Add revert method

src/FontLib/BinaryStream.php

@@ -18,6 +18,7 @@ class BinaryStream {
    * @var resource The file pointer
    */
   protected $f;
+  protected $f2;
 
   const uint8        = 1;
   const  int8        = 2;
@@ -66,6 +67,9 @@ public function open($filename, $mode = self::modeRead) {
       throw new \Exception("Unknown file open mode");
     }
 
+    if ($this->f != null && $this->f != false) {
+      $this->f2 = $this->f;
+    }
     $this->f = fopen($filename, $mode);
 
     return $this->f != false;
@@ -75,9 +79,22 @@ public function open($filename, $mode = self::modeRead) {
    * Close the internal file pointer
    */
   public function close() {
+    if ($this->f2 !== null && $this->f2 !== false) {
+      fclose($this->f2);
+    }
     return fclose($this->f) != false;
   }
 
+  public function revert() {
+    if ($this->f2 !== null && $this->f !== null && $this->f !== false) {
+      fclose($this->f);
+      $this->f = $this->f2;
+      $this->f2 = null;
+      return true;
+    }
+    return false;
+  }
+
   /**
    * Change the internal file pointer
    *