How to write RIFF chunk header when store image from url?

I just tried to download webp image from url, but I found something different when I try to process the stored image.

If I download the image from the browser, it can be decoded using x/image/webp package, but if I store the image using http.Get() then create a new file then io.Copy() the image, it says:

"missing RIFF chunk header"

I assume that I need to write some RIFF chunk header when I store it using golang code.

func main(){
    response, e := http.Get(URL)
    if e != nil {
        log.Fatal(e)
    }
    defer response.Body.Close()

    //open a file for writing
    file, err := os.Create('tv.webp')
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    // Use io.Copy to just dump the response body to the file. This supports huge files
    _, err = io.Copy(file, response.Body)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println("Success!")

    imgData, err := os.Open("tv.webp")
    if err != nil {
        fmt.Println(err)
        return
    }
    log.Printf("%+v", imgData)
    image, err := webp.Decode(imgData)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(image.Bounds())
}

Here is the URL IMG URL

download file is not webp type. it's png.

package main

import (
    "fmt"
    "image"
    "io"
    "log"
    "net/http"
    "os"

    _ "image/png"
)

func main() {
    response, e := http.Get("https://www.sony.com/is/image/gwtprod/0abe7672ff4c6cb4a0a4d4cc143fd05b?fmt=png-alpha")
    if e != nil {
        log.Fatal(e)
    }
    defer response.Body.Close()

    file, err := os.Create("dump")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    _, err = io.Copy(file, response.Body)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println("Success!")

    imageFile, err := os.Open("dump")
    if err != nil {
        panic(err)
    }

    m, name, err := image.Decode(imageFile)
    if err != nil {
        panic(err)
    }

    fmt.Println("image type is ", name, m.Bounds())
}