add content_length configuration

flight/net/Response.php

@@ -34,6 +34,13 @@ class Response {
      */
     protected $sent = false;
     
+    /**
+     * header Content-Length
+     *
+     * @var boolean
+     */
+    public $content_length = true;
+
     /**
      * @var array HTTP status codes
      */
@@ -251,12 +258,14 @@ class Response {
             }
         }
 
+        if ($this->content_length) {
             // Send content length
             $length = $this->getContentLength();
 
             if ($length > 0) {
                 header('Content-Length: '.$length);
             }
+        }
 
         return $this;
     }