/*

Copyright (c) 2014-2017, 2019-2020, Arvid Norberg

Copyright (c) 2016-2018, 2020, Alden Torres

All rights reserved.

Redistribution and use in source and binary forms, with or without

modification, are permitted provided that the following conditions

are met:

    * Redistributions of source code must retain the above copyright

      notice, this list of conditions and the following disclaimer.

    * Redistributions in binary form must reproduce the above copyright

      notice, this list of conditions and the following disclaimer in

      the documentation and/or other materials provided with the distribution.

    * Neither the name of the author nor the names of its

      contributors may be used to endorse or promote products derived

      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE

LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR

CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN

CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

POSSIBILITY OF SUCH DAMAGE.

*/

#include "libtorrent/aux_/resolver.hpp"

#include "libtorrent/debug.hpp"

#include "libtorrent/aux_/time.hpp"

namespace libtorrent {

namespace aux {

  constexpr resolver_flags resolver_interface::cache_only;

  constexpr resolver_flags resolver_interface::abort_on_shutdown;

  resolver::resolver(io_context& ios)

    : m_ios(ios)

    , m_resolver(ios)

    , m_critical_resolver(ios)

    , m_max_size(700)

    , m_timeout(seconds(1200))

  {}

namespace {

  void callback(resolver_interface::callback_t h

    , error_code const& ec, std::vector<address> const& ips)

  {

    try {

      h(ec, ips);

    } catch (std::exception&) {

      TORRENT_ASSERT_FAIL();

    }

  }

}

  void resolver::on_lookup(error_code const& ec, tcp::resolver::results_type ips

    , std::string const& hostname)

  {

    COMPLETE_ASYNC("resolver::on_lookup");

    if (ec)

    {

      failed_dns_cache_entry& ce = m_failed_cache[hostname];

      ce.last_seen = time_now();

      ce.error = ec;

      // if the cache grows too big, weed out the

      // oldest entries

      if (int(m_failed_cache.size()) > m_max_size)

      {

        auto oldest = m_failed_cache.begin();

        for (auto k = m_failed_cache.begin(); k != m_failed_cache.end(); ++k)

        {

          if (k->second.last_seen < oldest->second.last_seen)

            oldest = k;

        }

        // remove the oldest entry

        m_failed_cache.erase(oldest);

      }

      auto const range = m_callbacks.equal_range(hostname);

      for (auto c = range.first; c != range.second; ++c)

        callback(std::move(c->second), ec, {});

      m_callbacks.erase(range.first, range.second);

      return;

    }

    {

      auto const k = m_failed_cache.find(hostname);

      if (k != m_failed_cache.end())

        m_failed_cache.erase(k);

    }

    dns_cache_entry& ce = m_cache[hostname];

    ce.last_seen = time_now();

    ce.addresses.clear();

    for (auto i : ips)

      ce.addresses.push_back(i.endpoint().address());

    auto const range = m_callbacks.equal_range(hostname);

    for (auto c = range.first; c != range.second; ++c)

      callback(std::move(c->second), ec, ce.addresses);

    m_callbacks.erase(range.first, range.second);

    // if m_cache grows too big, weed out the

    // oldest entries

    if (int(m_cache.size()) > m_max_size)

    {

      auto oldest = m_cache.begin();

      for (auto k = m_cache.begin(); k != m_cache.end(); ++k)

      {

        if (k->second.last_seen < oldest->second.last_seen)

          oldest = k;

      }

      // remove the oldest entry

      m_cache.erase(oldest);

    }

  }

  void resolver::async_resolve(std::string const& host, resolver_flags const flags

    , resolver_interface::callback_t h)

  {

    // special handling for raw IP addresses. There's no need to get in line

    // behind actual lookups if we can just resolve it immediately.

    error_code ec;

    address const ip = make_address(host, ec);

    if (!ec)

    {

      post(m_ios, [h, ec, ip]{ callback(h, ec, std::vector<address>{ip}); });

      return;

    }

    ec.clear();

    auto const i = m_cache.find(host);

    if (i != m_cache.end())

    {

      // keep cache entries valid for m_timeout seconds

      if ((flags & resolver_interface::cache_only)

        || i->second.last_seen + m_timeout >= time_now())

      {

        std::vector<address> ips = i->second.addresses;

        post(m_ios, [h, ec, ips] { callback(h, ec, ips); });

        return;

      }

    }

    auto const k = m_failed_cache.find(host);

    if (k != m_failed_cache.end())

    {

      // keep cache entries valid for m_timeout seconds

      // failures are cached for a shorter time to optimistically retry

      if ((flags & resolver_interface::cache_only)

        || k->second.last_seen + m_timeout / 8 >= time_now())

      {

        error_code error_code = k->second.error;

        post(m_ios, [h, error_code] { callback(h, error_code, {}); });

        return;

      }

    }

    if (flags & resolver_interface::cache_only)

    {

      // we did not find a cache entry, fail the lookup

      post(m_ios, [h] {

        callback(h, boost::asio::error::host_not_found, std::vector<address>{});

      });

      return;

    }

    auto iter = m_callbacks.find(host);

    bool const done = (iter != m_callbacks.end());

    m_callbacks.insert(iter, {host, std::move(h)});

    // if there is an existing outtanding lookup, our callback will be

    // called once it completes. We're done here.

    if (done) return;

    // the port is ignored

    using namespace std::placeholders;

    ADD_OUTSTANDING_ASYNC("resolver::on_lookup");

    if (flags & resolver_interface::abort_on_shutdown)

    {

      m_resolver.async_resolve(host, "80", std::bind(&resolver::on_lookup, this, _1, _2

        , host));

    }

    else

    {

      m_critical_resolver.async_resolve(host, "80", std::bind(&resolver::on_lookup, this, _1, _2

        , host));

    }

  }

  void resolver::abort()

  {

    m_resolver.cancel();

  }

  void resolver::set_cache_timeout(seconds const timeout)

  {

    if (timeout >= seconds(0))

      m_timeout = timeout;

    else

      m_timeout = seconds(0);

  }

}

}