Deprecated Functional error on Magento 2.4.5

Question

I'm getting following error while compiling magento 2.4.5 which is newly upgraded from Magento 2.4.3

 Deprecated Functionality: Zend_Http_UserAgent implements the Serializable interface, which is deprecated. Implement __serialize() and __unserialize() instead (or in addition, if support for old PHP versions is necessary) in /var/www/html/wff/vendor/magento/zendframework1/library/Zend/Http/  
  UserAgent.php on line 37 

                                                                                                                      
                                                      



 report.ERROR: Deprecated Functionality: Zend_Http_UserAgent implements the Serializable interface, which is deprecated. Implement __serialize() and __unserialize() instead (or in addition, if support for old PHP versions is necessary) in /var/www/html/wff/vendor/magento/zendframework1/library/Zend/Http/UserAgent.php on line 37
#0 /var/www/html/wff/vendor/magento/zendframework1/library/Zend/Http/UserAgent.php(37): Magento\Framework\App\ErrorHandler->handler()
#1 /var/www/html/wff/vendor/composer/ClassLoader.php(480): include('...')
#2 /var/www/html/wff/vendor/composer/ClassLoader.php(346): Composer\Autoload\includeFile()
#3 [internal function]: Composer\Autoload\ClassLoader->loadClass()
#4 /var/www/html/wff/vendor/magento/framework/GetParameterClassTrait.php(34): ReflectionClass->__construct()
#5 /var/www/html/wff/vendor/magento/framework/Code/Reader/ClassReader.php(42): Magento\Framework\Code\Reader\ClassReader->getParameterClass()
#6 /var/www/html/wff/setup/src/Magento/Setup/Module/Di/Code/Reader/ClassReaderDecorator.php(35): Magento\Framework\Code\Reader\ClassReader->getConstructor()
#7 /var/www/html/wff/setup/src/Magento/Setup/Module/Di/Code/Reader/Decorator/Area.php(53): Magento\Setup\Module\Di\Code\Reader\ClassReaderDecorator->getConstructor()
#8 /var/www/html/wff/setup/src/Magento/Setup/Module/Di/App/Task/Operation/Area.php(116): Magento\Setup\Module\Di\Code\Reader\Decorator\Area->getList()
#9 /var/www/html/wff/setup/src/Magento/Setup/Module/Di/App/Task/Operation/Area.php(87): Magento\Setup\Module\Di\App\Task\Operation\Area->getDefinitionsCollection()
#10 /var/www/html/wff/setup/src/Magento/Setup/Module/Di/App/Task/Manager.php(56): Magento\Setup\Module\Di\App\Task\Operation\Area->doOperation()
#11 /var/www/html/wff/setup/src/Magento/Setup/Console/Command/DiCompileCommand.php(216): Magento\Setup\Module\Di\App\Task\Manager->process()
#12 /var/www/html/wff/vendor/symfony/console/Command/Command.php(255): Magento\Setup\Console\Command\DiCompileCommand->execute()
#13 /var/www/html/wff/vendor/symfony/console/Application.php(1021): Symfony\Component\Console\Command\Command->run()
#14 /var/www/html/wff/vendor/symfony/console/Application.php(275): Symfony\Component\Console\Application->doRunCommand()
#15 /var/www/html/wff/vendor/magento/framework/Console/Cli.php(116): Symfony\Component\Console\Application->doRun()
#16 /var/www/html/wff/vendor/symfony/console/Application.php(149): Magento\Framework\Console\Cli->doRun()
#17 /var/www/html/wff/bin/magento(23): Symfony\Component\Console\Application->run()
#18 {main} [] []

Can any one help me how to fix this php version 8.1

Answer 1

One of your custom modules or a 3rd-party module (extension) caused this issue.

I never get this error before but I guess a module (extension) called Zend_Http_UserAgent class which has an error as you mentioned.

To detect which file (module) caused this error, go to your Magento root directory, and run the following command:

grep -r --exclude-dir=vendor/magento/zendframework1/library/Zend/Http Zend_Http_UserAgent .

If you still need to use this module and need to use Zend_Http_UserAgent class, apply the following patch to make Zend_Http_UserAgent compatible with PHP 8.1:

Patch file to allow Zend_Http_UserAgent compatible with PHP 8.1 by Tu Van

diff --git a/vendor/magento/zendframework1/library/Zend/Http/UserAgent.php b/vendor/magento/zendframework1/library/Zend/Http/UserAgent.php
index a06402f8..17ff4490 100644
--- a/vendor/magento/zendframework1/library/Zend/Http/UserAgent.php
+++ b/vendor/magento/zendframework1/library/Zend/Http/UserAgent.php
@@ -34,7 +34,7 @@
  * @copyright  Copyright (c) 2005-2015 Zend Technologies USA Inc. (http://www.zend.com)
  * @license    http://framework.zend.com/license/new-bsd     New BSD License
  */
-class Zend_Http_UserAgent implements Serializable
+class Zend_Http_UserAgent implements \Serializable
 {
     /**
      * 'desktop' by default if the sequence return false for each item or is empty
@@ -164,12 +164,21 @@ class Zend_Http_UserAgent implements Serializable
         }
     }

+    /**
+     * Compatible with PHP 8.1
+     *
+     * @return string
+     */
+    public function serialize() {
+        return serialize($this->__serialize());
+    }
+
     /**
      * Serialized representation of the object
      *
      * @return string
      */
-    public function serialize()
+    public function __serialize()
     {
         $device = $this->getDevice();
         $spec = array(
@@ -180,7 +189,17 @@ class Zend_Http_UserAgent implements Serializable
             'user_agent'   => $this->getServerValue('http_user_agent'),
             'http_accept'  => $this->getServerValue('http_accept'),
         );
-        return serialize($spec);
+        return $spec;
+    }
+
+    /**
+     * Compatible with PHP 8.1
+     *
+     * @param string $serialized
+     * @return void
+     */
+    public function unserialize($serialized) {
+        return $this->__unserialize($serialized);
     }

     /**
@@ -189,7 +208,7 @@ class Zend_Http_UserAgent implements Serializable
      * @param  string $serialized
      * @return void
      */
-    public function unserialize($serialized)
+    public function __unserialize($serialized)
     {
         $spec = unserialize($serialized);

Take a look at this guide to know how to apply custom patch in Magento 2: https://experienceleague.adobe.com/docs/commerce-operations/upgrade-guide/patches/apply.html

I highly recommend apply patch using Composer.