continuity/Server.Packets/PacketForwardingService.cs

using System.Collections.Immutable;
using System.Reflection;

namespace Server.Packets;

public class PacketForwardingService
{
	private ImmutableDictionary<PacketId, System.Reflection.ConstructorInfo> _packets = null!;

	public PacketForwardingService()
	{
		InitializePackets(typeof(IPacket).Assembly);
	}

	private void InitializePackets(Assembly assembly)
	{
		// Get all types that implement IPacket and have a PacketIdAttribute
		_packets = assembly.GetTypes()
			.Select(x => (attr: x.GetCustomAttribute<PacketIdAttribute>(), ctor: x.GetConstructor(Type.EmptyTypes)))
			.Where(x => x.GetType().IsAssignableTo(typeof(IPacket)) && x.GetType().IsClass)
			.Where(x => x.attr != null && x.ctor != null)
			.ToImmutableDictionary(x => x.attr!.PacketId, x => x.ctor)!;
	}

	public IPacket Dispatch(Span<Byte> bytes)
	{
		// Get constructor according to packet id
		IPacket packet = _packets[GetPacketId(bytes)].Invoke(Array.Empty<object>()) as IPacket ??
		                 throw new InvalidOperationException();
		// Slice off packet id
		packet.Deserialize(bytes.Slice(2));
		return packet;
	}

	private PacketId GetPacketId(Span<Byte> bytes)
	{
		var id = (PacketId)BitConverter.ToUInt16(new[] { bytes[0], bytes[1] });
		return id;
	}
}