//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2012, 2013 Ripple Labs Inc.

    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.

    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================

#ifndef RIPPLE_SERVER_DOOR_H_INCLUDED
#define RIPPLE_SERVER_DOOR_H_INCLUDED

#include <xrpl/basics/Log.h>
#include <xrpl/basics/contract.h>
#include <xrpl/server/detail/PlainHTTPPeer.h>
#include <xrpl/server/detail/SSLHTTPPeer.h>
#include <xrpl/server/detail/io_list.h>

#include <boost/asio/basic_waitable_timer.hpp>
#include <boost/asio/buffer.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/post.hpp>
#include <boost/asio/spawn.hpp>
#include <boost/asio/steady_timer.hpp>
#include <boost/beast/core/detect_ssl.hpp>
#include <boost/beast/core/multi_buffer.hpp>
#include <boost/beast/core/tcp_stream.hpp>
#include <boost/container/flat_map.hpp>
#include <boost/predef.h>

#if !BOOST_OS_WINDOWS
#include <sys/resource.h>

#include <dirent.h>
#include <unistd.h>
#endif

#include <algorithm>
#include <chrono>
#include <cstdint>
#include <functional>
#include <memory>
#include <optional>
#include <sstream>

namespace ripple {

/** A listening socket. */
template <class Handler>
class Door : public io_list::work,
             public std::enable_shared_from_this<Door<Handler>>
{
private:
    using clock_type = std::chrono::steady_clock;
    using timer_type = boost::asio::basic_waitable_timer<clock_type>;
    using error_code = boost::system::error_code;
    using yield_context = boost::asio::yield_context;
    using protocol_type = boost::asio::ip::tcp;
    using acceptor_type = protocol_type::acceptor;
    using endpoint_type = protocol_type::endpoint;
    using socket_type = boost::asio::ip::tcp::socket;
    using stream_type = boost::beast::tcp_stream;

    // Detects SSL on a socket
    class Detector : public io_list::work,
                     public std::enable_shared_from_this<Detector>
    {
    private:
        Port const& port_;
        Handler& handler_;
        boost::asio::io_context& ioc_;
        stream_type stream_;
        socket_type& socket_;
        endpoint_type remote_address_;
        boost::asio::strand<boost::asio::io_context::executor_type> strand_;
        beast::Journal const j_;

    public:
        Detector(
            Port const& port,
            Handler& handler,
            boost::asio::io_context& ioc,
            stream_type&& stream,
            endpoint_type remote_address,
            beast::Journal j);
        void
        run();
        void
        close() override;

    private:
        void
        do_detect(yield_context yield);
    };

    beast::Journal const j_;
    Port const& port_;
    Handler& handler_;
    boost::asio::io_context& ioc_;
    acceptor_type acceptor_;
    boost::asio::strand<boost::asio::io_context::executor_type> strand_;
    bool ssl_;
    bool plain_;
    static constexpr std::chrono::milliseconds INITIAL_ACCEPT_DELAY{50};
    static constexpr std::chrono::milliseconds MAX_ACCEPT_DELAY{2000};
    std::chrono::milliseconds accept_delay_{INITIAL_ACCEPT_DELAY};
    boost::asio::steady_timer backoff_timer_;
    static constexpr double FREE_FD_THRESHOLD = 0.70;

    struct FDStats
    {
        std::uint64_t used{0};
        std::uint64_t limit{0};
    };

    void
    reOpen();

    std::optional<FDStats>
    query_fd_stats() const;

    bool
    should_throttle_for_fds();

public:
    Door(
        Handler& handler,
        boost::asio::io_context& io_context,
        Port const& port,
        beast::Journal j);

    // Work-around because we can't call shared_from_this in ctor
    void
    run();

    /** Close the Door listening socket and connections.
        The listening socket is closed, and all open connections
        belonging to the Door are closed.
        Thread Safety:
            May be called concurrently
    */
    void
    close() override;

    endpoint_type
    get_endpoint() const
    {
        return acceptor_.local_endpoint();
    }

private:
    template <class ConstBufferSequence>
    void
    create(
        bool ssl,
        ConstBufferSequence const& buffers,
        stream_type&& stream,
        endpoint_type remote_address);

    void
    do_accept(yield_context yield);
};

template <class Handler>
Door<Handler>::Detector::Detector(
    Port const& port,
    Handler& handler,
    boost::asio::io_context& ioc,
    stream_type&& stream,
    endpoint_type remote_address,
    beast::Journal j)
    : port_(port)
    , handler_(handler)
    , ioc_(ioc)
    , stream_(std::move(stream))
    , socket_(stream_.socket())
    , remote_address_(remote_address)
    , strand_(boost::asio::make_strand(ioc_))
    , j_(j)
{
}

template <class Handler>
void
Door<Handler>::Detector::run()
{
    util::spawn(
        strand_,
        std::bind(
            &Detector::do_detect,
            this->shared_from_this(),
            std::placeholders::_1));
}

template <class Handler>
void
Door<Handler>::Detector::close()
{
    stream_.close();
}

template <class Handler>
void
Door<Handler>::Detector::do_detect(boost::asio::yield_context do_yield)
{
    boost::beast::multi_buffer buf(16);
    stream_.expires_after(std::chrono::seconds(15));
    boost::system::error_code ec;
    bool const ssl = async_detect_ssl(stream_, buf, do_yield[ec]);
    stream_.expires_never();
    if (!ec)
    {
        if (ssl)
        {
            if (auto sp = ios().template emplace<SSLHTTPPeer<Handler>>(
                    port_,
                    handler_,
                    ioc_,
                    j_,
                    remote_address_,
                    buf.data(),
                    std::move(stream_)))
                sp->run();
            return;
        }
        if (auto sp = ios().template emplace<PlainHTTPPeer<Handler>>(
                port_,
                handler_,
                ioc_,
                j_,
                remote_address_,
                buf.data(),
                std::move(stream_)))
            sp->run();
        return;
    }
    if (ec != boost::asio::error::operation_aborted)
    {
        JLOG(j_.trace()) << "Error detecting ssl: " << ec.message() << " from "
                         << remote_address_;
    }
}

//------------------------------------------------------------------------------

template <class Handler>
void
Door<Handler>::reOpen()
{
    error_code ec;

    if (acceptor_.is_open())
    {
        acceptor_.close(ec);
        if (ec)
        {
            std::stringstream ss;
            ss << "Can't close acceptor: " << port_.name << ", "
               << ec.message();
            JLOG(j_.error()) << ss.str();
            Throw<std::runtime_error>(ss.str());
        }
    }

    endpoint_type const local_address = endpoint_type(port_.ip, port_.port);

    acceptor_.open(local_address.protocol(), ec);
    if (ec)
    {
        JLOG(j_.error()) << "Open port '" << port_.name
                         << "' failed:" << ec.message();
        Throw<std::exception>();
    }

    acceptor_.set_option(
        boost::asio::ip::tcp::acceptor::reuse_address(true), ec);
    if (ec)
    {
        JLOG(j_.error()) << "Option for port '" << port_.name
                         << "' failed:" << ec.message();
        Throw<std::exception>();
    }

    acceptor_.bind(local_address, ec);
    if (ec)
    {
        JLOG(j_.error()) << "Bind port '" << port_.name
                         << "' failed:" << ec.message();
        Throw<std::exception>();
    }

    acceptor_.listen(boost::asio::socket_base::max_listen_connections, ec);
    if (ec)
    {
        JLOG(j_.error()) << "Listen on port '" << port_.name
                         << "' failed:" << ec.message();
        Throw<std::exception>();
    }

    JLOG(j_.info()) << "Opened " << port_;
}

template <class Handler>
Door<Handler>::Door(
    Handler& handler,
    boost::asio::io_context& io_context,
    Port const& port,
    beast::Journal j)
    : j_(j)
    , port_(port)
    , handler_(handler)
    , ioc_(io_context)
    , acceptor_(io_context)
    , strand_(boost::asio::make_strand(io_context))
    , ssl_(
          port_.protocol.count("https") > 0 ||
          port_.protocol.count("wss") > 0 || port_.protocol.count("wss2") > 0 ||
          port_.protocol.count("peer") > 0)
    , plain_(
          port_.protocol.count("http") > 0 || port_.protocol.count("ws") > 0 ||
          port_.protocol.count("ws2"))
    , backoff_timer_(io_context)
{
    reOpen();
}

template <class Handler>
void
Door<Handler>::run()
{
    util::spawn(
        strand_,
        std::bind(
            &Door<Handler>::do_accept,
            this->shared_from_this(),
            std::placeholders::_1));
}

template <class Handler>
void
Door<Handler>::close()
{
    if (!strand_.running_in_this_thread())
        return boost::asio::post(
            strand_,
            std::bind(&Door<Handler>::close, this->shared_from_this()));
    backoff_timer_.cancel();
    error_code ec;
    acceptor_.close(ec);
}

//------------------------------------------------------------------------------

template <class Handler>
template <class ConstBufferSequence>
void
Door<Handler>::create(
    bool ssl,
    ConstBufferSequence const& buffers,
    stream_type&& stream,
    endpoint_type remote_address)
{
    if (ssl)
    {
        if (auto sp = ios().template emplace<SSLHTTPPeer<Handler>>(
                port_,
                handler_,
                ioc_,
                j_,
                remote_address,
                buffers,
                std::move(stream)))
            sp->run();
        return;
    }
    if (auto sp = ios().template emplace<PlainHTTPPeer<Handler>>(
            port_,
            handler_,
            ioc_,
            j_,
            remote_address,
            buffers,
            std::move(stream)))
        sp->run();
}

template <class Handler>
void
Door<Handler>::do_accept(boost::asio::yield_context do_yield)
{
    while (acceptor_.is_open())
    {
        if (should_throttle_for_fds())
        {
            backoff_timer_.expires_after(accept_delay_);
            boost::system::error_code tec;
            backoff_timer_.async_wait(do_yield[tec]);
            accept_delay_ = std::min(accept_delay_ * 2, MAX_ACCEPT_DELAY);
            JLOG(j_.warn()) << "Throttling do_accept for "
                            << accept_delay_.count() << "ms.";
            continue;
        }

        error_code ec;
        endpoint_type remote_address;
        stream_type stream(ioc_);
        socket_type& socket = stream.socket();
        acceptor_.async_accept(socket, remote_address, do_yield[ec]);
        if (ec)
        {
            if (ec == boost::asio::error::operation_aborted)
                break;

            if (ec == boost::asio::error::no_descriptors ||
                ec == boost::asio::error::no_buffer_space)
            {
                JLOG(j_.warn()) << "accept: Too many open files. Pausing for "
                                << accept_delay_.count() << "ms.";

                backoff_timer_.expires_after(accept_delay_);
                boost::system::error_code tec;
                backoff_timer_.async_wait(do_yield[tec]);

                accept_delay_ = std::min(accept_delay_ * 2, MAX_ACCEPT_DELAY);
            }
            else
            {
                JLOG(j_.error()) << "accept error: " << ec.message();
            }
            continue;
        }

        accept_delay_ = INITIAL_ACCEPT_DELAY;

        if (ssl_ && plain_)
        {
            if (auto sp = ios().template emplace<Detector>(
                    port_,
                    handler_,
                    ioc_,
                    std::move(stream),
                    remote_address,
                    j_))
                sp->run();
        }
        else if (ssl_ || plain_)
        {
            create(
                ssl_,
                boost::asio::null_buffers{},
                std::move(stream),
                remote_address);
        }
    }
}

template <class Handler>
std::optional<typename Door<Handler>::FDStats>
Door<Handler>::query_fd_stats() const
{
#if BOOST_OS_WINDOWS
    return std::nullopt;
#else
    FDStats s;
    struct rlimit rl;
    if (getrlimit(RLIMIT_NOFILE, &rl) != 0 || rl.rlim_cur == RLIM_INFINITY)
        return std::nullopt;
    s.limit = static_cast<std::uint64_t>(rl.rlim_cur);
#if BOOST_OS_LINUX
    constexpr char const* kFdDir = "/proc/self/fd";
#else
    constexpr char const* kFdDir = "/dev/fd";
#endif
    if (DIR* d = ::opendir(kFdDir))
    {
        std::uint64_t cnt = 0;
        while (::readdir(d) != nullptr)
            ++cnt;
        ::closedir(d);
        // readdir counts '.', '..', and the DIR* itself shows in the list
        s.used = (cnt >= 3) ? (cnt - 3) : 0;
        return s;
    }
    return std::nullopt;
#endif
}

template <class Handler>
bool
Door<Handler>::should_throttle_for_fds()
{
#if BOOST_OS_WINDOWS
    return false;
#else
    auto const stats = query_fd_stats();
    if (!stats || stats->limit == 0)
        return false;

    auto const& s = *stats;
    auto const free = (s.limit > s.used) ? (s.limit - s.used) : 0ull;
    double const free_ratio =
        static_cast<double>(free) / static_cast<double>(s.limit);
    if (free_ratio < FREE_FD_THRESHOLD)
    {
        return true;
    }
    return false;
#endif
}

}  // namespace ripple

#endif