Added static-file response to r.u.response

@@ -1,4 +1,5 @@
-(ns ring.util.response)
+(ns ring.util.response
+  (:import java.io.File))
 
 (defn redirect-to
   "Returns a Ring response for an HTTP redirect. 
@@ -8,3 +9,43 @@
   {:status  (:status opts 302)
    :headers {"Location" url}
    :body    ""})
+
+(defn- safe-path?
+  "Is a filepath safe for a particular root?"
+  [root path]
+  (.startsWith (.getCanonicalPath (File. root path))
+               (.getCanonicalPath (File. root))))
+
+(defn- find-index-file
+  "Search the directory for an index file."
+  [dir]
+  (first
+    (filter
+      #(.startsWith (.toLowerCase (.getName %)) "index.")
+       (.listFiles dir))))
+
+(defn- get-file
+  "Safely retrieve the correct file. See serve-file for an explanation of
+  options."
+  [path opts]
+  (let [file (if-let [root (:root opts)]
+               (if (safe-path? root path)
+                 (File. root path))
+               (File. path))]
+    (if (.exists file)
+      (if (.isDirectory file)
+        (if (:index-files? opts true)
+          (find-index-file file))
+        file))))
+
+(defn static-file
+  "Returns a Ring response to serve a static file, or nil if the file does
+  not exist.
+  Options:
+    :root         - take the filepath relative to this root path
+    :index-files? - look for index.* files in directories, defaults to true"
+  [filepath & [opts]]
+  (if-let [file (get-file filepath opts)]
+    {:status  200
+     :headers {}
+     :body    file}))