1 /*
2  * Handy secure string adapter functions for mbedTLS,
3  * converting from `StringCchVPrintfEx` to `_vsnprintf_s`.
4  *
5  * Copyright 2015 Ismael Ferreras Morezuelas <swyterzone+ros@gmail.com>
6  *
7  * This library is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * This library is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with this library; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
20  */
21 
22 #include <windef.h>
23 #include <strsafe.h>
24 
25 int _vsnprintf_s(char *buffer, size_t sizeOfBuffer, size_t count, const char *format, va_list argptr)
26 {
27     size_t cchRemaining;
28 
29     HRESULT ret = StringCchVPrintfEx(buffer, sizeOfBuffer, NULL, &cchRemaining, 0, format, argptr);
30 
31     // EXAMPLE //////////////////////////
32     // -------- > Size of provided buffer in chars (8).
33     // ABC0____ > Buffer contents after StringCchVPrintfEx gets called.
34     // ---      > What we actually need to return (3).
35     //    ----- > Remaining chars in buffer, including post string NULL, returned by StringCchVPrintfEx (5).
36 
37     /* _vsnprintf_s returns the number of characters written, not including
38        the terminating null, or a negative value if an output error occurs.  */
39 
40     switch (ret)
41     {
42         case S_OK:
43             return (sizeOfBuffer - cchRemaining);
44 
45         case STRSAFE_E_INVALID_PARAMETER:
46         case STRSAFE_E_INSUFFICIENT_BUFFER:
47         default:
48             return -1;
49     }
50 }