Hewer

https://www.npmjs.com/package/hewer

A small, extensible, easy-to-use, zero-dependency logging library for node.js

Index

• Motivation
• Installation
• Basic Usage
• API
• Filters
• Formatters
• Writers
• Contributing
• Testing
• License

Motivation

This library was written to solve a need I had for a simple log standardization solution that would be very easy to extend and adapt without increasing the already possibly excessively big dependency tree of my projects. So, instead of making it some internal solution, I decided to make it a stand-alone open-source library so other people could possibly benefit from it.

Installation

npm install --save hewer

Basic Usage

var hewer = require('hewer');

var Logger = new hewer.Logger();

Logger.log({ // A JSON of data to be logged
  'name'  : 'Aragorn',
  'class' : 'Ranger'
})
.with('level', '99') // Add more meta data
.with('kingdom', 'Gondor') // And a few more meta data
.info('Here comes the king');

// 2016-04-05T03:32:15.604 INFO Here comes the king {"name":"Aragorn","class":"Ranger","level":"99","kingdom":"Gondor"}

API

class Logger(filters, writers, formatter)

Parameters

1. filters: Array of Filter - OPTIONAL - A list of filters that will be applied to the log message.
2. writers: Array of Writer - OPTIONAL - A list of writers that will be used to write the log message to some output. If no writer is provided then the ConsoleWriter will be used.
3. formatter: Formatter - OPTIONAL - A formatter that may transform and format the message before sending it to a writer. If no formatter is provided then the DefaultFormatter will be used.

Logger.log(meta) returns Log

Creates a new log instance with the optional provided meta data.

Parameters

1. meta : JSON - OPTIONAL - A JSON with a any arbitrary meta.

Logger.addFilter(filter) returns [Logger]

Adds a Filter to the filters pool

Parameters

1. filter : Filter - MANDATORY -

Logger.addWriter(writer) returns [Logger]

Adds a Writer to the writers pool

Parameters

1. writer : Writer - MANDATORY -

Logger.setFormatter(formatter) returns [Logger]

Defines the Formatter that's going to be used

Parameters

1. formatter : Formatter - MANDATORY

class Log(meta, logger)

Parameters

1. meta : JSON - MANDATORY - A JSON with a any arbitrary meta.
2. logger : Logger - MANDATORY

Log.with(key, value) returns Log

Appends some meta data to the log.

Parameters

1. key : STRING - MANDATORY - The name of your meta data.
2. value : ANY - MANDATORY - Your actual data.

Log.info(message) returns Promise

Commits the message and the meta provided to the set of writers with log level INFO.

Parameters

1. message : STRING - `OPTIONAL - Some arbitrary log message.

Log.warn(message) returns Promise

Just like Log.info but with log level WARN.

Log.error(message) returns Promise

Just like Log.info but with log level ERROR.

Log.debug(message) returns Promise

Just like Log.info but with log level DEBUG.

---

Filters

A filter receives a formatted log message and then applies some string-transformation rule over it.

Usage

var hewer = require('hewer');
var PatternFilter = hewer.filters.PatternFilter;

var nameErasingFilter = new PatternFilter(/(\"name\"\:)(\".*?\")/, '$1[REDACTED]');

var Logger = new hewer.Logger([nameErasingFilter]);

Logger.log({ // A JSON of data to be logged
  'name'  : 'Aragorn',
  'class' : 'Ranger'
})
.with('level', '99') // Add more meta data
.with('kingdom', 'Gondor') // And a few more meta data
.info('Here comes the king');
// 2016-04-08T15:02:54.022 INFO Here comes the king {"name":[REDACTED],"class":"Ranger","level":"99","kingdom":"Gondor"}

Built-in Filters

class IdentityFilter

The default filter used in case you don't pick any. Just returns the string as it is.

Usage

var IdentityFilter = require('hewer').filters.IdentityFilter;

var filter = new IdentityFilter();

console.log(filter.apply('You shall not pass!'));
//You shall not pass!

class PatternFilter(pattern, replacement)

A filter that applies a pattern or substring and replaces it by a pattern or substring

Parameters

1. pattern : STRING or REGEXP - MANDATORY - The pattern for matching some string
2. replacement : STRING - MANDATORY - The string for which the pattern should be replaced

Usage

var PatternFilter = require('hewer').filters.PatternFilter;

var filter = new PatternFilter(/(Aragorn)/, '$1 (A.K.A Strider)');

console.log(filter.apply("I am Aragorn son of Arathorn"));
//I am Aragorn (A.K.A Strider) son of Arathorn

class KeyFilter(key, replacement)

Replaces the value of a key in a serialized JSON

Parameters

1. key : STRING - MANDATORY - The name of the key that must be replaced
2. replacement : STRING - MANDATORY - The string for which the value of the key should be replaced

Usage

var KeyFilter = require('hewer').filters.KeyFilter;

var filter = new KeyFilter('name', '[REDACTED]');

console.log(filter.apply('Here comes the king {"name":"Aragorn","class":"Ranger","level":"99","kingdom":"Gondor"}'));
//Here comes the king {"name":"[REDACTED]","class":"Ranger","level":"99","kingdom":"Gondor"}

Custom filter

A filter is simply a class that has an apply method that takes a string as parameter and returns a string

API

interface Filter()

Filter.apply(message) returns STRING

Parameters

1. message : STRING - MANDATORY - The log string that will be sent to a writer

Usage

var hewer = require('hewer');

function CustomFilter() {
	this.apply = function(str) {
		//Do something with the string
		return str + " That's what Bilbo Baggins hates!";
	}
}

var Logger = new hewer.Logger([new CustomFilter()])

Logger.log().warn('Smash the bottles and burn the corks!');
//2016-04-10T15:30:50.546 WARN Smash the bottles and burn the corks! {} That's what Bilbo Baggins hates!
Logger.log().warn('Chip the glasses and crack the plates!');
//2016-04-10T15:30:50.551 WARN Chip the glasses and crack the plates! {} That's what Bilbo Baggins hates!

Formatters

Built-in formatters

class DefaultFormatter()

Usage

var DefaultFormatter =  require('hewer').formatters.DefaultFormatter;

var formatter = new DefaultFormatter();

console.log(formatter.format("There is only one Lord of the Ring, only one who can bend it to his will", "INFO", {}));
//2016-04-10T16:16:13.763 INFO There is only one Lord of the Ring, only one who can bend it to his will {}

Custom formatter

A formatter is simply a class that has a format method that receives some message, some log level name, and some meta data and returns a formatted string.

API

interface Formatter

Formatter.format(message, level, meta) returns STRING

Parameters

1. message : STRING - MANDATORY - The log message
2. level : STRING - MANDATORY - Some log level name
3. meta : JSON - MANDATORY - Some meta data object

Usage

var hewer = require('hewer');

var function CustomFormatter() {
    this.format = function(message, level, meta) {
        return `${level} ${message} ${JSON.stringify(meta)}`;
    }
}

var Logger = new hewer.Logger(null, null, new CustomFormatter())

Logger.log({ titles : [
    'The gray',
    'The white'] })
    .info('Gandalf!');
// "INFO Gandalf! {"titles":["The gray","The white"]}"

Writers

A writer is the final destiny of any log message. A writer is where the message is going to be printed to the console, be sent to a database etc.

Built-in Writers

class ConsoleWriter()

Writes the log message to the console

Usage

var ConsoleWriter =  require('hewer').writers.ConsoleWriter;

var writer = new ConsoleWriter();


function saySomeElficWhisper() {
    console.log('Elfic whispering!');
}

writer.info('The world has changed', saySomeElficWhisper);
//The world has changed
//Elfic whispering

writer.debug('I feel it in the water', saySomeElficWhisper);
//I feel it in the water
//Elfic whispering

writer.warn('I feel it in the earth', saySomeElficWhisper);
//I feel it in the earth
//Elfic whispering

writer.error('I smell it in the air', saySomeElficWhisper);
//I smell it in the air
//Elfic whispering

Custom writers

API

interface Writer

Writer.info(message, callback)

Writes message with INFO log level

Parameters

1. message : STRING - MANDATORY - The log message
2. callback(error) : FUNCTION - MANDATORY - A callback function to be called after the writer task has been executed

Writer.debug(message, callback)

Just like Writer.info but with DEBUG log level

Writer.warn(message, callback)

Just like Writer.info but with WARN log level

Writer.error(message, callback)

Just like Writer.info but with ERROR log level

Usage

var hewer = require('hewer');

function CustomWriter() {
    this.info = function(message, callback) {
    	//Do something with the message
        callback();
    }

    this.debug = function(message, callback) {
    	//Do something with the message
        callback();
    }

    this.error = function(message, callback) {
    	//Do something with the message
	callback();   
    }

    this.warn = function(message, callback) {
    	//Do something with the message
        callback();
    }
}

var Logger = new hewer.Logger(null, [new CustomWriter()])

Logger.log({ titles : [
    'The gray',
    'The white'] })
    .info('Gandalf!');

Contributing

If you want to contribute to the project with new Filters, Formatters, Writers, fixes, functionalities, optimizations, documentation, issues etc. All you have to do is open an issue and, if needed, fork this project and open a pull request.

Testing

npm test

License

The MIT License (MIT)

Copyright (c) 2016 Mateus Chagas

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.