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#reitit
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2021-04-06
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wonderlastking13:04:45

Hello! Its time to add my question too, Can someone explain me how the compiled middlewares (:compile) work? For example, this web-app example https://github.com/PrestanceDesign/usermanager-reitit-integrant-example defines a middleware-db this way:

(def middleware-db
  {:name ::db
   :compile (fn [{:keys [db]} _]
              (fn [handler]
                (fn [req]
                  (handler (assoc req :db db)))))})
My question is which are the 2 arguments from the fn {:keys [db]} _ ] and where they come from?

ikitommi13:04:20

• 1st arg: the full route data • 2nd arg: router options

ikitommi13:04:45

hope this helps

wonderlastking14:04:17

nice! Thanks 🙂

Jonas Svalin17:04:20

In bidi you can define your route and handler separately and then have them mapped through the bidi/make-handler function, for example:

(def route 
 [""
   [["/" :index]
    ["/ping" :ping])

(def handlers
 {:index ...
  :ping ...})

(bidi/make-handler route handlers)
In reitit implementations I’ve only seen the handlers defined in-line in the route-definition, such as:
(def routes
  [["/" {:get {:handler ...}}]
   ["/ping" {:get {:handler ...}}]])
Can I do the same in reitit as the bidi-example out of the box somehow, or would I have to write the equivalent to the make-handler function myself? I’ve inspected the reitit-ring/ring-handler function signature, but if I understand it correctly it does not have an overload that would support this. Does this functionality exist somewhere else that I’m missing?

Jonas Svalin07:04:37

Excellent, thanks for you help @ikitommi :thumbsup:

Jonas Svalin08:04:46

Perfectly solved my problem, much appreciated

stopa17:04:58

Hey team, a bit of a noob question. I am writing my own custom exception / logging middleware. I put them at the end of reitit/router, etc A: wrap at end

(-> (ring/ring-handler (ring/router ...)
    wrap-logging
    wrap-uncaught-exception)
But, here’s the problem: My expectation is, since the middleware is wrapping ring/ring-handler, all the parsing of parameters, etc, should happen before it gets to wrap-logging
(defn wrap-logging [handler]
  (fn [req] ...))
But, it does not, the request in wrap-logging does not have :parameters `:session`, etc However, if I instead move this middleware into the :middleware key: A: wrap in :middleware
(defn api-routes []
  ["/api"
   {:middleware [;; uncaught exceptions
                 middleware/wrap-uncaught-exception
                 ;; logging
                 middleware/wrap-logging
                 ;; query-params & form-params
Then it does have those keys. This is surprising to me. I would expect that both A and B should have had :session and :`parameters` Am sure I’m misunderstanding something. If you have thoughts would love to hear!

ikitommi18:04:32

In the first A, the logging is applied before the router is invoked. In ring, the middleware chain in run in reverse order. Inside reitit router, mw is run in reverse-reverse order, e.g. in "right" order.

stopa19:04:35

Thanks for jumping in @ikitommi Would you mind expanding a bit deeper, on how A is being applied before the router is invoked? If it’s

(-> (ring/ring-handler (ring/router ...)
    wrap-logging
    wrap-uncaught-exception)
Wouldn’t this imply that first ring/router is run, than ring-handler, then ring-logging, etc? (or does ring/router doesn’t quite invoke it yet?