Showing the changes to sys/src/cmd/python/Python/mysnprintf.c (1 of 3706 files). Show all
Unified · Split
| @@ -0,0 +1,93 @@ | |||
| 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 | #ifndef HAVE_SNPRINTF | ||
| 58 | char *buffer; | ||
| 59 | #endif | ||
| 60 | assert(str != NULL); | ||
| 61 | assert(size > 0); | ||
| 62 | assert(format != NULL); | ||
| 63 | |||
| 64 | #ifdef HAVE_SNPRINTF | ||
| 65 | len = vsnprintf(str, size, format, va); | ||
| 66 | #else | ||
| 67 | /* Emulate it. */ | ||
| 68 | buffer = PyMem_MALLOC(size + 512); | ||
| 69 | if (buffer == NULL) { | ||
| 70 | len = -666; | ||
| 71 | goto Done; | ||
| 72 | } | ||
| 73 | |||
| 74 | len = vsprintf(buffer, format, va); | ||
| 75 | if (len < 0) | ||
| 76 | /* ignore the error */; | ||
| 77 | |||
| 78 | else if ((size_t)len >= size + 512) | ||
| 79 | Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf"); | ||
| 80 | |||
| 81 | else { | ||
| 82 | const size_t to_copy = (size_t)len < size ? | ||
| 83 | (size_t)len : size - 1; | ||
| 84 | assert(to_copy < size); | ||
| 85 | memcpy(str, buffer, to_copy); | ||
| 86 | str[to_copy] = '\0'; | ||
| 87 | } | ||
| 88 | PyMem_FREE(buffer); | ||
| 89 | Done: | ||
| 90 | #endif | ||
| 91 | str[size-1] = '\0'; | ||
| 92 | return len; | ||
| 93 | } | ||