中間件是一種計算機軟件，可爲操作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。廣泛用於web應用和麪向服務的體系結構等。
縱觀GO語言，中間件應用比較普遍，主要應用：
- 記錄對服務器發送的請求（request）
- 處理服務器響應（response ）
- 請求和處理之間做一個權限認證工作
- 遠程調用
- 安全
- 等等
中間件處理程序是簡單的http.Handler，它包裝另一個http.Handler做請求的一些預處理和/或後處理。它被稱爲“中間件”，因爲它位於Go Web服務器和實際處理程序之間的中間位置。
下面是一些中間件例子
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
返回結果
foo
將上面示例修改下，也可以實現相同的功能。
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
返回結果
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)
}中間件本身只是將其http.HandlerFunc作爲其參數之一，包裝它並返回一個新http.HandlerFunc的服務器來調用。在這裏，我們定義了一種新類型Middleware，最終可以更容易地將多箇中間件鏈接在一起。
當然我們也可以改成如下形式
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() 創建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() 創建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")
}以上示例也可改爲
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"之後）。
更多gin中間件示例可參考 https://github.com/gin-gonic/gin
參考資料