Fix #2925

Author: JimBobSquarePants

src/ImageSharp/Formats/Webp/WebpDecoderCore.cs

@@ -220,7 +220,7 @@ private WebpImageInfo ReadVp8Info(BufferedReadStream stream, ImageMetadata metad
                     else
                     {
                         // Ignore unknown chunks.
-                        uint chunkSize = ReadChunkSize(stream, buffer);
+                        uint chunkSize = ReadChunkSize(stream, buffer, false);
                         stream.Skip((int)chunkSize);
                     }
                 }
@@ -498,17 +498,24 @@ private static WebpChunkType ReadChunkType(BufferedReadStream stream, Span<byte>
     /// </summary>
     /// <param name="stream">The stream to decode from.</param>
     /// <param name="buffer">Temporary buffer.</param>
+    /// <param name="required">If true, the chunk size is required to be read, otherwise it can be skipped.</param>
     /// <returns>The chunk size in bytes.</returns>
     /// <exception cref="ImageFormatException">Invalid data.</exception>
-    private static uint ReadChunkSize(BufferedReadStream stream, Span<byte> buffer)
+    private static uint ReadChunkSize(BufferedReadStream stream, Span<byte> buffer, bool required = true)
     {
         if (stream.Read(buffer, 0, 4) == 4)
         {
             uint chunkSize = BinaryPrimitives.ReadUInt32LittleEndian(buffer);
             return (chunkSize % 2 == 0) ? chunkSize : chunkSize + 1;
         }
 
-        throw new ImageFormatException("Invalid Webp data.");
+        if (required)
+        {
+            throw new ImageFormatException("Invalid Webp data.");
+        }
+
+        // Return the size of the remaining data in the stream.
+        return (uint)(stream.Length - stream.Position);
     }
 
     /// <inheritdoc/>

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

@@ -549,4 +549,14 @@ public void Identify_VerifyRatio(string imagePath)
         Assert.Equal(37.8, meta.VerticalResolution);
         Assert.Equal(PixelResolutionUnit.PixelsPerCentimeter, meta.ResolutionUnits);
     }
+
+    [Theory]
+    [WithFile(Lossy.Issue2925, PixelTypes.Rgba32)]
+    public void WebpDecoder_CanDecode_Issue2925<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(WebpDecoder.Instance);
+        image.DebugSave(provider);
+        image.CompareToOriginal(provider, ReferenceDecoder);
+    }
 }

tests/ImageSharp.Tests/TestImages.cs

@@ -873,6 +873,7 @@ public static class Lossy
             public const string Issue2763 = "Webp/issues/Issue2763.png";
             public const string Issue2801 = "Webp/issues/Issue2801.webp";
             public const string Issue2866 = "Webp/issues/Issue2866.webp";
+            public const string Issue2925 = "Webp/issues/Issue2925.webp";
         }
 
         public const string AlphaBlend = "Webp/alpha-blend.webp";

tests/Images/Input/Webp/issues/Issue2925.webp

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:e12207babf122af7a62246938c2e78faa0d3f730edb3182f4f9d6adae6bfc602
+size 262144