mirror of
https://github.com/sheumann/hush.git
synced 2024-12-23 05:29:58 +00:00
76b680c7a8
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
488 lines
14 KiB
C
488 lines
14 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* bare bones sendmail
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*
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* Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
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*
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* Licensed under GPLv2, see file LICENSE in this source tree.
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*/
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//kbuild:lib-$(CONFIG_SENDMAIL) += sendmail.o mail.o
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//usage:#define sendmail_trivial_usage
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//usage: "[OPTIONS] [RECIPIENT_EMAIL]..."
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//usage:#define sendmail_full_usage "\n\n"
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//usage: "Read email from stdin and send it\n"
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//usage: "\nStandard options:"
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//usage: "\n -t Read additional recipients from message body"
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//usage: "\n -f SENDER For use in MAIL FROM:<sender>. Can be empty string"
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//usage: "\n Default: -auUSER, or username of current UID"
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//usage: "\n -o OPTIONS Various options. -oi implied, others are ignored"
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//usage: "\n -i -oi synonym. implied and ignored"
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//usage: "\n"
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//usage: "\nBusybox specific options:"
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//usage: "\n -v Verbose"
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//usage: "\n -w SECS Network timeout"
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//usage: "\n -H 'PROG ARGS' Run connection helper"
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//usage: "\n Examples:"
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//usage: "\n -H 'exec openssl s_client -quiet -tls1 -starttls smtp"
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//usage: "\n -connect smtp.gmail.com:25' <email.txt"
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//usage: "\n [4<username_and_passwd.txt | -auUSER -apPASS]"
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//usage: "\n -H 'exec openssl s_client -quiet -tls1"
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//usage: "\n -connect smtp.gmail.com:465' <email.txt"
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//usage: "\n [4<username_and_passwd.txt | -auUSER -apPASS]"
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//usage: "\n -S HOST[:PORT] Server"
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//usage: "\n -auUSER Username for AUTH LOGIN"
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//usage: "\n -apPASS Password for AUTH LOGIN"
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////usage: "\n -amMETHOD Authentication method. Ignored. LOGIN is implied"
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//usage: "\n"
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//usage: "\nOther options are silently ignored; -oi -t is implied"
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//usage: IF_MAKEMIME(
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//usage: "\nUse makemime to create emails with attachments"
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//usage: )
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/* Currently we don't sanitize or escape user-supplied SENDER and RECIPIENT_EMAILs.
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* We may need to do so. For one, '.' in usernames seems to require escaping!
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*
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* From http://cr.yp.to/smtp/address.html:
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*
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* SMTP offers three ways to encode a character inside an address:
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*
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* "safe": the character, if it is not <>()[].,;:@, backslash,
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* double-quote, space, or an ASCII control character;
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* "quoted": the character, if it is not \012, \015, backslash,
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* or double-quote; or
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* "slashed": backslash followed by the character.
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*
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* An encoded box part is either (1) a sequence of one or more slashed
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* or safe characters or (2) a double quote, a sequence of zero or more
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* slashed or quoted characters, and a double quote. It represents
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* the concatenation of the characters encoded inside it.
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*
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* For example, the encoded box parts
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* angels
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* \a\n\g\e\l\s
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* "\a\n\g\e\l\s"
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* "angels"
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* "ang\els"
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* all represent the 6-byte string "angels", and the encoded box parts
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* a\,comma
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* \a\,\c\o\m\m\a
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* "a,comma"
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* all represent the 7-byte string "a,comma".
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*
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* An encoded address contains
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* the byte <;
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* optionally, a route followed by a colon;
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* an encoded box part, the byte @, and a domain; and
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* the byte >.
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*
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* It represents an Internet mail address, given by concatenating
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* the string represented by the encoded box part, the byte @,
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* and the domain. For example, the encoded addresses
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* <God@heaven.af.mil>
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* <\God@heaven.af.mil>
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* <"God"@heaven.af.mil>
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* <@gateway.af.mil,@uucp.local:"\G\o\d"@heaven.af.mil>
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* all represent the Internet mail address "God@heaven.af.mil".
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*/
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#include "libbb.h"
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#include "mail.h"
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// limit maximum allowed number of headers to prevent overflows.
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// set to 0 to not limit
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#define MAX_HEADERS 256
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static void send_r_n(const char *s)
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{
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if (verbose)
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bb_error_msg("send:'%s'", s);
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printf("%s\r\n", s);
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}
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static int smtp_checkp(const char *fmt, const char *param, int code)
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{
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char *answer;
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char *msg = send_mail_command(fmt, param);
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// read stdin
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// if the string has a form NNN- -- read next string. E.g. EHLO response
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// parse first bytes to a number
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// if code = -1 then just return this number
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// if code != -1 then checks whether the number equals the code
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// if not equal -> die saying msg
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while ((answer = xmalloc_fgetline(stdin)) != NULL) {
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if (verbose)
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bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer);
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if (strlen(answer) <= 3 || '-' != answer[3])
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break;
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free(answer);
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}
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if (answer) {
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int n = atoi(answer);
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if (timeout)
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alarm(0);
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free(answer);
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if (-1 == code || n == code) {
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free(msg);
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return n;
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}
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}
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bb_error_msg_and_die("%s failed", msg);
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}
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static int smtp_check(const char *fmt, int code)
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{
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return smtp_checkp(fmt, NULL, code);
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}
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// strip argument of bad chars
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static char *sane_address(char *str)
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{
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char *s;
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trim(str);
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s = str;
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while (*s) {
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if (!isalnum(*s) && !strchr("_-.@", *s)) {
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bb_error_msg("bad address '%s'", str);
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/* returning "": */
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str[0] = '\0';
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return str;
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}
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s++;
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}
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return str;
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}
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// check for an address inside angle brackets, if not found fall back to normal
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static char *angle_address(char *str)
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{
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char *s, *e;
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trim(str);
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e = last_char_is(str, '>');
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if (e) {
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s = strrchr(str, '<');
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if (s) {
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*e = '\0';
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str = s + 1;
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}
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}
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return sane_address(str);
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}
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static void rcptto(const char *s)
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{
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if (!*s)
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return;
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// N.B. we don't die if recipient is rejected, for the other recipients may be accepted
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if (250 != smtp_checkp("RCPT TO:<%s>", s, -1))
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bb_error_msg("Bad recipient: <%s>", s);
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}
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// send to a list of comma separated addresses
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static void rcptto_list(const char *list)
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{
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char *str = xstrdup(list);
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char *s = str;
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char prev = 0;
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int in_quote = 0;
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while (*s) {
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char ch = *s++;
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if (ch == '"' && prev != '\\') {
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in_quote = !in_quote;
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} else if (!in_quote && ch == ',') {
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s[-1] = '\0';
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rcptto(angle_address(str));
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str = s;
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}
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prev = ch;
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}
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if (prev != ',')
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rcptto(angle_address(str));
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free(str);
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}
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int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int sendmail_main(int argc UNUSED_PARAM, char **argv)
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{
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char *opt_connect = opt_connect;
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char *opt_from = NULL;
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char *s;
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llist_t *list = NULL;
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char *host = sane_address(safe_gethostname());
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unsigned nheaders = 0;
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int code;
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enum {
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HDR_OTHER = 0,
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HDR_TOCC,
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HDR_BCC,
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} last_hdr = 0;
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int check_hdr;
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int has_to = 0;
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enum {
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//--- standard options
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OPT_t = 1 << 0, // read message for recipients, append them to those on cmdline
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OPT_f = 1 << 1, // sender address
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OPT_o = 1 << 2, // various options. -oi IMPLIED! others are IGNORED!
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OPT_i = 1 << 3, // IMPLIED!
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//--- BB specific options
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OPT_w = 1 << 4, // network timeout
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OPT_H = 1 << 5, // use external connection helper
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OPT_S = 1 << 6, // specify connection string
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OPT_a = 1 << 7, // authentication tokens
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OPT_v = 1 << 8, // verbosity
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};
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// init global variables
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INIT_G();
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// save initial stdin since body is piped!
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xdup2(STDIN_FILENO, 3);
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G.fp0 = xfdopen_for_read(3);
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// parse options
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// -v is a counter, -H and -S are mutually exclusive, -a is a list
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opt_complementary = "vv:w+:H--S:S--H:a::";
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// N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect
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// -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
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// it is still under development.
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opts = getopt32(argv, "tf:o:iw:H:S:a::v", &opt_from, NULL,
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&timeout, &opt_connect, &opt_connect, &list, &verbose);
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//argc -= optind;
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argv += optind;
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// process -a[upm]<token> options
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if ((opts & OPT_a) && !list)
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bb_show_usage();
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while (list) {
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char *a = (char *) llist_pop(&list);
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if ('u' == a[0])
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G.user = xstrdup(a+1);
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if ('p' == a[0])
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G.pass = xstrdup(a+1);
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// N.B. we support only AUTH LOGIN so far
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//if ('m' == a[0])
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// G.method = xstrdup(a+1);
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}
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// N.B. list == NULL here
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//bb_error_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);
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// connect to server
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// connection helper ordered? ->
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if (opts & OPT_H) {
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const char *args[] = { "sh", "-c", opt_connect, NULL };
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// plug it in
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launch_helper(args);
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// Now:
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// our stdout will go to helper's stdin,
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// helper's stdout will be available on our stdin.
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// Wait for initial server message.
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// If helper (such as openssl) invokes STARTTLS, the initial 220
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// is swallowed by helper (and not repeated after TLS is initiated).
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// We will send NOOP cmd to server and check the response.
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// We should get 220+250 on plain connection, 250 on STARTTLSed session.
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//
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// The problem here is some servers delay initial 220 message,
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// and consider client to be a spammer if it starts sending cmds
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// before 220 reached it. The code below is unsafe in this regard:
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// in non-STARTTLSed case, we potentially send NOOP before 220
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// is sent by server.
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// Ideas? (--delay SECS opt? --assume-starttls-helper opt?)
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code = smtp_check("NOOP", -1);
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if (code == 220)
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// we got 220 - this is not STARTTLSed connection,
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// eat 250 response to our NOOP
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smtp_check(NULL, 250);
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else
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if (code != 250)
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bb_error_msg_and_die("SMTP init failed");
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} else {
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// vanilla connection
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int fd;
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// host[:port] not explicitly specified? -> use $SMTPHOST
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// no $SMTPHOST? -> use localhost
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if (!(opts & OPT_S)) {
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opt_connect = getenv("SMTPHOST");
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if (!opt_connect)
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opt_connect = (char *)"127.0.0.1";
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}
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// do connect
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fd = create_and_connect_stream_or_die(opt_connect, 25);
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// and make ourselves a simple IO filter
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xmove_fd(fd, STDIN_FILENO);
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xdup2(STDIN_FILENO, STDOUT_FILENO);
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// Wait for initial server 220 message
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smtp_check(NULL, 220);
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}
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// we should start with modern EHLO
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if (250 != smtp_checkp("EHLO %s", host, -1))
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smtp_checkp("HELO %s", host, 250);
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// perform authentication
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if (opts & OPT_a) {
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smtp_check("AUTH LOGIN", 334);
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// we must read credentials unless they are given via -a[up] options
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if (!G.user || !G.pass)
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get_cred_or_die(4);
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encode_base64(NULL, G.user, NULL);
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smtp_check("", 334);
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encode_base64(NULL, G.pass, NULL);
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smtp_check("", 235);
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}
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// set sender
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// N.B. we have here a very loosely defined algorythm
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// since sendmail historically offers no means to specify secrets on cmdline.
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// 1) server can require no authentication ->
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// we must just provide a (possibly fake) reply address.
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// 2) server can require AUTH ->
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// we must provide valid username and password along with a (possibly fake) reply address.
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// For the sake of security username and password are to be read either from console or from a secured file.
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// Since reading from console may defeat usability, the solution is either to read from a predefined
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// file descriptor (e.g. 4), or again from a secured file.
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// got no sender address? use auth name, then UID username as a last resort
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if (!opt_from) {
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opt_from = xasprintf("%s@%s",
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G.user ? G.user : xuid2uname(getuid()),
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xgethostbyname(host)->h_name);
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}
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free(host);
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smtp_checkp("MAIL FROM:<%s>", opt_from, 250);
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// process message
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// read recipients from message and add them to those given on cmdline.
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// this means we scan stdin for To:, Cc:, Bcc: lines until an empty line
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// and then use the rest of stdin as message body
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code = 0; // set "analyze headers" mode
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while ((s = xmalloc_fgetline(G.fp0)) != NULL) {
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dump:
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// put message lines doubling leading dots
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if (code) {
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// escape leading dots
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// N.B. this feature is implied even if no -i (-oi) switch given
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// N.B. we need to escape the leading dot regardless of
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// whether it is single or not character on the line
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if ('.' == s[0] /*&& '\0' == s[1] */)
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bb_putchar('.');
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// dump read line
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send_r_n(s);
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free(s);
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continue;
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}
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// analyze headers
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// To: or Cc: headers add recipients
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check_hdr = (0 == strncasecmp("To:", s, 3));
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has_to |= check_hdr;
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if (opts & OPT_t) {
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if (check_hdr || 0 == strncasecmp("Bcc:" + 1, s, 3)) {
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rcptto_list(s+3);
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last_hdr = HDR_TOCC;
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goto addheader;
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}
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// Bcc: header adds blind copy (hidden) recipient
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if (0 == strncasecmp("Bcc:", s, 4)) {
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rcptto_list(s+4);
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free(s);
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last_hdr = HDR_BCC;
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continue; // N.B. Bcc: vanishes from headers!
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}
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}
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check_hdr = (list && isspace(s[0]));
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if (strchr(s, ':') || check_hdr) {
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// other headers go verbatim
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// N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines.
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// Continuation is denoted by prefixing additional lines with whitespace(s).
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// Thanks (stefan.seyfried at googlemail.com) for pointing this out.
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if (check_hdr && last_hdr != HDR_OTHER) {
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rcptto_list(s+1);
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if (last_hdr == HDR_BCC)
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continue;
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// N.B. Bcc: vanishes from headers!
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} else {
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last_hdr = HDR_OTHER;
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}
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addheader:
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// N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
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if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
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goto bail;
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llist_add_to_end(&list, s);
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} else {
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// a line without ":" (an empty line too, by definition) doesn't look like a valid header
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// so stop "analyze headers" mode
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reenter:
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// put recipients specified on cmdline
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check_hdr = 1;
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while (*argv) {
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char *t = sane_address(*argv);
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rcptto(t);
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//if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
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// goto bail;
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if (!has_to) {
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const char *hdr;
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if (check_hdr && argv[1])
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hdr = "To: %s,";
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else if (check_hdr)
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hdr = "To: %s";
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else if (argv[1])
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hdr = "To: %s," + 3;
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else
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hdr = "To: %s" + 3;
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llist_add_to_end(&list,
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xasprintf(hdr, t));
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check_hdr = 0;
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}
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argv++;
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}
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// enter "put message" mode
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// N.B. DATA fails iff no recipients were accepted (or even provided)
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// in this case just bail out gracefully
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if (354 != smtp_check("DATA", -1))
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goto bail;
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// dump the headers
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while (list) {
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send_r_n((char *) llist_pop(&list));
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}
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// stop analyzing headers
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code++;
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// N.B. !s means: we read nothing, and nothing to be read in the future.
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// just dump empty line and break the loop
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if (!s) {
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send_r_n("");
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break;
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}
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// go dump message body
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// N.B. "s" already contains the first non-header line, so pretend we read it from input
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goto dump;
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}
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}
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// odd case: we didn't stop "analyze headers" mode -> message body is empty. Reenter the loop
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// N.B. after reenter code will be > 0
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if (!code)
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goto reenter;
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// finalize the message
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smtp_check(".", 250);
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bail:
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// ... and say goodbye
|
|
smtp_check("QUIT", 221);
|
|
// cleanup
|
|
if (ENABLE_FEATURE_CLEAN_UP)
|
|
fclose(G.fp0);
|
|
|
|
return EXIT_SUCCESS;
|
|
}
|