Redirect 服务

pub struct Redirect<ResBody> {
    status_code: StatusCode,
    location: HeaderValue,
    // Covariant over ResBody, no dropping of ResBody
    _marker: PhantomData<fn() -> ResBody>,
}

    pub fn with_status_code(status_code: StatusCode, uri: Uri) -> Self {
        assert!(
            status_code.is_redirection(),
            "not a redirection status code"
        );

        Self {
            status_code,
            location: HeaderValue::try_from(uri.to_string())
                .expect("URI isn't a valid header value"),
            _marker: PhantomData,
        }
    }

impl<R, ResBody> Service<R> for Redirect<ResBody>
where
    ResBody: Default,
{
    type Response = Response<ResBody>;
    type Error = Infallible;
    type Future = ResponseFuture<ResBody>;
    // poll_ready：永远 Ready
    fn call(&mut self, _req: R) -> Self::Future {
        ResponseFuture {
            status_code: self.status_code,
            location: Some(self.location.clone()),
            _marker: PhantomData,
        }
    }
}

tower-http = { version = "=0.7.1", features = ["redirect"] }
tower = { version = "=0.5.3", features = ["util"] }
axum = "=0.8.9"
tokio = { version = "=1.54.1", features = ["macros", "rt"] }
http = "1"

use axum::{body::Body, response::IntoResponse, Router};
use http::{header, Request, StatusCode, Uri};
use tower::ServiceExt;
use tower_http::services::Redirect;

fn show(tag: &str, status: StatusCode, loc: Option<&http::HeaderValue>) {
  println!("{tag:<38} {status} location={loc:?}");
}

#[tokio::main(flavor = "current_thread")]
async fn main() {
  std::panic::set_hook(Box::new(|_| {}));

  // 1. 请求是什么都行，连 () 都可以
  let res = Redirect::<Body>::temporary(Uri::from_static("/login")).oneshot(()).await.unwrap();
  show("temporary, request = ()", res.status(), res.headers().get(header::LOCATION));

  // 2. 当 fallback：目标固定，不带上原来的路径
  let app = Router::new().fallback_service(Redirect::<Body>::permanent(Uri::from_static("https://example.com/")));
  let res = app.oneshot(Request::get("http://example.com/docs/a?x=1").body(Body::empty()).unwrap()).await.unwrap();
  show("permanent as fallback, GET /docs/a?x=1", res.status(), res.headers().get(header::LOCATION));

  // 3. 304 也算 3xx
  let res = Redirect::<Body>::with_status_code(StatusCode::NOT_MODIFIED, Uri::from_static("/x")).oneshot(()).await.unwrap();
  show("with_status_code(304)", res.status(), res.headers().get(header::LOCATION));

  // 4. 不是 3xx：构造时 panic
  let r = std::panic::catch_unwind(|| Redirect::<Body>::with_status_code(StatusCode::OK, Uri::from_static("/x")));
  println!("{:<38} panic: {:?}", "with_status_code(200)", r.err().and_then(|e| e.downcast_ref::<&str>().map(|s| s.to_string())));

  // 5. Uri 能不能装下 HeaderValue 不接受的字节
  for s in ["/a\tb", "/a\nb", "/a\x7fb"] {
    println!("{:<38} {:?}", format!("Uri parse {s:?}"), s.parse::<Uri>().map(|u| u.to_string()));
  }
  let res = Redirect::<Body>::temporary("/中文".parse().unwrap()).oneshot(()).await.unwrap();
  show("temporary(\"/中文\")", res.status(), res.headers().get(header::LOCATION));

  // 6. axum 的 Redirect：响应，不是服务；坏 Location 回 500
  for (tag, r) in [("axum Redirect::to", axum::response::Redirect::to("/next")), ("axum Redirect::to(\"/a\\nb\")", axum::response::Redirect::to("/a\nb"))] {
    let res = r.into_response();
    show(tag, res.status(), res.headers().get(header::LOCATION));
  }
}

temporary, request = ()                307 Temporary Redirect location=Some("/login")
permanent as fallback, GET /docs/a?x=1 308 Permanent Redirect location=Some("https://example.com/")
with_status_code(304)                  304 Not Modified location=Some("/x")
with_status_code(200)                  panic: Some("not a redirection status code")
Uri parse "/a\tb"                      Err(InvalidUri(InvalidUriChar))
Uri parse "/a\nb"                      Err(InvalidUri(InvalidUriChar))
Uri parse "/a\u{7f}b"                  Err(InvalidUri(InvalidUriChar))
temporary("/中文")                       307 Temporary Redirect location=Some("/\xe4\xb8\xad\xe6\x96\x87")
axum Redirect::to                      303 See Other location=Some("/next")
axum Redirect::to("/a\nb")             500 Internal Server Error location=None