Don't start a session if it's known to be empty.

If an app only reads/checks the session there's no need to start a
session to know that the read/checked session value is empty.

Fixes #1981

lib/Cake/Model/Datasource/CakeSession.php

@@ -127,6 +127,13 @@ class CakeSession {
  */
 	protected static $_initialized = false;
 
+/**
+ * Session cookie name
+ *
+ * @var string
+ */
+	protected static $_cookieName = null;
+
 /**
  * Pseudo constructor.
  *
@@ -222,12 +229,10 @@ class CakeSession {
  * @return boolean True if variable is there
  */
 	public static function check($name = null) {
-		if (!self::start()) {
+		if (empty($name) || !self::_hasSession() || !self::start()) {
-			return false;
-		}
-		if (empty($name)) {
 			return false;
 		}
+
 		return Hash::get($_SESSION, $name) !== null;
 	}
 
@@ -321,7 +326,7 @@ class CakeSession {
  * @return boolean Success
  */
 	public static function valid() {
-		if (self::read('Config')) {
+		if (self::start() && self::read('Config')) {
 			if (self::_validAgentAndTime() && self::$error === false) {
 				self::$valid = true;
 			} else {
@@ -369,18 +374,19 @@ class CakeSession {
  * Returns given session variable, or all of them, if no parameters given.
  *
  * @param string|array $name The name of the session variable (or a path as sent to Set.extract)
- * @return mixed The value of the session variable
+ * @return mixed The value of the session variable, null if session not available,
+ *   session not started, or provided name not found in the session.
  */
 	public static function read($name = null) {
-		if (!self::start()) {
+		if (empty($name) && $name !== null) {
 			return false;
 		}
+		if (!self::_hasSession() || !self::start()) {
+			return null;
+		}
 		if ($name === null) {
 			return self::_returnSessionVars();
 		}
-		if (empty($name)) {
-			return false;
-		}
 		$result = Hash::get($_SESSION, $name);
 
 		if (isset($result)) {
@@ -410,12 +416,10 @@ class CakeSession {
  * @return boolean True if the write was successful, false if the write failed
  */
 	public static function write($name, $value = null) {
-		if (!self::start()) {
+		if (empty($name) || !self::start()) {
-			return false;
-		}
-		if (empty($name)) {
 			return false;
 		}
+
 		$write = $name;
 		if (!is_array($name)) {
 			$write = array($name => $value);
@@ -443,6 +447,7 @@ class CakeSession {
 
 		$_SESSION = null;
 		self::$id = null;
+		self::$_cookieName = null;
 	}
 
 /**
@@ -482,9 +487,12 @@ class CakeSession {
 		if (!isset($sessionConfig['ini']['session.cookie_lifetime'])) {
 			$sessionConfig['ini']['session.cookie_lifetime'] = $sessionConfig['cookieTimeout'] * 60;
 		}
+
 		if (!isset($sessionConfig['ini']['session.name'])) {
 			$sessionConfig['ini']['session.name'] = $sessionConfig['cookie'];
 		}
+		self::$_cookieName = $sessionConfig['ini']['session.name'];
+
 		if (!empty($sessionConfig['handler'])) {
 			$sessionConfig['ini']['session.save_handler'] = 'user';
 		}
@@ -522,6 +530,39 @@ class CakeSession {
 		self::$sessionTime = self::$time + ($sessionConfig['timeout'] * 60);
 	}
 
+/**
+ * Get session cookie name.
+ *
+ * @return string
+ */
+	protected static function _cookieName() {
+		if (self::$_cookieName !== null) {
+			return self::$_cookieName;
+		}
+
+		self::init();
+
+		$sessionConfig = Configure::read('Session');
+		if (isset($sessionConfig['ini']['session.name'])) {
+			return self::$_cookieName = $sessionConfig['ini']['session.name'];
+		}
+
+		$defaults = self::_defaultConfig($sessionConfig['defaults']);
+		if ($defaults) {
+			return self::$_cookieName = $defaults['cookie'];
+		}
+
+		return self::$_cookieName = ini_get('session.name');
+	}
+
+/**
+ * Returns whether a session exists
+ * @return boolean
+ */
+	protected static function _hasSession() {
+		return self::started() || isset($_COOKIE[self::_cookieName()]);
+	}
+
 /**
  * Find the handler class and make sure it implements the correct interface.
  *

lib/Cake/Test/Case/Controller/Component/SessionComponentTest.php

@@ -135,10 +135,6 @@ class SessionComponentTest extends CakeTestCase {
  * @return void
  */
 	public function testSessionIdConsistentAcrossRequestAction() {
-		$Session = new SessionComponent($this->ComponentCollection);
-		$Session->check('Test');
-		$this->assertTrue(isset($_SESSION));
-
 		$Object = new Object();
 		$Session = new SessionComponent($this->ComponentCollection);
 		$expected = $Session->id();
@@ -274,7 +270,7 @@ class SessionComponentTest extends CakeTestCase {
 	public function testSessionId() {
 		unset($_SESSION);
 		$Session = new SessionComponent($this->ComponentCollection);
-		$Session->check('test');
+		CakeSession::start();
 		$this->assertEquals(session_id(), $Session->id());
 	}
 

lib/Cake/Test/Case/I18n/I18nTest.php

@@ -17,6 +17,7 @@
  */
 
 App::uses('I18n', 'I18n');
+App::uses('CakeSession', 'Model/Datasource');
 
 /**
  * I18nTest class
@@ -1517,7 +1518,7 @@ class I18nTest extends CakeTestCase {
  * @return void
  */
 	public function testSetLanguageWithSession() {
-		$_SESSION['Config']['language'] = 'po';
+		CakeSession::write('Config.language', 'po');
 		$singular = $this->_singular();
 		$this->assertEquals('Po (translated)', $singular);
 
@@ -1548,7 +1549,7 @@ class I18nTest extends CakeTestCase {
 		$this->assertTrue(in_array('23 everything else (po translated)', $plurals));
 		$this->assertTrue(in_array('24 everything else (po translated)', $plurals));
 		$this->assertTrue(in_array('25 everything else (po translated)', $plurals));
-		unset($_SESSION['Config']['language']);
+		CakeSession::delete('Config.language');
 	}
 
 /**

lib/Cake/Test/Case/Model/Datasource/CakeSessionTest.php

@@ -114,7 +114,6 @@ class CakeSessionTest extends CakeTestCase {
 			'cookieTimeout' => 120,
 			'ini' => array(),
 		));
-		TestCakeSession::init();
 	}
 
 /**