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Bug ReportVersionPlatformCrates
DescriptionWhen trying to use the // Cargo.toml
//
// [package]
// name = "mvp"
// version = "0.1.0"
// edition = "2021"
//
// [dependencies]
// axum = "0.8.4"
// axum-extra = "0.10.1"
// tokio = { version = "1.47.1", features = ["full"] }
// tower-http = { version = "0.6.6", features = ["trace"] }
use axum::{Router, routing};
use tower_http::trace::TraceLayer;
use axum_extra::middleware::option_layer;
#[tokio::main]
async fn main() {
let trace_layer = TraceLayer::new_for_http();
let app = Router::new()
.route("/", routing::get(|| async { "Hello, World!" }))
.layer(trace_layer)
.layer(option_layer(Some(trace_layer)));
//
// ^^ Expect this to work, but get following error. (Of course a dummy setup, but it should illustrate that the trace layer works without the option_layer wrapper).
//
// error[E0271]: type mismatch resolving `<Route as Service<Request<Body>>>::Response == Response<ResponseBody<Body, NeverClassifyEos<ServerErrorsFailureClass>>>`
// --> src/main.rs:12:10
// |
// 12 | .layer(option_layer(Some(trace_layer)));
// | ^^^^^ expected `Response<ResponseBody<..., ...>>`, found `Response<Body>`
// |
// = note: expected struct `Response<ResponseBody<Body, NeverClassifyEos<ServerErrorsFailureClass>>>`
// found struct `Response<Body>`
// = note: required for `Either<Trace<Route, SharedClassifier<ServerErrorsAsFailures>>, Route>` to implement `tower_service::Service<axum::http::Request<Body>>`
//
// For more information about this error, try `rustc --explain E0271`.
let listener = tokio::net::TcpListener::bind("0.0.0.0:3001").await.unwrap();
axum::serve(listener, app).await.unwrap();
} |
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Replies: 1 comment 3 replies
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Without testing the setup, what I think happens is that the trace layer changes the body type of the response, which the optional layer does not support though it doesn't seem to be documented. This doesn't work: let app = Router::new()
.layer(option_layer(Some(TraceLayer::new_for_http())))
.with_state(state);while this does: let app = Router::new()
.layer(option_layer(Some((
tower_http::map_response_body::MapResponseBodyLayer::new(axum::body::Body::new),
TraceLayer::new_for_http(),
))))
.with_state(state);What happens is By using a tuple as shown, it first applies the trace layer but then wraps it again in the same body, changing it back. |
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Thank you for a through response, that does clarify things (and makes my example work after your changes). Certainly a bit unergonomic, though fully understandable from a strongly typed perspective. |
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I think we might do the conversion automatically. We already do it for |
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That would be great! I think I might be overcomplicating things, as my type-foo is not too great, though after some fiddeling I got a helper function sorta working. fn erased_option_layer<L, B>(
layer: Option<L>,
) -> Either<
(
MapResponseBodyLayer<impl Fn(B) -> axum::body::Body + Clone>,
//MapResponseBodyLayer<fn(B) -> axum::body::Body>,
// Would prefer the latter, but get an mismatched types
// regarding the unique type of the function pointer:
// = note: expected enum `std::option::Option<(MapResponseBodyLayer<fn(_) -> axum::body::Body>, _)>`
// found enum `std::option::Option<(MapResponseBodyLayer<fn(_) -> axum::body::Body {axum::body::Body::new::<B>}>, _)>`
L,
),
Identity,
>
where
B: HttpBody<Data = Bytes> + Send + 'static,
<B as HttpBody>::Error: Error + Send + Sync + 'static,
{
let eraser = MapResponseBodyLayer::new(axum::body::Body::new::<B>);
option_layer(layer.map(move |m| (eraser, m)))
} |
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Without testing the setup, what I think happens is that the trace layer changes the body type of the response, which the optional layer does not support though it doesn't seem to be documented.
This doesn't work:
while this does:
What happens is
optinal_layercreatesEither<T, Idnetity>which implementsLayerbut the returned service imple…