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1 : : // Copyright (c) 2016-2022 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 <policy/rbf.h>
6 : :
7 : : #include <consensus/amount.h>
8 : : #include <kernel/mempool_entry.h>
9 : : #include <policy/feerate.h>
10 : : #include <primitives/transaction.h>
11 : : #include <sync.h>
12 : : #include <tinyformat.h>
13 : : #include <txmempool.h>
14 : : #include <uint256.h>
15 : : #include <util/check.h>
16 : : #include <util/moneystr.h>
17 : : #include <util/rbf.h>
18 : :
19 : : #include <limits>
20 : : #include <vector>
21 : :
22 : : #include <compare>
23 : :
24 : 0 : RBFTransactionState IsRBFOptIn(const CTransaction& tx, const CTxMemPool& pool)
25 : : {
26 : 0 : AssertLockHeld(pool.cs);
27 : :
28 : : // First check the transaction itself.
29 [ # # ]: 0 : if (SignalsOptInRBF(tx)) {
30 : : return RBFTransactionState::REPLACEABLE_BIP125;
31 : : }
32 : :
33 : : // If this transaction is not in our mempool, then we can't be sure
34 : : // we will know about all its inputs.
35 [ # # ]: 0 : if (!pool.exists(GenTxid::Txid(tx.GetHash()))) {
36 : : return RBFTransactionState::UNKNOWN;
37 : : }
38 : :
39 : : // If all the inputs have nSequence >= maxint-1, it still might be
40 : : // signaled for RBF if any unconfirmed parents have signaled.
41 : 0 : const auto& entry{*Assert(pool.GetEntry(tx.GetHash()))};
42 : 0 : auto ancestors{pool.AssumeCalculateMemPoolAncestors(__func__, entry, CTxMemPool::Limits::NoLimits(),
43 : 0 : /*fSearchForParents=*/false)};
44 : :
45 [ # # ]: 0 : for (CTxMemPool::txiter it : ancestors) {
46 [ # # # # ]: 0 : if (SignalsOptInRBF(it->GetTx())) {
47 : : return RBFTransactionState::REPLACEABLE_BIP125;
48 : : }
49 : : }
50 : : return RBFTransactionState::FINAL;
51 : 0 : }
52 : :
53 : 0 : RBFTransactionState IsRBFOptInEmptyMempool(const CTransaction& tx)
54 : : {
55 : : // If we don't have a local mempool we can only check the transaction itself.
56 [ # # ]: 0 : return SignalsOptInRBF(tx) ? RBFTransactionState::REPLACEABLE_BIP125 : RBFTransactionState::UNKNOWN;
57 : : }
58 : :
59 : 9 : std::optional<std::string> GetEntriesForConflicts(const CTransaction& tx,
60 : : CTxMemPool& pool,
61 : : const CTxMemPool::setEntries& iters_conflicting,
62 : : CTxMemPool::setEntries& all_conflicts)
63 : : {
64 : 9 : AssertLockHeld(pool.cs);
65 : 9 : const uint256 txid = tx.GetHash();
66 : 9 : uint64_t nConflictingCount = 0;
67 [ + + ]: 41 : for (const auto& mi : iters_conflicting) {
68 [ + + ]: 33 : nConflictingCount += mi->GetCountWithDescendants();
69 : : // Rule #5: don't consider replacing more than MAX_REPLACEMENT_CANDIDATES
70 : : // entries from the mempool. This potentially overestimates the number of actual
71 : : // descendants (i.e. if multiple conflicts share a descendant, it will be counted multiple
72 : : // times), but we just want to be conservative to avoid doing too much work.
73 [ + + ]: 33 : if (nConflictingCount > MAX_REPLACEMENT_CANDIDATES) {
74 [ + - ]: 2 : return strprintf("rejecting replacement %s; too many potential replacements (%d > %d)\n",
75 : 2 : txid.ToString(),
76 : : nConflictingCount,
77 : 1 : MAX_REPLACEMENT_CANDIDATES);
78 : : }
79 : : }
80 : : // Calculate the set of all transactions that would have to be evicted.
81 [ + + ]: 36 : for (CTxMemPool::txiter it : iters_conflicting) {
82 : 28 : pool.CalculateDescendants(it, all_conflicts);
83 : : }
84 : 8 : return std::nullopt;
85 : : }
86 : :
87 : 8 : std::optional<std::string> HasNoNewUnconfirmed(const CTransaction& tx,
88 : : const CTxMemPool& pool,
89 : : const CTxMemPool::setEntries& iters_conflicting)
90 : : {
91 : 8 : AssertLockHeld(pool.cs);
92 : 8 : std::set<uint256> parents_of_conflicts;
93 [ + + ]: 31 : for (const auto& mi : iters_conflicting) {
94 [ + + ]: 46 : for (const CTxIn& txin : mi->GetTx().vin) {
95 [ + - ]: 23 : parents_of_conflicts.insert(txin.prevout.hash);
96 : : }
97 : : }
98 : :
99 [ + + ]: 16 : for (unsigned int j = 0; j < tx.vin.size(); j++) {
100 : : // Rule #2: We don't want to accept replacements that require low feerate junk to be
101 : : // mined first. Ideally we'd keep track of the ancestor feerates and make the decision
102 : : // based on that, but for now requiring all new inputs to be confirmed works.
103 : : //
104 : : // Note that if you relax this to make RBF a little more useful, this may break the
105 : : // CalculateMempoolAncestors RBF relaxation which subtracts the conflict count/size from the
106 : : // descendant limit.
107 [ + + ]: 11 : if (!parents_of_conflicts.count(tx.vin[j].prevout.hash)) {
108 : : // Rather than check the UTXO set - potentially expensive - it's cheaper to just check
109 : : // if the new input refers to a tx that's in the mempool.
110 [ + - + - ]: 3 : if (pool.exists(GenTxid::Txid(tx.vin[j].prevout.hash))) {
111 : 3 : return strprintf("replacement %s adds unconfirmed input, idx %d",
112 [ + - + - ]: 9 : tx.GetHash().ToString(), j);
113 : : }
114 : : }
115 : : }
116 : 5 : return std::nullopt;
117 : 8 : }
118 : :
119 : 108 : std::optional<std::string> EntriesAndTxidsDisjoint(const CTxMemPool::setEntries& ancestors,
120 : : const std::set<Txid>& direct_conflicts,
121 : : const uint256& txid)
122 : : {
123 [ + + ]: 124 : for (CTxMemPool::txiter ancestorIt : ancestors) {
124 : 19 : const Txid& hashAncestor = ancestorIt->GetTx().GetHash();
125 [ + + ]: 19 : if (direct_conflicts.count(hashAncestor)) {
126 [ + - ]: 9 : return strprintf("%s spends conflicting transaction %s",
127 : 3 : txid.ToString(),
128 [ + - ]: 9 : hashAncestor.ToString());
129 : : }
130 : : }
131 : 105 : return std::nullopt;
132 : : }
133 : :
134 : 10 : std::optional<std::string> PaysMoreThanConflicts(const CTxMemPool::setEntries& iters_conflicting,
135 : : CFeeRate replacement_feerate,
136 : : const uint256& txid)
137 : : {
138 [ + + ]: 16 : for (const auto& mi : iters_conflicting) {
139 : : // Don't allow the replacement to reduce the feerate of the mempool.
140 : : //
141 : : // We usually don't want to accept replacements with lower feerates than what they replaced
142 : : // as that would lower the feerate of the next block. Requiring that the feerate always be
143 : : // increased is also an easy-to-reason about way to prevent DoS attacks via replacements.
144 : : //
145 : : // We only consider the feerates of transactions being directly replaced, not their indirect
146 : : // descendants. While that does mean high feerate children are ignored when deciding whether
147 : : // or not to replace, we do require the replacement to pay more overall fees too, mitigating
148 : : // most cases.
149 : 11 : CFeeRate original_feerate(mi->GetModifiedFee(), mi->GetTxSize());
150 [ + + ]: 11 : if (replacement_feerate <= original_feerate) {
151 [ + - ]: 15 : return strprintf("rejecting replacement %s; new feerate %s <= old feerate %s",
152 [ + - ]: 10 : txid.ToString(),
153 [ + - ]: 10 : replacement_feerate.ToString(),
154 : 15 : original_feerate.ToString());
155 : : }
156 : : }
157 : 5 : return std::nullopt;
158 : : }
159 : :
160 : 12 : std::optional<std::string> PaysForRBF(CAmount original_fees,
161 : : CAmount replacement_fees,
162 : : size_t replacement_vsize,
163 : : CFeeRate relay_fee,
164 : : const uint256& txid)
165 : : {
166 : : // Rule #3: The replacement fees must be greater than or equal to fees of the
167 : : // transactions it replaces, otherwise the bandwidth used by those conflicting transactions
168 : : // would not be paid for.
169 [ + + ]: 12 : if (replacement_fees < original_fees) {
170 [ + - ]: 4 : return strprintf("rejecting replacement %s, less fees than conflicting txs; %s < %s",
171 [ + - + - ]: 6 : txid.ToString(), FormatMoney(replacement_fees), FormatMoney(original_fees));
172 : : }
173 : :
174 : : // Rule #4: The new transaction must pay for its own bandwidth. Otherwise, we have a DoS
175 : : // vector where attackers can cause a transaction to be replaced (and relayed) repeatedly by
176 : : // increasing the fee by tiny amounts.
177 : 10 : CAmount additional_fees = replacement_fees - original_fees;
178 [ + + ]: 10 : if (additional_fees < relay_fee.GetFee(replacement_vsize)) {
179 [ + - ]: 6 : return strprintf("rejecting replacement %s, not enough additional fees to relay; %s < %s",
180 [ + - ]: 6 : txid.ToString(),
181 [ + - ]: 6 : FormatMoney(additional_fees),
182 : 6 : FormatMoney(relay_fee.GetFee(replacement_vsize)));
183 : : }
184 : 7 : return std::nullopt;
185 : : }
186 : :
187 : 6 : std::optional<std::pair<DiagramCheckError, std::string>> ImprovesFeerateDiagram(CTxMemPool& pool,
188 : : const CTxMemPool::setEntries& direct_conflicts,
189 : : const CTxMemPool::setEntries& all_conflicts,
190 : : CAmount replacement_fees,
191 : : int64_t replacement_vsize)
192 : : {
193 : : // Require that the replacement strictly improves the mempool's feerate diagram.
194 : 6 : const auto chunk_results{pool.CalculateChunksForRBF(replacement_fees, replacement_vsize, direct_conflicts, all_conflicts)};
195 : :
196 [ + + ]: 6 : if (!chunk_results.has_value()) {
197 [ + - ]: 2 : return std::make_pair(DiagramCheckError::UNCALCULABLE, util::ErrorString(chunk_results).original);
198 : : }
199 : :
200 [ + - + + ]: 5 : if (!std::is_gt(CompareChunks(chunk_results.value().second, chunk_results.value().first))) {
201 [ + - ]: 2 : return std::make_pair(DiagramCheckError::FAILURE, "insufficient feerate: does not improve feerate diagram");
202 : : }
203 : 3 : return std::nullopt;
204 : 6 : }
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