morgan

What is morgan?

Morgan is a middleware for Node.js that enables HTTP request logging. It is commonly used with Express.js applications to log information about incoming requests, which can be helpful for debugging, monitoring, and analytics purposes.

What are morgan's main functionalities?

Logging HTTP requests

This code sets up an Express server and uses Morgan to log all incoming HTTP requests in the 'combined' Apache format.

const express = require('express');
const morgan = require('morgan');
const app = express();

app.use(morgan('combined'));

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

Customizing log formats

This code demonstrates how to customize the log format to include specific details such as the HTTP method, URL, status code, content length, and response time.

const express = require('express');
const morgan = require('morgan');
const app = express();

app.use(morgan(':method :url :status :res[content-length] - :response-time ms'));

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

Creating custom tokens

This code shows how to create a custom token 'id' that can be used in the log format. The token function returns a value from the request object, which is then logged.

const express = require('express');
const morgan = require('morgan');
const app = express();

morgan.token('id', function getId(req) {
  return req.id;
});

app.use(morgan(':id :method :url'));

app.get('/', (req, res) => {
  req.id = 'abc123';
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

Writing logs to a file

This code snippet demonstrates how to configure Morgan to write logs to a file named 'access.log' instead of outputting to the console.

const fs = require('fs');
const express = require('express');
const morgan = require('morgan');
const path = require('path');
const app = express();

const accessLogStream = fs.createWriteStream(path.join(__dirname, 'access.log'), { flags: 'a' });

app.use(morgan('combined', { stream: accessLogStream }));

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(3000, () => {
  console.log('Server running on port 3000');
});

Other packages similar to morgan

winston

Winston is a versatile logging library for Node.js. Unlike Morgan, which is specifically designed for HTTP request logging, Winston can be used for general-purpose application logging. It supports multiple transports (e.g., console, file, database) and is highly configurable.

pino

Pino is a very low-overhead Node.js logger. It is designed for speed and can be significantly faster than other logging solutions like Morgan, especially in high-throughput scenarios. Pino focuses on JSON logging and offers different log levels and custom serializers.

bunyan

Bunyan is a simple and fast JSON logging library for Node.js services. Like Pino, it focuses on JSON logging. Bunyan provides a set of standard log levels and includes a CLI tool for pretty-printing log files. It is more similar to Winston in terms of features but with a focus on JSON.

README

morgan

HTTP request logger middleware for node.js

Named after Dexter, a show you should not watch until completion.

API

var morgan = require('morgan')

morgan(format, options)

Create a new morgan logger middleware function using the given format and options. The format argument may be a string of a predefined name (see below for the names), a string of a format string, or a function that will produce a log entry.

The format function will be called with three arguments tokens, req, and res, where tokens is an object with all defined tokens, req is the HTTP request and res is the HTTP response. The function is expected to return a string that will be the log line, or undefined / null to skip logging.

Using a predefined format string

morgan('tiny')

Using format string of predefined tokens

morgan(':method :url :status :res[content-length] - :response-time ms')

Using a custom format function

morgan(function (tokens, req, res) {
  return [
    tokens.method(req, res),
    tokens.url(req, res),
    tokens.status(req, res),
    tokens.res(req, res, 'content-length'), '-',
    tokens['response-time'](req, res), 'ms'
  ].join(' ')
})

Options

Morgan accepts these properties in the options object.

immediate

Write log line on request instead of response. This means that a requests will be logged even if the server crashes, but data from the response (like the response code, content length, etc.) cannot be logged.

skip

Function to determine if logging is skipped, defaults to false. This function will be called as skip(req, res).

// EXAMPLE: only log error responses
morgan('combined', {
  skip: function (req, res) { return res.statusCode < 400 }
})

stream

Output stream for writing log lines, defaults to process.stdout.

Predefined Formats

There are various pre-defined formats provided:

combined

Standard Apache combined log output.

:remote-addr - :remote-user [:date[clf]] ":method :url HTTP/:http-version" :status :res[content-length] ":referrer" ":user-agent"

common

Standard Apache common log output.

:remote-addr - :remote-user [:date[clf]] ":method :url HTTP/:http-version" :status :res[content-length]

dev

Concise output colored by response status for development use. The :status token will be colored green for success codes, red for server error codes, yellow for client error codes, cyan for redirection codes, and uncolored for information codes.

:method :url :status :response-time ms - :res[content-length]

short

Shorter than default, also including response time.

:remote-addr :remote-user :method :url HTTP/:http-version :status :res[content-length] - :response-time ms

tiny

The minimal output.

:method :url :status :res[content-length] - :response-time ms

Tokens

Creating new tokens

To define a token, simply invoke morgan.token() with the name and a callback function. This callback function is expected to return a string value. The value returned is then available as ":type" in this case:

morgan.token('type', function (req, res) { return req.headers['content-type'] })

Calling morgan.token() using the same name as an existing token will overwrite that token definition.

The token function is expected to be called with the arguments req and res, representing the HTTP request and HTTP response. Additionally, the token can accept further arguments of it's choosing to customize behavior.

:date[format]

The current date and time in UTC. The available formats are:

• clf for the common log format ("10/Oct/2000:13:55:36 +0000")
• iso for the common ISO 8601 date time format (2000-10-10T13:55:36.000Z)
• web for the common RFC 1123 date time format (Tue, 10 Oct 2000 13:55:36 GMT)

If no format is given, then the default is web.

:http-version

The HTTP version of the request.

:method

The HTTP method of the request.

:referrer

The Referrer header of the request. This will use the standard mis-spelled Referer header if exists, otherwise Referrer.

:remote-addr

The remote address of the request. This will use req.ip, otherwise the standard req.connection.remoteAddress value (socket address).

:remote-user

The user authenticated as part of Basic auth for the request.

:req[header]

The given header of the request. If the header is not present, the value will be displayed as "-" in the log.

:res[header]

The given header of the response. If the header is not present, the value will be displayed as "-" in the log.

:response-time[digits]

The time between the request coming into morgan and when the response headers are written, in milliseconds.

The digits argument is a number that specifies the number of digits to include on the number, defaulting to 3, which provides microsecond precision.

:status

The status code of the response.

If the request/response cycle completes before a response was sent to the client (for example, the TCP socket closed prematurely by a client aborting the request), then the status will be empty (displayed as "-" in the log).

:total-time[digits]

The time between the request coming into morgan and when the response has finished being written out to the connection, in milliseconds.

The digits argument is a number that specifies the number of digits to include on the number, defaulting to 3, which provides microsecond precision.

:url

The URL of the request. This will use req.originalUrl if exists, otherwise req.url.

:user-agent

The contents of the User-Agent header of the request.

morgan.compile(format)

Compile a format string into a format function for use by morgan. A format string is a string that represents a single log line and can utilize token syntax. Tokens are references by :token-name. If tokens accept arguments, they can be passed using [], for example: :token-name[pretty] would pass the string 'pretty' as an argument to the token token-name.

The function returned from morgan.compile takes three arguments tokens, req, and res, where tokens is object with all defined tokens, req is the HTTP request and res is the HTTP response. The function will return a string that will be the log line, or undefined / null to skip logging.

Normally formats are defined using morgan.format(name, format), but for certain advanced uses, this compile function is directly available.

Examples

express/connect

Simple app that will log all request in the Apache combined format to STDOUT

var express = require('express')
var morgan = require('morgan')

var app = express()

app.use(morgan('combined'))

app.get('/', function (req, res) {
  res.send('hello, world!')
})

vanilla http server

Simple app that will log all request in the Apache combined format to STDOUT

var finalhandler = require('finalhandler')
var http = require('http')
var morgan = require('morgan')

// create "middleware"
var logger = morgan('combined')

http.createServer(function (req, res) {
  var done = finalhandler(req, res)
  logger(req, res, function (err) {
    if (err) return done(err)

    // respond to request
    res.setHeader('content-type', 'text/plain')
    res.end('hello, world!')
  })
})

write logs to a file

single file

Simple app that will log all requests in the Apache combined format to the file access.log.

var express = require('express')
var fs = require('fs')
var morgan = require('morgan')
var path = require('path')

var app = express()

// create a write stream (in append mode)
var accessLogStream = fs.createWriteStream(path.join(__dirname, 'access.log'), { flags: 'a' })

// setup the logger
app.use(morgan('combined', { stream: accessLogStream }))

app.get('/', function (req, res) {
  res.send('hello, world!')
})

log file rotation

Simple app that will log all requests in the Apache combined format to one log file per day in the log/ directory using the rotating-file-stream module.

var express = require('express')
var morgan = require('morgan')
var path = require('path')
var rfs = require('rotating-file-stream') // version 2.x

var app = express()

// create a rotating write stream
var accessLogStream = rfs.createStream('access.log', {
  interval: '1d', // rotate daily
  path: path.join(__dirname, 'log')
})

// setup the logger
app.use(morgan('combined', { stream: accessLogStream }))

app.get('/', function (req, res) {
  res.send('hello, world!')
})

split / dual logging

The morgan middleware can be used as many times as needed, enabling combinations like:

• Log entry on request and one on response
• Log all requests to file, but errors to console
• ... and more!

Sample app that will log all requests to a file using Apache format, but error responses are logged to the console:

var express = require('express')
var fs = require('fs')
var morgan = require('morgan')
var path = require('path')

var app = express()

// log only 4xx and 5xx responses to console
app.use(morgan('dev', {
  skip: function (req, res) { return res.statusCode < 400 }
}))

// log all requests to access.log
app.use(morgan('common', {
  stream: fs.createWriteStream(path.join(__dirname, 'access.log'), { flags: 'a' })
}))

app.get('/', function (req, res) {
  res.send('hello, world!')
})

use custom token formats

Sample app that will use custom token formats. This adds an ID to all requests and displays it using the :id token.

var express = require('express')
var morgan = require('morgan')
var uuid = require('node-uuid')

morgan.token('id', function getId (req) {
  return req.id
})

var app = express()

app.use(assignId)
app.use(morgan(':id :method :url :response-time'))

app.get('/', function (req, res) {
  res.send('hello, world!')
})

function assignId (req, res, next) {
  req.id = uuid.v4()
  next()
}

License

MIT