Version: 214.2.2

(cherry picked from commit 025d90d281)
(cherry picked from commit 799702b814)
(cherry picked from commit 4600ee8e5788891f1b610e2d5141fb4e1228d323)

.github/workflows/publish-client.yml

@@ -33,10 +33,10 @@ jobs:
         mkdir "release/${{ steps.parse_version.outputs.version }}"
         mv release/*.zip "release/${{ steps.parse_version.outputs.version }}"
 
-    - name: Upload files to centcomm
+    - name: Upload files to Suns
       uses: appleboy/scp-action@master
       with:
-        host: centcomm.spacestation14.io
+        host: suns.spacestation14.com
         username: robust-build-push
         key: ${{ secrets.CENTCOMM_ROBUST_BUILDS_PUSH_KEY }}
         source: "release/${{ steps.parse_version.outputs.version }}"
@@ -46,7 +46,7 @@ jobs:
     - name: Update manifest JSON
       uses: appleboy/ssh-action@master
       with:
-        host: centcomm.spacestation14.io
+        host: suns.spacestation14.com
         username: robust-build-push
         key: ${{ secrets.CENTCOMM_ROBUST_BUILDS_PUSH_KEY }}
         script: /home/robust-build-push/push.ps1 ${{ steps.parse_version.outputs.version }}

Directory.Packages.props

@@ -1,4 +1,14 @@
 <Project>
+  <PropertyGroup>
+    <!--
+    We actually set ManagePackageVersionsCentrally manually in another import file.
+    Since .NET SDK 8.0.300, ManagePackageVersionsCentrally is automatically set if Directory.Packages.props exists.
+    https://github.com/NuGet/NuGet.Client/pull/5572
+    We actively negate this here, as we have some packages in tree we don't want such automatic behavior for.
+    We use Directory.Build.props to get copy the state *after* our MSBuild config but before Nuget's config.
+    -->
+    <ManagePackageVersionsCentrally />
+  </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="BenchmarkDotNet" Version="0.13.12" />
     <PackageVersion Include="DiscordRichPresence" Version="1.2.1.24" />
@@ -45,7 +55,7 @@
     <PackageVersion Include="Serilog" Version="3.1.1" />
     <PackageVersion Include="Serilog.Sinks.Loki" Version="4.0.0-beta3" />
     <PackageVersion Include="SharpZstd.Interop" Version="1.5.2-beta2" />
-    <PackageVersion Include="SixLabors.ImageSharp" Version="3.1.3" />
+    <PackageVersion Include="SixLabors.ImageSharp" Version="3.1.5" />
     <PackageVersion Include="SpaceWizards.HttpListener" Version="0.1.0" />
     <PackageVersion Include="SpaceWizards.NFluidsynth" Version="0.1.1" />
     <PackageVersion Include="SpaceWizards.SharpFont" Version="1.0.2" />

MSBuild/Robust.Engine.Version.props

@@ -1,4 +1,4 @@
 <Project>
 
-    <!-- This file automatically reset by Tools/version.py -->
+    <!-- This file automatically reset by Tools/version.py -->
 

RELEASE-NOTES.md

@@ -54,6 +54,80 @@ END TEMPLATE-->
 *None yet*
 
 
+## 214.2.2
+
+
+## 214.2.1
+
+
+## 214.2.0
+
+### New features
+
+* Added a `Undetachable` entity metadata flag, which stops the client from moving an entity to nullspace when it moves out of PVS range.
+
+### Bugfixes
+
+* Fix tooltips not clamping to the left side of the viewport.
+* Fix global audio property not being properly set.
+
+### Internal
+
+* The server game state / PVS code has been rewritten. It should be somewhat faster now, albeit at the cost of using more memory. The current engine version may be unstable.
+
+
+## 214.1.1
+
+### Bugfixes
+
+* Fixed connection denial always causing redial.
+
+
+## 214.1.0
+
+### New features
+
+* Added the `pvs_override_info` command for debugging PVS overrides.
+
+### Bugfixes
+
+* Fix VV for prototype structs.
+* Fix audio limits for clientside audio.
+
+
+## 214.0.0
+
+### Breaking changes
+
+* `NetStructuredDisconnectMessages` has received a complete overhaul and has been moved to `NetDisconnectMessage`. The API is no longer designed such that consumers must pass around JSON nodes, as they are not in sandbox (and clunky).
+
+### New features
+
+* Add a basic default concurrent audio limit of 16 for a single filepath to avoid overflowing audio sources.
+* `NetConnectingArgs.Deny()` can now pass along structured data that will be received by the client.
+
+### Bugfixes
+
+* Fixed cursor position bugs when an empty `TextEdit` has a multi-line place holder.
+* Fixed empty `TextEdit` throwing exception if cursor is moved left.
+
+
+## 213.0.0
+
+### Breaking changes
+
+* Remove obsoleted BaseContainer methods.
+
+### New features
+
+* Add EntityManager.RaiseSharedEvent where the event won't go to the attached client but will be predicted locally on their end.
+* Add GetEntitiesInRange override that takes in EntityCoordinates and an EntityUid hashset.
+
+### Bugfixes
+
+* Check if a sprite entity is deleted before drawing in SpriteView.
+
+
 ## 212.2.0
 
 ### New features

Resources/Locale/en-US/commands.ftl

@@ -566,3 +566,9 @@ cmd-reloadtiletextures-help = Usage: reloadtiletextures
 cmd-audio_length-desc = Shows the length of an audio file
 cmd-audio_length-help = Usage: audio_length { cmd-audio_length-arg-file-name }
 cmd-audio_length-arg-file-name = <file name>
+
+## PVS
+cmd-pvs-override-info-desc = Prints information about any PVS overrides associated with an entity.
+cmd-pvs-override-info-empty = Entity {$nuid} has no PVS overrides.
+cmd-pvs-override-info-global = Entity {$nuid} has a global override.
+cmd-pvs-override-info-clients = Entity {$nuid} has a session override for {$clients}.

Robust.Client/Audio/AudioSystem.Limits.cs

@@ -0,0 +1,57 @@
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using Robust.Shared;
+using Robust.Shared.GameObjects;
+
+namespace Robust.Client.Audio;
+
+public sealed partial class AudioSystem
+{
+    /*
+     * Handles limiting concurrent sounds for audio to avoid blowing the source budget on one sound getting spammed.
+     */
+
+    private readonly Dictionary<string, int> _playingCount = new();
+
+    private int _maxConcurrent;
+
+    private void InitializeLimit()
+    {
+        Subs.CVar(CfgManager, CVars.AudioDefaultConcurrent, SetConcurrentLimit, true);
+    }
+
+    private void SetConcurrentLimit(int obj)
+    {
+        _maxConcurrent = obj;
+    }
+
+    private bool TryAudioLimit(string sound)
+    {
+        if (string.IsNullOrEmpty(sound))
+            return true;
+
+        ref var count = ref CollectionsMarshal.GetValueRefOrAddDefault(_playingCount, sound, out _);
+
+        if (count >= _maxConcurrent)
+            return false;
+
+        count++;
+        return true;
+    }
+
+    private void RemoveAudioLimit(string sound)
+    {
+        if (!_playingCount.TryGetValue(sound, out var count))
+            return;
+
+        count--;
+
+        if (count <= 0)
+        {
+            _playingCount.Remove(sound);
+            return;
+        }
+
+        _playingCount[sound] = count;
+    }
+}

Robust.Client/Audio/AudioSystem.cs

@@ -41,6 +41,7 @@ public sealed partial class AudioSystem : SharedAudioSystem
     [Dependency] private readonly IParallelManager _parMan = default!;
     [Dependency] private readonly IRuntimeLog _runtimeLog = default!;
     [Dependency] private readonly IAudioInternal _audio = default!;
+    [Dependency] private readonly MetaDataSystem _metadata = default!;
     [Dependency] private readonly SharedTransformSystem _xformSys = default!;
     [Dependency] private readonly SharedPhysicsSystem _physics = default!;
 
@@ -51,6 +52,7 @@ public sealed partial class AudioSystem : SharedAudioSystem
     private EntityUid? _listenerGrid;
     private UpdateAudioJob _updateAudioJob;
 
+
     private EntityQuery<PhysicsComponent> _physicsQuery;
 
     private float _maxRayLength;
@@ -108,6 +110,7 @@ public sealed partial class AudioSystem : SharedAudioSystem
 
         Subs.CVar(CfgManager, CVars.AudioAttenuation, OnAudioAttenuation, true);
         Subs.CVar(CfgManager, CVars.AudioRaycastLength, OnRaycastLengthChanged, true);
+        InitializeLimit();
     }
 
     private void OnAudioState(EntityUid uid, AudioComponent component, ref AfterAutoHandleStateEvent args)
@@ -163,26 +166,37 @@ public sealed partial class AudioSystem : SharedAudioSystem
             return;
         }
 
-        SetupSource(component, audioResource);
+        SetupSource((uid, component), audioResource);
         component.Loaded = true;
     }
 
-    private void SetupSource(AudioComponent component, AudioResource audioResource, TimeSpan? length = null)
+    private void SetupSource(Entity<AudioComponent> entity, AudioResource audioResource, TimeSpan? length = null)
     {
-        var source = _audio.CreateAudioSource(audioResource);
-
-        if (source == null)
+        var component = entity.Comp;
+    
+        if (TryAudioLimit(component.FileName))
         {
-            Log.Error($"Error creating audio source for {audioResource}");
-            DebugTools.Assert(false);
-            source = component.Source;
+            var newSource = _audio.CreateAudioSource(audioResource);
+
+            if (newSource == null)
+            {
+                Log.Error($"Error creating audio source for {audioResource}");
+                DebugTools.Assert(false);
+            }
+            else
+            {
+                component.Source = newSource;
+            }
         }
 
-        component.Source = source;
+        if ((component.Flags & AudioFlags.GridAudio) != 0x0)
+        {
+            _metadata.SetFlag(entity.Owner, MetaDataFlags.Undetachable, true);
+        }
 
         // Need to set all initial data for first frame.
         ApplyAudioParams(component.Params, component);
-        source.Global = component.Global;
+        component.Source.Global = component.Global;
 
         // Don't play until first frame so occlusion etc. are correct.
         component.Gain = 0f;
@@ -202,6 +216,8 @@ public sealed partial class AudioSystem : SharedAudioSystem
     {
         // Breaks with prediction?
         component.Source.Dispose();
+
+        RemoveAudioLimit(component.FileName);
     }
 
     private void OnAudioAttenuation(int obj)
@@ -576,13 +592,13 @@ public sealed partial class AudioSystem : SharedAudioSystem
         return PlayGlobal(filename, audioParams);
     }
 
-    public override void LoadStream<T>(AudioComponent component, T stream)
+    public override void LoadStream<T>(Entity<AudioComponent> entity, T stream)
     {
         if (stream is AudioStream audioStream)
         {
             TryGetAudio(audioStream, out var audio);
-            SetupSource(component, audio!, audioStream.Length);
-            component.Loaded = true;
+            SetupSource(entity, audio!, audioStream.Length);
+            entity.Comp.Loaded = true;
         }
     }
 
@@ -621,7 +637,7 @@ public sealed partial class AudioSystem : SharedAudioSystem
         var audioP = audioParams ?? AudioParams.Default;
         var entity = EntityManager.CreateEntityUninitialized("Audio", MapCoordinates.Nullspace);
         var comp = SetupAudio(entity, null, audioP, stream.Length);
-        LoadStream(comp, stream);
+        LoadStream((entity, comp), stream);
         EntityManager.InitializeAndStartEntity(entity);
         var source = comp.Source;
 

Robust.Client/Console/Commands/DumpMetadataMembersCommand.cs

@@ -11,7 +11,7 @@ namespace Robust.Client.Console.Commands
 
         public override void Execute(IConsoleShell shell, string argStr, string[] args)
         {
-            var type = Type.GetType(args[0]);
+            var type = GetType(args[0]);
 
             if (type == null)
             {
@@ -25,6 +25,17 @@ namespace Robust.Client.Console.Commands
                 shell.WriteLine(sig);
             }
         }
+
+        private Type? GetType(string name)
+        {
+            foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
+            {
+                if (assembly.GetType(name) is { } type)
+                    return type;
+            }
+
+            return null;
+        }
     }
 #endif
 }

Robust.Client/Console/Commands/UITestCommand.cs

@@ -165,7 +165,7 @@ Suspendisse hendrerit blandit urna ut laoreet. Suspendisse ac elit at erat males
     {
         var textEdit = new TextEdit
         {
-            Placeholder = new Rope.Leaf("You deleted the lipsum OwO")
+            Placeholder = new Rope.Leaf("You deleted the lipsum\nOwO")
         };
         TabContainer.SetTabTitle(textEdit, "TextEdit");
 

Robust.Client/GameObjects/ClientEntityManager.cs

@@ -8,6 +8,7 @@ using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
 using Robust.Shared.Network;
 using Robust.Shared.Network.Messages;
+using Robust.Shared.Player;
 using Robust.Shared.Replays;
 using Robust.Shared.Utility;
 
@@ -134,6 +135,24 @@ namespace Robust.Client.GameObjects
             EventBus.RaiseEvent(EventSource.Local, new EntitySessionMessage<T>(eventArgs, msg));
         }
 
+        /// <inheritdoc />
+        public override void RaiseSharedEvent<T>(T message, EntityUid? user = null)
+        {
+            if (user == null || user != _playerManager.LocalEntity || !_gameTiming.IsFirstTimePredicted)
+                return;
+
+            EventBus.RaiseEvent(EventSource.Local, ref message);
+        }
+
+        /// <inheritdoc />
+        public override void RaiseSharedEvent<T>(T message, ICommonSession? user = null)
+        {
+            if (user == null || user != _playerManager.LocalSession || !_gameTiming.IsFirstTimePredicted)
+                return;
+
+            EventBus.RaiseEvent(EventSource.Local, ref message);
+        }
+
         #region IEntityNetworkManager impl
 
         public override IEntityNetworkManager EntityNetManager => this;

Robust.Client/GameStates/ClientGameStateManager.cs

@@ -1120,7 +1120,7 @@ namespace Robust.Client.GameStates
                     continue;
                 }
 
-                if ((meta.Flags & MetaDataFlags.Detached) != 0)
+                if ((meta.Flags & (MetaDataFlags.Detached | MetaDataFlags.Undetachable)) != 0)
                     continue;
 
                 if (lastStateApplied.HasValue)

Robust.Client/UserInterface/Controls/Range.cs

@@ -13,6 +13,7 @@ namespace Robust.Client.UserInterface.Controls
         private float _value;
         private float _page;
         private bool _rounded;
+        private int _roundingDecimals = 0;
 
         public event Action<Range>? OnValueChanged;
 
@@ -86,6 +87,17 @@ namespace Robust.Client.UserInterface.Controls
             }
         }
 
+        [ViewVariables]
+        public int RoundingDecimals
+        {
+            get => _roundingDecimals;
+            set
+            {
+                _roundingDecimals = value;
+                _ensureValueClamped();
+            }
+        }
+
         public virtual void SetValueWithoutEvent(float newValue)
         {
             newValue = ClampValue(newValue);
@@ -107,7 +119,7 @@ namespace Robust.Client.UserInterface.Controls
         {
             if (_rounded)
             {
-                value = MathF.Round(value);
+                value = MathF.Round(value, _roundingDecimals);
             }
             return MathHelper.Clamp(value, _minValue, _maxValue-_page);
         }

Robust.Client/UserInterface/Controls/SpriteView.cs

@@ -16,7 +16,7 @@ namespace Robust.Client.UserInterface.Controls
     {
         private SpriteSystem? _sprite;
         private SharedTransformSystem? _transform;
-        IEntityManager _entMan;
+        private readonly IEntityManager _entMan;
 
         [ViewVariables]
         public SpriteComponent? Sprite => Entity?.Comp1;
@@ -143,6 +143,8 @@ namespace Robust.Client.UserInterface.Controls
             if (netEnt == NetEnt)
                 return;
 
+            // The Entity is getting set later in the ResolveEntity method
+            // because the client may not have received it yet.
             Entity = null;
             NetEnt = netEnt;
         }
@@ -256,28 +258,19 @@ namespace Robust.Client.UserInterface.Controls
             [NotNullWhen(true)] out SpriteComponent? sprite,
             [NotNullWhen(true)] out TransformComponent? xform)
         {
+            if (NetEnt != null && Entity == null && _entMan.TryGetEntity(NetEnt, out var ent))
+                SetEntity(ent);
+
             if (Entity != null)
             {
                 (uid, sprite, xform) = Entity.Value;
-                return true;
+                return !_entMan.Deleted(uid);
             }
 
             sprite = null;
             xform = null;
             uid = default;
-
-            if (NetEnt == null)
-                return false;
-
-            if (!_entMan.TryGetEntity(NetEnt, out var ent))
-                return false;
-
-            SetEntity(ent);
-            if (Entity == null)
-                return false;
-
-            (uid, sprite, xform) = Entity.Value;
-            return true;
+            return false;
         }
     }
 }

Robust.Client/UserInterface/Controls/TextEdit.cs

@@ -576,7 +576,7 @@ public sealed class TextEdit : Control
 
                 var newPos = CursorShiftedLeft();
                 // Explicit newlines work kinda funny with bias, so keep it at top there.
-                var bias = Rope.Index(TextRope, newPos) == '\n'
+                var bias = _cursorPosition.Index == TextLength || Rope.Index(TextRope, newPos) == '\n'
                     ? LineBreakBias.Top
                     : LineBreakBias.Bottom;
 
@@ -940,6 +940,13 @@ public sealed class TextEdit : Control
 
     private CursorPos GetIndexAtHorizontalPos(int line, float horizontalPos)
     {
+        // If the placeholder is visible, this function does not return correct results because it looks at TextRope,
+        // but _lineBreaks is configured for the display rope.
+        // Bail out early in this case, the function is not currently used in any situation in any location
+        // where something else is desired if the placeholder is visible.
+        if (IsPlaceholderVisible)
+            return default;
+
         var contentBox = PixelSizeBox;
         var font = GetFont();
         var uiScale = UIScale;

Robust.Client/UserInterface/Tooltips.cs

@@ -1,4 +1,5 @@
-using System.Numerics;
+using System;
+using System.Numerics;
 using Robust.Client.UserInterface.Controls;
 using Robust.Shared.Maths;
 
@@ -41,20 +42,16 @@ namespace Robust.Client.UserInterface
             tooltip.Measure(Vector2Helpers.Infinity);
             var combinedMinSize = tooltip.DesiredSize;
 
-            LayoutContainer.SetPosition(tooltip, new Vector2(screenPosition.X, screenPosition.Y - combinedMinSize.Y));
+            // If it overflows right bounds then just place left on the edge.
+            var right = MathF.Min(screenPosition.X + combinedMinSize.X, screenBounds.X);
 
-            var right = tooltip.Position.X + combinedMinSize.X;
-            var top = tooltip.Position.Y;
+            // However, better to clamp the end of the tooltip instead of the start.
+            var left = MathF.Max(0f, right - combinedMinSize.X);
 
-            if (right > screenBounds.X)
-            {
-                LayoutContainer.SetPosition(tooltip, new(screenPosition.X - combinedMinSize.X, tooltip.Position.Y));
-            }
+            var bottom = MathF.Min(screenPosition.Y, screenBounds.Y);
+            var top = MathF.Max(0f, bottom - combinedMinSize.Y);
 
-            if (top < 0f)
-            {
-                LayoutContainer.SetPosition(tooltip, new(tooltip.Position.X, 0f));
-            }
+            LayoutContainer.SetPosition(tooltip, new Vector2(left, top));
         }
     }
 }

Robust.Client/ViewVariables/ClientViewVariablesManager.cs

@@ -126,6 +126,22 @@ namespace Robust.Client.ViewVariables
                 return new VVPropEditorString();
             }
 
+            if (type == typeof(EntProtoId) ||
+                type == typeof(EntProtoId?))
+            {
+                return new VVPropEditorEntProtoId();
+            }
+
+            if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(ProtoId<>))
+            {
+                var editor =
+                    (VVPropEditor)Activator.CreateInstance(
+                        typeof(VVPropEditorProtoId<>).MakeGenericType(type.GenericTypeArguments[0]))!;
+
+                IoCManager.InjectDependencies(editor);
+                return editor;
+            }
+
             if (typeof(IPrototype).IsAssignableFrom(type) || typeof(ViewVariablesBlobMembers.PrototypeReferenceToken).IsAssignableFrom(type))
             {
                 return (VVPropEditor)Activator.CreateInstance(typeof(VVPropEditorIPrototype<>).MakeGenericType(type))!;

Robust.Client/ViewVariables/Editors/VVPropEditorEntProtoId.cs

@@ -0,0 +1,28 @@
+using Robust.Client.UserInterface;
+using Robust.Client.UserInterface.Controls;
+using Robust.Shared.Prototypes;
+
+namespace Robust.Client.ViewVariables.Editors;
+
+internal sealed class VVPropEditorEntProtoId : VVPropEditor
+{
+    protected override Control MakeUI(object? value)
+    {
+        var lineEdit = new LineEdit
+        {
+            Text = (EntProtoId) (value ?? ""),
+            Editable = !ReadOnly,
+            HorizontalExpand = true,
+        };
+
+        if (!ReadOnly)
+        {
+            lineEdit.OnTextEntered += e =>
+            {
+                ValueChanged((EntProtoId) e.Text);
+            };
+        }
+
+        return lineEdit;
+    }
+}

Robust.Client/ViewVariables/Editors/VVPropEditorProtoId.cs

@@ -0,0 +1,38 @@
+using Robust.Client.UserInterface;
+using Robust.Client.UserInterface.Controls;
+using Robust.Shared.IoC;
+using Robust.Shared.Prototypes;
+
+namespace Robust.Client.ViewVariables.Editors;
+
+internal sealed class VVPropEditorProtoId<T> : VVPropEditor where T : class, IPrototype
+{
+    [Dependency] private readonly IPrototypeManager _protoManager = default!;
+
+    protected override Control MakeUI(object? value)
+    {
+        var lineEdit = new LineEdit
+        {
+            Text = (ProtoId<T>) (value ?? ""),
+            Editable = !ReadOnly,
+            HorizontalExpand = true,
+        };
+
+        if (!ReadOnly)
+        {
+            lineEdit.OnTextEntered += e =>
+            {
+                var id = (ProtoId<T>)e.Text;
+
+                if (!_protoManager.HasIndex(id))
+                {
+                    return;
+                }
+
+                ValueChanged(id);
+            };
+        }
+
+        return lineEdit;
+    }
+}

Robust.Server/Audio/AudioSystem.cs

@@ -238,7 +238,8 @@ public sealed partial class AudioSystem : SharedAudioSystem
         }
     }
 
-    public override void LoadStream<T>(AudioComponent component, T stream)
+    public override void LoadStream<T>(Entity<AudioComponent> entity, T stream)
     {
+        // TODO: Yeah remove this...
     }
 }

Robust.Server/BaseServer.cs

@@ -653,8 +653,8 @@ namespace Robust.Server
             _playerManager.PlayerStatusChanged -= OnPlayerStatusChanged;
 
             // shut down networking, kicking all players.
-            var shutdownReasonWithRedial = NetStructuredDisconnectMessages.Encode($"Server shutting down: {_shutdownReason}", true);
-            _network.Shutdown(shutdownReasonWithRedial);
+            var shutdownReasonWithRedial = new NetDisconnectMessage($"Server shutting down: {_shutdownReason}", true);
+            _network.Shutdown(shutdownReasonWithRedial.Encode());
 
             // shutdown entities
             _entityManager.Cleanup();

Robust.Server/GameObjects/EntitySystems/VisibilitySystem.cs

@@ -1,4 +1,5 @@
 using System;
+using Robust.Server.GameStates;
 using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
 using Robust.Shared.ViewVariables;
@@ -7,6 +8,7 @@ namespace Robust.Server.GameObjects
 {
     public sealed class VisibilitySystem : EntitySystem
     {
+        [Dependency] private readonly PvsSystem _pvs = default!;
         [Dependency] private readonly IViewVariablesManager _vvManager = default!;
 
         private EntityQuery<TransformComponent> _xformQuery;
@@ -133,6 +135,7 @@ namespace Robust.Server.GameObjects
 
             var xform = _xformQuery.GetComponent(uid);
             meta.VisibilityMask = mask;
+            _pvs.SyncMetadata(meta);
 
             foreach (var child in xform._children)
             {

Robust.Server/GameObjects/ServerEntityManager.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using JetBrains.Annotations;
 using Prometheus;
+using Robust.Server.GameStates;
 using Robust.Server.Player;
 using Robust.Shared;
 using Robust.Shared.Configuration;
@@ -42,7 +43,7 @@ namespace Robust.Server.GameObjects
 #endif
 
         private ISawmill _netEntSawmill = default!;
-        private EntityQuery<ActorComponent> _actorQuery;
+        private PvsSystem _pvs = default!;
 
         public override void Initialize()
         {
@@ -57,7 +58,7 @@ namespace Robust.Server.GameObjects
         public override void Startup()
         {
             base.Startup();
-            _actorQuery = GetEntityQuery<ActorComponent>();
+            _pvs = System<PvsSystem>();
         }
 
         EntityUid IServerEntityManagerInternal.AllocEntity(EntityPrototype? prototype)
@@ -103,6 +104,40 @@ namespace Robust.Server.GameObjects
             return entity;
         }
 
+        /// <inheritdoc />
+        public override void RaiseSharedEvent<T>(T message, EntityUid? user = null)
+        {
+            if (user != null)
+            {
+                var filter = Filter.Broadcast().RemoveWhereAttachedEntity(e => e == user.Value);
+                foreach (var session in filter.Recipients)
+                {
+                    EntityNetManager.SendSystemNetworkMessage(message, session.Channel);
+                }
+            }
+            else
+            {
+                EntityNetManager.SendSystemNetworkMessage(message);
+            }
+        }
+
+        /// <inheritdoc />
+        public override void RaiseSharedEvent<T>(T message, ICommonSession? user = null)
+        {
+            if (user != null)
+            {
+                var filter = Filter.Broadcast().RemovePlayer(user);
+                foreach (var session in filter.Recipients)
+                {
+                    EntityNetManager.SendSystemNetworkMessage(message, session.Channel);
+                }
+            }
+            else
+            {
+                EntityNetManager.SendSystemNetworkMessage(message);
+            }
+        }
+
         private void ClearTicks(EntityUid entity, EntityPrototype prototype)
         {
             foreach (var (netId, component) in GetNetComponents(entity))
@@ -116,6 +151,12 @@ namespace Robust.Server.GameObjects
             }
         }
 
+        internal override void SetLifeStage(MetaDataComponent meta, EntityLifeStage stage)
+        {
+            base.SetLifeStage(meta, stage);
+            _pvs.SyncMetadata(meta);
+        }
+
         #region IEntityNetworkManager impl
 
         public override IEntityNetworkManager EntityNetManager => this;

Robust.Server/GameStates/PvsChunk.cs

@@ -42,7 +42,7 @@ internal sealed class PvsChunk
     /// <remarks>
     /// This already includes <see cref="Map"/>, <see cref="Root"/>, and <see cref="Children"/>
     /// </remarks>
-    public readonly List<Entity<MetaDataComponent>> Contents = new();
+    public readonly List<ChunkEntity> Contents = new();
 
     /// <summary>
     /// The unique location identifier for this chunk.
@@ -68,8 +68,8 @@ internal sealed class PvsChunk
     // the same chunk can be repopulated more than once.
     private List<HashSet<EntityUid>> _childSets = new();
     private List<HashSet<EntityUid>> _nextChildSets = new();
-    private List<Entity<MetaDataComponent>> _lowPriorityChildren = new();
-    private List<Entity<MetaDataComponent>> _anchoredChildren = new();
+    private List<ChunkEntity> _lowPriorityChildren = new();
+    private List<ChunkEntity> _anchoredChildren = new();
 
     /// <summary>
     /// Effective "counts" of <see cref="Contents"/> that should be used to limit the number of entities in a chunk that
@@ -151,11 +151,11 @@ internal sealed class PvsChunk
             childMeta.LastPvsLocation = Location;
 
             if ((childMeta.Flags & MetaDataFlags.PvsPriority) == MetaDataFlags.PvsPriority)
-                Contents.Add((child, childMeta));
+                Contents.Add(new ChunkEntity(child, childMeta));
             else if (childXform.Anchored)
-                _anchoredChildren.Add((child, childMeta));
+                _anchoredChildren.Add(new(child, childMeta));
             else
-                _lowPriorityChildren.Add((child, childMeta));
+                _lowPriorityChildren.Add(new(child, childMeta));
 
             var subCount = childXform._children.Count;
             if (subCount == 0)
@@ -196,7 +196,7 @@ internal sealed class PvsChunk
                     }
 
                     childMeta.LastPvsLocation = Location;
-                    Contents.Add((child, childMeta));
+                    Contents.Add(new(child, childMeta));
 
                     var subCount = childXform._children.Count;
                     if (subCount == 0)
@@ -241,10 +241,10 @@ internal sealed class PvsChunk
         set.Add(Map.Owner);
         foreach (var child in Contents)
         {
-            var parent = query.GetComponent(child).ParentUid;
+            var parent = query.GetComponent(child.Uid).ParentUid;
             DebugTools.Assert(set.Contains(parent),
                 "A child's parent is not in the chunk, or is not listed first.");
-            DebugTools.Assert(set.Add(child), "Child appears more than once in the chunk.");
+            DebugTools.Assert(set.Add(child.Uid), "Child appears more than once in the chunk.");
         }
     }
 
@@ -274,4 +274,11 @@ internal sealed class PvsChunk
             ? $"map-{Root.Owner}-{Location.Indices}"
             : $"grid-{Root.Owner}-{Location.Indices}";
     }
+
+    public readonly struct ChunkEntity(EntityUid uid, MetaDataComponent meta)
+    {
+        public readonly EntityUid Uid = uid;
+        public readonly PvsIndex Ptr = meta.PvsData;
+        public readonly MetaDataComponent Meta = meta;
+    }
 }

Robust.Server/GameStates/PvsData.cs

@@ -1,9 +1,10 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Robust.Shared.Collections;
 using Robust.Shared.GameObjects;
 using Robust.Shared.GameStates;
-using Robust.Shared.Maths;
 using Robust.Shared.Network;
 using Robust.Shared.Player;
 using Robust.Shared.Timing;
@@ -14,26 +15,24 @@ namespace Robust.Server.GameStates;
 /// <summary>
 /// Class for storing session specific PVS data.
 /// </summary>
-internal sealed class PvsSession(ICommonSession session)
+internal sealed class PvsSession(ICommonSession session, ResizableMemoryRegion<PvsData> memoryRegion)
 {
     public readonly ICommonSession Session = session;
+
+    public readonly ResizableMemoryRegion<PvsData> DataMemory = memoryRegion;
+
     public INetChannel Channel => Session.Channel;
 
     /// <summary>
-    /// All <see cref="EntityUid"/>s that this session saw during the last <see cref="PvsSystem.DirtyBufferSize"/> ticks.
+    /// All entities that this session saw during the last <see cref="PvsSystem.DirtyBufferSize"/> ticks.
     /// </summary>
-    public readonly OverflowDictionary<GameTick, List<PvsData>> PreviouslySent = new(PvsSystem.DirtyBufferSize);
-
-    /// <summary>
-    /// Dictionary containing data about all entities that this client has ever seen.
-    /// </summary>
-    public readonly Dictionary<NetEntity, PvsData> Entities = new();
+    public readonly OverflowDictionary<GameTick, List<PvsIndex>> PreviouslySent = new(PvsSystem.DirtyBufferSize);
 
     /// <summary>
     /// <see cref="PreviouslySent"/> overflow in case a player's last ack is more than
     /// <see cref="PvsSystem.DirtyBufferSize"/> ticks behind the current tick.
     /// </summary>
-    public (GameTick Tick, List<PvsData> SentEnts)? Overflow;
+    public (GameTick Tick, List<PvsIndex> SentEnts)? Overflow;
 
     /// <summary>
     /// The client's current visibility mask.
@@ -43,13 +42,13 @@ internal sealed class PvsSession(ICommonSession session)
     /// <summary>
     /// The list that is currently being prepared for sending.
     /// </summary>
-    public List<PvsData>? ToSend;
+    public List<PvsIndex>? ToSend;
 
     /// <summary>
     /// The <see cref="ToSend"/> list from the previous tick. Also caches the current tick that the PVS leave message
     /// should belong to, in case the processing is ever run asynchronously with normal system/game ticking.
     /// </summary>
-    public (GameTick ToTick, List<PvsData> PreviouslySent)? LastSent;
+    public (GameTick ToTick, List<PvsIndex> PreviouslySent)? LastSent;
 
     /// <summary>
     /// Visible chunks, sorted by proximity to the clients's viewers;
@@ -126,10 +125,12 @@ internal sealed class PvsSession(ICommonSession session)
 /// <summary>
 /// Class for storing session-specific information about when an entity was last sent to a player.
 /// </summary>
-internal sealed class PvsData(NetEntity entity) : IEquatable<PvsData>
+/// <remarks>
+/// Size is padded to 16 bytes so
+/// </remarks>
+[StructLayout(LayoutKind.Sequential, Size = 16)]
+internal struct PvsData
 {
-    public readonly NetEntity NetEntity = entity;
-
     /// <summary>
     /// Tick at which this entity was last sent to a player.
     /// </summary>
@@ -146,22 +147,55 @@ internal sealed class PvsData(NetEntity entity) : IEquatable<PvsData>
     /// present in that state.
     /// </summary>
     public GameTick EntityLastAcked;
+}
 
-    public bool Equals(PvsData? other)
-    {
-        DebugTools.Assert((NetEntity != other?.NetEntity) || ReferenceEquals(this, other));
-        return NetEntity == other?.NetEntity;
-    }
+/// <summary>
+/// Specialized struct with the same size as <see cref="PvsData"/> that is used to store metadata in the pinned PVsData array
+/// </summary>
+[StructLayout(LayoutKind.Sequential, Size = 16)]
+internal struct PvsMetadata
+{
+    /// <summary>
+    /// Tick at which this entity was last sent to a player.
+    /// </summary>
+    public NetEntity NetEntity;
 
-    public override int GetHashCode()
+    public GameTick LastModifiedTick;
+    public ushort VisMask;
+    public EntityLifeStage LifeStage;
+#if DEBUG
+    // This struct is padded to a size of 16 so it's aligned to cache boundaries nicely.
+    // We have this extra space that isn't being used,
+    // so I'm opting to use them to make debugging the free list easier.
+    // "Marker" overlaps with the field used by the free list (which occupies the unused memory of PvsMetadata).
+    // So we set it to a bogus value and BAM! Errors are obvious!
+    private byte Pad0;
+    public uint Marker;
+#endif
+}
+
+[StructLayout(LayoutKind.Sequential, Size = 16)]
+internal struct PvsMetadataFreeLink
+{
+#if DEBUG
+    static unsafe PvsMetadataFreeLink()
     {
-        return NetEntity.GetHashCode();
+        DebugTools.Assert(sizeof(PvsMetadataFreeLink) == sizeof(PvsMetadata));
     }
+#endif
+
+    public int Pad0;
+    public int Pad1;
+    public int Pad2;
+    // We offset the NextFree to be at the end of the struct.
+    // This is so that it overlaps with the debug Marker field of PvsMetadata instead of real data.
+    public PvsIndex NextFree;
 }
 
 /// <summary>
 /// Struct for storing information about the current number of entities that are being sent to the player this tick.
 /// Used to enforce pvs budgets.
+/// </summary>
 internal struct PvsBudget
 {
     public int NewLimit;

Robust.Server/GameStates/PvsOverrideSystem.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using Robust.Server.Player;
+using Robust.Shared.Console;
 using Robust.Shared.Enums;
 using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
@@ -12,6 +14,7 @@ namespace Robust.Server.GameStates;
 public sealed class PvsOverrideSystem : EntitySystem
 {
     [Dependency] private readonly IPlayerManager _player = default!;
+    [Dependency] private readonly IConsoleHost _console = default!;
 
     private readonly HashSet<EntityUid> _hasOverride = new();
 
@@ -28,8 +31,64 @@ public sealed class PvsOverrideSystem : EntitySystem
         SubscribeLocalEvent<MapChangedEvent>(OnMapChanged);
         SubscribeLocalEvent<GridInitializeEvent>(OnGridCreated);
         SubscribeLocalEvent<GridRemovalEvent>(OnGridRemoved);
+
+        // TODO console commands for adding/removing overrides?
+        _console.RegisterCommand(
+            "pvs_override_info",
+            Loc.GetString("cmd-pvs-override-info-desc"),
+            "pvs_override_info",
+            GetPvsInfo,
+            GetCompletion);
     }
 
+    #region Console Commands
+
+    /// <summary>
+    /// Debug command for displaying PVS override information.
+    /// </summary>
+    private void GetPvsInfo(IConsoleShell shell, string argstr, string[] args)
+    {
+        if (args.Length != 1)
+        {
+            shell.WriteError(Loc.GetString("cmd-invalid-arg-number-error"));
+            return;
+        }
+
+        if (!NetEntity.TryParse(args[0], out var nuid) || !TryGetEntity(nuid, out var uid))
+        {
+            shell.WriteError(Loc.GetString("cmd-parse-failure-uid"));
+            return;
+        }
+
+        if (!_hasOverride.Contains(uid.Value))
+        {
+            shell.WriteLine(Loc.GetString("cmd-pvs-override-info-empty", ("nuid", args[0])));
+            return;
+        }
+
+        if (GlobalOverride.Contains(uid.Value) || ForceSend.Contains(uid.Value))
+            shell.WriteLine(Loc.GetString("cmd-pvs-override-info-global", ("nuid", args[0])));
+
+        HashSet<ICommonSession> sessions = new();
+        sessions.UnionWith(SessionOverrides.Where(x => x.Value.Contains(uid.Value)).Select(x => x.Key));
+        sessions.UnionWith(SessionForceSend.Where(x => x.Value.Contains(uid.Value)).Select(x => x.Key));
+        if (sessions.Count == 0)
+            return;
+
+        var clients = string.Join(", ", sessions.Select(x => x.ToString()));
+        shell.WriteLine(Loc.GetString("cmd-pvs-override-info-clients", ("nuid", args[0]), ("clients", clients)));
+    }
+
+    private CompletionResult GetCompletion(IConsoleShell shell, string[] args)
+    {
+        if (args.Length != 1)
+            return CompletionResult.Empty;
+
+        return CompletionResult.FromHintOptions(CompletionHelper.NetEntities(args[0], EntityManager), "NetEntity");
+    }
+
+    #endregion
+
     private void OnPlayerStatusChanged(object? sender, SessionStatusEventArgs ev)
     {
         if (ev.NewStatus != SessionStatus.Disconnected)

Robust.Server/GameStates/PvsSystem.Ack.cs

@@ -4,6 +4,7 @@ using System.Runtime.InteropServices;
 using System.Threading;
 using Prometheus;
 using Robust.Shared.Enums;
+using Robust.Shared.GameObjects;
 using Robust.Shared.Log;
 using Robust.Shared.Player;
 using Robust.Shared.Threading;
@@ -105,7 +106,7 @@ internal sealed partial class PvsSystem
     private void ProcessQueuedAck(PvsSession session)
     {
         var ackedTick = session.LastReceivedAck;
-        List<PvsData>? ackedEnts;
+        List<PvsIndex>? ackedEnts;
 
         if (session.Overflow != null && session.Overflow.Value.Tick <= ackedTick)
         {
@@ -125,12 +126,12 @@ internal sealed partial class PvsSystem
         else if (!session.PreviouslySent.TryGetValue(ackedTick, out ackedEnts))
             return;
 
-        foreach (var data in CollectionsMarshal.AsSpan(ackedEnts))
+        foreach (ref var intPtr in CollectionsMarshal.AsSpan(ackedEnts))
         {
-            data.EntityLastAcked = ackedTick;
+            ref var data = ref session.DataMemory.GetRef(intPtr.Index);
+            DebugTools.AssertNotEqual(data.LastSeen, GameTick.Zero);
             DebugTools.Assert(data.LastSeen >= ackedTick); // LastSent may equal ackedTick if the packet was sent reliably.
-            DebugTools.Assert(!session.Entities.TryGetValue(data.NetEntity, out var old)
-                              || ReferenceEquals(data, old));
+            data.EntityLastAcked = ackedTick;
         }
 
         // The client acked a tick. If they requested a full state, this ack happened some time after that, so we can safely set this to false

Robust.Server/GameStates/PvsSystem.DataStorage.cs

@@ -0,0 +1,384 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Threading;
+using Robust.Shared;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Threading;
+using Robust.Shared.Timing;
+using Robust.Shared.Utility;
+
+namespace Robust.Server.GameStates;
+
+// This partial class handles the PvsData memory. This array stores information about when each entity was last sent to
+// each player. This is somewhat faster than using a per-player Dictionary<EntityUid, PvsData>, though it can be less
+// memory efficient.
+internal sealed partial class PvsSystem
+{
+    // This is used for asserts.
+    private HashSet<PvsIndex> _assignedEnts = new();
+
+    /// <summary>
+    /// Recently returned indexes from deleted entities. These get moved to <see cref="_pendingReturns"/> before
+    /// moving back into the free list.
+    /// </summary>
+    private List<PvsIndex> _incomingReturns = new();
+
+    /// <summary>
+    /// Recently returned pointers from deleted entities. These will get returned to the free list
+    /// after a minimum amount of time has passed, to ensure that processing late game-state ack messages doesn't
+    /// write data to deleted entities.
+    /// </summary>
+    private List<PvsIndex> _pendingReturns = new();
+
+    /// <summary>
+    /// Tick at which the <see cref="_pendingReturns"/> were last processed.
+    /// </summary>
+    private GameTick _lastReturn = GameTick.Zero;
+
+    /// <summary>
+    /// Memory region to store <see cref="PvsMetadata"/> instances and the free list.
+    /// </summary>
+    /// <remarks>
+    /// Unused elements form a linked list out of <see cref="PvsMetadataFreeLink"/> elements.
+    /// </remarks>
+    private ResizableMemoryRegion<PvsMetadata> _metadataMemory = default!;
+
+    /// <summary>
+    /// The head of the PVS data free list. This is the first element that will be used if a new one is needed.
+    /// </summary>
+    /// <remarks>
+    /// If the value is <see cref="PvsIndex.Invalid"/>,
+    /// there are no more free elements and the next allocation must expand the memory.
+    /// </remarks>
+    private PvsIndex _dataFreeListHead;
+
+    private WaitHandle? _deletionTask;
+
+    /// <summary>
+    /// Expand the size of <see cref="_metadataMemory"/> (and all session data stores) one iteration.
+    /// </summary>
+    /// <remarks>
+    /// This ensures that we have at least one free list slot.
+    /// </remarks>
+    private void ExpandEntityCapacity()
+    {
+        var initial = _metadataMemory.CurrentSize;
+
+        var entityGrowth = _configManager.GetCVar(CVars.NetPvsEntityGrowth);
+        var newSize = initial + (entityGrowth <= 0 ? initial : entityGrowth);
+        newSize = Math.Min(newSize, _metadataMemory.MaxSize);
+        if (newSize == initial)
+            throw new InvalidOperationException("Out of PVS entity capacity! Increase net.pvs_entity_max!");
+
+        Log.Debug($"Growing PvsData memory from {initial} -> {newSize} entities");
+
+        _metadataMemory.Expand(newSize);
+        foreach (var playerSession in PlayerData.Values)
+        {
+            playerSession.DataMemory.Expand(newSize);
+        }
+
+        var newSlots = _metadataMemory.GetSpan<PvsMetadataFreeLink>()[initial..];
+        InitializeFreeList(newSlots, initial, ref _dataFreeListHead);
+    }
+
+    /// <summary>
+    /// Initialize <see cref="_metadataMemory"/> and the free list.
+    /// </summary>
+    private void InitializePvsArray()
+    {
+        var initialCount = _configManager.GetCVar(CVars.NetPvsEntityInitial);
+        var maxCount = _configManager.GetCVar(CVars.NetPvsEntityMax);
+
+        if (initialCount <= 0 || maxCount <= 0)
+            throw new InvalidOperationException("net.pvs_entity_initial and net.pvs_entity_max must be positive");
+
+        _metadataMemory = new ResizableMemoryRegion<PvsMetadata>(maxCount, initialCount);
+
+        ResetDataMemory();
+    }
+
+    /// <summary>
+    /// Initialize a section of the free list.
+    /// </summary>
+    /// <param name="memory">The section of the free list to initialize.</param>
+    /// <param name="baseOffset">What offset in the total PVS data this section starts at.</param>
+    /// <param name="head">The current head storage of the free list to update.</param>
+    private static void InitializeFreeList(Span<PvsMetadataFreeLink> memory, int baseOffset, ref PvsIndex head)
+    {
+        for (var i = 0; i < memory.Length; i++)
+        {
+            memory[i].NextFree = new PvsIndex(baseOffset + i + 1);
+        }
+
+        memory[^1].NextFree = head;
+        head = new PvsIndex(baseOffset);
+    }
+
+    /// <summary>
+    /// Clear all PVS data. After this function is called,
+    /// <see cref="ResetDataMemory"/> must be called if the system isn't being shut down.
+    /// </summary>
+    private void ClearPvsData()
+    {
+        _leaveTask?.WaitOne();
+        _leaveTask = null;
+
+        _deletionTask?.WaitOne();
+        _deletionTask = null;
+
+        _incomingReturns.Clear();
+        _pendingReturns.Clear();
+        _deletionJob.ToClear.Clear();
+        _assignedEnts.Clear();
+
+        // Remove all pointers stored in any player's PVS send-histories. Required to avoid accidentally writing to
+        // invalid bits of memory while processing late game-state acks. This also forces all players to receive a full
+        // game state, in lieu of sending the required PVS leave messages.
+        foreach (var session in PlayerData.Values)
+        {
+            session.DataMemory.Clear();
+            ForceFullState(session);
+        }
+
+        _metadataMemory.Clear();
+    }
+
+    /// <summary>
+    /// Re-initialize the memory in <see cref="_metadataMemory"/> after it was fully cleared on reset.
+    /// </summary>
+    private void ResetDataMemory()
+    {
+        _dataFreeListHead = PvsIndex.Invalid;
+        InitializeFreeList(_metadataMemory.GetSpan<PvsMetadataFreeLink>(), 0, ref _dataFreeListHead);
+    }
+
+    /// <summary>
+    /// Shrink <see cref="_metadataMemory"/> (and all sessions) back down to initial entity size after clear.
+    /// </summary>
+    private void ShrinkDataMemory()
+    {
+        DebugTools.Assert(EntityManager.EntityCount == 0);
+
+        var initialCount = _configManager.GetCVar(CVars.NetPvsEntityInitial);
+
+        if (initialCount != _metadataMemory.CurrentSize)
+        {
+            Log.Debug($"Shrinking PVS data from {_metadataMemory.CurrentSize} -> {initialCount} entities");
+
+            _metadataMemory.Shrink(initialCount);
+            foreach (var player in PlayerData.Values)
+            {
+                player.DataMemory.Shrink(initialCount);
+            }
+        }
+    }
+
+    /// <summary>
+    /// This method shuffles the entity free list. This is used to avoid accidental / unrealistic cache locality
+    /// in benchmarks.
+    /// </summary>
+    internal void ShufflePointers(int seed)
+    {
+        throw new NotImplementedException();
+        /*List<IntPtr> ptrs = new(_pointerPool);
+        _pointerPool.Clear();
+
+        var rng = new Random(seed);
+        var n = ptrs.Count;
+        while (n > 0)
+        {
+            var k = rng.Next(n);
+            _pointerPool.Push(ptrs[k]);
+            ptrs[k] = ptrs[^1];
+            ptrs.RemoveAt(--n);
+        }*/
+    }
+
+    /// <summary>
+    /// Clear all of this sessions' PvsData for all entities. This effectively means that PVS will act as if the player
+    /// had never been sent information about any entity. Used when returning the player's index offset to the pool.
+    /// </summary>
+    private void ClearPlayerPvsData(PvsSession session)
+    {
+        session.DataMemory.Clear();
+    }
+
+    /// <summary>
+    /// Clear all of this entity' PvsData entries. This effectively means that PVS will act as if no player
+    /// had never been sent information about this entity. Used when returning the entity's index back to the free list.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private void ClearEntityPvsData(PvsIndex index)
+    {
+        foreach (var playerData in PlayerData.Values)
+        {
+            ref var entry = ref playerData.DataMemory.GetRef(index.Index);
+            entry = default;
+        }
+    }
+
+    /// <summary>
+    /// Get the NetEntity associated with a given <see cref="PvsIndex"/>.
+    /// </summary>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private NetEntity IndexToNetEntity(PvsIndex index)
+    {
+        DebugTools.Assert(_assignedEnts.Contains(index));
+        return _metadataMemory.GetRef(index.Index).NetEntity;
+    }
+
+    /// <summary>
+    /// Create a new <see cref="ResizableMemoryRegion{T}"/> suitable for assigning to a new <see cref="PvsSession"/>.
+    /// </summary>
+    private ResizableMemoryRegion<PvsData> CreateSessionDataMemory()
+    {
+        return new ResizableMemoryRegion<PvsData>(_metadataMemory.MaxSize, _metadataMemory.CurrentSize);
+    }
+
+    private static void FreeSessionDataMemory(PvsSession session)
+    {
+        session.DataMemory.Dispose();
+    }
+
+    private void OnEntityAdded(Entity<MetaDataComponent> entity)
+    {
+        DebugTools.Assert(entity.Comp.PvsData.Index == default);
+
+        AssignEntityPointer(entity.Comp);
+    }
+
+    /// <summary>
+    /// Retrieve a free entity index and assign it to an entity.
+    /// </summary>
+    private void AssignEntityPointer(MetaDataComponent meta)
+    {
+        if (_dataFreeListHead == PvsIndex.Invalid)
+        {
+            ExpandEntityCapacity();
+            DebugTools.Assert(_dataFreeListHead != PvsIndex.Invalid);
+        }
+
+        var index = _dataFreeListHead;
+        DebugTools.Assert(_assignedEnts.Add(index));
+        ref var metadata = ref _metadataMemory.GetRef(index.Index);
+        ref var freeLink = ref Unsafe.As<PvsMetadata, PvsMetadataFreeLink>(ref metadata);
+        _dataFreeListHead = freeLink.NextFree;
+
+        // TODO: re-introduce this assert.
+        // DebugTools.AssertEqual(((PvsMetadata*) ptr)->NetEntity, NetEntity.Invalid);
+        DebugTools.AssertNotEqual(meta.NetEntity, NetEntity.Invalid);
+
+        meta.PvsData = index;
+        metadata.NetEntity = meta.NetEntity;
+        metadata.LastModifiedTick = meta.LastModifiedTick;
+        metadata.VisMask = meta.VisibilityMask;
+        metadata.LifeStage = meta.EntityLifeStage;
+#if DEBUG
+        metadata.Marker = uint.MaxValue;
+#endif
+    }
+
+    /// <summary>
+    /// Return an entity's index in the data array back to the free list of available indices.
+    /// </summary>
+    private void OnEntityDeleted(Entity<MetaDataComponent> entity)
+    {
+        var ptr = entity.Comp.PvsData;
+        entity.Comp.PvsData = default;
+
+        if (ptr == default)
+            return;
+
+        _incomingReturns.Add(ptr);
+    }
+
+    /// <summary>
+    /// Immediately return all data indexes back to the pool after flushing all entities.
+    /// </summary>
+    private void AfterEntityFlush()
+    {
+        DebugTools.Assert(EntityManager.EntityCount == 0);
+
+        ClearPvsData();
+        ShrinkDataMemory();
+        ResetDataMemory();
+    }
+
+    /// <summary>
+    /// This update method periodically returns entity indices back to the pool, once we are sure no old
+    /// game state acks will use indices to that entity.
+    /// </summary>
+    private void ProcessDeletions()
+    {
+        var curTick = _gameTiming.CurTick;
+
+        if (curTick < _lastReturn + (uint)ForceAckThreshold + 1)
+            return;
+
+        if (curTick < _lastReturn)
+            throw new InvalidOperationException($"Time travel is not supported");
+
+        _leaveTask?.WaitOne();
+        _leaveTask = null;
+
+        _deletionTask?.WaitOne();
+        _deletionTask = null;
+
+        _lastReturn = curTick;
+
+        foreach (var index in CollectionsMarshal.AsSpan(_deletionJob.ToClear))
+        {
+            ReturnEntity(index);
+        }
+        _deletionJob.ToClear.Clear();
+
+        // Cycle lists.
+        (_deletionJob.ToClear, _pendingReturns, _incomingReturns) = (_pendingReturns, _incomingReturns, _deletionJob.ToClear);
+
+        if (_deletionJob.ToClear.Count == 0)
+            return;
+
+        #if DEBUG
+        foreach (var index in CollectionsMarshal.AsSpan(_deletionJob.ToClear))
+        {
+            DebugTools.Assert(_assignedEnts.Remove(index));
+        }
+        #endif
+
+        if (_deletionJob.ToClear.Count > 16)
+        {
+            _deletionTask = _parallelManager.Process(_deletionJob, _deletionJob.Count);
+            return;
+        }
+
+        foreach (var index in CollectionsMarshal.AsSpan(_deletionJob.ToClear))
+        {
+            ClearEntityPvsData(index);
+        }
+    }
+
+    private void ReturnEntity(PvsIndex index)
+    {
+        DebugTools.Assert(!_assignedEnts.Contains(index));
+        ref var freeLink = ref _metadataMemory.GetRef<PvsMetadataFreeLink>(index.Index);
+        freeLink.NextFree = _dataFreeListHead;
+        _dataFreeListHead = index;
+    }
+
+    private record struct PvsDeletionsJob(PvsSystem _pvs) : IParallelRobustJob
+    {
+        public int BatchSize => 8;
+        private PvsSystem _pvs = _pvs;
+        public List<PvsIndex> ToClear = new();
+
+        public int Count => ToClear.Count;
+
+        public void Execute(int index)
+        {
+            _pvs.ClearEntityPvsData(ToClear[index]);
+        }
+    }
+}

Robust.Server/GameStates/PvsSystem.Dirty.cs

@@ -49,6 +49,12 @@ namespace Robust.Server.GameStates
 
         private void OnEntityDirty(Entity<MetaDataComponent> uid)
         {
+            if (uid.Comp.PvsData != default)
+            {
+                ref var meta = ref _metadataMemory.GetRef(uid.Comp.PvsData.Index);
+                meta.LastModifiedTick = uid.Comp.EntityLastModifiedTick;
+            }
+
             if (!_addEntities[_currentIndex].Contains(uid))
                 _dirtyEntities[_currentIndex].Add(uid);
         }

Robust.Server/GameStates/PvsSystem.Entity.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Diagnostics;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Map.Components;
@@ -25,11 +26,6 @@ internal sealed partial class PvsSystem
     {
         var meta = ev.Entity.Comp;
 
-        foreach (var sessionData in PlayerData.Values)
-        {
-            sessionData.Entities.Remove(meta.NetEntity);
-        }
-
         _deletedEntities.Add(meta.NetEntity);
         _deletedTick.Add(_gameTiming.CurTick);
         RemoveEntityFromChunk(ev.Entity.Owner, meta);
@@ -111,4 +107,14 @@ internal sealed partial class PvsSystem
         DebugTools.AssertNull(xform.MapUid);
         AssertNullspace(xform.ParentUid);
     }
+
+    internal void SyncMetadata(MetaDataComponent meta)
+    {
+        if (meta.PvsData == default)
+            return;
+
+        ref var ptr = ref _metadataMemory.GetRef(meta.PvsData.Index);
+        ptr.VisMask = meta.VisibilityMask;
+        ptr.LifeStage = meta.EntityLifeStage;
+    }
 }

Robust.Server/GameStates/PvsSystem.Leave.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Threading;
 using Prometheus;
@@ -47,12 +48,14 @@ internal sealed partial class PvsSystem
             return;
 
         var (toTick, lastSent) = session.LastSent.Value;
-        foreach (var data in CollectionsMarshal.AsSpan(lastSent))
+
+        foreach (var intPtr in CollectionsMarshal.AsSpan(lastSent))
         {
+            ref var data = ref session.DataMemory.GetRef(intPtr.Index);
             if (data.LastSeen == toTick)
                 continue;
 
-            session.LeftView.Add(data.NetEntity);
+            session.LeftView.Add(IndexToNetEntity(intPtr));
             data.LastLeftView = toTick;
         }
 

Robust.Server/GameStates/PvsSystem.Overrides.cs

@@ -1,4 +1,6 @@
 using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Timing;
 
@@ -8,21 +10,23 @@ namespace Robust.Server.GameStates;
 // range/chunk restrictions.
 internal sealed partial class PvsSystem
 {
-    private readonly List<Entity<MetaDataComponent>> _cachedForceOverride = new();
-    private readonly List<Entity<MetaDataComponent>> _cachedGlobalOverride = new();
+    private readonly List<PvsChunk.ChunkEntity> _cachedForceOverride = new();
+    private readonly List<PvsChunk.ChunkEntity> _cachedGlobalOverride = new();
 
     private readonly HashSet<EntityUid> _forceOverrideSet = new();
     private readonly HashSet<EntityUid> _globalOverrideSet = new();
 
     private void AddAllOverrides(PvsSession session)
     {
+        var mask = session.VisMask;
         var fromTick = session.FromTick;
         RaiseExpandEvent(session, fromTick);
 
-        foreach (var entity in _cachedGlobalOverride)
+        foreach (ref var ent in CollectionsMarshal.AsSpan(_cachedGlobalOverride))
         {
-            if (!AddEntity(session, entity, fromTick))
-                break;
+            ref var meta = ref _metadataMemory.GetRef(ent.Ptr.Index);
+            if ((mask & meta.VisMask) == meta.VisMask)
+                AddEntity(session, ref ent, ref meta, fromTick);
         }
 
         if (!_pvsOverride.SessionOverrides.TryGetValue(session.Session, out var sessionOverrides))
@@ -42,10 +46,13 @@ internal sealed partial class PvsSystem
         // Ignore PVS budgets
         session.Budget = new() {NewLimit = int.MaxValue, EnterLimit = int.MaxValue};
 
+        var mask = session.VisMask;
         var fromTick = session.FromTick;
-        foreach (var entity in _cachedForceOverride)
+        foreach (ref var ent in CollectionsMarshal.AsSpan(_cachedForceOverride))
         {
-            AddEntity(session, entity, fromTick);
+            ref var meta = ref _metadataMemory.GetRef(ent.Ptr.Index);
+            if ((mask & meta.VisMask) == meta.VisMask)
+                AddEntity(session, ref ent, ref meta, fromTick);
         }
 
         foreach (var uid in session.Viewers)
@@ -156,7 +163,7 @@ internal sealed partial class PvsSystem
 
     private bool CacheOverrideParents(
         EntityUid uid,
-        List<Entity<MetaDataComponent>> list,
+        List<PvsChunk.ChunkEntity> list,
         HashSet<EntityUid> set,
         out TransformComponent xform)
     {
@@ -175,11 +182,11 @@ internal sealed partial class PvsSystem
             return false;
         }
 
-        list.Add((uid, meta));
+        list.Add(new(uid, meta));
         return true;
     }
 
-    private void CacheOverrideChildren(TransformComponent xform, List<Entity<MetaDataComponent>> list, HashSet<EntityUid> set)
+    private void CacheOverrideChildren(TransformComponent xform, List<PvsChunk.ChunkEntity> list, HashSet<EntityUid> set)
     {
         foreach (var child in xform._children)
         {
@@ -190,7 +197,7 @@ internal sealed partial class PvsSystem
             }
 
             if (set.Add(child))
-                list.Add((child, _metaQuery.GetComponent(child)));
+                list.Add(new(child, _metaQuery.GetComponent(child)));
 
             CacheOverrideChildren(childXform, list, set);
         }

Robust.Server/GameStates/PvsSystem.Pooling.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using Microsoft.Extensions.ObjectPool;
 using Robust.Shared.GameObjects;
@@ -15,8 +16,8 @@ internal sealed partial class PvsSystem
     /// </summary>
     private const int MaxVisPoolSize = 1024;
 
-    private readonly ObjectPool<List<PvsData>> _entDataListPool
-        = new DefaultObjectPool<List<PvsData>>(new ListPolicy<PvsData>(), MaxVisPoolSize);
+    private readonly ObjectPool<List<PvsIndex>> _entDataListPool
+        = new DefaultObjectPool<List<PvsIndex>>(new ListPolicy<PvsIndex>(), MaxVisPoolSize);
 
     private readonly ObjectPool<HashSet<EntityUid>> _uidSetPool
         = new DefaultObjectPool<HashSet<EntityUid>>(new SetPolicy<EntityUid>(), MaxVisPoolSize);

Robust.Server/GameStates/PvsSystem.Session.cs

@@ -72,7 +72,10 @@ internal sealed partial class PvsSystem
     private PvsSession GetOrNewPvsSession(ICommonSession session)
     {
         if (!PlayerData.TryGetValue(session, out var pvsSession))
-            PlayerData[session] = pvsSession = new(session);
+        {
+            var memoryRegion = CreateSessionDataMemory();
+            PlayerData[session] = pvsSession = new(session, memoryRegion);
+        }
 
         return pvsSession;
     }
@@ -193,6 +196,5 @@ internal sealed partial class PvsSystem
 
         session.PreviouslySent.Clear();
         session.LastSent = null;
-        session.Entities.Clear();
     }
 }

Robust.Server/GameStates/PvsSystem.ToSendSet.cs

@@ -61,71 +61,91 @@ internal sealed partial class PvsSystem
         for (var i = 0; i < limit; i++)
         {
             var ent = span[i];
-            if ((mask & ent.Comp.VisibilityMask) != ent.Comp.VisibilityMask)
+            ref var meta = ref _metadataMemory.GetRef(ent.Ptr.Index);
+
+            if ((mask & meta.VisMask) != meta.VisMask)
                 continue;
 
             // TODO PVS improve this somehow
             // Having entities "leave" pvs view just because the pvs entry budget was exceeded sucks.
             // This probably requires changing client game state manager to support receiving entities with unknown parents.
             // Probably needs to do something similar to pending net entity states, but for entity spawning.
-            if (!AddEntity(session, ent, fromTick))
+            if (!AddEntity(session, ref ent, ref meta, fromTick))
                 limit = directChildren;
         }
     }
 
+    /// <summary>
+    /// Attempt to add an entity to the to-send lists, while respecting pvs budgets.
+    /// </summary>
+    /// <returns>Returns false if the entity would exceed the client's PVS budget.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private bool AddEntity(PvsSession session, ref PvsChunk.ChunkEntity ent, ref PvsMetadata meta,
+        GameTick fromTick)
+    {
+        DebugTools.Assert(fromTick < _gameTiming.CurTick);
+        ref var data = ref session.DataMemory.GetRef(ent.Ptr.Index);
+
+        if (data.LastSeen == _gameTiming.CurTick)
+            return true;
+
+        if (meta.LifeStage >= EntityLifeStage.Terminating)
+        {
+            Log.Error($"Attempted to send deleted entity: {ToPrettyString(ent.Uid)}");
+            EntityManager.QueueDeleteEntity(ent.Uid);
+            return true;
+        }
+
+        var (entered,budgetExceeded) = IsEnteringPvsRange(ref data, fromTick, ref session.Budget);
+
+        if (budgetExceeded)
+            return false;
+
+        data.LastSeen = _gameTiming.CurTick;
+        session.ToSend!.Add(ent.Ptr);
+
+        if (session.RequestedFull)
+        {
+            var state = GetFullEntityState(session.Session, ent.Uid, ent.Meta);
+            session.States.Add(state);
+            return true;
+        }
+
+        if (entered)
+        {
+            var state = GetEntityState(session.Session, ent.Uid, data.EntityLastAcked, ent.Meta);
+            session.States.Add(state);
+            return true;
+        }
+
+        if (meta.LastModifiedTick <= fromTick)
+            return true;
+
+        var entState = GetEntityState(session.Session, ent.Uid, fromTick , ent.Meta);
+
+        if (!entState.Empty)
+            session.States.Add(entState);
+
+        return true;
+    }
+
     /// <summary>
     /// Attempt to add an entity to the to-send lists, while respecting pvs budgets.
     /// </summary>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private bool AddEntity(PvsSession session, Entity<MetaDataComponent> entity, GameTick fromTick)
     {
-        var nuid = entity.Comp.NetEntity;
-        ref var data = ref CollectionsMarshal.GetValueRefOrAddDefault(session.Entities, nuid, out var exists);
-        if (!exists)
-            data = new(nuid);
+        DebugTools.Assert(fromTick < _gameTiming.CurTick);
+        ref var data = ref session.DataMemory.GetRef(entity.Comp.PvsData.Index);
 
-        if (entity.Comp.Deleted)
-        {
-            Log.Error($"Attempted to send deleted entity: {ToPrettyString(entity, entity)}");
-            session.Entities.Remove(entity.Comp.NetEntity);
-            return false;
-        }
-
-        DebugTools.AssertEqual(data!.NetEntity, entity.Comp.NetEntity);
         if (data.LastSeen == _gameTiming.CurTick)
             return true;
 
-        var (entered,budgetExceeded) = IsEnteringPvsRange(data, fromTick, ref session.Budget);
+        var (entered,budgetExceeded) = IsEnteringPvsRange(ref data, fromTick, ref session.Budget);
 
         if (budgetExceeded)
             return false;
 
-        if (!AddToSendList(session, data, entity, fromTick, entered))
-            return false;
-
-        DebugTools.AssertNotEqual(data.LastSeen, GameTick.Zero);
-        return true;
-    }
-
-    /// <summary>
-    /// This method adds an entity to the list of visible entities, updates the last-seen tick, and computes any
-    /// required game states.
-    /// </summary>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private bool AddToSendList(PvsSession session, PvsData data, Entity<MetaDataComponent> entity, GameTick fromTick,
-        bool entered)
-    {
-        DebugTools.Assert(fromTick < _gameTiming.CurTick);
-
-        // ReSharper disable once ConditionIsAlwaysTrueOrFalseAccordingToNullableAPIContract
-        if (data == null)
-        {
-            Log.Error($"Encountered null EntityData.");
-            return false;
-        }
-
-        DebugTools.AssertNotEqual(data.LastSeen, _gameTiming.CurTick);
-        DebugTools.Assert(data.EntityLastAcked <= fromTick || fromTick == GameTick.Zero);
         var (uid, meta) = entity;
 
         // ReSharper disable once ConditionIsAlwaysTrueOrFalseAccordingToNullableAPIContract
@@ -147,19 +167,18 @@ internal sealed partial class PvsSystem
         }
 
         data.LastSeen = _gameTiming.CurTick;
-        session.ToSend!.Add(data);
-        EntityState state;
+        session.ToSend!.Add(entity.Comp.PvsData);
 
         if (session.RequestedFull)
         {
-            state = GetFullEntityState(session.Session, uid, meta);
+            var state = GetFullEntityState(session.Session, uid, meta);
             session.States.Add(state);
             return true;
         }
 
         if (entered)
         {
-            state = GetEntityState(session.Session, uid, data.EntityLastAcked, meta);
+            var state = GetEntityState(session.Session, uid, data.EntityLastAcked, meta);
             session.States.Add(state);
             return true;
         }
@@ -167,10 +186,10 @@ internal sealed partial class PvsSystem
         if (meta.EntityLastModifiedTick <= fromTick)
             return true;
 
-        state = GetEntityState(session.Session, uid, fromTick , meta);
+        var entState = GetEntityState(session.Session, uid, fromTick , meta);
 
-        if (!state.Empty)
-            session.States.Add(state);
+        if (!entState.Empty)
+            session.States.Add(entState);
 
         return true;
     }
@@ -181,7 +200,7 @@ internal sealed partial class PvsSystem
     /// </summary>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private (bool Entering, bool BudgetExceeded) IsEnteringPvsRange(
-        PvsData data,
+        ref PvsData data,
         GameTick fromTick,
         ref PvsBudget budget)
     {

Robust.Server/GameStates/PvsSystem.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Numerics;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading.Tasks;
@@ -15,6 +16,8 @@ using Robust.Server.Replays;
 using Robust.Shared;
 using Robust.Shared.Configuration;
 using Robust.Shared.GameObjects;
+using Robust.Shared.GameStates;
+using Robust.Shared.IoC;
 using Robust.Shared.Log;
 using Robust.Shared.Map;
 using Robust.Shared.Network;
@@ -75,6 +78,7 @@ internal sealed partial class PvsSystem : EntitySystem
     private PvsAckJob _ackJob;
     private PvsChunkJob _chunkJob;
     private PvsLeaveJob _leaveJob;
+    private PvsDeletionsJob _deletionJob;
 
     private EntityQuery<EyeComponent> _eyeQuery;
     private EntityQuery<MetaDataComponent> _metaQuery;
@@ -110,6 +114,10 @@ internal sealed partial class PvsSystem : EntitySystem
     {
         base.Initialize();
 
+        if (Marshal.SizeOf<PvsMetadata>() != Marshal.SizeOf<PvsData>())
+            throw new Exception($"Pvs struct sizes must match");
+
+        _deletionJob = new PvsDeletionsJob(this);
         _leaveJob = new PvsLeaveJob(this);
         _chunkJob = new PvsChunkJob(this);
         _ackJob = new PvsAckJob(this);
@@ -125,6 +133,9 @@ internal sealed partial class PvsSystem : EntitySystem
 
         _playerManager.PlayerStatusChanged += OnPlayerStatusChanged;
         _transform.OnGlobalMoveEvent += OnEntityMove;
+        EntityManager.EntityAdded += OnEntityAdded;
+        EntityManager.EntityDeleted += OnEntityDeleted;
+        EntityManager.AfterEntityFlush += AfterEntityFlush;
 
         Subs.CVar(_configManager, CVars.NetPVS, SetPvs, true);
         Subs.CVar(_configManager, CVars.NetMaxUpdateRange, OnViewsizeChanged, true);
@@ -135,10 +146,10 @@ internal sealed partial class PvsSystem : EntitySystem
 
         _serverGameStateManager.ClientAck += OnClientAck;
         _serverGameStateManager.ClientRequestFull += OnClientRequestFull;
+        _parallelMgr.ParallelCountChanged += ResetParallelism;
 
         InitializeDirty();
-
-        _parallelMgr.ParallelCountChanged += ResetParallelism;
+        InitializePvsArray();
     }
 
     public override void Shutdown()
@@ -147,15 +158,22 @@ internal sealed partial class PvsSystem : EntitySystem
 
         _playerManager.PlayerStatusChanged -= OnPlayerStatusChanged;
         _transform.OnGlobalMoveEvent -= OnEntityMove;
+        EntityManager.EntityAdded -= OnEntityAdded;
+        EntityManager.EntityDeleted -= OnEntityDeleted;
+        EntityManager.AfterEntityFlush -= AfterEntityFlush;
 
         _parallelMgr.ParallelCountChanged -= ResetParallelism;
 
         _serverGameStateManager.ClientAck -= OnClientAck;
         _serverGameStateManager.ClientRequestFull -= OnClientRequestFull;
 
+        ClearPvsData();
         ShutdownDirty();
-        _leaveTask?.WaitOne();
-        _leaveTask = null;
+    }
+
+    public override void Update(float frameTime)
+    {
+        ProcessDeletions();
     }
 
     /// <summary>
@@ -253,6 +271,7 @@ internal sealed partial class PvsSystem : EntitySystem
         session.LastReceivedAck = _gameTiming.CurTick;
         session.RequestedFull = true;
         ClearSendHistory(session);
+        ClearPlayerPvsData(session);
     }
 
     private void OnViewsizeChanged(float value)
@@ -342,19 +361,20 @@ internal sealed partial class PvsSystem : EntitySystem
     {
         var toSend = pvsSession.ToSend;
         var toSendSet = new HashSet<NetEntity>(toSend!.Count);
-        foreach (var data in toSend)
+
+        foreach (var intPtr in toSend)
         {
-            toSendSet.Add(data.NetEntity);
+            toSendSet.Add(IndexToNetEntity(intPtr));
         }
         DebugTools.AssertEqual(toSend.Count, toSendSet.Count);
 
-        foreach (var data in CollectionsMarshal.AsSpan(toSend))
+        foreach (var intPtr in CollectionsMarshal.AsSpan(toSend))
         {
+            ref var data = ref pvsSession.DataMemory.GetRef(intPtr.Index);
             DebugTools.AssertEqual(data.LastSeen, _gameTiming.CurTick);
-            DebugTools.Assert(ReferenceEquals(data, pvsSession.Entities[data.NetEntity]));
 
             // if an entity is visible, its parents should always be visible.
-            if (_xformQuery.GetComponent(GetEntity(data.NetEntity)).ParentUid is not {Valid: true} pUid)
+            if (_xformQuery.GetComponent(GetEntity(IndexToNetEntity(intPtr))).ParentUid is not {Valid: true} pUid)
                 continue;
 
             DebugTools.Assert(toSendSet.Contains(GetNetEntity(pUid)),
@@ -362,11 +382,11 @@ internal sealed partial class PvsSystem : EntitySystem
         }
 
         pvsSession.PreviouslySent.TryGetValue(_gameTiming.CurTick - 1, out var lastSent);
-        foreach (var data in CollectionsMarshal.AsSpan(lastSent))
+        foreach (var intPtr in CollectionsMarshal.AsSpan(lastSent))
         {
-            DebugTools.Assert(!pvsSession.Entities.TryGetValue(data.NetEntity, out var old) || ReferenceEquals(data, old));
+            ref var data = ref pvsSession.DataMemory.GetRef(intPtr.Index);
             DebugTools.Assert(data.LastSeen != GameTick.Zero);
-            DebugTools.AssertEqual(toSendSet.Contains(data.NetEntity), data.LastSeen == _gameTiming.CurTick);
+            DebugTools.AssertEqual(toSendSet.Contains(IndexToNetEntity(intPtr)), data.LastSeen == _gameTiming.CurTick);
             DebugTools.Assert(data.LastSeen == _gameTiming.CurTick
                               || data.LastSeen == _gameTiming.CurTick - 1);
         }
@@ -409,7 +429,10 @@ internal sealed partial class PvsSystem : EntitySystem
         foreach (var session in _disconnected)
         {
             if (PlayerData.Remove(session, out var pvsSession))
+            {
                 ClearSendHistory(pvsSession);
+                FreeSessionDataMemory(pvsSession);
+            }
         }
 
         var ackJob = ProcessQueuedAcks();

Robust.Server/Replays/ReplayRecordingManager.cs

@@ -5,6 +5,7 @@ using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
 using Robust.Shared.Replays;
 using Robust.Shared.Timing;
+using Robust.Shared.Utility;
 
 namespace Robust.Server.Replays;
 
@@ -13,7 +14,7 @@ internal sealed class ReplayRecordingManager : SharedReplayRecordingManager, ISe
     [Dependency] private readonly IEntitySystemManager _sysMan = default!;
 
     private PvsSystem _pvs = default!;
-    private PvsSession _pvsSession = new(default!) { DisableCulling = true };
+    private PvsSession _pvsSession = new(default!, new ResizableMemoryRegion<PvsData>(1)) { DisableCulling = true };
 
     public override void Initialize()
     {

Robust.Shared.Maths/MathHelper.cs

@@ -697,6 +697,32 @@ namespace Robust.Shared.Maths
 
         #endregion
 
+        /// <summary>
+        /// Round up (ceiling) a value to a multiple of a known power of two.
+        /// </summary>
+        /// <param name="value">The value to round up.</param>
+        /// <param name="powerOfTwo">
+        /// The power of two to round up to a multiple of. The result is undefined if this is not a power of two.
+        /// </param>
+        /// <remarks>
+        /// The result is undefined if either value is negative.
+        /// </remarks>
+        /// <typeparam name="T">The type of integer to operate on.</typeparam>
+        /// <example>
+        /// <code>
+        /// MathHelper.CeilMultiplyPowerOfTwo(5, 4) // 8
+        /// MathHelper.CeilMultiplyPowerOfTwo(4, 4) // 4
+        /// MathHelper.CeilMultiplyPowerOfTwo(8, 4) // 8
+        /// </code>
+        /// </example>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static T CeilMultipleOfPowerOfTwo<T>(T value, T powerOfTwo) where T : IBinaryInteger<T>
+        {
+            var mask = powerOfTwo - T.One;
+            var remainder = value & mask;
+            return remainder == T.Zero ? value : (value | mask) + T.One;
+        }
+
         #endregion Public Members
     }
 }

Robust.Shared/Audio/Systems/SharedAudioSystem.cs

@@ -266,7 +266,7 @@ public abstract partial class SharedAudioSystem : EntitySystem
         return sound == null ? null : PlayGlobal(GetSound(sound), recipient, sound.Params);
     }
 
-    public abstract void LoadStream<T>(AudioComponent component, T stream);
+    public abstract void LoadStream<T>(Entity<AudioComponent> entity, T stream);
 
     /// <summary>
     /// Play an audio file globally, without position.

Robust.Shared/CVars.cs

@@ -183,6 +183,30 @@ namespace Robust.Shared
         public static readonly CVarDef<bool> NetPVS =
             CVarDef.Create("net.pvs", true, CVar.ARCHIVE | CVar.REPLICATED | CVar.SERVER);
 
+        /// <summary>
+        /// Size increments for the automatic growth of Pvs' entity data storage. 0 will increase it by factors of 2
+        /// </summary>
+        public static readonly CVarDef<int> NetPvsEntityGrowth =
+            CVarDef.Create("net.pvs_entity_growth", 1 << 16, CVar.ARCHIVE | CVar.SERVERONLY);
+
+        /// <summary>
+        /// Initial size of PVS' entity data storage.
+        /// </summary>
+        public static readonly CVarDef<int> NetPvsEntityInitial =
+            CVarDef.Create("net.pvs_entity_initial", 1 << 16, CVar.ARCHIVE | CVar.SERVERONLY);
+
+        /// <summary>
+        /// Maximum ever size of PVS' entity data storage.
+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// Arbitrarily set to a default of 16 million entities.
+        /// Increasing this parameter does not increase real memory usage, only virtual.
+        /// </para>
+        /// </remarks>
+        public static readonly CVarDef<int> NetPvsEntityMax =
+            CVarDef.Create("net.pvs_entity_max", 1 << 24, CVar.ARCHIVE | CVar.SERVERONLY);
+
         /// <summary>
         /// If false, this will run more parts of PVS synchronously. This will generally slow it down, can be useful
         /// for collecting tick timing metrics.
@@ -1031,6 +1055,12 @@ namespace Robust.Shared
          * AUDIO
          */
 
+        /// <summary>
+        /// Default limit for concurrently playing an audio file.
+        /// </summary>
+        public static readonly CVarDef<int> AudioDefaultConcurrent =
+            CVarDef.Create("audio.default_concurrent", 16, CVar.CLIENTONLY | CVar.ARCHIVE);
+
         public static readonly CVarDef<int> AudioAttenuation =
             CVarDef.Create("audio.attenuation", (int) Attenuation.LinearDistanceClamped, CVar.REPLICATED | CVar.ARCHIVE);
 

Robust.Shared/Containers/BaseContainer.cs

@@ -71,46 +71,6 @@ namespace Robust.Shared.Containers
         [DataField("showEnts")]
         public bool ShowContents { get; set; }
 
-        [Obsolete("Use container system method")]
-        public bool Insert(
-            EntityUid toinsert,
-            IEntityManager? entMan = null,
-            TransformComponent? transform = null,
-            TransformComponent? ownerTransform = null,
-            MetaDataComponent? meta = null,
-            PhysicsComponent? physics = null,
-            bool force = false)
-        {
-            IoCManager.Resolve(ref entMan);
-            return entMan.System<SharedContainerSystem>().Insert((toinsert, transform, meta, physics), this, ownerTransform, force);
-        }
-
-        /// <summary>
-        /// Whether the given entity can be inserted into this container.
-        /// </summary>
-        /// <param name="assumeEmpty">Whether to assume that the container is currently empty.</param>
-        protected internal virtual bool CanInsert(EntityUid toInsert, bool assumeEmpty, IEntityManager entMan) => true;
-
-        [Obsolete("Use container system method")]
-        public bool Remove(
-            EntityUid toRemove,
-            IEntityManager? entMan = null,
-            TransformComponent? xform = null,
-            MetaDataComponent? meta = null,
-            bool reparent = true,
-            bool force = false,
-            EntityCoordinates? destination = null,
-            Angle? localRotation = null
-        )
-        {
-            IoCManager.Resolve(ref entMan);
-            return entMan.System<SharedContainerSystem>().Remove((toRemove, xform, meta), this, reparent, force, destination, localRotation);
-        }
-
-        [Obsolete("Use container system method")]
-        public void ForceRemove(EntityUid toRemove, IEntityManager? entMan = null, MetaDataComponent? meta = null)
-            => Remove(toRemove, entMan, meta: meta, reparent: false, force: true);
-
         /// <summary>
         /// Checks if the entity is contained in this container.
         /// This is not recursive, so containers of children are not checked.
@@ -120,18 +80,10 @@ namespace Robust.Shared.Containers
         public abstract bool Contains(EntityUid contained);
 
         /// <summary>
-        /// Clears the container and marks it as deleted.
+        /// Whether the given entity can be inserted into this container.
         /// </summary>
-        [Obsolete("use system method")]
-        public void Shutdown(IEntityManager? entMan = null, INetManager? _ = null)
-        {
-            IoCManager.Resolve(ref entMan);
-            entMan.System<SharedContainerSystem>().ShutdownContainer(this);
-        }
-
-        /// <inheritdoc />
-        [Access(typeof(SharedContainerSystem))]
-        protected internal abstract void InternalShutdown(IEntityManager entMan, SharedContainerSystem system, bool isClient);
+        /// <param name="assumeEmpty">Whether to assume that the container is currently empty.</param>
+        protected internal virtual bool CanInsert(EntityUid toInsert, bool assumeEmpty, IEntityManager entMan) => true;
 
         /// <summary>
         /// Implement to store the reference in whatever form you want
@@ -148,5 +100,14 @@ namespace Robust.Shared.Containers
         /// <param name="entMan"></param>
         [Access(typeof(SharedContainerSystem))]
         protected internal abstract void InternalRemove(EntityUid toRemove, IEntityManager entMan);
+
+        /// <summary>
+        /// Implement to clear the container and mark it as deleted.
+        /// </summary>
+        /// <param name="entMan"></param>
+        /// <param name="system"></param>
+        /// <param name=isClient"></param>
+        [Access(typeof(SharedContainerSystem))]
+        protected internal abstract void InternalShutdown(IEntityManager entMan, SharedContainerSystem system, bool isClient);
     }
 }

Robust.Shared/ContentPack/AssemblyTypeChecker.Parsing.cs

@@ -32,7 +32,7 @@ namespace Robust.Shared.ContentPack
             String("short").ThenReturn(PrimitiveTypeCode.Int16);
 
         private static readonly Parser<char, PrimitiveTypeCode> UInt16TypeParser =
-            String("ushort").ThenReturn(PrimitiveTypeCode.UInt32);
+            String("ushort").ThenReturn(PrimitiveTypeCode.UInt16);
 
         private static readonly Parser<char, PrimitiveTypeCode> Int32TypeParser =
             String("int").ThenReturn(PrimitiveTypeCode.Int32);

Robust.Shared/ContentPack/Sandbox.yml

@@ -84,12 +84,146 @@ Types:
       - "bool get_HasContents()"
   Lidgren.Network:
     NetBuffer:
-      All: True
+      Methods:
+      - "byte[] get_Data()"
+      - "void set_Data(byte[])"
+      - "int get_LengthBytes()"
+      - "void set_LengthBytes(int)"
+      - "int get_LengthBits()"
+      - "void set_LengthBits(int)"
+      - "long get_Position()"
+      - "void set_Position(long)"
+      - "int get_PositionInBytes()"
+      - "byte[] PeekDataBuffer()"
+      - "bool PeekBoolean()"
+      - "byte PeekByte()"
+      - "sbyte PeekSByte()"
+      - "byte PeekByte(int)"
+      - "System.Span`1<byte> PeekBytes(System.Span`1<byte>)"
+      - "byte[] PeekBytes(int)"
+      - "void PeekBytes(byte[], int, int)"
+      - "short PeekInt16()"
+      - "ushort PeekUInt16()"
+      - "int PeekInt32()"
+      - "int PeekInt32(int)"
+      - "uint PeekUInt32()"
+      - "uint PeekUInt32(int)"
+      - "ulong PeekUInt64()"
+      - "long PeekInt64()"
+      - "ulong PeekUInt64(int)"
+      - "long PeekInt64(int)"
+      - "float PeekFloat()"
+      - "System.Half PeekHalf()"
+      - "float PeekSingle()"
+      - "double PeekDouble()"
+      - "string PeekString()"
+      - "int PeekStringSize()"
+      - "bool ReadBoolean()"
+      - "byte ReadByte()"
+      - "bool ReadByte(ref byte)"
+      - "sbyte ReadSByte()"
+      - "byte ReadByte(int)"
+      - "System.Span`1<byte> ReadBytes(System.Span`1<byte>)"
+      - "byte[] ReadBytes(int)"
+      - "bool ReadBytes(int, ref byte[])"
+      - "bool TryReadBytes(System.Span`1<byte>)"
+      - "void ReadBytes(byte[], int, int)"
+      - "void ReadBits(System.Span`1<byte>, int)"
+      - "void ReadBits(byte[], int, int)"
+      - "short ReadInt16()"
+      - "ushort ReadUInt16()"
+      - "int ReadInt32()"
+      - "bool ReadInt32(ref int)"
+      - "int ReadInt32(int)"
+      - "uint ReadUInt32()"
+      - "bool ReadUInt32(ref uint)"
+      - "uint ReadUInt32(int)"
+      - "ulong ReadUInt64()"
+      - "long ReadInt64()"
+      - "ulong ReadUInt64(int)"
+      - "long ReadInt64(int)"
+      - "float ReadFloat()"
+      - "System.Half ReadHalf()"
+      - "float ReadSingle()"
+      - "bool ReadSingle(ref float)"
+      - "double ReadDouble()"
+      - "uint ReadVariableUInt32()"
+      - "bool ReadVariableUInt32(ref uint)"
+      - "int ReadVariableInt32()"
+      - "long ReadVariableInt64()"
+      - "ulong ReadVariableUInt64()"
+      - "float ReadSignedSingle(int)"
+      - "float ReadUnitSingle(int)"
+      - "float ReadRangedSingle(float, float, int)"
+      - "int ReadRangedInteger(int, int)"
+      - "long ReadRangedInteger(long, long)"
+      - "string ReadString()"
+      - "bool ReadString(ref string)"
+      - "double ReadTime(Lidgren.Network.NetConnection, bool)"
+      - "System.Net.IPEndPoint ReadIPEndPoint()"
+      - "void SkipPadBits()"
+      - "void ReadPadBits()"
+      - "void SkipPadBits(int)"
+      - "void EnsureBufferSize(int)"
+      - "void Write(bool)"
+      - "void Write(byte)"
+      - "void WriteAt(int, byte)"
+      - "void Write(sbyte)"
+      - "void Write(byte, int)"
+      - "void Write(byte[])"
+      - "void Write(System.ReadOnlySpan`1<byte>)"
+      - "void Write(byte[], int, int)"
+      - "void Write(ushort)"
+      - "void WriteAt(int, ushort)"
+      - "void Write(ushort, int)"
+      - "void Write(short)"
+      - "void WriteAt(int, short)"
+      - "void Write(int)"
+      - "void WriteAt(int, int)"
+      - "void Write(uint)"
+      - "void WriteAt(int, uint)"
+      - "void Write(uint, int)"
+      - "void Write(int, int)"
+      - "void Write(ulong)"
+      - "void WriteAt(int, ulong)"
+      - "void Write(ulong, int)"
+      - "void Write(long)"
+      - "void Write(long, int)"
+      - "void Write(System.Half)"
+      - "void Write(float)"
+      - "void Write(double)"
+      - "int WriteVariableUInt32(uint)"
+      - "int WriteVariableInt32(int)"
+      - "int WriteVariableInt64(long)"
+      - "int WriteVariableUInt64(ulong)"
+      - "void WriteSignedSingle(float, int)"
+      - "void WriteUnitSingle(float, int)"
+      - "void WriteRangedSingle(float, float, float, int)"
+      - "int WriteRangedInteger(int, int, int)"
+      - "int WriteRangedInteger(long, long, long)"
+      - "void Write(string)"
+      - "void Write(System.Net.IPEndPoint)"
+      - "void WriteTime(bool)"
+      - "void WriteTime(double, bool)"
+      - "void WritePadBits()"
+      - "void WritePadBits(int)"
+      - "void Write(Lidgren.Network.NetBuffer)"
+      - "void Zero(int)"
+      - "void .ctor()"
     NetDeliveryMethod: { }
     NetIncomingMessage:
-      All: True
+      Methods:
+      - "Lidgren.Network.NetIncomingMessageType get_MessageType()"
+      - "Lidgren.Network.NetDeliveryMethod get_DeliveryMethod()"
+      - "int get_SequenceChannel()"
+      - "System.Net.IPEndPoint get_SenderEndPoint()"
+      - "Lidgren.Network.NetConnection get_SenderConnection()"
+      - "double get_ReceiveTime()"
+      - "double ReadTime(bool)"
+      - "string ToString()"
     NetOutgoingMessage:
-      All: True
+      Methods:
+      - "string ToString()"
   Nett:
     CommentLocation: { } # Enum
     Toml:

Robust.Shared/ContentPack/WritableDirProvider.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
+using System.Threading;
 using Robust.Shared.Utility;
 
 namespace Robust.Shared.ContentPack
@@ -135,11 +136,37 @@ namespace Robust.Shared.ContentPack
                 path = path.Directory;
 
             var fullPath = GetFullPath(path);
-            Process.Start(new ProcessStartInfo
+            if (OperatingSystem.IsWindows())
             {
-                UseShellExecute = true,
-                FileName = fullPath,
-            });
+                Process.Start(new ProcessStartInfo
+                {
+                    FileName = "explorer.exe",
+                    Arguments = ".",
+                    WorkingDirectory = fullPath,
+                });
+            }
+            else if (OperatingSystem.IsMacOS())
+            {
+                Process.Start(new ProcessStartInfo
+                {
+                    FileName = "open",
+                    Arguments = ".",
+                    WorkingDirectory = fullPath,
+                });
+            }
+            else if (OperatingSystem.IsLinux() || OperatingSystem.IsFreeBSD())
+            {
+                Process.Start(new ProcessStartInfo
+                {
+                    FileName = "xdg-open",
+                    Arguments = ".",
+                    WorkingDirectory = fullPath,
+                });
+            }
+            else
+            {
+                throw new NotSupportedException("Opening OS windows not supported on this OS");
+            }
         }
 
         #endregion

Robust.Shared/GameObjects/Components/MetaDataComponent.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using Robust.Shared.GameStates;
 using Robust.Shared.Maths;
 using Robust.Shared.Prototypes;
@@ -199,6 +200,11 @@ namespace Robust.Shared.GameObjects
             // (Creation can still be cleared though)
             ClearCreationTick();
         }
+
+        /// <summary>
+        /// Offset into internal PVS data.
+        /// </summary>
+        internal PvsIndex PvsData;
     }
 
     [Flags]
@@ -221,16 +227,32 @@ namespace Robust.Shared.GameObjects
         /// </summary>
         Detached = 1 << 2,
 
+        /// <summary>
+        /// Indicates this entity can never be handled by the client as PVS detached.
+        /// </summary>
+        Undetachable = 1 << 3,
+
         /// <summary>
         /// If true, then this entity is considered a "high priority" entity and will be sent to players from further
         /// away. Useful for things like light sources and occluders. Only works if the entity is directly parented to
         /// a grid or map.
         /// </summary>
-        PvsPriority = 1 << 3,
+        PvsPriority = 1 << 4,
     }
 
     /// <summary>
     /// Key struct for uniquely identifying a PVS chunk.
     /// </summary>
     internal readonly record struct PvsChunkLocation(EntityUid Uid, Vector2i Indices);
+
+    /// <summary>
+    /// An opaque index into the PVS data arrays on the server.
+    /// </summary>
+    internal readonly record struct PvsIndex(int Index)
+    {
+        /// <summary>
+        /// An invalid index. This is also used as a marker value in the free list.
+        /// </summary>
+        public static readonly PvsIndex Invalid = new PvsIndex(-1);
+    }
 }

Robust.Shared/GameObjects/EntityManager.Network.cs

@@ -32,6 +32,7 @@ public partial class EntityManager
     /// </summary>
     internal void SetNetEntity(EntityUid uid, NetEntity netEntity, MetaDataComponent component)
     {
+        DebugTools.Assert(component.NetEntity == NetEntity.Invalid || _netMan.IsClient);
         DebugTools.Assert(!NetEntityLookup.ContainsKey(netEntity));
         NetEntityLookup[netEntity] = (uid, component);
         component.NetEntity = netEntity;

Robust.Shared/GameObjects/EntityManager.cs

@@ -906,6 +906,16 @@ namespace Robust.Shared.GameObjects
             DebugTools.Assert("Why are you raising predictive events on the server?");
         }
 
+        /// <summary>
+        /// Raises an event locally on client or networked on server.
+        /// </summary>
+        public abstract void RaiseSharedEvent<T>(T message, EntityUid? user = null) where T : EntityEventArgs;
+
+        /// <summary>
+        /// Raises an event locally on client or networked on server.
+        /// </summary>
+        public abstract void RaiseSharedEvent<T>(T message, ICommonSession? user = null) where T : EntityEventArgs;
+
         /// <summary>
         ///     Factory for generating a new EntityUid for an entity currently being created.
         /// </summary>

Robust.Shared/GameObjects/Systems/EntityLookup.Queries.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using JetBrains.Annotations;
 using Robust.Shared.Collections;
 using Robust.Shared.Map;
 using Robust.Shared.Map.Components;
@@ -744,9 +745,20 @@ public sealed partial class EntityLookupSystem
     }
 
     public HashSet<EntityUid> GetEntitiesInRange(EntityCoordinates coordinates, float range, LookupFlags flags = DefaultFlags)
+    {
+        var ents = new HashSet<EntityUid>();
+        GetEntitiesInRange(coordinates, range, ents, flags);
+        return ents;
+    }
+
+    public void GetEntitiesInRange(EntityCoordinates coordinates, float range, HashSet<EntityUid> entities, LookupFlags flags = DefaultFlags)
     {
         var mapPos = coordinates.ToMap(EntityManager, _transform);
-        return GetEntitiesInRange(mapPos, range, flags);
+
+        if (mapPos.MapId == MapId.Nullspace)
+            return;
+
+        GetEntitiesInRange(mapPos.MapId, mapPos.Position, range, entities, flags);
     }
 
     #endregion

Robust.Shared/GameObjects/Systems/SharedTransformSystem.Component.cs

@@ -616,7 +616,7 @@ public abstract partial class SharedTransformSystem
         TransformComponent? newParent = null,
         TransformComponent? oldParent = null)
     {
-        SetCoordinates((uid, xform, MetaData(uid)), value, rotation, unanchor, newParent, oldParent);
+        SetCoordinates((uid, xform, _metaQuery.GetComponent(uid)), value, rotation, unanchor, newParent, oldParent);
     }
 
     #endregion

Robust.Shared/Network/NetChannelArgs.cs

@@ -1,7 +1,6 @@
 using System;
+using System.Collections.Generic;
 using System.Net;
-using System.Text.Json;
-using System.Text.Json.Nodes;
 
 namespace Robust.Shared.Network
 {
@@ -31,9 +30,10 @@ namespace Robust.Shared.Network
     /// </summary>
     public sealed class NetConnectingArgs : EventArgs
     {
-        public bool IsDenied => DenyReason != null;
+        public bool IsDenied => DenyReasonData != null;
 
-        public string? DenyReason { get; private set; }
+        public string? DenyReason => DenyReasonData?.Text;
+        public NetDenyReason? DenyReasonData { get; private set; }
 
         public NetUserData UserData { get; }
 
@@ -48,7 +48,12 @@ namespace Robust.Shared.Network
 
         public void Deny(string reason)
         {
-            DenyReason = reason;
+            Deny(new NetDenyReason(reason));
+        }
+
+        public void Deny(NetDenyReason reason)
+        {
+            DenyReasonData = reason;
         }
 
         /// <summary>
@@ -65,12 +70,29 @@ namespace Robust.Shared.Network
         }
     }
 
+    /// <summary>
+    /// Contains a reason for denying a client connection to the game server.
+    /// </summary>
+    /// <param name="Text">The textual reason, presented to the user.</param>
+    /// <param name="AdditionalProperties">
+    /// Additional JSON properties that will be included in the <see cref="NetDisconnectMessage"/>.
+    /// Valid value types are: string, int, float, bool.
+    /// </param>
+    /// <seealso cref="NetDisconnectMessage"/>
+    /// <seealso cref="NetConnectingArgs"/>
+    public record NetDenyReason(string Text, Dictionary<string, object> AdditionalProperties)
+    {
+        public NetDenyReason(string Text) : this(Text, new Dictionary<string, object>())
+        {
+        }
+    }
+
     /// <summary>
     /// Structured reason common interface.
     /// </summary>
     public interface INetStructuredReason
     {
-        JsonObject StructuredReason { get; }
+        NetDisconnectMessage Message { get; }
         string Reason { get; }
         bool RedialFlag { get; }
     }
@@ -80,33 +102,33 @@ namespace Robust.Shared.Network
     /// </summary>
     public sealed class NetConnectFailArgs : EventArgs, INetStructuredReason
     {
-        public NetConnectFailArgs(string reason) : this(NetStructuredDisconnectMessages.Decode(reason))
+        public NetConnectFailArgs(string reason) : this(NetDisconnectMessage.Decode(reason))
         {
         }
 
-        public NetConnectFailArgs(JsonObject reason)
+        internal NetConnectFailArgs(NetDisconnectMessage reason)
         {
-            StructuredReason = reason;
+            Message = reason;
         }
 
-        public JsonObject StructuredReason { get; }
-        public string Reason => NetStructuredDisconnectMessages.ReasonOf(StructuredReason);
-        public bool RedialFlag => NetStructuredDisconnectMessages.RedialFlagOf(StructuredReason);
+        public NetDisconnectMessage Message { get; }
+        public string Reason => Message.Reason;
+        public bool RedialFlag => Message.RedialFlag;
     }
 
     public sealed class NetDisconnectedArgs : NetChannelArgs, INetStructuredReason
     {
-        public NetDisconnectedArgs(INetChannel channel, string reason) : this(channel, NetStructuredDisconnectMessages.Decode(reason))
+        public NetDisconnectedArgs(INetChannel channel, string reason) : this(channel, NetDisconnectMessage.Decode(reason))
         {
         }
 
-        public NetDisconnectedArgs(INetChannel channel, JsonObject reason) : base(channel)
+        internal NetDisconnectedArgs(INetChannel channel, NetDisconnectMessage reason) : base(channel)
         {
-            StructuredReason = reason;
+            Message = reason;
         }
 
-        public JsonObject StructuredReason { get; }
-        public string Reason => NetStructuredDisconnectMessages.ReasonOf(StructuredReason);
-        public bool RedialFlag => NetStructuredDisconnectMessages.RedialFlagOf(StructuredReason);
+        public NetDisconnectMessage Message { get; }
+        public string Reason => Message.Reason;
+        public bool RedialFlag => Message.RedialFlag;
     }
 }

Robust.Shared/Network/NetDisconnectMessage.cs

@@ -0,0 +1,259 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Text.Json;
+using Robust.Shared.Utility;
+
+namespace Robust.Shared.Network;
+
+// Why did this dinky class grow to this LOC...
+
+/// <summary>
+/// Stores structured information about why a connection was denied or disconnected.
+/// </summary>
+/// <remarks>
+/// <para>
+/// The core networking layer (Lidgren) allows passing plain strings for disconnect reasons.
+/// We can beam a structured format (like JSON) over this,
+/// but Lidgren also generates messages internally (such as on timeout).
+/// This class is responsible for bridging the two to produce consistent results.
+/// </para>
+/// <para>
+/// Disconnect messages are just a simple key/value format.
+/// Valid value types are <see cref="int"/>, <see cref="float"/>, <see cref="bool"/>, and <see cref="string"/>.
+/// </para>
+/// </remarks>
+public sealed class NetDisconnectMessage
+{
+    private const string LidgrenDisconnectedPrefix = "Disconnected: ";
+
+    /// <summary>
+    /// The reason given if none was included in the structured message.
+    /// </summary>
+    internal const string DefaultReason = "unknown reason";
+
+    /// <summary>
+    /// The default redial flag given if none was included in the structured message.
+    /// </summary>
+    internal const bool DefaultRedialFlag = false;
+
+    /// <summary>
+    /// The key of the <see cref="Reason"/> value.
+    /// </summary>
+    public const string ReasonKey = "reason";
+
+    /// <summary>
+    /// The key of the <see cref="RedialFlag"/> value.
+    /// </summary>
+    public const string RedialKey = "redial";
+
+    internal readonly Dictionary<string, object> Values;
+
+    internal NetDisconnectMessage(Dictionary<string, object> values)
+    {
+        Values = values;
+    }
+
+    internal NetDisconnectMessage(
+        string reason = DefaultReason,
+        bool redialFlag = DefaultRedialFlag)
+    {
+        Values = new Dictionary<string, object>
+        {
+            { ReasonKey, reason },
+            { RedialKey, redialFlag }
+        };
+    }
+
+    /// <summary>
+    /// The human-readable reason for why the disconnection happened.
+    /// </summary>
+    /// <seealso cref="ReasonKey"/>
+    public string Reason => StringOf(ReasonKey, DefaultReason);
+
+    /// <summary>
+    /// Whether the client should "redial" to reconnect to the server.
+    /// </summary>
+    /// <remarks>
+    /// Redial means the client gets restarted by the launcher, to enable an update to occur.
+    /// This is generally set if the disconnection reason is some sort of version mismatch.
+    /// </remarks>
+    /// <seealso cref="RedialKey"/>
+    public bool RedialFlag => BoolOf(RedialKey, DefaultRedialFlag);
+
+    /// <summary>
+    /// Decode from a disconnect message.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// If structured JSON can be extracted, it is used.
+    /// Otherwise, or if the format is invalid, the entire input is returned as disconnect reason.
+    /// </para>
+    /// <para>Invalid JSON values (e.g. arrays) are discarded.</para>
+    /// </remarks>
+    /// <param name="text">The disconnect reason from Lidgren's disconnect message.</param>
+    internal static NetDisconnectMessage Decode(string text)
+    {
+        var start = text.AsMemory().TrimStart();
+        // Lidgren generates this prefix internally.
+        if (start.Span.StartsWith(LidgrenDisconnectedPrefix))
+            start = start[LidgrenDisconnectedPrefix.Length..];
+        // If it starts with { it's probably a JSON object.
+        if (start.Span.StartsWith("{"))
+        {
+            try
+            {
+                using var node = JsonDocument.Parse(start);
+                DebugTools.Assert(node.RootElement.ValueKind == JsonValueKind.Object);
+                return JsonToReason(node.RootElement);
+            }
+            catch (Exception)
+            {
+                // Discard the exception
+            }
+        }
+
+        // Something went wrong. That probably means it's not a structured reason.
+        // Or worst case scenario, some poor end-user has to look at half-broken JSON.
+        return new NetDisconnectMessage(new Dictionary<string, object>
+        {
+            { ReasonKey, text }
+        });
+    }
+
+    /// <summary>
+    /// Encode to a textual string, that can be embedded into a disconnect message.
+    /// </summary>
+    internal string Encode()
+    {
+        return JsonSerializer.Serialize(Values);
+    }
+
+    private static NetDisconnectMessage JsonToReason(JsonElement obj)
+    {
+        DebugTools.Assert(obj.ValueKind == JsonValueKind.Object);
+
+        var dict = new Dictionary<string, object>();
+        foreach (var property in obj.EnumerateObject())
+        {
+            object value;
+            switch (property.Value.ValueKind)
+            {
+                case JsonValueKind.String:
+                    value = property.Value.GetString()!;
+                    break;
+                case JsonValueKind.Number:
+                    if (property.Value.TryGetInt32(out var valueInt))
+                        value = valueInt;
+                    else
+                        value = property.Value.GetSingle();
+                    break;
+                case JsonValueKind.True:
+                case JsonValueKind.False:
+                    value = property.Value.GetBoolean();
+                    break;
+                default:
+                    // Discard invalid values intentionally.
+                    continue;
+            }
+
+            dict[property.Name] = value;
+        }
+
+        return new NetDisconnectMessage(dict);
+    }
+
+    /// <summary>
+    /// Get a value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <returns>
+    /// Null if no such value exists, otherwise an object of one of the valid types (int, float, string, bool).
+    /// </returns>
+    public object? ValueOf(string key)
+    {
+        return Values.GetValueOrDefault(key);
+    }
+
+    /// <summary>
+    /// Get a <see cref="string"/> value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <param name="defaultValue">Default value to return if the value does not exist or is the wrong type.</param>
+    /// <returns>
+    /// The <see cref="string"/> value with the given key,
+    /// or <paramref name="defaultValue"/> if no such value exists or it's a different type.
+    /// </returns>
+    [return: NotNullIfNotNull(nameof(defaultValue))]
+    public string? StringOf(string key, string? defaultValue = null)
+    {
+        if (ValueOf(key) is not string valueString)
+            return defaultValue;
+
+        return valueString;
+    }
+
+    /// <summary>
+    /// Get a <see cref="bool"/> value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <returns>
+    /// The <see cref="bool"/> value with the given key, or <see langword="null" /> if no such value exists or it's a different type.
+    /// </returns>
+    public bool? BoolOf(string key) => ValueOf(key) as bool?;
+
+    /// <summary>
+    /// Get a <see cref="bool"/> value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <param name="defaultValue">Default value to return if the value does not exist or is the wrong type.</param>
+    /// <returns>
+    /// The <see cref="bool"/> value with the given key,
+    /// or <paramref name="defaultValue"/> if no such value exists or it's a different type.
+    /// </returns>
+    public bool BoolOf(string key, bool defaultValue) => BoolOf(key) ?? defaultValue;
+
+    /// <summary>
+    /// Get a <see cref="int"/> value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <returns>
+    /// The <see cref="int"/> value with the given key, or <see langword="null" /> if no such value exists or it's a different type.
+    /// </returns>
+    public int? Int32Of(string key) => ValueOf(key) as int?;
+
+    /// <summary>
+    /// Get an <see cref="Int32"/> value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <param name="defaultValue">Default value to return if the value does not exist or is the wrong type.</param>
+    /// <returns>
+    /// The <see cref="Int32"/> value with the given key,
+    /// or <paramref name="defaultValue"/> if no such value exists or it's a different type.
+    /// </returns>
+    public int Int32Of(string key, int defaultValue) => Int32Of(key) ?? defaultValue;
+
+    /// <summary>
+    /// Get a <see cref="float"/> value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <returns>
+    /// The <see cref="float"/> value with the given key, or <see langword="null" /> if no such value exists or it's a different type.
+    /// </returns>
+    public float? SingleOf(string key)
+    {
+        var value = ValueOf(key);
+        return value as float? ?? value as int?;
+    }
+
+    /// <summary>
+    /// Get a <see cref="Single"/> value by its key.
+    /// </summary>
+    /// <param name="key">The key of the value to look up.</param>
+    /// <param name="defaultValue">Default value to return if the value does not exist or is the wrong type.</param>
+    /// <returns>
+    /// The <see cref="Single"/> value with the given key,
+    /// or <paramref name="defaultValue"/> if no such value exists or it's a different type.
+    /// </returns>
+    public float SingleOf(string key, float defaultValue) => SingleOf(key) ?? defaultValue;
+}

Robust.Shared/Network/NetManager.ServerAuth.cs

@@ -16,7 +16,7 @@ namespace Robust.Shared.Network
 {
     partial class NetManager
     {
-        private readonly static string DisconnectReasonWrongKey = NetStructuredDisconnectMessages.Encode("Token decryption failed.\nPlease reconnect to this server from the launcher.", true);
+        private static readonly string DisconnectReasonWrongKey = new NetDisconnectMessage("Token decryption failed.\nPlease reconnect to this server from the launcher.", true).Encode();
 
         private readonly byte[] _cryptoPrivateKey = new byte[CryptoBox.SecretKeyBytes];
 
@@ -211,9 +211,15 @@ namespace Robust.Shared.Network
 
                 var endPoint = connection.RemoteEndPoint;
                 var connect = await OnConnecting(endPoint, userData, type);
-                if (connect.IsDenied)
+                if (connect.DenyReasonData is { } deny)
                 {
-                    connection.Disconnect($"Connection denied: {connect.DenyReason}");
+                    var denyMsg = $"Connect denied: {deny.Text}";
+                    var structured = new NetDisconnectMessage(denyMsg);
+                    foreach (var (k, v) in deny.AdditionalProperties)
+                    {
+                        structured.Values[k] = v;
+                    }
+                    connection.Disconnect(structured.Encode());
                     return;
                 }
 

Robust.Shared/Network/NetStructuredDisconnectMessages.cs

@@ -1,119 +0,0 @@
-using System;
-using System.Net;
-using System.Text.Json;
-using System.Text.Json.Nodes;
-
-namespace Robust.Shared.Network;
-
-/// <summary>
-/// Structured disconnection utilities.
-/// These use JsonNode so that Content may add it's own data.
-/// Note that to prevent encoding a NetStructuredDisco value within a NetStructuredDisco value,
-/// these should be encoded at the "highest level".
-/// Whatever generates the final "reason" value is responsible for performing NetStructuredDisco.Encode.
-/// </summary>
-public static class NetStructuredDisconnectMessages
-{
-    public const string ReasonKey = "reason";
-    public const string RedialKey = "redial";
-
-    /// <summary>
-    /// Encodes a structured disconnect message into a JsonObject.
-    /// That can then be extended with additional properties.
-    /// </summary>
-    public static JsonObject EncodeObject(string text, bool redialFlag = false)
-    {
-        JsonObject obj = new();
-        obj[ReasonKey] = text;
-        obj[RedialKey] = redialFlag;
-        return obj;
-    }
-
-    /// <summary>
-    /// Encodes a structured disconnect message.
-    /// Note that using this kind of gets in the way of adding content properties.
-    /// </summary>
-    public static string Encode(string text, bool redialFlag = false) => Encode(EncodeObject(text, redialFlag));
-
-    /// <summary>
-    /// Encodes a structured disconnect message from a JsonObject.
-    /// </summary>
-    public static string Encode(JsonObject obj) => obj.ToJsonString();
-
-    /// <summary>
-    /// Decodes a structured disconnect message.
-    /// This is designed assuming the input isn't necessarily a structured disconnect message.
-    /// As such this will always produce output that can be passed to ReasonOf.
-    /// </summary>
-    public static JsonObject Decode(string text)
-    {
-        var start = text.AsSpan().TrimStart();
-        // Lidgren generates this prefix internally.
-        var lidgrenDisconnectedPrefix = "Disconnected: ";
-        if (start.StartsWith(lidgrenDisconnectedPrefix))
-            start = start.Slice(lidgrenDisconnectedPrefix.Length);
-        // If it starts with { it's probably a JSON object.
-        if (start.StartsWith("{"))
-        {
-            try
-            {
-                var node = JsonNode.Parse(new string(start));
-                if (node != null)
-                    return (JsonObject)node;
-            }
-            catch (Exception)
-            {
-                // Discard the exception
-            }
-        }
-
-        // Something went wrong, so...
-        JsonObject fallback = new();
-        fallback[ReasonKey] = text;
-        return fallback;
-    }
-
-    /// <summary>
-    /// Get a property as a JsonValue.
-    /// </summary>
-    public static JsonValue? ValueOf(JsonObject obj, string key)
-    {
-        if (obj.TryGetPropertyValue(key, out var val))
-            if (val is JsonValue)
-                return ((JsonValue) val);
-        return null;
-    }
-
-    /// <summary>
-    /// Decode a string property.
-    /// </summary>
-    public static string StringOf(JsonObject obj, string key, string def)
-    {
-        var val = ValueOf(obj, key);
-        if (val != null && val.TryGetValue(out string? res))
-            return res;
-        return def;
-    }
-
-    /// <summary>
-    /// Grab the redial flag.
-    /// </summary>
-    public static bool BoolOf(JsonObject obj, string key, bool def)
-    {
-        var val = ValueOf(obj, key);
-        if (val != null && val.TryGetValue(out bool res))
-            return res;
-        return def;
-    }
-
-    /// <summary>
-    /// Decode a reason.
-    /// </summary>
-    public static string ReasonOf(JsonObject obj) => StringOf(obj, ReasonKey, "unknown reason");
-
-    /// <summary>
-    /// Grab the redial flag.
-    /// </summary>
-    public static bool RedialFlagOf(JsonObject obj) => BoolOf(obj, RedialKey, false);
-}
-

Robust.Shared/Utility/ResizableMemoryRegion.cs

@@ -0,0 +1,338 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.Metrics;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using Robust.Shared.Maths;
+using static TerraFX.Interop.Windows.Windows;
+using static TerraFX.Interop.Windows.MEM;
+using static TerraFX.Interop.Windows.PAGE;
+
+namespace Robust.Shared.Utility;
+
+/// <summary>
+/// Implementation detail to store metrics for <see cref="ResizableMemoryRegion{T}"/>.
+/// </summary>
+internal static class ResizableMemoryRegionMetrics
+{
+    public static readonly Meter Meter = new("Robust.Shared.Utility.ResizableMemoryRegion");
+
+    public const string GaugeName = "robust_resizable_memory_used_bytes";
+}
+
+// TODO: Proper implementation on Linux that uses mmap()/madvise()/mprotect().
+
+/// <summary>
+/// An unmanaged region of memory that can be dynamically resized without requiring copying.
+/// </summary>
+/// <remarks>
+/// <para>
+/// The maximum size of the memory region must be specified in the constructor. This reserves virtual memory for later,
+/// but does not charge actual physical memory or commit charge and therefore costs nothing.
+/// </para>
+/// <para>
+/// The "real" allocated memory region can be expanded by calling <see cref="Expand"/>.
+/// This will increase resource consumption and make more memory available for use.
+/// </para>
+/// <para>
+/// Allocated memory starts initialized to 0.
+/// </para>
+/// </remarks>
+/// <typeparam name="T">The type of elements stored in the memory region.</typeparam>
+internal sealed unsafe class ResizableMemoryRegion<T> : IDisposable where T : unmanaged
+{
+    private static readonly UpDownCounter<long> MemoryUsageGauge =
+        ResizableMemoryRegionMetrics.Meter.CreateUpDownCounter<long>(
+            ResizableMemoryRegionMetrics.GaugeName,
+            "bytes",
+            "The amount of committed memory used by ResizableMemoryRegion<T> instances.",
+            new[] { new KeyValuePair<string, object?>("type", typeof(T).FullName) });
+
+    /// <summary>
+    /// The pointer to the start of the allocated memory region. Use with care!
+    /// </summary>
+    public T* BaseAddress { get; private set; }
+
+    /// <summary>
+    /// The maximum amount of elements that can be stored in this memory region.
+    /// </summary>
+    public int MaxSize { get; }
+
+    /// <summary>
+    /// The current space (in elements) commit that is directly accessible.
+    /// </summary>
+    public int CurrentSize { get; private set; }
+
+    /// <summary>
+    /// Create a new <see cref="ResizableMemoryRegion{T}"/> with a certain maximum and initial size.
+    /// </summary>
+    /// <param name="maxElementSize">The maximum amount of elements ever stored in this memory region.</param>
+    /// <param name="initialElementSize">
+    /// The initial amount of elements that will be immediately accessible without using <see cref="Expand"/>.
+    /// </param>
+    /// <exception cref="InvalidOperationException">
+    /// Thrown if the memory region is already initialized.
+    /// </exception>
+    /// <exception cref="ArgumentException">
+    /// Thrown if <paramref name="maxElementSize"/> is zero
+    /// or <paramref name="initialElementSize"/> is greater than <paramref name="maxElementSize"/>.
+    /// </exception>
+    public ResizableMemoryRegion(int maxElementSize, int initialElementSize = 0)
+    {
+        if (BaseAddress != null)
+            throw new InvalidOperationException("Memory region is already initialized!");
+
+        if (initialElementSize > maxElementSize)
+            throw new ArgumentException("initialSize must be smaller than maxSize");
+
+        if (maxElementSize == 0)
+            throw new ArgumentException("Cannot allocate a 0-byte memory region!");
+
+        var maxByteSize = checked((nuint)sizeof(T) * (nuint)maxElementSize);
+
+        if (OperatingSystem.IsWindows())
+        {
+            // On Windows, we MEM_RESERVE a large chunk of memory and then MEM_COMMIT it later when expanding.
+
+            BaseAddress = (T*)VirtualAlloc(null, maxByteSize, MEM_RESERVE, PAGE_NOACCESS);
+            if (BaseAddress == null)
+                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
+        }
+        else
+        {
+            // Non-Windows systems use some form of overcommit,
+            // and therefore we don't need to separately reserve and commit memory.
+            // So we can just calloc() a fuck-huge chunk of memory and call it a day.
+            //
+            // It's important that we use calloc() and don't manually fill the memory region,
+            // as that will avoid immediately assigning unused memory pages.
+            //
+            // Note that we still pretend to client code that this works the same as on Windows,
+            // e.g. the memory is not writable until expanded into. We do this so that client code does not prematurely
+            // populate the memory, e.g. PVS code filling it with a free list.
+            BaseAddress = (T*)NativeMemory.AllocZeroed(maxByteSize);
+
+            // What about Linux with overcommit disabled? Not a real use case, ignored.
+        }
+
+        MaxSize = maxElementSize;
+
+        Expand(initialElementSize);
+    }
+
+    /// <summary>
+    /// Expand the committed space for this <see cref="ResizableMemoryRegion{T}"/> to have space for at least
+    /// <paramref name="newElementSize"/> elements.
+    /// </summary>
+    /// <remarks>
+    /// This operation happens without copying and existing references to the memory region remain valid.
+    /// </remarks>
+    /// <param name="newElementSize">The minimum amount of elements that should fit in the memory region.</param>
+    /// <exception cref="ArgumentException">
+    /// Thrown if <paramref name="newElementSize"/> is greater than <see cref="MaxSize"/>.
+    /// </exception>
+    public void Expand(int newElementSize)
+    {
+        ThrowIfDisposed();
+
+        if (newElementSize > MaxSize)
+            throw new ArgumentException("Cannot expand memory region past max size.", nameof(newElementSize));
+
+        if (newElementSize <= CurrentSize)
+            return;
+
+        var previousSize = CurrentSize;
+
+        var newByteSize = (nuint)sizeof(T) * (nuint)newElementSize;
+
+        if (OperatingSystem.IsWindows())
+        {
+            var ret = VirtualAlloc(BaseAddress, newByteSize, MEM_COMMIT, PAGE_READWRITE);
+            if (ret == null)
+                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
+        }
+        else
+        {
+            // Nada. On overcommit systems we don't need to do anything.
+        }
+
+        CurrentSize = newElementSize;
+
+        MemoryUsageGauge.Add((newElementSize - previousSize) * sizeof(T));
+    }
+
+    /// <summary>
+    /// Shrink this <see cref="ResizableMemoryRegion{T}"/> to reduce the amount of memory used.
+    /// </summary>
+    /// <remarks>
+    /// Existing references inside the shrank-away region of memory become undefined to read or write from,
+    /// and can cause access violations.
+    /// </remarks>
+    /// <param name="newElementSize">
+    /// The new size of the committed region of memory.
+    /// </param>
+    /// <exception cref="ArgumentException">
+    /// Thrown if trying to shrink to a size larger than the current size, or when trying to shrink to a negative size.
+    /// </exception>
+    public void Shrink(int newElementSize)
+    {
+        ThrowIfDisposed();
+
+        if (newElementSize > CurrentSize)
+            throw new ArgumentException("Cannot shrink to a larger size!", nameof(newElementSize));
+
+        if (newElementSize < 0)
+            throw new ArgumentException("Cannot shrink to a negative size!", nameof(newElementSize));
+
+        var currentByteSize = (nuint)sizeof(T) * (nuint)CurrentSize;
+        var newByteSize = (nuint)sizeof(T) * (nuint)newElementSize;
+
+        // If the new max size cuts a page in the middle we can't free it so round up to the next page.
+        var newPageSize = MathHelper.CeilMultipleOfPowerOfTwo(newByteSize, (nuint) Environment.SystemPageSize);
+        if (OperatingSystem.IsWindows())
+        {
+            var freeBaseAddress = (byte*)BaseAddress + newPageSize;
+            var freeLength = currentByteSize - newPageSize;
+            var result = VirtualFree(freeBaseAddress, freeLength, MEM_DECOMMIT);
+            if (!result)
+                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
+        }
+        else
+        {
+            // Nothing to do on operating systems without advanced memory management.
+        }
+
+        CurrentSize = newElementSize;
+    }
+
+    /// <summary>
+    /// Get a <see cref="Span{T}"/> over the committed region of memory.
+    /// </summary>
+    /// <returns>A <see cref="Span{T}"/> over the committed region of memory.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public Span<T> GetSpan()
+    {
+        // If the memory region is disposed, CurrentSize is 0 so it's impossible to use the (nullptr) BaseAddress.
+        // This means you can't dereference the span anyways, so that works out fine!
+        return new Span<T>(BaseAddress, CurrentSize);
+    }
+
+    /// <summary>
+    /// Get a <see cref="Span{T}"/> over the committed region of memory, cast to a different type.
+    /// </summary>
+    /// <remarks>
+    /// This is equivalent to using <see cref="MemoryMarshal.Cast{TFrom, TTo}(Span{TFrom})"/> on the result of <see cref="GetSpan"/>.
+    /// </remarks>
+    /// <typeparam name="TCast">The type to cast the memory region to.</typeparam>
+    /// <returns>A <see cref="Span{T}"/> over the committed region of memory.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public Span<TCast> GetSpan<TCast>() where TCast : unmanaged
+    {
+        return MemoryMarshal.Cast<T, TCast>(GetSpan());
+    }
+
+    /// <summary>
+    /// Get a mutable reference to a single element of the memory region.
+    /// </summary>
+    /// <param name="index">The index of the element desired.</param>
+    /// <exception cref="IndexOutOfRangeException">
+    /// Thrown if <paramref name="index"/> is greater or equal to <see cref="CurrentSize"/>.
+    /// </exception>
+    /// <returns>A mutable reference to the element.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ref T GetRef(int index)
+    {
+        // If the memory region is disposed, CurrentSize is 0 and this check always fails.
+        if (index >= CurrentSize)
+            ThrowIndexOutOfRangeException();
+
+        return ref *(BaseAddress + index);
+    }
+
+    /// <summary>
+    /// Get a mutable reference to a single element of the memory region, cast to a different type.
+    /// </summary>
+    /// <remarks>
+    /// This is equivalent to using <see cref="M:System.Runtime.CompilerServices.Unsafe.As``2(``0@)"/> on the result of <see cref="GetSpan"/>.
+    /// </remarks>
+    /// <param name="index">The index of the element desired.</param>
+    /// <exception cref="IndexOutOfRangeException">
+    /// Thrown if <paramref name="index"/> is greater or equal to <see cref="CurrentSize"/>.
+    /// </exception>
+    /// <returns>A mutable reference to the element.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public ref TCast GetRef<TCast>(int index) where TCast : unmanaged
+    {
+        return ref Unsafe.As<T, TCast>(ref GetRef(index));
+    }
+
+    /// <summary>
+    /// Clear the contents of the memory stored in this <see cref="ResizableMemoryRegion{T}"/> back to zero.
+    /// </summary>
+    /// <remarks>
+    /// This does not change the <see cref="CurrentSize"/>.
+    /// </remarks>
+    public void Clear()
+    {
+        GetSpan().Clear();
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private void ThrowIfDisposed()
+    {
+        if (BaseAddress == null)
+            ThrowNotInitialized();
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void ThrowNotInitialized()
+    {
+        throw new InvalidOperationException("Memory region is not initialized!");
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static void ThrowIndexOutOfRangeException()
+    {
+        throw new IndexOutOfRangeException();
+    }
+
+    private void ReleaseUnmanagedResources()
+    {
+        if (BaseAddress == null)
+            return;
+
+        if (OperatingSystem.IsWindows())
+        {
+            var result = VirtualFree(BaseAddress, 0, MEM_RELEASE);
+            if (!result)
+                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
+        }
+        else
+        {
+            NativeMemory.Free(BaseAddress);
+        }
+
+        MemoryUsageGauge.Add(-CurrentSize * sizeof(T));
+
+        BaseAddress = null;
+        CurrentSize = 0;
+    }
+
+    /// <summary>
+    /// Release the backing memory for this <see cref="ResizableMemoryRegion{T}"/>.
+    /// </summary>
+    /// <remarks>
+    /// Existing references to memory of the memory region become invalid and should no longer be used.
+    /// </remarks>
+    public void Dispose()
+    {
+        ReleaseUnmanagedResources();
+
+        GC.SuppressFinalize(this);
+    }
+
+    ~ResizableMemoryRegion()
+    {
+        ReleaseUnmanagedResources();
+    }
+}

Robust.UnitTesting/Client/UserInterface/Controls/TextEditTest.cs

@@ -0,0 +1,52 @@
+using System.Numerics;
+using NUnit.Framework;
+using Robust.Client.UserInterface;
+using Robust.Client.UserInterface.Controls;
+using Robust.Shared.Input;
+using Robust.Shared.IoC;
+using Robust.Shared.Map;
+using Robust.Shared.Maths;
+using Robust.Shared.Utility;
+
+namespace Robust.UnitTesting.Client.UserInterface.Controls;
+
+[TestFixture]
+[TestOf(typeof(TextEdit))]
+public sealed class TextEditTest : RobustUnitTest
+{
+    public override UnitTestProject Project => UnitTestProject.Client;
+
+    [OneTimeSetUp]
+    public void Setup()
+    {
+        IoCManager.Resolve<IUserInterfaceManagerInternal>().InitializeTesting();
+    }
+
+    // Regression test for https://github.com/space-wizards/RobustToolbox/issues/4953
+    // It was possible to move the cursor up/down if there was multi-line placeholder text.
+    [Test]
+    public void TestInvalidMoveInPlaceholder()
+    {
+        var textEdit = new TextEdit { Placeholder = new Rope.Leaf("Foo\nBar") };
+        textEdit.Arrange(new UIBox2(0, 0, 200, 200));
+
+        var click = new GUIBoundKeyEventArgs(EngineKeyFunctions.TextCursorDown, BoundKeyState.Down, new ScreenCoordinates(), true, Vector2.Zero, Vector2.Zero);
+        textEdit.KeyBindDown(click);
+        textEdit.KeyBindUp(click);
+
+        Assert.That(textEdit.CursorPosition.Index, Is.Zero);
+    }
+
+    // Regression test for https://github.com/space-wizards/RobustToolbox/issues/4957
+    // Moving left (with the arrow keys) in an empty TextEdit would cause an exception.
+    [Test]
+    public void TestEmptyMoveLeft()
+    {
+        var textEdit = new TextEdit();
+        textEdit.Arrange(new UIBox2(0, 0, 200, 200));
+
+        var click = new GUIBoundKeyEventArgs(EngineKeyFunctions.TextCursorLeft, BoundKeyState.Down, new ScreenCoordinates(), true, Vector2.Zero, Vector2.Zero);
+        textEdit.KeyBindDown(click);
+        textEdit.KeyBindUp(click);
+    }
+}

Robust.UnitTesting/Shared/Map/SingleTileRemoveTest.cs

@@ -139,4 +139,3 @@ public sealed class GridDeleteSingleTileRemoveTestTest : RobustIntegrationTest
         Assert.That(cQuery.GetComponent(cEntity.Value).ParentUid, Is.EqualTo(cMap));
     }
 }
-

Robust.UnitTesting/Shared/Networking/NetDisconnectMessageTest.cs

@@ -0,0 +1,113 @@
+using NUnit.Framework;
+using Robust.Shared.Network;
+
+namespace Robust.UnitTesting.Shared.Networking;
+
+[TestFixture]
+[Parallelizable(ParallelScope.All)]
+[TestOf(typeof(NetDisconnectMessage))]
+internal sealed class NetDisconnectMessageTest
+{
+    [Test]
+    [TestCase("Disconnected: bye", "Disconnected: bye", NetDisconnectMessage.DefaultRedialFlag)]
+    [TestCase("Disconnected: {\"reason\": \"bye\"}", "bye", NetDisconnectMessage.DefaultRedialFlag)]
+    [TestCase("Disconnected: {}", NetDisconnectMessage.DefaultReason, NetDisconnectMessage.DefaultRedialFlag)]
+    [TestCase("Disconnected: {\"redial\": true}", NetDisconnectMessage.DefaultReason, true)]
+    [TestCase("Disconnected: {\"redial\": true, \"foobar\": 5}", NetDisconnectMessage.DefaultReason, true)]
+    [TestCase("Disconnected: {\"redial\": true, \"foobar\": 5, \"reason\": \"asdf\"}", "asdf", true)]
+    [TestCase("Disconnected: {", "Disconnected: {", NetDisconnectMessage.DefaultRedialFlag)]
+    [TestCase("Disconnected: {\"a\":[]}", NetDisconnectMessage.DefaultReason, NetDisconnectMessage.DefaultRedialFlag)]
+    [TestCase("{\"redial\": true, \"foobar\": 5, \"reason\": \"asdf\"}", "asdf", true)]
+    public void TestBasicDecode(string encoded, string reasonExpected, bool redialExpected)
+    {
+        var parsed = NetDisconnectMessage.Decode(encoded);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(parsed.Reason, Is.EqualTo(reasonExpected));
+            Assert.That(parsed.RedialFlag, Is.EqualTo(redialExpected));
+        });
+    }
+
+    [Test]
+    public void TestEncode()
+    {
+        var value = new NetDisconnectMessage("foobar", true)
+        {
+            Values =
+            {
+                ["asdf"] = 20.5f
+            }
+        };
+
+        var encoded = value.Encode();
+        TestContext.Write($"Encoded: {encoded}\n");
+        var decodedAgain = NetDisconnectMessage.Decode(encoded);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(decodedAgain.Reason, Is.EqualTo("foobar"));
+            Assert.That(decodedAgain.RedialFlag, Is.EqualTo(true));
+            Assert.That(decodedAgain.SingleOf("asdf"), Is.EqualTo(20.5f));
+        });
+    }
+
+    [Test]
+    public void TestDefaultConstructor()
+    {
+        var value = new NetDisconnectMessage("foobar");
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(value.Reason, Is.EqualTo("foobar"));
+            Assert.That(value.RedialFlag, Is.EqualTo(false));
+        });
+    }
+
+    [Test]
+    public void TestValueOfInt()
+    {
+        var parsed = NetDisconnectMessage.Decode("{\"foobar\": 5}");
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(parsed.Int32Of("foobar"), Is.EqualTo(5));
+            Assert.That(parsed.Int32Of("asdf"), Is.Null);
+            Assert.That(parsed.Int32Of("asdf", 7), Is.EqualTo(7));
+        });
+    }
+
+    [Test]
+    public void TestValueOfFloat()
+    {
+        var parsed = NetDisconnectMessage.Decode("{\"foobar\": 5.5}");
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(parsed.SingleOf("foobar"), Is.EqualTo(5.5f));
+            Assert.That(parsed.SingleOf("asdf"), Is.Null);
+            Assert.That(parsed.SingleOf("asdf", 7), Is.EqualTo(7f));
+        });
+    }
+
+    [Test]
+    public void TestValueOfFloatInt()
+    {
+        var parsed = NetDisconnectMessage.Decode("{\"foobar\": 5}");
+
+        Assert.That(parsed.SingleOf("foobar"), Is.EqualTo(5f));
+    }
+
+    [Test]
+    public void TestValueOfString()
+    {
+        var parsed = NetDisconnectMessage.Decode("{\"foobar\": \"real\"}");
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(parsed.StringOf("foobar"), Is.EqualTo("real"));
+            Assert.That(parsed.StringOf("asdf"), Is.Null);
+            Assert.That(parsed.StringOf("asdf", "honk"), Is.EqualTo("honk"));
+        });
+    }
+}

Robust.UnitTesting/Shared/Utility/MathHelper_Test.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Numerics;
 using NUnit.Framework;
 using Robust.Shared.Maths;
 
@@ -304,5 +305,23 @@ namespace Robust.UnitTesting.Shared.Utility
 
             Assert.That(MathHelper.Mod(val, mod), Is.EqualTo(result).Within(0.00000000001));
         }
+
+        [Test]
+        [TestCase(4, 4, ExpectedResult = 4)]
+        [TestCase(5, 4, ExpectedResult = 8)]
+        [TestCase(7, 4, ExpectedResult = 8)]
+        [TestCase(8, 4, ExpectedResult = 8)]
+        [TestCase(4U, 4U, ExpectedResult = 4U)]
+        [TestCase(5U, 4U, ExpectedResult = 8U)]
+        [TestCase(7U, 4U, ExpectedResult = 8U)]
+        [TestCase(8U, 4U, ExpectedResult = 8U)]
+        [TestCase(4L, 4L, ExpectedResult = 4L)]
+        [TestCase(5L, 4L, ExpectedResult = 8L)]
+        [TestCase(7L, 4L, ExpectedResult = 8L)]
+        [TestCase(8L, 4L, ExpectedResult = 8L)]
+        public T TestCeilMultipleOfPowerOfTwo<T>(T value, T powerOfTwo) where T : IBinaryInteger<T>
+        {
+            return MathHelper.CeilMultipleOfPowerOfTwo(value, powerOfTwo);
+        }
     }
 }