Logging with dot-log in Zend Expressive and Dotkernel

Adding the config provider

• Open config/config.php.
• If there's no entry for the dot-log config provider, add \Dot\Log\ConfigProvider::class.
• Make sure it's added before application-specific components, e.g. Frontend\App\ConfigProvider::class, Admin\App\ConfigProvider::class, MyProject\ConfigProvider::class.
• Inside Dot\Log\ConfigProvider, the dependencies section registers an abstract factory, LoggerAbstractServiceFactory::class. This class responds to "selectors" instead of class names - instead of requesting Zend\Log\Logger::class from the container, you request dot-log.my_logger (or just my_logger if using zend-log).
• Create a log.global.php file within /config/autoload, returning an empty array to start.

Configuring the logger

For this tutorial, the created logger is named my_logger (the name is the developer's choice and should reflect its purpose, e.g. db_error_logger).

In log.global.php:

1. Add a top-level key dot-log (or log if using zend-log) with an array value.
2. Inside it, add a loggers key.
3. Inside that, add the logger name key (my_logger) with an empty array.

For the logger to actually log somewhere, a writer is required - without one, log calls are received but there's nowhere to write the message.

Configuring the writer(s)

Loggers must have at least one writer. A writer is an object that inherits from Zend\Log\Writer\AbstractWriter, responsible for recording log data to a storage backend (see the zend-log writer documentation).

It's possible to separate logs into multiple files using writers and filters (e.g. warnings.log, errors.log, all_messages.log). In the simplest example, all log messages are written to one file, e.g. /data/logs/dk.log, under a writers key inside my_logger.

Notes on writer configuration:

• The writer key name (e.g. FileWriter) is optional - otherwise the writers array would be enumerative instead of associative.
• The writer's name key is a developer-provided name for that writer and is mandatory.
• The writer's priority key doesn't affect which errors get written - it's only a way to organize writers (e.g. 1 - FILE, 2 - SQL, 3 - E-mail), reflecting that writing to a file is the most reliable since SQL or e-mail servers can be external and offline. The priority key is optional.
• To write to a file, the stream key must be present in the writer's options array (required only when writing to streams/files).

More writer examples: Streams, Databases, FirePHP, ChromePHP, Mail, MongoDB, Syslog, Zend Monitor.

(Optional) Configuring the filters

A filter prevents a message from being written to the log (see the zend-log filters documentation).

Per PSR-3, the log levels, in order of priority/importance, are:

Level	Priority number
emergency	0
alert	1
critical	2
error	3
warn	4
notice	5
info	6
debug	7

Although the plain Logger in Zend Log is not fully PSR-3 compatible, it provides a way to log all of these message types. The developer can optionally use keys to name filters. Important: the operator for "more important" messages is <=, because a smaller number represents a more important message.

More on filters: zend-log filters documentation.

(Optional) Configuring the formatter

The logged value isn't limited to a string - arrays can be logged too, and for readability they can be serialized. Zend Log provides String, XML, JSON and FirePHP formatting.

The formatter config accepts:

• name - the formatter class (must implement Zend\Log\Formatter\FormatterInterface)
• options - options passed to the formatter constructor, if required

More on formatters: Simple, JSON, XML, FirePHP.

Full example (described)

A complete configuration, as described in the article, does the following:

• Uses the log through dot-log
• Names the logger my_logger
• Writes to file: data/logs/dk.log
• Explicitly allows all messages to be written
• Formats the message as JSON

Usage

Basic usage of the logger:

use Zend\Log\Logger;

$logger = $container->get('dot-log.my_logger');

/** @var Logger $logger */
$logger->emerg('0 EMERG');
$logger->alert('1 ALERT');
$logger->crit('2 CRITICAL');
$logger->err('3 ERR');
$logger->warn('4 WARN');
$logger->notice('5 NOTICE');
$logger->info('6 INF');
$logger->debug('7 debug');
$logger->log(Logger::NOTICE, 'NOTICE from log()');

Frequently Asked Questions