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_EVICTION_H
6#define BITCOIN_NODE_EVICTION_H
7
8#include <node/connection_types.h>
9#include <net_permissions.h>
10
11#include <chrono>
12#include <cstdint>
13#include <optional>
14#include <vector>
15
16typedef int64_t NodeId;
17
18struct NodeEvictionCandidate {
19    NodeId id;
20    NodeClock::time_point m_connected;
21    NodeClock::duration m_min_ping_time;
22    std::chrono::seconds m_last_block_time;
23    std::chrono::seconds m_last_tx_time;
24    bool fRelevantServices;
25    bool m_relay_txs;
26    bool fBloomFilter;
27    uint64_t nKeyedNetGroup;
28    bool prefer_evict;
29    bool m_is_local;
30    Network m_network;
31    bool m_noban;
32    ConnectionType m_conn_type;
33};
34
35/**
36 * Select an inbound peer to evict after filtering out (protecting) peers having
37 * distinct, difficult-to-forge characteristics. The protection logic picks out
38 * fixed numbers of desirable peers per various criteria, followed by (mostly)
39 * ratios of desirable or disadvantaged peers. If any eviction candidates
40 * remain, the selection logic chooses a peer to evict.
41 */
42[[nodiscard]] std::optional<NodeId> SelectNodeToEvict(std::vector<NodeEvictionCandidate>&& vEvictionCandidates);
43
44/** Protect desirable or disadvantaged inbound peers from eviction by ratio.
45 *
46 * This function protects half of the peers which have been connected the
47 * longest, to replicate the non-eviction implicit behavior and preclude attacks
48 * that start later.
49 *
50 * Half of these protected spots (1/4 of the total) are reserved for the
51 * following categories of peers, sorted by longest uptime, even if they're not
52 * longest uptime overall:
53 *
54 * - onion peers connected via our tor control service
55 *
56 * - localhost peers, as manually configured hidden services not using
57 *   `-bind=addr[:port]=onion` will not be detected as inbound onion connections
58 *
59 * - I2P peers
60 *
61 * - CJDNS peers
62 *
63 * This helps protect these privacy network peers, which tend to be otherwise
64 * disadvantaged under our eviction criteria for their higher min ping times
65 * relative to IPv4/IPv6 peers, and favorise the diversity of peer connections.
66 */
67void ProtectEvictionCandidatesByRatio(std::vector<NodeEvictionCandidate>& vEvictionCandidates);
68
69#endif // BITCOIN_NODE_EVICTION_H
70