wallet: add utxo filter function.

Allows to attach a utxo filter function when creating a transaction
funded by the internal wallet.

wallet/createtx.go

@@ -140,7 +140,9 @@ func (w *Wallet) txToOutputs(outputs []*wire.TxOut,
 	coinSelectKeyScope, changeKeyScope *waddrmgr.KeyScope,
 	account uint32, minconf int32, feeSatPerKb btcutil.Amount,
 	strategy CoinSelectionStrategy, dryRun bool,
-	selectedUtxos []wire.OutPoint) (*txauthor.AuthoredTx, error) {
+	selectedUtxos []wire.OutPoint,
+	allowUtxo func(utxo wtxmgr.Credit) bool) (
+	*txauthor.AuthoredTx, error) {
 
 	chainClient, err := w.requireChainClient()
 	if err != nil {
@@ -168,7 +170,8 @@ func (w *Wallet) txToOutputs(outputs []*wire.TxOut,
 		}
 
 		eligible, err := w.findEligibleOutputs(
-			dbtx, coinSelectKeyScope, account, minconf, bs,
+			dbtx, coinSelectKeyScope, account, minconf,
+			bs, allowUtxo,
 		)
 		if err != nil {
 			return err
@@ -322,7 +325,8 @@ func (w *Wallet) txToOutputs(outputs []*wire.TxOut,
 
 func (w *Wallet) findEligibleOutputs(dbtx walletdb.ReadTx,
 	keyScope *waddrmgr.KeyScope, account uint32, minconf int32,
-	bs *waddrmgr.BlockStamp) ([]wtxmgr.Credit, error) {
+	bs *waddrmgr.BlockStamp,
+	allowUtxo func(utxo wtxmgr.Credit) bool) ([]wtxmgr.Credit, error) {
 
 	addrmgrNs := dbtx.ReadBucket(waddrmgrNamespaceKey)
 	txmgrNs := dbtx.ReadBucket(wtxmgrNamespaceKey)
@@ -341,6 +345,13 @@ func (w *Wallet) findEligibleOutputs(dbtx walletdb.ReadTx,
 	for i := range unspent {
 		output := &unspent[i]
 
+		// Restrict the selected utxos if a filter function is provided.
+		if allowUtxo != nil &&
+			!allowUtxo(*output) {
+
+			continue
+		}
+
 		// Only include this output if it meets the required number of
 		// confirmations. Coinbase transactions must have reached
 		// maturity before their outputs may be spent.

wallet/createtx_test.go

@@ -28,6 +28,8 @@ var (
 			"02a4",
 	)
 	testBlockHeight int32 = 276425
+
+	alwaysAllowUtxo = func(utxo wtxmgr.Credit) bool { return true }
 )
 
 // TestTxToOutput checks that no new address is added to he database if we
@@ -79,7 +81,7 @@ func TestTxToOutputsDryRun(t *testing.T) {
 	// database us not inflated.
 	dryRunTx, err := w.txToOutputs(
 		txOuts, nil, nil, 0, 1, 1000, CoinSelectionLargest, true,
-		nil,
+		nil, alwaysAllowUtxo,
 	)
 	if err != nil {
 		t.Fatalf("unable to author tx: %v", err)
@@ -97,7 +99,7 @@ func TestTxToOutputsDryRun(t *testing.T) {
 
 	dryRunTx2, err := w.txToOutputs(
 		txOuts, nil, nil, 0, 1, 1000, CoinSelectionLargest, true,
-		nil,
+		nil, alwaysAllowUtxo,
 	)
 	if err != nil {
 		t.Fatalf("unable to author tx: %v", err)
@@ -133,7 +135,7 @@ func TestTxToOutputsDryRun(t *testing.T) {
 	// to the database.
 	tx, err := w.txToOutputs(
 		txOuts, nil, nil, 0, 1, 1000, CoinSelectionLargest, false,
-		nil,
+		nil, alwaysAllowUtxo,
 	)
 	if err != nil {
 		t.Fatalf("unable to author tx: %v", err)
@@ -283,7 +285,7 @@ func TestTxToOutputsRandom(t *testing.T) {
 	createTx := func() *txauthor.AuthoredTx {
 		tx, err := w.txToOutputs(
 			txOuts, nil, nil, 0, 1, feeSatPerKb,
-			CoinSelectionRandom, true, nil,
+			CoinSelectionRandom, true, nil, alwaysAllowUtxo,
 		)
 		require.NoError(t, err)
 		return tx
@@ -355,7 +357,7 @@ func TestCreateSimpleCustomChange(t *testing.T) {
 	}
 	tx1, err := w.txToOutputs(
 		[]*wire.TxOut{targetTxOut}, nil, nil, 0, 1, 1000,
-		CoinSelectionLargest, true, nil,
+		CoinSelectionLargest, true, nil, alwaysAllowUtxo,
 	)
 	require.NoError(t, err)
 
@@ -381,7 +383,7 @@ func TestCreateSimpleCustomChange(t *testing.T) {
 	tx2, err := w.txToOutputs(
 		[]*wire.TxOut{targetTxOut}, &waddrmgr.KeyScopeBIP0086,
 		&waddrmgr.KeyScopeBIP0084, 0, 1, 1000, CoinSelectionLargest,
-		true, nil,
+		true, nil, alwaysAllowUtxo,
 	)
 	require.NoError(t, err)
 
@@ -465,7 +467,7 @@ func TestSelectUtxosTxoToOutpoint(t *testing.T) {
 	}
 	tx1, err := w.txToOutputs(
 		[]*wire.TxOut{targetTxOut}, nil, nil, 0, 1, 1000,
-		CoinSelectionLargest, true, selectUtxos,
+		CoinSelectionLargest, true, selectUtxos, alwaysAllowUtxo,
 	)
 	require.NoError(t, err)
 

wallet/wallet.go

@@ -1201,6 +1201,7 @@ type (
 		dryRun                bool
 		resp                  chan createTxResponse
 		selectUtxos           []wire.OutPoint
+		allowUtxo             func(wtxmgr.Credit) bool
 	}
 	createTxResponse struct {
 		tx  *txauthor.AuthoredTx
@@ -1239,9 +1240,10 @@ out:
 			}
 
 			tx, err := w.txToOutputs(
-				txr.outputs, txr.coinSelectKeyScope, txr.changeKeyScope,
-				txr.account, txr.minconf, txr.feeSatPerKB,
-				txr.coinSelectionStrategy, txr.dryRun, txr.selectUtxos,
+				txr.outputs, txr.coinSelectKeyScope,
+				txr.changeKeyScope, txr.account, txr.minconf,
+				txr.feeSatPerKB, txr.coinSelectionStrategy,
+				txr.dryRun, txr.selectUtxos, txr.allowUtxo,
 			)
 
 			release()
@@ -1259,6 +1261,7 @@ out:
 type txCreateOptions struct {
 	changeKeyScope *waddrmgr.KeyScope
 	selectUtxos    []wire.OutPoint
+	allowUtxo      func(wtxmgr.Credit) bool
 }
 
 // TxCreateOption is a set of optional arguments to modify the tx creation
@@ -1289,6 +1292,15 @@ func WithCustomSelectUtxos(utxos []wire.OutPoint) TxCreateOption {
 	}
 }
 
+// WithUtxoFilter is used to restrict the selection of the internal wallet
+// inputs by further external conditions. Utxos which pass the filter are
+// considered when creating the transaction.
+func WithUtxoFilter(allowUtxo func(utxo wtxmgr.Credit) bool) TxCreateOption {
+	return func(opts *txCreateOptions) {
+		opts.allowUtxo = allowUtxo
+	}
+}
+
 // CreateSimpleTx creates a new signed transaction spending unspent outputs with
 // at least minconf confirmations spending to any number of address/amount
 // pairs. Only unspent outputs belonging to the given key scope and account will
@@ -1333,6 +1345,7 @@ func (w *Wallet) CreateSimpleTx(coinSelectKeyScope *waddrmgr.KeyScope,
 		dryRun:                dryRun,
 		resp:                  make(chan createTxResponse),
 		selectUtxos:           opts.selectUtxos,
+		allowUtxo:             opts.allowUtxo,
 	}
 	w.createTxRequests <- req
 	resp := <-req.resp