func (f *FilePointer) GetLine(pos int64, len int) []byte {
	buf := make([]byte, len)
	_, _ = f.File.ReadAt(buf, pos)
	return buf
}
GetLine of the file
package main
import "os"
type FilePointer struct {
	Filename string
	File     *os.File
}
func NewFilePointer(filename string) *FilePointer {
	f := &FilePointer{
		Filename: filename,
	}
	f.File, _ = os.Open(f.Filename)
	return f
}