extract::Path doesn't work with types using serde::Deserializer::deserialize_any

[paolobarbolini]

Feature Request

Motivation

PathDeserializer doesn't support deserialize_any ¹ so it doesn't work with things like time::Date ²

Proposal

Add support for deserialize_any. I might be able to look into it in the following days.

Alternatives

Create a wrapper around the type and force it to use a specific deserializer

Footnotes

1. https://github.com/tokio-rs/axum/blob/87a80ec47bfd2c39ac4ea3d1acffb5d1ff540f63/axum/src/extract/path/de.rs#L59 ↩

2. https://github.com/time-rs/time/blob/d97594b9f5cfeab0335c16687e26a8b51c56a526/time/src/serde/mod.rs#L124 ↩

[davidpdrsn]

What would such an implementation look like? Afaik URL params aren't a self describing format so when you encounter some key/value pair how do you know what to deserialize that into?

I check and the Path extractors in poem actix-web don't support deserialize_any either, though there is a PR for actix-web for forwards it to deserialize_str (actix/actix-web#2881). I'm not sure thats right 🤔

[jplatte]

I think if we support it, deserialize_str is the right implementation.

[paolobarbolini]

serde_urlencoded forwards deserialize_any to deserialize_map and it seems to work fine for them, so it should make sense for us to forward it to deserialize_str
https://github.com/nox/serde_urlencoded/blob/d8bc15d16adf6b3ba6ae46d199d7109cf5079efa/src/de.rs#L102

The playground doesn't enable the right time features for it to work, but you can test it locally:

Cargo.toml

[package]
name = "test123"
version = "0.1.0"
edition = "2021"

[dependencies]
serde = { version = "1", features = ["derive"] }
time = { version = "0.3", features = ["serde-human-readable", "parsing"] }
serde_urlencoded = "0.7"

main.rs

use serde::Deserialize;
use time::Date;

fn main() {
    #[derive(Debug, Deserialize)]
    struct Stuff {
        date: Date,
    }

    let deserialized: Stuff = serde_urlencoded::from_str("date=2022-01-01").unwrap();
    println!("{deserialized:?}");
}

stdout

Stuff { date: 2022-01-01 }

[jplatte]

I think the more interesting question for serde_urlencoded is, what does deserialize_any do for the individual keys and values (represented as Part<'de> internally)?

[davidpdrsn]

It seems serde_urlencoded also just calls deserialize_str for values (https://github.com/nox/serde_urlencoded/blob/master/src/de.rs#L194-L202), so thats probably also what axum should do (#1693)