Blazor Hybrid CSS Hot Reload Fixes (#9645)

* Stop copying content stream in .NET MAUI Blazor Windows

Fixes: #9206

microsoft/CsWinRT#670 and https://task.ms/31565319 have been marked as resolved. This PR removes the existing logic which copies the content into a memory stream, and replaces it with a call to `AsRandomAccessStream()` (`IRandomAccessStream` is still required per the `CoreWebView2` API).

I tried out CSS hot reload with this change and things are working as expected. Not sure if there's a particular behavior/technique we can use to verify the validity of this change. Spoke with @Eilon regarding this, and per his recollection things were immediately hanging, and that's why this change was necessitated.

* AutoCloseOnReadCompleteStream

* Ensure old response content is closed out for hot reload

* PR Feedback

Microsoft.Maui.sln

@@ -196,6 +196,7 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MauiBlazorWebView.DeviceTes
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "SharedSource", "SharedSource", "{4F2926C8-43AB-4328-A735-D9EAD699F81D}"
  ProjectSection(SolutionItems) = preProject
+ src\BlazorWebView\src\SharedSource\AutoCloseOnReadCompleteStream.cs = src\BlazorWebView\src\SharedSource\AutoCloseOnReadCompleteStream.cs
  src\BlazorWebView\src\SharedSource\QueryStringHelper.cs = src\BlazorWebView\src\SharedSource\QueryStringHelper.cs
  src\BlazorWebView\src\SharedSource\UrlLoadingEventArgs.cs = src\BlazorWebView\src\SharedSource\UrlLoadingEventArgs.cs
  src\BlazorWebView\src\SharedSource\UrlLoadingStrategy.cs = src\BlazorWebView\src\SharedSource\UrlLoadingStrategy.cs

src/BlazorWebView/src/SharedSource/AutoCloseOnReadCompleteStream.cs

@@ -0,0 +1,51 @@
+#if WEBVIEW2_WINFORMS || WEBVIEW2_WPF
+
+using System.IO;
+
+namespace Microsoft.AspNetCore.Components.WebView.WebView2
+{
+ internal class AutoCloseOnReadCompleteStream : Stream
+ {
+ private readonly Stream _baseStream;
+
+ public AutoCloseOnReadCompleteStream(Stream baseStream)
+ {
+ _baseStream = baseStream;
+ }
+
+ public override bool CanRead => _baseStream.CanRead;
+
+ public override bool CanSeek => _baseStream.CanSeek;
+
+ public override bool CanWrite => _baseStream.CanWrite;
+
+ public override long Length => _baseStream.Length;
+
+ public override long Position { get => _baseStream.Position; set => _baseStream.Position = value; }
+
+ public override void Flush() => _baseStream.Flush();
+
+ public override int Read(byte[] buffer, int offset, int count)
+ {
+ var bytesRead = _baseStream.Read(buffer, offset, count);
+
+ // Stream.Read only returns 0 when it has reached the end of stream
+ // and no further bytes are expected. Otherwise it blocks until
+ // one or more (and at most count) bytes can be read.
+ if (bytesRead == 0)
+ {
+ _baseStream.Close();
+ }
+
+ return bytesRead;
+ }
+
+ public override long Seek(long offset, SeekOrigin origin) => _baseStream.Seek(offset, origin);
+
+ public override void SetLength(long value) => _baseStream.SetLength(value);
+
+ public override void Write(byte[] buffer, int offset, int count) => _baseStream.Write(buffer, offset, count);
+ }
+}
+
+#endif

src/BlazorWebView/src/SharedSource/StaticContentHotReloadManager.cs

@@ -67,6 +67,7 @@ public static bool TryReplaceResponseContent(string contentRootRelativePath, str
  if (_updatedContent.TryGetValue((assemblyName, relativePath), out var values))
  {
  responseStatusCode = 200;
+ responseContent.Close();
  responseContent = new MemoryStream(values.Content);
  if (!string.IsNullOrEmpty(values.ContentType))
  {

src/BlazorWebView/src/SharedSource/WebView2WebViewManager.cs

@@ -304,7 +304,10 @@ protected virtual Task HandleWebResourceRequest(CoreWebView2WebResourceRequested
  StaticContentHotReloadManager.TryReplaceResponseContent(_contentRootRelativeToAppRoot, requestUri, ref statusCode, ref content, headers);
 
  var headerString = GetHeaderString(headers);
- eventArgs.Response = _coreWebView2Environment!.CreateWebResourceResponse(content, statusCode, statusMessage, headerString);
+
+ var autoCloseStream = new AutoCloseOnReadCompleteStream(content);
+
+ eventArgs.Response = _coreWebView2Environment!.CreateWebResourceResponse(autoCloseStream, statusCode, statusMessage, headerString);
  }
 #elif WEBVIEW2_MAUI
  // No-op here because all the work is done in the derived WinUIWebViewManager