/*      $NetBSD: expandm.c,v 1.13 2024/10/04 08:37:20 rillig Exp $      */

/*-
 * Copyright (c) 2019 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Christos Zoulas.
 *
 * 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */
#include <sys/cdefs.h>
__RCSID("$NetBSD: expandm.c,v 1.13 2024/10/04 08:37:20 rillig Exp $");

#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>

#include "expandm.h"

#ifdef TEST
#undef INT_MAX
#define INT_MAX 31
#endif


const char * __attribute__((__format_arg__(1)))
expandm(const char *fmt, const char *sf, char **rbuf)
{
        const int err = errno;
        const char *e = NULL;
        char *buf, *nbuf;
        const char *ptr, *m;

        buf = NULL;
        for (ptr = fmt; (m = strstr(ptr, "%m")) != NULL; ptr = m + 2) {
                size_t cnt = 0;
                size_t nlen;

                for (const char *p = m; p >= ptr && *p == '%'; p--)
                        cnt++;

                nlen = (size_t)(m - ptr);
                /*
                 * we can't exceed INT_MAX because int is used as 
                 * a format width
                 */
                if (__predict_false(nlen >= INT_MAX)) {
                        size_t blen = buf ? strlen(buf) : 0;
                        size_t tlen;

                        /*
                         * if we would overflow a ptrdiff_t when computing
                         * tlen, then don't bother.  The format string is
                         * simply too large to be converted.
                         */
                        if (blen >= PTRDIFF_MAX ||
                            nlen >= PTRDIFF_MAX - blen ||
                            nlen >= SIZE_T_MAX - blen)
                                goto out;

                        tlen = nlen + blen;

                        nbuf = realloc(buf, tlen + 1);
                        if (nbuf == NULL)
                                goto out;

                        memcpy(nbuf + blen, ptr, nlen);
                        nbuf[tlen] = '\0';
                        ptr += nlen;
                        buf = nbuf;
                }

                if (__predict_true(e == NULL && (cnt & 1) != 0))
                        e = strerror(err);
                if (asprintf(&nbuf, "%s%.*s%s", buf ? buf : "",
                    (int)(m - ptr), ptr, (cnt & 1) ? e : "%m") == -1)
                        goto out;
                free(buf);
                buf = nbuf;
        }

        if (asprintf(&nbuf, "%s%s%s", buf ? buf : "", ptr, sf ? sf : "") == -1)
                goto out;

        free(buf);
        if (rbuf)
                *rbuf = nbuf;
        errno = err;
        return nbuf;
out:
        free(buf);
        if (rbuf)
                *rbuf = NULL;
        errno = err;
        return fmt;
}

#ifdef TEST
int
main(int argc, char *argv[])
{
        errno = ERANGE;
        printf("%s\n", expandm(argc > 1 ? argv[1] : "Message %%m=%m: %%%m%%",
            "...", NULL));
        return 0;
}
#endif