Release v36 (beta)

app/.idea/.idea.DiscordHistoryTracker/.idea/avalonia.xml

@@ -8,11 +8,13 @@
         <entry key="Desktop/Dialogs/Message/MessageDialog.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Dialogs/Progress/ProgressDialog.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/AboutWindow.axaml" value="Desktop/Desktop.csproj" />
+        <entry key="Desktop/Main/Controls/AttachmentFilterPanel.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/Controls/MessageFilterPanel.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/Controls/ServerConfigurationPanel.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/Controls/StatusBar.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/MainWindow.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/Pages/AdvancedPage.axaml" value="Desktop/Desktop.csproj" />
+        <entry key="Desktop/Main/Pages/AttachmentsPage.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/Pages/DatabasePage.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/Pages/DebugPage.axaml" value="Desktop/Desktop.csproj" />
         <entry key="Desktop/Main/Pages/TrackingPage.axaml" value="Desktop/Desktop.csproj" />

app/Desktop/App.axaml

@@ -7,6 +7,7 @@
     <Application.Styles>
 
         <FluentTheme Mode="Light" />
+        <StyleInclude Source="avares://Avalonia.Controls.DataGrid/Themes/Default.xaml"/>
 
         <Style Selector="Button, CheckBox, RadioButton, Expander /template/ ToggleButton#ExpanderHeader">
             <Setter Property="Cursor" Value="Hand" />
@@ -105,6 +106,7 @@
     <Application.Resources>
 
         <common:NumberValueConverter x:Key="NumberValueConverter" />
+        <common:BytesValueConverter x:Key="BytesValueConverter" />
 
         <system:Double x:Key="ControlContentThemeFontSize">14</system:Double>
         <CornerRadius x:Key="ControlCornerRadius">0</CornerRadius>
@@ -154,7 +156,7 @@
         <SolidColorBrush x:Key="TextControlPlaceholderForegroundDisabled" Color="#AAAAAA" />
 
         <Thickness x:Key="ExpanderHeaderPadding">15,0</Thickness>
-        <Thickness x:Key="ExpanderContentPadding">15</Thickness>
+        <Thickness x:Key="ExpanderContentPadding">12</Thickness>
         <SolidColorBrush x:Key="ExpanderBorderBrush" Color="#697DAB" />
         <SolidColorBrush x:Key="ExpanderBackground" Color="#697DAB" />
         <SolidColorBrush x:Key="ExpanderForeground" Color="#FFFFFF" />

app/Desktop/Common/BytesValueConverter.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Globalization;
+using Avalonia.Data.Converters;
+
+namespace DHT.Desktop.Common {
+	sealed class BytesValueConverter : IValueConverter {
+		private static readonly string[] Units = {
+			"B",
+			"kB",
+			"MB",
+			"GB",
+			"TB"
+		};
+
+		private const int Scale = 1000;
+
+		private static string Convert(ulong size) {
+			int power = size == 0L ? 0 : (int) Math.Log(size, Scale);
+			int unit = power >= Units.Length ? Units.Length - 1 : power;
+			if (unit == 0) {
+				return string.Format(Program.Culture, "{0:n0}", size) + " " + Units[unit];
+			}
+			else {
+				double humanReadableSize = size / Math.Pow(Scale, unit);
+				return string.Format(Program.Culture, "{0:n0}", humanReadableSize) + " " + Units[unit];
+			}
+		}
+
+		public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture) {
+			if (value is long size and >= 0L) {
+				return Convert((ulong) size);
+			}
+			else if (value is ulong usize) {
+				return Convert(usize);
+			}
+			else {
+				return "-";
+			}
+		}
+
+		public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture) {
+			throw new NotSupportedException();
+		}
+	}
+}

app/Desktop/Desktop.csproj

@@ -21,9 +21,10 @@
     <DebugType>none</DebugType>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="Avalonia" Version="0.10.13" />
+    <PackageReference Include="Avalonia" Version="0.10.14" />
-    <PackageReference Include="Avalonia.Desktop" Version="0.10.13" />
+    <PackageReference Include="Avalonia.Controls.DataGrid" Version="0.10.14" />
-    <PackageReference Include="Avalonia.Diagnostics" Version="0.10.13" Condition=" '$(Configuration)' == 'Debug' " />
+    <PackageReference Include="Avalonia.Desktop" Version="0.10.14" />
+    <PackageReference Include="Avalonia.Diagnostics" Version="0.10.14" Condition=" '$(Configuration)' == 'Debug' " />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Server\Server.csproj" />

app/Desktop/Main/Controls/AttachmentFilterPanel.axaml

@@ -0,0 +1,51 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:controls="clr-namespace:DHT.Desktop.Main.Controls"
+             mc:Ignorable="d"
+             x:Class="DHT.Desktop.Main.Controls.AttachmentFilterPanel">
+
+    <Design.DataContext>
+        <controls:AttachmentFilterPanelModel />
+    </Design.DataContext>
+
+    <UserControl.Styles>
+        <Style Selector="WrapPanel > StackPanel">
+            <Setter Property="Margin" Value="0 20 40 0" />
+            <Setter Property="Spacing" Value="4" />
+        </Style>
+        <Style Selector="WrapPanel > StackPanel:nth-last-child(1)">
+            <Setter Property="Margin" Value="0 20 0 0" />
+        </Style>
+        <Style Selector="Grid > Label">
+            <Setter Property="VerticalAlignment" Value="Center" />
+        </Style>
+        <Style Selector="ComboBox">
+            <Setter Property="Margin" Value="8 0 0 0" />
+        </Style>
+        <Style Selector="Button">
+            <Setter Property="Margin" Value="0 0 0 8" />
+        </Style>
+    </UserControl.Styles>
+
+    <StackPanel>
+        <TextBlock Text="{Binding FilterStatisticsText}" />
+        <WrapPanel>
+            <StackPanel>
+                <CheckBox IsChecked="{Binding LimitSize}">Limit Size</CheckBox>
+                <StackPanel Orientation="Horizontal">
+                    <TextBox Text="{Binding MaximumSize}" IsEnabled="{Binding LimitSize}" HorizontalContentAlignment="Right" />
+                    <ComboBox IsEnabled="{Binding LimitSize}" Items="{Binding Units}" SelectedItem="{Binding MaximumSizeUnit}">
+                        <ComboBox.ItemTemplate>
+                            <DataTemplate>
+                                <TextBlock Text="{Binding Name}" />
+                            </DataTemplate>
+                        </ComboBox.ItemTemplate>
+                    </ComboBox>
+                </StackPanel>
+            </StackPanel>
+        </WrapPanel>
+    </StackPanel>
+
+</UserControl>

app/Desktop/Main/Controls/AttachmentFilterPanel.axaml.cs

@@ -0,0 +1,17 @@
+using System.Diagnostics.CodeAnalysis;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace DHT.Desktop.Main.Controls {
+	[SuppressMessage("ReSharper", "MemberCanBeInternal")]
+	public sealed class AttachmentFilterPanel : UserControl {
+		public AttachmentFilterPanel() {
+			InitializeComponent();
+		}
+
+		private void InitializeComponent() {
+			AvaloniaXamlLoader.Load(this);
+		}
+	}
+}
+

app/Desktop/Main/Controls/AttachmentFilterPanelModel.cs

@@ -0,0 +1,125 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using DHT.Desktop.Common;
+using DHT.Server.Data.Filters;
+using DHT.Server.Database;
+using DHT.Utils.Models;
+using DHT.Utils.Tasks;
+
+namespace DHT.Desktop.Main.Controls {
+	sealed class AttachmentFilterPanelModel : BaseModel, IDisposable {
+		public sealed record Unit(string Name, int Scale);
+
+		private static readonly Unit[] AllUnits = {
+			new ("B", 1),
+			new ("kB", 1024),
+			new ("MB", 1024 * 1024)
+		};
+
+		private static readonly HashSet<string> FilterProperties = new () {
+			nameof(LimitSize),
+			nameof(MaximumSize),
+			nameof(MaximumSizeUnit)
+		};
+
+		public string FilterStatisticsText { get; private set; } = "";
+
+		private bool limitSize = false;
+		private int maximumSize = 0;
+		private Unit maximumSizeUnit = AllUnits[0];
+
+		public bool LimitSize {
+			get => limitSize;
+			set => Change(ref limitSize, value);
+		}
+
+		public int MaximumSize {
+			get => maximumSize;
+			set => Change(ref maximumSize, value);
+		}
+
+		public Unit MaximumSizeUnit {
+			get => maximumSizeUnit;
+			set => Change(ref maximumSizeUnit, value);
+		}
+
+		public IEnumerable<Unit> Units => AllUnits;
+
+		private readonly IDatabaseFile db;
+		private readonly string verb;
+
+		private readonly AsyncValueComputer<long> matchingAttachmentCountComputer;
+		private long? matchingAttachmentCount;
+		private long? totalAttachmentCount;
+
+		[Obsolete("Designer")]
+		public AttachmentFilterPanelModel() : this(DummyDatabaseFile.Instance) {}
+
+		public AttachmentFilterPanelModel(IDatabaseFile db, string verb = "Matches") {
+			this.db = db;
+			this.verb = verb;
+
+			this.matchingAttachmentCountComputer = AsyncValueComputer<long>.WithResultProcessor(SetAttachmentCounts).Build();
+
+			UpdateFilterStatistics();
+			
+			PropertyChanged += OnPropertyChanged;
+			db.Statistics.PropertyChanged += OnDbStatisticsChanged;
+		}
+
+		public void Dispose() {
+			db.Statistics.PropertyChanged -= OnDbStatisticsChanged;
+		}
+
+		private void OnPropertyChanged(object? sender, PropertyChangedEventArgs e) {
+			if (e.PropertyName != null && FilterProperties.Contains(e.PropertyName)) {
+				UpdateFilterStatistics();
+			}
+		}
+
+		private void OnDbStatisticsChanged(object? sender, PropertyChangedEventArgs e) {
+			if (e.PropertyName == nameof(DatabaseStatistics.TotalAttachments)) {
+				totalAttachmentCount = db.Statistics.TotalAttachments;
+				UpdateFilterStatistics();
+			}
+		}
+
+		private void UpdateFilterStatistics() {
+			var filter = CreateFilter();
+			if (filter.IsEmpty) {
+				matchingAttachmentCountComputer.Cancel();
+				matchingAttachmentCount = totalAttachmentCount;
+				UpdateFilterStatisticsText();
+			}
+			else {
+				matchingAttachmentCount = null;
+				UpdateFilterStatisticsText();
+				matchingAttachmentCountComputer.Compute(() => db.CountAttachments(filter));
+			}
+		}
+
+		private void SetAttachmentCounts(long matchingAttachmentCount) {
+			this.matchingAttachmentCount = matchingAttachmentCount;
+			UpdateFilterStatisticsText();
+		}
+
+		private void UpdateFilterStatisticsText() {
+			var matchingAttachmentCountStr = matchingAttachmentCount?.Format() ?? "(...)";
+			var totalAttachmentCountStr = totalAttachmentCount?.Format() ?? "(...)";
+
+			FilterStatisticsText = verb + " " + matchingAttachmentCountStr + " out of " + totalAttachmentCountStr + " attachment" + (totalAttachmentCount is null or 1 ? "." : "s.");
+			OnPropertyChanged(nameof(FilterStatisticsText));
+		}
+
+		public AttachmentFilter CreateFilter() {
+			AttachmentFilter filter = new();
+
+			if (LimitSize) {
+				filter.MaxBytes = maximumSize * maximumSizeUnit.Scale;
+			}
+
+			return filter;
+		}
+	}
+}

app/Desktop/Main/Controls/MessageFilterPanelModel.cs

@@ -91,6 +91,7 @@ namespace DHT.Desktop.Main.Controls {
 
 		private readonly Window window;
 		private readonly IDatabaseFile db;
+		private readonly string verb;
 
 		private readonly AsyncValueComputer<long> exportedMessageCountComputer;
 		private long? exportedMessageCount;
@@ -99,13 +100,14 @@ namespace DHT.Desktop.Main.Controls {
 		[Obsolete("Designer")]
 		public MessageFilterPanelModel() : this(null!, DummyDatabaseFile.Instance) {}
 
-		public MessageFilterPanelModel(Window window, IDatabaseFile db) {
+		public MessageFilterPanelModel(Window window, IDatabaseFile db, string verb = "Matches") {
 			this.window = window;
 			this.db = db;
+			this.verb = verb;
 			
 			this.exportedMessageCountComputer = AsyncValueComputer<long>.WithResultProcessor(SetExportedMessageCount).Build();
 
-			UpdateFilterStatisticsText();
+			UpdateFilterStatistics();
 			UpdateChannelFilterLabel();
 			UpdateUserFilterLabel();
 
@@ -147,13 +149,14 @@ namespace DHT.Desktop.Main.Controls {
 		private void UpdateFilterStatistics() {
 			var filter = CreateFilter();
 			if (filter.IsEmpty) {
+				exportedMessageCountComputer.Cancel();
 				exportedMessageCount = totalMessageCount;
 				UpdateFilterStatisticsText();
 			}
 			else {
 				exportedMessageCount = null;
 				UpdateFilterStatisticsText();
-				exportedMessageCountComputer.Compute(_ => db.CountMessages(filter));
+				exportedMessageCountComputer.Compute(() => db.CountMessages(filter));
 			}
 		}
 
@@ -166,7 +169,7 @@ namespace DHT.Desktop.Main.Controls {
 			var exportedMessageCountStr = exportedMessageCount?.Format() ?? "(...)";
 			var totalMessageCountStr = totalMessageCount?.Format() ?? "(...)";
 			
-			FilterStatisticsText = "Will export " + exportedMessageCountStr + " out of " + totalMessageCountStr + " message" + (totalMessageCount is null or > 0 ? "s." : ".");
+			FilterStatisticsText = verb + " " + exportedMessageCountStr + " out of " + totalMessageCountStr + " message" + (totalMessageCount is null or 0 ? "." : "s.");
 			OnPropertyChanged(nameof(FilterStatisticsText));
 		}
 

app/Desktop/Main/MainWindow.axaml

@@ -8,7 +8,7 @@
         Title="{Binding Title}"
         Icon="avares://DiscordHistoryTracker/Resources/icon.ico"
         Width="800" Height="500"
-        MinWidth="500" MinHeight="275"
+        MinWidth="520" MinHeight="300"
         WindowStartupLocation="CenterScreen"
         Closed="OnClosed">
 

app/Desktop/Main/Pages/AttachmentsPage.axaml

@@ -0,0 +1,54 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:pages="clr-namespace:DHT.Desktop.Main.Pages"
+             xmlns:controls="clr-namespace:DHT.Desktop.Main.Controls"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             x:Class="DHT.Desktop.Main.Pages.AttachmentsPage">
+
+    <Design.DataContext>
+        <pages:AttachmentsPageModel />
+    </Design.DataContext>
+
+    <UserControl.Styles>
+        <Style Selector="Expander">
+            <Setter Property="Margin" Value="0 5 0 0" />
+        </Style>
+        <Style Selector="DataGridColumnHeader">
+            <Setter Property="FontWeight" Value="Medium" />
+        </Style>
+        <Style Selector="DataGridColumnHeader:nth-child(2)">
+            <Setter Property="HorizontalContentAlignment" Value="Right" />
+        </Style>
+        <Style Selector="DataGridColumnHeader:nth-child(3)">
+            <Setter Property="HorizontalContentAlignment" Value="Right" />
+        </Style>
+        <Style Selector="DataGridCell.right">
+            <Setter Property="HorizontalContentAlignment" Value="Right" />
+        </Style>
+    </UserControl.Styles>
+
+    <StackPanel Orientation="Vertical" Spacing="20">
+        <DockPanel>
+            <Button Command="{Binding OnClickToggleDownload}" Content="{Binding ToggleDownloadButtonText}" IsEnabled="{Binding IsToggleDownloadButtonEnabled}" DockPanel.Dock="Left" />
+            <TextBlock Text="{Binding DownloadMessage}" Margin="10 0 0 0" VerticalAlignment="Center" DockPanel.Dock="Left" />
+            <ProgressBar Value="{Binding DownloadProgress}" IsVisible="{Binding IsDownloading}" Margin="15 0" VerticalAlignment="Center" DockPanel.Dock="Right" />
+        </DockPanel>
+        <controls:AttachmentFilterPanel DataContext="{Binding FilterModel}" IsEnabled="{Binding !DataContext.IsDownloading, RelativeSource={RelativeSource AncestorType=UserControl}}" />
+        <StackPanel Orientation="Vertical" Spacing="12">
+            <Expander Header="Download Status" IsExpanded="True">
+                <DataGrid Items="{Binding StatisticsRows}" AutoGenerateColumns="False" CanUserReorderColumns="False" CanUserResizeColumns="False" CanUserSortColumns="False" IsReadOnly="True">
+                    <DataGrid.Columns>
+                        <DataGridTextColumn Header="State" Binding="{Binding State}" Width="*" />
+                        <DataGridTextColumn Header="Attachments" Binding="{Binding Items, Converter={StaticResource NumberValueConverter}}" Width="*" CellStyleClasses="right" />
+                        <DataGridTextColumn Header="Size" Binding="{Binding Size, Converter={StaticResource BytesValueConverter}}" Width="*" CellStyleClasses="right" />
+                    </DataGrid.Columns>
+                </DataGrid>
+            </Expander>
+            <StackPanel Orientation="Horizontal" Spacing="10">
+                <Button Command="{Binding OnClickRetryFailedDownloads}" IsEnabled="{Binding HasFailedDownloads}">Retry Failed Downloads</Button>
+            </StackPanel>
+        </StackPanel>
+    </StackPanel>
+</UserControl>

app/Desktop/Main/Pages/AttachmentsPage.axaml.cs

@@ -0,0 +1,16 @@
+using System.Diagnostics.CodeAnalysis;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace DHT.Desktop.Main.Pages {
+	[SuppressMessage("ReSharper", "MemberCanBeInternal")]
+	public sealed class AttachmentsPage : UserControl {
+		public AttachmentsPage() {
+			InitializeComponent();
+		}
+
+		private void InitializeComponent() {
+			AvaloniaXamlLoader.Load(this);
+		}
+	}
+}

app/Desktop/Main/Pages/AttachmentsPageModel.cs

@@ -0,0 +1,201 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using DHT.Desktop.Common;
+using DHT.Desktop.Main.Controls;
+using DHT.Server.Data;
+using DHT.Server.Data.Aggregations;
+using DHT.Server.Data.Filters;
+using DHT.Server.Database;
+using DHT.Server.Download;
+using DHT.Utils.Models;
+using DHT.Utils.Tasks;
+
+namespace DHT.Desktop.Main.Pages {
+	sealed class AttachmentsPageModel : BaseModel, IDisposable {
+		private static readonly DownloadItemFilter EnqueuedItemFilter = new() {
+			IncludeStatuses = new HashSet<DownloadStatus> {
+				DownloadStatus.Enqueued
+			}
+		};
+
+		private bool isThreadDownloadButtonEnabled = true;
+
+		public string ToggleDownloadButtonText => downloadThread == null ? "Start Downloading" : "Stop Downloading";
+
+		public bool IsToggleDownloadButtonEnabled {
+			get => isThreadDownloadButtonEnabled;
+			set => Change(ref isThreadDownloadButtonEnabled, value);
+		}
+
+		public string DownloadMessage { get; set; } = "";
+		public double DownloadProgress => allItemsCount is null or 0 ? 0.0 : 100.0 * doneItemsCount / allItemsCount.Value;
+
+		public AttachmentFilterPanelModel FilterModel { get; }
+
+		private readonly StatisticsRow statisticsEnqueued = new ("Enqueued");
+		private readonly StatisticsRow statisticsDownloaded = new ("Downloaded");
+		private readonly StatisticsRow statisticsFailed = new ("Failed");
+		private readonly StatisticsRow statisticsSkipped = new ("Skipped");
+
+		public List<StatisticsRow> StatisticsRows {
+			get {
+				return new List<StatisticsRow> {
+					statisticsEnqueued,
+					statisticsDownloaded,
+					statisticsFailed,
+					statisticsSkipped
+				};
+			}
+		}
+
+		public bool IsDownloading => downloadThread != null;
+		public bool HasFailedDownloads => statisticsFailed.Items > 0;
+
+		private readonly IDatabaseFile db;
+		private readonly AsyncValueComputer<DownloadStatusStatistics>.Single downloadStatisticsComputer;
+		private BackgroundDownloadThread? downloadThread;
+
+		private int doneItemsCount;
+		private int? allItemsCount;
+
+		public AttachmentsPageModel() : this(DummyDatabaseFile.Instance) {}
+
+		public AttachmentsPageModel(IDatabaseFile db) {
+			this.db = db;
+			this.FilterModel = new AttachmentFilterPanelModel(db);
+
+			this.downloadStatisticsComputer = AsyncValueComputer<DownloadStatusStatistics>.WithResultProcessor(UpdateStatistics).WithOutdatedResults().BuildWithComputer(db.GetDownloadStatusStatistics);
+			this.downloadStatisticsComputer.Recompute();
+
+			db.Statistics.PropertyChanged += OnDbStatisticsChanged;
+		}
+
+		public void Dispose() {
+			db.Statistics.PropertyChanged -= OnDbStatisticsChanged;
+
+			FilterModel.Dispose();
+			DisposeDownloadThread();
+		}
+
+		private void OnDbStatisticsChanged(object? sender, PropertyChangedEventArgs e) {
+			if (e.PropertyName == nameof(DatabaseStatistics.TotalAttachments)) {
+				if (IsDownloading) {
+					EnqueueDownloadItems();
+				}
+				else {
+					downloadStatisticsComputer.Recompute();
+				}
+			}
+		}
+
+		private void EnqueueDownloadItems() {
+			var filter = FilterModel.CreateFilter();
+			filter.DownloadItemRule = AttachmentFilter.DownloadItemRules.OnlyNotPresent;
+			db.EnqueueDownloadItems(filter);
+
+			downloadStatisticsComputer.Recompute();
+		}
+
+		private void UpdateStatistics(DownloadStatusStatistics statusStatistics) {
+			var hadFailedDownloads = HasFailedDownloads;
+
+			statisticsEnqueued.Items = statusStatistics.EnqueuedCount;
+			statisticsEnqueued.Size = statusStatistics.EnqueuedSize;
+
+			statisticsDownloaded.Items = statusStatistics.SuccessfulCount;
+			statisticsDownloaded.Size = statusStatistics.SuccessfulSize;
+
+			statisticsFailed.Items = statusStatistics.FailedCount;
+			statisticsFailed.Size = statusStatistics.FailedSize;
+
+			statisticsSkipped.Items = statusStatistics.SkippedCount;
+			statisticsSkipped.Size = statusStatistics.SkippedSize;
+
+			OnPropertyChanged(nameof(StatisticsRows));
+
+			if (hadFailedDownloads != HasFailedDownloads) {
+				OnPropertyChanged(nameof(HasFailedDownloads));
+			}
+
+			allItemsCount = doneItemsCount + statisticsEnqueued.Items;
+			UpdateDownloadMessage();
+		}
+
+		private void UpdateDownloadMessage() {
+			DownloadMessage = IsDownloading ? doneItemsCount.Format() + " / " + (allItemsCount?.Format() ?? "?") : "";
+
+			OnPropertyChanged(nameof(DownloadMessage));
+			OnPropertyChanged(nameof(DownloadProgress));
+		}
+
+		private void DownloadThreadOnOnItemFinished(object? sender, DownloadItem e) {
+			++doneItemsCount;
+
+			UpdateDownloadMessage();
+			downloadStatisticsComputer.Recompute();
+		}
+
+		private void DownloadThreadOnOnServerStopped(object? sender, EventArgs e) {
+			downloadStatisticsComputer.Recompute();
+			IsToggleDownloadButtonEnabled = true;
+		}
+
+		public void OnClickToggleDownload() {
+			if (downloadThread == null) {
+				EnqueueDownloadItems();
+				downloadThread = new BackgroundDownloadThread(db);
+				downloadThread.OnItemFinished += DownloadThreadOnOnItemFinished;
+				downloadThread.OnServerStopped += DownloadThreadOnOnServerStopped;
+			}
+			else {
+				IsToggleDownloadButtonEnabled = false;
+				DisposeDownloadThread();
+
+				db.RemoveDownloadItems(EnqueuedItemFilter, FilterRemovalMode.RemoveMatching);
+				
+				doneItemsCount = 0;
+				allItemsCount = null;
+				UpdateDownloadMessage();
+			}
+
+			OnPropertyChanged(nameof(ToggleDownloadButtonText));
+			OnPropertyChanged(nameof(IsDownloading));
+		}
+
+		public void OnClickRetryFailedDownloads() {
+			var allExceptFailedFilter = new DownloadItemFilter {
+				IncludeStatuses = new HashSet<DownloadStatus> {
+					DownloadStatus.Enqueued,
+					DownloadStatus.Success
+				}
+			};
+
+			db.RemoveDownloadItems(allExceptFailedFilter, FilterRemovalMode.KeepMatching);
+			downloadStatisticsComputer.Recompute();
+
+			if (IsDownloading) {
+				EnqueueDownloadItems();
+			}
+		}
+
+		private void DisposeDownloadThread() {
+			if (downloadThread != null) {
+				downloadThread.OnItemFinished -= DownloadThreadOnOnItemFinished;
+				downloadThread.StopThread();
+			}
+
+			downloadThread = null;
+		}
+
+		public sealed class StatisticsRow {
+			public string State { get; }
+			public int Items { get; set; }
+			public ulong? Size { get; set; }
+
+			public StatisticsRow(string state) {
+				State = state;
+			}
+		}
+	}
+}

app/Desktop/Main/Pages/ViewerPage.axaml

@@ -13,16 +13,16 @@
 
     <UserControl.Styles>
         <Style Selector="Expander">
-            <Setter Property="Margin" Value="0 25 0 0" />
+            <Setter Property="Margin" Value="0 5 0 0" />
         </Style>
     </UserControl.Styles>
 
-    <StackPanel Orientation="Vertical">
+    <StackPanel Orientation="Vertical" Spacing="20">
         <StackPanel Orientation="Horizontal" VerticalAlignment="Top">
             <Button Command="{Binding OnClickOpenViewer}" Margin="0 0 5 0">Open Viewer</Button>
             <Button Command="{Binding OnClickSaveViewer}" Margin="5 0 0 0">Save Viewer</Button>
         </StackPanel>
-        <controls:MessageFilterPanel DataContext="{Binding FilterModel}" Margin="0 20 0 0" />
+        <controls:MessageFilterPanel DataContext="{Binding FilterModel}" />
         <Expander Header="Database Tools">
             <StackPanel Orientation="Vertical" Spacing="10">
                 <StackPanel Orientation="Vertical" Spacing="4">

app/Desktop/Main/Pages/ViewerPageModel.cs

@@ -43,7 +43,7 @@ namespace DHT.Desktop.Main.Pages {
 			this.window = window;
 			this.db = db;
 
-			FilterModel = new MessageFilterPanelModel(window, db);
+			FilterModel = new MessageFilterPanelModel(window, db, "Will export");
 			FilterModel.FilterPropertyChanged += OnFilterPropertyChanged;
 		}
 

app/Desktop/Main/Screens/MainContentScreen.axaml

@@ -73,14 +73,14 @@
     <DockPanel>
         <Border Classes="statusBar" DockPanel.Dock="Bottom">
             <DockPanel>
-                <TextBlock Classes="invisibleTabItem" DockPanel.Dock="Left">Advanced</TextBlock>
+                <TextBlock Classes="invisibleTabItem" DockPanel.Dock="Left">Attachments</TextBlock>
                 <controls:StatusBar DataContext="{Binding StatusBarModel}" DockPanel.Dock="Right" />
             </DockPanel>
         </Border>
         <TabControl x:Name="TabControl" TabStripPlacement="Left" DockPanel.Dock="Top">
             <TabControl.ItemsPanel>
                 <ItemsPanelTemplate>
-                    <Grid ColumnDefinitions="Auto" RowDefinitions="Auto,Auto,Auto,*,Auto,Auto" />
+                    <Grid ColumnDefinitions="Auto" RowDefinitions="Auto,Auto,Auto,Auto,*,Auto,Auto" />
                 </ItemsPanelTemplate>
             </TabControl.ItemsPanel>
             <TabItem x:Name="TabDatabase" Header="Database" Classes="first" Grid.Row="0">
@@ -93,17 +93,22 @@
                     <ContentPresenter Content="{Binding TrackingPage}" Classes="page" />
                 </ScrollViewer>
             </TabItem>
-            <TabItem x:Name="TabViewer" Header="Viewer" Grid.Row="2">
+            <TabItem x:Name="TabAttachments" Header="Attachments" Grid.Row="2">
+                <ScrollViewer>
+                    <ContentPresenter Content="{Binding AttachmentsPage}" Classes="page" />
+                </ScrollViewer>
+            </TabItem>
+            <TabItem x:Name="TabViewer" Header="Viewer" Grid.Row="3">
                 <ScrollViewer>
                     <ContentPresenter Content="{Binding ViewerPage}" Classes="page" />
                 </ScrollViewer>
             </TabItem>
-            <TabItem x:Name="TabAdvanced" Header="Advanced" Grid.Row="4">
+            <TabItem x:Name="TabAdvanced" Header="Advanced" Grid.Row="5">
                 <ScrollViewer>
                     <ContentPresenter Content="{Binding AdvancedPage}" Classes="page" />
                 </ScrollViewer>
             </TabItem>
-            <TabItem x:Name="TabDebug" Header="Debug" Grid.Row="5" IsVisible="{Binding HasDebugPage}">
+            <TabItem x:Name="TabDebug" Header="Debug" Grid.Row="6" IsVisible="{Binding HasDebugPage}">
                 <ScrollViewer>
                     <ContentPresenter Content="{Binding DebugPage}" Classes="page" />
                 </ScrollViewer>

app/Desktop/Main/Screens/MainContentScreenModel.cs

@@ -19,6 +19,9 @@ namespace DHT.Desktop.Main.Screens {
 		public TrackingPage TrackingPage { get; }
 		private TrackingPageModel TrackingPageModel { get; }
 
+		public AttachmentsPage AttachmentsPage { get; }
+		private AttachmentsPageModel AttachmentsPageModel { get; }
+
 		public ViewerPage ViewerPage { get; }
 		private ViewerPageModel ViewerPageModel { get; }
 
@@ -63,6 +66,9 @@ namespace DHT.Desktop.Main.Screens {
 			TrackingPageModel = new TrackingPageModel(window);
 			TrackingPage = new TrackingPage { DataContext = TrackingPageModel };
 
+			AttachmentsPageModel = new AttachmentsPageModel(db);
+			AttachmentsPage = new AttachmentsPage { DataContext = AttachmentsPageModel };
+
 			ViewerPageModel = new ViewerPageModel(window, db);
 			ViewerPage = new ViewerPage { DataContext = ViewerPageModel };
 
@@ -92,6 +98,7 @@ namespace DHT.Desktop.Main.Screens {
 
 		public void Dispose() {
 			ServerLauncher.ServerManagementExceptionCaught -= ServerLauncherOnServerManagementExceptionCaught;
+			AttachmentsPageModel.Dispose();
 			ViewerPageModel.Dispose();
 			serverManager.Dispose();
 		}

app/Resources/Tracker/styles/controller.css

@@ -2,6 +2,10 @@
   margin-bottom: 48px !important;
 }
 
+#app-mount div[class*="app-"] > div[class*="app-"] {
+  margin-bottom: 0 !important;
+}
+
 #dht-ctrl {
   position: absolute;
   bottom: 0;

app/Server/Data/Aggregations/DownloadStatusStatistics.cs

@@ -0,0 +1,15 @@
+namespace DHT.Server.Data.Aggregations {
+	public sealed class DownloadStatusStatistics {
+		public int EnqueuedCount { get; internal set; }
+		public ulong EnqueuedSize { get; internal set; }
+
+		public int SuccessfulCount { get; internal set; }
+		public ulong SuccessfulSize { get; internal set; }
+
+		public int FailedCount { get; internal set; }
+		public ulong FailedSize { get; internal set; }
+
+		public int SkippedCount { get; internal set; }
+		public ulong SkippedSize { get; internal set; }
+	}
+}

app/Server/Data/Download.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Net;
+
+namespace DHT.Server.Data {
+	public readonly struct Download {
+		internal static Download NewEnqueued(string url, ulong size) {
+			return new Download(url, DownloadStatus.Enqueued, size);
+		}
+
+		internal static Download NewSuccess(string url, byte[] data) {
+			return new Download(url, DownloadStatus.Success, (ulong) Math.Max(data.LongLength, 0), data);
+		}
+
+		internal static Download NewFailure(string url, HttpStatusCode? statusCode, ulong size) {
+			return new Download(url, statusCode.HasValue ? (DownloadStatus) (int) statusCode : DownloadStatus.GenericError, size);
+		}
+
+		public string Url { get; }
+		public DownloadStatus Status { get; }
+		public ulong Size { get; }
+		public byte[]? Data { get; }
+
+		private Download(string url, DownloadStatus status, ulong size, byte[]? data = null) {
+			Url = url;
+			Status = status;
+			Size = size;
+			Data = data;
+		}
+	}
+}

app/Server/Data/DownloadStatus.cs

@@ -0,0 +1,12 @@
+using System.Net;
+
+namespace DHT.Server.Data {
+	/// <summary>
+	/// Extends <see cref="HttpStatusCode"/> with custom status codes in the range 0-99.
+	/// </summary>
+	public enum DownloadStatus {
+		Enqueued = 0,
+		GenericError = 1,
+		Success = HttpStatusCode.OK
+	}
+}

app/Server/Data/Filters/AttachmentFilter.cs

@@ -0,0 +1,15 @@
+namespace DHT.Server.Data.Filters {
+	public sealed class AttachmentFilter {
+		public long? MaxBytes { get; set; } = null;
+
+		public DownloadItemRules? DownloadItemRule { get; set; } = null;
+
+		public bool IsEmpty => MaxBytes == null &&
+		                       DownloadItemRule == null;
+
+		public enum DownloadItemRules {
+			OnlyNotPresent,
+			OnlyPresent
+		}
+	}
+}

app/Server/Data/Filters/DownloadItemFilter.cs

@@ -0,0 +1,10 @@
+using System.Collections.Generic;
+
+namespace DHT.Server.Data.Filters {
+	public sealed class DownloadItemFilter {
+		public HashSet<DownloadStatus>? IncludeStatuses { get; set; } = null;
+		public HashSet<DownloadStatus>? ExcludeStatuses { get; set; } = null;
+
+		public bool IsEmpty => IncludeStatuses == null && ExcludeStatuses == null;
+	}
+}

app/Server/Database/DatabaseStatistics.cs

@@ -6,6 +6,7 @@ namespace DHT.Server.Database {
 		private long totalChannels;
 		private long totalUsers;
 		private long? totalMessages;
+		private long? totalAttachments;
 
 		public long TotalServers {
 			get => totalServers;
@@ -27,12 +28,18 @@ namespace DHT.Server.Database {
 			internal set => Change(ref totalMessages, value);
 		}
 
+		public long? TotalAttachments {
+			get => totalAttachments;
+			internal set => Change(ref totalAttachments, value);
+		}
+
 		public DatabaseStatistics Clone() {
 			return new DatabaseStatistics {
 				totalServers = totalServers,
 				totalChannels = totalChannels,
 				totalUsers = TotalUsers,
-				totalMessages = totalMessages
+				totalMessages = totalMessages,
+				totalAttachments = totalAttachments
 			};
 		}
 	}

app/Server/Database/DummyDatabaseFile.cs

@@ -1,6 +1,8 @@
 using System.Collections.Generic;
 using DHT.Server.Data;
+using DHT.Server.Data.Aggregations;
 using DHT.Server.Data.Filters;
+using DHT.Server.Download;
 
 namespace DHT.Server.Database {
 	public sealed class DummyDatabaseFile : IDatabaseFile {
@@ -41,6 +43,24 @@ namespace DHT.Server.Database {
 
 		public void RemoveMessages(MessageFilter filter, FilterRemovalMode mode) {}
 
+		public int CountAttachments(AttachmentFilter? filter = null) {
+			return new();
+		}
+
+		public void AddDownloads(IEnumerable<Data.Download> downloads) {}
+
+		public void EnqueueDownloadItems(AttachmentFilter? filter = null) {}
+		
+		public List<DownloadItem> GetEnqueuedDownloadItems(int count) {
+			return new();
+		}
+
+		public void RemoveDownloadItems(DownloadItemFilter? filter, FilterRemovalMode mode) {}
+
+		public DownloadStatusStatistics GetDownloadStatusStatistics() {
+			return new();
+		}
+
 		public void Vacuum() {}
 
 		public void Dispose() {}

app/Server/Database/IDatabaseFile.cs

@@ -1,7 +1,9 @@
 using System;
 using System.Collections.Generic;
 using DHT.Server.Data;
+using DHT.Server.Data.Aggregations;
 using DHT.Server.Data.Filters;
+using DHT.Server.Download;
 
 namespace DHT.Server.Database {
 	public interface IDatabaseFile : IDisposable {
@@ -22,6 +24,14 @@ namespace DHT.Server.Database {
 		List<Message> GetMessages(MessageFilter? filter = null);
 		void RemoveMessages(MessageFilter filter, FilterRemovalMode mode);
 
+		int CountAttachments(AttachmentFilter? filter = null);
+
+		void AddDownloads(IEnumerable<Data.Download> downloads);
+		void EnqueueDownloadItems(AttachmentFilter? filter = null);
+		List<DownloadItem> GetEnqueuedDownloadItems(int count);
+		void RemoveDownloadItems(DownloadItemFilter? filter, FilterRemovalMode mode);
+		DownloadStatusStatistics GetDownloadStatusStatistics();
+
 		void Vacuum();
 	}
 }

app/Server/Database/Sqlite/Schema.cs

@@ -6,7 +6,7 @@ using DHT.Utils.Logging;
 
 namespace DHT.Server.Database.Sqlite {
 	sealed class Schema {
-		internal const int Version = 3;
+		internal const int Version = 4;
 
 		private static readonly Log Log = Log.ForType<Schema>();
 
@@ -94,6 +94,7 @@ namespace DHT.Server.Database.Sqlite {
 
 			CreateMessageEditTimestampTable();
 			CreateMessageRepliedToTable();
+			CreateDownloadsTable();
 
 			Execute("CREATE INDEX attachments_message_ix ON attachments(message_id)");
 			Execute("CREATE INDEX embeds_message_ix ON embeds(message_id)");
@@ -114,6 +115,14 @@ namespace DHT.Server.Database.Sqlite {
 			        replied_to_id INTEGER NOT NULL)");
 		}
 
+		private void CreateDownloadsTable() {
+			Execute(@"CREATE TABLE downloads (
+                      url TEXT NOT NULL PRIMARY KEY,
+                      status INTEGER NOT NULL,
+                      size INTEGER NOT NULL,
+                      blob BLOB)");
+		}
+
 		private void UpgradeSchemas(int dbVersion) {
 			var perf = Log.Start("from version " + dbVersion);
 
@@ -145,6 +154,11 @@ namespace DHT.Server.Database.Sqlite {
 				perf.Step("Vacuum");
 			}
 
+			if (dbVersion <= 3) {
+				CreateDownloadsTable();
+				perf.Step("Upgrade to version 4");
+			}
+
 			perf.End();
 		}
 	}

app/Server/Database/Sqlite/SqliteDatabaseFile.cs

@@ -2,11 +2,12 @@ using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Text;
-using System.Threading;
 using System.Threading.Tasks;
 using DHT.Server.Data;
+using DHT.Server.Data.Aggregations;
 using DHT.Server.Data.Filters;
 using DHT.Server.Database.Sqlite.Utils;
+using DHT.Server.Download;
 using DHT.Utils.Collections;
 using DHT.Utils.Logging;
 using DHT.Utils.Tasks;
@@ -39,11 +40,14 @@ namespace DHT.Server.Database.Sqlite {
 		private readonly Log log;
 		private readonly SqliteConnectionPool pool;
 		private readonly AsyncValueComputer<long>.Single totalMessagesComputer;
+		private readonly AsyncValueComputer<long>.Single totalAttachmentsComputer;
 
 		private SqliteDatabaseFile(string path, SqliteConnectionPool pool) {
 			this.log = Log.ForType(typeof(SqliteDatabaseFile), System.IO.Path.GetFileName(path));
 			this.pool = pool;
+			
 			this.totalMessagesComputer = AsyncValueComputer<long>.WithResultProcessor(UpdateMessageStatistics).WithOutdatedResults().BuildWithComputer(ComputeMessageStatistics);
+			this.totalAttachmentsComputer = AsyncValueComputer<long>.WithResultProcessor(UpdateAttachmentStatistics).WithOutdatedResults().BuildWithComputer(ComputeAttachmentStatistics);
 
 			this.Path = path;
 			this.Statistics = new DatabaseStatistics();
@@ -55,6 +59,7 @@ namespace DHT.Server.Database.Sqlite {
 			}
 
 			totalMessagesComputer.Recompute();
+			totalAttachmentsComputer.Recompute();
 		}
 
 		public void Dispose() {
@@ -194,6 +199,8 @@ namespace DHT.Server.Database.Sqlite {
 				cmd.ExecuteNonQuery();
 			}
 			
+			bool addedAttachments = false;
+
 			using (var conn = pool.Take()) {
 				using var tx = conn.BeginTransaction();
 
@@ -274,6 +281,8 @@ namespace DHT.Server.Database.Sqlite {
 					}
 
 					if (!message.Attachments.IsEmpty) {
+						addedAttachments = true;
+						
 						foreach (var attachment in message.Attachments) {
 							attachmentCmd.Set(":message_id", messageId);
 							attachmentCmd.Set(":attachment_id", attachment.Id);
@@ -309,6 +318,10 @@ namespace DHT.Server.Database.Sqlite {
 			}
 
 			totalMessagesComputer.Recompute();
+
+			if (addedAttachments) {
+				totalAttachmentsComputer.Recompute();
+			}
 		}
 
 		public int CountMessages(MessageFilter? filter = null) {
@@ -358,25 +371,123 @@ LEFT JOIN replied_to rt ON m.message_id = rt.message_id" + filter.GenerateWhereC
 
 		public void RemoveMessages(MessageFilter filter, FilterRemovalMode mode) {
 			var whereClause = filter.GenerateWhereClause(invert: mode == FilterRemovalMode.KeepMatching);
-			if (string.IsNullOrEmpty(whereClause)) {
-				return;
-			}
 			
+			if (!string.IsNullOrEmpty(whereClause)) {
 				var perf = log.Start();
 				
-			// Rider is being stupid...
+				DeleteFromTable("messages", whereClause);
-			StringBuilder build = new StringBuilder()
+				totalMessagesComputer.Recompute();
-			                      .Append("DELETE ")
-			                      .Append("FROM messages")
-			                      .Append(whereClause);
 				
-			using (var conn = pool.Take()) {
+				perf.End();
-				using var cmd = conn.Command(build.ToString());
+			}
+		}
+
+		public int CountAttachments(AttachmentFilter? filter = null) {
+			using var conn = pool.Take();
+			using var cmd = conn.Command("SELECT COUNT(*) FROM attachments a" + filter.GenerateWhereClause("a"));
+			using var reader = cmd.ExecuteReader();
+
+			return reader.Read() ? reader.GetInt32(0) : 0;
+		}
+
+		public void AddDownloads(IEnumerable<Data.Download> downloads) {
+			using var conn = pool.Take();
+			using var tx = conn.BeginTransaction();
+
+			using var cmd = conn.Upsert("downloads", new[] {
+				("url", SqliteType.Text),
+				("status", SqliteType.Integer),
+				("size", SqliteType.Integer),
+				("blob", SqliteType.Blob)
+			});
+
+			foreach (var download in downloads) {
+				cmd.Set(":url", download.Url);
+				cmd.Set(":status", (int) download.Status);
+				cmd.Set(":size", download.Size);
+				cmd.Set(":blob", download.Data);
 				cmd.ExecuteNonQuery();
 			}
 
-			totalMessagesComputer.Recompute();
+			tx.Commit();
-			perf.End();
+		}
+
+		public void EnqueueDownloadItems(AttachmentFilter? filter = null) {
+			using var conn = pool.Take();
+			using var cmd = conn.Command("INSERT INTO downloads (url, status, size) SELECT a.url, :enqueued, a.size FROM attachments a" + filter.GenerateWhereClause("a"));
+			cmd.AddAndSet(":enqueued", SqliteType.Integer, (int) DownloadStatus.Enqueued);
+			cmd.ExecuteNonQuery();
+		}
+
+		public List<DownloadItem> GetEnqueuedDownloadItems(int count) {
+			var list = new List<DownloadItem>();
+			
+			using var conn = pool.Take();
+			using var cmd = conn.Command("SELECT url, size FROM downloads WHERE status = :enqueued LIMIT :limit");
+			cmd.AddAndSet(":enqueued", SqliteType.Integer, (int) DownloadStatus.Enqueued);
+			cmd.AddAndSet(":limit", SqliteType.Integer, Math.Max(0, count));
+			
+			using var reader = cmd.ExecuteReader();
+			
+			while (reader.Read()) {
+				list.Add(new DownloadItem {
+					Url = reader.GetString(0),
+					Size = reader.GetUint64(1)
+				});
+			}
+			
+			return list;
+		}
+
+		public void RemoveDownloadItems(DownloadItemFilter? filter, FilterRemovalMode mode) {
+			var whereClause = filter.GenerateWhereClause(invert: mode == FilterRemovalMode.KeepMatching);
+			
+			if (!string.IsNullOrEmpty(whereClause)) {
+				DeleteFromTable("downloads", whereClause);
+			}
+		}
+
+		public DownloadStatusStatistics GetDownloadStatusStatistics() {
+			static void LoadUndownloadedStatistics(ISqliteConnection conn, DownloadStatusStatistics result) {
+				using var cmd = conn.Command("SELECT IFNULL(COUNT(filtered.size), 0), IFNULL(SUM(filtered.size), 0) FROM (SELECT DISTINCT a.url, a.size FROM attachments a  WHERE a.url NOT IN (SELECT d.url FROM downloads d)) filtered");
+				using var reader = cmd.ExecuteReader();
+
+				if (reader.Read()) {
+					result.SkippedCount = reader.GetInt32(0);
+					result.SkippedSize = reader.GetUint64(1);
+				}
+			}
+
+			static void LoadSuccessStatistics(ISqliteConnection conn, DownloadStatusStatistics result) {
+				using var cmd = conn.Command(@"SELECT
+IFNULL(SUM(CASE WHEN status = :enqueued THEN 1 ELSE 0 END), 0),
+IFNULL(SUM(CASE WHEN status = :enqueued THEN size ELSE 0 END), 0),
+IFNULL(SUM(CASE WHEN status = :success THEN 1 ELSE 0 END), 0),
+IFNULL(SUM(CASE WHEN status = :success THEN size ELSE 0 END), 0),
+IFNULL(SUM(CASE WHEN status != :enqueued AND status != :success THEN 1 ELSE 0 END), 0),
+IFNULL(SUM(CASE WHEN status != :enqueued AND status != :success THEN size ELSE 0 END), 0)
+FROM downloads");
+				cmd.AddAndSet(":enqueued", SqliteType.Integer, (int) DownloadStatus.Enqueued);
+				cmd.AddAndSet(":success", SqliteType.Integer, (int) DownloadStatus.Success);
+				
+				using var reader = cmd.ExecuteReader();
+
+				if (reader.Read()) {
+					result.EnqueuedCount = reader.GetInt32(0);
+					result.EnqueuedSize = reader.GetUint64(1);
+					result.SuccessfulCount = reader.GetInt32(2);
+					result.SuccessfulSize = reader.GetUint64(3);
+					result.FailedCount = reader.GetInt32(4);
+					result.FailedSize = reader.GetUint64(5);
+				}
+			}
+
+			var result = new DownloadStatusStatistics();
+
+			using var conn = pool.Take();
+			LoadUndownloadedStatistics(conn, result);
+			LoadSuccessStatistics(conn, result);
+			return result;
 		}
 
 		private MultiDictionary<ulong, Attachment> GetAllAttachments() {
@@ -440,6 +551,19 @@ LEFT JOIN replied_to rt ON m.message_id = rt.message_id" + filter.GenerateWhereC
 			return dict;
 		}
 
+		private void DeleteFromTable(string table, string whereClause) {
+			// Rider is being stupid...
+			StringBuilder build = new StringBuilder()
+			                      .Append("DELETE ")
+			                      .Append("FROM ")
+			                      .Append(table)
+			                      .Append(whereClause);
+
+			using var conn = pool.Take();
+			using var cmd = conn.Command(build.ToString());
+			cmd.ExecuteNonQuery();
+		}
+
 		public void Vacuum() {
 			using var conn = pool.Take();
 			using var cmd = conn.Command("VACUUM");
@@ -458,7 +582,7 @@ LEFT JOIN replied_to rt ON m.message_id = rt.message_id" + filter.GenerateWhereC
 			Statistics.TotalUsers = conn.SelectScalar("SELECT COUNT(*) FROM users") as long? ?? 0;
 		}
 
-		private long ComputeMessageStatistics(CancellationToken token) {
+		private long ComputeMessageStatistics() {
 			using var conn = pool.Take();
 			return conn.SelectScalar("SELECT COUNT(*) FROM messages") as long? ?? 0L;
 		}
@@ -466,5 +590,14 @@ LEFT JOIN replied_to rt ON m.message_id = rt.message_id" + filter.GenerateWhereC
 		private void UpdateMessageStatistics(long totalMessages) {
 			Statistics.TotalMessages = totalMessages;
 		}
+
+		private long ComputeAttachmentStatistics() {
+			using var conn = pool.Take();
+			return conn.SelectScalar("SELECT COUNT(*) FROM attachments") as long? ?? 0L;
+		}
+
+		private void UpdateAttachmentStatistics(long totalAttachments) {
+			Statistics.TotalAttachments = totalAttachments;
+		}
 	}
 }

app/Server/Database/Sqlite/SqliteFilters.cs

@@ -0,0 +1,83 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using DHT.Server.Data;
+using DHT.Server.Data.Filters;
+using DHT.Server.Database.Sqlite.Utils;
+
+namespace DHT.Server.Database.Sqlite {
+	static class SqliteFilters {
+		public static string GenerateWhereClause(this MessageFilter? filter, string? tableAlias = null, bool invert = false) {
+			if (filter == null) {
+				return "";
+			}
+
+			var where = new SqliteWhereGenerator(tableAlias, invert);
+
+			if (filter.StartDate != null) {
+				where.AddCondition("timestamp >= " + new DateTimeOffset(filter.StartDate.Value).ToUnixTimeMilliseconds());
+			}
+
+			if (filter.EndDate != null) {
+				where.AddCondition("timestamp <= " + new DateTimeOffset(filter.EndDate.Value).ToUnixTimeMilliseconds());
+			}
+
+			if (filter.ChannelIds != null) {
+				where.AddCondition("channel_id IN (" + string.Join(",", filter.ChannelIds) + ")");
+			}
+
+			if (filter.UserIds != null) {
+				where.AddCondition("sender_id IN (" + string.Join(",", filter.UserIds) + ")");
+			}
+
+			if (filter.MessageIds != null) {
+				where.AddCondition("message_id IN (" + string.Join(",", filter.MessageIds) + ")");
+			}
+
+			return where.Generate();
+		}
+
+		public static string GenerateWhereClause(this AttachmentFilter? filter, string? tableAlias = null, bool invert = false) {
+			if (filter == null) {
+				return "";
+			}
+
+			var where = new SqliteWhereGenerator(tableAlias, invert);
+
+			if (filter.MaxBytes != null) {
+				where.AddCondition("size <= " + filter.MaxBytes);
+			}
+
+			if (filter.DownloadItemRule == AttachmentFilter.DownloadItemRules.OnlyNotPresent) {
+				where.AddCondition("url NOT IN (SELECT url FROM downloads)");
+			}
+			else if (filter.DownloadItemRule == AttachmentFilter.DownloadItemRules.OnlyPresent) {
+				where.AddCondition("url IN (SELECT url FROM downloads)");
+			}
+			
+			return where.Generate();
+		}
+
+		public static string GenerateWhereClause(this DownloadItemFilter? filter, string? tableAlias = null, bool invert = false) {
+			if (filter == null) {
+				return "";
+			}
+
+			var where = new SqliteWhereGenerator(tableAlias, invert);
+
+			if (filter.IncludeStatuses != null) {
+				where.AddCondition("status IN (" + filter.IncludeStatuses.In() + ")");
+			}
+
+			if (filter.ExcludeStatuses != null) {
+				where.AddCondition("status NOT IN (" + filter.ExcludeStatuses.In() + ")");
+			}
+
+			return where.Generate();
+		}
+
+		private static string In(this ISet<DownloadStatus> statuses) {
+			return string.Join(",", statuses.Select(static status => (int) status));
+		}
+	}
+}

app/Server/Database/Sqlite/SqliteMessageFilter.cs

@@ -1,50 +0,0 @@
-using System;
-using System.Collections.Generic;
-using DHT.Server.Data.Filters;
-
-namespace DHT.Server.Database.Sqlite {
-	static class SqliteMessageFilter {
-		public static string GenerateWhereClause(this MessageFilter? filter, string? tableAlias = null, bool invert = false) {
-			if (filter == null) {
-				return "";
-			}
-
-			if (tableAlias != null) {
-				tableAlias += ".";
-			}
-
-			List<string> conditions = new();
-
-			if (filter.StartDate != null) {
-				conditions.Add(tableAlias + "timestamp >= " + new DateTimeOffset(filter.StartDate.Value).ToUnixTimeMilliseconds());
-			}
-
-			if (filter.EndDate != null) {
-				conditions.Add(tableAlias + "timestamp <= " + new DateTimeOffset(filter.EndDate.Value).ToUnixTimeMilliseconds());
-			}
-
-			if (filter.ChannelIds != null) {
-				conditions.Add(tableAlias + "channel_id IN (" + string.Join(",", filter.ChannelIds) + ")");
-			}
-
-			if (filter.UserIds != null) {
-				conditions.Add(tableAlias + "sender_id IN (" + string.Join(",", filter.UserIds) + ")");
-			}
-
-			if (filter.MessageIds != null) {
-				conditions.Add(tableAlias + "message_id IN (" + string.Join(",", filter.MessageIds) + ")");
-			}
-
-			if (conditions.Count == 0) {
-				return "";
-			}
-
-			if (invert) {
-				return " WHERE NOT (" + string.Join(" AND ", conditions) + ")";
-			}
-			else {
-				return " WHERE " + string.Join(" AND ", conditions);
-			}
-		}
-	}
-}

app/Server/Database/Sqlite/Utils/SqliteConnectionPool.cs

@@ -13,6 +13,7 @@ namespace DHT.Server.Database.Sqlite.Utils {
 		}
 
 		private readonly object monitor = new ();
+		private readonly Random rand = new ();
 		private volatile bool isDisposed;
 
 		private readonly BlockingCollection<PooledConnection> free = new (new ConcurrentStack<PooledConnection>());
@@ -49,7 +50,7 @@ namespace DHT.Server.Database.Sqlite.Utils {
 			while (conn == null) {
 				ThrowIfDisposed();
 				lock (monitor) {
-					if (free.TryTake(out conn, TimeSpan.FromMilliseconds(100))) {
+					if (free.TryTake(out conn, TimeSpan.FromMilliseconds(rand.Next(100, 200)))) {
 						used.Add(conn);
 						break;
 					}

app/Server/Database/Sqlite/Utils/SqliteExtensions.cs

@@ -56,6 +56,10 @@ namespace DHT.Server.Database.Sqlite.Utils {
 			}
 		}
 
+		public static void AddAndSet(this SqliteCommand cmd, string key, SqliteType type, object? value) {
+			cmd.Parameters.Add(key, type).Value = value ?? DBNull.Value;
+		}
+
 		public static void Set(this SqliteCommand cmd, string key, object? value) {
 			cmd.Parameters[key].Value = value ?? DBNull.Value;
 		}

app/Server/Database/Sqlite/Utils/SqliteWhereGenerator.cs

@@ -0,0 +1,31 @@
+using System.Collections.Generic;
+
+namespace DHT.Server.Database.Sqlite.Utils {
+	sealed class SqliteWhereGenerator {
+		private readonly string? tableAlias;
+		private readonly bool invert;
+		private readonly List<string> conditions = new ();
+
+		public SqliteWhereGenerator(string? tableAlias, bool invert) {
+			this.tableAlias = tableAlias;
+			this.invert = invert;
+		}
+
+		public void AddCondition(string condition) {
+			conditions.Add(tableAlias == null ? condition : tableAlias + '.' + condition);
+		}
+
+		public string Generate() {
+			if (conditions.Count == 0) {
+				return "";
+			}
+
+			if (invert) {
+				return " WHERE NOT (" + string.Join(" AND ", conditions) + ")";
+			}
+			else {
+				return " WHERE " + string.Join(" AND ", conditions);
+			}
+		}
+	}
+}

app/Server/Download/BackgroundDownloadThread.cs

@@ -0,0 +1,129 @@
+using System;
+using System.Collections.Concurrent;
+using System.Net;
+using System.Threading;
+using DHT.Server.Database;
+using DHT.Utils.Logging;
+using DHT.Utils.Models;
+
+namespace DHT.Server.Download {
+	public sealed class BackgroundDownloadThread : BaseModel {
+		private static readonly Log Log = Log.ForType<BackgroundDownloadThread>();
+
+		public event EventHandler<DownloadItem>? OnItemFinished {
+			add => parameters.OnItemFinished += value;
+			remove => parameters.OnItemFinished -= value;
+		}
+		
+		public event EventHandler? OnServerStopped {
+			add => parameters.OnServerStopped += value;
+			remove => parameters.OnServerStopped -= value;
+		}
+
+		private readonly CancellationTokenSource cancellationTokenSource;
+		private readonly ThreadInstance.Parameters parameters;
+
+		public BackgroundDownloadThread(IDatabaseFile db) {
+			this.cancellationTokenSource = new CancellationTokenSource();
+			this.parameters = new ThreadInstance.Parameters(db, cancellationTokenSource);
+
+			var thread = new Thread(new ThreadInstance().Work) {
+				Name = "DHT download thread"
+			};
+
+			thread.Start(parameters);
+		}
+
+		public void StopThread() {
+			try {
+				cancellationTokenSource.Cancel();
+			} catch (ObjectDisposedException) {
+				Log.Warn("Attempted to stop background download thread after the cancellation token has been disposed.");
+			}
+		}
+
+		private sealed class ThreadInstance {
+			private const int QueueSize = 32;
+
+			public sealed class Parameters {
+				public event EventHandler<DownloadItem>? OnItemFinished;
+				public event EventHandler? OnServerStopped;
+
+				public IDatabaseFile Db { get; }
+				public CancellationTokenSource CancellationTokenSource { get; }
+
+				public Parameters(IDatabaseFile db, CancellationTokenSource cancellationTokenSource) {
+					Db = db;
+					CancellationTokenSource = cancellationTokenSource;
+				}
+
+				public void FireOnItemFinished(DownloadItem item) {
+					OnItemFinished?.Invoke(null, item);
+				}
+
+				public void FireOnServerStopped() {
+					OnServerStopped?.Invoke(null, EventArgs.Empty);
+				}
+			}
+
+			private readonly WebClient client = new ();
+
+			public ThreadInstance() {
+				client.Headers[HttpRequestHeader.UserAgent] = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.51 Safari/537.36";
+			}
+
+			public void Work(object? obj) {
+				var parameters = (Parameters) obj!;
+
+				var cancellationTokenSource = parameters.CancellationTokenSource;
+				var cancellationToken = cancellationTokenSource.Token;
+
+				var db = parameters.Db;
+				var queue = new ConcurrentQueue<DownloadItem>();
+
+				cancellationToken.Register(client.CancelAsync);
+
+				try {
+					while (!cancellationToken.IsCancellationRequested) {
+						FillQueue(db, queue, cancellationToken);
+
+						while (!cancellationToken.IsCancellationRequested && queue.TryDequeue(out var item)) {
+							var url = item.Url;
+							Log.Debug("Downloading " + url + "...");
+
+							try {
+								db.AddDownloads(new [] { Data.Download.NewSuccess(url, client.DownloadData(url)) });
+							} catch (WebException e) {
+								db.AddDownloads(new [] { Data.Download.NewFailure(url, e.Response is HttpWebResponse response ? response.StatusCode : null, item.Size) });
+								Log.Error(e);
+							} finally {
+								parameters.FireOnItemFinished(item);
+							}
+						}
+					}
+				} catch (OperationCanceledException) {
+					//
+				} catch (ObjectDisposedException) {
+					//
+				} finally {
+					cancellationTokenSource.Dispose();
+					parameters.FireOnServerStopped();
+				}
+			}
+
+			private static void FillQueue(IDatabaseFile db, ConcurrentQueue<DownloadItem> queue, CancellationToken cancellationToken) {
+				while (!cancellationToken.IsCancellationRequested && queue.IsEmpty) {
+					var newItems = db.GetEnqueuedDownloadItems(QueueSize);
+					if (newItems.Count == 0) {
+						Thread.Sleep(TimeSpan.FromMilliseconds(50));
+					}
+					else {
+						foreach (var item in newItems) {
+							queue.Enqueue(item);
+						}
+					}
+				}
+			}
+		}
+	}
+}

app/Server/Download/DownloadItem.cs

@@ -0,0 +1,6 @@
+namespace DHT.Server.Download {
+	public readonly struct DownloadItem {
+		public string Url { get; init; }
+		public ulong Size { get; init; }
+	}
+}

app/Utils/Tasks/AsyncValueComputer.cs

@@ -11,8 +11,10 @@ namespace DHT.Utils.Tasks {
 
 		private readonly object stateLock = new ();
 
-		private CancellationTokenSource? currentCancellationTokenSource;
+		private SoftHardCancellationToken? currentCancellationTokenSource;
-		private Func<CancellationToken, TValue>? currentComputeFunction;
+		private bool wasHardCancelled = false;
+		
+		private Func<TValue>? currentComputeFunction;
 		private bool hasComputeFunctionChanged = false;
 
 		private AsyncValueComputer(Action<TValue> resultProcessor, TaskScheduler resultTaskScheduler, bool processOutdatedResults) {
@@ -21,12 +23,21 @@ namespace DHT.Utils.Tasks {
 			this.processOutdatedResults = processOutdatedResults;
 		}
 
-		public void Compute(Func<CancellationToken, TValue> func) {
+		public void Cancel() {
 			lock (stateLock) {
+				wasHardCancelled = true;
+				currentCancellationTokenSource?.RequestHardCancellation();
+			}
+		}
+
+		public void Compute(Func<TValue> func) {
+			lock (stateLock) {
+				wasHardCancelled = false;
+				
 				if (currentComputeFunction != null) {
 					currentComputeFunction = func;
 					hasComputeFunctionChanged = true;
-					currentCancellationTokenSource?.Cancel();
+					currentCancellationTokenSource?.RequestSoftCancellation();
 				}
 				else {
 					EnqueueComputation(func);
@@ -35,19 +46,18 @@ namespace DHT.Utils.Tasks {
 		}
 
 		[SuppressMessage("ReSharper", "MethodSupportsCancellation")]
-		private void EnqueueComputation(Func<CancellationToken, TValue> func) {
+		private void EnqueueComputation(Func<TValue> func) {
-			var cancellationTokenSource = new CancellationTokenSource();
+			var cancellationTokenSource = new SoftHardCancellationToken();
-			var cancellationToken = cancellationTokenSource.Token;
 
-			currentCancellationTokenSource?.Cancel();
+			currentCancellationTokenSource?.RequestSoftCancellation();
 			currentCancellationTokenSource = cancellationTokenSource;
 			currentComputeFunction = func;
 			hasComputeFunctionChanged = false;
 
-			var task = Task.Run(() => func(cancellationToken));
+			var task = Task.Run(func);
 
 			task.ContinueWith(t => {
-				if (processOutdatedResults || !cancellationToken.IsCancellationRequested) {
+				if (!cancellationTokenSource.IsCancelled(processOutdatedResults)) {
 					resultProcessor(t.Result);
 				}
 			}, CancellationToken.None, TaskContinuationOptions.NotOnFaulted, resultTaskScheduler);
@@ -60,11 +70,12 @@ namespace DHT.Utils.Tasks {
 						currentCancellationTokenSource = null;
 					}
 
-					if (hasComputeFunctionChanged) {
+					if (hasComputeFunctionChanged && !wasHardCancelled) {
 						EnqueueComputation(currentComputeFunction);
 					}
 					else {
 						currentComputeFunction = null;
+						hasComputeFunctionChanged = false;
 					}
 				}
 			});
@@ -72,9 +83,9 @@ namespace DHT.Utils.Tasks {
 
 		public sealed class Single {
 			private readonly AsyncValueComputer<TValue> baseComputer;
-			private readonly Func<CancellationToken, TValue> resultComputer;
+			private readonly Func<TValue> resultComputer;
 
-			internal Single(AsyncValueComputer<TValue> baseComputer, Func<CancellationToken, TValue> resultComputer) {
+			internal Single(AsyncValueComputer<TValue> baseComputer, Func<TValue> resultComputer) {
 				this.baseComputer = baseComputer;
 				this.resultComputer = resultComputer;
 			}
@@ -107,7 +118,7 @@ namespace DHT.Utils.Tasks {
 				return new AsyncValueComputer<TValue>(resultProcessor, resultTaskScheduler, processOutdatedResults);
 			}
 
-			public Single BuildWithComputer(Func<CancellationToken, TValue> resultComputer) {
+			public Single BuildWithComputer(Func<TValue> resultComputer) {
 				return new Single(Build(), resultComputer);
 			}
 		}

app/Utils/Tasks/SoftHardCancellationToken.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Threading;
+
+namespace DHT.Utils.Tasks {
+	/// <summary>
+	/// Manages a pair of cancellation tokens that follow these rules:
+	/// <list type="number">
+	/// <item><description>If the soft token is cancelled, the hard token remains uncancelled.</description></item>
+	/// <item><description>If the hard token is cancelled, the soft token is also cancelled.</description></item>
+	/// </list>
+	/// </summary>
+	sealed class SoftHardCancellationToken : IDisposable {
+		private readonly CancellationTokenSource soft;
+		private readonly CancellationTokenSource hard;
+		
+		public SoftHardCancellationToken() {
+			this.soft = new CancellationTokenSource();
+			this.hard = new CancellationTokenSource();
+		}
+
+		public bool IsCancelled(bool onlyHardCancellation) {
+			return (onlyHardCancellation ? hard : soft).IsCancellationRequested;
+		}
+
+		public void RequestSoftCancellation() {
+			soft.Cancel();
+		}
+
+		public void RequestHardCancellation() {
+			soft.Cancel();
+			hard.Cancel();
+		}
+
+		public void Dispose() {
+			soft.Dispose();
+			hard.Dispose();
+		}
+	}
+}

app/Version.cs

@@ -7,6 +7,6 @@ using DHT.Utils;
 
 namespace DHT.Utils {
 	static class Version {
-		public const string Tag = "35.3.0.0";
+		public const string Tag = "36.0.0.0";
 	}
 }