QL-Win/QuickLook · warning · InvalidDataException

DS_Store: wrong magic (expected 'Bud1')

Error message

DS_Store: wrong magic (expected 'Bud1')

What it means

Thrown by DSStoreAllocator.ReadHeader when bytes 4-7 (big-endian) are not 0x42756431, the ASCII string 'Bud1'. This is the canonical .DS_Store format signature; its absence means the file is not a real .DS_Store B-tree allocator image.

Source

Thrown at QuickLook.Plugin/QuickLook.Plugin.ArchiveViewer/DSStore/DSStoreExtractor.cs:76

            _root = NewBlock(offset, size);
            ReadOffsets();
            ReadToc();
            ReadFreeList();
        }

        private (uint offset, uint size) ReadHeader()
        {
            if (_data.Length < 32)
                throw new InvalidDataException("DS_Store header too short");

            uint magic1 = ReadUint32BE(_data, (int)_pos);
            if (magic1 != 1)
                throw new InvalidDataException("DS_Store: wrong magic (expected 0x00000001)");
            _pos += 4;

            uint magic = ReadUint32BE(_data, (int)_pos);
            if (magic != 0x42756431u)
                throw new InvalidDataException("DS_Store: wrong magic (expected 'Bud1')");
            _pos += 4;

            uint offset = ReadUint32BE(_data, (int)_pos); _pos += 4;
            uint size   = ReadUint32BE(_data, (int)_pos); _pos += 4;
            uint offset2 = ReadUint32BE(_data, (int)_pos);
            if (offset != offset2)
                throw new InvalidDataException("DS_Store: root-block offset mismatch");
            _pos += 4;

            return (offset, size);
        }

        private DSStoreBlock NewBlock(uint pos, uint size)
        {
            if (_data.Length < pos + 4 + size)
                throw new InvalidDataException("DS_Store: not enough data for block");
            var buf = new byte[size];
            Buffer.BlockCopy(_data, (int)pos + 4, buf, 0, (int)size);

View on GitHub (pinned to cb5d9c429c)

Solutions

1. Validate the 'Bud1' signature at offset 4 before parsing.
2. Skip files that fail the signature check.
3. Re-copy the file from the original macOS source.
4. Catch InvalidDataException and return an empty list.

Example fix

// before
var names = DSStoreExtractor.GetFileNames(path);

// after
var data = File.ReadAllBytes(path);
if (data.Length < 8 || System.Text.Encoding.ASCII.GetString(data, 4, 4) != "Bud1")
    return new List<string>();
var names = DSStoreExtractor.GetFileNames(path);

// Validate the .DS_Store 'Bud1' signature at offset 4.
public static bool IsValidDsStoreHeader(string path)
{
    var data = File.ReadAllBytes(path);
    return data.Length >= 8
        && System.Text.Encoding.ASCII.GetString(data, 4, 4) == "Bud1";
}

try { var names = DSStoreExtractor.GetFileNames(path); }
catch (InvalidDataException ex) when (ex.Message.Contains("Bud1"))
{
    // 'Bud1' signature missing; file is not a valid .DS_Store.
}

When it happens

Trigger: Calling GetFileNames on a file whose bytes 4-7 are not 'Bud1': a non-.DS_Store file, a corrupt file, or a file produced by a tool that does not emit the Bud1 signature.

Common situations: Generic binary or text file renamed .DS_Store; corrupt/truncated file from a flaky transfer; a macOS version or third-party tool that writes a different structure.

Related errors

• DS_Store: wrong magic (expected 0x00000001)
• DS_Store header too short
• DS_Store: root-block offset mismatch
• DS_Store: not enough data for block
• DS_Store: block id out of range

AI-assisted analysis of QL-Win/QuickLook@cb5d9c429c (2026-08-13). Data as JSON: /api/errors/2a52268af97e5799. Report an issue: GitHub.