open62541/examples/tutorial_server_events.c

/* This work is licensed under a Creative Commons CCZero 1.0 Universal License.
 * See http://creativecommons.org/publicdomain/zero/1.0/ for more information. */

#include <open62541/plugin/log_stdout.h>
#include <open62541/server.h>

/**
 * Generating events
 * -----------------
 * To make sense of the many things going on in a server, monitoring items can
 * be useful. Though in many cases, data change does not convey enough
 * information to be the optimal solution. Events can be generated at any time,
 * hold a lot of information and can be filtered so the client only receives the
 * specific attributes of interest.
 *
 * Emitting events by calling methods
 * ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 * The following example will be based on the server method tutorial. We will be
 * creating a method node which generates an event from the server node.
 *
 * The event we want to generate should be very simple. Since the `BaseEventType` is abstract,
 * we will have to create our own event type. `EventTypes` are saved internally as `ObjectTypes`,
 * so add the type as you would a new `ObjectType`. */

static UA_NodeId eventType;

static UA_StatusCode
addNewEventType(UA_Server *server) {
    UA_ObjectTypeAttributes attr = UA_ObjectTypeAttributes_default;
    attr.displayName = UA_LOCALIZEDTEXT("en-US", "SimpleEventType");
    attr.description = UA_LOCALIZEDTEXT("en-US", "The simple event type we created");
    return UA_Server_addObjectTypeNode(server, UA_NODEID_NULL,
                                       UA_NS0ID(BASEEVENTTYPE), UA_NS0ID(HASSUBTYPE),
                                       UA_QUALIFIEDNAME(0, "SimpleEventType"),
                                       attr, NULL, &eventType);
}

/**
 * Setting up an event
 * ^^^^^^^^^^^^^^^^^^^
 * In order to set up the event, we can first use ``UA_Server_createEvent`` to
 * give us a node representation of the event. All we need for this is our
 * `EventType`. Once we have our event node, which is saved internally as an
 * `ObjectNode`, we can define the attributes the event has the same way we
 * would define the attributes of an object node. It is not necessary to define
 * the attributes `EventId`, `ReceiveTime`, `SourceNode` or `EventType` since
 * these are set automatically by the server. In this example, we will be
 * setting the fields 'Message' and 'Severity' in addition to `Time` which is
 * needed to make the example UaExpert compliant.
 */

static UA_StatusCode
setUpEvent(UA_Server *server, UA_NodeId *outId) {
    UA_StatusCode retval = UA_Server_createEvent(server, eventType, outId);
    if (retval != UA_STATUSCODE_GOOD) {
        UA_LOG_WARNING(UA_Log_Stdout, UA_LOGCATEGORY_SERVER,
                       "createEvent failed. StatusCode %s", UA_StatusCode_name(retval));
        return retval;
    }

    /* Set the Event Attributes */
    /* Setting the Time is required or else the event will not show up in UAExpert! */
    UA_DateTime eventTime = UA_DateTime_now();
    UA_Server_writeObjectProperty_scalar(server, *outId, UA_QUALIFIEDNAME(0, "Time"),
                                         &eventTime, &UA_TYPES[UA_TYPES_DATETIME]);

    UA_UInt16 eventSeverity = 100;
    UA_Server_writeObjectProperty_scalar(server, *outId, UA_QUALIFIEDNAME(0, "Severity"),
                                         &eventSeverity, &UA_TYPES[UA_TYPES_UINT16]);

    UA_LocalizedText eventMessage = UA_LOCALIZEDTEXT("en-US", "An event has been generated.");
    UA_Server_writeObjectProperty_scalar(server, *outId, UA_QUALIFIEDNAME(0, "Message"),
                                         &eventMessage, &UA_TYPES[UA_TYPES_LOCALIZEDTEXT]);

    UA_String eventSourceName = UA_STRING("Server");
    UA_Server_writeObjectProperty_scalar(server, *outId, UA_QUALIFIEDNAME(0, "SourceName"),
                                         &eventSourceName, &UA_TYPES[UA_TYPES_STRING]);

    return UA_STATUSCODE_GOOD;
}

/**
 * Triggering an event
 * ^^^^^^^^^^^^^^^^^^^
 * First a node representing an event is generated using ``setUpEvent``. Once
 * our event is good to go, we specify a node which emits the event - in this
 * case the server node. We can use ``UA_Server_triggerEvent`` to trigger our
 * event onto said node. Passing ``NULL`` as the second-last argument means we
 * will not receive the `EventId`. The last boolean argument states whether the
 * node should be deleted. */

static UA_StatusCode
generateEventMethodCallback(UA_Server *server,
                         const UA_NodeId *sessionId, void *sessionHandle,
                         const UA_NodeId *methodId, void *methodContext,
                         const UA_NodeId *objectId, void *objectContext,
                         size_t inputSize, const UA_Variant *input,
                         size_t outputSize, UA_Variant *output) {

    UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "Creating event");

    /* set up event */
    UA_NodeId eventNodeId;
    UA_StatusCode retval = setUpEvent(server, &eventNodeId);
    if(retval != UA_STATUSCODE_GOOD) {
        UA_LOG_WARNING(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                       "Creating event failed. StatusCode %s", UA_StatusCode_name(retval));
        return retval;
    }

    retval = UA_Server_triggerEvent(server, eventNodeId, UA_NS0ID(SERVER), NULL, UA_TRUE);
    if(retval != UA_STATUSCODE_GOOD)
        UA_LOG_WARNING(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                       "Triggering event failed. StatusCode %s", UA_StatusCode_name(retval));

    return retval;
}

/**
 * Now, all that is left to do is to create a method node which uses our
 * callback. We do not require any input and as output we will be using the
 * `EventId` we receive from ``triggerEvent``. The `EventId` is generated by the
 * server internally and is a random unique ID which identifies that specific
 * event.
 *
 * This method node will be added to a basic server setup.
 */

static void
addGenerateEventMethod(UA_Server *server) {
    UA_MethodAttributes generateAttr = UA_MethodAttributes_default;
    generateAttr.description = UA_LOCALIZEDTEXT("en-US","Generate an event.");
    generateAttr.displayName = UA_LOCALIZEDTEXT("en-US","Generate Event");
    generateAttr.executable = true;
    generateAttr.userExecutable = true;
    UA_Server_addMethodNode(server, UA_NODEID_NUMERIC(1, 62541),
                            UA_NS0ID(OBJECTSFOLDER), UA_NS0ID(HASCOMPONENT),
                            UA_QUALIFIEDNAME(1, "Generate Event"),
                            generateAttr, &generateEventMethodCallback,
                            0, NULL, 0, NULL, NULL, NULL);
}

/** It follows the main server code, making use of the above definitions. */

int main(void) {
    UA_Server *server = UA_Server_new();

    addNewEventType(server);
    addGenerateEventMethod(server);

    UA_Server_runUntilInterrupt(server);
    UA_Server_delete(server);
    return 0;
}