Attempt to implement data for fixed bitset reading

apps/amethyst/lib/data.ex

@@ -142,7 +142,7 @@ defmodule Amethyst.Minecraft.Write do
   end
 
   def bitset(list) do
-    unaligned = Enum.reduce(list, <<>>, &(if &1 do <<&2::bitstring, 1::1>> else <<&2::bitstring, 0::1>> end))
+    unaligned = Enum.reduce(list, <<>>, &(if &1 do <<1::1, &2::bitstring>> else <<0::1, &2::bitstring>> end))
     aligned = if rem(bit_size(unaligned), 64) == 0 do
       unaligned
     else
@@ -150,6 +150,18 @@ defmodule Amethyst.Minecraft.Write do
     end
     varint(div(byte_size(aligned), 8)) <> aligned
   end
+  def fixed_bitset(list, length) do
+    unaligned = Enum.reduce(list, <<>>, &(if &1 do <<1::1, &2::bitstring>> else <<0::1, &2::bitstring>> end))
+    if bit_size(unaligned) != length do
+      raise ArgumentError, "Fixed bitset is not the correct length"
+    end
+    aligned = if rem(bit_size(unaligned), 64) == 0 do
+      unaligned
+    else
+      <<0::size(64 - rem(bit_size(unaligned), 64)), unaligned::bitstring>>
+    end
+    aligned
+  end
 end
 
 defmodule Amethyst.Minecraft.Read do
@@ -282,4 +294,10 @@ defmodule Amethyst.Minecraft.Read do
   def raw({acc, data, :reversed}) do
     {[data | acc], "", :reversed}
   end
+  def fixed_bitset({acc, data, :reversed}, length) do
+    bytes = ceil(length / 8)
+    <<value::binary-size(bytes), rest::binary>> = data
+    value = :binary.bin_to_list(value, 0, 1) |> Enum.reverse() |> Enum.take(length) |> Enum.map(& &1 != 0)
+    {[value | acc], rest, :reversed}
+  end
 end

apps/amethyst/lib/states/play.ex

@@ -157,6 +157,14 @@ defmodule Amethyst.ConnectionState.Play do
   def ge_start_waiting_for_level_chunks(767), do: %{packet_type: :game_event, event: 13, value: 0}
 
   Macros.defpacket_serverbound :confirm_teleportation, 0x00, 767, [teleport_id: :varint]
+  Macros.defpacket_serverbound :chat_message, 0x06, 767, [
+    message: :string,
+    timestamp: :long,
+    salt: :long,
+    signature: {:optional, :byte_array},
+    message_count: :varint,
+    acknowledged: {:fixed_bitset, 20}
+  ]
   Macros.defpacket_serverbound :serverbound_plugin_message, 0x12, 767, [channel: :string, data: :raw]
   Macros.defpacket_serverbound :keep_alive, 0x18, 767, [id: :long]
   Macros.defpacket_serverbound :set_player_position, 0x1A, 767, [