From cfcc9a9bba2baf1c91a16fff6303d73fe47e61bc Mon Sep 17 00:00:00 2001
From: Stephen Crawford <65832608+scrawfor99@users.noreply.github.com>
Date: Thu, 9 Nov 2023 18:22:58 -0500
Subject: [PATCH] Manually backport #11060 (simple regex normalization
 refactor) (#11148)

* Manually backport 11060

Signed-off-by: Stephen Crawford <steecraw@amazon.com>

* spotless

Signed-off-by: Stephen Crawford <steecraw@amazon.com>

---------

Signed-off-by: Stephen Crawford <steecraw@amazon.com>
---
 CHANGELOG.md                                  |  2 +
 .../org/opensearch/common/regex/Regex.java    | 54 +++++++++----------
 .../opensearch/common/regex/RegexTests.java   | 15 ++++++
 3 files changed, 44 insertions(+), 27 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 56fb5aacd00ee..6c9c28f3a7758 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Bump `netty` from 4.1.96.Final to 4.1.97.Final ([#9553](https://github.com/opensearch-project/OpenSearch/pull/9553))
 
 ### Changed
+- Use iterative approach to evaluate Regex.simpleMatch ([#11060](https://github.com/opensearch-project/OpenSearch/pull/11060))
+
 ### Deprecated
 ### Removed
 ### Fixed
diff --git a/server/src/main/java/org/opensearch/common/regex/Regex.java b/server/src/main/java/org/opensearch/common/regex/Regex.java
index dc42b09848e36..4b0ccc39f2db2 100644
--- a/server/src/main/java/org/opensearch/common/regex/Regex.java
+++ b/server/src/main/java/org/opensearch/common/regex/Regex.java
@@ -124,35 +124,35 @@ public static boolean simpleMatch(String pattern, String str, boolean caseInsens
     }
 
     private static boolean simpleMatchWithNormalizedStrings(String pattern, String str) {
-        final int firstIndex = pattern.indexOf('*');
-        if (firstIndex == -1) {
-            return pattern.equals(str);
-        }
-        if (firstIndex == 0) {
-            if (pattern.length() == 1) {
-                return true;
-            }
-            final int nextIndex = pattern.indexOf('*', firstIndex + 1);
-            if (nextIndex == -1) {
-                // str.endsWith(pattern.substring(1)), but avoiding the construction of pattern.substring(1):
-                return str.regionMatches(str.length() - pattern.length() + 1, pattern, 1, pattern.length() - 1);
-            } else if (nextIndex == 1) {
-                // Double wildcard "**" - skipping the first "*"
-                return simpleMatchWithNormalizedStrings(pattern.substring(1), str);
-            }
-            final String part = pattern.substring(1, nextIndex);
-            int partIndex = str.indexOf(part);
-            while (partIndex != -1) {
-                if (simpleMatchWithNormalizedStrings(pattern.substring(nextIndex), str.substring(partIndex + part.length()))) {
-                    return true;
-                }
-                partIndex = str.indexOf(part, partIndex + 1);
+        int sIdx = 0, pIdx = 0, match = 0, wildcardIdx = -1;
+        while (sIdx < str.length()) {
+            // both chars matching, incrementing both pointers
+            if (pIdx < pattern.length() && str.charAt(sIdx) == pattern.charAt(pIdx)) {
+                sIdx++;
+                pIdx++;
+            } else if (pIdx < pattern.length() && pattern.charAt(pIdx) == '*') {
+                // wildcard found, only incrementing pattern pointer
+                wildcardIdx = pIdx;
+                match = sIdx;
+                pIdx++;
+            } else if (wildcardIdx != -1) {
+                // last pattern pointer was a wildcard, incrementing string pointer
+                pIdx = wildcardIdx + 1;
+                match++;
+                sIdx = match;
+            } else {
+                // current pattern pointer is not a wildcard, last pattern pointer was also not a wildcard
+                // characters do not match
+                return false;
             }
-            return false;
         }
-        return str.regionMatches(0, pattern, 0, firstIndex)
-            && (firstIndex == pattern.length() - 1 // only wildcard in pattern is at the end, so no need to look at the rest of the string
-                || simpleMatchWithNormalizedStrings(pattern.substring(firstIndex), str.substring(firstIndex)));
+
+        // check for remaining characters in pattern
+        while (pIdx < pattern.length() && pattern.charAt(pIdx) == '*') {
+            pIdx++;
+        }
+
+        return pIdx == pattern.length();
     }
 
     /**
diff --git a/server/src/test/java/org/opensearch/common/regex/RegexTests.java b/server/src/test/java/org/opensearch/common/regex/RegexTests.java
index b92fcdad56d74..4a3772b77fde7 100644
--- a/server/src/test/java/org/opensearch/common/regex/RegexTests.java
+++ b/server/src/test/java/org/opensearch/common/regex/RegexTests.java
@@ -97,6 +97,21 @@ public void testDoubleWildcardMatch() {
         assertTrue(Regex.simpleMatch("fff*******ddd", "fffabcddd"));
         assertTrue(Regex.simpleMatch("fff*******ddd", "FffAbcdDd", true));
         assertFalse(Regex.simpleMatch("fff******ddd", "fffabcdd"));
+        assertFalse(Regex.simpleMatch("fff*******ddd", "FffAbcdDd", false));
+        assertTrue(Regex.simpleMatch("abCDefGH******ddd", "abCDefGHddd", false));
+        assertTrue(Regex.simpleMatch("******", "a"));
+        assertTrue(Regex.simpleMatch("***WILDcard***", "aaaaaaaaWILDcardZZZZZZ", false));
+        assertFalse(Regex.simpleMatch("***xxxxx123456789xxxxxx***", "xxxxxabcdxxxxx", false));
+        assertFalse(Regex.simpleMatch("***xxxxxabcdxxxxx***", "xxxxxABCDxxxxx", false));
+        assertTrue(Regex.simpleMatch("***xxxxxabcdxxxxx***", "xxxxxABCDxxxxx", true));
+        assertTrue(Regex.simpleMatch("**stephenIsSuperCool**", "ItIsTrueThatStephenIsSuperCoolSoYouShouldLetThisIn", true));
+        assertTrue(
+            Regex.simpleMatch(
+                "**w**X**y**Z**",
+                "abcdeFGHIJKLMNOPqrstuvwabcdeFGHIJKLMNOPqrstuvwXabcdeFGHIJKLMNOPqrstuvwXyabcdeFGHIJKLMNOPqrstuvwXyZ",
+                false
+            )
+        );
     }
 
     public void testSimpleMatch() {