Middleware usage

[kevin-sakemaer]

Is there a way to use Middleware with this package?

And better to annotate a Route with some middleware we want to use for this route ?

[jonasfj]

I think it's technically possible by simply return null from an .all( handler, example:

router.all('/<ignored|.*>', (Request request) {
  // Do something here....
  return null;
});

router.get(....);

Maybe we should create a router.middleware method, and a @Middleware annotation.
I'm not sure middleware is the best name, but I'm open to suggestions.

[kevin-sakemaer]

router.all('/<ignored|.*>', (Request request) {
  // Do something here....
  return null;
});

router.get(....);

the callback on the router.all is only called before and not after the router.get. Which is not how Middleware work.
With Middleware we can hook some code before and/or after the innerHandler.

maybe we can add a named parameter to router.get/all/post/etc called middleware where we can pass a Middleware object.
and same with the annotation we can maybe pass a Middleware object.

[kevin-sakemaer]

maybe something like that ?

    router.get('/say-hi/<name>', (Request request, String name) {
      return Response.ok('hi $name');
    }, requestHandler: (req) {
      return req.change(context: {'logHandlerTime': Stopwatch()..start()});
    }, responseHandler: (res, req) {
      final sw = req.context['logHandlerTime'] as Stopwatch;
      print(sw.elapsed);
      return null;
    });

trying some API

this example raised a problem which is we can't reuse middleware across different route :/
Maybe we can have a custom Middleware (or with an other name) class to wrap this two functions with some shared context.

[jonasfj]

@kleak, another option is to leave middleware to shelf.Pipeline, see shelf middleware docs.

Looking at: https://pub.dev/documentation/shelf/latest/shelf/Pipeline-class.html
That might be a fine solution for middleware..

Mostly, you'll want middleware to wrap all requests, so one would do something like:

final router = Router();
router.get(...); // setup routes + handlers

final pipeline = Pipeline()
    .addMiddleware(loggingMiddleware)
    .addMiddleware(cachingMiddleware)
    .addHandler(router.handler);

In the rare case that we need a set of middlewares that wraps all end-points under /api/ we could create a new sub-router for /api/ and simply have an router.all('/api/' handler that forwards to a new pipeline and sub-router.

That way we keep the logic simple, and reuse the constructs given in package:shelf. If anyone is interested, I think it would be worth while to document this pattern in the example for package:shelf_router or package:shelf_router_generator. Or maybe by adding a section in the README.md..

[kevin-sakemaer]

That's seems great, I always forget the Pipeline class 🙁.

I can make a PR to add this as an example.

[kevin-sakemaer]

In fact there is a little problem.
If I want to use a middleware only on specific route I have to wrap it in a Router.
For example a middleware that check if the user is authenticated.

[jonasfj]

If I want to use a middleware only on specific route I have to wrap it in a Router.
For example a middleware that check if the user is authenticated.

Yes.

I wish we could do some sort of middleware annotations too.. Like:

class MyService {

  @shelf_router.Route.get('/my-path/<param>')
  @WithAuthorization(permission: 'user-read')
  shelf.Response myHandler(shelf.Request req, String param) {...}
}

class WithAuthorization extends shelf_router.MiddlewareAnnotation {
  /// Required permissions
  final String permission;

  const WithAuthorization({this.permission})

  @override
  shelf.Response wrapHandler(shelf.Request req, shelf.Response Function(shelf.Request) handler) {
     if (!getUser(req).permissions.contains(this.permission)) {
        return shelf.Response.unauthorized();
     }
     return handler(req);
  }
}

Such that we can create custom annotations by extending MiddlewareAnnotation. This would be super cool... But I'm not sure exactly how this should be designed or exactly how it should work.

[jonasfj]

If someone wants to draft a design and implement this, I'll be happy to help with reviews.