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AIX reports the CODESET as "ISO8859-1" in the POSIX locale.
Treating that as a safe encoding is OK because even when other
systems return that string for real ISO8859-1, it is still
safe in the sense that it is ASCII-compatible and stateless.

Issue reported by Val dot Baranov at duke dot edu.  Additional
information provided by Michael dot Felt at felt dot demon dot nl.
Tested by Michael Felt on AIX 6.1 and by Val Baranov on AIX 7.1.
Tweak and OK djm@.

/* $OpenBSD: utf8.c,v 1.8 2018/08/21 13:56:27 schwarze Exp $ */
/*
 * Copyright (c) 2016 Ingo Schwarze <schwarze@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*
 * Utility functions for multibyte-character handling,
 * in particular to sanitize untrusted strings for terminal output.
 */

#include <sys/types.h>
#include <langinfo.h>
#include <limits.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <vis.h>
#include <wchar.h>

#include "utf8.h"

static int	 dangerous_locale(void);
static int	 grow_dst(char **, size_t *, size_t, char **, size_t);
static int	 vasnmprintf(char **, size_t, int *, const char *, va_list);


/*
 * For US-ASCII and UTF-8 encodings, we can safely recover from
 * encoding errors and from non-printable characters.  For any
 * other encodings, err to the side of caution and abort parsing:
 * For state-dependent encodings, recovery is impossible.
 * For arbitrary encodings, replacement of non-printable
 * characters would be non-trivial and too fragile.
 * The comments indicate what nl_langinfo(CODESET)
 * returns for US-ASCII on various operating systems.
 */

static int
dangerous_locale(void) {
	char	*loc;

	loc = nl_langinfo(CODESET);
	return strcmp(loc, "UTF-8") != 0 &&
	    strcmp(loc, "US-ASCII") != 0 &&		/* OpenBSD */
	    strcmp(loc, "ANSI_X3.4-1968") != 0 &&	/* Linux */
	    strcmp(loc, "ISO8859-1") != 0 &&		/* AIX */
	    strcmp(loc, "646") != 0 &&			/* Solaris, NetBSD */
	    strcmp(loc, "") != 0;			/* Solaris 6 */
}

static int
grow_dst(char **dst, size_t *sz, size_t maxsz, char **dp, size_t need)
{
	char	*tp;
	size_t	 tsz;

	if (*dp + need < *dst + *sz)
		return 0;
	tsz = *sz + 128;
	if (tsz > maxsz)
		tsz = maxsz;
	if ((tp = recallocarray(*dst, *sz, tsz, 1)) == NULL)
		return -1;
	*dp = tp + (*dp - *dst);
	*dst = tp;
	*sz = tsz;
	return 0;
}

/*
 * The following two functions limit the number of bytes written,
 * including the terminating '\0', to sz.  Unless wp is NULL,
 * they limit the number of display columns occupied to *wp.
 * Whichever is reached first terminates the output string.
 * To stay close to the standard interfaces, they return the number of
 * non-NUL bytes that would have been written if both were unlimited.
 * If wp is NULL, newline, carriage return, and tab are allowed;
 * otherwise, the actual number of columns occupied by what was
 * written is returned in *wp.
 */

static int
vasnmprintf(char **str, size_t maxsz, int *wp, const char *fmt, va_list ap)
{
	char	*src;	/* Source string returned from vasprintf. */
	char	*sp;	/* Pointer into src. */
	char	*dst;	/* Destination string to be returned. */
	char	*dp;	/* Pointer into dst. */
	char	*tp;	/* Temporary pointer for dst. */
	size_t	 sz;	/* Number of bytes allocated for dst. */
	wchar_t	 wc;	/* Wide character at sp. */
	int	 len;	/* Number of bytes in the character at sp. */
	int	 ret;	/* Number of bytes needed to format src. */
	int	 width;	/* Display width of the character wc. */
	int	 total_width, max_width, print;

	src = NULL;
	if ((ret = vasprintf(&src, fmt, ap)) <= 0)
		goto fail;

	sz = strlen(src) + 1;
	if ((dst = malloc(sz)) == NULL) {
		free(src);
		ret = -1;
		goto fail;
	}

	if (maxsz > INT_MAX)
		maxsz = INT_MAX;

	sp = src;
	dp = dst;
	ret = 0;
	print = 1;
	total_width = 0;
	max_width = wp == NULL ? INT_MAX : *wp;
	while (*sp != '\0') {
		if ((len = mbtowc(&wc, sp, MB_CUR_MAX)) == -1) {
			(void)mbtowc(NULL, NULL, MB_CUR_MAX);
			if (dangerous_locale()) {
				ret = -1;
				break;
			}
			len = 1;
			width = -1;
		} else if (wp == NULL &&
		    (wc == L'\n' || wc == L'\r' || wc == L'\t')) {
			/*
			 * Don't use width uninitialized; the actual
			 * value doesn't matter because total_width
			 * is only returned for wp != NULL.
			 */
			width = 0;
		} else if ((width = wcwidth(wc)) == -1 &&
		    dangerous_locale()) {
			ret = -1;
			break;
		}

		/* Valid, printable character. */

		if (width >= 0) {
			if (print && (dp - dst >= (int)maxsz - len ||
			    total_width > max_width - width))
				print = 0;
			if (print) {
				if (grow_dst(&dst, &sz, maxsz,
				    &dp, len) == -1) {
					ret = -1;
					break;
				}
				total_width += width;
				memcpy(dp, sp, len);
				dp += len;
			}
			sp += len;
			if (ret >= 0)
				ret += len;
			continue;
		}

		/* Escaping required. */

		while (len > 0) {
			if (print && (dp - dst >= (int)maxsz - 4 ||
			    total_width > max_width - 4))
				print = 0;
			if (print) {
				if (grow_dst(&dst, &sz, maxsz,
				    &dp, 4) == -1) {
					ret = -1;
					break;
				}
				tp = vis(dp, *sp, VIS_OCTAL | VIS_ALL, 0);
				width = tp - dp;
				total_width += width;
				dp = tp;
			} else
				width = 4;
			len--;
			sp++;
			if (ret >= 0)
				ret += width;
		}
		if (len > 0)
			break;
	}
	free(src);
	*dp = '\0';
	*str = dst;
	if (wp != NULL)
		*wp = total_width;

	/*
	 * If the string was truncated by the width limit but
	 * would have fit into the size limit, the only sane way
	 * to report the problem is using the return value, such
	 * that the usual idiom "if (ret < 0 || ret >= sz) error"
	 * works as expected.
	 */

	if (ret < (int)maxsz && !print)
		ret = -1;
	return ret;

fail:
	if (wp != NULL)
		*wp = 0;
	if (ret == 0) {
		*str = src;
		return 0;
	} else {
		*str = NULL;
		return -1;
	}
}

int
snmprintf(char *str, size_t sz, int *wp, const char *fmt, ...)
{
	va_list	 ap;
	char	*cp;
	int	 ret;

	va_start(ap, fmt);
	ret = vasnmprintf(&cp, sz, wp, fmt, ap);
	va_end(ap);
	if (cp != NULL) {
		(void)strlcpy(str, cp, sz);
		free(cp);
	} else
		*str = '\0';
	return ret;
}

/*
 * To stay close to the standard interfaces, the following functions
 * return the number of non-NUL bytes written.
 */

int
vfmprintf(FILE *stream, const char *fmt, va_list ap)
{
	char	*str;
	int	 ret;

	if ((ret = vasnmprintf(&str, INT_MAX, NULL, fmt, ap)) < 0)
		return -1;
	if (fputs(str, stream) == EOF)
		ret = -1;
	free(str);
	return ret;
}

int
fmprintf(FILE *stream, const char *fmt, ...)
{
	va_list	 ap;
	int	 ret;

	va_start(ap, fmt);
	ret = vfmprintf(stream, fmt, ap);
	va_end(ap);
	return ret;
}

int
mprintf(const char *fmt, ...)
{
	va_list	 ap;
	int	 ret;

	va_start(ap, fmt);
	ret = vfmprintf(stdout, fmt, ap);
	va_end(ap);
	return ret;
}