Remove request body type param

[davidpdrsn]

Fixes #1110

This removes the request body type param from everything (Router, FromRequest, RequestParts, etc...). The goal being to improve usability and solve issues like #1110.

The general approach is to implement Service like this:

impl<B> Service<Request<B>> for Router
where
    B: http_body::Body,
{
    fn call(&mut self, req: Request<B>) -> Self::Future {
        let req = req.map(|body| hyper::Body::wrap_body(body));
        // ...
    }
}

This allows us to accept any impl http_body::Body on the outside but convert that to a hyper::Body on the inside.

We need to accept any impl http_body::Body instead of only hyper::Body to support middleware that change the request body (such as RequestBodyLimit).

I also considered using BoxBody rather than hyper::Body but that means users cannot extract Request<hyper::Body> which I think would confuse many users.

Note that hyper::Body:wrap_body isn't shipped yet. I have made a PR to hyper that adds that. If hyper decides not to merge that then our only option is to use BoxBody. We need that to construct a hyper::Body from a generic impl http_body::Body.

This is also a win in another elsewhere because it removes a type param from FromRequest and RequestParts. In #1121 and a WIP fix for #1142 I'm adding two more type params to those types. So by removing the body we'll only have two type params instead of three.

TODO

• Update docs
• Update changelog, including guide on how to upgrade

[davidpdrsn]

Note this makes hyper a public dependency of axum-core. I think thats a little unfortunate but its required to make impl FromRequest for Request<hyper::Body> work. I think thats an okay trade-off.

[davidpdrsn]

It also does mean that any crate that depends on axum-core now also depends on hyper. Thats pretty unfortunate 🤔 But yeah not sure there is a way around it.

[davidpdrsn]

One solution would be to keep the type param on FromRequest and RequestParts but that would mean they get three type params in 0.6 😬

[davidpdrsn]

Perhaps its also worth considering adding our own body type to axum-core, to avoid the dependency on hyper. I believe hyper's Body will be moved into hyper-utils for 1.0 and we don't wanna have a public dependency on hyper-utils. So we'll probably need our own body type eventually.

Though we have to consider compatibility with things like reqwest. I probably should be possible to extract the body with axum for send it somewhere else with reqwest or a hyper::Client.

[davidpdrsn]

Note to self: Wo can remove this method and just use the one in hyper.

[davidpdrsn]

I wrote about why hyper::Body::wrap_body is necessary here.

[jplatte]

I never used a non-default body type so I don't really have a good overview of what kinds of things this makes harder / pessimizes (if any). If this doesn't have any serious downsides I'd be in favor of course :)

[jplatte]

Err, why is there a request_parts module, but RequestParts is defined elsewhere?

[davidpdrsn]

The main downside is that it locks us into one body type for extractors. I think a lot depends on the hyper/hyper-util split for their 1.0 and where stuff ends up. We cannot publicly depend on the body from hyper-util and hyper probably won't have a single body type.

[davidpdrsn]

I'm gonna close this. All this is gonna have to change anyway when we get closer to hyper 1.0 so I'd rather deal with it then. See #1110 (comment).

This PR is also too large to review so if/when we do this we have to do it in smaller chunks.