code: func (r *bufferingReaderAt) recycleBuf(b []byte) {
  	if cap(b) != r.blockSize {
  		panic("trying to return a buffer not initially requested via grabBuf")
  	}
  	if len(r.pool)+1 > cap(r.pool) {
  		panic("unexpected growth of byte buffer pool beyond capacity")
  	}
  	r.pool = append(r.pool, b[:cap(b)])
  }
docs: // recycleBuf is called when the buffer is no longer needed to put it for reuse.