#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.  At least MS _vsnprintf returns a

   negative value instead, and fills the entire buffer with non-\0 data.

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

   PyOS_snprintf and PyOS_vsnprintf never write more than size bytes

   (including the trailing '\0') 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 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 in this case.

    When rv < 0, "something bad happened".  str[size-1] is \0 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 */

#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';

    }

    PyMem_FREE(buffer);

#endif

Done:

    if (size > 0)

        str[size-1] = '\0';

    return len;

#undef _PyOS_vsnprintf_EXTRA_SPACE

}