node_modules/log4js/lib/appenders/dateFile.js

const streams = require('streamroller');
const os = require('os');

const eol = os.EOL;

function openTheStream(filename, pattern, options) {
  const stream = new streams.DateRollingFileStream(
    filename,
    pattern,
    options
  );
  stream.on('error', (err) => {
    console.error('log4js.dateFileAppender - Writing to file %s, error happened ', filename, err); //eslint-disable-line
  });
  stream.on("drain", () => {
    process.emit("log4js:pause", false);
  });
  return stream;
}

/**
 * File appender that rolls files according to a date pattern.
 * @param filename base filename.
 * @param pattern the format that will be added to the end of filename when rolling,
 *          also used to check when to roll files - defaults to '.yyyy-MM-dd'
 * @param layout layout function for log messages - defaults to basicLayout
 * @param options - options to be passed to the underlying stream
 * @param timezoneOffset - optional timezone offset in minutes (default system local)
 */
function appender(
  filename,
  pattern,
  layout,
  options,
  timezoneOffset
) {
  // the options for file appender use maxLogSize, but the docs say any file appender
  // options should work for dateFile as well.
  options.maxSize = options.maxLogSize;

  const writer = openTheStream(filename, pattern, options);

  const app = function (logEvent) {
    if (!writer.writable) {
      return;
    }
    if (!writer.write(layout(logEvent, timezoneOffset) + eol, "utf8")) {
      process.emit("log4js:pause", true);
    }
  };

  app.shutdown = function (complete) {
    writer.end('', 'utf-8', complete);
  };

  return app;
}

function configure(config, layouts) {
  let layout = layouts.basicLayout;
  if (config.layout) {
    layout = layouts.layout(config.layout.type, config.layout);
  }

  if (!config.alwaysIncludePattern) {
    config.alwaysIncludePattern = false;
  }

  // security default (instead of relying on streamroller default)
  config.mode = config.mode || 0o600;

  return appender(
    config.filename,
    config.pattern,
    layout,
    config,
    config.timezoneOffset
  );
}

module.exports.configure = configure;