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// Copyright (c) 2024-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_POLICY_EPHEMERAL_POLICY_H
#define BITCOIN_POLICY_EPHEMERAL_POLICY_H
#include <policy/packages.h>
#include <policy/policy.h>
#include <primitives/transaction.h>
#include <txmempool.h>
/** These utility functions ensure that ephemeral dust is safely
* created and spent without unduly risking them entering the utxo
* set.
* This is ensured by requiring:
* - PreCheckEphemeralTx checks are respected
* - The parent has no child (and 0-fee as implied above to disincentivize mining)
* - OR the parent transaction has exactly one child, and the dust is spent by that child
*
* Imagine three transactions:
* TxA, 0-fee with two outputs, one non-dust, one dust
* TxB, spends TxA's non-dust
* TxC, spends TxA's dust
*
* All the dust is spent if TxA+TxB+TxC is accepted, but the mining template may just pick
* up TxA+TxB rather than the three "legal configurations:
* 1) None
* 2) TxA+TxB+TxC
* 3) TxA+TxC
* By requiring the child transaction to sweep any dust from the parent txn, we ensure that
* there is a single child only, and this child, or the child's descendants,
* are the only way to bring fees.
*/
/** Returns true if transaction contains dust */
bool HasDust(const CTransaction& tx, CFeeRate dust_relay_rate);
/* All the following checks are only called if standardness rules are being applied. */
/** Must be called for each transaction once transaction fees are known.
* Does context-less checks about a single transaction.
* Returns false if the fee is non-zero and dust exists, populating state. True otherwise.
*/
bool PreCheckEphemeralTx(const CTransaction& tx, CFeeRate dust_relay_rate, CAmount base_fee, CAmount mod_fee, TxValidationState& state);
/** Must be called for each transaction(package) if any dust is in the package.
* Checks that each transaction's parents have their dust spent by the child,
* where parents are either in the mempool or in the package itself.
* The function returns std::nullopt if all dust is properly spent, or the txid of the violating child spend.
*/
std::optional<Txid> CheckEphemeralSpends(const Package& package, CFeeRate dust_relay_rate, const CTxMemPool& tx_pool);
#endif // BITCOIN_POLICY_EPHEMERAL_POLICY_H
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