made configurable custom settings prefix

Author: chernser

client-v2/src/main/java/com/clickhouse/client/api/ClientConfigProperties.java

@@ -182,6 +182,13 @@ public Object parseValue(String value) {
      * SNI SSL parameter that will be set for each outbound SSL socket.
      */
     SSL_SOCKET_SNI("ssl_socket_sni", String.class,""),
+
+    /**
+     *  Prefix for custom settings. Should be aligned with server configuration.
+     *  See <a href="https://clickhouse.com/docs/operations/settings/query-level#custom_settings">ClickHouse Docs</a>
+     */
+    CUSTOM_SETTINGS_PREFIX("clickhouse_setting_", String.class, "custom_"),
+
     ;
 
     public static final String NO_THROW_ON_UNKNOWN_CONFIG = "no_throw_on_unknown_config";
@@ -224,8 +231,6 @@ public <T> T getDefObjVal() {
 
     public static final String SERVER_SETTING_PREFIX = "clickhouse_setting_";
 
-    public static final String CUSTOM_SETTING_PREFIX = "custom_";
-
     // Key used to identify default value in configuration map
     public static final String DEFAULT_KEY = "_default_";
 
@@ -338,10 +343,12 @@ public static Map<String, Object> parseConfigMap(Map<String, String> configMap)
             }
         }
 
+        final String customSettingsPrefix = configMap.getOrDefault(ClientConfigProperties.CUSTOM_SETTINGS_PREFIX.getKey(),
+                CUSTOM_SETTINGS_PREFIX.getDefaultValue());
         for (String key : new HashSet<>(tmpMap.keySet())) {
             if (key.startsWith(HTTP_HEADER_PREFIX) || key.startsWith(SERVER_SETTING_PREFIX)) {
                 parsedConfig.put(key, tmpMap.remove(key));
-            } else if (key.startsWith(CUSTOM_SETTING_PREFIX)) {
+            } else if (key.startsWith(customSettingsPrefix)) {
                 parsedConfig.put(serverSetting(key), tmpMap.remove(key));
             }
         }

client-v2/src/test/java/com/clickhouse/client/ClientTests.java

@@ -109,6 +109,8 @@ public static Object[][] secureClientProvider() throws Exception {
     public void testRawSettings() {
         Client client = newClient()
                 .setOption("custom_setting_1", "value_1")
+                .setOption(ClientConfigProperties.CUSTOM_SETTINGS_PREFIX.getKey(), isCloud()? "SQL_" :
+                        ClientConfigProperties.CUSTOM_SETTINGS_PREFIX.getDefaultValue())
                 .build();
 
         client.execute("SELECT 1");