如果使用异步读取接口UA_Client_readValueAttribute_async，请实现客户端和服务端-Go服务器开发

以下是一个使用异步读取接口UA_Client_readValueAttribute_async的简单示例，包括客户端和服务端的实现。

客户端（C++代码）：

#include <open62541/client_config_default.h>
#include <open62541/client_highlevel.h>
int main() {
    UA_Client *client = UA_Client_new();
    UA_ClientConfig_setDefault(UA_Client_getConfig(client));
    // 连接到服务器
    UA_StatusCode status = UA_Client_connect(client, "opc.tcp://localhost:4840");
    if (status != UA_STATUSCODE_GOOD) {
        printf("连接到服务器失败\n");
        return status;
    }
    // 创建异步读取请求
    UA_ReadRequest request;
    UA_ReadRequest_init(&request);
    request.nodesToRead = UA_Array_new(1, &UA_TYPES[UA_TYPES_READVALUEID]);
    request.nodesToReadSize = 1;
    // 设置要读取的节点信息
    request.nodesToRead[0].nodeId = UA_NODEID_NUMERIC(0, 2258);  // 修改为实际的节点ID
    // 发送异步读取请求
    status = UA_Client_Service_readAsync(client, &request);
    if (status != UA_STATUSCODE_GOOD) {
        printf("发送异步读取请求失败\n");
        return status;
    }
    // 等待响应
	UA_Boolean responseReceived = false;
	while (!responseReceived) {
		status = UA_Client_run_iterate(client, 1000);  // 等待响应时间间隔为1秒
		if (status == UA_STATUSCODE_BADCONNECTIONCLOSED) {
			printf("与服务器的连接已关闭\n");
			break;
		} else if (status != UA_STATUSCODE_GOOD) {
			printf("等待响应时发生错误\n");
			break;
		}
		if (request.response == NULL)
			continue;
        // 处理读取结果
		if (request.response->responseHeader.serviceResult == UA_STATUSCODE_GOOD) {
            for (size_t i = 0; i < request.response->resultsSize; ++i) {
                UA_DataValue *value = &(request.response->results[i]);
                printf("节点值: %f\n", *(UA_Double *)value->value.data);
            }
		}
        responseReceived = true;
	}
    // 清理资源
    UA_ReadRequest_deleteMembers(&request);
    UA_Client_disconnect(client);
    UA_Client_delete(client);
    return 0;
}

服务端（C++代码）：

#include <open62541/server.h>
int main() {
	UA_Server *server = UA_Server_new();
	UA_ServerConfig_setDefault(UA_Server_getConfig(server));
    // 在服务器上创建一个叫做"Temperature"的变量节点，并设置其初始值为25.0
	UA_VariableAttributes attr = UA_VariableAttributes_default;
	attr.displayName = UA_LOCALIZEDTEXT("en-US", "Temperature");
	UA_Double temperature = 25.0;
	UA_Variant_setScalarCopy(&attr.value, &temperature, &UA_TYPES[UA_TYPES_DOUBLE]);
	UA_NodeId nodeId = UA_NODEID_STRING(1, "Temperature");
	UA_QualifiedName browseName = UA_QUALIFIEDNAME(1, "Temperature");
    // 将变量节点添加到服务器上
    status = UA_Server_addVariableNode(server, nodeId,
                                       parentNodeId,  // 修改为实际的父节点ID
                                       referenceTypeId,  // 修改为实际的引用类型ID
                                       browseName,
                                       UA_NODEID_NUMERIC(0, UA_NS0ID_BASEDATAVARIABLETYPE),
                                       attr, NULL, NULL);
    // 启动服务器
	UA_StatusCode status = UA_Server_run(server, &running);
    // 关闭服务器
	UA_Server_delete(server);
	return status;
}