utilities: Implement real function iio_snprintf

Everything in libiio expects iio_snprintf() to return an error when the
data to be written overflows the buffer, but it is not how snprintf()
behaves; instead, it returns the number of characters that would have
been written if there was enough space in the buffer.

Therefore, to know that the data was truncated, it is required to
compare the return value with the size of the buffer, and nothing in
libiio does that.

Address this issue by returning -ERANGE if an overflow is detected.

Signed-off-by: Paul Cercueil <[email protected]>

Author: pcercuei

iio-private.h

@@ -32,13 +32,19 @@
 
 #ifdef _MSC_BUILD
 #define inline __inline
-#define iio_snprintf sprintf_s
 #define iio_sscanf sscanf_s
 #else
-#define iio_snprintf snprintf
 #define iio_sscanf sscanf
 #endif
 
+#if defined(__MINGW32__)
+#   define __iio_printf __attribute__((__format__(ms_printf, 3, 4)))
+#elif defined(__GNUC__)
+#   define __iio_printf __attribute__((__format__(gnu_printf, 3, 4)))
+#else
+#   define __iio_printf
+#endif
+
 #define ARRAY_SIZE(x) (sizeof(x) ? sizeof(x) / sizeof((x)[0]) : 0)
 #define BIT(x) (1 << (x))
 #define BIT_MASK(bit) BIT((bit) % 32)
@@ -287,6 +293,8 @@ struct iio_context_pdata * iio_context_get_pdata(const struct iio_context *ctx);
 int add_iio_dev_attr(struct iio_dev_attrs *attrs, const char *attr,
 		     const char *type, const char *dev_id);
 
+ssize_t __iio_printf iio_snprintf(char *buf, size_t len, const char *fmt, ...);
+
 #undef __api
 
 #endif /* __IIO_PRIVATE_H__ */

utilities.c

@@ -15,6 +15,7 @@
 
 #include <errno.h>
 #include <locale.h>
+#include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -315,3 +316,17 @@ char * iio_getenv (char * envvar)
 #endif
 	return NULL;
 }
+
+ssize_t __iio_printf iio_snprintf(char *buf, size_t len, const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	va_start(ap, fmt);
+	ret = vsnprintf(buf, len, fmt, ap);
+	if (len && ret >= (ssize_t)len)
+		ret = -ERANGE;
+	va_end(ap);
+
+	return (ssize_t)ret;
+}