From e9f8471a280d99db6825ef5057f1f67f5af5fe38 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Mon, 2 Jun 2025 10:46:15 +0300
Subject: [PATCH] BAN: Return UTF::invalid from byte_length instead of 0

---
 BAN/include/BAN/UTF8.h                   | 2 +-
 userspace/libraries/LibC/stdlib.cpp      | 9 ++++++---
 userspace/libraries/LibFont/PSF.cpp      | 2 +-
 userspace/programs/Terminal/Terminal.cpp | 2 +-
 4 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/BAN/include/BAN/UTF8.h b/BAN/include/BAN/UTF8.h
index 5718f12b13..1976172b05 100644
--- a/BAN/include/BAN/UTF8.h
+++ b/BAN/include/BAN/UTF8.h
@@ -18,7 +18,7 @@ namespace BAN::UTF8
 			return 3;
 		if ((first_byte & 0xF8) == 0xF0)
 			return 4;
-		return 0;
+		return UTF8::invalid;
 	}
 
 	template<typename T> requires (sizeof(T) == 1)
diff --git a/userspace/libraries/LibC/stdlib.cpp b/userspace/libraries/LibC/stdlib.cpp
index 42056228d7..41317673b1 100644
--- a/userspace/libraries/LibC/stdlib.cpp
+++ b/userspace/libraries/LibC/stdlib.cpp
@@ -560,9 +560,12 @@ int mblen(const char* s, size_t n)
 		case LOCALE_POSIX:
 			return 1;
 		case LOCALE_UTF8:
-			if (const auto bytes = BAN::UTF8::byte_length(*s); n >= bytes)
-				return bytes;
-			return -1;
+			const auto bytes = BAN::UTF8::byte_length(*s);
+			if (bytes == BAN::UTF8::invalid)
+				return -1;
+			if (n < bytes)
+				return -1;
+			return bytes;
 	}
 	ASSERT_NOT_REACHED();
 }
diff --git a/userspace/libraries/LibFont/PSF.cpp b/userspace/libraries/LibFont/PSF.cpp
index 9bab58b0bf..242b587944 100644
--- a/userspace/libraries/LibFont/PSF.cpp
+++ b/userspace/libraries/LibFont/PSF.cpp
@@ -176,7 +176,7 @@ namespace LibFont
 
 					uint32_t len = BAN::UTF8::byte_length(bytes[0]);
 
-					if (len == 0)
+					if (len == BAN::UTF8::invalid)
 					{
 						invalid_utf = true;
 						byte_index = 0;
diff --git a/userspace/programs/Terminal/Terminal.cpp b/userspace/programs/Terminal/Terminal.cpp
index 6ab8480885..315183227b 100644
--- a/userspace/programs/Terminal/Terminal.cpp
+++ b/userspace/programs/Terminal/Terminal.cpp
@@ -748,7 +748,7 @@ Rectangle Terminal::putchar(uint8_t ch)
 	m_utf8_bytes[m_utf8_index++] = ch;
 
 	const size_t utf8_len = BAN::UTF8::byte_length(m_utf8_bytes[0]);
-	if (utf8_len == 0)
+	if (utf8_len == BAN::UTF8::invalid)
 	{
 		dwarnln("invalid utf8 leading byte 0x{2H}", ch);
 		m_utf8_index = 0;