example middleware

example.rs

type Handler = Box<Fn(i32) -> i32>;
type Middleware = fn(Handler) -> Handler;

struct Router {
    middleware: Vec<Middleware>,
}

impl Router {
    pub fn new() -> Router {
        Router {
            middleware: Vec::new(),
        }
    }

    pub fn add_middleware(mut self, middleware: Middleware) -> Self {
        self.middleware.push(middleware);
        self
    }

    fn middleware(&self, next: Handler) -> Handler {
        if self.middleware.len() == 0 {
            next
        } else {
            self.next_middleware(self.middleware.len() - 1, next)
        }
    }

    fn next_middleware(&self, index: usize, next: Handler) -> Handler {
        let current = self.middleware.get(index).unwrap();
        match index == 0 {
            true => current(next),
            false => current(self.next_middleware(index - 1, next))
        }
    }
}

fn my_middleware(next: Handler) -> Handler {
    println!("middleware");
    let f = move |req: i32| -> i32 {
        next(req - 1)
    };
    Box::new(f)
}

fn handler(req: i32) -> i32 {
    println!("handler");
    req + 1
}

pub fn main() {
    let r = Router::new().add_middleware(my_middleware);
    let result = r.middleware(Box::new(handler))(31);
    println!("{}", result);
}