Showing the changes to sys/src/cmd/python/Python/mysnprintf.c (1 of 3706 files). Show all
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| 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 | +} | |