void getBlockChecksum(DataInputStream in,
VersionAndOpcode versionAndOpcode) throws IOException {
// header
BlockChecksumHeader blockChecksumHeader =
new BlockChecksumHeader(versionAndOpcode);
blockChecksumHeader.readFields(in);
final int namespaceId = blockChecksumHeader.getNamespaceId();
final Block block = new Block(blockChecksumHeader.getBlockId(), 0,
blockChecksumHeader.getGenStamp());
DataOutputStream out = null;