#include "Python.h"

/* snprintf() wrappers. If the platform has vsnprintf, we use it, else we
 emulate it in a half-hearted way. Even if the platform has it, we wrap
 it because platforms differ in what vsnprintf does in case the buffer
 is too small: C99 behavior is to return the number of characters that
 would have been written had the buffer not been too small, and to set
 the last byte of the buffer to 0円. At least MS _vsnprintf returns a
 negative value instead, and fills the entire buffer with non-0円 data.

 The wrappers ensure that str[size-1] is always 0円 upon return.

 PyOS_snprintf and PyOS_vsnprintf never write more than size bytes
 (including the trailing '0円') into str.

 If the platform doesn't have vsnprintf, and the buffer size needed to
 avoid truncation exceeds size by more than 512, Python aborts with a
 Py_FatalError.

 Return value (rv):

 When 0 <= rv < size, the output conversion was unexceptional, and
 rv characters were written to str (excluding a trailing 0円 byte at
 str[rv]).

 When rv >= size, output conversion was truncated, and a buffer of
 size rv+1 would have been needed to avoid truncation. str[size-1]
 is 0円 in this case.

 When rv < 0, "something bad happened". str[size-1] is 0円 in this
 case too, but the rest of str is unreliable. It could be that
 an error in format codes was detected by libc, or on platforms
 with a non-C99 vsnprintf simply that the buffer wasn't big enough
 to avoid truncation, or on platforms without any vsnprintf that
 PyMem_Malloc couldn't obtain space for a temp buffer.

 CAUTION: Unlike C99, str != NULL and size > 0 are required.
*/

int
PyOS_snprintf(char *str, size_t size, const char *format, ...)
{
 int rc;
 va_list va;

 va_start(va, format);
 rc = PyOS_vsnprintf(str, size, format, va);
 va_end(va);
 return rc;
}

int
PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
{
 int len; /* # bytes written, excluding 0円 */
#ifdef HAVE_SNPRINTF
#define _PyOS_vsnprintf_EXTRA_SPACE 1
#else
#define _PyOS_vsnprintf_EXTRA_SPACE 512
 char *buffer;
#endif
 assert(str != NULL);
 assert(size > 0);
 assert(format != NULL);
 /* We take a size_t as input but return an int. Sanity check
 * our input so that it won't cause an overflow in the
 * vsnprintf return value or the buffer malloc size. */
 if (size > INT_MAX - _PyOS_vsnprintf_EXTRA_SPACE) {
 len = -666;
 goto Done;
 }

#ifdef HAVE_SNPRINTF
 len = vsnprintf(str, size, format, va);
#else
 /* Emulate it. */
 buffer = PyMem_MALLOC(size + _PyOS_vsnprintf_EXTRA_SPACE);
 if (buffer == NULL) {
 len = -666;
 goto Done;
 }

 len = vsprintf(buffer, format, va);
 if (len < 0)
 /* ignore the error */;

 else if ((size_t)len >= size + _PyOS_vsnprintf_EXTRA_SPACE)
 Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf");

 else {
 const size_t to_copy = (size_t)len < size ?
 (size_t)len : size - 1;
 assert(to_copy < size);
 memcpy(str, buffer, to_copy);
 str[to_copy] = '0円';
 }
 PyMem_FREE(buffer);
#endif
Done:
 if (size > 0)
 str[size-1] = '0円';
 return len;
#undef _PyOS_vsnprintf_EXTRA_SPACE
}