When Hot Reload change fails to apply in the browser send full error … (

#33471)

src/BuiltInTools/BrowserRefresh/WebSocketScriptInjection.js

@@ -43,7 +43,8 @@ setTimeout(async function () {
       const payload = JSON.parse(message.data);
       const action = {
         'UpdateStaticFile': () => updateStaticFile(payload.path),
-        'BlazorHotReloadDeltav1': () => applyBlazorDeltas(payload.sharedSecret, payload.deltas),
+        'BlazorHotReloadDeltav1': () => applyBlazorDeltas(payload.sharedSecret, payload.deltas, false),
+        'BlazorHotReloadDeltav2': () => applyBlazorDeltas(payload.sharedSecret, payload.deltas, true),
         'HotReloadDiagnosticsv1': () => displayDiagnostics(payload.diagnostics),
         'BlazorRequestApplyUpdateCapabilities': getBlazorWasmApplyUpdateCapabilities,
         'AspNetCoreHotReloadApplied': () => aspnetCoreHotReloadApplied()
@@ -123,14 +124,14 @@ setTimeout(async function () {
     styleElement.parentNode.insertBefore(newElement, styleElement.nextSibling);
   }
 
-  function applyBlazorDeltas(serverSecret, deltas) {
+  function applyBlazorDeltas(serverSecret, deltas, sendErrorToClient) {
     if (sharedSecret && (serverSecret != sharedSecret.encodedSharedSecret)) {
       // Validate the shared secret if it was specified. It might be unspecified in older versions of VS
       // that do not support this feature as yet.
       throw 'Unable to validate the server. Rejecting apply-update payload.';
     }
 
-    let applyFailed = false;
+    let applyError = undefined;
     if (window.Blazor?._internal?.applyHotReload) {
       // Only apply hot reload deltas if Blazor has been initialized.
       // It's possible for Blazor to start after the initial page load, so we don't consider skipping this step
@@ -140,7 +141,7 @@ setTimeout(async function () {
           window.Blazor._internal.applyHotReload(d.moduleId, d.metadataDelta, d.ilDelta, d.pdbDelta)
         } catch (error) {
           console.warn(error);
-          applyFailed = true;
+          applyError = error;
         }
       }); 
     }
@@ -153,8 +154,8 @@ setTimeout(async function () {
         }
       });
 
-    if (applyFailed) {
-      sendDeltaNotApplied();
+    if (applyError) {
+      sendDeltaNotApplied(sendErrorToClient ? applyError : undefined);
     } else {
       sendDeltaApplied();
       notifyHotReloadApplied();
@@ -202,8 +203,13 @@ setTimeout(async function () {
     connection.send(new Uint8Array([1]).buffer);
   }
 
-  function sendDeltaNotApplied() {
-    connection.send(new Uint8Array([0]).buffer);
+  function sendDeltaNotApplied(error) {
+    if (error) {
+      let encoder = new TextEncoder()
+      connection.send(encoder.encode("\0" + error.message + "\0" + error.stack));
+    } else {
+      connection.send(new Uint8Array([0]).buffer);
+    }
   }
 
   async function getSecret(serverKeyString) {

src/BuiltInTools/dotnet-watch/HotReload/BlazorWebAssemblyDeltaApplier.cs

@@ -105,30 +105,46 @@ public override async Task<ApplyStatus> Apply(DotNetWatchContext context, Immuta
 
         private async Task<bool> ReceiveApplyUpdateResult(BrowserRefreshServer browserRefresh, CancellationToken cancellationToken)
         {
-            var _receiveBuffer = new byte[1];
-            var result = await browserRefresh.ReceiveAsync(_receiveBuffer, cancellationToken);
-            if (result is null)
+            var buffer = new byte[1];
+
+            var result = await browserRefresh.ReceiveAsync(buffer, cancellationToken);
+            if (result is not { MessageType: WebSocketMessageType.Binary })
             {
                 // A null result indicates no clients are connected. No deltas could have been applied in this state.
                 _reporter.Verbose("Apply confirmation: No browser is connected");
                 return false;
             }
 
-            if (IsDeltaReceivedMessage(result.Value))
+            if (result is { Count: 1, EndOfMessage: true })
             {
-                // 1 indicates success.
-                return _receiveBuffer[0] == 1;
+                return buffer[0] == 1;
             }
 
-            return false;
+            _reporter.Verbose("Browser failed to apply the change and reported error:");
+
+            buffer = new byte[1024];
+            var messageStream = new MemoryStream();
 
-            bool IsDeltaReceivedMessage(ValueWebSocketReceiveResult result)
+            while (true)
             {
-                _reporter.Verbose($"Apply confirmation: Received {_receiveBuffer[0]} from browser in [Count: {result.Count}, MessageType: {result.MessageType}, EndOfMessage: {result.EndOfMessage}].");
-                return result.Count == 1 // Should have received 1 byte on the socket for the acknowledgement
-                    && result.MessageType is WebSocketMessageType.Binary
-                    && result.EndOfMessage;
+                result = await browserRefresh.ReceiveAsync(buffer, cancellationToken);
+                if (result is not { MessageType: WebSocketMessageType.Binary })
+                {
+                    _reporter.Verbose("Failed to receive error message");
+                    break;
+                }
+
+                messageStream.Write(buffer, 0, result.Value.Count);
+
+                if (result is { EndOfMessage: true })
+                {
+                    // message and stack trace are separated by '\0'
+                    _reporter.Verbose(Encoding.UTF8.GetString(messageStream.ToArray()).Replace("\0", Environment.NewLine));
+                    break;
+                }
             }
+
+            return false;
         }
 
         public override void Dispose()
@@ -138,7 +154,7 @@ public override void Dispose()
 
         private readonly struct UpdatePayload
         {
-            public string Type => "BlazorHotReloadDeltav1";
+            public string Type => "BlazorHotReloadDeltav2";
             public string? SharedSecret { get; init; }
             public IEnumerable<UpdateDelta> Deltas { get; init; }
         }