在golang中，使用net / http时如何调用带有或不带有后括号的函数

Question

In the main function, I have a gorilla mux router, and a function to handle the route.

var router = mux.NewRouter()
func main() {   
    router.HandleFunc("/", ParseSlash)
    http.Handle("/", router)
    http.ListenAndServe(":8000", nil)
}

and ParseSlash looks like

const slash = `<h1>Login</h1>
<form method="post" action="/login">
  <label for="name">User name</label>
  <input type="text" id="name" name="name">
  <label for="password">Password</label>
  <input type="password" id="password" name="password">
  <button type="submit">Login</button>
</form>`

func ParseSlash(response http.ResponseWriter, request *http.Request)  {
    fmt.Fprintf(response, slash)
}

However, in main, we are not calling the function as ParseSlash(), but ParseSlash inside router.HandleFunc(). Where do the function get the parameters from, if we are not providing explicitely? What is this way of calling a function termed as?

Thank you.

Answer 1

You are not "calling" the function from main, you are providing it as a argument to HandleFunc, registering it to be called for the path "/" in the mux.Router. This pattern of providing a function to be called later is typically known as a "callback".

Your ParseSlash function is of the type http.HandlerFunc

type HandlerFunc func(ResponseWriter, *Request)

Your function is eventually called by the http.Server via its ServeHTTP method (here, via the mux.Router), passing the arguments shown. When the function is called, the http.ResponseWriter and *http.Request arguments are for the individual http request being handled.