Proof of concept for bringing your own JSON library

project.clj

@@ -11,7 +11,8 @@
                                     :sign-releases false}]]
   :plugins [[lein-cljfmt "0.6.4"]]
   :global-vars {*warn-on-reflection* true}
-  :profiles {:dev {:dependencies [[org.clojure/clojure "1.10.1"]
+  :profiles {:dev {:dependencies [[org.clojure/clojure "1.11.1"]
+                                  [org.clojure/data.json "2.4.0"]
                                   [cheshire "5.10.0"]
                                   [ring/ring-core "1.9.0"]
                                   [javax.servlet/servlet-api "2.5"]

src/hato/middleware.clj

@@ -22,15 +22,25 @@
    (java.util.zip
     GZIPInputStream InflaterInputStream ZipException Inflater)))
 
-;; Cheshire is an optional dependency, so we check for it at compile time.
+(def ^:dynamic *json-lib* nil)
 
+(defmulti decode-json
+  (fn [[lib & _]]
+    lib))
 
-(def json-enabled?
-  (try
-    (require
-     'cheshire.core)
-    true
-    (catch Throwable _ false)))
+(defmethod decode-json :default [& _]
+  (throw (ex-info "JSON library not loaded!"
+                  {:type           :json-lib-not-loaded
+                   :json-lib-value *json-lib*})))
+
+(defmulti encode-json
+  (fn [[lib & _]]
+    lib))
+
+(defmethod encode-json :default [& _]
+  (throw (ex-info "JSON library not loaded!"
+                  {:type           :json-lib-not-loaded
+                   :json-lib-value *json-lib*})))
 
 ;; Transit is an optional dependency, so check at compile time.
 (def transit-enabled?
@@ -69,14 +79,12 @@
 (defn ^:dynamic json-encode
   "Resolve and apply cheshire's json encoding dynamically."
   [& args]
-  {:pre [json-enabled?]}
-  (apply (ns-resolve (symbol "cheshire.core") (symbol "encode")) args))
+  (encode-json (cons *json-lib* args)))
 
 (defn ^:dynamic json-decode-stream-strict
   "Resolve and apply cheshire's json decoding dynamically (with lazy parsing disabled)."
   [& args]
-  {:pre [json-enabled?]}
-  (apply (ns-resolve (symbol "cheshire.core") (symbol "parse-stream-strict")) args))
+  (decode-json (cons *json-lib* args)))
 
 ;;;
 
@@ -168,7 +176,7 @@
   [{:keys [coerce]} {:keys [body status] :as resp} keyword?]
   (let [^String charset (or (-> resp :content-type-params :charset) "UTF-8")
         decode-func json-decode-stream-strict]
-    (if json-enabled?
+    (if *json-lib*
       (cond
         (and (unexceptional-status? status)
              (or (nil? coerce) (= coerce :unexceptional)))
@@ -501,10 +509,10 @@
 
 (defmethod coerce-form-params :application/json
   [{:keys [form-params json-opts]}]
-  (when-not json-enabled?
+  (when-not *json-lib*
     (throw (ex-info (str "Can't encode form params as \"application/json\". "
-                         "Cheshire dependency not loaded.")
-                    {:type        :cheshire-not-loaded
+                         "Requires cheshire or clojure.data.json library.")
+                    {:type        :json-lib-not-loaded
                      :form-params form-params
                      :json-opts   json-opts})))
   (json-encode form-params json-opts))

src/hato/optional/cheshire.clj

@@ -0,0 +1,11 @@
+(ns hato.optional.cheshire
+  (:require [cheshire.core :as cheshire]
+            [hato.middleware :refer [decode-json encode-json]]))
+
+(defmethod decode-json 'cheshire [[_ & args]]
+  (apply cheshire/parse-stream-strict args))
+
+(defmethod encode-json 'cheshire [[_ & args]]
+  (apply cheshire/encode args))
+
+(alter-var-root #'hato.middleware/*json-lib* (constantly 'cheshire))

src/hato/optional/data_json.clj

@@ -0,0 +1,16 @@
+(ns hato.optional.data-json
+  (:require [clojure.data.json :as json]
+            [hato.middleware :refer [decode-json encode-json]]))
+
+(defmethod decode-json 'clojure.data.json [[_ reader key-fn & args]]
+  (apply json/read reader
+                   :key-fn (if (true? key-fn)
+                             keyword
+                             identity)
+                   args))
+
+(defmethod encode-json 'clojure.data.json [[_ & args]]
+  ;; Mimicks the behavior of cheshire.core/encode
+  (apply json/write-str args))
+
+(alter-var-root #'hato.middleware/*json-lib* (constantly 'clojure.data.json))