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

@@ -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

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)

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();
 }