usr.bin/tail/forward.c

/*-
 * Copyright (c) 1991 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 */

#ifndef lint
static char sccsid[] = "@(#)forward.c   5.4 (Berkeley) 2/12/92";
#endif /* not lint */

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "extern.h"

static void rlines __P((FILE *, long, struct stat *));

/*
 * 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(fp, style, off, sbp)
        FILE *fp;
        enum STYLE style;
        long off;
        struct stat *sbp;
{
        register int ch;
        struct timeval second;
        fd_set zero;

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

        /*
         * We pause for one second after displaying any data that has
         * accumulated since we read the file.
         */
        if (fflag) {
                FD_ZERO(&zero);
                second.tv_sec = 1;
                second.tv_usec = 0;
        }

        for (;;) {
                while ((ch = getc(fp)) != EOF)
                        if (putchar(ch) == EOF)
                                oerr();
                if (ferror(fp))
                        ierr();
                (void)fflush(stdout);
                if (!fflag)
                        break;
                /* Sleep is eight system calls.  Do it fast. */
                if (select(0, &zero, &zero, &zero, &second) == -1)
                        err("select: %s", strerror(errno));
                clearerr(fp);
        }
}

/*
 * rlines -- display the last offset lines of the file.
 */
static void
rlines(fp, off, sbp)
        FILE *fp;
        long off;
        struct stat *sbp;
{
        register off_t size;
        register char *p;

        if (!(size = sbp->st_size))
                return;

        if ((p = mmap(NULL,
            size, PROT_READ, MAP_FILE, fileno(fp), (off_t)0)) == (caddr_t)-1)
                err("%s", strerror(errno));

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

        /* Set the file pointer to reflect the length displayed. */
        size = sbp->st_size - size;
        WR(p, size);
        if (fseek(fp, sbp->st_size, SEEK_SET) == -1)
                ierr();
}