rippled/include/xrpl/core/HashRouter.h

#pragma once

#include <xrpl/basics/CountedObject.h>
#include <xrpl/basics/UnorderedContainers.h>
#include <xrpl/basics/base_uint.h>
#include <xrpl/basics/chrono.h>
#include <xrpl/basics/hardened_hash.h>
#include <xrpl/beast/container/aged_unordered_map.h>

#include <chrono>
#include <cstdint>
#include <mutex>
#include <optional>
#include <set>
#include <type_traits>
#include <utility>

namespace xrpl {

enum class HashRouterFlags : std::uint16_t {
    // Public flags
    UNDEFINED = 0x00,
    BAD = 0x02,  // Temporarily bad
    SAVED = 0x04,
    HELD = 0x08,     // Held by LedgerMaster after potential processing failure
    TRUSTED = 0x10,  // Comes from a trusted source

    // Private flags. Each group is owned by one file; do not read, set, or
    // reuse a flag outside the file noted.
    // Used in apply.cpp
    PRIVATE1 = 0x0100,
    PRIVATE2 = 0x0200,
    PRIVATE3 = 0x0400,
    PRIVATE4 = 0x0800,
    // Used in EscrowFinish.cpp
    PRIVATE5 = 0x1000,
    PRIVATE6 = 0x2000
};

constexpr HashRouterFlags
operator|(HashRouterFlags lhs, HashRouterFlags rhs)
{
    return static_cast<HashRouterFlags>(
        static_cast<std::underlying_type_t<HashRouterFlags>>(lhs) |
        static_cast<std::underlying_type_t<HashRouterFlags>>(rhs));
}

constexpr HashRouterFlags&
operator|=(HashRouterFlags& lhs, HashRouterFlags rhs)
{
    lhs = lhs | rhs;
    return lhs;
}

constexpr HashRouterFlags
operator&(HashRouterFlags lhs, HashRouterFlags rhs)
{
    return static_cast<HashRouterFlags>(
        static_cast<std::underlying_type_t<HashRouterFlags>>(lhs) &
        static_cast<std::underlying_type_t<HashRouterFlags>>(rhs));
}

constexpr HashRouterFlags&
operator&=(HashRouterFlags& lhs, HashRouterFlags rhs)
{
    lhs = lhs & rhs;
    return lhs;
}

constexpr bool
any(HashRouterFlags flags)
{
    return static_cast<std::underlying_type_t<HashRouterFlags>>(flags) != 0;
}

/**
 * Routing table for objects identified by hash.
 *
 * This table keeps track of which hashes have been received by which peers.
 * It is used to manage the routing and broadcasting of messages in the peer
 * to peer overlay.
 */
class HashRouter
{
public:
    // The type here *MUST* match the type of Peer::id_t
    using PeerShortID = std::uint32_t;

    /**
     * Structure used to customize @ref HashRouter behavior.
     *
     * Even though these items are configurable, they are undocumented. Don't
     * change them unless there is a good reason, and network-wide coordination
     * to do it.
     *
     * Configuration is processed in setup_HashRouter.
     */
    struct Setup
    {
        /**
         * Default constructor
         */
        explicit Setup() = default;

        using seconds = std::chrono::seconds;

        /**
         * Expiration time for a hash entry
         */
        seconds holdTime{300};

        /**
         * Amount of time required before a relayed item will be relayed again.
         */
        seconds relayTime{30};
    };

private:
    /**
     * An entry in the routing table.
     */
    class Entry : public CountedObject<Entry>
    {
    public:
        Entry() = default;

        void
        addPeer(PeerShortID peer)
        {
            if (peer != 0)
                peers_.insert(peer);
        }

        [[nodiscard]] HashRouterFlags
        getFlags() const
        {
            return flags_;
        }

        void
        setFlags(HashRouterFlags flagsToSet)
        {
            flags_ |= flagsToSet;
        }

        /**
         * Return set of peers we've relayed to and reset tracking
         */
        std::set<PeerShortID>
        releasePeerSet()
        {
            return std::move(peers_);
        }

        /**
         * Return seated relay time point if the message has been relayed
         */
        [[nodiscard]] std::optional<Stopwatch::time_point>
        relayed() const
        {
            return relayed_;
        }

        /**
         * Determines if this item should be relayed.
         *
         * Checks whether the item has been recently relayed.
         * If it has, return false. If it has not, update the
         * last relay timestamp and return true.
         */
        bool
        shouldRelay(Stopwatch::time_point const& now, std::chrono::seconds relayTime)
        {
            if (relayed_ && *relayed_ + relayTime > now)
                return false;
            relayed_.emplace(now);
            return true;
        }

        bool
        shouldProcess(Stopwatch::time_point now, std::chrono::seconds interval)
        {
            if (processed_ && ((*processed_ + interval) > now))
                return false;
            processed_.emplace(now);
            return true;
        }

    private:
        HashRouterFlags flags_ = HashRouterFlags::UNDEFINED;
        std::set<PeerShortID> peers_;
        // This could be generalized to a map, if more
        // than one flag needs to expire independently.
        std::optional<Stopwatch::time_point> relayed_;
        std::optional<Stopwatch::time_point> processed_;
    };

public:
    HashRouter(Setup const& setup, Stopwatch& clock) : setup_(setup), suppressionMap_(clock)
    {
    }

    HashRouter&
    operator=(HashRouter const&) = delete;

    virtual ~HashRouter() = default;

    // VFALCO TODO Replace "Suppression" terminology with something more
    // semantically meaningful.
    void
    addSuppression(uint256 const& key);

    bool
    addSuppressionPeer(uint256 const& key, PeerShortID peer);

    /**
     * Add a suppression peer and get message's relay status.
     * Return pair:
     * element 1: true if the peer is added.
     * element 2: optional is seated to the relay time point or
     * is unseated if has not relayed yet.
     */
    std::pair<bool, std::optional<Stopwatch::time_point>>
    addSuppressionPeerWithStatus(uint256 const& key, PeerShortID peer);

    bool
    addSuppressionPeer(uint256 const& key, PeerShortID peer, HashRouterFlags& flags);

    // Add a peer suppression and return whether the entry should be processed
    bool
    shouldProcess(
        uint256 const& key,
        PeerShortID peer,
        HashRouterFlags& flags,
        std::chrono::seconds txInterval);

    /**
     * Set the flags on a hash.
     *
     * @return `true` if the flags were changed. `false` if unchanged.
     */
    bool
    setFlags(uint256 const& key, HashRouterFlags flags);

    HashRouterFlags
    getFlags(uint256 const& key);

    /**
     * Determines whether the hashed item should be relayed.
     *
     * Effects:
     *
     *     If the item should be relayed, this function will not
     *     return a seated optional again until the relay time has expired.
     *     The internal set of peers will also be reset.
     *
     * @return A `std::optional` set of peers which do not need to be
     *     relayed to. If the result is unseated, the item should
     *     _not_ be relayed.
     */
    std::optional<std::set<PeerShortID>>
    shouldRelay(uint256 const& key);

private:
    // pair.second indicates whether the entry was created
    std::pair<Entry&, bool>
    emplace(uint256 const&);

    std::mutex mutable mutex_;

    // Configurable parameters
    Setup const setup_;

    // Stores all suppressed hashes and their expiration time
    beast::aged_unordered_map<uint256, Entry, Stopwatch::clock_type, HardenedHash<strong_hash>>
        suppressionMap_;
};

}  // namespace xrpl