diff --git a/src/GatewayChecksum.php b/src/GatewayChecksum.php
index b112fa3..585dd59 100644
--- a/src/GatewayChecksum.php
+++ b/src/GatewayChecksum.php
@@ -11,8 +11,8 @@
 class GatewayChecksum
 {
     public static $checksum = "";
-    public static $baseChecksum = "8f5eedd22eee69780abd2eb4d7ca7f1f";
-    public static $versionNo = "P8.11";
+    public static $baseChecksum = "a25b794b7ab3ce7af7ef7d73c3aad975";
+    public static $versionNo = "P8.12";
 
 //////////////////////////////////////////////////////////////////////
 //
@@ -30,7 +30,7 @@ static function SetVersion()
             md5_file($dirName . "/GatewayCodes.php");
         GatewayChecksum::$checksum = md5($baseString);
         if (GatewayChecksum::$checksum != GatewayChecksum::$baseChecksum) {
-            GatewayChecksum::$versionNo = "P8.11m";
+            GatewayChecksum::$versionNo = "P8.12m";
         }
     }
 }
diff --git a/src/GatewayService.php b/src/GatewayService.php
index 442efa5..263b95b 100644
--- a/src/GatewayService.php
+++ b/src/GatewayService.php
@@ -61,6 +61,11 @@ class GatewayService
 //
     private $curlCallback;
 
+//
+// Optional curl response callback function after curl_exec()
+//
+    private $curlResponseCallback;
+
 //////////////////////////////////////////////////////////////////////
 //
 //	GatewayService() - Constructor for class.
@@ -426,6 +431,20 @@ function SetCurlCallback($callback)
         $this->curlCallback = $callback;
     }
 
+//////////////////////////////////////////////////////////////////////
+//
+//	SetCurlResponseCallback() - Set optional curl response callback
+//			 that will allow to manipulate
+//			 with CURL instance after curl_exec().
+//
+//////////////////////////////////////////////////////////////////////
+//
+    function SetCurlResponseCallback($callback)
+    {
+        $this->curlResponseCallback = $callback;
+    }
+
+
 //////////////////////////////////////////////////////////////////////
 //
 //	PerformTransaction() - Perform the transaction outlined
@@ -715,11 +734,21 @@ function PerformConfirmation(GatewayRequest $request, GatewayResponse $response)
 //
     function PerformCURLTransaction($host, GatewayRequest $request, GatewayResponse $response)
     {
+
+        $results_headers = [];
 //
 //	Reset the response object and turn the request into
 //	a string that can be transmitted.
 //
         $response->Reset();// Clear old contents
+//
+// indicate in version that a user function has been used
+//
+        if (is_callable($this->curlCallback) || is_callable($this->curlResponseCallback)) {
+            $request->Set(GatewayRequest::VERSION_INDICATOR(),
+                GatewayChecksum::$versionNo. "c");
+        }
+
         $requestBytes = $request->ToXMLString();// Change to XML request
 
 //
@@ -853,12 +882,34 @@ function PerformCURLTransaction($host, GatewayRequest $request, GatewayResponse
 //
         if (is_callable($this->curlCallback)) {
             $handle = call_user_func($this->curlCallback, $handle);
+
+            curl_setopt($handle, CURLOPT_HEADERFUNCTION,
+                function($curl, $header) use (&$results_headers)
+                {
+                    $len = strlen($header);
+                    $header = explode(':', $header, 2);
+                    if (count($header) < 2) // ignore invalid headers
+                        return $len;
+
+                    $results_headers[strtolower(trim($header[0]))][] = trim($header[1]);
+
+                    return $len;
+                }
+            );
         }
 
 //
 //	Execute the operation.
 //
         $results = curl_exec($handle);// Execute the operation
+
+//
+//  Apply optional curlResponseCallback if available
+//
+        if (is_callable($this->curlResponseCallback)) {
+            call_user_func($this->curlResponseCallback, $handle, $request, $response, $results_headers, $results);
+        }
+
         if (!($results)) {// Did it fail?
             $errorCode = curl_errno($handle);// Get the error code
             if (!$errorCode) {