support 2nd RCPT TO and PRDR

[ghsmtp.git] / Session.cpp

#include <algorithm>
#include <charconv>
#include <iomanip>
#include <iostream>
#include <string>
#include <vector>

#include "DNS.hpp"
#include "Domain.hpp"
#include "IP.hpp"
#include "IP4.hpp"
#include "IP6.hpp"
#include "MessageStore.hpp"
#include "Session.hpp"
#include "esc.hpp"
#include "iequal.hpp"
#include "is_ascii.hpp"
#include "osutil.hpp"

#include <fmt/format.h>
#include <fmt/ostream.h>

#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/split.hpp>

#include <boost/xpressive/xpressive.hpp>

#include <syslog.h>

#include <gflags/gflags.h>

using namespace std::string_literals;

namespace Config {
/*
char const* wls[]{
    "list.dnswl.org",
};
*/

/*
<https://www.dnswl.org/?page_id=15#query>

Return codes

The return codes are structured as 127.0.x.y, with “x” indicating the category
of an entry and “y” indicating how trustworthy an entry has been judged.

Categories (127.0.X.y):

    2 – Financial services
    3 – Email Service Providers
    4 – Organisations (both for-profit [ie companies] and non-profit)
    5 – Service/network providers
    6 – Personal/private servers
    7 – Travel/leisure industry
    8 – Public sector/governments
    9 – Media and Tech companies
    10 – some special cases
    11 – Education, academic
    12 – Healthcare
    13 – Manufacturing/Industrial
    14 – Retail/Wholesale/Services
    15 – Email Marketing Providers
    20 – Added through Self Service without specific category

Trustworthiness / Score (127.0.x.Y):

    0 = none – only avoid outright blocking (eg large ESP mailservers, -0.1)
    1 = low – reduce chance of false positives (-1.0)
    2 = medium – make sure to avoid false positives but allow override for clear
cases (-10.0) 3 = high – avoid override (-100.0).

The scores in parantheses are typical SpamAssassin scores.

Special return code 127.0.0.255

In cases where your nameserver issues more than 100’000 queries / 24 hours, you
may be blocked from further queries. The return code “127.0.0.255” indicates
this situation.

*/

char const* bls[]{
    "b.barracudacentral.org",
    "sbl-xbl.spamhaus.org",
};

/*** Last octet from A record returned by blocklists ***

<https://www.spamhaus.org/faq/section/DNSBL%20Usage#200>

 Spamhaus uses this general convention for return codes:

Return Code     Description
127.0.0.0/24    Spamhaus IP Blocklists
127.0.1.0/24    Spamhaus Domain Blocklists
127.0.2.0/24    Spamhaus Zero Reputation Domains list
127.255.255.0/24        ERRORS (not implying a "listed" response)

Currently used return codes for Spamhaus public IP zones:

Return Code     Zone    Description
127.0.0.2       SBL     Spamhaus SBL Data
127.0.0.3       SBL     Spamhaus SBL CSS Data
127.0.0.4       XBL     CBL Data
127.0.0.9       SBL     Spamhaus DROP/EDROP Data
                        (in addition to 127.0.0.2, since 01-Jun-2016)
127.0.0.10      PBL     ISP Maintained
127.0.0.11      PBL     Spamhaus Maintained

127.0.0.5-7 are allocated to XBL for possible future use;
127.0.0.8 is allocated to SBL for possible future use.

From <https://www.spamhaus.org/faq/section/Spamhaus%20DBL#291>

Return Codes    Data Source
127.0.1.2       spam domain
127.0.1.4       phish domain
127.0.1.5       malware domain
127.0.1.6       botnet C&C domain
127.0.1.102     abused legit spam
127.0.1.103     abused spammed redirector domain
127.0.1.104     abused legit phish
127.0.1.105     abused legit malware
127.0.1.106     abused legit botnet C&C
127.0.1.255     IP queries prohibited!

The following special codes indicate an error condition and should not
be taken to imply that the queried domain is "listed":

Return Code      Description
127.255.255.252  Typing error in DNSBL name
127.255.255.254  Anonymous query through public resolver
127.255.255.255  Excessive number of queries


From <http://www.surbl.org/lists#multi>

last octet indicates which lists it belongs to. The bit positions in
that last octet for membership in the different lists are:

  8 = listed on PH
 16 = listed on MW
 64 = listed on ABUSE
128 = listed on CR

*/

/*
char const* uribls[]{
    "dbl.spamhaus.org",
    "multi.uribl.com",
};
*/

constexpr auto greeting_wait              = std::chrono::seconds{6};
constexpr int  max_recipients_per_message = 100;
constexpr int  max_unrecognized_cmds      = 20;

// Read timeout value gleaned from RFC-1123 section 5.3.2 and RFC-5321
// section 4.5.3.2.7.
constexpr auto read_timeout  = std::chrono::minutes{5};
constexpr auto write_timeout = std::chrono::seconds{30};
} // namespace Config

DEFINE_bool(immortal, false, "don't set process timout");

DEFINE_uint64(max_read, 0, "max data to read");
DEFINE_uint64(max_write, 0, "max data to write");

DEFINE_bool(test_mode, false, "ease up on some checks");

DEFINE_bool(use_binarymime, true, "support BINARYMIME extension, RFC 3030");
DEFINE_bool(use_chunking, true, "support CHUNKING extension, RFC 3030");
DEFINE_bool(use_pipelining, true, "support PIPELINING extension, RFC 2920");
DEFINE_bool(use_rrvs, false, "support RRVS extension, RFC 7293");
DEFINE_bool(use_smtputf8, true, "support SMTPUTF8 extension, RFC 6531");

boost::xpressive::mark_tag     secs_(1);
boost::xpressive::sregex const all_rex = boost::xpressive::icase("wait-all-") >>
                                         (secs_ = +boost::xpressive::_d);

Session::Session(fs::path                  config_path,
                 std::function<void(void)> read_hook,
                 int                       fd_in,
                 int                       fd_out)
  : config_path_(config_path)
  , res_(config_path)
  , sock_(fd_in, fd_out, read_hook, Config::read_timeout, Config::write_timeout)
//, send_(config_path, "smtp")
//, srs_(config_path)
{
  auto accept_db_name  = config_path_ / "accept_domains";
  auto allow_db_name   = config_path_ / "allow";
  auto block_db_name   = config_path_ / "block";
  auto forward_db_name = config_path_ / "forward";

  accept_domains_.open(accept_db_name);
  allow_.open(allow_db_name);
  block_.open(block_db_name);
  forward_.open(forward_db_name);

  if (sock_.has_peername() && !IP::is_private(sock_.us_c_str())) {
    auto fcrdns = DNS::fcrdns(res_, sock_.us_c_str());
    for (auto const& fcr : fcrdns) {
      server_fcrdns_.emplace_back(fcr);
    }
  }

  server_identity_ = [this] {
    auto const id_from_env{getenv("GHSMTP_SERVER_ID")};
    if (id_from_env)
      return std::string{id_from_env};

    auto const hostname{osutil::get_hostname()};
    if (hostname.find('.') != std::string::npos)
      return hostname;

    if (!server_fcrdns_.empty()) {
      // first result should be shortest
      return server_fcrdns_.front().ascii();
    }

    auto const us_c_str = sock_.us_c_str();
    if (us_c_str && !IP::is_private(us_c_str)) {
      return IP::to_address_literal(us_c_str);
    }

    LOG(FATAL) << "can't determine my server ID, set GHSMTP_SERVER_ID maybe";
    return ""s;
  }();

  // send_.set_sender(server_identity_);

  max_msg_size(Config::max_msg_size_initial);
}

void Session::max_msg_size(size_t max)
{
  max_msg_size_ = max; // number to advertise via RFC 1870

  if (FLAGS_max_read) {
    sock_.set_max_read(FLAGS_max_read);
  }
  else {
    auto const overhead = std::max(max / 10, size_t(2048));
    sock_.set_max_read(max + overhead);
  }
}

void Session::bad_host_(char const* msg) const
{
  if (sock_.has_peername()) {
    // On my systems, this pattern triggers a fail2ban rule that
    // blocks connections from this IP address on port 25 for a few
    // days.  See <https://www.fail2ban.org/> for more info.
    syslog(LOG_MAIL | LOG_WARNING, "bad host [%s] %s", sock_.them_c_str(), msg);
  }
  std::exit(EXIT_SUCCESS);
}

void Session::reset_()
{
  // RSET does not force another EHLO/HELO, the one piece of per
  // transaction data saved is client_identity_:

  // client_identity_.clear(); <-- not cleared!

  reverse_path_.clear();
  forward_path_.clear();
  spf_received_.clear();
  // fwd_path_.clear();
  // fwd_from_.clear();
  // rep_info_.clear();

  binarymime_ = false;
  smtputf8_   = false;
  // prdr_     = false;

  if (msg_) {
    msg_.reset();
  }

  max_msg_size(max_msg_size());

  state_ = xact_step::mail;
  // send_.rset();
}

// Return codes from connection establishment are 220 or 554, according
// to RFC 5321.  That's it.

void Session::greeting()
{
  CHECK(state_ == xact_step::helo);

  if (sock_.has_peername()) {
    close(2); // if we're a networked program, never send to stderr

    std::string error_msg;
    if (!verify_ip_address_(error_msg)) {
      LOG(INFO) << error_msg;
      bad_host_(error_msg.c_str());
    }

    /******************************************************************
    <https://tools.ietf.org/html/rfc5321#section-4.3.1> says:

    4.3.  Sequencing of Commands and Replies

    4.3.1.  Sequencing Overview

    The communication between the sender and receiver is an alternating
    dialogue, controlled by the sender.  As such, the sender issues a
    command and the receiver responds with a reply.  Unless other
    arrangements are negotiated through service extensions, the sender
    MUST wait for this response before sending further commands.  One
    important reply is the connection greeting.  Normally, a receiver
    will send a 220 "Service ready" reply when the connection is
    completed.  The sender SHOULD wait for this greeting message before
    sending any commands.

    So which is it?

    “…the receiver responds with a reply.”
    “…the sender MUST wait for this response…”
    “One important reply is the connection greeting.”
    “The sender SHOULD wait for this greeting…”

    So is it MUST or SHOULD?  I enforce MUST.
    *******************************************************************/

    // Wait a bit of time for pre-greeting traffic.
    if (!(ip_allowed_ || fcrdns_allowed_)) {
      if (sock_.input_ready(Config::greeting_wait)) {
        out_() << "421 4.3.2 not accepting network messages\r\n" << std::flush;
        LOG(INFO) << "input before any greeting from " << client_;
        bad_host_("input before any greeting");
      }
      // Give a half greeting and wait again.
      out_() << "220-" << server_id_() << " ESMTP slowstart - ghsmtp\r\n"
             << std::flush;
      if (sock_.input_ready(Config::greeting_wait)) {
        out_() << "421 4.3.2 not accepting network messages\r\n" << std::flush;
        LOG(INFO) << "input before full greeting from " << client_;
        bad_host_("input before full greeting");
      }
      /*
        <https://www.rfc-editor.org/rfc/rfc5321#section-4.2>

        An SMTP client MUST determine its actions only by the reply code, not
        by the text (except for the "change of address" 251 and 551 and, if
        necessary, 220, 221, and 421 replies); in the general case, any text,
        including no text at all (although senders SHOULD NOT send bare
        codes), MUST be acceptable.  The space (blank) following the reply
        code is considered part of the text.  Whenever possible, a receiver-
        SMTP SHOULD test the first digit (severity indication) of the reply
        code.

        Except the following chokes a lot of senders:

        out_() << "220\r\n" << std::flush;

      */
      out_() << "220 " << server_id_() << " ESMTP - ghsmtp\r\n" << std::flush;
    }
    else {
      out_() << "220 " << server_id_() << " ESMTP faststart - ghsmtp\r\n"
             << std::flush;
    }
  }
  else {
    out_() << "220 " << server_id_() << " ESMTP - ghsmtp\r\n" << std::flush;
  }

  LOG(INFO) << "connect from " << client_;

  if ((!FLAGS_immortal) && (getenv("GHSMTP_IMMORTAL") == nullptr)) {
    alarm(2 * 60); // initial alarm
  }
}

void Session::flush() { out_() << std::flush; }

void Session::last_in_group_(std::string_view verb)
{
  if (sock_.input_ready(std::chrono::seconds(0))) {
    LOG(WARNING) << "pipelining error; input ready processing " << verb;
  }
}

void Session::check_for_pipeline_error_(std::string_view verb)
{
  if (!(FLAGS_use_pipelining && extensions_)) {
    if (sock_.input_ready(std::chrono::seconds(0))) {
      LOG(WARNING) << "pipelining error; input ready processing " << verb;
    }
  }
}

void Session::lo_(char const* verb, std::string_view client_identity)
{
  last_in_group_(verb);
  reset_();

  if (client_identity_ != client_identity) {
    client_identity_ = client_identity;

    std::string error_msg;
    if (!verify_client_(client_identity_, error_msg)) {
      LOG(INFO) << "client identity blocked: " << error_msg;
      bad_host_(error_msg.c_str());
    }
  }

  if (*verb == 'H') {
    extensions_ = false;
    out_() << "250 " << server_id_() << "\r\n";
  }

  if (*verb == 'E') {
    extensions_ = true;

    if (sock_.has_peername()) {
      out_() << "250-" << server_id_() << " at your service, " << client_
             << "\r\n";
    }
    else {
      out_() << "250-" << server_id_() << "\r\n";
    }

    // https://datatracker.ietf.org/doc/draft-freed-smtp-limits/
    out_() << "250-LIMITS RCPTMAX=" << Config::max_recipients_per_message
           << "\r\n";
    out_() << "250-SIZE " << max_msg_size() << "\r\n"; // RFC 1870
    out_() << "250-8BITMIME\r\n";                      // RFC 6152

    if (FLAGS_use_rrvs) {
      out_() << "250-RRVS\r\n"; // RFC 7293
    }

    // out_() << "250-PRDR\r\n"; // draft-hall-prdr-00.txt

    if (sock_.tls()) {
      // Check sasl sources for auth types.
      // out_() << "250-AUTH PLAIN\r\n";
      out_() << "250-REQUIRETLS\r\n"; // RFC 8689
    }
    else {
      // If we're not already TLS, offer TLS
      out_() << "250-STARTTLS\r\n"; // RFC 3207
    }

    out_() << "250-ENHANCEDSTATUSCODES\r\n"; // RFC 2034

    if (FLAGS_use_pipelining) {
      out_() << "250-PIPELINING\r\n"; // RFC 2920
    }

    if (FLAGS_use_binarymime) {
      out_() << "250-BINARYMIME\r\n"; // RFC 3030
    }

    if (FLAGS_use_chunking) {
      out_() << "250-CHUNKING\r\n"; // RFC 3030
    }

    if (FLAGS_use_smtputf8) {
      out_() << "250-SMTPUTF8\r\n"; // RFC 6531
    }

    out_() << "250 HELP\r\n";
  }

  out_() << std::flush;

  if (sock_.has_peername()) {
    if (std::find(begin(client_fcrdns_), end(client_fcrdns_),
                  client_identity_) != end(client_fcrdns_)) {
      LOG(INFO) << verb << " " << client_identity << " from "
                << sock_.them_address_literal();
    }
    else {
      LOG(INFO) << verb << " " << client_identity << " from " << client_;
    }
  }
  else {
    LOG(INFO) << verb << " " << client_identity;
  }
}

void Session::mail_from(Mailbox&& reverse_path, parameters_t const& parameters)
{
  check_for_pipeline_error_("MAIL FROM");

  switch (state_) {
  case xact_step::helo:
    out_() << "503 5.5.1 sequence error, expecting HELO/EHLO\r\n" << std::flush;
    LOG(WARNING) << "'MAIL FROM' before HELO/EHLO"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  case xact_step::mail: break;
  case xact_step::rcpt:
    out_() << "503 5.5.1 sequence error, expecting RCPT\r\n" << std::flush;
    LOG(WARNING) << "nested MAIL command"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  case xact_step::data:
  case xact_step::bdat:
    out_() << "503 5.5.1 sequence error, expecting DATA/BDAT\r\n" << std::flush;
    LOG(WARNING) << "nested MAIL command"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  case xact_step::rset:
    out_() << "503 5.5.1 sequence error, expecting RSET\r\n" << std::flush;
    LOG(WARNING) << "error state must be cleared with a RSET"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  }

  if (!verify_from_params_(parameters)) {
    return;
  }

  if (!smtputf8_ && !is_ascii(reverse_path.local_part())) {
    LOG(WARNING) << "non ascii reverse_path \"" << reverse_path
                 << "\" without SMTPUTF8 paramater";
  }

  std::string error_msg;
  if (!verify_sender_(reverse_path, error_msg)) {
    LOG(INFO) << "verify sender failed: " << error_msg;
    bad_host_(error_msg.c_str());
  }

  reverse_path_ = std::move(reverse_path);
  // fwd_path_.clear();
  // fwd_from_.clear();
  forward_path_.clear();
  out_() << "250 2.1.0 MAIL FROM OK\r\n";
  // No flush RFC-2920 section 3.1, this could be part of a command group.

  fmt::memory_buffer params;
  for (auto const& [name, value] : parameters) {
    fmt::format_to(std::back_inserter(params), " {}", name);
    if (!value.empty()) {
      fmt::format_to(std::back_inserter(params), "={}", value);
    }
  }
  LOG(INFO) << "MAIL FROM:<" << reverse_path_ << ">" << fmt::to_string(params);

  state_ = xact_step::rcpt;
}

// bool Session::forward_to_(std::string const& forward, Mailbox const& rcpt_to)
// {
//   // If we're already forwarding or replying, reject
//   if (!fwd_path_.empty() || !rep_info_.empty()) {
//     out_() << "432 4.3.0 Recipient's incoming mail queue has been
//     stopped\r\n"
//            << std::flush;
//     LOG(WARNING) << "failed to forward to <" << forward
//                  << "> already forwarding or replying for: " << rcpt_to;
//     return false;
//   }

//   fwd_path_ = Mailbox(forward);
//   fwd_from_ = rcpt_to;

//   // New bounce address
//   Reply::from_to bounce;
//   bounce.mail_from = reverse_path_.as_string();

//   auto const new_bounce = srs_.enc_bounce(bounce, server_id_().c_str());

//   auto const mail_from = Mailbox(new_bounce);

//   std::string error_msg;
//   if (!send_.mail_from_rcpt_to(res_, mail_from, fwd_path_, error_msg)) {
//     out_() << error_msg << std::flush;
//     LOG(WARNING) << "failed to forward <" << fwd_path_ << "> " << error_msg;
//     return false;
//   }

//   LOG(INFO) << "RCPT TO:<" << rcpt_to << "> forwarding to == <" << fwd_path_
//             << ">";
//   return true;
// }

// bool Session::reply_to_(Reply::from_to const& reply_info, Mailbox const&
// rcpt_to)
// {
//   // If we're already forwarding or replying, reject
//   if (!fwd_path_.empty() || !rep_info_.empty()) {
//     out_() << "432 4.3.0 Recipient's incoming mail queue has been
//     stopped\r\n"
//            << std::flush;
//     LOG(WARNING) << "failed to reply to <" << reply_info.mail_from
//                  << "> already forwarding or replying for: " << rcpt_to;
//     return false;
//   }

//   rep_info_ = reply_info;

//   Mailbox const from(rep_info_.rcpt_to_local_part, server_identity_);
//   Mailbox const to(rep_info_.mail_from);

//   std::string error_msg;
//   if (!send_.mail_from_rcpt_to(res_, from, to, error_msg)) {
//     out_() << error_msg << std::flush;
//     LOG(WARNING) << "failed to reply from <" << from << "> to <" << to << ">
//     "
//                  << error_msg;
//     return false;
//   }

//   LOG(INFO) << "RCPT TO:<" << rcpt_to << "> is a reply to "
//             << rep_info_.mail_from << " from " <<
//             rep_info_.rcpt_to_local_part;
//   return true;
// }

void Session::rcpt_to(Mailbox&& forward_path, parameters_t const& parameters)
{
  check_for_pipeline_error_("RCPT TO");

  switch (state_) {
  case xact_step::helo:
    out_() << "503 5.5.1 sequence error, expecting HELO/EHLO\r\n" << std::flush;
    LOG(WARNING) << "'RCPT TO' before HELO/EHLO"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  case xact_step::mail:
    out_() << "503 5.5.1 sequence error, expecting MAIL\r\n" << std::flush;
    LOG(WARNING) << "'RCPT TO' before 'MAIL FROM'"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  case xact_step::rcpt:
  case xact_step::data: break;
  case xact_step::bdat:
    out_() << "503 5.5.1 sequence error, expecting BDAT\r\n" << std::flush;
    LOG(WARNING) << "'RCPT TO' during BDAT transfer"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  case xact_step::rset:
    out_() << "503 5.5.1 sequence error, expecting RSET\r\n" << std::flush;
    LOG(WARNING) << "error state must be cleared with a RSET"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return;
  }

  if (!verify_rcpt_params_(parameters))
    return;

  if (!verify_recipient_(forward_path))
    return;

  if (!smtputf8_ && !is_ascii(forward_path.local_part())) {
    LOG(WARNING) << "non ascii forward_path \"" << forward_path
                 << "\" without SMTPUTF8 paramater";
  }

  if (forward_path_.size() >= Config::max_recipients_per_message) {
    out_() << "452 4.5.3 too many recipients\r\n" << std::flush;
    LOG(WARNING) << "too many recipients <" << forward_path << ">";
    return;
  }
  // no check for dups, postfix doesn't
  forward_path_.emplace_back(std::move(forward_path));

  Mailbox const& rcpt_to_mbx = forward_path_.back();

  LOG(INFO) << "RCPT TO:<" << rcpt_to_mbx << ">";

  // auto const rcpt_to_str = rcpt_to_mbx.as_string();

  // if (auto reply = srs_.dec_reply(rcpt_to_mbx.local_part()); reply) {
  //   if (!reply_to_(*reply, rcpt_to_mbx))
  //     return;
  // }
  // else if (auto const forward = forward_.find(rcpt_to_str.c_str()); forward)
  // {
  //   if (!forward_to_(*forward, rcpt_to_mbx))
  //     return;
  // }
  // else {
  //   LOG(INFO) << "RCPT TO:<" << rcpt_to_str << ">";
  // }

  // No flush RFC-2920 section 3.1, this could be part of a command group.
  out_() << "250 2.1.5 RCPT TO OK\r\n";

  state_ = xact_step::data;
}

// The headers Return-Path:, Received-SPF:, and Received: are returned
// as a string.

std::string Session::added_headers_(MessageStore const& msg)
{
  auto const protocol{[this]() {
    if (sock_.tls() && !extensions_) {
      LOG(WARNING) << "TLS active without extensions";
    }
    // <https://www.iana.org/assignments/mail-parameters/mail-parameters.xhtml#mail-parameters-5>
    if (smtputf8_)
      return sock_.tls() ? "UTF8SMTPS" : "UTF8SMTP";
    else if (sock_.tls())
      return "ESMTPS";
    else if (extensions_)
      return "ESMTP";
    else
      return "SMTP";
  }()};

  fmt::memory_buffer headers;

  // Return-Path:
  fmt::format_to(std::back_inserter(headers), "Return-Path: <{}>\r\n",
                 reverse_path_.as_string());

  // Received-SPF:
  if (!spf_received_.empty()) {
    fmt::format_to(std::back_inserter(headers), "{}\r\n", spf_received_);
  }

  // Received:
  // <https://tools.ietf.org/html/rfc5321#section-4.4>
  fmt::format_to(std::back_inserter(headers), "Received: from {}",
                 client_identity_.utf8());
  if (sock_.has_peername()) {
    fmt::format_to(std::back_inserter(headers), " ({})", client_);
  }
  fmt::format_to(std::back_inserter(headers), "\r\n\tby {} with {} id {}",
                 server_identity_.utf8(), protocol, msg.id().as_string_view());
  if (forward_path_.size()) {
    fmt::format_to(std::back_inserter(headers), "\r\n\tfor <{}>",
                   forward_path_[0].as_string());
    // From <https://datatracker.ietf.org/doc/html/rfc5321#section-4.4>:
    // “If the FOR clause appears, it MUST contain exactly one <path>
    //  entry, even when multiple RCPT commands have been given.  Multiple
    //  <path>s raise some security issues and have been deprecated, see
    //  Section 7.2.”
    // for (auto i = 1u; i < forward_path_.size(); ++i)
    //   fmt::format_to(headers, ",\r\n\t   <{}>", forward_path_[i]);
  }
  std::string const tls_info{sock_.tls_info()};
  if (tls_info.length()) {
    fmt::format_to(std::back_inserter(headers), "\r\n\t({})", tls_info);
  }
  fmt::format_to(std::back_inserter(headers), ";\r\n\t{}\r\n",
                 msg.when().as_string_view());

  return fmt::to_string(headers);
}

namespace {
bool lookup_domain(CDB& cdb, Domain const& domain)
{
  if (!domain.empty()) {
    if (cdb.contains(domain.ascii())) {
      return true;
    }
    if (domain.is_unicode() && cdb.contains(domain.utf8())) {
      return true;
    }
  }
  return false;
}
} // namespace

std::tuple<Session::SpamStatus, std::string> Session::spam_status_()
{
  if (spf_result_ == SPF::Result::FAIL && !ip_allowed_)
    return {SpamStatus::spam, "SPF failed"};

  // These should have already been rejected by verify_client_().
  if ((reverse_path_.domain() == "localhost.local") ||
      (reverse_path_.domain() == "localhost"))
    return {SpamStatus::spam, "bogus reverse_path"};

  std::vector<std::string> why_ham;

  // Anything enciphered tastes a lot like ham.
  if (sock_.tls())
    why_ham.emplace_back("they used TLS");

  if (spf_result_ == SPF::Result::PASS) {
    if (lookup_domain(allow_, spf_sender_domain_)) {
      why_ham.emplace_back(fmt::format("SPF sender domain ({}) is allowed",
                                       spf_sender_domain_.utf8()));
    }
    else {
      auto tld_dom{tld_db_.get_registered_domain(spf_sender_domain_.ascii())};
      if (tld_dom && allow_.contains(tld_dom)) {
        why_ham.emplace_back(fmt::format(
            "SPF sender registered domain ({}) is allowed", tld_dom));
      }
    }
  }

  if (fcrdns_allowed_)
    why_ham.emplace_back(
        fmt::format("FCrDNS (or it's registered domain) is allowed"));

  if (!why_ham.empty())
    return {SpamStatus::ham,
            fmt::format("{}", fmt::join(std::begin(why_ham), std::end(why_ham),
                                        ", and "))};

  return {SpamStatus::spam, "it's not ham"};
}

static std::string folder(Session::SpamStatus         status,
                          std::vector<Mailbox> const& forward_path,
                          Mailbox const&              reverse_path)
{
  if (reverse_path ==
      Mailbox("gene.hightower+caf_=forwarded-gmail=digilicious.com@gmail.com"))
    return ".Gmail";

  if (reverse_path == Mailbox("ietf-smtp-bounces@ietf.org"))
    return ".smtp";

  struct assignment {
    std::string_view local_part;
    std::string_view folder;
  };

  assignment assignments[] = {
      {"Emailcore", ".emailcore"},
      {"bootstrappable", ".bootstrappable"},
      {"coreboot.org", ".coreboot"},
      {"dmarc", ".dmarc"},
      {"dns-privacy", ".dns-privacy"},
      {"fucking-facebook", ".FB"},
      {"gene-ebay", ".EBay"},
      {"i-hate-facebook", ".FB"},
      {"i-hate-linked-in", ".linkedin"},
      {"mailop", ".INBOX.mailop"},
      {"modelfkeyboards.com", ""},
      {"nest", ".INBOX.Nest"},
      {"opendmarc-dev", ".dmarc"},
      {"opendmarc-users", ".dmarc"},
      {"postmaster-rua", ".INBOX.rua"},
      {"quic=ietf.org", ".INBOX.quic"},
      {"shadowserver-reports@digilicious.com", ".INBOX.shadowserver"},
      {"theatlantic.com", ""},
      {"time-nutz", ".time-nutz"},
      {"zfsonlinux.topicbox.com", ".INBOX.zfs"},
  };

  for (auto ass : assignments) {
    if (forward_path[0].local_part() == ass.local_part)
      return std::string(ass.folder);
  }

  if (iends_with(forward_path[0].local_part(), "-at-duck"))
    return ".JunkDuck";

  if (status == Session::SpamStatus::spam)
    return ".Junk";

  return "";
}

bool Session::msg_new()
{
  CHECK((state_ == xact_step::data) || (state_ == xact_step::bdat));

  auto const& [status, reason]{spam_status_()};

  LOG(INFO) << ((status == SpamStatus::ham) ? "ham since " : "spam since ")
            << reason;

  // All sources of ham get a fresh 5 minute timeout per message.
  if (status == SpamStatus::ham) {
    if ((!FLAGS_immortal) && (getenv("GHSMTP_IMMORTAL") == nullptr))
      alarm(5 * 60);
  }

  msg_ = std::make_unique<MessageStore>();

  if (!FLAGS_max_write)
    FLAGS_max_write = max_msg_size();

  try {
    msg_->open(server_id_(), FLAGS_max_write,
               folder(status, forward_path_, reverse_path_));
    auto const hdrs{added_headers_(*(msg_.get()))};
    msg_->write(hdrs);

    // fmt::memory_buffer spam_status;
    // fmt::format_to(spam_status, "X-Spam-Status: {}, {}\r\n",
    //                ((status == SpamStatus::spam) ? "Yes" : "No"), reason);
    // msg_->write(spam_status.data(), spam_status.size());

    LOG(INFO) << "Spam-Status: "
              << ((status == SpamStatus::spam) ? "Yes" : "No") << ", "
              << reason;

    return true;
  }
  catch (std::system_error const& e) {
    switch (errno) {
    case ENOSPC:
      out_() << "452 4.3.1 insufficient system storage\r\n" << std::flush;
      LOG(ERROR) << "no space";
      msg_->trash();
      msg_.reset();
      return false;

    default:
      out_() << "451 4.0.0 mail system error\r\n" << std::flush;
      LOG(ERROR) << "errno==" << errno << ": " << strerror(errno);
      LOG(ERROR) << e.what();
      msg_->trash();
      msg_.reset();
      return false;
    }
  }
  catch (std::exception const& e) {
    out_() << "451 4.0.0 mail system error\r\n" << std::flush;
    LOG(ERROR) << e.what();
    msg_->trash();
    msg_.reset();
    return false;
  }

  out_() << "451 4.0.0 mail system error\r\n" << std::flush;
  LOG(ERROR) << "msg_new failed with no exception caught";
  msg_->trash();
  msg_.reset();
  return false;
}

bool Session::msg_write(char const* s, std::streamsize count)
{
  if ((state_ != xact_step::data) && (state_ != xact_step::bdat))
    return false;

  if (!msg_)
    return false;

  try {
    if (msg_->write(s, count))
      return true;
  }
  catch (std::system_error const& e) {
    switch (errno) {
    case ENOSPC:
      out_() << "452 4.3.1 insufficient system storage\r\n" << std::flush;
      LOG(ERROR) << "no space";
      msg_->trash();
      msg_.reset();
      return false;

    default:
      out_() << "451 4.0.0 mail system error\r\n" << std::flush;
      LOG(ERROR) << "errno==" << errno << ": " << strerror(errno);
      LOG(ERROR) << e.what();
      msg_->trash();
      msg_.reset();
      return false;
    }
  }
  catch (std::exception const& e) {
    out_() << "451 4.0.0 mail system error\r\n" << std::flush;
    LOG(ERROR) << e.what();
    msg_->trash();
    msg_.reset();
    return false;
  }

  out_() << "451 4.0.0 mail system error\r\n" << std::flush;
  LOG(ERROR) << "msg_write failed with no exception caught";
  msg_->trash();
  msg_.reset();
  return false;
}

bool Session::data_start()
{
  last_in_group_("DATA");

  switch (state_) {
  case xact_step::helo:
    out_() << "503 5.5.1 sequence error, expecting HELO/EHLO\r\n" << std::flush;
    LOG(WARNING) << "'DATA' before HELO/EHLO"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  case xact_step::mail:
    out_() << "503 5.5.1 sequence error, expecting MAIL\r\n" << std::flush;
    LOG(WARNING) << "'DATA' before 'MAIL FROM'"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  case xact_step::rcpt:

    /******************************************************************
    <https://tools.ietf.org/html/rfc5321#section-3.3> says:

    The DATA command can fail at only two points in the protocol exchange:

    If there was no MAIL, or no RCPT, command, or all such commands were
    rejected, the server MAY return a "command out of sequence" (503) or
    "no valid recipients" (554) reply in response to the DATA command.

    However, <https://tools.ietf.org/html/rfc2033#section-4.2> says:

    The additional restriction is that when there have been no successful
    RCPT commands in the mail transaction, the DATA command MUST fail
    with a 503 reply code.

    Therefore I will send the reply code that is valid for both, and
    do the same for the BDAT case.
    *******************************************************************/

    out_() << "503 5.5.1 sequence error, expecting RCPT\r\n" << std::flush;
    LOG(WARNING) << "no valid recipients"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  case xact_step::data: break;
  case xact_step::bdat:
    out_() << "503 5.5.1 sequence error, expecting BDAT\r\n" << std::flush;
    LOG(WARNING) << "'DATA' during BDAT transfer"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  case xact_step::rset:
    out_() << "503 5.5.1 sequence error, expecting RSET\r\n" << std::flush;
    LOG(WARNING) << "error state must be cleared with a RSET"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  }

  if (binarymime_) {
    out_() << "503 5.5.1 sequence error, DATA does not support BINARYMIME\r\n"
           << std::flush;
    LOG(WARNING) << "DATA does not support BINARYMIME";
    state_ = xact_step::rset; // RFC 3030 section 3 page 5
    return false;
  }

  if (!msg_new()) {
    LOG(ERROR) << "msg_new() failed";
    return false;
  }

  out_() << "354 go, end with <CR><LF>.<CR><LF>\r\n" << std::flush;
  LOG(INFO) << "DATA";
  return true;
}

// bool Session::do_forward_(message::parsed& msg)
// {
//   auto msg_fwd = msg;

//   // Generate a reply address
//   Reply::from_to reply;
//   reply.mail_from          = msg_fwd.dmarc_from;
//   reply.rcpt_to_local_part = fwd_from_.local_part();

//   auto const reply_addr =
//       fmt::format("{}@{}", srs_.enc_reply(reply), server_id_());

//   auto const munging = false;

//   auto const sender   = server_identity_.ascii().c_str();
//   auto const selector = FLAGS_selector.c_str();
//   auto const key_file =
//       (config_path_ / FLAGS_selector).replace_extension("private");
//   CHECK(fs::exists(key_file)) << "can't find key file " << key_file;

//   if (munging) {
//     auto const from_hdr =
//         fmt::format("From: \"{} via\" <@>", msg_fwd.dmarc_from, reply_addr);
//     message::rewrite_from_to(msg_fwd, from_hdr, "", sender, selector,
//     key_file);
//   }
//   else {
//     auto const reply_to_hdr = fmt::format("Reply-To: {}", reply_addr);
//     message::rewrite_from_to(msg_fwd, "", reply_to_hdr, sender, selector,
//                              key_file);
//   }

//   // Forward it on
//   if (!send_.send(msg_fwd.as_string())) {
//     out_() << "432 4.3.0 Recipient's incoming mail queue has been "
//               "stopped\r\n"
//            << std::flush;

//     LOG(ERROR) << "failed to send for " << fwd_path_;
//     return false;
//   }

//   LOG(INFO) << "successfully sent for " << fwd_path_;
//   return true;
// }

// bool Session::do_reply_(message::parsed& msg)
// {
//   Mailbox to_mbx(rep_info_.mail_from);
//   Mailbox from_mbx(rep_info_.rcpt_to_local_part, server_identity_);

//   auto reply = std::make_unique<MessageStore>();
//   reply->open(server_id_(), FLAGS_max_write, ".Drafts");

//   auto const date{Now{}};
//   auto const pill{Pill{}};
//   auto const mid_str =
//       fmt::format("<{}.{}@{}>", date.sec(), pill, server_identity_);

//   fmt::memory_buffer bfr;

//   fmt::format_to(bfr, "From: <{}>\r\n", from_mbx);
//   fmt::format_to(bfr, "To: <{}>\r\n", to_mbx);

//   fmt::format_to(bfr, "Date: {}\r\n", date.c_str());

//   fmt::format_to(bfr, "Message-ID: {}\r\n", mid_str.c_str());

//   if (!msg.get_header(message::Subject).empty()) {
//     fmt::format_to(bfr, "{}: {}\r\n", message::Subject,
//                    msg.get_header(message::Subject));
//   }
//   else {
//     fmt::format_to(bfr, "{}: {}\r\n", message::Subject,
//                    "Reply to your message");
//   }

//   if (!msg.get_header(message::In_Reply_To).empty()) {
//     fmt::format_to(bfr, "{}: {}\r\n", message::In_Reply_To,
//                    msg.get_header(message::In_Reply_To));
//   }

//   if (!msg.get_header(message::MIME_Version).empty() &&
//       msg.get_header(message::Content_Type).empty()) {
//     fmt::format_to(bfr, "{}: {}\r\n", message::MIME_Version,
//                    msg.get_header(message::MIME_Version));
//     fmt::format_to(bfr, "{}: {}\r\n", message::Content_Type,
//                    msg.get_header(message::Content_Type));
//   }

//   reply->write(fmt::to_string(bfr));

//   if (!msg.body.empty()) {
//     reply->write("\r\n");
//     reply->write(msg.body);
//   }

//   auto const      msg_data = reply->freeze();
//   message::parsed msg_reply;
//   CHECK(msg_reply.parse(msg_data));

//   auto const sender   = server_identity_.ascii().c_str();
//   auto const selector = FLAGS_selector.c_str();
//   auto const key_file =
//       (config_path_ / FLAGS_selector).replace_extension("private");
//   CHECK(fs::exists(key_file)) << "can't find key file " << key_file;

//   message::dkim_sign(msg_reply, sender, selector, key_file);

//   if (!send_.send(msg_reply.as_string())) {
//     out_() << "432 4.3.0 Recipient's incoming mail queue has been "
//               "stopped\r\n"
//            << std::flush;

//     LOG(ERROR) << "send failed for reply to " << to_mbx << " from " <<
//     from_mbx; return false;
//   }

//   LOG(INFO) << "successful reply to " << to_mbx << " from " << from_mbx;
//   return true;
// }

bool Session::do_deliver_()
{
  CHECK(msg_);

  // auto const sender   = server_identity_.ascii().c_str();
  // auto const selector = FLAGS_selector.c_str();
  // auto const key_file =
  //     (config_path_ / FLAGS_selector).replace_extension("private");
  // CHECK(fs::exists(key_file)) << "can't find key file " << key_file;

  try {
    // auto const msg_data = msg_->freeze();

    // message::parsed msg;

    // // Only deal in RFC-5322 Mail Objects.
    // bool const message_parsed = msg.parse(msg_data);
    // if (message_parsed) {

    //   // remove any Return-Path
    //   message::remove_delivery_headers(msg);

    //   auto const authentic =
    //       message_parsed &&
    //       message::authentication(msg, sender, selector, key_file);

    // // write a new Return-Path
    // msg_->write(fmt::format("Return-Path: <{}>\r\n", reverse_path_));

    //   for (auto const h : msg.headers) {
    //     msg_->write(h.as_string());
    //     msg_->write("\r\n");
    //   }
    //   if (!msg.body.empty()) {
    //     msg_->write("\r\n");
    //     msg_->write(msg.body);
    //   }

    msg_->deliver();

    // if (authentic && !fwd_path_.empty()) {
    //   if (!do_forward_(msg))
    //     return false;
    // }
    // if (authentic && !rep_info_.empty()) {
    //   if (!do_reply_(msg))
    //     return false;
    // }
    // }

    msg_->close();
  }
  catch (std::system_error const& e) {
    switch (errno) {
    case ENOSPC:
      out_() << "452 4.3.1 mail system full\r\n" << std::flush;
      LOG(ERROR) << "no space";
      msg_->trash();
      reset_();
      return false;

    default:
      out_() << "550 5.0.0 mail system error\r\n" << std::flush;
      if (errno)
        LOG(ERROR) << "errno==" << errno << ": " << strerror(errno);
      LOG(ERROR) << e.what();
      msg_->trash();
      reset_();
      return false;
    }
  }

  return true;
}

void Session::data_done()
{
  CHECK((state_ == xact_step::data));

  if (msg_ && msg_->size_error()) {
    data_size_error();
    return;
  }

  // if (prdr_) {
  //   out_() << "353\r\n";
  //   for (auto fp : forward_path_) {
  //     out_() << "250 2.1.5 RCPT TO OK\r\n";
  //   }
  // }

  // Check for and act on magic "wait" address.
  {
    using namespace boost::xpressive;

    sregex const rex = icase("wait-data-") >> (secs_ = +_d);
    smatch       what;

    for (auto fp : forward_path_) {
      if (regex_match(fp.local_part(), what, rex) ||
          regex_match(fp.local_part(), what, all_rex)) {
        auto const str = what[secs_].str();
        LOG(INFO) << "waiting at DATA " << str << " seconds";
        long value = 0;
        std::from_chars(str.data(), str.data() + str.size(), value);
        google::FlushLogFiles(google::INFO);
        out_() << std::flush;
        sleep(value);
        LOG(INFO) << "done waiting";
      }
    }
  }

  if (do_deliver_()) {
    auto temp_fail_db_name = config_path_ / "temp_fail_data";
    CDB  temp_fail;

    for (auto fp : forward_path_) {
      if (temp_fail.open(temp_fail_db_name) &&
          temp_fail.contains(fp.local_part())) {
        out_() << "450 4.2.2 Mailbox full.\r\n" << std::flush;
        LOG(WARNING) << "temp fail at DATA for recipient " << fp;
        reset_();
        return;
      }
    }
  }

  // Check for addresses we reject after data.
  {
    auto bad_recipients_db_name = config_path_ / "bad_recipients_data";
    CDB  bad_recipients_db;
    if (bad_recipients_db.open(bad_recipients_db_name)) {
      for (auto fp : forward_path_) {
        std::string loc = fp.local_part();
        std::transform(loc.begin(), loc.end(), loc.begin(),
                       [](unsigned char c) { return std::tolower(c); });
        if (bad_recipients_db.contains(loc)) {
          out_() << "550 5.1.1 bad recipient " << fp << "\r\n" << std::flush;
          LOG(WARNING) << "bad recipient " << fp;
          reset_();
          return;
        }
        else {
          LOG(INFO) << "unbad recipient " << fp.local_part();
        }
      }
    }
    else {
      LOG(WARNING) << "can't open bad_recipients_data";
    }
  }

  out_() << "250 2.0.0 DATA OK\r\n" << std::flush;
  LOG(INFO) << "message delivered, " << msg_->size() << " octets, with id "
            << msg_->id();
  reset_();
}

void Session::data_size_error()
{
  out_().clear(); // clear possible eof from input side
  out_() << "552 5.3.4 message size limit exceeded\r\n" << std::flush;
  if (msg_) {
    msg_->trash();
  }
  LOG(WARNING) << "DATA size error";
  reset_();
}

void Session::data_error()
{
  out_().clear(); // clear possible eof from input side
  out_() << "554 5.3.0 message error of some kind\r\n" << std::flush;
  if (msg_) {
    msg_->trash();
  }
  LOG(WARNING) << "DATA error";
  reset_();
}

bool Session::bdat_start(size_t n)
{
  // In practice, this one gets pipelined.
  // last_in_group_("BDAT");

  switch (state_) {
  case xact_step::helo:
    out_() << "503 5.5.1 sequence error, expecting HELO/EHLO\r\n" << std::flush;
    LOG(WARNING) << "'BDAT' before HELO/EHLO"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  case xact_step::mail:
    out_() << "503 5.5.1 sequence error, expecting MAIL\r\n" << std::flush;
    LOG(WARNING) << "'BDAT' before 'MAIL FROM'"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  case xact_step::rcpt:
    // See comment in data_start()
    out_() << "503 5.5.1 sequence error, expecting RCPT\r\n" << std::flush;
    LOG(WARNING) << "no valid recipients"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  case xact_step::data: // first bdat
    break;
  case xact_step::bdat: return true;
  case xact_step::rset:
    out_() << "503 5.5.1 sequence error, expecting RSET\r\n" << std::flush;
    LOG(WARNING) << "error state must be cleared with a RSET"
                 << (sock_.has_peername() ? " from " : "") << client_;
    return false;
  }

  state_ = xact_step::bdat;

  return msg_new();
}

void Session::bdat_done(size_t n, bool last)
{
  if (state_ != xact_step::bdat) {
    bdat_seq_error();
    return;
  }

  if (!msg_) {
    return;
  }

  if (msg_->size_error()) {
    bdat_size_error();
    return;
  }

  if (!last) {
    out_() << "250 2.0.0 BDAT " << n << " OK\r\n" << std::flush;
    LOG(INFO) << "BDAT " << n;
    return;
  }

  // Check for and act on magic "wait" address.
  {
    using namespace boost::xpressive;

    sregex const rex = icase("wait-bdat-") >> (secs_ = +_d);
    smatch       what;

    for (auto fp : forward_path_) {
      if (regex_match(fp.local_part(), what, rex) ||
          regex_match(fp.local_part(), what, all_rex)) {
        auto const str = what[secs_].str();
        LOG(INFO) << "waiting at BDAT " << str << " seconds";
        long value = 0;
        std::from_chars(str.data(), str.data() + str.size(), value);
        google::FlushLogFiles(google::INFO);
        out_() << std::flush;
        sleep(value);
        LOG(INFO) << "done waiting";
      }
    }
  }

  do_deliver_();

  out_() << "250 2.0.0 BDAT " << n << " LAST OK\r\n" << std::flush;
  LOG(INFO) << "BDAT " << n << " LAST";
  LOG(INFO) << "message delivered, " << msg_->size() << " octets, with id "
            << msg_->id();
  reset_();
}

void Session::bdat_size_error()
{
  out_().clear(); // clear possible eof from input side
  out_() << "552 5.3.4 message size limit exceeded\r\n" << std::flush;
  if (msg_) {
    msg_->trash();
  }
  LOG(WARNING) << "BDAT size error";
  reset_();
}

void Session::bdat_seq_error()
{
  out_().clear(); // clear possible eof from input side
  out_() << "503 5.5.1 BDAT sequence error\r\n" << std::flush;
  if (msg_) {
    msg_->trash();
  }
  LOG(WARNING) << "BDAT sequence error";
  reset_();
}

void Session::bdat_io_error()
{
  out_().clear(); // clear possible eof from input side
  out_() << "503 5.5.1 BDAT I/O error\r\n" << std::flush;
  if (msg_) {
    msg_->trash();
  }
  LOG(WARNING) << "BDAT I/O error";
  reset_();
}

void Session::rset()
{
  out_() << "250 2.1.5 RSET OK\r\n";
  // No flush RFC-2920 section 3.1, this could be part of a command group.
  LOG(INFO) << "RSET";
  reset_();
}

void Session::noop(std::string_view str)
{
  last_in_group_("NOOP");
  out_() << "250 2.0.0 NOOP OK\r\n" << std::flush;
  LOG(INFO) << "NOOP" << (str.length() ? " " : "") << str;
}

void Session::vrfy(std::string_view str)
{
  last_in_group_("VRFY");
  out_() << "252 2.1.5 try it\r\n" << std::flush;
  LOG(INFO) << "VRFY" << (str.length() ? " " : "") << str;
}

void Session::help(std::string_view str)
{
  if (iequal(str, "help\r\n")) {
    out_() << "214 2.0.0 Now you're sounding desperate.\r\n" << std::flush;
  }
  else {
    out_() << "214 2.0.0 see https://digilicious.com/smtp.html\r\n"
           << std::flush;
  }
  LOG(INFO) << "HELP" << (str.length() ? " " : "") << str;
}

void Session::quit()
{
  // send_.quit();
  // last_in_group_("QUIT");
  out_() << "221 2.0.0 closing connection\r\n" << std::flush;
  LOG(INFO) << "QUIT";
  exit_();
}

void Session::auth()
{
  out_() << "454 4.7.0 authentication failure\r\n" << std::flush;
  LOG(INFO) << "AUTH";
  bad_host_("auth");
}

void Session::error(std::string_view log_msg)
{
  out_() << "421 4.3.5 system error: " << log_msg << "\r\n" << std::flush;
  LOG(WARNING) << log_msg;
}

void Session::cmd_unrecognized(std::string_view cmd)
{
  auto const escaped{esc(cmd)};
  LOG(WARNING) << "command unrecognized: \"" << escaped << "\"";

  if (++n_unrecognized_cmds_ >= Config::max_unrecognized_cmds) {
    out_() << "500 5.5.1 command unrecognized: \"" << escaped
           << "\" exceeds limit\r\n"
           << std::flush;
    LOG(WARNING) << n_unrecognized_cmds_
                 << " unrecognized commands is too many";
    exit_();
  }

  out_() << "500 5.5.1 command unrecognized: \"" << escaped << "\"\r\n"
         << std::flush;
}

void Session::bare_lf()
{
  // Error code used by Office 365.
  out_() << "554 5.6.11 bare LF\r\n" << std::flush;
  LOG(WARNING) << "bare LF";
  exit_();
}

void Session::max_out()
{
  out_() << "552 5.3.4 message size limit exceeded\r\n" << std::flush;
  LOG(WARNING) << "message size maxed out";
  exit_();
}

void Session::time_out()
{
  out_() << "421 4.4.2 time-out\r\n" << std::flush;
  LOG(WARNING) << "time-out" << (sock_.has_peername() ? " from " : "")
               << client_;
  exit_();
}

void Session::starttls()
{
  last_in_group_("STARTTLS");
  if (sock_.tls()) {
    out_() << "554 5.5.1 TLS already active\r\n" << std::flush;
    LOG(WARNING) << "STARTTLS issued with TLS already active";
  }
  else if (!extensions_) {
    out_() << "554 5.5.1 TLS not avaliable without using EHLO\r\n"
           << std::flush;
    LOG(WARNING) << "STARTTLS issued without using EHLO";
  }
  else {
    out_() << "220 2.0.0 STARTTLS OK\r\n" << std::flush;
    if (sock_.starttls_server(config_path_)) {
      reset_();
      max_msg_size(Config::max_msg_size_bro);
      LOG(INFO) << "STARTTLS " << sock_.tls_info();
    }
    else {
      LOG(INFO) << "failed STARTTLS";
    }
  }
}

void Session::exit_()
{
  // sock_.log_totals();

  timespec time_used{};
  clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time_used);

  LOG(INFO) << "CPU time " << time_used.tv_sec << "." << std::setw(9)
            << std::setfill('0') << time_used.tv_nsec << " seconds";

  std::exit(EXIT_SUCCESS);
}

/////////////////////////////////////////////////////////////////////////////

// All of the verify_* functions send their own error messages back to
// the client on failure, and return false.

bool Session::verify_ip_address_(std::string& error_msg)
{
  auto ip_block_db_name = config_path_ / "ip-block";
  CDB  ip_block;
  if (ip_block.open(ip_block_db_name) &&
      ip_block.contains(sock_.them_c_str())) {
    error_msg =
        fmt::format("IP address {} on static blocklist", sock_.them_c_str());
    out_() << "554 5.7.1 " << error_msg << "\r\n" << std::flush;
    return false;
  }

  client_fcrdns_.clear();

  if ((sock_.them_address_literal() == IP4::loopback_literal) ||
      (sock_.them_address_literal() == IP6::loopback_literal)) {
    LOG(INFO) << "loopback address allowed";
    ip_allowed_ = true;
    client_fcrdns_.emplace_back("localhost");
    client_ = fmt::format("localhost {}", sock_.them_address_literal());
    return true;
  }

  auto const fcrdns = DNS::fcrdns(res_, sock_.them_c_str());
  for (auto const& fcr : fcrdns) {
    client_fcrdns_.emplace_back(fcr);
  }

  if (IP::is_private(sock_.them_address_literal())) {
    LOG(INFO) << "private address allowed";
    ip_allowed_ = true;
    client_     = sock_.them_address_literal();
    return true;
  }

  if (!client_fcrdns_.empty()) {
    client_ = fmt::format("{} {}", client_fcrdns_.front().ascii(),
                          sock_.them_address_literal());
    // check allow list
    for (auto const& client_fcrdns : client_fcrdns_) {
      if (allow_.contains(client_fcrdns.ascii())) {
        LOG(INFO) << "FCrDNS " << client_fcrdns << " allowed";
        fcrdns_allowed_ = true;
        return true;
      }
      auto const tld{tld_db_.get_registered_domain(client_fcrdns.ascii())};
      if (tld) {
        if (allow_.contains(tld)) {
          LOG(INFO) << "FCrDNS registered domain " << tld << " allowed";
          fcrdns_allowed_ = true;
          return true;
        }
      }
    }
    // check blocklist
    for (auto const& client_fcrdns : client_fcrdns_) {
      if (block_.contains(client_fcrdns.ascii())) {
        error_msg =
            fmt::format("FCrDNS {} on static blocklist", client_fcrdns.ascii());
        out_() << "554 5.7.1 blocklisted\r\n" << std::flush;
        return false;
      }

      auto const tld{tld_db_.get_registered_domain(client_fcrdns.ascii())};
      if (tld) {
        if (block_.contains(tld)) {
          error_msg = fmt::format(
              "FCrDNS registered domain {} on static blocklist", tld);
          out_() << "554 5.7.1 blocklisted\r\n" << std::flush;
          return false;
        }
      }
    }
  }
  else {
    client_ = fmt::format("{}", sock_.them_address_literal());
  }

  if (IP4::is_address(sock_.them_c_str())) {

    auto const reversed{IP4::reverse(sock_.them_c_str())};

    /*
    // Check with allow list.
    std::shuffle(std::begin(Config::wls), std::end(Config::wls),
                 random_device_);

    for (auto wl : Config::wls) {
      DNS::Query q(res_, DNS::RR_type::A, reversed + wl);
      if (q.has_record()) {
        using namespace boost::xpressive;

        auto const as = q.get_strings()[0];
        LOG(INFO) << "on allow list " << wl << " as " << as;

        mark_tag     x_(1);
        mark_tag     y_(2);
        sregex const rex = as_xpr("127.0.") >> (x_ = +_d) >> '.' >> (y_ = +_d);
        smatch       what;

        if (regex_match(as, what, rex)) {
          auto const x = what[x_].str();
          auto const y = what[y_].str();

          int value = 0;
          std::from_chars(y.data(), y.data() + y.size(), value);
          if (value > 0) {
            ip_allowed_ = true;
            LOG(INFO) << "allowed";
          }
        }

        LOG(INFO) << "Any A record skips check on block list";
        return true;
      }
    }
    */

    // Check with block lists. <https://en.wikipedia.org/wiki/DNSBL>
    std::shuffle(std::begin(Config::bls), std::end(Config::bls),
                 random_device_);

    for (auto bl : Config::bls) {
      DNS::Query q(res_, DNS::RR_type::A, reversed + bl);
      if (q.has_record()) {
        const auto a_strings = q.get_strings();
        for (auto const& as : a_strings) {
          LOG(INFO) << bl << " returned " << as;
        }
        for (auto const& as : a_strings) {
          if (as == "127.0.0.1") {
            LOG(INFO) << "Should never get 127.0.0.1, from " << bl;
          }
          else if (as == "127.0.0.10" || as == "127.0.0.11") {
            LOG(INFO) << "PBL listed, ignoring " << bl;
          }
          else if (as == "127.255.255.252") {
            LOG(INFO) << "Typing error in DNSBL name " << bl;
          }
          else if (as == "127.255.255.254") {
            LOG(INFO) << "Anonymous query through public resolver " << bl;
          }
          else if (as == "127.255.255.255") {
            LOG(INFO) << "Excessive number of queries " << bl;
          }
          else {
            error_msg = fmt::format("IP address {} blocked: {} returned {}",
                                    sock_.them_c_str(), bl, as);
            out_() << "554 5.7.1 " << error_msg << "\r\n" << std::flush;
            return false;
          }
        }
      }
    }
    // LOG(INFO) << "IP address " << sock_.them_c_str() << " cleared by dnsbls";
  }

  LOG(INFO) << "IP address okay";
  return true;
}

bool domain_blocked(DNS::Resolver& res, Domain const& identity)
{
  Domain     lookup{fmt::format("{}.dbl.spamhaus.org", identity.ascii())};
  DNS::Query q(res, DNS::RR_type::A, lookup.ascii());
  if (q.has_record()) {
    const auto a_strings = q.get_strings();
    for (auto const& as : a_strings) {
      if (istarts_with(as, "127.0.1.")) {
        LOG(INFO) << "Domain " << identity << " blocked by spamhaus, " << as;
        return true;
      }
    }
  }
  return false;
}

// check the identity from HELO/EHLO
bool Session::verify_client_(Domain const& client_identity,
                             std::string&  error_msg)
{
  if (!client_fcrdns_.empty()) {
    if (auto id = std::find(begin(client_fcrdns_), end(client_fcrdns_),
                            client_identity);
        id != end(client_fcrdns_)) {
      // If the HELO ident is one of the FCrDNS names...
      if (id != begin(client_fcrdns_)) {
        // ...then rotate that one to the front of the list
        std::rotate(begin(client_fcrdns_), id, id + 1);
      }
      client_ = fmt::format("{} {}", client_fcrdns_.front().ascii(),
                            sock_.them_address_literal());
      return true;
    }
    LOG(INFO) << "claimed identity " << client_identity
              << " does NOT match any FCrDNS: ";
    for (auto const& client_fcrdns : client_fcrdns_) {
      LOG(INFO) << "                 " << client_fcrdns;
    }
  }

  // Bogus clients claim to be us or some local host.
  if (sock_.has_peername() && ((client_identity == server_identity_) ||
                               (client_identity == "localhost") ||
                               (client_identity == "localhost.localdomain"))) {

    if ((sock_.them_address_literal() == IP4::loopback_literal) ||
        (sock_.them_address_literal() == IP6::loopback_literal)) {
      return true;
    }

    // Give 'em a pass.
    if (ip_allowed_) {
      LOG(INFO) << "allow-listed IP address can claim to be "
                << client_identity;
      return true;
    }

    // Ease up in test mode.
    if (FLAGS_test_mode || getenv("GHSMTP_TEST_MODE")) {
      return true;
    }

    error_msg = fmt::format("liar, claimed to be {}", client_identity.ascii());
    out_() << "550 5.7.1 liar\r\n" << std::flush;
    return false;
  }

  std::vector<std::string> labels;
  boost::algorithm::split(labels, client_identity.ascii(),
                          boost::algorithm::is_any_of("."));
  if (labels.size() < 2) {
    error_msg =
        fmt::format("claimed bogus identity {}", client_identity.ascii());
    out_() << "550 4.7.1 bogus identity\r\n" << std::flush;
    return false;
    // // Sometimes we may want to look at mail from non conforming
    // // sending systems.
    // LOG(WARNING) << "invalid sender" << (sock_.has_peername() ? " " : "")
    //              << client_ << " claiming " << client_identity;
    // return true;
  }

  if (lookup_domain(block_, client_identity)) {
    error_msg =
        fmt::format("claimed blocked identity {}", client_identity.ascii());
    out_() << "550 4.7.1 blocked identity\r\n" << std::flush;
    return false;
  }

  auto const tld{tld_db_.get_registered_domain(client_identity.ascii())};
  if (!tld) {
    // Sometimes we may want to look at mail from misconfigured
    // sending systems.
    // LOG(WARNING) << "claimed identity has no registered domain";
    // return true;
  }
  else if (block_.contains(tld)) {
    error_msg =
        fmt::format("claimed identity has blocked registered domain {}", tld);
    out_() << "550 4.7.1 blocked registered domain\r\n" << std::flush;
    return false;
  }

  if (domain_blocked(res_, client_identity) ||
      domain_blocked(res_, Domain(tld))) {
    error_msg = fmt::format("claimed identity {} blocked by spamhaus",
                            client_identity.ascii());
    out_() << "550 4.7.1 blocked identity\r\n" << std::flush;
    return false;
  }

  DNS::Query q(res_, DNS::RR_type::A, client_identity.ascii());
  if (!q.has_record()) {
    LOG(WARNING) << "claimed identity " << client_identity.ascii()
                 << " not DNS resolvable";
  }

  // not otherwise objectionable
  return true;
}

// check sender from RFC5321 MAIL FROM:
bool Session::verify_sender_(Mailbox const& sender, std::string& error_msg)
{
  do_spf_check_(sender);

  std::string const sender_str{sender};

  if (sender.empty()) {
    // MAIL FROM:<>
    // is used to send bounce messages.
    return true;
  }

  if (domain_blocked(res_, sender.domain())) {
    error_msg = fmt::format("{} sender domain blocked by spamhaus", sender_str);
    out_() << "550 5.1.8 " << error_msg << "\r\n" << std::flush;
    return false;
  }

  auto bad_senders_db_name = config_path_ / "bad_senders";
  CDB  bad_senders;
  if (bad_senders.open(bad_senders_db_name) &&
      bad_senders.contains(sender_str)) {
    error_msg = fmt::format("{} bad sender", sender_str);
    out_() << "550 5.1.8 " << error_msg << "\r\n" << std::flush;
    return false;
  }

  // We don't accept mail /from/ a domain we are expecting to accept
  // mail for on an external network connection.

  if (sock_.them_address_literal() != sock_.us_address_literal()) {
    if ((accept_domains_.is_open() &&
         (accept_domains_.contains(sender.domain().ascii()) ||
          accept_domains_.contains(sender.domain().utf8()))) ||
        (sender.domain() == server_identity_)) {

      // Ease up in test mode.
      if (FLAGS_test_mode || getenv("GHSMTP_TEST_MODE")) {
        return true;
      }
      out_() << "550 5.7.1 liar\r\n" << std::flush;
      error_msg = fmt::format("liar, claimed to be {}", sender.domain().utf8());
      return false;
    }
  }

  if (sender.domain().is_address_literal()) {
    if (sender.domain() != sock_.them_address_literal()) {
      LOG(WARNING) << "sender domain " << sender.domain() << " does not match "
                   << sock_.them_address_literal();
    }
    return true;
  }

  if (!verify_sender_domain_(sender.domain(), error_msg)) {
    return false;
  }

  return true;
}

// this sender is the RFC5321 MAIL FROM: domain part
bool Session::verify_sender_domain_(Domain const& sender,
                                    std::string&  error_msg)
{
  if (sender.empty()) {
    // MAIL FROM:<>
    // is used to send bounce messages.
    return true;
  }

  // Break sender domain into labels:

  std::vector<std::string> labels;
  boost::algorithm::split(labels, sender.ascii(),
                          boost::algorithm::is_any_of("."));

  if (labels.size() < 2) { // This is not a valid domain.
    error_msg = fmt::format("{} invalid syntax", sender.ascii());
    out_() << "550 5.7.1 " << error_msg << "\r\n" << std::flush;
    return false;
  }

  if (lookup_domain(block_, sender)) {
    error_msg = fmt::format("SPF sender domain ({}) is blocked",
                            spf_sender_domain_.ascii());
    out_() << "550 5.7.1 " << error_msg << "\r\n" << std::flush;
    return false;
  }

  if (spf_result_ == SPF::Result::PASS) {
    if (allow_.contains(spf_sender_domain_.ascii())) {
      LOG(INFO) << "sender " << spf_sender_domain_.ascii() << " allowed";
      return true;
    }

    auto const reg_dom{
        tld_db_.get_registered_domain(spf_sender_domain_.ascii())};
    if (reg_dom) {
      if (allow_.contains(reg_dom)) {
        LOG(INFO) << "sender registered domain \"" << reg_dom << "\" allowed";
        return true;
      }
    }
  }

  LOG(INFO) << "sender \"" << sender << "\" not disallowed";
  return true;
}

void Session::do_spf_check_(Mailbox const& sender)
{
  if (!sock_.has_peername()) {
    auto const ip_addr = "127.0.0.1"; // use localhost for local socket
    spf_received_      = fmt::format(
             "Received-SPF: pass ({}: allow-listed) client-ip={}; "
                  "envelope-from={}; helo={};",
             server_id_(), ip_addr, sender.as_string(), client_identity_.ascii());
    spf_sender_domain_ = "localhost";
    return;
  }

  auto const spf_srv     = SPF::Server{server_id_().c_str()};
  auto       spf_request = SPF::Request{spf_srv};

  if (IP4::is_address(sock_.them_c_str())) {
    spf_request.set_ipv4_str(sock_.them_c_str());
  }
  else if (IP6::is_address(sock_.them_c_str())) {
    spf_request.set_ipv6_str(sock_.them_c_str());
  }
  else {
    LOG(FATAL) << "bogus address " << sock_.them_address_literal() << ", "
               << sock_.them_c_str();
  }

  auto const from{static_cast<std::string>(sender)};

  spf_request.set_env_from(from.c_str());
  spf_request.set_helo_dom(client_identity_.ascii().c_str());

  auto const spf_res{SPF::Response{spf_request}};
  spf_result_        = spf_res.result();
  spf_received_      = spf_res.received_spf();
  spf_sender_domain_ = spf_request.get_sender_dom();

  LOG(INFO) << "spf_received_ == " << spf_received_;

  if (spf_result_ == SPF::Result::FAIL) {
    LOG(INFO) << "FAIL " << spf_res.header_comment();
  }
  else if (spf_result_ == SPF::Result::NEUTRAL) {
    LOG(INFO) << "NEUTRAL " << spf_res.header_comment();
  }
  else if (spf_result_ == SPF::Result::PASS) {
    LOG(INFO) << "PASS " << spf_res.header_comment();
  }
  else {
    LOG(INFO) << "INVALID/SOFTFAIL/NONE/xERROR " << server_id_().c_str();
  }
}

bool Session::verify_from_params_(parameters_t const& parameters)
{
  // Take a look at the optional parameters:
  for (auto const& [name, value] : parameters) {
    if (iequal(name, "BODY")) {
      if (iequal(value, "8BITMIME")) {
        // everything is cool, this is our default...
      }
      else if (iequal(value, "7BIT")) {
        // nothing to see here, move along...
      }
      else if (iequal(value, "BINARYMIME")) {
        binarymime_ = true;
      }
      else {
        LOG(WARNING) << "unrecognized BODY type \"" << value << "\" requested";
      }
    }
    else if (iequal(name, "SMTPUTF8")) {
      if (!value.empty()) {
        LOG(WARNING) << "SMTPUTF8 parameter has a value: " << value;
      }
      smtputf8_ = true;
    }

    // else if (iequal(name, "PRDR")) {
    //   LOG(INFO) << "using PRDR";
    //   prdr_ = true;
    // }

    else if (iequal(name, "SIZE")) {
      if (value.empty()) {
        LOG(WARNING) << "SIZE parameter has no value.";
      }
      else {
        try {
          auto const sz = stoull(value);
          if (sz > max_msg_size()) {
            out_() << "552 5.3.4 message size limit exceeded\r\n" << std::flush;
            LOG(WARNING) << "SIZE parameter too large: " << sz;
            return false;
          }
        }
        catch (std::invalid_argument const& e) {
          LOG(WARNING) << "SIZE parameter has invalid value: " << value;
        }
        catch (std::out_of_range const& e) {
          LOG(WARNING) << "SIZE parameter has out-of-range value: " << value;
        }
        // I guess we just ignore bad size parameters.
      }
    }
    else if (iequal(name, "REQUIRETLS")) {
      if (!sock_.tls()) {
        out_() << "554 5.7.1 REQUIRETLS needed\r\n" << std::flush;
        LOG(WARNING) << "REQUIRETLS needed";
        return false;
      }
    }
    else {
      LOG(WARNING) << "unrecognized 'MAIL FROM' parameter " << name << "="
                   << value;
    }
  }

  return true;
}

bool Session::verify_rcpt_params_(parameters_t const& parameters)
{
  // Take a look at the optional parameters:
  for (auto const& [name, value] : parameters) {
    if (iequal(name, "RRVS")) {
      // rrvs-param = "RRVS=" date-time [ ";" ( "C" / "R" ) ]
      LOG(INFO) << name << "=" << value;
    }
    else {
      LOG(WARNING) << "unrecognized 'RCPT TO' parameter " << name << "="
                   << value;
    }
  }

  return true;
}

// check recipient from RFC5321 RCPT TO:
bool Session::verify_recipient_(Mailbox const& recipient)
{
  if ((recipient.local_part() == "Postmaster") && (recipient.domain() == "")) {
    LOG(INFO) << "magic Postmaster address";
    return true;
  }

  auto const accepted_domain{[this, &recipient] {
    if (recipient.domain().is_address_literal()) {
      if (recipient.domain() != sock_.us_address_literal()) {
        LOG(WARNING) << "recipient.domain address " << recipient.domain()
                     << " does not match ours " << sock_.us_address_literal();
        /*
            return false;
        */
      }
      return true;
    }

    // Domains we accept mail for.
    if (accept_domains_.is_open()) {
      if (accept_domains_.contains(recipient.domain().ascii()) ||
          accept_domains_.contains(recipient.domain().utf8())) {
        return true;
      }
    }
    else {
      // If we have no list of domains to accept, at least take our own.
      if (recipient.domain() == server_id_()) {
        return true;
      }
    }

    return false;
  }()};

  if (!accepted_domain) {
    out_() << "550 5.7.1 relay access denied\r\n" << std::flush;
    LOG(WARNING) << "relay access denied for domain " << recipient.domain();
    return false;
  }

  if (recipient.local_part() == "gene" && client_fcrdns_.size() &&
      client_fcrdns_[0].ascii().ends_with("outlook.com")) {
    // Getting Spam'ed by MS
    if (reverse_path_.empty() || (reverse_path_.length() > 40) ||
        reverse_path_.domain().ascii().ends_with(".onmicrosoft.com")) {
      std::string error_msg = fmt::format("rejecting spammy message from {}",
                                          client_fcrdns_[0].ascii());
      LOG(WARNING) << error_msg;
      out_() << "550 5.7.0 " << error_msg << "\r\n" << std::flush;
      return false;
    }
  }

  // Check for local addresses we reject.
  {
    auto bad_recipients_db_name = config_path_ / "bad_recipients";
    CDB  bad_recipients_db;

    std::string loc = recipient.local_part();
    std::transform(loc.begin(), loc.end(), loc.begin(),
                   [](unsigned char c) { return std::tolower(c); });

    if (bad_recipients_db.open(bad_recipients_db_name) &&
        bad_recipients_db.contains(loc)) {
      out_() << "550 5.1.1 bad recipient " << recipient << "\r\n" << std::flush;
      LOG(WARNING) << "bad recipient " << recipient;
      return false;
    }
  }

  {
    auto fail_db_name = config_path_ / "fail_554";
    if (fs::exists(fail_db_name)) {
      CDB fail_db;
      if (fail_db.open(fail_db_name) &&
          fail_db.contains(recipient.local_part())) {
        out_() << "554 5.7.1 prohibited for policy reasons" << recipient
               << "\r\n"
               << std::flush;
        LOG(WARNING) << "fail_554 recipient " << recipient;
        return false;
      }
    }
  }

  {
    auto temp_fail_db_name = config_path_ / "temp_fail";
    CDB  temp_fail;
    if (temp_fail.open(temp_fail_db_name) &&
        temp_fail.contains(recipient.local_part())) {
      out_() << "432 4.3.0 recipient's incoming mail queue has been stopped\r\n"
             << std::flush;
      LOG(WARNING) << "temp fail for recipient " << recipient;
      return false;
    }
  }

  // Check for and act on magic "wait" address.
  {
    using namespace boost::xpressive;

    sregex const rex = icase("wait-rcpt-") >> (secs_ = +_d);
    smatch       what;

    if (regex_match(recipient.local_part(), what, rex) ||
        regex_match(recipient.local_part(), what, all_rex)) {
      auto const str = what[secs_].str();
      LOG(INFO) << "waiting at RCPT TO " << str << " seconds";
      long value = 0;
      std::from_chars(str.data(), str.data() + str.size(), value);
      google::FlushLogFiles(google::INFO);
      out_() << std::flush;
      sleep(value);
      LOG(INFO) << "done waiting";
    }
  }

  // This is a trap for a probe done by some senders to see if we
  // accept just any old local-part.
  // if (!extensions_) {
  //   if (recipient.local_part().length() > 8) {
  //     out_() << "550 5.1.1 unknown recipient " << recipient << "\r\n"
  //            << std::flush;
  //     LOG(WARNING) << "unknown recipient for HELO " << recipient;
  //     return false;
  //   }
  // }

  return true;
}