Golang服务响应文件

How can I return a file from a service more efficiently in Go? For example, I receive a file like this

Here is an example that i use to receive a file from the service:

func (b *BenefitListHandler) UploadAppend(w http.ResponseWriter, r *http.Request) {
    r.ParseMultipartForm(32 << 20)
    file, handler, err := r.FormFile("benefitlistuploadfile")
    if err != nil {
        libhttp.EncodeErrorResponse(w, err, http.StatusInternalServerError)
        return
    }
defer file.Close()
f, err := os.OpenFile("./"+handler.Filename, os.O_WRONLY|os.O_CREATE, 0666)
if err != nil {
    libhttp.EncodeErrorResponse(w, err, http.StatusInternalServerError)
    return
}

defer f.Close()
io.Copy(f, file)

go b.readFileAppend("./" + handler.Filename)

libhttp.EncodeOKResponse(w, true)}

After that, I am confused how I can send another file from that request like a binary, to improve the time and consumption.

after look information about the question i get that solution

to specify a browser that is a file i put that header to the response:

w.Header().Set("Content-Disposition", "attachment; filename=NameOfFile")

after that i read the file with ioutil:

files, err := ioutil.ReadFile(result)

and at the end i use the http.ResponseWriter to write the []byte of the file to the response

w.Write(files)