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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.
#include <policy/v3_policy.h>
#include <coins.h>
#include <consensus/amount.h>
#include <logging.h>
#include <tinyformat.h>
#include <util/check.h>
#include <algorithm>
#include <numeric>
#include <vector>
/** Helper for PackageV3Checks: Returns a vector containing the indices of transactions (within
* package) that are direct parents of ptx. */
std::vector<size_t> FindInPackageParents(const Package& package, const CTransactionRef& ptx)
{
std::vector<size_t> in_package_parents;
std::set<Txid> possible_parents;
for (auto &input : ptx->vin) {
possible_parents.insert(input.prevout.hash);
}
for (size_t i{0}; i < package.size(); ++i) {
const auto& tx = package.at(i);
// We assume the package is sorted, so that we don't need to continue
// looking past the transaction itself.
if (&(*tx) == &(*ptx)) break;
if (possible_parents.count(tx->GetHash())) {
in_package_parents.push_back(i);
}
}
return in_package_parents;
}
/** Helper for PackageV3Checks, storing info for a mempool or package parent. */
struct ParentInfo {
/** Txid used to identify this parent by prevout */
const Txid& m_txid;
/** Wtxid used for debug string */
const Wtxid& m_wtxid;
/** nVersion used to check inheritance of v3 and non-v3 */
decltype(CTransaction::nVersion) m_version;
/** If parent is in mempool, whether it has any descendants in mempool. */
bool m_has_mempool_descendant;
ParentInfo() = delete;
ParentInfo(const Txid& txid, const Wtxid& wtxid, decltype(CTransaction::nVersion) version, bool has_mempool_descendant) :
m_txid{txid}, m_wtxid{wtxid}, m_version{version},
m_has_mempool_descendant{has_mempool_descendant}
{}
};
std::optional<std::string> PackageV3Checks(const CTransactionRef& ptx, int64_t vsize,
const Package& package,
const CTxMemPool::setEntries& mempool_ancestors)
{
// This function is specialized for these limits, and must be reimplemented if they ever change.
static_assert(V3_ANCESTOR_LIMIT == 2);
static_assert(V3_DESCENDANT_LIMIT == 2);
const auto in_package_parents{FindInPackageParents(package, ptx)};
// Now we have all ancestors, so we can start checking v3 rules.
if (ptx->nVersion == 3) {
if (mempool_ancestors.size() + in_package_parents.size() + 1 > V3_ANCESTOR_LIMIT) {
return strprintf("tx %s (wtxid=%s) would have too many ancestors",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString());
}
const bool has_parent{mempool_ancestors.size() + in_package_parents.size() > 0};
if (has_parent) {
// A v3 child cannot be too large.
if (vsize > V3_CHILD_MAX_VSIZE) {
return strprintf("v3 child tx %s (wtxid=%s) is too big: %u > %u virtual bytes",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString(),
vsize, V3_CHILD_MAX_VSIZE);
}
// Exactly 1 parent exists, either in mempool or package. Find it.
const auto parent_info = [&] {
if (mempool_ancestors.size() > 0) {
auto& mempool_parent = *mempool_ancestors.begin();
Assume(mempool_parent->GetCountWithDescendants() == 1);
return ParentInfo{mempool_parent->GetTx().GetHash(),
mempool_parent->GetTx().GetWitnessHash(),
mempool_parent->GetTx().nVersion,
/*has_mempool_descendant=*/mempool_parent->GetCountWithDescendants() > 1};
} else {
auto& parent_index = in_package_parents.front();
auto& package_parent = package.at(parent_index);
return ParentInfo{package_parent->GetHash(),
package_parent->GetWitnessHash(),
package_parent->nVersion,
/*has_mempool_descendant=*/false};
}
}();
// If there is a parent, it must have the right version.
if (parent_info.m_version != 3) {
return strprintf("v3 tx %s (wtxid=%s) cannot spend from non-v3 tx %s (wtxid=%s)",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString(),
parent_info.m_txid.ToString(), parent_info.m_wtxid.ToString());
}
for (const auto& package_tx : package) {
// Skip same tx.
if (&(*package_tx) == &(*ptx)) continue;
for (auto& input : package_tx->vin) {
// Fail if we find another tx with the same parent. We don't check whether the
// sibling is to-be-replaced (done in SingleV3Checks) because these transactions
// are within the same package.
if (input.prevout.hash == parent_info.m_txid) {
return strprintf("tx %s (wtxid=%s) would exceed descendant count limit",
parent_info.m_txid.ToString(),
parent_info.m_wtxid.ToString());
}
// This tx can't have both a parent and an in-package child.
if (input.prevout.hash == ptx->GetHash()) {
return strprintf("tx %s (wtxid=%s) would have too many ancestors",
package_tx->GetHash().ToString(), package_tx->GetWitnessHash().ToString());
}
}
}
// It shouldn't be possible to have any mempool siblings at this point. SingleV3Checks
// catches mempool siblings and sibling eviction is not extended to packages. Also, if the package consists of connected transactions,
// any tx having a mempool ancestor would mean the package exceeds ancestor limits.
if (!Assume(!parent_info.m_has_mempool_descendant)) {
return strprintf("tx %s (wtxid=%s) would exceed descendant count limit",
parent_info.m_txid.ToString(), parent_info.m_wtxid.ToString());
}
}
} else {
// Non-v3 transactions cannot have v3 parents.
for (auto it : mempool_ancestors) {
if (it->GetTx().nVersion == 3) {
return strprintf("non-v3 tx %s (wtxid=%s) cannot spend from v3 tx %s (wtxid=%s)",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString(),
it->GetSharedTx()->GetHash().ToString(), it->GetSharedTx()->GetWitnessHash().ToString());
}
}
for (const auto& index: in_package_parents) {
if (package.at(index)->nVersion == 3) {
return strprintf("non-v3 tx %s (wtxid=%s) cannot spend from v3 tx %s (wtxid=%s)",
ptx->GetHash().ToString(),
ptx->GetWitnessHash().ToString(),
package.at(index)->GetHash().ToString(),
package.at(index)->GetWitnessHash().ToString());
}
}
}
return std::nullopt;
}
std::optional<std::pair<std::string, CTransactionRef>> SingleV3Checks(const CTransactionRef& ptx,
const CTxMemPool::setEntries& mempool_ancestors,
const std::set<Txid>& direct_conflicts,
int64_t vsize)
{
// Check v3 and non-v3 inheritance.
for (const auto& entry : mempool_ancestors) {
if (ptx->nVersion != 3 && entry->GetTx().nVersion == 3) {
return std::make_pair(strprintf("non-v3 tx %s (wtxid=%s) cannot spend from v3 tx %s (wtxid=%s)",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString(),
entry->GetSharedTx()->GetHash().ToString(), entry->GetSharedTx()->GetWitnessHash().ToString()),
nullptr);
} else if (ptx->nVersion == 3 && entry->GetTx().nVersion != 3) {
return std::make_pair(strprintf("v3 tx %s (wtxid=%s) cannot spend from non-v3 tx %s (wtxid=%s)",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString(),
entry->GetSharedTx()->GetHash().ToString(), entry->GetSharedTx()->GetWitnessHash().ToString()),
nullptr);
}
}
// This function is specialized for these limits, and must be reimplemented if they ever change.
static_assert(V3_ANCESTOR_LIMIT == 2);
static_assert(V3_DESCENDANT_LIMIT == 2);
// The rest of the rules only apply to transactions with nVersion=3.
if (ptx->nVersion != 3) return std::nullopt;
// Check that V3_ANCESTOR_LIMIT would not be violated.
if (mempool_ancestors.size() + 1 > V3_ANCESTOR_LIMIT) {
return std::make_pair(strprintf("tx %s (wtxid=%s) would have too many ancestors",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString()),
nullptr);
}
// Remaining checks only pertain to transactions with unconfirmed ancestors.
if (mempool_ancestors.size() > 0) {
// If this transaction spends V3 parents, it cannot be too large.
if (vsize > V3_CHILD_MAX_VSIZE) {
return std::make_pair(strprintf("v3 child tx %s (wtxid=%s) is too big: %u > %u virtual bytes",
ptx->GetHash().ToString(), ptx->GetWitnessHash().ToString(), vsize, V3_CHILD_MAX_VSIZE),
nullptr);
}
// Check the descendant counts of in-mempool ancestors.
const auto& parent_entry = *mempool_ancestors.begin();
// If there are any ancestors, this is the only child allowed. The parent cannot have any
// other descendants. We handle the possibility of multiple children as that case is
// possible through a reorg.
const auto& children = parent_entry->GetMemPoolChildrenConst();
// Don't double-count a transaction that is going to be replaced. This logic assumes that
// any descendant of the V3 transaction is a direct child, which makes sense because a V3
// transaction can only have 1 descendant.
const bool child_will_be_replaced = !children.empty() &&
std::any_of(children.cbegin(), children.cend(),
[&direct_conflicts](const CTxMemPoolEntry& child){return direct_conflicts.count(child.GetTx().GetHash()) > 0;});
if (parent_entry->GetCountWithDescendants() + 1 > V3_DESCENDANT_LIMIT && !child_will_be_replaced) {
// Allow sibling eviction for v3 transaction: if another child already exists, even if
// we don't conflict inputs with it, consider evicting it under RBF rules. We rely on v3 rules
// only permitting 1 descendant, as otherwise we would need to have logic for deciding
// which descendant to evict. Skip if this isn't true, e.g. if the transaction has
// multiple children or the sibling also has descendants due to a reorg.
const bool consider_sibling_eviction{parent_entry->GetCountWithDescendants() == 2 &&
children.begin()->get().GetCountWithAncestors() == 2};
// Return the sibling if its eviction can be considered. Provide the "descendant count
// limit" string either way, as the caller may decide not to do sibling eviction.
return std::make_pair(strprintf("tx %u (wtxid=%s) would exceed descendant count limit",
parent_entry->GetSharedTx()->GetHash().ToString(),
parent_entry->GetSharedTx()->GetWitnessHash().ToString()),
consider_sibling_eviction ? children.begin()->get().GetSharedTx() : nullptr);
}
}
return std::nullopt;
}
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