DynamoDB BatchGetItem should return UnprocessedKeys when response exceeds 16MB

[sirrus233]

What I expect to happen:
A BatchGetItem call to a moto dynamodb instance which would return > 16 MB of data should only return a partial result, with any unprocessed keys being returned under a separate key in the response.

What is happening:
BatchGetItem returns all results, regardless of the size of the response.

Documentation: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_BatchGetItem.html

Specifically:

A single operation can retrieve up to 16 MB of data, which can contain as many as 100 items. BatchGetItem returns a partial result if the response size limit is exceeded, the table's provisioned throughput is exceeded, or an internal processing failure occurs. If a partial result is returned, the operation returns a value for UnprocessedKeys. You can use this value to retry the operation starting with the next item to get.

Today it seems that although moto does provide an UnprocessedKeys key in the response, the value is hard-coded to an empty list.

moto version: 3.1.6

[bblommers]

Thanks for raising this @sirrus233 - will mark it as an enhancement to implement this validation.

If this is something you'd like to contribute yourself, PR's are always welcome!