feat: Add CLP UDF docs

presto-clp/src/main/java/com/facebook/presto/plugin/clp/ClpFunctions.java

@@ -97,4 +97,12 @@ public static boolean clpWildcardBoolColumn()
     {
         throw new UnsupportedOperationException("CLP_WILDCARD_BOOL_COLUMN is a placeholder function without implementation.");
     }
+
+    @ScalarFunction(value = "CLP_GET_JSON_STRING", deterministic = false)
+    @Description("Converts an entire log record into a JSON string.")
+    @SqlType(StandardTypes.VARCHAR)
+    public static Slice clpGetJSONString()
+    {
+        throw new UnsupportedOperationException("CLP_GET_JSON_STRING is a placeholder function without implementation.");
+    }
 }

presto-clp/src/main/java/com/facebook/presto/plugin/clp/optimization/ClpUdfRewriter.java

@@ -58,6 +58,7 @@
 public final class ClpUdfRewriter
         implements ConnectorPlanOptimizer
 {
+    public static final String JSON_STRING_PLACEHOLDER = "__json_string";
     private final FunctionMetadataManager functionManager;
 
     public ClpUdfRewriter(FunctionMetadataManager functionManager)
@@ -123,7 +124,7 @@ public PlanNode visitProject(ProjectNode node, RewriteContext<Void> context)
             for (Map.Entry<VariableReferenceExpression, RowExpression> entry : node.getAssignments().getMap().entrySet()) {
                 newAssignments.put(
                         entry.getKey(),
-                        rewriteClpUdfs(entry.getValue(), functionManager, variableAllocator));
+                        rewriteClpUdfs(entry.getValue(), functionManager, variableAllocator, true));
             }
 
             PlanNode newSource = rewritePlanSubtree(node.getSource());
@@ -148,20 +149,32 @@ public PlanNode visitFilter(FilterNode node, RewriteContext<Void> context)
          * @param expression the input expression to analyze and possibly rewrite
          * @param functionManager function manager used to resolve function metadata
          * @param variableAllocator variable allocator used to create new variable references
+         * @param inProjectNode whether the CLP UDFs are in a {@link ProjectNode}
          * @return a possibly rewritten {@link RowExpression} with <code>CLP_GET_*</code> calls
          * replaced
          */
         private RowExpression rewriteClpUdfs(
                 RowExpression expression,
                 FunctionMetadataManager functionManager,
-                VariableAllocator variableAllocator)
+                VariableAllocator variableAllocator,
+                boolean inProjectNode)
         {
             // Handle CLP_GET_* function calls
             if (expression instanceof CallExpression) {
                 CallExpression call = (CallExpression) expression;
                 String functionName = functionManager.getFunctionMetadata(call.getFunctionHandle()).getName().getObjectName().toUpperCase();
 
-                if (functionName.startsWith("CLP_GET_")) {
+                if (inProjectNode && functionName.equals("CLP_GET_JSON_STRING")) {
+                    VariableReferenceExpression newValue = variableAllocator.newVariable(
+                            expression.getSourceLocation(),
+                            JSON_STRING_PLACEHOLDER,
+                            call.getType());
+                    ClpColumnHandle targetHandle = new ClpColumnHandle(JSON_STRING_PLACEHOLDER, call.getType());
+
+                    globalColumnVarMap.put(targetHandle, newValue);
+                    return newValue;
+                }
+                else if (functionName.startsWith("CLP_GET_")) {
                     if (call.getArguments().size() != 1 || !(call.getArguments().get(0) instanceof ConstantExpression)) {
                         throw new PrestoException(CLP_PUSHDOWN_UNSUPPORTED_EXPRESSION,
                                 "CLP_GET_* UDF must have a single constant string argument");
@@ -187,7 +200,7 @@ private RowExpression rewriteClpUdfs(
 
                 // Recurse into arguments
                 List<RowExpression> rewrittenArgs = call.getArguments().stream()
-                        .map(arg -> rewriteClpUdfs(arg, functionManager, variableAllocator))
+                        .map(arg -> rewriteClpUdfs(arg, functionManager, variableAllocator, inProjectNode))
                         .collect(toImmutableList());
 
                 return new CallExpression(call.getDisplayName(), call.getFunctionHandle(), call.getType(), rewrittenArgs);
@@ -198,7 +211,7 @@ private RowExpression rewriteClpUdfs(
                 SpecialFormExpression special = (SpecialFormExpression) expression;
 
                 List<RowExpression> rewrittenArgs = special.getArguments().stream()
-                        .map(arg -> rewriteClpUdfs(arg, functionManager, variableAllocator))
+                        .map(arg -> rewriteClpUdfs(arg, functionManager, variableAllocator, inProjectNode))
                         .collect(toImmutableList());
 
                 return new SpecialFormExpression(special.getSourceLocation(), special.getForm(), special.getType(), rewrittenArgs);
@@ -298,7 +311,7 @@ private TableScanNode buildNewTableScanNode(TableScanNode node)
          */
         private FilterNode buildNewFilterNode(FilterNode node)
         {
-            RowExpression newPredicate = rewriteClpUdfs(node.getPredicate(), functionManager, variableAllocator);
+            RowExpression newPredicate = rewriteClpUdfs(node.getPredicate(), functionManager, variableAllocator, false);
             PlanNode newSource = rewritePlanSubtree(node.getSource());
             return new FilterNode(node.getSourceLocation(), idAllocator.getNextId(), newSource, newPredicate);
         }

presto-clp/src/test/java/com/facebook/presto/plugin/clp/TestClpUdfRewriter.java

@@ -72,6 +72,7 @@
 import static com.facebook.presto.plugin.clp.metadata.ClpSchemaTreeNodeType.Float;
 import static com.facebook.presto.plugin.clp.metadata.ClpSchemaTreeNodeType.Integer;
 import static com.facebook.presto.plugin.clp.metadata.ClpSchemaTreeNodeType.VarString;
+import static com.facebook.presto.plugin.clp.optimization.ClpUdfRewriter.JSON_STRING_PLACEHOLDER;
 import static com.facebook.presto.sql.planner.assertions.MatchResult.NO_MATCH;
 import static com.facebook.presto.sql.planner.assertions.MatchResult.match;
 import static com.facebook.presto.sql.planner.assertions.PlanMatchPattern.anyTree;
@@ -140,7 +141,7 @@ public void tearDown()
     }
 
     @Test
-    public void testScanFilter()
+    public void testClpGetScanFilter()
     {
         TransactionId transactionId = localQueryRunner.getTransactionManager().beginTransaction(false);
         Session session = testSessionBuilder().setCatalog("clp").setSchema("default").setTransactionId(transactionId).build();
@@ -179,7 +180,7 @@ public void testScanFilter()
     }
 
     @Test
-    public void testScanProject()
+    public void testClpGetScanProject()
     {
         TransactionId transactionId = localQueryRunner.getTransactionManager().beginTransaction(false);
         Session session = testSessionBuilder().setCatalog("clp").setSchema("default").setTransactionId(transactionId).build();
@@ -229,7 +230,7 @@ public void testScanProject()
     }
 
     @Test
-    public void testScanProjectFilter()
+    public void testClpGetScanProjectFilter()
     {
         TransactionId transactionId = localQueryRunner.getTransactionManager().beginTransaction(false);
         Session session = testSessionBuilder().setCatalog("clp").setSchema("default").setTransactionId(transactionId).build();
@@ -265,6 +266,38 @@ public void testScanProjectFilter()
                                                         city))))));
     }
 
+    @Test
+    public void testClpGetJsonString()
+    {
+        TransactionId transactionId = localQueryRunner.getTransactionManager().beginTransaction(false);
+        Session session = testSessionBuilder().setCatalog("clp").setSchema("default").setTransactionId(transactionId).build();
+
+        Plan plan = localQueryRunner.createPlan(
+                session,
+                "SELECT CLP_GET_JSON_STRING() from test WHERE CLP_GET_BIGINT('user_id') = 0",
+                WarningCollector.NOOP);
+        ClpUdfRewriter udfRewriter = new ClpUdfRewriter(functionAndTypeManager);
+        PlanNode optimizedPlan = udfRewriter.optimize(plan.getRoot(), session.toConnectorSession(), variableAllocator, planNodeIdAllocator);
+        ClpComputePushDown optimizer = new ClpComputePushDown(functionAndTypeManager, functionResolution, splitFilterProvider);
+        optimizedPlan = optimizer.optimize(optimizedPlan, session.toConnectorSession(), variableAllocator, planNodeIdAllocator);
+
+        PlanAssert.assertPlan(
+                session,
+                localQueryRunner.getMetadata(),
+                (node, sourceStats, lookup, s, types) -> PlanNodeStatsEstimate.unknown(),
+                new Plan(optimizedPlan, plan.getTypes(), StatsAndCosts.empty()),
+                anyTree(
+                        project(
+                                ImmutableMap.of(
+                                        "clp_get_json_string",
+                                        PlanMatchPattern.expression(JSON_STRING_PLACEHOLDER)),
+                                ClpTableScanMatcher.clpTableScanPattern(
+                                        new ClpTableLayoutHandle(table, Optional.of("user_id: 0"), Optional.empty()),
+                                        ImmutableSet.of(
+                                                new ClpColumnHandle("user_id", BIGINT),
+                                                new ClpColumnHandle(JSON_STRING_PLACEHOLDER, VARCHAR))))));
+    }
+
     private static final class ClpTableScanMatcher
             implements Matcher
     {

presto-docs/src/main/sphinx/connector/clp.rst

@@ -320,6 +320,125 @@ Each JSON log maps to this unified ``ROW`` type, with absent fields represented
 ``status``, ``thread_num``, ``backtrace``) become fields within the ``ROW``, clearly reflecting the nested and varying
 structures of the original JSON logs.
 
+*************
+CLP Functions
+*************
+
+Semi-structured logs can have many potential keys, which can lead to very wide Presto tables. To keep table metadata
+concise and still preserve access to dynamic fields, the connector provides two sets of functions that are specific to
+the CLP connector. These functions are not part of standard Presto SQL.
+
+- JSON path functions (e.g., ``CLP_GET_STRING``)
+- Wildcard column matching functions for use in filter predicates (e.g., ``CLP_WILDCARD_STRING_COLUMN``)
+
+There is **no performance penalty** when using these functions. During query optimization, the connector rewrites these
+functions into references to concrete schema-backed columns or valid symbols in KQL queries. This avoids additional
+parsing overhead and delivers performance comparable to querying standard columns.
+
+Path-based Functions
+====================
+
+.. function:: CLP_GET_STRING(varchar) -> varchar
+
+    Returns the string value at the given JSON path, where the column type is one of: ``ClpString``, ``VarString``, or
+    ``DateString``. Returns a Presto ``VARCHAR``.
+
+.. function:: CLP_GET_BIGINT(varchar) -> bigint
+
+    Returns the integer value at the given JSON path, where the column type is ``Integer``. Returns a Presto ``BIGINT``.
+
+.. function:: CLP_GET_DOUBLE(varchar) -> double
+
+    Returns the double value at the given JSON path, where the column type is ``Float``.  Returns a Presto ``DOUBLE``.
+
+.. function:: CLP_GET_BOOL(varchar) -> boolean
+
+    Returns the boolean value at the given JSON path, where the column type is ``Boolean``. Returns a Presto ``BOOLEAN``.
+
+.. function:: CLP_GET_STRING_ARRAY(varchar) -> array(varchar)
+
+    Returns the array value at the given JSON path, where the column type is ``UnstructuredArray`` and converts each
+    element into a string. Returns a Presto ``ARRAY(VARCHAR)``.
+
+.. note::
+
+   - JSON paths must be **constant string literals**; variables are not supported.
+   - Wildcards (e.g., ``msg.*.ts``) are **not supported**.
+   - If a path is invalid or missing, the function returns ``NULL`` rather than raising an error.
+
+Examples
+--------
+
+.. code-block:: sql
+
+    SELECT CLP_GET_STRING(msg.author) AS author
+    FROM clp.default.table_1
+    WHERE CLP_GET_INT('msg.timestamp') > 1620000000;
+
+    SELECT CLP_GET_STRING_ARRAY(msg.tags) AS tags
+    FROM clp.default.table_2
+    WHERE CLP_GET_BOOL('msg.is_active') = true;
+
+
+Wildcard Column Functions
+=========================
+
+These functions are used to apply filter predicates across all columns of a certain type. They are useful for searching
+across unknown or dynamic schemas without specifying exact column names. Similar to the path-based functions, these
+functions are rewritten during query optimization to a KQL query that matches the appropriate columns.
+
+.. function:: CLP_WILDCARD_STRING_COLUMN() -> varchar
+
+   Represents all columns whose CLP types are ``ClpString``, ``VarString``, or ``DateString``.
+
+.. function:: CLP_WILDCARD_INT_COLUMN() -> bigint
+
+   Represents all columns whose CLP type is ``Integer``.
+
+.. function:: CLP_WILDCARD_FLOAT_COLUMN() -> double
+
+   Represents all columns whose CLP type is ``Float``.
+
+.. function:: CLP_WILDCARD_BOOL_COLUMN() -> boolean
+
+   Represents all columns whose CLP type is ``Boolean``.
+
+.. note::
+
+   - Wildcard functions must appear **only in filter conditions** (`WHERE` clause). They cannot be selected and cannot
+     be passed as arguments to other functions.
+   - Supported operators include:
+
+     ::
+
+         =   (EQUAL)
+         !=  (NOT_EQUAL)
+         <   (LESS_THAN)
+         <=  (LESS_THAN_OR_EQUAL)
+         >   (GREATER_THAN)
+         >=  (GREATER_THAN_OR_EQUAL)
+         LIKE
+         BETWEEN
+         IN
+
+     Use of other operators (e.g., arithmetic or function calls) with wildcard functions is not allowed and will result
+     in a query error.
+
+Examples
+--------
+
+.. code-block:: sql
+
+   -- Matches if any string column contains "Beijing"
+   SELECT *
+   FROM clp.default.table_1
+   WHERE CLP_WILDCARD_STRING_COLUMN() = 'Beijing';
+
+   -- Matches if any integer column equals 1
+   SELECT *
+   FROM clp.default.table_2
+   WHERE CLP_WILDCARD_INT_COLUMN() = 1;
+
 ***********
 SQL support
 ***********