private_broadcast.h

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// Copyright (c) 2023-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or https://opensource.org/license/mit/.

#ifndef BITCOIN_PRIVATE_BROADCAST_H
#define BITCOIN_PRIVATE_BROADCAST_H

#include <net.h>
#include <primitives/transaction.h>
#include <primitives/transaction_identifier.h>
#include <sync.h>
#include <threadsafety.h>
#include <util/time.h>

#include <optional>
#include <tuple>
#include <unordered_map>
#include <vector>

class PrivateBroadcast
{
public:
    struct PeerSendInfo {
        CService address;
        NodeClock::time_point sent;
        std::optional<NodeClock::time_point> received;
    };

    struct TxBroadcastInfo {
        CTransactionRef tx;
        std::vector<PeerSendInfo> peers;
    };

    bool Add(const CTransactionRef& tx)
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    std::optional<size_t> Remove(const CTransactionRef& tx)
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    std::optional<CTransactionRef> PickTxForSend(const NodeId& will_send_to_nodeid, const CService& will_send_to_address)
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    std::optional<CTransactionRef> GetTxForNode(const NodeId& nodeid)
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    void NodeConfirmedReception(const NodeId& nodeid)
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    bool DidNodeConfirmReception(const NodeId& nodeid)
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    bool HavePendingTransactions()
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    std::vector<CTransactionRef> GetStale() const
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    std::vector<TxBroadcastInfo> GetBroadcastInfo() const
        EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

private:
    struct SendStatus {
        const NodeId nodeid; 
        const CService address; 
        const NodeClock::time_point picked; 
        std::optional<NodeClock::time_point> confirmed; 

        SendStatus(const NodeId& nodeid, const CService& address, const NodeClock::time_point& picked) : nodeid{nodeid}, address{address}, picked{picked} {}
    };

    struct Priority {
        size_t num_picked{0}; 
        NodeClock::time_point last_picked{}; 
        size_t num_confirmed{0}; 
        NodeClock::time_point last_confirmed{}; 

        auto operator<=>(const Priority& other) const
        {
            // Invert `other` and `this` in the comparison because smaller num_picked, num_confirmed or
            // earlier times mean greater priority. In other words, if this.num_picked < other.num_picked
            // then this > other.
            return std::tie(other.num_picked, other.num_confirmed, other.last_picked, other.last_confirmed) <=>
                   std::tie(num_picked, num_confirmed, last_picked, last_confirmed);
        }
    };

    struct TxAndSendStatusForNode {
        const CTransactionRef& tx;
        SendStatus& send_status;
    };

    // No need for salted hasher because we are going to store just a bunch of locally originating transactions.

    struct CTransactionRefHash {
        size_t operator()(const CTransactionRef& tx) const
        {
            return static_cast<size_t>(tx->GetWitnessHash().ToUint256().GetUint64(0));
        }
    };

    struct CTransactionRefComp {
        bool operator()(const CTransactionRef& a, const CTransactionRef& b) const
        {
            return a->GetWitnessHash() == b->GetWitnessHash(); // If wtxid equals, then txid also equals.
        }
    };

    static Priority DerivePriority(const std::vector<SendStatus>& sent_to);

    std::optional<TxAndSendStatusForNode> GetSendStatusByNode(const NodeId& nodeid)
        EXCLUSIVE_LOCKS_REQUIRED(m_mutex);

    mutable Mutex m_mutex;
    std::unordered_map<CTransactionRef, std::vector<SendStatus>, CTransactionRefHash, CTransactionRefComp>
        m_transactions GUARDED_BY(m_mutex);
};

#endif // BITCOIN_PRIVATE_BROADCAST_H