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Edit File: class-debug-log.php

<?php

/**
 * Class MC4WP_Debug_Log
 *
 * Simple logging class which writes to a file, loosely based on PSR-3.
 */
class MC4WP_Debug_Log
{
    /**
     * Detailed debug information
     */
    public const DEBUG = 100;

/**
     * Interesting events
     *
     * Examples: Visitor subscribed
     */
    public const INFO = 200;

/**
     * Exceptional occurrences that are not errors
     *
     * Examples: User already subscribed
     */
    public const WARNING = 300;

/**
     * Runtime errors
     */
    public const ERROR = 400;

/**
     * Logging levels from syslog protocol defined in RFC 5424
     *
     * @var array $levels Logging levels
     */
    protected static $levels = [
        self::DEBUG   => 'DEBUG',
        self::INFO    => 'INFO',
        self::WARNING => 'WARNING',
        self::ERROR   => 'ERROR',
    ];

/**
     * @var string The file to which messages should be written.
     */
    public $file;

/**
     * @var int Only write messages with this level or higher
     */
    public $level;

/**
     * @var resource
     */
    protected $stream;

/**
     * MC4WP_Debug_Log constructor.
     *
     * @param string $file
     * @param mixed $level;
     */
    public function __construct($file, $level = self::DEBUG)
    {
        $this->file  = $file;
        $this->level = self::to_level($level);
    }

/**
     * @param mixed $level
     * @param string $message
     * @return boolean
     */
    public function log($level, $message)
    {
        $level = self::to_level($level);

// only log if message level is higher than log level
        if ($level < $this->level) {
            return false;
        }

// obfuscate email addresses in log message since log might be public.
        $message = mc4wp_obfuscate_email_addresses((string) $message);

// first, get rid of everything between "invisible" tags
        $message = preg_replace('/<(?:style|script|head)>.+?<\/(?:style|script|head)>/is', '', $message);

// then, strip tags (while retaining content of these tags)
        $message = wp_strip_all_tags($message);
        $message = trim($message);

/**
         * Modifies the message that is written to the debug log.
         * Return an empty string to skip logging this message altogether.
         *
         * @param string $message
         */
        $message = apply_filters('mc4wp_debug_log_message', $message);
        if (empty($message)) {
            return false;
        }

// generate line
        $level_name = self::get_level_name($level);
        $datetime   = gmdate('Y-m-d H:i:s', time() + ( get_option('gmt_offset', 0) * HOUR_IN_SECONDS ));
        $message    = sprintf('[%s] %s: %s', $datetime, $level_name, $message) . PHP_EOL;

// did we open stream yet?
        if (! is_resource($this->stream)) {
            // attempt to open stream
            $this->stream = @fopen($this->file, 'c+'); // phpcs:ignore
            if (! is_resource($this->stream)) {
                return false;
            }

// make sure first line of log file is a PHP tag + exit statement (to prevent direct file access)
            $line            = fgets($this->stream);
            $php_exit_string = '<?php exit; ?>';
            if (strpos($line, $php_exit_string) !== 0) {
                rewind($this->stream);
                fwrite($this->stream, $php_exit_string . PHP_EOL . $line); // phpcs:ignore
            }

// place pointer at end of file
            fseek($this->stream, 0, SEEK_END);
        }

// lock file while we write, ignore errors (not much we can do)
        flock($this->stream, LOCK_EX);

// write the message to the file
        fwrite($this->stream, $message); // phpcs:ignore

// unlock file again, but don't close it for remainder of this request
        flock($this->stream, LOCK_UN);

// Maybe send email on level errors and up
        if ($level >= self::ERROR) {
            $opts = mc4wp_get_options();
            if (! empty($opts['email_on_error'])) {
                $last_sent = get_transient('mc4wp_error_email_sent');
                if (! $last_sent) {
                    $subject = sprintf('[%s] MC4WP Error on your site', get_bloginfo('name'));
                    $body    = sprintf('A MC4WP error occurred on your site: %s', $message);
                    wp_mail($opts['email_on_error'], $subject, $body);
                    set_transient('mc4wp_error_email_sent', time(), DAY_IN_SECONDS);
                }
            }
        }

return true;
    }

/**
     * @param string $message
     * @return boolean
     */
    public function warning($message)
    {
        return $this->log(self::WARNING, $message);
    }

/**
     * @param string $message
     * @return boolean
     */
    public function info($message)
    {
        return $this->log(self::INFO, $message);
    }

/**
     * @param string $message
     * @return boolean
     */
    public function error($message)
    {
        return $this->log(self::ERROR, $message);
    }

/**
     * @param string $message
     * @return boolean
     */
    public function debug($message)
    {
        return $this->log(self::DEBUG, $message);
    }

/**
     * Converts PSR-3 levels to local ones if necessary
     *
     * @param string|int $level Number or name of logging level (PSR-3)
     * @return int
     */
    public static function to_level($level)
    {
        if (is_string($level)) {
            $level = strtoupper($level);
            if (defined(__CLASS__ . '::' . $level)) {
                return constant(__CLASS__ . '::' . $level);
            }

// phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- Exception text is not direct output and is escaped at render time.
            throw new InvalidArgumentException('Level "' . $level . '" is not defined, use one of: ' . implode(', ', array_keys(self::$levels)));
        }

return $level;
    }

/**
     * Gets the name of the logging level.
     *
     * @param  int    $level
     * @return string
     */
    public static function get_level_name($level)
    {
        if (! isset(self::$levels[ $level ])) {
            // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- Exception text is not direct output and is escaped at render time.
            throw new InvalidArgumentException('Level "' . $level . '" is not defined, use one of: ' . implode(', ', array_keys(self::$levels)));
        }

return self::$levels[ $level ];
    }

/**
     * Tests if the log file is writable
     *
     * @return bool
     */
    public function test()
    {
        $handle   = @fopen($this->file, 'a'); // phpcs:ignore
        $writable = false;

if (is_resource($handle)) {
            $writable = true;
            fclose($handle); // phpcs:ignore
        }

return $writable;
    }
}