func newChecksumBlockOp(block *hdfs.LocatedBlockProto) *hdfs.OpBlockChecksumProto {
	return &hdfs.OpBlockChecksumProto{
		Header: &hdfs.BaseHeaderProto{
			Block: block.GetB(),
			Token: block.GetBlockToken(),
		},
	}
}

func newBlockReadOp(block *hdfs.LocatedBlockProto, offset, length uint64) *hdfs.OpReadBlockProto {
	return &hdfs.OpReadBlockProto{
		Header: &hdfs.ClientOperationHeaderProto{
			BaseHeader: &hdfs.BaseHeaderProto{
				Block: block.GetB(),
				Token: block.GetBlockToken(),
			},
			ClientName: proto.String(ClientName),
		},
		Offset: proto.Uint64(offset),
		Len:    proto.Uint64(length),
	}
}

// NewChecksumReader creates a new ChecksumReader for the given block.
func NewChecksumReader(block *hdfs.LocatedBlockProto) *ChecksumReader {
	locs := block.GetLocs()
	datanodes := make([]string, len(locs))
	for i, loc := range locs {
		dn := loc.GetId()
		datanodes[i] = fmt.Sprintf("%s:%d", dn.GetIpAddr(), dn.GetXferPort())
	}

	return &ChecksumReader{
		block:     block,
		datanodes: newDatanodeFailover(datanodes),
	}
}

// NewBlockReader returns a new BlockReader, given the block information and
// security token from the namenode. It will connect (lazily) to one of the
// provided datanode locations based on which datanodes have seen failures.
func NewBlockReader(block *hdfs.LocatedBlockProto, offset int64, clientName string) *BlockReader {
	locs := block.GetLocs()
	datanodes := make([]string, len(locs))
	for i, loc := range locs {
		datanodes[i] = getDatanodeAddress(loc)
	}

	return &BlockReader{
		clientName: clientName,
		block:      block,
		datanodes:  newDatanodeFailover(datanodes),
		offset:     offset,
	}
}