Handle range lock sector

Directory.csproj.props

@@ -11,7 +11,7 @@
   <!-- Packaging -->
   <PropertyGroup>
     <Version>3.0.0.0</Version>
-    <PackageVersion>$(Version)-preview.4</PackageVersion>
+    <PackageVersion>$(Version)-preview.5</PackageVersion>
     <Authors>ironfede,jeremy-visionaid</Authors>
     <Copyright>Copyright © 2010-2024, Federico Blaseotto, Jeremy Powell</Copyright>
     <PackageProjectUrl>https://github.com/ironfede/openmcdf</PackageProjectUrl>

OpenMcdf.Tests/RootStorageTests.cs

@@ -252,4 +252,28 @@ public void V3ThrowsIOExceptionAt2GB()
 
         Assert.ThrowsException<IOException>(() => stream.Write(buffer, 0, buffer.Length));
     }
+
+    [TestMethod]
+    [DoNotParallelize] // High memory usage
+    public void ValidateRangeLockSector()
+    {
+        RecyclableMemoryStreamManager manager = new();
+        using RecyclableMemoryStream baseStream = new(manager);
+        baseStream.Capacity64 = RootContext.RangeLockSectorOffset;
+
+        using var rootStorage = RootStorage.Create(baseStream, Version.V4);
+        using (CfbStream stream = rootStorage.CreateStream("Test"))
+        {
+            byte[] buffer = TestData.CreateByteArray(4096);
+            while (baseStream.Length <= RootContext.RangeLockSectorOffset)
+                stream.Write(buffer, 0, buffer.Length);
+        }
+
+        Assert.IsTrue(rootStorage.Validate());
+
+        rootStorage.Delete("Test");
+        rootStorage.Flush();
+
+        Assert.IsTrue(rootStorage.Validate());
+    }
 }

OpenMcdf/Fat.cs

@@ -15,11 +15,20 @@ internal sealed class Fat : ContextBase, IEnumerable<FatEntry>, IDisposable
     Sector cachedSector = Sector.EndOfChain;
     private bool isDirty;
 
+    public Func<FatEntry, bool> IsUsed { get; }
+
     public Fat(RootContextSite rootContextSite)
         : base(rootContextSite)
     {
         fatSectorEnumerator = new(rootContextSite);
         cachedSectorBuffer = new byte[Context.SectorSize];
+
+        if (Context.Version == Version.V3)
+            IsUsed = entry => entry.Value is not SectorType.Free;
+        else if (Context.Version == Version.V4)
+            IsUsed = entry => entry.Value is not SectorType.Free && entry.Index is not RootContext.RangeLockSectorId;
+        else
+            throw new NotSupportedException($"Unsupported major version: {Context.Version}.");
     }
 
     public void Dispose()
@@ -143,14 +152,14 @@ public uint Add(FatEnumerator fatEnumerator, uint startIndex)
 
     public Sector GetLastUsedSector()
     {
-        uint lastUsedSectorIndex = uint.MaxValue;
+        FatEntry lastUsedSectorIndex = new(uint.MaxValue, uint.MaxValue);
         foreach (FatEntry entry in this)
         {
-            if (!entry.IsFree)
-                lastUsedSectorIndex = entry.Index;
+            if (IsUsed(entry))
+                lastUsedSectorIndex = entry;
         }
 
-        return new(lastUsedSectorIndex, Context.SectorSize);
+        return new(lastUsedSectorIndex.Index, Context.SectorSize);
     }
 
     public IEnumerator<FatEntry> GetEnumerator() => new FatEnumerator(Context.Fat);
@@ -172,7 +181,7 @@ internal void WriteTrace(TextWriter writer)
         foreach (FatEntry entry in this)
         {
             Sector sector = new(entry.Index, Context.SectorSize);
-            if (entry.IsFree)
+            if (entry.Value is SectorType.Free)
             {
                 freeCount++;
                 writer.WriteLine($"{entry}");
@@ -194,7 +203,7 @@ internal void WriteTrace(TextWriter writer)
     }
 
     [ExcludeFromCodeCoverage]
-    internal void Validate()
+    internal bool Validate()
     {
         long fatSectorCount = 0;
         long difatSectorCount = 0;
@@ -213,8 +222,21 @@ internal void Validate()
             throw new FileFormatException($"FAT sector count mismatch. Expected: {Context.Header.FatSectorCount} Actual: {fatSectorCount}.");
         if (Context.Header.DifatSectorCount != difatSectorCount)
             throw new FileFormatException($"DIFAT sector count mismatch: Expected: {Context.Header.DifatSectorCount} Actual: {difatSectorCount}.");
+
+        if (Context.Length < RootContext.RangeLockSectorOffset)
+        {
+            if (this.TryGetValue(RootContext.RangeLockSectorId, out uint value) && value != SectorType.Free)
+                throw new FileFormatException($"Range lock FAT entry is not free.");
+        }
+        else
+        {
+            if (this[RootContext.RangeLockSectorId] != SectorType.EndOfChain)
+                throw new FileFormatException($"Range lock sector is not at the end of the chain.");
+        }
+
+        return true;
     }
 
     [ExcludeFromCodeCoverage]
-    internal long GetFreeSectorCount() => this.Count(entry => entry.IsFree);
+    internal long GetFreeSectorCount() => this.Count(entry => entry.Value == SectorType.Free);
 }

OpenMcdf/FatEntry.cs

@@ -7,8 +7,6 @@ namespace OpenMcdf;
 /// </summary>
 internal record struct FatEntry(uint Index, uint Value)
 {
-    public readonly bool IsFree => Value == SectorType.Free;
-
     [ExcludeFromCodeCoverage]
     public override readonly string ToString() => $"#{Index}: {Value}";
 }

OpenMcdf/FatEnumerator.cs

@@ -77,7 +77,7 @@ public bool MoveNextFreeEntry()
     {
         while (MoveNext())
         {
-            if (value == SectorType.Free)
+            if (value is SectorType.Free)
                 return true;
         }
 

OpenMcdf/FatStream.cs

@@ -1,4 +1,6 @@
-namespace OpenMcdf;
+using System.Diagnostics;
+
+namespace OpenMcdf;
 
 /// <summary>
 /// Provides a <inheritdoc cref="Stream"/> for a stream object in a compound file./>
@@ -185,6 +187,7 @@ public override void Write(byte[] buffer, int offset, int count)
             long writeLength = Math.Min(remaining, sector.Length - sectorOffset);
             writer.Write(buffer, localOffset, (int)writeLength);
             Context.ExtendStreamLength(sector.EndPosition);
+            Debug.Assert(Context.Length >= Context.Stream.Length);
             position += writeLength;
             writeCount += (int)writeLength;
             sectorOffset = 0;

OpenMcdf/MiniFat.cs

@@ -133,7 +133,7 @@ public uint Add(MiniFatEnumerator miniFatEnumerator, uint startIndex)
         FatEntry entry = miniFatEnumerator.Current;
         this[entry.Index] = SectorType.EndOfChain;
 
-        Debug.Assert(entry.IsFree);
+        Debug.Assert(entry.Value is SectorType.Free);
         MiniSector miniSector = new(entry.Index, Context.MiniSectorSize);
         if (Context.MiniStream.Length < miniSector.EndPosition)
             Context.MiniStream.SetLength(miniSector.EndPosition);
@@ -153,7 +153,7 @@ internal void WriteTrace(TextWriter writer)
     }
 
     [ExcludeFromCodeCoverage]
-    internal void Validate()
+    internal bool Validate()
     {
         using MiniFatEnumerator miniFatEnumerator = new(ContextSite);
 
@@ -165,5 +165,7 @@ internal void Validate()
                 throw new FileFormatException($"Mini FAT entry {current} is beyond the end of the mini stream.");
             }
         }
+
+        return true;
     }
 }

OpenMcdf/RootContext.cs

@@ -16,7 +16,9 @@ enum IOContextFlags
 /// </summary>
 internal sealed class RootContext : ContextBase, IDisposable
 {
-    const long MaximumV3StreamLength = 2147483648;
+    internal const long MaximumV3StreamLength = 2147483648;
+    internal const uint RangeLockSectorOffset = 0x7FFFFF00;
+    internal const uint RangeLockSectorId = RangeLockSectorOffset / (1 << Header.SectorShiftV4) - 1;
 
     readonly IOContextFlags contextFlags;
     readonly CfbBinaryWriter? writer;
@@ -187,11 +189,14 @@ public void Flush()
 
     public void ExtendStreamLength(long length)
     {
+        if (Length >= length)
+            return;
+
         if (Version is Version.V3 && length > MaximumV3StreamLength)
             throw new IOException("V3 compound files are limited to 2 GB.");
-
-        if (Length < length)
-            Length = length;
+        else if (Version is Version.V4 && Length < RangeLockSectorOffset && length >= RangeLockSectorOffset)
+            Fat[RangeLockSectorId] = SectorType.EndOfChain;
+        Length = length;
     }
 
     void TrimBaseStream()
@@ -200,6 +205,9 @@ void TrimBaseStream()
         if (!lastUsedSector.IsValid)
             throw new FileFormatException("Last used sector is invalid");
 
+        if (Version is Version.V4 && lastUsedSector.EndPosition < RangeLockSectorOffset)
+            Fat.TrySetValue(RangeLockSectorId, SectorType.Free);
+
         Length = lastUsedSector.EndPosition;
         BaseStream.SetLength(Length);
     }

OpenMcdf/RootStorage.cs

@@ -244,10 +244,11 @@ internal void Trace(TextWriter writer)
         Context.MiniFat.WriteTrace(writer);
     }
 
+    // TODO: Move checks to Tests project as Asserts
     [ExcludeFromCodeCoverage]
-    internal void Validate()
+    internal bool Validate()
     {
-        Context.Fat.Validate();
-        Context.MiniFat.Validate();
+        return Context.Fat.Validate()
+            && Context.MiniFat.Validate();
     }
 }