Issue while using local IPC for messaging between two local component

Question

publish("test/test",message={"a":1})  
  
 def publish(self, topic, message, message_format="json"):  
        """Publishes message to a topic of AWS IOT   
  
        Args:  
            topic (string): AWS IoT Core Topic  
            message (dict / string): Message to be published  
            message_format  
        """  
  
        request = PublishToTopicRequest()  
        request.topic_name = topic  
        publish_message = PublishMessage()  
        if message_format != "json":  
            publish_message.binary_message = BinaryMessage(message=bytes(message, "utf-8"))  
            # publish_message.binary_message.message = bytes(message, "utf-8")  
        else:  
            publish_message.json_message = JsonMessage(message=message)  
            # publish_message.json_message.message = message  
  
        request.publish_message = publish_message  
        operation = self.ipc_client.new_publish_to_topic()  
        operation.activate(request)  
        future = operation.get_response()  
        future.result(TIMEOUT)

**accessControl permissions are:**  
          com.test.test:pubsub:1:  
          policyDescription: "Allows communication with other components"  
          operations:  
          - "aws.greengrass#PublishToTopic"  
          resources:  
          - "test/test"

**and Greengrass.log are:**

2021-01-06T10:30:13.515Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.RpcServer: New connection code \[AWS_ERROR_SUCCESS] for \[Id 816, Class ServerConnection, Refs 1](2021-01-06T10:30:13.515Z) - . {}  
2021-01-06T10:30:13.515Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: aws.greengrass#GreengrassCoreIPC authenticated identity: com.test.test. {}  
2021-01-06T10:30:13.515Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: Connection accepted for com.test.test. {}  
2021-01-06T10:30:13.515Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: Sending connect response for com.test.test. {}  
2021-01-06T10:30:13.517Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.RpcServer: New connection code \[AWS_ERROR_SUCCESS] for \[Id 818, Class ServerConnection, Refs 1](2021-01-06T10:30:13.517Z) - . {}  
2021-01-06T10:30:13.517Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: aws.greengrass#GreengrassCoreIPC authenticated identity: com.test.test {}  
2021-01-06T10:30:13.517Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: Connection accepted for com.test.test. {}  
2021-01-06T10:30:13.517Z \[INFO] (Thread-6) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: Sending connect response for com.test.test. {}  
2021-01-06T10:30:13.518Z \[ERROR] (Thread-6) com.aws.greengrass.ipc.common.ExceptionUtil: Unhandled exception in IPC. {}  
java.lang.NullPointerException  
  
Edited by: allenkallz on Jan 6, 2021 3:21 AM

Answer

Hi and thanks for using Greengrass v2.  
  
Is there any additional logging after the NullPointerException? There ought to be a stacktrace which would tells us exactly what the problem is.  
  
Thanks!  
  
Michael Dombrowski.

Answer

Hi   
Thanks for your reply.  
  
The issue is in AWS IoT Python SDK v2 that for communication with the local component we have to create request instance **PublishToTopicRequest**  that accept topic with-param name "topic"  
  
but when we have to communicate with Cloud then we have to create request instance **PublishToIoTTopicRequest** and this class accepts topic with-param name   **topic_name**.    I have one question why you don`t have the same param name at both places. It`s confusing  
  
See the param names of both classes in the attachment.  
 And previously it`s not mentioned in Greengrass v2 documentation.  
  
Edited by: allenkallz on Jan 8, 2021 8:37 AM

Answer

I think I am also getting same error. Here is the complete stack trace:  
  
```  
2021-01-07T14:31:08.759Z \[INFO] (Thread-17) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: Connection accepted for com.example.IPCExample. {}  
2021-01-07T14:31:08.760Z \[INFO] (Thread-17) software.amazon.awssdk.eventstreamrpc.ServiceOperationMappingContinuationHandler: Sending connect response for com.example.IPCExample. {}  
2021-01-07T14:31:08.760Z \[ERROR] (Thread-17) com.aws.greengrass.ipc.common.ExceptionUtil: Unhandled exception in IPC. {}  
java.lang.NullPointerException  
        at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936)  
        at com.aws.greengrass.builtin.services.pubsub.PubSubIPCEventStreamAgent.handlePublishToTopicRequest(PubSubIPCEventStreamAgent.java:113)  
        at com.aws.greengrass.builtin.services.pubsub.PubSubIPCEventStreamAgent.access$100(PubSubIPCEventStreamAgent.java:44)  
        at com.aws.greengrass.builtin.services.pubsub.PubSubIPCEventStreamAgent$PublishToTopicOperationHandler.lambda$handleRequest$0(PubSubIPCEventStreamAgent.java:192)  
        at com.aws.greengrass.ipc.common.ExceptionUtil.translateExceptions(ExceptionUtil.java:33)  
        at com.aws.greengrass.builtin.services.pubsub.PubSubIPCEventStreamAgent$PublishToTopicOperationHandler.handleRequest(PubSubIPCEventStreamAgent.java:176)  
        at com.aws.greengrass.builtin.services.pubsub.PubSubIPCEventStreamAgent$PublishToTopicOperationHandler.handleRequest(PubSubIPCEventStreamAgent.java:160)  
        at software.amazon.awssdk.eventstreamrpc.OperationContinuationHandler.onContinuationMessage(OperationContinuationHandler.java:271)  
        at software.amazon.awssdk.crt.eventstream.ServerConnectionContinuationHandler.onContinuationMessageShim(ServerConnectionContinuationHandler.java:53)  
  
```  
  
Edited by: kunupat on Jan 7, 2021 6:46 AM

Answer

Based on that stacktrace, that must mean that the topic is null. Please ensure that you have set a non-null topic name in the publish request.  
  
request.topic = "my/topic/name"  
  
Thanks.  
Michael Dombrowski  
  
Edited by: MichaelDombrowski-AWS on Jan 7, 2021 9:08 AM

Issue while using local IPC for messaging between two local component

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