Interface IFeeWallet

Namespace

NArk.Abstractions.Blockchain

Assembly

NArk.Abstractions.dll

Provides confirmed on-chain UTXOs and signing capability for fee funding. Used by CPFP child transactions during unilateral exit broadcasting.

Host applications implement this to connect to their on-chain wallet:

• BTCPay Server: uses the store's on-chain wallet (signs internally)
• HSM / hardware-wallet integrations: never expose raw keys
• Standalone apps with an in-memory key: see TestFeeWallet for the pattern

The contract is sighash-callback shaped (mirroring Sign(OutputDescriptor, uint256, CancellationToken)) — the SDK never sees the underlying signing material. Implementations can sign with a raw Key, proxy to a hardware wallet, call out to a remote signer, or delegate to BTCPay's own wallet manager; the choice is opaque to the SDK.

public interface IFeeWallet

Methods

GetChangeScriptAsync(CancellationToken)

Gets a script for receiving change from CPFP child transactions.

Task<Script> GetChangeScriptAsync(CancellationToken cancellationToken = default)

Parameters

cancellationToken CancellationToken

Returns

Task<Script>

SelectFeeUtxoAsync(Money, CancellationToken)

Selects a confirmed on-chain UTXO with at least minAmount value to fund CPFP child transaction fees. Returns NBitcoin's standard NBitcoin.ICoin shape (outpoint + previous output) — no signing material is exposed; signing is requested separately via SignFeeUtxoAsync(OutPoint, uint256, TaprootSigHash, CancellationToken).

Task<ICoin?> SelectFeeUtxoAsync(Money minAmount, CancellationToken cancellationToken = default)

Parameters

minAmount Money

cancellationToken CancellationToken

Returns

Task<ICoin>

A coin suitable for funding fees, or null if no UTXO meets the threshold. Implementations may return any NBitcoin.ICoin subtype (a plain NBitcoin.Coin, a NBitcoin.ScriptCoin for future script-path fee inputs, etc.).

SignFeeUtxoAsync(OutPoint, uint256, TaprootSigHash, CancellationToken)

Signs a P2TR keypath spend of a previously-selected fee UTXO. The SDK computes the sighash (using the standard taproot algorithm with all prevouts) and asks the wallet to return a Schnorr signature over it — without ever requiring the wallet to surface its private key.

Task<SecpSchnorrSignature> SignFeeUtxoAsync(OutPoint feeOutpoint, uint256 sighash, TaprootSigHash sighashType, CancellationToken cancellationToken = default)

Parameters

feeOutpoint OutPoint

The fee UTXO being spent. Used by wallets that hold multiple keys to disambiguate which signing material to use.

sighash uint256

Precomputed taproot sighash.

sighashType TaprootSigHash

Sighash type (typically NBitcoin.TaprootSigHash.Default).

cancellationToken CancellationToken

Cancellation token.

Returns

Task<SecpSchnorrSignature>