Re: Idempotency-Key for resuming requests (TUS Resumable Uploads Protocol)

[Marius Kleidl <[e-mail]>]

Dear Austin,

you brought up a good point by throwing Idempotency-Key into the recent
Interim meeting. Idempotency and resumability are related but not the same,
because when resuming an upload you want to start the data transfer at a
different offset to avoid transmitting the same data again. I am missing
this part from your proposal. How does the client obtain the information
which data the server has already received and which part it must still
transmit? Or did I just miss that piece?

That being said, I think that an idempotency key could play an important
role in resumable uploads, especially considering the creation of uploads
resources.

Best regards,
Marius


El jue., 6 oct. 2022 1:11, Austin William Wright <[e-mail]> escribió:

> Hello HTTP WG,
>
> It occurred to me that, in general, where a client wants resumable
> requests, it also wants those requests be idempotent. I noted the HTTP APIs
> WG is considering an Idempotency-Key header, and it seems to me these
> should be part of the same mechanism. Let me explain how that might work:
>
> If the client sends an Idempotency-Key, then the server can respond with a
> 1xx (Resumption Supported) confirming that the key will be honored for
> resuming the request.
>
> Clients that want resumption SHOULD send Idempotency-Key, but they don’t
> have to (for example, to minimize UA fingerprinting). If the client does
> not send Idempotency-Key, the server should still send 1xx (Resumption
> Supported) to assign the request an Idempotency-Key. But it doesn’t have to
> (for example, 1xx is filtered by gateways).
>
> Then when the request is interrupted, the client may resume the request
> with the same URI and Idempotency-Key of the request being resumed. By
> defining a RESUME method, a client could attempt to send a RESUME request
> in the hopes the server supports resumption, even if it didn’t receive a
> 1xx response. (Using the same URI allows the server to partition incomplete
> requests/uploads by the resource URI. There should be little need to
> re-send the method, since the server must store the details of the original
> request anyways, but a header could be defined if such a need is found.)
>
> I see few downsides with this technique. There’s some builtin redundancy
> so resumption will work even if one party is buggy, and if a new method is
> used, there’s no possibility that a server could misinterpret the request.
> Idempotency-Key would replace "Upload-Token” entirely.
>
> Thoughts?
>
> Thanks,
>
> Austin.
>