/* vi: set sw=4 ts=4: */
/*
 * bare bones sendmail
 *
 * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
 *
 * Licensed under GPLv2, see file LICENSE in this tarball for details.
 */
#include "libbb.h"
#include "mail.h"

static int smtp_checkp(const char *fmt, const char *param, int code)
{
        char *answer;
        const char *msg = command(fmt, param);
        // read stdin
        // if the string has a form \d\d\d- -- read next string. E.g. EHLO response
        // parse first bytes to a number
        // if code = -1 then just return this number
        // if code != -1 then checks whether the number equals the code
        // if not equal -> die saying msg
        while ((answer = xmalloc_fgetline(stdin)) != NULL)
                if (strlen(answer) <= 3 || '-' != answer[3])
                        break;
        if (answer) {
                int n = atoi(answer);
                if (timeout)
                        alarm(0);
                free(answer);
                if (-1 == code || n == code)
                        return n;
        }
        bb_error_msg_and_die("%s failed", msg);
}

static int smtp_check(const char *fmt, int code)
{
        return smtp_checkp(fmt, NULL, code);
}

// strip argument of bad chars
static char *sane_address(char *str)
{
        char *s = str;
        char *p = s;
        while (*s) {
                if (isalnum(*s) || '_' == *s || '-' == *s || '.' == *s || '@' == *s) {
                        *p++ = *s;
                }
                s++;
        }
        *p = '\0';
        return str;
}

static void rcptto(const char *s)
{
        smtp_checkp("RCPT TO:<%s>", s, 250);
}

int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int sendmail_main(int argc UNUSED_PARAM, char **argv)
{
        char *opt_connect = opt_connect;
        char *opt_from;
        char *s;
        llist_t *list = NULL;
        char *domain = sane_address(safe_getdomainname());
        int code;

        enum {
        //--- standard options
                OPT_t = 1 << 0,         // read message for recipients, append them to those on cmdline
                OPT_f = 1 << 1,         // sender address
                OPT_o = 1 << 2,         // various options. -oi IMPLIED! others are IGNORED!
        //--- BB specific options
                OPT_w = 1 << 3,         // network timeout
                OPT_H = 1 << 4,         // use external connection helper
                OPT_S = 1 << 5,         // specify connection string
                OPT_a = 1 << 6,         // authentication tokens
        };

        // init global variables
        INIT_G();

        // save initial stdin since body is piped!
        xdup2(STDIN_FILENO, 3);
        G.fp0 = fdopen(3, "r");

        // parse options
        // -f is required. -H and -S are mutually exclusive
        opt_complementary = "f:w+:H--S:S--H:a::";
        // N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect
        // -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
        // it is still under development.
        opts = getopt32(argv, "tf:o:w:H:S:a::", &opt_from, NULL, &timeout, &opt_connect, &opt_connect, &list);
        //argc -= optind;
        argv += optind;

        // process -a[upm]<token> options
        if ((opts & OPT_a) && !list)
                bb_show_usage();
        while (list) {
                char *a = (char *) llist_pop(&list);
                if ('u' == a[0])
                        G.user = xstrdup(a+1);
                if ('p' == a[0])
                        G.pass = xstrdup(a+1);
                // N.B. we support only AUTH LOGIN so far
                //if ('m' == a[0])
                //      G.method = xstrdup(a+1);
        }
        // N.B. list == NULL here
        //bb_info_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);

        // connect to server

        // connection helper ordered? ->
        if (opts & OPT_H) {
                const char *args[] = { "sh", "-c", opt_connect, NULL };
                // plug it in
                launch_helper(args);
        // vanilla connection
        } else {
                int fd;
                // host[:port] not explicitly specified? -> use $SMTPHOST
                // no $SMTPHOST ? -> use localhost
                if (!(opts & OPT_S)) {
                        opt_connect = getenv("SMTPHOST");
                        if (!opt_connect)
                                opt_connect = (char *)"127.0.0.1";
                }
                // do connect
                fd = create_and_connect_stream_or_die(opt_connect, 25);
                // and make ourselves a simple IO filter
                xmove_fd(fd, STDIN_FILENO);
                xdup2(STDIN_FILENO, STDOUT_FILENO);
        }
        // N.B. from now we know nothing about network :)

        // wait for initial server OK
        // N.B. if we used openssl the initial 220 answer is already swallowed during openssl TLS init procedure
        // so we need to kick the server to see whether we are ok
        code = smtp_check("NOOP", -1);
        // 220 on plain connection, 250 on openssl-helped TLS session
        if (220 == code)
                smtp_check(NULL, 250); // reread the code to stay in sync
        else if (250 != code)
                bb_error_msg_and_die("INIT failed");

        // we should start with modern EHLO
        if (250 != smtp_checkp("EHLO %s", domain, -1)) {
                smtp_checkp("HELO %s", domain, 250);
        }
        if (ENABLE_FEATURE_CLEAN_UP)
                free(domain);

        // perform authentication
        if (opts & OPT_a) {
                smtp_check("AUTH LOGIN", 334);
                // we must read credentials unless they are given via -a[up] options
                if (!G.user || !G.pass)
                        get_cred_or_die(4);
                encode_base64(NULL, G.user, NULL);
                smtp_check("", 334);
                encode_base64(NULL, G.pass, NULL);
                smtp_check("", 235);
        }

        // set sender
        // N.B. we have here a very loosely defined algotythm
        // since sendmail historically offers no means to specify secrets on cmdline.
        // 1) server can require no authentication ->
        //      we must just provide a (possibly fake) reply address.
        // 2) server can require AUTH ->
        //      we must provide valid username and password along with a (possibly fake) reply address.
        //      For the sake of security username and password are to be read either from console or from a secured file.
        //      Since reading from console may defeat usability, the solution is either to read from a predefined
        //      file descriptor (e.g. 4), or again from a secured file.

        // got no sender address? -> use system username as a resort
        // N.B. we marked -f as required option!
        //if (!G.user) {
        //      // N.B. IMHO getenv("USER") can be way easily spoofed!
        //      G.user = xuid2uname(getuid());
        //      opt_from = xasprintf("%s@%s", G.user, domain);
        //}
        //if (ENABLE_FEATURE_CLEAN_UP)
        //      free(domain);
        smtp_checkp("MAIL FROM:<%s>", opt_from, 250);

        // process message

        // read recipients from message and add them to those given on cmdline.
        // this means we scan stdin for To:, Cc:, Bcc: lines until an empty line
        // and then use the rest of stdin as message body
        code = 0; // set "analyze headers" mode
        while ((s = xmalloc_fgetline(G.fp0)) != NULL) {
                // put message lines doubling leading dots
                if (code) {
                        // escape leading dots
                        // N.B. this feature is implied even if no -i (-oi) switch given
                        // N.B. we need to escape the leading dot regardless of
                        // whether it is single or not character on the line
                        if ('.' == s[0] /*&& '\0' == s[1] */)
                                printf(".");
                        // dump read line
                        printf("%s\r\n", s);
                        free(s);
                        continue;
                }

                // analyze headers
                // To: or Cc: headers add recipients
                if (0 == strncasecmp("To: ", s, 4) || 0 == strncasecmp("Bcc: " + 1, s, 4)) {
                        rcptto(sane_address(s+4));
//                      goto addh;
                        llist_add_to_end(&list, s);
                // Bcc: header adds blind copy (hidden) recipient
                } else if (0 == strncasecmp("Bcc: ", s, 5)) {
                        rcptto(sane_address(s+5));
                        free(s);
                        // N.B. Bcc: vanishes from headers!
                // other headers go verbatim
                } else if (s[0]) {
// addh:
                        llist_add_to_end(&list, s);
                // the empty line stops analyzing headers
                } else {
                        free(s);
                        // put recipients specified on cmdline
                        while (*argv) {
                                s = sane_address(*argv);
                                rcptto(s);
                                llist_add_to_end(&list, xasprintf("To: %s", s));
                                argv++;
                        }
                        // enter "put message" mode
                        smtp_check("DATA", 354);
                        // dump the headers
                        while (list) {
                                printf("%s\r\n", (char *) llist_pop(&list));
                        }
                        printf("%s\r\n" + 2); // quirk for format string to be reused
                        // stop analyzing headers
                        code++;
                }
        }

        // finalize the message
        smtp_check(".", 250);
        // ... and say goodbye
        smtp_check("QUIT", 221);
        // cleanup
        if (ENABLE_FEATURE_CLEAN_UP)
                fclose(G.fp0);

        return EXIT_SUCCESS;
}