D2C messages sent over 1MB in size via AMQP are currently being retried by the SDK

[abhipsaMisra]

When a D2C message over 1MB in size is sent to IoT Hub over AMQP, instead of throwing a MessageTooLargeException immediately, the operation is instead retried and an OperationCancelledException is eventually thrown.

[abhipsaMisra]

This issue happens because the service exhibits different behaviors for different sizes of D2C messages when over the 256KB limit.

• For messages between 256KB and 1MB in size, service returns an amqp outcome of “rejected” with the specified error code. This outcome is translated by the sdk to a MessageTooLargeException and is returned to the caller.
• For messages over 1MB, the message is rejected by the amqp layer itself, even before it reaches the service’s application layer. As a result, the amqp layer rejects the message and closes the accompanying links ungracefully. This link closure is detected by the sdk as an OperationCancelledException and it tries to recover. This causes the sdk to retry the failed operation, resulting in the sdk resending the overly large data.

[abhipsaMisra]

Even though service should exhibit the same behavior for all messages exceeding the hub specified limit of 256kb, the sdk will also be updated the inspect the inner exception details in case of ungraceful link closures.

[abhipsaMisra]

This fix has been released in our latest release: https://github.com/Azure/azure-iot-sdk-csharp/releases/tag/2021-8-11
Closing this issue.