1 #include "Python.h"
2
3 /* snprintf() and vsnprintf() wrappers.
4
5 If the platform has vsnprintf, we use it, else we
6 emulate it in a half-hearted way. Even if the platform has it, we wrap
7 it because platforms differ in what vsnprintf does in case the buffer
8 is too small: C99 behavior is to return the number of characters that
9 would have been written had the buffer not been too small, and to set
10 the last byte of the buffer to \0. At least MS _vsnprintf returns a
11 negative value instead, and fills the entire buffer with non-\0 data.
12 Unlike C99, our wrappers do not support passing a null buffer.
13
14 The wrappers ensure that str[size-1] is always \0 upon return.
15
16 PyOS_snprintf and PyOS_vsnprintf never write more than size bytes
17 (including the trailing '\0') into str.
18
19 Return value (rv):
20
21 When 0 <= rv < size, the output conversion was unexceptional, and
22 rv characters were written to str (excluding a trailing \0 byte at
23 str[rv]).
24
25 When rv >= size, output conversion was truncated, and a buffer of
26 size rv+1 would have been needed to avoid truncation. str[size-1]
27 is \0 in this case.
28
29 When rv < 0, "something bad happened". str[size-1] is \0 in this
30 case too, but the rest of str is unreliable. It could be that
31 an error in format codes was detected by libc, or on platforms
32 with a non-C99 vsnprintf simply that the buffer wasn't big enough
33 to avoid truncation, or on platforms without any vsnprintf that
34 PyMem_Malloc couldn't obtain space for a temp buffer.
35
36 CAUTION: Unlike C99, str != NULL and size > 0 are required.
37 Also, size must be smaller than INT_MAX.
38 */
39
40 int
PyOS_snprintf(char * str,size_t size,const char * format,...)41 PyOS_snprintf(char *str, size_t size, const char *format, ...)
42 {
43 int rc;
44 va_list va;
45
46 va_start(va, format);
47 rc = PyOS_vsnprintf(str, size, format, va);
48 va_end(va);
49 return rc;
50 }
51
52 int
PyOS_vsnprintf(char * str,size_t size,const char * format,va_list va)53 PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
54 {
55 assert(str != NULL);
56 assert(size > 0);
57 assert(size <= (INT_MAX - 1));
58 assert(format != NULL);
59
60 int len; /* # bytes written, excluding \0 */
61 /* We take a size_t as input but return an int. Sanity check
62 * our input so that it won't cause an overflow in the
63 * vsnprintf return value. */
64 if (size > INT_MAX - 1) {
65 len = -666;
66 goto Done;
67 }
68
69 #if defined(_MSC_VER)
70 len = _vsnprintf(str, size, format, va);
71 #else
72 len = vsnprintf(str, size, format, va);
73 #endif
74
75 Done:
76 if (size > 0) {
77 str[size-1] = '\0';
78 }
79 return len;
80 }
81