ch.c

/*
 * Copyright (C) 1984-2022  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, 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

#if HAVE_STAT_INO
#include <sys/stat.h>
extern dev_t curr_dev;
extern ino_t curr_ino;
#endif

#if HAVE_PROCFS
#include <sys/statfs.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".
 */
struct bufnode {
    struct bufnode *next, *prev;
    struct bufnode *hnext, *hprev;
};

#define LBUFSIZE        8192
struct buf {
    struct bufnode node;
    BLOCKNUM block;
    unsigned int datasize;
    unsigned char data[LBUFSIZE];
};
#define bufnode_buf(bn)  ((struct buf *) bn)

/*
 * The file state is maintained in a filestate structure.
 * A pointer to the filestate is kept in the ifile structure.
 */
#define BUFHASH_SIZE    1024
struct filestate {
    struct bufnode buflist;
    struct bufnode hashtbl[BUFHASH_SIZE];
    int file;
    int flags;
    POSITION fpos;
    int nbufs;
    BLOCKNUM block;
    unsigned int offset;
    POSITION fsize;
};

#define ch_bufhead      thisfile->buflist.next
#define ch_buftail      thisfile->buflist.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    (&thisfile->buflist)
#define END_OF_HCHAIN(h) (&thisfile->hashtbl[h])
#define BUFHASH(blk)    ((blk) & (BUFHASH_SIZE-1))

/*
 * Macros to manipulate the list of buffers in thisfile->buflist.
 */
#define FOR_BUFS(bn) \
    for (bn = ch_bufhead;  bn != END_OF_CHAIN;  bn = bn->next)

#define BUF_RM(bn) \
    (bn)->next->prev = (bn)->prev; \
    (bn)->prev->next = (bn)->next;

#define BUF_INS_HEAD(bn) \
    (bn)->next = ch_bufhead; \
    (bn)->prev = END_OF_CHAIN; \
    ch_bufhead->prev = (bn); \
    ch_bufhead = (bn);

#define BUF_INS_TAIL(bn) \
    (bn)->next = END_OF_CHAIN; \
    (bn)->prev = ch_buftail; \
    ch_buftail->next = (bn); \
    ch_buftail = (bn);

/*
 * Macros to manipulate the list of buffers in thisfile->hashtbl[n].
 */
#define FOR_BUFS_IN_CHAIN(h,bn) \
    for (bn = thisfile->hashtbl[h].hnext;  \
         bn != END_OF_HCHAIN(h);  bn = bn->hnext)

#define BUF_HASH_RM(bn) \
    (bn)->hnext->hprev = (bn)->hprev; \
    (bn)->hprev->hnext = (bn)->hnext;

#define BUF_HASH_INS(bn,h) \
    (bn)->hnext = thisfile->hashtbl[h].hnext; \
    (bn)->hprev = END_OF_HCHAIN(h); \
    thisfile->hashtbl[h].hnext->hprev = (bn); \
    thisfile->hashtbl[h].hnext = (bn);

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

extern int autobuf;
extern int sigs;
extern int secure;
extern int screen_trashed;
extern int follow_mode;
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.
 */
    int
ch_get(VOID_PARAM)
{
    struct buf *bp;
    struct bufnode *bn;
    int n;
    int slept;
    int h;
    POSITION pos;
    POSITION len;

    if (thisfile == NULL)
        return (EOI);

    /*
     * Quick check for the common case where
     * the desired char is in the head buffer.
     */
    if (ch_bufhead != END_OF_CHAIN)
    {
        bp = bufnode_buf(ch_bufhead);
        if (ch_block == bp->block && ch_offset < bp->datasize)
            return bp->data[ch_offset];
    }

    slept = FALSE;

    /*
     * Look for a buffer holding the desired block.
     */
    h = BUFHASH(ch_block);
    FOR_BUFS_IN_CHAIN(h, bn)
    {
        bp = bufnode_buf(bn);
        if (bp->block == ch_block)
        {
            if (ch_offset >= bp->datasize)
                /*
                 * Need more data in this buffer.
                 */
                break;
            goto found;
        }
    }
    if (bn == END_OF_HCHAIN(h))
    {
        /*
         * 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 ||
            bufnode_buf(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;
        }
        bn = ch_buftail;
        bp = bufnode_buf(bn);
        BUF_HASH_RM(bn); /* Remove from old hash chain. */
        bp->block = ch_block;
        bp->datasize = 0;
        BUF_HASH_INS(bn, 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, SEEK_SET) == 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)
        (void)! 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);
            }
            sleep_ms(2); /* Reduce system load */
            slept = TRUE;

#if HAVE_STAT_INO
            if (follow_mode == FOLLOW_NAME)
            {
                /* See whether the file's i-number has changed,
                 * or the file has shrunk.
                 * If so, force the file to be closed and
                 * reopened. */
                struct stat st;
                POSITION curr_pos = ch_tell();
                int r = stat(get_filename(curr_ifile), &st);
                if (r == 0 && (st.st_ino != curr_ino ||
                    st.st_dev != curr_dev ||
                    (curr_pos != NULL_POSITION && st.st_size < curr_pos)))
                {
                    /* screen_trashed=2 causes
                     * make_display to reopen the file. */
                    screen_trashed = 2;
                    return (EOI);
                }
            }
#endif
        }
        if (sigs)
            return (EOI);
    }

    found:
    if (ch_bufhead != bn)
    {
        /*
         * Move the buffer to the head of the buffer chain.
         * This orders the buffer chain, most- to least-recently used.
         */
        BUF_RM(bn);
        BUF_INS_HEAD(bn);

        /*
         * Move to head of hash chain too.
         */
        BUF_HASH_RM(bn);
        BUF_HASH_INS(bn, 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(VOID_PARAM)
{
    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;
    free(namelogfile);
    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(VOID_PARAM)
{
    struct buf *bp;
    struct bufnode *bn;
    int warned = FALSE;
    BLOCKNUM block;
    BLOCKNUM nblocks;

    nblocks = (ch_fpos + LBUFSIZE - 1) / LBUFSIZE;
    for (block = 0;  block < nblocks;  block++)
    {
        int wrote = FALSE;
        FOR_BUFS(bn)
        {
            bp = bufnode_buf(bn);
            if (bp->block == block)
            {
                (void)! write(logfile, (char *) bp->data, bp->datasize);
                wrote = TRUE;
                break;
            }
        }
        if (!wrote && !warned)
        {
            error("Warning: log file is incomplete",
                NULL_PARG);
            warned = TRUE;
        }
    }
}

#endif

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

    h = BUFHASH(block);
    FOR_BUFS_IN_CHAIN(h, bn)
    {
        bp = bufnode_buf(bn);
        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)
    POSITION pos;
{
    BLOCKNUM new_block;
    POSITION len;

    if (thisfile == NULL)
        return (0);

    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(VOID_PARAM)
{
    POSITION len;

    if (thisfile == NULL)
        return (0);

    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 last position in the file that is currently buffered.
 */
    public int
ch_end_buffer_seek(VOID_PARAM)
{
    struct buf *bp;
    struct bufnode *bn;
    POSITION buf_pos;
    POSITION end_pos;

    if (thisfile == NULL || (ch_flags & CH_CANSEEK))
        return (ch_end_seek());

    end_pos = 0;
    FOR_BUFS(bn)
    {
        bp = bufnode_buf(bn);
        buf_pos = (bp->block * LBUFSIZE) + bp->datasize;
        if (buf_pos > end_pos)
            end_pos = buf_pos;
    }

    return (ch_seek(end_pos));
}

/*
 * 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(VOID_PARAM)
{
    struct bufnode *bn;
    struct bufnode *firstbn;

    /*
     * 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.
     */
    firstbn = ch_bufhead;
    if (firstbn == END_OF_CHAIN)
        return (1);
    FOR_BUFS(bn)
    {
        if (bufnode_buf(bn)->block < bufnode_buf(firstbn)->block)
            firstbn = bn;
    }
    ch_block = bufnode_buf(firstbn)->block;
    ch_offset = 0;
    return (0);
}

/*
 * Return the length of the file, if known.
 */
    public POSITION
ch_length(VOID_PARAM)
{
    if (thisfile == NULL)
        return (NULL_POSITION);
    if (ignore_eoi)
        return (NULL_POSITION);
    if (ch_flags & CH_HELPFILE)
        return (size_helpdata);
    if (ch_flags & CH_NODATA)
        return (0);
    return (ch_fsize);
}

/*
 * Return the current position in the file.
 */
    public POSITION
ch_tell(VOID_PARAM)
{
    if (thisfile == NULL)
        return (NULL_POSITION);
    return (ch_block * LBUFSIZE) + ch_offset;
}

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

    if (thisfile == NULL)
        return (EOI);
    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(VOID_PARAM)
{
    if (thisfile == NULL)
        return (EOI);
    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(VOID_PARAM)
{
    struct bufnode *bn;

    if (thisfile == NULL)
        return;

    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_BUFS(bn)
    {
        bufnode_buf(bn)->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 HAVE_PROCFS
    /*
     * 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)
    {
        struct statfs st;
        if (fstatfs(ch_file, &st) == 0)
        {
            if (st.f_type == PROC_SUPER_MAGIC)
            {
                ch_fsize = NULL_POSITION;
                ch_flags &= ~CH_CANSEEK;
            }
        }
    }
#endif

    if (lseek(ch_file, (off_t)0, SEEK_SET) == 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(VOID_PARAM)
{
    struct buf *bp;
    struct bufnode *bn;

    /*
     * 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;
    bn = &bp->node;

    BUF_INS_TAIL(bn);
    BUF_HASH_INS(bn, 0);
    return (0);
}

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

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

/*
 * Delete all buffers for this file.
 */
    static void
ch_delbufs(VOID_PARAM)
{
    struct bufnode *bn;

    while (ch_bufhead != END_OF_CHAIN)
    {
        bn = ch_bufhead;
        BUF_RM(bn);
        free(bufnode_buf(bn));
    }
    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, SEEK_SET) != BAD_LSEEK);
}

/*
 * Force EOF to be at the current read position.
 * This is used after an ignore_eof read, during which the EOF may change.
 */
    public void
ch_set_eof(VOID_PARAM)
{
    if (ch_fsize != NULL_POSITION && ch_fsize < ch_fpos)
        ch_fsize = ch_fpos;
}


/*
 * 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 *)
                ecalloc(1, sizeof(struct filestate));
        thisfile->buflist.next = thisfile->buflist.prev = END_OF_CHAIN;
        thisfile->nbufs = 0;
        thisfile->flags = flags;
        thisfile->fpos = 0;
        thisfile->block = 0;
        thisfile->offset = 0;
        thisfile->file = -1;
        thisfile->fsize = NULL_POSITION;
        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(VOID_PARAM)
{
    int keepstate = FALSE;

    if (thisfile == NULL)
        return;

    if ((ch_flags & (CH_CANSEEK|CH_POPENED|CH_HELPFILE)) && !(ch_flags & CH_KEEPOPEN))
    {
        /*
         * 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(VOID_PARAM)
{
    if (thisfile == NULL)
        return (0);
    return (ch_flags);
}

#if 0
    public void
ch_dump(struct filestate *fs)
{
    struct buf *bp;
    struct bufnode *bn;
    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 (bn = fs->next; bn != &fs->buflist;  bn = bn->next)
    {
        bp = bufnode_buf(bn);
        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