From 5cb97cc6de7422054e210fd8c757f7aefd6adb13 Mon Sep 17 00:00:00 2001
From: Kamron Batman <3953314+kamronbatman@users.noreply.github.com>
Date: Wed, 30 Apr 2025 19:33:15 -0700
Subject: [PATCH] fix: Fixes BitArray serialization (#2170)

Fixes serialization/deserialization edge cases with BitArray. If you use BitArray, you will need to migrate.

1. Change the type in the migration JSON file (if there is one) from `BitArray` to `byte[]` for all the versions you need to migrate.
2. Then in the `MigrateFrom`, use the following function to convert the field from a byte[] back to the BitArray.

Example Migration JSON:
```json
    {
      "name": "RestrictedSpells",
      "type": "byte[]",
      "rule": "ArrayMigrationRule",
      "ruleArguments": [
        "byte",
        "PrimitiveTypeMigrationRule",
        ""
      ]
    },
```

Migration function to use in MigrateFrom:
```cs
public static BitArray MigrateBitArray(byte[] data, int bitLength) => new(data) { Length = bitLength };
```

Example use:
```cs
    private void MigrateFrom(V0Content content)
    {
        // ... deserialize
        _restrictedSpells = content.RestrictedSpells.MigrateBitArray(SpellRegistry.Types.Length);
        _restrictedSkills = content.RestrictedSkills.MigrateBitArray(SkillInfo.Table.Length);
        // ... rest of deserialize
    }

```
---
 .../Server/Serialization/IGenericReader.cs    | 22 ++++++++++++-------
 .../Server/Serialization/IGenericWriter.cs    | 19 +++++++++++-----
 2 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/Projects/Server/Serialization/IGenericReader.cs b/Projects/Server/Serialization/IGenericReader.cs
index e3fe07deb..4e59e4e98 100644
--- a/Projects/Server/Serialization/IGenericReader.cs
+++ b/Projects/Server/Serialization/IGenericReader.cs
@@ -14,6 +14,7 @@
  *************************************************************************/
 
 using System;
+using System.Buffers;
 using System.Collections;
 using System.IO;
 using System.Net;
@@ -51,7 +52,7 @@ public interface IGenericReader
             var delta     => new DateTime(delta + DateTime.UtcNow.Ticks, DateTimeKind.Utc)
         };
     }
-    decimal ReadDecimal() => new(stackalloc int[4] { ReadInt(), ReadInt(), ReadInt(), ReadInt() });
+    decimal ReadDecimal() => new([ReadInt(), ReadInt(), ReadInt(), ReadInt()]);
     int ReadEncodedInt()
     {
         int v = 0, shift = 0;
@@ -119,14 +120,19 @@ public interface IGenericReader
 
     public BitArray ReadBitArray()
     {
-        var byteArrayLength = ReadEncodedInt();
+        int bitLength = ReadEncodedInt();
+        int byteLength = (bitLength + 7) / 8;
 
-        // We need an exact array size since the ctor doesn't allow for offset/length, not much we can do at this point.
-        var byteArray = new byte[byteArrayLength];
-
-        Read(byteArray);
-
-        return new BitArray(byteArray);
+        var buffer = ArrayPool<byte>.Shared.Rent(byteLength);
+        try
+        {
+            Read(buffer.AsSpan(0, byteLength));
+            return new BitArray(buffer) { Length = bitLength };
+        }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(buffer);
+        }
     }
 
     TextDefinition ReadTextDefinition()
diff --git a/Projects/Server/Serialization/IGenericWriter.cs b/Projects/Server/Serialization/IGenericWriter.cs
index 63ac04970..72a8728d0 100644
--- a/Projects/Server/Serialization/IGenericWriter.cs
+++ b/Projects/Server/Serialization/IGenericWriter.cs
@@ -163,14 +163,21 @@ public interface IGenericWriter
 
     public void Write(BitArray bitArray)
     {
-        var bytesLength = (bitArray.Length - 1 + (1 << 3)) >>> 3;
-        var arrayBuffer = ArrayPool<byte>.Shared.Rent(bytesLength);
+        int bitLength = bitArray.Length;
+        int byteLength = (bitLength + 7) / 8;
 
-        WriteEncodedInt(bytesLength);
-        bitArray.CopyTo(arrayBuffer, 0);
+        WriteEncodedInt(bitLength);
 
-        Write(arrayBuffer.AsSpan(0, bytesLength));
-        ArrayPool<byte>.Shared.Return(arrayBuffer);
+        var arrayBuffer = ArrayPool<byte>.Shared.Rent(byteLength);
+        try
+        {
+            bitArray.CopyTo(arrayBuffer, 0);
+            Write(arrayBuffer.AsSpan(0, byteLength));
+        }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(arrayBuffer);
+        }
     }
 
     void Write(TextDefinition def)