bolyan

A tiny (bunyan compatible) JSON logger

This is bascically Bole but output is even more bunyan compatible. @rvagg has written about 99% of this and I've just diddled some object keys, added some output levels, and copy+pasta'd some code from bunyan for serialization so that if you log an object that has any of the keys req, res, err, an attempt will be made to use the applicable bunyan serializer on those values

Log JSON from within Node.js applications. The log format is obviously inspired by the excellent Bunyan and is likely to be output-compatible in most cases. The difference is that bolyan/bole aims for even more simplicity, supporting only the common-case basics.

bolyan is designed for global singleton use. Your application has many log sources, but they all aggregate to the same sources. You configure output in one place for an application, regardless of how many modules and dependencies are also using bolyan for logging.

Example

mymodule.js

var log = require('bolyan')('mymodule')

module.exports.derp = function derp() {
  log.debug('W00t!')
  log.info('Starting mymodule#derp()')
}

main.js

var bolyan = require('bolyan')
var mod  = require('./mymodule')

bolyan.output({
  level: 'info',
  stream: process.stdout
})

mod.derp()

$ node main
{"time":"2014-05-18T23:47:06.545Z","hostname":"tweedy","pid":27374,"level":"info","name":"mymodule","message":"Starting mymodule#derp()"}

Features

• Arbitrary log names, create a logger by calling var log = bolyan('logname') and 'logname' will be attached to the output
• Loggers have 6 levels / methods: log.trace(), log.debug(), log.info(), log.warn(), log.error(), log.fatal()``
• Log methods accept console.log() style strfmt output ( usingutil.format()): log.warn('foo %s', 'bar')
• Log methods accept arbitrary objects that extend the log output data, each property on the object is attached to the debug output object
• Log methods accept Error objects and print appropriate Error properties, including a full stack trace (including any cause where supported)
• Log methods accept http.IncomingMessage for simple logging of an HTTP server's req object. URL, method, headers, remote host details will be included in the log output.
• Newline separated JSON output to arbitrary streams
• Any number of output streams, each with configurable minimum log-levels
• Fast short-circuit where no loggers are configured for the log-level, effectively making log statements a noop where they don't output
• Sub-logger to split a logger for grouping types of events, such as individual HTTP request

API

bolyan(name)

Create a new logger with the supplied name to be attached to each output. If you keep a logger-per module you don't need to pass loggers around, keep your concerns separated.

logger#trace(), logger#debug(), logger#info(), logger#warn(), logger#error(), logger#fatal()

Loggers have 6 roughly identical log methods, one for each of the supports log-levels. Log levels are recorded on the output and can be used to determine the level of detail passed to the output.

Log methods support the following types of input:

• Error objects: log output will include the error name, message, complete stack and also a code where there is one. Additionally you can supply further arguments which are passed to util.format() and attached as a "message" property to the output: log.warn(err, 'error occurred while fetching session for user %s', user.name)

• http.IncomingMessage for simple access-log style logging. URL, method, headers, remote address and remote port are logged: log.info(req), further data can be provided for a "message" property if required.

• Arbitrary objects whose properties will be placed directly on the logged output object. Be careful passing objects with large numbers of properties, in most cases you are best to construct your own objects: log.debug({ dbHost: 'foo', dbPort: 8080 }, 'connecting to database'), further data can be provided for a "message" property if required.

• console.log style output so you can treat loggers just like console.log(): log.info('logging a string'), log.info('it has been said that %d is the meaning of %s', 42, 'life'), log.debug('foo', 'bar', 'baz').

If you require more sophisticated serialisation of your objects, then write a utility function to convert those objects to loggable objects.

logger()

The logger object returned by bolyan(name) is also a function that accepts a name argument. It returns a new logger whose name is the parent logger with the new name appended after a ':' character. This is useful for splitting a logger up for grouping events. Consider the HTTP server case where you may want to group all events from a particular request together:

var log = bolyan('server')

http.createServer(function (req, res) {
  req.log = log(uuid.v4()) // make a new sub-logger
  req.log.info(req)

  //...

  // log an error against this sub-logger
  req.log.error(err)
})

In this case, your events would be listed as something like "name":"server:93f57a1a-ae59-46da-a625-8d084a77028a" and each event for a particular request would have the same "name" property, distinct from the rest.

Sub-loggers can even be split in to sub-sub loggers, the rabbit hole is ~bottomless.

bolyan.output()

Add outputs for application-wide logging, accepts either an object for defining a single output or an array of objects defining multiple outputs. Each output requires only a 'level' and a 'stream', where the level defines the minimum debug level to print to this stream and the stream is any WritableStream that accepts a .write() method.

bolyan.output([
  { level: 'debug', fs.createWriteStream('app.log') },
  { level: 'info', process.stdout }
])

bolyan.reset()

Clears all output streams from the application

Additional features

If you need to serialise specific types of objects then write a utility function to convert to a loggable object.

If you need a special kind of output then write a stream to accept output data.

If you need to filter a present output data in a special way, write a package to do it and publish it in npm.

License

bole is Copyright (c) 2014 Rod Vagg @rvagg and licensed under the MIT License. All rights not explicitly granted in the MIT License are reserved. See the included LICENSE.md file for more details. bolyan is Copyright (c) 2014 James Butler (https://sandfox.co.uk) bunyan is Copyright (c) 2014 Trent Mick & Joyent Inc. All rights reserved.