Send settings from server to client

programs/client/Client.cpp

@@ -476,6 +476,17 @@ void Client::connect()
                 connection_parameters.timeouts, server_name, server_version_major, server_version_minor, server_version_patch, server_revision);
             config().setString("host", connection_parameters.host);
             config().setInt("port", connection_parameters.port);
+
+            /// Apply setting changes received from server, but with lower priority than settings
+            /// changed from command line.
+            SettingsChanges settings_from_server = assert_cast<Connection &>(*connection).settingsFromServer();
+            const Settings & settings = global_context->getSettingsRef();
+            std::erase_if(settings_from_server, [&](const SettingChange & change)
+            {
+                return settings.isChanged(change.name);
+            });
+            global_context->applySettingsChanges(settings_from_server);
+
             break;
         }
         catch (const Exception & e)

src/Client/Connection.cpp

@@ -5,6 +5,7 @@
 #include <Core/Settings.h>
 #include <Compression/CompressedReadBuffer.h>
 #include <Compression/CompressedWriteBuffer.h>
+#include <IO/LimitReadBuffer.h>
 #include <IO/ReadHelpers.h>
 #include <IO/WriteHelpers.h>
 #include <IO/copyData.h>
@@ -74,6 +75,7 @@ namespace ErrorCodes
     extern const int SUPPORT_IS_DISABLED;
     extern const int BAD_ARGUMENTS;
     extern const int EMPTY_DATA_PASSED;
+    extern const int CANNOT_READ_ALL_DATA;
 }
 
 Connection::~Connection()
@@ -575,6 +577,22 @@ void Connection::receiveHello(const Poco::Timespan & handshake_timeout)
             readIntBinary(read_nonce, *in);
             nonce.emplace(read_nonce);
         }
+        if (server_revision >= DBMS_MIN_REVISION_WITH_SERVER_HELLO_EXTRAS)
+        {
+            UInt64 extras_size;
+            readVarUInt(extras_size, *in);
+            LimitReadBuffer extras(*in, extras_size, /*throw_exception_*/ false, /*exact_limit_*/ extras_size);
+
+            if (server_revision >= DBMS_MIN_REVISION_WITH_SERVER_SETTINGS)
+            {
+                Settings settings;
+                settings.read(extras, SettingsWriteFormat::STRINGS_WITH_FLAGS);
+                settings_from_server = settings.changes();
+            }
+
+            if (!extras.eof())
+                throw Exception(ErrorCodes::CANNOT_READ_ALL_DATA, "Unexpected size of Hello message extras: expected {}, got {}", extras.count(), extras_size);
+        }
     }
     else if (packet_type == Protocol::Server::Exception)
         receiveException()->rethrow();
@@ -600,6 +618,12 @@ const String & Connection::getDefaultDatabase() const
     return default_database;
 }
 
+const SettingsChanges & Connection::settingsFromServer() const
+{
+    chassert(connected);
+    return settings_from_server;
+}
+
 const String & Connection::getDescription(bool with_extra) const /// NOLINT
 {
     if (with_extra)
@@ -833,9 +857,23 @@ void Connection::sendQuery(
     /// Per query settings.
     if (settings)
     {
+        std::optional<Settings> modified_settings;
+        const Settings * settings_to_send = settings;
+        if (!settings_from_server.empty())
+        {
+            /// Don't send settings that we got from the server in the first place.
+            modified_settings.emplace(*settings);
+            for (const SettingChange & change : settings_from_server)
+            {
+                if (settings->get(change.name) == change.value)
+                    modified_settings->setDefaultValue(change.name);
+            }
+            settings_to_send = &*modified_settings;
+        }
+
         auto settings_format = (server_revision >= DBMS_MIN_REVISION_WITH_SETTINGS_SERIALIZED_AS_STRINGS) ? SettingsWriteFormat::STRINGS_WITH_FLAGS
                                                                                                           : SettingsWriteFormat::BINARY;
-        settings->write(*out, settings_format);
+        settings_to_send->write(*out, settings_format);
     }
     else
         writeStringBinary("" /* empty string is a marker of the end of settings */, *out);

src/Client/Connection.h

@@ -89,6 +89,8 @@ public:
     const String & getServerTimezone(const ConnectionTimeouts & timeouts) override;
     const String & getServerDisplayName(const ConnectionTimeouts & timeouts) override;
 
+    const SettingsChanges & settingsFromServer() const;
+
     /// For log and exception messages.
     const String & getDescription(bool with_extra = false) const override; /// NOLINT
     const String & getHost() const;
@@ -213,6 +215,7 @@ private:
     UInt64 server_parallel_replicas_protocol_version = 0;
     String server_timezone;
     String server_display_name;
+    SettingsChanges settings_from_server;
 
     std::unique_ptr<Poco::Net::StreamSocket> socket;
     std::shared_ptr<ReadBufferFromPocoSocketChunked> in;

src/Core/ProtocolDefines.h

@@ -3,6 +3,8 @@
 namespace DB
 {
 
+/// In the names below, "REVISION" and "PROTOCOL_VERSION" are synonyms.
+
 static constexpr auto DBMS_MIN_REVISION_WITH_CLIENT_INFO = 54032;
 static constexpr auto DBMS_MIN_REVISION_WITH_SERVER_TIMEZONE = 54058;
 static constexpr auto DBMS_MIN_REVISION_WITH_QUOTA_KEY_IN_CLIENT_INFO = 54060;
@@ -90,6 +92,10 @@ static constexpr auto DBMS_MIN_PROTOCOL_VERSION_WITH_CHUNKED_PACKETS = 54470;
 
 static constexpr auto DBMS_MIN_REVISION_WITH_VERSIONED_PARALLEL_REPLICAS_PROTOCOL = 54471;
 
+static constexpr auto DBMS_MIN_REVISION_WITH_SERVER_HELLO_EXTRAS = 54472;
+
+static constexpr auto DBMS_MIN_REVISION_WITH_SERVER_SETTINGS = 54472;
+
 /// Version of ClickHouse TCP protocol.
 ///
 /// Should be incremented manually on protocol changes.
@@ -97,6 +103,6 @@ static constexpr auto DBMS_MIN_REVISION_WITH_VERSIONED_PARALLEL_REPLICAS_PROTOCO
 /// NOTE: DBMS_TCP_PROTOCOL_VERSION has nothing common with VERSION_REVISION,
 /// later is just a number for server version (one number instead of commit SHA)
 /// for simplicity (sometimes it may be more convenient in some use cases).
-static constexpr auto DBMS_TCP_PROTOCOL_VERSION = 54471;
+static constexpr auto DBMS_TCP_PROTOCOL_VERSION = 54472;
 
 }

src/Core/ServerSettings.cpp

@@ -192,6 +192,7 @@ namespace DB
     DECLARE(UInt64, parts_killer_pool_size, 128, "Threads for cleanup of shared merge tree outdated threads. Only available in ClickHouse Cloud", 0) \
     DECLARE(UInt64, keeper_multiread_batch_size, 10'000, "Maximum size of batch for MultiRead request to [Zoo]Keeper that support batching. If set to 0, batching is disabled. Available only in ClickHouse Cloud.", 0) \
     DECLARE(Bool, use_legacy_mongodb_integration, true, "Use the legacy MongoDB integration implementation. Note: it's highly recommended to set this option to false, since legacy implementation will be removed in the future. Please submit any issues you encounter with the new implementation.", 0) \
+    DECLARE(Bool, send_settings_to_client, true, "Send user settings from server configuration to clients (in the server Hello message).", 0) \
 
 /// If you add a setting which can be updated at runtime, please update 'changeable_settings' map in dumpToSystemServerSettingsColumns below
 

src/Core/Settings.cpp

@@ -6284,6 +6284,11 @@ void Settings::read(ReadBuffer & in, SettingsWriteFormat format)
     impl->read(in, format);
 }
 
+void Settings::writeEmpty(WriteBuffer & out)
+{
+    BaseSettingsHelpers::writeString("", out);
+}
+
 void Settings::addToProgramOptions(boost::program_options::options_description & options)
 {
     addProgramOptions(*impl, options);

src/Core/Settings.h

@@ -139,6 +139,8 @@ struct Settings
 
     void write(WriteBuffer & out, SettingsWriteFormat format = SettingsWriteFormat::DEFAULT) const;
     void read(ReadBuffer & in, SettingsWriteFormat format = SettingsWriteFormat::DEFAULT);
+    /// Equivalent to Settings().write(out, <any format>) but faster.
+    static void writeEmpty(WriteBuffer & out);
 
     void addToProgramOptions(boost::program_options::options_description & options);
     void addToProgramOptions(std::string_view setting_name, boost::program_options::options_description & options);

src/IO/WriteBufferFromString.h

@@ -9,7 +9,7 @@ namespace DB
 {
 
 /** Writes the data to a string.
-  * Note: before using the resulting string, destroy this object.
+  * Note: before using the resulting string, destroy this object or call finalize().
   */
 using WriteBufferFromString = WriteBufferFromVector<std::string>;
 

src/Server/TCPHandler.cpp

@@ -105,6 +105,7 @@ namespace Setting
 namespace ServerSetting
 {
     extern const ServerSettingsBool validate_tcp_client_information;
+    extern const ServerSettingsBool send_settings_to_client;
 }
 }
 
@@ -1752,6 +1753,24 @@ void TCPHandler::sendHello()
         nonce.emplace(thread_local_rng());
         writeIntBinary(nonce.value(), *out);
     }
+
+    if (client_tcp_protocol_version >= DBMS_MIN_REVISION_WITH_SERVER_HELLO_EXTRAS)
+    {
+        /// Write newly added fields as one length-prefixed blob to allow proxies to skip them
+        /// without parsing. Needed only for Hello message because it can't use chunked protocol.
+        WriteBufferFromOwnString extras;
+
+        if (client_tcp_protocol_version >= DBMS_MIN_REVISION_WITH_SERVER_SETTINGS)
+        {
+            if (is_interserver_mode || !Context::getGlobalContextInstance()->getServerSettings()[ServerSetting::send_settings_to_client])
+                Settings::writeEmpty(extras); // send empty list of setting changes
+            else
+                session->sessionContext()->getSettingsRef().write(extras, SettingsWriteFormat::STRINGS_WITH_FLAGS);
+        }
+
+        writeStringBinary(extras.str(), *out);
+    }
+
     out->next();
 }
 

tests/integration/test_settings_from_server/configs/users.d/users.xml

@@ -0,0 +1,21 @@
+<clickhouse>
+    <profiles>
+        <default>
+            <output_format_json_quote_64bit_integers>0</output_format_json_quote_64bit_integers>
+        </default>
+        <second_profile>
+            <output_format_json_quote_64bit_integers>1</output_format_json_quote_64bit_integers>
+            <output_format_json_array_of_rows>1</output_format_json_array_of_rows>
+        </second_profile>
+    </profiles>
+    <users>
+        <default>
+            <password></password>
+            <profile>default</profile>
+        </default>
+        <second_user>
+            <password></password>
+            <profile>second_profile</profile>
+        </second_user>
+    </users>
+</clickhouse>

tests/integration/test_settings_from_server/test.py

@@ -0,0 +1,47 @@
+import pytest
+
+from helpers.client import QueryRuntimeException
+from helpers.cluster import ClickHouseCluster
+from helpers.network import PartitionManager
+
+cluster = ClickHouseCluster(__file__)
+node = cluster.add_instance(
+    "node",
+    main_configs=[],
+    user_configs=[
+        "configs/users.d/users.xml",
+    ],
+)
+
+@pytest.fixture(scope="module")
+def started_cluster():
+    try:
+        cluster.start()
+        yield cluster
+    finally:
+        cluster.shutdown()
+
+def test_settings_from_server(started_cluster):
+    # Setting changed by server (default user).
+    res = node.query("select 42::UInt64 as x format JSON")
+    assert '"x": 42' in res, "should be unquoted"
+
+    # Setting changed by server to a different value (other user).
+    res = node.query("select 42::UInt64 as x format JSON", user='second_user')
+    assert '"x": "42"' in res, "should be quoted"
+
+    # Setting not changed by server (default user).
+    res = node.query("select 42::UInt64 as x format JSONEachRow")
+    assert '[' not in res, "should not be formatted as a JSON array"
+
+    # Setting changed by server (other user).
+    res = node.query("select 42::UInt64 as x format JSONEachRow", user='second_user')
+    assert '[' in res, "should be formatted as a JSON array"
+
+    # Setting changed by server but changed back by the query.
+    res = node.query("select 42::UInt64 as x settings output_format_json_array_of_rows=0 format JSONEachRow", user='second_user')
+    assert '[' not in res, "should not be formatted as a JSON array"
+
+    # Setting changed by server but changed back client command line.
+    res = node.query("select 42::UInt64 as x format JSONEachRow", user='second_user', settings={"output_format_json_array_of_rows": "0"})
+    assert '[' not in res, "should not be formatted as a JSON array"