Writer for Mono-logger

Writer extension for Mono-logger 1.5+. Please refer to its documentation before jumping into configuring the Writer.

This effect allows you to write logs to a file with minimum configuration.

import { Logger } from '@zodyac/mono-logger';
import { WriterEffect } from '@zodyac/mono-logger-writer';

const writerEffect = new WriterEffect({
  path: 'logs',
});

const logger = new Logger("writer", {
  effect: writerEffect,
});

logger.info("Hello, World!");

// Console: 7/29/2024, 16:16:16 [INF] writer Hello, world!
//
// + file: logs/mono-logger-2024629-0.log:
// 2024-07-29T13:18:07.235Z [INF] writer Hello, world!

Changelog

Please see CHANGELOG for latest changes.

Prerequisites

• Node.js 12+
• Mono-logger 1.5+

Installation

Assuming you have already installed Mono-logger 1.5+:

yarn add @zodyac/mono-logger-writer

Or

npm i @zodyac/mono-logger-writer

Configuration

• level (LogLevel) – The minimum log level to write (e.g. debug, info, warn, error, fatal). Default: debug;

• path (string) – The directory to write logs. Default: logs;

• filename (function) – Function to generate the filename that accepts the current date and file iterator (starts with 0) and returns a file name string;

• transform (function) – Function to transform the log message before writing to the file. Default: undefined;

• max_file_size (number) – The maximum file size in kilobytes before creating a new file. Default: 5 * 1024KB (~5MB);

import { Logger, type LogLevel } from '@zodyac/mono-logger';
import { WriterEffect } from '@zodyac/mono-logger-writer';

const transformer = (ts: Date, level: LogLevel, topics: string[], ...messages: any[]) => {
  const timestamp = ts.toString();
  const lvl_str = level.toUpperCase();
  return `${timestamp} [${lvl_str}] ${topics.join(':')} ${messages.join(' ')}`;
};

const writerEffect = new WriterEffect({
  level: 'info',
  path: 'logs',
  filename: (date, i) => `my-log-${date.toISOString()}-${i}.log`,
  max_file_size: 20 * 1024, // 20MB
  transform: transformer,
});

const logger = new Logger("root", {
  effect: writerEffect,
});

logger.info("Hello, World!");

// Output:
// + file: logs/my-log-2024-07-29T13:34:40.782Z-0.log
// Mon Jul 29 2024 16:35:25 GMT+0300 (Istanbul Standard time) [INFO] root Hello, World!

Size based rotation

The Writer will create a new file when the current file size exceeds the max_file_size limit. File size is provided in kilobytes. Default file size is around 5MB, which can be changed by setting the max_file_size option. If you don't want your files to be rotated, you can just pass Infinity to this field. In this case, the iterator will not have any effect.

If you stop the app and run it again with all the same configuration, iterator will be pointed to the next of the last file number. If you want to start from scratch, you can delete those files or change the filename function.

Daily rotation

By setting daily_rotation to true, you can effortlessly make the Writer create a new file every day. This is useful when you want to keep logs separated by days, not file size.

Note: This will cancel Size based rotation behavior.

How to screw things up

Common problems that can possibly happen fall into one (or more) of these categories:

• fs cannot write to the directory because of it's access rules;

• fs cannot write because the disk is full;

• File is being overwritten because it happened to have same filename and path (check the path and filename function);

• Provided max_file_size is smaller than a given record, so the file will be rotated immediately (and possibly infinitely if you dump MASSIVE amount of data in one record);

Contributing

Contribution is always welcomed! These are several points of special interest:

• Improve test coverage (Jest);
• Edge case exploration;
• Stability and efficiency improvements (KISS);

You are also welcome to extend and improve Mono-logger plugin ecosystem.

License

MIT