Multicast DNS Discovery Driver

An OPC UA application can announce / retract a server via multicast DNS. Also it receives multicast-based information about other servers. This functionality is implemented as a driver that integrates with open62541 servers. Internally, the drivers use the EventLoop of the server to create and manage UDP sockets. They further use the UA_APPLICATIONNOTIFICATIONTYPE_DISCOVERY category for server notifications to receive relevant updates from the server at runtime.

The following configuration parameters are forwarded in a key-value map during driver instantiation and/or set in the key-value map inside the generic driver structure before starting the driver.

0:listen [bool]

Receive information about OPC UA servers on the network via mDNS. Calls UA_Server_registerServerOnNetwork and UA_Server_deregisterServerOnNetwork to store the server information locally.

0:announce [bool]

Announce registered servers over mDNS. This receives register/deregister notifications from UA_Server_registerServerOnNetwork and forwards the information.

0:announce-ttl [uint32]

Default TTL in seconds for announced mDNS records.

0:query-presence [bool]

Send an mDNS PTR query for _opcua-tcp._tcp.local. on startup. Defaults to false.

0:query-details [bool]

Send targeted SRV/TXT follow-up queries for partially received OPC UA service instances. Defaults to false.

0:query-interval [uint32]

Interval in seconds for repeated presence queries. A value of zero disables repeated queries. Defaults to zero.

0:interface [string]

Network interface for listening or sending. Can be either the IP address of the network interface or the interface name (e.g. ‘eth0’). Cf. the UDP ConnectionManager parameters.

typedef struct UA_MdnsDriver UA_MdnsDriver;

struct UA_MdnsDriver {
    UA_Driver drv; /* Must be the first member */

    /* Manually publish/remove address records. This is separate from the
     * ServerOnNetwork announcement path as PTR/SRV/TXT records are always
     * derived from the ServerOnNetwork data. The address strings are numeric
     * IPv4/IPv6 literals. */
    UA_StatusCode (*addARecord)(UA_MdnsDriver *mdns, UA_String hostname,
                                UA_String address, UA_UInt32 ttl);
    UA_StatusCode (*removeARecord)(UA_MdnsDriver *mdns, UA_String hostname,
                                   UA_String address);
    UA_StatusCode (*addAAAARecord)(UA_MdnsDriver *mdns, UA_String hostname,
                                   UA_String address, UA_UInt32 ttl);
    UA_StatusCode (*removeAAAARecord)(UA_MdnsDriver *mdns, UA_String hostname,
                                      UA_String address);
};

/* Based on the libmdnsd dependency */
UA_MdnsDriver *
UA_MdnsDriver_Mdnsd(const UA_KeyValueMap params);

/* Based on the libavahi dependency */
UA_MdnsDriver *
UA_MdnsDriver_Avahi(const UA_KeyValueMap params);