isolate fwrite to allow override

src/Monolog/Handler/StreamHandler.php

@@ -113,13 +113,23 @@ class StreamHandler extends AbstractProcessingHandler
             flock($this->stream, LOCK_EX);
         }
 
-        fwrite($this->stream, (string) $record['formatted']);
+        $this->streamWrite($this->stream, $record);
 
         if ($this->useLocking) {
             flock($this->stream, LOCK_UN);
         }
     }
 
+    /**
+     * Write to stream
+     * @param resource $stream
+     * @param array $record
+     */
+    protected function streamWrite($stream, array $record)
+    {
+        fwrite($stream, (string)$record['formatted']);
+    }
+
     private function customErrorHandler($code, $msg)
     {
         $this->errorMessage = preg_replace('{^(fopen|mkdir)\(.*?\): }', '', $msg);