add idempotency key

[idelvall]

Adds an idempotency key to the headers sent by the requests and its retries so the server can use this header to avoid processing multiple times a non-idempotent implementation.

Idempotency keys are unique tokens that you submit as a request header, that guarantee that only one resource will be created regardless of how many times a request is sent to us.

[johanbrandhorst]

This seems like a reasonable idea, but couldn't it just be another interceptor? Why does it need to be part of the retry logic? Also please add some tests.

[idelvall]

This seems like a reasonable idea, but couldn't it just be another interceptor? Why does it need to be part of the retry logic? Also please add some tests.

Hi @johanbrandhorst, yes I considered that option, but my reasoning was that given that non-idempotent RPCs should not be retried, this is something that falls into the library scope.

Happy to add those tests if you think the change is worth it.

[johanbrandhorst]

Ah, you mean that the use of the retry interceptor implies that the request must be idempotent? I suppose I follow that logic.

[johanbrandhorst]

Yes, please do add the tests and fix the build, thanks