1// Copyright (c) 2022-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#ifndef BITCOIN_NODE_TXRECONCILIATION_H
6#define BITCOIN_NODE_TXRECONCILIATION_H
7
8#include <net.h>
9#include <sync.h>
10
11#include <memory>
12#include <tuple>
13
14/** Supported transaction reconciliation protocol version */
15inline constexpr uint32_t TXRECONCILIATION_VERSION{1};
16
17enum class ReconciliationRegisterResult {
18    NOT_FOUND,
19    SUCCESS,
20    ALREADY_REGISTERED,
21    PROTOCOL_VIOLATION,
22};
23
24/**
25 * Transaction reconciliation is a way for nodes to efficiently announce transactions.
26 * This object keeps track of all txreconciliation-related communications with the peers.
27 * The high-level protocol is:
28 * 0.  Txreconciliation protocol handshake.
29 * 1.  Once we receive a new transaction, add it to the set instead of announcing immediately.
30 * 2.  At regular intervals, a txreconciliation initiator requests a sketch from a peer, where a
31 *     sketch is a compressed representation of short form IDs of the transactions in their set.
32 * 3.  Once the initiator received a sketch from the peer, the initiator computes a local sketch,
33 *     and combines the two sketches to attempt finding the difference in *sets*.
34 * 4a. If the difference was not larger than estimated, see SUCCESS below.
35 * 4b. If the difference was larger than estimated, initial txreconciliation fails. The initiator
36 *     requests a larger sketch via an extension round (allowed only once).
37 *     - If extension succeeds (a larger sketch is sufficient), see SUCCESS below.
38 *     - If extension fails (a larger sketch is insufficient), see FAILURE below.
39 *
40 * SUCCESS. The initiator knows full symmetrical difference and can request what the initiator is
41 *          missing and announce to the peer what the peer is missing.
42 *
43 * FAILURE. The initiator notifies the peer about the failure and announces all transactions from
44 *          the corresponding set. Once the peer received the failure notification, the peer
45 *          announces all transactions from their set.
46
47 * This is a modification of the Erlay protocol (https://arxiv.org/abs/1905.10518) with two
48 * changes (sketch extensions instead of bisections, and an extra INV exchange round), both
49 * are motivated in BIP-330.
50 */
51class TxReconciliationTracker
52{
53private:
54    class Impl;
55    const std::unique_ptr<Impl> m_impl;
56
57public:
58    explicit TxReconciliationTracker(uint32_t recon_version);
59    ~TxReconciliationTracker();
60
61    /**
62     * Step 0. Generates initial part of the state (salt) required to reconcile txs with the peer.
63     * The salt is used for short ID computation required for txreconciliation.
64     * The function returns the salt.
65     * A peer can't participate in future txreconciliations without this call.
66     * This function must be called only once per peer.
67     */
68    uint64_t PreRegisterPeer(NodeId peer_id);
69
70    /**
71     * Step 0. Once the peer agreed to reconcile txs with us, generate the state required to track
72     * ongoing reconciliations. Must be called only after pre-registering the peer and only once.
73     */
74    ReconciliationRegisterResult RegisterPeer(NodeId peer_id, bool is_peer_inbound,
75                                              uint32_t peer_recon_version, uint64_t remote_salt);
76
77    /**
78     * Attempts to forget txreconciliation-related state of the peer (if we previously stored any).
79     * After this, we won't be able to reconcile transactions with the peer.
80     */
81    void ForgetPeer(NodeId peer_id);
82
83    /**
84     * Check if a peer is registered to reconcile transactions with us.
85     */
86    bool IsPeerRegistered(NodeId peer_id) const;
87};
88
89#endif // BITCOIN_NODE_TXRECONCILIATION_H
90