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// Copyright (c) 2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_NODE_TXRECONCILIATION_H
#define BITCOIN_NODE_TXRECONCILIATION_H
#include <net.h>
#include <sync.h>
#include <memory>
#include <tuple>
/** Whether transaction reconciliation protocol should be enabled by default. */
static constexpr bool DEFAULT_TXRECONCILIATION_ENABLE{false};
/** Supported transaction reconciliation protocol version */
static constexpr uint32_t TXRECONCILIATION_VERSION{1};
enum class ReconciliationRegisterResult {
NOT_FOUND,
SUCCESS,
ALREADY_REGISTERED,
PROTOCOL_VIOLATION,
};
/**
* Transaction reconciliation is a way for nodes to efficiently announce transactions.
* This object keeps track of all txreconciliation-related communications with the peers.
* The high-level protocol is:
* 0. Txreconciliation protocol handshake.
* 1. Once we receive a new transaction, add it to the set instead of announcing immediately.
* 2. At regular intervals, a txreconciliation initiator requests a sketch from a peer, where a
* sketch is a compressed representation of short form IDs of the transactions in their set.
* 3. Once the initiator received a sketch from the peer, the initiator computes a local sketch,
* and combines the two sketches to attempt finding the difference in *sets*.
* 4a. If the difference was not larger than estimated, see SUCCESS below.
* 4b. If the difference was larger than estimated, initial txreconciliation fails. The initiator
* requests a larger sketch via an extension round (allowed only once).
* - If extension succeeds (a larger sketch is sufficient), see SUCCESS below.
* - If extension fails (a larger sketch is insufficient), see FAILURE below.
*
* SUCCESS. The initiator knows full symmetrical difference and can request what the initiator is
* missing and announce to the peer what the peer is missing.
*
* FAILURE. The initiator notifies the peer about the failure and announces all transactions from
* the corresponding set. Once the peer received the failure notification, the peer
* announces all transactions from their set.
* This is a modification of the Erlay protocol (https://arxiv.org/abs/1905.10518) with two
* changes (sketch extensions instead of bisections, and an extra INV exchange round), both
* are motivated in BIP-330.
*/
class TxReconciliationTracker
{
private:
class Impl;
const std::unique_ptr<Impl> m_impl;
public:
explicit TxReconciliationTracker(uint32_t recon_version);
~TxReconciliationTracker();
/**
* Step 0. Generates initial part of the state (salt) required to reconcile txs with the peer.
* The salt is used for short ID computation required for txreconciliation.
* The function returns the salt.
* A peer can't participate in future txreconciliations without this call.
* This function must be called only once per peer.
*/
uint64_t PreRegisterPeer(NodeId peer_id);
/**
* Step 0. Once the peer agreed to reconcile txs with us, generate the state required to track
* ongoing reconciliations. Must be called only after pre-registering the peer and only once.
*/
ReconciliationRegisterResult RegisterPeer(NodeId peer_id, bool is_peer_inbound,
uint32_t peer_recon_version, uint64_t remote_salt);
/**
* Attempts to forget txreconciliation-related state of the peer (if we previously stored any).
* After this, we won't be able to reconcile transactions with the peer.
*/
void ForgetPeer(NodeId peer_id);
/**
* Check if a peer is registered to reconcile transactions with us.
*/
bool IsPeerRegistered(NodeId peer_id) const;
};
#endif // BITCOIN_NODE_TXRECONCILIATION_H
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