add config and fix style check

src/Core/Settings.h

@@ -584,6 +584,8 @@ static constexpr UInt64 operator""_GiB(unsigned long long value)
     \
     M(Bool, allow_unrestricted_reads_from_keeper, false, "Allow unrestricted (without condition on path) reads from system.zookeeper table, can be handy, but is not safe for zookeeper", 0) \
     \
+    M(Bool, allow_writes_to_zookeeper, false, "Allow writes to system.zookeeper table, can be handy, but is not safe for zookeeper", 0) \
+    \
     /** Experimental functions */ \
     M(Bool, allow_experimental_funnel_functions, false, "Enable experimental functions for funnel analysis.", 0) \
     M(Bool, allow_experimental_nlp_functions, false, "Enable experimental functions for natural language processing.", 0) \

src/Storages/System/StorageSystemZooKeeper.cpp

@@ -21,7 +21,7 @@
 #include <boost/algorithm/string.hpp>
 #include <algorithm>
 #include <deque>
-#include <limits.h>
+#include <climits>
 
 
 namespace DB
@@ -53,7 +53,7 @@ struct ZkNodeCache
     {
         /// If this node has an empty name, just skip it.
         /// Possibly a "/a//b///c//d/" will cause empty node.
-        while(index < nodes.size() && nodes[index].empty())
+        while (index < nodes.size() && nodes[index].empty())
             ++index;
 
         if (index == nodes.size())
@@ -130,7 +130,8 @@ public:
                 throw Exception("Column `name` should not be empty", ErrorCodes::BAD_ARGUMENTS);
             }
 
-            if (path.size() + name.size() > PATH_MAX) {
+            if (path.size() + name.size() > PATH_MAX)
+            {
                 throw Exception("Sum of `name` length and `path` length should not exceed PATH_MAX", ErrorCodes::BAD_ARGUMENTS);
             }
 
@@ -151,6 +152,8 @@ public:
 
 SinkToStoragePtr StorageSystemZooKeeper::write(const ASTPtr &, const StorageMetadataPtr &, ContextPtr context)
 {
+    if (!context->getSettingsRef().allow_writes_to_zookeeper)
+        throw Exception("Prohibit writing to system.zookeeper unless `set allow_writes_to_zookeeper = 'true'`", ErrorCodes::BAD_ARGUMENTS);
     Block write_header;
     write_header.insert(ColumnWithTypeAndName(std::make_shared<DataTypeString>(), "name"));
     write_header.insert(ColumnWithTypeAndName(std::make_shared<DataTypeString>(), "value"));

tests/queries/0_stateless/02311_system_zookeeper_insert.sql

@@ -1,6 +1,9 @@
 -- Tags: zookeeper
 
+insert into system.zookeeper (name, path, value) values ('a', '/b', 'y'); -- { serverError 36 }
+
 set allow_unrestricted_reads_from_keeper = 'true';
+set allow_writes_to_zookeeper = 'true';
 
 drop table if exists test_zkinsert;