lnwallet+mock: add new PSBT methods

lntest/mock/walletcontroller.go

@@ -10,6 +10,7 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
+	"github.com/btcsuite/btcutil/psbt"
 	"github.com/btcsuite/btcwallet/wallet/txauthor"
 	"github.com/btcsuite/btcwallet/wtxmgr"
 
@@ -141,6 +142,18 @@ func (w *WalletController) ReleaseOutput(wtxmgr.LockID, wire.OutPoint) error {
 	return nil
 }
 
+// FundPsbt currently does nothing.
+func (w *WalletController) FundPsbt(_ *psbt.Packet,
+	_ chainfee.SatPerKWeight) (int32, error) {
+
+	return 0, nil
+}
+
+// FinalizePsbt currently does nothing.
+func (w *WalletController) FinalizePsbt(_ *psbt.Packet) error {
+	return nil
+}
+
 // PublishTransaction sends a transaction to the PublishedTransactions chan.
 func (w *WalletController) PublishTransaction(tx *wire.MsgTx, _ string) error {
 	w.PublishedTransactions <- tx

lnwallet/btcwallet/btcwallet.go

@@ -13,6 +13,7 @@ import (
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
+	"github.com/btcsuite/btcutil/psbt"
 	"github.com/btcsuite/btcwallet/chain"
 	"github.com/btcsuite/btcwallet/waddrmgr"
 	base "github.com/btcsuite/btcwallet/wallet"
@@ -690,6 +691,51 @@ func (b *BtcWallet) ListTransactionDetails(startHeight,
 	return txDetails, nil
 }
 
+// FundPsbt creates a fully populated PSBT packet that contains enough
+// inputs to fund the outputs specified in the passed in packet with the
+// specified fee rate. If there is change left, a change output from the
+// internal wallet is added and the index of the change output is returned.
+// Otherwise no additional output is created and the index -1 is returned.
+//
+// NOTE: If the packet doesn't contain any inputs, coin selection is
+// performed automatically. If the packet does contain any inputs, it is
+// assumed that full coin selection happened externally and no
+// additional inputs are added. If the specified inputs aren't enough to
+// fund the outputs with the given fee rate, an error is returned.
+// No lock lease is acquired for any of the selected/validated inputs.
+// It is in the caller's responsibility to lock the inputs before
+// handing them out.
+//
+// This is a part of the WalletController interface.
+func (b *BtcWallet) FundPsbt(packet *psbt.Packet,
+	feeRate chainfee.SatPerKWeight) (int32, error) {
+
+	// The fee rate is passed in using units of sat/kw, so we'll convert
+	// this to sat/KB as the CreateSimpleTx method requires this unit.
+	feeSatPerKB := btcutil.Amount(feeRate.FeePerKVByte())
+
+	// Let the wallet handle coin selection and/or fee estimation based on
+	// the partial TX information in the packet.
+	return b.wallet.FundPsbt(packet, defaultAccount, feeSatPerKB)
+}
+
+// FinalizePsbt expects a partial transaction with all inputs and
+// outputs fully declared and tries to sign all inputs that belong to
+// the wallet. Lnd must be the last signer of the transaction. That
+// means, if there are any unsigned non-witness inputs or inputs without
+// UTXO information attached or inputs without witness data that do not
+// belong to lnd's wallet, this method will fail. If no error is
+// returned, the PSBT is ready to be extracted and the final TX within
+// to be broadcast.
+//
+// NOTE: This method does NOT publish the transaction after it's been
+// finalized successfully.
+//
+// This is a part of the WalletController interface.
+func (b *BtcWallet) FinalizePsbt(packet *psbt.Packet) error {
+	return b.wallet.FinalizePsbt(packet)
+}
+
 // txSubscriptionClient encapsulates the transaction notification client from
 // the base wallet. Notifications received from the client will be proxied over
 // two distinct channels.

lnwallet/interface.go

@@ -10,6 +10,7 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
+	"github.com/btcsuite/btcutil/psbt"
 	"github.com/btcsuite/btcwallet/wallet/txauthor"
 	"github.com/btcsuite/btcwallet/wtxmgr"
 	"github.com/lightningnetwork/lnd/input"
@@ -273,6 +274,37 @@ type WalletController interface {
 	// is set. Labels must not be empty, and they are limited to 500 chars.
 	LabelTransaction(hash chainhash.Hash, label string, overwrite bool) error
 
+	// FundPsbt creates a fully populated PSBT packet that contains enough
+	// inputs to fund the outputs specified in the passed in packet with the
+	// specified fee rate. If there is change left, a change output from the
+	// internal wallet is added and the index of the change output is
+	// returned. Otherwise no additional output is created and the index -1
+	// is returned.
+	//
+	// NOTE: If the packet doesn't contain any inputs, coin selection is
+	// performed automatically. If the packet does contain any inputs, it is
+	// assumed that full coin selection happened externally and no
+	// additional inputs are added. If the specified inputs aren't enough to
+	// fund the outputs with the given fee rate, an error is returned.
+	// No lock lease is acquired for any of the selected/validated inputs.
+	// It is in the caller's responsibility to lock the inputs before
+	// handing them out.
+	FundPsbt(packet *psbt.Packet, feeRate chainfee.SatPerKWeight) (int32,
+		error)
+
+	// FinalizePsbt expects a partial transaction with all inputs and
+	// outputs fully declared and tries to sign all inputs that belong to
+	// the wallet. Lnd must be the last signer of the transaction. That
+	// means, if there are any unsigned non-witness inputs or inputs without
+	// UTXO information attached or inputs without witness data that do not
+	// belong to lnd's wallet, this method will fail. If no error is
+	// returned, the PSBT is ready to be extracted and the final TX within
+	// to be broadcast.
+	//
+	// NOTE: This method does NOT publish the transaction after it's been
+	// finalized successfully.
+	FinalizePsbt(packet *psbt.Packet) error
+
 	// SubscribeTransactions returns a TransactionSubscription client which
 	// is capable of receiving async notifications as new transactions
 	// related to the wallet are seen within the network, or found in