Tidy up AstcDecoder and add more guards

Author: Erik-White

src/ImageSharp.Textures/TextureFormats/Decoding/AstcDecoder.cs

@@ -10,17 +10,30 @@ namespace SixLabors.ImageSharp.Textures.TextureFormats.Decoding;
 /// </summary>
 internal static class AstcDecoder
 {
+    internal const int AstcBlockSize = 16;
+
     /// <summary>
     /// Decodes an ASTC block into RGBA pixels.
     /// </summary>
     /// <param name="blockData">The 16-byte ASTC block data.</param>
     /// <param name="blockWidth">The width of the block footprint (4-12).</param>
     /// <param name="blockHeight">The height of the block footprint (4-12).</param>
     /// <param name="decodedPixels">The output span for decoded RGBA pixels.</param>
-    /// <param name="isSrgb">Optional flag to indicate if the output should be in sRGB color space.</param>
+    /// <exception cref="ArgumentException">Thrown if blockData is not 16 bytes or decodedPixels is the wrong size.</exception>
     /// <exception cref="ArgumentOutOfRangeException">Thrown if the block dimensions are invalid.</exception>
-    public static void DecodeBlock(ReadOnlySpan<byte> blockData, int blockWidth, int blockHeight, Span<byte> decodedPixels, bool isSrgb = false)
+    public static void DecodeBlock(ReadOnlySpan<byte> blockData, int blockWidth, int blockHeight, Span<byte> decodedPixels)
     {
+        if (blockData.Length != AstcBlockSize)
+        {
+            throw new ArgumentException($"ASTC block data must be exactly {AstcBlockSize} bytes. Received {blockData.Length} bytes.", nameof(blockData));
+        }
+
+        int expectedDecodedSize = blockWidth * blockHeight * 4;
+        if (decodedPixels.Length < expectedDecodedSize)
+        {
+            throw new ArgumentException($"Output buffer must be at least {expectedDecodedSize} bytes for {blockWidth}x{blockHeight} block. Received {decodedPixels.Length} bytes.", nameof(decodedPixels));
+        }
+
         Footprint footprint = Footprint.FromFootprintType(FootprintFromDimensions(blockWidth, blockHeight));
 
         AstcSharp.AstcDecoder.DecompressBlock(blockData, footprint, decodedPixels);
@@ -36,6 +49,9 @@ public static void DecodeBlock(ReadOnlySpan<byte> blockData, int blockWidth, int
     /// <param name="blockHeight">The height of the block footprint.</param>
     /// <param name="compressedBytesPerBlock">The number of compressed bytes per block.</param>
     /// <returns>The decompressed RGBA pixel data.</returns>
+    /// <exception cref="ArgumentNullException">Thrown if blockData is null.</exception>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if dimensions or block parameters are invalid.</exception>
+    /// <exception cref="ArgumentException">Thrown if blockData length is invalid.</exception>
     public static byte[] DecompressImage(
         byte[] blockData,
         int width,
@@ -44,8 +60,28 @@ public static byte[] DecompressImage(
         int blockHeight,
         byte compressedBytesPerBlock)
     {
+        ArgumentNullException.ThrowIfNull(blockData);
+        ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(0, width);
+        ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(0, height);
+
+        if (compressedBytesPerBlock != AstcBlockSize)
+        {
+            throw new ArgumentOutOfRangeException(nameof(compressedBytesPerBlock), compressedBytesPerBlock, $"ASTC blocks must be {AstcBlockSize} bytes.");
+        }
+
+        // Validate block dimensions (will throw if invalid)
+        _ = FootprintFromDimensions(blockWidth, blockHeight);
+
         int blocksWide = (width + blockWidth - 1) / blockWidth;
         int blocksHigh = (height + blockHeight - 1) / blockHeight;
+        int totalBlocks = blocksWide * blocksHigh;
+        int expectedDataLength = totalBlocks * compressedBytesPerBlock;
+
+        if (blockData.Length < expectedDataLength)
+        {
+            throw new ArgumentException($"Block data is too small. Expected at least {expectedDataLength} bytes for {width}x{height} texture with {blockWidth}x{blockHeight} blocks, but received {blockData.Length} bytes.", nameof(blockData));
+        }
+
         byte[] decompressedData = new byte[width * height * 4];
         byte[] decodedBlock = new byte[blockWidth * blockHeight * 4];
 
@@ -105,6 +141,6 @@ private static FootprintType FootprintFromDimensions(int width, int height)
             (10, 10) => FootprintType.Footprint10x10,
             (12, 10) => FootprintType.Footprint12x10,
             (12, 12) => FootprintType.Footprint12x12,
-            _ => throw new ArgumentOutOfRangeException(nameof(width), "Invalid footprint type."),
+            _ => throw new ArgumentOutOfRangeException(nameof(width), $"Invalid ASTC block dimensions: {width}x{height}. Valid sizes are 4x4, 5x4, 5x5, 6x5, 6x6, 8x5, 8x6, 8x8, 10x5, 10x6, 10x8, 10x10, 12x10, 12x12."),
         };
 }