在循环中向ServeMux声明和分配处理程序不起作用。

Question

我有下面的代码，它不像预期的那样工作。具体来说，对任何端点的所有请求都是作为对/banana/auth或/banana/description端点的请求处理的。

type Route struct {
    AuthRoute        string
    DescriptionRoute string
}

var routes = [2]Route{
    {
        AuthRoute:        "/apple/auth",
        DescriptionRoute: "/apple/description",
    },
    {
        AuthRoute:        "/banana/auth",
        DescriptionRoute: "/banana/description",
    },
}

// ...
sm := http.NewServeMux()

for i, authServerConfig := range authServerConfigs {
    authHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.Auth(w, r)
    }
    sm.Handle(routes[i].AuthRoute, authHandler)

    descriptionHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.ServeDescription(w, r)
    }
    sm.Handle(routes[i].DescriptionRoute, descriptionHandler)
}

server := &http.Server{
    // ...
    Handler: sm,
    // ...
}
server.ListenAndServe()

当我继续用这些语句替换for-循环时，它完全符合我的要求：

    authHandlerApple := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.Auth(w, r)
    }
    sm.Handle(routes[0].AuthRoute, authHandlerApple)

    descriptionHandlerApple := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.ServeDescription(w, r)
    }
    sm.Handle(routes[0].DescriptionRoute, descriptionHandlerApple)

    authHandlerBanana := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.Auth(w, r)
    }
    sm.Handle(routes[1].AuthRoute, authHandlerBanana)

    descriptionHandlerBanana := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.ServeDescription(w, r)
    }
    sm.Handle(routes[1].DescriptionRoute, descriptionHandlerBanana)

问题是，我最初做错了什么，如何避免像第二个示例那样编写笨重的代码？

Answer 1

根据FAQ -当闭包作为goroutines运行时会发生什么？，每个闭包共享for循环中的单变量authServerConfig。要修复它，只需在循环中添加authServerConfig := authServerConfig即可。

for i, authServerConfig := range authServerConfigs {
     authServerConfig := authServerConfig

    authHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.Auth(w, r)
    })
    sm.Handle(routes[i].AuthRoute, authHandler)

    descriptionHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        authServerConfig.ServeDescription(w, r)
    })
    sm.Handle(routes[i].DescriptionRoute, descriptionHandler)
}