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`. .. code-block:: c 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_NODEID_NUMERIC(0, UA_NS0ID_BASEEVENTTYPE), UA_NODEID_NUMERIC(0, 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. .. code-block:: c 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. .. code-block:: c 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_NODEID_NUMERIC(0, 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. .. code-block:: c 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_NODEID_NUMERIC(0, UA_NS0ID_OBJECTSFOLDER), UA_NODEID_NUMERIC(0, 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. .. code-block:: c int main(void) { UA_Server *server = UA_Server_new(); addNewEventType(server); addGenerateEventMethod(server); UA_StatusCode retval = UA_Server_runUntilInterrupt(server); UA_Server_delete(server); return retval == UA_STATUSCODE_GOOD ? EXIT_SUCCESS : EXIT_FAILURE; }