Streaming custom QVariant?

[wysota]

Shouldn't serialization framework automatically handle Qt types and provide mechanism for custom types?

It does. But not through QVariant

I do override the QDataStream streaming operators, but that doesn't say anything about the header (type, size, etc.) that should be handled automatically.

That's your task in the implementation of the operator.

QDataStream is a mechanism do stream binary data to/from a device. It is not a general-purpose serialization mechanism but it can be used to create one. It's main task is to provide a way to store (and retrieve) binary data in some well known internal data format where you know what data you expect.