class DbLog

class DbLog implements LoggerInterface {
  use RfcLoggerTrait;
  use DependencySerializationTrait;
  
  /**
   * The dedicated database connection target to use for log entries.
   */
  const DEDICATED_DBLOG_CONNECTION_TARGET = 'dedicated_dblog';
  
  /**
   * The database connection object.
   *
   * @var \Drupal\Core\Database\Connection
   */
  protected $connection;
  
  /**
   * The message's placeholders parser.
   *
   * @var \Drupal\Core\Logger\LogMessageParserInterface
   */
  protected $parser;
  
  /**
   * Constructs a DbLog object.
   *
   * @param \Drupal\Core\Database\Connection $connection
   *   The database connection object.
   * @param \Drupal\Core\Logger\LogMessageParserInterface $parser
   *   The parser to use when extracting message variables.
   */
  public function __construct(Connection $connection, LogMessageParserInterface $parser) {
    $this->connection = $connection;
    $this->parser = $parser;
  }
  
  /**
   * {@inheritdoc}
   */
  public function log($level, $message, array $context = []) {
    // Remove any backtraces since they may contain an unserializable variable.
    unset($context['backtrace']);
    // Convert PSR3-style messages to \Drupal\Component\Render\FormattableMarkup
    // style, so they can be translated too in runtime.
    $message_placeholders = $this->parser
      ->parseMessagePlaceholders($message, $context);
    try {
      $this->connection
        ->insert('watchdog')
        ->fields([
        'uid' => $context['uid'],
        'type' => mb_substr($context['channel'], 0, 64),
        'message' => $message,
        'variables' => serialize($message_placeholders),
        'severity' => $level,
        'link' => $context['link'],
        'location' => $context['request_uri'],
        'referer' => $context['referer'],
        'hostname' => mb_substr($context['ip'], 0, 128),
        'timestamp' => $context['timestamp'],
      ])
        ->execute();
    } catch (\Exception $e) {
      // When running Drupal on MySQL or MariaDB you can run into several errors
      // that corrupt the database connection. Some examples for these kind of
      // errors on the database layer are "1100 - Table 'xyz' was not locked
      // with LOCK TABLES" and "1153 - Got a packet bigger than
      // 'max_allowed_packet' bytes". If such an error happens, the MySQL server
      // invalidates the connection and answers all further requests in this
      // connection with "2006 - MySQL server had gone away". In that case the
      // insert statement above results in a database exception. To ensure that
      // the causal error is written to the log we try once to open a dedicated
      // connection and write again.
      if (($e instanceof DatabaseException || $e instanceof \PDOException) && $this->connection
        ->getTarget() != self::DEDICATED_DBLOG_CONNECTION_TARGET) {
        // Open a dedicated connection for logging.
        $key = $this->connection
          ->getKey();
        $info = Database::getConnectionInfo($key);
        Database::addConnectionInfo($key, self::DEDICATED_DBLOG_CONNECTION_TARGET, $info['default']);
        $this->connection = Database::getConnection(self::DEDICATED_DBLOG_CONNECTION_TARGET, $key);
        // Now try once to log the error again.
        $this->log($level, $message, $context);
      }
      else {
        throw $e;
      }
    }
  }

}