createwithtransport_unsubscribe

Can you Unsubscribe from C2D Message Callback when using AMQP Multiplexing?

Short answer is, no.

Explanation

If you try unsubscribing from the Message Callback using SetMessageCallback, you may see the following error:

File:E:\GitRepos\azure-iot-sdk-c\iothub_client\src\iothub_client_core_ll.c Func:_IoTHubClientCore_LL_SetMessageCallback_Ex Line:1927 Invalid workflow sequence. Please unsubscribe using the IoTHubClientCore_LL_SetMessageCallback function.

What's going on? Here's the investigation:

IoTHubClientCore_LL_SetMessageCallback -> SYNC IoTHubClientCore_LL_SetMessageCallback_Ex ->ASYNC

messageCallback == NULL (unsub)

IoTHubClientCore_LL_SetMessageCallback_Ex

OR

iotHubClientInstance->created_with_transport_handle != 0

IoTHubClientCore_LL_SetMessageCallback

iotHubClientInstance->created_with_transport_handle == 0

IoTHubClientCore_LL_SetMessageCallback_Ex

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create_iothub_instance

starts with: result->created_with_transport_handle = 0;

if deviceConfig.transportHandle != NULL

result->created_with_transport_handle = 1;

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create_iothub_instance

if (config != NULL) if (transportHandle != NULL) deviceConfig.transportHandle = IoTHubTransport_GetLLTransport(transportHandle);

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transportHandle is 3rd arg of create_iothub_instance

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IoTHubClientCore_CreateFromConnectionString -> transportHandle is NULL IoTHubClientCore_Create -> transportHandle is NULL IoTHubClientCore_CreateFromEnvironment -> transportHandle is NULL IoTHubClientCore_CreateWithTransport -> transportHandle is NOT NULL (!!!!!!) IoTHubClientCore_CreateFromDeviceAuth -> transportHandle is NULL

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IoTHubClient_CreateWithTransport calls IoTHubClientCore_CreateWithTransport

IoTHubDeviceClient_CreateWithTransport calls IoTHubClientCore_CreateWithTransport

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Conclusion: created_with_transport_handle indicates if device multiplexing is used (1) or not (0). if using dev mux, SYNC SetMessageCallback is used. Unsubscribing for Messages (C2D) only calls IoTHubClientCore_LL_SetMessageCallback_Ex.

SO: if using dev mux, you cannot unsubscribe for C2D messages.