Reduced memory usage and fixed several memory leaks (#933)

app/MindWork AI Studio/Dialogs/DocumentCheckDialog.razor.cs

@@ -21,11 +21,41 @@ public partial class DocumentCheckDialog : MSGComponentBase
     [Parameter]
     public string FileContent { get; set; } = string.Empty;
 
+    /// <summary>
+    /// How many characters we show at most. Rendering a huge document costs us a large Markdown
+    /// syntax tree and an equally large render tree. This dialog answers the question of how we
+    /// read the file, though — the beginning of the document is enough for that, and the AI still
+    /// receives the entire content.
+    /// </summary>
+    private const int PREVIEW_CHARACTER_LIMIT = 200_000;
+
     /// <summary>
     /// Set when reading the file failed, so the dialog shows the reason instead of empty content.
     /// </summary>
     private string? loadFailureMessage;
 
+    /// <summary>
+    /// What we show to the user: either the entire file content, or its beginning. We keep this in
+    /// its own field so that we cut the content only once, instead of on every render.
+    /// </summary>
+    private string previewContent = string.Empty;
+
+    /// <summary>
+    /// How many characters we cut off from the preview. Zero when we show the entire content.
+    /// </summary>
+    private int previewCutOffCharacters;
+
+    /// <summary>
+    /// Ends the extraction when this dialog is gone before the file was read completely.
+    /// </summary>
+    private readonly CancellationTokenSource extractionCancellation = new();
+
+    /// <summary>
+    /// True once this dialog was disposed. The extraction runs across awaits, so it may return
+    /// long after the user closed the dialog — it must not touch this component afterwards.
+    /// </summary>
+    private bool isDisposed;
+
     /// <summary>
     /// True while we extract the file content. Reading happens after the first render, so the
     /// dialog can tell the user that it is working instead of showing an empty document.
@@ -54,6 +84,7 @@ public partial class DocumentCheckDialog : MSGComponentBase
             this.Document.Exists &&
             string.IsNullOrWhiteSpace(this.FileContent);
 
+        this.UpdatePreview();
         await base.OnInitializedAsync();
     }
 
@@ -66,7 +97,10 @@ public partial class DocumentCheckDialog : MSGComponentBase
 
             try
             {
-                var extraction = await UserFile.LoadFileData(this.Document.FilePath, this.RustService, this.DialogService);
+                var extraction = await UserFile.LoadFileData(this.Document.FilePath, this.RustService, this.DialogService, this.extractionCancellation.Token);
+                if (this.isDisposed)
+                    return;
+
                 this.FileContent = extraction.Content;
 
                 //
@@ -76,6 +110,10 @@ public partial class DocumentCheckDialog : MSGComponentBase
                 if (!extraction.HasUsableContent)
                     this.loadFailureMessage = extraction.ToUserMessage(this.Document.FileName);
             }
+            catch (OperationCanceledException)
+            {
+                // The user closed this dialog while we were reading the file. Nothing left to do.
+            }
             catch (Exception ex)
             {
                 this.Logger.LogError(ex, "Failed to load file content from '{FilePath}'", this.Document);
@@ -84,14 +122,67 @@ public partial class DocumentCheckDialog : MSGComponentBase
             }
             finally
             {
-                this.isLoadingContent = false;
-                this.StateHasChanged();
+                if (!this.isDisposed)
+                {
+                    this.isLoadingContent = false;
+                    this.UpdatePreview();
+                    this.StateHasChanged();
+                }
             }
         }
         else if (firstRender)
             this.Logger.LogWarning("Document check dialog opened without a valid file path.");
     }
     
+    /// <summary>
+    /// Called when the user loads a file through this dialog. We don't use a two-way binding here,
+    /// since we have to refresh the preview whenever the content changes.
+    /// </summary>
+    /// <param name="fileContent">The content of the file the user has loaded.</param>
+    private void ApplyLoadedFileContent(string fileContent)
+    {
+        this.FileContent = fileContent;
+        this.UpdatePreview();
+    }
+
+    /// <summary>
+    /// Determines what part of the file content we show to the user.
+    /// </summary>
+    private void UpdatePreview()
+    {
+        if (this.FileContent.Length <= PREVIEW_CHARACTER_LIMIT)
+        {
+            this.previewContent = this.FileContent;
+            this.previewCutOffCharacters = 0;
+            return;
+        }
+
+        //
+        // We cut at the last line break before our limit. Otherwise, we might tear apart a Markdown
+        // construct like a table row or a code fence in the middle of a line:
+        //
+        var cutIndex = this.FileContent.LastIndexOf('\n', PREVIEW_CHARACTER_LIMIT - 1) + 1;
+        if (cutIndex < 1)
+            cutIndex = PREVIEW_CHARACTER_LIMIT;
+
+        this.previewContent = this.FileContent[..cutIndex];
+        this.previewCutOffCharacters = this.FileContent.Length - cutIndex;
+    }
+
+    /// <summary>
+    /// Ends a running extraction. Without this, reading a large document would continue after the
+    /// user closed this dialog and would keep this component, the extracted content, and the
+    /// response stream alive until the runtime is done.
+    /// </summary>
+    protected override void DisposeResources()
+    {
+        this.isDisposed = true;
+        this.extractionCancellation.Cancel();
+        this.extractionCancellation.Dispose();
+
+        base.DisposeResources();
+    }
+
     private CodeBlockTheme CodeColorPalette => this.SettingsManager.IsDarkMode ? CodeBlockTheme.Dark : CodeBlockTheme.Default;
 
     private MudMarkdownStyling MarkdownStyling => new()