Large Packets

Minecraft limits the size of a single custom packet. If a payload can exceed that limit, attach a SplitPacketTransformer, which transparently splits the payload on send and reassembles it on receive.

Adding a split transformer

Both the registration overloads accept a List<PacketTransformer>. Add a SplitPacketTransformer to it on both sides of the connection.

For a C2S packet:

NetworkManager.registerReceiver(NetworkManager.Side.C2S,
    BigDataPayload.TYPE, BigDataPayload.CODEC,
    List.of(new SplitPacketTransformer()),
    (payload, context) -> context.queue(() -> {
        // handle the (reassembled) payload
    }));

For an S2C packet, add it to both the type declaration and the client receiver:

// Server: declare the type with the transformer
NetworkManager.registerS2CPayloadType(BigDataPayload.TYPE, BigDataPayload.CODEC,
    List.of(new SplitPacketTransformer()));

// Client: register the receiver with the transformer
NetworkManager.registerReceiver(NetworkManager.Side.S2C,
    BigDataPayload.TYPE, BigDataPayload.CODEC,
    List.of(new SplitPacketTransformer()),
    (payload, context) -> context.queue(() -> { /* ... */ }));

Sending is unchanged - call sendToServer / sendToPlayer as usual; the transformer handles the splitting.

Experimental

The packet-transformer overloads are marked experimental and may change. SplitPacketTransformer is the ready-made transformer for oversized packets; PacketTransformer is the general interface behind it if you ever need custom byte-level transformation.