Keep public interface for QCBOREncode_AddBytesLenOnly

[BrianSipos]

I see that the current public function QCBOREncode_AddBytesLenOnly() is marked as being obsoleted for version 2.0, but this is a valuable use case for me implementing COSE sign and MAC with large (10s of MiB) detached payloads.

If this is not available in the future, can there be some similar public function to write just the CBOR head and defer the content to the user?

[laurencelundblade]

There are several options. The most direct replacement is QCBOREncode_EncodeHead(). It is available in QCBORv1. Presumably you are already writing bytes into the UsefulBuf directly. You will need to do that if you use QCBOREncode_EncodeHead().

In QCBORv2 there is QCBOREncode_OpenBytes() and streaming mode. QCBOREncode_OpenBytes() is not supported in streaming mode, but it could easily be if the length was known when QCBOREncode_OpenBytes() is called. Maybe I'll fix that.

When you write the very large COSE payload, is it all at once or a block at a time? It's even OK to use indefinite lengths for the COSE payload bstr. Though the protocol using COSE may not allow that, COSE does.