Basic Middleware

Volga provides several tools to help you build middleware pipelines, whether for individual routes, route groups, or the entire application.

Enabling Middleware

If you're not using the full feature set, make sure to explicitly enable the middleware feature in your Cargo.toml:

[dependencies]
volga = { version = "0.6.0", features = ["middleware"] }

Filters

The filter() method allows you to define conditional logic (such as validation or access control) for a specific route or a group of routes.

use volga::App;

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let mut app = App::new();

    // Allow only positive numbers
    app
        .map_group("/positive")
        .filter(|x: i32, y: i32| async move { x >= 0 && y >= 0 })
        .map_get("/sum/{x}/{y}", sum);
    
    // Allow only negative numbers
    app
        .map_get("/negative/sum/{x}/{y}", sum)
        .filter(|x: i32, y: i32| async move { x < 0 && y < 0 });

    app.run().await
}

async fn sum(x: i32, y: i32) -> i32 {
    x + y
}

Handling Incoming Requests

The tap_req() method gives you access to the HttpRequest, allowing you to inspect or mutate it before request processing.

use volga::{App, HttpRequest, headers::HeaderValue};

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let mut app = App::new();

    app
        .map_get("/sum", |x: i32, y: i32| async move { x + y })
        .tap_req(|mut req: HttpRequest| async move { 
            req.headers_mut()
                .insert("X-Custom-Header", HeaderValue::from_static("Custom Value"));
            req
        });

    app.run().await
}

Handling Successful Responses

Use the map_ok() method to transform or augment successful HTTP responses.

use volga::{App, HttpResponse, headers::HeaderValue};

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let mut app = App::new();

    app
        .map_group("/positive")
        .map_ok(group_response)
        .map_get("/sum/{x}/{y}", sum);

    app
        .map_get("/negative/sum/{x}/{y}", sum)
        .map_ok(route_response);

    app.run().await
}

async fn group_response(mut resp: HttpResponse) -> HttpResponse {
    resp.headers_mut()
        .insert("x-custom-header", HeaderValue::from_static("for-group"));
    resp
}

async fn route_response(mut resp: HttpResponse) -> HttpResponse {
    resp.headers_mut()
        .insert("x-custom-header", HeaderValue::from_static("for-route"));
    resp
}

async fn sum(x: i32, y: i32) -> i32 {
    x + y
}

Handling Errors

The map_err() method lets you define custom error handlers - globally, per route, or for route groups.

use volga::{App, HttpResult, error::Error, problem};
use std::io::Error as IoError;

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let mut app = App::new();
    
    app
        .map_get("/error", produce_err)
        .map_err(handle_err);

    app.run().await
}

async fn handle_err(error: Error) -> HttpResult {
    let (status, instance, err) = error.into_parts();
    problem! {
        "status": status.as_u16(),
        "detail": err.to_string(),
        "instance": instance,
    }
}

async fn produce_err() -> IoError {
    IoError::other("some error")
}

Tips

By attaching map_err() to the App, you configure a global error handler. You can read more about advanced error handling here.