rust - 在actix-web中用作查询参数时，如何将无效的枚举变量转换为“无”

Question

通过documentation中提供的actix_web::web::Query示例，当提供未知变体时，如何使response_type诉诸None？
如果我有以下内容:

use actix_web::{web, App, HttpServer};
use serde::Deserialize;

#[derive(Debug, Deserialize)]
pub enum ResponseType {
    Token,
    Code,
}

#[derive(Deserialize)]
pub struct AuthRequest {
    id: u64,
    response_type: Option<ResponseType>,
}

async fn index(web::Query(info): web::Query<AuthRequest>) -> String {
    format!(
        "Authorization request for client with id={} and type={:?}!",
        info.id, info.response_type
    )
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| App::new().route("/", web::get().to(index)))
        .bind(("127.0.0.1", 8080))?
        .run()
        .await
}

并且我访问http://localhost:8080/?id=1&response_type=foo，得到了这个400的响应:

Query deserialize error: unknown variant foo, expected Token or Code

相反，当我希望它仅接受Enum的值作为有效值，并且如果未提供值或无效值时，我希望将其设置为None。

Answer 1

这可以用deserialize_with处理。

use actix_web::{web, App, HttpServer};
use serde::Deserialize;
use serde::de::{Deserializer};

#[derive(Debug, Deserialize)]
pub enum ResponseType {
    Token,
    Code,
}

fn from_response_type<'de, D>(deserializer: D) -> Result<Option<ResponseType>, D::Error>
where
    D: Deserializer<'de>,
{
    let res: Option<ResponseType> = Deserialize::deserialize(deserializer).unwrap_or(None);
    Ok(res)
}

#[derive(Debug, Deserialize)]
pub struct AuthRequest {
    id: u64,
    #[serde(deserialize_with = "from_response_type")]
    response_type: Option<ResponseType>,
}

async fn index(web::Query(info): web::Query<AuthRequest>) -> String {
    format!(
        "Authorization request for client with id={} and type={:?}!",
        info.id, info.response_type
    )
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| App::new().route("/", web::get().to(index)))
        .bind(("127.0.0.1", 8080))?
        .run()
        .await
}

任何无效值都被视为None。关键是

let res: Option<ResponseType> = Deserialize::deserialize(deserializer).unwrap_or(None);