/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * John B. Roll Jr.
 *
 * 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.
 *
 * $xMach: xargs.c,v 1.6 2002/02/23 05:27:47 tim Exp $
 */

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/limits.h>
#include <sys/resource.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <langinfo.h>
#include <locale.h>
#include <paths.h>
#include <regex.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "pathnames.h"

static void     parse_input(int, char *[]);
static void     prerun(int, char *[]);
static int      prompt(void);
static void     run(char **);
static void     usage(void);
bool            strnsubst(char **, const char *, const char *, size_t);
static pid_t    xwait(int block, int *status);
static void     xexit(const char *, const int);
static void     waitchildren(const char *, int);
static void     pids_init(void);
static int      pids_empty(void);
static int      pids_full(void);
static void     pids_add(pid_t pid);
static int      pids_remove(pid_t pid);
static int      findslot(pid_t pid);
static int      findfreeslot(void);
static void     clearslot(int slot);

static char echo[] = _PATH_ECHO;
static char **av, **bxp, **ep, **endxp, **xp;
static char *argp, *bbp, *ebp, *inpline, *p, *replstr;
static const char *eofstr;
static long eoflen;
static int count, insingle, indouble, oflag, pflag, tflag, Rflag, rval, zflag;
static int cnt, Iflag, jfound, Lflag, Sflag, wasquoted, xflag;
static int curprocs, maxprocs;
static pid_t *childpids;

static volatile int childerr;

extern char **environ;

static const char *optstr = "+0E:I:J:L:n:oP:pR:S:s:rtx";

static const struct option long_options[] =
{
        {"exit",                no_argument,            NULL,   'x'},
        {"interactive",         no_argument,            NULL,   'p'},
        {"max-args",            required_argument,      NULL,   'n'},
        {"max-chars",           required_argument,      NULL,   's'},
        {"max-procs",           required_argument,      NULL,   'P'},
        {"no-run-if-empty",     no_argument,            NULL,   'r'},
        {"null",                no_argument,            NULL,   '0'},
        {"verbose",             no_argument,            NULL,   't'},

        {NULL,                  no_argument,            NULL,   0},
};

int
main(int argc, char *argv[])
{
        long arg_max;
        int ch, Jflag, nargs, nflag, nline;
        size_t linelen;
        struct rlimit rl;
        const char *errstr;

        inpline = replstr = NULL;
        ep = environ;
        eofstr = "";
        eoflen = 0;
        Jflag = nflag = 0;

        (void)setlocale(LC_ALL, "");

        /*
         * POSIX.2 limits the exec line length to ARG_MAX - 2K.  Running that
         * caused some E2BIG errors, so it was changed to ARG_MAX - 4K.  Given
         * that the smallest argument is 2 bytes in length, this means that
         * the number of arguments is limited to:
         *
         *       (ARG_MAX - 4K - LENGTH(utility + arguments)) / 2.
         *
         * We arbitrarily limit the number of arguments to 5000.  This is
         * allowed by POSIX.2 as long as the resulting minimum exec line is
         * at least LINE_MAX.  Realloc'ing as necessary is possible, but
         * probably not worthwhile.
         */
        nargs = 5000;
        if ((arg_max = sysconf(_SC_ARG_MAX)) == -1)
                errx(1, "sysconf(_SC_ARG_MAX) failed");
        nline = arg_max - 4 * 1024;
        while (*ep != NULL) {
                /* 1 byte for each '\0' */
                nline -= strlen(*ep++) + 1 + sizeof(*ep);
        }
        maxprocs = 1;
        while ((ch = getopt_long(argc, argv, optstr, long_options, NULL)) != -1)
                switch (ch) {
                case 'E':
                        eofstr = optarg;
                        eoflen = strlen(eofstr);
                        break;
                case 'I':
                        Jflag = 0;
                        Iflag = 1;
                        Lflag = 1;
                        replstr = optarg;
                        break;
                case 'J':
                        Iflag = 0;
                        Jflag = 1;
                        replstr = optarg;
                        break;
                case 'L':
                        Lflag = (int)strtonum(optarg, 1, INT_MAX, &errstr);
                        if (errstr)
                                errx(1, "-%c %s: %s", ch, optarg, errstr);
                        break;
                case 'n':
                        nflag = 1;
                        nargs = (int)strtonum(optarg, 1, arg_max, &errstr);
                        if (errstr)
                                errx(1, "-%c %s: %s", ch, optarg, errstr);
                        break;
                case 'o':
                        oflag = 1;
                        break;
                case 'P':
                        maxprocs = (int)strtonum(optarg, 0, INT_MAX, &errstr);
                        if (errstr)
                                errx(1, "-%c %s: %s", ch, optarg, errstr);
                        if (getrlimit(RLIMIT_NPROC, &rl) != 0)
                                errx(1, "getrlimit failed");
                        if (maxprocs == 0 || maxprocs > rl.rlim_cur)
                                maxprocs = rl.rlim_cur;
                        break;
                case 'p':
                        pflag = 1;
                        break;
                case 'R':
                        Rflag = (int)strtonum(optarg, INT_MIN, INT_MAX, &errstr);
                        if (errstr)
                                errx(1, "-%c %s: %s", ch, optarg, errstr);
                        if (!Rflag)
                                errx(1, "-%c %s: %s", ch, optarg, "must be non-zero");
                        break;
                case 'r':
                        /* GNU compatibility */
                        break;
                case 'S':
                        Sflag = (int)strtonum(optarg, 0, INT_MAX, &errstr);
                        if (errstr)
                                errx(1, "-%c %s: %s", ch, optarg, errstr);
                        break;
                case 's':
                        nline = (int)strtonum(optarg, 0, INT_MAX, &errstr);
                        if (errstr)
                                errx(1, "-%c %s: %s", ch, optarg, errstr);
                        break;
                case 't':
                        tflag = 1;
                        break;
                case 'x':
                        xflag = 1;
                        break;
                case '0':
                        zflag = 1;
                        break;
                case '?':
                default:
                        usage();
        }
        argc -= optind;
        argv += optind;

        if (!Iflag && Rflag)
                usage();
        if (!Iflag && Sflag)
                usage();
        if (Iflag && !Rflag)
                Rflag = 5;
        if (Iflag && !Sflag)
                Sflag = 255;
        if (xflag && !nflag)
                usage();
        if (Iflag || Lflag)
                xflag = 1;
        if (replstr != NULL && *replstr == '\0')
                errx(1, "replstr may not be empty");

        pids_init();

        /*
         * Allocate pointers for the utility name, the utility arguments,
         * the maximum arguments to be read from stdin and the trailing
         * NULL.
         */
        linelen = 1 + argc + (size_t)nargs + 1;
        if ((av = bxp = malloc(linelen * sizeof(char *))) == NULL)
                errx(1, "malloc failed");

        /*
         * Use the user's name for the utility as argv[0], just like the
         * shell.  Echo is the default.  Set up pointers for the user's
         * arguments.
         */
        if (*argv == NULL)
                cnt = strlen(*bxp++ = echo);
        else {
                do {
                        if (Jflag && strcmp(*argv, replstr) == 0) {
                                char **avj;
                                jfound = 1;
                                argv++;
                                for (avj = argv; *avj; avj++)
                                        cnt += strlen(*avj) + 1;
                                break;
                        }
                        cnt += strlen(*bxp++ = *argv) + 1;
                } while (*++argv != NULL);
        }

        /*
         * Set up begin/end/traversing pointers into the array.  The -n
         * count doesn't include the trailing NULL pointer, so the malloc
         * added in an extra slot.
         */
        endxp = (xp = bxp) + nargs;

        /*
         * Allocate buffer space for the arguments read from stdin and the
         * trailing NULL.  Buffer space is defined as the default or specified
         * space, minus the length of the utility name and arguments.  Set up
         * begin/end/traversing pointers into the array.  The -s count does
         * include the trailing NULL, so the malloc didn't add in an extra
         * slot.
         */
        nline -= cnt;
        if (nline <= 0)
                errx(1, "insufficient space for command");

        if ((bbp = malloc((size_t)(nline + 1))) == NULL)
                errx(1, "malloc failed");
        ebp = (argp = p = bbp) + nline - 1;
        for (;;)
                parse_input(argc, argv);
}

static void
parse_input(int argc, char *argv[])
{
        int ch, foundeof;
        char **avj;

        foundeof = 0;

        switch (ch = getchar()) {
        case EOF:
                /* No arguments since last exec. */
                if (p == bbp) {
                        waitchildren(*av, 1);
                        exit(rval);
                }
                goto arg1;
        case ' ':
        case '\t':
                /* Quotes escape tabs and spaces. */
                if (insingle || indouble || zflag)
                        goto addch;
                goto arg2;
        case '\0':
                if (zflag) {
                        /*
                         * Increment 'count', so that nulls will be treated
                         * as end-of-line, as well as end-of-argument.  This
                         * is needed so -0 works properly with -I and -L.
                         */
                        count++;
                        goto arg2;
                }
                goto addch;
        case '\n':
                if (zflag)
                        goto addch;
                count++;            /* Indicate end-of-line (used by -L) */

                /* Quotes do not escape newlines. */
arg1:           if (insingle || indouble) {
                        warnx("unterminated quote");
                        xexit(*av, 1);
                }
arg2:
                foundeof = eoflen != 0 && p - argp == eoflen &&
                    strncmp(argp, eofstr, eoflen) == 0;

                /* Do not make empty args unless they are quoted */
                if ((argp != p || wasquoted) && !foundeof) {
                        *p++ = '\0';
                        *xp++ = argp;
                        if (Iflag) {
                                size_t curlen;

                                if (inpline == NULL)
                                        curlen = 0;
                                else {
                                        /*
                                         * If this string is not zero
                                         * length, append a space for
                                         * separation before the next
                                         * argument.
                                         */
                                        if ((curlen = strlen(inpline)))
                                                strcat(inpline, " ");
                                }
                                curlen++;
                                /*
                                 * Allocate enough to hold what we will
                                 * be holding in a second, and to append
                                 * a space next time through, if we have
                                 * to.
                                 */
                                inpline = realloc(inpline, curlen + 2 +
                                    strlen(argp));
                                if (inpline == NULL) {
                                        warnx("realloc failed");
                                        xexit(*av, 1);
                                }
                                if (curlen == 1)
                                        strcpy(inpline, argp);
                                else
                                        strcat(inpline, argp);
                        }
                }

                /*
                 * If max'd out on args or buffer, or reached EOF,
                 * run the command.  If xflag and max'd out on buffer
                 * but not on args, object.  Having reached the limit
                 * of input lines, as specified by -L is the same as
                 * maxing out on arguments.
                 */
                if (xp == endxp || p > ebp || ch == EOF ||
                    (Lflag <= count && xflag) || foundeof) {
                        if (xflag && xp != endxp && p > ebp) {
                                warnx("insufficient space for arguments");
                                xexit(*av, 1);
                        }
                        if (jfound) {
                                for (avj = argv; *avj; avj++)
                                        *xp++ = *avj;
                        }
                        prerun(argc, av);
                        if (ch == EOF || foundeof) {
                                waitchildren(*av, 1);
                                exit(rval);
                        }
                        p = bbp;
                        xp = bxp;
                        count = 0;
                }
                argp = p;
                wasquoted = 0;
                break;
        case '\'':
                if (indouble || zflag)
                        goto addch;
                insingle = !insingle;
                wasquoted = 1;
                break;
        case '"':
                if (insingle || zflag)
                        goto addch;
                indouble = !indouble;
                wasquoted = 1;
                break;
        case '\\':
                if (zflag)
                        goto addch;
                /* Backslash escapes anything, is escaped by quotes. */
                if (!insingle && !indouble && (ch = getchar()) == EOF) {
                        warnx("backslash at EOF");
                        xexit(*av, 1);
                }
                /* FALLTHROUGH */
        default:
addch:          if (p < ebp) {
                        *p++ = ch;
                        break;
                }

                /* If only one argument, not enough buffer space. */
                if (bxp == xp) {
                        warnx("insufficient space for argument");
                        xexit(*av, 1);
                }
                /* Didn't hit argument limit, so if xflag object. */
                if (xflag) {
                        warnx("insufficient space for arguments");
                        xexit(*av, 1);
                }

                if (jfound) {
                        for (avj = argv; *avj; avj++)
                                *xp++ = *avj;
                }
                prerun(argc, av);
                xp = bxp;
                cnt = ebp - argp;
                memcpy(bbp, argp, (size_t)cnt);
                p = (argp = bbp) + cnt;
                *p++ = ch;
                break;
        }
}

/*
 * Do things necessary before run()'ing, such as -I substitution,
 * and then call run().
 */
static void
prerun(int argc, char *argv[])
{
        char **tmp, **tmp2, **avj;
        int repls;

        repls = Rflag;

        if (argc == 0 || repls == 0) {
                *xp = NULL;
                run(argv);
                return;
        }

        avj = argv;

        /*
         * Allocate memory to hold the argument list, and
         * a NULL at the tail.
         */
        tmp = malloc((argc + 1) * sizeof(char *));
        if (tmp == NULL) {
                warnx("malloc failed");
                xexit(*argv, 1);
        }
        tmp2 = tmp;

        /*
         * Save the first argument and iterate over it, we
         * cannot do strnsubst() to it.
         */
        if ((*tmp++ = strdup(*avj++)) == NULL) {
                warnx("strdup failed");
                xexit(*argv, 1);
        }

        /*
         * For each argument to utility, if we have not used up
         * the number of replacements we are allowed to do, and
         * if the argument contains at least one occurrence of
         * replstr, call strnsubst(), else just save the string.
         * Iterations over elements of avj and tmp are done
         * where appropriate.
         */
        while (--argc) {
                *tmp = *avj++;
                if (repls && strstr(*tmp, replstr) != NULL) {
                        if (strnsubst(tmp++, replstr, inpline, (size_t)Sflag)) {
                                warnx("command line cannot be assembled, too long");
                                xexit(*argv, 1);
                        }
                        if (repls > 0)
                                repls--;
                } else {
                        if ((*tmp = strdup(*tmp)) == NULL) {
                                warnx("strdup failed");
                                xexit(*argv, 1);
                        }
                        tmp++;
                }
        }

        /*
         * Run it.
         */
        *tmp = NULL;
        run(tmp2);

        /*
         * Walk from the tail to the head, free along the way.
         */
        for (; tmp2 != tmp; tmp--)
                free(*tmp);
        /*
         * Now free the list itself.
         */
        free(tmp2);

        /*
         * Free the input line buffer, if we have one.
         */
        if (inpline != NULL) {
                free(inpline);
                inpline = NULL;
        }
}

static void
run(char **argv)
{
        pid_t pid;
        int fd;
        char **avec;

        /*
         * If the user wants to be notified of each command before it is
         * executed, notify them.  If they want the notification to be
         * followed by a prompt, then prompt them.
         */
        if (tflag || pflag) {
                (void)fprintf(stderr, "%s", *argv);
                for (avec = argv + 1; *avec != NULL; ++avec)
                        (void)fprintf(stderr, " %s", *avec);
                /*
                 * If the user has asked to be prompted, do so.
                 */
                if (pflag)
                        /*
                         * If they asked not to exec, return without execution
                         * but if they asked to, go to the execution.  If we
                         * could not open their tty, break the switch and drop
                         * back to -t behaviour.
                         */
                        switch (prompt()) {
                        case 0:
                                return;
                        case 1:
                                goto exec;
                        case 2:
                                break;
                        }
                (void)fprintf(stderr, "\n");
                (void)fflush(stderr);
        }
exec:
        childerr = 0;
        switch (pid = vfork()) {
        case -1:
                warn("vfork");
                xexit(*argv, 1);
        case 0:
                if (oflag) {
                        if ((fd = open(_PATH_TTY, O_RDONLY)) == -1)
                                err(1, "can't open /dev/tty");
                } else {
                        fd = open(_PATH_DEVNULL, O_RDONLY);
                }
                if (fd > STDIN_FILENO) {
                        if (dup2(fd, STDIN_FILENO) != 0)
                                err(1, "can't dup2 to stdin");
                        close(fd);
                }
                execvp(argv[0], argv);
                childerr = errno;
                _exit(1);
        }
        pids_add(pid);
        waitchildren(*argv, 0);
}

/*
 * Wait for a tracked child to exit and return its pid and exit status.
 *
 * Ignores (discards) all untracked child processes.
 * Returns -1 and sets errno to ECHILD if no tracked children exist.
 * If block is set, waits indefinitely for a child process to exit.
 * If block is not set and no children have exited, returns 0 immediately.
 */
static pid_t
xwait(int block, int *status) {
        pid_t pid;

        if (pids_empty()) {
                errno = ECHILD;
                return (-1);
        }

        while ((pid = waitpid(-1, status, block ? 0 : WNOHANG)) > 0)
                if (pids_remove(pid))
                        break;

        return (pid);
}

static void
xexit(const char *name, const int exit_code) {
        waitchildren(name, 1);
        exit(exit_code);
}

static void
waitchildren(const char *name, int waitall)
{
        pid_t pid;
        int status;
        int cause_exit = 0;

        while ((pid = xwait(waitall || pids_full(), &status)) > 0) {
                /*
                 * If we couldn't invoke the utility or if utility exited
                 * because of a signal or with a value of 255, warn (per
                 * POSIX), and then wait until all other children have
                 * exited before exiting 1-125. POSIX requires us to stop
                 * reading if child exits because of a signal or with 255,
                 * but it does not require us to exit immediately; waiting
                 * is preferable to orphaning.
                 */
                if (childerr != 0 && cause_exit == 0) {
                        errno = childerr;
                        waitall = 1;
                        cause_exit = errno == ENOENT ? 127 : 126;
                        warn("%s", name);
                } else if (WIFSIGNALED(status)) {
                        waitall = cause_exit = 1;
                        warnx("%s: terminated with signal %d; aborting",
                            name, WTERMSIG(status));
                } else if (WEXITSTATUS(status) == 255) {
                        waitall = cause_exit = 1;
                        warnx("%s: exited with status 255; aborting", name);
                } else if (WEXITSTATUS(status))
                        rval = 1;
        }

        if (cause_exit)
                exit(cause_exit);
        if (pid == -1 && errno != ECHILD)
                err(1, "waitpid");
}

#define NOPID   (0)

static void
pids_init(void)
{
        int i;

        if ((childpids = malloc(maxprocs * sizeof(*childpids))) == NULL)
                errx(1, "malloc failed");

        for (i = 0; i < maxprocs; i++)
                clearslot(i);
}

static int
pids_empty(void)
{

        return (curprocs == 0);
}

static int
pids_full(void)
{

        return (curprocs >= maxprocs);
}

static void
pids_add(pid_t pid)
{
        int slot;

        slot = findfreeslot();
        childpids[slot] = pid;
        curprocs++;
}

static int
pids_remove(pid_t pid)
{
        int slot;

        if ((slot = findslot(pid)) < 0)
                return (0);

        clearslot(slot);
        curprocs--;
        return (1);
}

static int
findfreeslot(void)
{
        int slot;

        if ((slot = findslot(NOPID)) < 0)
                errx(1, "internal error: no free pid slot");
        return (slot);
}

static int
findslot(pid_t pid)
{
        int slot;

        for (slot = 0; slot < maxprocs; slot++)
                if (childpids[slot] == pid)
                        return (slot);
        return (-1);
}

static void
clearslot(int slot)
{

        childpids[slot] = NOPID;
}

/*
 * Prompt the user about running a command.
 */
static int
prompt(void)
{
        regex_t cre;
        size_t rsize = 0;
        int match;
        char *response = NULL;
        FILE *ttyfp;

        if ((ttyfp = fopen(_PATH_TTY, "r")) == NULL)
                return (2);     /* Indicate that the TTY failed to open. */
        (void)fprintf(stderr, "?...");
        (void)fflush(stderr);
        if (getline(&response, &rsize, ttyfp) < 0 ||
            regcomp(&cre, nl_langinfo(YESEXPR), REG_EXTENDED) != 0) {
                (void)fclose(ttyfp);
                return (0);
        }
        match = regexec(&cre, response, 0, NULL, 0);
        free(response);
        (void)fclose(ttyfp);
        regfree(&cre);
        return (match == 0);
}

static void
usage(void)
{

        fprintf(stderr,
"usage: xargs [-0opt] [-E eofstr] [-I replstr [-R replacements] [-S replsize]]\n"
"             [-J replstr] [-L number] [-n number [-x]] [-P maxprocs]\n"
"             [-s size] [utility [argument ...]]\n");
        exit(1);
}