From 348391616d447cf814198c44d670bd0b22aec32e Mon Sep 17 00:00:00 2001
From: Thanabodee Charoenpiriyakij <thanabodee.c@linecorp.com>
Date: Tue, 3 Jan 2023 23:44:46 +0700
Subject: [PATCH 1/2] Optimize Cloak.Tags.Decoder.decode/1

Do not copying `message` to calculate tag length. This could reduce
memory pressure during decode the tag.
---
 lib/cloak/tags/decoder.ex | 30 +++++++++++-------------------
 1 file changed, 11 insertions(+), 19 deletions(-)

diff --git a/lib/cloak/tags/decoder.ex b/lib/cloak/tags/decoder.ex
index 7884e10..bcebaf4 100644
--- a/lib/cloak/tags/decoder.ex
+++ b/lib/cloak/tags/decoder.ex
@@ -16,11 +16,17 @@ defmodule Cloak.Tags.Decoder do
   @byte_length 256
   @half_byte 128
 
-  def decode(message) do
-    length = tag_length(message)
+  def decode(<<_type::size(8), len::size(8), rest::binary>> = message) do
+    tag_length =
+      if len >= @half_byte do
+        <<value::binary-size(len - @half_byte), _::binary>> = rest
+        @offset + len - @half_byte + value_bytes(:binary.bin_to_list(value))
+      else
+        @offset + len
+      end
 
     case message do
-      <<tlv::binary-size(length), remainder::binary>> ->
+      <<tlv::binary-size(tag_length), remainder::binary>> ->
         %{tag: tag(tlv), remainder: remainder}
 
       _other ->
@@ -28,18 +34,6 @@ defmodule Cloak.Tags.Decoder do
     end
   end
 
-  defp tag_length(message) do
-    <<_type::size(8), len::size(8), rest::binary>> = message
-
-    tag_length(len, :binary.bin_to_list(rest))
-  end
-
-  defp tag_length(num, list) when num >= @half_byte do
-    @offset + num - @half_byte + value_bytes(list, num - @half_byte)
-  end
-
-  defp tag_length(num, _list), do: @offset + num
-
   defp tag(<<_type::size(8), len::size(8), rest::binary>>) when len >= @half_byte do
     size = len - @half_byte
     <<_value_bytes::binary-size(size), tag::binary>> = rest
@@ -51,9 +45,7 @@ defmodule Cloak.Tags.Decoder do
     tag
   end
 
-  defp value_bytes(list, num_bytes) do
-    list
-    |> Enum.take(num_bytes)
-    |> Enum.reduce(0, fn value, acc -> acc * @byte_length + value end)
+  defp value_bytes(list) do
+    Enum.reduce(list, 0, fn value, acc -> acc * @byte_length + value end)
   end
 end

From d9399116f0789bcf8738c64b021d26032286ef50 Mon Sep 17 00:00:00 2001
From: Thanabodee Charoenpiriyakij <thanabodee.c@linecorp.com>
Date: Mon, 6 Feb 2023 16:52:59 +0700
Subject: [PATCH 2/2] Calculate size before use in pattern matching

---
 lib/cloak/tags/decoder.ex | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/cloak/tags/decoder.ex b/lib/cloak/tags/decoder.ex
index bcebaf4..c7ff9d0 100644
--- a/lib/cloak/tags/decoder.ex
+++ b/lib/cloak/tags/decoder.ex
@@ -19,7 +19,8 @@ defmodule Cloak.Tags.Decoder do
   def decode(<<_type::size(8), len::size(8), rest::binary>> = message) do
     tag_length =
       if len >= @half_byte do
-        <<value::binary-size(len - @half_byte), _::binary>> = rest
+        size = len - @half_byte
+        <<value::binary-size(size), _::binary>> = rest
         @offset + len - @half_byte + value_bytes(:binary.bin_to_list(value))
       else
         @offset + len