egametang/ET · error · IOException

Unsupported compression type {compressionType}

Error message

Unsupported compression type {compressionType}

What it means

BundleFileReader.DecompressBytes (line 115) throws IOException for a CompressionType value outside None/Lzma/Lz4/Lz4HC. The reader does not know how to decompress that block, so it refuses. This typically signals a newer Unity bundle format with a compression flag this reader predates.

Source

Thrown at Packages/cn.etetet.hybridclr/Scripts/Editor/Share/3rds/UnityFS/BundleFileReader.cs:115

                        using (var compressedStream = new MemoryStream(compressedBytes))
                        {
                            ComparessHelper.Decompress7Zip(compressedStream, uncompressedStream, m_Header.compressedBlocksInfoSize, m_Header.uncompressedBlocksInfoSize);
                        }
                        return uncompressedStream.ReadAllBytes();
                    }
                case CompressionType.Lz4:
                case CompressionType.Lz4HC:
                    {
                        var uncompressedBytes = new byte[uncompressedSize];
                        var numWrite = LZ4Codec.Decode(compressedBytes, 0, compressedBytes.Length, uncompressedBytes, 0, uncompressedBytes.Length, true);
                        if (numWrite != uncompressedSize)
                        {
                            throw new IOException($"Lz4 decompression error, write {numWrite} bytes but expected {uncompressedSize} bytes");
                        }
                        return uncompressedBytes;
                    }
                default:
                    throw new IOException($"Unsupported compression type {compressionType}");
            }
        }

        private void ReadMetadata(EndianBinaryReader reader)
        {
            byte[] compressMetadataBytes = ReadBlocksInfoAndDirectoryMetadataUnCompressedBytes(reader);
            MemoryStream metadataStream = new MemoryStream(DecompressBytes((CompressionType)(m_Header.flags & ArchiveFlags.CompressionTypeMask), compressMetadataBytes, m_Header.uncompressedBlocksInfoSize));
            using (var blocksInfoReader = new EndianBinaryReader(metadataStream))
            {
                var uncompressedDataHash = blocksInfoReader.ReadBytes(16);
                var blocksInfoCount = blocksInfoReader.ReadInt32();
                m_BlocksInfo = new StorageBlock[blocksInfoCount];
                for (int i = 0; i < blocksInfoCount; i++)
                {
                    m_BlocksInfo[i] = new StorageBlock
                    {
                        uncompressedSize = blocksInfoReader.ReadUInt32(),
                        compressedSize = blocksInfoReader.ReadUInt32(),

View on GitHub (pinned to 5cab01f7a8)

Solutions

1. Rebuild/export the bundle with a compression type this reader supports (None/Lz4/Lz4HC/Lzma).
2. Use a Unity/editor version whose BundleFileReader understands the bundle's compression flag.
3. If the flags field is corrupted, re-fetch/rebuild the bundle.
4. Extend the switch with the new compression type if you must support it.

CompressionType ct = (CompressionType)(flags & CompressionTypeMask);
if (ct != CompressionType.None && ct != CompressionType.Lzma && ct != CompressionType.Lz4 && ct != CompressionType.Lz4HC)
    throw new NotSupportedException($"unsupported compression {ct}; rebuild bundle with Lz4/Lz4HC");

try { reader.Load(...); }
catch (IOException e) when (e.Message.Contains("Unsupported compression type"))
{ Log.Error($"unsupported compression in bundle: {e.Message}"); /* rebuild with supported codec */ }

When it happens

Trigger: Loading a UnityFS bundle whose block/metadata flags encode a compression type not handled (e.g. a newer Unity LZSS/zstd variant), or a malformed flags field yielding a bogus CompressionType after masking.

Common situations: Opening bundles built by a newer Unity version than the reader supports, a corrupted flags header producing an unknown enum value, or a custom compression the toolchain never registered.

Related errors

• Lz4 decompression error, write {numWrite} bytes but expected
• too fig file
• btenv not found key: {key} {typeof(T).FullName}
• 不能把{value.GetType()}转换为{typeof (T)}
• condition root child count error: {node.Children.Count}

AI-assisted analysis of egametang/ET@5cab01f7a8 (2026-08-13). Data as JSON: /api/errors/c7c0e2b788d2ab1f. Report an issue: GitHub.