Go Web 示例: 中间件(高级)

中间件(高级)

个例子将展示如何在 Go 中创建一个更高级的中间件版本。

中间件本身只是简单地将 http.HandlerFunc 作为其参数之一,包装它并返回一个新的 http.HandlerFunc 供服务器调用。

在这里,我们定义了一种新类型的中间件,它最终可以更容易地将多个中间件链接在一起。 这个想法的灵感来自 Mat Ryers 关于构建 API 的演讲。 你可以找到更详细的解释,包括这里的谈话。

此代码段详细解释了如何创建新中间件。 在下面的完整示例中,我们通过一些样板代码减少了这个版本。

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func createNewMiddleware() Middleware {

    // Create a new Middleware
    middleware := func(next http.HandlerFunc) http.HandlerFunc {

        // Define the http.HandlerFunc which is called by the server eventually
        handler := func(w http.ResponseWriter, r *http.Request) {

            // ... do middleware things

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

        // Return newly created handler
        return handler
    }

    // Return newly created middleware
    return middleware
}

完整代码:

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// advanced-middleware.go
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)
}
$ go run advanced-middleware.go
2017/02/11 00:34:53 / 0s

$ curl -s http://localhost:8080/
hello world

$ curl -s -XPOST http://localhost:8080/
Bad Request

本文翻译自:https://gowebexamples.com/advanced-middleware/

updatedupdated2021-06-132021-06-13
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