使用MQTT开发即时通讯时远程服务器连接失败求助

我正在使用MQTT开发即时通讯功能，本人是MQTT新手，相关知识储备不足，若有错误恳请指正。发送消息时出现连接错误，错误发生在ConnectClient方法的await client.ConnectAsync(options);处，已确认所有凭证正确，且通过Broker仪表盘能看到服务器有响应。

错误日志 #

{MQTTnet.Exceptions.MqttCommunicationException: Unable to connect to the remote server ---> System.Net.WebSockets.WebSocketException: Unable to connect to the remote server ---> System.Net.WebSockets.WebSocketException: Unable to connect to the remote server ---> System.Net.Http.WinHttpException: A security error occurred
   --- End of inner exception stack trace ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
   at System.Net.WebSockets.WinHttpWebSocket.<ConnectAsync>d__18.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.WebSockets.WebSocketHandle.<ConnectAsyncCore>d__20.MoveNext()
   --- End of inner exception stack trace ---
   at System.Net.WebSockets.WebSocketHandle.<ConnectAsyncCore>d__20.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Net.WebSockets.ClientWebSocket.<ConnectAsyncCore>d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MQTTnet.Implementations.MqttWebSocketChannel.<ConnectAsync>d__8.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MQTTnet.Internal.TaskExtensions.<TimeoutAfterAsync>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MQTTnet.Adapter.MqttChannelAdapter.<ConnectAsync>d__20.MoveNext()
   --- End of inner exception stack trace ---
   at MQTTnet.Adapter.MqttChannelAdapter.WrapException(Exception exception)
   at MQTTnet.Adapter.MqttChannelAdapter.<ConnectAsync>d__20.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MQTTnet.Client.MqttClient.<ConnectAsync>d__30.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at MQTTnet.Client.MqttClient.<ConnectAsync>d__30.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at VCL_Communications.MQTTClient.<ConnectClient>d__32.MoveNext() in C:\Users\oms\source\Workspaces\Workspace\VolunteerSuite\H2-branch\VCL_CommunicationsSTD\MQTT\MQTTClient.cs:line 280}

出错代码 #

private async Task ConnectClient()
{
    try
    {
        stopFlag = false; //reset the stop flag
        Guid theGuid = Guid.NewGuid();// new Guid();

        // Use WebSocket connection.
        var options = new MqttClientOptionsBuilder()
                .WithWebSocketServer(SERVER_URL)
                .WithCredentials(SERVER_USER, SERVER_PW)
                .WithClientId(TOPIC_SERVER_PREFIX + "|" + SYSTEM_TYPE + "|" + senderProfileId.ToString() + "|" + theGuid.ToString().Substring(0, 10))
                .WithCleanSession(true)
                .Build();

        //add tls if app
        if (_isApp)
        {
            options.ChannelOptions.TlsOptions.UseTls = true;
            options.ChannelOptions.TlsOptions.SslProtocol = System.Security.Authentication.SslProtocols.Tls12;
        }

        // **Here it is failing, returning error**
        await client.ConnectAsync(options);
        if (verbose)
        {
            WriteLog("MQTT c: Connected to MQTT Server");
        }
    }catch (Exception ex)
    {
        WriteLog("MQTT c: Error connecting: " + ex.Message);
    }
}

解决方案建议 #

1. 排查TLS证书验证问题 #

• 如果服务器使用自签名证书（仅测试环境适用，生产环境禁止），可以临时禁用证书验证：
  在TLS配置中添加证书验证回调：

  options.ChannelOptions.TlsOptions.CertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true;
  

• 生产环境需确保服务器证书有效且被客户端信任，可将证书导入客户端系统的信任存储。

2. 确认WebSocket URL格式正确性 #

• 若启用TLS，URL必须以wss://开头，非TLS用ws://；多数MQTT Broker的WebSocket端点路径为/mqtt，例如：wss://your-broker.com:8084/mqtt，需确认SERVER_URL包含正确的路径和端口。

3. 匹配TLS协议版本 #

• 确认服务器支持TLS 1.2，若服务器支持更高版本，可尝试同时指定多个协议：

  options.ChannelOptions.TlsOptions.SslProtocol = 
      System.Security.Authentication.SslProtocols.Tls12 | 
      System.Security.Authentication.SslProtocols.Tls13;
  

4. 优化客户端配置方式 #

建议通过MqttClientOptionsBuilder链式配置TLS，避免Build后修改导致配置不生效：

private async Task ConnectClient()
{
    try
    {
        stopFlag = false;
        Guid theGuid = Guid.NewGuid();
        string clientId = $"{TOPIC_SERVER_PREFIX}|{SYSTEM_TYPE}|{senderProfileId}|{theGuid.ToString().Substring(0, 10)}";

        var optionsBuilder = new MqttClientOptionsBuilder()
                .WithWebSocketServer(SERVER_URL)
                .WithCredentials(SERVER_USER, SERVER_PW)
                .WithClientId(clientId)
                .WithCleanSession(true);

        if (_isApp)
        {
            optionsBuilder.WithTls(tlsOptions =>
            {
                tlsOptions.UseTls = true;
                tlsOptions.SslProtocol = System.Security.Authentication.SslProtocols.Tls12;
                // 测试环境可添加证书验证回调
                // tlsOptions.CertificateValidationCallback = (_, _, _, _) => true;
            });
        }

        var options = optionsBuilder.Build();
        await client.ConnectAsync(options);
        
        if (verbose)
        {
            WriteLog("MQTT c: Connected to MQTT Server");
        }
    }
    catch (Exception ex)
    {
        WriteLog($"MQTT c: Error connecting: {ex.Message}\n{ex.StackTrace}");
    }
}

5. 检查网络与代理 #

• 确认客户端防火墙/杀毒软件未拦截WebSocket端口；
• 若使用代理，需配置MQTT客户端的代理设置，或确保代理允许WebSocket流量。

内容的提问来源于stack exchange，提问作者TheHunter Shergill