Logging Information

• Configuration
  • Using Multiple Log Handlers
• Modifying the Message With Context
• Using Third-Party Loggers
• LoggerAware Trait

You can log information to the local log files by using the log_message() method. You must supplythe “level” of the error in the first parameter, indicating what type of message it is (debug, error, etc).The second parameter is the message itself:

if ($some_var == '')
{
        log_message('error', 'Some variable did not contain a value.');
}

There are eight different log levels, matching to the RFC 5424 levels, and they are as follows:

• debug - Detailed debug information.
• info - Interesting events in your application, like a user logging in, logging SQL queries, etc.
• notice - Normal, but significant events in your application.
• warning - Exceptional occurrences that are not errors, like the use of deprecated APIs, poor use of an API, or other undesirable things that are not necessarily wrong.
• error - Runtime errors that do not require immediate action but should typically be logged and monitored.
• critical - Critical conditions, like an application component not available, or an unexpected exception.
• alert - Action must be taken immediately, like when an entire website is down, the database unavailable, etc.
• emergency - The system is unusable.

The logging system does not provide ways to alert sysadmins or webmasters about these events, they solely logthe information. For many of the more critical event levels, the logging happens automatically by theError Handler, described above.

Configuration

You can modify which levels are actually logged, as well as assign different Loggers to handle different levels, withinthe /app/Config/Logger.php configuration file.

The threshold value of the config file determines which levels are logged across your application. If any levelsare requested to be logged by the application, but the threshold doesn’t allow them to log currently, they will beignored. The simplest method to use is to set this value to the minimum level that you want to have logged. For example,if you want to log debug messages, and not information messages, you would set the threshold to 5. Any log requests witha level of 5 or less (which includes runtime errors, system errors, etc) would be logged and info, notices, and warningswould be ignored:

public $threshold = 5;

A complete list of levels and their corresponding threshold value is in the configuration file for your reference.

You can pick and choose the specific levels that you would like logged by assigning an array of log level numbersto the threshold value:

// Log only debug and info type messages
public $threshold = [5, 8];

Using Multiple Log Handlers

The logging system can support multiple methods of handling logging running at the same time. Each handler canbe set to handle specific levels and ignore the rest. Currently, two handlers come with a default install:

• File Handler is the default handler and will create a single file for every day locally. This is therecommended method of logging.
• ChromeLogger Handler If you have the ChromeLogger extensioninstalled in the Chrome web browser, you can use this handler to display the log information inChrome’s console window.

The handlers are configured in the main configuration file, in the $handlers property, which is simplyan array of handlers and their configuration. Each handler is specified with the key being the fullyname-spaced class name. The value will be an array of varying properties, specific to each handler.Each handler’s section will have one property in common: handles, which is an array of log levelnames that the handler will log information for.

public $handlers = [
 
        //--------------------------------------------------------------------
        // File Handler
        //--------------------------------------------------------------------
 
        'CodeIgniter\Log\Handlers\FileHandler' => [
 
                'handles' => ['critical', 'alert', 'emergency', 'debug', 'error', 'info', 'notice', 'warning'],
        ]
];

Modifying the Message With Context

You will often want to modify the details of your message based on the context of the event being logged.You might need to log a user id, an IP address, the current POST variables, etc. You can do this by useplaceholders in your message. Each placeholder must be wrapped in curly braces. In the third parameter,you must provide an array of placeholder names (without the braces) and their values. These will be insertedinto the message string:

// Generates a message like: User 123 logged into the system from 127.0.0.1
$info = [
        'id' => $user->id,
        'ip_address' => $this->request->ip_address()
];
 
log_message('info', 'User {id} logged into the system from {ip_address}', $info);

If you want to log an Exception or an Error, you can use the key of ‘exception’, and the value being theException or Error itself. A string will be generated from that object containing the error message, thefile name and line number. You must still provide the exception placeholder in the message:

try
{
        ... Something throws error here
}
catch (\Exception $e)
{
        log_message('error', '[ERROR] {exception}', ['exception' => $e]);
}

Several core placeholders exist that will be automatically expanded for you based on the current page request:

Using Third-Party Loggers

You can use any other logger that you might like as long as it extends from eitherPsr\Log\LoggerInterface and is PSR3 compatible. This meansthat you can easily drop in use for any PSR3-compatible logger, or create your own.

You must ensure that the third-party logger can be found by the system, by adding it to eitherthe /app/Config/Autoload.php configuration file, or through another autoloader,like Composer. Next, you should modify /app/Config/Services.php to point the loggeralias to your new class name.

Now, any call that is done through the log_message() function will use your library instead.

LoggerAware Trait

If you would like to implement your libraries in a framework-agnostic method, you can usethe CodeIgniter\Log\LoggerAwareTrait which implements the setLogger() method for you.Then, when you use your library under different environments for frameworks, your library shouldstill be able to log as it would expect, as long as it can find a PSR3 compatible logger.