Missing `OptionalFromRequestParts` implementation for the `Host` extractor from the axum-extra crate

[dnlsndr]

• I have looked for existing issues (including closed) about this

Bug Report

Version

v0.8.1

Platform

UNIX

Crates

axum
axum-extra

Description

Now that the Host extractor was moved to the axum-extra crate and with the new changes to how Option extractors work, it's not possible to do something like this anymore:

use axum_extra::extract::Host;

async fn handler(host: Option<Host>){}

as the compiler complains with this error:

the trait bound `axum_extra::extract::Host: OptionalFromRequestParts<Arc<AppState>>` is not satisfied
you can use `cargo tree` to explore your dependency tree
required for `std::option::Option<axum_extra::extract::Host>` to implement `FromRequestParts<Arc<AppState>>`

[taladar]

The Query extractor is still missing one of those too.

[taladar]

Specifically I meant the one from axum but axum_extra seems to have one too that is also affected.

[dnlsndr]

@taladar Check this out: #3079 although their reasoning does not apply to extractors such as Host

[taladar]

I see, so in case someone comes across this OptionalQuery from axum_extra looks like the correct replacement for the situation where the whole query value is optional, not just individual fields.

[Turbo87]

@taladar OptionalQuery is close to being deprecated too. I would recommend to wrap all your query fields with Option instead, since that best reflects reality of how query parameters work.

[taladar]

Semantically 99% of the time when I even want several query parameters stored in the same value I want to know if all of them have been specified though, not a mess of several Option values, some of them potentially None that I have to check manually again anyway.

[jplatte]

Could you give an example? I have the exact opposite experience, I have never seen a set of query parameters that are optional as a group, rather than individually.

[jplatte]

@dnlsndr Want to send a PR for Host?

[taladar]

Usually that occurs when you have related information that is useless if you only have some of it, e.g. you have a map API with x, y and z parameters or a sort by and sort direction parameter.

[dnlsndr]

I'd be happy to! PR incoming.

[Turbo87]

you have a map API with x, y and z parameters

let (x, y, z) = match (x, y, z) {
  (Some(x), Some(y), Some(z)) => (x, y, z),
  _ => return Err(...),
}

I think something like this should work?

a sort by and sort direction parameter.

you can use #[serde(default = ...)] in this case without having to use Option inside the struct

[taladar]

That is the kind of code that I would consider "manually checking". Obviously it is not impossible but there definitely is a use-case for not having that check inside the handler.

[Turbo87]

I haven't tried it, but another alternative could be to use something like this if you always need these params to be present together:

struct QueryParams {
  #[serde(flatten)]
  xyz: Option<XYZ>
}

struct XYZ {
  x: f32,
  y: f32,
  z: f32,
}