How should I json encode an exception in clojure?

I would like to be able to json encode an exception object. I am pushing my logs to sumologic and would like to be able to push json encoded exception's so that I can parse and filter these logs in sumo too.

However, I can't json encode the exception and get this error:

Cannot JSON encode object of class: class java.lang.Class: class clojure.lang.ExceptionInfo

Here is my exception handler for compojure-api:

(defn exception-handler
  "Handles exceptions."
  [f]

  (fn [^Exception ex data request]
    (log/error (json/generate-string {:request-id log-helper/*request-id*
                                      :error    ex}))

    (f (.getMessage ex))))

Solution

Applications will have different needs in this regards, but one strategy can be to use Throwable->map:

(Throwable->map 
  (ex-info 
    "The Holy Grail me be found in the castle of-aaaaaaaaaaaaaaaarrrgh" 
    {:film "Monty Python and the Holy Grail (1975)"} 
    (IllegalStateException. "aaaaargh")))
=> 
{:cause "aaaaargh",
 :via
 [{:type clojure.lang.ExceptionInfo,
   :message
   "The Holy Grail me be found in the castle of-aaaaaaaaaaaaaaaarrrgh",
   :data {:film "Monty Python and the Holy Grail (1975)"},
   :at [clojure.core$ex_info invokeStatic "core.clj" 4739]}
  {:type java.lang.IllegalStateException,
   :message "aaaaargh",
   :at [user$eval13 invokeStatic "NO_SOURCE_FILE" 2]}],
 :trace
 [[user$eval13 invokeStatic "NO_SOURCE_FILE" 2]
  [user$eval13 invoke "NO_SOURCE_FILE" 2]
  [clojure.lang.Compiler eval "Compiler.java" 7062]
  [clojure.lang.Compiler eval "Compiler.java" 7025]
  [clojure.core$eval invokeStatic "core.clj" 3206]
  [clojure.core$eval invoke "core.clj" 3202]
  [clojure.main$repl$read_eval_print__8572$fn__8575
   invoke
   "main.clj"
   243]
  [clojure.main$repl$read_eval_print__8572 invoke "main.clj" 243]
  [clojure.main$repl$fn__8581 invoke "main.clj" 261]
  [clojure.main$repl invokeStatic "main.clj" 261]
  [clojure.main$repl_opt invokeStatic "main.clj" 325]
  [clojure.main$main invokeStatic "main.clj" 424]
  [clojure.main$main doInvoke "main.clj" 387]
  [clojure.lang.RestFn invoke "RestFn.java" 397]
  [clojure.lang.AFn applyToHelper "AFn.java" 152]
  [clojure.lang.RestFn applyTo "RestFn.java" 132]
  [clojure.lang.Var applyTo "Var.java" 702]
  [clojure.main main "main.java" 37]]}

If you want to make a custom data representation of Exceptions, I recommend you have a look at the source of Throwable->map to know how to fetch the relevant information.