public static RpcRequestHeaderProto makeRpcRequestHeader(RPC.RpcKind rpcKind,
      RpcRequestHeaderProto.OperationProto operation, int callId,
      int retryCount, byte[] uuid) {
    return makeRpcRequestHeader(rpcKind, operation, callId, retryCount, uuid,
        null);
  }
@Test
  public void testRpcClientId() {
    byte[] uuid = ClientId.getClientId();
    RpcRequestHeaderProto header = ProtoUtil.makeRpcRequestHeader(
        RpcKind.RPC_PROTOCOL_BUFFER, OperationProto.RPC_FINAL_PACKET, 0,
        RpcConstants.INVALID_RETRY_COUNT, uuid);
    assertTrue(Arrays.equals(uuid, header.getClientId().toByteArray()));
  }