source: MondoRescue/branches/2.2.5/mindi-busybox/coreutils/tail.c@ 1772

/* vi: set sw=4 ts=4: */
/*
 * Mini tail implementation for busybox
 *
 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */

/* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
 *
 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
 * 1) mixing printf/write without fflush()ing stdout
 * 2) no check that any open files are present
 * 3) optstring had -q taking an arg
 * 4) no error checking on write in some cases, and a warning even then
 * 5) q and s interaction bug
 * 6) no check for lseek error
 * 7) lseek attempted when count==0 even if arg was +0 (from top)
 */

#include "libbb.h"

static const struct suffix_mult tail_suffixes[] = {
    { "b", 512 },
    { "k", 1024 },
    { "m", 1024*1024 },
    { }
};

struct globals {
    bool status;
};
#define G (*(struct globals*)&bb_common_bufsiz1)

static void tail_xprint_header(const char *fmt, const char *filename)
{
    if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
        bb_perror_nomsg_and_die();
}

static ssize_t tail_read(int fd, char *buf, size_t count)
{
    ssize_t r;
    off_t current;
    struct stat sbuf;

    /* (A good comment is missing here) */
    current = lseek(fd, 0, SEEK_CUR);
    /* /proc files report zero st_size, don't lseek them. */
    if (fstat(fd, &sbuf) == 0 && sbuf.st_size)
        if (sbuf.st_size < current)
            lseek(fd, 0, SEEK_SET);

    r = safe_read(fd, buf, count);
    if (r < 0) {
        bb_perror_msg(bb_msg_read_error);
        G.status = EXIT_FAILURE;
    }

    return r;
}

static const char header_fmt[] ALIGN1 = "\n==> %s <==\n";

static unsigned eat_num(const char *p)
{
    if (*p == '-')
        p++;
    else if (*p == '+') {
        p++;
        G.status = EXIT_FAILURE;
    }
    return xatou_sfx(p, tail_suffixes);
}

int tail_main(int argc, char **argv);
int tail_main(int argc, char **argv)
{
    unsigned count = 10;
    unsigned sleep_period = 1;
    bool from_top;
    int header_threshhold = 1;
    const char *str_c, *str_n;
    USE_FEATURE_FANCY_TAIL(const char *str_s;)

    char *tailbuf;
    size_t tailbufsize;
    int taillen = 0;
    int newline = 0;
    int nfiles, nread, nwrite, seen, i, opt;

    int *fds;
    char *s, *buf;
    const char *fmt;

#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
    /* Allow legacy syntax of an initial numeric option without -n. */
    if (argc >= 2 && (argv[1][0] == '+' || argv[1][0] == '-')
     && isdigit(argv[1][1])
    ) {
        /* replacing arg[0] with "-n" can segfault, so... */
        argv[1] = xasprintf("-n%s", argv[1]);
#if 0 /* If we ever decide to make tail NOFORK */
        char *s = alloca(strlen(argv[1]) + 3);
        sprintf(s, "-n%s", argv[1]);
        argv[1] = s;
#endif
    }
#endif

    opt = getopt32(argv, "fc:n:" USE_FEATURE_FANCY_TAIL("qs:v"),
            &str_c, &str_n USE_FEATURE_FANCY_TAIL(,&str_s));
#define FOLLOW (opt & 0x1)
#define COUNT_BYTES (opt & 0x2)
    //if (opt & 0x1) // -f
    if (opt & 0x2) count = eat_num(str_c); // -c
    if (opt & 0x4) count = eat_num(str_n); // -n
#if ENABLE_FEATURE_FANCY_TAIL
    if (opt & 0x8) header_threshhold = INT_MAX; // -q
    if (opt & 0x10) sleep_period = xatou(str_s); // -s
    if (opt & 0x20) header_threshhold = 0; // -v
#endif
    argc -= optind;
    argv += optind;
    from_top = G.status;

    /* open all the files */
    fds = xmalloc(sizeof(int) * (argc + 1));
    nfiles = i = 0;
    G.status = EXIT_SUCCESS;
    if (argc == 0) {
        struct stat statbuf;

        if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
            opt &= ~1; /* clear FOLLOW */
        }
        *argv = (char *) bb_msg_standard_input;
    }
    do {
        FILE* fil = fopen_or_warn_stdin(argv[i]);
        if (!fil) {
            G.status = EXIT_FAILURE;
            continue;
        }
        fds[nfiles] = fileno(fil);
        argv[nfiles++] = argv[i];
    } while (++i < argc);

    if (!nfiles)
        bb_error_msg_and_die("no files");

    tailbufsize = BUFSIZ;

    /* tail the files */
    if (!from_top && COUNT_BYTES) {
        if (tailbufsize < count) {
            tailbufsize = count + BUFSIZ;
        }
    }

    buf = tailbuf = xmalloc(tailbufsize);

    fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
    i = 0;
    do {
        /* Be careful.  It would be possible to optimize the count-bytes
         * case if the file is seekable.  If you do though, remember that
         * starting file position may not be the beginning of the file.
         * Beware of backing up too far.  See example in wc.c.
         */
        if (!(count | from_top) && lseek(fds[i], 0, SEEK_END) >= 0) {
            continue;
        }

        if (nfiles > header_threshhold) {
            tail_xprint_header(fmt, argv[i]);
            fmt = header_fmt;
        }

        buf = tailbuf;
        taillen = 0;
        seen = 1;
        newline = 0;

        while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
            if (from_top) {
                nwrite = nread;
                if (seen < count) {
                    if (COUNT_BYTES) {
                        nwrite -= (count - seen);
                        seen = count;
                    } else {
                        s = buf;
                        do {
                            --nwrite;
                            if (*s++ == '\n' && ++seen == count) {
                                break;
                            }
                        } while (nwrite);
                    }
                }
                xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
            } else if (count) {
                if (COUNT_BYTES) {
                    taillen += nread;
                    if (taillen > count) {
                        memmove(tailbuf, tailbuf + taillen - count, count);
                        taillen = count;
                    }
                } else {
                    int k = nread;
                    int nbuf = 0;

                    while (k) {
                        --k;
                        if (buf[k] == '\n') {
                            ++nbuf;
                        }
                    }

                    if (newline + nbuf < count) {
                        newline += nbuf;
                        taillen += nread;
                    } else {
                        int extra = 0;

                        if (buf[nread-1] != '\n')
                            extra = 1;
                        k = newline + nbuf + extra - count;
                        s = tailbuf;
                        while (k) {
                            if (*s == '\n') {
                                --k;
                            }
                            ++s;
                        }
                        taillen += nread - (s - tailbuf);
                        memmove(tailbuf, s, taillen);
                        newline = count - extra;
                    }
                    if (tailbufsize < taillen + BUFSIZ) {
                        tailbufsize = taillen + BUFSIZ;
                        tailbuf = xrealloc(tailbuf, tailbufsize);
                    }
                }
                buf = tailbuf + taillen;
            }
        }

        if (!from_top) {
            xwrite(STDOUT_FILENO, tailbuf, taillen);
        }

        taillen = 0;
    } while (++i < nfiles);

    buf = xrealloc(tailbuf, BUFSIZ);

    fmt = NULL;

    if (FOLLOW) while (1) {
        sleep(sleep_period);
        i = 0;
        do {
            if (nfiles > header_threshhold) {
                fmt = header_fmt;
            }
            while ((nread = tail_read(fds[i], buf, sizeof(buf))) > 0) {
                if (fmt) {
                    tail_xprint_header(fmt, argv[i]);
                    fmt = NULL;
                }
                xwrite(STDOUT_FILENO, buf, nread);
            }
        } while (++i < nfiles);
    }
    if (ENABLE_FEATURE_CLEAN_UP) {
        free(fds);
    }
    return G.status;
}