Better error message on invalid PSBT in Sign with Seed (#6920)

* Better error message on invalid PSBT in Sign with Seed

* Improve error reporting if a PSBT built by SendWallet is not signable

BTCPayServer/Controllers/UIWalletsController.PSBT.cs

@@ -86,6 +86,7 @@ namespace BTCPayServer.Controllers
                     BackUrl = vm.BackUrl
                 });
             }
+
             switch (command)
             {
                 case "vault":
@@ -170,6 +171,7 @@ namespace BTCPayServer.Controllers
             {
                 return View("WalletPSBT", vm);
             }
+
             switch (command)
             {
                 case "createpending":
@@ -373,14 +375,25 @@ namespace BTCPayServer.Controllers
                 vm.FeeRate = feeRate.ToString();
             }
 
-            var sanityErrors = psbtObject.CheckSanity();
+            if (!psbtObject.IsAllFinalized())
-            if (sanityErrors.Count != 0)
             {
-                vm.SetErrors(sanityErrors);
+                var sanityErrors = new List<PSBTError>();
-            }
+                foreach (var input in psbtObject.Inputs)
-            else if (!psbtObject.IsAllFinalized() && !psbtObject.TryFinalize(out var errors))
+                {
-            {
+                    if (input.IsFinalized())
-                vm.SetErrors(errors);
+                        continue;
+
+                    if (input.GetSignableCoin(out var missingCoin) is null)
+                    {
+                        sanityErrors.Add(new PSBTError(input.Index, missingCoin));
+                    }
+                    else if (!input.TryFinalizeInput(out var err))
+                    {
+                        sanityErrors.Add(err[0]);
+                    }
+                }
+                if (sanityErrors.Count > 0)
+                    vm.SetErrors(sanityErrors);
             }
 
             var combinedTypeIds = inputToObjects.Values.SelectMany(ids => ids).Concat(outputToObjects.Values)

BTCPayServer/Controllers/UIWalletsController.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
 using System.Net.Mime;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using BTCPayServer.Abstractions.Constants;
@@ -1289,6 +1290,9 @@ namespace BTCPayServer.Controllers
                 ChangeAddress = psbtResponse.ChangeAddress?.ToString(),
                 PSBT = psbt.ToHex()
             };
+
+            if (!psbt.IsReadyToSign() && command == "sign")
+                command = "analyze-psbt";
             switch (command)
             {
                 case "createpending":
@@ -1512,9 +1516,9 @@ namespace BTCPayServer.Controllers
 
             var psbt = PSBT.Parse(viewModel.SigningContext.PSBT, network.NBitcoinNetwork);
 
-            if (!psbt.IsReadyToSign())
+            if (!psbt.IsReadyToSign(out var errors))
             {
-                ModelState.AddModelError(nameof(viewModel.SigningContext.PSBT), "PSBT is not ready to be signed");
+                ModelState.AddModelError(nameof(viewModel.SigningContext.PSBT), BuildErrorMessage(errors));
             }
 
             if (!ModelState.IsValid)
@@ -1580,6 +1584,27 @@ namespace BTCPayServer.Controllers
             });
         }
 
+        private static string BuildErrorMessage(PSBTError[] errors)
+        {
+            StringBuilder errorMessage = new();
+            errorMessage.Append("PSBT is not ready to be signed.");
+            if (errors.Length == 1)
+            {
+                errorMessage.Append($" ({errors[0]})");
+            }
+            else
+            {
+                errorMessage.AppendLine();
+                foreach (var error in errors.Take(5))
+                {
+                    errorMessage.AppendLine(error.ToString());
+                }
+            }
+            if (errors.Length > 5)
+                errorMessage.Append($"{errors.Length - 5} more errors...");
+            return errorMessage.ToString();
+        }
+
         private WalletPSBTReadyViewModel.StringAmounts ValueToString(Money v, BTCPayNetworkBase network,
             FiatRate? rate) =>
             new(