winston-stream-wrapper

This package provides a type-safe wrapper for winston Logger instances that allows them to easily be used as a Node.js WritableStream.

Motivation

I wrote this package because I needed to pipe a subprocess' output to a Logger instance. I tried using winston-stream, but it had a few issues around buffered streams that are solved by the splitLines option in this package.

Installation

npm install winston-stream-wrapper

Usage

The following example shows how to pipe a subprocess' stdout and stderr to a Logger instance:

import { spawn } from "child_process";
import { createLogger, format, transports } from 'winston';

import LogStreamWrapper from 'winston-stream-wrapper';

const logger = createLogger({
    format: format.combine(
        format.timestamp(),
        format.json(),
    ),
    transports: [
        new transports.Console(),
    ],
});

const infoStream = new LogStreamWrapper(logger, {
    level: 'info',
    splitLines: true,
});

const errorStream = new LogStreamWrapper(logger, {
    level: 'error',
    splitLines: true,
});

const subprocess = spawn('some-command', ['some', 'args']);

// This will log each line of the subprocess' output as a separate log message.
subprocess.stdout.pipe(infoStream);
subprocess.stderr.pipe(errorStream);

API

The package exports a single class, LogStreamWrapper, which is a WritableStream that can be used to pipe data to a Logger instance.

LogStreamWrapper

class LogStreamWrapper extends Writable {
    constructor(logger: Logger, options: LogStreamWrapperOptions);
}

Options

The LogStreamWrapper constructor takes an options object with the following properties:

• level: The level to log messages at.
• splitLines: Whether to split the stream's input into separate log messages on newlines. If false, every chunk of data will be logged as a single log message. Defaults to true.
• skipEmptyLines: Whether to skip empty lines when splitLines is true. Defaults to true.
• lineSeparator: The line separator to use when splitLines is true. Defaults to \n.

Issues

If you find any issues with this package, please open an issue on GitHub.