How to log errors and exceptions

[manojLondhe]

Hi,

1. We added a 500 page, which works, but is there a way to catch errors and show them on 500 page when debug mode is on 500.
2. Additionally, how can we log such errors to to log files?

[johanjanssens]

Exceptions in Pages are exposed as events. They can easily be intercepted through event subscribers. Based on the type of exception different event handlers could do different things, for example:

• handling 404 not found exceptions
• handling error logging
• rendering debug information

What exceptions does Pages capture

If Pages is activate all errors and exceptions will be captured, exceptions can be triggered anywhere. Depending on your Joomla exception and error handling settings Pages will also capture exceptions in Joomla extensions and plugins that are triggered in the request/response cycle.

Pages does that by registering itself as a Joomla exception callback handler through: JError::setErrorHandling(E_ERROR, 'callback', array($this, 'handleException'));

See: event/subscriber/exception.php#L24

Basic exception event subscriber

This is an example of a custom exception handler you can add to your own site. Add it to: /joomlatools-pages/extensions/pages/event/subscriber/exception.php

class ExtPagesEventSubscriberException extends ComPagesEventSubscriberAbstract
{
    public function onException(KEvent $event)
    {
        $exception = $event->exception;

        if($exception->getCode() == 500)
        {
             //Handle exception here
        }
    }
}

Exception logger using Monolog

This is an example of a Monolog exception logger you can add to your own site. Add it to: /joomlatools-pages/extensions/pages/event/subscriber/error.php

Object properties:

• enabled: An event subscriber has an enabled property to to allow you to disable it dynamically, by default a subscriber is enabled. Here i'm disabling it if debug is off. If you want to always enable it, take out this code.
• base_path: Using the pages logs path to store the error logs

<?php

use Monolog\Logger;
use Monolog\Handler\StreamHandler;
use Monolog\Processor\WebProcessor;
use Monolog\Formatter\LineFormatter;

class ExtPagesEventSubscriberError extends ComPagesEventSubscriberAbstract
{
    protected function _initialize(KObjectConfig $config)
    {
        $config->append([
            'enabled'  => JDEBUG ? true : false,
            'base_path'  => $this->getObject('com:pages.config')->getSitePath('logs'),
        ]);

        parent::_initialize($config);
    }

    public function getFile()
    {
        return $this->getConfig()->base_path.'/'.'error.log';
    }

    //https://chrishewett.com/blog/monolog-human-readable-exception-email-with-stack-trace/
    //http://www.inanzzz.com/index.php/post/xj81/handling-and-logging-exceptions-in-symfony-api-applications
    public function onException(KEvent $event)
    {
        if(class_exists('Monolog\Logger'))
        {
            $exception = $event->exception;
            
             //If the exception code does not correspond to a http status message, use 500
            $code = $exception->getCode();
            if(!isset(KHttpResponse::$status_messages[$code])) {
                $code = '500';
            }

            if($code >= 500)
            {
                //Log invalid requests exception
                $file = $this->getFile();

                // Create a logger
                $logger  = new Logger('error');
                $handler = new StreamHandler($file);
                $handler->setFormatter(new PrintRLineFormatter());

                $logger->pushHandler($handler);
                $logger->pushProcessor(new WebProcessor());
                $logger->pushProcessor(function ($record)
                {
                    if( !empty( $_SERVER ) ){
                        $record['extra']['_SERVER'] = $_SERVER;
                    }
                    if( !empty( $_SESSION ) ){
                        $record['extra']['_SESSION'] = $_SESSION;
                    }
                    if( !empty( $_POST ) ){
                        $record['extra']['_POST'] = $_POST;
                    }
                    return $record;

                });

                $log = [
                    'code' => $exception->getCode(),
                    'message' => $exception->getMessage(),
                    'file' => $exception->getFile(),
                    'line' => $exception->getLine(),
                ];

                if ($exception->getPrevious() instanceof Exception)
                {
                    $log += [
                        'previous' => [
                            'message' => $exception->getPrevious()->getMessage(),
                            'exception' => get_class($exception->getPrevious()),
                            'file' => $exception->getPrevious()->getFile(),
                            'line' => $exception->getPrevious()->getLine(),
                        ],
                    ];
                }

                $logger->error($exception->getMessage(), $log);
            }
        }
    }
}

class PrintrLineFormatter extends LineFormatter
{
    public function format(array $record)
    {
        return print_r( $record, true );
    }
}

Logrotation

The exception logger is build to be used during development to log exceptions. If you want to use it production it's advised tot setup a log rotator.

You can use the Monolog RotatingFileHandler to handle log rotation.

You should use logrotate for high profile setups though, this is just meant as a quick and dirty solution.