Provide cross platform vsnprintf wrapper
diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 9d9c529..24c6362 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -55,17 +55,33 @@
* \{
*/
+/* The older Microsoft Windows common runtime provides non-conforming
+ * implementations of some standard library functions, including snprintf
+ * and vsnprintf. This affects MSVC and MinGW builds.
+ */
+#if defined(_MSC_VER) && _MSC_VER <= 1900
+#define MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF
+#define MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF
+#endif
+
#if !defined(MBEDTLS_PLATFORM_NO_STD_FUNCTIONS)
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#if !defined(MBEDTLS_PLATFORM_STD_SNPRINTF)
-#if defined(_WIN32)
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF)
#define MBEDTLS_PLATFORM_STD_SNPRINTF mbedtls_platform_win32_snprintf /**< The default \c snprintf function to use. */
#else
#define MBEDTLS_PLATFORM_STD_SNPRINTF snprintf /**< The default \c snprintf function to use. */
#endif
#endif
+#if !defined(MBEDTLS_PLATFORM_STD_VSNPRINTF)
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF)
+#define MBEDTLS_PLATFORM_STD_VSNPRINTF mbedtls_platform_win32_vsnprintf /**< The default \c vsnprintf function to use. */
+#else
+#define MBEDTLS_PLATFORM_STD_VSNPRINTF vsnprintf /**< The default \c vsnprintf function to use. */
+#endif
+#endif
#if !defined(MBEDTLS_PLATFORM_STD_PRINTF)
#define MBEDTLS_PLATFORM_STD_PRINTF printf /**< The default \c printf function to use. */
#endif
@@ -201,7 +217,7 @@
* - however it is acceptable to return -1 instead of the required length when
* the destination buffer is too short.
*/
-#if defined(_WIN32)
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF)
/* For Windows (inc. MSYS2), we provide our own fixed implementation */
int mbedtls_platform_win32_snprintf( char *s, size_t n, const char *fmt, ... );
#endif
@@ -228,6 +244,41 @@
#endif /* MBEDTLS_PLATFORM_SNPRINTF_ALT */
/*
+ * The function pointers for vsnprintf
+ *
+ * The vsnprintf implementation should conform to C99:
+ * - it *must* always correctly zero-terminate the buffer
+ * (except when n == 0, then it must leave the buffer untouched)
+ * - however it is acceptable to return -1 instead of the required length when
+ * the destination buffer is too short.
+ */
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF)
+/* For Older Windows (inc. MSYS2), we provide our own fixed implementation */
+int mbedtls_platform_win32_vsnprintf( char *s, size_t n, const char *fmt, va_list arg );
+#endif
+
+#if defined(MBEDTLS_PLATFORM_VSNPRINTF_ALT)
+#include <stdarg.h>
+extern int (*mbedtls_vsnprintf)( char * s, size_t n, const char * format, va_list arg );
+
+/**
+ * \brief Set your own snprintf function pointer
+ *
+ * \param vsnprintf_func the snprintf function implementation
+ *
+ * \return 0
+ */
+int mbedtls_platform_set_vsnprintf( int (*vsnprintf_func)( char * s, size_t n,
+ const char * format, va_list arg ) );
+#else /* MBEDTLS_PLATFORM_VSNPRINTF_ALT */
+#if defined(MBEDTLS_PLATFORM_VSNPRINTF_MACRO)
+#define mbedtls_vsnprintf MBEDTLS_PLATFORM_VSNPRINTF_MACRO
+#else
+#define mbedtls_vsnprintf vsnprintf
+#endif /* MBEDTLS_PLATFORM_VSNPRINTF_MACRO */
+#endif /* MBEDTLS_PLATFORM_VSNPRINTF_ALT */
+
+/*
* The function pointers for exit
*/
#if defined(MBEDTLS_PLATFORM_EXIT_ALT)