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ch.c

/*
 * Copyright (C) 1984-2004  Mark Nudelman
 *
 * You may distribute under the terms of either the GNU General Public
 * License or the Less License, as specified in the README file.
 *
 * For more information about less, or for information on how to 
 * contact the author, see the README file.
 */


/*
 * Low level character input from the input file.
 * We use these special purpose routines which optimize moving
 * both forward and backward from the current read pointer.
 */

#include "less.h"
#if MSDOS_COMPILER==WIN32C
#include <errno.h>
#include <windows.h>
#endif

typedef POSITION BLOCKNUM;

public int ignore_eoi;

/*
 * Pool of buffers holding the most recently used blocks of the input file.
 * The buffer pool is kept as a doubly-linked circular list,
 * in order from most- to least-recently used.
 * The circular list is anchored by the file state "thisfile".
 */
#define     LBUFSIZE    8192
struct buf {
      struct buf *next, *prev;
      struct buf *hnext, *hprev;
      BLOCKNUM block;
      unsigned int datasize;
      unsigned char data[LBUFSIZE];
};

struct buflist {
      /* -- Following members must match struct buf */
      struct buf *buf_next, *buf_prev;
      struct buf *buf_hnext, *buf_hprev;
};

/*
 * The file state is maintained in a filestate structure.
 * A pointer to the filestate is kept in the ifile structure.
 */
#define     BUFHASH_SIZE      64
struct filestate {
      struct buf *buf_next, *buf_prev;
      struct buflist hashtbl[BUFHASH_SIZE];
      int file;
      int flags;
      POSITION fpos;
      int nbufs;
      BLOCKNUM block;
      unsigned int offset;
      POSITION fsize;
};

#define     ch_bufhead  thisfile->buf_next
#define     ch_buftail  thisfile->buf_prev
#define     ch_nbufs    thisfile->nbufs
#define     ch_block    thisfile->block
#define     ch_offset   thisfile->offset
#define     ch_fpos           thisfile->fpos
#define     ch_fsize    thisfile->fsize
#define     ch_flags    thisfile->flags
#define     ch_file           thisfile->file

#define     END_OF_CHAIN      ((struct buf *)&thisfile->buf_next)
#define     END_OF_HCHAIN(h) ((struct buf *)&thisfile->hashtbl[h])
#define BUFHASH(blk)    ((blk) & (BUFHASH_SIZE-1))

#define     FOR_BUFS_IN_CHAIN(h,bp) \
      for (bp = thisfile->hashtbl[h].buf_hnext;  \
           bp != END_OF_HCHAIN(h);  bp = bp->hnext)

#define     HASH_RM(bp) \
      (bp)->hnext->hprev = (bp)->hprev; \
      (bp)->hprev->hnext = (bp)->hnext;

#define     HASH_INS(bp,h) \
      (bp)->hnext = thisfile->hashtbl[h].buf_hnext; \
      (bp)->hprev = END_OF_HCHAIN(h); \
      thisfile->hashtbl[h].buf_hnext->hprev = (bp); \
      thisfile->hashtbl[h].buf_hnext = (bp);

static struct filestate *thisfile;
static int ch_ungotchar = -1;
static int maxbufs = -1;

extern int autobuf;
extern int sigs;
extern int secure;
extern constant char helpdata[];
extern constant int size_helpdata;
extern IFILE curr_ifile;
#if LOGFILE
extern int logfile;
extern char *namelogfile;
#endif

static int ch_addbuf();


/*
 * Get the character pointed to by the read pointer.
 * ch_get() is a macro which is more efficient to call
 * than fch_get (the function), in the usual case 
 * that the block desired is at the head of the chain.
 */
#define     ch_get()   ((ch_block == ch_bufhead->block && \
                 ch_offset < ch_bufhead->datasize) ? \
                  ch_bufhead->data[ch_offset] : fch_get())
      int
fch_get()
{
      register struct buf *bp;
      register int n;
      register int slept;
      register int h;
      POSITION pos;
      POSITION len;

      slept = FALSE;

      /*
       * Look for a buffer holding the desired block.
       */
      h = BUFHASH(ch_block);
      FOR_BUFS_IN_CHAIN(h, bp)
      {
            if (bp->block == ch_block)
            {
                  if (ch_offset >= bp->datasize)
                        /*
                         * Need more data in this buffer.
                         */
                        goto read_more;
                  goto found;
            }
      }
      /*
       * Block is not in a buffer.  
       * Take the least recently used buffer 
       * and read the desired block into it.
       * If the LRU buffer has data in it, 
       * then maybe allocate a new buffer.
       */
      if (ch_buftail == END_OF_CHAIN || ch_buftail->block != -1)
      {
            /*
             * There is no empty buffer to use.
             * Allocate a new buffer if:
             * 1. We can't seek on this file and -b is not in effect; or
             * 2. We haven't allocated the max buffers for this file yet.
             */
            if ((autobuf && !(ch_flags & CH_CANSEEK)) ||
                (maxbufs < 0 || ch_nbufs < maxbufs))
                  if (ch_addbuf())
                        /*
                         * Allocation failed: turn off autobuf.
                         */
                        autobuf = OPT_OFF;
      }
      bp = ch_buftail;
      HASH_RM(bp); /* Remove from old hash chain. */
      bp->block = ch_block;
      bp->datasize = 0;
      HASH_INS(bp, h); /* Insert into new hash chain. */

    read_more:
      pos = (ch_block * LBUFSIZE) + bp->datasize;
      if ((len = ch_length()) != NULL_POSITION && pos >= len)
            /*
             * At end of file.
             */
            return (EOI);

      if (pos != ch_fpos)
      {
            /*
             * Not at the correct position: must seek.
             * If input is a pipe, we're in trouble (can't seek on a pipe).
             * Some data has been lost: just return "?".
             */
            if (!(ch_flags & CH_CANSEEK))
                  return ('?');
            if (lseek(ch_file, (off_t)pos, 0) == BAD_LSEEK)
            {
                  error("seek error", NULL_PARG);
                  clear_eol();
                  return (EOI);
            }
            ch_fpos = pos;
      }

      /*
       * Read the block.
       * If we read less than a full block, that's ok.
       * We use partial block and pick up the rest next time.
       */
      if (ch_ungotchar != -1)
      {
            bp->data[bp->datasize] = ch_ungotchar;
            n = 1;
            ch_ungotchar = -1;
      } else if (ch_flags & CH_HELPFILE)
      {
            bp->data[bp->datasize] = helpdata[ch_fpos];
            n = 1;
      } else
      {
            n = iread(ch_file, &bp->data[bp->datasize], 
                  (unsigned int)(LBUFSIZE - bp->datasize));
      }

      if (n == READ_INTR)
            return (EOI);
      if (n < 0)
      {
#if MSDOS_COMPILER==WIN32C
            if (errno != EPIPE)
#endif
            {
                  error("read error", NULL_PARG);
                  clear_eol();
            }
            n = 0;
      }

#if LOGFILE
      /*
       * If we have a log file, write the new data to it.
       */
      if (!secure && logfile >= 0 && n > 0)
            write(logfile, (char *) &bp->data[bp->datasize], n);
#endif

      ch_fpos += n;
      bp->datasize += n;

      /*
       * If we have read to end of file, set ch_fsize to indicate
       * the position of the end of file.
       */
      if (n == 0)
      {
            ch_fsize = pos;
            if (ignore_eoi)
            {
                  /*
                   * We are ignoring EOF.
                   * Wait a while, then try again.
                   */
                  if (!slept)
                  {
                        PARG parg;
                        parg.p_string = wait_message();
                        ierror("%s", &parg);
                  }
#if !MSDOS_COMPILER
                  sleep(1);
#else
#if MSDOS_COMPILER==WIN32C
                  Sleep(1000);
#endif
#endif
                  slept = TRUE;
            }
            if (sigs)
                  return (EOI);
      }

    found:
      if (ch_bufhead != bp)
      {
            /*
             * Move the buffer to the head of the buffer chain.
             * This orders the buffer chain, most- to least-recently used.
             */
            bp->next->prev = bp->prev;
            bp->prev->next = bp->next;
            bp->next = ch_bufhead;
            bp->prev = END_OF_CHAIN;
            ch_bufhead->prev = bp;
            ch_bufhead = bp;

            /*
             * Move to head of hash chain too.
             */
            HASH_RM(bp);
            HASH_INS(bp, h);
      }

      if (ch_offset >= bp->datasize)
            /*
             * After all that, we still don't have enough data.
             * Go back and try again.
             */
            goto read_more;

      return (bp->data[ch_offset]);
}

/*
 * ch_ungetchar is a rather kludgy and limited way to push 
 * a single char onto an input file descriptor.
 */
      public void
ch_ungetchar(c)
      int c;
{
      if (c != -1 && ch_ungotchar != -1)
            error("ch_ungetchar overrun", NULL_PARG);
      ch_ungotchar = c;
}

#if LOGFILE
/*
 * Close the logfile.
 * If we haven't read all of standard input into it, do that now.
 */
      public void
end_logfile()
{
      static int tried = FALSE;

      if (logfile < 0)
            return;
      if (!tried && ch_fsize == NULL_POSITION)
      {
            tried = TRUE;
            ierror("Finishing logfile", NULL_PARG);
            while (ch_forw_get() != EOI)
                  if (ABORT_SIGS())
                        break;
      }
      close(logfile);
      logfile = -1;
      namelogfile = NULL;
}

/*
 * Start a log file AFTER less has already been running.
 * Invoked from the - command; see toggle_option().
 * Write all the existing buffered data to the log file.
 */
      public void
sync_logfile()
{
      register struct buf *bp;
      int warned = FALSE;
      BLOCKNUM block;
      BLOCKNUM nblocks;

      nblocks = (ch_fpos + LBUFSIZE - 1) / LBUFSIZE;
      for (block = 0;  block < nblocks;  block++)
      {
            for (bp = ch_bufhead;  ;  bp = bp->next)
            {
                  if (bp == END_OF_CHAIN)
                  {
                        if (!warned)
                        {
                              error("Warning: log file is incomplete",
                                    NULL_PARG);
                              warned = TRUE;
                        }
                        break;
                  }
                  if (bp->block == block)
                  {
                        write(logfile, (char *) bp->data, bp->datasize);
                        break;
                  }
            }
      }
}

#endif

/*
 * Determine if a specific block is currently in one of the buffers.
 */
      static int
buffered(block)
      BLOCKNUM block;
{
      register struct buf *bp;
      register int h;

      h = BUFHASH(block);
      FOR_BUFS_IN_CHAIN(h, bp)
      {
            if (bp->block == block)
                  return (TRUE);
      }
      return (FALSE);
}

/*
 * Seek to a specified position in the file.
 * Return 0 if successful, non-zero if can't seek there.
 */
      public int
ch_seek(pos)
      register POSITION pos;
{
      BLOCKNUM new_block;
      POSITION len;

      len = ch_length();
      if (pos < ch_zero() || (len != NULL_POSITION && pos > len))
            return (1);

      new_block = pos / LBUFSIZE;
      if (!(ch_flags & CH_CANSEEK) && pos != ch_fpos && !buffered(new_block))
      {
            if (ch_fpos > pos)
                  return (1);
            while (ch_fpos < pos)
            {
                  if (ch_forw_get() == EOI)
                        return (1);
                  if (ABORT_SIGS())
                        return (1);
            }
            return (0);
      }
      /*
       * Set read pointer.
       */
      ch_block = new_block;
      ch_offset = pos % LBUFSIZE;
      return (0);
}

/*
 * Seek to the end of the file.
 */
      public int
ch_end_seek()
{
      POSITION len;

      if (ch_flags & CH_CANSEEK)
            ch_fsize = filesize(ch_file);

      len = ch_length();
      if (len != NULL_POSITION)
            return (ch_seek(len));

      /*
       * Do it the slow way: read till end of data.
       */
      while (ch_forw_get() != EOI)
            if (ABORT_SIGS())
                  return (1);
      return (0);
}

/*
 * Seek to the beginning of the file, or as close to it as we can get.
 * We may not be able to seek there if input is a pipe and the
 * beginning of the pipe is no longer buffered.
 */
      public int
ch_beg_seek()
{
      register struct buf *bp, *firstbp;

      /*
       * Try a plain ch_seek first.
       */
      if (ch_seek(ch_zero()) == 0)
            return (0);

      /*
       * Can't get to position 0.
       * Look thru the buffers for the one closest to position 0.
       */
      firstbp = bp = ch_bufhead;
      if (bp == END_OF_CHAIN)
            return (1);
      while ((bp = bp->next) != END_OF_CHAIN)
            if (bp->block < firstbp->block)
                  firstbp = bp;
      ch_block = firstbp->block;
      ch_offset = 0;
      return (0);
}

/*
 * Return the length of the file, if known.
 */
      public POSITION
ch_length()
{
      if (ignore_eoi)
            return (NULL_POSITION);
      if (ch_flags & CH_HELPFILE)
            return (size_helpdata);
      return (ch_fsize);
}

/*
 * Return the current position in the file.
 */
      public POSITION
ch_tell()
{
      return (ch_block * LBUFSIZE) + ch_offset;
}

/*
 * Get the current char and post-increment the read pointer.
 */
      public int
ch_forw_get()
{
      register int c;

      c = ch_get();
      if (c == EOI)
            return (EOI);
      if (ch_offset < LBUFSIZE-1)
            ch_offset++;
      else
      {
            ch_block ++;
            ch_offset = 0;
      }
      return (c);
}

/*
 * Pre-decrement the read pointer and get the new current char.
 */
      public int
ch_back_get()
{
      if (ch_offset > 0)
            ch_offset --;
      else
      {
            if (ch_block <= 0)
                  return (EOI);
            if (!(ch_flags & CH_CANSEEK) && !buffered(ch_block-1))
                  return (EOI);
            ch_block--;
            ch_offset = LBUFSIZE-1;
      }
      return (ch_get());
}

/*
 * Set max amount of buffer space.
 * bufspace is in units of 1024 bytes.  -1 mean no limit.
 */
      public void
ch_setbufspace(bufspace)
      int bufspace;
{
      if (bufspace < 0)
            maxbufs = -1;
      else
      {
            maxbufs = ((bufspace * 1024) + LBUFSIZE-1) / LBUFSIZE;
            if (maxbufs < 1)
                  maxbufs = 1;
      }
}

/*
 * Flush (discard) any saved file state, including buffer contents.
 */
      public void
ch_flush()
{
      register struct buf *bp;

      if (!(ch_flags & CH_CANSEEK))
      {
            /*
             * If input is a pipe, we don't flush buffer contents,
             * since the contents can't be recovered.
             */
            ch_fsize = NULL_POSITION;
            return;
      }

      /*
       * Initialize all the buffers.
       */
      for (bp = ch_bufhead;  bp != END_OF_CHAIN;  bp = bp->next)
            bp->block = -1;

      /*
       * Figure out the size of the file, if we can.
       */
      ch_fsize = filesize(ch_file);

      /*
       * Seek to a known position: the beginning of the file.
       */
      ch_fpos = 0;
      ch_block = 0; /* ch_fpos / LBUFSIZE; */
      ch_offset = 0; /* ch_fpos % LBUFSIZE; */

#if 1
      /*
       * This is a kludge to workaround a Linux kernel bug: files in
       * /proc have a size of 0 according to fstat() but have readable 
       * data.  They are sometimes, but not always, seekable.
       * Force them to be non-seekable here.
       */
      if (ch_fsize == 0)
      {
            ch_fsize = NULL_POSITION;
            ch_flags &= ~CH_CANSEEK;
      }
#endif

      if (lseek(ch_file, (off_t)0, 0) == BAD_LSEEK)
      {
            /*
             * Warning only; even if the seek fails for some reason,
             * there's a good chance we're at the beginning anyway.
             * {{ I think this is bogus reasoning. }}
             */
            error("seek error to 0", NULL_PARG);
      }
}

/*
 * Allocate a new buffer.
 * The buffer is added to the tail of the buffer chain.
 */
      static int
ch_addbuf()
{
      register struct buf *bp;

      /*
       * Allocate and initialize a new buffer and link it 
       * onto the tail of the buffer list.
       */
      bp = (struct buf *) calloc(1, sizeof(struct buf));
      if (bp == NULL)
            return (1);
      ch_nbufs++;
      bp->block = -1;
      bp->next = END_OF_CHAIN;
      bp->prev = ch_buftail;
      ch_buftail->next = bp;
      ch_buftail = bp;
      HASH_INS(bp, 0);
      return (0);
}

/*
 *
 */
      static void
init_hashtbl()
{
      register int h;

      for (h = 0;  h < BUFHASH_SIZE;  h++)
      {
            thisfile->hashtbl[h].buf_hnext = END_OF_HCHAIN(h);
            thisfile->hashtbl[h].buf_hprev = END_OF_HCHAIN(h);
      }
}

/*
 * Delete all buffers for this file.
 */
      static void
ch_delbufs()
{
      register struct buf *bp;

      while (ch_bufhead != END_OF_CHAIN)
      {
            bp = ch_bufhead;
            bp->next->prev = bp->prev;;
            bp->prev->next = bp->next;
            free(bp);
      }
      ch_nbufs = 0;
      init_hashtbl();
}

/*
 * Is it possible to seek on a file descriptor?
 */
      public int
seekable(f)
      int f;
{
#if MSDOS_COMPILER
      extern int fd0;
      if (f == fd0 && !isatty(fd0))
      {
            /*
             * In MS-DOS, pipes are seekable.  Check for
             * standard input, and pretend it is not seekable.
             */
            return (0);
      }
#endif
      return (lseek(f, (off_t)1, 0) != BAD_LSEEK);
}

/*
 * Initialize file state for a new file.
 */
      public void
ch_init(f, flags)
      int f;
      int flags;
{
      /*
       * See if we already have a filestate for this file.
       */
      thisfile = (struct filestate *) get_filestate(curr_ifile);
      if (thisfile == NULL)
      {
            /*
             * Allocate and initialize a new filestate.
             */
            thisfile = (struct filestate *) 
                        calloc(1, sizeof(struct filestate));
            thisfile->buf_next = thisfile->buf_prev = END_OF_CHAIN;
            thisfile->nbufs = 0;
            thisfile->flags = 0;
            thisfile->fpos = 0;
            thisfile->block = 0;
            thisfile->offset = 0;
            thisfile->file = -1;
            thisfile->fsize = NULL_POSITION;
            ch_flags = flags;
            init_hashtbl();
            /*
             * Try to seek; set CH_CANSEEK if it works.
             */
            if ((flags & CH_CANSEEK) && !seekable(f))
                  ch_flags &= ~CH_CANSEEK;
            set_filestate(curr_ifile, (void *) thisfile);
      }
      if (thisfile->file == -1)
            thisfile->file = f;
      ch_flush();
}

/*
 * Close a filestate.
 */
      public void
ch_close()
{
      int keepstate = FALSE;

      if (ch_flags & (CH_CANSEEK|CH_POPENED|CH_HELPFILE))
      {
            /*
             * We can seek or re-open, so we don't need to keep buffers.
             */
            ch_delbufs();
      } else
            keepstate = TRUE;
      if (!(ch_flags & CH_KEEPOPEN))
      {
            /*
             * We don't need to keep the file descriptor open
             * (because we can re-open it.)
             * But don't really close it if it was opened via popen(),
             * because pclose() wants to close it.
             */
            if (!(ch_flags & (CH_POPENED|CH_HELPFILE)))
                  close(ch_file);
            ch_file = -1;
      } else
            keepstate = TRUE;
      if (!keepstate)
      {
            /*
             * We don't even need to keep the filestate structure.
             */
            free(thisfile);
            thisfile = NULL;
            set_filestate(curr_ifile, (void *) NULL);
      }
}

/*
 * Return ch_flags for the current file.
 */
      public int
ch_getflags()
{
      return (ch_flags);
}

#if 0
      public void
ch_dump(struct filestate *fs)
{
      struct buf *bp;
      unsigned char *s;

      if (fs == NULL)
      {
            printf(" --no filestate\n");
            return;
      }
      printf(" file %d, flags %x, fpos %x, fsize %x, blk/off %x/%x\n",
            fs->file, fs->flags, fs->fpos, 
            fs->fsize, fs->block, fs->offset);
      printf(" %d bufs:\n", fs->nbufs);
      for (bp = fs->buf_next; bp != (struct buf *)fs;  bp = bp->next)
      {
            printf("%x: blk %x, size %x \"",
                  bp, bp->block, bp->datasize);
            for (s = bp->data;  s < bp->data + 30;  s++)
                  if (*s >= ' ' && *s < 0x7F)
                        printf("%c", *s);
                  else
                        printf(".");
            printf("\"\n");
      }
}
#endif

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