Express default log component morgan's method

morgan is express's default logging middleware. This article mainly introduces the method of express's default logging component morgan. Now I will share it with you and give you a reference.

Chapter Overview

Morgan is express's default logging middleware. It can also be used as a node.js logging component without express. Use alone. This article goes from shallow to deep, and the content mainly includes:

1. Getting started with morgan examples

2. How to save logs to local files

3. Core API usage instructions and examples

4. Advanced usage: 1. Log splitting 2. Write logs to the database

5. Source code analysis: morgan’s log format and pre-compilation

Getting Started Example

First, initialize the project .

npm install express morgan

Then, add the following code in basic.js.

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

app.use(morgan('short'));
app.use(function(req, res, next){
 res.send('ok');
});

app.listen(3000);

node basic.jsRun the program and access http://127.0.0.1:3000 in the browser to print the log As follows

➜ 2016.12.11-advanced-morgan git:(master) ✗ node basic.js
::ffff:127.0.0.1 - GET / HTTP/1.1 304 - - 3.019 ms
: :ffff:127.0.0.1 - GET /favicon.ico HTTP/1.1 200 2 - 0.984 ms

Print log to local file

morgan supports stream Configuration item, you can use it to achieve the effect of landing the log. The code is as follows:

var express = require('express');
var app = express();
var morgan = require('morgan');
var fs = require('fs');
var path = require('path');
var accessLogStream = fs.createWriteStream(path.join(__dirname, 'access.log'), {flags: 'a'});
app.use(morgan('short', {stream: accessLogStream}));
app.use(function(req, res, next){
 res.send('ok');
});
app.listen(3000);

Usage explanation

Core API

morgan has very few APIs. The most frequently used one is morgan(), which returns an express log middleware.

morgan(format, options)

The parameter description is as follows:

1. format: optional, morgan and defined There are several log formats. Each format has a corresponding name, such as combined, short, etc. The default is default. The differences between different formats can be found here. The following will explain how to customize the log format.

2. options: Optional, configuration items, including stream (commonly used), skip, and immediate.

3. stream: Log output stream configuration, the default is process.stdout.

4. skip: Whether to skip logging, please refer to here for usage.

5. immediate: Boolean value, default is false. When true, the log will be logged as soon as the request is received; if false, the log will be logged after the request returns.
   

Custom log format

First understand the two concepts in morgan: format and token. Very simple:

1. #format: log format, which is essentially a string representing the log format, such as: method :url :status :res[content-length] - :response- time ms.

2. Token: The component of format, such as :method and :url above are so-called tokens.

After clarifying the difference between format and token, you can take a look at the key APIs about custom log formats in morgan.

morgan.format(name, format); // 自定义日志格式
morgan.token(name, fn); // 自定义token

Custom format

is very simple, first pass morgan.format() Define the log format named joke, and then call it through morgan('joke').

var express = require('express');
var app = express();
var morgan = require('morgan');
morgan.format('joke', '[joke] :method :url :status');
app.use(morgan('joke'));
app.use(function(req, res, next){
 res.send('ok');
});
app.listen(3000);

Let’s take a look at the running results

➜ 2016.12.11-advanced-morgan git:(master) ✗ node morgan .format.js
[joke] GET / 304
[joke] GET /favicon.ico 200

Custom token

Code As follows, customize the token through morgan.token(), and then add the customized token to the customized format.

var express = require('express');
var app = express();
var morgan = require('morgan');
// 自定义token
morgan.token('from', function(req, res){
 return req.query.from || '-';
});
// 自定义format，其中包含自定义的token
morgan.format('joke', '[joke] :method :url :status :from');

// 使用自定义的format
app.use(morgan('joke'));
app.use(function(req, res, next){
 res.send('ok');
});
app.listen(3000);

Run the program and visit http://127.0.0.1:3000/hello?from=app and http: //127.0.0.1:3000/hello?from=pc

➜ 2016.12.11-advanced-morgan git:(master) ✗ node morgan.token.js
[joke] GET / hello?from=app 200 app
[joke] GET /favicon.ico 304 -
[joke] GET /hello?from=pc 200 pc
[joke] GET /favicon.ico 304 -

Advanced Usage

Log Cutting

An online application, if All logs are stored in the same local file. Over time, the file will become very large, which affects performance and is inconvenient to view. At this time, you need to use log segmentation.

With the help of the file-stream-rotator plug-in, log splitting can be easily completed. Except for the configuration code related to file-stream-rotator, the rest is similar to the previous example, so I won’t go into details here.

var FileStreamRotator = require('file-stream-rotator')
var express = require('express')
var fs = require('fs')
var morgan = require('morgan')
var path = require('path')

var app = express()
var logDirectory = path.join(__dirname, 'log')

// ensure log directory exists
fs.existsSync(logDirectory) || fs.mkdirSync(logDirectory)

// create a rotating write stream
var accessLogStream = FileStreamRotator.getStream({
 date_format: 'YYYYMMDD',
 filename: path.join(logDirectory, 'access-%DATE%.log'),
 frequency: 'daily',
 verbose: false
})

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

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

Write logs to the database

Sometimes, we have such a need to Access logs are written to the database. This requirement is common in log systems that require real-time query statistics.

在morgan里该如何实现呢？从文档上，并没有看到适合的扩展接口。于是查阅了下morgan的源码，发现实现起来非常简单。

回顾下之前日志写入本地文件的例子，最关键的两行代码如下。通过stream指定日志的输出流。

var accessLogStream = fs.createWriteStream(path.join(__dirname, 'access.log'), {flags: 'a'});
app.use(morgan('short', {stream: accessLogStream}));

在morgan内部，大致实现是这样的（简化后）。

// opt为配置文件
var stream = opts.stream || process.stdout;
var logString = createLogString(); // 伪代码，根据format、token的定义，生成日志
stream.write(logString);

于是，可以用比较取巧的方式来实现目的：声明一个带write方法的对象，并作为stream配置传入。

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

// 带write方法的对象
var dbStream = {
 write: function(line){
 saveToDatabase(line); // 伪代码，保存到数据库
 }
};

// 将 dbStream 作为 stream 配置项的值
app.use(morgan('short', {stream: dbStream}));
app.use(function(req, res, next){
 res.send('ok');
});

app.listen(3000);

深入剖析

morgan的代码非常简洁，从设计上来说，morgan的生命周期包含：

token定义 --> 日志格式定义 -> 日志格式预编译 --> 请求达到/返回 --> 写日志

其中，token定义、日志格式定义前面已经讲到，这里就只讲下 日志格式预编译 的细节。

跟模板引擎预编译一样，日志格式预编译，也是为了提升性能。源码如下，最关键的代码就是compile(fmt)。

 function getFormatFunction (name) {
 // lookup format
 var fmt = morgan[name] || name || morgan.default

 // return compiled format
 return typeof fmt !== 'function'
 ? compile(fmt)
 : fmt
}

compile()方法的实现细节这里不赘述，着重看下compile(fmt)返回的内容：

var morgan = require('morgan');
var format = morgan['tiny'];
var fn = morgan.compile(format);

console.log(fn.toString());

运行上面程序，输出内容如下，其中tokens其实就是morgan。 

function anonymous(tokens, req, res
/**/) {
 return ""
 + (tokens["method"](req, res, undefined) || "-") + " "
 + (tokens["url"](req, res, undefined) || "-") + " "
 + (tokens["status"](req, res, undefined) || "-") + " "
 + (tokens["res"](req, res, "content-length") || "-") + " - "
 + (tokens["response-time"](req, res, undefined) || "-") + " ms";
}

看下morgan.token()的定义，就很清晰了

function token (name, fn) {
 morgan[name] = fn
 return this
}

上面是我整理给大家的，希望今后会对大家有帮助。

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