salvo-middleware（齐射中间件）

Salvo Middleware

In Salvo, middleware is just a Handler that calls ctrl.call_next(...). Attach it with hoop(); it runs for the current router and all descendants.

Basic middleware

use salvo::prelude::*;

#[handler]
async fn logger(
    req: &mut Request,
    depot: &mut Depot,
    res: &mut Response,
    ctrl: &mut FlowCtrl,
) {
    println!("--> {} {}", req.method(), req.uri().path());
    ctrl.call_next(req, depot, res).await;
    println!("<-- {}", res.status_code().unwrap_or(StatusCode::OK));
}

let router = Router::new().hoop(logger).get(handler);

Omit ctrl.call_next(...) only at the end of the chain; otherwise downstream handlers will not run.

Scoping

hoop() on a router applies to that router and its descendants. Compose scopes with push():

let router = Router::new()
    .hoop(logger)                                       // global
    .push(
        Router::with_path("api")
            .hoop(auth_check)                           // only /api/**
            .hoop(rate_limiter)
            .push(Router::with_path("users").get(list_users))
    )
    .push(Router::with_path("public").get(public_handler));  // no auth

FlowCtrl

• call_next(req, depot, res).await — run the next handler
• skip_rest() — skip all remaining handlers (the response you set is returned)
• cease() — skip_rest() plus mark as ceased; subsequent middleware should check is_ceased()
• is_ceased() — has the flow been explicitly ceased

Salvo also auto-skips the rest of the chain when a handler sets an error (4xx/5xx) or redirect (3xx) status.

Authentication pattern

#[handler]
async fn auth_check(
    req: &mut Request,
    depot: &mut Depot,
    res: &mut Response,
    ctrl: &mut FlowCtrl,
) {
    let token = req.header::<String>("Authorization");
    match token.as_deref().and_then(validate_token) {
        Some(user) => {
            depot.insert("user", user);
            ctrl.call_next(req, depot, res).await;
        }
        None => {
            res.render(StatusError::unauthorized());
            ctrl.skip_rest();
        }
    }
}

Setting an error status via StatusError auto-stops the chain, but calling skip_rest() explicitly is clearer.

Depot for sharing data

#[handler]
async fn protected(depot: &mut Depot) -> String {
    // Depot::get returns Result<&V, _>, not Option
    let user: &User = depot.get("user").unwrap();
    format!("hello, {}", user.name)
}

Depot API:

• depot.insert(key, value) — stores by string key
• depot.get::<V>(key) — returns Result<&V, Option<&Box<dyn Any>>>
• depot.inject(value) — stores by type (single value per type)
• depot.obtain::<V>() — retrieves by type, returns Result

Prefer inject / obtain when the type itself is the key; use insert / get when you need multiple values of the same type distinguished by name.

Early response

#[handler]
async fn guard(
    req: &mut Request,
    _depot: &mut Depot,
    res: &mut Response,
    ctrl: &mut FlowCtrl,
) {
    if !is_valid(req) {
        res.render(StatusError::bad_request().brief("invalid input"));
        ctrl.skip_rest();
    }
    // fall through to call_next if you want to continue
}

CORS

use salvo::cors::Cors;
use salvo::http::Method;

let cors = Cors::new()
    .allow_origin("https://example.com")
    .allow_methods(vec![Method::GET, Method::POST])
    .allow_headers(vec!["Content-Type", "Authorization"])
    .into_handler();

let router = Router::new().hoop(cors).get(handler);

Cors is a builder; call .into_handler() before passing to hoop(). Cors::permissive() also requires .into_handler().

Rate limiting

use salvo::rate_limiter::{BasicQuota, FixedGuard, MokaStore, RateLimiter, RemoteIpIssuer};

let limiter = RateLimiter::new(
    FixedGuard::new(),
    MokaStore::new(),
    RemoteIpIssuer,
    BasicQuota::per_second(10),
);

let router = Router::new().hoop(limiter).get(handler);

Built-in middleware

use std::time::Duration;
use salvo::logging::Logger;
use salvo::compression::Compression;
use salvo::timeout::Timeout;

let router = Router::new()
    .hoop(Logger::new())
    .hoop(Compression::new())
    .hoop(Timeout::new(Duration::from_secs(30)));

Execution order (onion model)

Router::new()
    .hoop(a)  // outermost
    .hoop(b)
    .hoop(c)  // innermost
    .get(handler);
// a-before -> b-before -> c-before -> handler
//                                  -> c-after -> b-after -> a-after

Code after ctrl.call_next(...) runs on the way out. Put logging/timing outermost, auth before authorization, body parsing before handlers that need it.

Related Skills

• salvo-auth: Authentication and authorization middleware
• salvo-cors: CORS middleware configuration
• salvo-compression: Response compression middleware
• salvo-logging: Request logging and tracing middleware