From 0240baa42de554a7eb103020c2d53373d3468b31 Mon Sep 17 00:00:00 2001
From: Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
Date: Sun, 16 Aug 2020 01:37:32 +0200
Subject: [PATCH] AK+Kernel: Support snprintf

In contrast to sprintf, which might overflow the given buffer.

I feel bad about the code duplication, but that is a pre-existing issue.
---
 AK/kstdio.h        |  1 +
 Kernel/kprintf.cpp | 28 ++++++++++++++++++++++++++++
 Kernel/kstdio.h    |  1 +
 3 files changed, 30 insertions(+)

diff --git a/AK/kstdio.h b/AK/kstdio.h
index 78ca52bc9a6374..98f69caeb2a8a7 100644
--- a/AK/kstdio.h
+++ b/AK/kstdio.h
@@ -37,6 +37,7 @@ int vdbgprintf(const char* fmt, va_list);
 int dbgprintf(const char* fmt, ...);
 ssize_t dbgputstr(const char*, ssize_t);
 int sprintf(char* buf, const char* fmt, ...);
+int snprintf(char* buffer, size_t, const char* fmt, ...);
 }
 #    endif
 #else
diff --git a/Kernel/kprintf.cpp b/Kernel/kprintf.cpp
index 3e2eff5b04c41b..6834ce00bd0fe0 100644
--- a/Kernel/kprintf.cpp
+++ b/Kernel/kprintf.cpp
@@ -144,6 +144,34 @@ int sprintf(char* buffer, const char* fmt, ...)
     return ret;
 }
 
+static size_t __vsnprintf_space_remaining;
+ALWAYS_INLINE void sized_buffer_putch(char*& bufptr, char ch)
+{
+    if (__vsnprintf_space_remaining) {
+        *bufptr++ = ch;
+        --__vsnprintf_space_remaining;
+    }
+}
+
+int snprintf(char* buffer, size_t size, const char* fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+    if (size) {
+        __vsnprintf_space_remaining = size - 1;
+    } else {
+        __vsnprintf_space_remaining = 0;
+    }
+    int ret = printf_internal(sized_buffer_putch, buffer, fmt, ap);
+    if (__vsnprintf_space_remaining) {
+        buffer[ret] = '\0';
+    } else if (size > 0) {
+        buffer[size - 1] = '\0';
+    }
+    va_end(ap);
+    return ret;
+}
+
 static void debugger_out(char ch)
 {
     if (serial_debug)
diff --git a/Kernel/kstdio.h b/Kernel/kstdio.h
index b6f3d17cf96328..32f3b1adda32b1 100644
--- a/Kernel/kstdio.h
+++ b/Kernel/kstdio.h
@@ -34,6 +34,7 @@ int dbgputstr(const char*, int);
 int kernelputstr(const char*, int);
 int kprintf(const char* fmt, ...);
 int sprintf(char* buf, const char* fmt, ...);
+int snprintf(char* buf, size_t, const char* fmt, ...);
 void set_serial_debug(bool on_or_off);
 int get_serial_debug();
 }