Default Middleware

[metosin/reitit-middleware "0.3.4"]

Any Ring middleware can be used with reitit-ring, but using data-driven middleware is preferred as they are easier to manage and in many cases, yield better performance. reitit-middleware contains a set of common ring middleware, lifted into data-driven middleware.

• Parameter Handling
• Exception Handling
• Content Negotiation
• Multipart Request Handling
• Inspecting Middleware Chain

Parameters Handling

reitit.ring.middleware.parameters/parameters-middleware to capture query- and form-params. Wraps ring.middleware.params/wrap-params.

NOTE: will be factored into two parts: a query-parameters middleware and a Muuntaja format responsible for the the application/x-www-form-urlencoded body format.

Exception Handling

A polished version of compojure-api exception handling. Catches all exceptions and invokes configured exception handler.

(require '[reitit.ring.middleware.exception :as exception])

exception/exception-middleware

A preconfigured middleware using exception/default-handlers. Catches:

• Request & response Coercion exceptions
• Muuntaja decode exceptions
• Exceptions with :type of :reitit.ring/response, returning :response key from ex-data.
• Safely all other exceptions

(require '[reitit.ring :as ring])

(def app
  (ring/ring-handler
    (ring/router
      ["/fail" (fn [_] (throw (Exception. "fail")))]
      {:data {:middleware [exception/exception-middleware]}})))

(app {:request-method :get, :uri "/fail"})
;{:status 500
; :body {:type "exception"
;        :class "java.lang.Exception"}}

exception/create-exception-middleware

Creates the exception-middleware with custom options. Takes a map of identifier => exception request => response that is used to select the exception handler for the thrown/raised exception identifier. Exception idenfier is either a Keyword or a Exception Class.

The following handlers are available by default:

key	description
:reitit.ring/response	value in ex-data key :response will be returned
:muuntaja/decode	handle Muuntaja decoding exceptions
:reitit.coercion/request-coercion	request coercion errors (http 400 response)
:reitit.coercion/response-coercion	response coercion errors (http 500 response)
::exception/default	a default exception handler if nothing else matched (default exception/default-handler).
::exception/wrap	a 3-arity handler to wrap the actual handler handler exception request => response (no default).

The handler is selected from the options map by exception idenfitifier in the following lookup order:

1. :type of exception ex-data
2. Class of exception
3. :type ancestors of exception ex-data
4. Super Classes of exception
5. The ::default handler

;; type hierarchy
(derive ::error ::exception)
(derive ::failure ::exception)
(derive ::horror ::exception)

(defn handler [message exception request]
  {:status 500
   :body {:message message
          :exception (.getClass exception)
          :data (ex-data exception)
          :uri (:uri request)}})

(def exception-middleware
  (exception/create-exception-middleware
    (merge
      exception/default-handlers
      {;; ex-data with :type ::error
       ::error (partial handler "error")

       ;; ex-data with ::exception or ::failure
       ::exception (partial handler "exception")

       ;; SQLException and all it's child classes
       java.sql.SQLException (partial handler "sql-exception")

       ;; override the default handler
       ::exception/default (partial handler "default")

       ;; print stack-traces for all exceptions
       ::exception/wrap (fn [handler e request]
                          (println "ERROR" (pr-str (:uri request)))
                          (handler e request))})))

(def app
  (ring/ring-handler
    (ring/router
      ["/fail" (fn [_] (throw (ex-info "fail" {:type ::failue})))]
      {:data {:middleware [exception-middleware]}})))

(app {:request-method :get, :uri "/fail"})
; ERROR "/fail"
; => {:status 500,
;     :body {:message "default"
;            :exception clojure.lang.ExceptionInfo
;            :data {:type :user/failue}
;            :uri "/fail"}}

Content Negotiation

Wrapper for Muuntaja middleware for content-negotiation, request decoding and response encoding. Takes explicit configuration via :muuntaja key in route data. Emit's 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, 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])

(def app
  (ring/ring-handler
    (ring/router
      [["/math"
        {: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)}})}}]
       ["/xml"
        {: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
                           rrc/coerce-exceptions-middleware
                           rrc/coerce-request-middleware
                           rrc/coerce-response-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)

<kikka>kukka</kikka>

Multipart Request Handling

Wrapper for Ring Multipart Middleware. Emits swagger :consumes definitions automatically.

Expected route data:

key	description
[:parameters :multipart]	mounts only if defined for a route.

(require '[reitit.ring.middleware.multipart :as multipart])

• multipart/multipart-middleware a preconfigured middleware for multipart handling
• multipart/create-multipart-middleware to generate with custom configuration

Inspecting Middleware Chain

reitit.ring.middleware.dev/print-request-diffs is a middleware chain transforming function. It prints a request and response diff between each middleware. To use it, add the following router option:

:reitit.middleware/transform reitit.ring.middleware.dev/print-request-diffs

Partial sample output:

Example app

See an example app with the default middleware in action: https://github.com/metosin/reitit/blob/master/examples/ring-swagger/src/example/server.clj.