From eab266faa93175b33b06d6ada9ff998ef5de0824 Mon Sep 17 00:00:00 2001
From: Firat Hajiyev <fi189352@ucf.edu>
Date: Sun, 18 Oct 2026 18:14:42 -0400
Subject: [PATCH] Handle String::toInt overflow

---
 api/String.cpp                 | 29 ++++++++++++++++++++++++--
 test/src/String/test_toInt.cpp | 37 ++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/api/String.cpp b/api/String.cpp
index 4f176374..be8fd748 100644
--- a/api/String.cpp
+++ b/api/String.cpp
@@ -25,6 +25,7 @@
 #include "deprecated-avr-comp/avr/dtostrf.h"
 
 #include <float.h>
+#include <limits.h>
 
 namespace arduino {
 
@@ -732,8 +733,32 @@ void String::trim(void)
 
 long String::toInt(void) const
 {
-	if (buffer) return atol(buffer);
-	return 0;
+	if (!buffer) return 0;
+
+	char const *p = buffer;
+	while (isspace(static_cast<unsigned char>(*p))) p++;
+
+	bool const negative = *p == '-';
+	if (negative || *p == '+') p++;
+
+	unsigned long value = 0;
+	unsigned long const negative_limit = static_cast<unsigned long>(-(LONG_MIN + 1L)) + 1UL;
+	unsigned long const limit = negative
+		? negative_limit
+		: static_cast<unsigned long>(LONG_MAX);
+	unsigned long const cutoff = limit / 10UL;
+	unsigned long const cutlim = limit % 10UL;
+
+	while (isdigit(static_cast<unsigned char>(*p))) {
+		unsigned long const digit = static_cast<unsigned long>(*p - '0');
+		if (value > cutoff || (value == cutoff && digit > cutlim)) return 0;
+		value = value * 10UL + digit;
+		p++;
+	}
+
+	if (!negative) return static_cast<long>(value);
+	if (value == negative_limit) return LONG_MIN;
+	return -static_cast<long>(value);
 }
 
 float String::toFloat(void) const
diff --git a/test/src/String/test_toInt.cpp b/test/src/String/test_toInt.cpp
index c93fcc4a..40d13bc1 100644
--- a/test/src/String/test_toInt.cpp
+++ b/test/src/String/test_toInt.cpp
@@ -10,6 +10,9 @@
 
 #include <catch2/catch_test_macros.hpp>
 
+#include <climits>
+#include <string>
+
 #include <api/String.h>
 
 #include "StringPrinter.h"
@@ -45,3 +48,37 @@ TEST_CASE ("Testing String::toInt when string does not have a buffer", "[String-
   arduino::String str(buffer);
   REQUIRE(str.toInt() == 0);
 }
+
+TEST_CASE ("Testing String::toInt when string exceeds the long range", "[String-toInt-05]")
+{
+  unsigned long const minimum_magnitude = static_cast<unsigned long>(-(LONG_MIN + 1L)) + 1UL;
+  std::string const one_past_maximum = std::to_string(static_cast<unsigned long>(LONG_MAX) + 1UL);
+  std::string const one_past_minimum = "-" + std::to_string(minimum_magnitude + 1UL);
+  arduino::String positive_boundary(one_past_maximum.c_str());
+  arduino::String negative_boundary(one_past_minimum.c_str());
+  arduino::String positive("999999999999999999999999999999999999");
+  arduino::String negative("-999999999999999999999999999999999999");
+
+  REQUIRE(positive_boundary.toInt() == 0);
+  REQUIRE(negative_boundary.toInt() == 0);
+  REQUIRE(positive.toInt() == 0);
+  REQUIRE(negative.toInt() == 0);
+}
+
+TEST_CASE ("Testing String::toInt at the long range limits", "[String-toInt-06]")
+{
+  arduino::String maximum(std::to_string(LONG_MAX).c_str());
+  arduino::String minimum(std::to_string(LONG_MIN).c_str());
+
+  REQUIRE(maximum.toInt() == LONG_MAX);
+  REQUIRE(minimum.toInt() == LONG_MIN);
+}
+
+TEST_CASE ("Testing String::toInt keeps atol parsing behavior", "[String-toInt-07]")
+{
+  arduino::String negative(" \t-123abc");
+  arduino::String positive("+456xyz");
+
+  REQUIRE(negative.toInt() == -123);
+  REQUIRE(positive.toInt() == 456);
+}