u/truncate_printf: Add truncating helpers

src/xrt/auxiliary/util/u_truncate_printf.h

@@ -0,0 +1,88 @@
+// Copyright 2023, Collabora, Ltd.
+// SPDX-License-Identifier: BSL-1.0
+/*!
+ * @file
+ * @brief  Truncating versions of string printing functions.
+ * @author Jakob Bornecrantz <jakob@collabora.com>
+ * @ingroup aux_util
+ */
+
+#pragma once
+
+#include "xrt/xrt_compiler.h"
+
+#include <stdio.h>
+#include <stdarg.h>
+#include <limits.h>
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/*!
+ * We want to truncate the value, not get the possible written.
+ *
+ * There are no version of the *many* Windows versions of this functions that
+ * truncates and returns the number of bytes written (not including null). Also
+ * need to have the same behaviour on Linux.
+ *
+ * @ingroup @aux_util
+ */
+static inline int
+u_truncate_vsnprintf(char *chars, size_t char_count, const char *fmt, va_list args)
+{
+	/*
+	 * We always want to be able to write null terminator, and
+	 * something propbly went wrong if char_count larger then INT_MAX.
+	 */
+	if (char_count == 0 || char_count > INT_MAX) {
+		return -1;
+	}
+
+	// Will always be able to write null terminator.
+	int ret = vsnprintf(chars, char_count, fmt, args);
+	if (ret < 0) {
+		return ret;
+	}
+
+	// Safe, ret is checked for negative above.
+	if ((size_t)ret > char_count - 1) {
+		return (int)char_count - 1;
+	}
+
+	return ret;
+}
+
+/*!
+ * We want to truncate the value, not get the possible written, and error when
+ * we can not write out anything.
+ *
+ * See @ref u_truncate_vsnprintf for more info.
+ *
+ * @ingroup @aux_util
+ */
+static inline int
+u_truncate_snprintf(char *chars, size_t char_count, const char *fmt, ...)
+{
+	/*
+	 * We always want to be able to write null terminator, and
+	 * something propbly went wrong if char_count larger then INT_MAX.
+	 */
+	if (char_count == 0 || char_count > INT_MAX) {
+		return -1;
+	}
+
+	va_list args;
+	va_start(args, fmt);
+	int ret = u_truncate_vsnprintf(chars, char_count, fmt, args);
+	va_end(args);
+
+	return ret;
+}
+
+
+#ifdef __cplusplus
+}
+#endif