open62541 事件

概述

监控项目能够监测到数据的变化，但是有时候并不能传递足够的信息，使用事件可以带有信息以及其可以在任何时候进行触发，同时其属性可以被客户端进行过滤，只接收自己感兴趣的特定属性。本文将描述server端事件的触发以及client端事件的过滤及接收。

编译

在使用之前我们需要编译open62541，我们使用CMake勾选对应的选项进行编译即可得到对应的.h和.c文件，勾选选项如下

重新编译后即可得到对应.h和.c文件。

Server端触发事件

这里以例程tutorial_server_events.c为例，描述server端去触发事件，代码如下

/* 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>
//#include <open62541/server_config_default.h>
#include "open62541.h"

#include <signal.h>
#include <stdlib.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 he is interested in.
 *
 * 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_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.
 */
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 = 500;
    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_NODEID_NUMERIC(0, UA_NS0ID_SERVER_SERVERSTATUS),
                                    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_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. */

static volatile UA_Boolean running = true;
static void stopHandler(int sig) {
    running = false;
}

int main (void) {
    /* default server values */
    signal(SIGINT, stopHandler);
    signal(SIGTERM, stopHandler);

    UA_Server *server = UA_Server_new();
    UA_ServerConfig_setDefault(UA_Server_getConfig(server));

    addNewEventType(server);
    addGenerateEventMethod(server);

    UA_StatusCode retval = UA_Server_run(server, &running);

    UA_Server_delete(server);
    return retval == UA_STATUSCODE_GOOD ? EXIT_SUCCESS : EXIT_FAILURE;
}

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在这个例程中我们创建了自己的事件类型SimpleEventType，其继承于BaseEventType。另外添加了一个方法节点用于进行事件的触发，在每次触发前都需要先创建一个新的事件，同时设置事件的字段值，此例程设置了四个字段，Time、Severity、Message和SourceName。我们也可以添加其他一些字段信息，其他定义我们可以使用Uaexpert来进行查看

可以看到总共有9个字段，我们可以单独的进行设置。我们调用Generate Event方法后就会通过回调去触发一个事件。我们可以使用Uaexpert来进行验证，

添加事件窗口后我们需要添加Server对象节点

我们调用生成事件方法，在event view中能看到接收到的事件

点击这个事件可以获取相关的信息。

client端接收事件

这里以例程tutorial_client_events.c为例，描述client端如何去接收server端发出的事件，代码如下

/* 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/client.h>
//#include <open62541/client_config_default.h>
//#include <open62541/client_highlevel.h>
//#include <open62541/client_subscriptions.h>
//#include <open62541/plugin/log_stdout.h>
//#include <open62541/server.h>
//#include <open62541/server_config_default.h>
//#include <open62541/util.h>
#include "open62541.h"

#include <signal.h>

#ifdef _MSC_VER
#pragma warning(disable:4996) // warning C4996: 'UA_Client_Subscriptions_addMonitoredEvent': was declared deprecated
#endif

#ifdef __clang__
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
#endif

#ifdef __GNUC__
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
#endif

static UA_Boolean running = true;
static void stopHandler(int sig) {
    UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "received ctrl-c");
    running = false;
}

#ifdef UA_ENABLE_SUBSCRIPTIONS

static void
handler_events(UA_Client *client, UA_UInt32 subId, void *subContext,
               UA_UInt32 monId, void *monContext,
               size_t nEventFields, UA_Variant *eventFields) {
    UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "Notification");

    /* The context should point to the monId on the stack */
    UA_assert(*(UA_UInt32*)monContext == monId);

    for(size_t i = 0; i < nEventFields; ++i) {
        if(UA_Variant_hasScalarType(&eventFields[i], &UA_TYPES[UA_TYPES_UINT16])) {
            UA_UInt16 severity = *(UA_UInt16 *)eventFields[i].data;
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "Severity: %u", severity);
        } else if (UA_Variant_hasScalarType(&eventFields[i], &UA_TYPES[UA_TYPES_LOCALIZEDTEXT])) {
            UA_LocalizedText *lt = (UA_LocalizedText *)eventFields[i].data;
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                        "Message: '%.*s'", (int)lt->text.length, lt->text.data);
        }
        else {
#ifdef UA_ENABLE_TYPEDESCRIPTION
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                        "Don't know how to handle type: '%s'", eventFields[i].type->typeName);
#else
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                        "Don't know how to handle type, enable UA_ENABLE_TYPEDESCRIPTION "
                        "for typename");
#endif
        }
    }
}

const size_t nSelectClauses = 2;

static UA_SimpleAttributeOperand *
setupSelectClauses(void) {
    UA_SimpleAttributeOperand *selectClauses = (UA_SimpleAttributeOperand*)
        UA_Array_new(nSelectClauses, &UA_TYPES[UA_TYPES_SIMPLEATTRIBUTEOPERAND]);
    if(!selectClauses)
        return NULL;

    for(size_t i =0; i<nSelectClauses; ++i) {
        UA_SimpleAttributeOperand_init(&selectClauses[i]);
    }

    selectClauses[0].typeDefinitionId = UA_NODEID_NUMERIC(0, UA_NS0ID_BASEEVENTTYPE);
    selectClauses[0].browsePathSize = 1;
    selectClauses[0].browsePath = (UA_QualifiedName*)
        UA_Array_new(selectClauses[0].browsePathSize, &UA_TYPES[UA_TYPES_QUALIFIEDNAME]);
    if(!selectClauses[0].browsePath) {
        UA_SimpleAttributeOperand_delete(selectClauses);
        return NULL;
    }
    selectClauses[0].attributeId = UA_ATTRIBUTEID_VALUE;
    selectClauses[0].browsePath[0] = UA_QUALIFIEDNAME_ALLOC(0, "Message");

    selectClauses[1].typeDefinitionId = UA_NODEID_NUMERIC(0, UA_NS0ID_BASEEVENTTYPE);
    selectClauses[1].browsePathSize = 1;
    selectClauses[1].browsePath = (UA_QualifiedName*)
        UA_Array_new(selectClauses[1].browsePathSize, &UA_TYPES[UA_TYPES_QUALIFIEDNAME]);
    if(!selectClauses[1].browsePath) {
        UA_SimpleAttributeOperand_delete(selectClauses);
        return NULL;
    }
    selectClauses[1].attributeId = UA_ATTRIBUTEID_VALUE;
    selectClauses[1].browsePath[0] = UA_QUALIFIEDNAME_ALLOC(0, "Severity");

    return selectClauses;
}

#endif

int main(int argc, char *argv[]) {
    signal(SIGINT, stopHandler);
    signal(SIGTERM, stopHandler);

    UA_Client *client = UA_Client_new();
    UA_ClientConfig_setDefault(UA_Client_getConfig(client));

    /* opc.tcp://uademo.prosysopc.com:53530/OPCUA/SimulationServer */
    /* opc.tcp://opcua.demo-this.com:51210/UA/SampleServer */
    UA_StatusCode retval = UA_Client_connect(client, "opc.tcp://127.0.0.1:4840");
    if(retval != UA_STATUSCODE_GOOD) {
        UA_Client_delete(client);
        return EXIT_FAILURE;
    }

#ifdef UA_ENABLE_SUBSCRIPTIONS
    /* Create a subscription */
    UA_CreateSubscriptionRequest request = UA_CreateSubscriptionRequest_default();
    UA_CreateSubscriptionResponse response = UA_Client_Subscriptions_create(client, request,
                                                                            NULL, NULL, NULL);
    if(response.responseHeader.serviceResult != UA_STATUSCODE_GOOD) {
        UA_Client_disconnect(client);
        UA_Client_delete(client);
        return EXIT_FAILURE;
    }
    UA_UInt32 subId = response.subscriptionId;
    UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "Create subscription succeeded, id %u", subId);

    /* Add a MonitoredItem */
    UA_MonitoredItemCreateRequest item;
    UA_MonitoredItemCreateRequest_init(&item);
    item.itemToMonitor.nodeId = UA_NODEID_NUMERIC(0, 2253); // Root->Objects->Server
    item.itemToMonitor.attributeId = UA_ATTRIBUTEID_EVENTNOTIFIER;
    item.monitoringMode = UA_MONITORINGMODE_REPORTING;

    UA_EventFilter filter;
    UA_EventFilter_init(&filter);
    filter.selectClauses = setupSelectClauses();
    filter.selectClausesSize = nSelectClauses;

    item.requestedParameters.filter.encoding = UA_EXTENSIONOBJECT_DECODED;
    item.requestedParameters.filter.content.decoded.data = &filter;
    item.requestedParameters.filter.content.decoded.type = &UA_TYPES[UA_TYPES_EVENTFILTER];

    UA_UInt32 monId = 0;

    UA_MonitoredItemCreateResult result =
        UA_Client_MonitoredItems_createEvent(client, subId,
                                             UA_TIMESTAMPSTORETURN_BOTH, item,
                                             &monId, handler_events, NULL);

    if(result.statusCode != UA_STATUSCODE_GOOD) {
        UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                    "Could not add the MonitoredItem with %s", UA_StatusCode_name(retval));
        goto cleanup;
    } else {
        UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                    "Monitoring 'Root->Objects->Server', id %u", response.subscriptionId);
    }

    monId = result.monitoredItemId;

    while(running)
        retval = UA_Client_run_iterate(client, 100);

    /* Delete the subscription */
 cleanup:
    UA_MonitoredItemCreateResult_clear(&result);
    UA_Client_Subscriptions_deleteSingle(client, response.subscriptionId);
    UA_Array_delete(filter.selectClauses, nSelectClauses, &UA_TYPES[UA_TYPES_SIMPLEATTRIBUTEOPERAND]);
#endif

    UA_Client_disconnect(client);
    UA_Client_delete(client);
    return retval == UA_STATUSCODE_GOOD ? EXIT_SUCCESS : EXIT_FAILURE;
}

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这里与监控变量操作大致一致，只是这里监控的是server节点下的事件通知，

	item.itemToMonitor.nodeId = UA_NODEID_NUMERIC(0, 2253); // Root->Objects->Server
    item.itemToMonitor.attributeId = UA_ATTRIBUTEID_EVENTNOTIFIER;
    item.monitoringMode = UA_MONITORINGMODE_REPORTING;
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同时这里使用的事件过滤器，只选择了Message和Severity两个字段。调用UA_Client_MonitoredItems_createEvent设置好接收事件回调函数后我们只需在回调函数中做处理即可

static void
handler_events(UA_Client *client, UA_UInt32 subId, void *subContext,
               UA_UInt32 monId, void *monContext,
               size_t nEventFields, UA_Variant *eventFields) {
    UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "Notification");

    /* The context should point to the monId on the stack */
    UA_assert(*(UA_UInt32*)monContext == monId);

    for(size_t i = 0; i < nEventFields; ++i) {
        if(UA_Variant_hasScalarType(&eventFields[i], &UA_TYPES[UA_TYPES_UINT16])) {
            UA_UInt16 severity = *(UA_UInt16 *)eventFields[i].data;
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "Severity: %u", severity);
        } else if (UA_Variant_hasScalarType(&eventFields[i], &UA_TYPES[UA_TYPES_LOCALIZEDTEXT])) {
            UA_LocalizedText *lt = (UA_LocalizedText *)eventFields[i].data;
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                        "Message: '%.*s'", (int)lt->text.length, lt->text.data);
        }
        else {
#ifdef UA_ENABLE_TYPEDESCRIPTION
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                        "Don't know how to handle type: '%s'", eventFields[i].type->typeName);
#else
            UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND,
                        "Don't know how to handle type, enable UA_ENABLE_TYPEDESCRIPTION "
                        "for typename");
#endif
        }
    }
}
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这里打印了事件相关字段的值。我们使用Uaexpert触发事件，

这样我们client就能正常接收事件信息了，如果想获取更多信息，在过滤字段那里进行添加即可。

结尾

在server例程中我们创建了自定义的事件类型，其注释表面BaseEventType是抽象的不能直接实例化对象，但实际uaexpert中查看它并不是抽象的，

尝试使用BaseEventType去创建事件也是OK的。打个问号*-*