Upcaster

[m1l4n54v1c]

• Enable schema evolution and backward compatibility by allowing payload upcasting at the state machine boundary.
• Provide Upcasters with enough context (such as the core message type and selected header keys) to make informed transformation decisions.
• Ensure system robustness: failures during upcasting must not break invocation processing.

Upcaster:

public interface Upcaster {
  boolean canUpcast(Slice body, Map<String, String> headers);

  Slice upcast(Slice body, Map<String, String> headers);
}

The upcaster is invoked for relevant protocol messages before handed over to the current state of the StateMachine. Messages carrying any form of payload. It could be that certain messages could be left out.

To help Upcaster implementations, metadata is constructed that includes the name of the core message and, where applicable, relevant information.

Since there is no hierarchy/generalization in messages, DefaultInvocationInputUpcaster is a bit verbose. I'm open to suggestions on how to improve it.

I see this as a conversation starter rather than a final solution. Looking forward to the feedback.

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[m1l4n54v1c]

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