/* $NetBSD: forward.c,v 1.34 2024/01/14 17:37:32 christos Exp $ */

/* $NetBSD: forward.c,v 1.34 2024/01/14 17:37:32 christos Exp $ */

/*-
* Copyright (c) 1991, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Edward Sze-Tyan Wang.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/

#include <sys/cdefs.h>
#ifndef lint
#if 0
static char sccsid[] = "@(#)forward.c 8.1 (Berkeley) 6/6/93";
#endif
__RCSID("$NetBSD: forward.c,v 1.34 2024/01/14 17:37:32 christos Exp $");
#endif /* not lint */

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/event.h>

#include <limits.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "extern.h"

static int rlines(FILE *, off_t, struct stat *);

/* defines for inner loop actions */
#define USE_SLEEP 0
#define USE_KQUEUE 1
#define ADD_EVENTS 2

/*
* forward -- display the file, from an offset, forward.
*
* There are eight separate cases for this -- regular and non-regular
* files, by bytes or lines and from the beginning or end of the file.
*
* FBYTES byte offset from the beginning of the file
* REG seek
* NOREG read, counting bytes
*
* FLINES line offset from the beginning of the file
* REG read, counting lines
* NOREG read, counting lines
*
* RBYTES byte offset from the end of the file
* REG seek
* NOREG cyclically read characters into a wrap-around buffer
*
* RLINES
* REG mmap the file and step back until reach the correct offset.
* NOREG cyclically read lines into a wrap-around array of buffers
*/
void
forward(FILE *fp, enum STYLE style, off_t off, struct stat *sbp)
{
int ch, n;
int kq=-1, action=USE_SLEEP;
struct stat statbuf;
struct kevent ev[2];

switch(style) {
case FBYTES:
if (off == 0)
break;
if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
if (sbp->st_size < off)
off = sbp->st_size;
if (fseeko(fp, off, SEEK_SET) == -1) {
ierr();
return;
}
} else while (off--)
if ((ch = getc(fp)) == EOF) {
if (ferror(fp)) {
ierr();
return;
}
break;
}
break;
case FLINES:
if (off == 0)
break;
for (;;) {
if ((ch = getc(fp)) == EOF) {
if (ferror(fp)) {
ierr();
return;
}
break;
}
if (ch == '\n' && !--off)
break;
}
break;
case RBYTES:
if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
if (sbp->st_size >= off &&
fseeko(fp, -off, SEEK_END) == -1) {
ierr();
return;
}
} else if (off == 0) {
while (getc(fp) != EOF);
if (ferror(fp)) {
ierr();
return;
}
} else {
if (displaybytes(fp, off))
return;
}
break;
case RLINES:
if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
if (!off) {
if (fseek(fp, 0L, SEEK_END) == -1) {
ierr();
return;
}
} else {
if (rlines(fp, off, sbp))
return;
}
} else if (off == 0) {
while (getc(fp) != EOF);
if (ferror(fp)) {
ierr();
return;
}
} else {
if (displaylines(fp, off))
return;
}
break;
default:
break;
}

if (fflag) {
kq = kqueue();
if (kq < 0)
xerr(1, "kqueue");
action = ADD_EVENTS;
}

for (;;) {
while ((ch = getc(fp)) != EOF) {
if (putchar(ch) == EOF)
oerr();
}
if (ferror(fp)) {
ierr();
return;
}
(void)fflush(stdout);
if (!fflag)
break;

clearerr(fp);

switch (action) {
case ADD_EVENTS:
n = 0;

memset(ev, 0, sizeof(ev));
if (fflag == 2 && fp != stdin) {
EV_SET(&ev[n], fileno(fp), EVFILT_VNODE,
EV_ADD | EV_ENABLE | EV_CLEAR,
NOTE_DELETE | NOTE_RENAME, 0, 0);
n++;
}
EV_SET(&ev[n], fileno(fp), EVFILT_READ,
EV_ADD | EV_ENABLE, 0, 0, 0);
n++;

if (kevent(kq, ev, n, NULL, 0, NULL) == -1) {
close(kq);
kq = -1;
action = USE_SLEEP;
} else {
action = USE_KQUEUE;
}
break;

case USE_KQUEUE:
if (kevent(kq, NULL, 0, ev, 1, NULL) == -1)
xerr(1, "kevent");

if (ev[0].filter == EVFILT_VNODE) {
/* file was rotated, wait until it reappears */
action = USE_SLEEP;
} else if (ev[0].data < 0) {
/* file shrank, reposition to end */
if (fseek(fp, 0L, SEEK_END) == -1) {
ierr();
return;
}
}
break;

case USE_SLEEP:
/*
* We pause for one second after displaying any data
* that has accumulated since we read the file.
*/
(void) sleep(1);

if (fflag == 2 && fp != stdin &&
stat(fname, &statbuf) != -1) {
if (statbuf.st_ino != sbp->st_ino ||
statbuf.st_dev != sbp->st_dev ||
statbuf.st_rdev != sbp->st_rdev ||
statbuf.st_nlink == 0) {
fp = freopen(fname, "r", fp);
if (fp == NULL) {
ierr();
goto out;
}
*sbp = statbuf;
if (kq != -1)
action = ADD_EVENTS;
} else if (kq != -1)
action = USE_KQUEUE;
}
break;
}
}
out:
if (fflag && kq != -1)
close(kq);
}

/*
* rlines -- display the last offset lines of the file.
*
* Non-zero return means than a (non-fatal) error occurred.
*/
static int
rlines(FILE *fp, off_t off, struct stat *sbp)
{
off_t file_size;
off_t file_remaining;
char *p = NULL;
char *start = NULL;
off_t mmap_size;
off_t mmap_offset;
off_t mmap_remaining = 0;

#define MMAP_MAXSIZE (10 * 1024 * 1024)

if (!(file_size = sbp->st_size))
return 0;
file_remaining = file_size;

if (file_remaining > MMAP_MAXSIZE) {
mmap_size = MMAP_MAXSIZE;
mmap_offset = file_remaining - MMAP_MAXSIZE;
} else {
mmap_size = file_remaining;
mmap_offset = 0;
}

while (off) {
start = mmap(NULL, (size_t)mmap_size, PROT_READ,
MAP_FILE|MAP_SHARED, fileno(fp), mmap_offset);
if (start == MAP_FAILED) {
xerr(0, "%s", fname);
return 1;
}

mmap_remaining = mmap_size;
/* Last char is special, ignore whether newline or not. */
for (p = start + mmap_remaining - 1 ; --mmap_remaining ; )
if (*--p == '\n' && !--off) {
++p;
break;
}

file_remaining -= mmap_size - mmap_remaining;

if (off == 0)
break;

if (file_remaining == 0)
break;

if (munmap(start, mmap_size)) {
xerr(0, "%s", fname);
return 1;
}

if (mmap_offset >= MMAP_MAXSIZE) {
mmap_offset -= MMAP_MAXSIZE;
} else {
mmap_offset = 0;
mmap_size = file_remaining;
}
}

/*
* Output the (perhaps partial) data in this mmap'd block.
*/
WR(p, mmap_size - mmap_remaining);
file_remaining += mmap_size - mmap_remaining;
if (munmap(start, mmap_size)) {
xerr(0, "%s", fname);
return 1;
}

/*
* Set the file pointer to reflect the length displayed.
* This will cause the caller to redisplay the data if/when
* needed.
*/
if (fseeko(fp, file_remaining, SEEK_SET) == -1) {
ierr();
return 1;
}
return 0;
}