PSR Logger

A PSR-3 compatible logger factory with namespace breadcrumbs, log-level filtering, and context placeholder interpolation. See the full PSR-3 specification for the interface contract this library implements.

Requirements

• PHP 8.2 or higher
• psr/log ^2.0 || ^3.0

Installation

With composer:

composer require helsingborg-stad/psr-logger

Basic usage

use PsrLogger\LoggerFactory;
use PsrLogger\Loggers\PhpErrorLogger;
use Psr\Log\LogLevel;

$factory = new LoggerFactory(
    namespace: 'MyPlugin',
    loggers: [['logger' => new PhpErrorLogger(), 'logLevel' => LogLevel::ERROR]]
);

$logger = $factory->createLogger();
$logger->error('Something went wrong');
// → [ERROR]:[MyPlugin]: Something went wrong
$logger->debug('Verbose detail');  // suppressed — below ERROR threshold
$logger->info('Just FYI');         // suppressed — below ERROR threshold

Child loggers (namespace tree)

createLogger() returns a LoggerInterface & LoggerFactoryInterface, so you can branch the namespace tree by calling createLogger(['namespace' => '...']) on any logger.

$app       = $factory->createLogger();
$moduleA   = $app->createLogger(['namespace' => 'ModuleA']);
$component = $moduleA->createLogger(['namespace' => 'Component']);

$app->error('app');
// → [ERROR]:[MyPlugin]: app

$moduleA->error('moduleA');
// → [ERROR]:[MyPlugin/ModuleA]: moduleA

$component->error('component');
// → [ERROR]:[MyPlugin/ModuleA/Component]: component

Namespace display defaults to breadcrumbMaxCount: -1 — all segments are shown. Set breadcrumbMaxCount to a positive integer to limit how many are displayed (e.g. 2 shows only the first and last segment).

Context placeholders

{key} tokens in the message are replaced with matching values from the $context array.

$logger->error('User {user.name} failed to log in', ['user' => ['name' => 'Alice']]);
// → [ERROR]:[MyPlugin]: User Alice failed to log in

$logger->debug('Payload: {data}', ['data' => ['id' => 1, 'status' => 'fail']]);
// → [DEBUG]:[MyPlugin]: Payload: {
//       "id": 1,
//       "status": "fail"
//   }

$logger->debug('Response: {res}', ['res' => $someObject]);
// → [DEBUG]:[MyPlugin]: Response: {
//       "prop": "value"
//   }

• Valid key characters are A-Za-z0-9_. — hyphens, whitespace, or other characters leave the token unreplaced
• No whitespace inside braces: { name } is never interpolated
• Dot notation resolves nested arrays (user.name → $context['user']['name'])
• A flat key ('user.name') takes precedence over dot-notation traversal when both exist in context
• Scalars (int, float) are cast to string; Stringable objects call __toString(); arrays and objects are JSON-encoded
• Unresolved keys (missing from context or no matching resolver) are left as the original {key} token
• When using custom resolvers, the first matching resolver wins — later ones are not evaluated
• Arrays and objects are JSON-encoded with JSON_PRETTY_PRINT by default. Pass a custom jsonResolverFlag per-logger to change the encoding flags

Custom logger implementation

Any class implementing LoggerInterface can be used as a destination. The simplest approach is to extend Psr\Log\NullLogger and override only log() — NullLogger provides no-op implementations of all the level-specific methods (debug(), info(), etc.) that forward to log().

use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use Stringable;

class FileLogger extends NullLogger implements LoggerInterface
{
    public function __construct(private string $path) {}

    public function log($level, string|Stringable $message, array $context = []): void
    {
        file_put_contents($this->path, $message . PHP_EOL, FILE_APPEND);
    }
}

$factory = new LoggerFactory(
    namespace: 'MyPlugin',
    loggers: [['logger' => new FileLogger('/tmp/app.log'), 'logLevel' => LogLevel::DEBUG]]
);

The two built-in loggers follow the same pattern:

• PhpErrorLogger — passes the formatted message to error_log().
• InMemoryLogger — appends each record to a public $records array; useful for testing.

LoggerFactory Constructor options

Parameter	Default	Description
$namespace	'PluginNameSpace'	Root namespace label
$loggers	[['logger' => NullLogger, 'logLevel' => ERROR]]	One or more logger + level pairs
$logLevel	LogLevel::ERROR	Default threshold for all loggers

Per-logger options (inside $loggers entries)

Key	Description
logger	Any LoggerInterface instance
logLevel	Minimum level for this logger. Available levels (high → low): emergency, alert, critical, error, warning, notice, info, debug
breadcrumbMaxCount	Max namespace segments shown (-1 = all, default -1)
breadcrumbDirection	Which end to trim: 'left' (default) or 'right'
formatStr	sprintf format string — receives LEVEL, namespace, message
jsonResolverFlag	json_encode flags for array/object placeholders (default JSON_PRETTY_PRINT)
resolvers	Custom [callable $test, callable $transform][] pairs for placeholder resolution