Don't submit directories to MIME type checks or any other checks which depend upon them.

httphandlers.go

@@ -71,6 +71,12 @@ func GetHandler(config Config) http.HandlerFunc {
 			http.Error(w, "File not world-readable.", http.StatusForbidden)
 			return
 		}
+		// If this is a directory, nothing below makes sense, so just
+		// serve it!
+		if info.IsDir() {
+			http.ServeFile(w, r, path)
+			return
+		}
 
 		// Get MIME type
 		ext := filepath.Ext(path)