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Content Negotiation

Wrapper for Muuntaja middleware for content negotiation, request decoding and response encoding. Takes explicit configuration via :muuntaja key in route data. Emits swagger :produces and :consumes definitions automatically based on the Muuntaja configuration.

Negotiates a request body based on Content-Type header and response body based on Accept and Accept-Charset headers. Publishes the negotiation results as :muuntaja/request and :muuntaja/response keys into the request.

Decodes the request body into :body-params using the :muuntaja/request key in request if the :body-params doesn't already exist.

Encodes the response body using the :muuntaja/response key in request if the response doesn't have Content-Type header already set.

Expected route data:

key description
:muuntaja muuntaja.core/Muuntaja instance, does not mount if not set.
(require '[reitit.ring.middleware.muuntaja :as muuntaja])
  • muuntaja/format-middleware - Negotiation, request decoding and response encoding in a single Middleware
  • muuntaja/format-negotiate-middleware - Negotiation
  • muuntaja/format-request-middleware - Request decoding
  • muuntaja/format-response-middleware - Response encoding
(require '[reitit.ring :as ring])
(require '[reitit.ring.coercion :as rrc])
(require '[reitit.coercion.spec :as rcs])
(require '[ring.adapter.jetty :as jetty])
(require '[muuntaja.core :as m])

(def app
        {:post {:summary "negotiated request & response (json, edn, transit)"
                :parameters {:body {:x int?, :y int?}}
                :responses {200 {:body {:total int?}}}
                :handler (fn [{{{:keys [x y]} :body} :parameters}]
                           {:status 200
                            :body {:total (+ x y)}})}}]
        {:get {:summary "forced xml response"
               :handler (fn [_]
                          {:status 200
                           :headers {"Content-Type" "text/xml"}
                           :body "<kikka>kukka</kikka>"})}}]]
      {:data {:muuntaja m/instance
              :coercion rcs/coercion
              :middleware [muuntaja/format-middleware

(jetty/run-jetty #'app {:port 3000, :join? false})

Testing with httpie:

> http POST :3000/math x:=1 y:=2

HTTP/1.1 200 OK
Content-Length: 11
Content-Type: application/json; charset=utf-8
Date: Wed, 22 Aug 2018 16:59:54 GMT
Server: Jetty(9.2.21.v20170120)

 "total": 3
> http :3000/xml

HTTP/1.1 200 OK
Content-Length: 20
Content-Type: text/xml
Date: Wed, 22 Aug 2018 16:59:58 GMT
Server: Jetty(9.2.21.v20170120)


Changing default parameters

The current JSON formatter used by reitit already has the option to parse keys as keyword which is a sane default in Clojure. However, if you would like to parse all the double as bigdecimal you'd need to change an option of the JSON formatter

(def new-muuntaja-instance
    [:formats "application/json" :decoder-opts :bigdecimals]

Now you should change the m/instance installed in the router with the new-muuntaja-instance.

Here you can find more options for JSON and EDN.

Adding custom encoder

The example below is from muuntaja explaining how to add a custom encoder to parse a java.util.Date instance.

(def muuntaja-instance
      [:formats "application/json" :encoder-opts]
      {:date-format "yyyy-MM-dd"})))

(->> {:value (java.util.Date.)}
     (m/encode m "application/json")
; => "{\"value\":\"2019-10-15\"}"

Putting it all together

If you inspect m/default-options you'll find it's only a map. This means you can compose your new muuntaja instance with as many options as you need.

(def new-muuntaja
   (-> m/default-options
       (assoc-in [:formats "application/json" :decoder-opts :bigdecimals] true)
       (assoc-in [:formats "application/json" :encoder-opts :date-format] "yyyy-MM-dd"))))

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Phil Hofmann, Ronny Løvtangen & Wanderson Ferreira
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