POLL_MSEC);
 if (which) {
 assert (which == node1);
 char *ipaddress, *received;
 zstr_recvx (node1, &ipaddress, &received, NULL);
 assert (streq (received, "NODE/2"));
 zstr_free (&ipaddress);
 zstr_free (&received);
zpoller_destroy (&poller);

// Stop listening
zstr_sendx (node1, "UNSUBSCRIBE", NULL);

// Stop all node broadcasts
zstr_sendx (node1, "SILENCE", NULL);
zstr_sendx (node2, "SILENCE", NULL);
zstr_sendx (node3, "SILENCE", NULL);

// Destroy the test nodes
zactor_destroy (&node1);
zactor_destroy (&node2); zactor_destroy (&node3);


The czmq manual was written by the authors in the AUTHORS file.


Main web site:

Report bugs to the email <gro.qmorez.stsil|ved-qmorez#gro.qmorez.stsil|ved-qmorez>


Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for ØMQ: http://czmq.zeromq.org. This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/. LICENSE included with the czmq distribution.