1 #include "Python.h" 2 #include <ctype.h> 3 4 /* snprintf() wrappers. If the platform has vsnprintf, we use it, else we 5 emulate it in a half-hearted way. Even if the platform has it, we wrap 6 it because platforms differ in what vsnprintf does in case the buffer 7 is too small: C99 behavior is to return the number of characters that 8 would have been written had the buffer not been too small, and to set 9 the last byte of the buffer to \0. At least MS _vsnprintf returns a 10 negative value instead, and fills the entire buffer with non-\0 data. 11 12 The wrappers ensure that str[size-1] is always \0 upon return. 13 14 PyOS_snprintf and PyOS_vsnprintf never write more than size bytes 15 (including the trailing '\0') into str. 16 17 If the platform doesn't have vsnprintf, and the buffer size needed to 18 avoid truncation exceeds size by more than 512, Python aborts with a 19 Py_FatalError. 20 21 Return value (rv): 22 23 When 0 <= rv < size, the output conversion was unexceptional, and 24 rv characters were written to str (excluding a trailing \0 byte at 25 str[rv]). 26 27 When rv >= size, output conversion was truncated, and a buffer of 28 size rv+1 would have been needed to avoid truncation. str[size-1] 29 is \0 in this case. 30 31 When rv < 0, "something bad happened". str[size-1] is \0 in this 32 case too, but the rest of str is unreliable. It could be that 33 an error in format codes was detected by libc, or on platforms 34 with a non-C99 vsnprintf simply that the buffer wasn't big enough 35 to avoid truncation, or on platforms without any vsnprintf that 36 PyMem_Malloc couldn't obtain space for a temp buffer. 37 38 CAUTION: Unlike C99, str != NULL and size > 0 are required. 39 */ 40 41 int 42 PyOS_snprintf(char *str, size_t size, const char *format, ...) 43 { 44 int rc; 45 va_list va; 46 47 va_start(va, format); 48 rc = PyOS_vsnprintf(str, size, format, va); 49 va_end(va); 50 return rc; 51 } 52 53 int 54 PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va) 55 { 56 int len; /* # bytes written, excluding \0 */ 57 #ifdef HAVE_SNPRINTF 58 #define _PyOS_vsnprintf_EXTRA_SPACE 1 59 #else 60 #define _PyOS_vsnprintf_EXTRA_SPACE 512 61 char *buffer; 62 #endif 63 assert(str != NULL); 64 assert(size > 0); 65 assert(format != NULL); 66 /* We take a size_t as input but return an int. Sanity check 67 * our input so that it won't cause an overflow in the 68 * vsnprintf return value or the buffer malloc size. */ 69 if (size > INT_MAX - _PyOS_vsnprintf_EXTRA_SPACE) { 70 len = -666; 71 goto Done; 72 } 73 74 #ifdef HAVE_SNPRINTF 75 len = vsnprintf(str, size, format, va); 76 #else 77 /* Emulate it. */ 78 buffer = PyMem_MALLOC(size + _PyOS_vsnprintf_EXTRA_SPACE); 79 if (buffer == NULL) { 80 len = -666; 81 goto Done; 82 } 83 84 len = vsprintf(buffer, format, va); 85 if (len < 0) 86 /* ignore the error */; 87 88 else if ((size_t)len >= size + _PyOS_vsnprintf_EXTRA_SPACE) 89 Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf"); 90 91 else { 92 const size_t to_copy = (size_t)len < size ? 93 (size_t)len : size - 1; 94 assert(to_copy < size); 95 memcpy(str, buffer, to_copy); 96 str[to_copy] = '\0'; 97 } 98 PyMem_FREE(buffer); 99 #endif 100 Done: 101 if (size > 0) 102 str[size-1] = '\0'; 103 return len; 104 #undef _PyOS_vsnprintf_EXTRA_SPACE 105 } 106
