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Dynamic Extensions

ring-handler injects the Match into a request and it can be extracted at runtime with reitit.ring/get-match. This can be used to build ad-hoc extensions to the system.

Example middleware to guard routes based on user roles:

(require '[reitit.ring :as ring])
(require '[clojure.set :as set])

(defn wrap-enforce-roles [handler]
  (fn [{:keys [::roles] :as request}]
    (let [required (some-> request (ring/get-match) :data ::roles)]
      (if (and (seq required) (not (set/subset? required roles)))
        {:status 403, :body "forbidden"}
        (handler request)))))

Mounted to an app via router data (effecting all routes):

(def handler (constantly {:status 200, :body "ok"}))

(def app
  (ring/ring-handler
    (ring/router
      [["/api"
        ["/ping" handler]
        ["/admin" {::roles #{:admin}}
         ["/ping" handler]]]]
      {:data {:middleware [wrap-enforce-roles]}})))

Anonymous access to public route:

(app {:request-method :get, :uri "/api/ping"})
; {:status 200, :body "ok"}

Anonymous access to guarded route:

(app {:request-method :get, :uri "/api/admin/ping"})
; {:status 403, :body "forbidden"}

Authorized access to guarded route:

(app {:request-method :get, :uri "/api/admin/ping", ::roles #{:admin}})
; {:status 200, :body "ok"}

Dynamic extensions are nice, but we can do much better. See data-driven middleware and compiling routes.

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