SixLabors/ImageSharp · error · ImageFormatException

Invalid Webp data, could not read chunk type.

Error message

Invalid Webp data, could not read chunk type.

What it means

WebpChunkParsingUtils.ReadChunkType throws ImageFormatException when the 4-byte chunk type (FourCC) cannot be read from the stream. Unknown chunk types are normally skipped, but a chunk type must still be readable to parse the RIFF structure; failing to read 4 bytes means the data is truncated or not WebP at that offset.

Solutions

1. Verify file integrity and re-download; check the file starts with RIFF....WEBP.
2. Catch ImageFormatException around decoding to classify input as corrupt.
3. Validate chunk structure with a tool (webpinfo) to find where the file diverges from the RIFF spec.
4. Ensure no other code has advanced the stream before the decoder receives it.

Example fix

// before
using var image = Image.Load(maybeWebp);
// after
using var ms = new MemoryStream();
maybeWebp.CopyTo(ms); ms.Position = 0;
try { using var image = Image.Load(ms); }
catch (ImageFormatException) { /* not valid/truncated WebP */ }

try { using var image = Image.Load(stream); }
catch (ImageFormatException ex) { log.Warn(ex, "Could not read WebP chunk type — file truncated/corrupt"); }

When it happens

Trigger: Decoding a WebP where the stream ends inside a chunk's FourCC field; also reached when the header structure is misplaced so the reader expects a chunk type at end-of-data.

Common situations: Truncated downloads; files where a prior chunk size was corrupted causing the parser to seek past real data; saving a partial file during an in-progress transfer.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• Invalid Webp data, could not read chunk size.
• Invalid Webp data, could not read unsigned 24 bit integer.
• The ANI file does not contain any frame resources.
• The stream does not contain an ANI RIFF container.
• The ANI RIFF container size is invalid.

AI-assisted analysis of SixLabors/ImageSharp@59ce6af6fc (2026-09-13). Data as JSON: /api/errors/f9abbd45ccfae98f. Report an issue: GitHub.

Appendix: source

Thrown at src/ImageSharp/Formats/Webp/WebpChunkParsingUtils.cs:364

    /// <summary>
    /// Identifies the chunk type from the chunk.
    /// </summary>
    /// <param name="stream">The stream to read the data from.</param>
    /// <param name="buffer">Buffer to store the data read from the stream.</param>
    /// <exception cref="ImageFormatException">
    /// Thrown if the input stream is not valid.
    /// </exception>
    public static WebpChunkType ReadChunkType(BufferedReadStream stream, Span<byte> buffer)
    {
        if (stream.Read(buffer) == 4)
        {
            return (WebpChunkType)BinaryPrimitives.ReadUInt32BigEndian(buffer);
        }

        // While we ignore unknown chunks we still need a to be a ble to read a chunk type
        // known or otherwise from the stream.
        throw new ImageFormatException("Invalid Webp data, could not read chunk type.");
    }

    /// <summary>
    /// Reads the ICCP chunk from the stream.
    /// </summary>
    /// <param name="stream">The stream to decode from.</param>
    /// <param name="metadata">The image metadata.</param>
    /// <param name="ignoreMetadata">If true, metadata will be ignored.</param>
    /// <param name="executeAncillarySegmentAction">Executes profile parsing under the decoder's integrity policy.</param>
    public static void ReadIccProfile(
        BufferedReadStream stream,
        ImageMetadata metadata,
        bool ignoreMetadata,
        Action<Action> executeAncillarySegmentAction)
    {
        ulong chunkSize = ReadPaddedChunkSize(stream, stackalloc byte[4], true);

        // ICCP precedes image/frame data. Its framing must be readable even when

View on GitHub (pinned to 59ce6af6fc)