func setContentType(w http.ResponseWriter, name string, file http.File) {
t := mime.TypeByExtension(filepath.Ext(name))
if t == "" {
var buffer [512]byte
n, _ := io.ReadFull(file, buffer[:])
t = http.DetectContentType(buffer[:n])
if _, err := file.Seek(0, os.SEEK_SET); err != nil {
http.Error(w, "Can't seek", http.StatusInternalServerError)
return
}
}
w.Header().Set("Content-Type", t)
}
