Add useful Write functions

lib/data.ex

@@ -101,6 +101,28 @@ defmodule Amethyst.Minecraft.Write do
   def position({x, y, z}) do
     <<x::signed-big-26, z::signed-big-26, y::signed-big-12>>
   end
+
+  @doc """
+  Writes a list of elements with the given `callback` function. This does not
+  prefix the list with a length, remember to do that yourself if needed.
+
+     iex> Amethyst.Minecraft.Write.list([1, 2, 3, 4], &Amethyst.Minecraft.Write.byte/1)
+     <<1, 2, 3, 4>>
+  """
+  def list(list, callback) do
+    Enum.reduce(list, "", &(&2 <> callback.(&1)))
+  end
+
+  @doc """
+  Shorthand function for writing a value which may not be present. If `value` is `nil`,
+  writes `false`, otherwise writes `true` followed by the value using `callback`.
+  """
+  def option(value, callback) do
+    case value do
+      nil -> bool(false)
+      v -> bool(true) <> callback.(v)
+    end
+  end
 end
 
 defmodule Amethyst.Minecraft.Read do

lib/servers/configuration.ex

@@ -143,16 +143,12 @@ defmodule Amethyst.Server.Configuration do
   end
   # Remove Resource Pack https://wiki.vg/Protocol#Remove_Resource_Pack_(configuration)
   def serialize({:remove_resource_pack, id}) do
-    if id == nil do
+    Write.option(id, &Write.string/1)
-      Write.varint(0x08) <> <<0x00>>
-    else
-      Write.varint(0x08) <> <<0x01>> <> Write.string(id)
-    end
   end
   # Add Resource Pack https://wiki.vg/Protocol#Add_Resource_Pack_(configuration)
   def serialize({:add_resource_pack, id, url, hash, forced, msg}) do
     Write.varint(0x09) <> Write.string(id) <> Write.string(url) <> Write.string(hash) <>
-    if(forced, do: <<0x01>>, else: <<0x00>>) <> if(msg == nil, do: <<0x00>>, else: <<0x01>> <> Write.string(msg))
+    Write.bool(forced) <> Write.option(msg, &Write.string/1)
   end
   # Store Cookie https://wiki.vg/Protocol#Store_Cookie_(configuration)
   def serialize({:store_cookie, id, data}) do
@@ -164,7 +160,7 @@ defmodule Amethyst.Server.Configuration do
   end
   # Feature Flags https://wiki.vg/Protocol#Feature_Flags
   def serialize({:feature_flags, flags}) do
-    Write.varint(0x0C) <> Write.varint(length(flags)) <> Enum.reduce(flags, "", fn id, acc -> acc <> Write.string(id) end)
+    Write.varint(0x0C) <> Write.varint(length(flags)) <> Write.list(flags, &Write.string/1)
   end
   # Update Tags https://wiki.vg/Protocol#Update_Tags
   def serialize({:update_tags, tags}) do
@@ -174,19 +170,17 @@ defmodule Amethyst.Server.Configuration do
   # Clientbound Known Packs https://wiki.vg/Protocol#Clientbound_Known_Packs
   def serialize({:clientbound_known_packs, packs}) do
     Write.varint(0x0E) <> Write.varint(length(packs)) <>
-    Enum.reduce(packs, "", fn {namespace, id, version}, acc -> acc <> Write.string(namespace) <> Write.string(id) <> Write.string(version) end)
+    Write.list(packs, fn {namespace, id, version} -> Write.string(namespace) <> Write.string(id) <> Write.string(version) end)
   end
   # Custom Report Details https://wiki.vg/Protocol#Custom_Report_Details
   def serialize({:custom_report_details, details}) do
     Write.varint(0x0F) <> Write.varint(length(details)) <>
-    Enum.reduce(details, "", fn {id, data}, acc -> acc <> Write.string(id) <> Write.string(data) end)
+    Write.list(details, fn {id, data} -> Write.string(id) <> Write.string(data) end)
   end
   # Server Links https://wiki.vg/Protocol#Server_Links_(configuration)
   def serialize({:server_links, links}) do
     Write.varint(0x10) <> Write.varint(length(links)) <>
-    Enum.reduce(links, "", fn {label, url}, acc ->
+    Write.list(links, fn {label, url} -> serialize_link_label(label) <> Write.string(url) end)
-      acc <> serialize_link_label(label) <> Write.string(url)
-    end)
   end
   def serialize(packet) do
     raise ArgumentError, "Tried serializing unknown packet #{inspect(packet)}"
@@ -196,8 +190,10 @@ defmodule Amethyst.Server.Configuration do
     acc <> Write.string(id) <> Write.varint(length(elements)) <> serialize_elements(elements)
   end
   defp serialize_elements(elements) do
-    Enum.reduce(elements, "", fn {id, ids}, acc -> acc <> Write.string(id) <> Write.varint(length(ids)) <>
+    Write.list(elements, fn {id, ids} ->
-      Enum.reduce(ids, "", fn id, acc -> acc <> Write.varint(id) end) end)
+      Write.string(id) <> Write.varint(length(ids)) <>
+      Write.list(ids, &Write.varint/1)
+    end)
   end
   defp serialize_link_label(:bug_report) do
     <<0x01>> <> Write.varint(0x00)