preserve extra appended null bytes for archengius + trumank zen project

UAssetAPI.Tests/AssetUnitTests.cs

@@ -575,6 +575,7 @@ public void TestTraditionalUE5_4()
             TestUE5_4Subsection("BlankGame", EngineVersion.VER_UE5_4, new Usmap(Path.Combine("TestAssets", "TestUE5_4", "BlankGame", "BlankGame_Dumper-7.usmap")));
             TestUE5_4Subsection("Bellwright", EngineVersion.VER_UE5_4, new Usmap(Path.Combine("TestAssets", "TestUE5_4", "Bellwright", "Bellwright.usmap")));
             TestUE5_4Subsection("TheForeverWinter", EngineVersion.VER_UE5_4, new Usmap(Path.Combine("TestAssets", "TestUE5_4", "TheForeverWinter", "TheForeverWinter.usmap")));
+            TestUE5_4Subsection("Billiards", EngineVersion.VER_UE5_4, new Usmap(Path.Combine("TestAssets", "TestUE5_4", "Billiards", "5.4.3-34507850+++UE5+Release-5.4-DeepSpace7.usmap")));
         }
 
         /// <summary>

UAssetAPI.Tests/UAssetAPI.Tests.csproj

@@ -440,6 +440,15 @@
     <None Update="TestAssets\TestUE5_4\Bellwright\UMG_TreeViewDemo.uasset">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>
+    <None Update="TestAssets\TestUE5_4\Billiards\5.4.3-34507850+++UE5+Release-5.4-DeepSpace7.usmap">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+    <None Update="TestAssets\TestUE5_4\Billiards\BP_Table_Lamp.uasset">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+    <None Update="TestAssets\TestUE5_4\Billiards\BP_Table_Lamp.uexp">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
     <None Update="TestAssets\TestUE5_4\BlankGame\BP_CubePawn.combined">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>
     </None>

UAssetAPI/UAsset.cs

@@ -289,6 +289,12 @@ public bool HasUnversionedProperties
         /// </summary>
         public FWorldTileInfo WorldTileInfo;
 
+        /// <summary>
+        /// The number of null bytes appended to the end of the package header (.uasset file).
+        /// This should typically be zero, but may be greater when reading assets generated by external tools.
+        /// </summary>
+        public int AppendedNullBytes;
+
         /// <summary>
         /// In MapProperties that have StructProperties as their keys or values, there is no universal, context-free way to determine the type of the struct.
         /// <para />
@@ -1872,8 +1878,10 @@ public virtual void Read(AssetBinaryReader reader, int[] manualSkips = null, int
             // SeaOfThievesGarbageData
             if (SeaOfThievesGarbageDataOffset > 0 && SeaOfThievesGarbageDataLength > 0)
             {
+                long before = reader.BaseStream.Position;
                 reader.BaseStream.Seek(SeaOfThievesGarbageDataOffset, SeekOrigin.Begin);
                 SeaOfThievesGarbageData = reader.ReadBytes(SeaOfThievesGarbageDataLength);
+                reader.BaseStream.Seek(before, SeekOrigin.Begin);
             }
             else if (SeaOfThievesGarbageDataOffset == 0 || SeaOfThievesGarbageDataLength == 0)
             {
@@ -1887,8 +1895,10 @@ public virtual void Read(AssetBinaryReader reader, int[] manualSkips = null, int
             BulkData = [];
             if (BulkDataStartOffset > 0 && reader.LoadUexp)
             {
+                long before = reader.BaseStream.Position;
                 reader.BaseStream.Seek(BulkDataStartOffset, SeekOrigin.Begin);
                 BulkData = reader.ReadBytes((int)(reader.BaseStream.Length - BulkDataStartOffset));
+                reader.BaseStream.Seek(before, SeekOrigin.Begin);
             }
 
             // WorldTileInfoDataOffset
@@ -1905,9 +1915,11 @@ public virtual void Read(AssetBinaryReader reader, int[] manualSkips = null, int
             }
 
             // PreloadDependencies
+            if (PreloadDependencyOffset > 0) reader.BaseStream.Seek(PreloadDependencyOffset, SeekOrigin.Begin); // needed so that we're at a sensible offset for AppendedNullBytes if no preload deps
             for (int i = 0; i < Exports.Count; i++)
             {
-                if (Exports[i].FirstExportDependencyOffset < 0) continue;
+                if (PreloadDependencyOffset <= 0) continue;
+                if (Exports[i].FirstExportDependencyOffset < 0) continue; // not <= 0
                 this.UsesEventDrivenLoader = true;
 
                 reader.BaseStream.Seek(PreloadDependencyOffset, SeekOrigin.Begin);
@@ -1949,6 +1961,20 @@ public virtual void Read(AssetBinaryReader reader, int[] manualSkips = null, int
                 }
             }
 
+            // possible for some null bytes to exist at end of .uasset file as part of Archengius + trumank zen to legacy conversion project
+            // as with other changes made by external tools that are accepted by the engine, we would like to maintain these bytes
+            if (Exports.Count > 0)
+            {
+                long offsetDiff = Exports[0].SerialOffset - reader.BaseStream.Position;
+                byte[] paddingBytes = reader.ReadBytes((int)offsetDiff);
+                foreach (byte byt in paddingBytes)
+                {
+                    // if non-null then we expect that some serialization problem has occurred
+                    if (byt != 0) throw new FormatException("Encountered additional non-null data at end of legacy header data");
+                }
+                AppendedNullBytes = paddingBytes.Length; // int rather than byte[] so easy to understand in JSON
+            }
+
             if (reader.LoadUexp)
             {
                 bool skipParsingExports = CustomSerializationFlags.HasFlag(CustomSerializationFlags.SkipParsingExports);
@@ -2575,6 +2601,12 @@ public virtual MemoryStream WriteData()
                     }
                 }
 
+                if (AppendedNullBytes > 0)
+                {
+                    // new arrays guaranteed to be zero'd
+                    writer.Write(new byte[AppendedNullBytes]);
+                }
+
                 // Export data
                 int oldOffset = this.SectionSixOffset;
                 this.SectionSixOffset = (int)writer.BaseStream.Position;