Detailed introduction of express default log component morgan
This time I will bring you a detailed introduction to express's default log component morgan. What are the precautions when using express's default log component morgan? The following is a practical case, let's take a look.
Chapter Overview
Morgan is express's default logging middleware. It can also be used independently from express as a node.js logging component. This article goes from shallow to deep, and the content mainly includes:
Getting started with morgan examples
How to save logs to local files
Core API usage instructions and examples
Advanced usage: 1. Log splitting 2. Write logs to database
Source code analysis: Morgan’s log format and pre-compilation
##Getting started example
First ,Initialization project.
npm install express morgan
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. The print log is 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 the log to a local file
#morgan supports the stream configuration item, which can be used to implement The effect of log implementation, 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 APImorgan has very few APIs, and the most frequently used one is morgan( ), its function is to return an express log middleware.morgan(format, options)
- format: Optional, morgan has defined 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.
- options: Optional, configuration items, including stream (commonly used), skip, and immediate.
- stream: Log output stream configuration, the default is process.stdout.
- skip: Whether to skip logging, please refer to here for usage.
- 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:- format: log format, which is essentially a string representing the log format, such as :method :url :status :res[content-length] - :response-time ms.
- Token: The component of format, such as :method and :url above are so-called tokens.
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 define the log format named joke through morgan.format(), and then call it through morgan('joke') Can.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);➜ 2016.12.11-advanced-morgan git:(master) ✗ node morgan.format.js[joke] GET / 304
[joke] GET /favicon.ico 200
Custom token
The code is as follows, customize the token through morgan.token(), Then add the custom token to the custom 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);➜ 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 -
高级使用
日志切割
一个线上应用，如果所有的日志都落地到同一个本地文件，时间久了，文件会变得非常大，既影响性能，又不便于查看。这时候，就需要用到日志分割了。
借助file-stream-rotator插件，可以轻松完成日志分割的工作。除了file-stream-rotator相关的配置代码，其余跟之前的例子差不多，这里不赘述。
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!')
})日志写入数据库
有的时候，我们会有这样的需求，将访问日志写入数据库。这种需求常见于需要实时查询统计的日志系统。
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
}相信看了本文案例你已经掌握了方法，更多精彩请关注php中文网其它相关文章！
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