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Go 代理模式讲解和代码示例

代理是一种结构型设计模式， 让你能提供真实服务对象的替代品给客户端使用。 代理接收客户端的请求并进行一些处理 （访问控制和缓存等）， 然后再将请求传递给服务对象。

代理对象拥有和服务对象相同的接口， 这使得当其被传递给客户端时可与真实对象互换。

** 进一步了解代理模式 **

概念示例

Nginx 这样的 Web 服务器可充当应用程序服务器的代理：

• 提供了对应用程序服务器的受控访问权限。
• 可限制速度。
• 可缓存请求。

** server.go:  主体

package main

type server interface {
    handleRequest(string, string) (int, string)
}

** nginx.go:  代理

package main

type Nginx struct {
    application       *Application
    maxAllowedRequest int
    rateLimiter       map[string]int
}

func newNginxServer() *Nginx {
    return &Nginx{
        application:       &Application{},
        maxAllowedRequest: 2,
        rateLimiter:       make(map[string]int),
    }
}

func (n *Nginx) handleRequest(url, method string) (int, string) {
    allowed := n.checkRateLimiting(url)
    if !allowed {
        return 403, "Not Allowed"
    }
    return n.application.handleRequest(url, method)
}

func (n *Nginx) checkRateLimiting(url string) bool {
    if n.rateLimiter[url] == 0 {
        n.rateLimiter[url] = 1
    }
    if n.rateLimiter[url] > n.maxAllowedRequest {
        return false
    }
    n.rateLimiter[url] = n.rateLimiter[url] + 1
    return true
}

** application.go:  真实主体

package main

type Application struct {
}

func (a *Application) handleRequest(url, method string) (int, string) {
    if url == "/app/status" && method == "GET" {
        return 200, "Ok"
    }

    if url == "/create/user" && method == "POST" {
        return 201, "User Created"
    }
    return 404, "Not Ok"
}

** main.go:  客户端代码

package main

import "fmt"

func main() {

    nginxServer := newNginxServer()
    appStatusURL := "/app/status"
    createuserURL := "/create/user"

    httpCode, body := nginxServer.handleRequest(appStatusURL, "GET")
    fmt.Printf("\nUrl: %s\nHttpCode: %d\nBody: %s\n", appStatusURL, httpCode, body)

    httpCode, body = nginxServer.handleRequest(appStatusURL, "GET")
    fmt.Printf("\nUrl: %s\nHttpCode: %d\nBody: %s\n", appStatusURL, httpCode, body)

    httpCode, body = nginxServer.handleRequest(appStatusURL, "GET")
    fmt.Printf("\nUrl: %s\nHttpCode: %d\nBody: %s\n", appStatusURL, httpCode, body)

    httpCode, body = nginxServer.handleRequest(createuserURL, "POST")
    fmt.Printf("\nUrl: %s\nHttpCode: %d\nBody: %s\n", appStatusURL, httpCode, body)

    httpCode, body = nginxServer.handleRequest(createuserURL, "GET")
    fmt.Printf("\nUrl: %s\nHttpCode: %d\nBody: %s\n", appStatusURL, httpCode, body)
}

** output.txt:  执行结果

Url: /app/status
HttpCode: 200
Body: Ok

Url: /app/status
HttpCode: 200
Body: Ok

Url: /app/status
HttpCode: 403
Body: Not Allowed

Url: /app/status
HttpCode: 201
Body: User Created

Url: /app/status
HttpCode: 404
Body: Not Ok