Allow HttpServer::new's arg factory function to return a Result

[jayvdb]

We use functions to build the App like

pub fn build_app() -> App<
    impl ServiceFactory<
        ServiceRequest,
        Config = (),
        Response = ServiceResponse,
        Error = actix_web::Error,
        InitError = (),
    >,
> { ...}

However there is quite a bit of logic in these functions, with lots of bits that can fail, and we'd like to have structured errors for those, so something like

pub fn build_app() -> Result<App<
    impl ServiceFactory<
        ServiceRequest,
        Config = (),
        Response = ServiceResponse,
        Error = actix_web::Error,
        InitError = (),
    >>, Error
> { ... }

Is this possible already somehow? If not, is it feasible to add?

The InitError there is very curious...

The way we work around this atm is the have a fn setup_data(..) -> Result<AppData, ..> and a fn build_app(app_data: AppData) -> App<impl ServiceFactory<..>> { } and then join them using

let data = setup_data(&env)?;

actix_web::HttpServer::new(move || build_app(data.clone()))....

[robjtede]

It's not currently possible and would require a breaking change; worth opening an issue imo.

There's some limited ways to do it for app data using .data_factory() but it's not quite what you're asking.

For now you just have to do all the fallible stuff before HttpServer::new.