Route and service types #346

kellytk · 2021-09-25T16:00:43Z

kellytk
Sep 25, 2021

I can use a service inline:

.route("/Cargo.toml", service::get(ServeFile::new("Cargo.toml")))

And separately if I have a handler:

async fn handle() -> String {
    String::from("handle")
}

I can use it:

.route("/", handler::get(handle))

How can the same be done with the service, moving its body into a separate function?

async fn file_service() -> ServeFile {
    ServeFile::new("Cargo.toml")
}

.route("/Cargo.toml", service::get(file_service))

Generates the error:

error[E0277]: the trait bound `fn() -> impl Future {file_service}: tower_service::Service<Request<axum::body::Body>>` is not satisfied
  --> src/main.rs:11:31
   |
11 |         .route("/Cargo.toml", service::get(file_service));
   |                               ^^^^^^^^^^^^ the trait `tower_service::Service<Request<axum::body::Body>>` is not implemented for `fn() -> impl Future {file_service}`

Answered by davidpdrsn

Sep 25, 2021

You can make a handler that calls a service and returns it's response. The most common way is some_service.oneshot(request).await but there are a number useful methods on tower::ServiceExt.

View full answer

davidpdrsn · 2021-09-25T16:24:07Z

davidpdrsn
Sep 25, 2021
Collaborator

You can make a handler that calls a service and returns it's response. The most common way is some_service.oneshot(request).await but there are a number useful methods on tower::ServiceExt.

3 replies

kellytk Sep 25, 2021
Author

Thank you. How should the return value of some_service.oneshot(request).await be converted to a value acceptable to handler::get()?

.route("/Cargo.toml", handler::get(file_handler))

async fn file_handler(
    request: Request<Body>,
) -> Result<Response<ServeFileResponseBody>, std::io::Error> {
    ServeFile::new("Cargo.toml")
        .oneshot(request)
        .await
}

Generates the error:

error[E0277]: the trait bound `fn(Request<axum::body::Body>) -> impl Future {file_handler}: Handler<_, _>` is not satisfied
   --> src/main.rs:13:44
    |
13  |         .route("/Cargo.toml", handler::get(file_handler));
    |                                            ^^^^^^^^^^^^ the trait `Handler<_, _>` is not implemented for `fn(Request<axum::body::Body>) -> impl Future {file_handler}`

davidpdrsn Sep 25, 2021
Collaborator

As mentioned in the docs handlers must return something that implements IntoResponse which std::io::Error does not. So you have to somehow convert that into a response that's appropriate for your app. You can match on the result or use Result::map_err.

kellytk Sep 25, 2021
Author

By [temporarily] adding unwrap to oneshot's await and stripping the Result and Error from the return type the code now compiles. Thanks again.

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Route and service types #346

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Route and service types #346

kellytk Sep 25, 2021

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davidpdrsn Sep 25, 2021 Collaborator

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