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Pipeline (Legacy Pattern)

Pipeline is a legacy pattern for composing middleware, see Middleware for the modern approach.

Overview​

The Pipeline class is a helper that makes it easy to compose a set of [Middleware] and a [Handler]. It provides a fluent API for building middleware chains that process requests and responses in a specific order.

import 'package:relic/relic.dart';

final handler = const Pipeline()
  .addMiddleware(logRequests())
  .addMiddleware(corsMiddleware())
  .addMiddleware(authMiddleware())
  .addHandler(myHandler);

How Pipeline Works​

The Pipeline class uses a recursive composition pattern where each middleware wraps the next one in the chain:

  1. Request Flow: Middleware processes requests from outermost to innermost.
  2. Response Flow: Middleware processes responses from innermost to outermost.

When you call addMiddleware(), it creates a new Pipeline instance that stores the current middleware and a reference to the parent composition. When addHandler() is finally called, it recursively builds the middleware chain by wrapping each handler with its middleware.

This creates a nested structure where each middleware wraps the next, forming a Russian doll pattern of function composition.

Migration from Pipeline to router.use()​

Old Pipeline approach:

final router = Router<Handler>()
  ..get('/users', usersHandler)
  ..get('/posts', postsHandler);

final handler = const Pipeline()
  .addMiddleware(logRequests())
  .addMiddleware(authMiddleware())
  .addMiddleware(routeWith(router))
  .addHandler(respondWith((_) => Response.notFound()));

New router.use() approach:

final router = RelicRouter()
  ..use('/', logRequests())
  ..use('/', authMiddleware())
  ..get('/users', usersHandler)
  ..get('/posts', postsHandler)
  ..fallback = respondWith((_) => Response.notFound());

final handler = router.asHandler;

The new approach is more concise, provides better path-specific middleware control, and integrates more naturally with Relic's routing system.

Examples​

Check out these examples to see pipeline in action: