convert: add range checking conversion helpers

include/re.h

@@ -25,6 +25,7 @@ extern "C" {
 #include "re_bfcp.h"
 #include "re_btrace.h"
 #include "re_conf.h"
+#include "re_convert.h"
 #include "re_crc32.h"
 #include "re_dns.h"
 #include "re_hash.h"

include/re_convert.h

@@ -0,0 +1,79 @@
+/**
+ * @file re_convert.h  Conversion helpers
+ *
+ * Copyright (C) 2022 Sebastian Reimers
+ */
+#include <limits.h>
+
+static inline int try_into_u16_from_size(uint16_t *dest, const size_t src)
+{
+	*dest = 0;
+
+	if (src > UINT16_MAX)
+		return ERANGE;
+
+	*dest = (uint16_t)src;
+
+	return 0;
+}
+
+
+static inline int try_into_u16_from_int(uint16_t *dest, const int src)
+{
+	*dest = 0;
+
+	if (src > UINT16_MAX)
+		return ERANGE;
+
+	if (src < 0)
+		return ERANGE;
+
+	*dest = (uint16_t)src;
+
+	return 0;
+}
+
+
+static inline int try_into_int_from_size(int *dest, const size_t src)
+{
+	*dest = 0;
+
+	if (src > INT_MAX)
+		return ERANGE;
+
+	*dest = (int)src;
+
+	return 0;
+}
+
+
+static inline int try_into_err(void *dest, ...)
+{
+	(void)dest;
+
+	return ENOTSUP;
+}
+
+
+/**
+ * Try to convert safely from one type (src) into another (dest).
+ * Types are auto detected.
+ *
+ * @param dest Destination
+ * @param src  Source value
+ *
+ * @return 0 if success, ERANGE if value overflow and ENOTSUP if not supported
+ */
+#define try_into(dest, src)						      \
+	_Generic((dest), 						      \
+		uint16_t: _Generic((src),				      \
+				size_t: try_into_u16_from_size, 	      \
+				int: try_into_u16_from_int,		      \
+				default: try_into_err			      \
+			),						      \
+		int: _Generic((src),					      \
+				size_t: try_into_int_from_size,		      \
+				default: try_into_err			      \
+			)						      \
+		)							      \
+	(&(dest), (src))