Basic Wonolog Concepts

Monolog-based logging package for WordPress.

Basic Wonolog Concepts

Table of contents

Wonolog Main Logging Hook

One of the goals of Wonolog is to allow for plugins and themes to be compatible with it, without requiring it as a dependency.

For this reason, logging in Wonolog is done via a WordPress function: do_action().

The main hook to use for the scope is 'wonolog.log'.

A bare-minimum example of logging with Wonolog could look like so:

do_action( 'wonolog.log', 'Something happened.' );

This is nice and easy, however, there are a few thing missing, the most important ones being the channel and the level of the log event.

It still works because Wonolog will kindly set them according to defaults, but in general it is better to take control over this.

Log Record Data

In Monolog (and Wonolog), every log record comes with the following information:

Data Key Type Description
'message' string Textual description of the event.
'channel'° string The name of the logger to use. Every logger will handle the log differently.
'level'°° integer “Severity” of the event.
'context' array Arbitrary data providing context to the log record.

° There are no default channels in Monolog, but there are some default channels in Wonolog. These are accessible via class constants on the Channels class. More on this below.

°° The log level is normally represented by an integer, that can be compared in order of severity with the levels defined by PSR-3, which assign to each of the eight log levels a name (as interface constant) and an integer (as constant value).

An example of logging an array of data with Wonolog could be this:

do_action( 'wonolog.log', [
    'message' => 'Something happened.',
    'channel' => 'DEBUG',
    'level'   => 100,
    'context' => [],
] );

By using arrays containing log data, and do_action() to trigger the actual logging, Wonolog allows plugins and themes to be compatible without requiring Wonolog as a dependency. If code like the above is executed without Wonolog being available, nothing (bad) happens.

Moreover, at any point it would be possible to hook the log event with some other logging package, being able to log data in a different way without changing any code.

Log Record Data as Wonolog Objects

Even if arrays are a good way to make code to be logged not dependent on Wonolog, there are cases when it is desirable to write code that is dependent on Wonolog on purpose (e.g., when you are developing a Wonolog extension).

In those cases, it’s important to know that, internally, Wonolog handles log data in the form of objects implementing Inpsyde\Wonolog\Data\LogDatainterface.

There are a few of them. The simplest one is Inpsyde\Wonolog\Data\Log, whose constructor signature is the following:

public function __construct(
    $message = '',
    $level = Logger::DEBUG,
    $channel = Channels::DEBUG,
    array $context = []

By using this object, a log event that does the same as the array example from above looks like so:

do_action( 'wonolog.log', new Data\Log( 'Something happened.', Logger::CRITICAL ) );

Wonolog also ships with a series of objects that represent specific error levels, making the triggering of events less verbose. All the objects are in the Inpsyde\Wonolog\Data namespace, and there’s an object for each log level.

The constructor of those objects is the same as Inpsyde\Wonolog\Data\Log, except that they don’t take any $level, as it is specific per object.

For example, the same result of the example above could be obtained with this:

do_action( 'wonolog.log', new Data\Critical( 'Something happened.' ) );

Log Record Data from WP_Error Objects

When dealing with WordPress code, it’s easy to encounter functions that return WP_Error instances when something goes wrong.

To integrate with such code easier, Wonolog supports log record data to be passed as WP_Error objects.

The log record will include both the message and context of the WP_Error object, taken via WP_Error::get_error_message() and WP_Error::get_error_data(), respectively.

Both the channel and level can be passed explicitly, or Wonolog will try to guess them from the error code.

While this guessing has higher chances to work with WP_Error instances returned by WordPress core, it could not work that well with custom error objects.

For example, assuming a WP_Error like this:

global $wpdb;

$wp_error = new \WP_Error( $wpdb->last_error, 'wpdb_error', [ 'query' => $wpdb->last_query ] );

With this, it is possible to do the following:

do_action( 'wonolog.log', $wp_error );

Wonolog will recognize the message, the context, the channel (Channels::DB), and it will set the level to Logger::ERROR.

The level can also be set explicitly including a second argument in the do_action call, like so:

do_action( 'wonolog.log', $wp_error, Logger::CRITICAL );

Also, the channel can be set explicitly, providing a third argument:

do_action( 'wonolog.log', $wp_error, Logger::WARNING, Channels::DEBUG );

Log Record Data from Exceptions

Another common use case is to log an exception thrown during execution of code.

While it might be worth noting that uncaught exceptions will be logged by Wonolog automatically (by default), your code, hopefully, catches any thrown exception, and hence you might want to log them manually.

An example usage could be like the following:

try {
    // Do somethig here.
} catch( \Exception $exception ) {
    // Log the exception, by directly passing it to Wonolog.
    do_action( 'wonolog.log', $exception );

    if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
        // When in debugging mode, we want to see this popping up.
        throw $exception;

    // Debugging is turned off, silence is golden in production.

Note that Wonolog also works well with PHP 7+ \Throwable.

When the only argument passed to the wonolog.log action is the exception instance, the level of the log event is assumed to be LogLevel::ERROR, and the channel Channels::DEBUG. However, it is possible to explicitly pass error level and error channel, like this:

do_action( 'wonolog.log', $exception, Logger::CRITICAL, Channels::DB );

Level-rich Log Hooks

So far, we only used a single Wonolog action: 'wonolog.log'.

However, there are more action hooks that can be used to log data.

These are hooks that embed error level.

For example, the following log code:

do_action( 'wonolog.log', [ 'message' => 'Please log me!', 'level' => 'INFO' ] );

can also be written like so:

do_action( '', [ 'message' => 'Please log me!' ] );

This could make logging action calls more concise, even without relying on Wonolog objects (and thus not making code using these hooks dependent on Wonolog).

There is one hook for each of the PSR-3 log levels, so we have:

  • 'wonolog.log.emergency'
  • 'wonolog.log.alert'
  • 'wonolog.log.critical'
  • 'wonolog.log.error'
  • 'wonolog.log.warning'
  • 'wonolog.log.notice'
  • ''
  • 'wonolog.log.debug'

In case one of the above hook is used passing some data that also contains hook level information, the level with higher severity wins.

Let’s have some examples:

// In this case, the logged level will be "ERROR", because it has a higher severity than "DEBUG".
do_action( 'wonolog.log.debug', [ 'message' => 'Please log me!', 'level' => 'ERROR' ] );

// In this case, the logged level will be "CRITICAL", because it has higher severity than "ERROR".
do_action( 'wonolog.log.critical', [ 'message' => 'Please log me!', 'level' => 'ERROR' ] );

The same applies if the data is provided as Wonolog log data object:

// In this case, the logged level will be "ERROR", because it has higher severity than "DEBUG".
do_action( 'wonolog.log.error', new Data\Debug( 'Please log me!' ) );

// In this case, the logged level will be "CRITICAL", because it has higher severity than "ERROR".
do_action( 'wonolog.log.critical', new Data\Error( 'Please log me!' ) );

Read next:

  • 03 - A Deeper Look at Wonolog to learn more advanced concepts and features of Wonolog.
  • 04 - Hook Listeners to read about hook listeners, the powerful feature of Wonolog that allows for logging any WordPress code.
  • 05 - Wonolog Customization for a deep travel through all the possible configurations available for any aspect of the package.
  • 06 - Custom Hook Listeners to see a complete example of a custom hook listener, its integration in Wonolog, and all the things that you need to know in order to write reusable Wonolog extensions.

Read previous:

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