Winston, a logger for just about everything.

In this article, we review a package called Winston.

Now, this is something I found in logger.ts file in n8n codebase and at line number 16, you will find this below import.


import winston from 'winston';

and it got me wondering what this package is about. So, when I quickly googled Winston, I found this npm package.

Winston

Winstom is a logger for just about everything. Winston is designed to be a simple and universal logging library with support for multiple transports. A transport is essentially a storage device for your logs. Each Winston logger can have multiple transports. So I think mainly what it does is you can provide a file name and all the logs can go into that file. That’s what I understood.

for example, you may want error logs to be stored in a persistent remote location like database, but all logs output to the console or a local file. So Winston aims to decouple parts of the logging process to make it more flexible and extensible. Attention is given to supporting flexibility in log formatting.

Usage


const winston = require('winston');

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.json(),
  defaultMeta: { service: 'user-service' },
  transports: [
    //
    // - Write all logs with importance level of `error` 
    // or higher to `error.log`
    //   (i.e., error, fatal, but not other levels)
    //
    new winston.transports.File({ filename: 'error.log', level: 'error' }),
    //
    // - Write all logs with importance level of `info` or higher 
    // to `combined.log`
    //   (i.e., fatal, error, warn, and info, but not trace)
    //
    new winston.transports.File({ filename: 'combined.log' }),
  ],
});

//
// If we're not in production then log to the `console` with the format:
// `${info.level}: ${info.message} JSON.stringify({ ...rest }) `
//
if (process.env.NODE_ENV !== 'production') {
  logger.add(new winston.transports.Console({
    format: winston.format.simple(),
  }));
}

This usage example in documentation demonstrates how you could write to a console and also to a file. Keep this in mind as we are going to need this information to understand how Winston transports are configured in n8n logger.ts file.

Winston usage in n8n


this.internalLogger = winston.createLogger({
   level: this.level,
   silent: isSilent,
});

This code snippet is picked from L44 in logger.ts. Notice how it does not have any transports configured yet.

Console transport


private setConsoleTransport() {
  const format =
   this.level === 'debug' && inDevelopment
    ? this.debugDevConsoleFormat()
    : this.level === 'debug' && inProduction
     ? this.debugProdConsoleFormat()
     : winston.format.printf(({ message }: { message: string }) => message);

  this.internalLogger.add(new winston.transports.Console({ format }));
 }

This code snippet is picked from L116 in logger.ts.

File transport


 private setFileTransport() {
  const format = winston.format.combine(
   winston.format.timestamp(),
   winston.format.metadata(),
   winston.format.json(),
  );

  const filename = path.join(
   this.instanceSettingsConfig.n8nFolder,
   this.globalConfig.logging.file.location,
  );

  const { fileSizeMax, fileCountMax } = this.globalConfig.logging.file;

  this.internalLogger.add(
   new winston.transports.File({
    filename,
    format,
    maxsize: fileSizeMax * 1_048_576, // config * 1 MiB in bytes
    maxFiles: fileCountMax,
   }),
  );
 }

This code snippet is picked from L189 in logger.ts.

About me:

Hey, my name is Ramu Narasinga. I study large open-source projects and create content about their codebase architecture and best practices, sharing it through articles, videos.

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