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 #ifdef HAVE_SNPRINTF

    58 #define _PyOS_vsnprintf_EXTRA_SPACE 1

    59 #else

    60 #define _PyOS_vsnprintf_EXTRA_SPACE 512

    61 	char *buffer;

    62 #endif

    63 	assert(str != NULL);

    64 	assert(size > 0);

    65 	assert(format != NULL);

    66 	/* We take a size_t as input but return an int.  Sanity check

    67 	 * our input so that it won't cause an overflow in the

    68          * vsnprintf return value or the buffer malloc size.  */

    69 	if (size > INT_MAX - _PyOS_vsnprintf_EXTRA_SPACE) {

    70 		len = -666;

    71 		goto Done;

    72 	}

    73 

    74 #ifdef HAVE_SNPRINTF

    75 	len = vsnprintf(str, size, format, va);

    76 #else

    77 	/* Emulate it. */

    78 	buffer = PyMem_MALLOC(size + _PyOS_vsnprintf_EXTRA_SPACE);

    79 	if (buffer == NULL) {

    80 		len = -666;

    81 		goto Done;

    82 	}

    83 

    84 	len = vsprintf(buffer, format, va);

    85 	if (len < 0)

    86 		/* ignore the error */;

    87 

    88 	else if ((size_t)len >= size + _PyOS_vsnprintf_EXTRA_SPACE)

    89 		Py_FatalError("Buffer overflow in PyOS_snprintf/PyOS_vsnprintf");

    90 

    91 	else {

    92 		const size_t to_copy = (size_t)len < size ?

    93 					(size_t)len : size - 1;

    94 		assert(to_copy < size);

    95 		memcpy(str, buffer, to_copy);

    96 		str[to_copy] = '\0';

    97 	}

    98 	PyMem_FREE(buffer);

    99 #endif

   100 Done:

   101 	if (size > 0)

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

   103 	return len;

   104 #undef _PyOS_vsnprintf_EXTRA_SPACE

   105 }