如何对open62541.h/open62541.c的UA_Client进行状态（在线/掉线）监控

背景

目前在利用open62541.h/open62541.c编写了一个与PLC进行OPCUA通讯的上位机程序。
上位机这边会定时对PLC的某个opcua变量进行写操作。但是假如PLC离线或者说拔掉网线，上位机就会直接崩溃死机，并且报如下的错误：

[2024-08-12 10:07:25.528 (UTC+0800)] warn/channel	Connection 2516 | SecureChannel 28 | Receiving the response failed with StatusCode BadConnectionClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/client	Received Publish Response with code BadSecureChannelClosed
[2024-08-12 10:07:25.528 (UTC+0800)] warn/channel	Connection 0 | SecureChannel 0 | Could not receive with StatusCode BadConnectionClosed
[2024-08-12 10:07:25.528 (UTC+0800)] info/client	Client Status: ChannelState: Closed, SessionState: Created, ConnectStatus: Good

有没有什么办法可以监控client的状态，了解其是什么时候掉线，掉线了我就不写就行了。

解决方案

幸亏，是有这么一个回调函数的，参考官方的例子【open62541/examples/client_async.c】可以发现，我们可以对UA_ClientConfig中的stateCallback进行赋值，也就是注册一个状态回调函数，从而获取客户端的状态变化。

static void
onConnect(UA_Client *client, UA_SecureChannelState channelState,UA_SessionState sessionState, UA_StatusCode connectStatus) {printf("Async connect returned with status code %s\n",UA_StatusCode_name(connectStatus));
}---UA_ClientConfig *cc = UA_Client_getConfig(client);cc->stateCallback = onConnect;

一般检测channelState就行

// 状态变化回调函数，可以通过这个监测客户端是否断开连接
// 此回调函数的线程，貌似就是UA_Client_run_iterate所在的线程？起始应该不是，恐怕是在哪个线程调用了UA_Client相关的函数，就在那个线程；
static void
onStateChanged(UA_Client *client,UA_SecureChannelState channelState,UA_SessionState sessionState,UA_StatusCode connectStatus)
{if(channelState == UA_SECURECHANNELSTATE_CLOSED) // 连接已断开{qDebug() << "callback thread:" << QThread::currentThread();qDebug() << "连接已断开--------" << QDateTime::currentDateTime();---}
}

注意事项

这个opcua库对多线程的处理比较差，很容易造成冲突。一定要自己加个线程锁，否则程序很容易就崩掉。

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参考：
【open62541/examples/client_async.c】