}
@Override
public void blockChecksum(final ExtendedBlock blk,
final Token<BlockTokenIdentifier> blockToken) throws IOException {
OpBlockChecksumProto proto = OpBlockChecksumProto.newBuilder()
.setHeader(DataTransferProtoUtil.buildBaseHeader(blk, blockToken))
.build();
send(out, Op.BLOCK_CHECKSUM, proto);
}