/*
 * Copyright (c) 2000-2001, 2004 Sendmail, Inc. and its suppliers.
 *      All rights reserved.
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * By using this file, you agree to the terms and conditions set
 * forth in the LICENSE file which can be found at the top level of
 * the sendmail distribution.
 */

#include <sm/gen.h>
SM_RCSID("@(#)$Id: fseek.c,v 1.47 2005/06/14 23:07:20 ca Exp $")
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <errno.h>
#include <setjmp.h>
#include <sm/time.h>
#include <sm/signal.h>
#include <sm/io.h>
#include <sm/assert.h>
#include <sm/clock.h>
#include "local.h"

#define POS_ERR (-(off_t)1)

static void     seekalrm __P((int));
static jmp_buf SeekTimeOut;

/*
**  SEEKALRM -- handler when timeout activated for sm_io_seek()
**
**  Returns flow of control to where setjmp(SeekTimeOut) was set.
**
**      Parameters:
**              sig -- unused
**
**      Returns:
**              does not return
**
**      Side Effects:
**              returns flow of control to setjmp(SeekTimeOut).
**
**      NOTE:   THIS CAN BE CALLED FROM A SIGNAL HANDLER.  DO NOT ADD
**              ANYTHING TO THIS ROUTINE UNLESS YOU KNOW WHAT YOU ARE
**              DOING.
*/

/* ARGSUSED0 */
static void
seekalrm(sig)
        int sig;
{
        longjmp(SeekTimeOut, 1);
}

/*
**  SM_IO_SEEK -- position the file pointer
**
**      Parameters:
**              fp -- the file pointer to be seek'd
**              timeout -- time to complete seek (milliseconds)
**              offset -- seek offset based on 'whence'
**              whence -- indicates where seek is relative from.
**                      One of SM_IO_SEEK_{CUR,SET,END}.
**      Returns:
**              Failure: returns -1 (minus 1) and sets errno
**              Success: returns 0 (zero)
*/

int
sm_io_seek(fp, timeout, offset, whence)
        register SM_FILE_T *fp;
        int SM_NONVOLATILE timeout;
        long SM_NONVOLATILE offset;
        int SM_NONVOLATILE whence;
{
        bool havepos;
        off_t target, curoff;
        size_t n;
        struct stat st;
        int ret;
        SM_EVENT *evt = NULL;
        register off_t (*seekfn) __P((SM_FILE_T *, off_t, int));

        SM_REQUIRE_ISA(fp, SmFileMagic);

        /* make sure stdio is set up */
        if (!Sm_IO_DidInit)
                sm_init();

        /* Have to be able to seek. */
        if ((seekfn = fp->f_seek) == NULL)
        {
                errno = ESPIPE;                 /* historic practice */
                return -1;
        }

        if (timeout == SM_TIME_DEFAULT)
                timeout = fp->f_timeout;
        if (timeout == SM_TIME_IMMEDIATE)
        {
                /*
                **  Filling the buffer will take time and we are wanted to
                **  return immediately. So...
                */

                errno = EAGAIN;
                return -1;
        }

#define SM_SET_ALARM()                                          \
        if (timeout != SM_TIME_FOREVER)                         \
        {                                                       \
                if (setjmp(SeekTimeOut) != 0)                   \
                {                                               \
                        errno = EAGAIN;                         \
                        return -1;                              \
                }                                               \
                evt = sm_seteventm(timeout, seekalrm, 0);       \
        }

        /*
        **  Change any SM_IO_SEEK_CUR to SM_IO_SEEK_SET, and check `whence'
        **  argument. After this, whence is either SM_IO_SEEK_SET or
        **  SM_IO_SEEK_END.
        */

        switch (whence)
        {
          case SM_IO_SEEK_CUR:

                /*
                **  In order to seek relative to the current stream offset,
                **  we have to first find the current stream offset a la
                **  ftell (see ftell for details).
                */

                /* may adjust seek offset on append stream */
                sm_flush(fp, (int *) &timeout);
                SM_SET_ALARM();
                if (fp->f_flags & SMOFF)
                        curoff = fp->f_lseekoff;
                else
                {
                        curoff = (*seekfn)(fp, (off_t) 0, SM_IO_SEEK_CUR);
                        if (curoff == -1L)
                        {
                                ret = -1;
                                goto clean;
                        }
                }
                if (fp->f_flags & SMRD)
                {
                        curoff -= fp->f_r;
                        if (HASUB(fp))
                                curoff -= fp->f_ur;
                }
                else if (fp->f_flags & SMWR && fp->f_p != NULL)
                        curoff += fp->f_p - fp->f_bf.smb_base;

                offset += curoff;
                whence = SM_IO_SEEK_SET;
                havepos = true;
                break;

          case SM_IO_SEEK_SET:
          case SM_IO_SEEK_END:
                SM_SET_ALARM();
                curoff = 0;             /* XXX just to keep gcc quiet */
                havepos = false;
                break;

          default:
                errno = EINVAL;
                return -1;
        }

        /*
        **  Can only optimise if:
        **      reading (and not reading-and-writing);
        **      not unbuffered; and
        **      this is a `regular' Unix file (and hence seekfn==sm_stdseek).
        **  We must check SMNBF first, because it is possible to have SMNBF
        **  and SMSOPT both set.
        */

        if (fp->f_bf.smb_base == NULL)
                sm_makebuf(fp);
        if (fp->f_flags & (SMWR | SMRW | SMNBF | SMNPT))
                goto dumb;
        if ((fp->f_flags & SMOPT) == 0)
        {
                if (seekfn != sm_stdseek ||
                    fp->f_file < 0 || fstat(fp->f_file, &st) ||
                    (st.st_mode & S_IFMT) != S_IFREG)
                {
                        fp->f_flags |= SMNPT;
                        goto dumb;
                }
                fp->f_blksize = st.st_blksize;
                fp->f_flags |= SMOPT;
        }

        /*
        **  We are reading; we can try to optimise.
        **  Figure out where we are going and where we are now.
        */

        if (whence == SM_IO_SEEK_SET)
                target = offset;
        else
        {
                if (fstat(fp->f_file, &st))
                        goto dumb;
                target = st.st_size + offset;
        }

        if (!havepos)
        {
                if (fp->f_flags & SMOFF)
                        curoff = fp->f_lseekoff;
                else
                {
                        curoff = (*seekfn)(fp, (off_t) 0, SM_IO_SEEK_CUR);
                        if (curoff == POS_ERR)
                                goto dumb;
                }
                curoff -= fp->f_r;
                if (HASUB(fp))
                        curoff -= fp->f_ur;
        }

        /*
        **  Compute the number of bytes in the input buffer (pretending
        **  that any ungetc() input has been discarded).  Adjust current
        **  offset backwards by this count so that it represents the
        **  file offset for the first byte in the current input buffer.
        */

        if (HASUB(fp))
        {
                curoff += fp->f_r;      /* kill off ungetc */
                n = fp->f_up - fp->f_bf.smb_base;
                curoff -= n;
                n += fp->f_ur;
        }
        else
        {
                n = fp->f_p - fp->f_bf.smb_base;
                curoff -= n;
                n += fp->f_r;
        }

        /*
        **  If the target offset is within the current buffer,
        **  simply adjust the pointers, clear SMFEOF, undo ungetc(),
        **  and return.  (If the buffer was modified, we have to
        **  skip this; see getln in fget.c.)
        */

        if (target >= curoff && target < curoff + (off_t) n)
        {
                register int o = target - curoff;

                fp->f_p = fp->f_bf.smb_base + o;
                fp->f_r = n - o;
                if (HASUB(fp))
                        FREEUB(fp);
                fp->f_flags &= ~SMFEOF;
                ret = 0;
                goto clean;
        }

        /*
        **  The place we want to get to is not within the current buffer,
        **  but we can still be kind to the kernel copyout mechanism.
        **  By aligning the file offset to a block boundary, we can let
        **  the kernel use the VM hardware to map pages instead of
        **  copying bytes laboriously.  Using a block boundary also
        **  ensures that we only read one block, rather than two.
        */

        curoff = target & ~(fp->f_blksize - 1);
        if ((*seekfn)(fp, curoff, SM_IO_SEEK_SET) == POS_ERR)
                goto dumb;
        fp->f_r = 0;
        fp->f_p = fp->f_bf.smb_base;
        if (HASUB(fp))
                FREEUB(fp);
        fp->f_flags &= ~SMFEOF;
        n = target - curoff;
        if (n)
        {
                /* Note: SM_TIME_FOREVER since fn timeout already set */
                if (sm_refill(fp, SM_TIME_FOREVER) || fp->f_r < (int) n)
                        goto dumb;
                fp->f_p += n;
                fp->f_r -= n;
        }

        ret = 0;
clean:
        /*  We're back. So undo our timeout and handler */
        if (evt != NULL)
                sm_clrevent(evt);
        return ret;
dumb:
        /*
        **  We get here if we cannot optimise the seek ... just
        **  do it.  Allow the seek function to change fp->f_bf.smb_base.
        */

        /* Note: SM_TIME_FOREVER since fn timeout already set */
        ret = SM_TIME_FOREVER;
        if (sm_flush(fp, &ret) != 0 ||
            (*seekfn)(fp, (off_t) offset, whence) == POS_ERR)
        {
                ret = -1;
                goto clean;
        }

        /* success: clear SMFEOF indicator and discard ungetc() data */
        if (HASUB(fp))
                FREEUB(fp);
        fp->f_p = fp->f_bf.smb_base;
        fp->f_r = 0;
        fp->f_flags &= ~SMFEOF;
        ret = 0;
        goto clean;
}