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);
----

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);
----
