Implement SLP

lib/apps/tcp_listener.ex

@@ -34,18 +34,4 @@ defmodule Amethyst.TCPListener do
     Logger.info("Received connection from #{inspect(client)}, assigned to PID #{inspect(pid)}")
     loop_acceptor(socket)
   end
-
-  defp serve(socket) do
-    socket |> read_line() |> write_line(socket)
-    serve(socket)
-  end
-
-  defp read_line(socket) do
-    {:ok, data} = :gen_tcp.recv(socket, 0)
-    data
-  end
-
-  defp write_line(line, socket) do
-    :gen_tcp.send(socket, line)
-  end
 end

lib/servers/stage1.ex

@@ -24,14 +24,16 @@ defmodule Amethyst.Server.Stage1 do
   @spec serve(:gen_tcp.socket()) :: no_return()
   def serve(client) do
     {id, data} = Amethyst.Server.Generic.get_packet(client)
-    case deserialize(id, data) do
-      {:handshake, ver, addr, port, next} -> Logger.info("Got handshake on ver #{ver}, #{addr}:#{port} moving to #{next}")
-    end
+    packet = deserialize(id, data)
+    Logger.debug("Got packet #{inspect(packet)}")
+    handle(packet, client)
     serve(client)
   end
 
   ## DESERIALIZATION
   # Handshake https://wiki.vg/Protocol#Handshake
+  @spec deserialize(0, binary()) ::
+          {:handshake, any(), any(), any(), :login | :status | :transfer}
   def deserialize(0x00, <<data::binary>>) do
     {[ver, addr, port, next], ""} = Read.start(data) |> Read.varint() |> Read.string() |> Read.ushort() |> Read.varint() |> Read.stop()
     next = case next do
@@ -45,4 +47,18 @@ defmodule Amethyst.Server.Stage1 do
   def deserialize(type, _) do
     raise RuntimeError, "Got unknown packet type #{type}!"
   end
+
+  ## HANDLING
+  # Handshake https://wiki.vg/Protocol#Handshake
+  @spec handle(any(), any()) :: no_return()
+  def handle({:handshake, ver, addr, port, next}, client) do
+    Logger.info("Got handshake, version #{ver} on #{addr}:#{port}. Wants to move to #{next}")
+    case next do
+      :status -> Amethyst.Server.Status.serve(client)
+      _ -> raise RuntimeError, "Unhandled move to next mode #{next}"
+    end
+  end
+  def handle(tuple, _) do
+    Logger.error("Unhandled but known packet #{elem(tuple, 0)}")
+  end
 end

lib/servers/status.ex

@@ -0,0 +1,89 @@
+# 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.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.
+  """
+  require Logger
+  alias Amethyst.Minecraft.Read
+  alias Amethyst.Minecraft.Write
+
+  @spec serve(:gen_tcp.socket()) :: no_return()
+  def serve(client) do
+    {id, data} = Amethyst.Server.Generic.get_packet(client)
+    packet = deserialize(id, data)
+    Logger.debug("Got packet #{inspect(packet)}")
+    handle(packet, client)
+    serve(client)
+  end
+
+  def transmit(packet, client) do
+    Logger.debug("Transmitting #{inspect(packet)}")
+    data = serialize(packet)
+    length = byte_size(data) |> Write.varint()
+    :gen_tcp.send(client, length <> data)
+  end
+
+  ## DESERIALIZATION
+  # Status Request https://wiki.vg/Protocol#Status_Request
+  def deserialize(0x00, _) do
+    {:status_request}
+  end
+  # Ping Request https://wiki.vg/Protocol#Ping_Request
+  def deserialize(0x01, <<data::binary>>) do
+    {[payload], ""} = Read.start(data) |> Read.long() |> Read.stop()
+    {:ping_request, payload}
+  end
+  def deserialize(type, _) do
+    raise RuntimeError, "Got unknown packet type #{type}!"
+  end
+
+  ## SERIALIZATION
+  # Status Response https://wiki.vg/Protocol#Status_Response
+  def serialize({:status_response, data}) do
+    Write.varint(0x00) <> Write.string(data)
+  end
+  def serialize({:ping_response, payload}) do
+    Write.varint(0x01) <> <<payload::64-big-signed>>
+  end
+  def serialize(packet) do
+    raise ArgumentError, "Tried serializing unknown packet #{inspect(packet)}"
+  end
+
+  ## HANDLING
+  # Status Request https://wiki.vg/Protocol#Status_Request
+  def handle({:status_request}, client) do
+    # We want to make this more dynamic in the future, but this works for now
+    packet = {:status_response, ~s({
+"version": {"name": "1.21", "protocol": 767},
+"players": {"max": -1, "online": 69, "sample": [{"name": "§dAmethyst§r", "id": "4566e69f-c907-48ee-8d71-d7ba5aa00d20"}]},
+"description": {"text":"Amethyst is an experimental server written in Elixir"},
+"enforcesSecureChat": false,
+"previewsChat": false,
+"preventsChatReports": true
+})}
+    transmit(packet, client)
+  end
+  def handle({:ping_request, payload}, client) do
+    packet = {:ping_response, payload}
+    transmit(packet, client)
+  end
+  def handle(tuple, _) do
+    Logger.error("Unhandled but known packet #{elem(tuple, 0)}")
+  end
+end