Passing state as parameter to a ring handler?

Question

How does one inject state into ring handlers most conveniently (without using global vars)?

Here is an example:

(defroutes main-routes
  (GET \"/api/         


        

Answer 1

In addition to what Alex described some routing frameworks for ring have a place for additional arguments which can be accessed by all handlers. In reitit this would work by putting custom objects under :data:

 (reiti.ring/ring-handler
   (reiti.ring/router
    [ ["/api"
      ["/math" {:get {:parameters {:query {:x int?, :y int?}}
                      :responses  {200 {:body {:total pos-int?}}}
                      :handler    (fn [{{{:keys [x y]} :query} :parameters}]
                                    {:status 200
                                     :body   {:total (+ x y)}})}}]] ]
    {:syntax    :bracket
     :exception pretty/exception
     :data      {:your-custom-data your-custom-data
                 :coercion   reitit.coercion.spec/coercion
                 :muuntaja   m/instance
                 :middleware []}}))

In your handler you're supposed to only work with :parameters, but you will be able to access your custom data by selecting :reitit.core/match and :data. The argument that the handler receives is based entirely on this:

(defrecord Match [template data result path-params path])
(defrecord PartialMatch [template data result path-params required])