Middleware 🍔

Middleware in Dart Frog allows you to execute code before and after a request is processed. You can modify the inbound request and outbound responses, provide dependencies, and more!

In Dart Frog, a piece of middleware consists of a middleware function exported from a _middleware.dart file within a subdirectory of the routes folder. There can only ever be one piece of middleware per route directory with routes/_middleware.dart being middleware that is executed for all inbound requests.

import 'package:dart_frog/dart_frog.dart';

Handler middleware(Handler handler) {
  return (context) async {
    // Execute code before request is handled.

    // Forward the request to the respective handler.
    final response = await handler(context);

    // Execute code after request is handled.

    // Return a response.
    return response;
  };
}

We can chain built-in middleware, such as the requestLogger middleware via the use API. For example, if we create routes/_middleware.dart with the following contents, we will automatically log all requests to our server.

import 'package:dart_frog/dart_frog.dart';

Handler middleware(Handler handler) {
  return handler.use(requestLogger());
}

Creating Middleware

To create new middleware on a Dart Frog project, run the following command:

# Creates routes/hello/_middleware.dart
dart_frog new middleware "/hello"

tip

Install and use the Dart Frog VS Code extension to easily create new middleware within your IDE.