feat: add Sign trait

[flaneur2020]

background: apache/opendal#4960 (comment)

this PR introduced a Sign trait, which is suitable on the cases like when we want customize signing logics like apache/iceberg-rust#506

[Xuanwo]

Thanks a lot for your PR! However I'm thinking of a big refactor that build a Sign for entire reqsign. And we can remove the SignableRequest concept entirely by just support http. Do you have interest in this?

[flaneur2020]

hmm, it'd be a big refactor, but i have interest about this.

let me have a try, but maybe it's better to make this refactor in a seperate pr.

i'll change the newly added Sign trait to http first.

[flaneur2020]

i found that it's not that easy to get the mut ref of the Parts inside http::request::Request<T>, to mut the req, it seems that it's still easier to pass &mut http::request::Request<T> here if we'd like to pass a concerete Request struct here.

[Xuanwo]

i found that it's not that easy to get the mut ref of the Parts inside http::request::Request<T>, to mut the req

Would you like to elaborate further? It should be as straightforward as into_parts and from_parts. I want to avoid introduce an generice body in sign.

[flaneur2020]

we have to have the ownership of Request in the caller side, like this:

let (mut parts, body) = req.into_parts();
signer.sign(mut parts);
let req = Request::from_parts(parts, body);

if all you have is a &mut Request, you can not easily get the parts from it in the caller site.

[Xuanwo]

I proposed an RFC to http: hyperium/http#712

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we have to have the ownership of Request in the caller side, like this:

In read use cases, caller will always have the ownership of Request. I still think it's better for us to just take Parts in our API. So all imples and users don't need to play with Body generic type.

[flaneur2020]

this RFC makes sense.

i've made the changes, PTAL

[flaneur2020]

if hyperium/http is not planned to exposes parts_mut() (in hyperium/http#712 (comment)), i'm afraid that it might be better api to allow accepting a generic parameter in the Sign trait.

in the current code base, there're a lot of call sites that only have got &mut Request instead of an owned Request. it's hard to get the mutable reference of Parts.

[Xuanwo]

I strongly disagree with accepting a generic parameter. I prefer refactoring the entire codebase.

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In opendal, we use reqsign in this way:

let req = balabala_build_request();
sign(&mut req);
client.send(req)

So it's totally fine for me to have:

let (head, body) = balabala_build_request().into_parts();
sign(&mut head);
client.send(Request::from_parts(head, body))

[Xuanwo]

Looks good to me. Thanks a lot for carrying this work!