//write the header.
ReadBlockHeader readBlockHeader = new ReadBlockHeader(
dataTransferVersion, namespaceId, blockId, genStamp, startOffset, len,
clientName, reuseConnection, cliData != null);
readBlockHeader.setReadOptions(options);
readBlockHeader.writeVersionAndOpCode(out);
readBlockHeader.write(out);
out.flush();
//
// Get bytes in block, set streams