interceptors.md

Interceptors

Reitit has also support for interceptors as an alternative to using middleware. Basic interceptor handling is implemented in reitit.interceptor package. There is no interceptor executor shipped, but you can use libraries like Pedestal Interceptor or Sieppari to execute the chains.

Reitit-http

[metosin/reitit-http "0.5.12"]

A module for http-routing using interceptors instead of middleware. Builds on top of the reitit-ring module having all the same features.

The differences:

• :interceptors key used in route data instead of :middleware
• reitit.http/http-router requires an extra option :executor of type reitit.interceptor/Executor to execute the interceptor chain
  • optionally, a routing interceptor can be used - it enqueues the matched interceptors into the context. See reitit.http/routing-interceptor for details.

Simple example

(require '[reitit.ring :as ring])
(require '[reitit.http :as http])
(require '[reitit.interceptor.sieppari :as sieppari])

(defn interceptor [number]
  {:enter (fn [ctx] (update-in ctx [:request :number] (fnil + 0) number))})

(def app
  (http/ring-handler
    (http/router
      ["/api"
       {:interceptors [(interceptor 1)]}

       ["/number"
        {:interceptors [(interceptor 10)]
         :get {:interceptors [(interceptor 100)]
               :handler (fn [req]
                          {:status 200
                           :body (select-keys req [:number])})}}]])

    ;; the default handler
    (ring/create-default-handler)

    ;; executor
    {:executor sieppari/executor}))


(app {:request-method :get, :uri "/"})
; {:status 404, :body "", :headers {}}

(app {:request-method :get, :uri "/api/number"})
; {:status 200, :body {:number 111}}

Why interceptors?

• https://quanttype.net/posts/2018-08-03-why-interceptors.html
• https://www.reddit.com/r/Clojure/comments/9csmty/why_interceptors/