GO中間件(Middleware )

時間 2019-12-08

標籤中間件 middleware 简体版

原文原文鏈接

中間件是一種計算機軟件，可爲操做系統提供的軟件應用程序提供服務，以便於各個軟件之間的溝通，特別是系統軟件和應用軟件。普遍用於web應用和麪向服務的體系結構等。git

縱觀GO語言，中間件應用比較廣泛，主要應用：github

記錄對服務器發送的請求（request）
處理服務器響應（response ）
請求和處理之間作一個權限認證工做
遠程調用
安全
等等

中間件處理程序是簡單的http.Handler，它包裝另外一個http.Handler作請求的一些預處理和/或後處理。它被稱爲「中間件」，由於它位於Go Web服務器和實際處理程序之間的中間位置。golang

下面是一些中間件例子web

記錄日誌中間件

package main

import (
   "fmt"
   "log"
   "net/http"
)

func logging(f http.HandlerFunc) http.HandlerFunc {
   return func(w http.ResponseWriter, r *http.Request) {
      log.Println(r.URL.Path)
      f(w, r)
   }
}
func foo(w http.ResponseWriter, r *http.Request) {
   fmt.Fprintln(w, "foo")
}

func bar(w http.ResponseWriter, r *http.Request) {
   fmt.Fprintln(w, "bar")
}

func main() {
   http.HandleFunc("/foo", logging(foo))
   http.HandleFunc("/bar", logging(bar))
   http.ListenAndServe(":8080", nil)
}

訪問 http://localhost:8080/foo安全

返回結果服務器

fooapp

將上面示例修改下，也能夠實現相同的功能。框架

package main

import (
   "fmt"
   "log"
   "net/http"
)

func foo(w http.ResponseWriter, r *http.Request) {
   fmt.Fprintln(w, "foo")
}
func bar(w http.ResponseWriter, r *http.Request) {
   fmt.Fprintln(w, "bar")
}

func loggingMiddleware(next http.Handler) http.Handler {
   return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
      log.Println(r.URL.Path)
      next.ServeHTTP(w, r)
   })
}

func main() {

   http.Handle("/foo", loggingMiddleware(http.HandlerFunc(foo)))
   http.Handle("/bar", loggingMiddleware(http.HandlerFunc(bar)))
   http.ListenAndServe(":8080", nil)
}

訪問 http://localhost:8080/foo學習

返回結果url

foo

多中間件例子

package main

import (
   "fmt"
   "log"
   "net/http"
   "time"
)

type Middleware func(http.HandlerFunc) http.HandlerFunc

// Logging logs all requests with its path and the time it took to process
func Logging() Middleware {

   // Create a new Middleware
   return func(f http.HandlerFunc) http.HandlerFunc {

      // Define the http.HandlerFunc
      return func(w http.ResponseWriter, r *http.Request) {

         // Do middleware things
         start := time.Now()
         defer func() { log.Println(r.URL.Path, time.Since(start)) }()

         // Call the next middleware/handler in chain
         f(w, r)
      }
   }
}

// Method ensures that url can only be requested with a specific method, else returns a 400 Bad Request
func Method(m string) Middleware {

   // Create a new Middleware
   return func(f http.HandlerFunc) http.HandlerFunc {

      // Define the http.HandlerFunc
      return func(w http.ResponseWriter, r *http.Request) {

         // Do middleware things
         if r.Method != m {
            http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
            return
         }

         // Call the next middleware/handler in chain
         f(w, r)
      }
   }
}

// Chain applies middlewares to a http.HandlerFunc
func Chain(f http.HandlerFunc, middlewares ...Middleware) http.HandlerFunc {
   for _, m := range middlewares {
      f = m(f)
   }
   return f
}

func Hello(w http.ResponseWriter, r *http.Request) {
   fmt.Fprintln(w, "hello world")
}

func main() {
   http.HandleFunc("/", Chain(Hello, Method("GET"), Logging()))
   http.ListenAndServe(":8080", nil)
}

中間件自己只是將其http.HandlerFunc做爲其參數之一，包裝它並返回一個新http.HandlerFunc的服務器來調用。在這裏，咱們定義了一種新類型Middleware，最終能夠更容易地將多箇中間件連接在一塊兒。

固然咱們也能夠改爲以下形式

package main

import (
   "fmt"
   "log"
   "net/http"
   "time"
)

type Middleware func(http.Handler) http.Handler

func Hello(w http.ResponseWriter, r *http.Request) {
   fmt.Fprintln(w, "hello world")
}

func Chain(f http.Handler, mmap ...Middleware) http.Handler {
   for _, m := range mmap {
      f = m(f)
   }
   return f
}
func Method(m string) Middleware {
   return func(f http.Handler) http.Handler {
      return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
         log.Println(r.URL.Path)
         if r.Method != m {
            http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
            return
         }
         f.ServeHTTP(w, r)
      })
   }

}
func Logging() Middleware {
   return func(f http.Handler) http.Handler {
      return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
         //log.Println(r.URL.Path)
         // Do middleware things
         start := time.Now()
         defer func() { log.Println(r.URL.Path, time.Since(start)) }()
         f.ServeHTTP(w, r)
      })
   }
}

func main() {
   http.Handle("/", Chain(http.HandlerFunc(Hello), Method("GET"), Logging()))
   http.ListenAndServe(":8080", nil)
}

在gin框架下實現中間件

r := gin.Default() 建立帶有默認中間件的路由，默認是包含logger和recovery中間件的
r :=gin.new()      建立帶有沒有中間件的路由

示例

package main

import (
   "github.com/gin-gonic/gin"
   "log"
   "time"
)

func Logger() gin.HandlerFunc {
   return func(c *gin.Context) {
      t := time.Now()
      // Set example variable
      c.Set("example", "12345")
      // before request
      c.Next()
      // after request
      latency := time.Since(t)
      log.Print(latency) //時間  0s
      // access the status we are sending
      status := c.Writer.Status()
      log.Println(status) //狀態 200
   }
}
func main() {
   r := gin.New()
   r.Use(Logger())

   r.GET("/test", func(c *gin.Context) {
      example := c.MustGet("example").(string)

      // it would print: "12345"
      log.Println(example)
   })

   // Listen and serve on 0.0.0.0:8080
   r.Run(":8080")
}

以上示例也可改成

package main

import (
   "github.com/gin-gonic/gin"
   "log"
   "time"
)

func Logger() gin.HandlerFunc {
   return func(c *gin.Context) {
      t := time.Now()
      // Set example variable
      c.Set("example", "12345")
      // before request
      c.Next()
      // after request
      latency := time.Since(t)
      log.Print(latency) //時間  0s
      // access the status we are sending
      status := c.Writer.Status()
      log.Println(status) //狀態 200
   }
}

func main() {
   r := gin.New()
   r.GET("/test", Logger(), func(c *gin.Context) {
      example := c.MustGet("example").(string)
      // it would print: "12345"
      log.Println(example)
   })
   // Listen and serve on 0.0.0.0:8080
   r.Run(":8080")
}

即不用r.use添加中間件，直接將Logger() 寫到r.GET 方法的參數裏（"/test"以後）。

更多gin中間件示例可參考 https://github.com/gin-gonic/gin

參考資料

https://drstearns.github.io/t...

https://gowebexamples.com/adv...