/* 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 source tree.
 */
/* 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)
 */
//config:config TAIL
//config:       bool "tail (6.8 kb)"
//config:       default y
//config:       help
//config:       tail is used to print the last specified number of lines
//config:       from files.
//config:
//config:config FEATURE_FANCY_TAIL
//config:       bool "Enable -q, -s, -v, and -F options"
//config:       default y
//config:       depends on TAIL
//config:       help
//config:       These options are provided by GNU tail, but
//config:       are not specified in the SUSv3 standard:
//config:               -q      Never output headers giving file names
//config:               -s SEC  Wait SEC seconds between reads with -f
//config:               -v      Always output headers giving file names
//config:               -F      Same as -f, but keep retrying

//applet:IF_TAIL(APPLET(tail, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_TAIL) += tail.o

/* 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 */

//usage:#define tail_trivial_usage
//usage:       "[OPTIONS] [FILE]..."
//usage:#define tail_full_usage "\n\n"
//usage:       "Print last 10 lines of FILEs (or stdin) to.\n"
//usage:       "With more than one FILE, precede each with a filename header.\n"
//usage:     "\n        -c [+]N[bkm]    Print last N bytes"
//usage:     "\n        -n N[bkm]       Print last N lines"
//usage:     "\n        -n +N[bkm]      Start on Nth line and print the rest"
//usage:     "\n                        (b:*512 k:*1024 m:*1024^2)"
//usage:        IF_FEATURE_FANCY_TAIL(
//usage:     "\n        -q              Never print headers"
//usage:     "\n        -v              Always print headers"
//usage:        )
//usage:     "\n        -f              Print data as file grows"
//usage:        IF_FEATURE_FANCY_TAIL(
//usage:     "\n        -F              Same as -f, but keep retrying"
//usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
//usage:        )
//usage:
//usage:#define tail_example_usage
//usage:       "$ tail -n 1 /etc/resolv.conf\n"
//usage:       "nameserver 10.0.0.1\n"

#include "libbb.h"
#include "common_bufsiz.h"

struct globals {
        bool from_top;
        bool exitcode;
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { setup_common_bufsiz(); } while (0)

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;

        r = full_read(fd, buf, count);
        if (r < 0) {
                bb_simple_perror_msg(bb_msg_read_error);
                G.exitcode = EXIT_FAILURE;
        }

        return r;
}

#define header_fmt_str "\n==> %s <==\n"

static unsigned eat_num(const char *p)
{
        if (*p == '-')
                p++;
        else if (*p == '+') {
                p++;
                G.from_top = 1;
        }
        return xatou_sfx(p, bkm_suffixes);
}

int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tail_main(int argc, char **argv)
{
        unsigned count = 10;
        unsigned sleep_period = 1;
        const char *str_c, *str_n;

        char *tailbuf;
        size_t tailbufsize;
        unsigned header_threshold = 1;
        unsigned nfiles;
        int i, opt;

        int *fds;
        const char *fmt;
        int prev_fd;

        INIT_G();

#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
        /* Allow legacy syntax of an initial numeric option without -n. */
        if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
         && isdigit(argv[1][1])
        ) {
                count = eat_num(argv[1]);
                argv++;
                argc--;
        }
#endif

        /* -s NUM, -F imlies -f */
        opt = getopt32(argv, IF_FEATURE_FANCY_TAIL("^")
                        "fc:n:"IF_FEATURE_FANCY_TAIL("qs:+vF")
                        IF_FEATURE_FANCY_TAIL("\0" "Ff"),
                        &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period)
        );
#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
        /* q: make it impossible for nfiles to be > header_threshold */
        if (opt & 0x8) header_threshold = UINT_MAX; // -q
        //if (opt & 0x10) // -s
        if (opt & 0x20) header_threshold = 0; // -v
# define FOLLOW_RETRY (opt & 0x40)
#else
# define FOLLOW_RETRY 0
#endif
        argc -= optind;
        argv += optind;

        /* open all the files */
        fds = xmalloc(sizeof(fds[0]) * (argc + 1));
        if (!argv[0]) {
                struct stat statbuf;

                if (fstat(STDIN_FILENO, &statbuf) == 0
                 && S_ISFIFO(statbuf.st_mode)
                ) {
                        opt &= ~1; /* clear FOLLOW */
                }
                argv[0] = (char *) bb_msg_standard_input;
        }
        nfiles = i = 0;
        do {
                int fd = open_or_warn_stdin(argv[i]);
                if (fd < 0 && !FOLLOW_RETRY) {
                        G.exitcode = EXIT_FAILURE;
                        continue;
                }
                fds[nfiles] = fd;
                argv[nfiles++] = argv[i];
        } while (++i < argc);

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

        /* prepare the buffer */
        tailbufsize = BUFSIZ;
        if (!G.from_top && COUNT_BYTES) {
                if (tailbufsize < count + BUFSIZ) {
                        tailbufsize = count + BUFSIZ;
                }
        }
        /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
         * (In fact, it doesn't need ANY memory). So delay allocation.
         */
        tailbuf = NULL;

        /* tail the files */

        fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
        i = 0;
        do {
                char *buf;
                int taillen;
                int newlines_seen;
                unsigned seen;
                int nread;
                int fd = fds[i];

                if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
                        continue; /* may happen with -F */

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

                if (!G.from_top) {
                        off_t current = lseek(fd, 0, SEEK_END);
                        if (current > 0) {
                                unsigned off;
                                if (COUNT_BYTES) {
                                /* Optimizing count-bytes case if the file is seekable.
                                 * Beware of backing up too far.
                                 * Also we exclude files with size 0 (because of /proc/xxx) */
                                        if (count == 0)
                                                continue; /* showing zero bytes is easy :) */
                                        current -= count;
                                        if (current < 0)
                                                current = 0;
                                        xlseek(fd, current, SEEK_SET);
                                        bb_copyfd_size(fd, STDOUT_FILENO, count);
                                        continue;
                                }
#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
                                /* Optimizing count-lines case if the file is seekable.
                                 * We assume the lines are <64k.
                                 * (Users complain that tail takes too long
                                 * on multi-gigabyte files) */
                                off = (count | 0xf); /* for small counts, be more paranoid */
                                if (off > (INT_MAX / (64*1024)))
                                        off = (INT_MAX / (64*1024));
                                current -= off * (64*1024);
                                if (current < 0)
                                        current = 0;
                                xlseek(fd, current, SEEK_SET);
#endif
                        }
                }

                if (!tailbuf)
                        tailbuf = xmalloc(tailbufsize);

                buf = tailbuf;
                taillen = 0;
                /* "We saw 1st line/byte".
                 * Used only by +N code ("start from Nth", 1-based): */
                seen = 1;
                newlines_seen = 0;
                while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
                        if (G.from_top) {
                                int nwrite = nread;
                                if (seen < count) {
                                        /* We need to skip a few more bytes/lines */
                                        if (COUNT_BYTES) {
                                                nwrite -= (count - seen);
                                                seen += nread;
                                        } else {
                                                char *s = buf;
                                                do {
                                                        --nwrite;
                                                        if (*s++ == '\n' && ++seen == count) {
                                                                break;
                                                        }
                                                } while (nwrite);
                                        }
                                }
                                if (nwrite > 0)
                                        xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
                        } else if (count) {
                                if (COUNT_BYTES) {
                                        taillen += nread;
                                        if (taillen > (int)count) {
                                                memmove(tailbuf, tailbuf + taillen - count, count);
                                                taillen = count;
                                        }
                                } else {
                                        int k = nread;
                                        int newlines_in_buf = 0;

                                        do { /* count '\n' in last read */
                                                k--;
                                                if (buf[k] == '\n') {
                                                        newlines_in_buf++;
                                                }
                                        } while (k);

                                        if (newlines_seen + newlines_in_buf < (int)count) {
                                                newlines_seen += newlines_in_buf;
                                                taillen += nread;
                                        } else {
                                                int extra = (buf[nread-1] != '\n');
                                                char *s;

                                                k = newlines_seen + newlines_in_buf + extra - count;
                                                s = tailbuf;
                                                while (k) {
                                                        if (*s == '\n') {
                                                                k--;
                                                        }
                                                        s++;
                                                }
                                                taillen += nread - (s - tailbuf);
                                                memmove(tailbuf, s, taillen);
                                                newlines_seen = count - extra;
                                        }
                                        if (tailbufsize < (size_t)taillen + BUFSIZ) {
                                                tailbufsize = taillen + BUFSIZ;
                                                tailbuf = xrealloc(tailbuf, tailbufsize);
                                        }
                                }
                                buf = tailbuf + taillen;
                        }
                } /* while (tail_read() > 0) */
                if (!G.from_top) {
                        xwrite(STDOUT_FILENO, tailbuf, taillen);
                }
        } while (++i < nfiles);
        prev_fd = fds[i-1];

        tailbuf = xrealloc(tailbuf, BUFSIZ);

        fmt = NULL;

        if (FOLLOW) while (1) {
                sleep(sleep_period);

                i = 0;
                do {
                        int nread;
                        const char *filename = argv[i];
                        int fd = fds[i];
                        int new_fd = -1;
                        struct stat sbuf;

                        if (FOLLOW_RETRY) {
                                struct stat fsbuf;

                                if (fd < 0
                                 || fstat(fd, &fsbuf) < 0
                                 || stat(filename, &sbuf) < 0
                                 || fsbuf.st_dev != sbuf.st_dev
                                 || fsbuf.st_ino != sbuf.st_ino
                                ) {
                                        /* Looks like file has been created/renamed/deleted */
                                        new_fd = open(filename, O_RDONLY);
                                        if (new_fd >= 0) {
                                                bb_error_msg("%s has %s; following end of new file",
                                                        filename, (fd < 0) ? "appeared" : "been replaced"
                                                );
                                                if (fd < 0) {
                                                        /* No previously open fd for this file,
                                                         * start using new_fd immediately. */
                                                        fds[i] = fd = new_fd;
                                                        new_fd = -1;
                                                }
                                        } else if (fd >= 0) {
                                                bb_perror_msg("%s has been renamed or deleted", filename);
                                        }
                                }
                        }
                        if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
                                continue;
                        if (nfiles > header_threshold) {
                                fmt = header_fmt_str;
                        }
                        for (;;) {
                                /* tail -f keeps following files even if they are truncated */
                                /* /proc files report zero st_size, don't lseek them */
                                if (fstat(fd, &sbuf) == 0
                                 /* && S_ISREG(sbuf.st_mode) TODO? */
                                 && sbuf.st_size > 0
                                ) {
                                        off_t current = lseek(fd, 0, SEEK_CUR);
                                        if (sbuf.st_size < current) {
                                                //bb_perror_msg("%s: file truncated", filename); - says coreutils 8.32
                                                xlseek(fd, 0, SEEK_SET);
                                        }
                                }

                                nread = tail_read(fd, tailbuf, BUFSIZ);
                                if (nread <= 0) {
                                        if (new_fd < 0)
                                                break;
                                        /* Switch to "tail -F"ing the new file */
                                        xmove_fd(new_fd, fd);
                                        new_fd = -1;
                                        continue;
                                }
                                if (fmt && (fd != prev_fd)) {
                                        tail_xprint_header(fmt, filename);
                                        fmt = NULL;
                                        prev_fd = fd;
                                }
                                xwrite(STDOUT_FILENO, tailbuf, nread);
                        }
                } while (++i < nfiles);
        } /* while (1) */

        if (ENABLE_FEATURE_CLEAN_UP) {
                free(fds);
                free(tailbuf);
        }
        return G.exitcode;
}