reitit/doc/ring/dynamic_extensions.md
2021-07-27 18:33:17 +02:00

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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.
This example shows a middleware to guard routes based on user roles:
```clj
(require '[reitit.ring :as ring])
(require '[clojure.set :as set])
(defn wrap-enforce-roles [handler]
(fn [{:keys [my-roles] :as request}]
(let [required (some-> request (ring/get-match) :data ::roles)]
(if (and (seq required) (not (set/subset? required my-roles)))
{:status 403, :body "forbidden"}
(handler request)))))
```
Mounted to an app via router data (affecting all routes):
```clj
(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:
```clj
(app {:request-method :get, :uri "/api/ping"})
; {:status 200, :body "ok"}
```
Anonymous access to guarded route:
```clj
(app {:request-method :get, :uri "/api/admin/ping"})
; {:status 403, :body "forbidden"}
```
Authorized access to guarded route:
```clj
(app {:request-method :get, :uri "/api/admin/ping", :my-roles #{:admin}})
; {:status 200, :body "ok"}
```
Dynamic extensions are nice, but we can do much better. See [data-driven middleware](data_driven_middleware.md) and [compiling routes](compiling_middleware.md).