在HTTP路由器中将未知的URL路径设置为错误

Problem:

I am having trouble finding the answer to a question, which there is a BIG possibility I do not know how to ask.

I am having problem with Go Server. I do not have any big knowledge of go programming but I did make a server with it. This server will display a JSON file which will then be pulled my other HTML file which is now irrelevant. This works. My problem is the path to the server.

Code

package main

import (
    "encoding/json"
    "fmt"
    "net/http"
    "os"
    "time"
)

type Event struct {
    Start     time.Time `json:"start"`
    End       time.Time `json:"end"`
    Summary   string    `json:"summary"`
    Organizer string    `json:"organizer"`
    MeetURL   string    `json:"meet_url"`
}

type EventSlice struct {
    Events []Event `json:"events"`
}

func loadEvents(filename string) (EventSlice, error) {
    // Open events file.
    file, err := os.Open(filename)
    if err != nil {
        return EventSlice{}, err
    }
    var list EventSlice

    // Parse events from json file to events slice.
    err = json.NewDecoder(file).Decode(&list)
    if err != nil {
        fmt.Println("Displays", err)
        return EventSlice{}, err
    }
    return list, nil
}

func handler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Access-Control-Allow-Origin", "*")
    events, err := loadEvents("json.json")
    if err != nil {
        fmt.Fprintln(w, err)
    }

    // Reduntant step in real life
    err = json.NewEncoder(w).Encode(events)
    if err != nil {
        fmt.Fprintln(w, err)
    }
}

func handler_over(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "This is my server. Hello.")
}

func main() {
    http.HandleFunc("/", handler_over)
    http.HandleFunc("/events", handler)
    http.ListenAndServe(":8080", nil)
}

And if I go run the server and then on this url change the path to example: http://0.0.0.0:8080/otherpath, it will still display function for handler_over. Which will display a string: This is my server.Hello.

What would I have to do, so when you change the URL to unknown path (which is not a path) that it will display an Error like 404 Page not found. In meaning, that only 2 paths will be recognisable on the server: "/" path and "/events" path.

Note This question has already probably been asked before, but I do not know how to ask the question. Any help or redirections to the answers would be gladly appreciated.

func handler_over(w http.ResponseWriter, r *http.Request) {
    // The "/" pattern matches everything, so we need to check
    // that we're at the root here.
    if r.URL.Path != "/" {
        http.NotFound(w, req)
        return
    }
    fmt.Fprintf(w, "This is my server. Hello.")
}