From 875f4c0c484f5f679d83e665cb65817c3eb6ded9 Mon Sep 17 00:00:00 2001
From: Sabith Saheb <shabi7204192361@gmail.com>
Date: Sun, 18 Oct 2026 15:41:03 +0530
Subject: [PATCH] Count code points, not UTF-16 units, in XPath string
 functions

XPath 1.0 defines substring(), string-length() and translate() over
characters, but CoreFunction indexed and counted UTF-16 code units.
A supplementary character in the input was counted twice by
string-length(), could be split by substring() into a lone surrogate,
and was matched or emitted half at a time by translate().

Count and offset by code point instead. Strings without supplementary
characters behave as before.
---
 .../jxpath/ri/compiler/CoreFunction.java      | 38 +++++++++++--------
 .../jxpath/ri/compiler/CoreFunctionTest.java  | 15 ++++++++
 2 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreFunction.java b/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreFunction.java
index 2c6548991..49f56fda4 100644
--- a/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreFunction.java
+++ b/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreFunction.java
@@ -650,7 +650,7 @@ protected Object functionStringLength(final EvalContext context) {
             assertArgCount(1);
             s = InfoSetUtil.stringValue(getArg1().computeValue(context));
         }
-        return Double.valueOf(s.length());
+        return Double.valueOf(s.codePointCount(0, s.length()));
     }
 
     /**
@@ -665,19 +665,20 @@ protected Object functionSubstring(final EvalContext context) {
         assertArgRange(minArgs, maxArgs);
         final int ac = getArgumentCount();
         final String s1 = InfoSetUtil.stringValue(getArg1().computeValue(context));
+        final int s1Length = s1.codePointCount(0, s1.length());
         double from = InfoSetUtil.doubleValue(getArg2().computeValue(context));
         if (Double.isNaN(from)) {
             return "";
         }
         from = Math.round(from);
-        if (from > s1.length() + 1) {
+        if (from > s1Length + 1) {
             return "";
         }
         if (ac == 2) {
             if (from < 1) {
                 from = 1;
             }
-            return s1.substring((int) from - 1);
+            return s1.substring(s1.offsetByCodePoints(0, (int) from - 1));
         }
         double length = InfoSetUtil.doubleValue(getArg3().computeValue(context));
         length = Math.round(length);
@@ -688,16 +689,16 @@ protected Object functionSubstring(final EvalContext context) {
         if (to < 1) {
             return "";
         }
-        if (to > s1.length() + 1) {
+        if (to > s1Length + 1) {
             if (from < 1) {
                 from = 1;
             }
-            return s1.substring((int) from - 1);
+            return s1.substring(s1.offsetByCodePoints(0, (int) from - 1));
         }
         if (from < 1) {
             from = 1;
         }
-        return s1.substring((int) from - 1, (int) (to - 1));
+        return s1.substring(s1.offsetByCodePoints(0, (int) from - 1), s1.offsetByCodePoints(0, (int) (to - 1)));
     }
 
     /**
@@ -770,20 +771,27 @@ protected Object functionTranslate(final EvalContext context) {
         final String s1 = InfoSetUtil.stringValue(getArg1().computeValue(context));
         final String s2 = InfoSetUtil.stringValue(getArg2().computeValue(context));
         final String s3 = InfoSetUtil.stringValue(getArg3().computeValue(context));
-        final char[] chars = s1.toCharArray();
-        int out = 0;
-        for (int in = 0; in < chars.length; in++) {
-            final char c = chars[in];
-            final int inx = s2.indexOf(c);
+        final int[] codePoints = s1.codePoints().toArray();
+        final int[] fromCodePoints = s2.codePoints().toArray();
+        final int[] toCodePoints = s3.codePoints().toArray();
+        final StringBuilder buffer = new StringBuilder(s1.length());
+        for (final int c : codePoints) {
+            int inx = -1;
+            for (int i = 0; i < fromCodePoints.length; i++) {
+                if (fromCodePoints[i] == c) {
+                    inx = i;
+                    break;
+                }
+            }
             if (inx != -1) {
-                if (inx < s3.length()) {
-                    chars[out++] = s3.charAt(inx);
+                if (inx < toCodePoints.length) {
+                    buffer.appendCodePoint(toCodePoints[inx]);
                 }
             } else {
-                chars[out++] = c;
+                buffer.appendCodePoint(c);
             }
         }
-        return new String(chars, 0, out);
+        return buffer.toString();
     }
 
     /**
diff --git a/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreFunctionTest.java b/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreFunctionTest.java
index db68bde51..5cf435e2c 100644
--- a/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreFunctionTest.java
+++ b/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreFunctionTest.java
@@ -132,6 +132,21 @@ void testNumberConversionIsXPathConformant() {
         assertXPathValue(context, "'1e3' = 1000", Boolean.FALSE);
     }
 
+    @Test
+    void testStringFunctionsCountCodePoints() {
+        // U+1D11E MUSICAL SYMBOL G CLEF is one XPath character but two UTF-16 chars.
+        context.getVariables().declareVariable("clef", "𝄞abc");
+        assertXPathValue(context, "string-length($clef)", Double.valueOf(4));
+        assertXPathValue(context, "substring($clef, 2)", "abc");
+        assertXPathValue(context, "substring($clef, 1, 1)", "𝄞");
+        assertXPathValue(context, "substring($clef, 2, 2)", "ab");
+        assertXPathValue(context, "substring($clef, 0, 2)", "𝄞");
+        assertXPathValue(context, "substring($clef, 5)", "");
+        assertXPathValue(context, "translate($clef, 'a', '-')", "𝄞-bc");
+        assertXPathValue(context, "translate($clef, substring($clef, 1, 1), 'x')", "xabc");
+        assertXPathValue(context, "translate('abc', 'b', $clef)", "a𝄞c");
+    }
+
     @Test
     void testExtendedKeyFunction() {
         context.setKeyManager(new ExtendedKeyManager() {