1// Copyright (c) 2024-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#include <consensus/validation.h>
6#include <policy/ephemeral_policy.h>
7#include <policy/feerate.h>
8#include <policy/packages.h>
9#include <policy/policy.h>
10#include <primitives/transaction.h>
11#include <txmempool.h>
12#include <util/check.h>
13#include <util/hasher.h>
14
15#include <algorithm>
16#include <cstdint>
17#include <map>
18#include <memory>
19#include <unordered_set>
20#include <utility>
21#include <vector>
22
23bool PreCheckEphemeralTx(const CTransaction& tx, CFeeRate dust_relay_rate, CAmount base_fee, CAmount mod_fee, TxValidationState& state)
24{
25    // We never want to give incentives to mine this transaction alone
26    if ((base_fee != 0 || mod_fee != 0) && !GetDust(tx, dust_relay_rate).empty()) {
27        return state.Invalid(TxValidationResult::TX_NOT_STANDARD, "dust", "tx with dust output must be 0-fee");
28    }
29
30    return true;
31}
32
33bool CheckEphemeralSpends(const Package& package, CFeeRate dust_relay_rate, const CTxMemPool& tx_pool, TxValidationState& out_child_state, Wtxid& out_child_wtxid)
34{
35    if (!Assume(std::ranges::all_of(package, [](const auto& tx){return tx != nullptr;}))) {
36        // Bail out of spend checks if caller gave us an invalid package
37        return true;
38    }
39
40    std::map<Txid, CTransactionRef> map_txid_ref;
41    for (const auto& tx : package) {
42        map_txid_ref[tx->GetHash()] = tx;
43    }
44
45    for (const auto& tx : package) {
46        std::unordered_set<Txid, SaltedTxidHasher> processed_parent_set;
47        std::unordered_set<COutPoint, SaltedOutpointHasher> unspent_parent_dust;
48
49        for (const auto& tx_input : tx->vin) {
50            const Txid& parent_txid{tx_input.prevout.hash};
51            // Skip parents we've already checked dust for
52            if (processed_parent_set.contains(parent_txid)) continue;
53
54            // We look for an in-package or in-mempool dependency
55            CTransactionRef parent_ref = nullptr;
56            if (auto it = map_txid_ref.find(parent_txid); it != map_txid_ref.end()) {
57                parent_ref = it->second;
58            } else {
59                parent_ref = tx_pool.get(parent_txid);
60            }
61
62            // Check for dust on parents
63            if (parent_ref) {
64                for (uint32_t out_index = 0; out_index < parent_ref->vout.size(); out_index++) {
65                    const auto& tx_output = parent_ref->vout[out_index];
66                    if (IsDust(tx_output, dust_relay_rate)) {
67                        unspent_parent_dust.insert(COutPoint(parent_txid, out_index));
68                    }
69                }
70            }
71
72            processed_parent_set.insert(parent_txid);
73        }
74
75        if (unspent_parent_dust.empty()) {
76            continue;
77        }
78
79        // Now that we have gathered parents' dust, make sure it's spent
80        // by the child
81        for (const auto& tx_input : tx->vin) {
82            unspent_parent_dust.erase(tx_input.prevout);
83        }
84
85        if (!unspent_parent_dust.empty()) {
86            const Txid& out_child_txid = tx->GetHash();
87            out_child_wtxid = tx->GetWitnessHash();
88            out_child_state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "missing-ephemeral-spends",
89                                strprintf("tx %s (wtxid=%s) did not spend parent's ephemeral dust", out_child_txid.ToString(), out_child_wtxid.ToString()));
90            return false;
91        }
92    }
93
94    return true;
95}
96