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csplit(1): Fix extraneous output in edge case
When the input to csplit contains fewer lines than the number of matches
specified, extra output was mistakenly included in some output files.
From FreeBSD via Tim Chase.

/*	$OpenBSD: csplit.c,v 1.10 2021/07/08 00:38:42 millert Exp $	*/
/*	$FreeBSD: src/usr.bin/csplit/csplit.c,v 1.9 2004/03/22 11:15:03 tjr Exp $	*/

/*-
 * Copyright (c) 2002 Tim J. Robbins.
 * All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 */

/*
 * csplit -- split files based on context
 *
 * This utility splits its input into numbered output files by line number
 * or by a regular expression. Regular expression matches have an optional
 * offset with them, allowing the split to occur a specified number of
 * lines before or after the match.
 *
 * To handle negative offsets, we stop reading when the match occurs and
 * store the offset that the file should have been split at, then use
 * this output file as input until all the "overflowed" lines have been read.
 * The file is then closed and truncated to the correct length.
 *
 * We assume that the output files can be seeked upon (ie. they cannot be
 * symlinks to named pipes or character devices), but make no such
 * assumption about the input.
 */

#include <sys/types.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <limits.h>
#include <regex.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

void	 cleanup(void);
void	 do_lineno(const char *);
void	 do_rexp(const char *);
char	*get_line(void);
void	 handlesig(int);
FILE	*newfile(void);
void	 toomuch(FILE *, long);
static void __dead usage(void);

/*
 * Command line options
 */
const char *prefix;		/* File name prefix */
long	 sufflen;		/* Number of decimal digits for suffix */
int	 sflag;			/* Suppress output of file names */
int	 kflag;			/* Keep output if error occurs */

/*
 * Other miscellaneous globals (XXX too many)
 */
long	 lineno;		/* Current line number in input file */
long	 reps;			/* Number of repetitions for this pattern */
long	 nfiles;		/* Number of files output so far */
long	 maxfiles;		/* Maximum number of files we can create */
char	 currfile[PATH_MAX];	/* Current output file */
const char *infn;		/* Name of the input file */
FILE	*infile;		/* Input file handle */
FILE	*overfile;		/* Overflow file for toomuch() */
off_t	 truncofs;		/* Offset this file should be truncated at */
int	 doclean;		/* Should cleanup() remove output? */

int
main(int argc, char *argv[])
{
	struct sigaction sa;
	long i;
	int ch;
	const char *expr;
	char *ep, *p;
	FILE *ofp;

	if (pledge("stdio rpath wpath cpath", NULL) == -1)
		err(1, "pledge");

	kflag = sflag = 0;
	prefix = "xx";
	sufflen = 2;
	while ((ch = getopt(argc, argv, "f:kn:s")) != -1) {
		switch (ch) {
		case 'f':
			prefix = optarg;
			break;
		case 'k':
			kflag = 1;
			break;
		case 'n':
			errno = 0;
			sufflen = strtol(optarg, &ep, 10);
			if (sufflen <= 0 || *ep != '\0' || errno != 0)
				errx(1, "%s: bad suffix length", optarg);
			break;
		case 's':
			sflag = 1;
			break;
		default:
			usage();
		}
	}

	if (sufflen + strlen(prefix) >= PATH_MAX)
		errx(1, "name too long");

	argc -= optind;
	argv += optind;

	if ((infn = *argv++) == NULL)
		usage();
	if (strcmp(infn, "-") == 0) {
		infile = stdin;
		infn = "stdin";
	} else if ((infile = fopen(infn, "r")) == NULL)
		err(1, "%s", infn);

	if (!kflag) {
		doclean = 1;
		atexit(cleanup);
		sa.sa_flags = 0;
		sa.sa_handler = handlesig;
		sigemptyset(&sa.sa_mask);
		sigaddset(&sa.sa_mask, SIGHUP);
		sigaddset(&sa.sa_mask, SIGINT);
		sigaddset(&sa.sa_mask, SIGTERM);
		sigaction(SIGHUP, &sa, NULL);
		sigaction(SIGINT, &sa, NULL);
		sigaction(SIGTERM, &sa, NULL);
	}

	lineno = 0;
	nfiles = 0;
	truncofs = 0;
	overfile = NULL;

	/* Ensure 10^sufflen < LONG_MAX. */
	for (maxfiles = 1, i = 0; i < sufflen; i++) {
		if (maxfiles > LONG_MAX / 10)
			errx(1, "%ld: suffix too long (limit %ld)",
			    sufflen, i);
		maxfiles *= 10;
	}

	/* Create files based on supplied patterns. */
	while (nfiles < maxfiles - 1 && (expr = *argv++) != NULL) {
		/* Look ahead & see if this pattern has any repetitions. */
		if (*argv != NULL && **argv == '{') {
			errno = 0;
			reps = strtol(*argv + 1, &ep, 10);
			if (reps < 0 || *ep != '}' || errno != 0)
				errx(1, "%s: bad repetition count", *argv + 1);
			argv++;
		} else
			reps = 0;

		if (*expr == '/' || *expr == '%') {
			do {
				do_rexp(expr);
			} while (reps-- != 0 && nfiles < maxfiles - 1);
		} else if (isdigit((unsigned char)*expr))
			do_lineno(expr);
		else
			errx(1, "%s: unrecognised pattern", expr);
	}

	/* Copy the rest into a new file. */
	if (!feof(infile)) {
		ofp = newfile();
		while ((p = get_line()) != NULL && fputs(p, ofp) == 0)
			;
		if (!sflag)
			printf("%jd\n", (intmax_t)ftello(ofp));
		if (fclose(ofp) != 0)
			err(1, "%s", currfile);
	}

	toomuch(NULL, 0);
	doclean = 0;

	return (0);
}

static void __dead
usage(void)
{
	extern char *__progname;

	fprintf(stderr,
	    "usage: %s [-ks] [-f prefix] [-n number] file args ...\n",
	    __progname);
	exit(1);
}

/* ARGSUSED */
void
handlesig(int sig)
{
	const char msg[] = "csplit: caught signal, cleaning up\n";

	write(STDERR_FILENO, msg, sizeof(msg) - 1);
	cleanup();
	_exit(2);
}

/* Create a new output file. */
FILE *
newfile(void)
{
	FILE *fp;

	if ((size_t)snprintf(currfile, sizeof(currfile), "%s%0*ld", prefix,
	    (int)sufflen, nfiles) >= sizeof(currfile))
		errc(1, ENAMETOOLONG, "%s", currfile);
	if ((fp = fopen(currfile, "w+")) == NULL)
		err(1, "%s", currfile);
	nfiles++;

	return (fp);
}

/* Remove partial output, called before exiting. */
void
cleanup(void)
{
	char fnbuf[PATH_MAX];
	long i;

	if (!doclean)
		return;

	/*
	 * NOTE: One cannot portably assume to be able to call snprintf() from
	 * inside a signal handler.  It is, however, safe to do on OpenBSD.
	 */
	for (i = 0; i < nfiles; i++) {
		snprintf(fnbuf, sizeof(fnbuf), "%s%0*ld", prefix,
		    (int)sufflen, i);
		unlink(fnbuf);
	}
}

/* Read a line from the input into a static buffer. */
char *
get_line(void)
{
	static char lbuf[LINE_MAX];
	FILE *src;

	src = overfile != NULL ? overfile : infile;

again: if (fgets(lbuf, sizeof(lbuf), src) == NULL) {
		if (src == overfile) {
			src = infile;
			goto again;
		}
		return (NULL);
	}
	if (ferror(src))
		err(1, "%s", infn);
	lineno++;

	return (lbuf);
}

/* Conceptually rewind the input (as obtained by get_line()) back `n' lines. */
void
toomuch(FILE *ofp, long n)
{
	char buf[BUFSIZ];
	size_t i, nread;

	if (overfile != NULL) {
		/*
		 * Truncate the previous file we overflowed into back to
		 * the correct length, close it.
		 */
		if (fflush(overfile) != 0)
			err(1, "overflow");
		if (ftruncate(fileno(overfile), truncofs) != 0)
			err(1, "overflow");
		if (fclose(overfile) != 0)
			err(1, "overflow");
		overfile = NULL;
	}

	if (n == 0)
		/* Just tidying up */
		return;

	lineno -= n;

	/*
	 * Wind the overflow file backwards to `n' lines before the
	 * current one.
	 */
	do {
		if (ftello(ofp) < (off_t)sizeof(buf))
			rewind(ofp);
		else
			fseeko(ofp, -(off_t)sizeof(buf), SEEK_CUR);
		if (ferror(ofp))
			errx(1, "%s: can't seek", currfile);
		if ((nread = fread(buf, 1, sizeof(buf), ofp)) == 0)
			errx(1, "can't read overflowed output");
		if (fseeko(ofp, -(off_t)nread, SEEK_CUR) != 0)
			err(1, "%s", currfile);
		for (i = 1; i <= nread; i++)
			if (buf[nread - i] == '\n' && n-- == 0)
				break;
		if (ftello(ofp) == 0)
			break;
	} while (n > 0);
	if (fseeko(ofp, (off_t)(nread - i + 1), SEEK_CUR) != 0)
		err(1, "%s", currfile);

	/*
	 * get_line() will read from here. Next call will truncate to
	 * truncofs in this file.
	 */
	overfile = ofp;
	truncofs = ftello(overfile);
}

/* Handle splits for /regexp/ and %regexp% patterns. */
void
do_rexp(const char *expr)
{
	regex_t cre;
	intmax_t nwritten;
	long ofs;
	int first;
	char *ecopy, *ep, *p, *pofs, *re;
	FILE *ofp;

	if ((ecopy = strdup(expr)) == NULL)
		err(1, "strdup");

	re = ecopy + 1;
	if ((pofs = strrchr(ecopy, *expr)) == NULL || pofs[-1] == '\\')
		errx(1, "%s: missing trailing %c", expr, *expr);
	*pofs++ = '\0';

	if (*pofs != '\0') {
		errno = 0;
		ofs = strtol(pofs, &ep, 10);
		if (*ep != '\0' || errno != 0)
			errx(1, "%s: bad offset", pofs);
	} else
		ofs = 0;

	if (regcomp(&cre, re, REG_BASIC|REG_NOSUB) != 0)
		errx(1, "%s: bad regular expression", re);

	if (*expr == '/')
		/* /regexp/: Save results to a file. */
		ofp = newfile();
	else {
		/* %regexp%: Make a temporary file for overflow. */
		if ((ofp = tmpfile()) == NULL)
			err(1, "tmpfile");
	}

	/* Read and output lines until we get a match. */
	first = 1;
	while ((p = get_line()) != NULL) {
		if (fputs(p, ofp) != 0)
			break;
		if (!first && regexec(&cre, p, 0, NULL, 0) == 0)
			break;
		first = 0;
	}

	if (p == NULL) {
		toomuch(NULL, 0);
		errx(1, "%s: no match", re);
	}

	if (ofs <= 0) {
		/*
		 * Negative (or zero) offset: throw back any lines we should
		 * not have read yet.
		  */
		if (p != NULL) {
			toomuch(ofp, -ofs + 1);
			nwritten = (intmax_t)truncofs;
		} else
			nwritten = (intmax_t)ftello(ofp);
	} else {
		/*
		 * Positive offset: copy the requested number of lines
		 * after the match.
		 */
		while (--ofs > 0 && (p = get_line()) != NULL)
			fputs(p, ofp);
		toomuch(NULL, 0);
		nwritten = (intmax_t)ftello(ofp);
		if (fclose(ofp) != 0)
			err(1, "%s", currfile);
	}

	if (!sflag && *expr == '/')
		printf("%jd\n", nwritten);

	regfree(&cre);
	free(ecopy);
}

/* Handle splits based on line number. */
void
do_lineno(const char *expr)
{
	long lastline, tgtline;
	char *ep, *p;
	FILE *ofp;

	errno = 0;
	tgtline = strtol(expr, &ep, 10);
	if (tgtline <= 0 || errno != 0 || *ep != '\0')
		errx(1, "%s: bad line number", expr);
	lastline = tgtline;
	if (lastline <= lineno)
		errx(1, "%s: can't go backwards", expr);

	while (nfiles < maxfiles - 1) {
		ofp = newfile();
		while (lineno + 1 != lastline) {
			if ((p = get_line()) == NULL)
				errx(1, "%ld: out of range", lastline);
			if (fputs(p, ofp) != 0)
				break;
		}
		if (!sflag)
			printf("%jd\n", (intmax_t)ftello(ofp));
		if (fclose(ofp) != 0)
			err(1, "%s", currfile);
		if (reps-- == 0)
			break;
		lastline += tgtline;
	} 
}