doc: improve ring example in README.md

- format-response-middleware wasn't doing anything, use
  format-middleware instead as that's what the users usually want
- add exception handling
- document middleware stack a bit

README.md

@@ -109,6 +109,7 @@ A Ring routing app with input & output coercion using [data-specs](https://githu
 (require '[reitit.ring :as ring])
 (require '[reitit.coercion.spec])
 (require '[reitit.ring.coercion :as rrc])
+(require '[reitit.ring.middleware.exception :as exception])
 (require '[reitit.ring.middleware.muuntaja :as muuntaja])
 (require '[reitit.ring.middleware.parameters :as parameters])
 
@@ -124,39 +125,45 @@ A Ring routing app with input & output coercion using [data-specs](https://githu
       ;; router data affecting all routes
       {:data {:coercion   reitit.coercion.spec/coercion
               :muuntaja   m/instance
-              :middleware [parameters/parameters-middleware
+              :middleware [parameters/parameters-middleware ; decoding query & form params
+                           muuntaja/format-middleware       ; content negotiation
+                           exception/exception-middleware   ; converting exceptions to HTTP responses
                            rrc/coerce-request-middleware
-                           muuntaja/format-response-middleware
                            rrc/coerce-response-middleware]}})))
 ```
 
 Valid request:
 
 ```clj
-(app {:request-method :get
+(-> (app {:request-method :get
-      :uri "/api/math"
+          :uri "/api/math"
-      :query-params {:x "1", :y "2"}})
+          :query-params {:x "1", :y "2"}})
+    (update :body slurp))
 ; {:status 200
-;  :body {:total 3}}
+;  :body "{\"total\":3}"
+;  :headers {"Content-Type" "application/json; charset=utf-8"}}
 ```
 
 Invalid request:
 
 ```clj
-(app {:request-method :get
+(-> (app {:request-method :get
-      :uri "/api/math"
+          :uri "/api/math"
-      :query-params {:x "1", :y "a"}})
+          :query-params {:x "1", :y "a"}})
-;{:status 400,
+    (update :body jsonista.core/read-value))
-; :body {:type :reitit.coercion/request-coercion,
+; {:status 400
-;        :coercion :spec,
+;  :headers {"Content-Type" "application/json; charset=utf-8"}
-;        :spec "(spec-tools.core/spec {:spec (clojure.spec.alpha/keys :req-un [:$spec20745/x :$spec20745/y]), :type :map, :keys #{:y :x}, :keys/req #{:y :x}})",
+;  :body {"spec" "(spec-tools.core/spec {:spec (clojure.spec.alpha/keys :req-un [:spec$8974/x :spec$8974/y]), :type :map, :leaf? false})"
-;        :problems [{:path [:y],
+;         "value" {"x" "1"
-;                    :pred "clojure.core/int?",
+;                  "y" "a"}
-;                    :val "a",
+;         "problems" [{"via" ["spec$8974/y"]
-;                    :via [:$spec20745/y],
+;                      "path" ["y"]
-;                    :in [:y]}],
+;                      "pred" "clojure.core/int?"
-;        :value {:x "1", :y "a"},
+;                      "in" ["y"]
-;        :in [:request :query-params]}}
+;                      "val" "a"}]
+;         "type" "reitit.coercion/request-coercion"
+;         "coercion" "spec"
+;         "in" ["request" "query-params"]}}
 ```
 
 ## More examples