Add documentation for SQL filter expression limits (#1224)

* Refs #24181. Add properties in non-consolidated QoS.

Signed-off-by: Miguel Company <miguelcompany@eprosima.com>

* Refs #24181. Add example.

Signed-off-by: Miguel Company <miguelcompany@eprosima.com>

* Refs #24181. Add link from the filtering section.

Signed-off-by: Miguel Company <miguelcompany@eprosima.com>

* Refs #24181. Fix doc8.

Signed-off-by: Miguel Company <miguelcompany@eprosima.com>

* Refs #24181. Apply suggestions.

Signed-off-by: Miguel Company <miguelcompany@eprosima.com>

---------

Signed-off-by: Miguel Company <miguelcompany@eprosima.com>
(cherry picked from commit 7bb4e28)

Author: MiguelCompany

code/DDSCodeTester.cpp

@@ -995,6 +995,19 @@ void dds_domain_examples()
             "true"); // true or True or TRUE or 1
         //!--
     }
+
+    {
+        // DDS_SQL_LIMITS_PROPERTY
+        DomainParticipantQos pqos;
+
+        pqos.properties().properties().emplace_back(
+            "dds.sql.expression.max_expression_length",
+            "20000");
+        pqos.properties().properties().emplace_back(
+            "dds.sql.expression.max_subexpressions",
+            "10");
+        //!--
+    }
 }
 
 //DOMAINPARTICIPANTLISTENER-DISCOVERY-CALLBACKS

code/XMLTester.xml

@@ -3317,6 +3317,34 @@
 -->
 <!--><-->
 
+<!-->DDS_SQL_LIMITS_PROPERTY<-->
+<!--
+<?xml version="1.0" encoding="UTF-8" ?>
+<dds xmlns="http://www.eprosima.com">
+    <profiles>
+-->
+        <participant profile_name="custom_sql_limits_domainparticipant_xml_profile">
+            <rtps>
+                <propertiesPolicy>
+                    <properties>
+                        <property>
+                            <name>dds.sql.expression.max_expression_length</name>
+                            <value>20000</value>
+                        </property>
+                        <property>
+                            <name>dds.sql.expression.max_subexpressions</name>
+                            <value>10</value>
+                        </property>
+                    </properties>
+                </propertiesPolicy>
+            </rtps>
+        </participant>
+<!--
+    </profiles>
+</dds>
+-->
+<!--><-->
+
 <!-->FASTDDS_STATISTICS_MODULE<-->
 <participant profile_name="statistics_domainparticipant_conf_xml_profile">
     <rtps>

docs/fastdds/dds_layer/topic/contentFilteredTopic/defaultFilter.rst

@@ -9,6 +9,9 @@ The default SQL-like filter
 Filter expressions used by :ref:`dds_layer_topic_contentFilteredTopic` API may use a subset of SQL syntax, extended with
 the possibility to use program variables in the SQL expression.
 This section shows this default SQL-like syntax and how to use it.
+Apart from the syntax described in this section, certain restrictions apply to the allowed SQL expressions.
+These restrictions can be relaxed or tightened by the user, as explained in
+:ref:`properties_sql_filter_expression_limits`.
 
 * :ref:`default_sql_filter_grammar`
 * :ref:`default_sql_filter_like`

docs/fastdds/property_policies/non_consolidated_qos.rst

@@ -543,3 +543,46 @@ The following table lists all the optional QoS that can be serialized in the dis
         :start-after: <!-->SERIALIZE_OPTIONAL_QOS_PROPERTY<-->
         :end-before: <!--><-->
         :lines: 2-4,6-17,19-20
+
+.. _properties_sql_filter_expression_limits:
+
+SQL Filter Expression limits
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When creating content-filtered topics using the
+:ref:`default SQL-like filter <dds_layer_topic_contentFilteredTopic_default_filter>`, some restrictions apply to the
+SQL expressions that can be used for content-based filtering.
+The default limits are set to values that should be enough for most use cases, but they can be customized using the
+following properties when a participant is created:
+
+.. list-table::
+   :header-rows: 1
+   :align: left
+
+   * - PropertyPolicyQos name
+     - PropertyPolicyQos value
+     - Default value
+   * - ``"dds.sql.expression.max_expression_length"``
+     - Maximum length of the SQL expression, in characters.
+     - ``16384``
+   * - ``"dds.sql.expression.max_subexpressions"``
+     - Maximum number of sub-expressions in the SQL expression.
+     - ``256``
+
+Creating content-filtered topics with expressions exceeding any of these limits will fail.
+Expressions received in discovery messages exceeding any of these limits will be ignored, and filtering will happen
+in the reader side.
+
+.. tab-set-code::
+
+    .. literalinclude:: /../code/DDSCodeTester.cpp
+        :language: c++
+        :start-after: // DDS_SQL_LIMITS_PROPERTY
+        :end-before: //!--
+        :dedent: 8
+
+    .. literalinclude:: /../code/XMLTester.xml
+        :language: xml
+        :start-after: <!-->DDS_SQL_LIMITS_PROPERTY<-->
+        :end-before: <!--><-->
+        :lines: 2-4,6-21,23-24