英文:
What means foo()(bar) in go and how it works?
问题
在auth0的Golang快速入门教程中，我找到了这段代码：
router.Handle("/api/private", middleware.EnsureValidToken()(
http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)
w.Write([]byte(`{"message":"Hello from a private endpoint! You need to be authenticated to see this."}`))
}),
))
然后我将其简化为以下形式：
func handler(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)
w.Write([]byte(`{"message":"Hello from test"}`))
}
func preHandler() func(next http.Handler) http.Handler {
log.Println("in preHandler")
return func(next http.Handler) http.Handler {
return check(next)
}
}
func main() {
http.Handle("/test/", preHandler()(http.HandlerFunc(handler)))
http.ListenAndServe(":80", nil)
}
但是我无法理解这段代码preHandler()(http.HandlerFunc(handler))的工作原理和含义是什么。
谢谢帮助！
附：
我尝试在谷歌上找到答案，但没有找到。我只是想弄清楚它是如何工作的。
英文:
In auth0 QuickStart tutorial for Golang I had found this piece of code:
router.Handle("/api/private", middleware.EnsureValidToken()(
http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)
w.Write([]byte(`{"message":"Hello from a private endpoint! You need to be authenticated to see this."}`))
}),
))
Then I had simplify it to this form:
func handler(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)
w.Write([]byte(`{"message":"Hello from test"}`))
}
func preHandler() func(next http.Handler) http.Handler {
log.Println("in preHandler")
return func(next http.Handler) http.Handler {
return check(next)
}
}
func main() {
http.Handle("/test/", preHandler()(http.HandlerFunc(handler)))
http.ListenAndServe(":80", nil)
}
But I can't figure out how is working and what is meaning of this piece of code preHandler()(http.HandlerFunc(handler))
Thnx for help!
P.s.
I tried to find answer in google but nothing. I just want to find out how it works
答案1
得分: 3
这个语句
http.Handle("/test/", preHandler()(http.HandlerFunc(handler)))
包含了三个函数调用和一个类型转换。我将把这个语句拆分成四个语句来解释：
f := preHandler() // f 是一个类型为 func(next http.Handler) http.Handler 的函数
h := http.HandlerFunc(handler) // 类型转换为 http.HandlerFunc
hw := f(h) // 调用 f 并传入 h，结果是一个 http.Handler
http.Handle("/test/", hw) // 注册这个处理器
英文:
The statement
http.Handle("/test/", preHandler()(http.HandlerFunc(handler)))
has three function calls and a type conversion. I'll explain what's going on by splitting the one statement into four statements:
f := preHandler() // f is function with type func(next http.Handler) http.Handler
h := http.HandlerFunc(handler) // type conversion to http.HandlerFunc
hw := f(h) // call f with h, result is an http.Handler
http.Handle("/test/", hw) // register the handler
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