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sfdcseekable.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*          Copyright (c) 1985-2009 AT&T Intellectual Property          *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                    by AT&T Intellectual Property                     *
*                                                                      *
*                A copy of the License is available at                 *
*            http://www.opensource.org/licenses/cpl1.0.txt             *
*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                 Glenn Fowler <gsf@research.att.com>                  *
*                  David Korn <dgk@research.att.com>                   *
*                   Phong Vo <kpv@research.att.com>                    *
*                                                                      *
***********************************************************************/
#include    "sfdchdr.h"

/*    Discipline to make an unseekable read stream seekable
**
**    sfraise(f,SFSK_DISCARD,0) discards previous seek data
**    but seeks from current offset on still allowed
**
**    Written by Kiem-Phong Vo, kpv@research.att.com, 03/18/1998.
*/

typedef struct _skable_s
{     Sfdisc_t    disc; /* sfio discipline */
      Sfio_t*           shadow;     /* to shadow data */
      Sfoff_t           discard;/* sfseek(f,-1,SEEK_SET) discarded data */
      Sfoff_t           extent; /* shadow extent */
      int         eof;  /* if eof has been reached */
} Seek_t;

#if __STD_C
static ssize_t skwrite(Sfio_t* f, const Void_t* buf, size_t n, Sfdisc_t* disc)
#else
static ssize_t skwrite(f, buf, n, disc)
Sfio_t*           f;    /* stream involved */
Void_t*           buf;  /* buffer to read into */
size_t            n;    /* number of bytes to read */
Sfdisc_t*   disc; /* discipline */
#endif
{
      return (ssize_t)(-1);
}

#if __STD_C
static ssize_t skread(Sfio_t* f, Void_t* buf, size_t n, Sfdisc_t* disc)
#else
static ssize_t skread(f, buf, n, disc)
Sfio_t*           f;    /* stream involved */
Void_t*           buf;  /* buffer to read into */
size_t            n;    /* number of bytes to read */
Sfdisc_t*   disc; /* discipline */
#endif
{
      Seek_t*           sk;
      Sfio_t*           sf;
      Sfoff_t           addr;
      ssize_t           r, w, p;

      sk = (Seek_t*)disc;
      sf = sk->shadow;
      if(sk->eof)
            return sfread(sf,buf,n);

      addr = sfseek(sf,(Sfoff_t)0,SEEK_CUR);

      if(addr+n <= sk->extent)
            return sfread(sf,buf,n);

      if((r = (ssize_t)(sk->extent-addr)) > 0)
      {     if((w = sfread(sf,buf,r)) != r)
                  return w;
            buf = (char*)buf + r;
            n -= r;
      }

      /* do a raw read */
      if((w = sfrd(f,buf,n,disc)) <= 0)
      {     sk->eof = 1;
            w = 0;
      }
      else
      {
            if((p = sfwrite(sf,buf,w)) != w)
                  sk->eof = 1;
            if(p > 0)
                  sk->extent += p;
      }

      return r+w;
}

#if __STD_C
static Sfoff_t skseek(Sfio_t* f, Sfoff_t addr, int type, Sfdisc_t* disc)
#else
static Sfoff_t skseek(f, addr, type, disc)
Sfio_t*           f;
Sfoff_t           addr;
int         type;
Sfdisc_t*   disc;
#endif
{
      Seek_t*           sk;
      Sfio_t*           sf;
      char        buf[SF_BUFSIZE];
      ssize_t           r, w;

      sk = (Seek_t*)disc;
      sf = sk->shadow;

      switch (type)
      {
      case SEEK_SET:
            addr -= sk->discard;
            break;
      case SEEK_CUR:
            addr += sftell(sf);
            break;
      case SEEK_END:
            addr += sk->extent;
            break;
      default:
            return -1;
      }

      if(addr < 0)
            return (Sfoff_t)(-1);
      else if(addr > sk->extent)
      {     if(sk->eof)
                  return (Sfoff_t)(-1);

            /* read enough to reach the seek point */
            while(addr > sk->extent)
            {     if(addr > sk->extent+sizeof(buf) )
                        w = sizeof(buf);
                  else  w = (int)(addr-sk->extent);
                  if((r = sfrd(f,buf,w,disc)) <= 0)
                        w = r-1;
                  else if((w = sfwrite(sf,buf,r)) > 0)
                        sk->extent += w;
                  if(w != r)
                  {     sk->eof = 1;
                        break;
                  }
            }

            if(addr > sk->extent)
                  return (Sfoff_t)(-1);
      }

      return sfseek(sf,addr,SEEK_SET) + sk->discard;
}

/* on close, remove the discipline */
#if __STD_C
static int skexcept(Sfio_t* f, int type, Void_t* data, Sfdisc_t* disc)
#else
static int skexcept(f,type,data,disc)
Sfio_t*           f;
int         type;
Void_t*           data;
Sfdisc_t*   disc;
#endif
{
      Seek_t*           sk;

      sk = (Seek_t*)disc;

      switch (type)
      {
      case SF_FINAL:
      case SF_DPOP:
            sfclose(sk->shadow);
            free(disc);
            break;
      case SFSK_DISCARD:
            sk->eof = 0;
            sk->discard += sk->extent;
            sk->extent = 0;
            sfseek(sk->shadow,(Sfoff_t)0,SEEK_SET);
            break;
      }
      return 0;
}

#if __STD_C
int sfdcseekable(Sfio_t* f)
#else
int sfdcseekable(f)
Sfio_t*     f;
#endif
{
      reg Seek_t* sk;

      /* see if already seekable */
      if(sfseek(f,(Sfoff_t)0,SEEK_CUR) >= 0)
            return 0;

      if(!(sk = (Seek_t*)malloc(sizeof(Seek_t))) )
            return -1;
      memset(sk, 0, sizeof(*sk));

      sk->disc.readf = skread;
      sk->disc.writef = skwrite;
      sk->disc.seekf = skseek;
      sk->disc.exceptf = skexcept;
      sk->shadow = sftmp(SF_BUFSIZE);
      sk->discard = 0;
      sk->extent = 0;
      sk->eof = 0;

      if(sfdisc(f, (Sfdisc_t*)sk) != (Sfdisc_t*)sk)
      {     sfclose(sk->shadow);
            free(sk);
            return -1;
      }

      return 0;
}

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