Middleware

🏗️ Middleware

Middleware components are interceptors that can process HTTP requests before they reach the final route handler. They are ideal for cross-cutting concerns like logging, authentication, and header manipulation.

📚 The Middleware Interface

Levtus uses a functional interface Middleware which provides the current LevtusContext and a Runnable to trigger the next step in the chain.

@FunctionalInterface
public interface Middleware {
    void handle(LevtusContext ctx, Runnable next);
}

⚙️ How it Works

1. Execution Chain: Middleware are executed in the order they are registered using app.use().
2. Passing Control: You must call next.run() to pass control to the next middleware or the final route handler.
3. Short-circuiting: If you don't call next.run(), the request stops there. This is useful for unauthorized access or early exits.

📝 Examples

Simple Logger

app.use((ctx, next) -> {
    System.out.println("Incoming: " + ctx.req().method() + " " + ctx.req().path());
    next.run();
});

Authentication Guard

app.use((ctx, next) -> {
    String auth = ctx.header("Authorization");
    if ("secret-token".equals(auth)) {
        next.run(); // Authorized
    } else {
        ctx.status(401).send("Unauthorized"); // Short-circuit
    }
});

Response Timer

app.use((ctx, next) -> {
    long start = System.currentTimeMillis();
    next.run();
    long end = System.currentTimeMillis();
    System.out.println("Handled in " + (end - start) + "ms");
});