/*      $OpenBSD: forward.c,v 1.33 2019/06/28 13:35:04 deraadt Exp $    */
/*      $NetBSD: forward.c,v 1.7 1996/02/13 16:49:10 ghudson 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/types.h>
#include <sys/stat.h>
#include <sys/event.h>

#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

static int rlines(struct tailfile *, off_t);
static inline void tfprint(FILE *fp);
static int tfqueue(struct tailfile *tf);
static const struct timespec *tfreopen(struct tailfile *tf);

static int kq = -1;

/*
 * 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     step back until the correct offset is reached.
 *      NOREG   cyclically read lines into a wrap-around array of buffers
 */
void
forward(struct tailfile *tf, int nfiles, enum STYLE style, off_t origoff)
{
        int ch;
        struct tailfile *ctf, *ltf;
        struct kevent ke;
        const struct timespec *ts = NULL;
        int i;
        int nevents;

        if (nfiles < 1)
                return;

        if (fflag && (kq = kqueue()) == -1)
                warn("kqueue");

        for (i = 0; i < nfiles; i++) {
                off_t off = origoff;
                if (nfiles > 1)
                        printfname(tf[i].fname);

                switch(style) {
                case FBYTES:
                        if (off == 0)
                                break;
                        if (S_ISREG(tf[i].sb.st_mode)) {
                                if (tf[i].sb.st_size < off)
                                        off = tf[i].sb.st_size;
                                if (fseeko(tf[i].fp, off, SEEK_SET) == -1) {
                                        ierr(tf[i].fname);
                                        return;
                                }
                        } else while (off--)
                                if ((ch = getc(tf[i].fp)) == EOF) {
                                        if (ferror(tf[i].fp)) {
                                                ierr(tf[i].fname);
                                                return;
                                        }
                                        break;
                                }
                        break;
                case FLINES:
                        if (off == 0)
                                break;
                        for (;;) {
                                if ((ch = getc(tf[i].fp)) == EOF) {
                                        if (ferror(tf[i].fp)) {
                                                ierr(tf[i].fname);
                                                return;
                                        }
                                        break;
                                }
                                if (ch == '\n' && !--off)
                                        break;
                        }
                        break;
                case RBYTES:
                        if (S_ISREG(tf[i].sb.st_mode)) {
                                if (tf[i].sb.st_size >= off &&
                                    fseeko(tf[i].fp, -off, SEEK_END) == -1) {
                                        ierr(tf[i].fname);
                                        return;
                                }
                        } else if (off == 0) {
                                while (getc(tf[i].fp) != EOF)
                                        ;
                                if (ferror(tf[i].fp)) {
                                        ierr(tf[i].fname);
                                        return;
                                }
                        } else {
                                if (bytes(&(tf[i]), off))
                                        return;
                        }
                        break;
                case RLINES:
                        if (S_ISREG(tf[i].sb.st_mode)) {
                                if (!off) {
                                        if (fseeko(tf[i].fp, (off_t)0,
                                            SEEK_END) == -1) {
                                                ierr(tf[i].fname);
                                                return;
                                        }
                                } else if (rlines(&(tf[i]), off) != 0)
                                        lines(&(tf[i]), off);
                        } else if (off == 0) {
                                while (getc(tf[i].fp) != EOF)
                                        ;
                                if (ferror(tf[i].fp)) {
                                        ierr(tf[i].fname);
                                        return;
                                }
                        } else {
                                if (lines(&(tf[i]), off))
                                        return;
                        }
                        break;
                default:
                        err(1, "Unsupported style");
                }

                tfprint(tf[i].fp);
                if (fflag && tfqueue(&(tf[i])) == -1)
                        warn("Unable to follow %s", tf[i].fname);

        }
        ltf = &(tf[i-1]);

        (void)fflush(stdout);
        if (!fflag || kq == -1)
                return;

        while (1) {
                if ((nevents = kevent(kq, NULL, 0, &ke, 1, ts)) <= 0) {
                        if (errno == EINTR) {
                                close(kq);
                                return;
                        }
                }

                ctf = ke.udata;
                if (nevents > 0) {
                        if (ke.filter == EVFILT_READ) {
                                if (ctf != ltf) {
                                        printfname(ctf->fname);
                                        ltf = ctf;
                                }
                                clearerr(ctf->fp);
                                tfprint(ctf->fp);
                                if (ferror(ctf->fp)) {
                                        ierr(ctf->fname);
                                        fclose(ctf->fp);
                                        warn("Lost file %s", ctf->fname);
                                        continue;
                                }
                                (void)fflush(stdout);
                                clearerr(ctf->fp);
                        } else if (ke.filter == EVFILT_VNODE) {
                                if (ke.fflags & (NOTE_DELETE | NOTE_RENAME)) {
                                        /*
                                         * File was deleted or renamed.
                                         *
                                         * Continue to look at it until
                                         * a new file reappears with
                                         * the same name. 
                                         */
                                        (void) tfreopen(ctf);
                                } else if (ke.fflags & NOTE_TRUNCATE) {
                                        warnx("%s has been truncated, "
                                            "resetting.", ctf->fname);
                                        fpurge(ctf->fp);
                                        rewind(ctf->fp);
                                }
                        }
                }
                ts = tfreopen(NULL);
        }
}

/*
 * rlines -- display the last offset lines of the file.
 */
static int
rlines(struct tailfile *tf, off_t off)
{
        off_t pos;
        int ch;

        pos = tf->sb.st_size;
        if (pos == 0)
                return (0);

        /*
         * Position before char.
         * Last char is special, ignore it whether newline or not.
         */
        pos -= 2;
        ch = EOF;
        for (; off > 0 && pos >= 0; pos--) {
                /* A seek per char isn't a problem with a smart stdio */
                if (fseeko(tf[0].fp, pos, SEEK_SET) == -1) {
                        ierr(tf->fname);
                        return (1);
                }
                if ((ch = getc(tf[0].fp)) == '\n')
                        off--;
                else if (ch == EOF) {
                        if (ferror(tf[0].fp)) {
                                ierr(tf->fname);
                                return (1);
                        }
                        break;
                }
        }
        /* If we read until start of file, put back last read char */
        if (pos < 0 && off > 0 && ch != EOF && ungetc(ch, tf[0].fp) == EOF) {
                ierr(tf->fname);
                return (1);
        }

        while (!feof(tf[0].fp) && (ch = getc(tf[0].fp)) != EOF)
                if (putchar(ch) == EOF)
                        oerr();
        if (ferror(tf[0].fp)) {
                ierr(tf->fname);
                return (1);
        }

        return (0);
}

static inline void
tfprint(FILE *fp)
{
        int ch;

        while (!feof(fp) && (ch = getc(fp)) != EOF)
                if (putchar(ch) == EOF)
                        oerr();
}

static int
tfqueue(struct tailfile *tf)
{
        struct kevent ke[2];
        int i = 1;

        if (kq < 0) {
                errno = EBADF;
                return -1;
        }

        EV_SET(&(ke[0]), fileno(tf->fp), EVFILT_READ,
            EV_ENABLE | EV_ADD | EV_CLEAR, 0, 0, tf);

        if (S_ISREG(tf->sb.st_mode)) {
                i = 2;
                EV_SET(&(ke[1]), fileno(tf->fp), EVFILT_VNODE,
                    EV_ENABLE | EV_ADD | EV_CLEAR,
                    NOTE_DELETE | NOTE_RENAME | NOTE_TRUNCATE,
                    0, tf);
        }
        if (kevent(kq, ke, i, NULL, 0, NULL) == -1) {
                ierr(tf->fname);
                return -1;
        }
        return 0;
}

#define AFILESINCR 8
static const struct timespec *
tfreopen(struct tailfile *tf) {
        static struct tailfile          **reopen = NULL;
        static int                        nfiles = 0, afiles = 0;
        static const struct timespec      ts = {1, 0};

        struct stat                       sb;
        struct tailfile                 **treopen, *ttf;
        int                               i;

        if (tf && !(tf->fp == stdin) &&
            ((stat(tf->fname, &sb) != 0) || sb.st_ino != tf->sb.st_ino)) {
                if (afiles < ++nfiles) {
                        afiles += AFILESINCR;
                        treopen = reallocarray(reopen, afiles, sizeof(*reopen));
                        if (treopen)
                                reopen = treopen;
                        else
                                afiles -= AFILESINCR;
                }
                if (nfiles <= afiles) {
                        for (i = 0; i < nfiles - 1; i++)
                                if (strcmp(reopen[i]->fname, tf->fname) == 0)
                                        break;
                        if (i < nfiles - 1)
                                nfiles--;
                        else
                                reopen[nfiles-1] = tf;
                } else {
                        warnx("Lost track of %s", tf->fname);
                        nfiles--;
                }
        }

        for (i = 0; i < nfiles; i++) {
                ttf = reopen[i];
                if (stat(ttf->fname, &sb) == -1)
                        continue;
                if (sb.st_ino != ttf->sb.st_ino) {
                        (void) memcpy(&(ttf->sb), &sb, sizeof(ttf->sb));
                        ttf->fp = freopen(ttf->fname, "r", ttf->fp);
                        if (ttf->fp == NULL)
                                ierr(ttf->fname);
                        else {
                                warnx("%s has been replaced, reopening.",
                                    ttf->fname);
                                tfqueue(ttf);
                        }
                }
                reopen[i] = reopen[--nfiles];
        }

        return nfiles ? &ts : NULL;
}