LoggerInterface PSR Proposal

LoggerInterface.php

<?php

namespace PSR\Log;

/**
 * Describes a logger instance
 *
 * The $message MUST be a string.
 * The $message MAY contain variable expressions like "%var%" which reference $data['var'].
 * The "%var%" notation MUST NOT reference values of nested arrays (eg no "%parent.child%" notation).
 * The $message SHOULD NOT include runtime data using plain string concatenation.
 *
 * The context array can contain arbitrary data, the only assumption that
 * can be made by implementors is that if an Exception instance is given
 * to produce a stack trace, it MUST be in a key named "exception".
 *
 * Example:
 * <code>
 * $log->info('LDAP authentication for "%user%" failed due to LDAP communication error with "%server%"', array(
 *   'user' => $submittedUser,
 *   'server' => $configuredServer,
 * ));
 * </code>
 */
interface LoggerInterface
{
    /**
     * System is unusable.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function emergency($message, array $context = array());

    /**
     * Action must be taken immediately. 
     *
     * Example: Entire website down, database unavailable, etc. This should 
     * trigger the SMS alerts and wake you up.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function alert($message, array $context = array());

    /**
     * Critical conditions. 
     *
     * Example: Application component unavailable, unexpected exception.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function critical($message, array $context = array());

    /**
     * Runtime errors that do not require immediate action but should typically
     * be logged and monitored.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function error($message, array $context = array());

    /**
     * Exceptional occurrences that are not errors. 
     *
     * Example: Use of deprecated APIs, poor use of an API, undesirable things
     * that are not necessarily wrong.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function warning($message, array $context = array());

    /**
     * Normal but significant events.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function notice($message, array $context = array());

    /**
     * Interesting events. 
     *
     * Example: User logs in, SQL logs.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function info($message, array $context = array());

    /**
     * Detailed debug information.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function debug($message, array $context = array());
}

NoopLogger.php

<?php

namespace PSR\Log;

/**
 * This Logger can be used to avoid conditional log calls
 * 
 * Logging should always be optional, and if no logger is provided to your
 * library creating a NullLogger instance to have something to throw logs at
 * is a good way to avoid littering your code with `if ($this->logger) { }`
 * blocks.
 */
class NullLogger implements LoggerInterface
{
    /**
     * {@inheritDoc}
     */
    public function emergency($message, array $context = array())
    {
        // noop
    }

    /**
     * {@inheritDoc}
     */
    public function alert($message, array $context = array())
    {
        // noop
    }

    /**
     * {@inheritDoc}
     */
    public function critical($message, array $context = array())
    {
        // noop
    }

    /**
     * {@inheritDoc}
     */
    public function error($message, array $context = array())
    {
        // noop
    }

    /**
     * {@inheritDoc}
     */
    public function warning($message, array $context = array())
    {
        // noop
    }

    /**
     * {@inheritDoc}
     */
    public function notice($message, array $context = array())
    {
        // noop
    }

    /**
     * {@inheritDoc}
     */
    public function info($message, array $context = array())
    {
        // noop
    }

    /**
     * {@inheritDoc}
     */
    public function debug($message, array $context = array())
    {
        // noop
    }
}