code: func (ch *Chunk) Drain() {
  	bytesAhead := ch.Size - ch.Pos
  	for bytesAhead > 0 {
  		readSize := int64(bytesAhead)
  
  		if _, err := io.CopyN(ioutil.Discard, ch.R, readSize); err != nil {
  			return
  		}
  		bytesAhead -= int(readSize)
  	}
  }
docs: // Drain discards the rest of the chunk