Move to login mode when client wants to

lib/apps/tcp_listener.ex

@@ -29,7 +29,7 @@ defmodule Amethyst.TCPListener do
   @spec loop_acceptor(socket :: :gen_tcp.socket()) :: no_return()
   defp loop_acceptor(socket) do
     {:ok, client} = :gen_tcp.accept(socket)
-    {:ok, pid} = Task.Supervisor.start_child(Amethyst.ConnectionSupervisor, fn -> Amethyst.Server.Stage1.serve(client) end)
+    {:ok, pid} = Task.Supervisor.start_child(Amethyst.ConnectionSupervisor, fn -> Amethyst.Server.Handshake.serve(client) end)
     :ok = :gen_tcp.controlling_process(client, pid)
     Logger.info("Received connection from #{inspect(client)}, assigned to PID #{inspect(pid)}")
     loop_acceptor(socket)

lib/data.ex

@@ -22,6 +22,10 @@ defmodule Amethyst.Minecraft.Write do
   than simple binary data.
   """
 
+  def uuid(uuid) do
+    UUID.string_to_binary!(uuid)
+  end
+
   def varint(value) when value in -2_147_483_648..2_147_483_647 do
     <<value::32-unsigned>> = <<value::32-signed>> # This is a trick to allow the arithmetic shift to act as a logical shift
     varnum("", value)
@@ -115,6 +119,15 @@ defmodule Amethyst.Minecraft.Read do
     {[value | acc], rest, :reversed}
   end
 
+  def uuid({acc, <<uuid::16-binary, rest::binary>>, :reversed}) do
+    {[UUID.binary_to_string!(uuid) | acc], rest, :reversed}
+  end
+
+  def raw({acc, data, :reversed}, amount) do
+    <<data::binary-size(amount), rest::binary>> = data
+    {[data | acc], rest, :reversed}
+  end
+
   def varint(tuple, read \\ 0, nacc \\ 0)
   def varint({acc, <<1::1, value::7, rest::binary>>, :reversed}, read, nacc) when read < 5 do
     varint({acc, rest, :reversed}, read + 1, nacc + (value <<< (7 * read)))

lib/servers/handhsake.ex

@@ -14,9 +14,9 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-defmodule Amethyst.Server.Stage1 do
+defmodule Amethyst.Server.Handshake do
   @moduledoc """
-  This module contains the stage 1 (Handshaking) server logic.
+  This module contains the logic for the Handshake stage of the server.
   """
   require Logger
   use Amethyst.Server
@@ -53,6 +53,7 @@ defmodule Amethyst.Server.Stage1 do
     Logger.info("Got handshake, version #{ver} on #{addr}:#{port}. Wants to move to #{next}")
     case next do
       :status -> Amethyst.Server.Status.serve(client)
+      :login -> Amethyst.Server.Login.serve(client)
       _ -> raise RuntimeError, "Unhandled move to next mode #{next}"
     end
   end

lib/servers/login.ex

@@ -0,0 +1,105 @@
+# Amethyst - An experimental Minecraft server written in Elixir.
+# Copyright (C) 2024 KodiCraft
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+defmodule Amethyst.Server.Login do
+  @moduledoc """
+  This module contains the logic for the Handshake stage of the server.
+  """
+  require Logger
+  use Amethyst.Server
+
+  alias Amethyst.Minecraft.Read
+  alias Amethyst.Minecraft.Write
+
+  ## DESERIALIZATION
+  # Login Start https://wiki.vg/Protocol#Login_Start
+  def deserialize(0x00, data) do
+    {[name, uuid], ""} = Read.start(data) |> Read.string() |> Read.uuid() |> Read.stop()
+    {:login_start, name, uuid}
+  end
+  # Encryption Response https://wiki.vg/Protocol#Encryption_Response
+  def deserialize(0x01, data) do
+    {[secret_length], rest} = Read.start(data) |> Read.varint() |> Read.stop()
+    {[secret, verify_token_length], rest} = Read.start(rest) |> Read.raw(secret_length) |> Read.varint() |> Read.stop()
+    {[verify_token], ""} = Read.start(rest) |> Read.raw(verify_token_length) |> Read.stop()
+    {:encryption_response, secret, verify_token}
+  end
+  # Login Plugin Response https://wiki.vg/Protocol#Login_Plugin_Response
+  def deserialize(0x02, data) do
+    {[message_id, success], rest} = Read.start(data) |> Read.varint() |> Read.bool() |> Read.stop()
+    if success do
+      {:login_plugin_response, message_id, rest}
+    else
+      {:login_plugin_response, message_id, nil}
+    end
+  end
+  # Login Acknowledged https://wiki.vg/Protocol#Login_Acknowledged
+  def deserialize(0x03, "") do
+    {:login_acknowledged}
+  end
+  # Cookie Response https://wiki.vg/Protocol#Cookie_Response_(login)
+  def deserialize(0x04, data) do
+    {[key, exists], rest} = Read.start(data) |> Read.string() |> Read.bool() |> Read.stop()
+    if exists do
+      {[length], rest} = Read.start(rest) |> Read.varint() |> Read.stop()
+      {[data], _} = Read.start(rest) |> Read.raw(length) |> Read.stop()
+      {:cookie_response, key, data}
+    else
+      {:cookie_response, key, nil}
+    end
+  end
+  def deserialize(type, _) do
+    raise RuntimeError, "Got unknown packet type #{type}!"
+  end
+
+  ## SERIALIZATION
+  # Disconnect (login) https://wiki.vg/Protocol#Disconnect_(login)
+  def serialize({:disconnect, reason}) do
+    Write.varint(0x00) <> Write.string(reason)
+  end
+  # Encryption Request https://wiki.vg/Protocol#Encryption_Request
+  def serialize({:encryption_request, id, pubkey, verify_token, auth}) do
+    Write.varint(0x01) <> Write.string(id) <> Write.varint(byte_size(pubkey)) <> pubkey <> Write.varint(byte_size(verify_token)) <> verify_token <> <<auth::8>>
+  end
+  # Login Success https://wiki.vg/Protocol#Login_Success
+  def serialize({:login_success, uuid, username, props, strict}) do
+    Write.varint(0x02) <> Write.uuid(uuid) <> Write.string(username) <> Write.varint(length(props)) <>
+    Enum.reduce(props, "", fn {name, value, signature}, acc -> acc <> Write.string(name) <> Write.string(value) <> case signature do
+      nil -> <<0x00>>
+      signature -> <<0x01>> <> Write.string(signature)
+    end end) <> <<strict::8>>
+  end
+  # Set Compression https://wiki.vg/Protocol#Set_Compression
+  def serialize({:set_compression, threshold}) do
+    Write.varint(0x03) <> Write.varint(threshold)
+  end
+  # Login Plugin Request https://wiki.vg/Protocol#Login_Plugin_Request
+  def serialize({:login_plugin_request, id, channel, data}) do
+    Write.varint(0x04) <> Write.varint(id) <> Write.string(channel) <> data
+  end
+  # Cookie Request (login) https://wiki.vg/Protocol#Cookie_Request_(login)
+  def serialize({:cookie_request_login, id}) do
+    Write.varint(0x05) <> Write.string(id)
+  end
+  def serialize(packet) do
+    raise ArgumentError, "Tried serializing unknown packet #{inspect(packet)}"
+  end
+
+  ## HANDLING
+  def handle(tuple, _) do
+    Logger.error("Unhandled but known packet #{elem(tuple, 0)}")
+  end
+end

lib/servers/status.ex

@@ -16,8 +16,7 @@
 
 defmodule Amethyst.Server.Status do
   @moduledoc """
-  This module contains the Status logic, this is not really its own login state since the client
-  is only asking a bit of information.
+  This module contains the logic for the Status stage of the server.
   """
   require Logger
   use Amethyst.Server

mix.exs

@@ -22,7 +22,8 @@ defmodule Amethyst.MixProject do
   # Run "mix help deps" to learn about dependencies.
   defp deps do
     [
-      {:credo, "~> 1.7", only: [:dev, :test], runtime: false}
+      {:credo, "~> 1.7", only: [:dev, :test], runtime: false},
+      {:uuid, "~> 1.1"}
     ]
   end
 end

mix.lock

@@ -3,4 +3,5 @@
   "credo": {:hex, :credo, "1.7.7", "771445037228f763f9b2afd612b6aa2fd8e28432a95dbbc60d8e03ce71ba4446", [:mix], [{:bunt, "~> 0.2.1 or ~> 1.0", [hex: :bunt, repo: "hexpm", optional: false]}, {:file_system, "~> 0.2 or ~> 1.0", [hex: :file_system, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "8bc87496c9aaacdc3f90f01b7b0582467b69b4bd2441fe8aae3109d843cc2f2e"},
   "file_system": {:hex, :file_system, "1.0.0", "b689cc7dcee665f774de94b5a832e578bd7963c8e637ef940cd44327db7de2cd", [:mix], [], "hexpm", "6752092d66aec5a10e662aefeed8ddb9531d79db0bc145bb8c40325ca1d8536d"},
   "jason": {:hex, :jason, "1.4.3", "d3f984eeb96fe53b85d20e0b049f03e57d075b5acda3ac8d465c969a2536c17b", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "9a90e868927f7c777689baa16d86f4d0e086d968db5c05d917ccff6d443e58a3"},
+  "uuid": {:hex, :uuid, "1.1.8", "e22fc04499de0de3ed1116b770c7737779f226ceefa0badb3592e64d5cfb4eb9", [:mix], [], "hexpm", "c790593b4c3b601f5dc2378baae7efaf5b3d73c4c6456ba85759905be792f2ac"},
 }