为什么http.HandleFunc对一个请求执行两次？ [重复]

I build a very simple web sever with golang to understand the http package, but I find the HandleFunc function executed two times for one request, and there's a favicon.ico I have not expected.

Here's the web server code:

package main

import (
    "fmt"
    "log"
    "net/http"
    "strings"
)

// sayHelloName a basic web function
func sayHelloName(w http.ResponseWriter, r *http.Request) {
    r.ParseForm() // Parse parameters
    fmt.Println(r.Form)
    fmt.Println("path", r.URL.Path)
    fmt.Println("scheme", r.URL.Scheme)
    fmt.Println(r.Form["url_long"])

    for k, v := range r.Form {
        fmt.Println("key", k)
        fmt.Println("val", strings.Join(v, ""))
    }

    fmt.Fprintf(w, "hello Go-web")
}

func main() {
    http.HandleFunc("/", sayHelloName)
    // log.Println("Serve listen at http://localhost:8900/")
    err := http.ListenAndServe(":8900", nil)

    if err != nil {
        log.Fatal("Listen & Serve Error", err)
    }
}

visit http://localhost:9090/?url_long=111&url_long=222

Real Output
map[url_long:[111 222]]
path /
scheme
[111 222]
key url_long
val 111222
map[]
path /favicon.ico
scheme
[]
I don't understand why there's a favicon.ico here.
Any help will be appreciated.

</div>

The /favicon.ico is actually requested by your browser. If you run a curl request from shell you won't see two HandleFunc requests.

curl http://localhost:9090/?url_long=111&url_long=222

If you want to handle the /favicon.ico path you can do something like this:

func faviconPath(w http.ResponseWriter, r *http.Request) {
    http.ServeFile(w, r, "path/to/favicon.ico")
}

func main() {
  http.HandleFunc("/favicon.ico", faviconPath)
}