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, blockHeight int32) bool) (
+	*txauthor.AuthoredTx, error) {
 
 	chainClient, err := w.requireChainClient()
 	if err != nil {
@@ -181,6 +183,13 @@ func (w *Wallet) txToOutputs(outputs []*wire.TxOut,
 			)
 
 			for _, e := range eligible {
+				// Restrict the selected utxos if a filter
+				// function is provided.
+				if allowUtxo != nil &&
+					!allowUtxo(e, bs.Height) {
+
+					continue
+				}
 				eligibleByOutpoint[e.OutPoint] = e
 			}
 
@@ -206,6 +215,14 @@ func (w *Wallet) txToOutputs(outputs []*wire.TxOut,
 			// according to the selected coin selection strategy.
 			wrappedEligible := make([]Coin, len(eligible))
 			for i := range eligible {
+				// Restrict the selected utxos if a filter
+				// function is provided.
+				if allowUtxo != nil &&
+					!allowUtxo(eligible[i], bs.Height) {
+
+					continue
+				}
+
 				wrappedEligible[i] = Coin{
 					TxOut: wire.TxOut{
 						Value: int64(

wallet/wallet.go

@@ -1201,6 +1201,7 @@ type (
 		dryRun                bool
 		resp                  chan createTxResponse
 		selectUtxos           []wire.OutPoint
+		allowUtxo             func(wtxmgr.Credit, int32) 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, int32) bool
 }
 
 // TxCreateOption is a set of optional arguments to modify the tx creation
@@ -1289,6 +1292,15 @@ func WithCustomSelectUtxos(utxos []wire.OutPoint) TxCreateOption {
 	}
 }
 
+// WithAllowUtxo is used to restrict the selection of the internal wallet inputs
+// by further external conditions.
+func WithAllowUtxo(allowUtxo func(utxo wtxmgr.Credit,
+	blockHeight int32) 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