usr/src/lib/libast/common/sfio/sfpeek.c

   1 /***********************************************************************
   2 *                                                                      *
   3 *               This software is part of the ast package               *
   4 *          Copyright (c) 1985-2010 AT&T Intellectual Property          *
   5 *                      and is licensed under the                       *
   6 *                  Common Public License, Version 1.0                  *
   7 *                    by AT&T Intellectual Property                     *
   8 *                                                                      *
   9 *                A copy of the License is available at                 *
  10 *            http://www.opensource.org/licenses/cpl1.0.txt             *
  11 *         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
  12 *                                                                      *
  13 *              Information and Software Systems Research               *
  14 *                            AT&T Research                             *
  15 *                           Florham Park NJ                            *
  16 *                                                                      *
  17 *                 Glenn Fowler <gsf@research.att.com>                  *
  18 *                  David Korn <dgk@research.att.com>                   *
  19 *                   Phong Vo <kpv@research.att.com>                    *
  20 *                                                                      *
  21 ***********************************************************************/
  22 #include        "sfhdr.h"
  23
  24 /*      Safe access to the internal stream buffer.
  25 **      This function is obsolete. sfreserve() should be used.
  26 **
  27 **      Written by Kiem-Phong Vo (06/27/90).
  28 */
  29
  30 #if _BLD_sfio && defined(__EXPORT__)
  31 #define extern  __EXPORT__
  32 #endif
  33
  34 #if __STD_C
  35 extern ssize_t sfpeek(reg Sfio_t* f, Void_t** bp, reg size_t size)
  36 #else
  37 extern ssize_t sfpeek(f,bp,size)
  38 reg Sfio_t*     f;      /* file to peek */
  39 Void_t**        bp;     /* start of data area */
  40 reg size_t      size;   /* size of peek */
  41 #endif
  42 {       reg ssize_t     n, sz;
  43         reg int         mode;
  44
  45         /* query for the extent of the remainder of the buffer */
  46         if((sz = size) == 0 || !bp)
  47         {       if(f->mode&SF_INIT)
  48                         (void)_sfmode(f,0,0);
  49
  50                 if((f->flags&SF_RDWRSTR) == SF_RDWRSTR)
  51                 {       SFSTRSIZE(f);
  52                         n = (f->data+f->here) - f->next;
  53                 }
  54                 else    n = f->endb - f->next;
  55
  56                 if(!bp)
  57                         return n;
  58                 else if(n > 0)  /* size == 0 */
  59                 {       *bp = (Void_t*)f->next;
  60                         return 0;
  61                 }
  62                 /* else fall down and fill buffer */
  63         }
  64
  65         if(!(mode = f->flags&SF_READ) )
  66                 mode = SF_WRITE;
  67         if((int)f->mode != mode && _sfmode(f,mode,0) < 0)
  68                 return -1;
  69
  70         *bp = sfreserve(f, sz <= 0 ? 0 : sz > f->size ? f->size : sz, 0);
  71
  72         if(*bp && sz >= 0)
  73                 return sz;
  74
  75         if((n = sfvalue(f)) > 0)
  76         {       *bp = (Void_t*)f->next;
  77                 if(sz < 0)
  78                 {       f->mode |= SF_PEEK;
  79                         f->endr = f->endw = f->data;
  80                 }
  81                 else
  82                 {       if(sz > n)
  83                                 sz = n;
  84                         f->next += sz;
  85                 }
  86         }
  87
  88         return (sz >= 0 && n >= sz) ? sz : n;
  89 }