private void handleCommands(List<CommandOperation> ops, ConfigOverlay overlay)
        throws IOException {
      for (CommandOperation op : ops) {
        switch (op.name) {
          case SET_PROPERTY:
            overlay = applySetProp(op, overlay);
            break;
          case UNSET_PROPERTY:
            overlay = applyUnset(op, overlay);
            break;
          case SET_USER_PROPERTY:
            overlay = applySetUserProp(op, overlay);
            break;
          case UNSET_USER_PROPERTY:
            overlay = applyUnsetUserProp(op, overlay);
            break;
          case UPDATE_REQHANDLER:
          case CREATE_REQHANDLER:
            overlay = applyRequestHandler(op, overlay);
            break;
          case DELETE_REQHANDLER:
            overlay = applyDeleteHandler(op, overlay);
            break;
        }
      }
      List errs = CommandOperation.captureErrors(ops);
      if (!errs.isEmpty()) {
        resp.add(CommandOperation.ERR_MSGS, errs);
        return;
      }

      SolrResourceLoader loader = req.getCore().getResourceLoader();
      if (loader instanceof ZkSolrResourceLoader) {
        ZkController.persistConfigResourceToZooKeeper(
            loader,
            overlay.getZnodeVersion(),
            ConfigOverlay.RESOURCE_NAME,
            overlay.toByteArray(),
            true);

      } else {
        SolrResourceLoader.persistConfLocally(
            loader, ConfigOverlay.RESOURCE_NAME, overlay.toByteArray());
        req.getCore().getCoreDescriptor().getCoreContainer().reload(req.getCore().getName());
      }
    }
    private void handlePOST() throws IOException {
      Iterable<ContentStream> streams = req.getContentStreams();
      if (streams == null) {
        throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "missing content stream");
      }
      ArrayList<CommandOperation> ops = new ArrayList<>();

      for (ContentStream stream : streams) ops.addAll(CommandOperation.parse(stream.getReader()));
      List<Map> errList = CommandOperation.captureErrors(ops);
      if (!errList.isEmpty()) {
        resp.add(CommandOperation.ERR_MSGS, errList);
        return;
      }

      try {
        for (; ; ) {
          ArrayList<CommandOperation> opsCopy = new ArrayList<>(ops.size());
          for (CommandOperation op : ops) opsCopy.add(op.getCopy());
          try {
            if (parts.size() > 1 && RequestParams.NAME.equals(parts.get(1))) {
              RequestParams params =
                  RequestParams.getFreshRequestParams(
                      req.getCore().getResourceLoader(),
                      req.getCore().getSolrConfig().getRequestParams());
              handleParams(opsCopy, params);
            } else {
              ConfigOverlay overlay =
                  SolrConfig.getConfigOverlay(req.getCore().getResourceLoader());
              handleCommands(opsCopy, overlay);
            }
            break; // succeeded . so no need to go over the loop again
          } catch (ZkController.ResourceModifiedInZkException e) {
            // retry
            log.info(
                "Race condition, the node is modified in ZK by someone else " + e.getMessage());
          }
        }
      } catch (Exception e) {
        resp.setException(e);
        resp.add(CommandOperation.ERR_MSGS, singletonList(SchemaManager.getErrorStr(e)));
      }
    }
    private void handleParams(ArrayList<CommandOperation> ops, RequestParams params) {
      for (CommandOperation op : ops) {
        switch (op.name) {
          case CREATE:
          case UPDATE:
            {
              Map<String, Object> map = op.getDataMap();
              if (op.hasError()) break;

              for (Map.Entry<String, Object> entry : map.entrySet()) {

                Map val = null;
                String key = entry.getKey();
                if (key == null || key.trim().isEmpty()) {
                  op.addError("null key ");
                  continue;
                }
                key = key.trim();
                if (!validName(key)) {
                  op.addError(
                      MessageFormat.format(
                          "''{0}'' name should only have chars [a-zA-Z_-.0-9] ", key));
                  continue;
                }

                try {
                  val = (Map) entry.getValue();
                } catch (Exception e1) {
                  op.addError("invalid params for key : " + key);
                  continue;
                }

                if (val.containsKey("")) {
                  op.addError("Empty keys are not allowed in params");
                  continue;
                }

                MapSolrParams old = params.getParams(key);
                if (op.name.equals(UPDATE)) {
                  LinkedHashMap m = new LinkedHashMap(old.getMap());
                  m.putAll(val);
                  val = m;
                }
                params = params.setParams(key, val);
              }
              break;
            }
          case "delete":
            {
              List<String> name = op.getStrs(CommandOperation.ROOT_OBJ);
              if (op.hasError()) break;
              for (String s : name) {
                if (params.getParams(s) == null) {
                  op.addError(
                      MessageFormat.format("can't delete . No such params ''{0}'' exist", s));
                }
                params = params.setParams(s, null);
              }
            }
        }
      }

      List errs = CommandOperation.captureErrors(ops);
      if (!errs.isEmpty()) {
        resp.add(CommandOperation.ERR_MSGS, errs);
        return;
      }

      SolrResourceLoader loader = req.getCore().getResourceLoader();
      if (loader instanceof ZkSolrResourceLoader) {
        ZkController.persistConfigResourceToZooKeeper(
            loader, params.getZnodeVersion(), RequestParams.RESOURCE, params.toByteArray(), true);

      } else {
        SolrResourceLoader.persistConfLocally(
            loader, ConfigOverlay.RESOURCE_NAME, params.toByteArray());
        req.getCore().getSolrConfig().refreshRequestParams();
      }
    }