Routing requests

Routing Requests

This is an action in the default HTTP sequence. Its responsibility is to find a route that can handle a given http request. By default, the FindRoute action uses the RoutingTable from @loopback/rest to match requests against registered routes including controller methods using request.method and request.path. For example:

• GET /orders => OrderController.getOrders (@get('/orders'))
• GET /orders/123 => OrderController.getOrderById (@get('/orders/{id}'))
• GET /orders/count => OrderController.getOrderCount (@get('/orders/count'))
• POST /orders => OrderController.createOrder (@post('/orders'))

Customize the FindRoute action

The FindRoute action is bound to SequenceActions.FIND_ROUTE ('rest.sequence.actions.findRoute') and injected into the default sequence.

To create your own FindRoute action, bind your implementation as follows:

const yourFindRoute: FindRoute = ...;
app.bind(SequenceActions.FIND_ROUTE).to(yourFindRoute);

Customize the REST Router

Instead of rewriting FindRoute action completely, LoopBack 4 also allows you to simply replace the RestRouter implementation.

The @loopback/rest module ships two built-in routers:

• TrieRouter: it keeps routes as a trie tree and uses traversal to match request to routes based on the hierarchy of the path
• RegExpRouter: it keeps routes as an array and uses path-to-regexp to match request to routes based on the path pattern

For both routers, routes without variables are optimized in a map so that any requests matching to a fixed path can be resolved quickly.

By default, @loopback/rest uses TrieRouter as it performs better than RegExpRouter. There is a simple benchmarking for RegExpRouter and TrieRouter at https://githhub.com/loopbackio/loopback-next/benchmark/src/rest-routing/routing-table.ts.

To change the router for REST routing, we can bind the router class as follows:

import {RestBindings, RegExpRouter} from '@loopback/rest';
app.bind(RestBindings.ROUTER).toClass(RegExpRouter);

It's also possible to have your own implementation of RestRouter interface below:

/**
 * Interface for router implementation
 */
export interface RestRouter {
  /**
   * Add a route to the router
   * @param route - A route entry
   */
  add(route: RouteEntry): boolean;

  /**
   * Find a matching route for the given http request
   * @param request - Http request
   * @returns The resolved route, if not found, `undefined` is returned
   */
  find(request: Request): ResolvedRoute | undefined;

  /**
   * List all routes
   */
  list(): RouteEntry[];
}

See examples at:

• TrieRouter
• RegExpRouter