Revert "Remove unused Error.cshtml"

This reverts commit 7b2ef9aec2.

BTCPayServer/Controllers/HomeController.cs

@@ -14,5 +14,24 @@ namespace BTCPayServer.Controllers
         {
             return View("Home");
         }
+
+        public IActionResult About()
+        {
+            ViewData["Message"] = "Your application description page.";
+
+            return View();
+        }
+
+        public IActionResult Contact()
+        {
+            ViewData["Message"] = "Your contact page.";
+
+            return View();
+        }
+
+        public IActionResult Error()
+        {
+            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
+        }
     }
 }

BTCPayServer/Models/ErrorViewModel.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace BTCPayServer.Models
+{
+    public class ErrorViewModel
+    {
+        public string RequestId { get; set; }
+
+        public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
+    }
+}

BTCPayServer/Views/Shared/Error.cshtml

@@ -0,0 +1,22 @@
+@model ErrorViewModel
+@{
+    ViewData["Title"] = "Error";
+}
+
+<h1 class="text-danger">Error.</h1>
+<h2 class="text-danger">An error occurred while processing your request.</h2>
+
+@if(Model.ShowRequestId)
+{
+    <p>
+        <strong>Request ID:</strong> <code>@Model.RequestId</code>
+    </p>
+}
+
+<h3>Development Mode</h3>
+<p>
+    Swapping to <strong>Development</strong> environment will display more detailed information about the error that occurred.
+</p>
+<p>
+    <strong>Development environment should not be enabled in deployed applications</strong>, as it can result in sensitive information from exceptions being displayed to end users. For local debugging, development environment can be enabled by setting the <strong>ASPNETCORE_ENVIRONMENT</strong> environment variable to <strong>Development</strong>, and restarting the application.
+</p>