Add utility tool to decode PSBT

BTCPayServer/BTCPayServer.csproj

@@ -182,6 +182,9 @@
 	  <Content Update="Views\Wallets\ListWallets.cshtml">
 	    <Pack>$(IncludeRazorContentInPack)</Pack>
 	  </Content>
+	  <Content Update="Views\Wallets\WalletPSBT.cshtml">
+	    <Pack>$(IncludeRazorContentInPack)</Pack>
+	  </Content>
 	  <Content Update="Views\Wallets\WalletRescan.cshtml">
 	    <Pack>$(IncludeRazorContentInPack)</Pack>
 	  </Content>

BTCPayServer/Controllers/WalletsController.cs

@@ -247,6 +247,12 @@ namespace BTCPayServer.Controllers
                 try
                 {
                     var psbt = await CreatePSBT(network, derivationScheme, sendModel, cancellation);
+                    if (command == "analyze-psbt")
+                        return View(nameof(WalletPSBT), new WalletPSBTViewModel()
+                        {
+                            Decoded = psbt.PSBT.ToString(),
+                            PSBT = psbt.PSBT.ToBase64()
+                        });
                     return File(psbt.PSBT.ToBytes(), "application/octet-stream", $"Send-{vm.Amount.Value}-{network.CryptoCode}-to-{destination[0].ToString()}.psbt");
                 }
                 catch (NBXplorerException ex)
@@ -331,6 +337,31 @@ namespace BTCPayServer.Controllers
             }
         }
 
+        [HttpGet]
+        [Route("{walletId}/psbt")]
+        public IActionResult WalletPSBT()
+        {
+            return View(new WalletPSBTViewModel());
+        }
+        [HttpPost]
+        [Route("{walletId}/psbt")]
+        public IActionResult WalletPSBT(
+            [ModelBinder(typeof(WalletIdModelBinder))]
+            WalletId walletId, 
+            WalletPSBTViewModel vm)
+        {
+            try
+            {
+                if (!string.IsNullOrEmpty(vm.PSBT))
+                    vm.Decoded = PSBT.Parse(vm.PSBT, NetworkProvider.GetNetwork(walletId.CryptoCode).NBitcoinNetwork).ToString();
+            }
+            catch (FormatException ex)
+            {
+                ModelState.AddModelError(nameof(vm.PSBT), ex.Message);
+            }
+            return View(vm);
+        }
+
         [HttpGet]
         [Route("{walletId}/rescan")]
         public async Task<IActionResult> WalletRescan(

BTCPayServer/Models/WalletViewModels/WalletPSBTViewModel.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace BTCPayServer.Models.WalletViewModels
+{
+    public class WalletPSBTViewModel
+    {
+        public string Decoded { get; set; }
+        public string PSBT { get; set; }
+    }
+}

BTCPayServer/Views/Wallets/WalletPSBT.cshtml

@@ -0,0 +1,29 @@
+@model WalletPSBTViewModel
+@{
+    Layout = "../Shared/_NavLayout.cshtml";
+    ViewData["Title"] = "PSBT";
+    ViewData.SetActivePageAndTitle(WalletsNavPages.PSBT);
+}
+<div class="row">
+    <div class="col-md-10">
+        @if (!string.IsNullOrEmpty(Model.Decoded))
+        {
+            <h3>Decoded PSBT</h3>
+            <pre><code class="json">@Model.Decoded</code></pre>
+        }
+        <h3>PSBT to decode</h3>
+        <form class="form-group" method="post" asp-action="WalletPSBT">
+            <div class="form-group">
+                <textarea class="form-control" rows="5" asp-for="PSBT"></textarea>
+                <span asp-validation-for="PSBT" class="text-danger"></span>
+            </div>
+            <button type="submit" class="btn btn-primary">Decode</button>
+        </form>
+    </div>
+</div>
+
+@section Scripts {
+    <link rel="stylesheet" href="~/vendor/highlightjs/default.min.css">
+    <script src="~/vendor/highlightjs/highlight.min.js"></script>
+    <script>hljs.initHighlightingOnLoad();</script>
+}

BTCPayServer/Views/Wallets/WalletSend.cshtml

@@ -90,6 +90,7 @@
                     <div class="dropdown-menu" aria-labelledby="SendMenu">
                         <button name="command" type="submit" class="dropdown-item" value="ledger">... your Ledger Wallet device</button>
                         <button name="command" type="submit" class="dropdown-item" value="save-psbt">... a wallet supporting PSBT</button>
+                        <button name="command" type="submit" class="dropdown-item" value="analyze-psbt">... analyze the PSBT</button>
                     </div>
                 </div>
             </div>

BTCPayServer/Views/Wallets/WalletsNavPages.cs

@@ -9,6 +9,7 @@ namespace BTCPayServer.Views.Wallets
     {
         Send,
         Transactions,
-        Rescan
+        Rescan,
+        PSBT
     }
 }

BTCPayServer/Views/Wallets/_Nav.cshtml

@@ -4,5 +4,6 @@
     <a class="nav-link @ViewData.IsActivePage(WalletsNavPages.Transactions)" asp-action="WalletTransactions">Transactions</a>
     <a class="nav-link @ViewData.IsActivePage(WalletsNavPages.Send)" asp-action="WalletSend">Send</a>
     <a class="nav-link @ViewData.IsActivePage(WalletsNavPages.Rescan)" asp-action="WalletRescan">Rescan</a>
+    <a class="nav-link @ViewData.IsActivePage(WalletsNavPages.PSBT)" asp-action="WalletPSBT">PSBT</a>
 </div>