@uswitch/koa-signal

🚦 Koa Signal

A hackable & configurable console logger designed to integrate perfectly with @uswitch/koa libraries

Overview | Usage | Api | Configuration | Contributors

Overview

This package is a library inspired by Signale, to provide customisable and consistent logging for Node* services.

It tries to address the following;

• 🍽 Comletely Customisable - Control everything with a single JSON file
• 📏 Extensible - Add your own signals and components

This allows you to create consistent logs decoupled from the actual implementation of your code.

---

Usage

koa-signal was designed to work seamlessly with @uswitch/koa-access & @uswitch/koa-tracer. If you use either of these, you can just plug it in like so;

import Koa from 'koa'

import Signal from '@uswitch/koa-signal'
import access, { eventAccess } from '@uswitch/koa-access'
import tracer, { eventTrace, eventError } from '@uswitch/koa-tracer'

const app = new Koa()
const signal = Signal({ /* Config overrides */ })

app.use(tracer())
app.use(access())

app.on(eventAccess, signal.access)
app.on(eventTrace, ({ ctx,key,trace }) => signal.trace({ ...ctx, ...trace, scope: key }))
app.on(eventError, ({ ctx, error }) => signal.error(ctx, error.original))


app.listen(3000, () => signal.start(Listening on port 3000))

N.B. See koa-core

However, you can use it entirely independently of these two libraries as a log formatter. Creating an instance of koa-signal will provide you with a bunch of different logging functions, e.g.

import Signal from '@uswitch/koa-signal'
const signal = Signal({ /* config overrides */ })

signal.info('My really useful info message')

Production vs Development

koa-signal's formatting is useful for logging in Development to give a good understanding of what's happening in your application, however, in Production you probably want your output to be machine readable.

To change the formatting for Production, you can just provide a new config file, e.g.

import Signal from '@uswitch/koa-signal'
const signal = Signal({
  levels: {
    info: { format: [] },
    trace: { format: [] },
    warn: { format: [] },
    error: { format: [] },
    access: { format: [ 'json' ] }
  },
  components: {
    json: { properties: [ 'id', 'errors', 'errorsCount', 'traces' ] }
  }
})

N.B. See koa-core

In Production it's a common practice to save the logs to a file as well. koa-signal supports both console and file outputs which can be used independently or together e.g.

outputs

import Signal from '@uswitch/koa-signal'
const signal = Signal({
  levels: {
    info: { format: [] },
    trace: { format: [] },
    warn: { format: [] },
    error: { format: [] },
    access: { format: [ 'json' ] }
  },
  components: {
    json: { properties: [ 'id', 'errors', 'errorsCount', 'traces' ] }
  },
  outputs: [
    { type: 'console' },
    { type: 'file', file: './path/to/file.json' }
  ]
})

API

Each Signal function is defined with a format property (See configuration) which dictates how the log output is built. For example, let's take the trace function with the following output;

🤦 Doh!   [9ee...498] | +2546ms | |  +123ms | [SCOPE] >  First scoped traced message

The whole output is a LEVEL, but is made up of multiple COMPONENTS;

                                  TRACE LEVEL FUNCTION
╭──────────────────────────────────────────┴────────────────────────────────────────╮
🤦 Doh!   [9ee...498] | +2546ms | |  +123ms | [SCOPE] >  First scoped traced message
╰───┬───╯ ╰────┬────╯ ╰────┬────╯ ╰────┬────╯ ╰────┬────╯╰─────────────┬────────────╯
COMPONENT  COMPONENT   COMPONENT   COMPONENT   COMPONENT           COMPONENT

This is defined in config as the following;

{
  "levels": {
    "trace": {
      "badge": "🤦",
      "label": "Doh!",
      "format": [ "level", "id", "time-diff-init", "time-diff-scope", "scope", "message" ]
    }
  }
}

Where [ "level", ..., "message" ] is the list of Components being used. Components also have their own configuration defined separately.

API Functions

These functions are available by default and require the following properties when called.

Function	API
success	({ state: { id: STRING }, msg: STRING })
info	({ state: { id: STRING }, msg: STRING })
warn	({ state: { id: STRING }, msg: STRING })
access	({ state: { id: STRING }, req: OBJECT, res: OBJECT }, extras: OBJECT)
trace	({ state: { id: STRING }, initDiff: INT, timeDiff: INT, scope: STRING, msg: STRING })
zipkin	({ kind: CLIENT/SERVER, state: { parent: STRING, trace: STRING }, req: OBJECT, res: OBJECT })
error	({ state: { id: STRING }, msg: STRING }, ERROR)
start	({ msg: SRTING })
end	({ msg: STRING })

Configuration

You can see the default configuration of koa-signal here

Contributors

Thanks goes to these wonderful people (emoji key):

Dom Charlesworth 📖 💻 🤔 🔌	David Annez 💻 🤔 🔌

This project follows the all-contributors specification. Contributions of any kind welcome!