improve session ID assignment to avoid possible overlaps.

Signed-off-by: Taylor Otwell <taylorotwell@gmail.com>

laravel/session/drivers/driver.php

@@ -1,6 +1,6 @@
-<?php namespace Laravel\Session\Drivers;
+<?php namespace Laravel\Session\Drivers; use Laravel\Config, Laravel\Str;
 
-interface Driver {
+abstract class Driver {
 
 	/**
 	 * Load a session from storage by a given ID.
@@ -10,7 +10,7 @@ interface Driver {
 	 * @param  string  $id
 	 * @return array
 	 */
-	public function load($id);
+	abstract public function load($id);
 
 	/**
 	 * Save a given session to storage.
@@ -20,7 +20,7 @@ interface Driver {
 	 * @param  bool   $exists
 	 * @return void
 	 */
-	public function save($session, $config, $exists);
+	abstract public function save($session, $config, $exists);
 
 	/**
 	 * Delete a session from storage by a given ID.
@@ -28,6 +28,43 @@ interface Driver {
 	 * @param  string  $id
 	 * @return void
 	 */
-	public function delete($id);
+	abstract public function delete($id);
+
+	/**
+	 * Insert a fresh session and return the payload array.
+	 *
+	 * @return array
+	 */
+	public function fresh()
+	{
+		// We will simply generate an empty session payload array, using an ID
+		// that is not currently assigned to any existing session within the
+		// application and return it to the driver.
+		return array('id' => $this->id(), 'data' => array(
+			':new:' => array(),
+			':old:' => array(),
+		));
+	}
+
+	/**
+	 * Get a new session ID that isn't assigned to any current session.
+	 *
+	 * @return string
+	 */
+	public function id()
+	{
+		$session = array();
+
+		// We'll containue generating random IDs until we find an ID that is
+		// not currently assigned to a session. This is almost definitely
+		// going to happen on the first iteration.
+		do {
+
+			$session = $this->load($id = Str::random(40));			
+
+		} while ( ! is_null($session));
+
+		return $id;
+	}
 
 }