From 2464fccadd38e93313fdf44912b753560f38cf6a Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Sat, 19 Oct 2024 12:43:23 +0300
Subject: [PATCH] LibC: Fix *scanf consuming extra characters

---
 userspace/libraries/LibC/include/scanf_impl.h |  2 +-
 userspace/libraries/LibC/scanf_impl.cpp       | 10 +++---
 userspace/libraries/LibC/stdio.cpp            | 33 +++++++++++++++----
 3 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/userspace/libraries/LibC/include/scanf_impl.h b/userspace/libraries/LibC/include/scanf_impl.h
index 87411dbd..0479e254 100644
--- a/userspace/libraries/LibC/include/scanf_impl.h
+++ b/userspace/libraries/LibC/include/scanf_impl.h
@@ -2,4 +2,4 @@
 
 #include <stdarg.h>
 
-int scanf_impl(const char* format, va_list arguments, int (*getc_fun)(void*), void* data);
+int scanf_impl(const char* format, va_list arguments, int (*getc_fun)(bool advance, void*), void* data);
diff --git a/userspace/libraries/LibC/scanf_impl.cpp b/userspace/libraries/LibC/scanf_impl.cpp
index 0a3afb9e..b5b35c1f 100644
--- a/userspace/libraries/LibC/scanf_impl.cpp
+++ b/userspace/libraries/LibC/scanf_impl.cpp
@@ -112,9 +112,9 @@ using BASE_TYPE = BAN::integral_constant<int, BASE>;
 template<bool UNSIGNED>
 using IS_UNSIGNED = BAN::integral_constant<bool, UNSIGNED>;
 
-int scanf_impl(const char* format, va_list arguments, int (*__getc_fun)(void*), void* data)
+int scanf_impl(const char* format, va_list arguments, int (*__getc_fun)(bool advance, void*), void* data)
 {
-	static constexpr int DONE = -1;
+	static constexpr int DONE = EOF;
 	static constexpr int NONE = -2;
 
 	int nread = 0;
@@ -134,11 +134,9 @@ int scanf_impl(const char* format, va_list arguments, int (*__getc_fun)(void*),
 		{
 			if (in == DONE)
 				return;
-			if (advance || in == NONE)
-			{
-				in = __getc_fun(data);
+			in = __getc_fun(advance, data);
+			if (advance)
 				nread++;
-			}
 		};
 
 	auto parse_integer_internal =
diff --git a/userspace/libraries/LibC/stdio.cpp b/userspace/libraries/LibC/stdio.cpp
index bea1a6a3..90f05a56 100644
--- a/userspace/libraries/LibC/stdio.cpp
+++ b/userspace/libraries/LibC/stdio.cpp
@@ -794,11 +794,10 @@ char* tmpnam(char* storage)
 	return storage;
 }
 
-int ungetc(int c, FILE* stream)
+int ungetc_unlocked(int c, FILE* stream)
 {
 	if (c == EOF)
 		return EOF;
-	ScopeLock _(stream);
 	if (stream->unget_char != EOF)
 		return EOF;
 	stream->unget_char = c;
@@ -806,6 +805,12 @@ int ungetc(int c, FILE* stream)
 	return (unsigned char)c;
 }
 
+int ungetc(int c, FILE* stream)
+{
+	ScopeLock _(stream);
+	return ungetc_unlocked(c, stream);
+}
+
 int vfprintf(FILE* file, const char* format, va_list arguments)
 {
 	ScopeLock _(file);
@@ -815,7 +820,18 @@ int vfprintf(FILE* file, const char* format, va_list arguments)
 int vfscanf(FILE* file, const char* format, va_list arguments)
 {
 	ScopeLock _(file);
-	return scanf_impl(format, arguments, [](void* file) { return getc_unlocked(static_cast<FILE*>(file)); }, file);
+	return scanf_impl(format, arguments,
+		[](bool advance, void* data)
+		{
+			FILE* fp = static_cast<FILE*>(data);
+
+			if (advance)
+				getc_unlocked(fp);
+			const int ret = getc_unlocked(fp);
+			ungetc_unlocked(ret, fp);
+			return ret;
+		}, file
+	);
 }
 
 int vprintf(const char* format, va_list arguments)
@@ -883,12 +899,15 @@ int vsprintf(char* buffer, const char* format, va_list arguments)
 int vsscanf(const char* s, const char* format, va_list arguments)
 {
 	return scanf_impl(format, arguments,
-		[](void* data) -> int
+		[](bool advance, void* data) -> int
 		{
-			char ret = **static_cast<char**>(data);
-			(*static_cast<char**>(data))++;
+			const char** ptr = static_cast<const char**>(data);
+
+			if (advance)
+				(*ptr)++;
+			const char ret = **ptr;
 			if (ret == '\0')
-				return -1;
+				return EOF;
 			return ret;
 		}, &s
 	);