Add expert mode to BTCPay with No Change UTXO option

BTCPayServer/Controllers/WalletsController.cs

@@ -146,7 +146,7 @@ namespace BTCPayServer.Controllers
         [Route("{walletId}/send")]
         public async Task<IActionResult> WalletSend(
             [ModelBinder(typeof(WalletIdModelBinder))]
-            WalletId walletId, string defaultDestination = null, string defaultAmount = null)
+            WalletId walletId, string defaultDestination = null, string defaultAmount = null, bool advancedMode = false)
         {
             if (walletId?.StoreId == null)
                 return NotFound();
@@ -195,6 +195,7 @@ namespace BTCPayServer.Controllers
                 }
                 catch (Exception ex) { model.RateError = ex.Message; }
             }
+            model.AdvancedMode = advancedMode;
             return View(model);
         }
 
@@ -202,7 +203,7 @@ namespace BTCPayServer.Controllers
         [Route("{walletId}/send")]
         public async Task<IActionResult> WalletSend(
             [ModelBinder(typeof(WalletIdModelBinder))]
-            WalletId walletId, WalletSendModel vm)
+            WalletId walletId, WalletSendModel vm, string command = null)
         {
             if (walletId?.StoreId == null)
                 return NotFound();
@@ -212,6 +213,14 @@ namespace BTCPayServer.Controllers
             var network = this.NetworkProvider.GetNetwork(walletId?.CryptoCode);
             if (network == null)
                 return NotFound();
+
+            if (command == "noob" || command == "expert")
+            {
+                ModelState.Clear();
+                vm.AdvancedMode = command == "expert";
+                return View(vm);
+            }
+
             var destination = ParseDestination(vm.Destination, network.NBitcoinNetwork);
             if (destination == null)
                 ModelState.AddModelError(nameof(vm.Destination), "Invalid address");
@@ -231,7 +240,8 @@ namespace BTCPayServer.Controllers
                 Destination = vm.Destination,
                 Amount = vm.Amount.Value,
                 SubstractFees = vm.SubstractFees,
-                FeeSatoshiPerByte = vm.FeeSatoshiPerByte
+                FeeSatoshiPerByte = vm.FeeSatoshiPerByte,
+                NoChange = vm.NoChange
             });
         }
 
@@ -403,6 +413,7 @@ namespace BTCPayServer.Controllers
             // getxpub
             int account = 0,
             // sendtoaddress
+            bool noChange = false,
             string destination = null, string amount = null, string feeRate = null, string substractFees = null
             )
         {
@@ -487,24 +498,16 @@ namespace BTCPayServer.Controllers
                         var strategy = GetDirectDerivationStrategy(derivationScheme);
                         var wallet = _walletProvider.GetWallet(network);
                         var change = wallet.GetChangeAddressAsync(derivationScheme);
-
+                        var keypaths = new Dictionary<Script, KeyPath>();
-                        var unspentCoins = await wallet.GetUnspentCoins(derivationScheme);
+                        List<Coin> availableCoins = new List<Coin>();
-                        var changeAddress = await change;
+                        foreach (var c in await wallet.GetUnspentCoins(derivationScheme))
-                        var send = new[] { (
-                        destination: destinationAddress as IDestination,
-                        amount: amountBTC,
-                        substractFees: subsctractFeesValue) };
-
-                        foreach (var element in send)
                         {
-                            if (element.destination == null)
+                            keypaths.TryAdd(c.Coin.ScriptPubKey, c.KeyPath);
-                                throw new ArgumentNullException(nameof(element.destination));
+                            availableCoins.Add(c.Coin);
-                            if (element.amount == null)
-                                throw new ArgumentNullException(nameof(element.amount));
-                            if (element.amount <= Money.Zero)
-                                throw new ArgumentOutOfRangeException(nameof(element.amount), "The amount should be above zero");
                         }
 
+                        var changeAddress = await change;
+
                         var storeBlob = storeData.GetStoreBlob();
                         var paymentId = new Payments.PaymentMethodId(cryptoCode, Payments.PaymentTypes.BTCLike);
                         var foundKeyPath = storeBlob.GetWalletKeyPathRoot(paymentId);
@@ -520,10 +523,25 @@ namespace BTCPayServer.Controllers
                             storeData.SetStoreBlob(storeBlob);
                             await Repository.UpdateStore(storeData);
                         }
+retry:
+                        var send = new[] { (
+                        destination: destinationAddress as IDestination,
+                        amount: amountBTC,
+                        substractFees: subsctractFeesValue) };
+
+                        foreach (var element in send)
+                        {
+                            if (element.destination == null)
+                                throw new ArgumentNullException(nameof(element.destination));
+                            if (element.amount == null)
+                                throw new ArgumentNullException(nameof(element.amount));
+                            if (element.amount <= Money.Zero)
+                                throw new ArgumentOutOfRangeException(nameof(element.amount), "The amount should be above zero");
+                        }
 
                         TransactionBuilder builder = network.NBitcoinNetwork.CreateTransactionBuilder();
                         builder.StandardTransactionPolicy.MinRelayTxFee = summary.Status.BitcoinStatus.MinRelayTxFee;
-                        builder.AddCoins(unspentCoins.Select(c => c.Coin).ToArray());
+                        builder.AddCoins(availableCoins);
 
                         foreach (var element in send)
                         {
@@ -531,6 +549,7 @@ namespace BTCPayServer.Controllers
                             if (element.substractFees)
                                 builder.SubtractFees();
                         }
+
                         builder.SetChange(changeAddress.Item1);
 
                         if (network.MinFee == null)
@@ -547,13 +566,15 @@ namespace BTCPayServer.Controllers
                         }
                         var unsigned = builder.BuildTransaction(false);
 
-                        var keypaths = new Dictionary<Script, KeyPath>();
+                        var hasChange = unsigned.Outputs.Any(o => o.ScriptPubKey == changeAddress.Item1.ScriptPubKey);
-                        foreach (var c in unspentCoins)
+                        if (noChange && hasChange)
                         {
-                            keypaths.TryAdd(c.Coin.ScriptPubKey, c.KeyPath);
+                            availableCoins = builder.FindSpentCoins(unsigned).Cast<Coin>().ToList();
+                            amountBTC = builder.FindSpentCoins(unsigned).Select(c => c.TxOut.Value).Sum();
+                            subsctractFeesValue = true;
+                            goto retry;
                         }
 
-                        var hasChange = unsigned.Outputs.Count == 2;
                         var usedCoins = builder.FindSpentCoins(unsigned);
 
                         Dictionary<uint256, Transaction> parentTransactions = new Dictionary<uint256, Transaction>();

BTCPayServer/Models/WalletViewModels/WalletSendLedgerModel.cs

@@ -11,5 +11,6 @@ namespace BTCPayServer.Models.WalletViewModels
         public bool SubstractFees { get; set; }
         public decimal Amount { get; set; }
         public string Destination { get; set; }
+        public bool NoChange { get; set; }
     }
 }

BTCPayServer/Models/WalletViewModels/WalletSendModel.cs

@@ -28,6 +28,10 @@ namespace BTCPayServer.Models.WalletViewModels
         [Display(Name = "Fee rate (satoshi per byte)")]
         [Required]
         public int FeeSatoshiPerByte { get; set; }
+
+        [Display(Name = "Make sure no change UTXO is created")]
+        public bool NoChange { get; set; }
+        public bool AdvancedMode { get; set; }
         public decimal? Rate { get; set; }
         public int Divisibility { get; set; }
         public string Fiat { get; set; }

BTCPayServer/Views/Wallets/WalletSend.cshtml

@@ -55,7 +55,23 @@
                 <label asp-for="SubstractFees"></label>
                 <input asp-for="SubstractFees" class="form-check" />
             </div>
-            <button type="submit" class="btn btn-primary">Confirm</button>
+            @if (Model.AdvancedMode)
+            {
+            <div class="form-group">
+                <label asp-for="NoChange"></label>
+                <a href="https://docs.btcpayserver.org/features/wallet#make-sure-no-change-utxo-is-created-expert-mode" target="_blank"><span class="fa fa-question-circle-o" title="More information..."></span></a>
+                <input asp-for="NoChange" class="form-check" />
+            </div>
+            }
+            <button name="command" type="submit" class="btn btn-primary">Confirm</button>
+            @if (Model.AdvancedMode)
+            {
+                <button name="command" type="submit" value="noob" class="btn btn-secondary">Use noob mode</button>
+            }
+            else
+            {
+                <button name="command" type="submit" value="expert" class="btn btn-secondary">Use expert mode</button>
+            }
         </form>
     </div>
 </div>

BTCPayServer/Views/Wallets/WalletSendLedger.cshtml

@@ -16,6 +16,7 @@
         <input type="hidden" asp-for="Amount" />
         <input type="hidden" asp-for="FeeSatoshiPerByte" />
         <input type="hidden" asp-for="SubstractFees" />
+        <input type="hidden" asp-for="NoChange" />
         <p>
             You can send money received by this store to an address with the help of your Ledger Wallet. <br />
             If you don't have a Ledger Wallet, use Electrum with your favorite hardware wallet to transfer crypto. <br />

BTCPayServer/wwwroot/js/WalletSendLedger.js

@@ -3,6 +3,7 @@
     var amount = $("#Amount").val();
     var fee = $("#FeeSatoshiPerByte").val();
     var substractFee = $("#SubstractFees").val();
+    var noChange = $("#NoChange").val();
 
     var loc = window.location, ws_uri;
     if (loc.protocol === "https:") {
@@ -48,8 +49,14 @@
         args += "&amount=" + amount;
         args += "&feeRate=" + fee;
         args += "&substractFees=" + substractFee;
+        args += "&noChange=" + noChange;
 
-        WriteAlert("warning", 'Please validate the transaction on your ledger');
+        if (noChange === "True") {
+            WriteAlert("warning", 'WARNING: Because you want to make sure no change UTXO is created, you will end up sending more than the chosen amount to your destination. Please validate the transaction on your ledger');
+        }
+        else {
+            WriteAlert("warning", 'Please validate the transaction on your ledger');
+        }        
 
         var confirmButton = $("#confirm-button");
         confirmButton.prop("disabled", true);