BitReader now uses stream extension to read the data from the stream

src/ImageSharp/Formats/WebP/BitReader/BitReaderBase.cs

@@ -29,23 +29,7 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.BitReader
         {
             this.Data = memoryAllocator.Allocate<byte>(bytesToRead);
             Span<byte> dataSpan = this.Data.Memory.Span;
-
-            using (IManagedByteBuffer buffer = memoryAllocator.AllocateManagedByteBuffer(4096))
-            {
-                Span<byte> bufferSpan = buffer.GetSpan();
-                int read;
-                while (bytesToRead > 0 && (read = input.Read(buffer.Array, 0, Math.Min(bufferSpan.Length, bytesToRead))) > 0)
-                {
-                    buffer.Array.AsSpan(0, read).CopyTo(dataSpan);
-                    bytesToRead -= read;
-                    dataSpan = dataSpan.Slice(read);
-                }
-
-                if (bytesToRead > 0)
-                {
-                    WebPThrowHelper.ThrowImageFormatException("webp image file has insufficient data");
-                }
-            }
+            input.Read(dataSpan.Slice(0, bytesToRead), 0, bytesToRead);
         }
 
         /// <inheritdoc/>

src/ImageSharp/Formats/WebP/Lossless/WebPLosslessDecoder.cs

@@ -945,17 +945,23 @@ namespace SixLabors.ImageSharp.Formats.Experimental.WebP.Lossless
         /// <param name="length">The number of pixels to copy.</param>
         private static void CopyBlock(Span<uint> pixelData, int decodedPixels, int dist, int length)
         {
+            int start = decodedPixels - dist;
+            if (start < 0)
+            {
+                WebPThrowHelper.ThrowImageFormatException("webp image data seems to be invalid");
+            }
+
             if (dist >= length)
             {
                 // no overlap.
-                Span<uint> src = pixelData.Slice(decodedPixels - dist, length);
+                Span<uint> src = pixelData.Slice(start, length);
                 Span<uint> dest = pixelData.Slice(decodedPixels);
                 src.CopyTo(dest);
             }
             else
             {
                 // There is overlap between the backward reference distance and the pixels to copy.
-                Span<uint> src = pixelData.Slice(decodedPixels - dist);
+                Span<uint> src = pixelData.Slice(start);
                 Span<uint> dest = pixelData.Slice(decodedPixels);
                 for (int i = 0; i < length; i++)
                 {

tests/ImageSharp.Tests/Formats/WebP/WebPDecoderTests.cs

@@ -321,8 +321,19 @@ namespace SixLabors.ImageSharp.Tests.Formats.WebP
         [Theory]
         [WithFile(Lossless.LossLessCorruptImage1, PixelTypes.Rgba32)]
         [WithFile(Lossless.LossLessCorruptImage2, PixelTypes.Rgba32)]
-        [WithFile(Lossless.LossLessCorruptImage3, PixelTypes.Rgba32)]
         [WithFile(Lossless.LossLessCorruptImage4, PixelTypes.Rgba32)]
+        public void WebpDecoder_CanDecodeLosslessWithIssues<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            // Just make sure no exception is thrown. The reference decoder fails to load the image.
+            using (Image<TPixel> image = provider.GetImage(WebpDecoder))
+            {
+                image.DebugSave(provider);
+            }
+        }
+
+        [Theory]
+        [WithFile(Lossless.LossLessCorruptImage3, PixelTypes.Rgba32)]
         public void WebpDecoder_ThrowImageFormatException_OnInvalidImages<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel>
         {