gistfile1.txt

+(defn decorate! [proxy-instance method fun]
+  (update-proxy
+   proxy-instance
+   (update-in (proxy-mappings proxy-instance)
+              [(name method)]
+              fun))
+  proxy-instance)
+
+;; should use reflection to generate method bodies
+(defmacro dummy-up [classes constructor-args methods]
+  `(proxy [~@classes] [~@constructor-args]
+     ~@(for [[name arities] methods]
+         `(~name
+           ~@(for [arity arities
+                   :let [args (map gensym (range arity))]]
+               `(~(vec args)
+                 (proxy-super ~name ~@args)))))))
+
+(defn ensured-inputstream [stream byte-count]
+  (doto (dummy-up [CountingInputStream] [stream]
+                  {read #{0 1 3}})
+    (decorate!
+     :read
+     (fn [read-fn]
+       (fn [this & args]
+         (let [r (apply read-fn this args)]
+           (when (and (= -1 r)
+                      (> byte-count (.getCount this)))
+             (throw (IllegalStateException.
+                     (format "inputstream expected length %s actual %s"
+                             byte-count
+                             (.getCount this)))))
+           r))))))