Invoice: Improve zero amount invoice handling (#6199)

This is for the checkout page to properly redirect paid invoices with no payment methods (e.g. free invoices with zero amount) to either the receipt page or redirect URL. Only fall back to 404 if there is neither.

Fixes #6123.

BTCPayServer.Tests/BTCPayServer.Tests.csproj

@@ -34,7 +34,7 @@
     <PackageReference Include="Newtonsoft.Json.Schema" Version="3.0.15" />
     <PackageReference Include="Selenium.Support" Version="4.1.1" />
     <PackageReference Include="Selenium.WebDriver" Version="4.22.0" />
-	<PackageReference Include="Selenium.WebDriver.ChromeDriver" Version="125.0.6422.14100" />
+	<PackageReference Include="Selenium.WebDriver.ChromeDriver" Version="128.0.6613.11900" />
 	<PackageReference Include="xunit" Version="2.6.6" />
 	<PackageReference Include="xunit.runner.visualstudio" Version="2.5.6">
       <PrivateAssets>all</PrivateAssets>

BTCPayServer.Tests/SeleniumTester.cs

@@ -55,6 +55,7 @@ namespace BTCPayServer.Tests
             options.AddArguments($"window-size={windowSize.Width}x{windowSize.Height}");
             options.AddArgument("shm-size=2g");
             options.AddArgument("start-maximized");
+            options.AddArgument("disable-search-engine-choice-screen");
             if (Server.PayTester.InContainer)
             {
                 // Shot in the dark to fix https://stackoverflow.com/questions/53902507/unknown-error-session-deleted-because-of-page-crash-from-unknown-error-cannot

BTCPayServer.Tests/SeleniumTests.cs

@@ -745,6 +745,14 @@ namespace BTCPayServer.Tests
             s.Driver.FindElement(By.CssSelector("[data-invoice-state-badge] .dropdown-toggle")).Click();
             s.Driver.FindElements(By.CssSelector("[data-invoice-state-badge] .dropdown-menu button"))[0].Click();
             TestUtils.Eventually(() => Assert.Contains("Settled (marked)", s.Driver.PageSource));
+            
+            // zero amount invoice should redirect to receipt
+            var zeroAmountId = s.CreateInvoice(0);
+            s.GoToUrl($"/i/{zeroAmountId}");
+            Assert.EndsWith("/receipt", s.Driver.Url);
+            Assert.Contains("$0.00", s.Driver.PageSource);
+            s.GoToInvoice(zeroAmountId);
+            Assert.Equal("Settled", s.Driver.FindElement(By.CssSelector("[data-invoice-state-badge]")).Text);
         }
 
         [Fact(Timeout = TestTimeout)]

BTCPayServer/Controllers/UIInvoiceController.UI.cs

@@ -199,16 +199,13 @@ namespace BTCPayServer.Controllers
                 return NotFound();
 
             var receipt = InvoiceDataBase.ReceiptOptions.Merge(store.GetStoreBlob().ReceiptOptions, i.ReceiptOptions);
-
             if (receipt.Enabled is not true)
             {
-                if (i.RedirectURL is not null)
+                return i.RedirectURL is not null
-                {
+                    ? Redirect(i.RedirectURL.ToString())
-                    return Redirect(i.RedirectURL.ToString());
+                    : NotFound();
-                }
-                return NotFound();
-
             }
+
             var storeBlob = store.GetStoreBlob();
             var vm = new InvoiceReceiptViewModel
             {
@@ -699,7 +696,16 @@ namespace BTCPayServer.Controllers
 
             var model = await GetInvoiceModel(invoiceId, paymentMethodId == null ? null : PaymentMethodId.Parse(paymentMethodId), lang);
             if (model == null)
-                return NotFound();
+            {
+                // see if the invoice actually exists and is in a state for which we do not display the checkout
+                var invoice = await _InvoiceRepository.GetInvoice(invoiceId);
+                var store = invoice != null ? await _StoreRepository.GetStoreByInvoiceId(invoice.Id) : null;
+                var receipt = invoice != null && store != null ? InvoiceDataBase.ReceiptOptions.Merge(store.GetStoreBlob().ReceiptOptions, invoice.ReceiptOptions) : null;
+                var redirectUrl = invoice?.RedirectURL?.ToString();
+                return receipt?.Enabled is true
+                    ? RedirectToAction(nameof(InvoiceReceipt), new { invoiceId })
+                    : !string.IsNullOrEmpty(redirectUrl) ? Redirect(redirectUrl) : NotFound();
+            }
 
             if (view == "modal")
                 model.IsModal = true;