webcit/snprintf.c

   1 /*
   2  * $Id$
   3  */
   4
   5 /**
   6  *  Replacements for snprintf() and vsnprintf()
   7  *
   8  * Use it only if you have the "spare" cycles needed to effectively
   9  * do every snprintf operation twice! Why is that? Because everything
  10  * is first vfprintf()'d to /dev/null to determine the number of bytes.
  11  * Perhaps a bit slow for demanding applications on slow machines,
  12  * no problem for a fast machine with some spare cycles.
  13  *
  14  * You don't have a /dev/null? Every Linux contains one for free!
  15  *
  16  * Because the format string is never even looked at, all current and
  17  * possible future printf-conversions should be handled just fine.
  18  *
  19  * Written July 1997 by Sten Gunterberg (gunterberg@ergon.ch)
  20  */
  21
  22 #include "webcit.h"
  23 #include "webserver.h"
  24
  25 /**
  26  *  is it needed????
  27  *  fmt the formatstring?
  28  *  argp how many params?
  29  */
  30 static int needed(const char *fmt, va_list argp)
  31 {
  32         static FILE *sink = NULL;
  33
  34         /**
  35          * ok, there's a small race here that could result in the sink being
  36          * opened more than once if we're threaded, but I'd rather ignore it than
  37          * spend cycles synchronizing :-) */
  38
  39         if (sink == NULL) {
  40                 if ((sink = fopen("/dev/null", "w")) == NULL) {
  41                         perror("/dev/null");
  42                         exit(1);
  43                 }
  44         }
  45         return vfprintf(sink, fmt, argp);
  46 }
  47
  48 /**
  49  *  vsnprintf wrapper
  50  *  buf the output charbuffer
  51  *  max maximal size of the buffer
  52  *  fmt the formatstring (see man printf)
  53  *  argp the variable argument list
  54  */
  55 int vsnprintf(char *buf, size_t max, const char *fmt, va_list argp)
  56 {
  57         char *p;
  58         int size;
  59
  60         if ((p = malloc(needed(fmt, argp) + 1)) == NULL) {
  61                 lprintf(1, "vsnprintf: malloc failed, aborting\n");
  62                 abort();
  63         }
  64         if ((size = vsprintf(p, fmt, argp)) >= max)
  65                 size = -1;
  66
  67         strncpy(buf, p, max);
  68         buf[max - 1] = 0;
  69         free(p);
  70         return size;
  71 }
  72
  73 /**
  74  *  snprintf wrapper
  75  *  buf the output charbuffer
  76  *  max maximal size of the buffer
  77  *  fmt the formatstring (see man printf)
  78  *  ... the variable argument list
  79  */
  80 int snprintf(char *buf, size_t max, const char *fmt,...)
  81 {
  82         va_list argp;
  83         int bytes;
  84
  85         va_start(argp, fmt);
  86         bytes = vsnprintf(buf, max, fmt, argp);
  87         va_end(argp);
  88
  89         return bytes;
  90 }
  91
  92