Go Paradigm - Decorator

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示例

示例 1

func decorator(f func(s string)) func(s string) {
    return func(s string) {
        fmt.Println("Started")
        f(s)
        fmt.Println("Done")
    }
}

func Hello(s string) {
    fmt.Println(s)
}

func main() {
    decorator(Hello)("Hello, World!")
}

// output:
//     Started
//     Hello, World!
//     Done

示例 2

type SumFunc func(int64, int64) int64

func getFunctionName(i any) string {
    return runtime.FuncForPC(reflect.ValueOf(i).Pointer()).Name()
}

func timedSumFunc(f SumFunc) SumFunc {
    return func(start int64, end int64) int64 {
        defer func(t time.Time) {
            fmt.Printf("--- Time Elapsed (%s): %v ---\n", getFunctionName(f), time.Since(t))
        }(time.Now())

        return f(start, end)
    }
}

func sum(start int64, end int64) int64 {
    var sum int64
    for i := start; i <= end; i++ {
        sum += i
    }
    return sum
}

func main() {
    timedSumFunc(sum)(1, 1000000000) // --- Time Elapsed (main.sum): 317.173167ms ---
}

示例 3

func WithServerHeader(h http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        log.Println("--->WithServerHeader")
        w.Header().Set("Server", "HelloServer v0.0.1")
        h(w, r)
    }
}

func hello(w http.ResponseWriter, r *http.Request) {
    log.Printf("Recieved Request %s from %s\n", r.URL.Path, r.RemoteAddr)
    _, _ = fmt.Fprintf(w, "Hello, World! "+r.URL.Path)
}

func main() {
    http.Handle("/v1/hello", WithServerHeader(hello)) // decorate the handler function with WithServerHeader
    err := http.ListenAndServe(":8000", nil)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

$ curl -v 127.1:8000/v1/hello
*   Trying 127.0.0.1:8000...
* Connected to 127.0.0.1 (127.0.0.1) port 8000 (#0)
> GET /v1/hello HTTP/1.1
> Host: 127.0.0.1:8000
> User-Agent: curl/7.88.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: HelloServer v0.0.1
< Date: Fri, 15 Dec 2022 14:11:31 GMT
< Content-Length: 23
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host 127.0.0.1 left intact
Hello, World! /v1/hello

Pipeline

type HttpHandlerDecorator func(http.HandlerFunc) http.HandlerFunc

func Handler(h http.HandlerFunc, decors ...HttpHandlerDecorator) http.HandlerFunc {
    for i := range decors {
        h = decors[len(decors)-1-i](h)
    }
    return h
}

func WithServerHeader(h http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        log.Println("--->WithServerHeader")
        w.Header().Set("Server", "HelloServer v0.0.1")
        h(w, r)
    }
}

func WithAuthCookie(h http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        log.Println("--->WithAuthCookie")
        cookie := http.Cookie{Name: "Auth", Value: "SimpleAuth"}
        http.SetCookie(w, &cookie)
        h(w, r)
    }
}

func hello(w http.ResponseWriter, r *http.Request) {
    log.Printf("Recieved Request %s from %s\n", r.URL.Path, r.RemoteAddr)
    _, _ = fmt.Fprintf(w, "Hello, World! "+r.URL.Path)
}

func main() {
    http.Handle("/v1/hello", Handler(hello, WithServerHeader, WithAuthCookie))
    err := http.ListenAndServe(":8000", nil)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

$ curl -v 127.1:8000/v1/hello
*   Trying 127.0.0.1:8000...
* Connected to 127.0.0.1 (127.0.0.1) port 8000 (#0)
> GET /v1/hello HTTP/1.1
> Host: 127.0.0.1:8000
> User-Agent: curl/7.88.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: HelloServer v0.0.1
< Set-Cookie: Auth=SimpleAuth
< Date: Fri, 15 Dec 2022 14:18:21 GMT
< Content-Length: 23
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host 127.0.0.1 left intact
Hello, World! /v1/hello