From 5bec2604a3565f6db31419a4630e0317384ebe61 Mon Sep 17 00:00:00 2001
From: Michael Brown <mcb30@ipxe.org>
Date: Thu, 28 Aug 2025 15:12:41 +0100
Subject: [PATCH] [libc] Add wcsnlen()

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/core/wchar.c        | 19 ++++++++++++++++---
 src/include/wchar.h     |  1 +
 src/tests/string_test.c | 18 ++++++++++++++++++
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/src/core/wchar.c b/src/core/wchar.c
index 860322820..b06cf452a 100644
--- a/src/core/wchar.c
+++ b/src/core/wchar.c
@@ -36,12 +36,25 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  * Calculate length of wide-character string
  *
  * @v string		String
- * @ret len		Length (excluding terminating NUL)
+ * @v max		Maximum length (in wide characters)
+ * @ret len		Length (in wide characters, excluding terminating NUL)
  */
-size_t wcslen ( const wchar_t *string ) {
+size_t wcsnlen ( const wchar_t *string, size_t max ) {
 	size_t len = 0;
 
-	while ( *(string++) )
+	while ( max-- && *(string++) )
 		len++;
 	return len;
 }
+
+/**
+ * Calculate length of wide-character string
+ *
+ * @v string		String
+ * @ret len		Length (in wide characters, excluding terminating NUL)
+ */
+size_t wcslen ( const wchar_t *string ) {
+
+	return wcsnlen ( string, ( ( ~( ( size_t ) 0 ) ) /
+				   sizeof ( string[0] ) ) );
+}
diff --git a/src/include/wchar.h b/src/include/wchar.h
index d054b8d5b..a7e9de4f2 100644
--- a/src/include/wchar.h
+++ b/src/include/wchar.h
@@ -24,6 +24,7 @@ size_t wcrtomb ( char *buf, wchar_t wc, mbstate_t *ps __unused ) {
 	return 1;
 }
 
+extern size_t wcsnlen ( const wchar_t *string, size_t max );
 extern size_t wcslen ( const wchar_t *string );
 
 #endif /* WCHAR_H */
diff --git a/src/tests/string_test.c b/src/tests/string_test.c
index c0436c3ad..6662848d3 100644
--- a/src/tests/string_test.c
+++ b/src/tests/string_test.c
@@ -38,6 +38,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <stdio.h>
 #include <string.h>
 #include <strings.h>
+#include <wchar.h>
 #include <ipxe/string.h>
 #include <ipxe/test.h>
 
@@ -322,6 +323,23 @@ static void string_test_exec ( void ) {
 			 + 17 ) * 26 + 10 ) );
 		ok ( endp == &string[6] );
 	}
+
+	/* Test wcslen() */
+	ok ( wcslen ( L"" ) == 0 );
+	ok ( wcslen ( L"Helloo" ) == 6 );
+	ok ( wcslen ( L"Helloo woorld!" ) == 14 );
+	ok ( wcslen ( L"Helloo\0woorld!" ) == 6 );
+
+	/* Test wcsnlen() */
+	ok ( wcsnlen ( L"", 0 ) == 0 );
+	ok ( wcsnlen ( L"", 10 ) == 0 );
+	ok ( wcsnlen ( L"Helloo", 0 ) == 0 );
+	ok ( wcsnlen ( L"Helloo", 3 ) == 3 );
+	ok ( wcsnlen ( L"Helloo", 5 ) == 5 );
+	ok ( wcsnlen ( L"Helloo", 16 ) == 6 );
+	ok ( wcsnlen ( L"Helloo woorld!", 5 ) == 5 );
+	ok ( wcsnlen ( L"Helloo woorld!", 11 ) == 11 );
+	ok ( wcsnlen ( L"Helloo woorld!", 16 ) == 14 );
 }
 
 /** String self-test */