@foxxmd/logging

A typed, opinionated, batteries-included, Pino-based logging solution for backend TS/JS projects.

Features:

• Fully typed for Typescript projects
• One-line, turn-key logging to console and rotating file
• Child (nested) loggers with hierarchical label prefixes for log messages
• Per-destination level filtering configurable via ENV or arguments
• Clean, opinionated log output format powered by pino-pretty:
  • Colorized output when stream is TTY and supports it
  • Automatically serialize passed objects and Errors, including Error Cause
  • Automatically redact current working directory from log output
• Bring-Your-Own settings
  • Add or use your own streams/transports for destinations
  • All pino-pretty configs are exposed and extensible
• Build-Your-Own Logger
  • Don't want to use any of the pre-built transports? Leverage the convenience of @foxxmd/logging wrappers and default settings but build your logger from scratch

Documentation best viewed on https://foxxmd.github.io/logging

Install

npm install @foxxmd/logging
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Quick Start

import { loggerAppRolling, loggerApp } from "@foxxmd/logging";

const logger = loggerApp();
logger.info('Test');
/*
 * Logs to -> console, colorized
 * Logs to -> CWD/logs/app.log
 * 
 * [2024-03-07 10:31:34.963 -0500] DEBUG: Test
 * */


// or for rolling log files we need to scan logs dir before opening a file
// and need to await initial logger
const rollingLogger = await loggerAppRolling();
rollingLogger.info('Test');
/*
 * Logs to -> console, colorized
 * Logs to daily log file, max 10MB size -> CWD/logs/app.1.log
 * 
 * [2024-03-07 10:31:34.963 -0500] DEBUG: Test
 * */
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Loggers

The package exports 4 top-level loggers.

App Loggers

These are the loggers that should be used for the majority of your application. They accept an optional configuration object for configuring log destinations.

• loggerApp - Logs to console and a fixed file destination
• loggerAppRolling - Logs to console and a rolling file destination

Helper Loggers

These loggers are pre-defined for specific use cases:

• loggerDebug - Logs ONLY to console at minimum debug level. Can be used during application startup before a logger app configuration has been parsed.
• loggerTest - A noop logger (will not log anywhere) for use in tests/mockups.

Configuring

The App Loggers take an optional LogOptions to configure LogLevel globally or individually for Console and File outputs. file in LogOptions may also be an object that specifies more behavior for log file output.

const infoLogger = loggerApp({
 level: 'info' // console and file will log any levels `info` and above
});

const logger = loggerApp({
  console: 'debug', // console will log `debug` and higher
  file: 'warn' // file will log `warn` and higher
});

const fileLogger = loggerRollingApp({
  // no level specified => console defaults to `info` level
  file: {
      level: 'warn', // file will log `warn` and higher
      path: '/my/cool/path/output.log', // output to log file at this path
      frequency: 'daily', // rotate hourly
      size: '20MB', // rotate if file size grows larger than 20MB
      timestamp: 'unix' // use unix epoch timestamp instead of iso8601 in rolling file
  }
});
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An optional second parameter, LoggerAppExtras, may be passed that allows adding additional log destinations or pino-pretty customization to the App Loggers. Some defaults and convenience variables for pino-pretty options are also available in @foxxmd/logging/factory prefixed with PRETTY_.

An example using LoggerAppExtras:

import { loggerApp } from '@foxxmd/logging';
import {
    PRETTY_ISO8601,
    buildDestinationFile 
} from "@foxxmd/logging/factory";

// additional file logging but only at `warn` or higher
const warnFileDestination = buildDestinationFile('warn', {path: './myLogs/warn.log'});

const logger = loggerApp({
  level: 'debug', // console AND built-in file logging will log `debug` and higher
  }, {
   destinations: [warnFileDestination],
   pretty: {
     translateTime: PRETTY_ISO8601 // replaces standard timestamp with ISO8601 format
   }
});
logger.debug('Test');
// [2024-03-07T11:27:41-05:00] DEBUG: Test
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See Building A Logger for more information.

Colorizing Docker Logs

Color output to STD out/err is normally automatically detected by colorette or can manually be set using colorize anywhere PrettyOptions are accepted. However docker output can be hard to detect as supporting colorizing, or the output may not be TTY at the container interface but is viewed by a terminal or web app that does support colorizing.

Therefore @foxxmd/logging will look for a COLORED_STD environmental variable and, if no other colorize option is set and the ENV is not empty, will use the truthy value of this variable to set colorize for any buildDestinationStdout or buildDestinationStderr transports. This includes the built-in stdout transports for loggerApp and loggerAppRolling.

Thus you could set COLORED_STD=true in your Dockerfile to coerce colored output to docker logs. If a user does not want colored output for any reason they can simply override the environmental variable like COLORED_STD=false

Usage

Child Loggers

Pino Child loggers can be created using the childLogger function with the added ability to inherit Labels from their parent loggers.

Labels are inserted between the log level and message contents of a log. The child logger inherits all labels from all its parent loggers.

childLogger accepts a single string label or an array of string labels.

import {loggerApp, childLogger} from '@foxxmd/logging';

logger = loggerApp();
logger.debug('Test');
// [2024-03-07 11:27:41.944 -0500] DEBUG: Test

const nestedChild1 = childLogger(logger, 'First');
nestedChild1.debug('I am nested one level');
// [2024-03-07 11:27:41.945 -0500] DEBUG: [First] I am nested one level

const nestedChild2 = childLogger(nestedChild1, ['Second', 'Third']);
nestedChild2.warn('I am nested two levels but with more labels');
// [2024-03-07 11:27:41.945 -0500] WARN: [First] [Second] [Third] I am nested two levels but with more labels

const siblingLogger = childLogger(logger, ['1Sib','2Sib']);
siblingLogger.info('Test');
// [2024-03-07 11:27:41.945 -0500] INFO: [1Sib] [2Sib] Test
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Labels can also be added at "runtime" by passing an object with labels prop to the logger level function. These labels will be appended to any existing labels on the logger.

logger.debug({labels: ['MyLabel']}, 'My log message');
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Serializing Objects and Errors

Passing an object or array as the first argument to the logger will cause the object to be JSONified and pretty printed below the log message

logger.debug({myProp: 'a string', nested: {anotherProps: ['val1', 'val2'], boolProp: true}}, 'Test');
 /*
[2024-03-07 11:39:37.687 -0500] DEBUG: Test
  myProp: "a string"
  nested: {
    "anotherProps": [
      "val1",
      "val2"
     ],
   "boolProp": true
  }
  */
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Passing an Error as the first argument will pretty print the error stack including any causes.

const er = new Error('This is the original error');
const causeErr = new ErrorWithCause('A top-level error', {cause: er});
logger.debug(causeErr, 'Test');
/*
[2024-03-07 11:43:27.453 -0500] DEBUG: Test
Error: A top-level error
    at <anonymous> (/my/dir/src/index.ts:55:18)
caused by: Error: This is the original error
    at <anonymous> (/my/dir/src/index.ts:54:12)
 */
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Passing an Error without a second argument (message) will cause the top-level error's message to be printed instead of log message.

Building A Logger

All the functionality required to build your own logger is exported by @foxxmd/logging/factory. You can customize almost every facet of logging.

A logger is composed of a minimum default level and array of objects that implement StreamEntry, the same interface used by pino.multistream. The only constraint is that your streams must accept the same levels as @foxxmd/logging using the LogLevelStreamEntry interface that extends StreamEntry.

import {LogLevelStreamEntry} from '@foxxmd/logging';
import { buildLogger } from "@foxxmd/logging/factory";

const myStreams: LogLevelStreamEntry[] = [];
// build streams

const logger = buildLogger('debug', myStreams);
logger.debug('Test');
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factory exports several "destination" LogLevelStreamEntry function creators with default configurations that can be overridden.

import {
    buildLogger,
    buildDestinationStream,     // generic NodeJS.WriteableStream or SonicBoom DestinationStream
    buildDestinationStdout,     // stream to STDOUT
    buildDestinationStderr,     // stream to STDERR
    buildDestinationFile,       // write to static file
    buildDestinationRollingFile // write to rolling file
} from "@foxxmd/logging/factory";
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All buildDestination functions take args:

• level (first arg) - minimum level to log at
• options (second arg) - an object extending pino-pretty options, PrettyOptions

options inherits a default pino-pretty configuration that comprises @foxxmd/logging's opinionated logging format. The common default config can be generated using prettyOptsFactory which accepts an optional PrettyOptions object to override defaults:

import { prettyOptsFactory } from "@foxxmd/logging/factory";

const defaultConfig = prettyOptsFactory();

// override with your own config
const myCustomizedConfig = prettyOptsFactory({ colorize: false });
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Pre-configured PrettyOptions are also provided for different destinations:

import {
  PRETTY_OPTS_CONSOLE, // default config
  PRETTY_OPTS_FILE     // disables colorize
} from "@foxxmd/logging/factory";
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Specific buildDestinations also require passing a stream or path:

buildDestinationStream must pass a NodeJS.WriteableStream or SonicBoom DestinationStream to options as destination

import {buildDestinationStream} from "@foxxmd/logging/factory";

const myStream = new WritableStream();
const dest = buildDestinationStream('debug', {destination: myStream});
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buildDestinationStdout and buildDestinationStderr do not require a destination as they are fixed to STDOUT/STDERR

buildDestinationFile and buildDestinationRollingFile must pass a path to options

import {buildDestinationFile} from "@foxxmd/logging/factory";

const dest = buildDestinationFile('debug', {path: '/path/to/file.log'});
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Example

Putting everything above together

import {
  buildDestinationStream,
  buildDestinationFile,
  prettyOptsFactory,
  buildDestinationStdout,
  buildLogger
} from "@foxxmd/logging/factory";
import { PassThrough } from "node:stream";

const hookStream = new PassThrough();
const hookDestination = buildDestinationStream('debug', {
  ...prettyOptsFactory({sync: true, ignore: 'pid'}),
  destination: hookStream
});

const debugFileDestination = buildDestinationFile('debug', {path: './myLogs/debug.log'});
const warnFileDestination = buildDestinationFile('warn', {path: './myLogs/warn.log'});

const logger = buildLogger('debug', [
  hookDestination,
  buildDestinationStdout('debug'),
  debugFileDestination,
  warnFileDestination
]);
hookStream.on('data', (log) => {console.log(log)});
logger.debug('Test')
// logs to hookStream
// logs to STDOUT
// logs to file ./myLogs/debug.log
// does NOT log to file ./myLogs/warn.log
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Parsing LogOptions

If you wish to use LogOptions to get default log levels for your destinations use parseLogOptions:

import {parseLogOptions, LogOptions} from '@foxxmd/logging';

const parsedOptions: LogOptions = parseLogOptions(myConfig);
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Examples

Various use-cases for @foxxmd/logging and how to configure a logger for them.

Remember, loggerApp and loggerAppRolling accept the same arguments. The examples below use loggerApp but loggerAppRolling can be used as a drop-in replacement in order to use a rolling log file.

Log to Console and File

import {loggerApp, loggerAppRolling} from '@foxxmd/logging';

// static log file at ./logs/app.log
const staticLogger = loggerApp();

// rolling log file at ./logs/app.1.log
const rollingLogger = loggerAppRolling();
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Log At Specific Level Or Higher for Console and File

import {loggerApp} from '@foxxmd/logging';

// INFO is the default level
// when 'console' is not specified it logs to 'info' or higher
// when 'file' is not specified it logs to 'info' or higher
const infoLogger = loggerApp();

// logs to console and log at 'debug' level and higher
const debugLogger = loggerApp({level: 'debug'});
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Log At debug for Console and warn for File

import {loggerApp} from '@foxxmd/logging';

const logger = loggerApp({
  console: 'debug',
  file: 'warn'
});
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Do not log to File

import {loggerApp} from '@foxxmd/logging';

// also logs to console at 'info' level
const logger = loggerApp({
  file: false
});
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Log to Specific File

import {loggerApp} from '@foxxmd/logging';

// also logs to console at 'info' level
const logger = loggerApp({
  file: {
      path: './path/to/file.log'
  }
});
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Log to Rolling File with Unix Timestamp

import {loggerApp} from '@foxxmd/logging';

// also logs to console at 'info' level
const logger = loggerApp({
  file: {
      timestamp: 'unix'
  }
});
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Log to Rolling File with no timestamp

import {loggerApp} from '@foxxmd/logging';

// also logs to console at 'info' level
const logger = loggerApp({
  file: {
      // specify size but NOT 'frequency' to disable timestamps in filename
      size: '10M'
  }
});
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Log to additional File for 'error' only

import {loggerApp} from '@foxxmd/logging';
import { buildDestinationFile } from "@foxxmd/logging/factory";

const errorFileDestination = buildDestinationFile('error', {path: './myLogs/warn.log'});

// also logs to console and file at 'info' level
const logger = loggerApp({}, {
    destinations: [errorFileDestination]
});
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Log raw, newline-delimited json logs to additional File

import {loggerApp} from '@foxxmd/logging';
import { buildDestinationFile } from "@foxxmd/logging/factory";
import fs from 'node:fs';

const rawFile = fs.createWriteStream('myRawFile.log');

// also logs to console and file at 'info' level
const logger = loggerApp({}, {
    destinations: [
      {
          level: 'debug',
          stream: rawFile // logs are NOT prettified, only raw data from pino
      }
    ]
});
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Log prettified data to additional stream

This could be used to trigger something when a log object with a specific property is found. Or to stream prettified log json to a client over websockets.

To emit data as an object (LogDataPretty) set objectMode and object to true.

import {loggerApp} from '@foxxmd/logging';
import { buildDestinationJsonPrettyStream } from "@foxxmd/logging/factory";
import { PassThrough } from "node:stream";

const prettyObjectStream = new Passthrough({objectMode: true}); // objectMode MUST be true to get objects from the stream
const prettyObjectDestination = buildDestinationJsonPrettyStream('debug', {
  destination: prettyObjectStream,
  object: true, // must be set to true to use with objectMode stream
  colorize: true
});

const prettyStringStream = new Passthrough(); // will emit data as a json string
const prettyStringDestination = buildDestinationJsonPrettyStream('debug', {
  destination: prettyStringStream,
  object: false,
  colorize: true
});

// also logs to console and file at 'info' level
const logger = loggerApp({}, {
    destinations: [
      prettyObjectDestination,
      prettyStringDestination
    ]
});

prettyObjectStream.on('data', (log) => {
  // do something with log object (LogDataPretty) 
});

prettyStringStream.on('data', (log) => {
  // do something with log string
});
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Log to additional Pino Transports

Log to a Pino Transport like pino-elasticsearch:

import {loggerApp} from '@foxxmd/logging';
import pinoElastic from 'pino-elasticsearch'

const streamToElastic = pinoElastic({
  index: 'an-index',
  node: 'http://localhost:9200',
  esVersion: 7,
  flushBytes: 1000
});

// also logs to console and file at 'info' level
const logger = loggerApp({}, {
    destinations: [
      {
          level: 'debug',
          stream: streamToElastic
      }
    ]
});
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