node.js - 如何解决 : premature close at onclosenexttick in Node. js 服务器？

Question

如何解决这个错误，我用 AWS IoT 运行我的 Node.js 然后它有时会显示这个错误:

      throw er; // Unhandled 'error' event
      ^

Error: How  (/home/ec2-user/work/nodejs_27_01/node_modules/end-of-stream/index.js:54:                                                                                                     86)
    at processTicksAndRejections (internal/process/task_queues.js:79:11)
Emitted 'error' event on DeviceClient instance at:
    at MqttClient.<anonymous> (/home/ec2-user/work/nodejs_27_01/node_modules/aws-iot-device-sdk/                                                                                                     device/index.js:772:15)
    at MqttClient.emit (events.js:333:22)
    at MqttClient.EventEmitter.emit (domain.js:485:12)
    at TLSSocket.f (/home/ec2-user/work/nodejs_27_01/node_modules/once/once.js:25:25)
    at onclosenexttick (/home/ec2-user/work/nodejs_27_01/node_modules/end-of-stream/index.js:54:                                                                                                     73)

Answer 1

这可能有多种原因:

具有相同 ClientId 的多个连接

clientId 一次只能用于一个连接。如果您在建立另一个连接时使用相同的 clientId 进行连接，则旧连接将被丢弃(这会导致过早关闭错误)并建立新连接。

The client is using a client ID that is already in use. In this case, the client that is already connected will be disconnected [...]. (Source)

权限

如果设备(来自 aws-iot-device-sdk-js 的 mqtt.Client)没有正确的权限来连接和/或发布/订阅/接收给定主题的消息，就会发生此错误。

有关更多文档，请参阅此处:https://docs.aws.amazon.com/iot/latest/developerguide/pub-sub-policy.html

策略应如下所示(示例显示 Cloudformation Iot Policy 资源):

MyIotThingsPolicy:
  Type: AWS::IoT::Policy
  Properties:
    PolicyDocument:
      Version: "2012-10-17"
      Statement:
        - Action: iot:Connect
          Effect: Allow
          Resource: !Join [ "", [!Sub "arn:aws:iot:${AWS::Region}:${AWS::AccountId}:client/",
                                 "${iot:ClientId}"] ]
        - Action: iot:Receive
          Effect: Allow
          Resource: !Join [ "", [!Sub "arn:aws:iot:${AWS::Region}:${AWS::AccountId}:topic/",
                                "${iot:ClientId}/eg/your/broadcast/topic"] ]
        - Action: iot:Subscribe
          Effect: Allow
          Resource: !Join [ "", [!Sub "arn:aws:iot:${AWS::Region}:${AWS::AccountId}:topicfilter/",
                                 "${iot:ClientId}/eg/your/broadcast/topic"] ]
        - Action: iot:Publish
          Effect: Allow
          Resource: !Join [ "", [!Sub "arn:aws:iot:${AWS::Region}:${AWS::AccountId}:topic/",
                                 "${iot:ClientId}/eg/your/publish/topic"] ]

!Join是必要的，因为 Cloudformation 会尝试解析 ${iot:ClientId} ，这是一个运行时值，在部署期间未知。

疑难解答

• 作为Sandeep Patel还建议，如果你想在客户端对这种情况采取行动，你应该实现错误回调:

  device.on('error', (error) => {
    // error.message might be 'premature close'
  });
  

• 您还可以查找 disconnectReason关于主题$aws/events/presence/disconnected/<clientId> ，参见:https://docs.aws.amazon.com/iot/latest/developerguide/life-cycle-events.html