The whole bot

Everything broken into pieces in First bot, in one file: connection, handler, read loop, phase switching. The same code sits in the repository as examples/MinimalBot and runs without changes, from the root of the McProtoNet clone:

dotnet run --project examples/MinimalBot -- 127.0.0.1 25565 McProtoBot

The arguments are address, port, and bot name. If they are missing, the defaults are 127.0.0.1, 25565, and McProtoBot. The protocol number is set by the Pv constant at the top of the listing. The server needs online-mode=false: the example stops at the Mojang session check.

What shows up in the console

The output is shortened: in play there are noticeably more skipped packets. There is no line about the compression threshold, because compression is off on this server.

MinimalBot: McProtoBot -> 127.0.0.1:25565 (pv 772)
[net] connection open
[login] handshake + login start sent
[login] cipher on: AES/CFB8
[login] success: McProtoBot ccf52582-9c5b-304f-a243-15437255b5eb
[config] in configuration, client information sent
[config] known packs: 1, acknowledged
  .. [Configuration] skipped 0x07 (1611 bytes) - and every later one
[play] configuration finished, in play
  .. [Play] skipped 0x7E (16779 bytes) - and every later one
  .. [Play] skipped 0x45 (8 bytes) - and every later one
[play] position: x=40,6 y=63,0 z=-58,6 - teleport 1 confirmed
[play] spawned
  .. [Play] skipped EntityMetadata (11 bytes) - and every later one
[play] health: 20, food 20
[play] keep-alive #1 - answered and waved

The dotted lines are packets the library has no method for: the number is not described for this version, phase, and direction, or it is described but no code has been generated for it yet. A packet whose On<Name> is not overridden gets parsed and quietly dropped - it does not show up in the console. Each dotted line prints once per phase, or there would be hundreds of them. A name instead of a number appears when the packet is found in the registry.

The listing has no CancellationTokenSource loop: the example stops on a kick or at the end of the stream. The token from the Read loop section gets added by anyone who needs an outside stop.

Listing

// dotnet run [host] [port] [name] - defaults are 127.0.0.1 25565 McProtoBot (pv 772)

using McProtoNet;
using McProtoNet.Primitives;
using McProtoNet.Protocol;
using McProtoNet.Transport.Cryptography;
using ConfCb = McProtoNet.Protocol.Packets.Configuration.Clientbound;
using ConfSb = McProtoNet.Protocol.Packets.Configuration.Serverbound;
using HandshakeSb = McProtoNet.Protocol.Packets.Handshaking.Serverbound;
using LoginCb = McProtoNet.Protocol.Packets.Login.Clientbound;
using LoginSb = McProtoNet.Protocol.Packets.Login.Serverbound;
using PlayCb = McProtoNet.Protocol.Packets.Play.Clientbound;
using PlaySb = McProtoNet.Protocol.Packets.Play.Serverbound;

const int Pv = 772;

var host = args.Length > 0 ? args[0] : "127.0.0.1";
var port = args.Length > 1 && int.TryParse(args[1], out var typed) ? typed : 25565;
var name = args.Length > 2 ? args[2] : "McProtoBot";

Console.WriteLine($"MinimalBot: {name} -> {host}:{port} (pv {Pv})");

await using var client = new MinecraftClient(new MinecraftClientOptions { Host = host, Port = port });
await client.ConnectAsync();
Console.WriteLine("[net] connection open");

await client.SendAsync(new HandshakeSb.SetProtocolPacket(Pv, host, port, 2), Pv);
await client.SendAsync(new LoginSb.LoginStartPacket(name, V764_Last: new(Guid.NewGuid())), Pv);
Console.WriteLine("[login] handshake + login start sent");

var bot = new Bot(client, Pv);

try
{
    await foreach (var packet in client.ReadPacketsAsync())
    {
        await bot.HandleAsync(in packet, Pv);
        if (bot.Stopped) break;
    }
}
catch (EndOfStreamException)
{
    // the server closed the connection - a normal end of session, the reason is logged above
}

Console.WriteLine("Connection closed.");

sealed class Bot(MinecraftClient client, int pv) : ClientboundHandler
{
    private readonly HashSet<(PacketPhase, int)> _unknownSeen = [];
    private int _keepAlives;
    private bool _spawned;

    /// <summary>The session is over: a kick, a login failure or the end of the stream.</summary>
    public bool Stopped { get; private set; }

    protected override ValueTask OnLoginCompress(LoginCb.LoginCompressPacket packet)
    {
        client.CompressionThreshold = packet.Threshold;
        Console.WriteLine($"[login] compression on, threshold {packet.Threshold}");
        return default;
    }

    protected override async ValueTask OnEncryptionRequest(LoginCb.EncryptionRequestPacket packet)
    {
        if (packet.V766_Last is { ShouldAuthenticate: true })
        {
            Console.WriteLine("[login] the server wants Mojang authentication - this example is offline only");
            Stopped = true;
            return;
        }

        using var rsa = EncryptionHelpers.DecodeRSAPublicKey(packet.PublicKey)
                        ?? throw new InvalidOperationException("could not parse the server public key");
        var secret = EncryptionHelpers.GenerateAESPrivateKey();

        await client.SendAsync(new LoginSb.EncryptionResponsePacket(
            rsa.Encrypt(secret, false),
            rsa.Encrypt(packet.VerifyToken, false)), pv);

        client.EnableEncryption(secret);
        Console.WriteLine("[login] cipher on: AES/CFB8");
    }

    protected override ValueTask OnLoginPluginRequest(LoginCb.LoginPluginRequestPacket packet)
        => client.SendAsync(new LoginSb.LoginPluginResponsePacket(packet.MessageId, null), pv);

    protected override async ValueTask OnLoginSuccess(LoginCb.LoginSuccessPacket packet)
    {
        Console.WriteLine($"[login] success: {packet.Username} {packet.Uuid}");
        await client.SendAsync(new LoginSb.LoginAcknowledgedPacket(), pv);
        Phase = PacketPhase.Configuration;

        await client.SendAsync(new ConfSb.ClientInformationPacket(
            "en_us", 2, 0, true, 0x7F, 1, false, true, V768_Last: new(ParticleStatus.All)), pv);
        Console.WriteLine("[config] in configuration, client information sent");
    }

    protected override ValueTask OnLoginDisconnect(LoginCb.LoginDisconnectPacket packet)
        => Kicked("login", packet.Reason);

    protected override ValueTask OnConfigurationKeepAlive(ConfCb.KeepAlivePacket packet)
        => client.SendAsync(new ConfSb.KeepAlivePacket(packet.KeepAliveId), pv);

    protected override ValueTask OnConfigurationPing(ConfCb.PingPacket packet)
        => client.SendAsync(new ConfSb.PongPacket(packet.Id), pv);

    protected override async ValueTask OnSelectKnownPacks(ConfCb.SelectKnownPacksPacket packet)
    {
        await client.SendAsync(new ConfSb.SelectKnownPacksPacket(packet.Packs), pv);
        Console.WriteLine($"[config] known packs: {packet.Packs.Length}, acknowledged");
    }

    protected override async ValueTask OnFinishConfiguration(ConfCb.FinishConfigurationPacket packet)
    {
        await client.SendAsync(new ConfSb.FinishConfigurationPacket(), pv);
        Phase = PacketPhase.Play;
        Console.WriteLine("[play] configuration finished, in play");
    }

    protected override ValueTask OnDisconnect(ConfCb.DisconnectPacket packet)
        => Kicked("config", packet.V764?.ReasonJson ?? packet.V765_Last?.Reason.ToString());

    protected override async ValueTask OnKeepAlive(PlayCb.KeepAlivePacket packet)
    {
        await client.SendAsync(new PlaySb.KeepAlivePacket(packet.KeepAliveId), pv);
        await client.SendAsync(new PlaySb.ArmAnimationPacket(0), pv);
        Console.WriteLine($"[play] keep-alive #{++_keepAlives} - answered and waved");
    }

    protected override ValueTask OnPing(PlayCb.PingPacket packet)
        => client.SendAsync(new PlaySb.PongPacket(packet.Id), pv);

    protected override async ValueTask OnStartConfiguration(PlayCb.StartConfigurationPacket packet)
    {
        await client.SendAsync(new PlaySb.ConfigurationAcknowledgedPacket(), pv);
        Phase = PacketPhase.Configuration;
        Console.WriteLine("[config] the server sent us back to configuration");
    }

    protected override async ValueTask OnPlayerPosition(PlayCb.PlayerPositionPacket packet)
    {
        await client.SendAsync(new PlaySb.TeleportConfirmPacket(packet.TeleportId), pv);
        Console.WriteLine(
            $"[play] position: x={packet.X:F1} y={packet.Y:F1} z={packet.Z:F1} - teleport {packet.TeleportId} confirmed");

        if (!_spawned)
        {
            _spawned = true;
            Console.WriteLine("[play] spawned");
        }
    }

    protected override ValueTask OnUpdateHealth(PlayCb.UpdateHealthPacket packet)
    {
        Console.WriteLine($"[play] health: {packet.Health}, food {packet.Food}");
        return default;
    }

    protected override ValueTask OnKickDisconnect(PlayCb.KickDisconnectPacket packet)
        => Kicked("play", packet.VUntil764?.ReasonJson ?? packet.V765_Last?.Reason.ToString());

    protected override ValueTask OnUnknown(in IncomingPacket raw)
    {
        if (_unknownSeen.Add((Phase, raw.Id)))
        {
            var packetName = PacketRegistry.TryResolve(raw.Id, pv, Phase, Direction, out var desc)
                ? desc.Identity.Name
                : $"0x{raw.Id:X2}";
            Console.WriteLine($"  .. [{Phase}] skipped {packetName} ({raw.Body.Length} bytes) - and every later one");
        }

        return default;
    }

    private ValueTask Kicked(string phase, string? reason)
    {
        Console.WriteLine($"[{phase}] kick: {reason ?? "no reason given"}");
        Stopped = true;
        return default;
    }
}

Chat and movement get added directly to the Bot class: the methods from Life in play sit next to the other handlers.

Next

• Phase and direction
• Handlers and unknown packets
• Cancellation, errors, closing