Partial decoding

[Dementiy]

Things to check first

• I have searched the existing issues and didn't find my feature already requested there

Feature description

Is it possible to decode only the desired keys and not the whole blob? Something like cbor2.load_keys(...) or specify some hook in the load method to keep only desired keys.

Use case

I think it would be useful to decode only part of data to save some RAM in different use cases. For example, I can read only the header and then forward the blob to another service or collect blobs as chunks and read only metadata from each blob.

[agronholm]

This would require a major architectural change to allow for streaming decode. If I get to that point, it will likely come in the next major release.

[agronholm]

Oh, and there won't be specific convenience functions like that. I think you're assuming that the incoming object is a mapping, which it may not be. Nevertheless, with a streaming decoder this could be implemented with relative ease.