Clear up error cases

Author: SteveSandersonMS

src/Components/Endpoints/src/RazorComponentEndpointInvoker.cs

@@ -3,14 +3,14 @@
 
 using System.Buffers;
 using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
 using System.Text;
 using System.Text.Encodings.Web;
 using Microsoft.AspNetCore.Antiforgery;
 using Microsoft.AspNetCore.Antiforgery.Infrastructure;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.WebUtilities;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
 
 namespace Microsoft.AspNetCore.Components.Endpoints;
 
@@ -110,32 +110,38 @@ private async Task<RequestValidationState> ValidateRequestAsync(IAntiforgery? an
             if (!valid)
             {
                 _context.Response.StatusCode = StatusCodes.Status400BadRequest;
+
+                if (_context.RequestServices.GetService<IHostEnvironment>()?.IsDevelopment() == true)
+                {
+                    await _context.Response.WriteAsync("A valid antiforgery token was not provided with the request. Add an antiforgery token, or disable antiforgery validation for this endpoint.");
+                }
             }
-            var formValid = TryGetFormHandler(out var handler);
-            return new(valid && formValid, isPost, handler);
+
+            var handler = GetFormHandler(out var isBadRequest);
+            return new(valid && !isBadRequest, isPost, handler);
         }
 
         return new(true, false, null);
     }
 
-    private bool TryGetFormHandler([NotNullWhen(true)] out string? handler)
+    private string? GetFormHandler(out bool isBadRequest)
     {
-        handler = "";
+        isBadRequest = false;
+
         if (_context.Request.Form.TryGetValue("handler", out var value))
         {
             if (value.Count != 1)
             {
                 _context.Response.StatusCode = StatusCodes.Status400BadRequest;
-                handler = null;
-                return false;
+                isBadRequest = true;
             }
             else
             {
-                handler = value[0]!;
+                return value[0]!;
             }
         }
 
-        return true;
+        return null;
     }
 
     private static TextWriter CreateResponseWriter(Stream bodyStream)

src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.EventDispatch.cs

@@ -30,7 +30,9 @@ internal Task DispatchSubmitEventAsync(string? handlerName)
         }
 
         var eventHandlerId = FindEventHandlerIdForNamedEvent("onsubmit", frameLocation.ComponentId, frameLocation.FrameIndex);
-        return DispatchEventAsync(eventHandlerId, null, EventArgs.Empty, quiesce: true);
+        return eventHandlerId.HasValue
+            ? DispatchEventAsync(eventHandlerId.Value, null, EventArgs.Empty, quiesce: true)
+            : Task.CompletedTask;
     }
 
     private void UpdateNamedEvents(in RenderBatch renderBatch)
@@ -81,7 +83,7 @@ private void UpdateNamedEvents(in RenderBatch renderBatch)
         }
     }
 
-    private ulong FindEventHandlerIdForNamedEvent(string eventType, int componentId, int frameIndex)
+    private ulong? FindEventHandlerIdForNamedEvent(string eventType, int componentId, int frameIndex)
     {
         var frames = GetCurrentRenderTreeFrames(componentId);
         ref var frame = ref frames.Array[frameIndex];
@@ -114,8 +116,8 @@ private ulong FindEventHandlerIdForNamedEvent(string eventType, int componentId,
             }
         }
 
-        // This won't be possible if the Razor compiler requires @onsubmit:name to be used only when there's an @onsubmit.
-        throw new InvalidOperationException($"The event named '{frame.NamedEventAssignedName}' in component {componentId} at index {frameIndex} does not match a preceding event handler.");
+        // No match found
+        return default;
     }
 
     private string GenerateComponentPath(int componentId)

src/Components/Web/src/Forms/EditForm.cs

@@ -144,7 +144,7 @@ protected override void BuildRenderTree(RenderTreeBuilder builder)
         {
             var combinedFormName = MappingContext.GetCombinedFormName(FormHandlerName) ?? string.Empty;
             builder.AddNamedEvent(5, "onsubmit", combinedFormName);
-            RenderSSRFormHandlingChildren(builder, 6, combinedFormName);
+            RenderSSRFormHandlingChildren(builder, 6);
         }
 
         builder.OpenComponent<CascadingValue<EditContext>>(7);
@@ -158,7 +158,7 @@ protected override void BuildRenderTree(RenderTreeBuilder builder)
         builder.CloseRegion();
     }
 
-    private void RenderSSRFormHandlingChildren(RenderTreeBuilder builder, int sequence, string submitEventName)
+    private void RenderSSRFormHandlingChildren(RenderTreeBuilder builder, int sequence)
     {
         builder.OpenRegion(sequence);
 
@@ -169,12 +169,6 @@ private void RenderSSRFormHandlingChildren(RenderTreeBuilder builder, int sequen
         builder.OpenComponent<AntiforgeryToken>(3);
         builder.CloseComponent();
 
-        builder.OpenElement(4, "input");
-        builder.AddAttribute(5, "type", "hidden");
-        builder.AddAttribute(6, "name", "handler");
-        builder.AddAttribute(7, "value", submitEventName);
-        builder.CloseElement();
-
         builder.CloseRegion();
     }
 

src/Components/Web/test/Forms/EditFormTest.cs

@@ -147,8 +147,8 @@ public async Task AddSSRContentWhenMappingContextPresent()
 
         // Assert
         Assert.Collection(editFormFrames.AsEnumerable(),
-            frame => AssertFrame.Region(frame, 17),
-            frame => AssertFrame.Element(frame, "form", 16),
+            frame => AssertFrame.Region(frame, 13),
+            frame => AssertFrame.Element(frame, "form", 12),
 
             // Sets "method" to "post" by default
             frame => AssertFrame.Attribute(frame, "method", "post"),
@@ -157,7 +157,7 @@ public async Task AddSSRContentWhenMappingContextPresent()
             frame => AssertFrame.Attribute(frame, "onsubmit"),
             frame => AssertFrame.NamedEvent(frame, "onsubmit", "mapping-context-name.my-form"),
 
-            frame => AssertFrame.Region(frame, 8),
+            frame => AssertFrame.Region(frame, 4),
 
             // Adds FormMappingValidator child
             frame => AssertFrame.Component<FormMappingValidator>(frame, 2),
@@ -166,12 +166,6 @@ public async Task AddSSRContentWhenMappingContextPresent()
             // Adds AntiforgeryToken child
             frame => AssertFrame.Component<AntiforgeryToken>(frame, 1),
 
-            // Adds hidden input specifying handler name
-            frame => AssertFrame.Element(frame, "input", 4),
-            frame => AssertFrame.Attribute(frame, "type", "hidden"),
-            frame => AssertFrame.Attribute(frame, "name", "handler"),
-            frame => AssertFrame.Attribute(frame, "value", "mapping-context-name.my-form"),
-
             frame => AssertFrame.Component<CascadingValue<EditContext>>(frame, 4),
             frame => AssertFrame.Attribute(frame, "IsFixed", true),
             frame => AssertFrame.Attribute(frame, "Value"),