From 1bfd4c936112a2fea8b07a8f390e60952b59c48f Mon Sep 17 00:00:00 2001
From: Robin Friedmann <robinfriedmann.rf@gmail.com>
Date: Thu, 1 Feb 2024 15:58:23 +0100
Subject: [PATCH] Refactor FilterPath parse function (#12067) Signed-off-by:
 Robin Friedmann <robinfriedmann.rf@gmail.com>

---
 .../core/xcontent/filtering/FilterPath.java   | 26 +++++++------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/libs/core/src/main/java/org/opensearch/core/xcontent/filtering/FilterPath.java b/libs/core/src/main/java/org/opensearch/core/xcontent/filtering/FilterPath.java
index 5389538a8c7dd..d37a6aaaef4fc 100644
--- a/libs/core/src/main/java/org/opensearch/core/xcontent/filtering/FilterPath.java
+++ b/libs/core/src/main/java/org/opensearch/core/xcontent/filtering/FilterPath.java
@@ -99,32 +99,26 @@ public static FilterPath[] compile(Set<String> filters) {
 
         List<FilterPath> paths = new ArrayList<>();
         for (String filter : filters) {
-            if (filter != null) {
+            if (filter != null && !filter.isEmpty()) {
                 filter = filter.trim();
                 if (filter.length() > 0) {
-                    paths.add(parse(filter, filter));
+                    paths.add(parse(filter));
                 }
             }
         }
         return paths.toArray(new FilterPath[0]);
     }
 
-    private static FilterPath parse(final String filter, final String segment) {
-        int end = segment.length();
+    private static FilterPath parse(final String filter) {
+        String[] segments = filter.split("(?<!\\\\)\\.");
+        FilterPath next = EMPTY;
 
-        for (int i = 0; i < end;) {
-            char c = segment.charAt(i);
-
-            if (c == '.') {
-                String current = segment.substring(0, i).replaceAll("\\\\.", ".");
-                return new FilterPath(filter, current, parse(filter, segment.substring(i + 1)));
-            }
-            ++i;
-            if ((c == '\\') && (i < end) && (segment.charAt(i) == '.')) {
-                ++i;
-            }
+        for (int i = segments.length - 1; i >= 0; i--) {
+            String segment = segments[i].replaceAll("\\\\.", ".");
+            next = new FilterPath(filter, segment, next);
         }
-        return new FilterPath(filter, segment.replaceAll("\\\\.", "."), EMPTY);
+
+        return next;
     }
 
     @Override