source: MondoRescue/branches/3.3/mindi-busybox/mailutils/sendmail.c@ 3621

/* 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 source tree.
 */

//kbuild:lib-$(CONFIG_SENDMAIL) += sendmail.o mail.o

//usage:#define sendmail_trivial_usage
//usage:       "[OPTIONS] [RECIPIENT_EMAIL]..."
//usage:#define sendmail_full_usage "\n\n"
//usage:       "Read email from stdin and send it\n"
//usage:     "\nStandard options:"
//usage:     "\n    -t      Read additional recipients from message body"
//usage:     "\n    -f SENDER   For use in MAIL FROM:<sender>. Can be empty string"
//usage:     "\n            Default: -auUSER, or username of current UID"
//usage:     "\n    -o OPTIONS  Various options. -oi implied, others are ignored"
//usage:     "\n    -i      -oi synonym. implied and ignored"
//usage:     "\n"
//usage:     "\nBusybox specific options:"
//usage:     "\n    -v      Verbose"
//usage:     "\n    -w SECS     Network timeout"
//usage:     "\n    -H 'PROG ARGS'  Run connection helper"
//usage:     "\n            Examples:"
//usage:     "\n            -H 'exec openssl s_client -quiet -tls1 -starttls smtp"
//usage:     "\n                -connect smtp.gmail.com:25' <email.txt"
//usage:     "\n                [4<username_and_passwd.txt | -auUSER -apPASS]"
//usage:     "\n            -H 'exec openssl s_client -quiet -tls1"
//usage:     "\n                -connect smtp.gmail.com:465' <email.txt"
//usage:     "\n                [4<username_and_passwd.txt | -auUSER -apPASS]"
//usage:     "\n    -S HOST[:PORT]  Server"
//usage:     "\n    -auUSER     Username for AUTH LOGIN"
//usage:     "\n    -apPASS     Password for AUTH LOGIN"
////usage:     "\n  -amMETHOD   Authentication method. Ignored. LOGIN is implied"
//usage:     "\n"
//usage:     "\nOther options are silently ignored; -oi -t is implied"
//usage:    IF_MAKEMIME(
//usage:     "\nUse makemime to create emails with attachments"
//usage:    )

/* Currently we don't sanitize or escape user-supplied SENDER and RECIPIENT_EMAILs.
 * We may need to do so. For one, '.' in usernames seems to require escaping!
 *
 * From http://cr.yp.to/smtp/address.html:
 *
 * SMTP offers three ways to encode a character inside an address:
 *
 * "safe": the character, if it is not <>()[].,;:@, backslash,
 *  double-quote, space, or an ASCII control character;
 * "quoted": the character, if it is not \012, \015, backslash,
 *   or double-quote; or
 * "slashed": backslash followed by the character.
 *
 * An encoded box part is either (1) a sequence of one or more slashed
 * or safe characters or (2) a double quote, a sequence of zero or more
 * slashed or quoted characters, and a double quote. It represents
 * the concatenation of the characters encoded inside it.
 *
 * For example, the encoded box parts
 *  angels
 *  \a\n\g\e\l\s
 *  "\a\n\g\e\l\s"
 *  "angels"
 *  "ang\els"
 * all represent the 6-byte string "angels", and the encoded box parts
 *  a\,comma
 *  \a\,\c\o\m\m\a
 *  "a,comma"
 * all represent the 7-byte string "a,comma".
 *
 * An encoded address contains
 *  the byte <;
 *  optionally, a route followed by a colon;
 *  an encoded box part, the byte @, and a domain; and
 *  the byte >.
 *
 * It represents an Internet mail address, given by concatenating
 * the string represented by the encoded box part, the byte @,
 * and the domain. For example, the encoded addresses
 *     <God@heaven.af.mil>
 *     <\God@heaven.af.mil>
 *     <"God"@heaven.af.mil>
 *     <@gateway.af.mil,@uucp.local:"\G\o\d"@heaven.af.mil>
 * all represent the Internet mail address "God@heaven.af.mil".
 */

#include "libbb.h"
#include "mail.h"

// limit maximum allowed number of headers to prevent overflows.
// set to 0 to not limit
#define MAX_HEADERS 256

static void send_r_n(const char *s)
{
    if (verbose)
        bb_error_msg("send:'%s'", s);
    printf("%s\r\n", s);
}

static int smtp_checkp(const char *fmt, const char *param, int code)
{
    char *answer;
    char *msg = send_mail_command(fmt, param);
    // read stdin
    // if the string has a form NNN- -- 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 (verbose)
            bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer);
        if (strlen(answer) <= 3 || '-' != answer[3])
            break;
        free(answer);
    }
    if (answer) {
        int n = atoi(answer);
        if (timeout)
            alarm(0);
        free(answer);
        if (-1 == code || n == code) {
            free(msg);
            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;

    trim(str);
    s = str;
    while (*s) {
        if (!isalnum(*s) && !strchr("_-.@", *s)) {
            bb_error_msg("bad address '%s'", str);
            /* returning "": */
            str[0] = '\0';
            return str;
        }
        s++;
    }
    return str;
}

// check for an address inside angle brackets, if not found fall back to normal
static char *angle_address(char *str)
{
    char *s, *e;

    trim(str);
    e = last_char_is(str, '>');
    if (e) {
        s = strrchr(str, '<');
        if (s) {
            *e = '\0';
            str = s + 1;
        }
    }
    return sane_address(str);
}

static void rcptto(const char *s)
{
    if (!*s)
        return;
    // N.B. we don't die if recipient is rejected, for the other recipients may be accepted
    if (250 != smtp_checkp("RCPT TO:<%s>", s, -1))
        bb_error_msg("Bad recipient: <%s>", s);
}

// send to a list of comma separated addresses
static void rcptto_list(const char *list)
{
    char *str = xstrdup(list);
    char *s = str;
    char prev = 0;
    int in_quote = 0;

    while (*s) {
        char ch = *s++;

        if (ch == '"' && prev != '\\') {
            in_quote = !in_quote;
        } else if (!in_quote && ch == ',') {
            s[-1] = '\0';
            rcptto(angle_address(str));
            str = s;
        }
        prev = ch;
    }
    if (prev != ',')
        rcptto(angle_address(str));
    free(str);
}

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 = NULL;
    char *s;
    llist_t *list = NULL;
    char *host = sane_address(safe_gethostname());
    unsigned nheaders = 0;
    int code;
    enum {
        HDR_OTHER = 0,
        HDR_TOCC,
        HDR_BCC,
    } last_hdr = 0;
    int check_hdr;
    int has_to = 0;

    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!
        OPT_i = 1 << 3,         // IMPLIED!
    //--- BB specific options
        OPT_w = 1 << 4,         // network timeout
        OPT_H = 1 << 5,         // use external connection helper
        OPT_S = 1 << 6,         // specify connection string
        OPT_a = 1 << 7,         // authentication tokens
        OPT_v = 1 << 8,         // verbosity
    };

    // init global variables
    INIT_G();

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

    // parse options
    // -v is a counter, -H and -S are mutually exclusive, -a is a list
    opt_complementary = "vv: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:iw:H:S:a::v", &opt_from, NULL,
            &timeout, &opt_connect, &opt_connect, &list, &verbose);
    //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_error_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);
        // Now:
        // our stdout will go to helper's stdin,
        // helper's stdout will be available on our stdin.

        // Wait for initial server message.
        // If helper (such as openssl) invokes STARTTLS, the initial 220
        // is swallowed by helper (and not repeated after TLS is initiated).
        // We will send NOOP cmd to server and check the response.
        // We should get 220+250 on plain connection, 250 on STARTTLSed session.
        //
        // The problem here is some servers delay initial 220 message,
        // and consider client to be a spammer if it starts sending cmds
        // before 220 reached it. The code below is unsafe in this regard:
        // in non-STARTTLSed case, we potentially send NOOP before 220
        // is sent by server.
        // Ideas? (--delay SECS opt? --assume-starttls-helper opt?)
        code = smtp_check("NOOP", -1);
        if (code == 220)
            // we got 220 - this is not STARTTLSed connection,
            // eat 250 response to our NOOP
            smtp_check(NULL, 250);
        else
        if (code != 250)
            bb_error_msg_and_die("SMTP init failed");
    } else {
        // vanilla connection
        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);

        // Wait for initial server 220 message
        smtp_check(NULL, 220);
    }

    // we should start with modern EHLO
    if (250 != smtp_checkp("EHLO %s", host, -1))
        smtp_checkp("HELO %s", host, 250);

    // 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 algorythm
    // 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 auth name, then UID username as a last resort
    if (!opt_from) {
        opt_from = xasprintf("%s@%s",
                             G.user ? G.user : xuid2uname(getuid()),
                             xgethostbyname(host)->h_name);
    }
    free(host);

    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) {
 dump:
        // 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] */)
                bb_putchar('.');
            // dump read line
            send_r_n(s);
            free(s);
            continue;
        }

        // analyze headers
        // To: or Cc: headers add recipients
        check_hdr = (0 == strncasecmp("To:", s, 3));
        has_to |= check_hdr;
        if (opts & OPT_t) {
            if (check_hdr || 0 == strncasecmp("Bcc:" + 1, s, 3)) {
                rcptto_list(s+3);
                last_hdr = HDR_TOCC;
                goto addheader;
            }
            // Bcc: header adds blind copy (hidden) recipient
            if (0 == strncasecmp("Bcc:", s, 4)) {
                rcptto_list(s+4);
                free(s);
                last_hdr = HDR_BCC;
                continue; // N.B. Bcc: vanishes from headers!
            }
        }
        check_hdr = (list && isspace(s[0]));
        if (strchr(s, ':') || check_hdr) {
            // other headers go verbatim
            // N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines.
            // Continuation is denoted by prefixing additional lines with whitespace(s).
            // Thanks (stefan.seyfried at googlemail.com) for pointing this out.
            if (check_hdr && last_hdr != HDR_OTHER) {
                rcptto_list(s+1);
                if (last_hdr == HDR_BCC)
                    continue;
                    // N.B. Bcc: vanishes from headers!
            } else {
                last_hdr = HDR_OTHER;
            }
 addheader:
            // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
            if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
                goto bail;
            llist_add_to_end(&list, s);
        } else {
            // a line without ":" (an empty line too, by definition) doesn't look like a valid header
            // so stop "analyze headers" mode
 reenter:
            // put recipients specified on cmdline
            check_hdr = 1;
            while (*argv) {
                char *t = sane_address(*argv);
                rcptto(t);
                //if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
                //  goto bail;
                if (!has_to) {
                    const char *hdr;

                    if (check_hdr && argv[1])
                        hdr = "To: %s,";
                    else if (check_hdr)
                        hdr = "To: %s";
                    else if (argv[1])
                        hdr = "To: %s," + 3;
                    else
                        hdr = "To: %s" + 3;
                    llist_add_to_end(&list,
                            xasprintf(hdr, t));
                    check_hdr = 0;
                }
                argv++;
            }
            // enter "put message" mode
            // N.B. DATA fails iff no recipients were accepted (or even provided)
            // in this case just bail out gracefully
            if (354 != smtp_check("DATA", -1))
                goto bail;
            // dump the headers
            while (list) {
                send_r_n((char *) llist_pop(&list));
            }
            // stop analyzing headers
            code++;
            // N.B. !s means: we read nothing, and nothing to be read in the future.
            // just dump empty line and break the loop
            if (!s) {
                send_r_n("");
                break;
            }
            // go dump message body
            // N.B. "s" already contains the first non-header line, so pretend we read it from input
            goto dump;
        }
    }
    // odd case: we didn't stop "analyze headers" mode -> message body is empty. Reenter the loop
    // N.B. after reenter code will be > 0
    if (!code)
        goto reenter;

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

    return EXIT_SUCCESS;
}