From 9d335059fb915ff76fdad3a88f21f50740e88842 Mon Sep 17 00:00:00 2001
From: reginaldalfret <reginaldalfret@gmail.com>
Date: Fri, 23 Oct 2026 19:54:42 +0530
Subject: [PATCH] Replace recursive regex in PhoneNumberUtil.normalize() with
 linear scan

PR #4017 replaced VALID_ALPHA_PHONE_PATTERN with hasAtLeastThreeAlphaChars()
in PhoneNumberUtil.isAlphaNumber() to eliminate StackOverflowError caused by
recursive evaluation on long numeric inputs in java.util.regex. However,
PhoneNumberUtil.normalize(StringBuilder) still called
VALID_ALPHA_PHONE_PATTERN.matcher(number).matches(), leaving normalize()
vulnerable to the same recursion failure and leaving VALID_ALPHA_PHONE_PATTERN
in the codebase solely for that call.

This commit updates normalize(StringBuilder) to use hasAtLeastThreeAlphaChars(number)
and removes the unused VALID_ALPHA_PHONE_PATTERN, fully eliminating the pattern
and preventing StackOverflowError on long inputs.

Also adds a regression test and updates pending_code_changes.txt.

Signed-off-by: reginaldalfret <reginaldalfret@gmail.com>
---
 .../com/google/i18n/phonenumbers/PhoneNumberUtil.java    | 7 +------
 .../google/i18n/phonenumbers/PhoneNumberUtilTest.java    | 9 +++++++++
 pending_code_changes.txt                                 | 3 ++-
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/java/libphonenumber/src/com/google/i18n/phonenumbers/PhoneNumberUtil.java b/java/libphonenumber/src/com/google/i18n/phonenumbers/PhoneNumberUtil.java
index a1d83b3070..d741b0938b 100644
--- a/java/libphonenumber/src/com/google/i18n/phonenumbers/PhoneNumberUtil.java
+++ b/java/libphonenumber/src/com/google/i18n/phonenumbers/PhoneNumberUtil.java
@@ -277,10 +277,6 @@ public class PhoneNumberUtil {
   private static final String UNWANTED_END_CHARS = "[[\\P{N}&&\\P{L}]&&[^#]]+$";
   static final Pattern UNWANTED_END_CHAR_PATTERN = Pattern.compile(UNWANTED_END_CHARS);
 
-  // We use this pattern to check if the phone number has at least three letters in it - if so, then
-  // we treat it as a number where some phone-number digits are represented by letters.
-  private static final Pattern VALID_ALPHA_PHONE_PATTERN = Pattern.compile("(?:.*?[A-Za-z]){3}.*");
-
   // Regular expression of viable phone numbers. This is location independent. Checks we have at
   // least three leading digits, and only valid punctuation, alpha characters and
   // digits in the phone number. Does not include extension data.
@@ -802,8 +798,7 @@ static boolean isViablePhoneNumber(CharSequence number) {
    *     normalized in place
    */
   static StringBuilder normalize(StringBuilder number) {
-    Matcher m = VALID_ALPHA_PHONE_PATTERN.matcher(number);
-    if (m.matches()) {
+    if (hasAtLeastThreeAlphaChars(number)) {
       number.replace(0, number.length(), normalizeHelper(number, ALPHA_PHONE_MAPPINGS, true));
     } else {
       number.replace(0, number.length(), normalizeDigitsOnly(number));
diff --git a/java/libphonenumber/test/com/google/i18n/phonenumbers/PhoneNumberUtilTest.java b/java/libphonenumber/test/com/google/i18n/phonenumbers/PhoneNumberUtilTest.java
index 4da210ec1d..c7bd7f224e 100644
--- a/java/libphonenumber/test/com/google/i18n/phonenumbers/PhoneNumberUtilTest.java
+++ b/java/libphonenumber/test/com/google/i18n/phonenumbers/PhoneNumberUtilTest.java
@@ -476,6 +476,15 @@ public void testNormaliseOtherDigits() {
                  expectedOutput, PhoneNumberUtil.normalize(inputNumber).toString());
   }
 
+  public void testNormaliseLongNumericInputDoesNotThrow() {
+    StringBuilder inputNumber = new StringBuilder("+");
+    for (int i = 0; i < 5000; i++) {
+      inputNumber.append('1');
+    }
+    // Should not throw StackOverflowError and correctly normalize digits.
+    assertEquals(5000, PhoneNumberUtil.normalize(inputNumber).length());
+  }
+
   public void testNormaliseStripAlphaCharacters() {
     String inputNumber = "034-56&+a#234";
     String expectedOutput = "03456234";
diff --git a/pending_code_changes.txt b/pending_code_changes.txt
index 8b13789179..d312202c83 100644
--- a/pending_code_changes.txt
+++ b/pending_code_changes.txt
@@ -1 +1,2 @@
-
+Code changes:
+ - Fixed PhoneNumberUtil.normalize(StringBuilder) in Java to use a linear character scan instead of the recursive VALID_ALPHA_PHONE_PATTERN regex, preventing StackOverflowError on long inputs.