ZBEACON(3)

NAME
zbeacon - LAN discovery and presence

SYNOPSIS

//  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:
CZMQ_EXPORT void
    zbeacon (zsock_t *pipe, void *unused);
//  Self test of this class
CZMQ_EXPORT void
    zbeacon_test (bool verbose);
Please add '@interface' section in './../src/zbeacon.c'.

DESCRIPTION

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).

EXAMPLE

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);
        return;
    }
    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);

AUTHORS

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

RESOURCES

Main web site:

Report bugs to the email <zeromq-dev@lists.zeromq.org[1]>

COPYRIGHT

Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for 0MQ: 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.

NOTES

1.  zeromq-dev@lists.zeromq.org
    mailto:zeromq-dev@lists.zeromq.org