106 lines
3.3 KiB
C
106 lines
3.3 KiB
C
#include "Python.h"
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#include <ctype.h>
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/* snprintf() wrappers. If the platform has vsnprintf, we use it, else we
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emulate it in a half-hearted way. Even if the platform has it, we wrap
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it because platforms differ in what vsnprintf does in case the buffer
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is too small: C99 behavior is to return the number of characters that
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would have been written had the buffer not been too small, and to set
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the last byte of the buffer to \0. At least MS _vsnprintf returns a
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negative value instead, and fills the entire buffer with non-\0 data.
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The wrappers ensure that str[size-1] is always \0 upon return.
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PyOS_snprintf and PyOS_vsnprintf never write more than size bytes
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(including the trailing '\0') into str.
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If the platform doesn't have vsnprintf, and the buffer size needed to
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avoid truncation exceeds size by more than 512, Python aborts with a
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Py_FatalError.
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Return value (rv):
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When 0 <= rv < size, the output conversion was unexceptional, and
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rv characters were written to str (excluding a trailing \0 byte at
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str[rv]).
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When rv >= size, output conversion was truncated, and a buffer of
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size rv+1 would have been needed to avoid truncation. str[size-1]
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is \0 in this case.
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When rv < 0, "something bad happened". str[size-1] is \0 in this
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case too, but the rest of str is unreliable. It could be that
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an error in format codes was detected by libc, or on platforms
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with a non-C99 vsnprintf simply that the buffer wasn't big enough
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to avoid truncation, or on platforms without any vsnprintf that
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PyMem_Malloc couldn't obtain space for a temp buffer.
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CAUTION: Unlike C99, str != NULL and size > 0 are required.
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*/
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int
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PyOS_snprintf(char *str, size_t size, const char *format, ...)
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{
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int rc;
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va_list va;
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va_start(va, format);
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rc = PyOS_vsnprintf(str, size, format, va);
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va_end(va);
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return rc;
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}
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int
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PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
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{
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int len; /* # bytes written, excluding \0 */
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#ifdef HAVE_SNPRINTF
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#define _PyOS_vsnprintf_EXTRA_SPACE 1
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#else
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#define _PyOS_vsnprintf_EXTRA_SPACE 512
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char *buffer;
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#endif
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assert(str != NULL);
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assert(size > 0);
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assert(format != NULL);
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/* We take a size_t as input but return an int. Sanity check
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* our input so that it won't cause an overflow in the
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* vsnprintf return value or the buffer malloc size. */
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if (size > INT_MAX - _PyOS_vsnprintf_EXTRA_SPACE) {
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len = -666;
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goto Done;
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}
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#ifdef HAVE_SNPRINTF
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len = vsnprintf(str, size, format, va);
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#else
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/* Emulate it. */
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buffer = PyMem_MALLOC(size + _PyOS_vsnprintf_EXTRA_SPACE);
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if (buffer == NULL) {
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len = -666;
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goto Done;
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}
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len = vsprintf(buffer, format, va);
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if (len < 0)
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/* ignore the error */;
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else if ((size_t)len >= size + _PyOS_vsnprintf_EXTRA_SPACE)
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Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf");
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else {
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const size_t to_copy = (size_t)len < size ?
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(size_t)len : size - 1;
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assert(to_copy < size);
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memcpy(str, buffer, to_copy);
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str[to_copy] = '\0';
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}
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PyMem_FREE(buffer);
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#endif
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Done:
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if (size > 0)
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str[size-1] = '\0';
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return len;
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#undef _PyOS_vsnprintf_EXTRA_SPACE
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}
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