From 87272aeac2809feee8d8dba6f6ec25a78a0a7e96 Mon Sep 17 00:00:00 2001
From: Sandesh Kumar <sandeshkr419@gmail.com>
Date: Tue, 11 Jun 2024 17:13:17 -0700
Subject: [PATCH] grok validate pattern - change to iterative approach

Signed-off-by: Sandesh Kumar <sandeshkr419@gmail.com>
---
 .../main/java/org/opensearch/grok/Grok.java   | 91 ++++++++++++++-----
 1 file changed, 66 insertions(+), 25 deletions(-)

diff --git a/libs/grok/src/main/java/org/opensearch/grok/Grok.java b/libs/grok/src/main/java/org/opensearch/grok/Grok.java
index 7aa3347ba4f4b..e1ce499102632 100644
--- a/libs/grok/src/main/java/org/opensearch/grok/Grok.java
+++ b/libs/grok/src/main/java/org/opensearch/grok/Grok.java
@@ -39,11 +39,13 @@
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
 import java.util.Stack;
 import java.util.function.Consumer;
 
@@ -144,7 +146,7 @@ private Grok(
      */
     private void validatePatternBank() {
         for (String patternName : patternBank.keySet()) {
-            validatePatternBank(patternName, new Stack<>());
+            validatePatternBank(patternName);
         }
     }
 
@@ -156,33 +158,72 @@ private void validatePatternBank() {
      * a reference to another named pattern. This method will navigate to all these named patterns and
      * check for a circular reference.
      */
-    private void validatePatternBank(String patternName, Stack<String> path) {
-        String pattern = patternBank.get(patternName);
-        boolean isSelfReference = pattern.contains("%{" + patternName + "}") || pattern.contains("%{" + patternName + ":");
-        if (isSelfReference) {
-            throwExceptionForCircularReference(patternName, pattern);
-        } else if (path.contains(patternName)) {
-            // current pattern name is already in the path, fetch its predecessor
-            String prevPatternName = path.pop();
-            String prevPattern = patternBank.get(prevPatternName);
-            throwExceptionForCircularReference(prevPatternName, prevPattern, patternName, path);
-        }
-        path.push(patternName);
-        for (int i = pattern.indexOf("%{"); i != -1; i = pattern.indexOf("%{", i + 1)) {
-            int begin = i + 2;
-            int syntaxEndIndex = pattern.indexOf('}', begin);
-            if (syntaxEndIndex == -1) {
-                throw new IllegalArgumentException("Malformed pattern [" + patternName + "][" + pattern + "]");
+    private void validatePatternBank(String patternName) {
+        Stack<String> path = new Stack<>();
+        Stack<PatternState> stack = new Stack<>();
+        Set<String> visited = new HashSet<>();
+
+        stack.push(new PatternState(patternName, 0));
+
+        while (!stack.isEmpty()) {
+            PatternState currentState = stack.pop();
+            String currentPatternName = currentState.patternName;
+            int startIndex = currentState.startIndex;
+
+            if (path.contains(currentPatternName)) {
+                // Current pattern name is already in the path, indicating a circular reference.
+                String prevPatternName = path.pop();
+                String prevPattern = patternBank.get(prevPatternName);
+                throwExceptionForCircularReference(prevPatternName, prevPattern, currentPatternName, path);
+            }
+
+            path.push(currentPatternName);
+
+            String pattern = patternBank.get(currentPatternName);
+            if (pattern.contains("%{" + currentPatternName + "}") || pattern.contains("%{" + currentPatternName + ":")) {
+                throwExceptionForCircularReference(currentPatternName, pattern);
+            }
+
+            boolean hasDependencies = false;
+            for (int i = startIndex; i < pattern.length(); i = pattern.indexOf("%{", i + 1)) {
+                if (i == -1) {
+                    break;
+                }
+                int begin = i + 2;
+                int syntaxEndIndex = pattern.indexOf('}', begin);
+                if (syntaxEndIndex == -1) {
+                    throw new IllegalArgumentException("Malformed pattern [" + currentPatternName + "][" + pattern + "]");
+                }
+                int semanticNameIndex = pattern.indexOf(':', begin);
+                int end = syntaxEndIndex;
+                if (semanticNameIndex != -1) {
+                    end = Math.min(syntaxEndIndex, semanticNameIndex);
+                }
+                String dependsOnPattern = pattern.substring(begin, end);
+
+                if (!visited.contains(dependsOnPattern)) {
+                    stack.push(new PatternState(currentPatternName, i + 1));
+                    stack.push(new PatternState(dependsOnPattern, 0));
+                    hasDependencies = true;
+                    break;
+                }
             }
-            int semanticNameIndex = pattern.indexOf(':', begin);
-            int end = syntaxEndIndex;
-            if (semanticNameIndex != -1) {
-                end = Math.min(syntaxEndIndex, semanticNameIndex);
+
+            if (!hasDependencies) {
+                visited.add(currentPatternName);
+                path.pop();
             }
-            String dependsOnPattern = pattern.substring(begin, end);
-            validatePatternBank(dependsOnPattern, path);
         }
-        path.pop();
+    }
+
+    private static class PatternState {
+        String patternName;
+        int startIndex;
+
+        PatternState(String patternName, int startIndex) {
+            this.patternName = patternName;
+            this.startIndex = startIndex;
+        }
     }
 
     private static void throwExceptionForCircularReference(String patternName, String pattern) {