amethyst/lib/servers/generic.ex

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# 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.Generic do
@moduledoc """
This module includes generic logic which may be used by all stages of the server, including,
for instance, listening for packets.
"""
alias Amethyst.Minecraft.Read
def get_packet(client) do
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{[length], ""} = get_varint(client, "")
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recv = :gen_tcp.recv(client, length)
case recv do
{:ok, full_packet} -> ({[id], data} = Read.start(full_packet) |> Read.varint() |> Read.stop()
{id, data})
{:error, :closed} -> raise RuntimeError, "TODO: Handle disconnections reasonably"
{:error, error} -> raise RuntimeError, "An error has occured while waiting on a packet: #{error}"
end
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end
defp get_varint(client, acc) do
{:ok, byte} = :gen_tcp.recv(client, 1)
case byte do
<<0::1, _::7>> -> Read.start(acc <> byte) |> Read.varint() |> Read.stop()
<<1::1, _::7>> -> get_varint(client, acc <> byte)
end
end
end
defmodule Amethyst.Server do
@moduledoc """
This module includes shared boilerplate code for all stages of the server.
"""
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require Logger
@callback init(any()) :: any()
@callback deserialize(integer(), binary()) :: any()
@callback serialize(any()) :: binary()
@callback handle(any(), :gen_tcp.socket(), any()) :: {:ok, any()} | {:unhandled, any()}
defmacro __using__(_opts) do
quote do
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@behaviour Amethyst.Server
@spec serve(:gen_tcp.socket(), any()) :: no_return()
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def serve(client, state \\ []) do
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Logger.debug("#{__MODULE__} serving client #{inspect(client)}")
serve_loop(client, init(state))
end
defp serve_loop(client, state) do
{id, data} = Amethyst.Server.Generic.get_packet(client)
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Logger.debug("State: #{inspect(state)}")
packet = deserialize(id, data)
Logger.debug("Got packet #{inspect(packet)}")
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{result, state} = handle(packet, client, state)
if result != :ok do
Logger.warning("Handler returned result #{result}")
end
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serve_loop(client, state)
end
def transmit(packet, client) do
Logger.debug("Transmitting #{inspect(packet)}")
data = serialize(packet)
length = byte_size(data) |> Amethyst.Minecraft.Write.varint()
Logger.debug("Sending #{inspect(length <> data)}")
:gen_tcp.send(client, length <> data)
end
end
end
end