Branch data Line data Source code
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 41 : 179 : PyOS_snprintf(char *str, size_t size, const char *format, ...) 42 : : { 43 : : int rc; 44 : : va_list va; 45 : : 46 : 179 : va_start(va, format); 47 : 179 : rc = PyOS_vsnprintf(str, size, format, va); 48 : 179 : va_end(va); 49 : 179 : return rc; 50 : : } 51 : : 52 : : int 53 : 179 : 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 [ - + ]: 179 : if (size > INT_MAX - 1) { 65 : 0 : len = -666; 66 : 0 : goto Done; 67 : : } 68 : : 69 : : #if defined(_MSC_VER) 70 : : len = _vsnprintf(str, size, format, va); 71 : : #else 72 : 179 : len = vsnprintf(str, size, format, va); 73 : : #endif 74 : : 75 : 179 : Done: 76 [ + - ]: 179 : if (size > 0) { 77 : 179 : str[size-1] = '\0'; 78 : : } 79 : 179 : return len; 80 : : }