Middleware: Actix Web Documentation

# Middleware

Middleware in Actix Web is a layer that wraps around a Service. It allows you to inspect, modify, or reject requests before they reach your handler, and similarly modify responses before they are sent back to the client.

##Built-in Middleware

Actix Web provides several essential middlewares out of the box: - Logger: Logs request metadata (requires env_logger or similar). - Compress: Automatically compresses HTTP responses based on client headers. - NormalizePath: Normalizes trailing slashes. - Condition: Conditionally enables other middleware.

code_blocksrust

use actix_web::{middleware::Logger, App, HttpServer};

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    env_logger::init_from_env(env_logger::Env::new().default_filter_or("info"));

    HttpServer::new(|| {
        App::new()
            // Wrap the app with the Logger middleware
            .wrap(Logger::default())
            // ... routes
    })
    .bind("127.0.0.1:8080")?
    .run()
    .await
}

##Creating Custom Middleware

Creating custom middleware requires implementing the Service and Transform traits. This can be complex because it involves generic types and futures.

For simpler use cases, Actix Web 4 introduced actix_web::middleware::from_fn, allowing you to write middleware as a simple async function!

code_blocksrust

use actix_web::{dev::{ServiceRequest, ServiceResponse}, Error, middleware::Next};

async fn my_middleware(
    req: ServiceRequest,
    next: Next<impl actix_web::body::MessageBody>,
) -> Result<ServiceResponse<impl actix_web::body::MessageBody>, Error> {
    // Pre-processing: before handler is called
    println!("Request made to: {}", req.path());

    // Call the next service in the chain (the handler)
    let res = next.call(req).await?;

    // Post-processing: after handler returns
    println!("Response status: {}", res.status());

    Ok(res)
}

// Applying it:
// App::new().wrap(actix_web::middleware::from_fn(my_middleware))

This functional approach drastically lowers the barrier to entry for adding custom authentication checks, rate limiting, or custom logging.

Middleware

##Built-in Middleware

##Creating Custom Middleware

Was this page helpful?

Reference Implementation

Related Resources