@Override
 public long skip(long n) throws IOException {
   if (n > 0) {
     long curPos = getPos();
     long fileLen = getFileLength();
     if (n + curPos > fileLen) {
       n = fileLen - curPos;
     }
     seek(curPos + n);
     return n;
   }
   return n < 0 ? -1 : 0;
 }