Throw FileFormatException for invalid sectors

Additional fix for #354

Author: jeremy-visionaid

OpenMcdf/FatChainEnumerator.cs

@@ -79,6 +79,9 @@ public bool MoveNext()
             return false;
         }
 
+        if (value > SectorType.Maximum)
+            throw new FileFormatException($"Invalid FAT sector ID: {value}.");
+
         index++;
         if (index >= fat.Context.SectorCount)
         {

OpenMcdf/MiniFatChainEnumerator.cs

@@ -70,6 +70,9 @@ public bool MoveNext()
                 return false;
             }
 
+            if (value > SectorType.Maximum)
+                throw new FileFormatException($"Invalid mini FAT sector ID: {value}.");
+
             uint nextIndex = index + 1;
             if (nextIndex > SectorType.Maximum)
                 throw new FileFormatException("Mini FAT chain length is greater than the maximum.");

OpenMcdf/MiniSector.cs

@@ -9,37 +9,15 @@ namespace OpenMcdf;
 /// <param name="Length">The sector length</param>
 internal record struct MiniSector(uint Id, int Length)
 {
-    public readonly bool IsValid => Id <= SectorType.Maximum;
-
     /// <summary>
     /// The position of the mini sector in the mini FAT stream.
     /// </summary>
-    public readonly long Position
-    {
-        get
-        {
-            ThrowIfInvalid();
-            return Id * Length;
-        }
-    }
+    public readonly long Position => Id * Length;
 
     /// <summary>
     /// The end position of the mini sector in the mini FAT stream.
     /// </summary>
-    public readonly long EndPosition
-    {
-        get
-        {
-            ThrowIfInvalid();
-            return (Id + 1) * Length;
-        }
-    }
-
-    readonly void ThrowIfInvalid()
-    {
-        if (!IsValid)
-            throw new InvalidOperationException($"Invalid mini FAT sector ID: {Id}.");
-    }
+    public readonly long EndPosition => (Id + 1) * Length;
 
     [ExcludeFromCodeCoverage]
     public override readonly string ToString() => $"{Id}";

OpenMcdf/RootContext.cs

@@ -194,7 +194,7 @@ public void ExtendStreamLength(long length)
     void TrimBaseStream()
     {
         Sector lastUsedSector = Fat.GetLastUsedSector();
-        if (!lastUsedSector.IsValid)
+        if (lastUsedSector.Id > SectorType.Maximum)
             throw new FileFormatException("Last used sector is invalid");
 
         if (Version is Version.V4 && lastUsedSector.EndPosition < RangeLockSectorOffset)

OpenMcdf/Sector.cs

@@ -11,37 +11,15 @@ internal record struct Sector(uint Id, int Length)
 {
     public static readonly Sector EndOfChain = new(SectorType.EndOfChain, 0);
 
-    public readonly bool IsValid => Id <= SectorType.Maximum;
-
     /// <summary>
     /// The position of the sector in the compound file stream.
     /// </summary>
-    public readonly long Position
-    {
-        get
-        {
-            ThrowIfInvalid();
-            return (Id + 1) * Length;
-        }
-    }
+    public readonly long Position => (Id + 1) * Length;
 
     /// <summary>
     /// The end position of the sector in the compound file stream.
     /// </summary>
-    public readonly long EndPosition
-    {
-        get
-        {
-            ThrowIfInvalid();
-            return (Id + 2) * Length;
-        }
-    }
-
-    readonly void ThrowIfInvalid()
-    {
-        if (!IsValid)
-            throw new InvalidOperationException($"Invalid FAT sector ID: {Id}.");
-    }
+    public readonly long EndPosition => (Id + 2) * Length;
 
     [ExcludeFromCodeCoverage]
     public override readonly string ToString() => $"{Id}";