/*      $OpenBSD: from.c,v 1.28 2021/07/12 15:09:19 beck Exp $  */
/*      $NetBSD: from.c,v 1.6 1995/09/01 01:39:10 jtc Exp $     */

/*
 * Copyright (c) 1980, 1988, 1993
 *      The Regents of the University of California.  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.
 * 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.
 */

#include <sys/types.h>
#include <ctype.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <paths.h>
#include <string.h>
#include <err.h>
#include <errno.h>

int     match(char *, char *);
char    *mail_spool(char *file, const char *user);

int
main(int argc, char *argv[])
{
        int ch, newline, fflag = 0;
        char *file, *line, *sender, *p;
        size_t linesize = 0;
        ssize_t linelen;
        FILE *fp;

        file = line = sender = NULL;
        while ((ch = getopt(argc, argv, "f:s:")) != -1) {
                switch(ch) {
                case 'f':
                        fflag = 1;
                        file = optarg;
                        break;
                case 's':
                        sender = optarg;
                        for (p = sender; *p; ++p)
                                if (isupper((unsigned char)*p))
                                        *p = tolower((unsigned char)*p);
                        break;
                default:
                        fprintf(stderr,
                            "usage: from [-f file] [-s sender] [user]\n");
                        exit(EXIT_FAILURE);
                }
        }
        argv += optind;

        if (pledge("stdio unveil rpath getpw", NULL) == -1)
                err(1, "pledge");

        file = mail_spool(file, *argv);

        if (unveil(file, "r") == -1)
                err(1, "unveil %s", file);
        if (pledge("stdio rpath", NULL) == -1)
                err(1, "pledge");

        if ((fp = fopen(file, "r")) == NULL) {
                if (!fflag && errno == ENOENT)
                        exit(EXIT_SUCCESS);
                err(1, "%s", file);
        }

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

        for (newline = 1; (linelen = getline(&line, &linesize, fp)) != -1;) {
                if (*line == '\n') {
                        newline = 1;
                        continue;
                }
                if (newline && !strncmp(line, "From ", 5) &&
                    (!sender || match(line + 5, sender)))
                        printf("%s", line);
                newline = 0;
        }
        free(line);
        if (ferror(fp))
                err(EXIT_FAILURE, "getline");
        fclose(fp);
        exit(EXIT_SUCCESS);
}

char *
mail_spool(char *file, const char *user)
{
        struct passwd *pwd;

        /*
         * We find the mailbox by:
         *      1 -f flag
         *      2 _PATH_MAILDIR/user (from argv)
         *      2 MAIL environment variable
         *      3 _PATH_MAILDIR/user (from environment or passwd db)
         */
        if (file == NULL) {
                if (user == NULL) {
                        if ((file = getenv("MAIL")) == NULL) {
                                if ((user = getenv("LOGNAME")) == NULL &&
                                    (user = getenv("USER")) == NULL) {
                                        if (!(pwd = getpwuid(getuid())))
                                                errx(1, "no password file "
                                                    "entry for you");
                                        user = pwd->pw_name;
                                }
                        }
                }
                if (file == NULL) {
                        if (asprintf(&file, "%s/%s", _PATH_MAILDIR, user) == -1)
                                err(1, NULL);
                }
        }
        return(file);
}

int
match(char *line, char *sender)
{
        char ch, pch, first, *p, *t;

        for (first = *sender++;;) {
                if (isspace((unsigned char)(ch = *line)))
                        return(0);
                ++line;
                if (isupper((unsigned char)ch))
                        ch = tolower((unsigned char)ch);
                if (ch != first)
                        continue;
                for (p = sender, t = line;;) {
                        if (!(pch = *p++))
                                return(1);
                        if (isupper((unsigned char)(ch = *t++)))
                                ch = tolower((unsigned char)ch);
                        if (ch != pch)
                                break;
                }
        }
        /* NOTREACHED */
}