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Zstd Compression

The protocol supports both compressed and uncompressed packets using Zstd compression. This is configurable via the hytale.protocol.compressionLevel system property.

Compression Format​

When a packet is marked as compressed in the registry, the wire format changes:

Uncompressed:

[Length (LE)] [Packet ID (LE)] [Payload]

Compressed:

[Compressed Length (LE)] [Packet ID (LE)] [Zstd Compressed Payload]
Note

The Packet ID is never compressed. Only the payload following the ID is compressed.

Implementation Logic​

Sending (Encoding)​

if (info.compressed() && serializedSize > 0) {
    int compressBound = (int)Zstd.compressBound(serializedSize);
    out.ensureWritable(compressBound);
    
    // Compress payload into output buffer
    int compressedSize = compressToBuffer(payloadBuf, out, out.writerIndex(), compressBound);

    if (Zstd.isError(compressedSize))
        throw new ProtocolException("Zstd compression failed");

    // Write the compressed size into the length field
    out.setIntLE(lengthIndex, compressedSize);
}

Receiving (Decoding)​

if (info.compressed() && payloadLength > 0) {
    // Decompress payload
    payload = decompressFromBuffer(in, in.readerIndex(), payloadLength, info.maxSize());
    in.skipBytes(payloadLength);
}