Libraries for in-code service versioning?

I've read about an approach to handling multiple HTTP service versions running in parallel which I quite like. The layer above the serializer layer (in serializer->model->database architecture, maybe its an in-process middleware), inspects the incoming version requested and can select from a list of serializers for one that implements the requested API version. All of the versioning differences and backward compatibility concerns are handled in that serializer, or in the model layer, or somewhere between. Something like a database migration for APIs. Caveat is you need to have additive database changes so your physical schema is always backward-compatible.

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Anyway, I am looking for any and all libraries that might implement this pattern so that I can use them or use them as a reference. Does anyone know of any?