add image format checking to the animated gif handler

src/toascii/models/image.clj

@@ -1,7 +1,9 @@
 (ns toascii.models.image
   (:import (java.awt.image BufferedImage)
            (javax.imageio.stream ImageInputStream)
-           (java.io Writer))
+           (javax.imageio ImageIO ImageReader)
+           (java.io Writer)
+           (java.util Iterator))
   (:require [clojure.java.io :as io]
             [clj-image2ascii.core :as i2a]
             [toascii.util :refer [query-param-url->java-url stream-response]]))
@@ -38,4 +40,14 @@
       (.write w "</div>")
       (.write w "<script type=\"text/javascript\">")
       (.write w js-gif-animation)
-      (.write w "</script>"))))
+      (.write w "</script>"))))
+
+(defn gif? [^ImageInputStream image-stream]
+  (let [^Iterator readers (ImageIO/getImageReaders image-stream)]
+    (->> (loop [formats []]
+           (if (.hasNext readers)
+             (recur (conj formats (.next readers)))
+             formats))
+         (map (fn [^ImageReader r]
+                (.getFormatName r)))
+         (some #(= "gif" %)))))

src/toascii/routes/api/image.clj

@@ -5,7 +5,7 @@
             [liberator.core :refer [defresource]]
             [compojure.core :refer [ANY]]
             [toascii.route-utils :refer [register-routes]]
-            [toascii.models.image :refer [image->ascii gif->ascii get-image get-image-stream]]
+            [toascii.models.image :refer [image->ascii gif->ascii get-image get-image-stream gif?]]
             [toascii.util :refer [parse-int parse-boolean]]))
 
 (defresource render-image [{:keys [url width color format] :as params}]
@@ -54,7 +54,9 @@
   :exists?
   (fn [_]
     (if-let [stream (get-image-stream url)]
-      {:image stream}
+      (if-not (gif? stream)
+        (throw (new Exception "Invalid GIF image."))
+        {:image stream})
       [false {:error "Image could not be loaded."}]))
   :handle-ok
   (fn [ctx]