func fileExceed(file multipart.File, limitSize int64) bool {
var isExceed bool
read_buf := make([]byte, 1024)
var pos int64 = 0
for {
n, err := file.ReadAt(read_buf, pos)
if err != nil && err != io.EOF {
panic(err)
}
if n == 0 {
break
}
pos = pos + (int64)(n)
if pos > limitSize {
isExceed = true
break
}
}
return isExceed
}