Clojure.spec Coercion

The clojure.spec library specifies the structure of data, validates or destructures it, and can generate data based on the spec.

Warning

clojure.spec by itself doesn't support coercion. reitit uses spec-tools that adds coercion to spec. Like clojure.spec, it's alpha as it leans on clojure.spec.alpha/conform, which is concidered a spec internal, that might be changed or removed later.

For now, all leaf specs need to be wrapped into Spec Records to get the coercion working.

There are CLJ-2116 and CLJ-2251 that would help solve this elegantly.

Example

(require '[reitit.coercion.spec])
(require '[reitit.coercion :as coercion])
(require '[spec-tools.spec :as spec])
(require '[clojure.spec.alpha :as s])
(require '[reitit.core :as r])

;; need to wrap the primitives!
(s/def ::company spec/string?)
(s/def ::user-id spec/int?)
(s/def ::path-params (s/keys :req-un [::company ::user-id]))

(def router
  (r/router
    ["/:company/users/:user-id" {:name ::user-view
                                 :coercion reitit.coercion.spec/coercion
                                 :parameters {:path ::path-params}}]
    {:compile coercion/compile-request-coercers}))

(defn match-by-path-and-coerce! [path]
  (if-let [match (r/match-by-path router path)]
    (assoc match :parameters (coercion/coerce! match))))

Successful coercion:

(match-by-path-and-coerce! "/metosin/users/123")
; #Match{:template "/:company/users/:user-id",
;        :data {:name :user/user-view,
;               :coercion <<:spec>>
;               :parameters {:path ::path-params}},
;        :result {:path #object[reitit.coercion$request_coercer$]},
;        :path-params {:company "metosin", :user-id "123"},
;        :parameters {:path {:company "metosin", :user-id 123}}
;        :path "/metosin/users/123"}

Failing coercion:

(match-by-path-and-coerce! "/metosin/users/ikitommi")
; => ExceptionInfo Request coercion failed...