golang实现http server提供文件下载功能

func FileDownload(w http.ResponseWriter, r *http.Request) {
  filename := get_filename_from_request(r)

  file, _ := os.Open(filename)
  defer file.Close()

  fileHeader := make([]byte, 512)
  file.Read(fileHeader)

  fileStat, _ := file.Stat()

  w.Header().Set("Content-Disposition", "attachment; filename=" + filename)
  w.Header().Set("Content-Type", http.DetectContentType(fileHeader))
  w.Header().Set("Content-Length", strconv.FormatInt(fileStat.Size(), 10))

  file.Seek(0, 0)
  io.Copy(w, file)

  return
}

package main
import (
 "fmt"
 "io"
 "net/http"
)
func main() {
 http.HandleFunc("/", helloWorld)
 e:=http.ListenAndServe(":8888",nil)
 if e!=nil{
 fmt.Println(e.Error())
 }
}
func helloWorld(w http.ResponseWriter, r *http.Request) {
 str:="Hello World"
 n,e:=io.WriteString(w, str)
 if e!=nil{
 fmt.Println(e.Error())
 } else {
 fmt.Println(n," " ,len(str))
 }
}