Add default-handler support, #37

cognitect · Sep 5, 2019 · 972759a · 972759a
1 parent a64663e
commit 972759a
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Showing 2 changed files with 31 additions and 2 deletions.
diff --git a/src/cognitect/transit.clj b/src/cognitect/transit.clj
@@ -146,15 +146,19 @@
    with the default-handlers and then with the default handlers
    provided by transit-java.
 
+   :default-handler - a default WriteHandler to use if NO handler is
+   found for a type. If no default is specified, an error will be
+   thrown for an unknown type.
+
    :transform - a function of one argument that will transform values before
    they are written."
   ([out type] (writer out type {}))
-  ([^OutputStream out type {:keys [handlers transform]}]
+  ([^OutputStream out type {:keys [handlers default-handler transform]}]
      (if (#{:json :json-verbose :msgpack} type)
        (let [handler-map (if (instance? HandlerMapContainer handlers)
                            (handler-map handlers)
                            (merge default-write-handlers handlers))]
-         (Writer. (TransitFactory/writer (transit-format type) out handler-map nil
+         (Writer. (TransitFactory/writer (transit-format type) out handler-map default-handler
                     (when transform
                       (reify Function
                         (apply [_ x]

diff --git a/test/transit/test_handlers.clj b/test/transit/test_handlers.clj
@@ -0,0 +1,25 @@
+(ns transit.test-handlers
+  (:require [clojure.test :refer [deftest is run-tests]]
+            [cognitect.transit :as t])
+  (:import [java.io ByteArrayInputStream ByteArrayOutputStream]))
+
+(defrecord R [a])
+
+(deftest test-no-default
+  ;; no default handler: throws
+  (is (thrown? Exception
+        (let [out (ByteArrayOutputStream. 4096)
+              writer (t/writer out :json)]
+          (t/write writer (atom 1)))))
+
+  ;; add default handler: succeeds
+  (let [out (ByteArrayOutputStream. 4096)
+        default-handler (t/write-handler
+                          (fn [_] "atom")
+                          (fn [a] @a))
+        writer (t/writer out :json {:default-handler default-handler})]
+    (t/write writer (atom 1))))
+
+(comment
+  (run-tests)
+  )